Electrolyte, lithium ion battery and preparation method of lithium ion battery

Abstract

The invention relates to an electrolyte, a lithium ion battery and a preparation method of the lithium ion battery. The electrolyte comprises an electrolyte salt, an organic solvent and an additive, and the electrolyte comprises a first electrolyte used for liquid injection before battery formation treatment and a second electrolyte used for liquid injection after battery formation treatment; in the first electrolyte, the additives comprise a siloxane compound additive and a first nitrile compound additive; and in the second electrolyte, the additive comprises a second nitrile compound additive. According to the technical scheme, an interfacial film with low impedance and high stability can be formed, side reaction between the electrolyte and the electrode is reduced, the gas production phenomenon caused by the side reaction is inhibited, the cycle performance of the battery is effectively improved, the condition that the internal impedance of the battery is increased due to repeated charge-discharge cycles is improved, and the battery has good dynamic performance.

Description

Technical Field

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

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

[0003] In actual applications, as the number of charge and discharge cycles of lithium-ion batteries increases, the battery capacity will gradually decay, affecting the normal use of the equipment. In particular, long-term use in extreme environments such as high temperature or high voltage, or frequent overcharge or overdischarge during charge and discharge will lead to aggravated interface side reactions, which will reduce battery capacity and may also cause gas production. When gas production is severe, the battery will bulge, leading to battery shell rupture, electrolyte leakage, and even explosion. This will deteriorate the battery cycle life and seriously affect user experience and safety. Summary of the invention

[0004] In order to solve or partially solve the problems existing in the related art, the present application provides an electrolyte, a lithium-ion battery and a preparation method thereof, which can form an interface film with low impedance and high stability, reduce the side reactions between the electrolyte and the electrode, inhibit the gas production of the 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, so that the battery has good dynamic performance.

[0005] The first aspect of the present application provides an electrolyte, comprising an electrolyte salt, an organic solvent and an additive, wherein the electrolyte comprises 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 comprises a siloxane compound additive and a first nitrile compound additive; in the second electrolyte, the additive comprises a second nitrile compound additive.

[0006] In some embodiments of the present application, the structural formula of the siloxane compound additive is as follows: ; Wherein, each R group is independently selected from an alkane group, an alkene group, an alkoxy group, an alkylamine group, a halogen substituent group, a halogenated hydrocarbon group or a phenyl group, and n is a positive integer equal to or greater than 3.

[0007] In some preferred embodiments of the present application, the siloxane compound additive is selected from one or more of the following compounds: .

[0008] 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.

[0009] 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.

[0010] In some preferred embodiments of the present application, the dinitrile compound is selected from one or more of the following compounds: .

[0011] In some embodiments of the present application, 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 with cyano.

[0012] In some preferred embodiments of the present application, the polynitrile compound is .

[0013] In some embodiments of the present application, 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 6%.

[0014] In some embodiments of the present application, in the second electrolyte, the mass proportion of the second nitrile compound additive is 2% to 8%.

[0015] 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.

[0016] In some embodiments of the present application, the electrolyte salt includes one or more of lithium hexafluorophosphate, lithium difluorooxalatoborate, lithium difluorobisoxalatophosphate, lithium tetrafluoroborate, lithium bis(trifluoromethylsulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium difluorophosphate, and lithium cyano(trifluoromethanesulfonyl)imide.

[0017] In some preferred embodiments of the present application, the total mass of the electrolyte salt is 10% to 30% of the total mass of the electrolyte solution; more preferably, it is 12.5% ​​to 16%.

[0018] In some embodiments of the present application, the organic solvent includes a combination of 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.

[0019] In some preferred embodiments of the present application, 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, cyclopentane, 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 butyrate, methyl acrylate, and ethyl acrylate.

[0020] In some preferred embodiments of the present application, the total mass of the organic solvent is 20% to 80% of the total mass of the electrolyte.

[0021] In some embodiments of the present application, the additive also includes one or more of fluoroethylene carbonate, vinylene carbonate, 1,3-propane sultone, vinyl sulfate, propylene sultone, methylene disulfonate, pentafluoroethoxyphosphazene, dicyclohexylcarbonyl, trimethyl imide phosphate, and hexamethylene diisocyanate.

[0022] In some preferred embodiments of the present application, the total mass of the additive is 5% to 35% of the total mass of the electrolyte.

[0023] A second aspect of the present application provides a lithium-ion battery, comprising a positive electrode sheet, a negative electrode sheet, a separator and the above-mentioned electrolyte.

[0024] In some embodiments of the present application, 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 and the second electrolyte is between 8:2 and 9:1.

[0025] The third aspect of the present application provides a method for preparing a lithium-ion battery, comprising: stacking and winding a positive electrode sheet, a separator, and a negative electrode sheet in sequence to form a battery cell; Injecting a first electrolyte into the battery cell, allowing it to stand for a period of time before performing a formation treatment to obtain a preformed battery; The preformed battery is discharged to an empty state, injected with a second electrolyte, and then aged and capacity-separated to obtain a lithium-ion battery.

[0026] A fourth aspect of the present application provides an electrical device, comprising the above-mentioned lithium-ion battery or a lithium-ion battery prepared by the above-mentioned preparation method.

[0027] The technical solution provided by this application may have the following beneficial effects: The present application scheme adopts a siloxane compound and a first nitrile compound as additives in the first electrolyte, and utilizes the synergistic effect of the two when used in combination, so as to form a positive and negative interface film with low impedance and high stability, thereby improving the initial kinetic window, and at the same time effectively inhibiting the dissolution of positive electrode transition metal ions and the gas production of the battery cell, thereby improving the overall cycle performance of the lithium-ion battery. Furthermore, the battery cell is injected twice with the first electrolyte and the second electrolyte. After the first electrolyte is formed, a stable, low-impedance initial interface film can be formed. The injection of the second electrolyte can enhance the positive electrode interface complexation during the cycle, thereby improving the battery's cycle performance as a whole.

[0028] It should be understood that the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the present application. DETAILED DESCRIPTION

[0029] 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 specific embodiments described. It should also be understood that the terms used herein are only for describing specific embodiments and are not intended to be limiting.

[0030] The terms used in this application are for the purpose of describing specific embodiments only and are not intended to limit this application. The singular forms of "a", "said" and "the" used in this application and the appended claims are also intended to include plural forms unless the context clearly indicates other meanings. 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 associated listed items.

[0031] Where a numerical range is provided, it is to be understood that each intermediate value between the upper and lower limits of the range and any other provisions or intermediate values ​​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 explicitly excluded limits in the specified range. Where a specified range includes one or two limits, the scope excluding any or both of those included limits is also encompassed within the present invention. In the description of the present application, the meaning of "multiple" is two or more, unless otherwise clearly and specifically limited.

[0032] 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 invention belongs. Although any methods and materials or equivalent methods and materials described herein can also be used in the practice or testing of the present invention, preferred methods and materials are now described.

[0033] In actual applications, as the number of charge and discharge cycles of lithium-ion batteries increases, the electrochemical performance of the battery deteriorates, affecting the normal use of the equipment. In particular, long-term use in extreme environments such as high temperature or high voltage, or frequent overcharge or overdischarge during charge and discharge, will lead to aggravated interface side reactions, reducing battery capacity and may also cause gas production. When gas production is severe, the battery will bulge, leading to battery shell rupture, electrolyte leakage and even explosion, which will deteriorate the battery cycle life and put related electronic equipment at risk of damage. It will also pose a threat to the personal safety of users, seriously affecting user experience and safety.

[0034] In response to 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 interface film with low impedance and good stability, broaden the initial kinetic window, reduce gas production by side reactions, and improve the cycle life of the battery while enabling the battery to have both good kinetic performance and safety performance.

[0035] The electrolyte of the embodiment of the present application includes a first electrolyte for the first injection and a second electrolyte for the second injection. 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.

[0036] It should be noted that the first liquid injection described in the embodiment of the present application occurs before the battery formation treatment, and the second liquid injection occurs after the battery formation treatment.

[0037] Furthermore, in the embodiment of the present application, the additive of the second electrolyte does not include a siloxane compound additive.

[0038] Compared with traditional additives, siloxane compounds have high bond energy Si-O bonds and better heat resistance. When used as an additive for electrolyte components, they can effectively improve the overall thermal stability of the electrolyte, reduce the storage cost of the electrolyte, and improve the storage performance of the battery. In addition, 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 a stable, low-impedance positive and negative interface film, thereby effectively improving the initial kinetic window; at the same time, because it can act as an acid scavenger to remove HF generated by chemical reactions in the electrolyte, avoid a large amount of HF from corroding the battery's interface film, inhibit the hydrolysis of moisture-sensitive electrolyte salts such as lithium hexafluorophosphate, reduce side reactions between the electrolyte and the electrode, improve the battery's cycle stability, and inhibit the storage of gas production at high temperatures, improve the battery's high-temperature storage performance and cycle performance, and thus improve the battery's safety.

[0039] At the same time, the nitrile compound additives used in the first electrolyte and the second electrolyte can be adsorbed on the positive electrode plate through their lone electron pairs to complex the transition metal and inhibit its dissolution, thereby cooperating with the siloxane compound additive to effectively enhance the stability of the positive electrode interface during the cycle. In particular, the use of part of the first nitrile compound additive in the first electrolyte can avoid the increase in interface film impedance caused by the high content of nitrile compound additives before the battery formation treatment, thereby effectively widening the initial kinetic window of the battery; and the use of part of the second nitrile compound additive 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 battery cycle stability, and make the battery have good kinetic performance.

[0040] In some embodiments, the structural formula of the siloxane compound additive is as follows: ; The R groups are each 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.

[0041] Here, n is a positive integer greater than or equal to 3, such as n=3, 4, etc.

[0042] In some embodiments, the siloxane compound additive may be selected from one or more of the following compounds: .

[0043] The dissociation energy of the Si-O bond in the siloxane compound of the above structural formula is significantly higher than that of the CO bond, and the high bond energy gives the siloxane compound and its polymer excellent thermal stability. Therefore, after the first additive siloxane compound is added to the first electrolyte, the thermal stability of the first electrolyte itself is effectively improved. Moreover, the siloxane compound additive is beneficial to inhibit the dissolution of positive transition metal ions, improve the structural stability of the positive electrode, reduce the oxidation of the solvent on the positive electrode side, improve the storage performance of the battery, and make the battery have good kinetic performance through the synergistic effect with the second nitrile compound additive in the first electrolyte. The first additive siloxane compound can also polymerize at the interface between the electrolyte and the negative electrode plate to form an SEI film, effectively isolating the negative electrode plate 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. Furthermore, the siloxane compound additive can also be used as an acid scavenger to remove HF in the electrolyte, avoid the reaction between HF and the pole piece, prevent the corrosion of the interface protective film, and effectively improve the high temperature storage and cycle stability of the battery.

[0044] Preferably, the silicone compound additive may be: .

[0045] The additive is (3-aminopropyl) triethoxysilane, which can remove HF and stabilize PF5. First, the nucleophilic nitrogen atom with lone pair 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. Secondly, (3-aminopropyl) triethoxysilane can act as an HF scavenger by destroying its own Si-O bond, thereby preventing HF from further reacting with 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, and the formed polymer network can also serve as a protective layer on the electrode surface, inhibiting the side reactions of the electrode and the electrolyte at high temperatures, reducing the gas production of the side reactions, and improving the overall performance of the battery. Furthermore, the presence of amino groups in (3-aminopropyl) triethoxysilane can promote the transmission of lithium ions at the interface between the electrode and the electrolyte, and the combination with nitrile compound additives can effectively improve the stability of the positive and negative electrode interfaces, improve the overall cycle performance of lithium-ion batteries, and maintain good kinetic performance during long cycles.

[0046] In some embodiments, the nitrile compound additive may be one or more of a dinitrile compound and a polynitrile compound, wherein the polynitrile compound is a trinitrile or a compound containing more cyano groups; preferably, it is a chain nitrile compound.

[0047] In some embodiments, the dinitrile compound may be selected from one or more of the following compounds: .

[0048] In some embodiments, the polynitrile compound can be selected from the compounds shown in the following structural formula: ; 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 with cyano.

[0049] In some specific embodiments, the polynitrile compound may be: .

[0050] The nitrile compound additive of the above structural formula is a chain dinitrile or trinitrile compound, which can act synergistically with the siloxane compound additive to inhibit the dissolution of positive electrode transition metal ions and further reduce the oxidation of the solvent on the positive electrode side, thereby improving the high temperature storage performance and cycle stability of the battery.

[0051] Preferably, the dinitrile compound may be: .

[0052] Succinonitrile (BN) can cover the active sites on the surface of the positive electrode, effectively inhibit the dissolution of cobalt from the lithium cobalt oxide positive electrode under high voltage, and reduce the reactivity of the positive electrode to the electrolyte, thereby improving the battery's voltage resistance and high-temperature storage capacity. Its impedance is smaller than that of other commonly used nitriles, so that the battery has good kinetic performance.

[0053] Preferably, the trinitrile compound may be:

[0054] 1,3,6-Hexanetrinitrile (HTCN) can adsorb and form a strong complex with transition metals such as cobalt ions on the surface of the positive electrode, thereby inhibiting the dissolution of transition metals; it can also act as a dehydrating agent and an acid scavenger to synergize with siloxane compound additives to improve the stability of the positive and negative electrodes, while improving the density of the CEI film at the positive electrode interface, improving the stability of the battery when used in extreme environments such as high voltage and high temperature and in long-term charge and discharge cycles, and improving the battery cycle life.

[0055] Further preferably, the nitrile compound additive may be a combination of multiple nitrile compounds, specifically a combination of a dinitrile compound and a dinitrile compound, or a combination of a dinitrile compound and a trinitrile compound, preferably a combination of succinonitrile and 1,3,6-hexanetrinitrile.

[0056] 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 may be the same or different. In particular, when the nitrile compound additive in the electrolyte is a combination of succinonitrile and 1,3,6-hexanetrinitrile, any one of succinonitrile and 1,3,6-hexanetrinitrile may be used in the first electrolyte, and the other compound may be used in the second electrolyte, in which case the types of the first nitrile compound additive and the second nitrile compound additive are different; or the combination of succinonitrile and 1,3,6-hexanetrinitrile may be used in both the first electrolyte and the second electrolyte, in which case the types of the first nitrile compound additive and the second nitrile compound additive are the same.

[0057] In some embodiments, 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 6%.

[0058] Among them, the mass proportion of the siloxane compound additive can be, for example, 0.1%, 0.5%, 0.8%, 1%, 1.2%, 1.5%, 2%, 3%, 4%, 5%, etc., preferably 0.8% to 2%. When the content of the siloxane compound additive in the first electrolyte meets the above range, the effect of removing the decomposition products of the lithium salt is excellent, and an elastic interface protective film can be formed at the same time, which can effectively inhibit the occurrence of side reactions and improve the overall performance of the battery. If the content of the siloxane compound additive is too low, the effect of removing HF or PF5 is not obvious, and it cannot play a good role in improving the thermal stability, cycle performance and high-temperature storage performance of the battery; and if the content is too high, it will not be completely consumed in the formation stage. When the content of some siloxane compounds with larger molecular weight is too high, it will affect the overall viscosity of the electrolyte and deteriorate the kinetic properties of the electrolyte. By regulating the content of the siloxane compound additive in the first electrolyte, it is basically consumed in the formation stage.

[0059] The mass proportion of the first nitrile compound additive can be, for example, 2%, 2.5%, 3%, 3.5%, 4%, 5%, 6%, etc., preferably 2% to 4%. When the content of the first nitrile compound additive in the first electrolyte meets 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 plate, and obtains an initial interface with lower impedance, thereby improving the initial kinetic performance of the battery cell. If the content of the first nitrile compound additive is too low, the positive electrode cannot be effectively complexed; and if the content is too high, the interface impedance will increase, the initial kinetic window will deteriorate, and the battery performance will deteriorate.

[0060] In some embodiments, in the second electrolyte, the mass proportion of the second nitrile compound additive is 2% to 8%. For example, it can be 2%, 2.5%, 3%, 3.5%, 4%, 5%, 6%, 7%, 8%, etc., preferably 3% to 7%. When the content of the second nitrile compound additive in the second electrolyte meets the above range, the overall content of the nitrile compound in the electrolyte is controlled so that the total content of the nitrile compound in the electrolyte is less than 5%, which can avoid excessive cyanide from deteriorating the interface impedance, and can effectively complex with the positive electrode active material to reduce the side reaction between the electrolyte and the positive electrode plate.

[0061] 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. The smaller amount of the nitrile compound additive in the first electrolyte can not only play the role of complexing the positive electrode active material, but also avoid the excessive cyanide content increasing the interface film impedance, thereby playing a good synergistic effect with the siloxane compound additive in the first electrolyte; while the larger amount of the nitrile compound additive in the second electrolyte can effectively supplement the nitrile compound, ensure that the total electrolyte has a suitable cyanide content, meet its protection requirements for the positive electrode plate, and also ensure that the battery has good dynamic performance.

[0062] In some embodiments, the electrolyte salt includes one or more of lithium hexafluorophosphate (LiPF6), lithium difluorooxalatoborate (LiODFB), lithium difluorobis(oxalatophosphate) (LiDFOP), lithium tetrafluoroborate (LiBF4), lithium bis(trifluoromethylsulfonyl)imide (LiTFSI), lithium bis(fluorosulfonyl)imide (LiFSI), lithium difluorophosphate (LiPOF2), and lithium cyano(trifluoromethanesulfonyl)imide (LiCTFSI).

[0063] In some embodiments, the total mass of the electrolyte salt is 10% to 30% of the total mass of the electrolyte; 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 and the mass of the electrolyte salt in the second electrolyte, and the total mass of the electrolyte includes the first electrolyte and the second electrolyte. If the content of the lithium salt is too low, the mobility of the lithium ions decreases; if the concentration of the lithium salt is too high, the wettability of the electrolyte may decrease due to the excessive increase in the viscosity of the non-aqueous electrolyte, and the film-forming effect decreases accordingly.

[0064] In some embodiments, the organic solvent may include a cyclic carbonate organic solvent, a linear carbonate organic solvent, and other linear ester organic solvents.

[0065] The cyclic carbonate organic solvent can dissociate the lithium salt in the electrolyte well due to its high dielectric constant. A specific example of the cyclic carbonate organic solvent may be at least one organic solvent selected from ethylene carbonate (EC) and propylene carbonate (PC).

[0066] The linear carbonate organic solvent is an organic solvent with low viscosity and low dielectric constant, wherein a typical example of the linear carbonate organic solvent can 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.

[0067] Other linear ester organic solvents specifically include carboxylic acid ester organic solvents, which generally have a lower viscosity than carbonates and can ensure good fluidity of the liquid electrolyte. As a specific example, the linear ester organic solvent 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-amyl acetate, isoamyl acetate, methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), butyl propionate, methyl butyrate, ethyl butyrate, methyl acrylate, and ethyl acrylate.

[0068] In addition to the cyclic carbonate organic solvent and / or the linear carbonate organic solvent, the organic solvent may further include a cyclic ester organic solvent commonly used in lithium secondary battery electrolytes or a fluorine-substituted organic solvent of the ester organic solvent.

[0069] As a specific example, the cyclic ester organic solvent may include at least one organic solvent selected from γ-butyrolactone, γ-valerolactone, γ-caprolactone, δ-valerolactone, ε-caprolactone, and sulfolane.

[0070] As a specific example, the fluorine-substituted organic solvent may be one or more of fluoroethyl acetate (DFEA), fluoroethyl methyl carbonate (FEMC), fluorodimethyl carbonate (FDMC), and fluoropropylene carbonate (FPC).

[0071] In order 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.

[0072] In some embodiments, the total mass of the organic solvent is 20% to 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.

[0073] In some embodiments, the additive further includes a base additive, and the base additive includes one or more of fluoroethylene carbonate (FEC), vinylene carbonate (VC), 1,3-propane sultone (PS), diethylene sulfate (DTD), propene sultone (PST), methylene disulfonate (MMDS), pentafluoroethoxyphosphazene, dicyclohexylcarbonyl, trimethyl imide phosphate, and hexamethylene diisocyanate.

[0074] The specific ingredients of the basic additives can be selected according to the specific needs of the battery, such as fluoroethylene carbonate (FEC), vinylene carbonate (VC), 1,3-propane sultone (PS), etc., which can promote the formation of SEI film.

[0075] In some embodiments, the mass percentage of the basic additive in the first electrolyte is 5% to 35%.

[0076] In some embodiments, the mass percentage of the basic additive in the second electrolyte is 5% to 35%.

[0077] In some embodiments, the total mass of the additives is 5% to 35% of the total mass of the electrolyte. The total mass of the additives includes the mass of the additives in the first electrolyte and the mass of the additives in the second electrolyte, and the total mass of the electrolyte includes the first electrolyte and the second electrolyte.

[0078] In the first electrolyte, the additives include a base additive, a siloxane compound additive, and a first nitrile compound additive. In the second electrolyte, the additives include a base additive and a second nitrile compound additive. The types of the base additives in the first electrolyte and the second electrolyte may be the same or different.

[0079] Through the synergy between the additive components in the total electrolyte (basic additives, siloxane compound additives, nitrile compound additives), they can work together to form a film, further enhance the stability of the pole piece and interface, reduce side reactions at the interface between the electrolyte and the electrode, and improve the cycle stability and high-temperature storage performance of the battery.

[0080] It should be noted that the present application does not specifically limit the method for preparing the electrolyte, and those skilled in the art can prepare it into an electrolyte according to conventional technical means, for example, by uniformly mixing the raw materials according to a proportion.

[0081] The lithium-ion battery provided in the embodiment of the present application comprises a positive electrode sheet, a negative electrode sheet, a separator and the above-mentioned electrolyte.

[0082] 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 to the second electrolyte to meet the requirements, a low-impedance and high-stability interface film is formed on the electrode surface, the initial kinetic window is widened, and the side reaction gas production can be reduced, the thermal stability of the battery is improved, and the battery cycle life is improved. At the same time, the battery has good kinetic performance and safety performance, and the risk of thermal runaway of the battery is reduced.

[0083] In an embodiment of the present application, the positive electrode plate 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 the present 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 material known to be 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, and a carbon material such as carbon cloth and carbon paper; preferably aluminum foil.

[0084] 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 a positive electrode collector, and then dried and rolled to form a positive electrode material layer.

[0085] The positive electrode active material includes, but is not limited to, lithium cobalt oxide, and the lithium cobalt oxide is doped with one or more elements of aluminum, niobium, nickel, manganese, copper, tin, zirconium, chromium and titanium. The binder is a component that helps the bonding between the active material and the conductive agent and the bonding with the current collector. The binder can be polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, 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 an organic solvent such as N-methyl-2-pyrrolidone (NMP), and its amount can be such that the desired viscosity is obtained when the positive electrode active material and the optional binder and conductive agent are included.

[0086] In the embodiment of the present application, the negative electrode plate 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 enriched current collectors can be, for example, copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, foamed nickel, foamed copper or composite current collectors, etc.; preferably copper foil.

[0087] 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 a negative electrode collector, and then dried and rolled to form a negative electrode material layer.

[0088] The negative electrode active material may include a compound capable of reversibly inserting / deinserting lithium ions, including a carbon-based active material, a silicon-based active material, or a mixture thereof. Typical carbon active materials include at least one of carbon materials such as artificial graphite, natural graphite, acetylene black, needle coke, carbon nanotubes, and graphene. Typical silicon active materials include at least one of elemental silicon, silicon oxide compounds, pre-inserted lithium silicon oxide compounds, carbon-coated silicon materials, and silicon metal compounds. The binder may be polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer, styrene-butadiene rubber, and fluororubber. The solvent may include water, or an organic solvent, such as N-methyl-2-pyrrolidone (NMP), in an amount such that the desired viscosity is obtained when the negative electrode active material and optional binder and conductive agent are included.

[0089] In the lithium ion battery mentioned in the present application, the diaphragm is arranged between the positive electrode and the negative electrode to prevent short circuit. The present application embodiment has no particular restrictions on the material and shape of the diaphragm, as long as the effect of the present application is not significantly damaged. In some embodiments, the diaphragm can be used alone or in a stacked manner using a commonly used typical porous polymer film, such as a porous polymer film prepared by a polyolefin polymer (such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer and ethylene / methacrylate copolymer). Typical porous nonwoven fabrics can also be used, for example, nonwoven fabrics formed by high melting point glass fibers or polyethylene terephthalate fibers, etc.

[0090] The preparation process of the battery may include the following steps: overlapping the positive electrode sheet and the negative electrode sheet via the separator, and placing them into the shell after winding, folding, etc. as needed, injecting the electrolyte into the shell and sealing it, wherein the separator used is the separator provided in the present application. In addition, an overcurrent protection element, a guide plate, etc. may also be placed in the shell as needed to prevent the pressure inside the electrochemical device from rising and overcharging and discharging.

[0091] Further, it may include: S1, stacking and winding the positive electrode sheet, the separator and the negative electrode sheet in sequence to form a battery cell; S2, injecting a first electrolyte into the battery cell, allowing it to stand for a while and then performing a formation treatment to obtain a preformed battery; S3, discharging the preformed battery to an empty state, injecting a second electrolyte, and then performing aging and capacity separation treatments to obtain a lithium-ion battery.

[0092] That is, the first electrolyte and the second electrolyte are injected into the battery cell step by step using a secondary injection process. Specifically, the first electrolyte can be injected into the battery cell after vacuum baking, and then left to stand at room temperature for about 48 hours, and then left to stand at high temperature (40℃~60℃) for about 12 hours, and then pressurized to form a single battery with a surface pressure of 0.5 MPa~1.5MPa and a temperature between 25℃~85℃. After the formation, the battery is discharged to an empty state, and the second electrolyte is injected, followed by subsequent processes such as aging and capacity separation to obtain a lithium-ion battery.

[0093] 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.

[0094] The present application has no particular restrictions on the application fields of lithium-ion batteries, and they can be used in consumer electronics, new energy vehicles, energy storage and other fields.

[0095] In order to make the present invention easier to understand, the present invention will be further described in detail below in conjunction with examples, which are merely illustrative and are not intended to limit the scope of application of the present invention. The raw materials or components used in the present invention can be obtained by commercial routes or conventional methods unless otherwise specified.

[0096] Example 1 (1) Preparation of electrolyte First electrolyte: In a glove box filled with argon 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 0.8% (3-aminopropyl) triethoxysilane and 3.5% succinonitrile were added, and the first electrolyte was prepared after mixing evenly.

[0097] 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 <10ppm, 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 obtain the second electrolyte.

[0098] (2) Preparation of positive electrode sheet 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%). A 6μm aluminum foil was used as the current collector, and the solid content was 200mg / cm 2 The positive electrode slurry is coated on aluminum foil, dried, and rolled to a specific compaction density. It is then divided into strips, made into sheets, and glued to make positive electrode sheets that meet the winding requirements.

[0099] (3) Preparation of negative electrode sheet The negative electrode active material (graphite and carbon-coated silicon material, in which the silicon content is 10%) is mixed with a binder (SBR-CMC) and a conductive agent (carbon black) at a weight ratio of 95:3.5:1.5, and added to water as a solvent to prepare a negative electrode slurry (solid content is 60wt%). 8μm copper foil is used as the negative electrode current collector, and the solid content is 88mg / cm 2The negative electrode slurry is coated on the copper foil with a surface density of , dried, and rolled to prepare the negative electrode. Then, after the processes of striping, sheeting, and gluing, a negative electrode sheet that meets the winding requirements is made.

[0100] (4) Preparation of lithium-ion batteries A polyolefin porous membrane coated with inorganic particles (Al2O3) is used as the membrane.

[0101] The positive electrode sheet, separator and negative electrode sheet are stacked in order, so that the separator is in the middle of the positive and negative electrodes to play a role of isolation, and then the stacked electrode sheets and separators are wound to obtain a battery cell. The battery cell is placed in a battery shell and a lithium-ion battery is obtained through a secondary liquid injection process.

[0102] The secondary injection process includes: first, inject the first electrolyte after vacuum baking the battery cell, let it stand at room temperature for 48 hours, then let it stand at high temperature (60°C) for 12 hours, and then pressurize it, with a single battery surface pressure of 1MPa and a temperature of 80°C. After the formation, discharge the battery to an empty state, inject the second electrolyte, and then carry out subsequent processes such as capacity division and aging to obtain a lithium-ion battery.

[0103] Among them, the mass ratio of the first electrolyte to the second electrolyte is 8:2.

[0104] Embodiment 2 to Embodiment 21 The same method as in Example 1 is used, except that the components of the additives other than the basic additives in the first electrolyte or the second electrolyte and their corresponding contents (mass percentages) are different, or the mass ratio of the first electrolyte to the second electrolyte is different, as shown in Table 1.

[0105] Table 1

[0106] Comparative Example 1 The difference from Example 1 is that the content of (3-aminopropyl)triethoxysilane in the first electrolyte is 0.64%, the content of succinonitrile is 3.6%, and the lithium ion battery is prepared by a one-time injection process. That is, the formula of the electrolyte is consistent with the total electrolyte (first electrolyte + second electrolyte) in Example 1, and the only difference is that a one-time injection process is used.

[0107] Comparative Example 2 The same secondary injection process as in Example 1 is used, the difference being that both the first electrolyte and the second electrolyte contain 0.64% (3-aminopropyl)triethoxysilane, and the other formulas and contents in the electrolytes are consistent with those in Example 1.

[0108] Comparative Example 3 The same secondary injection process as that used in Example 1 is different in that the first electrolyte does not contain a siloxane compound additive.

[0109] Comparative Example 4 The same secondary injection process as in Example 1 is used, except that the first electrolyte does not contain nitrile compound additives.

[0110] Comparative Example 5 The same secondary injection process as in Example 1 is used, except that the second electrolyte does not contain nitrile compound additives.

[0111] Lithium-ion battery performance test (1) 0℃ cyclic interface state test Discharge to 3V at 0.2C at 25℃, then stand at 0℃ for 3H, charge to 4.53V at 0.34C constant current and constant voltage, cutoff current 0.05C, then discharge to 2.8V at 0.5C, repeat the cycle for 50cls, disassemble the fully charged battery and observe the lithium plating state of the interface.

[0112] (2) 60℃ cycle test Stand at 60℃ for 2h, charge to 4.53V at 0.5C constant current, cut-off current 0.05C, stand for 10min, test full charge thickness D0, then discharge to 3.0V at 0.5C, record discharge capacity C0 as initial capacity, repeat the cycle for 200cls, and get capacity C after 200 cycles 200 , thickness D 200 , then the capacity retention rate = C 200 / C0, thickness growth rate = D 200 / D0-1.

[0113] (3) 80℃ storage test Place the product at (85±2)℃ with full power and open circuit for 6 hours. Test the hot thickness immediately after taking it out of the box to see if the thickness changes. Determine whether there is gas generation based on the thickness change.

[0114] There were 5 batteries in each group and the results are recorded in the table below.

[0115] Table 2 Electrochemical performance test results of the battery

[0116] It can be seen from the embodiments, comparative examples and their electrochemical test performance that when a lithium-ion battery is prepared using the electrolyte and secondary injection process described in the present application, the low-impedance film-forming additive siloxane compound additive in the first electrolyte will undergo an oxidation-reduction reaction in the formation stage to form a dense, stable and low-impedance interface protection film, and the first nitrile compound additive can effectively complex the transition metal of the positive electrode. The combination of the two and other positive and negative electrode film-forming additives can effectively improve the initial kinetic window, while reducing the side reactions between the electrolyte and the electrodes, inhibiting the gas production of the battery cell at high temperatures and during the cycle, and improving the high-temperature storage performance, low-temperature and high-temperature cycle performance of the battery as a whole, and enabling the battery to have good kinetic performance, which is beneficial for its use under low temperature conditions.

[0117] According to Example 1 and Comparative Example 1, if conventional injection, i.e., a one-time injection process is used to prepare a lithium-ion battery, the interface film formed on the electrode surface after the formation treatment will cause the volume change caused by silicon-embedded lithium during long-term cycles, which will cause the SEI film to rupture, resulting in active lithium consumption and a decrease in capacity retention rate. At the same time, the thicker layer of side reaction products will increase the interface impedance and the thickness expansion rate. The siloxane compound additive can participate in the repair of the SEI film during the cycle, inhibit the battery thickness expansion and improve the battery cycle performance.

[0118] According to Example 1 and Comparative Example 2, if a large amount of the siloxane compound additive remains in the first electrolyte after formation, or continues to be introduced after formation, its property of polymerizing when in contact with water will cause it to continue to polymerize in any area of ​​the battery cell where there is water, thereby hindering the transport of lithium ions in the late cycle, reducing the kinetic performance of the battery, and deteriorating the cycle performance and storage performance of the battery, which is not conducive to the long-term cycle use of the battery.

[0119] According to Example 1 and Comparative Examples 3, 4 and 5, a siloxane compound additive having a high bond energy Si-O is used in combination with a low impedance nitrile compound additive in the first electrolyte, and a secondary liquid injection process is further combined, and a nitrile compound additive is used in the second electrolyte instead of a siloxane compound additive. The combination can effectively balance the interface protection of the positive and negative electrodes, can not only remove water and acid, but also form an interface protection film with good thermal stability and low impedance, and can effectively complex transition metal ions, that is, can effectively stabilize the positive electrode while reducing the degree of deterioration of the negative electrode, inhibit side reactions, thereby improving the overall performance of the lithium-ion battery as a whole, so that it has a good cycle life. According to Examples 1 to 5, when the electrolyte and secondary injection process described in this application are used to prepare lithium-ion batteries, when the additives in the electrolyte are siloxane compounds and nitrile compounds that conform to the structure defined in this application, they all have the effect of improving battery cycle performance, high-temperature storage performance, and inhibiting battery thickness expansion, while taking into account good battery dynamics performance. At the same time, (3-aminopropyl) triethoxysilane is used as a siloxane compound additive, which has a better effect on improving the performance of lithium-ion batteries.

[0120] According to Example 1, Example 6 and Example 7, when a combination of two nitrile compound additives is used in the electrolyte, the effect of improving the battery performance is better.

[0121] According to Example 1 and Example 8 to Example 12, when the content of the siloxane compound additive in the first electrolyte is within the range specified in the present application, especially in the range of 0.8% to 2%, the high temperature storage performance, high and low temperature cycle performance and dynamic performance of the battery are all improved.

[0122] According to Example 1 and Example 13 to Example 19, when the content of the first nitrile compound additive in the first electrolyte and the second nitrile compound additive in the second electrolyte are within the specified range of the present application, especially when the mass proportion of the first nitrile compound in the first electrolyte is 2% to 4%, the mass proportion of the second nitrile compound in the second electrolyte is 3% to 7%, and the content of the first nitrile compound is lower than the content of the second nitrile compound, the high temperature storage performance, high and low temperature cycle performance and dynamic performance of the battery are all improved.

[0123] According to Example 1, Example 20, and Example 21, the mass ratio of the first electrolyte to the second electrolyte is between 8:2 and 9:1, which has a good improvement effect on the high temperature storage performance, high and low temperature cycle performance, and dynamic performance of the battery. When there is less electrolyte during formation, the infiltration is not sufficient, which will affect the uniformity of the film formation and the high and low temperature cycle performance of the battery.

[0124] It should be noted that the embodiments described above are only used to explain the present application and do not constitute any limitation to the present application. The present application is described with reference to typical embodiments, but it should be understood that the words used therein are descriptive and explanatory words, rather than restrictive words. The present application may be modified as specified within the scope of the claims of the present application, and the present application may 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 additive includes a siloxane compound additive and a first nitrile compound additive; In the second electrolyte, the additive includes a second nitrile compound additive.

2. The electrolyte according to claim 1, characterized in that The structural formula of the siloxane compound additive is as follows: ； Wherein, each R group is independently selected from an alkane group, an alkene group, an alkoxy group, an alkylamine group, a halogen substituent group, a halogenated hydrocarbon group or a phenyl group, and n is a positive integer equal to or greater than 3.

3. The electrolyte according to claim 2, characterized in that The siloxane compound additive is selected from one or more of the following compounds: 。 4. 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 of dinitrile compounds and polynitrile compounds.

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

6. The electrolyte according to claim 4, characterized in that The dinitrile compound is selected from one or more of the following compounds: 。 7. The electrolyte according to claim 4, 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 with cyano.

8. The electrolyte according to claim 7, characterized in that The polynitrile compound is 。 9. 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 6%.

10. 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 8%.

11. The electrolyte according to claim 1, characterized in that 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.

12. 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, lithium difluorophosphate, and lithium cyano(trifluoromethanesulfonyl)imide.

13. The electrolyte according to claim 12, characterized in that The total mass of the electrolyte salt is 10% to 30% of the total mass of the electrolyte.

14. The electrolyte according to claim 13, characterized in that The total mass of the electrolyte salt is 12.5% ​​to 16% of the total mass of the electrolyte.

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

16. The electrolyte according to claim 15, 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.

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

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

19. The electrolyte according to claim 18, characterized in that The total mass of the additive is 5% to 35% of the total mass of the electrolyte.

20. A lithium ion battery, characterized in that: The invention comprises a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte as claimed in any one of claims 1 to 19.

21. The lithium ion battery according to claim 20, characterized in that 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.

22. A method for preparing a lithium ion battery, characterized in that: include: The positive electrode sheet, the separator and the negative electrode sheet are stacked and wound in sequence to form a battery cell; Injecting the first electrolyte according to any one of claims 1 to 19 into the battery cell, and performing a formation treatment after a static treatment to obtain a preformed battery; The preformed battery is discharged to an empty state, injected with the second electrolyte according to any one of claims 1 to 19, and then subjected to aging and capacity separation treatment to obtain a lithium-ion battery.

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