A compound additive for lithium battery electrolyte

Abstract

This invention discloses a compound additive for lithium battery electrolytes, comprising a high-voltage additive and an auxiliary additive capable of forming a film together with the high-voltage additive. The high-voltage additive is a polyphosphate compound containing a polysubstituted sulfonyl group and a polysubstituted alkyl group. The general structural formula of the high-voltage additive is: where R is an alkyl group with 1-8 carbon atoms, X1 is one of hydrogen, halogen, a hydrocarbon group with 1-8 carbon atoms, or a halogenated derivative of a hydrocarbon group with 1-8 carbon atoms, X2 is one of hydrogen, halogen, a hydrocarbon group with 1-8 carbon atoms, or a halogenated derivative of a hydrocarbon group with 1-8 carbon atoms, and n is the degree of polymerization.

Description

[0001] This application is a divisional application of application number "2021116740415" entitled "A high-voltage additive and electrolyte for lithium batteries". Technical Field

[0002] This invention relates to the field of materials technology, and in particular to a compound additive for lithium battery electrolytes. Background Technology

[0003] As a new type of energy source, lithium-ion batteries have been widely used in various fields since their invention due to their advantages such as no memory effect, rapid charging and discharging, high energy density, long cycle life, and no environmental pollution. Today, with the increasing demands on lithium-ion battery capacity from pure electric vehicles, hybrid vehicles, and portable energy storage devices, there is a growing expectation to develop lithium-ion batteries with higher energy and power densities to achieve longer driving range and energy storage.

[0004] Developing high-energy-density lithium batteries can be achieved by increasing the battery's operating voltage, allowing the positive and negative electrode materials to achieve higher specific capacities, thereby improving the mass and volumetric energy density of lithium-ion batteries. Simultaneously, it can reduce the cost of lithium batteries, making it a hot research topic in recent years. However, in the process of researching high-voltage lithium batteries, it has been found that as the operating voltage of lithium-ion batteries increases, traditional lithium battery electrolytes not only undergo self-oxidation and decomposition but also undergo irreversible chemical reactions with the positive electrode material, continuously consuming active lithium. This leads to increased battery impedance, low capacity retention, performance degradation, and a significant shortening of battery life. Therefore, developing electrolyte technologies specifically suited for high-voltage lithium batteries has become crucial. Summary of the Invention

[0005] This invention provides a compound additive for lithium battery electrolytes, which can form a uniform, dense, and stable positive electrode-electrolyte interface (CE I) film on the surface of the positive electrode material of lithium batteries, thereby improving the cycle performance and storage performance of lithium batteries.

[0006] In a first aspect, this embodiment provides a high-voltage additive for lithium battery electrolytes and an auxiliary additive capable of forming a film together with the high-voltage additive. The high-voltage additive is a polyphosphate compound containing polysubstituted sulfonyl groups and polysubstituted alkyl groups; the general structural formula of the high-voltage additive is:

[0007]

[0008] Wherein, R is an alkyl group with 1-8 carbon atoms, X1 is one of hydrogen, halogen, hydrocarbon group with 1-8 carbon atoms, or a halogenated derivative of hydrocarbon group with 1-8 carbon atoms, X2 is one of hydrogen, halogen, hydrocarbon group with 1-8 carbon atoms, or a halogenated derivative of hydrocarbon group with 1-8 carbon atoms, and n is the degree of polymerization.

[0009] Preferably, the halogen includes one or more of fluorine, chlorine, or bromine; the hydrocarbon group includes one or more of alkyl, alkenyl, cycloalkenyl, or aryl; and the halogenated derivative of the hydrocarbon group specifically refers to a halogen that partially or completely substitutes for hydrogen in the hydrocarbon group.

[0010] Secondly, this embodiment provides an electrolyte for high-voltage lithium batteries, the electrolyte comprising: lithium salt electrolyte, organic solvent, and the high-voltage additive and auxiliary additives described in the first aspect.

[0011] Preferably, the lithium salt electrolyte comprises one or more of lithium hexafluorophosphate, lithium hexafluoroarsenate, lithium perchlorate, lithium tetrafluoroborate, lithium difluorophosphate, lithium bis(oxalato)borate, lithium difluorooxalato)borate, lithium bis(trifluoromethanesulfonylimide), or lithium bis(fluorosulfonylimide).

[0012] Preferably, the organic solvent includes any one or more of the following: ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, 1,4-butyrolactone, methyl formate, ethyl acetate, methyl propionate, ethyl propionate, propyl propionate, butyl propionate, ethyl butyrate, and their halogenated derivatives.

[0013] Preferably, the auxiliary additives include one or more of the following: cyclic carbonate compounds, linear ester compounds containing unsaturated bonds, cyclic sulfate compounds, cyclic sulfonate compounds, silazane compounds, sulfonate amine salt compounds, phenylborane compounds, silanized phosphate compounds, cyclic carboxylate borate compounds, nitrile compounds, or sulfone compounds.

[0014] Preferably, the cyclic carbonate compounds, linear ester compounds containing unsaturated bonds, cyclic sulfate compounds, cyclic sulfonate compounds, silazane compounds, sulfonate ammonium salt compounds, phenylborane compounds, silicic phosphate compounds, cyclic carboxylate borate compounds, nitrile compounds, or sulfone compounds may also be substituted with fluorine-containing substituents.

[0015] Preferably, the cyclic carbonate compound includes one or more of vinylene carbonate and vinyl ethylene carbonate;

[0016] The linear ester compounds containing unsaturated bonds include vinyl acetate ester;

[0017] The cyclic sulfate compounds include one or more of vinyl sulfite, propylene sulfite, and vinyl sulfate;

[0018] The cyclic sulfonate compounds include one or more of 1,3-propanesulfonate lactone, propenyl-1,3-propanesulfonate lactone, 1,4-butanesulfonate lactone, and methylene disulfonate.

[0019] The silazane compounds include hexamethyldisilazane;

[0020] The silicon-containing phosphate compounds include tris(trimethylsilane) phosphate and tris(trimethylsilane) phosphite;

[0021] The sulfonate amine salt compounds include magnesium trifluoromethylsulfonate imine;

[0022] The phenylborane compounds include tris(pentafluorinated phenyl)boron;

[0023] The cyclic carboxylate borate compounds include lithium difluorooxalate borate.

[0024] Preferably, in the electrolyte, the lithium salt electrolyte accounts for 0.5wt%-20wt% of the total mass of the electrolyte;

[0025] The organic solvent accounts for 70wt%-90wt% of the total mass of the electrolyte;

[0026] The high-voltage additive accounts for 0.1wt%-5wt% of the total mass of the electrolyte;

[0027] The auxiliary additives account for 1wt%-5wt% of the total mass of the electrolyte.

[0028] Thirdly, this embodiment provides a high-voltage lithium battery, which includes the electrolyte for high-voltage lithium batteries described in the second aspect.

[0029] Preferably, the positive electrode material of the high-voltage lithium battery includes one or more of the following: lithium cobalt oxide, lithium manganese oxide, lithium nickel manganese oxide, lithium-rich materials, nickel-cobalt-manganese ternary materials, or nickel-cobalt-aluminum materials.

[0030] The high-voltage additive for lithium batteries provided in this invention is a polyphosphate compound containing polysubstituted sulfonyl and polysubstituted alkyl groups. In this structure, due to the influence of the polysubstituted groups on the sulfonyl functional groups, they are easily oxidized and decomposed under high voltage, forming some sulfur-containing inorganic compounds. Simultaneously, the polysubstituted alkyl groups are also oxidized, forming a uniform and dense CEI film on the surface of the cathode material with the sulfur-containing compounds. This CEI film contains phosphorus and sulfur, or halogens, has stable composition, and good mechanical properties, and can fully coat the surface of the cathode material, thereby inhibiting the breakage of cathode material particles under high voltage.

[0031] Under high voltage, a large number of phosphate ester functional groups can complex transition metal ions dissolved from the surface of the positive electrode material, thereby preventing highly oxidizing transition metal ions from entering the electrolyte and reaching the negative electrode material, reducing the continuous oxidation of the electrolyte and the damage to the negative electrode material.

[0032] This high-voltage additive modifies the electrode / electrolyte interface through multifunctional group interactions, preventing direct contact between the positive electrode material surface and the electrolyte, thereby reducing electrolyte oxidative decomposition. The resulting CEI film has stable composition and will not dissolve or regrow during battery charge-discharge cycles, improving CEI film uniformity, reducing CEI film thickness, lowering battery impedance, and minimizing polarization. Furthermore, this high-voltage additive can also form a composite negative electrode solid electrolyte interphase (SEI) film together with auxiliary additives at the negative electrode, improving the stability of the negative electrode SEI film and enhancing the electrochemical performance of lithium batteries under high-voltage conditions. Detailed Implementation

[0033] The present invention will be further described in detail below through specific embodiments. However, it should be understood that these embodiments are only for more detailed description and should not be construed as limiting the present invention in any way, that is, not intended to limit the scope of protection of the present invention.

[0034] This invention provides a high-voltage additive for lithium battery electrolytes. The high-voltage additive is a polyphosphate compound containing multi-substituted sulfonyl groups and multi-substituted alkyl groups. The general structural formula of the high-voltage additive is:

[0035]

[0036] Wherein, R is an alkyl group with 1-8 carbon atoms, X1 is one of hydrogen, halogen, hydrocarbon group with 1-8 carbon atoms, or a halogenated derivative of hydrocarbon group with 1-8 carbon atoms, X2 is one of hydrogen, halogen, hydrocarbon group with 1-8 carbon atoms, or a halogenated derivative of hydrocarbon group with 1-8 carbon atoms, and n is the degree of polymerization.

[0037] Halogens include one or more of fluorine, chlorine, or bromine; hydrocarbon groups include one or more of alkyl, alkenyl, cycloalkenyl, or aryl groups; halogenated derivatives of hydrocarbon groups are specifically those in which halogens partially or completely replace hydrogen in the hydrocarbon group.

[0038] This invention provides an electrolyte for high-voltage lithium batteries, comprising: lithium salt electrolyte, organic solvent, high-voltage additive, and auxiliary additive.

[0039] The lithium salt electrolyte includes one or more of the following: lithium hexafluorophosphate, lithium hexafluoroarsenate, lithium perchlorate, lithium tetrafluoroborate, lithium difluorophosphate, lithium bis(oxalato)borate, lithium difluorooxalato)borate, lithium bis(trifluoromethanesulfonylimide), or lithium bis(fluorosulfonylimide); wherein the mass of the lithium salt electrolyte accounts for 0.5wt%-20wt% of the total mass of the electrolyte.

[0040] The organic solvent includes any one or more of the following: ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, 1,4-butyrolactone, methyl formate, ethyl acetate, methyl propionate, ethyl propionate, propyl propionate, butyl propionate, ethyl butyrate, and their halogenated derivatives; wherein the organic solvent accounts for 70wt%-90wt% of the total mass of the electrolyte.

[0041] The high-voltage additive is a polyphosphate compound containing polysubstituted sulfonyl and polysubstituted alkyl groups, and its mass accounts for 0.1 wt%-5 wt% of the total electrolyte mass. Using this high-voltage additive, a uniform and dense CE I film can be preferentially formed on the positive electrode surface during battery charging and discharging, modifying the positive electrode material / electrolyte interface, reducing electrolyte oxidative decomposition, improving electrolyte stability under high voltage, and enhancing the high-voltage electrochemical performance of the lithium battery. After adding the high-voltage additive of this invention, within a suitable addition range, the high-voltage cycle capacity retention rate and high-voltage cycle life of the lithium battery are both improved to a certain extent.

[0042] The auxiliary additives include one or more of the following: vinylene carbonate, vinyl ethylene carbonate, vinyl vinyl acetate, vinyl sulfite, propylene sulfite, vinyl sulfate, 1,3-propanesulfonate lactone, propylene-1,3-propanesulfonate lactone, 1,4-butanesulfonate lactone, methylene disulfonate, hexamethyldisilazane, magnesium imine trifluoromethanesulfonate, tris(pentafluorinated phenyl)boron, tris(trimethylsilane) phosphate, tris(trimethylsilane) phosphite, lithium difluorooxalate boronate, nitrile compounds, or sulfone compounds; wherein the mass of the auxiliary additives accounts for 1wt%-5wt% of the total mass of the electrolyte. The auxiliary additives can form a composite SEI film at the negative electrode together with high-voltage additives, improving the stability of the negative electrode SEI film and enhancing the electrochemical performance of the lithium battery under high-voltage conditions.

[0043] This invention provides a high-voltage lithium battery, which includes the electrolyte described above. The positive electrode material of the high-voltage lithium battery includes one or more of the following: lithium cobalt oxide, lithium manganese oxide, lithium nickel manganese oxide, lithium-rich materials, nickel-cobalt-manganese ternary materials, or nickel-cobalt-aluminum materials.

[0044] To better understand the technical solution provided by this invention, the following uses several specific examples to illustrate the preparation of the electrolyte with high-voltage additives, the method of applying it to lithium batteries, and the battery characteristics.

[0045] Example 1

[0046] This embodiment provides a high-voltage additive A, with the following structural formula:

[0047]

[0048] In a glove box under an argon atmosphere with environmental parameters of H2O ≤ 0.5 ppm and O2 ≤ 2.0 ppm, organic solvents ethylene carbonate (EC), propylene carbonate (PC), fluoroethylene carbonate (FEC), and ethyl methyl carbonate (EMC) were mixed in a mass ratio of EC / PC / FEC / EMC = 15 / 10 / 5 / 70. Lithium hexafluorophosphate was then added to dissolve the mixture, preparing an electrolyte with a lithium hexafluorophosphate concentration of 1 mol / L. Then, auxiliary additives vinylene carbonate (VC), succinate (SN), and lithium difluorooxalate borate (LiDFOB) were added at mass fractions of 1%, 1%, and 0.5%, respectively. Finally, 1% of high-voltage additive A was added to obtain electrolyte I.

[0049] The electrolyte prepared in this embodiment was used to assemble a lithium battery and then tested. The specific steps are as follows:

[0050] (1) Lithium cobalt oxide, suitable for high voltage, was selected as the positive electrode material. The positive electrode material LiCoO2, carbon nanotubes (CNTs), and polyvinylidene fluoride (PVDF) were mixed uniformly in a ratio of 98:1:1, coated onto an aluminum foil current collector, dried in an oven, and then rolled on a roller press to a compaction density of 4.0 g / cm³. 3 The desired positive electrode sheet is obtained.

[0051] (2) Artificial graphite was selected as the negative electrode material. The artificial negative electrode, carboxymethyl cellulose (CMC), conductive agent Super P, and binder styrene-butadiene rubber (SBR) were mixed evenly in a ratio of 95:1.2:1.8:2 to obtain a negative electrode sheet with a compacted density of 1.65 g / cm³. 3 .

[0052] (3) Select 9μm PE as the base film, coat it with 3μm ceramic material to obtain (9+3) coated separator film, and make the electrode into a 2Ah small soft pack battery by stacking. The electrolyte is the electrolyte prepared in this embodiment.

[0053] The performance of the electrolyte in this embodiment was evaluated by testing small pouch batteries, specifically assessing the role of the high-voltage additive. Test conditions included a charge / discharge voltage window of 3.0-4.5V, cyclic testing at room temperature (25°C) and high temperature (45°C), with a cyclic charge / discharge current of 0.5C for both conditions.

[0054] The battery prepared in this embodiment is numbered 1#, and the test results are detailed in Table 1.

[0055] Example 2:

[0056] This embodiment provides a high-voltage additive B:

[0057]

[0058] In a glove box under an argon atmosphere with environmental parameters of H2O ≤ 0.5 ppm and O2 ≤ 2.0 ppm, organic solvents ethylene carbonate (EC), propylene carbonate (PC), fluoroethylene carbonate (FEC), and ethyl methyl carbonate (EMC) were mixed in a mass ratio of EC / PC / FEC / EMC = 15 / 10 / 5 / 70. Then, lithium hexafluorophosphate was added to dissolve the mixture, preparing an electrolyte with a lithium hexafluorophosphate concentration of 1 mol / L. Then, auxiliary additives VC, SN, and LiDFOB were added at mass fractions of 1%, 1%, and 0.5%, respectively. Finally, 1% of high-voltage additive B was added to obtain electrolyte II.

[0059] The electrolyte prepared in this embodiment was used to assemble a lithium battery and tested. Lithium manganese oxide was used as the positive electrode material. The specific steps of battery assembly and testing process were the same as in Embodiment 1. The battery prepared in this embodiment was numbered 2#. The test results are detailed in Table 1.

[0060] Example 3:

[0061] This embodiment provides a high-voltage additive C:

[0062]

[0063] In a glove box under an argon atmosphere with environmental parameters of H2O ≤ 0.5 ppm and O2 ≤ 2.0 ppm, organic solvents ethylene carbonate (EC), propylene carbonate (PC), fluoroethylene carbonate (FEC), and ethyl methyl carbonate (EMC) were mixed in a mass ratio of EC / PC / FEC / EMC = 15 / 10 / 5 / 70. Then, lithium hexafluorophosphate was added to dissolve the mixture, preparing an electrolyte with a lithium hexafluorophosphate concentration of 1 mol / L. Then, auxiliary additives VC, SN, and LiDFOB were added at mass fractions of 1%, 1%, and 0.5%, respectively. Finally, 1% of high-voltage additive C was added to obtain electrolyte III.

[0064] The electrolyte prepared in this embodiment was used to assemble a lithium battery and tested. Lithium cobalt oxide was used as the positive electrode material. The specific steps of battery assembly and testing process were the same as in Embodiment 1. The battery prepared in this embodiment was numbered 3#. The test results are detailed in Table 1.

[0065] Example 4:

[0066] This embodiment provides a high-voltage additive D:

[0067]

[0068] In a glove box under an argon atmosphere with environmental parameters of H2O ≤ 0.5 ppm and O2 ≤ 2.0 ppm, organic solvents ethylene carbonate (EC), propylene carbonate (PC), fluoroethylene carbonate (FEC), and ethyl methyl carbonate (EMC) were mixed in a mass ratio of EC / PC / FEC / EMC = 15 / 10 / 5 / 70. Then, lithium hexafluorophosphate was added to dissolve the mixture, preparing an electrolyte with a lithium hexafluorophosphate concentration of 1 mol / L. Then, auxiliary additives VC, SN, and LiDFOB were added at mass fractions of 1%, 1%, and 0.5%, respectively. Finally, 1% of high-voltage additive D was added to obtain electrolyte IV.

[0069] The electrolyte prepared in this embodiment was used to assemble a lithium battery and tested. Lithium nickel manganese oxide was used as the positive electrode material. The specific steps of battery assembly and testing process were the same as in Example 1. The battery prepared in this embodiment was numbered 4#. The test results are detailed in Table 1.

[0070] Example 5:

[0071] This embodiment uses the same high-voltage additive B as in Example 2:

[0072]

[0073] In a glove box under an argon atmosphere with environmental parameters of H2O ≤ 0.5 ppm and O2 ≤ 2.0 ppm, organic solvents ethylene carbonate (EC), propylene carbonate (PC), fluoroethylene carbonate (FEC), and ethyl methyl carbonate (EMC) were mixed in a mass ratio of EC / PC / FEC / EMC = 15 / 10 / 5 / 70. Lithium hexafluorophosphate was then added to dissolve the mixture, preparing an electrolyte with a lithium hexafluorophosphate concentration of 1 mol / L. Auxiliary additives VC, SN, and LiDFOB were then added at mass fractions of 1%, 1%, and 0.5%, respectively. Finally, 0.5% of high-voltage additive B was added to obtain electrolyte V.

[0074] The electrolyte prepared in this embodiment was used to assemble a lithium battery and tested. Nickel-cobalt-manganese ternary material was used as the positive electrode material. The specific steps of battery assembly and testing process were the same as in Example 1. The battery prepared in this embodiment was numbered 5#. The test results are detailed in Table 1.

[0075] Example 6:

[0076] This embodiment uses the same high-voltage additive B as in Example 2:

[0077]

[0078] In a glove box under an argon atmosphere with environmental parameters of H2O ≤ 0.5 ppm and O2 ≤ 2.0 ppm, organic solvents ethylene carbonate (EC), propylene carbonate (PC), fluoroethylene carbonate (FEC), and ethyl methyl carbonate (EMC) were mixed in a mass ratio of EC / PC / FEC / EMC = 15 / 10 / 5 / 70. Then, lithium hexafluorophosphate was added to dissolve the mixture, preparing an electrolyte with a lithium hexafluorophosphate concentration of 1 mol / L. Then, auxiliary additives VC, SN, and LiDFOB were added at mass fractions of 1%, 1%, and 0.5%, respectively. Finally, 1.5% of high-voltage additive B was added to obtain electrolyte VI.

[0079] The electrolyte prepared in this embodiment was used to assemble a lithium battery and tested. A lithium-rich material was used as the positive electrode material. The specific steps of battery assembly and testing process were the same as in Embodiment 1. The battery prepared in this embodiment was numbered 6#. The test results are detailed in Table 1.

[0080] Example 7:

[0081] This embodiment uses the same high-voltage additive B as in Example 2:

[0082]

[0083] In a glove box under an argon atmosphere with environmental parameters of H2O ≤ 0.5 ppm and O2 ≤ 2.0 ppm, organic solvents ethylene carbonate (EC), propylene carbonate (PC), fluoroethylene carbonate (FEC), and ethyl methyl carbonate (EMC) were mixed in a mass ratio of EC / PC / FEC / EMC = 15 / 10 / 5 / 70. Then, lithium hexafluorophosphate was added to dissolve the mixture, preparing an electrolyte with a lithium hexafluorophosphate concentration of 1 mol / L. Then, auxiliary additives VC, SN, and LiDFOB were added at mass fractions of 1%, 1%, and 0.5%, respectively. Finally, 2% of high-voltage additive B was added to obtain electrolyte VII.

[0084] The electrolyte prepared in this embodiment was used to assemble a lithium battery and tested. Nickel-cobalt-aluminum material was used as the positive electrode material. The specific steps of battery assembly and testing process were the same as in Example 1. The battery prepared in this embodiment was numbered 7#. The test results are detailed in Table 1.

[0085] To better illustrate the effects of the embodiments of the present invention, Comparative Example 1 is compared with the above embodiments.

[0086] Comparative Example 1:

[0087] High-voltage additives were not used in this comparative example.

[0088] In a glove box under an argon atmosphere with environmental parameters of H2O ≤ 0.5 ppm and O2 ≤ 2.0 ppm, organic solvents ethylene carbonate (EC), propylene carbonate (PC), fluoroethylene carbonate (FEC), and ethyl methyl carbonate (EMC) were mixed in a mass ratio of EC / PC / FEC / EMC = 15 / 10 / 5 / 70. Then, lithium hexafluorophosphate was added to dissolve the mixture to prepare an electrolyte with a lithium hexafluorophosphate concentration of 1 mol / L. Subsequently, auxiliary additives VC, SN, and LiDFOB were added at mass fractions of 1%, 1%, and 0.5%, respectively, to prepare control electrolyte 1.

[0089] The electrolyte prepared in this comparative example was used to assemble a lithium battery and tested. Lithium cobalt oxide was used as the positive electrode material. The specific steps of battery assembly and testing process were the same as in Example 1. The battery prepared in this comparative example was numbered 8#. The test results are detailed in Table 1.

[0090] Table 1 shows the electrical performance test results of the batteries assembled in Examples 1-7 and Comparative Example 1.

[0091]

[0092] Table 1

[0093] As can be seen from the data in Table 1, the initial efficiency and cycle capacity retention of the batteries in Examples 1-7 of this invention are better than those in Comparative Example 1. This indicates that, within a suitable addition range, the room-temperature initial efficiency, room-temperature cycle capacity retention, and high-temperature cycle capacity retention of high-voltage lithium batteries are all improved after using the high-voltage additive of this invention. This demonstrates that the high-voltage additive of this invention has excellent performance, and the high-voltage electrolyte prepared using it has good performance.

[0094] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A compound additive for lithium battery electrolyte, characterized in that, The compound additive includes a high-voltage additive and an auxiliary additive capable of forming a film together with the high-voltage additive. The high-voltage additive is a polyphosphate compound containing multi-substituted sulfonyl groups and multi-substituted alkyl groups. The general structural formula of the high-voltage additive is: ； Wherein, R is an alkyl group with 1-8 carbon atoms, X1 is one of hydrogen, halogen, hydrocarbon group with 1-8 carbon atoms, or a halogenated derivative of hydrocarbon group with 1-8 carbon atoms, X2 is one of hydrogen, halogen, hydrocarbon group with 1-8 carbon atoms, or a halogenated derivative of hydrocarbon group with 1-8 carbon atoms, and n is the degree of polymerization; by mass, the ratio of the high-voltage additive to the auxiliary additive is (1 part to 2 parts): 2.5 parts.

2. The compound additive for lithium battery electrolyte according to claim 1, characterized in that, The halogen includes one or more of fluorine, chlorine, or bromine; the hydrocarbon group includes one or more of alkyl, alkenyl, cycloalkenyl, or aryl; the halogenated derivative of the hydrocarbon group is specifically a halogen that partially or completely substitutes for hydrogen in the hydrocarbon group.

3. The compound additive for lithium battery electrolyte according to claim 1, characterized in that, The auxiliary additives include one or more of the following: cyclic carbonate compounds, linear ester compounds containing unsaturated bonds, cyclic sulfate compounds, cyclic sulfonate compounds, silazane compounds, sulfonate ammonium salt compounds, phenylborane compounds, silicic phosphate compounds, cyclic carboxylate borate compounds, nitrile compounds, or sulfone compounds.

4. The compound additive for lithium battery electrolyte according to claim 3, characterized in that, The cyclic carbonate compounds, linear ester compounds containing unsaturated bonds, cyclic sulfate compounds, cyclic sulfonates, silazane compounds, sulfonate amine salts, phenylborane compounds, silicic phosphate compounds, cyclic carboxylate borate compounds, nitrile compounds, or sulfone compounds are substituted with fluorine-containing substituents.

5. A compound additive for lithium battery electrolyte according to claim 3, characterized in that, The cyclic carbonate compounds include one or more of vinylene carbonate and vinyl ethylene carbonate; The linear ester compounds containing unsaturated bonds include vinyl acetate ester; The cyclic sulfate compounds include one or more of vinyl sulfite, propylene sulfite, and vinyl sulfate; The cyclic sulfonate compounds include one or more of 1,3-propanesulfonate lactone, propenyl-1,3-propanesulfonate lactone, 1,4-butanesulfonate lactone, and methylene disulfonate. The silazane compounds include hexamethyldisilazane; The silicon-containing phosphate compounds include tris(trimethylsilane) phosphate and tris(trimethylsilane) phosphite; The sulfonate amine salt compounds include magnesium trifluoromethylsulfonate imine; The phenylborane compounds include tris(pentafluorinated phenyl)boron; The cyclic carboxylate borate compounds include lithium difluorooxalate borate.

6. The use of the compound additive according to any one of claims 1-5 in the electrolyte.

7. The application according to claim 6, characterized in that, The electrolyte also includes lithium salt electrolyte and organic solvent.

8. The application according to claim 7, characterized in that, The lithium salt electrolyte includes one or more of the following: lithium hexafluorophosphate, lithium hexafluoroarsenate, lithium perchlorate, lithium tetrafluoroborate, lithium difluorophosphate, lithium bis(oxalato)borate, lithium difluorooxalato)borate, lithium bis(trifluoromethanesulfonylimide), or lithium bis(fluorosulfonylimide).

9. The application according to claim 7, characterized in that, The organic solvent includes any one or more of the following: ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, 1,4-butyrolactone, methyl formate, ethyl acetate, methyl propionate, ethyl propionate, propyl propionate, butyl propionate, ethyl butyrate, and their halogenated derivatives.

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