WO2025227462A1 - Electrolyte additive, electrolyte, and battery - Google Patents

Abstract

An electrolyte additive, an electrolyte, and a battery. The electrolyte additive comprises a first additive and a second additive, the first additive comprises a compound containing a silicon element and an unsaturated hydrocarbon group, and the second additive comprises a compound as shown in formula 1: (I), wherein X is selected from among O=S=O or C=O; R11 and R12 are each independently selected from among at least one of H, (II); R11 and R12 are not H at the same time; and R11 and R12 at least contain one sulfur atom. The electrolyte additive is added into a secondary battery, so that the high-temperature cycle performance and the high-temperature storage performance of the battery can be improved.

Description

Electrolyte additives, electrolytes and batteries

Priority information

This application claims priority and benefit to patent application 202410522374.3, filed with the China National Intellectual Property Administration on April 28, 2024, the entire contents of which are incorporated herein by reference.

Technical Field

This application belongs to the field of batteries, specifically relating to an electrolyte additive, an electrolyte, and a battery.

Background Technology

In recent years, the rapid development and widespread application of various portable electronic devices, new energy electric vehicles, and energy storage systems have created an increasingly urgent demand for rechargeable batteries with high energy density, long cycle life, safe use, and good rate performance.

However, the positive electrode materials of secondary batteries (such as sodium-ion batteries) may suffer from instability. High-temperature performance is particularly important for secondary batteries, as they are prone to poor storage performance, poor cycle performance, and gas generation at high temperatures, thus degrading their cycle performance, storage performance, and safety performance at high temperatures. Existing secondary batteries typically add various additives to the electrolyte, which can form an organic passivation film on the surface of the active material to improve the battery's cycle performance and high-temperature storage performance. However, the passivation film formed by conventional additives on the surface of the active material has high internal resistance, and this passivation film is insufficient to inhibit the continuous decomposition of the electrolyte on the positive electrode active material during battery cycling. This leads to a continuous increase in the thickness of the passivation film, resulting in a continuous increase in the internal resistance of the secondary battery during cycling, severely affecting its performance in high-temperature cycling and storage, and consequently impacting battery safety.

Given the above shortcomings, it is essential to develop an electrolyte that can significantly improve the cycle performance and high-temperature storage performance of secondary batteries.

Summary of the Invention

This application aims to at least partially address one of the technical problems in the related art. Therefore, one objective of this application is to provide an electrolyte additive, an electrolyte, and a battery, wherein adding the electrolyte additive to a secondary battery can improve the cycle performance and storage performance of the secondary battery at high temperatures.

The first aspect of this application discloses an electrolyte additive, which includes a first additive and a second additive, wherein the first additive includes a compound containing silicon and an unsaturated hydrocarbon group, and the second additive includes a compound represented by Formula 1:

Where X is selected from O=S=O or C=O, and _R11 and _R12 are each independently selected from H, At least one of them, _R11 and _R12 are not both H, and _R11 and _R12 contain at least one sulfur atom.

The combined use of a first additive containing carbon-carbon unsaturated bonds and silicon, and a second additive containing sulfone groups and cyclic carbonates, can significantly extend the cycle life of the battery at high temperatures, suppress gas production caused by the expansion of the secondary battery at high temperatures, and address the continuous increase in internal resistance during cycling, thereby improving the battery's high-temperature storage performance. The synergistic effect of the two additives stems from the combination of vinyl and sulfone functional groups to provide an SEI with a cross-linked protective network. The use of the first additive generates an SEI containing unsaturated bonds from an organic polymer on the negative electrode surface. The presence of this polymer component improves the stability of the SEI; however, with high-temperature cycling, this polymer component further decomposes, making the SEI on the electrode more porous and significantly increasing the SEI impedance. The use of the second additive generates an SEI containing alkyl sulfonate ( _RSO3Li ) on the negative electrode surface. The presence of alkyl sulfonate increases the lithium-ion conductivity of the SEI and can also react with the SEI containing unsaturated bonds of organic polymers generated by the first additive, inhibiting further decomposition of the organic polymer SEI and thus modifying the SEI. The synergistic effect of the two can form a protective layer with a three-dimensional network on the cathode of the battery, providing cross-linking protective layers and forming an SEI with high conductivity and high thermal stability. This effectively reduces the formation of secondary particles aggregated in the positive electrode of the battery, reduces the thickness of the SEI, reduces the SEI resistance, and improves the cycle performance and storage performance of the secondary battery at high temperatures.

In some embodiments, the mass ratio of the first additive to the second additive is (0.02-50):1. This can improve the battery's high-temperature cycle performance and high-temperature storage performance.

In some embodiments, the mass ratio of the first additive to the second additive is (0.03-30):1. This can improve the battery's high-temperature cycle performance and high-temperature storage performance.

In some embodiments, the first additive comprises at least one of the compounds shown in Formula 2 and Formula 3:

_R1 , _R2 , _R3 , R4, _R5 , _{R6 , R7} , _R8 , _R9 , and _R10 are each independently selected from H, _C1 - _C5 alkyl, C2 _{- C5} alkenyl, _C2 - _C5 alkynyl, and _C2 - _C5 alkoxy groups, and at least one of _R1 , _R2 , _R3 , _R4 , _R5 , _R6 , _R7 , _R8 , _R9 , and _R10 is an unsaturated hydrocarbon group.

In some embodiments, the first additive includes at least one selected from tetravinylsilane, tetramethyldivinyldisiloxane, vinyltrimethoxysilane, and allyloxytrimethylsilane. This can improve the battery's high-temperature cycle performance and high-temperature storage performance.

In some embodiments, the second additive includes at least one of the following substances:

This can improve the battery's high-temperature cycle performance and high-temperature storage performance.

The second aspect of this application discloses an electrolyte comprising the electrolyte additives described in the first aspect. Therefore, adding this electrolyte to a secondary battery can improve the battery's high-temperature cycle performance and high-temperature storage performance.

In some embodiments, the first additive accounts for 0.1%-5% of the total mass of the electrolyte. Therefore, adding this electrolyte to a secondary battery can improve the battery's high-temperature cycle performance and high-temperature storage performance.

In some embodiments, the first additive accounts for 0.1%-3% of the total mass of the electrolyte. Therefore, adding this electrolyte to a secondary battery can improve the battery's high-temperature cycle performance and high-temperature storage capacity. Storage performance.

In some embodiments, the second additive accounts for 0.1%-5% of the total mass of the electrolyte. Therefore, adding this electrolyte to a secondary battery can improve the battery's high-temperature cycle performance and high-temperature storage performance.

In some embodiments, the second additive accounts for 0.1%-3% of the total mass of the electrolyte. Therefore, adding this electrolyte to a secondary battery can improve the battery's high-temperature cycle performance and high-temperature storage performance.

A third aspect of this application discloses a battery comprising the electrolyte described in the second aspect. Consequently, this battery exhibits excellent high-temperature cycling performance and high-temperature storage performance.

In some embodiments, the positive electrode active material includes at _least one _{of LiCoO2} , _LiMn2O4 , LiMnO2, _Li2MnO4 , _LiFePO4 , Li1 _{+aMn1 - xMxO2} , _{LiCo1 - xMxO2} , LiFe1 _{- xMxPO4} , and _{Li2Mn1 - xO4} , where M is selected from at least one of Ni, Co, _Mn , Al, Cr, Mg, Zr, Mo, V, Ti, _B , and F, and 0 ≤ a _< 0.2, 0 ≤ x < ₁ .

In some embodiments, the battery includes a positive electrode active material, which includes at least one of Na _{_x1} _M ₁O₂, Na_{_x2}M₂[M₃(CN) _₆], NaFePO_₄, Na_₃V_₂ (PO_₄) _₃, Na₂M₄P₂O_₇, Na₂Fe₂(SO₄) _{3  , and} Na₂M_₄(SO₄)₂·2H₂O, wherein 0 < _x ₁ ≤ 1, M ₁ includes at least one of Ni, Co, Mn, Fe, and Cu, 0 <x₂< 6, M₂ includes at least one of Ni, Fe, and Mn, M₃ includes at least one of Fe and Mn, and M₄ includes at least one of Fe, Co, Mn, and Cu.

Additional aspects and advantages of this application will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of this application.

Detailed Implementation

The embodiments of this application are described in detail below and are intended to explain this application, but should not be construed as limiting this application.

Although the amount of electrolyte additives used accounts for only a small portion of the electrolyte in a secondary battery, appropriate amounts of additives can form an SEI (Solid Electrolyte Interface) on the surface of the negative electrode active material and a CEI (Cathode Electrolyte Interface) on the surface of the positive electrode active material. The SEI and CEI films formed on the surfaces of the negative and positive electrode active materials, respectively, reduce the risk of side reactions occurring after direct contact between the active materials and the electrolyte.

However, under high temperature or high pressure conditions, the cycle performance and storage performance of batteries are prone to significant degradation. Existing rechargeable batteries typically incorporate various additives into the electrolyte, which can form SEI and CEI on the surface of the active materials to improve cycle performance and high-temperature storage. However, the SEI and CEI formed by conventional additives on the surface of the active materials have high internal resistance, and these SEI and CEI are insufficient to suppress the continuous decomposition of the electrolyte on the positive electrode active material during battery cycling. This leads to a continuous increase in the thickness of the SEI and CEI, resulting in a continuous increase in the internal resistance of the rechargeable battery during cycling, which seriously affects its performance. This affects the battery's performance in areas such as cycling and storage at high temperatures, which in turn impacts the battery's safety performance.

In view of this, the first aspect of this application provides an electrolyte additive, which includes a first additive and a second additive, wherein the first additive includes a compound containing silicon and an unsaturated hydrocarbon group, and the second additive includes a compound represented by Formula 1:

Where X is selected from O=S=O or C=O, and _R11 and _R12 are each independently selected from H, At least one of them, _R11 and _R12 are not both H, and _R11 and _R12 contain at least one sulfur atom.

The electrolyte additives proposed in this application, using a first additive containing carbon-carbon unsaturated bonds and silicon, and a second additive containing sulfone groups and cyclic carbonates, can significantly extend the cycle life of the battery at high temperatures, suppress gas production caused by the expansion of the secondary battery at high temperatures, and address the continuous increase in internal resistance during cycling, thereby improving the battery's high-temperature storage performance. The synergistic effect of the two additives stems from the combination of vinyl and sulfone functional groups to provide an SEI with a cross-linked protective network. The use of the first additive generates an SEI containing an organic polymer with unsaturated bonds on the negative electrode surface of the battery. The presence of this polymer component improves the stability of the SEI; however, with high-temperature cycling, this polymer component further decomposes, making the film formed on the electrode more porous and significantly increasing the SEI impedance. The use of the second additive will generate an SEI containing alkyl sulfonate (RSO ₃ Li) on the negative electrode surface. The presence of alkyl sulfonate makes the SEI have higher lithium-ion conductivity and can also inhibit the further decomposition of the SEI containing unsaturated organic polymers generated by the first additive. The synergistic effect of the two can form a protective layer with a three-dimensional network on the cathode of the battery, providing cross-linking protective layers and forming an SEI with high conductivity and high thermal stability. This effectively reduces the formation of secondary particles aggregated in the positive electrode of the battery, reduces the thickness of the SEI, reduces the SEI resistance, and improves the cycle performance and storage performance of the secondary battery at high temperatures.

It is understandable that the presence of silicon in the first additive can suppress gas production in the battery, as shown in Formula 1. The presence of this group, as an electron-donating group, can promote the formation of unsaturated bonds between the sulfone group and the first additive. The SEI reaction of organic polymers inhibits further decomposition of the organic polymer SEI, which can form a protective layer with a three-dimensional network on the cathode of the battery. This provides cross-linking protective layers and forms an SEI with high conductivity and high thermal stability, thereby improving the cycle performance and storage performance of the secondary battery at high temperatures.

In some embodiments of this application, the mass ratio of the first additive to the second additive is (0.02-50):1. For example, the mass ratio of the first additive to the second additive can be 0.02:1, 0.5:1, 1:1, 10:1, 20:1, 30:1, 40:1, 50:1, etc. Therefore, by controlling the mass ratio of the first additive to the second additive within the above range, the synergistic effect of the first additive and the second additive can be fully utilized, enabling the formation of a three-dimensional network protective layer on the cathode of the battery, providing cross-linking protective layers, forming an SEI with high conductivity and high thermal stability, and improving the cycle performance and storage performance of the secondary battery at high temperatures. In other embodiments of this application, the mass ratio of the first additive to the second additive is (0.03-30):1.

In some embodiments of this application, the first additive includes at least one of the compounds shown in Formula 2 and Formula 3:

_R1 , _R2 , _R3 , R4, _R5 , _{R6 , R7} , _R8 , _R9 , and _R10 are each independently selected from H, _C1 - _C5 alkyl, C2 _{- C5} alkenyl, _C2 - _C5 alkynyl, and _C2 - _C5 alkoxy groups, and at least one of _R1 , _R2 , _R3 , _R4 , _R5 , _R6 , _R7 , _R8 , _R9 , and _R10 is an unsaturated hydrocarbon group.

As an example, when _R1 , _R2 , R3, _R4 , _R5 , _R6 , _R7 , _R8 , _R9 , and _R10 are each independently selected from _C1 - _C5 alkyl groups, _the number of carbon atoms can be 1-5, 2-4, 3-4, etc. When _R1 , _R2 , _R3 , _R4 , _R5 , _R6 , _R7 , _R8 , _R9 , and _R10 are each independently selected from any one of _C2 - _C5 alkenyl, C2 _{- C5} alkynyl, or C2 _{- C5} alkoxy groups, the number of carbon atoms can be 2-5, 3-5, 3-4, 4-5, etc.

In some embodiments of this application, the first additive includes at least one of tetravinylsilane, tetramethyldivinyldisiloxane, vinyltrimethoxysilane, and allyloxytrimethylsilane.

Specifically, the structural formula of the above-mentioned additive is as follows:

Specifically, the first additive uses at least one of the above-mentioned substances and can work synergistically with the second additive containing sulfone groups and cyclic carbonates to form a protective layer with a three-dimensional network on the cathode of the battery, respectively providing a cross-linked protective layer, forming an SEI with high electrical conductivity and high thermal stability, thereby improving the cycle performance and storage performance of the secondary battery at high temperatures.

In some embodiments of this application, the second additive includes at least one of the following substances:

Specifically, the CAS number of Formula 1-1 is 2520352-94-5, the CAS number of Formula 1-2 is 2507955-35-1, the CAS number of Formula 1-3 is 2943046-27-1, the CAS number of Formula 1-4 is 2846091-37-8, the CAS number of Formula 1-5 is 2520352-91-2, and the CAS number of Formula 1-6 is 2846091-42-5. Specifically, the above substances are added to the electrolyte additive, which can synergize with the first additive containing carbon-carbon unsaturated bonds and silicon to form a protective layer with a three-dimensional network on the cathode of the battery, respectively providing a cross-linked protective layer, forming an SEI with high conductivity and high thermal stability, and improving the cycle performance and storage performance of the secondary battery at high temperatures.

The second aspect of this application discloses an electrolyte comprising the electrolyte additives described in the first aspect. Therefore, adding this electrolyte to a secondary battery can improve the battery's high-temperature cycle performance and high-temperature storage performance.

In some embodiments of this application, based on the total mass of the electrolyte, the mass percentage of the first additive is 0.1%-5%, that is, each gram of electrolyte contains 0.1% to 5% of the first additive, for example, it can be 0.1%, 0.5%, 1.0%, etc. The electrolyte content can be 1.5%, 2.0%, 2.5%, 3.0%, 3.5%, 4.0%, 4.5%, 5%, etc. Therefore, adding this first additive content to the secondary battery allows the first and second additives to fully exert their synergistic effect, forming a three-dimensional network protective layer on the battery cathode, providing cross-linking protective layers, and forming an SEI with high conductivity and high thermal stability, thus improving the cycle performance and storage performance of the secondary battery at high temperatures. In other embodiments of this application, the mass percentage of the first additive is 0.1%-3%, for example, 0.1%-2%, based on the total mass of the electrolyte.

In some embodiments of this application, the second additive accounts for 0.1%-5% of the total mass of the electrolyte. That is, each gram of electrolyte contains 0.1% to 5% of the second additive, for example, 0.1%, 0.5%, 1.0%, 1.5%, 2.0%, 2.5%, 3.0%, 3.5%, 4.0%, 4.5%, 5%, etc. Therefore, adding this amount of second additive to the electrolyte in the secondary battery allows the first and second additives to fully exert their synergistic effect, forming a three-dimensional network protective layer on the cathode of the battery, providing cross-linking protective layers, forming an SEI with high conductivity and high thermal stability, and improving the cycle performance and storage performance of the secondary battery at high temperatures. In other embodiments of this application, the second additive accounts for 0.1%-3% of the total mass of the electrolyte, for example, 0.1%-2%.

In some embodiments of this application, the electrolyte further includes a solvent comprising at least one of ethylene carbonate, propylene carbonate, γ-butyrolactone, phenyl acetate, 1,4-butylsulfonyl lactone, 3,3,3-trifluoropropylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, methyl propyl carbonate, methyl formate, ethyl acetate, methyl acetate, propyl acetate, butyl acetate, methyl propionate, ethyl propionate, propyl propionate, butyl propionate, methyl butyrate, ethyl butyrate, ethylene glycol dimethyl ether, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, methyl trifluoroethyl carbonate, (2,2,2)-trifluoroethyl carbonate, 2,2-difluoroethyl acetate, 2,2-difluoroethyl propionate, and 2,2-difluoroethyl methyl carbonate. Using at least one of the aforementioned substances as the solvent in the electrolyte is beneficial for promoting the synergistic effect of the first and second additives, forming a three-dimensional network protective layer on the cathode of the battery, providing cross-linking protective layers, and forming an SEI with high conductivity and high thermal stability, thereby improving the cycle performance and storage performance of the secondary battery at high temperatures. In other embodiments of this application, the solvent includes at least one of ethylene carbonate, dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate.

In some embodiments of this application, the solvent accounts for 65%-87% of the total mass of the electrolyte. For example, 65%, 67%, 70%, 72%, 75%, 80%, 85%, 87%, etc. By controlling the solvent content within the above range, it is beneficial to further promote the synergistic effect of the first additive and the second additive, forming a protective layer with a three-dimensional network on the cathode of the battery, providing cross-linking protective layers, forming an SEI with high conductivity and high thermal stability, and improving the cycle performance and storage performance of the secondary battery at high temperatures.

In some embodiments of this application, the electrolyte further includes other additives selected from vinylene carbonate (VC), ethylene ethylene carbonate, vinyl sulfate, propylene carbonate, fluoroethylene carbonate, 1,3-propanesulfonate lactone, 1,3-propenesulfonate lactone, 1,4-butanesulfonate lactone, 2,4-butanesulfonate lactone, succinic anhydride, maleic anhydride, 2-methylmaleic anhydride, methyl carbonate-2-propynyl ester, triallyl isocyanurate, hexamethylene diisocyanate, o-phenanthroline, terephthalic diisocyanate, 2,4-toluene diisocyanate, N-phenylbis(trifluoromethanesulfonyl)imide, ethyl disulfide, etc. The additives are at least one selected from vinyl esters, phenyl methanesulfonate, vinyl disulfide, propylene dispironate, hydroquinone difluorosulfonate, triallyl phosphate, triargyl phosphate, 2,4-butane sulpholol, isocyanoethyl methacrylate, tris(trimethylsilane)borate, tris(trimethylsilane) phosphate, tris(vinyldimethylsilane) phosphate, 4,4'-bi-1,3-dioxolane-2,2'-dione, propyl dipropyl-2-alkynyl phosphate, ethyl dipropyl-2-alkynyl phosphate, tetramethylmethylene diphosphate, isocyanoethyl methacrylate, and 2-fluoropyridine. In some embodiments of this application, the other additives are selected from vinylene carbonate.

In some embodiments of this application, based on the total mass of the electrolyte, the mass percentage of the other additives is 0.1%-5%, that is, each gram of electrolyte contains 0.1%-5% of other additives, specifically selected from a range of 0.1%, 0.5%, 1.0%, 1.5%, 2.0%, 2.5%, 3.0%, 3.5%, 4.0%, 4.5%, 5.0%, or any combination thereof.

In some embodiments of this application, the electrolyte further includes a lithium salt, wherein the first lithium salt includes at least one of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium tetrafluoroborate, lithium bis(oxalate borate), lithium difluorooxalate borate, lithium difluorooxalate phosphate, lithium tetrafluorooxalate phosphate, and lithium bis(trifluoromethanesulfonyl)imide.

In some embodiments of this application, the mass percentage of the lithium salt is 5%-20% based on the total mass of the electrolyte, for example, it can be 5%, 10%, 15%, 20%, etc.

A third aspect of this application discloses a battery. According to an embodiment of this application, the battery includes the electrolyte described in the second aspect.

Therefore, in the battery containing this electrolyte, during battery formation and cycling, the synergistic effect of the simultaneous use of the first additive and the second additive can form a protective layer with a three-dimensional network on the cathode of the battery, providing a cross-linked protective layer, forming an SEI with high conductivity and high thermal stability, effectively reducing the formation of secondary particles aggregated in the positive electrode of the battery, reducing the thickness of the SEI, reducing the SEI resistance, and improving the cycling performance and storage performance of the secondary battery at high temperatures.

In some embodiments of this application, the battery includes a positive electrode active material. When the battery is a lithium- _ion battery, the positive electrode active material includes at least one of LiCoO2, _{LiMn2O4 , LiMnO2} , _Li2MnO4 , _LiFePO4 , Li1 _{+aMn1-xMxO2, LiCo1 - xMxO2 , LiFe1 - xMxPO4} , and _{Li2Mn1 -xO4 , where} M is selected from at least one of Ni, Co, Mn, _Al , Cr _, Mg, Zr, Mo, V, Ti, B, and F, and 0≤a＜0.2, 0≤x<1.

For example, 0≤a≤0.19, 0.05≤a≤0.15, 0.08≤a≤0.13, 0.1≤a≤0.12; 0≤x≤0.9, 0.1≤x≤0.8, 0.2≤x≤0.7, 0.3≤x≤0.6, 0.4≤x≤0.5, etc.

It is understandable that in Li _1+a Mn _1-x M _x O ₂ , LiCo _1-x M _x O ₂ and LiFe _1-x M _x PO ₄ , the choice of M in each chemical formula is independent of each other and does not affect each other. They can be the same or different. Similarly, in the above list of positive electrode active materials, the choices of a and x are also mutually exclusive and do not affect each other. They can be the same or different.

In other embodiments of this application, the positive electrode active material includes lithium iron phosphate positive electrode active materials ( _LiFePO4 , _{LiFe1- xMxPO4 )} . Specifically, compared to other positive electrode active materials (such as ternary materials), lithium iron phosphate... Lithium-based cathode active materials have a lower voltage plateau and better stability, which allows the battery of this application to be charged and discharged at low voltage. At high temperature and low pressure, lithium iron phosphate cathode active materials, when matched with the additives of this application, can further reduce the probability of SEI decomposition of the three-dimensional network, reduce battery gas production, and improve the battery's cycle performance and storage performance at high temperature.

When the battery is a sodium-ion battery, the positive electrode active material may include at least one of the following materials:

Na _x MO ₂ , wherein M includes at least one of Ti, V, Mn, Co, Ni, Fe, Zn, V, Zr, Ce, Cr, and Cu, and 0 < x ≤ 1.

Polyanionic compounds: _at least _one of NaFePO4, _Na3V2 ( _PO4 ) ₃ (sodium vanadium phosphate, abbreviated as NVP), _Na4Fe3 ( _{PO4 ) 2} ( _P2O7 ), _NaM'PO4F (M' includes at least one of V, Fe, Mn _and Ni) and _Na3 ( _VOy ) _{2 (PO4)2F3-2y ( 0≤y≤1} ).

Prussian blue compounds: Na _a Me _b Me' _c (CN) ₆ , wherein Me and Me' each independently include at least one of Ni, Cu, Fe, Mn, Co, and Zn, 0 < a ≤ 2, 0 < b < 1, 0 < c < 1.

In some embodiments, the battery includes a positive electrode active material, which includes at least one of Na _{_x1} _M ₁O₂, Na_{_x2}M₂[M₃(CN) _₆], NaFePO_₄, Na_₃V_₂ (PO_₄) _₃, Na₂M₄P₂O_₇, Na₂Fe₂(SO₄) _{3  , and} Na₂M_₄(SO₄)₂·2H₂O, wherein 0 < _x ₁ ≤ 1, M ₁ includes at least one of Ni, Co, Mn, Fe, and Cu, 0 <x₂< 6, M₂ includes at least one of Ni, Fe, and Mn, M₃ includes at least one of Fe and Mn, and M₄ includes at least one of Fe, Co, Mn, and Cu. The above-mentioned positive electrode active material has a high operating voltage. Combined with the electrolyte additives of the embodiments of this application, it can better generate a three-dimensional SEI network. Under high voltage, the SEI has strong stability, which can reduce battery gas production and improve the battery's cycle performance and storage performance at high temperatures.

Typically, a battery consists of a positive electrode, a negative electrode, an electrolyte, and a separator. During charging and discharging, active ions move back and forth between the positive and negative electrodes, inserting and releasing. The electrolyte acts as a conductor between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, primarily prevents short circuits while allowing ions to pass through.

The positive electrode sheet includes a positive current collector and a positive active material layer disposed on at least one side surface of the positive current collector, wherein the positive active material layer includes the aforementioned positive active material.

In some embodiments of this application, the positive current collector may include a metal foil or a composite positive current collector. For example, the metal foil may be aluminum foil. The composite positive current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. For example, the composite negative current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, etc.) on a polymer material substrate (such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), etc.).

In some embodiments of this application, the positive electrode active material layer may optionally include a conductive agent. As an example, the conductive agent may include superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. At least one of them.

In some embodiments of this application, the positive electrode active material layer may optionally include a binder. As an example, the binder may include at least one selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

In some embodiments of this application, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as positive active material, conductive agent, and binder, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto the positive current collector, and then obtaining the positive electrode sheet after drying, cold pressing, and other processes.

The negative electrode sheet includes a negative current collector and a negative active material layer disposed on at least one side surface of the negative current collector, wherein the negative active material layer includes a negative active material.

In some embodiments of this application, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), etc.).

In some embodiments of this application, the negative electrode active material may be a negative electrode active material known in the art for use in batteries. As an example, the negative electrode active material may include at least one of the following materials: natural graphite, artificial graphite, soft carbon, hard carbon, mesophase carbon microspheres, nano-carbon, elemental silicon, silicon oxide, silicon-carbon composite, silicon alloy, elemental tin, tin oxide, tin-carbon composite, tin alloy, and lithium titanate.

In some embodiments of this application, the negative electrode active material layer may optionally include a binder. The binder may include at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

In some embodiments of this application, the negative electrode active material layer may optionally include a conductive agent. The conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

In some embodiments of this application, the negative electrode active material layer may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

In some embodiments of this application, the negative electrode sheet can be prepared by dispersing the above-mentioned components for preparing the negative electrode sheet, such as negative electrode active material, conductive agent, binder and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto the negative electrode current collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained.

This application does not impose any particular restrictions on the type of separator membrane; any known porous separator membrane with good chemical and mechanical stability can be selected.

In some embodiments of this application, the material of the separator may include at least one of glass fiber, non-woven fabric, polyolefin membrane, aromatic polyamide membrane, polytetrafluoroethylene membrane, and polyethersulfone membrane.

In some embodiments of this application, the thickness of the separator can be 10μm-12μm, for example, 10μm, 11μm, 12μm, etc.

It should be noted that the features and advantages described above for the electrolyte also apply to this battery, and will not be repeated here.

It should be noted that the features and advantages described above for the battery also apply to this electrical device, and will not be repeated here.

The embodiments of the present invention are described in detail below. It should be noted that the embodiments described below are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention. In addition, unless otherwise specified, all reagents used in the following embodiments are commercially available or can be synthesized according to the methods described herein or known to others. For reaction conditions not listed, they are also readily available to those skilled in the art.

Example 1

1. Preparation of positive electrode sheet

Lithium iron phosphate (purchased from Defang Nano), carbon black, carbon nanotubes, and polyvinylidene fluoride (PVDF) were dispersed in N-methylpyrrolidone solvent at a mass ratio of 94.5:3.5:0.5:1.5 to obtain a positive electrode active material slurry. The positive electrode active material slurry was uniformly coated on the surface of the positive electrode current collector aluminum foil. After drying, rolling, baking, slitting, and spot welding of tabs, a positive electrode sheet was obtained with a total thickness of 90 μm.

2. Preparation of negative electrode sheet

The negative electrode active material graphite (purchased from Jiangxi Zichen), conductive agent carbon black, binder polyvinylidene fluoride and sodium carboxymethyl cellulose were dispersed in deionized water at a mass ratio of 94.5:2:2:1.5 and stirred evenly to obtain a negative electrode active material layer slurry. The negative electrode active material layer slurry was uniformly coated on the surface of the negative electrode current collector copper foil. After drying, rolling, baking, slitting and spot welding of electrode tabs, a negative electrode sheet was obtained with a total thickness of 128 μm.

3. Preparation of electrolyte

EC and EMC were mixed at a mass ratio of 3:7. After mixing, lithium salt, other additives, the first additive, and the second additive were added according to the molar concentration and mass fraction of each component, and mixed thoroughly to obtain the electrolyte. The organic solvents included ethylene carbonate (EC) and ethyl methyl carbonate (EMC) at a mass ratio of 3:7; the lithium salt included _LiPF6 , with a lithium salt concentration of 1 mol/L in the electrolyte; the other additive was VC, which accounted for 1% of the total mass of the electrolyte. The first additive included tetravinylsilane at 0.2% of the total mass of the electrolyte; the second additive was compound 3-1, which accounted for 1% of the total mass of the electrolyte. 0.5% of the mass.

4. Separating membrane

A 10μm polyethylene film was used as the separator.

5. Lithium-ion battery manufacturing

The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to isolate them. The cells are then wound to obtain a bare cell. The tabs are welded on, and the bare cell is placed in an outer package. The electrolyte prepared above is injected into the dried cell. The cells are then encapsulated, left to stand, formed, and shaped to complete the preparation of the lithium-ion battery.

The lithium-ion battery preparation methods of Examples 2-28 and Comparative Examples 1-4 are the same as those of Example 1, except that the composition of additives in the electrolyte is different, as shown in Table 1.

Table 1

Example 29

1. Preparation of positive electrode sheet

The positive electrode active material Na(Ni _0.33 Fe _0.33 Mn _0.33 )O ₂ , conductive agent carbon black, conductive agent carbon nanotubes, and binder polyvinylidene fluoride were dispersed in the solvent N-methylpyrrolidone at a mass ratio of 94.5:3.5:0.5:1.5 to obtain a positive electrode active material slurry. The positive electrode active material slurry was uniformly coated on the surface of the positive electrode current collector aluminum foil. After drying, rolling, baking, slitting, and spot welding of electrode tabs, the positive electrode sheet was obtained with a total thickness of 90 μm.

2. Preparation of negative electrode sheet

The negative electrode active material graphite (purchased from Jiangxi Zichen), conductive agent carbon black, binder polyvinylidene fluoride and sodium carboxymethyl cellulose were dispersed in deionized water at a mass ratio of 94.5:2:2:1.5 and stirred evenly to obtain a negative electrode active material layer slurry. The negative electrode active material layer slurry was uniformly coated on the surface of the negative electrode current collector copper foil. After drying, rolling, baking, slitting and spot welding of electrode tabs, a negative electrode sheet was obtained with a total thickness of 128 μm.

3. Preparation of electrolyte

EC and EMC were mixed at a mass ratio of 3:7. After mixing, sodium salt, other additives, the first additive, and the second additive were added according to the molar concentration and mass fraction of each component, and mixed thoroughly to obtain the electrolyte. The organic solvents included ethylene carbonate (EC) and ethyl methyl carbonate (EMC) at a mass ratio of 3:7; the sodium salt included _NaPF6 , and the molar concentration of sodium in the electrolyte was 1 mol/L; the other additive was VC, which accounted for 1% of the total mass of the electrolyte. The first additive included tetravinylsilane at 0.2% of the total mass of the electrolyte; the second additive was compound 3-1, which accounted for 0.5% of the total mass of the electrolyte.

4. Separating membrane

A 10μm polyethylene film was used as the separator.

5. Sodium-ion battery preparation

Stack the positive electrode, separator, and negative electrode in sequence, with the separator positioned between the positive and negative electrodes to isolate the positive electrode from the negative electrode. The negative electrode is used to wind up the bare cell, the tabs are welded, the bare cell is placed in the outer packaging, the electrolyte prepared above is injected into the dried cell, and then it is packaged, left to stand, formed, shaped, etc. to complete the preparation of sodium-ion battery.

The sodium-ion batteries in Examples 30-33 are prepared in the same way as those in Example 29, except that the composition of the additives in the electrolyte is different, as shown in Table 2.

Table 2

The high-temperature storage performance and high-temperature cycling performance of the secondary batteries obtained in Examples 1-28 and Comparative Examples 1-4 were characterized, and the characterization results are shown in Table 3.

1. At 45℃, the battery is cycled 1500 times to test its capacity retention.

At 45℃, charge to 3.65V with 1C constant current and constant voltage, let stand for 5 minutes, and then discharge to 2.0V with 1C constant current. After 1500 cycles, calculate the capacity retention rate. The calculation method is: capacity retention rate (%) = (1500th discharge capacity / 1st discharge capacity) × 100%, see Table 3.

2. High-temperature storage performance test:

Expansion rate test: At 25℃, charge to 3.65V with 1C constant current and constant voltage, measure the initial thickness of the lithium-ion battery at this time, and then store at 60℃ for 30 days to test the thickness of the lithium-ion battery. Calculate the battery expansion rate according to the formula: Expansion rate (%) = (Thickness after storage - Initial thickness) / Initial thickness × 100%.

Cyclic performance test: After high-temperature storage, the lithium-ion battery is discharged to 2.0V at 1C, and the capacity retention rate of the battery is measured and calculated. The calculation formula is as follows: Capacity retention rate (%) = Retained capacity / Initial capacity × 100%.

DCR growth rate test: Secondary battery DC resistance (DCR) test: DCR test before storage: At an ambient temperature of 25℃, the battery is charged at a constant current of 1.0C to 3.65V, then at a constant voltage of 3.65V until the cutoff current is 0.05C. The battery is then left to rest for 30 minutes, followed by discharge at 1.0C for 30 minutes (adjusted to 50% SOC). The ending voltage V1 is recorded. After resting for 1 hour, the battery is discharged at 2.0C for 10 seconds, and the ending voltage V2 is recorded. The DCR1 before storage is (V1-V2)/(2.0C-1.0C). Storage at 60℃ for 30 minutes... The DCR test was conducted as follows: At an ambient temperature of 25°C, the stored battery was charged at a constant current of 1.0C to 3.65V, then at a constant voltage of 3.65V until the cutoff current reached 0.05C. The battery was then left to rest for 30 minutes, followed by a discharge at 1.0C for 30 minutes (adjusted to 50% SOC). The ending voltage V3 was recorded. After resting for 1 hour, the battery was discharged at 2.0C for 10 seconds, and the ending voltage V4 was recorded. The DCR2 before storage was calculated as (V3-V4)/(2.0C-1.0C); the DCR growth rate was calculated as (DCR2-DCR1)/DCR1×100%.

Table 3

As can be seen from Table 3, in Examples 1-28 of this application, the first additive and the second additive work synergistically when added to the secondary battery, which can reduce battery gas production, improve the high-temperature cycle performance and high-temperature storage performance of the battery, and suppress the growth of battery impedance (DCR).

Compared to Example 2, Comparative Examples 1-4 did not simultaneously add the first additive and the second additive, resulting in batteries with significantly lower gas generation performance, high-temperature cycle performance, and high-temperature storage performance, and significantly higher impedance. It can be seen that the electrolyte additives proposed in this application, with the first additive and the second additive working synergistically, when added to secondary batteries, can reduce battery gas generation, improve the high-temperature cycle performance and high-temperature storage performance of the battery, and suppress the increase in battery impedance.

The high-temperature cycling performance, high-temperature storage gas generation performance, capacity retention rate and DCR growth rate of the batteries in the other embodiments of Examples 1-6 are significantly better than those of Example 5. This is because the amount of the first additive added in Example 5 (5%) is higher than that in other embodiments. The possible reason is that the excessive use of the first additive causes the additive itself to continuously decompose into film, resulting in an increase in impedance and the occurrence of side reactions that generate gas, thereby degrading the battery performance.

The batteries in the other embodiments of Examples 8-13 have significantly better high-temperature cycling performance, high-temperature storage gas generation performance, capacity retention rate and DCR growth rate than those in Example 12. This is because the amount of the second additive added in Example 12 (5%) is higher than in the other embodiments. The possible reason is that the use of excessive second additive will lead to an increase in electrolyte viscosity, and the additive itself will undergo side reactions to generate gas, thereby degrading battery performance.

The high-temperature storage performance and high-temperature cycling performance of the secondary batteries obtained in Examples 29-33 were characterized, and the characterization results are shown in Table 4.

1. At 45℃, the battery is cycled 300 times to test its capacity retention.

The capacity retention rate of sodium-ion batteries after 300 cycles at high temperature (45℃) under 1C charge-discharge conditions was tested. Sodium-ion batteries with their capacity determined by the upper clamp were placed in a preset temperature environment and charged at a constant current and constant voltage of 1C to the upper limit cutoff voltage (cutoff current was 0.05C). Then, they were discharged at a constant current of 1C/1C to the lower limit cutoff voltage. This cycle was repeated, and the discharge capacity of the battery in the first and last cycles was recorded. The capacity retention rate was calculated using the following formula: Capacity retention rate = (Discharge capacity in the last cycle / Discharge capacity in the first cycle) × 100%.

2. High-temperature storage performance test:

Expansion rate test: At 25℃, charge the sodium-ion battery to the upper limit cutoff voltage using 1C constant current and constant voltage, measure the initial thickness of the sodium-ion battery at this time, and then store it at 60℃ for 30 days to test the thickness of the sodium-ion battery. Calculate the battery expansion rate according to the formula: Expansion rate (%) = (Thickness after storage - Initial thickness) / Initial thickness × 100%.

Cycle performance test: After the sodium-ion battery with the upper clamp has been capacity-graded, the clamp is removed and the battery is placed in a 25°C environment. It is charged at a constant current and constant voltage of 1C to the upper limit cutoff voltage, with a cutoff current of 0.05C. Then, it is discharged at a constant current of 1C to the lower limit cutoff voltage, and the discharge capacity at this point is recorded as C0. The battery is then charged again at a constant current and constant voltage of 1C to the upper limit cutoff voltage, with a cutoff current of 0.05C. The fully charged battery is then placed in a 60°C constant temperature oven for 30 days. After that, the battery is removed and placed in a 25°C environment for 2 hours. Then, it is discharged at a constant current of 1C to the lower limit cutoff voltage in a 25°C environment, and the discharge capacity at this point is recorded as C1. Capacity retention rate = (C1/C0) × 100%.

DCR growth rate test: Test DCR1 before storage and DCR2 after storage. Calculate the DCR growth rate according to the formula (DCR2-DCR1)/DCR1×100%.

Table 4

As shown in Table 4, in Examples 29-33 of this application, the first and second additives work synergistically when added to the secondary battery to reduce battery gas production, improve the battery's high-temperature cycle performance and high-temperature storage performance, and suppress the increase in battery impedance (DCR). Therefore, the electrolyte additives in the embodiments of this application are also applicable to sodium-ion batteries, and can improve the high-temperature cycle performance and high-temperature storage performance of sodium-ion batteries, and suppress the increase in battery impedance (DCR).

In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

Although embodiments of this application have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting this application. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of this application.

Claims (13)

An electrolyte additive, comprising a first additive and a second additive, wherein the first additive comprises a compound containing silicon and an unsaturated hydrocarbon group, and the second additive comprises a compound represented by Formula 1:
Where X is selected from O=S=O or C=O, and _R11 and _R12 are each independently selected from H, At least one of them, _R11 and _R12 are not both H, and _R11 and _R12 contain at least one sulfur atom. According to claim 1, the electrolyte additive is wherein the mass ratio of the first additive to the second additive is (0.02-50):1. According to claim 1, the electrolyte additive is wherein the mass ratio of the first additive to the second additive is (0.03-30):1. According to claim 1 or 2, the electrolyte additive, wherein the first additive comprises at least one of the compounds shown in Formula 2 and Formula 3:
_R1 , _R2 , _R3 , R4, _R5 , _R6 , _R7 , _R8 , _R9 , _{and R10} are each independently selected from H, _C1 - _C5 alkyl, C2 _{- C5} alkenyl, _C2 - _C5 alkynyl, and _C2 - _C5 alkoxy groups, and at least one of _R1 , _R2 , _R3 , _R4 , _R5 , _R6 , _R7 , _R8 , _R9 , and _R10 is an unsaturated hydrocarbon group. The electrolyte additive according to claim 1 or 2, wherein the first additive comprises tetravinylsilane. At least one of alkyl, tetramethyldivinyldisiloxane, vinyltrimethoxysilane and allyloxytrimethylsilane. According to claim 1 or 2, the electrolyte additive, wherein the second additive comprises at least one of the following substances:
An electrolyte comprising the electrolyte additive according to any one of claims 1-6. According to claim 7, the electrolyte contains, based on the total mass of the electrolyte, the mass percentage of the first additive is 0.1%-5%. According to claim 7, the electrolyte contains, based on the total mass of the electrolyte, the mass percentage of the first additive is 0.1%-3%. According to claim 7, the electrolyte, the mass percentage of the second additive is 0.1%-5% based on the total mass of the electrolyte. According to claim 7, the electrolyte, the mass percentage of the second additive is 0.1%-3% based on the total mass of the electrolyte. A battery comprising the electrolyte according to any one of claims 7-11. The battery according to claim 12, wherein the battery comprises a positive electrode active material, the positive electrode active material comprising at _{least one selected from LiCoO2, LiMn2O4, LiMnO2, Li2MnO4, LiFePO4, Li1+aMn1-xMxO2 , LiCo1 - xMxO2 , LiFe1 - xMxPO4 , and Li2Mn1 - xO4 , wherein M is selected from} at least one selected from Ni, Co, Mn, Al, Cr, Mg, Zr, Mo, V, Ti, B, and F, 0≤a＜0.2, 0≤x<1; or, The battery includes a positive electrode active material, which includes at least one selected from Na _{_X1} M₁O₂, Na_{_X2}M₂[M₃(CN)_₆], NaFePO_₄, Na _₃V_₂ (PO _₄)₃, Na _₂M₄P₂O_₇, Na_₂Fe_₂(SO_₄)_₃ _, and Na_₂M₄(SO₄)_₂·2H_₂ O. Wherein, 0 < x1 ≤ 1, M1 includes at least one of Ni, Co, Mn, Fe and Cu, 0 < x2 < 6, M2 includes at least one of Ni, Fe and Mn, M3 includes at least one of Fe and Mn, and M4 includes at least one of Fe, Co, Mn and Cu.