Non-aqueous electrolyte solution and lithium secondary battery

Abstract

The invention provides a non-aqueous electrolyte solution and a lithium secondary battery. The non-aqueous electrolyte comprises a carboxylic ester compound containing a cyano group and a phenoxy group as a component (A), a non-aqueous solvent as a component (B) and a lithium salt as a component (C); wherein the structural formula of the component (A) is as shown in formula (I): # imgabs0 # R1 represents a substituent group of a benzene ring, R1 is independently selected from cyano or substituent substituted or unsubstituted alkyl when appearing each time, and at least one R1 is cyano; r2 represents a divalent linking group; R3 represents a monovalent organic group; and n represents a positive integer of 1-5. The non-aqueous electrolyte provided by the invention has excellent low-temperature performance and high-pressure resistance.

Description

Technical Field

[0001] The invention relates to a non-aqueous electrolyte and a lithium secondary battery, belonging to the field of lithium ion batteries. Background Art

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

[0003] Further improving energy density is the main direction of lithium-ion battery development in the future, and increasing the operating voltage of the battery is one of the effective ways to increase the energy density of lithium-ion batteries. The reason why high-voltage lithium batteries are difficult to apply is that the electrochemical stability window of the current commercial carbonate-based electrolyte is low, which brings about the problem of decreased stability of lithium-ion batteries at high voltages, and also causes serious battery capacity decay. However, while maintaining high energy density, lithium-ion batteries will also seriously affect the battery capacity when facing extreme weather in application scenarios. This is mainly because the electrolyte conductivity is low under low temperature conditions, the interface impedance between the electrolyte and the positive and negative electrodes is large, and the slow migration speed of lithium ions in the positive and negative electrode materials limits the application of lithium-ion batteries.

[0004] Some documents disclose a cyanophenoxy-containing electrolyte, which uses cyanophenoxy-containing triester phosphate organic matter and / or phosphite triester organic matter as a high-voltage additive to improve the high-voltage stability of the battery. However, the carbonate solvent system used results in no improvement in 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, which uses a high concentration of LiPO2F2 as an additive to improve the high-voltage performance of the battery, but the solubility of LiPO2F2 in conventional cyclic carbonates, chain carbonates, 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 carboxylate-based electrolyte for low-temperature lithium batteries, which uses a carboxylate organic solvent as a base solvent to improve the low-temperature performance of the electrolyte. However, the high-voltage performance of carboxylate compounds is poor, so the electrolyte does not improve the high-voltage performance.

[0007] It can be seen that although a series of studies have been conducted in this field on electrolytes for improving high-voltage performance or low-temperature performance, it cannot be said that there is sufficient research on electrolytes that have both high-voltage performance and low-temperature performance, and there is room for further research. Summary of the invention

[0008] Problem that the invention aims to solve

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

[0010] In order to improve the high-voltage performance of the electrolyte, in the prior art, carbonates, sulfates, sulfites, phosphates or phosphites containing nitrile or fluorine-containing phosphates are added to the electrolyte as high-voltage additives to improve the high-voltage stability of the electrolyte. However, it has been found in practice that even if such additives are used, the low-temperature performance of the electrolyte will not be improved.

[0011] In addition, in order to improve the low-temperature performance of the electrolyte, the prior art has changed the lithium ion solvation structure in the electrolyte by (partially) replacing the carbonate solvent with a carboxylate solvent, reducing the desolvation energy of the lithium ions, improving the reaction kinetics of the battery, and improving the low-temperature performance. However, the high-pressure performance of carboxylate solvents is poor, and they are easily oxidized and decomposed under high pressure, resulting in the consumption of electrolyte and active lithium and the increase of positive electrode surface impedance, so it is difficult to achieve application under high pressure.

[0012] Therefore, at least for the reasons described above, it appears that there is some difficulty in trading off high voltage resistance and low temperature resistance in the electrolyte.

[0013] In addition, since the positive electrode material is prone to phase change under high pressure, resulting in material decomposition, metal ions dissolve after material decomposition and migrate to the electrolyte and the negative electrode to produce side reactions, which not only deteriorates the internal resistance of the lithium-ion battery, but also leads to the consumption of active lithium ions.

[0014] In order to solve the above problems, the present invention provides a non-aqueous electrolyte, which contains a carboxylic acid ester compound containing a cyano group and a phenoxy group of a specific structure. By using the compound as a co-solvent for the electrolyte, both low temperature performance and high voltage resistance can be achieved.

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

[0016] Solutions for solving problems

[0017] The present invention provides a non-aqueous electrolyte, wherein the non-aqueous electrolyte comprises a carboxylic acid ester compound containing a cyano group and a phenoxy group as a component (A), a non-aqueous solvent as a component (B), and a lithium salt as a component (C);

[0018] The structural formula of the carboxylic acid ester compound containing cyano and phenoxy groups in component (A) is shown in formula (I):

[0019]

[0020] R1 represents a substituent group of a benzene ring, and each occurrence of R1 is independently selected from a cyano group or a substituted or unsubstituted hydrocarbon group, 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] According to the non-aqueous electrolyte of the present invention, wherein the R1 is selected from at least one of a cyano group or a C1-C10 alkyl group which is substituted or unsubstituted.

[0024] According to the non-aqueous electrolyte of the present invention, wherein R2 is selected from a substituted or unsubstituted C1-C10 alkylene or heterocyclic group; and R3 is selected from a substituted or unsubstituted alkyl group.

[0025] According to the non-aqueous electrolyte of the present invention, wherein n is 1 or 2.

[0026] According to the non-aqueous electrolyte of the present invention, the content of the carboxylate compound containing cyano and phenoxy groups in component (A) is 0.5% to 30% by mass of the total mass of the non-aqueous electrolyte.

[0027] According to the non-aqueous electrolyte of the present invention, the component (B) non-aqueous solvent is selected from one or more of cyclic carbonate solvents, linear carbonate solvents, ether solvents, ester solvents, and ketone solvents.

[0028] According to the non-aqueous electrolyte of the present invention, the lithium salt of 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 - .

[0029] According to the non-aqueous electrolyte of the present invention, the non-aqueous electrolyte further comprises a functional additive as component (D).

[0030] In addition, the present invention 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 invention.

[0031] According to the lithium secondary battery of the present invention, the lithium secondary battery satisfies one or two of the following conditions:

[0032] i. The capacity retention rate of the lithium secondary battery at 25°C and a charge and discharge rate of 1C for 200 charge and discharge cycles is 89% or more;

[0033] ii. After the lithium secondary battery was stored at -20°C for 5 hours, it was discharged at a rate of 0.33C, and the discharge capacity retention rate was 80% or more.

[0034] Effects of the Invention

[0035] By implementing the above technical solution, the present invention can achieve the following technical effects:

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

[0037] 2) In addition, the cyano group in the carboxylate compound containing cyano and phenoxy groups can be complexed with the positive electrode metal to dissolve, and at the same time has the function of removing acid and water, further improving the high-voltage stability.

[0038] 3) In some preferred embodiments, the cyano- and phenoxy-containing carboxylic acid ester compounds contain (nitrogen-containing) heterocycles, wherein the introduced heteroatoms, such as nitrogen elements, enrich the electrode / electrolyte interface film components, improve the thermal stability of the interface film, and thus improve the high-temperature storage performance of lithium-ion batteries. DETAILED DESCRIPTION

[0039] The following is a detailed description of the present invention. The following description of the technical features is based on representative embodiments and specific examples of the present invention, but the present invention is not limited to these embodiments and specific examples. It should be noted that:

[0040] In this specification, the numerical range expressed using "a numerical value A to a numerical value B" means a range including the endpoints A and B.

[0041] In this specification, the numerical range expressed using "above" or "below" means a numerical range including the number.

[0042] In this specification, the word "may" includes both performing a certain process and not performing a certain process.

[0043] In this specification, the use of "optional" or "optional" indicates that certain substances, components, execution steps, application conditions and other factors are used or not used.

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

[0045] In this specification, the unit names used are all international standard unit names, and unless otherwise stated, the "%" used indicates weight or mass percentage.

[0046] In the present specification, the use of “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 this specification, when the terms “include” and / or “comprise” are used, they indicate the existence of features, steps, operations, devices, components and / or their combinations.

[0048] In this specification, the references to "some specific / preferred embodiments", "other specific / preferred embodiments", "embodiments", etc., mean that the specific elements (e.g., features, structures, properties and / or characteristics) described in connection with the embodiments are included in at least one embodiment described herein, and may or may not exist in other embodiments. In addition, it should be understood that the elements may be combined in various embodiments in any suitable manner.

[0049] The present invention mainly provides a non-aqueous electrolyte, which contains a carboxylate compound containing a cyano group and a phenoxy group. By adding the compound, the battery can have both excellent low-temperature performance and high-voltage stability.

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

[0051] In view of the problems of poor high-voltage stability and low conductivity at low temperatures in conventional carbonate-based electrolytes, the prior art proposes to improve the high-voltage performance or low-temperature performance of the electrolyte by adding different additives. However, the additives all have certain problems and cannot simultaneously improve the high-voltage performance and low-temperature performance of the electrolyte. Through long-term research, it is found that by adding a carboxylate compound containing cyano and phenoxy groups with a specific structure to the conventional carbonate-based electrolyte, the ionic conductivity is improved by the carboxylate compound structure and phenoxy groups in the compound, thereby improving the low-temperature performance. At the same time, the oxidation resistance of the cyano and phenoxy groups improves the high-voltage resistance of the carboxylate compound, thereby achieving the purpose of simultaneously improving the high-voltage resistance and low-temperature performance.

[0052] <First aspect>

[0053] A first aspect of the present invention provides a non-aqueous electrolyte solution comprising a carboxylate compound containing a cyano group and a phenoxy group as component (A), a non-aqueous solvent as component (B), and a lithium salt as component (C).

[0054] In addition, without limitation, various optional functional additive components may be used in the non-aqueous electrolyte as long as they do not hinder the realization of the technical effects of the present invention.

[0055] Component (A)

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

[0057]

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

[0059] The hydrocarbon group is not particularly limited in principle and can be selected from C1 to C10 alkyl groups, preferably C1 to C5 alkyl groups, and more preferably C1 to C3 alkyl groups.

[0060] The substituent in R1 is not particularly limited in principle, and can be selected from one of the halogen atoms, such as F atom.

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

[0062] R2 represents a divalent linking group. In some specific embodiments, the R2 may be a substituted or unsubstituted hydrocarbon group or a heterocyclic group. There is no particular limitation on the heterocyclic group, which may be an alicyclic or aromatic ring having 5 to 10 atoms, and the ring may have 1 or 2 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 may be a fluorine-substituted or unsubstituted alkylene group with 1 to 10 carbon atoms (e.g., methylene, 1,2-ethylene, etc.) or a five-membered or six-membered nitrogen-containing heterocycle. Preferably, the five-membered or six-membered nitrogen-containing heterocycle is used, and the electrode / electrolyte interface film component is enriched by introducing nitrogen elements, and the thermal stability of the interface film is improved, thereby improving the high-temperature storage performance of the lithium-ion battery.

[0064] R3 represents a monovalent organic group. In some specific embodiments, it can be a substituted or unsubstituted alkyl group, which can include methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl and other alkyl groups with 1 to 10 carbon atoms, and these alkyl groups can have F atom substituents.

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

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

[0067]

[0068] Component (B)

[0069] The present invention does not particularly limit the type of the non-aqueous solvent of component (B), as long as it is a non-aqueous solvent commonly used as a non-aqueous electrolyte.

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

[0071] Among them, the cyclic carbonate solvent can be selected from ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate (BC); the linear carbonate 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 solvent can be selected from methyl acetate, ethyl acetate, methyl propionate, and methyl pivalate, etc.; the ether 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 solvent can be selected from polymethyl vinyl ketone, etc. These nonaqueous solvents may be used alone or in admixture 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), and the like.

[0073] Component (C)

[0074] The present invention does not specifically limit the type of lithium salt of component (C), and it can be a lithium salt commonly used in the art. In some specific embodiments, the lithium salt can be selected from one or more 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 - wait.

[0075] In some preferred embodiments, the lithium salt may be selected from a combination of one or more of lithium hexafluorophosphate (LiPF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(fluorooxalatoborate) (LiDFOB) or lithium bis(trifluoromethylsulfonyl)imide (LiTFSI).

[0076] Other functional additives (D)

[0077] In principle, there is no particular limitation on other functional additives that can be used in the non-aqueous electrolyte of the present invention. For example, the use of some additives can promote film formation.

[0078] For such additives, vinyl ethylene carbonate (VC), fluoroethylene carbonate (FEC) or sulfur-containing additives can be cited. Among them, 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-propylene sultone (PST), vinyl sulfate (DTD), methylene disulfonate (MMDS), vinyl sulfite (ES), etc. These additives can be used alone or in the form of a mixture of two or more.

[0079] Composition of non-aqueous electrolyte

[0080] In the present invention, for the content of the carboxylate compound containing cyano and phenoxy groups in the component (A), in some specific embodiments, the content of the component (A) is 0.5% to 30% by mass of the total mass of the non-aqueous electrolyte, preferably 1% to 25% by mass, for example, 3%, 5%, 10%, 15%, 17%, 20%, 28% by mass, etc. When the content of the component (A) is 0.5% to 30% by mass of the total mass of the non-aqueous electrolyte, the low temperature performance and high voltage resistance of the battery can be improved at the same time.

[0081] In principle, there is no particular restriction on the content of the non-aqueous solvent of component (B). In some specific embodiments, the content of the non-aqueous solvent of component (B) is 60% to 80% by mass of the total mass of the non-aqueous electrolyte, such as 65%, 70%, 75% by mass, etc.

[0082] In principle, there is no particular restriction on the content of the lithium salt of the component (C). In some specific embodiments of the present invention, from the perspective of controlling the viscosity and cost of the electrolyte, the concentration of the lithium salt in the non-aqueous electrolyte can be 0.2 mol / L to 10 mol / L, 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, etc.

[0083] In principle, there is no particular restriction on the content of other functional additives of the component (D). In some specific embodiments of the present invention, the content of the component (D) is 0.5% to 5% by mass of the total mass of the non-aqueous electrolyte, for example, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5% by mass, etc.

[0084] <Second Aspect>

[0085] The lithium secondary battery described in the present invention includes non-aqueous electrolyte lithium secondary batteries, semi-solid lithium secondary batteries, quasi-solid lithium secondary batteries, etc.

[0086] The secondary battery of the present invention may be a power battery, that is, a battery used to provide power for transportation or vehicles, or a secondary battery used in energy storage equipment such as wind power, hydropower, solar power or traditional petrochemical energy power.

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

[0088] The lithium secondary battery of the present invention may 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. In principle, there is no particular limitation on the positive electrode active material. In some preferred embodiments, various lithium-containing oxides in the art can be used. In addition to lithium, other main group, sub-group or rare earth metal elements can be added to these oxides.

[0090] Furthermore, from the perspective of wide applicability, the positive electrode active material of the present invention may be a metal-doped lithium ion positive electrode active material, and more specifically, may be a positive electrode active material containing Mn, Co, Al and Ni elements.

[0091] In principle, there is no particular limitation on the negative electrode of the battery, and it can be a negative electrode commonly used in the art. Such a negative electrode 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 mesophase carbon spheres) and other carbon-based materials (hard carbon, soft carbon, and graphene); the non-carbon-based materials can be subdivided into titanium-based materials, silicon-based materials, tin-based materials, nitrides, and metallic lithium, etc.

[0092] In addition, there is no particular limitation on the battery of the present invention in principle, and a diaphragm may or may not be used. That is, the lithium secondary battery of the present invention may be a lithium secondary battery with a diaphragm or a lithium secondary battery without a diaphragm. When a diaphragm is used, it may be a diaphragm commonly used in the art, and preferably, a diaphragm having a high moisture retention capacity for the electrolyte solution and a low resistance to the transfer of electrolyte ions may be used. In the case of a lithium secondary battery without a diaphragm, the nonaqueous electrolyte of the present invention may be used in combination with a solid electrolyte, wherein the solid electrolyte may act as a diaphragm.

[0093] Example

[0094] The embodiments of the present invention will be described in detail below in conjunction with the examples, but those skilled in the art will appreciate that the following examples are only used to illustrate the present invention and should not be considered to limit the scope of the present invention. If no specific conditions are specified in the examples, they are carried out according to normal conditions or the conditions recommended by the manufacturer. If the manufacturer is not specified for the reagents or instruments used, they are all conventional products that can be obtained commercially.

[0095] Example 1

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

[0097] A non-aqueous electrolyte was prepared in a glove box with an argon atmosphere, wherein the moisture content in the box was less than 1 ppm. Solvents EC, PC and EMC were mixed in a volume ratio of 1:1:6, and then lithium salt (1 mol / L), the compound represented by formula (1-1), vinylene carbonate, 1,3-propane sultone and fluoroethylene carbonate were added thereto and stirred evenly 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, composite conductive agent ultrafine carbon powder (SP), single-walled carbon nanotubes (SWNT) and binder polyvinylidene fluoride (PVDF) are added to an appropriate amount of N-methyl-2-pyrrolidone (NMP) solvent and fully stirred, and the solid content is controlled to 73% to prepare a positive electrode mixture slurry. Thereafter, the formed positive electrode slurry is coated on aluminum foil, and after drying (positive electrode is dried at 90°C for 8h), roll-pressed and die-cut to form a positive electrode sheet.

[0100] Negative electrode preparation: Graphite, composite conductive agent ultrafine carbon powder (Super-P), thickener CMC, binder SBR were added to an appropriate amount of deionized water in a mass ratio of 95:2:1:2 and stirred thoroughly. The solid content was controlled to 55% to prepare a negative electrode mixture slurry. Afterwards, the formed negative electrode slurry was coated on copper foil and rolled and die-cut to form a negative electrode sheet after drying (negative electrode dried at 110°C for 8h).

[0101] Battery assembly: Take the positive electrode sheet, negative electrode sheet and separator, stack the negative electrode, separator and positive electrode in order, apply tape, then weld the tabs and use aluminum plastic film to package to obtain a soft-pack dry cell. The dry cell is dried at 80℃ for 12h, and then the lithium-ion battery is filled and sealed with the above non-aqueous electrolyte, left for 24h, formed, and sealed to prepare a lithium-ion soft-pack battery.

[0102] Embodiments 2 to 8

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

[0104] Comparative Example 1

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

[0106] Reference Example 1

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

[0108] Performance Testing

[0109] 1. Cycling performance at room temperature: The charging and discharging voltage range is 2.7V to 4.35V, the charging current at room temperature is 1C (5A) to 4.35V, 4.35V constant voltage charging to a cut-off current ≤ 0.05C (0.25A), after standing for 30 minutes, 1C (5A) discharge to 2.7V, stand for 30 minutes; get the initial capacity of the first cycle of the battery and record it as C1, and cycle charge and discharge in this way, the capacity after the 200th cycle discharge is recorded as C200, then the capacity retention rate (%) after 200 cycles at room temperature = C200 / C1×100%. The test results are shown in Table 2.

[0110] 2. Low-temperature discharge: At 25°C, the packaged lithium-ion battery is charged to 4.35V at 1C constant current and constant voltage after formation and capacity division steps. After half an hour of storage, 1C constant current discharge is performed to obtain the initial capacity of the battery and recorded as C0. Then the battery cell is placed in a high and low temperature box at -20°C, and after 5 hours of storage, it is discharged at a rate of 0.33C. The capacity obtained by discharge is recorded as C1. The capacity retention rate (%) of low-temperature discharge at -20°C = C1 / C0×100%. The test results are shown in Table 2.

[0111] 3. DCR test: Charge the battery before or after the cycle at 0.5C constant current to 4.35V at 25℃, charge at constant voltage to a current of 0.05C, leave it for 1 hour, then discharge it at 0.5C for 60 minutes (50% SOC), and continue to leave it for 1 hour; then discharge it at 0.1C for 10 seconds, record the voltage V1 at the end, and then discharge it at 1C for 1 second, record the voltage V2 at the end, then the DCR of the battery before or after the cycle = (V1-V2) / (I1C-I0.1C), the unit is mOhm. Calculate its growth rate based on the DCR value before and after the cycle, DCR growth rate = (battery DCR after the cycle - battery DCR before the cycle) / battery DCR before the cycle × 100%. The test results are shown in Table 2.

[0112] Table 1 Recipe

[0113]

[0114] Table 2 Test results

[0115]

[0116] It can be seen from the test data in Table 2 that the low-temperature discharge and high-voltage resistance performance of the non-aqueous electrolyte containing the carboxylic acid ester compound containing cyano and phenoxy groups described in the present invention are improved. Specifically, by comparing Examples 1 to 4 with Comparative Example 1, it can be seen that the introduction of the carboxylic acid ester compound containing cyano and phenoxy groups described in the present invention can effectively reduce the DCR growth rate of the non-aqueous electrolyte, improve the cycle capacity retention rate under high pressure, and improve the capacitance retention rate at low temperature.

[0117] In addition, it can be seen from Reference Example 1 that although component (A) is used, its dosage is too high, exceeding the conventional dosage of stability additives, which will also lead to a decrease in the low-temperature performance of the battery. This provides a recommended dosage range for component (A) of the present invention to a certain extent.

[0118] It should be noted that, although the technical solution of the present invention is introduced with specific examples, those skilled in the art will appreciate that the present invention should not be limited thereto.

[0119] The embodiments of the present invention have been described above, and the above description is exemplary, not exhaustive, and is not limited to the disclosed embodiments. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the described embodiments. The selection of terms used herein is intended to best explain the principles of the embodiments, practical applications, or technical improvements in the market, or to enable other persons of ordinary skill in the art to understand the embodiments disclosed herein.

Claims

1. A non-aqueous electrolyte, characterized in that: The non-aqueous electrolyte comprises a carboxylic acid ester compound containing a cyano group and a phenoxy group as component (A), a non-aqueous solvent as component (B), and a lithium salt as component (C); The structural formula of the carboxylic acid ester compound containing cyano and phenoxy groups in component (A) is shown in formula (I): R1 represents a substituent group of a benzene ring, and each occurrence of R1 is independently selected from a cyano group or a substituted or unsubstituted hydrocarbon group, and at least one R1 is a cyano group; R2 represents a divalent linking group, and R3 represents a monovalent organic group; n represents a positive integer of 1 to 5.

2. The non-aqueous electrolyte according to claim 1, characterized in that The R1 is at least one selected from a cyano group or a substituted or unsubstituted C1-C10 alkyl group.

3. The non-aqueous electrolyte according to claim 1 or 2, characterized in that The R2 is selected from a substituted or unsubstituted C1-C10 alkylene or heterocyclic group; and R3 is selected from a substituted or unsubstituted alkyl group.

4. The non-aqueous electrolyte according to any one of claims 1 to 3, characterized in that The n is 1 or 2.

5. The non-aqueous electrolyte according to any one of claims 1 to 4, characterized in that The content of the carboxylic acid ester compound containing cyano group and phenoxy group as component (A) is 0.5 mass % to 30 mass % of the total mass of the non-aqueous electrolyte.

6. The non-aqueous electrolyte according to any one of claims 1 to 5, 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, ester solvents, and ketone solvents.

7. The non-aqueous electrolyte according to any one of claims 1 to 6, characterized in that The lithium salt of 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 - .

8. The non-aqueous electrolyte according to any one of claims 1 to 7, characterized in that The non-aqueous electrolyte further comprises a functional additive as component (D).

9. A lithium secondary battery, characterized in that: The lithium secondary battery comprises a positive electrode, a negative electrode and the nonaqueous electrolyte according to any one of claims 1 to 8.

10. The lithium secondary battery according to claim 9, characterized in that: The lithium secondary battery meets one or both of the following conditions: i. The capacity retention rate of the lithium secondary battery at 25°C and a charge and discharge rate of 1C for 200 charge and discharge cycles is 89% or more; ii. After the lithium secondary battery was stored at -20°C for 5 hours, it was discharged at a rate of 0.33C, and the discharge capacity retention rate was 80% or more.

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