Lithium battery electrolyte, lithium battery and lithium battery preparation method

Abstract

The invention relates to the field of lithium batteries, and particularly discloses a lithium battery electrolyte, a lithium battery and a preparation method of the lithium battery. The lithium battery electrolyte comprises 8-20% of a lithium salt, 70-90% of an organic solvent and 0.01-5% of an electrolyte additive, wherein the electrolyte additive comprises at least one of a phosphite additive, siloxane and a film-forming additive. The lithium battery comprises a positive plate, a diaphragm, a negative plate and the lithium battery electrolyte. By adopting at least one of the phosphite additive, the siloxane and the film-forming additive, oxygen released during lithium removal of the lithium supplementing agent can be absorbed, the capacity, high-temperature circulation and high-temperature storage performance of a battery cell can be remarkably improved, the internal resistance of the battery can be reduced, the problem of gas production in the subsequent charging and discharging process of lithium supplementing of the positive electrode can be solved, and the service life of the battery cell can be prolonged. Therefore, the cycle performance and the service life of the lithium iron phosphate battery are improved.

Description

Technical Field

[0001] The present application relates to the technical field of lithium batteries, and in particular to a lithium battery electrolyte, a lithium battery, and a method for preparing a lithium battery. Background Art

[0002] Lithium batteries are widely used in mobile electronic devices, electric vehicles, digital products, energy storage power stations and other fields due to their high energy density, long cycle life and no memory effect. With the widespread use and continuous development of lithium batteries, people have put forward higher requirements for the energy density and cycle life of lithium batteries.

[0003] In the related technology, the commonly used positive electrode materials for lithium batteries include nickel-cobalt-manganese ternary materials, nickel-cobalt-aluminum ternary materials, lithium iron phosphate, lithium manganese-rich oxide, lithium iron manganese phosphate, lithium cobalt oxide, etc. Among them, lithium iron phosphate is one of the main positive electrode materials used in power batteries due to its high safety and good long-cycle stability. However, lithium iron phosphate consumes about 10% of active lithium in the first cycle of charging and discharging to form the solid electrolyte interface film (SEI film) of the negative electrode, which reduces the first efficiency of the lithium battery and also affects the subsequent cycle stability. Lithium replenishment technology is a method that can significantly improve the first efficiency of lithium iron phosphate batteries. Compared with negative electrode lithium replenishment, positive electrode lithium replenishment has the advantages of high safety and compatibility with existing battery manufacturing processes, and is expected to be industrialized. However, positive electrode lithium replenishment will produce gas during the subsequent charging and discharging process, causing a series of side effects such as electrolyte oxidation, which affects the cycle life of lithium batteries.

[0004] Therefore, how to solve the gas production problem that will occur during the subsequent charging and discharging process of positive electrode lithium replenishment in the above-mentioned related technologies, so as to improve the cycle performance and service life of lithium iron phosphate batteries, is a problem that needs to be solved at present. Summary of the invention

[0005] In order to improve the gas production problem that may occur during the subsequent charging and discharging process of positive electrode lithium supplementation, thereby improving the cycle performance and service life of lithium iron phosphate batteries, the present application provides a lithium battery electrolyte, a lithium battery and a lithium battery preparation method.

[0006] In a first aspect, the present application provides a lithium battery electrolyte, which adopts the following technical solution:

[0007] A lithium battery electrolyte comprises the following components in percentage by mass: 8-20% lithium salt, 70-90% organic solvent and 0.01-5% electrolyte additive, wherein the electrolyte additive comprises at least one of phosphite additive, siloxane and film-forming additive.

[0008] By adopting the above technical scheme, the film-forming additive can form a good SEI film on the electrode surface. The phosphite additive can combine with the oxygen on the surface of the positive electrode to form P=O, which can inhibit the oxidation and decomposition of the electrolyte at the positive electrode to produce gas. The Si-O bond in siloxane can react with H2O to generate -(Si-O)n-, or react with HF to generate Si-F bonds, inhibiting the hydrolysis of LiPF6. Through the coordinated cooperation of at least one of the phosphite additive, siloxane, and film-forming additive, the lithium battery electrolyte of the present application can absorb the oxygen released when the lithium supplement agent is de-lithium, significantly improve the capacity, high-temperature cycle and high-temperature storage performance of the battery cell, and can reduce the internal resistance of the battery, improve the gas production problem of the positive electrode supplement during the subsequent charging and discharging process, thereby improving the cycle performance and service life of the lithium iron phosphate lithium battery.

[0009] In a specific embodiment, the phosphite additive is one or more of trimethyl phosphite, tris(2,2,2-trifluoroethyl)phosphite triester, triphenyl phosphite, and tris(trimethylsilyl)phosphite.

[0010] By adopting the above technical solution, these phosphite additives can combine with oxygen on the surface of the positive electrode to form P=O, and can improve the wettability of the electrolyte to the battery separator and the positive and negative electrode materials, thereby improving the battery's charge and discharge efficiency and energy density.

[0011] In a specific embodiment, the siloxane is at least one of dimethoxydimethylsilane, diphenyldimethoxysilane, and vinyltri(2-methoxyethoxy)silane.

[0012] By adopting the above technical solutions, these siloxanes can inhibit the hydrolysis of LiPF6 and reduce the decomposition of the electrolyte during the charge and discharge process. In addition, the silicon-oxygen bonds in the siloxane molecules have high ion conductivity, which helps to improve the charge and discharge efficiency and energy density of lithium batteries.

[0013] In a specific embodiment, the film-forming additive is one or more of vinylene carbonate, fluoroethylene carbonate, lithium difluorooxalate phosphate, and vinyl sulfate.

[0014] By adopting the above technical solutions, these film-forming additives can form a strong and stable solid electrolyte interface (SEI) film on the electrode surface, reduce the occurrence of side reactions, improve the ion conductivity of the electrolyte, accelerate the migration of lithium ions in the electrolyte, and help improve the charge and discharge dynamics of lithium batteries.

[0015] In a specific embodiment, the lithium salt is one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(oxalatoborate), lithium difluorooxalatoborate, lithium difluorophosphate and lithium bis(fluorosulfonyl)imide.

[0016] In a specific embodiment, the organic solvent is one or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, dipropyl carbonate, ethyl acetate, methyl acetate, and ethyl propionate.

[0017] By adopting the above technical solution, the above lithium salt and organic solvent can form a good match with the electrolyte additive of the present application, and a lithium battery with excellent performance can be prepared.

[0018] In a second aspect, the present application provides an application of a lithium battery electrolyte, using the following technical solution:

[0019] An application of a lithium battery electrolyte, wherein the lithium battery electrolyte is applied to a lithium battery, and a positive electrode sheet of the lithium battery contains a lithium supplement.

[0020] By adopting the above technical solution, the lithium battery electrolyte of the present application is applied in a lithium battery whose positive electrode contains a lithium supplement agent, which can absorb the oxygen released when the lithium supplement agent is de-lithiated, improve the gas production problem of the lithium supplement agent during the subsequent charging and discharging process, thereby improving the cycle performance and service life of the lithium iron phosphate lithium-ion battery.

[0021] In a third aspect, the present application provides a lithium battery, which adopts the following technical solution:

[0022] A lithium battery, comprising a positive electrode sheet, a separator, a negative electrode sheet and the lithium battery electrolyte according to any one of claims 1 to 6; the positive electrode sheet comprises a positive electrode current collector carbon-coated aluminum foil and a positive electrode coating coated on the positive electrode current collector carbon-coated aluminum foil, and based on the total mass of the positive electrode coating, the positive electrode coating comprises the following components in mass percentage: 92-96% of positive electrode active material, 1-4% of lithium supplement, 1-2% of conductive agent and 2-3% of binder; the negative electrode sheet comprises a negative electrode current collector copper foil and a negative electrode coating coated on the negative electrode current collector copper foil, and based on the total mass of the negative electrode coating, the negative electrode coating comprises the following components in mass percentage: 92-97% of negative electrode active material, 0.5-3.5% of conductive agent and 2.5-4.5% of binder.

[0023] In a specific possible implementation scheme, the positive electrode active material is one or more of nickel-cobalt-manganese ternary material, nickel-cobalt-aluminum ternary material, lithium iron phosphate, lithium manganese-rich oxide, lithium manganese iron phosphate, and lithium cobalt oxide; the lithium supplement is one or more of lithium nickel-rich oxide, lithium iron-rich oxide, and lithium cobalt oxide; and the negative electrode active material is one or more of artificial graphite, natural graphite, soft carbon, hard carbon, silicon carbon, and silicon oxygen.

[0024] In a fourth aspect, the present application provides a method for preparing a lithium battery, which adopts the following technical solution:

[0025] A method for preparing a lithium battery comprises the following steps:

[0026] Preparation of positive electrode sheet: according to the proportion, weigh the positive electrode active material, lithium supplement agent, conductive agent and binder, add the positive electrode active material, lithium supplement agent, conductive agent and binder into N-methylpyrrolidone, disperse them evenly according to the homogenization process to obtain positive electrode slurry, evenly coat the positive electrode slurry on the carbon-coated aluminum foil, dry, roll and die-cut to obtain the positive electrode sheet;

[0027] Preparation of negative electrode sheet: according to the ratio, weigh the negative electrode active material, conductive agent and binder, add the negative electrode active material, conductive agent and binder into water, disperse them evenly according to the homogenization process to obtain negative electrode slurry, evenly coat the negative electrode slurry on the negative electrode current collector copper foil, dry, roll and die-cut to obtain the negative electrode sheet;

[0028] Preparation of lithium battery: bake the positive electrode at 90-100℃ and the negative electrode at 80-90℃ for 20-30h, stack the positive electrode, separator and negative electrode into bare cells, encapsulate the bare cells into stamped aluminum-plastic film bags to obtain dry cells, dry the dry cells at 80-95℃ for 15-30h, inject lithium battery electrolyte into the dry cells, perform high-temperature infiltration, formation, aging, vacuum sealing, and capacity separation to obtain lithium batteries.

[0029] By adopting the above technical solution, the above lithium battery component configuration and preparation method, a lithium battery with excellent charge and discharge performance and long service life can be prepared.

[0030] In summary, this application has the following beneficial effects:

[0031] 1. The present application adopts at least one of phosphite additives, siloxanes, and film-forming additives to absorb oxygen released when the lithium supplement agent is de-lithiated, thereby significantly improving the capacity, high-temperature cycle and high-temperature storage performance of the battery cell, and can reduce the internal resistance of the battery, improve the gas production problem caused by the positive electrode lithium supplement during the subsequent charging and discharging process, thereby improving the cycle performance and service life of the lithium iron phosphate battery.

[0032] 2. The method of the present application can produce a lithium battery with excellent charge and discharge performance and long service life. DETAILED DESCRIPTION

[0033] The present application found that positive electrode lithium replenishment technology, that is, adding a lithium replenisher to the positive electrode of a lithium battery, can effectively improve the initial efficiency and energy density of lithium iron phosphate batteries. However, gas production problems will occur during the subsequent charging and discharging process, causing a series of side effects such as electrolyte oxidation, affecting the cycle life of lithium-ion batteries. In view of the shortcomings of the prior art, the present application has developed a lithium battery electrolyte that is compatible with lithium iron phosphate batteries with added lithium replenishers, which can improve the gas production problem of the lithium replenisher during the subsequent charging and discharging process, thereby improving the cycle performance and service life of lithium iron phosphate lithium-ion batteries.

[0034] The components of the lithium battery electrolyte include lithium salt, organic solvent and electrolyte additive. The lithium salt can be one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bisoxalate borate, lithium difluorooxalate borate, lithium difluorophosphate and lithium bisfluorosulfonyl imide. The organic solvent can be one or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, dipropyl carbonate, ethyl acetate, methyl acetate, ethyl propionate. The phosphite additive can be one or more of trimethyl phosphite, tris (2,2,2-trifluoroethyl) phosphite triester, triphenyl phosphite, tris (trimethylsilyl) phosphite. Siloxane can be at least one of dimethoxydimethylsilane, diphenyldimethoxysilane, and vinyl tris (2-methoxyethoxy) silane. The film-forming additive can be one or more of vinylene carbonate, fluoroethylene carbonate, lithium difluorooxalate phosphate, and vinyl sulfate.

[0035] The lithium supplement added to the positive electrode sheet can be one or more of lithium nickel-rich lithium, lithium iron-rich lithium, and lithium cobalt-rich lithium. For these lithium supplements, the lithium battery electrolyte of the present application can improve the gas production problem of the lithium supplement in the subsequent charging and discharging process, and improve the cycle performance and service life of the lithium battery.

[0036] The present application also studies and develops a lithium battery, including a positive electrode sheet, a separator, a negative electrode sheet and the above-mentioned lithium battery electrolyte. Among them, the positive electrode sheet includes a positive electrode current collector carbon-coated aluminum foil and a positive electrode coating coated on the positive electrode current collector carbon-coated aluminum foil, and the positive electrode coating includes a positive electrode active material, a lithium supplement, a conductive agent and a binder. The negative electrode sheet includes a negative electrode current collector copper foil and a negative electrode coating coated on the negative electrode current collector copper foil, and the negative electrode coating includes a negative electrode active material, a conductive agent and a binder. The positive electrode active material is one or more of nickel-cobalt-manganese ternary material, nickel-cobalt-aluminum ternary material, lithium iron phosphate, lithium manganese-rich oxide, lithium iron manganese phosphate, and lithium cobalt oxide. The negative electrode active material is one or more of artificial graphite, natural graphite, soft carbon, hard carbon, silicon carbon, and silicon oxygen. The conductive agent is conductive carbon black (SP) or graphene (GOs). The binder is polyvinylidene fluoride (PVDF), styrene-butadiene rubber (SBR) or sodium carboxymethyl cellulose (CMC).

[0037] The present application is further described in detail below in conjunction with embodiments and comparative examples.

[0038] Example

[0039] Example 1

[0040] This embodiment provides a lithium-ion battery, including a positive electrode sheet, a separator, a negative electrode sheet and a lithium battery electrolyte.

[0041] The positive electrode sheet uses the following components in percentage by mass: 93% positive electrode active material LiFePO4, 2% lithium supplement Li5FeO4, 1.5% conductive agent SP, 1% conductive agent GOs and 2.5% binder PVDF.

[0042] The negative electrode sheet uses the following components in mass percentage: 96.5% negative electrode active material graphite, 0.5% conductive agent SP, 1.2% binder CMC and 1.8% binder SBR.

[0043] The preparation method of a lithium ion battery comprises the following steps:

[0044] Preparation of positive electrode sheet: LiFePO4, Li5FeO4, SP, GOs and PVDF are mixed according to the proportion, N-methylpyrrolidone is added, and the positive electrode slurry is fully stirred according to the homogenization step to obtain the positive electrode slurry, which is then coated on the positive electrode current collector carbon-coated aluminum foil. After drying, rolling and die-cutting, the positive electrode sheet is obtained.

[0045] Preparation of negative electrode sheet: Graphite, SP, CMC and SBR are mixed according to the proportion, deionized water is added, and the negative electrode slurry is fully stirred according to the homogenization step to obtain the negative electrode slurry, which is then coated on the negative electrode current collector copper foil. After drying, rolling and die-cutting, the negative electrode sheet is obtained.

[0046] Preparation of electrolyte: In an argon atmosphere glove box with water and oxygen content <0.01ppm, ethylene carbonate and ethyl methyl carbonate are mixed in a mass ratio of 3:7 to obtain an organic solvent. Lithium hexafluorophosphate and vinylene carbonate are dissolved in the organic solvent to obtain a lithium battery electrolyte. The concentration of lithium hexafluorophosphate in the lithium battery electrolyte is 1 mol / L; the mass percentage of vinylene carbonate in the total mass of the lithium battery electrolyte is 2%.

[0047] Preparation of lithium battery: stack the positive electrode sheet, separator and negative electrode sheet in order, so that the separator is in the middle of the positive and negative electrodes to play a role of isolation, and obtain dry battery cells. Place the dry battery cells in aluminum plastic film, dry them at 80-95℃ for 15-30h, inject the prepared electrolyte and package them. After high-temperature infiltration, formation, aging, vacuum sealing and capacity division, the lithium-ion battery is obtained.

[0048] Example 2

[0049] The only difference between this embodiment and embodiment 1 is that the lithium supplement Li5FeO4 is replaced by an equal amount of lithium supplement LiNiO2.

[0050] Example 3

[0051] The only difference between this embodiment and embodiment 1 is that the lithium supplement Li5FeO4 is replaced by an equal amount of lithium supplement LiCoO2.

[0052] Example 4

[0053] The difference between this embodiment and embodiment 1 is that, in the electrolyte preparation step of the lithium ion battery preparation method, lithium hexafluorophosphate, vinylene carbonate, and tris(trimethylsilyl)phosphite are dissolved in an organic solvent to obtain a lithium battery electrolyte. The concentration of lithium hexafluorophosphate in the lithium battery electrolyte is 1 mol / L; the mass percentage of vinylene carbonate in the total mass of the lithium battery electrolyte is 2%. The mass percentage of tris(trimethylsilyl)phosphite in the total mass of the lithium battery electrolyte is 0.5%.

[0054] Example 5

[0055] The difference between this embodiment and embodiment 1 is that, in the electrolyte preparation step of the lithium ion battery preparation method, lithium hexafluorophosphate, vinylene carbonate, and tris(trimethylsilyl)phosphite are dissolved in an organic solvent to obtain a lithium battery electrolyte. The concentration of lithium hexafluorophosphate in the lithium battery electrolyte is 1 mol / L; the mass percentage of vinylene carbonate in the total mass of the lithium battery electrolyte is 2%. The mass percentage of tris(trimethylsilyl)phosphite in the total mass of the lithium battery electrolyte is 1%.

[0056] Example 6

[0057] The difference between this embodiment and embodiment 1 is that, in the electrolyte preparation step of the lithium ion battery preparation method, lithium hexafluorophosphate, vinylene carbonate, and tris(trimethylsilyl)phosphite are dissolved in an organic solvent to obtain a lithium battery electrolyte. The concentration of lithium hexafluorophosphate in the lithium battery electrolyte is 1 mol / L; the mass percentage of vinylene carbonate in the total mass of the lithium battery electrolyte is 2%. The mass percentage of tris(trimethylsilyl)phosphite in the total mass of the lithium battery electrolyte is 3%.

[0058] Example 7

[0059] The difference between this embodiment and embodiment 1 is that in the electrolyte preparation step of the lithium ion battery preparation method, lithium hexafluorophosphate, vinylene carbonate, tris(trimethylsilyl)phosphite, and diphenyldimethoxysilane are dissolved in an organic solvent to obtain a lithium battery electrolyte. The concentration of lithium hexafluorophosphate in the lithium battery electrolyte is 1 mol / L; the mass percentage of vinylene carbonate in the total mass of the lithium battery electrolyte is 2%. The mass percentage of tris(trimethylsilyl)phosphite in the total mass of the lithium battery electrolyte is 1%, and the mass percentage of diphenyldimethoxysilane in the total mass of the lithium battery electrolyte is 0.5%.

[0060] Example 8

[0061] The difference between this embodiment and embodiment 1 is that in the electrolyte preparation step of the lithium ion battery preparation method, lithium hexafluorophosphate, vinylene carbonate, tris(trimethylsilyl)phosphite, and diphenyldimethoxysilane are dissolved in an organic solvent to obtain a lithium battery electrolyte. The concentration of lithium hexafluorophosphate in the lithium battery electrolyte is 1 mol / L; the mass percentage of vinylene carbonate in the total mass of the lithium battery electrolyte is 2%. The mass percentage of tris(trimethylsilyl)phosphite in the total mass of the lithium battery electrolyte is 1%, and the mass percentage of diphenyldimethoxysilane in the total mass of the lithium battery electrolyte is 1%.

[0062] Example 9

[0063] The difference between this embodiment and embodiment 1 is that in the electrolyte preparation step of the lithium ion battery preparation method, lithium hexafluorophosphate, vinylene carbonate, tris(trimethylsilyl)phosphite, and diphenyldimethoxysilane are dissolved in an organic solvent to obtain a lithium battery electrolyte. The concentration of lithium hexafluorophosphate in the lithium battery electrolyte is 1 mol / L; the mass percentage of vinylene carbonate in the total mass of the lithium battery electrolyte is 2%. The mass percentage of tris(trimethylsilyl)phosphite in the total mass of the lithium battery electrolyte is 1%, and the mass percentage of diphenyldimethoxysilane in the total mass of the lithium battery electrolyte is 3%.

[0064] Comparative Example

[0065] Comparative Example 1

[0066] The only difference between this comparative example and Example 1 is that the lithium supplement Li5FeO4 is not added. In the positive electrode sheet preparation step of the lithium ion battery preparation method, LiFePO4, SP, GOs and PVDF are mixed according to a ratio, N-methylpyrrolidone is added, and the positive electrode slurry is fully stirred according to the homogenization step to obtain the positive electrode slurry, which is then coated on the positive electrode current collector carbon-coated aluminum foil, and then dried, rolled, and die-cut to obtain the positive electrode sheet.

[0067] Comparative Example 2

[0068] The difference between this comparative example and Example 1 is that vinylene carbonate is not added in the electrolyte preparation step of the lithium ion battery preparation method. Lithium hexafluorophosphate is dissolved in an organic solvent to obtain a lithium battery electrolyte, and the concentration of lithium hexafluorophosphate in the lithium battery electrolyte is 1 mol / L.

[0069] Performance testing

[0070] For the lithium ion batteries prepared in Examples 1-9 and Comparative Examples 1-2, the initial charge and discharge efficiency, the capacity retention rate after 1000 cycles at 25° C., and the capacity retention rate after 500 cycles at 45° C. of the lithium ion batteries were tested. The test results are shown in Table 1.

[0071] Table 1

[0072]

[0073]

[0074] It can be seen from Examples 1-3 and Comparative Example 1 and Table 1 that adding a lithium supplement to the lithium iron phosphate positive electrode can improve the initial coulombic efficiency of the lithium ion battery. This is because the lithium supplement releases additional active lithium for the formation of the negative electrode SEI film during the first cycle of charging. At the same time, the increase in active lithium also improves the room temperature and high temperature cycle performance of the lithium ion battery, thereby extending the battery life.

[0075] It can be seen from Example 1 and Comparative Example 2 that when 2% of the negative electrode film-forming additive vinylene carbonate is added, an effective, dense and stable SEI film is formed on the surface of the graphite negative electrode, which can effectively inhibit the embedding of solvent molecules and solvated lithium ions, thereby improving the charge and discharge efficiency and cycle performance of the lithium-ion battery.

[0076] By comparing Examples 4-6 with Example 1, it can be seen that when a small amount of tris(trimethylsilyl)phosphite additive is added, since the phosphite additive can combine with the oxygen on the positive electrode surface to form P=O, it can inhibit the oxidation and decomposition of the electrolyte at the positive electrode to produce gas, so the cycle performance of the battery is significantly improved. The experimental results show that when the addition amount is 1%, the battery capacity retention rate is the highest.

[0077] By comparing Examples 7-9 with Example 5, it can be seen that when tris(trimethylsilyl)phosphite and diphenyldimethoxysilane are used as additives together, the cycle performance of the battery is further improved. This is mainly because the use of siloxane can react with H2O in the electrolyte to further inhibit the hydrolysis of LiPF6. This also verifies that a single additive has limited effect on improving the cycle performance of the battery. The synergistic effect of tris(trimethylsilyl)phosphite and diphenyldimethoxysilane further improves the room temperature and high temperature cycle performance of the lithium-ion battery, effectively improving the service life of the battery.

[0078] In summary, adding a positive electrode lithium replenisher can effectively improve the initial coulombic efficiency of a lithium iron phosphate battery, and the electrolyte provided in the present application is compatible with a lithium iron phosphate positive electrode and a graphite negative electrode lithium-ion battery containing a lithium iron oxide lithium replenisher at the positive electrode, which effectively improves the cycle performance of the lithium-ion battery and extends the service life of the battery.

[0079] This specific embodiment is merely an explanation of the present application and is not a limitation of the present application. After reading this specification, those skilled in the art may make modifications to the present embodiment without any creative contribution as needed, but such modifications are protected by the patent law as long as they are within the scope of the claims of the present application.

Claims

1. A lithium battery electrolyte, characterized in that: The invention comprises the following components in percentage by mass: 8-20% of lithium salt, 70-90% of organic solvent and 0.01-5% of electrolyte additive, wherein the electrolyte additive comprises at least one of phosphite additive, siloxane and film-forming additive.

2. A lithium battery electrolyte according to claim 1, characterized in that: The phosphite additive is one or more of trimethyl phosphite, tris(2,2,2-trifluoroethyl) phosphite triester, triphenyl phosphite, and tris(trimethylsilyl) phosphite.

3. A lithium battery electrolyte according to claim 1, characterized in that: The siloxane is at least one of dimethoxydimethylsilane, diphenyldimethoxysilane and vinyltri(2-methoxyethoxy)silane.

4. A lithium battery electrolyte according to claim 1, characterized in that: The film-forming additive is one or more of vinylene carbonate, fluoroethylene carbonate, lithium difluorooxalate phosphate, and vinyl sulfate.

5. A lithium battery electrolyte according to claim 1, characterized in that: The lithium salt is one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(oxalatoborate), lithium difluorooxalatoborate, lithium difluorophosphate and lithium bis(fluorosulfonyl)imide.

6. A lithium battery electrolyte according to claim 1, characterized in that: The organic solvent is one or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, dipropyl carbonate, ethyl acetate, methyl acetate, and ethyl propionate.

7. An application of the lithium battery electrolyte according to any one of claims 1 to 6, characterized in that: The lithium battery electrolyte is applied to a lithium battery, and the positive electrode of the lithium battery contains a lithium supplement.

8. A lithium battery, characterized in that: The invention comprises a positive electrode sheet, a separator, a negative electrode sheet and a lithium battery electrolyte as claimed in any one of claims 1 to 6; the positive electrode sheet comprises a positive electrode current collector carbon-coated aluminum foil and a positive electrode coating coated on the positive electrode current collector carbon-coated aluminum foil, and based on the total mass of the positive electrode coating, the positive electrode coating comprises the following components in mass percentage: 92-96% of positive electrode active material, 1-4% of lithium supplement, 1-2% of conductive agent and 2-3% of binder; the negative electrode sheet comprises a negative electrode current collector copper foil and a negative electrode coating coated on the negative electrode current collector copper foil, and based on the total mass of the negative electrode coating, the negative electrode coating comprises the following components in mass percentage: 92-97% of negative electrode active material, 0.5-3.5% of conductive agent and 2.5-4.5% of binder.

9. A lithium battery according to claim 8, characterized in that: The positive electrode active material is one or more of nickel-cobalt-manganese ternary material, nickel-cobalt-aluminum ternary material, lithium iron phosphate, lithium manganese-rich oxide, lithium manganese iron phosphate, and lithium cobalt oxide; the lithium supplement is one or more of lithium nickel-rich oxide, lithium iron-rich oxide, and lithium cobalt oxide; the negative electrode active material is one or more of artificial graphite, natural graphite, soft carbon, hard carbon, silicon carbon, and silicon oxygen.

10. A method for preparing a lithium battery according to claim 8, characterized in that: The steps include: Preparation of positive electrode sheet: according to the proportion, weigh the positive electrode active material, lithium supplement agent, conductive agent and binder, add the positive electrode active material, lithium supplement agent, conductive agent and binder into N-methylpyrrolidone, disperse them evenly according to the homogenization process to obtain positive electrode slurry, evenly coat the positive electrode slurry on the carbon-coated aluminum foil, dry, roll and die-cut to obtain the positive electrode sheet; Preparation of negative electrode sheet: according to the ratio, weigh the negative electrode active material, conductive agent and binder, add the negative electrode active material, conductive agent and binder into water, disperse them evenly according to the homogenization process to obtain negative electrode slurry, evenly coat the negative electrode slurry on the negative electrode current collector copper foil, dry, roll and die-cut to obtain the negative electrode sheet; Preparation of lithium battery: bake the positive electrode at 90-100℃ and the negative electrode at 80-90℃ for 20-30h, stack the positive electrode, separator and negative electrode into bare cells, encapsulate the bare cells into stamped aluminum-plastic film bags to obtain dry cells, dry the dry cells at 80-95℃ for 15-30h, inject lithium battery electrolyte into the dry cells, perform high-temperature infiltration, formation, aging, vacuum sealing, and capacity separation to obtain lithium batteries.

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