An electrolyte, a lithium-ion battery and a preparation method thereof

Abstract

This application relates to an electrolyte, a lithium-ion battery and a preparation method thereof. The electrolyte includes an electrolyte salt, an organic solvent and an additive. The electrolyte includes a first electrolyte for injection before battery formation treatment and a second electrolyte for injection after battery formation treatment. In the first electrolyte, the additive includes a siloxane compound additive and a first nitrile compound additive. In the second electrolyte, the additive includes a second nitrile compound additive. The technical solution of this application can form an interfacial film with low impedance and high stability, reduce side reactions between the electrolyte and the electrode, inhibit the gas generation phenomenon caused by side reactions, effectively improve the cycle performance of the battery and improve the increase in the internal impedance of the battery caused by repeated charge and discharge cycles, enabling the battery to have good kinetic performance.

Description

Technical Field

[0001] The present application relates to the technical field of lithium-ion batteries, and particularly to an electrolyte, a lithium-ion battery and a preparation method thereof. Background Art

[0002] A lithium-ion battery is a secondary battery that relies on the movement of lithium ions between the positive and negative electrodes to achieve charge and discharge purposes. It has advantages such as high energy density and long cycle life, and is widely used in the field of consumer electronic devices, such as smartphones, computers, electric vehicles, etc.

[0003] In actual applications of lithium-ion batteries, as the number of charge and discharge cycles increases, the battery capacity will gradually decay, affecting the normal use of the device. Especially when used in extreme environments such as high temperature or high voltage for a long time, or when overcharging or over-discharging frequently during charge and discharge, it will lead to an increase in interfacial side reactions, reduce the battery capacity, and may also cause gas generation. When the gas generation is severe, the battery will bulge, which may further lead to problems such as battery shell rupture, electrolyte leakage, and even explosion, deteriorating the battery cycle life and seriously affecting the user experience and safety. Summary of the Invention

[0004] To solve or partially solve the problems existing in the related technologies, the present application provides an electrolyte, a lithium-ion battery and a preparation method thereof, which can form an interfacial film with low impedance and high stability, reduce the side reactions between the electrolyte and the electrode, inhibit the gas generation phenomenon caused by side reactions, effectively improve the cycle performance of the battery, and improve the situation where the internal impedance of the battery increases due to repeated charge and discharge cycles, enabling the battery to have good kinetic performance.

[0005] In the first aspect of the present application, an electrolyte is provided, which includes an electrolyte salt, an organic solvent and an additive. The electrolyte includes a first electrolyte for injection before battery formation treatment and a second electrolyte for injection after battery formation treatment; in the first electrolyte, the additive includes a siloxane compound additive and a first nitrile compound additive; in the second electrolyte, the additive includes a second nitrile compound additive.

[0006] In some embodiments of the present application, the structural formula of the siloxane compound additive is as follows:

[0007] ;

[0008] Wherein, the R groups are each independently selected from an alkyl group, an alkene group, an alkoxy group, an alkylamine group, a halogen substituent, a halogenated hydrocarbon group or a phenyl group, and n is a positive integer equal to or greater than 3.

[0009] In some preferred embodiments of the present application, the siloxane compound additive is selected from one or more of the following compounds:

[0010] 。

[0011] In some embodiments of the present application, the first nitrile compound additive and the second nitrile compound are each independently selected from one or more of dinitrile compounds and polynitrile compounds.

[0012] In some preferred embodiments of the present application, the first nitrile compound additive and the second nitrile compound are each independently selected from chain nitrile compounds.

[0013] In some preferred embodiments of the present application, the dinitrile compound is selected from one or more of the following compounds:

[0014] 。

[0015] In some embodiments of the present application, the structural formula of the polynitrile compound is as follows:

[0016] ;

[0017] where A 2 represents ;R 21 、R 22 、R 23 、R 24 are each independently selected from a covalent single bond, an alkylene group having 1 to 5 carbon atoms, an alkenylene group having 2 to 4 carbon atoms, or represents a binding site with an adjacent atom; R 25 is independently selected from hydrogen, a cyano group, an alkyl group having 1 to 3 carbon atoms, or an alkyl group having 1 to 3 carbon atoms substituted with a cyano group.

[0018] In some preferred embodiments of the present application, the polynitrile compound is

[0019] 。

[0020] In some embodiments of the present application, in the first electrolyte, the mass ratio of the siloxane compound additive is 0.1% to 5%, and the mass ratio of the first nitrile compound additive is 2% to 6%.

[0021] In some embodiments of the present application, in the second electrolyte, the mass ratio of the second nitrile compound additive is 2% to 8%.

[0022] In some embodiments of the present application, the content of the first nitrile compound additive in the first electrolyte is lower than the content of the second nitrile compound additive in the second electrolyte.

[0023] In some embodiments of the present application, the electrolyte salt includes one or more of lithium hexafluorophosphate, lithium difluoro(oxalato)borate, lithium difluoro(oxalato)phosphate, lithium tetrafluoroborate, lithium bis(trifluoromethylsulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium difluorophosphate, and lithium cyano(trifluoromethanesulfonyl)imide.

[0024] In some preferred embodiments of the present application, the total mass of the electrolyte salt is 10% - 30% of the total mass of the electrolyte solution; more preferably 12.5% - 16%.

[0025] In some embodiments of the present application, the organic solvent includes one or more combinations of cyclic ester organic solvents, linear ester organic solvents, and fluorine-substituted organic solvents of the above ester organic solvents.

[0026] In some preferred embodiments of the present application, the organic solvent includes ethylene carbonate, propylene carbonate, diethyl carbonate, ethyl methyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, ethyl propionate, propyl propionate, ethyl fluoroacetate, ethyl methyl fluorocarbonate, dimethyl fluorocarbonate, propylene fluorocarbonate, γ-butyrolactone, sulfolane, methyl formate, ethyl formate, methyl acetate, ethyl acetate, propyl acetate, n-butyl acetate, isobutyl acetate, n-pentyl acetate, isopentyl acetate, methyl propionate, methyl butyrate, n-butyl butyrate, methyl acrylate, ethyl acrylate, etc.

[0027] In some preferred embodiments of the present application, the total mass of the organic solvent is 20% - 80% of the total mass of the electrolyte solution.

[0028] In some embodiments of the present application, the additive further includes one or more of fluorinated ethylene carbonate, vinylene carbonate, 1,3-propane sultone, ethylene sulfate, propene sultone, methylene methanedisulfonate, pentafluoroethoxyphosphazene, dicyclohexylcarbodiimide, trimethyl phosphite imide, hexamethylene diisocyanate.

[0029] In some preferred embodiments of the present application, the total mass of the additive is 5% - 35% of the total mass of the electrolyte solution.

[0030] The second aspect of the present application provides a lithium-ion battery, including a positive electrode sheet, a negative electrode sheet, a separator, and the above electrolyte solution.

[0031] In some embodiments of the present application, the first electrolyte solution is injected before the battery formation treatment, and the second electrolyte solution is injected after the battery formation treatment; the mass ratio of the injected first electrolyte solution and the second electrolyte solution is between 8:2 and 9:1.

[0032] The third aspect of the present application provides a method for preparing a lithium-ion battery, including: stacking and winding a positive electrode sheet, a separator, and a negative electrode sheet in sequence to form an electrode core;

[0033] Injecting a first electrolyte into the electrode core, performing a standing treatment, and then performing a formation treatment to obtain a preformed battery;

[0034] Discharging the preformed battery to an empty state, injecting a second electrolyte, and then performing an aging and grading treatment to obtain a lithium-ion battery.

[0035] The fourth aspect of the present application provides an electrical device, including the above-mentioned lithium-ion battery or a lithium-ion battery prepared by the above-mentioned preparation method.

[0036] The technical solution provided by the present application may include the following beneficial effects:

[0037] In the solution of the present application, by using a siloxane compound and a first nitrile compound as additives in the first electrolyte, and utilizing the synergistic effect when the two are used in combination, a positive and negative interface film with low impedance and high stability can be formed, improving the initial kinetic window, and at the same time effectively inhibiting the dissolution of positive electrode transition metal ions and the gas generation phenomenon of the electrode core, thereby improving the cycle performance of the lithium-ion battery as a whole.

[0038] Furthermore, through the secondary injection of the electrode core with the first electrolyte and the second electrolyte, a stable and low-impedance initial interface film can be formed after the first electrolyte is formed, and then the injection of the second electrolyte can strengthen the positive electrode interface complexation during the cycle, thereby improving the cycle performance of the battery as a whole.

[0039] It should be understood that the above general description and the following detailed description are only exemplary and explanatory, and cannot limit the present application. Detailed Embodiments

[0040] To make the present invention easy to understand, the present invention will be described in detail below. However, before describing the present invention in detail, it should be understood that the present invention is not limited to the described specific embodiments. It should also be understood that the terms used herein are only for describing specific embodiments and do not indicate restrictive.

[0041] The terms used in the present application are only for the purpose of describing specific embodiments and are not intended to limit the present application. The singular forms of "a", "the", and "said" used in the present application and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise. It should also be understood that the term "and / or" used herein refers to and includes any or all possible combinations of one or more of the associated listed items.

[0042] Where a numerical range is provided, it should be understood that each intermediate value between the upper and lower limits of the range and any other specified or intermediate value in the specified range is encompassed within the present invention. The upper and lower limits of these smaller ranges may be independently included in the smaller ranges and are also encompassed within the present invention, subject to any express exclusions in the specified range. Where the specified range includes one or both of the limits, ranges excluding either or both of the included limits are also included in the present invention. In the description of the present application, the meaning of "a plurality of" is two or more, unless otherwise specifically defined.

[0043] Unless otherwise defined, all terms used herein have the same meaning as commonly understood by those of ordinary skill in the art to which the present invention pertains. Although any methods and materials equivalent to those described herein may also be used in the implementation or testing of the present invention, the preferred methods and materials are now described.

[0044] In the practical application of lithium-ion batteries, as the number of charge-discharge cycles increases, the electrochemical performance of the battery deteriorates, affecting the normal use of the device. Especially when used in extreme environments such as high temperature or high voltage for a long time, or when overcharging or over-discharging frequently during charge and discharge, it will lead to an increase in interfacial side reactions, reduce the battery capacity, and may also cause gas generation. When the gas generation is severe, the battery will bulge, which may further lead to problems such as the rupture of the battery shell, leakage of electrolyte, and even explosion, deteriorating the battery cycle life. The related electronic devices are at risk of damage, and at the same time, it will pose a threat to the personal safety of users, seriously affecting the user experience and safety.

[0045] In view of the above problems, the embodiments of the present application provide an electrolyte, a lithium-ion battery, and a preparation method thereof, which can establish a positive and negative interfacial film with low impedance and good stability, broaden the initial kinetic window, reduce gas generation from side reactions, and improve the cycle life of the battery while enabling the battery to have good kinetic performance and safety performance.

[0046] The electrolyte of the embodiments of the present application includes a first electrolyte for the first injection and a second electrolyte for the second injection. Among them, the first electrolyte includes an electrolyte salt, an organic solvent, and an additive, and the second electrolyte also includes an electrolyte salt, an organic solvent, and an additive. In the first electrolyte, the additive includes a siloxane compound additive and a first nitrile compound additive; in the second electrolyte, the additive includes a second nitrile compound additive.

[0047] It should be noted that the first injection in the embodiments of the present application occurs before the battery formation treatment, and the second injection occurs after the battery formation treatment.

[0048] Furthermore, in the embodiments of the present application, the additive of the second electrolyte does not include a siloxane compound additive.

[0049] Compared with traditional additives, siloxane compounds have a high bond energy Si-O bond and better heat resistance. When used as an additive in the electrolyte composition, they can effectively improve the overall thermal stability of the electrolyte, reduce the storage cost of the electrolyte, and enhance the storage performance of the battery. Moreover, as an additive in the first electrolyte, the siloxane compound can preferentially form a film at the electrode interface through hydrolysis and condensation reactions during the formation stage, and can form stable and low-impedance positive and negative interface films, thereby effectively improving the initial kinetic window. At the same time, since it can act as an acid scavenger to remove HF generated by chemical reactions in the electrolyte, it can avoid a large amount of HF from corroding the interface film of the battery, inhibit the hydrolysis of moisture-sensitive electrolyte salts such as lithium hexafluorophosphate, reduce side reactions between the electrolyte and the electrode, enhance the cycle stability of the battery and inhibit gas generation during storage of the battery cell at high temperatures, improve the high-temperature storage performance and cycle performance of the battery, and further enhance the use safety of the battery.

[0050] Meanwhile, the nitrile compound additive used in the first electrolyte and the second electrolyte can adsorb complex transition metals on the positive electrode plate through its lone pair of electrons, inhibit their dissolution, and thus cooperate with the siloxane compound additive to effectively enhance the stability of the positive electrode interface during the cycle. In particular, using some of the first nitrile compound additives in the first electrolyte can avoid an increase in the interface film impedance caused by a high content of nitrile compound additives before the battery formation treatment, thereby effectively broadening the initial kinetic window of the battery; and using some of the second nitrile compound additives in the second electrolyte can serve as a supplement to effectively inhibit the dissolution of transition metals in the positive electrode plate, reduce side reactions, effectively improve the cycle stability of the battery while enabling the battery to have good kinetic performance.

[0051] In some embodiments, the structural formula of the siloxane compound additive is as follows:

[0052] ;

[0053] Among them, the R groups are each independently selected from an alkyl group, an alkene group, an alkoxy group, an alkylamine group, a halogen substituent, a halogenated hydrocarbon group, or a phenyl group, etc.

[0054] Among them, n is a positive integer greater than or equal to 3, such as n = 3, 4, etc.

[0055] In some specific embodiments, the siloxane compound additive can be selected from one or more of the following compounds:

[0056] 。

[0057] In the siloxane compound with the above structural formula, the dissociation energy of the Si-O bond is significantly higher than that of the C-O bond. The high bond energy endows the siloxane compound and its polymer with excellent thermal stability. Therefore, after adding the first additive, the siloxane compound, to the first electrolyte, the thermal stability of the first electrolyte itself is effectively improved. Moreover, through the synergistic effect with the second nitrile compound additive in the first electrolyte, the siloxane compound additive is beneficial to inhibiting the dissolution of transition metal ions in the positive electrode, improving the structural stability of the positive electrode, reducing the oxidation of the solvent on the positive electrode side, enhancing the storage performance of the battery, and endowing the battery with good kinetic performance. The first additive, the siloxane compound, can also polymerize to form a SEI film on the interface between the electrolyte and the negative electrode sheet, effectively isolating the negative electrode sheet from the electrolyte, reducing the rapid consumption of the electrolyte caused by a large number of side reactions between the two, and ensuring that the battery has good cycle performance and energy density. Further, the siloxane compound additive can also act as an acid scavenger to remove HF in the electrolyte, avoid the reaction between HF and the electrode sheet, prevent the interface protective film from being corroded, and effectively improve the high-temperature storage and cycle stability of the battery.

[0058] Preferably, the siloxane compound additive can be:

[0059] .

[0060] This additive is (3-aminopropyl)triethoxysilane, which can remove HF and stabilize PF5. First, the nucleophilic nitrogen atom with a lone pair of electrons may form a complex with the strongly electron-withdrawing PF5, inhibiting the formation of POF3, HF, or fluorophosphate, thereby enhancing the thermal stability of the electrolyte. Second, (3-aminopropyl)triethoxysilane can act as a HF scavenger by breaking its own Si-O bond, thus preventing further reaction between HF and the solvent. In addition to acting as an acid scavenger, (3-aminopropyl)triethoxysilane will also polymerize through a condensation reaction in the presence of water in the electrolyte. The formed polymer network can also serve as a protective layer on the electrode surface, inhibiting the side reactions between the electrode and the electrolyte at high temperatures, reducing the gas generation from side reactions, and improving the overall performance of the battery. Further, the presence of the amino group in (3-aminopropyl)triethoxysilane can promote the transport of lithium ions at the electrode and electrolyte interface. When used in combination with the nitrile compound additive, it can effectively improve the stability of the positive and negative electrode interfaces, enhance the overall cycle performance of the lithium-ion battery, and maintain good kinetic performance during long cycling.

[0061] In some embodiments, the nitrile compound additive can be one or more of a dinitrile compound and a polynitrile compound, and the polynitrile compound is a trinitrile or a compound containing more cyano groups; preferably a chain-like nitrile compound.

[0062] In some specific embodiments, the dinitrile compound can be selected from one or more of the following compounds:

[0063] 。

[0064] In some embodiments, the polynitrile compound may be selected from compounds represented by the following structural formulas:

[0065] ;

[0066] where A 2 represents ; R 21 、R 22 、R 23 、R 24 are each independently selected from a covalent single bond, a C1-C5 alkylene group, a C2-C4 alkenylene group or represents a binding site to an adjacent atom; R 25 is independently selected from hydrogen, a cyano group, a C1-C3 alkyl group or a C1-C3 alkyl group substituted with a cyano group.

[0067] In some specific embodiments, the polynitrile compound may be:

[0068] 。

[0069] The nitrile compound additive of the above structural formula is a chain-like dinitrile or trinitrile compound, which can cooperate with the silicone compound additive to inhibit the dissolution of the cathode transition metal ions and further reduce the oxidation of the solvent on the cathode side, improving the high-temperature storage performance and cycle stability performance of the battery.

[0070] Preferably, the dinitrile compound may be:

[0071] 。

[0072] Butanedinitrile (BN) can cover the active sites on the surface of the cathode electrode sheet, effectively inhibit the cobalt dissolution of the lithium cobalt oxide cathode at high voltage, reduce the reaction activity of the cathode to the electrolyte, thereby improving the voltage resistance and high-temperature storage ability of the battery, and its impedance is relatively small compared to other common nitriles, making the battery have good kinetic performance.

[0073] Preferably, the trinitrile compound may be:

[0074]

[0075] 1,3,6 - hexanetricarbonitrile (HTCN) can adsorb and form strong complexation with transition metals such as cobalt ions on the surface of the positive electrode plate, thereby inhibiting the dissolution of transition metals; it can also act as a water scavenger and acid scavenger to synergistically enhance the stability of the positive and negative electrodes with the silicone compound additive, while enhancing the compactness of the CEI film on the positive electrode interface, improving the stability of the battery under extreme environments such as high voltage and high temperature and during long - term charge - discharge cycling, and improving the battery cycle life.

[0076] Further preferably, the nitrile compound additive can be a combination of various nitrile compounds. Specifically, it can include a combination of dinitrile compounds and dinitrile compounds, or a combination of dinitrile compounds and trinitrile compounds. Preferably, it is a combination of succinonitrile and 1,3,6 - hexanetricarbonitrile.

[0077] It should be noted that the types of the first nitrile compound additive in the first electrolyte and the second nitrile compound additive in the second electrolyte can be the same or different. Particularly, when the nitrile compound additive in the electrolyte is a combination of succinonitrile and 1,3,6 - hexanetricarbonitrile, either of the two compounds, succinonitrile or 1,3,6 - hexanetricarbonitrile, can be used in the first electrolyte and the other compound can be used in the second electrolyte. In this case, the types of the first nitrile compound additive and the second nitrile compound additive are different; it is also possible to use the combination of succinonitrile and 1,3,6 - hexanetricarbonitrile in both the first electrolyte and the second electrolyte. In this case, the types of the first nitrile compound additive and the second nitrile compound additive are the same.

[0078] In some embodiments, in the first electrolyte, the mass ratio of the silicone compound additive is 0.1% - 5%, and the mass ratio of the first nitrile compound additive is 2% - 6%.

[0079] Among them, the mass ratio of the silicone compound additive can be, for example, 0.1%, 0.5%, 0.8%, 1%, 1.2%, 1.5%, 2%, 3%, 4%, 5%, etc., and preferably 0.8% - 2%. When the content of the silicone compound additive in the first electrolyte meets the above range, the effect of removing the decomposition products of lithium salts is excellent, and at the same time, an elastic interface protective film can be formed, which can effectively inhibit the occurrence of side reactions and improve the overall performance of the battery. If the content of the silicone compound additive is too low, the effect of removing HF or PF5 is not obvious, and it cannot achieve a good effect of improving the battery thermal stability, cycle performance, and high - temperature storage performance; while if the content is too high, it cannot be completely consumed during the formation stage. When the content of some silicone compounds with larger molecular weights is too high, it will affect the overall viscosity of the electrolyte and deteriorate the kinetic performance of the electrolyte. By regulating the content of the silicone compound additive in the first electrolyte, it is basically consumed during the formation stage.

[0080] The mass percentage of the first nitrile compound additive can be, for example, 2%, 2.5%, 3%, 3.5%, 4%, 5%, 6%, etc., and is preferably 2% - 4%. When the content of the first nitrile compound additive in the first electrolyte satisfies the above range, it has a good synergistic effect with the siloxane compound additive, effectively inhibits the dissolution of metal ions, reduces the side reaction between the electrolyte and the positive electrode sheet, and simultaneously obtains an initial interface with lower impedance, improving the initial kinetic performance of the battery cell. If the content of the first nitrile compound additive is too low, it cannot effectively complex the positive electrode; while if the content is too high, it will increase the interfacial impedance and deteriorate the initial kinetic window, thereby deteriorating the battery performance.

[0081] In some embodiments, in the second electrolyte, the mass percentage of the second nitrile compound additive is 2% - 8%. For example, it can be 2%, 2.5%, 3%, 3.5%, 4%, 5%, 6%, 7%, 8%, etc., and is preferably 3% - 7%. When the content of the second nitrile compound additive in the second electrolyte satisfies the above range, the total content of nitrile compounds in the electrolyte is controlled so that the total content of nitrile compounds in the electrolyte is below 5%, which can avoid excessive cyano groups from deteriorating the interfacial impedance, and at the same time can effectively complex with the positive electrode active material, reducing the side reaction between the electrolyte and the positive electrode sheet.

[0082] In some embodiments, the content of the first nitrile compound additive in the first electrolyte is lower than the content of the second nitrile compound additive in the second electrolyte. With a smaller amount of nitrile compound additive in the first electrolyte, it can not only play the role of complexing the positive electrode active material, but also avoid an excessive increase in the interfacial film impedance due to a high cyano group content, thus having a good synergistic effect with the siloxane compound additive in the first electrolyte; while a larger amount of nitrile compound additive in the second electrolyte can effectively supplement nitrile compounds, ensuring that the total electrolyte has an appropriate cyano group content to meet the requirement for protecting the positive electrode sheet and also ensuring that the battery has good kinetic performance.

[0083] In some embodiments, the electrolyte salt includes one or more of lithium hexafluorophosphate (LiPF6), lithium difluorooxalate borate (LiODFB), lithium difluorodioxalate phosphate (LiDFOP), lithium tetrafluoroborate (LiBF4), lithium bis(trifluoromethylsulfonyl)imide (LiTFSI), lithium bis(fluorosulfonyl)imide (LiFSI), lithium difluorophosphate (LiPOF2), lithium cyano(trifluoromethanesulfonyl)imide (LiCTFSI).

[0084] In some embodiments, the total mass of the electrolyte salt is 10% to 30% of the total mass of the electrolyte solution; more preferably 12.5% to 16%. That is, the total mass of the electrolyte salt includes the mass of the electrolyte salt in the first electrolyte solution and the mass of the electrolyte salt in the second electrolyte solution, and the total mass of the electrolyte solution includes the first electrolyte solution and the second electrolyte solution. If the content of the lithium salt is too low, the mobility of lithium ions decreases; if the concentration of the lithium salt is too high, the wettability of the electrolyte may decrease due to an excessive increase in the viscosity of the non-aqueous electrolyte solution, and the film-forming effect will decline accordingly.

[0085] In some embodiments, the organic solvent may include cyclic carbonate organic solvents, linear carbonate organic solvents, and other linear ester organic solvents, etc.

[0086] The cyclic carbonate organic solvent can dissociate the lithium salt in the electrolyte well due to its high dielectric constant. Among them, specific examples of the cyclic carbonate organic solvent may be at least one organic solvent selected from ethylene carbonate (EC) and propylene carbonate (PC).

[0087] The linear carbonate organic solvent is an organic solvent with low viscosity and low dielectric constant. Among them, typical examples of the linear carbonate organic solvent may be at least one organic solvent selected from dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), and ethyl propyl carbonate.

[0088] The other linear ester organic solvents specifically include carboxylic ester organic solvents, which usually have a lower viscosity than carbonate esters and can ensure good fluidity of the liquid electrolyte. As specific examples, the linear ester organic solvents may include at least one organic solvent selected from methyl formate, ethyl formate, methyl acetate, ethyl acetate, propyl acetate, n-butyl acetate, isobutyl acetate, n-pentyl acetate, isopentyl acetate, methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), butyl propionate, methyl butyrate, n-ethyl butyrate, methyl acrylate, and ethyl acrylate.

[0089] In addition to cyclic carbonate organic solvents and / or linear carbonate organic solvents, the organic solvent may further contain cyclic ester organic solvents commonly used in lithium secondary battery electrolytes or fluorine-substituted organic solvents of the above ester organic solvents.

[0090] As specific examples, the cyclic ester organic solvents may include at least one organic solvent selected from γ-butyrolactone, γ-valerolactone, γ-caprolactone, δ-valerolactone, ε-caprolactone, and sulfolane.

[0091] As a specific example, the fluorinated organic solvent can be one or more of ethyl fluoroacetate (DFEA), ethyl methyl fluoro carbonate (FEMC), dimethyl fluoro carbonate (FDMC), and fluoro propylene carbonate (FPC).

[0092] To prepare an electrolyte with high ionic conductivity, the volume ratio of the carbonate organic solvent to the carboxylate organic solvent is between 1:(1 - 9); preferably between 1:4 and 2:3.

[0093] In some embodiments, the total mass of the organic solvent is 20% - 80% of the total mass of the electrolyte. That is, the total mass of the organic solvent includes the mass of the organic solvent in the first electrolyte and the mass of the organic solvent in the second electrolyte, and the total mass of the electrolyte includes the first electrolyte and the second electrolyte.

[0094] In some embodiments, the additive further includes a basic additive, and the basic additive includes one or more of vinylene carbonate (FEC), vinylene carbonate (VC), 1,3 - propane sultone (PS), ethylene sulfate (DTD), propylene sultone (PST), methylene methanedisulfonate (MMDS), pentafluoroethoxy phosphazene, dicyclohexylcarbodiimide, trimethyl phosphate imide, and hexamethylene diisocyanate.

[0095] For the specific components of the basic additive, they can be selected according to the specific requirements of the battery. For example, vinylene carbonate (FEC), vinylene carbonate (VC), 1,3 - propane sultone (PS), etc. that can promote the formation of the SEI film are selected.

[0096] In some embodiments, the mass ratio of the basic additive in the first electrolyte is 5% - 35%.

[0097] In some embodiments, the mass ratio of the basic additive in the second electrolyte is 5% - 35%.

[0098] In some embodiments, the total mass of the additive is 5% - 35% of the total mass of the electrolyte. The total mass of the additive includes the mass of the additive in the first electrolyte and the mass of the additive in the second electrolyte, and the total mass of the electrolyte includes the first electrolyte and the second electrolyte.

[0099] In the first electrolyte, the additive includes a basic additive, a siloxane compound additive, and a first nitrile compound additive. In the second electrolyte, the additive includes a basic additive and a second nitrile compound additive. The types of the basic additives in the first electrolyte and the second electrolyte can be the same or different.

[0100] Through the synergy among the additive components (basic additives, silicone compound additives, nitrile compound additives) in the overall electrolyte, a film can be formed by joint cooperation, further enhancing the stability of the electrode sheet and the interface, reducing the side reactions at the electrolyte-electrode interface, and improving the cycle stability and high-temperature storage performance of the battery.

[0101] It should be noted that regarding the preparation method of the electrolyte, no special limitation is imposed in this application, and those skilled in the art can prepare it into an electrolyte according to conventional technical means. For example, it can be prepared by mixing each raw material evenly according to the ratio.

[0102] The lithium-ion battery provided by the embodiment of this application includes a positive electrode sheet, a negative electrode sheet, a separator, and the above-mentioned electrolyte.

[0103] In some embodiments, the first electrolyte is injected before the battery formation treatment, and the second electrolyte is injected after the battery formation treatment; the mass ratio of the injected first electrolyte to the second electrolyte is between 8:2 and 9:1. By controlling the mass ratio of the first electrolyte and the second electrolyte to meet the requirements, an interfacial film with low impedance and high stability is formed on the electrode surface, widening the initial kinetic window, and being able to reduce the gas generation from side reactions, improving the thermal stability of the battery, improving the battery cycle life while enabling the battery to have good kinetic performance and safety performance, and reducing the risk of battery thermal runaway.

[0104] In the embodiment of this application, the positive electrode sheet includes a positive electrode current collector and a positive electrode material layer coated on the surface of the positive electrode current collector. The positive electrode current collector mentioned in this application is not particularly limited as long as it has conductivity and does not cause adverse chemical changes in the battery, and can be any known material suitable for use as a positive electrode current collector. In one embodiment, the positive electrode current collector can be a metal material such as aluminum, stainless steel, nickel plating, titanium, tantalum, etc., and a carbon material such as carbon cloth and carbon paper; preferably, it is aluminum foil.

[0105] In some embodiments, a stable positive electrode slurry is prepared by mixing a positive electrode active material, a binder, a conductive agent, a solvent, etc., and then the slurry is coated on the positive electrode current collector, and then dried and roll-pressed to form a positive electrode material layer.

[0106] The positive electrode active material includes, but is not limited to, lithium cobaltate, and one or more elements selected from aluminum, niobium, nickel, manganese, copper, tin, zirconium, chromium, and titanium are doped in the lithium cobaltate. The binder is a component that helps the adhesion between the active material and the conductive agent and the adhesion to the current collector. The binder can be polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene terpolymer, styrene-butadiene rubber, and fluororubber, etc. The conductive agent can be carbon black, acetylene black, graphite powder, carbon fiber, or metal fiber, etc.; the solvent can include organic solvents such as N-methyl-2-pyrrolidone (NMP), and its dosage can be such that a desired viscosity is obtained when the positive electrode active material and optionally the binder and the conductive agent are included.

[0107] In an embodiment of the present application, the negative electrode sheet includes a negative electrode current collector and a negative electrode material layer located on the surface of the negative electrode current collector. The negative electrode current collector mentioned in the present application is not particularly limited as long as it has conductivity and does not cause adverse chemical changes in the battery. Typical current collectors such as copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, or composite current collectors, etc.; preferably copper foil.

[0108] In some embodiments, a stable negative electrode slurry is prepared by mixing a negative electrode active material, a binder, a conductive agent, a solvent, etc., and then the slurry is coated on the negative electrode current collector, and then dried and roll-pressed to form a negative electrode material layer.

[0109] The negative electrode active material can include compounds capable of reversibly intercalating / deintercalating lithium ions, including carbon-based active materials, silicon-based active materials, or mixtures thereof. Typical carbon active materials are at least one of carbon materials such as artificial graphite, natural graphite, acetylene black, needle coke, carbon nanotubes, graphene, etc. Typical silicon active materials are at least one of elemental silicon, silicon oxide, pre-lithiated silicon oxide, carbon-coated silicon materials, and silicon metal compounds. The binder can be polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer, styrene-butadiene rubber, and fluororubber. The solvent can include water, or organic solvents such as N-methyl-2-pyrrolidone (NMP), and its dosage can be such that a desired viscosity is obtained when the negative electrode active material and optionally the binder and the conductive agent are included.

[0110] In the lithium-ion battery mentioned in the present application, a separator is disposed between the positive electrode and the negative electrode to prevent short circuit. There are no particular limitations on the material and shape of the separator in the embodiments of the present application, as long as the effects of the present application are not significantly impaired. In some embodiments, the separator can be used alone or in a laminated manner with a typical porous polymer film commonly used, such as a porous polymer film prepared from polyolefin polymers (such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer). A typical porous non-woven fabric can also be used, for example, a non-woven fabric formed from high-melting-point glass fibers or polyethylene terephthalate fibers, etc.

[0111] The preparation process of the battery can include the following steps: overlapping the positive electrode sheet and the negative electrode sheet via the separator, and winding, folding, etc. as required and then placing them in a casing, injecting an electrolyte into the casing and sealing it, where the separator used is the separator provided by the present application. In addition, an overcurrent protection element, a guide plate, etc. can be placed in the casing as required to prevent the pressure rise and overcharge / discharge inside the electrochemical device.

[0112] Furthermore, it can include:

[0113] S1. Stack and wind the positive electrode sheet, the separator, and the negative electrode sheet in sequence to make an electrode core;

[0114] S2. Inject a first electrolyte into the electrode core, perform a static treatment and then a formation treatment to obtain a preformed battery;

[0115] S3. Discharge the preformed battery to an empty state, inject a second electrolyte and then perform an aging and grading treatment to obtain a lithium-ion battery.

[0116] That is, a two-step liquid injection process is adopted to inject the first electrolyte and the second electrolyte into the electrode core step by step. Specifically, it can be that the first electrolyte is injected after the electrode core is vacuum baked, left standing at room temperature for about 48H, then left standing at a high temperature (40°C - 60°C) for about 12H, and then a pressure formation is carried out, with the surface pressure of a single battery being 0.5 MPa - 1.5 MPa and the temperature being between 25°C and 85°C. After the formation is completed, the battery is discharged to an empty state, the second electrolyte is injected, and then subsequent processes such as aging and grading are carried out to obtain a lithium-ion battery.

[0117] In some embodiments, the mass ratio of the injection amount of the first electrolyte to the injection amount of the second electrolyte is between 8:2 and 9:1.

[0118] The present application has no particular limitations on the application fields of the lithium-ion battery, and it can be used in fields such as consumer electronic products, new energy vehicles, and energy storage.

[0119] To make the present invention easier to understand, the present invention will be further described in detail below with reference to the following examples. These examples are merely illustrative and do not limit the scope of application of the present invention. Unless otherwise specified, the raw materials or components used in the present invention can be obtained through commercial channels or conventional methods.

[0120] Example 1

[0121] (1) Preparation of electrolyte

[0122] First electrolyte: In an argon-filled glove box with a water content of <10ppm, ethylene carbonate (EC), propylene carbonate (PC), ethyl propionate (EP), and propyl propionate (PP) were mixed in a mass ratio of 1.5:1.5:4:3, and 12.5% LiPF6 was added; based on the total mass of the first electrolyte, 10% fluoroethylene carbonate (FEC), 4% 1,3-propane sultone (PS), and 0.3% vinylene carbonate (VC) were added as basic additives, and then 0.8% (3-aminopropyl) triethoxysilane and 3.5% succinonitrile were added and mixed evenly to prepare the first electrolyte.

[0123] Second electrolyte: EC / PC / EP / PP were mixed in a ratio of 1.5:1.5:4:3 in an argon-filled glove box with a water content of <10 ppm, 12.5% LiPF6 was added, and based on the total mass of the second electrolyte, 10% fluoroethylene carbonate (FEC), 4% 1,3-propane sultone (PS), and 0.3% vinylene carbonate (VC) were added as basic additives, and 4% succinonitrile was added and mixed evenly to prepare the second electrolyte.

[0124] (2) Preparation of positive electrode sheet

[0125] The cathode active material lithium cobalt oxide (LiCoO2), conductive agent carbon black, and binder polyvinylidene fluoride (PVDF) were added to the solvent N-methylpyrrolidone (NMP) at a mass ratio of 97.5:1:1.5, and stirred thoroughly to form a uniform cathode slurry (solid content of 50wt%). 6μm aluminum foil was used as the current collector and the concentration was 200mg / cm 2 The positive electrode slurry is coated on aluminum foil, dried, and rolled to a specific compaction density. It is then processed through processes such as slitting, sheeting, and gluing to produce positive electrode sheets that meet the winding requirements.

[0126] (3) Preparation of negative electrode sheet

[0127] Mix the negative electrode active material (graphite and carbon-coated silicon material with 10% silicon content), binder (SBR-CMC), and conductive agent (carbon black) in a weight ratio of 95:3.5:1.5, and add them to water as a solvent to prepare a negative electrode slurry (solid content: 60 wt%). Use an 8-μm copper foil as the negative electrode current collector, and coat the negative electrode slurry on the copper foil at a surface density of 88 mg / cm 2 and dry and roll it to prepare the negative electrode. Subsequently, through processes such as slitting, making into pieces, and pasting glue, a negative electrode sheet meeting the winding requirements is made.

[0128] (4) Preparation of lithium-ion battery

[0129] Use a polyolefin porous separator coated with inorganic particles (Al2O3) as the separator.

[0130] Stack the positive electrode sheet, separator, and negative electrode sheet in sequence, with the separator in the middle of the positive and negative electrodes to play an isolation role, and then wind the stacked electrode sheets and separator to obtain an electrode core. Place the electrode core into the battery case and obtain a lithium-ion battery through the secondary liquid injection process.

[0131] The secondary liquid injection process includes: First, inject the first electrolyte after vacuum baking the electrode core, let it stand at room temperature for 48H, then stand at a high temperature (60°C) for 12H, and then carry out pressure formation, with a surface pressure of 1 MPa for a single battery and a temperature of 80°C. After the formation is completed, discharge the battery to an empty state, inject the second electrolyte, and then carry out subsequent processes such as grading and aging to obtain a lithium-ion battery.

[0132] Among them, the mass ratio of the first electrolyte to the second electrolyte is 8:2.

[0133] Examples 2 to 21

[0134] Use the same method as in Example 1, the difference is that the components and their corresponding contents (mass percentages) of the additives other than the basic additives in the first electrolyte or the second electrolyte are different, or the mass ratio of the first electrolyte to the second electrolyte is different, as shown in Table 1 specifically.

[0135] Table 1

[0136]

[0137] Comparative Example 1

[0138] The difference from Example 1 is that the content of (3-aminopropyl)triethoxysilane in the first electrolyte is 0.64% and the content of succinonitrile is 3.6%, and a one-time injection process is used to prepare the lithium-ion battery. That is, the formula and content of this electrolyte are the same as those of the total electrolyte (the first electrolyte + the second electrolyte) in Example 1, and the only difference is the use of a one-time injection process.

[0139] Comparative Example 2

[0140] The same two-time injection process as in Example 1 is used, and the difference is that both the first electrolyte and the second electrolyte contain 0.64% of (3-aminopropyl)triethoxysilane, and the other formula and content in the electrolyte are the same as those in Example 1.

[0141] Comparative Example 3

[0142] The same two-time injection process as in Example 1 is used, and the difference is that the first electrolyte does not contain a siloxane compound additive.

[0143] Comparative Example 4

[0144] The same two-time injection process as in Example 1 is used, and the difference is that the first electrolyte does not contain a nitrile compound additive.

[0145] Comparative Example 5

[0146] The same two-time injection process as in Example 1 is used, and the difference is that the second electrolyte does not contain a nitrile compound additive.

[0147] Lithium-ion battery performance test

[0148] (1)0℃ cycle interface state test

[0149] Discharge at 0.2C to 3V at 25℃, then stand for 3H at 0℃, charge at a constant current and constant voltage of 0.34C to 4.53V with a cut-off current of 0.05C, then discharge at 0.5C to 2.8V, repeat the cycle 50cls, disassemble the fully charged battery, and observe the lithium deposition state at the interface.

[0150] (2)60℃ cycle test

[0151] Stand in an environment of 60℃ for 2h, charge at a constant current of 0.5C to 4.53V with a cut-off current of 0.05C, stand for 10min, measure the full charge thickness D0, then discharge at 0.5C to 3.0V, record the discharge capacity C0 as the initial capacity, repeat the cycle 200cls, and obtain the capacity C 200 、 thickness D 200 , then the capacity retention rate = C 200 / C0, and the thickness growth rate = D 200 / D0 - 1.

[0152] (3)Storage Test at 80°C

[0153] Open-circuit and fully charged at (85 ± 2) °C for 6 h, immediately test the hot state thickness after taking out of the box, and observe whether the thickness changes. Determine whether there is gas generation according to the thickness change.

[0154] There are 5 batteries in each group, and the obtained results are recorded in the following table.

[0155] Table 2 Electrochemical Performance Test of Batteries

[0156]

[0157] From the examples, comparative examples and their electrochemical test performances, it can be seen that when preparing lithium-ion batteries using the electrolyte and secondary injection process described in this application, the low-impedance film-forming additive siloxane compound additive in the first electrolyte will undergo redox reactions during the formation process, forming a dense, stable and low-impedance interfacial protective film. The first nitrile compound additive can effectively complex the transition metal of the positive electrode. The combination of the two and the cooperation with other positive and negative electrode film-forming additives can effectively improve the initial kinetic window, reduce the side reactions between the electrolyte and the electrode, inhibit the gas generation phenomenon of the battery core at high temperatures and during cycling, improve the high-temperature storage performance, low-temperature and high-temperature cycling performance of the battery as a whole, and endow the battery with good kinetic performance, which is beneficial to its use under low-temperature conditions.

[0158] According to Example 1 and Comparative Example 1, if a conventional injection method, that is, a one-time injection process, is used to prepare lithium-ion batteries, the interfacial film formed on the electrode surface after formation treatment will cause the SEI film to rupture due to the volume change brought by silicon lithium intercalation during long-term cycling, resulting in the consumption of active lithium and a decrease in the capacity retention rate. At the same time, due to the relatively thick side reaction product layer, the interfacial impedance will increase and the thickness expansion rate will increase; while the siloxane compound additive can participate in the repair of the SEI film during cycling, inhibit the thickness expansion of the battery and improve the cycling performance of the battery.

[0159] According to Example 1 and Comparative Example 2, if there is a large amount of residual siloxane compound additive in the first electrolyte after formation, or it is continuously introduced after formation, its water-polymerization property will cause it to continuously undergo polymerization reactions in any water-containing area of the battery core, thereby hindering the transport of lithium ions in the later stage of cycling, reducing the kinetic performance of the battery, and deteriorating the cycling performance and storage performance of the battery, which is not conducive to the long-term cycling use of the battery.

[0160] As shown in Example 1, Comparative Example 3, Comparative Example 4, and Comparative Example 5, in the first electrolyte, the combined use of a siloxane compound additive with high bond energy Si-O and a nitrile compound additive with low impedance, further combined with the secondary injection process, and the use of a nitrile compound additive in the second electrolyte without using a siloxane compound additive can effectively balance the interface protection of the positive and negative electrodes. It can not only remove water and acid, but also form an interface protective film with good thermal stability and low impedance, and can effectively complex transition metal ions, that is, it can effectively stabilize the positive electrode while causing less deterioration of the negative electrode, inhibit side reactions, and thus overall improve the overall performance of the lithium-ion battery and endow it with good cycle life.

[0161] As shown in Examples 1 to 5, when preparing a lithium-ion battery using the electrolyte and secondary injection process described in this application, when the additives in the electrolyte are siloxane compounds and nitrile compounds that meet the structures defined in this application, they all have the effects of improving the battery cycle performance, high-temperature storage performance, and inhibiting battery thickness expansion, and can also take into account good battery kinetic performance. At the same time, using (3-aminopropyl)triethoxysilane as a siloxane compound additive has a better effect on improving the performance of lithium-ion batteries.

[0162] As shown in Example 1, Example 6, and Example 7, when a combination of two nitrile compound additives is used in the electrolyte, the effect of improving battery performance is better.

[0163] As shown in Example 1, Examples 8 to 12, when the content of the siloxane compound additive in the first electrolyte is within the range defined in this application, especially within the range of 0.8% to 2%, it has good improvement effects on the high-temperature storage performance, high and low temperature cycle performance, and kinetic performance of the battery.

[0164] As shown in Example 1, Examples 13 to 19, when the contents of the first nitrile compound additive in the first electrolyte and the second nitrile compound additive in the second electrolyte are within the ranges defined in this application, especially when the mass ratio of the first nitrile compound in the first electrolyte is 2% to 4%, and the mass ratio of the second nitrile compound in the second electrolyte is 3% to 7%, and the content of the first nitrile compound is lower than that of the second nitrile compound, it has good improvement effects on the high-temperature storage performance, high and low temperature cycle performance, and kinetic performance of the battery.

[0165] As shown in Example 1, Example 20, and Example 21, when the mass ratio of the first electrolyte to the second electrolyte is between 8:2 and 9:1, it has good improvement effects on the high-temperature storage performance, high and low temperature cycle performance, and kinetic performance of the battery. When the electrolyte is less during formation, the infiltration is not sufficient, which will affect the uniformity of film formation and the high and low temperature cycle performance of the battery.

[0166] It should be noted that the above-described embodiments are only used to explain the present application and do not constitute any limitation to the present application. The present application has been described by referring to typical embodiments, but it should be understood that the words used therein are descriptive and explanatory words rather than limiting words. Modifications can be made to the present application within the scope of the claims of the present application as stipulated, and the present application can be revised without departing from the scope and spirit of the present application. Although the present application described therein relates to specific methods, materials and embodiments, it does not mean that the present application is limited to the specific examples disclosed therein. On the contrary, the present application can be extended to all other methods and applications with the same functions.

Claims

1. An electrolyte comprising an electrolyte salt, an organic solvent and an additive, characterized in that: The electrolyte includes a first electrolyte for injection before battery formation treatment and a second electrolyte for injection after battery formation treatment; In the first electrolyte, the additives include a siloxane compound additive and a first nitrile compound additive; In the second electrolyte, the additive includes a second nitrile compound additive; The content of the first nitrile compound additive in the first electrolyte is lower than the content of the second nitrile compound additive in the second electrolyte, and the total mass of the first nitrile compound additive and the second nitrile compound additive accounts for less than 5% of the total mass of the electrolyte; The structural formula of the silicone compound additive is shown below: ； Wherein, each R group is independently selected from an alkyl group, an alkene group, an alkoxy group, an alkylamino group, a halogen substituent, a halogenated hydrocarbon group or a phenyl group.

2. The electrolyte according to claim 1, characterized in that The silicone compound additive is selected from one or more of the following compounds: 。 3. The electrolyte according to claim 1, characterized in that The first nitrile compound additive and the second nitrile compound are each independently selected from one or more polynitrile compounds.

4. The electrolyte according to claim 3, characterized in that The first nitrile compound additive and the second nitrile compound are each independently selected from chain nitrile compounds.

5. The electrolyte according to claim 3, characterized in that The polynitrile compound is selected from one or more of the following compounds: 。 6. The electrolyte according to claim 3, characterized in that The structural formula of the polynitrile compound is as follows: ； Among them A 2 express ; R 21 、R 22 、R 23 、R 24 Each is independently selected from a covalent single bond, a C1-C5 alkylene group, a C2-C4 alkenylene group, or represents a binding site with an adjacent atom; R 25 Independently selected from hydrogen, cyano, C1~C3 alkyl or C1~C3 alkyl substituted by cyano.

7. The electrolyte according to claim 6, characterized in that The polynitrile compound is 。 8. The electrolyte according to claim 1, characterized in that In the first electrolyte, the mass proportion of the siloxane compound additive is 0.1% to 5%, and the mass proportion of the first nitrile compound additive is 2% to 4%.

9. The electrolyte according to claim 1, characterized in that In the second electrolyte, the mass proportion of the second nitrile compound additive is 2% to 4%.

10. The electrolyte according to claim 1, characterized in that The electrolyte salt includes one or more of lithium hexafluorophosphate, lithium difluorooxalatoborate, lithium difluorobisoxalatophosphate, lithium tetrafluoroborate, lithium bis(trifluoromethylsulfonyl)imide, lithium bis(fluorosulfonyl)imide, and lithium difluorophosphate.

11. The electrolyte according to claim 10, characterized in that The total mass of the electrolyte salt is 10% to 30% of the total mass of the electrolyte.

12. The electrolyte according to claim 11, characterized in that The total mass of the electrolyte salt is 12.5% to 16% of the total mass of the electrolyte solution.

13. The electrolyte according to claim 1, characterized in that The organic solvent includes one or more of a cyclic ester organic solvent, a linear ester organic solvent, and a fluorine-substituted organic solvent of the above ester organic solvents.

14. The electrolyte according to claim 13, characterized in that The organic solvent includes one or more of ethylene carbonate, propylene carbonate, diethyl carbonate, ethyl methyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, ethyl propionate, propyl propionate, ethyl fluoroacetate, ethyl methyl fluorocarbonate, dimethyl fluorocarbonate, propylene fluorocarbonate, γ-butyrolactone, sulfolane, methyl formate, ethyl formate, methyl acetate, ethyl acetate, propyl acetate, n-butyl acetate, isobutyl acetate, n-amyl acetate, isoamyl acetate, methyl propionate, methyl butyrate, ethyl n-butyrate, methyl acrylate, and ethyl acrylate.

15. The electrolyte according to claim 13, characterized in that The total mass of the organic solvent is 20% to 80% of the total mass of the electrolyte.

16. The electrolyte according to claim 1, characterized in that The additives further include one or more of fluoroethylene carbonate, vinylene carbonate, 1,3-propane sultone, vinyl sulfate, propene sultone, methylene disulfonate, pentafluoroethoxyphosphazene, dicyclohexylcarbonyl, trimethyl imide phosphate, and hexamethylene diisocyanate.

17. The electrolyte according to claim 16, characterized in that The total mass of the additives is greater than 5% of the total mass of the electrolyte and less than or equal to 35% of the total mass of the electrolyte.

18. A lithium ion battery, characterized in that: The invention comprises a positive electrode sheet, a negative electrode sheet, a separator and the electrolyte according to any one of claims 1 to 17.

19. The lithium-ion battery according to claim 18, wherein The first electrolyte is injected before the battery formation treatment, and the second electrolyte is injected after the battery formation treatment; the mass ratio of the injected first electrolyte to the second electrolyte is between 8:2 and 9:

1.

20. A method for preparing a lithium ion battery, characterized in that: The electrolyte uses the electrolyte according to any one of claims 1 to 17, and the preparation method comprises: The positive electrode sheet, separator and negative electrode sheet are stacked and wound in sequence to form a battery cell; injecting the first electrolyte into the battery cell, allowing it to stand for a period of time and then performing a formation treatment to obtain a preformed battery; The preformed battery is discharged to an empty state, injected with the second electrolyte, and then subjected to aging and capacity separation treatments to obtain a lithium-ion battery.

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