WO2025201570A1 - Negative electrode material, negative electrode sheet and secondary battery - Google Patents

Abstract

The present application relates to the field of electrochemical energy storage. Disclosed are a negative electrode material, a negative electrode sheet and a secondary battery. The negative electrode material comprises a carbon substrate and an active substance, wherein the carbon substrate is provided with pores, and the active substance is at least partially arranged inside the pores of the carbon substrate, with the deposition parameter γ of the active substance being greater than or equal to 0.85. In formula (1), m₁ is the mass of the negative electrode material; based on m₁, the mass percentage of the active substance is a₁, and the specific pore volume of the negative electrode material is p₁; m₂ is the mass of the negative electrode material after the active substance is removed; based on m₂, the mass percentage of the active substance is a₂, and the specific pore volume of the negative electrode material is p₂; and ρ is the density of the active substance. The secondary battery comprises the negative electrode material, and has a relatively high initial coulombic efficiency and good cycling stability.

Description

Negative electrode material, negative electrode sheet and secondary battery

This application claims priority to Chinese Patent Application No. 202411035149.3, filed on July 30, 2024, and Chinese Patent Application No. 202411369551.5, filed on September 27, 2024. This application incorporates the entirety of the aforementioned Chinese patent applications.

Technical Field

The present application relates to the field of electrochemical energy storage, and specifically to a negative electrode material, a negative electrode plate and a secondary battery.

Background Art

Lithium-ion batteries are widely used in the 3C industry due to their high energy density, long lifespan, and environmental friendliness. Silicon is one of the most promising anode materials for high-capacity lithium-ion batteries. However, silicon suffers from severe volume expansion during charge and discharge, leading to a rapid decrease in battery capacity over long cycles.

To address these technical issues, silicon materials are often combined with porous carbon materials to mitigate the volume expansion of the silicon material. However, when the silicon content reaches a certain level, there may be risks such as increased side reactions between the negative electrode material and the electrolyte and increased gas production, thereby reducing the battery's cycle performance and safety.

Summary of the Invention

The present application provides a negative electrode material, a negative electrode plate and a secondary battery to solve at least one of the above problems.

To achieve the above object, the present application provides a negative electrode material, comprising a carbon matrix and an active material, wherein the carbon matrix has pores, the active material is at least partially disposed in the pores of the carbon matrix, and the deposition parameter γ of the active material is greater than or equal to 0.85; Wherein, _m1 is the mass of the negative electrode material, based on _m1 , the mass percentage of the active material is _a1 , and the specific pore volume of the negative electrode material is _p1 ; _m2 is the mass of the negative electrode material after removing the active material, based on _m2 , the mass percentage of the active material is _a2 , and the specific pore volume of the negative electrode material after removing the active material is _p2 ; ρ is the density of the active material.

The present application also provides a negative electrode plate, comprising the above-mentioned negative electrode material.

The present application also provides a secondary battery, comprising the above-mentioned negative electrode material or the above-mentioned negative electrode plate.

The present application measures the pore volume change and mass change of the negative electrode material before and after removing the active material, and then characterizes the proportion of active material in the carbon matrix pores in the negative electrode material, that is, the deposition parameter γ. In the present application, the active material deposition parameter γ is greater than or equal to 0.85, so that most of the active material is attached to the pores of the carbon matrix, which can reduce the side reactions between the negative electrode material and the electrolyte during charging and discharging, improve the cycle performance of the battery, and reduce the hydrolysis of the active material during pulping and battery use, that is, reduce gas generation, and improve the safety performance of the battery. In addition, under the condition of a certain silicon content, the increase in the silicon content in the carbon matrix pores can also increase the particle strength of the negative electrode material.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a flow chart of the preparation of the negative electrode material provided in this application;

FIG2 is a scanning electron microscope (SEM) image of the negative electrode material provided in Example 17 of the present application;

FIG3 is an XRD pattern of the negative electrode material provided in Example 17 of the present application;

FIG4 is a graph showing the first charge and discharge curves of the negative electrode material provided in Example 17 of the present application;

FIG5 is a comparison chart of the electrical conductivity of the negative electrode material provided in Example 17 of the present application and the negative electrode material provided in Comparative Example 9.

DETAILED DESCRIPTION

The following describes the embodiments of the present application in detail. The following embodiments are illustrative and are only used to explain the present application, and should not be construed as limiting the present application. It should be noted that, unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which the present application belongs. In the absence of conflict, the embodiments of the present application and the features in the embodiments may be combined with each other. In the following description, many specific details are set forth to facilitate a full understanding of the present application, and the embodiments described are only a portion of the embodiments of the present application, not all of the embodiments.

An embodiment of the present application provides a secondary battery, comprising a housing, an electrode assembly, and an electrolyte. The electrode assembly and the electrolyte are both located within the housing.

The outer shell can be a packaging bag encapsulated by an encapsulation film (such as an aluminum-plastic film), such as a soft-pack battery. In other embodiments, the secondary battery can also be, but is not limited to, a steel-shell battery, an aluminum-shell battery, etc.

The electrolyte may be in one or more of a gel state, a solid state, and a liquid state. In some embodiments, the liquid electrolyte comprises a lithium salt and an organic solvent. The lithium salt may be selected from, but is not limited to, one or more of lithium hexafluorophosphate (LiPF ₆ ), lithium tetrafluoroborate (LiBF ₄ ), lithium hexafluoroarsenate (LiAsF ₆ ), lithium perchlorate (LiClO ₄ ), lithium tetraphenylborate (LiB(C ₆ H ₅ ) ₄ ), lithium methanesulfonate (LiCH ₃ SO ₃ ), lithium bisfluorosulfonyl imide (LiFSI), lithium bistrifluoromethanesulfonyl imide (LiTFSI), lithium trifluoromethanesulfonate (LiCF ₃ SO ₃ ), lithium bis(trifluoromethylsulfonyl)imide (LiN(SO ₂ CF ₃ ) ₂ , tris(trifluoromethylsulfonyl)methyl lithium (LiC(SO ₂ CF ₃ ) ₃ ), lithium bisoxalatoborate (LiBOB) and lithium difluorophosphate (LiPO ₂ F ₂ ). For example, the lithium salt may be selected from LiPF ₆ Because it can give high ionic conductivity and improve cycle characteristics. The organic solvent can be a carbonate compound, a carboxylate compound, an ether compound, a nitrile compound, other organic solvents or a combination thereof. Examples of carbonate compounds include but are not limited to diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), ethylmethyl carbonate (MEC), ethylene carbonate (EC), propylene carbonate (PC), Butylene carbonate (BC), vinyl ethylene carbonate (VEC), fluoroethylene carbonate (FEC), 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-difluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate, trifluoromethylethylene carbonate, or a combination thereof.

The electrode assembly includes a positive electrode sheet, a negative electrode sheet, and a separator, with the separator disposed between the positive and negative electrode sheets. The electrode assembly can be a laminated structure, formed by alternating layers of positive electrode sheets, separators, and negative electrode sheets. In other embodiments, the electrode assembly can also be a wound structure, formed by stacking the positive electrode sheet, separators, and negative electrode sheets in sequence and then winding them.

positive electrode

The positive electrode sheet includes a positive electrode current collector and a positive electrode active layer disposed on at least one surface of the positive electrode current collector. The positive electrode current collector can be aluminum foil or nickel foil, or any composite current collector disclosed in the prior art, such as, but not limited to, a current collector formed by combining the aforementioned conductive foil and a polymer substrate. The positive electrode active layer contains a positive electrode active material, which includes a compound that reversibly intercalates and deintercalates lithium ions (i.e., a lithiated intercalation compound). In some embodiments, the positive electrode active material may include a lithium transition metal composite oxide. The lithium transition metal composite oxide contains lithium and at least one element selected from cobalt, manganese, and nickel. In some embodiments, the positive electrode active material may include, but is not limited to _, at least one _of lithium cobalt oxide ( _LiCoO2 ), lithium nickel manganese cobalt ternary material (NCM), lithium manganese oxide ( _LiMn2O4 ), lithium nickel manganese oxide ( _{LiNi0.5Mn1.5O4 )} , or lithium iron phosphate ( _LiFePO4 ).

The positive electrode active layer also includes a binder to bond the positive electrode active material particles to facilitate film formation and improve the bonding strength between the positive electrode active layer and the positive electrode current collector. In some embodiments, the binder may include, but is not limited to, at least one of polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, a polymer containing ethylene oxide, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, or nylon.

The positive electrode active layer may further include a conductive material, including but not limited to carbon-based materials, metal-based materials, conductive polymers, or any combination thereof. In some embodiments, the carbon-based material may include but is not limited to natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, or any combination thereof. In some embodiments, the metal-based material may include but is not limited to metal powder or metal fiber, such as copper, nickel, aluminum, or silver. In some embodiments, the conductive polymer may be a polyphenylene derivative.

negative electrode

The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector. The negative electrode current collector can be made of at least one of copper foil, nickel foil, stainless steel foil, titanium foil, or a carbon-based current collector. It can also be any composite current collector disclosed in the prior art, such as, but not limited to, a current collector formed by combining the aforementioned conductive foil and a polymer substrate. The negative electrode active material layer includes a negative electrode material, a binder, and a conductive material.

The negative electrode material includes a carbon matrix and an active substance. The carbon matrix is provided with pores, and the active substance is at least partially provided in the pores of the carbon matrix.

The carbon matrix has pores, which provide more sites for the deposition of active materials, allowing them to deposit at least within the pores of the carbon matrix. Furthermore, the porous framework of the carbon matrix forms a conductive network that facilitates electron transport during charge and discharge, thereby reducing polarization of the battery material and improving conductivity and cycling stability.

In the present application, the deposition parameter γ of the active material in the negative electrode material is greater than or equal to 85%, and the deposition parameter γ is obtained by formula I, which is:

Wherein, _m1 is the mass of the negative electrode material, based on _m1 , the mass percentage of the active material is _a1 , and the specific pore volume of the negative electrode material is _p1 ; _m2 is the mass of the negative electrode material after removing the active material, based on _m2 , the mass percentage of the active material is _a2 , and the specific pore volume of the negative electrode material after removing the active material is _p2 ; ρ is the density of the active material.

In Formula I, the polynomial m ₂ × p ₂ -m ₁ × p ₁ represents the difference between the pore volume of the negative electrode material after active material removal and the pore volume of the provided negative electrode material, and is used to characterize the volume of the active material located within the pores of the carbon matrix in the provided negative electrode material. The polynomial m ₁ × a ₁ -m ₂ × a ₂ represents the difference between the mass of the active material in the provided negative electrode material and the mass of the active material in the negative electrode material after active material removal, and is used to characterize the total mass of the active material in the provided negative electrode material after acid removal (including all active material located within the pores of the carbon matrix and elsewhere in the carbon matrix). The ratio of the polynomial m ₁ × a ₁ -m ₂ × a ₂ to the density ρ of the active material corresponds to the total volume of the active material in the provided negative electrode material. Therefore, Formula I as a whole is used to characterize the proportion of active material located within the pores of the carbon matrix to the total active material in the negative electrode material. In some embodiments, taking silicon-based materials as active materials, ρ in Formula I can be 2.34, with the unit of g/cm ³ . The deposition parameter γ of the silicon-based material is calculated by Formula I, which can further characterize the proportion of the silicon-based material deposited in the pores of the carbon matrix.

In the related art, when the silicon-based material content reaches a certain level, some silicon-based material particles will begin to adhere to the surface of the carbon matrix, thereby significantly increasing the specific surface area of the composite material, resulting in increased contact between the composite material and the electrolyte and increased side reactions during the charge and discharge process, making it more difficult to maintain a stable SEI film; and, the silicon-based material particles attached to the surface of the carbon matrix are easily hydrolyzed during slurry preparation and battery use, producing a large amount of gas, thereby leading to decreased slurry stability and potential battery safety hazards; in addition, when the silicon-based material content is certain, a higher silicon-based material content on the surface of the carbon matrix means that the carbon matrix is filled with less silicon-based material, so that excess pores may be generated inside the particles, resulting in a decrease in the strength of the composite material particles.

The present application measures the pore volume change and mass change of the negative electrode material before and after removing the active material, and then characterizes the proportion of active material in the carbon matrix pores in the negative electrode material, that is, the deposition parameter γ. In the present application, the active material deposition parameter γ is greater than or equal to 0.85, so that most of the active material is attached to the pores of the carbon matrix, which can reduce the side reactions between the negative electrode material and the electrolyte during charging and discharging, improve the cycle performance of the battery, and reduce the hydrolysis of the active material during pulping and battery use, that is, reduce the generation of gas, and improve the safety performance of the battery. In addition, when the content of active material such as silicon-based material is certain, an increase in the content of active material such as silicon-based material in the carbon matrix pores can also increase the particle strength of the negative electrode material. In other embodiments, when the deposition parameter γ is less than 0.85, the specific pore volume, specific surface area, proportion of micropores (pores with a pore diameter less than or equal to 2 nm) and gas production of the obtained negative electrode material increase significantly, which is not conducive to achieving good electrochemical performance. This also shows that the present application has important practical application value in obtaining negative electrode materials with relatively more active substances in the pores of the carbon matrix by setting the deposition parameter γ to be greater than or equal to 0.85.

Specifically, the parameter γ can be any value between 0.85, 0.91, 0.93, 0.94, 0.95, 0.96, 0.97, 0.98, 0.99, etc., or other values not less than 0.85, and is not limited here. When γ ≥ 0.85, it indicates that a relatively large amount of active material is deposited in the pores inside the matrix.

In some embodiments, "removing active substances from the negative electrode material" includes mixing the negative electrode material with an acid solution. The negative electrode material is mixed with an acid solution of sufficient concentration, stirred thoroughly, and etched with the acid solution to remove, to a certain extent, the active substances within the pores of the carbon matrix of the negative electrode material and on the surface of the carbon matrix. The active substances are removed by washing and drying the etched negative electrode material. In some embodiments, the acid solution includes one or more of hydrochloric acid, nitric acid, and hydrofluoric acid.

In some embodiments, the distribution parameter M of the active material in the negative electrode material is 0.015≤M≤5. The distribution parameter M of the active material in the negative electrode material is obtained by the following formula: M=σ/a1; wherein, based on the mass of the negative electrode material, the mass percentage of the active material in the negative electrode material is a1%, the conductivity of the negative electrode material is σS/cm, and 16≤a1≤65 is defined, resulting in a value of M between 0.015 and 5.

The negative electrode material provided in the present application is limited to 16≤a1≤65, and the value of M is limited to between 0.015 and 5. When the content of active material is within this range, it can fully fill the pores in the carbon matrix. While improving the conductivity of the negative electrode material, it can also ensure other properties of the negative electrode material, such as good cycle performance and first coulombic efficiency, and ultimately form a negative electrode material with excellent performance in all aspects.

The negative electrode material includes an appropriate amount of active material and has an appropriate electrical conductivity. It should be noted that, using silicon as an example, as a semiconductor material, silicon has inherently poor electrical conductivity, with an electrical conductivity of only approximately ^10-7 S/cm. When silicon is combined with a carbon matrix, if the silicon-based material accounts for too high a proportion of the negative electrode material or is distributed more on the surface of the carbon matrix, a thicker electron layer will form, reducing the conductivity of the negative electrode material. When a1 < 16, it indicates that the silicon-based material accounts for too low a proportion of the negative electrode material, and a large number of pores are distributed within the carbon matrix, some of which are not filled with active material. As a result, the resulting negative electrode material has a large specific surface area. During the charge and discharge process of a battery prepared with this negative electrode material, the contact area between the negative electrode material and the electrolyte increases, increasing side reactions between the negative electrode material and the electrolyte, and the SEI film on the surface of the negative electrode material continues to thicken, thereby consuming excessive lithium salt. Furthermore, the volume effect easily causes electrical separation between the particles, resulting in a reduction in the battery's reversible capacity and coulombic efficiency. When a1＞65, the proportion of active substances in the negative electrode material is too high, and some active substances will begin to adhere to the surface of the carbon matrix, thereby significantly increasing the specific surface area of the negative electrode material, resulting in increased contact between the composite material and the electrolyte and increased side reactions during the charge and discharge process, making it more difficult to maintain a stable SEI film; in addition, the silicon-based material particles attached to the surface of the carbon matrix are easily hydrolyzed during slurry preparation and battery use, producing a large amount of gas, which leads to a decrease in slurry stability and potential battery safety hazards.

Specifically, M can be any value between 0.015, 0.081, 0.16, 0.22, 0.36, 0.68, 1.24, 1.98, 2.25, 2.87, 3.33, 3.89, 4.41, 4.88, 5, or other values within 0.015 to 5, and is not limited here. Therefore, it can be understood that when the value of M is within this range, it means that the negative electrode material includes an appropriate amount of active material. At the same time, the deposition parameter γ is not less than 0.85, that is, a relatively large amount of active material is distributed in the pores in the carbon matrix. The two characteristics of M and γ that meet the numerical range assist each other, so that the active material is relatively more and evenly deposited inside the matrix, building a smooth electron channel in the pores of the carbon matrix, and improving the conductivity of the negative electrode material.

In some embodiments, the median particle size D50 of the negative electrode material is 1 μm to 15 μm, specifically 1 μm, 1.8 μm, 3 μm, 5 μm, 7.5 μm, 8 μm, 8.8 μm, 9.2 μm, 10 μm, 12 μm, and 15 μm, etc., and of course other values within the above range are also possible, and are not limited here. It can be understood that the negative electrode material has good mechanical strength and high specific surface area within the above range, which is conducive to improving the cycle performance of the negative electrode material.

In some embodiments, the particle size distribution of the negative electrode material satisfies the following relationship: the particle size distribution satisfies: 0.1≤(D90-D10)/D50≤2. Specifically, it can be any value among 0.1, 0.3, 0.8, 1.4, 1.8 and 2. Of course, it can also be other values within the above range, which is not limited here. When the particle size of the negative electrode material is within the above range, different particle sizes can cooperate with each other, and small particles can be used to fill the gaps between large particles, thereby increasing the tap density of the negative electrode material.

It should be noted that the volume-based cumulative particle size distribution D10 measured by the laser diffraction method represents the particle size corresponding to when the cumulative particle size distribution percentage of the powder reaches 10%, D50 represents the particle size corresponding to when the cumulative particle size distribution percentage reaches 50%, and D90 represents the particle size corresponding to when the cumulative particle size distribution percentage reaches 90%.

In some embodiments, the micropore ratio of the negative electrode material is 10% to 30%.

In some embodiments, the mesopore ratio of the negative electrode material is 30% to 80%.

In some embodiments, the macropores in the negative electrode material account for 0-10%.

Understandably, since the size of the molecules produced by the electrolyte is generally smaller than or equal to the pore size of the micropores, under the action of the strong capillary adsorption capacity of the micropores, the adsorption capacity of the negative electrode material is largely proportional to the pore volume of the micropores. For example, as the volume of the micropores increases, the adsorption capacity of the negative electrode material increases, thereby increasing the side reactions between the negative electrode material and the electrolyte. Therefore, controlling the volume ratio of micropores, mesopores, and macropores in the negative electrode material within this range can improve the uniformity of the distribution of silicon material within the negative electrode material. Specifically, the micropores are basically filled with active material, and the remaining majority of the pores are mesopores. This can effectively alleviate the volume expansion of the active material and reduce the excessive local expansion stress caused by the uneven volume change of the active material during the cycle of the negative electrode material, which leads to the rupture and pulverization of the negative electrode material.

In some embodiments, the specific surface area of the negative electrode material is 0.1 ^{m 2} /g to 5 m ² /g. Specifically, the specific surface area can be any value among 0.1 ^{m 2} /g, 0.8 m ² /g, 1.4 m ² /g, 1.8 ^{m 2} /g, ^{2.5 m 2} /g, 3.2 ^m 2 /g, 4.1 m ² /g, 4.8 m 2 /g, and 5 ^{m 2} /g, or other values within the foregoing range. It is understood that the specific surface area of the negative electrode material affects the contact area between the negative electrode material and the electrolyte. A specific surface area of the negative electrode material within the foregoing range can reduce the amount of lithium ions consumed by the SEI film formed during the initial charge and discharge process of the lithium-ion battery, thereby reducing the irreversible capacity loss of the lithium-ion battery.

In some embodiments, the carbon matrix is a porous carbon-based material, and the porous carbon-based material includes at least one of hard carbon, soft carbon, graphite, mesocarbon microbeads, activated carbon, carbon gel, and the like.

In some embodiments, the active material includes one or more of a silicon-based material, a tin-based material, a germanium-based material, and a lead-based material. For example, a silicon-based material used as a component of the negative electrode active material can increase the specific capacity of the negative electrode material, thereby increasing the energy density of the secondary battery.

In some embodiments, the silicon-based material includes one or more of amorphous silicon, crystalline silicon, a composite of crystalline silicon and amorphous silicon, silicon oxide, and a silicon alloy. For example, amorphous silicon expands isotropically during lithium insertion, which can reduce pore collapse, inhibit rapid capacity decay of the negative electrode material, and improve the lithium insertion cycle performance of the negative electrode material.

In some embodiments, the active material includes a silicon material, which includes at least one of crystalline silicon, silicon oxide, amorphous silicon, a silicon alloy, and a mixture of crystalline and amorphous silicon. Specifically, the silicon alloy may be a silicon-lithium alloy, a silicon-magnesium alloy, or the like. In some cases, the silicon alloy includes elemental silicon particles and alloys.

In some embodiments, the purity of the silicon material is greater than 99%. High-purity silicon material is conducive to Li-Si alloying with lithium, thereby improving the cycle performance of lithium-ion batteries.

In some embodiments, the average particle size of the silicon material is 1 nm to 500 nm. Specifically, the average particle size of the silicon material can be any value among 1 nm, 150 nm, 210 nm, 340 nm, 400 nm, 470 nm and 500 nm, or other values within the above range, which can be selected according to actual needs. The mechanical stress of the silicon material during expansion decreases as the particle size decreases, so that the secondary battery maintains a good battery capacity and reduces irreversible capacity loss. The size reduction can shorten the electron and ion transmission path. At the same time, when the particle size of the silicon material decreases, the gap between adjacent silicon materials increases, which can reserve space for expansion. Preferably, the average particle size of the silicon material is 1 nm to 50 nm, and more preferably, the average particle size of the silicon material is 1 nm to 10 nm.

In some embodiments, when the active material is a silicon-based material, the above-mentioned "removal of active material from negative electrode material" includes: using 70% hydrochloric acid and 50% hydrofluoric acid in a volume ratio of 2:1 to form an acid solution, placing the negative electrode material in the acid solution and stirring for at least 10 hours, and then cleaning and drying the negative electrode material.

In some embodiments, the morphology of the active material includes one or more of point-shaped, spherical, ellipsoidal, and flake-shaped. The morphology of the silicon material can be selected according to actual needs and is not limited here.

In some embodiments, the purity of the active material is greater than 99%. Taking silicon-based materials as an example, high-purity silicon-based materials are more conducive to Li-Si alloying with lithium, thereby improving the cycle performance of lithium-ion batteries.

In some embodiments, the average particle size of the active material (such as a silicon-based material) is 0.1 nm to 50 nm. For example, the average particle size of the active material can be 0.1 nm, 0.5 nm, 1 nm, 3 nm, 5 nm, 8 nm, 10 nm, 20 nm, 30 nm, 40 nm, 50 nm, or any value within the range of any two of the above values. By setting the average particle size of the active material, the mechanical stress of the active material during volume expansion can be reduced, so that the secondary battery maintains a good battery capacity, and reduces irreversible capacity loss. It can also shorten the electron and ion transmission path. At the same time, the size of the active material is reduced, and the gap between adjacent active materials is increased, which can reserve space for the volume expansion of the active material.

In some embodiments, the average particle size of the active material is further preferably 0.1 nm to 5 nm. For example, the average particle size of the active material can be 0.1 nm, 0.3 nm, 0.5 nm, 0.8 nm, 1 nm, 2 nm, 3 nm, 4 nm, 5 nm, or any value within a range formed by any two of the foregoing values.

In some embodiments, the carbon matrix includes one or more of artificial graphite, natural graphite, amorphous carbon, activated carbon, mesocarbon microbeads, carbon nanotubes, carbon nanofibers, and graphene. The carbon matrix selected from these materials can provide pore distribution sites for the active material and form a conductive network.

In some embodiments, the pores of the carbon matrix include micropores, and the volume fraction of the micropores in the carbon matrix is greater than or equal to 70%, and the pore diameter of the micropores is less than 2 nm. Preferably, it is ≥80%, and more preferably ≥90%. For example, the volume fraction of the micropores in the carbon matrix can be 70%, 75%, 80%, 85%, 90%, 95%, 99%, or any value within a range consisting of any two of the above values. Controlling the micropore fraction of the carbon matrix within the above range can reduce the aggregation of active materials on the surface of the carbon matrix, increase the content of active materials in the carbon matrix and the uniformity of the distribution of active materials, thereby improving the specific capacity and mechanical properties of the negative electrode material. It can be understood that the pores of the carbon matrix are mainly micropores, which is conducive to the deposition of active materials, such as silicon materials, on the micropores within the carbon matrix. In addition, a high micropore fraction leads to higher cycling performance and first coulombic efficiency of the resulting battery.

In some embodiments, the average pore size of the carbon matrix is 0.1 nm to 5 nm, preferably 0.1 nm to 2 nm, and more preferably 0.1 nm to 1.8 nm. Specifically, it can be any value between 0.1 nm, 0.4 nm, 0.8 nm, 1.8 nm, 2 nm, 2.5 nm, 3.4 nm, 4.5 nm, and 5 nm, or other values within the above range, without limitation. The pore size distribution within this range facilitates the deposition of the active material during the deposition process, thereby improving the density of the negative electrode material.

In some embodiments, the specific pore volume of the carbon matrix is 0.3 cm ³ /g to 2 cm ³ /g based on the mass of the carbon matrix. For example, the specific pore volume of the carbon matrix can be 0.3 ^{cm 3 /g, 0.5 cm 3} /g, 0.8 cm ³ /g, ^{1 cm 3} /g, 1.5 cm 3 /g, 1.8 cm ³ /g, 2 cm ³ /g, or any value within a range formed by any two of the foregoing values. When the carbon matrix has abundant pores, these pores can accommodate the active material and reserve space for the volume expansion of the active material.

In some embodiments, the specific pore volume of the carbon matrix is 0.5 cm ³ /g to 1.4 cm ³ /g. For example, the specific pore volume may be 0.5 ^{cm 3} /g, 0.8 ^{cm 3} /g, 1 cm 3 /g, 1.2 cm ³ /g, 1.4 cm ³ /g, or any value within a range formed by any two of the foregoing values.

In some embodiments, based on the mass of the carbon matrix, the pore volume of the carbon matrix is ≥0.4 ^{cm 3} /g, preferably ≥0.5 ^{cm 3} /g, and more preferably ≥0.7 ^{cm 3} /g. Specifically, it can be any value among 0.4 ^{cm 3} /g, 0.5 cm ³ /g, ^{0.6 cm 3 /} g, 0.7 cm 3 /g, 0.8 cm ³ /g, 0.9 cm ³ /g or other values within the above range, and is not limited here. It can be understood that when the carbon matrix has abundant pores, these pores can accommodate active substances and reserve space for the volume expansion of the active substances. In addition, the higher the pore volume of the carbon matrix, the more active substances can be accommodated inside it, so that more active substances are deposited inside the carbon matrix, thereby improving the conductivity and cycle performance of the negative electrode material.

In some embodiments, the average particle size of the carbon matrix is 1 μm to 50 μm, and specifically can be any value between 1 μm, 8 μm, 12 μm, 25 μm, 32 μm, 43 μm and 50 μm, or other values within the above range.

In some embodiments, based on the mass of the negative electrode material, the mass percentage of the carbon element is 30% to 75%. Specifically, the mass percentage of the carbon element can be any value of 30%, 38%, 45%, 51%, 60%, 70%, 75% or other values within the above range.

In some embodiments, the total pore volume of the negative electrode material is less than the total pore volume of the carbon matrix. In the present application, the total pore volume of the negative electrode material is significantly lower than the total pore volume of the carbon matrix. This is because the active material can be relatively evenly filled in the pores within the porous skeleton of the carbon matrix, so that the pore volume of most of the pores of the carbon matrix is reduced after being filled with the active material. This indicates that the pores of the carbon matrix are effectively and relatively evenly filled with the active material, thereby increasing the specific capacity of the negative electrode material.

In some embodiments, the specific pore volume of the negative electrode material is 0.001 ^{cm 3} /g to 0.1 cm ³ /g. For example, the specific pore volume of the negative electrode material can be 0.001 cm 3 /g, 0.003 ^{cm 3 /g, 0.005 cm 3 /} g, 0.008 cm ³ /g, 0.01 cm ³ /g, 0.03 cm ³ /g, 0.05 cm ³ /g, 0.08 cm ³ /g, 0.1 cm ³ /g, or any value within the range formed by any two of the above values. After the pores of the carbon matrix are filled with active material, the remaining pores in the carbon matrix can reserve space for the volume expansion of the active material, alleviate the expansion effect of the negative electrode material, and improve the cycle stability of the negative electrode material. The remaining pores in the carbon matrix can also adsorb or accommodate a small amount of gas generated by the reaction of part of the active material with the electrolyte or pulping, thereby improving the gas generation phenomenon of the negative electrode material.

In some embodiments, the average pore size of the negative electrode material is 0.45 nm to 50 nm. For example, the average pore size of the negative electrode material can be 0.45 nm, 0.65 nm, 0.85 nm, 1 nm, 3 nm, 5 nm, 8 nm, 10 nm, 20 nm, 30 nm, 40 nm, 50 nm, or any value within the range formed by any two of the above values. The distribution of the active material in the pores of the carbon matrix will affect the specific pore volume and average pore size of the negative electrode material. For example, if the active material adheres more to the surface of the carbon matrix, the pore volume of the negative electrode material will be larger and the average pore size will be slightly reduced. Controlling the average pore size of the pores in the negative electrode material will facilitate the passage of lithium ions through the pores of the negative electrode material, while improving the charge and discharge rate performance of the negative electrode material, and is conducive to buffering the volume expansion of the active material and improving the structural stability of the negative electrode material. In the present embodiment, most of the active material is distributed in the pores of the carbon matrix. Therefore, the average pore size of the negative electrode material formed will increase.

In some embodiments, the pores of the negative electrode material include micropores, the volume fraction of the micropores in the negative electrode material is less than or equal to 10%, and the pore diameter of the micropores is less than or equal to 2 nm. For example, the volume fraction of the micropores in the negative electrode material can be 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, or any value within a range formed by any two of the foregoing values. In some preferred embodiments, the volume fraction of the micropores in the negative electrode material is 1% to 9%.

In some embodiments, the pores of the negative electrode material include mesopores, and the volume fraction of the mesopores in the pores of the negative electrode material is greater than or equal to 80%, and the pore diameter of the mesopores is greater than 2 nm and less than or equal to 50 nm. For example, the volume fraction of the mesopores in the negative electrode material can be 80%, 85%, 90%, 95%, 96%, 97%, 98%, 99%, or any value within a range formed by any two of the foregoing values. In some preferred embodiments, the volume fraction of the mesopores in the negative electrode material is 85% to 94%.

In some embodiments, the pores of the negative electrode material include macropores, the macropores account for less than or equal to 20% of the volume of the pores in the negative electrode material, and the pore diameter of the macropores is greater than 50 nm. For example, the volume percentage of the macropores in the negative electrode material can be 1%, 3%, 5%, 8%, 10%, 13%, 15%, 18%, 20%, or any value within a range between any two of the foregoing values. In some preferred embodiments, the volume percentage of the macropores in the negative electrode material is 1% to 14%.

Since the size of the molecules produced by the electrolyte is generally smaller than or equal to the pore size of the micropores, under the action of the strong capillary adsorption capacity of the micropores, the adsorption capacity of the negative electrode material is largely proportional to the pore volume of the micropores. For example, as the volume of the micropores increases, the adsorption capacity of the negative electrode material increases, thereby increasing the side reaction between the negative electrode material and the electrolyte. Therefore, controlling the pore volume ratio of the micropores of the negative electrode material can reduce the reaction sites where the negative electrode material and the electrolyte undergo side reactions, thereby reducing the thickening of the solid electrolyte membrane (SEI membrane) caused by the continuous intrusion of the electrolyte, which is beneficial to improving the cycle performance of the negative electrode material. In addition, the distribution of pores is also closely related to the deposition of active substances. For example, if the active substance is deposited in the pores of the carbon matrix, the proportion of micropores in the material is small. If the active substance is deposited on the surface of the carbon matrix, a good sealing effect (especially micropores) cannot be achieved, which will increase the volume ratio of micropores in the material. Mesopores with an increased volume ratio can reserve sufficient buffer space for the volume expansion of active materials, effectively alleviate the volume expansion of active materials, and reduce the risk of excessive local expansion stress and pulverization of negative electrode materials due to uneven volume changes of active materials during the cycle, which is beneficial to improving the particle structure stability and cycle stability of negative electrode materials. Macropores with a smaller volume and area ratio (i.e., a small number of macropores and a small volume ratio) can increase the tap density and compaction density of negative electrode materials, reduce the problems of breakage and cracking of negative electrode materials during the roller pressing process, and improve the processing performance of negative electrode materials. Controlling the volume ratio of micropores, mesopores, and macropores in negative electrode materials within the above range can help improve the uniformity of the distribution of active materials inside the negative electrode materials.

In some embodiments, the specific surface area of the negative electrode material is ^0.5m2 /g to ^10m2 /g. For example, the specific surface area of the negative electrode material can be ^0.5m2 /g, ^1m2 /g, ^2m2 /g, 3m2/g, ^4m2 /g, ^5m2 /g, ^6m2 /g, ^7m2 /g, ^8m2 /g, ^9m2 / ^g , ^10m2 /g, or any value within the range formed by any two of the above values. When the specific surface area of the negative electrode material is large, the SEI film will consume excessive lithium salt, and the volume effect will easily cause electrical separation between the particles, resulting in a decrease in the reversible capacity and coulombic efficiency of the battery. Therefore, the specific surface area of this embodiment is small, which can effectively improve the first discharge specific capacity and first coulombic efficiency of the battery.

In some embodiments, the particle size D50 of the negative electrode material is 5 μm to 20 μm. For example, the particle size D50 of the negative electrode material can be 5 μm, 8 μm, 10 μm, 13 μm, 15 μm, 18 μm, 20 μm or any value within the range formed by any two of the above values. The D50 of the negative electrode material is within the above range, which is beneficial to the improvement of the cycle performance of the negative electrode material. In some embodiments, the particle size distribution (D90-D10)/D50 of the negative electrode material of the present application is 0.9 to 5. For example, the particle size distribution (D90-D10)/D50 of the negative electrode material can be 0.9, 1, 1.2, 1.5, 2, 2.6, 3, 3.5, 4, 4.3, 4.6, 4.8, 5 or any value within the range formed by any two of the above values.

In some embodiments, the negative electrode material has a compaction density at a pressure of 1 T of 0.8 g/cm ³ to 1.3 g/cm ³ . For example, the negative electrode material of the present application may have a compaction density at a pressure of 1 T of 0.8 g/cm ³ , 0.9 g/cm ³ , 1.0 g/cm ³ , 1.1 g/cm ³ , 1.2 g/cm ³ , 1.3 g/cm ³ , or any value within a range consisting of any two of the foregoing values. Controlling the compaction density within the foregoing range helps reduce the diffusion path of lithium ions in the negative electrode material, thereby improving the rate performance of the battery.

In some embodiments, the tap density of the negative electrode material after 3000 vibrations is between 0.5 g/cm ³ and 1.5 g/cm ³ . For example, the tap density can be 0.5 g/cm ³ , 0.7 g/cm ³ , 0.9 g/cm ³ , 1.1 g/cm ³ , 1.3 g/cm ³ , 1.5 g/cm ³ , or any value within a range formed by any two of the foregoing values. Controlling the tap density within the foregoing range facilitates forming an appropriate degree of compactness in the internal structure of the negative electrode material, thereby improving lithium ion transport and electron conduction, increasing battery energy density, extending cycle life, and enhancing safety performance.

In some embodiments, the powder conductivity of the negative electrode material under a pressure of 20 kN is 0.5 S/cm to 2 S/cm. For example, the powder conductivity of the negative electrode material can be 0.5 S/cm, 0.7 S/cm, 0.9 S/cm, 1.1 S/cm, 1.3 S/cm, 1.5 S/cm, 1.7 S/cm, 1.9 S/cm, 2.0 S/cm, or any value within a range formed by any two of the foregoing values.

In some embodiments, the average gas production of the negative electrode material at a temperature of 25°C over 7 days is less than or equal to 1 mL/g. For example, the average gas production of the negative electrode material at a temperature of 25°C over 7 days can be 0.1 mL/g, 0.3 mL/g, 0.5 mL/g, 0.7 mL/g, 0.9 mL/g, 1.0 mL/g, or any value within the range formed by any two of the above values. The gas production value of the negative electrode material is controlled within the above range, indicating that most of the active material can be relatively evenly distributed in the pores of the carbon matrix, and the direct contact between the active material and the electrolyte is reduced, thereby reducing the side reactions of the dissolved active material with the electrolyte or slurry (such as silicon hydrolysis into silicate and hydrogen), effectively reducing the gas production value of the negative electrode material.

In some embodiments, the average gas production of the negative electrode material over 24 hours at a temperature of 25°C is less than 0.15 mL/g. For example, the average gas production of the negative electrode material over 24 hours at a temperature of 25°C can be 0.052 mL/g, 0.07 mL/g, 0.09 mL/g, 0.1 mL/g, 0.11 mL/g, 0.13 mL/g, or any value within the range formed by any two of the above values. The gas production value of the negative electrode material is controlled within the above range, indicating that most of the active material can be relatively evenly distributed in the pores of the carbon matrix, and the direct contact between the active material and the electrolyte is reduced, thereby reducing the side reactions of the dissolved active material with the electrolyte or slurry (such as the hydrolysis of silicon into silicate and hydrogen), effectively reducing the gas production value of the negative electrode material.

In some embodiments, the mass percentage of carbon in the negative electrode material is 40% to 60% based on the mass of the negative electrode material. The carbon comprises both the carbon matrix and the carbon coating. When the mass percentage of carbon is within this range, a sufficient carbon-based matrix can be established, providing ample distribution sites for the active material, thereby forming an effective conductive network and improving the conductivity and cycle stability of the negative electrode material.

In some embodiments, the mass percentage of silicon in the negative electrode material is 37% to 55% based on the mass of the negative electrode material. When the mass percentage of silicon is within this range, the resulting lithium battery can store a higher amount of electricity, i.e., has a higher initial discharge specific capacity.

In some embodiments, the negative electrode material further comprises a coating layer, the coating layer being disposed on at least a portion of the surface of the carbon substrate, the coating layer comprising a carbon material, the carbon material comprising one or more of graphene, soft carbon, and hard carbon. The coating layer located on the outer layer of the negative electrode material has good electrical conductivity, which can improve the electrical conductivity of the negative electrode material. On the other hand, it can coat the active material exposed on the surface of the carbon substrate, thereby reducing the continuous oxidation of the exposed active material during storage, and reducing the reduction in the specific capacity and first coulombic efficiency (ICE) of the negative electrode material. The coating layer can also reduce direct contact between the active material and the electrolyte, improve the stability of the SEI film, and thus improve the first coulombic efficiency of the negative electrode material.

In some embodiments, the coating layer can be a single layer formed of a single material, a coating layer formed of a combination of multiple materials, a multi-layer coating layer formed of a single material, or a multi-layer coating layer formed of multiple materials. The layer structure of the coating layer can be selected according to actual needs. It is understood that a multi-layer coating structure has a higher density.

In some embodiments, the thickness of the coating layer is 1 nm to 300 nm. For example, the thickness of the coating layer can be 1 nm, 30 nm, 50 nm, 150 nm, 200 nm, 250 nm, 300 nm, or any value within the range formed by any two of the above values. The coating layer can reduce the solubility of the negative electrode material, thereby reducing the amount of gas produced by the reaction of the dissolved active material with the electrolyte. Controlling the thickness of the coating layer within the above range is beneficial to maintaining the stability of the particle structure of the negative electrode material during the cycle, can reduce the exposed active material on the surface of the negative electrode material, reduce the exposed active material causing a large amount of SEI to be generated during the charge and discharge process, and improve the specific capacity and electrochemical performance of the negative electrode material.

In some embodiments, the coating layer preferably has a thickness of 1 nm to 50 nm, more preferably 1 nm to 30 nm, thereby facilitating rapid and reversible intercalation and deintercalation of lithium ions.

In some embodiments, the mass percentage of the coating layer in the negative electrode material is less than or equal to 10%. For example, the mass percentage of the coating layer in the negative electrode material can be 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, 1%, or any value within the range formed by any two of the above values. The coating layer can reduce the solubility of the negative electrode material, thereby reducing the amount of gas generated by the reaction of the dissolved active material with the electrolyte. The mass percentage of the coating layer in the negative electrode material within the above range can ensure the amount of lithium that can be inserted into the negative electrode material, thereby ensuring the charge and discharge capacity of the lithium-ion battery prepared with the negative electrode material.

The negative electrode active layer also contains a binder for bonding the negative electrode material particles to facilitate the formation of a film layer, while also being able to improve the bonding force between the negative electrode active layer and the negative electrode current collector.

In some embodiments, the binder may include but is not limited to polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene 1,1-difluoride, polyethylene, polypropylene, sodium carboxymethyl cellulose, sodium alginate, sodium polyacrylate, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin or nylon, etc.

The separator includes a porous membrane layer, and its material includes, but is not limited to, at least one of polyethylene, polypropylene, polyvinylidene fluoride, polyethylene terephthalate, polyimide, or aramid. For example, the separator can be a polypropylene porous membrane, a polyethylene porous membrane, a polypropylene non-woven fabric, a polyethylene non-woven fabric, or a polypropylene-polyethylene-polypropylene porous composite membrane.

The above-mentioned battery is applied to an electronic device to power other electronic components in the electronic device. The use of the lithium-ion battery of the present application is not particularly limited, and it can be used in any electronic device known in the prior art. In some embodiments, the lithium-ion battery of the present application can be used for, but not limited to, laptop computers, pen-input computers, mobile computers, e-book players, portable phones, portable fax machines, portable copiers, portable printers, head-mounted stereo headphones, video recorders, LCD TVs, portable cleaners, portable CD players, mini-discs, transceivers, electronic notepads, calculators, memory cards, portable recorders, radios, backup power supplies, motors, cars, motorcycles, power-assisted bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, large household batteries and lithium-ion capacitors, etc.

Another embodiment of the present application provides a method for preparing a negative electrode material, comprising:

Step 1: Mix the carbon matrix, zinc salt and organic surfactant, which includes one or more of polyvinyl alcohol (PVA), polyvinyl pyrrolidone (PVP), and poloxamer (Pluronic F127). Heat under a reducing gas atmosphere to reduce the zinc ions in the zinc salt and attach them to the carbon matrix to obtain the first precursor.

The carbon matrix has pores, and the zinc ions can adhere to the surface of the carbon matrix or to the pores of the carbon matrix after reduction. The organic active agent can act to promote the deposition of the zinc salt on the carbon matrix. The first precursor is a carbon matrix precursor with elemental zinc metal attached both in the pores and on the surface. The organic active agent has amino and hydroxyl groups and can be a non-ionic active agent or an anionic active agent, which can promote the adhesion and reduction of the zinc salt on the surface and in the pores of the carbon matrix.

In some embodiments, the zinc salt includes one or more of zinc chloride, zinc nitrate, zinc acetate, and zinc sulfate.

In some embodiments, the reducing gas includes hydrogen. It is understood that the reducing gas atmosphere may further include an inert gas, for example, the reducing gas atmosphere may be hydrogen, a mixture of hydrogen and helium, a mixture of hydrogen and nitrogen, etc.

In some embodiments, the heating temperature is 600° C. to 800° C., and the heating time is 2 h to 6 h.

Step 2: Mix the first precursor with an acid solution with a concentration of 0.5 mol/L to 2 mol/L to dissolve and remove zinc attached to the surface of the carbon matrix. The dissolution time is 1 hour to 20 hours to obtain the second precursor.

The acid solution can act on the metallic zinc attached to the surface of the carbon matrix while also reducing the reaction between the metallic zinc within the pores of the carbon matrix and the acid solution, thereby producing a carbon matrix precursor with metallic zinc attached to the pores, i.e., the second precursor. By controlling the concentration of the acid solution and the dissolution time within the aforementioned ranges, the carbon matrix precursor dissolves in the acid solution, thereby cleaning and removing the zinc from the surface of the carbon matrix precursor while minimizing the reaction between the zinc within the pores of the carbon matrix precursor and the acid solution.

In some embodiments, the acid solution includes one or two of hydrochloric acid, sulfuric acid, nitric acid, and phosphoric acid.

Step 3: Mix the second precursor with the active material precursor and perform vapor deposition to deposit the active material in the pores of the carbon matrix to obtain the negative electrode material.

During the vapor deposition process, under the catalytic action of metallic elemental zinc, the active substance is deposited in the pores of the carbon matrix, so that the active substance in the prepared negative electrode material is mainly distributed in the pores of the carbon matrix, thereby reducing the reaction between the active substance attached to or dissolved from the surface of the negative electrode material and the electrolyte, effectively reducing the gas production value of the negative electrode material and increasing the powder conductivity of the negative electrode material, thereby improving the various performances of the battery prepared with the negative electrode material.

In some embodiments, the active material precursor includes a silicon-containing gas, and the silicon-containing gas includes one or more of silane, disilane, trisilane, and tetrasilane.

In some embodiments, the concentration of the silicon-containing gas is 10% to 80%. Further, the gas used to dilute the silicon-containing gas can be selected from one or both of an inert gas and hydrogen.

In some embodiments, the temperature of vapor deposition is 400°C to 600°C. For example, the temperature of vapor deposition can be 400°C, 420°C, 450°C, 470°C, 490°C, 500°C, 530°C, 550°C, 580°C, 600°C or any value within the range formed by any two of the above values.

In some embodiments, the vapor deposition time is 1 hour to 20 hours. For example, the vapor deposition time can be 1 hour, 2 hours, 5 hours, 8 hours, 10 hours, 15 hours, 18 hours, 20 hours, or any value within the range formed by any two of the above values.

The process conditions of vapor deposition (such as deposition temperature and deposition time) will affect the deposition of silicon particles in the pores of the carbon material. Controlling the temperature and time of vapor deposition within the above range can ensure that the reaction gas does not decompose and deposit before entering the pores of the carbon material, but quickly decomposes and deposits after entering the pores.

As shown in FIG1 , this application introduces a method for preparing a negative electrode material in conjunction with an embodiment, which includes the following steps:

S100: adding an active agent to the carbon-based raw material for activation, and then performing acid washing after activation to obtain a carbon-based precursor, and drying the carbon-based precursor to obtain a porous carbon precursor, wherein the active agent is a compound containing metal ions.

In some embodiments, the active agent includes at least one of potassium ferrate, nickel nitrate, ferric chloride, ferric nitrate, cobalt nitrate, nickel chloride, cobalt chloride, ferric bromide, cobalt bromide, nickel bromide, ferric carbonate, cobalt carbonate, nickel carbonate, etc., and the amount of the active agent added is 0.2% to 5% of the mass of the carbon-based raw material. The above-mentioned active agent has a strong activation ability and can form a large number of evenly distributed micropores in the porous carbon precursor, with the proportion of micropores not less than 70%, which is conducive to the subsequent filling of active substances in the micropores of the porous carbon precursor. If the amount of the activator added exceeds 5%, the pore size of the porous carbon precursor will be larger and the number of pores will be larger, which may easily lead to structural collapse of the negative electrode material during the deintercalation process, resulting in a decrease in the cycle performance of the negative electrode material. At the same time, the proportion of micropores in the porous carbon precursor is reduced, and the content of metal impurities is too high, which may easily affect other properties of the negative electrode material, such as reducing the first coulomb efficiency. If the amount of activator added is too small, it is impossible to form an appropriate number of activated pores with uniform distribution inside the porous carbon precursor, which is not conducive to the subsequent deposition of silicon material in the pores of the porous carbon precursor, causing a large amount of silicon material to be deposited on the surface of the porous carbon precursor, resulting in a large volume expansion of the negative electrode material. In addition, the silicon material deposited on the surface of the porous carbon precursor increases the contact area with the electrolyte, making it easier to contact the electrolyte, increasing the thickness of the SEI film on the surface of the negative electrode material, increasing the diffusion distance of lithium ions, hindering the smooth deintercalation of lithium ions, and ultimately causing the loss of the capacity of the negative electrode material. Moreover, since the silicon material cannot be deposited inside the porous carbon precursor, the M value and deposition coefficient γ of the negative electrode material are not within the preset value range of this application, and the conductivity of the formed negative electrode material is far lower than 1S/cm.

In some embodiments, the activation temperature is 500-1200° C., and the activation time is 0.5-20 h.

At this activation temperature and time, the activator is embedded in the internal structure of the carbon-based raw material, undergoes cross-linking or condensation reactions with the carbon atoms and heteroatoms in the carbon-based raw material, and volatilizes and removes non-carbon atoms N and H, causing some carbon atoms to be etched away. Holes appear at the etched locations, and the average pore size of the formed holes is small and the pore volume is high, which helps to accommodate more silicon material and allows silicon material to be deposited in the holes.

In some embodiments, the carbon-based material includes but is not limited to at least one of bamboo charcoal, coconut shell, graphite, peanut shell, fruit shell and resin. When the carbon-based raw material is a hard carbon-based raw material with an amorphous structure such as coconut shell, bamboo charcoal, peanut shell and fruit shell, it needs to be carbonized first, while for shaped raw materials such as graphite, it only needs to be directly mixed with an activator for activation. It should be noted that the carbon inside the carbon-based material with an amorphous structure is in an amorphous state, so the cost is low, and accordingly, the conductivity is also low, generally between 1 and 100 S/cm, while graphite, as a layered crystal structure, has a higher conductivity, but its processing cost is high. Therefore, in actual use, carbon-based raw materials with an amorphous structure are generally used. The carbon-based raw material is pre-treated so that it can evenly deposit the active material inside, thereby improving the conductivity of the formed negative electrode material and making up for the low conductivity of the active material itself.

In some embodiments, the activated carbon-based raw material is pickled with hydrochloric acid, wherein the concentration of the hydrochloric acid is 12% to 25%, and the pickling time is 5 hours to 6 hours to obtain a carbon-based precursor, and the pickled carbon-based precursor is dried to obtain a porous carbon precursor.

Hydrochloric acid cleaning is used to remove metal impurities in the carbon-based raw materials and impurities in the carbon-based materials themselves, thereby opening up the pore structure of the carbon-based raw materials and increasing the specific surface area and micropore diameter of the porous carbon precursor.

S200: Pre-treating the porous carbon precursor to obtain a carbon matrix.

The specific operation of the pretreatment is: placing the porous carbon precursor with a catalyst containing metal ions and an organic active agent in an aqueous solution, mixing and drying, then heating and reducing under a reducing atmosphere to obtain a carbon material with metal elements attached, and finally dispersing the carbon material in an acid solution for dissolution, removing the metal element particles on the surface of the carbon material, and obtaining a carbon matrix.

In some embodiments, the catalyst containing metal ions is specifically a catalyst containing zinc ions, and the compound can be a mixture of one or more of zinc chloride, zinc nitrate, zinc acetate, and zinc sulfate.

In some embodiments, the organic active agent is at least one of polyoxyethylene polyoxypropylene ether block copolymer (Pluronic F127), polyvinyl alcohol (PVA), and polyvinyl pyrrolidone (PVP).

In some embodiments, the reducing atmosphere is at least one of a mixed gas of hydrogen, helium, nitrogen, etc.

In some embodiments, the acid solution is at least one of dilute hydrochloric acid and dilute nitric acid, and the cleaning time of the acid solution is 1 to 12 hours, and the concentration is 0.5 to 1 mol/L. The acid solution is used to clean and remove metallic zinc attached to the surface of the carbon material, while also reducing the reaction between metallic zinc within the carbon material particles and the acid solution, thereby obtaining a carbon matrix with metallic zinc attached to the particles.

S300: performing vapor deposition on the carbon substrate using a silicon source to obtain a vapor deposition product.

In some embodiments, the silicon source includes at least one of monosilane, disilane, isosilane, and trisilane. The silicon source is vapor-deposited onto the carbon substrate to which the metallic zinc is attached. The metallic zinc catalyzes the deposition of the silicon material within the particles of the carbon substrate. In the prepared negative electrode material, the silicon material is primarily distributed within the particles of the carbon substrate, thereby facilitating electron transport and improving the powder conductivity of the negative electrode material.

In some embodiments, the deposition conditions for silicon deposition are: setting the ambient vacuum pressure to p Pa, the silane gas concentration to N%, the flow rate to V L/min, satisfying α=N*V2/p, and the value of α is: 0.1≤α≤50.

By regulating the vacuum pressure, silane gas concentration, and gas flow rate of the vapor deposition environment, uniform deposition of silicon is achieved within the carbon matrix. Specifically, the silicon source is precipitated into silicon material that is dispersed in the pores of the porous carbon matrix. The resulting negative electrode material has a uniform composition and a relatively dense structure. The volume expansion is buffered by the voids within the porous carbon matrix, resulting in a low expansion rate and excellent cycle performance. In addition, the carbon matrix skeleton is not only low in production cost, but also has excellent lithium storage capacity. In addition, the carbon matrix skeleton itself has a low density and light weight, which makes the formed negative electrode material have a high energy density. Moreover, when the value of α is between 0.1 and 50, a relatively large amount of silicon is uniformly deposited in the gaps within the porous carbon matrix. After testing, the deposition coefficient γ of the formed negative electrode material is not less than 0.85, and the value of M is between 0.015 and 5. In practical application, the conductivity is not less than 0.7S/cm, and the highest even reaches 80S/cm.

In some embodiments, the reaction temperature of silicon deposition is 400-800° C., and the time is 1-13 hours.

When the silicon deposition time is less than 1 hour, the overall content of the silicon material is low and it is difficult to deposit evenly inside the carbon matrix. When the silicon deposition time exceeds 13 hours, some silicon overflows and deposits on the surface of the carbon matrix. As a result, the silicon material on the surface of the carbon matrix is easily contacted and reacted with the electrolyte, thereby increasing the gas production value of the negative electrode material. In addition, after the silicon material is deposited on the surface of the carbon matrix, it continues to grow, which will cause the particles to pulverize and fall off, thereby reducing the electrochemical performance of the negative electrode material.

S400: mixing the vapor deposition product and the coating material and performing heat treatment to obtain a negative electrode material.

In some embodiments, the coating material includes at least one of a carbon material, a metal oxide, a conductive polymer, a fluoride, a phosphate, and a nitride, which are not specifically limited herein.

In some embodiments, the coating material includes a carbon material, and the carbon material includes at least one of soft carbon and hard carbon, which is not specifically limited herein.

In some embodiments, the coating material includes a metal oxide, and the metal oxide includes at least one of titanium oxide, aluminum oxide, lithium oxide, cobalt oxide, and vanadium oxide, which are not specifically limited herein.

In some embodiments, the coating material includes nitride, and the nitride includes at least one of titanium nitride, vanadium nitride, cobalt nitride, nickel nitride, and carbon nitride, which are not specifically limited herein.

In some embodiments, the coating material includes a conductive polymer, and the conductive polymer includes at least one of polyaniline, polyacetylene, polypyrrole, polythiophene, poly-3-hexylthiophene, poly(p-phenylene vinylene), polypyridine, and poly(phenylene vinylene), which are not specifically limited herein.

In some embodiments, the coating material includes a fluoride, and the fluoride includes at least one of vinyl fluoride, fluoropolymer, lithium fluoride, sodium fluoride, potassium fluoride, fluorocarbon polymer, fluorosilicone polymer, hexafluorobutyl acrylate, polytetrafluoroethylene, fluorinated ethylene-propylene copolymer, perfluoroalkoxy resin, polychlorotrifluoroethylene, ethylene-chlorotrifluoroethylene copolymer, polyvinylidene fluoride and polyvinyl fluoride, without specific limitation herein.

In some embodiments, the coating material includes phosphate, and the phosphate includes at least one of magnesium phosphate, calcium phosphate, aluminum phosphate, titanium phosphate, chromium phosphate, cobalt phosphate, nickel phosphate, germanium phosphate, zirconium phosphate, niobium phosphate, molybdenum phosphate, tantalum phosphate, tungsten phosphate, and lanthanum phosphate, without specific limitation herein.

In some embodiments, the coating material forms a coating layer on the surface of the carbon matrix, and the thickness of the coating layer is 1 to 500 nm. Specifically, the thickness of the coating layer can be 1 nm, 10 nm, 50 nm, 100 nm, 200 nm, 300 nm, or 500 nm. It can be understood that the coating layer can reduce the solubility of the negative electrode material, thereby reducing the amount of gas produced by the reaction of the dissolved silicon material with the electrolyte. Controlling the thickness of the coating layer within the above range is beneficial to maintaining the stability of the particle structure of the negative electrode material during the cycle, reducing the dissolution of the silicon material, and is beneficial to improving the transmission efficiency of lithium ions and enhancing the charge and discharge performance of the negative electrode material.

The present invention will be explained below in conjunction with the embodiments. It will be understood by those skilled in the art that the following examples are only used to explain the present invention and are not to be construed as limiting the present invention. Unless otherwise indicated, the reagents, software, and instruments not specifically described in the following examples are all conventional commercially available products or open source.

Example 1:

(1) Weigh 1.7 kg of zinc acetate and 360 g of Pluronic F127 and dissolve them in 20 L of water. Then add 4.4 kg of activated carbon, stir for 24 h, and filter and dry.

(2) placing the obtained material in a rotary kiln and calcining it at 800° C. in a 10 vol % hydrogen/argon mixed atmosphere for 4 h to obtain a first precursor;

(3) The first precursor was placed in 10 L 0.5 mol/L dilute hydrochloric acid and stirred for 6 h. The sample was then washed with pure water and dried for later use to obtain the second precursor.

(4) The second precursor was placed in a CVD device, and then silane was introduced into the CVD device, with the volume concentration ratio of silane and _N2 being 1:3 (the concentration of silicon-containing gas was 25%), the temperature was raised to 500°C, the reaction was carried out for 5 hours, and the deposition pressure was set to 10 kPa to obtain the negative electrode material.

Example 2:

The difference from Example 1 is that in step (1), zinc acetate is replaced by zinc chloride, and Pluronic F127 is replaced by PVA.

Example 3:

The difference from Example 1 is that in step (1), zinc acetate is replaced by zinc chloride.

Example 4:

The difference from Example 1 is that in step (1), zinc acetate is replaced by zinc nitrate, and Pluronic F127 is replaced by PVP.

Example 5:

The difference from Example 1 is that in step (1), zinc acetate is replaced by zinc nitrate.

Example 6:

The difference from Example 1 is that in step (1), Pluronic F127 is replaced by PVA.

Example 7:

The difference from Example 1 is that in step (3), 0.5 mol/L dilute hydrochloric acid is replaced by 0.75 mol/L dilute hydrochloric acid.

Example 8:

The difference from Example 1 is that in step (3), 0.5 mol/L dilute hydrochloric acid is replaced by 1 mol/L dilute hydrochloric acid.

Example 9:

The difference from Example 1 is that in step (3), the stirring time is adjusted to 1 hour.

Example 10:

The difference from Example 1 is that in step (3), the stirring time is adjusted to 12 hours.

Example 11:

The difference from Example 1 is that in step (3), 0.5 mol/L dilute hydrochloric acid is replaced by 2 mol/L dilute hydrochloric acid.

Example 12:

The difference from Example 1 is that in step (3), the stirring time is adjusted to 20 hours.

Example 13:

The difference from Example 1 is that in step (4), the deposition temperature is adjusted to 400°C.

Example 14:

The difference from Example 1 is that in step (4), the deposition time is adjusted to 20 h.

Example 15:

The difference from Example 1 is that in step (4), the deposition time is adjusted to 1 h.

Example 16:

The difference from Example 1 is that in step (4), the deposition temperature is adjusted to 600°C.

Comparative Example 1:

The difference from Example 1 is that step (3) is not performed.

Comparative Example 2:

The difference from Example 1 is that in step (3), 0.5 mol/L dilute hydrochloric acid is replaced by 0.2 mol/L dilute hydrochloric acid.

Comparative Example 3:

The difference from Example 1 is that in step (3), the stirring time is adjusted to 0.5 hours.

Comparative Example 4:

The difference from Example 1 is that in step (3), 0.5 mol/L dilute hydrochloric acid is replaced by 2.2 mol/L dilute hydrochloric acid.

Comparative Example 5:

The difference from Example 1 is that in step (3), the stirring time is adjusted to 21 hours.

Comparative Example 6:

The difference from Example 1 is that in step (1), Pluronic F127 is replaced by polyquaternium-16.

Comparative Example 7:

The difference from Example 1 is that in step (1), Pluronic F127 is replaced by benzalkonium bromide.

Comparative Example 8:

The difference from Example 1 is that in step (1), Pluronic F127 is eliminated and no other components are replaced.

Example 17:

(1) The coconut shell is placed in a carbonization furnace for carbonization at a specific carbonization temperature of 900°C and a carbonization time of 3 hours. The carbonized carbon-based material is mixed with potassium ferrate ( _K2FeO4 ), wherein the mass addition amount of potassium ferrate is 1% of the mass of _the coconut shell, and activated at 800°C for 10 hours. Then, hydrochloric acid is added for pickling at a concentration of 20% and a washing time of 5 hours to obtain a carbon-based precursor. The pickled carbon-based precursor is dried to obtain a porous carbon precursor.

(2) Weigh 1.7 kg of zinc acetate and 360 g of Pluronic F127 and dissolve them in 20 L of water. Then add 4.4 kg of porous carbon precursor, stir for 24 hours, and filter and dry. Then place the obtained material in a rotary kiln and calcine it at 800 ° C and 10 vol% hydrogen/argon mixed atmosphere for 4 hours to obtain a black powder sample. Finally, place the obtained black powder sample in 10 L of 0.5 mol/L dilute hydrochloric acid and stir for 6 hours. Then, wash the sample with pure water and dry it for use to obtain a carbon matrix.

(3) The carbon substrate was placed in a chemical vapor deposition (CVD) device, the vacuum degree was set to 8000 Pa, and then silane was introduced into the CVD device, the silane concentration was controlled to 50%, the gas velocity was 50 L/min, the temperature was raised to 600 ° C, and the reaction was carried out for 4 hours to obtain the vapor deposition product.

(4) The vapor deposition product and polyvinyl chloride were mixed in a mass ratio of 50:20, and then the mixed material was placed in a high-temperature box furnace, nitrogen was introduced, and heat treated at 660°C for 2 hours. The obtained sample was crushed, sieved and graded to obtain a negative electrode material.

In this embodiment, the negative electrode material includes a carbon matrix and a silicon material, and the silicon material is located in the carbon matrix. The deposition coefficient γ, M value, conductivity and silicon content of the negative electrode material are shown in Table 4.

As shown in FIG2 , it is a scanning electron microscope (SEM) image of the negative electrode material prepared in Example 17. It can be seen from the image that the particle shape is irregular.

As shown in FIG3 , this is the XRD pattern of the negative electrode material prepared in Example 17. It can be observed from the figure that the product is amorphous.

As shown in FIG4 , this is the first charge and discharge curve of the negative electrode material prepared in Example 17. It can be seen from the figure that the first charge and discharge capacity of the negative electrode material in Example 17 is 2098 mAh/g, and the first efficiency is 93.1%.

As shown in FIG5 , this is a diagram of the conductivity of the negative electrode material prepared in Example 17. It can be seen from the figure that the conductivity of Example 17 increases with increasing pressure and far exceeds the conductivity of the sample in Comparative Example 9.

Example 18

(1) Bamboo charcoal is placed in a carbonization furnace for carbonization at a specific carbonization temperature of 1200°C and a carbonization time of 4 hours. A mixture of nickel nitrate and potassium hydroxide (mass ratio of 1:89) is added to the treated carbon-based material, wherein the mass addition amount of the mixture of nickel nitrate and potassium hydroxide is 2.5% of the mass of the bamboo charcoal, and the mixture is activated at 800°C for 10 hours. Hydrochloric acid is then added for pickling at a pickling concentration of 12% and a cleaning time of 5 hours to obtain a carbon-based precursor. The pickled carbon-based precursor is dried to obtain a porous carbon precursor.

(2) Weigh 1.7 kg of zinc chloride and 360 g of Pluronic PVA and dissolve them in 20 L of water. Then add 4.4 kg of porous carbon precursor, stir for 24 hours, and filter and dry. Then place the obtained material in a rotary kiln and calcine it at 800 ° C and 10 vol% hydrogen/argon mixed atmosphere for 4 hours to obtain a black powder sample. The obtained black powder sample is placed in 10 L of 0.5 mol/L dilute hydrochloric acid and stirred for 6 hours. Then, the sample is washed with pure water and dried for use to obtain a carbon matrix.

(3) The carbon substrate was placed in a chemical vapor deposition (CVD) device, the vacuum degree was set to 10130 Pa, and then silane was introduced into the CVD device, the silane concentration was controlled to 80%, the gas rate was 72 L/min, the temperature was raised to 400 ° C, and the reaction was carried out for 4 hours to obtain the vapor deposition product.

(4) The vapor deposition product and sucrose were mixed in a mass ratio of 50:45, and then the mixed material was placed in a high-temperature box furnace, nitrogen was introduced, and heat treated at 920°C for 2 hours. The obtained sample was crushed, sieved and graded to obtain a negative electrode material.

In this embodiment, the negative electrode material includes a carbon matrix and a silicon material, and the silicon material is located in the carbon matrix. The deposition coefficient γ, M value, conductivity and silicon content of the negative electrode material are shown in Table 4.

Example 19

(1) Graphite is mixed with an activator, potassium hydroxide (KOH), wherein the mass addition amount of the activator KOH is 4.4% of the mass of the graphite, and activated at 1100°C for 10 hours. Then, hydrochloric acid is added for pickling, and the concentration of hydrochloric acid is 10%. The washing time is 6 hours to obtain a carbon-based precursor. The pickled carbon-based precursor is dried to obtain a porous carbon precursor.

(2) Weigh 1.7 kg of zinc sulfate and 360 g of F127 and dissolve them in 20 L of water. Then add 4.4 kg of porous carbon precursor, stir for 24 hours, and filter and dry. Then place the obtained material in a rotary kiln and calcine it at 800 ° C and 10 vol% hydrogen/argon mixed atmosphere for 4 hours. Then put the obtained black powder sample into 10 L of 0.5 mol/L dilute hydrochloric acid and stir for 6 hours. Then wash the sample with pure water and dry it for use to obtain a carbon matrix.

(3) The carbon substrate was placed in a chemical vapor deposition (CVD) device, the vacuum degree was set to 5000 Pa, and then silane was introduced into the CVD device with a silane concentration of 10% and a gas rate of 35 L/min. The temperature was raised to 500°C and the reaction was carried out for 3 hours to obtain a vapor deposition product.

(4) The vapor deposition product and epoxy resin were mixed in a mass ratio of 50:25, and then the mixed material was placed in a high-temperature box furnace, nitrogen was introduced, and heat treated at 620°C for 2 hours. The obtained sample was crushed, sieved and graded to obtain a negative electrode material.

In this embodiment, the negative electrode material includes a carbon matrix and a silicon material, and the silicon material is located in the carbon matrix. The deposition coefficient γ, M value, conductivity and silicon content of the negative electrode material are shown in Table 4.

Example 20

(1) The coconut shell is carbonized at a temperature of 800°C for 12 hours. A mixture of ferric chloride and KOH (mass ratio of 5:95) is added to the treated carbon-based material, wherein the mass addition amount of the mixture of ferric chloride and KOH is 3.9% of the mass of the coconut shell, and the mixture is activated at 850°C for 10 hours. Then, hydrochloric acid is added for pickling at a concentration of 25% and the washing time is 5 hours to obtain a carbon-based precursor. The pickled carbon-based precursor is dried to obtain a porous carbon precursor.

(2) Weigh 1.7 kg of zinc acetate and 360 g of Pluronic F127 and dissolve them in 20 L of water. Then add 4.4 kg of porous carbon precursor, stir for 24 hours, and filter and dry. Then place the obtained material in a rotary kiln and calcine it at 900 ° C and 12 vol% hydrogen/argon mixed atmosphere for 4 hours. Then put the obtained black powder sample into 12 L of 0.5 mol/L dilute hydrochloric acid and stir for 6 hours. Finally, wash the sample with pure water and dry it for use to obtain a carbon matrix.

(3) The carbon substrate was placed in a chemical vapor deposition (CVD) device, the vacuum degree was set to 500 Pa, and then silane was introduced into the CVD device, the silane concentration was controlled to 20%, the gas rate was 30 L/min, the temperature was raised to 600 ° C, and the reaction was carried out for 1 hour to obtain the vapor deposition product.

(4) The vapor deposition product and citric acid were mixed in a mass ratio of 50:20, and then the mixed material was placed in a high-temperature box furnace, nitrogen was introduced, and heat treated at 760°C for 2 hours. The obtained sample was crushed, sieved and graded to obtain a negative electrode material.

In this embodiment, the negative electrode material includes a carbon matrix and a silicon material, and the silicon material is located in the carbon matrix. The deposition coefficient γ, 2M value, conductivity and silicon content of the negative electrode material are shown in Table 4.

Example 21

The difference from Example 17 is that: step (1) is: placing the coconut shell in a carbonization furnace for carbonization, specifically the carbonization temperature is 900°C, the carbonization time is 3 hours, mixing the carbonized porous carbon-based material and potassium _ferrate ( _K2FeO4 ), wherein the mass addition amount of potassium ferrate is 0.2% of the mass of the coconut shell, activating at 800°C for 10 hours, then adding hydrochloric acid for pickling, wherein the hydrochloric acid concentration is 20%, and the washing time is 5 hours to obtain a carbon-based precursor, and drying the pickled carbon-based precursor to obtain a porous carbon precursor.

In this embodiment, the negative electrode material includes a carbon matrix and a silicon material, and the silicon material is located in the carbon matrix. The deposition coefficient γ, M value, conductivity and silicon content of the negative electrode material are shown in Table 4.

Example 22

The difference from Example 17 is that: step (1) is: placing the coconut shell in a carbonization furnace for carbonization, specifically the carbonization temperature is 900°C, the carbonization time is 3 hours, the carbonized carbon-based material and potassium _ferrate ( _K2FeO4 ) are mixed, wherein the mass addition amount of potassium ferrate is 3% of the mass of the coconut shell, and the mixture is activated at 800°C for 10 hours, and then hydrochloric acid is added for pickling, wherein the hydrochloric acid concentration is 20%, and the washing time is 5 hours to obtain a carbon-based precursor, and the pickled carbon-based precursor is dried to obtain a porous carbon precursor.

In this embodiment, the negative electrode material includes a carbon matrix and a silicon material, and the silicon material is located in the carbon matrix. The deposition coefficient γ, M value, conductivity and silicon content of the negative electrode material are shown in Table 4.

Example 23

The difference from Example 19 is that step (3) is: placing the carbon substrate in a chemical vapor deposition (CVD) device, setting the vacuum degree to 5000 Pa, and then introducing silane into the CVD device with a silane concentration of 10% and a gas rate of 35 L/min, heating to 500°C, reacting for 1.5 hours, and obtaining a vapor deposition product.

In this embodiment, the negative electrode material includes a carbon matrix and a silicon material, and the silicon material is located in the carbon matrix. The deposition coefficient γ, M value, conductivity and silicon content of the negative electrode material are shown in Table 4.

Example 24

The difference from Example 17 is that step (3) is: placing the carbon substrate in a chemical vapor deposition (CVD) device, setting the vacuum degree to 1250Pa, and then introducing silane into the CVD device with a silane concentration of 50% and a gas rate of 16L/min, heating to 500°C, reacting for 1.5h, and obtaining a vapor deposition product.

Example 25

The difference from Example 17 is that in step (3), the carbon substrate is placed in a chemical vapor deposition (CVD) device, the vacuum degree is set to 680 Pa, and then silane is introduced into the CVD device with a silane concentration of 50% and a gas rate of 26 L/min. The temperature is raised to 500°C and the reaction is carried out for 1.5 hours to obtain the vapor deposition product.

Example 26

The difference from Example 17 is that: step (1) is: placing the coconut shell in a carbonization furnace for carbonization, specifically the carbonization temperature is 900°C, the carbonization time is 3 hours, the carbonized carbon-based raw material and potassium _ferrate ( _K2FeO4 ) are mixed, wherein the mass addition amount of potassium ferrate is 5% of the mass of the coconut shell, and the mixture is activated at 800°C for 10 hours, and then hydrochloric acid is added for pickling, wherein the hydrochloric acid concentration is 20%, and the washing time is 5 hours to obtain a carbon-based precursor, and the pickled carbon-based precursor is dried to obtain a carbon precursor.

Example 27

The difference from Example 17 is that a mixture of nickel nitrate and potassium hydroxide (mass ratio of 1:89) is added to the treated carbon-based material, wherein the mass addition amount of the mixture of nickel nitrate and potassium hydroxide is 2.5% of the mass of the bamboo charcoal, and the material is activated at 800°C for 16 hours.

Example 28

The difference from Example 17 is that a mixture of nickel nitrate and potassium hydroxide (mass ratio of 1:89) is added to the treated carbon-based material, wherein the mass addition amount of the mixture of nickel nitrate and potassium hydroxide is 2.5% of the mass of the bamboo charcoal, and the material is activated at 800°C for 20 hours.

Comparative Example 9

The difference from Example 17 is that step (1) is: placing the coconut shell in a carbonization furnace for carbonization at a specific carbonization temperature of 900°C and a carbonization time of 3 hours, acid-washing the carbon-based material after carbonization at an acid washing concentration of 20% for 5 hours, and drying the acid-washed carbon-based precursor to obtain a porous carbon precursor. That is, the coconut shell is only carbonized and acid-washed without activation to obtain a carbon precursor.

Comparative Example 10

The difference from Example 17 is that: step (1) is: placing the coconut shell in a carbonization furnace for carbonization, specifically the carbonization temperature is 900°C, the carbonization time is 3 hours, the porous carbon-based material after carbonization treatment is mixed with potassium ferrate ( _K2FeO4 ), wherein the mass addition amount of potassium ferrate is 0.05% of the mass of the coconut shell, _and activated at 800°C for 10 hours, and then pickling is carried out, the pickling concentration is 20%, and the cleaning time is 5 hours. The carbon-based precursor after pickling is dried to obtain a porous carbon precursor.

Comparative Example 11

The difference from Example 17 is that: step (1) is: placing the coconut shell in a carbonization furnace for carbonization, specifically the carbonization temperature is 900°C, the carbonization time is 3 hours, the carbonized carbon-based material and potassium _ferrate ( _K2FeO4 ) are mixed, wherein the mass addition amount of potassium ferrate is 5.2% of the mass of the coconut shell, the mixture is activated at 800°C for 10 hours, and then acid-washed at an acid washing concentration of 20% for 5 hours. The acid-washed carbon-based precursor is dried to obtain a porous carbon precursor.

Comparative Example 12

The difference from Example 17 is that step (2) is not performed, that is, the porous carbon precursor is not pretreated.

Comparative Example 13

The difference from Example 17 is that step (3) is: placing the carbon substrate in a chemical vapor deposition (CVD) device, setting the vacuum degree to 8000 Pa, and then introducing silane into the CVD device with a silane concentration of 50% and a gas rate of 50 L/min, heating to 600°C, reacting for 0.5 h, and obtaining a vapor deposition product.

Comparative Example 14

The difference from Example 17 is that step (3) is: placing the carbon substrate in a chemical vapor deposition (CVD) device, setting the vacuum degree to 700 Pa, and then introducing silane into the CVD device with a silane concentration of 30% and a gas rate of 35 L/min, heating to 500°C, reacting for 1 hour, and obtaining a vapor deposition product.

Comparative Example 15

The difference from Example 17 is that step (3) is: placing the carbon substrate in a chemical vapor deposition (CVD) device, setting the vacuum degree to 8000 Pa, and then introducing silane into the CVD device with a silane concentration of 50% and a gas rate of 50 L/min, raising the temperature to 600°C, reacting for 14 hours, and obtaining a vapor deposition product.

Test method:

The method for testing the deposition parameter γ of silicon in anode materials includes: taking a sample of anode material with a mass of m ₁ and measuring its specific pore volume p ₁ using a Micromeritics ASAP2460 micropore surface area and pore size analyzer. The sample is then calcined in an oxygen atmosphere using a Nanyang Xinyu SA2-9-17TP box-type atmosphere furnace, causing the silicon and silicon oxide in the sample to react to form silicon dioxide. The carbon then burns and is released as carbon dioxide. The silicon content (a ₁ ) is then calculated by weighing. The anode material is placed in a solution of 70% HCl and 50% HF in a 2:1 volume ratio and stirred for over 10 hours. After washing and drying, the remaining material is then measured using the same method to determine its mass (m _{2 )} , specific pore volume (p _{2 )} , and silicon content (a _{2 )} . The density of the silicon particles is 2.34 (g/cm ^{3 )} . The deposition parameter γ of the silicon particles in the anode material is calculated using the following formula:

The test methods for the specific pore volume (PV), average pore size and volume ratio of micropores, mesopores and macropores of negative electrode materials include: using the ASAP2460 micropore specific surface area and pore size analyzer from Micromeritics, USA. The pore volume is calculated using the BJHDesorption cumulative volume of pores model. Calculated within a pore size range. Micropore and mesopore analysis was performed using the Micromeretics ASAP 2460. At liquid nitrogen temperature, the equilibrium amount of nitrogen adsorbed on a surface is related to properties such as pore size. By combining the relationship between the amount adsorbed and relative pressure during adsorption, various models can be fitted to calculate pore size. The software generates reports using density functional theory (DFT) to calculate pore size distribution, specific pore volume, and pore volume within a specific range.

The test method for the mass percentage of carbon element in the negative electrode material includes: using the G4 ICARUS HF infrared carbon-sulfur analyzer from Bruker of Germany, the sample is burned in a high-temperature, oxygen-rich state, and the carbon element it contains is oxidized into carbon dioxide. The generated gas enters the infrared detector with the carrier gas, and the carbon content can be calculated by quantitatively analyzing the changes in the carbon dioxide signal.

The test method for the mass percentage of silicon element in the negative electrode material includes: using Nanyang Xinyu SA2-9-17TP box-type atmosphere furnace, burning in an oxygen atmosphere, so that the silicon and silicon oxide in the sample react to form silicon dioxide, and the carbon is burned to become carbon dioxide and discharged, and the silicon content is calculated by weighing.

The test method for the specific surface area (SSA) of the negative electrode material includes: measuring using the American Micromeritics TriStar3000 specific surface area and pore size analyzer equipment.

The conductivity testing method for negative electrode material powder includes: using Mitsubishi Chemical's MCP-PD51 powder resistance test system to measure conductivity at a pressure point of 20 kN, and using the four-probe method to determine the sample's volume resistivity. This instrument measures the resistance of the powder, and a computer automatically calculates the powder's conductivity and resistivity.

The test method for the average gas production of the negative electrode material includes: (1) at room temperature, prepare each slurry in a certain proportion (carboxymethyl cellulose CMC is glued at a ratio of 1.4%, and after uniform dispersion, 10g of glue is taken and mixed with 10g of negative electrode material sample), and mix the above slurry components to form a slurry; (2) put the slurry into an aluminum-plastic film bag and record the slurry mass; (3) then seal it to form a sealed aluminum-plastic film bag; (4) measure the volume of gas generated: fix the sealed aluminum-plastic film bag at the bottom of the container, completely immerse it in water, and record the volume of the aluminum-plastic film bag; (5) after a fixed time (24h), record the volume of the aluminum-plastic film bag again; (6) calculate the gas production of the silicon negative electrode material based on the volume change of the aluminum-plastic film, unit: mL/g.

The D10, D50, and D90 measurements of negative electrode materials include: D50 is measured using a laser particle size analyzer, which exhibits a symmetrical, normal-like distribution. Within the volume-based distribution, the cumulative 50% diameter is D50. Similarly, the cumulative 90% diameter is D90, and the cumulative 10% diameter is D10. This provides the material's particle size distribution (D90 - D10)/D50.

The test method for the compaction density of negative electrode materials includes: using the American McNor CARVER 4350.22 powder compaction density meter, placing a sample of specified mass m in a mold and applying a pressure of 1.0T. After maintaining the pressure for 30S, the pressure is removed to test its thickness and calculate the compaction density.

The test method for the tap density of the negative electrode material includes: using the Meconta DAT-6-220 tap density meter, placing a specified mass of sample in a measuring cylinder, vibrating it a specified number of times (3000 times for conventional testing), reading the volume of the measuring cylinder after vibration and calculating the tap density.

The test method for the average particle size of the material is: observe the particles of the material through a field emission scanning electron microscope or a transmission electron microscope, randomly measure the particle size of 5 to 10 material particles using a scale, and take the average value of the particle size as the final average particle size of the material.

Please refer to Table 1-1, Table 1-2, Table 2, Table 3 and Table 4 for the above test results:

Table 1-1 Physical property test results of negative electrode materials of Examples 1-8 of the present application

Table 1-2 Physical property test results of negative electrode materials of Examples 9-16 of the present application

Table 2 Physical property test results of negative electrode materials of comparative examples 1-8 of this application

Table 3: Negative electrode material related parameter results of Examples 17-28 and Comparative Examples 9-15

Table 4: Related parameter results of negative electrode materials of Examples 17-28 and Comparative Examples 9-15

This application further utilizes the negative electrode materials of Examples 1-16 and Comparative Examples 1-8 to fabricate button-type batteries. Specifically, the process involves preparing a negative electrode slurry with a mass ratio of 70:15:15 between the negative electrode material, conductive carbon black, and PAA (polyacrylic acid), coating the mixture on copper foil, and drying the resulting negative electrode sheet. The button-type batteries were assembled in an Ar-filled glove box using a metallic lithium sheet as the counter electrode.

The coin-type batteries of Examples 1-16 and Comparative Examples 1-8 obtained above were tested for their initial discharge specific capacity and initial coulombic efficiency. The test conditions included charging and discharging the coin-type batteries at a current density of 0.1C within the charge and discharge range of 0.01-5V. As shown in Table 5, the coin-type batteries of Examples 1-16 exhibited significantly higher initial coulombic efficiencies than those of Comparative Examples 1-8.

Table 5. First discharge performance test results of button batteries of Examples 1-16 and Comparative Examples 1-8 of the present application

The present application further uses the negative electrode materials of Examples 1-16 and Comparative Examples 1-8 to respectively prepare button batteries. Specifically, the process comprises: preparing a negative electrode slurry by mixing a mixture of negative electrode material and graphite, Super-P, KS-6, CMC, and SBR in a mass ratio of 92:2:2:2:2, coating the mixture on copper foil, and drying the mixture to prepare a negative electrode sheet. The proportion of negative electrode material and graphite in the mixture of negative electrode material and graphite is determined by the initial discharge specific capacity of the two and the capacity required to be combined. A button battery is assembled in a glove box filled with Ar gas using a metal lithium sheet as the counter electrode.

The button cells of Examples 1-16 and Comparative Examples 1-8 were subjected to charge-discharge cycles and tested for capacity retention and electrode thickness expansion. The test conditions included repeating the charge-discharge test 50 times at a current density of 1C in the 0.01V-5V range. As shown in Table 6, compared to Comparative Examples 1-8, the button cells of Examples 1-16 exhibited significantly lower electrode thickness expansion and significantly higher capacity retention after 50 charge-discharge cycles.

Table 6. Test results of charge and discharge cycle performance of button batteries of Examples 1-16 and Comparative Examples 1-8 of the present application

Please refer to Tables 1-1 and 1-2. Examples 1-16 use the negative electrode material preparation method of the present application. Under the action of organic active agents such as PVA, PVP, and Pluronic F127, the carbon substrate is treated with zinc salt, so that elemental zinc is fully attached to the surface and pores of the carbon substrate. After acid washing, the zinc on the surface of the carbon substrate is removed while the zinc in the pores of the carbon substrate is retained. Under the action of the catalytic activity of the elemental zinc, silicon material is deposited in the pores of the carbon substrate. According to the characterization method of the present application, the deposition parameter γ of the silicon material in the negative electrode materials of Examples 1-16 is greater than 0.85, which can be used to indicate that relatively more silicon material is deposited in the pores of the carbon substrate and relatively less silicon material is attached to the surface of the carbon substrate.

Referring to Table 1-1, Table 1-2 and Table 5, the negative electrode materials of Examples 1-16 have a small specific surface area, a high powder conductivity, and suitable carbon and silicon content. For example, the specific surface area is controlled within a range of 0.5 m ² /g to 10 m ² /g, the powder conductivity is controlled within a range of 0.5 S/cm to 2 S/cm, the carbon content in the negative electrode material is controlled within a range of 40% to 62%, and the silicon content is controlled within a range of 37% to 55%.

The smaller specific surface area of the negative electrode material indicates that the SEI film consumes less lithium salt, which is beneficial to reducing the risk of electrical separation between particles caused by the volume effect. The higher powder conductivity of the negative electrode material indicates that it has better conductive properties. The appropriate carbon content of the negative electrode material indicates that it has an effective conductive network, and the appropriate silicon content indicates that it has sufficient power storage capacity. The above aspects enable the negative electrode materials of Examples 1-16 to have higher first discharge specific capacity and first coulomb efficiency (see Table 5).

Please refer to Table 1-1, Table 1-2 and Table 6. The negative electrode materials of Example 1-16 have a smaller specific pore volume, a lower gas production value, a smaller micropore ratio and a larger mesopore ratio. For example, the specific pore volume is maintained in the range of 0.001 cm ³ /g to 0.1 cm ³ /g, the 7-day average gas production at room temperature is less than 1 mL/g, the micropore ratio is maintained in the range of 0% to 10%, and the mesopore ratio is maintained in the range of 80% to 100%.

The smaller specific pore volume of the negative electrode material indicates that the pores of the carbon matrix are effectively filled with the silicon material, and the pores in the negative electrode material can reserve space for the volume expansion of the silicon material, thereby alleviating the expansion effect of the negative electrode material, making the expansion degree of the negative electrode materials of Examples 1-16 relatively low during the charge and discharge cycle (see Table 6); at the same time, the pores in the negative electrode material can also adsorb or accommodate a small amount of gas produced by the side reaction of part of the silicon material with the electrolyte, thereby improving the gas production phenomenon of the negative electrode material and significantly reducing the gas production of the negative electrode material.

The smaller proportion of micropores in the negative electrode material indicates that more than 70% of the micropores in the original carbon matrix are effectively filled with silicon materials, which can reduce the active sites for side reactions between the negative electrode material and the electrolyte, thereby reducing the SEI film thickening caused by the continuous intrusion of the electrolyte. The larger proportion of mesopores indicates that sufficient volume expansion buffer space is reserved for the silicon material in the negative electrode material, so that the negative electrode material has a certain ability to alleviate the volume expansion of the silicon material, reducing the excessive local expansion stress caused by the uneven volume change of silicon particles during the charge and discharge cycle, and thus causing the risk of rupture and pulverization of the negative electrode material. The above smaller proportion of micropores or larger proportion of mesopores makes the negative electrode materials of Examples 1-16 have higher cycle stability (see Table 6).

Please refer to Tables 2, 5, and 6. In Comparative Example 1, since the zinc on the surface of the carbon substrate was not pickled during its preparation, the proportion of silicon particles deposited in the pores of the carbon substrate was relatively small. The relatively large number of silicon particles attached to the surface of the carbon substrate resulted in a larger specific pore volume, a larger specific surface area, a larger proportion of micropores, and a smaller proportion of mesopores for the negative electrode material, which increased the gas production of the negative electrode material. Although it had a relatively high initial discharge capacity due to the large amount of silicon material attached to the surface, its initial coulombic efficiency was significantly low, and it expanded severely during the cycle and had poor cycle stability. Comparative Examples 2 and 3 respectively lowered the acid concentration and stirring time of the pickling during their preparation. Insufficient pickling resulted in incomplete removal of the zinc attached to the surface of the carbon substrate. As a result, similar to Comparative Example 1, although Comparative Examples 2 and 3 had a relatively high initial discharge capacity due to the large amount of silicon material attached to the surface, their initial coulombic efficiency was significantly low, and they expanded severely during the cycle and had poor cycle stability.

Referring to Tables 2, 5, and 6, Comparative Examples 4 and 5, respectively, increased the acid concentration and stirring time during the pickling process. Excessive pickling partially dissolves the zinc within the pores of the carbon matrix, resulting in a decrease in the total amount of silicon material distributed in the resulting negative electrode material. Excessive pickling results in a reduced amount of metallic zinc within the carbon matrix, which is not conducive to catalyzing the deposition of silicon material within the pores of the carbon matrix. The deposition parameter γ of the silicon material does not reach 0.85. Furthermore, although the relatively low silicon content results in some good physical properties or electrochemical cycling performance, the insufficient silicon material results in a significantly low first discharge specific capacity. Taking all factors into consideration, the overall performance of the negative electrode material is also suboptimal.

Please refer to Tables 2, 5, and 6. Comparative Examples 6 and 7 replaced the organic active agent during their preparation. The replaced components, polyquaternium-16 and benzalkonium bromide, did not meet the requirements for the selection of the organic active agent. Comparative Example 8 eliminated the original organic active agent during its preparation. During the preparation of Comparative Examples 6-8, the attachment or reduction of zinc on the surface and in the pores of the carbon matrix was affected, thereby affecting the subsequent deposition efficiency of the silicon material. Characterization showed that the silicon material deposition parameter γ in the negative electrode materials of Comparative Examples 6-8 was all low, and the silicon material could not be deposited more in the pores of the carbon matrix, resulting in the negative electrode material having a larger specific pore volume, a larger specific surface area, a larger proportion of micropores, and a smaller proportion of mesopores. This increased the gas production of the negative electrode material, and even though it had a relatively high first discharge specific capacity due to a certain amount of silicon material still attached to the surface, its first coulombic efficiency was significantly low, and it expanded severely during the cycle, and had poor cycle stability.

In summary, the deposition parameter γ of the silicon material in the negative electrode material of the present application is greater than or equal to 0.85, the average pore size is relatively large, and relatively more silicon material in the negative electrode material is distributed in the pores of the carbon matrix. The negative electrode material of the present application has a smaller specific surface area, a higher powder conductivity and a suitable carbon element content and silicon element content, thereby having a higher first discharge specific capacity and first coulombic efficiency. The negative electrode material of the present application also has a smaller specific pore volume, a lower gas production value, a smaller micropore ratio and a larger mesopore ratio, thereby having good resistance to expansion and higher cycle stability during the charge and discharge cycle, solving the problems of severe expansion and poor cycle stability of existing silicon-based negative electrode lithium-ion batteries.

The present application further uses the negative electrode materials of Examples 17-28 and Comparative Examples 9-15 to prepare button batteries, and conducts the following electrochemical performance tests:

1. Test methods for reversible capacity and 7C capacity retention rate:

1) Preparation of battery: The prepared negative electrode material, conductive agent and binder are dissolved in a solvent in a mass percentage of 94:1:5, and the solid content is controlled at 50%. The mixture is coated on a copper foil current collector and vacuum dried to obtain a negative electrode plate; then, a ternary positive electrode plate prepared by a traditional mature process, an electrolyte of 1 mol/L LiPF6/ethyl cellulose + dimethyl carbonate + ethyl methyl carbonate (v/v = 1:1:1), a polypropylene separator (Celgard2400), and a shell are assembled using a conventional production process to form an 18650 cylindrical single cell.

2) Testing: Charge and discharge tests were performed on the LAND battery testing system of Wuhan Jinnuo Electronics Co., Ltd. at room temperature using a 0.2C constant current charge and discharge with a charge and discharge voltage limited to 2.75-4.2V to obtain the initial reversible capacity. The reversible capacity was then obtained using a 7C constant current charge and discharge with a charge and discharge voltage limited to 2.75-4.2V. The ratio of the two was calculated to obtain the 7C capacity retention rate.

2. Test method for first coulombic efficiency (ICE):

1) Coin Cell Preparation: A negative electrode slurry was prepared using a negative electrode material, conductive carbon black, and polyacrylic acid (PPA) in a mass ratio of 75:15:10. This slurry was coated onto copper foil and dried to form a negative electrode sheet. A lithium metal sheet was used as the counter electrode, and the coin cell was assembled in an argon-filled glove box.

2) Testing: The button cell was charged and discharged at a current density of 0.1 C within the charge and discharge range of 0.01 V to 5 V to obtain the initial coulombic efficiency (ICE) of the button cell.

3. Test method for the thickness expansion rate of the pole piece after 50 cycles:

1) Preparation of button cells: A negative electrode slurry is prepared by mixing the negative electrode active material, conductive carbon black (Super-P), conductive graphite (KS-6), carboxymethyl cellulose (CMC), and styrene-butadiene rubber (SBR) in a mass ratio of 92:2:2:2:2, coating the mixture on copper foil, and drying to form a negative electrode sheet. The negative electrode active material is a mixture of the negative electrode material of this application and graphite, wherein the proportion of the negative electrode material and graphite is determined by the first discharge specific capacity of the two and the capacity required for the two to be combined. A button cell is assembled in an argon-filled glove box using a metal lithium sheet as the counter electrode.

2) Test: The button cell was subjected to 50 repetitive charge and discharge tests at a current density of 1C in the charge and discharge range of 0.01V-5V to obtain the electrode thickness expansion rate after 50 cycles.

The test results are shown in Table 7:

Table 7: Electrochemical performance characterization of negative electrode materials of Examples 17-28 and Comparative Examples 9-15

In combination with Examples 17-28 and Tables 3 and 4, by the preparation method of the negative electrode material of the present application, the mass addition amount of the activator is limited to 0.2% to 5% of the mass of the carbon-based raw material, which can form a large number of evenly distributed micropores in the porous carbon precursor, and the proportion of micropores is not less than 70%, which is conducive to the subsequent filling of active substances in the micropores. In the deposition process of active materials such as silicon materials, the deposition conditions are regulated and 0.1≤α≤50 is limited, so that the deposition parameter γ of the final negative electrode material is not less than 0.85, that is, relatively more active materials are deposited inside the matrix, reducing the direct contact between the negative electrode active material and the electrolyte during the charge and discharge process, and reducing the probability of active materials such as silicon materials being hydrolyzed in water to form silicates, thereby effectively reducing the gas production value of the negative electrode material; at the same time, the value of M is greater than 0.015 and less than 5, ensuring that a relatively large amount of silicon material is uniformly deposited in the carbon matrix, and the negative electrode material has a relatively high electrical conductivity. Importantly, the overall process does not introduce too much metal impurities, so the negative electrode material formed has high electrical conductivity, high charge and discharge efficiency and good cycle performance.

In combination with Examples 17-28, referring to Tables 3, 4 and 7, the content of mesopores in the negative electrode material is 30% to 80%, and the proportion of micropores is 10% to 30%, indicating that the micropores in the negative electrode material are basically filled with active substances such as silicon materials. The deposition parameters of the negative electrode material thus formed are relatively high, thereby constructing electron transmission channels in the pores of the carbon matrix, which is beneficial to improving the electrical conductivity of the negative electrode material, and also further improving the M value. The cycle performance and first coulombic efficiency of the battery thus formed are also higher.

In conjunction with Examples 17-28, referring to Tables 3 and 7, when the specific pore volume of the negative electrode material is between 0.001 and 0.1 cm ³ /g, the expansion rate of the formed negative electrode material is relatively low, all within 40%. This is because after the carbon matrix is filled with silicon material, the remaining pores in the carbon matrix can reserve space for the volume expansion of the silicon material, thereby alleviating the expansion effect of the negative electrode material and improving the cycle stability of the negative electrode material. The remaining pores in the carbon matrix can also absorb or accommodate a small amount of gas generated by the side reaction between the silicon material and the electrolyte, thereby reducing the gas generation value of the negative electrode material.

In combination with Examples 17-28, referring to Tables 3 and 7, when the average pore size of the negative electrode material is within the range of 0.45 to 50 nm, the lithium ion transmission channel can be unblocked, thereby improving the electrical conductivity and the first coulombic efficiency of the negative electrode material.

Compared with Example 17, in Comparative Example 9, potassium ferrate is not added, that is, the carbon-based raw material is not activated, and an appropriate number of activated pores with uniform distribution cannot be formed inside the material obtained by carbonization treatment. Active substances such as silicon materials are difficult to deposit in the pores of the carbon matrix, but are deposited on the surface of the carbon matrix, so that the formed negative electrode material has a large volume expansion and low electrical conductivity; in addition, the silicon material deposited on the surface of the carbon matrix increases the contact area with the electrolyte, increases the thickness of the SEI film, increases the diffusion distance of lithium ions, hinders the smooth deintercalation of lithium ions, and ultimately leads to a very low capacity retention rate of the negative electrode material.

Compared with Example 17, the amount of potassium ferrate added in Comparative Example 10 is lower, and an appropriate number of uniformly distributed activation pores cannot be formed inside the material obtained by carbonization treatment. Only a portion of the silicon material is deposited inside the carbon matrix, and more is deposited on the surface of the carbon matrix, resulting in the deposition coefficient γ and M value of the formed negative electrode material being lower than the preset values. The electrical conductivity of the negative electrode material is poor, and the electrochemical properties, especially the capacity retention rate, are far lower than the capacity retention rate of Example 1.

Compared with Example 17, the amount of potassium ferrate added in Comparative Example 11 is higher, the pore diameter of the pores formed during the activation process becomes larger, and the number of pores increases, which reduces the proportion of micropores in the carbon matrix and increases the size of the deposited silicon; in addition, the formed negative electrode material introduces more metal impurities, resulting in structural collapse of the negative electrode material during the deintercalation process, resulting in reduced cycle performance of the negative electrode material.

Compared with Example 17, in Comparative Example 12, the carbon matrix was not pretreated, and the silicon material was partially deposited on the surface of the carbon matrix. The obtained M value was only 0.002, which was about 1/10 of the value specified in this application. The deposition parameter γ was also lower than 0.85. The conductivity of the generated negative electrode material was only 0.1S/cm, which was far below the usage standard required by this application.

Compared with Example 17, Comparative Example 13 reduces the silicon deposition time, so the mass percentage of silicon in the obtained negative electrode material is only 15%. Although the M value, deposition coefficient γ and conductivity of the formed negative electrode material are all within the set values, the first discharge specific capacity and first coulombic efficiency of the negative electrode material are both low.

Compared with Example 17, Comparative Example 14 changes the deposition conditions of the silicon material, specifically, changes the vacuum degree of the silicon material deposition, so that the deposition condition α of the silicon material is 52.5%, which exceeds the preset range value, so that the specific pore volume of the negative electrode material is larger, and the silicon material is deposited more on the surface of the carbon matrix, thereby making the gas production value of the formed negative electrode material larger. The deposition coefficient γ and M value of the negative electrode material thus formed are both low, and the electrochemical performance of the formed battery is also poor.

Compared to Example 17, Comparative Example 15 increased the silicon material deposition time, resulting in a silicon mass percentage exceeding 65%. However, some silicon overflowed and deposited on the substrate surface, making it more susceptible to contact and reaction with the electrolyte, increasing the negative electrode material's gas production. Furthermore, after deposition on the carbon substrate, the silicon material continued to grow, causing particle pulverization and shedding, further degrading the negative electrode material's electrochemical performance. For example, the resulting battery performance, particularly the 7C capacity retention rate, was very low at only 2.5%, failing to meet the standards for use as an excellent battery material.

The above embodiments are only used to illustrate the technical solutions of the present application and are not intended to limit the present application. Although the present application has been described in detail with reference to the above preferred embodiments, those skilled in the art should understand that modifications or equivalent replacements of the technical solutions of the present application should not depart from the spirit and scope of the technical solutions of the present application.

Claims (15)

A negative electrode material, characterized in that the negative electrode material comprises a carbon matrix and an active material, the carbon matrix is provided with pores, the active material is at least partially provided in the pores of the carbon matrix, and the deposition parameter γ of the active material is greater than or equal to 0.85,
Wherein, _m1 is the mass of the negative electrode material, based on _m1 , the mass percentage of the active material is _a1 , and the specific pore volume of the negative electrode material is _p1 ; _m2 is the mass of the negative electrode material after removing the active material, based on _m2 , the mass percentage of the active material is _a2 , and the specific pore volume of the negative electrode material after removing the active material is _p2 ; ρ is the density of the active material. The negative electrode material according to claim 1, wherein the mass percentage of the active substance in the negative electrode material is a1%, based on the mass of the negative electrode material. The conductivity of the negative electrode material is σS/cm, wherein 16≤a1≤65, M=σ/a1 is defined, and the value of M is: 0.015≤M≤5. The negative electrode material according to claim 2, wherein the negative electrode material satisfies at least one of the following conditions: (1) The median particle size D50 of the negative electrode material is 1 μm to 15 μm; (2) The particle size distribution of the negative electrode material satisfies 0.1≤(D90-D10)/D50≤2; (3) The specific pore volume of the negative electrode material is 0.001 to 0.1 cm ³ /g; (4) The average pore size of the negative electrode material is 0.45 nm to 50 nm; (5) The specific surface area of the negative electrode material is 0.1 ^{m 2} /g to 5 m ² /g. The negative electrode material according to claim 2 or 3, characterized in that the negative electrode material satisfies at least one of the following conditions: (1) The micropores of the negative electrode material account for 10% to 30%, and the pore diameter of the micropores is less than or equal to 2 nm; (2) The mesopore ratio of the negative electrode material is 30% to 80%, and the pore size of the mesopore is greater than 2 nm and less than or equal to 50 nm; (3) The macropores of the negative electrode material account for 0 to 10%, and the pore diameter of the macropores is greater than 50 nm. The negative electrode material according to claim 1, wherein the negative electrode material satisfies at least one of the following conditions: (1) The specific pore volume of the negative electrode material is 0.001 cm ³ /g to 0.1 cm ³ /g; (2) The average pore size of the negative electrode material is 0.45 nm to 50 nm; (3) The pores of the negative electrode material include micropores, the volume of the micropores accounts for less than or equal to 10% of the pores, and the pore diameter of the micropores is less than or equal to 2 nm; (4) The pores of the negative electrode material include mesopores, the volume of the mesopores accounts for greater than or equal to 80% of the pores, and the pore diameter of the mesopores is greater than 2 nm and less than or equal to 50 nm; (5) The pores of the negative electrode material include macropores, the volume proportion of the macropores in the pores is less than or equal to 20%, and the pore diameter of the macropores is greater than 50 nm. The negative electrode material according to claim 1, wherein the negative electrode material satisfies at least one of the following conditions: (1) The specific surface area of the negative electrode material is 0.5 m ² /g to 10 m ² /g; (2) The particle size D50 of the negative electrode material is 5 μm to 20 μm; (3) The particle size distribution of the negative electrode material (D90-D10)/D50 is 0.9 to 5; (4) The compaction density of the negative electrode material under a pressure of 1T is 0.8g/ ^cm3 to 1.3g/ ^cm3 ; (5) The tap density of the negative electrode material after 3000 vibrations is 0.5 g/cm ³ to 1.5 g/cm ³ . The negative electrode material according to claim 1 or 2, characterized in that the active material comprises one or more of a silicon-based material, a tin-based material, a germanium-based material, and a lead-based material. The negative electrode material according to claim 1 or 2, characterized in that it includes at least one of the following features: (1) The active material comprises a silicon-based material, wherein the silicon-based material comprises one or more of amorphous silicon, crystalline silicon, a composite of crystalline silicon and amorphous silicon, silicon oxide, and a silicon alloy, and the average particle size of the active material is 0.1 nm to 50 nm; (2) The active material includes a silicon material, and the silicon material includes at least one of crystalline silicon, silicon oxide, amorphous silicon, a silicon alloy, and a mixture of crystalline and amorphous silicon; (3) The active material includes a silicon material, and the silicon material includes at least one of crystalline silicon, silicon oxide, amorphous silicon, a silicon alloy, and a mixture of crystalline and amorphous silicon; and the average particle size of the silicon material is 1 nm to 500 nm. The negative electrode material according to claim 8, wherein the purity of the silicon material is greater than 99%. The negative electrode material according to claim 1 or 2, characterized in that the negative electrode material satisfies at least one of the following conditions: (1) The powder conductivity of the negative electrode material under a pressure of 20 kN is 0.5 S/cm to 2 S/cm; (2) The average gas production of the negative electrode material at 25°C over 7 days is less than or equal to 1 mL/g; (3) Based on the mass of the negative electrode material, the mass percentage of carbon element in the negative electrode material is 40% to 60%; (4) Based on the mass of the negative electrode material, the mass percentage of silicon element in the negative electrode material is 37% to 55%. The negative electrode material according to claim 8, characterized in that removing the active substance from the negative electrode material comprises: using 70% hydrochloric acid and 50% hydrofluoric acid in a volume ratio of 2:1 to form an acid solution, placing the negative electrode material in the acid solution and stirring for at least 10 hours, and then washing and drying the negative electrode material. The negative electrode material according to claim 1 or 2, wherein the carbon matrix satisfies at least one of the following conditions: (1) The carbon matrix includes one or more of artificial graphite, natural graphite, amorphous carbon, activated carbon, mesophase carbon microbeads, carbon nanotubes, carbon nanofibers, and graphene; (2) The pores of the carbon matrix include micropores, the volume of the micropores in the pores of the carbon matrix accounts for greater than or equal to 70%, and the pore diameter of the micropores is less than 2 nm; (3) Based on the mass of the carbon matrix, the specific pore volume of the carbon matrix is 0.3 cm ³ /g to 2 cm ³ /g, or the pore volume of the carbon matrix is ≥ 0.4 cm ³ /g; (4) The carbon matrix includes at least one of hard carbon, soft carbon, graphite, mesocarbon microbeads, activated carbon, carbon gel, etc.; (5) The average pore size of the carbon matrix is 0.1 nm to 5 nm; (6) Based on the mass of the negative electrode material, the mass percentage of carbon element is 30% to 75%. The negative electrode material according to claim 1 or 2, characterized in that the negative electrode material further comprises a coating layer, the coating layer being provided on at least a portion of the surface of the carbon substrate, and the coating layer satisfies at least one of the following conditions: (1) The coating layer comprises at least one of a carbon material, a metal oxide, a conductive polymer, a fluoride, a phosphate, and a nitride, and the carbon material comprises one or more of graphene, soft carbon, and hard carbon; (2) The coating layer has a thickness of 1 nm to 300 nm; (3) The mass percentage of the coating layer in the negative electrode material is less than or equal to 10%. A negative electrode plate, characterized by comprising the negative electrode material according to any one of claims 1 to 13. A secondary battery, characterized by comprising the negative electrode material according to any one of claims 1 to 13 or the negative electrode plate according to claim 14.