CN109994710B - Composite negative electrode material and preparation method thereof, negative electrode sheet, battery - Google Patents

Abstract

The application provides a composite negative electrode material and a preparation method thereof, a negative electrode pole piece, and a battery. The composite negative electrode material includes a central core of the negative electrode material and a coating layer coated on the surface of the central core of the negative electrode material, and the coating layer includes Inorganic polymers or organic derivatives of inorganic polymers. The present application can effectively restrain the volume expansion of the negative electrode material during the charging and discharging process, restrain the rebound of the negative electrode pole piece, and improve the electrochemical performance of the battery.

Description

Composite negative electrode material and preparation method thereof, negative electrode sheet, and battery

technical field

The present application relates to the field of batteries, in particular to a composite negative electrode material and a preparation method thereof, a negative electrode pole piece, and a battery.

Background technique

Lithium-ion secondary batteries have the advantages of high capacity, long cycle, no memory effect, less self-discharge, wide operating temperature range, and high rate. They are widely used in mobile phones, computers, electric bicycles, and electric vehicles. During the use of the lithium ion secondary battery, due to the insertion and extraction of lithium ions, the positive and negative pole pieces will expand in volume, which affects the performance of the lithium ion secondary battery. Silicon-based anode materials have the advantages of high capacity, good cycle performance and good rate performance, and have been paid more and more attention by researchers. Its application is restricted.

In view of this, this application is hereby made.

SUMMARY OF THE INVENTION

In view of the problems existing in the background technology, the purpose of this application is to provide a composite negative electrode material and a preparation method thereof, a negative electrode pole piece, and a battery, which can effectively suppress the volume expansion of the negative electrode material during the charging and discharging process, and suppress the rebound of the negative electrode pole piece, Improve the electrochemical performance of the battery.

In order to achieve the above object, in a first aspect of the present application, the present application provides a composite negative electrode material, which comprises a central core of the negative electrode material and a coating layer coated on the surface of the central core of the negative electrode material, the coating layer comprising inorganic Organic derivatives of polymers or inorganic polymers.

In a second aspect of the present application, the present application provides a method for preparing a composite negative electrode material for preparing the composite negative electrode material described in the first aspect of the present application, comprising the steps of: adding the negative electrode material and an optional conductive agent to In the polymerizable small molecular substance solution, a curing agent is added to the solution under stirring to carry out a polymerization reaction, and after the reaction is completed, the solvent is dried and removed to obtain a composite negative electrode material.

In a third aspect of the present application, the present application provides a negative electrode sheet, which includes a negative electrode current collector and a negative electrode active material layer, the negative electrode active material layer is located on the surface of the negative electrode current collector, and the negative electrode active material layer comprises a negative electrode active material layer according to the present invention. The composite negative electrode material described in the first aspect of the application is applied.

In a fourth aspect of the present application, the present application provides a battery comprising the negative electrode sheet according to the third aspect of the present application.

Compared with the prior art, the present application at least includes the following beneficial effects:

In the present application, an inorganic polymer coating layer or an organic derivative coating layer of an inorganic polymer is formed by in-situ polymerization on the surface of the negative electrode material, which can significantly improve the adhesion of the negative electrode material and effectively inhibit the negative electrode material during the charging and discharging process. The volume expansion in the battery can inhibit the rebound of the negative electrode and improve the electrochemical performance of the battery.

Detailed ways

The composite negative electrode material and the preparation method thereof, the negative electrode sheet and the battery according to the present application will be described in detail below.

First, the composite negative electrode material according to the first aspect of the present application is described, which comprises a central core of the negative electrode material and a coating layer coated on the surface of the central core of the negative electrode material, the coating layer comprising an inorganic polymer or an organic derivative of the inorganic polymer .

In the composite negative electrode material of the first aspect of the present application, the inorganic polymer is selected from one or more of silicate inorganic polymers, phosphate inorganic polymers, and aluminosilicate inorganic polymers. The organic derivatives of the inorganic polymers refer to the introduction of organic groups containing carbon atoms into the structure of the inorganic polymers.

In the composite negative electrode material of the first aspect of the present application, in the composite negative electrode material, the content of the coating layer should not be too high, otherwise the capacity of the negative electrode material will be affected. Specifically, in the composite negative electrode material, the mass content of the coating layer is less than or equal to 40%, preferably, the mass content of the coating layer is less than or equal to 20%.

In the composite negative electrode material of the first aspect of the present application, the central core of the negative electrode material can be selected from one or more of silicon-based negative electrode materials and tin-based negative electrode materials. Preferably, the silicon-based negative electrode material is selected from one or more of silicon, silicon oxide, silicon-carbon composite, and silicon alloy. The silicon can be selected from one or more of silicon nanoparticles, silicon nanowires, silicon nanotubes, silicon thin films, 3D porous silicon, and hollow porous silicon. The tin-based negative electrode material is selected from one or more of tin, tin oxide and tin alloy.

In the composite negative electrode material of the first aspect of the present application, the negative electrode material can be subjected to surface hydroxylation treatment to facilitate the coating of the coating layer.

In the composite negative electrode material of the first aspect of the present application, the coating layer may further contain a conductive agent, and the conductive agent can further improve the conductivity of the negative electrode material, such as silicon-based negative electrode material and tin-based negative electrode material, and can also avoid The formation of an overly dense coating on the surface of the negative electrode material affects the transport of electrons.

In the composite negative electrode material of the first aspect of the present application, the coating layer is formed by in-situ polymerization of polymerizable small molecular substances on the surface of the negative electrode material. When the polymerization process of the polymerizable small molecular substances on the surface of the negative electrode material is in-situ polymerization, the inorganic polymer or organic derivative of the inorganic polymer in the coating layer can be closely attached to the negative electrode material, and it has high strength and toughness. Good feature, it can tolerate the expansion and contraction of the negative electrode material during the insertion and removal of lithium ions (or other ions), ensure the high elasticity and toughness of the SEI film on the surface of the negative electrode material, and reduce lithium ions (or other ions) during the cycle. consumption, significantly extending battery life. In particular, the present application is especially suitable for silicon-based anode materials, tin-based anode materials and other anode materials with large volume expansion during charging and discharging, which can effectively inhibit silicon-based anode materials and tin-based anode materials during the charging and discharging process. The volume expansion of the negative electrode can be suppressed, and the rebound of the negative electrode piece can be suppressed, and it can also help to obtain a battery with high capacity, good cycle performance and good rate performance. Preferably, the polymerizable small molecular substance is selected from one or more of inorganic silicates, inorganic phosphates, inorganic aluminates, ethyl orthosilicate, and kaolin. Among them, the types of cation moieties in inorganic silicates, inorganic phosphates, and inorganic aluminates are not limited, but alkali metals and alkaline earth metals are preferred, alkali metals are more preferred, and sodium or potassium is still more preferred. The inorganic phosphate can in turn be orthophosphate, dihydrogen phosphate, sesquihydrogen phosphate or hydrogen phosphate. Further preferably, the inorganic silicate may be water glass.

Taking water glass as an example, the polymerization process is:

Under the promotion of the curing agent, water glass will gradually hydrolyze in the aqueous solution to form [Si(OH) ₄ ] single molecules, which polymerize at different rates and gradually form monomeric Si(OH) 4 ] molecules with greater activity. ) ₄ and a silicate polymer with a lower degree of polymerization, and then combine with the hydroxyl group on the surface of the negative electrode material to form a nucleation point on the surface of the negative electrode material, and gradually form a coating layer in the form of amorphous SiO ₂ ·nH ₂ O, The reaction process is as follows:

Next, the preparation method of the composite negative electrode material according to the second aspect of the present application is described, which is used to prepare the composite negative electrode material described in the first aspect of the present application, including the steps of: adding the negative electrode material and an optional conductive agent to a polymerizable small In the molecular substance solution, a curing agent is added to the solution under stirring to carry out a polymerization reaction, and after the reaction is completed, the solvent is dried and removed to obtain a composite negative electrode material.

In the preparation method of the composite negative electrode material of the second aspect of the present application, the polymerizable small molecular substance is selected from one or more of inorganic silicates, inorganic phosphates, inorganic aluminates, and ethyl orthosilicate kind. Among them, the types of cation moieties in inorganic silicates, inorganic phosphates, and inorganic aluminates are not limited, but alkali metals and alkaline earth metals are preferred, alkali metals are more preferred, and sodium or potassium is still more preferred. The inorganic phosphate can in turn be orthophosphate, dihydrogen phosphate, sesquihydrogen phosphate or hydrogen phosphate.

In the preparation method of the composite negative electrode material of the second aspect of the present application, the type of the curing agent is not limited, and can be selected according to requirements. The curing agent can be inorganic, such as metal oxides, hydroxides, metal salts, and the curing agent can also be organic, such as silane coupling agent, ethyl acetate. Specifically, the curing agent can be selected from magnesium oxide, calcium oxide, aluminum oxide, copper oxide, sodium hydroxide, magnesium hydroxide, calcium hydroxide, calcium chloride, calcium nitrate, magnesium chloride, magnesium sulfate, aluminum chloride, One or more of hydrochloric acid, dilute sulfuric acid, nitric acid, acetic acid, citric acid, silane coupling agent and ethyl acetate.

In the preparation method of the composite negative electrode material of the second aspect of the present application, the type of solvent used in the polymerizable small molecular substance solution is not limited, and can be selected according to requirements, for example, deionized water, organic solvent or deionized water can be used. Mixed solution of water and organic solvent. Wherein, preferably, the organic solvent can be selected from one or more of ethanol, propylene glycol, N-methylpyrrolidone, and ethyl acetate.

In the preparation method of the composite negative electrode material of the second aspect of the present application, preferably, the mass fraction of the active material is 70% to 95%, the mass fraction of the conductive agent is 0% to 10%, and the mass fraction of the polymerizable small molecular substance is The fraction is 3% to 25%, and the mass fraction of the curing agent is 1% to 15%. If the proportion of polymerizable small molecular substances is small, it is not conducive to the formation of a complete, uniform and dense coating layer; if the proportion of curing agent is small, the system may not be effectively cured, which is not conducive to the formation of a complete, uniform and dense coating layer.

The negative pole piece according to the third aspect of the present application is described again, which includes a negative electrode current collector and a negative electrode active material layer, the negative electrode active material layer is located on the surface of the negative electrode current collector, and the negative electrode active material layer includes the negative electrode active material layer according to the first aspect of the present application. The composite anode material described above.

In the negative electrode sheet of the third aspect of the present application, in the negative electrode active material layer, only the composite negative electrode material described in the first aspect of the present application may be used as the negative electrode active material of the negative electrode sheet, or the first On the one hand, the composite negative electrode material is mixed with other common negative electrode materials. Preferably, the negative electrode active material layer may further include other commonly used negative electrode materials, such as soft carbon, hard carbon, artificial graphite, natural graphite, mesocarbon microspheres, lithium titanate, and metals that can form alloys with lithium. one or more.

In the negative electrode sheet of the third aspect of the present application, the negative electrode active material layer may further include a conductive agent and a binder. The types of conductive agents and binders are not limited and can be selected according to requirements.

In the negative pole piece of the third aspect of the present application, the preparation method of the negative pole piece may include the steps of: adding the negative electrode material and an optional conductive agent into the polymerizable small molecular substance solvent solution, and adding to it under stirring conditions. The curing agent is polymerized, and after stirring for a period of time, other commonly used negative electrode materials, binders and conductive agents are added, and the negative electrode slurry is obtained after stirring evenly; the negative electrode slurry is coated on the negative electrode current collector, and the Obtain the negative pole piece. In this way, when the polymerizable small molecular substance is in-situ cured, it can not only enhance the cohesive strength of the negative electrode active material layer, but also improve the bonding force between the negative electrode active material layer and the negative electrode current collector.

Next, the battery according to the fourth aspect of the present application will be described, which includes a positive pole piece, a negative pole piece, a separator, an electrolyte, and the like, wherein the negative pole piece is the negative pole piece described in the third aspect of the application.

The battery according to the fourth aspect of the present application may be a lithium ion secondary battery, a sodium ion secondary battery, a zinc ion secondary battery or a magnesium ion secondary battery. In the present application, only the lithium ion secondary battery is taken as an example for detailed description, but the present application is not limited thereto.

In the lithium ion secondary battery, the positive electrode active material can be selected from lithium transition metal composite oxides, including lithium transition metal oxides (such as lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel manganese oxide, Lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide), one or more of compounds obtained by adding other transition metals or non-transition metals to these lithium transition metal oxides.

The present application will be further described below with reference to the embodiments. It should be understood that these examples are only used to illustrate the present application and not to limit the scope of the present application.

Comparative Example 1

(1) Preparation of negative pole piece

The negative electrode active material, the conductive agent and the binder are fully stirred and mixed uniformly in the deionized water solvent system, and then coated on the Cu foil, dried and cold pressed to obtain the negative electrode pole piece. The negative active material is a mixture of artificial graphite and silicon oxide (SiO), the conductive agent is acetylene black, the binder is polyacrylic acid, and the mass ratio of artificial graphite, silicon oxide, acetylene black and polyacrylic acid is 76:20: 2:2.

(2) Preparation of positive electrode sheet

The positive active material LiNi _0.8 Mn _0.1 Co _0.1 O ₂ , the conductive agent acetylene black, and the binder polyvinylidene fluoride were fully stirred and mixed in the N-methylpyrrolidone solvent system in a mass ratio of 94:3:3, and then coated. Covered on Al foil, dried and cold pressed to obtain a positive pole piece.

(3) Preparation of separator

The PE porous polymer film is used as the separator.

(4) Preparation of electrolyte

In a mixed solvent of ethylene carbonate and ethyl methyl carbonate with a mass ratio of 30:70, lithium salt LiPF ₆ is added and mixed evenly to obtain an electrolyte, wherein the concentration of LiPF ₆ in the electrolyte is 1 mol/L.

(5) Preparation of lithium ion secondary battery

The positive pole piece, the separator and the negative pole piece are stacked in sequence, so that the separator is in the middle of the positive and negative pole pieces to play the role of isolation, and the bare cell is obtained by winding. Put the bare cell in the outer package, inject the prepared electrolyte and seal it.

Comparative Example 2

A lithium ion secondary battery was prepared in the same manner as in Comparative Example 1, except that the silicon oxide used in the preparation of the negative pole piece was silicon oxide coated with a layer of amorphous carbon.

Example 1

A lithium ion secondary battery was prepared in the same manner as in Comparative Example 1, except that:

(1) Preparation of negative pole piece

70 parts by mass of silicon oxide, 1 part by mass of acetylene black and 25 parts by mass of an aqueous solution of sodium silicate (the mass fraction is 20%, "25 parts by mass" means that the sodium silicate in the aqueous solution of sodium silicate is 25 parts by mass, the following examples Similar) add deionized water and mix evenly; under stirring conditions, slowly add 4 mass parts of CaCl ₂ aqueous solution (mass fraction is 10%, "4 mass parts" means that CaCl ₂ in the CaCl ₂ aqueous solution is 4 mass parts, the following examples Similar); after the dropwise addition, continue stirring for 2 hours to form a silicate inorganic polymer on the surface of silicon oxide; then add artificial graphite, acetylene black and polyacrylic acid, stir and mix well, and coat on Cu foil , after drying and cold pressing, a negative pole piece is obtained, wherein the mass ratio of artificial graphite, silicon oxide, acetylene black (acetylene black added for the second time) and polyacrylic acid is 76:20:2:2.

Example 2

A lithium ion secondary battery was prepared in the same manner as in Comparative Example 1, except that:

(1) Preparation of negative pole piece

Add 95 parts by mass of silicon oxide, 1 part by mass of acetylene black and 3 parts by mass of sodium silicate aqueous solution (mass fraction is 20%) into deionized water and mix well; under stirring conditions, slowly add 1 mass part of CaCl ₂ aqueous solution ( After the dropwise addition, continue to stir for 2 hours to form a silicate inorganic polymer on the surface of silicon oxide; then add artificial graphite, acetylene black and polyacrylic acid, stir and mix well, coat On the Cu foil, after drying and cold pressing, the negative pole piece is obtained. Among them, the mass ratio of artificial graphite, silicon oxide, acetylene black (acetylene black added for the second time), and polyacrylic acid is 76:20:2:2.

Example 3

A lithium ion secondary battery was prepared in the same manner as in Comparative Example 1, except that:

(1) Preparation of negative pole piece

Pour 75 parts by mass of silicon oxide, 10 parts by mass of acetylene black and 10 parts by mass of sodium silicate aqueous solution (mass fraction of 20%) into deionized water and mix well; under stirring conditions, slowly add 5 mass parts of CaCl ₂ aqueous solution dropwise (mass fraction is 10%); after the dropwise addition, continue stirring for 2 hours to form a silicate inorganic polymer on the surface of silicon oxide; then add artificial graphite, acetylene black and polyacrylic acid, stir and mix well, coat Covered on Cu foil, dried and cold pressed to obtain a negative pole piece. Among them, the mass ratio of artificial graphite, silicon oxide, acetylene black (acetylene black added for the second time), and polyacrylic acid is 76:20:2:2.

Example 4

A lithium ion secondary battery was prepared in the same manner as in Comparative Example 1, except that:

(1) Preparation of negative pole piece

Pour 70 parts by mass of silicon oxide, 10 parts by mass of acetylene black and 5 parts by mass of sodium silicate aqueous solution (mass fraction of 20%) into deionized water and mix well; under stirring conditions, slowly add 15 mass parts of CaCl ₂ aqueous solution dropwise (mass fraction is 10%); after the dropwise addition, continue stirring for 2 hours to form a silicate inorganic polymer on the surface of silicon oxide; then add artificial graphite, acetylene black and polyacrylic acid, stir and mix well, coat Covered on Cu foil, dried and cold pressed to obtain a negative pole piece. Among them, the mass ratio of artificial graphite, silicon oxide, acetylene black (acetylene black added for the second time), and polyacrylic acid is 76:20:2:2.

Example 5

A lithium ion secondary battery was prepared in the same manner as in Comparative Example 1, except that:

(1) Preparation of negative pole piece

Pour 70 parts by mass of silicon oxide and 25 parts by mass of sodium silicate aqueous solution (mass fraction of 20%) into deionized water and mix well; under stirring conditions, slowly add 5 mass parts of CaCl ₂ aqueous solution (mass fraction of 10%) ); after the dropwise addition, continue stirring for 2 hours to form a silicate inorganic polymer on the surface of silicon oxide; then add artificial graphite, acetylene black and polyacrylic acid, stir and mix well, coat on Cu foil, After drying and cold pressing, a negative pole piece is obtained. Among them, the mass ratio of artificial graphite, silicon oxide, acetylene black and polyacrylic acid is 76:20:2:2.

Example 6

A lithium ion secondary battery was prepared in the same manner as in Comparative Example 1, except that:

(1) Preparation of negative pole piece

Pour 70 parts by mass of silicon oxide and 25 parts by mass of aluminum phosphate aqueous solution (20% by mass) into deionized water and mix well; under stirring conditions, slowly add 5 parts by mass of copper oxide powder; after adding, continue stirring for 2 1 hour to form a phosphate inorganic polymer on the surface of silicon oxide; then add artificial graphite, acetylene black and polyacrylic acid, stir and mix well, coat on Cu foil, dry and cold press to obtain a negative pole piece . Among them, the mass ratio of artificial graphite, silicon oxide, acetylene black, and polyacrylic acid is 76:20:2:2.

Example 7

A lithium ion secondary battery was prepared in the same manner as in Comparative Example 1, except that:

(1) Preparation of negative pole piece

Pour 70 mass parts of silicon oxide and 25 mass parts of sodium aluminosilicate aqueous solution (mass fraction of 20%) into deionized water and mix well; under stirring conditions, slowly add 5 mass parts of CaCl ₂ aqueous solution (mass fraction of 10 %); after the dropwise addition, continue to stir for 2 hours to form aluminosilicate inorganic polymer on the surface of silicon oxide; then add artificial graphite, acetylene black and polyacrylic acid, stir and mix well, and coat on Cu foil After drying and cold pressing, a negative pole piece is obtained. Among them, the mass ratio of artificial graphite, silicon oxide, acetylene black and polyacrylic acid is 76:20:2:2.

Example 8

A lithium ion secondary battery was prepared in the same manner as in Comparative Example 1, except that:

(1) Preparation of negative pole piece

Pour 70 parts by mass of silicon oxide and 25 parts by mass of ethyl orthosilicate into N-methylpyrrolidone and mix well; under stirring conditions, slowly add 5 parts by mass of NaOH aqueous solution (mass fraction is 10%); After the end, stirring was continued for 2 hours to form organic derivatives of silicate inorganic polymers on the surface of silicon oxide; then artificial graphite, acetylene black and polyacrylic acid were added, and after stirring and mixing well, coated on Cu foil, After drying and cold pressing, a negative pole piece is obtained. Among them, the mass ratio of artificial graphite, silicon oxide, acetylene black, and polyacrylic acid is 76:20:2:2.

Next, the performance of the above-mentioned lithium ion secondary battery was tested.

Test 1: The first charge-discharge efficiency test of a lithium-ion secondary battery

The uncharged lithium-ion secondary batteries obtained in Comparative Examples 1-2 and 1-8 were charged to 3.5V with a constant current of 0.1C at room temperature, and then charged to 4.2V with a constant current of 0.3C, and then Constant voltage charging until the current is lower than 0.05C, the charging capacity during the entire charging process is recorded as C ₁ , and then discharged at a constant current of 0.5C to 2.8V, and the discharge capacity during the entire discharging process is recorded as D ₁ .

The first charge-discharge efficiency of the lithium ion secondary battery is E=D ₁ /C ₁ ×100%.

Table 1 The first charge-discharge efficiency test results of Comparative Example 1-2 and Example 1-8

Test 2: Rebound test of negative pole piece after charging

The thickness test of the negative pole piece in the initial state (that is, after cold pressing): take 3 pieces of the negative pole piece in Comparative Example 1-2 and Example 1-8, test the thickness of the negative pole piece in the initial state and record it as D ₀ .

Thickness test of negative pole piece after charging: Take 3 lithium ion secondary batteries in Comparative Example 1-2 and Example 1-8, charge them to 4.2V with a constant current of 0.5C at room temperature, and then use 4.2V Constant voltage charging until the current is below 0.05C, making it fully charged at 4.2V. The fully charged lithium ion secondary battery was disassembled, and the thickness of the negative pole piece was measured and recorded as D ₁ .

The thickness expansion rate of the negative pole piece after charging ε=(D ₁ -D ₀ )/D ₀ ×100%.

Table 2 The negative pole piece rebound test results of Comparative Example 1-2 and Example 1-8

Test 3: Discharge rate performance test of lithium-ion secondary battery

The lithium ion secondary batteries obtained in Comparative Examples 1-2 and 1-8 were charged to 4.2V with a constant current of 0.5C at room temperature, and then charged with a constant voltage of 4.2V until the current was lower than 0.05C, and then respectively press Different discharge rates (0.2C, 0.5C, 1.0C, 3.0C, 5.0C) were discharged to 2.8V, and the discharge capacity was tested. The discharge capacity obtained by 0.2C discharge was used as the reference value (ie, 100%).

Table 3 Test results of discharge rate performance of Comparative Examples 1-2 and Examples 1-8

Test 4: High-temperature storage performance test of lithium-ion secondary batteries

Three lithium ion secondary batteries from each group of Comparative Examples 1-2 and 1-8 were taken, and tested for high temperature storage performance.

At normal temperature, the lithium ion secondary battery is charged with constant current and constant voltage at a charging current of 1C until the upper limit voltage is 4.2V, and the thickness of the lithium ion secondary battery is measured at this time and recorded as D ₀ , and then the lithium ion secondary battery is charged. The secondary battery was placed in an 80°C incubator, and the thickness was measured every 4 hours.

Thickness expansion ratio of lithium ion secondary battery after high temperature storage=(lithium ion secondary battery thickness at Nth hour−D ₀ )/D ₀ ×100%.

Table 4 High-temperature storage expansion test results of Comparative Examples 1-2 and Examples 1-8

0 hours 4 hours 8 hours 12 hours Comparative Example 1 0% 8.2% 14.9% 28.7% Comparative Example 2 0% 6.1% 10.9% 20.2% Example 1 0% 5.2% 9.3% 13.6% Example 2 0% 7.3% 8.5% 15.7% Example 3 0% 6.3% 8.4% 14.7% Example 4 0% 6.4% 8.6% 15.5% Example 5 0% 5.5% 9.6% 13.9% Example 6 0% 5.9% 7.7% 14.2% Example 7 0% 6.1% 8.9% 13.3% Example 8 0% 6.0% 9.1% 14.9%

Test 5: Cyclic performance test of lithium ion secondary battery

Three lithium ion secondary batteries from each group of Comparative Examples 1-2 and 1-8 were taken, and the cycle performance was tested.

At room temperature and 45°C, the lithium-ion secondary battery was charged with constant current and constant voltage at a charging current of 1C, until the upper limit voltage was 4.2V, and then discharged at a constant current of 0.5C until the final The voltage was 2.75 V, and the discharge capacity of the first cycle was recorded; then 800 charge and discharge cycles were performed.

Lithium-ion battery cycle capacity retention rate=(discharge capacity at the 800th cycle/discharge capacity at the first cycle)×100%.

Table 5 Cycle performance test results of Comparative Examples 1-2 and Examples 1-8

Capacity retention rate at room temperature and 800 cycles Capacity retention rate at 45°C, 800 cycles Comparative Example 1 73.1% 68.8% Comparative Example 2 76.2% 71.3% Example 1 78.1% 73.1% Example 2 77.5% 72.7% Example 3 80.8% 74.9% Example 4 80.1% 75.2% Example 5 78.6% 73.6% Example 6 78.0% 73.2% Example 7 81.3% 75.4% Example 8 80.6% 75.7%

It can be seen from the test results in Tables 1 and 2 that in-situ coating of an inorganic polymer layer or an organic derivative layer of an inorganic polymer on the surface of silicon oxide can improve the first charge and discharge efficiency of the battery, indicating that the inorganic polymer The material layer or the organic derivative layer of the inorganic polymer has a certain role in promoting the formation of the SEI film, and also helps to ensure the high elasticity and toughness of the SEI film. The inorganic polymer layer can also inhibit the charging expansion of silicon oxide. This is because the polymerization process of polymerizable small molecular substances such as sodium silicate on the surface of silicon oxide is in-situ polymerization, which can realize the polymerization of inorganic polymers or inorganic polymers. The organic derivative is closely attached to the silicon oxide, and has the characteristics of high strength and good toughness, and can tolerate the charging expansion of the silicon oxide.

From the test results in Tables 3 to 5, it can be seen that in-situ coating of an inorganic polymer layer or an organic derivative layer of an inorganic polymer on the surface of silicon oxide can improve the electrochemical performance of the battery, and the rate performance, The cycle performance and storage performance have been improved to varying degrees. This is because the in-situ coating of an inorganic polymer layer or an organic derivative layer of an inorganic polymer on the surface of silicon oxide can tolerate the charge expansion of silicon oxide and improve the structural stability of silicon oxide during charging and discharging. This further ensures the stability of the SEI film on the surface of the silicon oxide, and at the same time protects the silicon oxide and reduces the probability of side reactions of the electrolyte on the surface of the silicon oxide at high temperatures. It can also be seen from the test results of Examples 1-8 that the comprehensive performance of the battery prepared in Example 4 is better, indicating that the combination of an appropriate amount of curing agent and silicate helps to form better quality on the surface of silicon oxide. The inorganic polymer layer, and the appropriate amount of conductive agent can further help to improve the electron transport of silicon oxide, and further improve the performance of the battery.

Claims (9)

1. The composite negative electrode material is characterized by comprising a negative electrode material central core and a coating layer coated on the surface of the negative electrode material central core, wherein the coating layer comprises an inorganic polymer, and the inorganic polymer is one or more selected from silicate inorganic polymers, phosphate inorganic polymers and aluminosilicate inorganic polymers; the coating layer also contains a conductive agent.

2. The composite anode material according to claim 1, wherein a mass content of the coating layer in the composite anode material is 40% or less.

3. The composite anode material according to claim 1, wherein the mass content of the coating layer in the composite anode material is 20%.

4. The composite anode material of claim 1, wherein the anode material central core is selected from one or more of silicon-based anode materials and tin-based anode materials.

5. A method for producing a composite anode material for use in producing the composite anode material according to any one of claims 1 to 4, comprising the steps of:

adding a negative electrode material and an optional conductive agent into a polymerizable micromolecular substance solution, adding a curing agent into the polymerizable micromolecular substance solution under the stirring condition for polymerization reaction, and drying to remove the solvent after the reaction is finished to obtain the composite negative electrode material.

6. The method for producing a composite anode material according to claim 5,

the polymerizable micromolecule substance is one or more selected from inorganic silicate, inorganic phosphate, inorganic aluminate, ethyl orthosilicate and kaolin.

7. A negative electrode sheet comprising:

a negative current collector; and

a negative electrode active material layer on a surface of the negative electrode current collector;

characterized in that the anode active material layer comprises the composite anode material according to any one of claims 1 to 4.

8. The negative electrode sheet according to claim 7, wherein the negative electrode active material layer further comprises a carbon-based negative electrode material, a conductive agent, and a binder.

9. A battery comprising a negative electrode tab according to any one of claims 7 to 8.