Non-aqueous electrolyte and lithium secondary battery

Abstract

The present application provides a kind of non-aqueous electrolyte and lithium secondary battery.The non-aqueous electrolyte includes as component (A) the carboxylic acid ester compound containing cyano and phenoxy, as component (B) non-aqueous solvent and as component (C) lithium salt;Wherein, the structure formula of the component (A) carboxylic acid ester compound containing cyano and phenoxy is as shown in formula (I) : R1 represents the substituent group of benzene ring, and R1 each occurrence, independently selected from cyano or substituted or unsubstituted hydrocarbyl, and at least one R1 is cyano;R2 represents divalent linking group, R3 represents monovalent organic group;N represents the positive integer of 1-5.The non-aqueous electrolyte provided by the present application has excellent low temperature performance and high pressure resistance.

Description

TECHNICAL FIELD

[0001] The present application relates to a non-aqueous electrolyte and a lithium secondary battery, and belongs to the field of lithium ion batteries. BACKGROUND

[0002] With the development of economic society, the ecological environment is facing great challenges, and in recent years, the development of new energy has become the focus of society. Among them, lithium ion batteries have become the first choice in the fields of 3C electronic products, energy storage, electric vehicles, aerospace, etc. due to their high specific energy, long service life, no memory effect and other advantages.

[0003] Further improving the energy density is the main direction of the future development of lithium ion batteries, and improving the working voltage of the battery is one of the effective ways to improve the energy density of lithium ion batteries. The reason why high-voltage lithium batteries are difficult to apply is that the current commercial carbonate-based electrolyte has a low electrochemical stability window, which leads to a decrease in the stability of lithium ion batteries at high voltage, and also causes serious capacity attenuation of the battery. However, while maintaining high energy density, lithium ion batteries also face extreme weather in application scenarios, which can seriously affect the capacity of the battery. The main reason is that the electrolyte has low conductivity at low temperature, the interface impedance between the electrolyte and the positive and negative electrodes is large, and the migration speed of lithium ions in the positive and negative electrode materials is slow, which limits the application of lithium ion batteries.

[0004] Some documents disclose an electrolyte containing a cyano phenoxy group, which uses a phosphoric acid triester organic compound and / or a phosphite triester organic compound containing a cyano phenoxy group as a high-voltage additive to improve the high-voltage stability of the battery. However, the use of carbonate solvent systems fails to improve the low-temperature performance.

[0005] Some documents disclose a high-voltage lithium ion battery electrolyte containing lithium difluorophosphate, a preparation method thereof and a lithium ion battery. The use of high-concentration LiPO2F2 as an additive improves the high-voltage performance of the battery, but the solubility of LiPO2F2 in conventional cyclic carbonate and chain carbonate and chain carboxylic acid ester mixed solvents is not high, usually around 1%, and decreases with the increase of lithium salt concentration. In addition, the electrolyte does not improve the low-temperature performance.

[0006] Some documents disclose a carboxylic acid ester-based electrolyte for low-temperature lithium batteries, which uses a carboxylic acid ester organic solvent as a base solvent to improve the low-temperature performance of the electrolyte. However, carboxylic acid ester compounds have poor high-voltage performance, so the electrolyte does not improve the high-voltage performance.

[0007] It can be seen that although the field has carried out a series of researches on electrolytes for improving high-voltage performance or low-temperature performance, the electrolyte that simultaneously has high-voltage performance and low-temperature performance cannot be said to be sufficient, and there is room for further research. SUMMARY

[0008] Problem to be solved by the invention

[0009] As described above, cyclic carbonates are often used as polar solvents because they have a strong lithium salt solubility and can reduce the occurrence of side reactions by forming a stable solid electrolyte interface (SEI), thereby improving compatibility with most electrode materials. However, the low electrochemical stability window of carbonate-based electrolytes results in poor stability at high voltage, and at low temperatures, the low conductivity and large interface impedance between the electrolyte and the positive and negative electrodes limit their application in high-voltage batteries.

[0010] In order to improve the high-voltage performance of the electrolyte, the prior art adds nitrile-containing carbonate, sulfate, sulfite, phosphate or phosphite compounds or fluorine-containing phosphate compounds as high-voltage additives in the electrolyte to improve the high-voltage stability of the electrolyte. However, it has been found in practice that even with such additives, the low-temperature performance of the electrolyte is not improved.

[0011] In addition, in order to improve the low-temperature performance of the electrolyte, the prior art replaces (partially) the carbonate solvent with a carboxylate solvent, changes the lithium ion solvation structure in the electrolyte, reduces the desolvation energy of lithium ions, improves the reaction kinetics of the battery, and improves the low-temperature performance. However, carboxylate solvents have poor high-voltage performance and are easily oxidized and decomposed at high voltage, leading to electrolyte and active lithium consumption and an increase in positive electrode surface impedance, so it is difficult to achieve high-voltage applications.

[0012] Therefore, due to at least the above reasons, it seems that there is a certain difficulty in balancing the high-pressure resistance and low-temperature resistance in the electrolyte.

[0013] In addition, since the positive electrode material is easily phase-transformed at high voltage, leading to material decomposition, metal ions are dissolved and migrate to the electrolyte and the negative electrode to produce side reactions, not only worsening the internal resistance of the lithium ion battery, but also leading to the consumption of active lithium ions.

[0014] To solve the above problems, the present application provides a non-aqueous electrolyte comprising a specific structure of a cyano and phenoxy-containing carboxylate compound, which can simultaneously have low-temperature performance and high-pressure resistance by using the compound as an electrolyte co-solvent.

[0015] In addition, the present application also provides a lithium secondary battery comprising the non-aqueous electrolyte of the present application.

[0016] Solution for solving the problem

[0017] The present application provides a nonaqueous electrolyte, wherein the nonaqueous electrolyte contains a carboxylic acid ester compound containing a cyano group and a phenoxy group as component (A), a nonaqueous solvent as component (B), and a lithium salt as component (C);

[0018] wherein the component (A) carboxylic acid ester compound containing a cyano group and a phenoxy group has a structural formula represented by formula (I):

[0019]

[0020] R1 represents a substituent group of a benzene ring, and R1 is independently selected from at least one of a cyano group or a substituted or unsubstituted hydrocarbon group at each occurrence, and at least one R1 is a cyano group;

[0021] R2 represents a divalent linking group, and R3 represents a monovalent organic group;

[0022] n represents a positive integer of 1 to 5.

[0023] The nonaqueous electrolyte according to the present application, wherein R1 is selected from at least one of a cyano group or a substituted or unsubstituted C1 to C10 alkyl group.

[0024] The nonaqueous electrolyte according to the present application, wherein R2 is selected from a substituted or unsubstituted C1 to C10 alkylene group or a heterocyclic group; and R3 is selected from a substituted or unsubstituted alkyl group.

[0025] The nonaqueous electrolyte according to the present application, wherein n is 1 or 2.

[0026] The nonaqueous electrolyte according to the present application, wherein the content of the component (A) carboxylic acid ester compound containing a cyano group and a phenoxy group is 0.5 mass% to 30 mass% of the total mass of the nonaqueous electrolyte.

[0027] The nonaqueous electrolyte according to the present application, wherein the component (B) nonaqueous solvent is selected from one or more of a cyclic carbonate solvent, a linear carbonate solvent, an ether solvent, an ester solvent, and a ketone solvent.

[0028] The nonaqueous electrolyte according to the present application, wherein the component (C) lithium salt is selected from one or more of a salt formed by a lithium ion and an anion selected from the group consisting of PF6 - , BF4 - , Cl - , Br - , I - , ClO4 - , AsF6 - , SiF6 2- , AlCl4 - , B(C2O4)2- CH3CO2 - CF3SO3 - N(CF3SO2)2 - N(FSO2)2 - C(CF2SO2)3 - C2BF2O4 - .

[0029] The non-aqueous electrolyte according to the present application, wherein the non-aqueous electrolyte further comprises a functional additive as component (D).

[0030] Further, the present application also provides a lithium secondary battery, wherein the lithium secondary battery comprises a positive electrode, a negative electrode and the non-aqueous electrolyte according to the present application.

[0031] The lithium secondary battery according to the present application, wherein the lithium secondary battery satisfies one or two of the following conditions:

[0032] i. the capacity retention rate of the lithium secondary battery is 89% or more when the lithium secondary battery is subjected to charge-discharge cycles at a charge-discharge rate of 1C at 25℃ for 200 times;

[0033] ii. the discharge capacity retention rate of the lithium secondary battery is 80% or more after the lithium secondary battery is stored at -20℃ for 5 hours and then discharged at a rate of 0.33C.

[0034] Effects of the invention

[0035] Through the implementation of the above technical solutions, the present application can obtain the following technical effects:

[0036] 1) The carboxylate compound containing cyano and phenoxy in the non-aqueous electrolyte provided by the present application can improve the high-pressure resistance and low-temperature performance as a functional additive or a co-solvent. The reason is that, on the one hand, compared with traditional carbonate solvents, the carboxylate compound has the characteristics of low viscosity and high dielectric constant, which is conducive to improving the ionic conductivity of the electrolyte, and the polar oxygen connected with the phenyl can combine with lithium ions, further improving the ionic conductivity, thereby improving the low-temperature performance; on the other hand, the cyano and benzene ring (conjugated) in the structure of the compound have the characteristics of oxidation resistance, which solves the problem of poor high-pressure stability of the carboxylate compound, and further realizes the purpose of excellent low-temperature performance and high-pressure resistance.

[0037] 2) In addition, the cyano in the carboxylate compound containing cyano and phenoxy can complex the positive electrode metal elution, and at the same time has the effect of removing acid and water, further improving the high-pressure stability.

[0038] 3) In some preferred embodiments, the cyano and phenoxy-containing carboxylate compound contains a (nitrogen-containing) heterocycle, wherein the introduced heteroatom, such as nitrogen element, enriches the electrode / electrolyte interface film component, improves the thermal stability of the interface film, and thus improves the high-temperature storage performance of the lithium ion battery. DETAILED DESCRIPTION

[0039] Hereinafter, the content of the present application will be described in detail. The description of the technical features described below is based on representative embodiments, specific examples of the present application, but the present application is not limited to these embodiments, specific examples. Note that:

[0040] In the present specification, the numerical range indicated by "numerical value A to numerical value B" means a range including the end point numerical values A and B.

[0041] In the present specification, the numerical range indicated by "above" or "below" means a numerical range including the number.

[0042] In the present specification, the meaning indicated by "may" includes both the meaning of performing a certain process and the meaning of not performing a certain process.

[0043] In the present specification, "optionally" or "optional" indicates the use or non-use of certain substances, components, execution steps, applied conditions, and the like.

[0044] In the present specification, "room temperature" or "ambient temperature" means an indoor environmental temperature of "23±2°C".

[0045] In the present specification, the unit names used are international standard unit names, and if not specifically stated, "%" used means a weight or mass percentage content.

[0046] In the present specification, "substantially" or "essentially" means that the standard deviation from a theoretical model, theoretical data, or target data is within a numerical range of 2%, preferably 1%, and more preferably 0.8%.

[0047] In the present specification, the term "comprising" and / or "including" means that the features, steps, operations, devices, components, and / or combinations thereof are present.

[0048] In the present specification, "some specific / preferred embodiments", "further specific / preferred embodiments", "embodiments", and the like mean that the specific elements (for example, features, structures, properties, and / or characteristics) described in relation to the embodiments are included in at least one embodiment described herein, and can be present in other embodiments or can not be present in other embodiments. In addition, it should be understood that the described elements can be combined in various embodiments in any suitable manner.

[0049] The present application mainly provides a non-aqueous electrolyte, the non-aqueous electrolyte comprises a carboxylic acid ester compound containing cyano and phenoxy, by adding the compound, the battery can have excellent low temperature performance and high pressure stability.

[0050] The present application is mainly obtained through the following insights:

[0051] In view of the problems of poor high pressure stability and low conductivity at low temperature of the conventional carbonate-based electrolyte, the prior art respectively proposes to add different additives to improve the high pressure performance or low temperature performance of the electrolyte, however, the additives all have certain problems, and cannot simultaneously improve the high pressure performance and low temperature performance of the electrolyte. Through long-term research, it is found that by adding a carboxylic acid ester compound containing cyano and phenoxy with a specific structure in the conventional carbonate-based electrolyte, the ion conductivity is improved through the structure of the carboxylic acid ester compound and the phenoxy, thereby improving the low temperature performance, and the oxidation resistance of the cyano and phenoxy improves the high pressure resistance of the carboxylic acid ester compound, thereby achieving the purpose of simultaneously improving the high pressure performance and low temperature performance.

[0052] <First aspect>

[0053] The first aspect of the present application provides a non-aqueous electrolyte comprising a carboxylic acid ester compound containing cyano and phenoxy as component (A), a non-aqueous solvent as component (B), and a lithium salt as component (C).

[0054] In addition, without limitation, as long as the implementation of the technical effects of the present application is not hindered, various functional additive components can also be used in the non-aqueous electrolyte.

[0055] Component (A)

[0056] The component (A) of the present application is a carboxylic acid ester compound containing cyano and phenoxy, which can effectively improve the high temperature performance and low temperature performance of the electrolyte as a co-solvent or functional additive of the electrolyte, and its structural formula is shown in formula (I):

[0057]

[0058] wherein R1 represents a substituent group of a benzene ring, and R1 is independently selected from cyano or a substituted or unsubstituted hydrocarbon group at each occurrence, and at least one R1 is cyano.

[0059] There is no particular limitation on the hydrocarbon group in principle, which can be selected from C1-C10 alkyl, preferably C1-C5 alkyl, and more preferably C1-C3 alkyl.

[0060] As for the substituent in R1, there is no particular limitation in principle, and one kind of halogen atom, for example, F atom, etc. can be selected.

[0061] Further, from the viewpoint of the conjugation effect, the cyano group in R1 is located at the ortho position or para position of the phenoxy group.

[0062] R2 represents a divalent linking group, and in some specific embodiments, R2 can be a substituted or unsubstituted hydrocarbon group or a heterocyclic group. As for the heterocyclic group, there is no particular limitation, and it can be an alicyclic or aromatic ring having 5 to 10 atoms, and the ring can have one or two heteroatoms. Preferably, the heteroatom in the heterocyclic group is a nitrogen atom, and more preferably, the nitrogen atom is directly connected to the ester group.

[0063] In some preferred embodiments, R2 can be a fluorine atom-substituted or unsubstituted alkylene group having 1 to 10 carbon atoms (e.g., methylene, 1,2-ethylene, etc.) or a five- or six-membered nitrogen-containing heterocyclic ring. Preferably, it is a five- or six-membered nitrogen-containing heterocyclic ring, which enriches the electrode / electrolyte interface film component by introducing a nitrogen element, improves the thermal stability of the interface film, and thus improves the high-temperature storage performance of the lithium ion battery.

[0064] R3 represents a monovalent organic group, and in some specific embodiments, it can be a substituted or unsubstituted alkyl group, and examples include a methyl group, an ethyl group, a n-propyl group, an i-propyl group, a n-butyl group, an i-butyl group, a t-butyl group, etc. alkyl groups having 1 to 10 carbon atoms, which can have a F atom substituent.

[0065] Further, n represents a positive integer of 1 to 5, and preferably, it is 1 or 2.

[0066] In further preferred embodiments of the present application, the carboxylic acid ester compound containing a cyano group and a phenoxy group in component (A) is selected from at least one of the following formulae (I-1), (I-2), (I-3), (I-4).

[0067]

[0068] Component (B)

[0069] As for the kind of the non-aqueous solvent of component (B), the present application is not particularly limited, and it can be any non-aqueous solvent generally used as a non-aqueous electrolyte.

[0070] In some specific embodiments, the non-aqueous solvent can be selected from one or more of a cyclic carbonate-based solvent, a linear carbonate-based solvent, an ether-based solvent, an ester-based solvent, and a ketone-based solvent.

[0071] The cyclic carbonate-based solvent can be selected from ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate (BC), etc.; the linear carbonate-based solvent can be selected from diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), ethyl methyl carbonate (EMC), and methyl propyl carbonate (MPC), methyl trifluoroethyl carbonate (FEMC), di(2,2,2-trifluoroethyl) carbonate (DFDEC), etc.; the ester-based solvent can be selected from methyl acetate, ethyl acetate, methyl propionate, and methyl neopentanoate, etc.; the ether-based solvent can be selected from dibutyl ether, tetrahydrofuran, 2-methyltetrahydrofuran, 1,4-dioxane, 1,2-dimethoxyethane, ethylene glycol dimethyl ether (DME), ethylene glycol diethyl ether (DEE), dioxane (DX), dioxolane (DOL), etc.; the ketone-based solvent can be selected from polymethyl vinyl ketone, etc. These non-aqueous solvents can be used alone or in the form of a mixture of two or more.

[0072] In some preferred embodiments, the non-aqueous solvent can be selected from at least one of ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dioxolane (DOL), ethylene glycol diethyl ether (DEE), etc.

[0073] Component (C)

[0074] As for the kind of lithium salt of component (C), the present application is not particularly limited, and can be a lithium salt commonly used in the art. In some specific embodiments, the lithium salt can be selected from one or more of the salts formed by lithium ions and the following anions: PF6 - , BF4 - , Cl - , Br - , I - , ClO4 - , AsF6 - , CH3CO2 - , CF3SO3 - , N(CF3SO2)2 - , N(FSO2)2 - , C(CF2SO2)3 - , C2BF2O4 - , etc.

[0075] In some preferred embodiments, the lithium salt can be selected from a combination of one or more of lithium hexafluorophosphate (LiPF6), lithium bisfluorosulfonylimide (LiFSI), lithium bisfluorooxalato borate (LiDFOB), or lithium bis-trifluoromethylsulfonylimide (LiTFSI).

[0076] Other functional additives (D)

[0077] Other functional additives that can be used in the nonaqueous electrolyte of the present application are not particularly limited in principle, and for example, film formation can be promoted by the use of some additives.

[0078] Examples of such additives include vinyl ethylene carbonate (VC), fluoroethylene carbonate (FEC), or a sulfur-containing additive, and the like. Among these, the sulfur-containing additive can be selected from 1,3-propane sultone (PS), 1,4-butane sultone (1,4-BS), 2,4-butane sultone (2,4-BS), 1,3-propene sultone (PST), ethylene sulfate (DTD), methane disulfonate methylene (MMDS), ethylene sulfite (ES), and the like. These additives can be used alone or in the form of a mixture of two or more.

[0079] Composition of the nonaqueous electrolyte

[0080] In the present application, the content of the carboxylic acid ester compound containing a cyano group and a phenoxy group in the component (A) is, in some specific embodiments, 0.5 mass% to 30 mass% of the total mass of the nonaqueous electrolyte, and preferably 1 mass% to 25 mass%, for example, 3 mass%, 5 mass%, 10 mass%, 15 mass%, 17 mass%, 20 mass%, 28 mass%, and the like. When the content of the component (A) is 0.5 mass% to 30 mass% of the total mass of the nonaqueous electrolyte, both the low-temperature performance and the high-pressure resistance of the battery can be improved.

[0081] The content of the nonaqueous solvent of the component (B) is not particularly limited in principle. In some specific embodiments, the content of the nonaqueous solvent of the component (B) is 60 mass% to 80 mass% of the total mass of the nonaqueous electrolyte, for example, 65 mass%, 70 mass%, 75 mass%, and the like.

[0082] The content of the lithium salt of the component (C) is also not particularly limited in principle. In some specific embodiments of the present application, the concentration of the lithium salt in the nonaqueous electrolyte can be 0.2 mol / L to 10 mol / L, and preferably 0.7 mol / L to 2 mol / L, for example, 0.5 mol / L, 1 mol / L, 1.5 mol / L, 2.5 mol / L, 5 mol / L, 8 mol / L, and the like, from the viewpoint of controlling the viscosity and the cost of the electrolyte.

[0083] The content of the other functional additives of the component (D) is not particularly limited in principle. In some specific embodiments of the present application, the content of the component (D) is 0.5 mass% to 5 mass% of the total mass of the nonaqueous electrolyte, for example, 1 mass%, 1.5 mass%, 2 mass%, 2.5 mass%, 3 mass%, 3.5 mass%, 4 mass%, 4.5 mass%, and the like.

[0084] <Second aspect>

[0085] The lithium secondary battery according to the present application includes a nonaqueous electrolyte lithium secondary battery, a semi-solid, quasi-solid, and the like.

[0086] The secondary battery according to the present application can be a power battery, i.e., a battery used for providing power to a transportation or a vehicle, or a secondary battery used for a power storage device such as a wind power, a hydroelectric power, a solar power, or a power from a conventional fossil fuel.

[0087] In some specific embodiments, the battery according to the present application is used in a single form, and in other specific embodiments, the battery according to the present application can be used in parallel or in series in any number of scales.

[0088] The lithium secondary battery according to the present application can include a positive electrode, a negative electrode, an electrolyte, and an optional separator.

[0089] The positive electrode includes a current collector and a positive electrode active material. The positive electrode active material is not particularly limited in principle, and in some preferred embodiments, various oxides containing lithium can be used in the art, and in addition to lithium, other main group, secondary group, or rare earth metal elements can be added to the oxides.

[0090] Further, from the viewpoint of the broad applicability, the positive electrode active material according to the present application can be a lithium ion positive electrode active material doped with a metal, and more specifically, a positive electrode active material containing Mn, Co, Al, and Ni elements.

[0091] The negative electrode of the battery is not particularly limited in principle, and can be a negative electrode generally used in the art, which includes a current collector and a negative electrode active material. Typically, the negative electrode active material can include carbon-based materials and non-carbon-based materials. The carbon-based materials include graphite materials (natural graphite, artificial graphite, and mesocarbon microbeads) and other carbon-based materials (hard carbon, soft carbon, and graphene); and the non-carbon-based materials can be classified into titanium-based materials, silicon-based materials, tin-based materials, nitrides, and metallic lithium, and the like.

[0092] Further, for the battery of the present application, there is no particular restriction in principle, and a separator can or can not be used. That is, the lithium secondary battery of the present application can be a lithium secondary battery with a separator, or a lithium secondary battery without a separator. In the case of using a separator, it can be a separator generally used in the art, and preferably, a separator having a high moisture retention ability for an electrolyte solution and a low resistance to electrolyte ion transfer can be used. In the case of a lithium secondary battery without a separator, the non-aqueous electrolyte of the present application can be used in combination with a solid-state electrolyte, in which the solid-state electrolyte can function as a separator.

[0093] Examples

[0094] The embodiments of the present application will be described in detail below with reference to Examples, but those skilled in the art will appreciate that the following Examples are for illustration only and should not be taken in a limiting sense. Where specific conditions are not mentioned in the Examples, they are carried out under conventional conditions or conditions recommended by the manufacturer. Where the manufacturer of the reagent or instrument is not mentioned, it is a conventional product that can be obtained commercially.

[0095] Example 1

[0096] (1) Preparation method of non-aqueous electrolyte:

[0097] The non-aqueous electrolyte was prepared in an argon atmosphere glove box, the water content in the box was less than 1 ppm, the solvents EC, PC and EMC were mixed in a ratio of 1:1:6 by volume, then the lithium salt (1 mol / L), the compound represented by formula (1-1), vinylene carbonate, 1,3-propane sultone, fluoroethylene carbonate were added thereto and stirred uniformly to obtain the required electrolyte, the specific contents are shown in Table 1;

[0098] (2) Preparation method of lithium ion secondary battery:

[0099] Positive electrode preparation: the positive electrode active material Li(Ni 0.8 Co 0.1 Mn 0.1 )O2, the composite conductive agent ultrafine carbon powder (SP), single-walled carbon nanotube (SWNT) and the binder polyvinylidene fluoride (PVDF) were added to an appropriate amount of N-methyl-2-pyrrolidone (NMP) solvent and stirred thoroughly, the solid content was controlled to 73%, and a positive electrode mixture slurry was prepared. Thereafter, the formed positive electrode slurry was coated on an aluminum foil, and after drying (positive electrode 90°C drying for 8h) and roll pressing, a positive electrode sheet was formed.

[0100] Negative electrode preparation: graphite, composite conductive agent superfine carbon powder (Super-P), thickening agent CMC, binder SBR were added into deionized water in a mass ratio of 95:2:1:2, and stirred well, the solid content was controlled to 55%, and the negative electrode mixture slurry was prepared. Then, the formed negative electrode slurry was coated on the copper foil, and after drying (negative electrode 110℃ drying for 8h) and rolling, the negative electrode sheet was formed.

[0101] Battery assembly: take the positive electrode sheet, negative electrode sheet and separator, stack them in the order of negative electrode, separator, positive electrode, paste the adhesive tape, then perform tab welding and use aluminum plastic film for packaging to obtain a soft package dry cell. The dry cell is dried at 80℃ for 12h, then the above non-aqueous electrolyte is used to inject the lithium ion battery, seal, stand for 24h, form, reseal, and prepare a lithium ion soft package battery.

[0102] Examples 2-8

[0103] The preparation method of Example 1 was used, and the raw material ratio of Examples 2-8 in Table 1 was used to prepare lithium ion batteries of Examples 2-8.

[0104] Comparative Example 1

[0105] The preparation method of Example 1 was used, and the raw material ratio of Comparative Example 1 in Table 1 was used to prepare lithium ion batteries of Comparative Examples 1-2.

[0106] Reference Example 1

[0107] The preparation method of Example 1 was used, and the raw material ratio of Reference Example 1 in Table 1 was used to prepare lithium ion batteries of Comparative Examples 1-2.

[0108] Performance test

[0109] 1. Room temperature cycle performance: the charge and discharge voltage range is 2.7V-4.35V, the charge current at room temperature is 1C (5A) to 4.35V, the constant voltage charge is stopped at 4.35V when the cutoff current is ≤0.05C (0.25A), after 30 minutes of standing, the discharge is 1C (5A) to 2.7V, and after 30 minutes of standing; the initial capacity of the first week of battery cycle is obtained and recorded as C1, and such cycle charging and discharging is carried out, and the capacity after the 200th week of discharge is recorded as C200, then the capacity retention rate (%) after 200 weeks of room temperature cycle = C200 / C1x100%. The test results are shown in Table 2.

[0110] 2. Low temperature discharge: after the completion of the packaging of the lithium ion battery, after the formation and distribution steps, the battery was charged at 25℃ with 1C constant current and constant voltage to 4.35V, and after 30 minutes, 1C constant current discharge was carried out to obtain the initial capacity of the battery and record it as C0, then the battery was placed in a high and low temperature box at -20℃, and after 5 hours, discharge was carried out at 0.33C rate, and the capacity obtained by discharge was recorded as C1, then the capacity retention rate (%) of low temperature discharge at -20℃ = C1 / C0 x 100%. The test results are shown in Table 2.

[0111] 3. DCR test: the battery before or after cycling was charged at 25℃ with 0.5C constant current to 4.35V, and the current was 0.05C, and after 1 hour, it was discharged at 0.5C for 60 minutes (50% SOC), and continued to stand for 1 hour; then discharged at 0.1C for 10 seconds, and the voltage V1 at the end was recorded, and then discharged at 1C for 1 second, and the voltage V2 at the end was recorded, then the DCR of the battery before or after cycling = (V1-V2) / (I1C-I0.1C), unit: mOhm. According to the DCR value before and after cycling, the growth rate was calculated, DCR growth rate = (battery DCR after cycling-battery DCR before cycling) / battery DCR before cycling x 100%. The test results are shown in Table 2.

[0112] Table 1 formula table

[0113]

[0114] Table 2 test results

[0115]

[0116] From the test data in Table 2, it can be seen that the low temperature discharge and high pressure resistance of the non-aqueous electrolyte containing the carboxylic acid ester compound containing cyano and phenoxy groups according to the application are improved. Specifically, by comparing Examples 1-4 and Comparative Example 1, it can be seen that the introduction of the carboxylic acid ester compound containing cyano and phenoxy groups according to the application can effectively reduce the DCR growth rate of the non-aqueous electrolyte, increase the cycle capacity retention rate at high pressure, and at the same time increase the capacity retention rate at low temperature

[0117] In addition, from Reference Example 1, it can be seen that although component (A) is used, the amount is too high, exceeding the conventional amount of stability additives, which also leads to a decrease in the low temperature performance of the battery, which to some extent gives the recommended amount range of component (A) according to the application.

[0118] It should be noted that although the technical solutions of the application are introduced with specific examples, those skilled in the art can understand that the application should not be limited thereto.

[0119] Having described various embodiments of the application, it is to be understood that the above description is meant not to limit and not to encompass all of the possible embodiments covered by the claims. Many modifications and variations of this application can be apparent to those of ordinary skill in the art without departing from the spirit and scope of the described embodiments. It is intended that the scope of the application should only be limited by the appended claims.

Claims

1. A non-aqueous electrolyte, characterized in that, The non-aqueous electrolyte comprises a cyano- and phenoxy-containing carboxylic acid ester compound as component A, a non-aqueous solvent as component B, and a lithium salt as component C. The structural formula of component A, a carboxylic acid ester compound containing cyano and phenoxy groups, is shown in Formula I-4: Ⅰ-4 The content of component A, which contains cyano and phenoxy carboxylic acid ester compounds, is 0.5% to 30% of the total mass of the non-aqueous electrolyte.

2. The non-aqueous electrolyte according to claim 1, characterized in that, The non-aqueous solvent of component B is selected from one or more of cyclic carbonate solvents, linear carbonate solvents, ether solvents, and ketone solvents.

3. The non-aqueous electrolyte according to claim 1, characterized in that, The non-aqueous solvent of component B is selected from ester solvents.

4. The non-aqueous electrolyte according to any one of claims 1 to 3, characterized in that, The lithium salt component C is selected from one or more salts formed by lithium ions and the following anions: PF6 - BF4 - Cl - ,Br - I - ClO4 - AsF6 - SiF6 2- AlCl4 - B(C2O4)2 - CH3CO2 - CF3SO3 - N(CF3SO2)2 - N(FSO2)2 - C(CF2SO2)3 - C2BF2O4 - .

5. The non-aqueous electrolyte according to any one of claims 1 to 3, characterized in that, The non-aqueous electrolyte also contains functional additives as component D.

6. A lithium secondary battery, characterized in that, The lithium secondary battery comprises a positive electrode, a negative electrode, and a non-aqueous electrolyte according to any one of claims 1 to 5.

7. The lithium secondary battery according to claim 6, characterized in that, The lithium secondary battery meets one or two of the following conditions: i. The lithium secondary battery retains more than 89% of its capacity after 200 charge-discharge cycles at 25°C and a charge-discharge rate of 1C. ii. After being stored at -20°C for 5 hours, the lithium secondary battery retains more than 80% of its discharge capacity when discharged at a rate of 0.33C.

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