Electrolyte additive, electrolyte and lithium ion battery

Abstract

The invention provides an electrolyte additive, an electrolyte and a lithium ion battery. The electrolyte additive comprises a benzotrifluoride compound and N-(4-aminophenyl) maleimide, and the mass ratio of the benzotrifluoride compound to the N-(4-aminophenyl) maleimide is (1-35): (1-35). According to the invention, trifluoromethyl (-CF3) in a trifluorotoluene compound is subjected to an oxidation reaction under a high-voltage condition, and the trifluoromethyl (-CF3) and acylamino (-CONH2) of N-(4-aminophenyl) maleimide generate a synergistic effect on the positive plate, so that a stable and compact catholyte interface layer (CEI) is constructed on the surface of the positive plate; therefore, the cycling stability of the lithium ion battery under high voltage is obviously improved.

Description

Technical Field

[0001] The present invention relates to the field of electrolytes, and in particular to an electrolyte additive, an electrolyte and a lithium ion battery. Background Art

[0002] Currently, the extensive use of non-renewable resources such as oil and coal has caused serious environmental pollution and energy crises, and the search for clean and efficient energy solutions has become a global focus. Lithium-ion batteries, due to their high energy conversion rate, long cycle life, and environmental friendliness, hold great promise for applications in electric vehicles, portable electronics, and smart grids. However, with the increasing demand for longer driving range in electric and hybrid vehicles, the market demand for higher energy density in lithium-ion batteries is also increasing. To this end, increasing the operating voltage of ternary materials has become an important technical approach.

[0003] However, this technical approach faces severe challenges. Traditional electrolytes have a narrow electrochemical window. When the operating voltage is increased, the electrolyte is prone to self-decomposition, which in turn exacerbates side reactions between the cathode material and the electrolyte, causing the transition metal in the cathode material to dissolve. This further accelerates the decomposition of the electrolyte, leading to decreased battery performance and shortened battery life. Therefore, it is of great significance to introduce electrolyte additives to construct an effective interface protection layer and improve the stability of the cathode material-electrolyte interface under high voltage conditions.

[0004] In view of this, this application is hereby filed. Summary of the Invention

[0005] The main purpose of the present invention is to provide an electrolyte additive, an electrolyte and a lithium-ion battery to solve the problem in the prior art that the electrolyte is easily decomposed under high voltage, resulting in a decrease in the cycle performance and shortened life of the battery under high voltage conditions.

[0006] To achieve the above object, according to one aspect of the present invention, there is provided an electrolyte additive comprising a trifluorotoluene compound and N-(4-aminophenyl)maleimide in a mass ratio of (1-35):(1-35); the trifluorotoluene compound has a structure shown in formula (I):

[0007]

[0008] wherein n is any integer from 0 to 5, and R is selected from substituted or unsubstituted C1-C 10 Alkyl, substituted or unsubstituted C2-C 10 Alkenyl, substituted or unsubstituted C2-C 10 Alkynyl, halogen, substituted or unsubstituted C1-C 10Carboxyl, substituted or unsubstituted C1-C 10 of cyano.

[0009] Further, n is 1 or 2, and R is selected from substituted or unsubstituted C1-C4 alkyl, substituted or unsubstituted C2-C4 alkenyl, substituted or unsubstituted C2-C4 alkynyl, halogen, substituted or unsubstituted C1-C4 carboxyl, and substituted or unsubstituted C1-C4 cyano.

[0010] Further, R is selected from *CH3, *CH2-CH3, *CH2-CH2-CH3, *CH-(CH3)2, *CH2-CH2-CH2-CH3, *CH2-CH-(CH3)2, *C(CH3)3, *F, *CF3, *CH2-CF3, *CH2-CH2-CF3, *CH-(CF3)2, *CH2-CH2-CH2-CF3, *CH2-CH-(CF3)2, *C(CF3)3, *CF2-CF3, *CF 2-CF2-CF3, *CF2-CF2-CF2-CF3, *CH=CH2, *CH=CH-CH3, *CH2-CH=CH2, *CH2-CH=CH-CH3, *CH=CH-CF3, *CF2-C H=CH2, *CH=CH-CH2-CF3, *C≡CH, *C≡C-CH3, *CH2-C≡CH, *CH2-C≡C-CH3, *C≡C-CF3, *CF2-C≡CH, *CH2-C≡C-CF3.

[0011] Furthermore, trifluorotoluene compounds include At least one of .

[0012] According to another aspect of the present invention, an electrolyte is provided, comprising: an organic solvent, a lithium salt and an electrolyte additive, wherein the electrolyte additive is the electrolyte additive provided in the first aspect.

[0013] Furthermore, based on the total mass of the electrolyte, the mass content of the trifluorotoluene compound is 0.1 to 3.5%, and further, the mass content of the trifluorotoluene compound is 0.8 to 2.5%.

[0014] Furthermore, based on the total mass of the electrolyte, the mass content of N-(4-aminophenyl)maleimide is 0.1 to 3.5%, and further, the mass content of N-(4-aminophenyl)maleimide is 0.5 to 2.2%.

[0015] Furthermore, the mass ratio of N-(4-aminophenyl)maleimide to the trifluorotoluene compound is (5-22):(8-25).

[0016] Furthermore, the organic solvent includes at least one of ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, fluoroethylene carbonate, 1,4-butyrolactone, methyl formate, ethyl acetate, methyl propionate, ethyl propionate, propyl propionate, butyl propionate, and ethyl butyrate.

[0017] Further, the lithium salt includes at least one of lithium hexafluorophosphate, lithium difluorobisoxalatophosphate, lithium tetrafluorooxalatophosphate, lithium difluorophosphate, lithium oxalatephosphate, lithium bisoxalatoborate, lithium difluorooxalatoborate, lithium tetrafluoroborate, bisfluorosulfonyl imide lithium salt and bisfluorosulfonyl imide lithium.

[0018] Furthermore, the concentration of the lithium salt is 0.5M to 1.5M.

[0019] Furthermore, the electrolyte further comprises a functional additive; and based on the total mass of the electrolyte, the mass content of the functional additive is 0.1 to 5%.

[0020] Furthermore, the functional additive includes at least one of vinylene carbonate, fluoroethylene carbonate, vinyl sulfate, tris(trimethylsilyl) phosphate, 1,3-propane sultone, methylene disulfonate, 1,3,6-hexanetrinitrile, tris(pentafluorophenyl)borane, lithium difluorophosphate, 3-hexylthiophene, hexafluorocyclotriphosphazene, and tris(hexafluoroisopropyl) phosphate.

[0021] Furthermore, based on the total mass of the electrolyte, the total mass content of the electrolyte additive and the functional additive is 0.3-12%.

[0022] According to a third aspect of the present invention, a lithium-ion battery is provided, comprising: a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte; wherein the electrolyte is the electrolyte provided in the second aspect above.

[0023] Applying the technical solution of the present invention, the electrolyte additive provided by the present application, by introducing trifluorotoluene compounds and N-(4-aminophenyl)maleimide, utilizes the trifluoromethyl (-CF3) in trifluorotoluene compounds to undergo oxidation reaction under high voltage conditions, and produces a synergistic effect with the amide group (-CONH2) of N-(4-aminophenyl)maleimide on the positive electrode sheet, thereby constructing a stable and dense cathode electrolyte interface layer (CEI) on the surface of the positive electrode sheet. The CEI layer effectively suppresses the decomposition reaction of the electrolyte under high voltage, and effectively blocks the direct contact between the electrolyte and the positive electrode material, suppresses the dissolution of transition metal ions in the positive electrode material, thereby enhancing the structural stability of the positive electrode material. In addition, the CEI layer also has excellent ionic conductivity, can serve as a high-speed lithium ion conduction channel, and accelerates the embedding and de-embedding process of lithium ions in the positive electrode material. Through the above-mentioned synergistic effect, the cycle stability of the lithium-ion battery at high voltage is significantly improved, the service life of the lithium-ion battery is extended, and an effective solution is provided for the performance improvement of the lithium-ion battery under high voltage conditions. DETAILED DESCRIPTION

[0024] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application can be combined with each other. The present invention will be described in detail below with reference to the embodiments.

[0025] As described in the background of this application, current electrolytes are prone to decomposition under high voltages, resulting in decreased cycle performance and shortened battery life under high voltage conditions. To address this issue, this application provides an electrolyte additive, an electrolyte, and a lithium-ion battery.

[0026] In a first typical embodiment of the present application, an electrolyte additive is provided, the electrolyte additive comprising a trifluorotoluene compound and N-(4-aminophenyl)maleimide, and the mass ratio of the two is (1-35): (1-35);

[0027] Trifluorotoluene compounds have the structure shown in formula (I): wherein n is any integer from 0 to 5, and R is selected from substituted or unsubstituted C1-C 10 Alkyl, substituted or unsubstituted C2-C 10 Alkenyl, substituted or unsubstituted C2-C 10 Alkynyl, halogen, substituted or unsubstituted C1-C 10 Carboxyl, substituted or unsubstituted C1-C 10 of cyano;

[0028] N-(4-aminophenyl)maleimide has the structure shown in formula (II):

[0029]

[0030] The electrolyte additive provided by the present application, by introducing trifluorotoluene compounds and N- (4-aminophenyl) maleimide, utilizes the trifluoromethyl (-CF3) in trifluorotoluene compounds to undergo oxidation reaction under high voltage conditions, under the synergistic effect of the amide group (-CONH2) of N- (4-aminophenyl) maleimide, a stable and dense cathode electrolyte interface layer (CEI) is constructed on the surface of the positive electrode sheet, and the final product obtained by the reaction is basically LiF and a portion of CO2. The CEI layer effectively suppresses the decomposition reaction of the electrolyte at high voltage, and effectively blocks the direct contact between the electrolyte and the positive electrode material, suppresses the dissolution of transition metal ions in the positive electrode material, thereby enhancing the structural stability of the positive electrode material. In addition, the CEI layer also has excellent ionic conductivity and can serve as a high-speed lithium ion conduction channel to accelerate the embedding and deintercalation process of lithium ions in the positive electrode material. Through the above-mentioned synergistic effect, the cycle stability of the lithium ion battery at high voltage is significantly improved, the service life of the lithium ion battery is extended, and an effective solution is provided for the performance improvement of the lithium ion battery under high voltage conditions.

[0031] In the present application, the term "substituted or unsubstituted" refers to substitution by one or more substituents selected from the group consisting of deuterium, a halogen group, a nitrile group, a nitro group, a hydroxyl group, a carbonyl group, an ester group, an imide group, an amino group, an alkoxy group, an aryloxy group, a silyl group, an alkyl group, a cycloalkyl group, an alkenyl group, an aryl group, an aralkyl group, an aralkenyl group, an alkylaryl group, an alkylamino group, or no substituent, or substitution by two or more substituents linked together from among the exemplified substituents, or no substituent. For example, the term "a substituent in which two or more substituents are linked together" may refer to a biphenyl group. That is, the biphenyl group may be an aryl group, or it may be interpreted as a substituent in which two phenyl groups are linked together.

[0032] In this application, C2-C 10 The alkenyl group in the alkenyl group can be in the middle or at the end of the chain segment; 10 The alkynyl group in the alkynyl group can be in the middle or at the end of the chain segment; 10 The general chemical formula of the carboxyl group is R1-COOH, where R1 is a C1-C9 alkyl group; 10 The general chemical formula of the cyano group is R2-C≡N, where R2 is a C1-C9 alkyl group.

[0033] In this application, the term "halogen" refers to fluorine. In addition, the range of carbon atoms in this article can be extended from the lower limit to the upper limit, such as C1-C 10 It means that the number of carbon atoms can be 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10.

[0034] In the present application, when n≥2, each R may be the same or different.

[0035] In order to further improve the cycle stability of the lithium ion battery at high voltage, preferably n is 1 or 2, preferably R is selected from substituted or unsubstituted C1-C4 alkyl, substituted or unsubstituted C2-C4 alkenyl, substituted or unsubstituted C2-C4 alkynyl, halogen, substituted or unsubstituted C1-C4 carboxyl, substituted or unsubstituted C1-C4 cyano; further preferably R is selected from H, *CH3, *CH2-CH3, *CH2-CH2-CH3, *CH-(CH3)2, *CH2-CH2-CH2-CH3, *CH2-CH-(CH3)2, *C(CH3)3, *F, *CF3, *CH2-CF3, *CH2-CH2-CF3, *C H-(CF3)2、*CH2-CH2-CH2-CF3、*CH2-CH-(CF3)2、*C(CF3)3、*CF2-CF3、*CF2-CF2-CF3、*CF2-CF2-CF2-CF3、*CH=CH2、*CH=CH-CH3、*CH2-CH=CH2、* CH2-CH=CH-CH3, *CH=CH-CF3, *CF2-CH=CH2, *CH=CH-CH2-CF3, *C≡CH, *C≡C-CH3, *CH2-C≡CH, *CH2-C≡C-CH3, *C≡C-CF3, *CF2-C≡CH, *CH2-C≡C-CF3.

[0036] In the structural formulas disclosed in this specification, unless otherwise specified, "*" indicates a linking site.

[0037] Typically but not limitatively, in the electrolyte provided in the present application, the mass ratio of N-(4-aminophenyl)maleimide and trifluorotoluene compounds is, for example, 1:35, 5:25, 8:22, 12:18, 15:15, 20:10, 22:8, 35:1 or a range consisting of any two values.

[0038] In some embodiments, when n=2, preferably two Rs are simultaneously located at the ortho or meta position of the trifluoromethyl group; when n=1, preferably R is located at the para position of the trifluoromethyl group.

[0039] In some embodiments, when the trifluorotoluene compound includes at least one of the following compounds, the synergistic effect produced by the trifluorotoluene compound and the amide group (-CONH2) of N-(4-aminophenyl)maleimide at the positive electrode is more obvious, and a more stable and denser cathode electrolyte interface film (CEI) can be constructed on the surface of the positive electrode sheet, thereby more effectively inhibiting the decomposition of the electrolyte at high voltage.

[0040]

[0041] At least one of .

[0042] In a second typical embodiment of the present application, an electrolyte is provided, comprising: an organic solvent, a lithium salt and an electrolyte additive; wherein the electrolyte additive is the electrolyte additive provided in the above-mentioned first typical embodiment.

[0043] This application adds an electrolyte additive to the electrolyte, utilizes the trifluoromethyl group (-CF3) in trifluorotoluene compounds to undergo an oxidation reaction under high voltage conditions, and produces a synergistic effect with the amide group (-CONH2) of N-(4-aminophenyl)maleimide at the positive electrode, thereby constructing a stable and dense cathode electrolyte interface layer (CEI) on the positive electrode surface. This effectively suppresses the decomposition reaction of the electrolyte under high voltage, effectively blocks the direct contact between the electrolyte and the positive electrode material, suppresses the dissolution of transition metal ions in the positive electrode material, and enhances the structural stability of the positive electrode material. This significantly improves the cycle stability of lithium-ion batteries under high voltage.

[0044] In order to further construct a more stable and dense positive electrode electrolyte interface film, thereby further inhibiting the decomposition reaction of the electrolyte under high voltage, and further improving the cycle stability of the battery under high voltage, based on the total mass of the electrolyte, the mass content of the trifluorotoluene compound is preferably 0.1-3.5%, and the mass content of the trifluorotoluene compound is further preferably 0.8-2.5%; the mass content of N-(4-aminophenyl)maleimide is preferably 0.1-3.5%, and the mass content of N-(4-aminophenyl)maleimide is further preferably 0.5%-2.2%.

[0045] Typically but not limitatively, in the electrolyte provided in the present application, based on the total mass of the electrolyte, the mass content of trifluorotoluene compounds is 0.1%, 0.8%, 1%, 1.5%, 1.8%, 2.2%, 2.5%, 3.5% or a range consisting of any two values; the mass content of N-(4-aminophenyl)maleimide is 0.1%, 0.5%, 0.8%, 1.2%, 1.5%, 2%, 2.2%, 3.5% or a range consisting of any two values.

[0046] In order to make N-(4-aminophenyl)maleimide and trifluorotoluene compounds better exert synergistic effects, the mass ratio of N-(4-aminophenyl)maleimide to trifluorotoluene compounds is preferably (5-22):(8-25).

[0047] In some embodiments, the organic solvent includes any one or more of ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, ethyl methyl carbonate, methylpropyl carbonate, ethylpropyl carbonate, fluoroethylene carbonate, 1,4-butyrolactone, methyl formate, ethyl acetate, methyl propionate, ethyl propionate, propyl propionate, butyl propionate, and ethyl butyrate. The above-mentioned organic solvents help promote the dissolution and uniform dispersion of the components, forming a more stable electrolyte, and can widen the electrochemical window and optimize the formation of the CEI layer, further making the electrolyte stable at higher voltages.

[0048] In order to further promote the dissolution and interaction of each component, so as to further improve the stability of the electrolyte and the efficient transmission of lithium ions inside the battery, the organic solvent is preferably a mixture of ethylene carbonate (EC) and ethyl methyl carbonate (EMC), and the mass ratio of the two is (2-4): (6-8); more preferably, the mass ratio of the two is 3:7.

[0049] Typically, but not limitatively, in the organic solvent provided herein, the mass ratio of ethylene carbonate (EC) to ethyl methyl carbonate (EMC) is 2:8, 3:7, 4:6, 2:6, 4:8 or a range consisting of any two values.

[0050] In some embodiments, the lithium salt includes any one or more of lithium hexafluorophosphate, lithium difluorobisoxalatophosphate, lithium tetrafluorooxalatophosphate, lithium difluorophosphate, lithium oxalate phosphate, lithium bisoxalatoborate, lithium difluorooxalatoborate, lithium tetrafluoroborate, lithium bisfluorosulfonyl imide, and lithium bisfluorosulfonyl imide. The lithium salt is further preferably lithium hexafluorophosphate (LiPF6) and / or lithium bisfluorosulfonyl imide (LiFSI). The above types of lithium salts have excellent electrical conductivity and compatibility, and can cooperate with different types of organic solvents and additives to further improve the cycle performance of the battery.

[0051] In order to further improve the lithium ion conductivity while avoiding the increase in viscosity and the decrease in lithium ion mobility caused by excessively high concentration, the concentration of the lithium salt is preferably 0.5M to 1.5M.

[0052] Typically, but not limitatively, in the electrolyte provided in the present application, the concentration of the lithium salt is 0.5M, 0.8M, 1.0M, 1.2M, 1.4M, 1.5M or a range consisting of any two values.

[0053] In order to further improve the electrolyte and obtain a lithium-ion battery with better comprehensive performance, it is preferred that the above-mentioned electrolyte also includes a functional additive, and the mass content of the functional additive is 0.1-5% based on the total mass of the electrolyte; further, it is preferred that the total mass content of the electrolyte additive and the functional additive is 0.3-12% based on the total mass of the electrolyte; further, it is preferred that the functional additive is selected from any one or more of vinylene carbonate, fluoroethylene carbonate, vinyl sulfate, tris(trimethylsilane) phosphate, tris(trimethylsilane) phosphate, 1,3-propane sultone, methanedisulfonic acid methylene ester, 1,3,6-hexane trinitrile, tris(pentafluorophenyl)borane, lithium difluorophosphate, 3-hexylthiophene, hexafluorocyclotriphosphazene, and tris(hexafluoroisopropyl) phosphate.

[0054] In a third typical embodiment of the present application, a lithium-ion battery is further provided, which includes a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte; wherein the electrolyte is any one of the electrolytes provided in the above-mentioned second typical embodiment.

[0055] Applying the technical solution of the present application, trifluorotoluene compounds and N-(4-aminophenyl)maleimide are introduced into the electrolyte as electrolyte additives. The lithium-ion battery assembled by the electrolyte utilizes the trifluoromethyl group (-CF3) in the trifluorotoluene compounds to undergo an oxidation reaction under high voltage conditions, and produces a synergistic effect with the amide group (-CONH2) of N-(4-aminophenyl)maleimide on the positive electrode sheet, thereby constructing a stable and dense cathode electrolyte interface layer (CEI) on the surface of the positive electrode sheet. The CEI layer effectively suppresses the decomposition reaction of the electrolyte under high voltage, and effectively blocks the direct contact between the electrolyte and the positive electrode material, suppresses the dissolution of transition metal ions in the positive electrode material, and thus enhances the structural stability of the positive electrode material. In addition, the CEI layer also has excellent ionic conductivity, can serve as a high-speed lithium ion conduction channel, and accelerates the embedding and de-embedding process of lithium ions in the positive electrode material. Through the above synergistic effect, the cycle stability of lithium-ion batteries under high voltage is significantly improved, the service life of lithium-ion batteries is extended, and an effective solution is provided for improving the performance of lithium-ion batteries under high voltage conditions.

[0056] In order to further improve the comprehensive performance of lithium-ion batteries, reduce costs and meet market demand, the positive electrode sheet preferably includes a positive electrode material, and the positive electrode material is an NCM ternary positive electrode material (lithium nickel cobalt manganese oxide). The ratio of the three elements of nickel, cobalt and manganese in the NCM ternary positive electrode material can be adjusted according to demand; the negative electrode sheet preferably includes a negative electrode material, and the negative electrode material is preferably graphite, such as natural graphite or artificial graphite.

[0057] The beneficial effects of the present application will be further illustrated below with reference to examples and comparative examples.

[0058] The structural formulas of compounds 1-8 used in the examples of this application are shown in Table 1.

[0059] Table 1

[0060]

[0061]

[0062]

[0063] Example 1

[0064] This embodiment provides a method for preparing an electrolyte, comprising the following steps: in an argon-filled glove box, ethylene carbonate (EC) and ethyl methyl carbonate (EMC) are mixed in a mass ratio of 3:7, followed by adding 1.0 M lithium hexafluorophosphate (LiPF6), and after the lithium salt is completely dissolved, 0.5 wt% of vinylene carbonate, 1.0 wt% of vinyl sulfate, and 0.8 wt% of lithium difluorooxalatoborate are added based on the total mass of the electrolyte, and then 1.5 wt% of N-(4-aminophenyl)maleimide and 1.5 wt% of compound 1 are added, and the mixture is stirred evenly to obtain an electrolyte.

[0065] Example 2

[0066] The difference from Example 1 is that in this example, the amount of N-(4-aminophenyl)maleimide is adjusted to 2.0 wt %, and the amount of Compound 1 is adjusted to 1.0 wt %;

[0067] The preparation method specifically includes the following steps: in a glove box filled with argon, ethylene carbonate (EC) and ethyl methyl carbonate (EMC) are mixed in a mass ratio of 3:7, and then 1.0M lithium hexafluorophosphate (LiPF6) is added. After the lithium salt is completely dissolved, 0.5wt% of vinylene carbonate, 1.0wt% of vinyl sulfate and 0.8wt% of lithium difluorooxalatoborate are added based on the total mass of the electrolyte, and then 2.0wt% of N-(4-aminophenyl)maleimide and 1.0wt% of compound 1 are added, and the electrolyte is obtained after stirring evenly.

[0068] Example 3

[0069] The difference from Example 1 is that in this example, the amount of N-(4-aminophenyl)maleimide is adjusted to 1.2 wt %, and the amount of Compound 1 is adjusted to 1.8 wt %;

[0070] The preparation method specifically includes the following steps: in a glove box filled with argon, ethylene carbonate (EC) and ethyl methyl carbonate (EMC) are mixed in a mass ratio of 3:7, and then 1.0M lithium hexafluorophosphate (LiPF6) is added. After the lithium salt is completely dissolved, 0.5wt% of vinylene carbonate, 1.0wt% of vinyl sulfate and 0.8wt% of lithium difluorooxalatoborate are added based on the total mass of the electrolyte, and then 1.2wt% of N-(4-aminophenyl)maleimide and 1.8wt% of compound 1 are added, and the electrolyte is obtained after stirring evenly.

[0071] Example 4

[0072] The difference from Example 1 is that in this example, the amount of N-(4-aminophenyl)maleimide is adjusted to 0.5 wt %, and the amount of Compound 1 is adjusted to 2.5 wt %;

[0073] The preparation method specifically includes the following steps: in a glove box filled with argon, ethylene carbonate (EC) and ethyl methyl carbonate (EMC) are mixed in a mass ratio of 3:7, and then 1.0M lithium hexafluorophosphate (LiPF6) is added. After the lithium salt is completely dissolved, 0.5wt% of vinylene carbonate, 1.0wt% of vinyl sulfate, and 0.8wt% of lithium difluorooxalatoborate are added based on the total mass of the electrolyte, and then 0.5wt% of N-(4-aminophenyl)maleimide and 2.5wt% of compound 1 are added, and the electrolyte is obtained after stirring evenly.

[0074] Example 5

[0075] The difference from Example 1 is that in this example, the amount of N-(4-aminophenyl)maleimide is adjusted to 2.2 wt %, and the amount of Compound 1 is adjusted to 0.8 wt %;

[0076] The preparation method specifically includes the following steps: in a glove box filled with argon, ethylene carbonate (EC) and ethyl methyl carbonate (EMC) are mixed in a mass ratio of 3:7, and then 1.0M lithium hexafluorophosphate (LiPF6) is added. After the lithium salt is completely dissolved, 0.5wt% of vinylene carbonate, 1.0wt% of vinyl sulfate and 0.8wt% of lithium difluorooxalatoborate are added based on the total mass of the electrolyte, and then 2.2wt% of N-(4-aminophenyl)maleimide and 0.8wt% of compound 1 are added, and the electrolyte is obtained after stirring evenly.

[0077] Example 6

[0078] The difference from Example 1 is that in this example, the amount of N-(4-aminophenyl)maleimide is adjusted to 0.8 wt %, and the amount of Compound 1 is adjusted to 2.2 wt %;

[0079] The preparation method specifically includes the following steps: in a glove box filled with argon, ethylene carbonate (EC) and ethyl methyl carbonate (EMC) are mixed in a mass ratio of 3:7, and then 1.0M lithium hexafluorophosphate (LiPF6) is added. After the lithium salt is completely dissolved, 0.5wt% of vinylene carbonate, 1.0wt% of vinyl sulfate and 0.8wt% of lithium difluorooxalatoborate are added based on the total mass of the electrolyte, and then 0.8wt% of N-(4-aminophenyl)maleimide and 2.2wt% of compound 1 are added, and the electrolyte is obtained after stirring evenly.

[0080] Example 7

[0081] The difference from Example 1 is that the dosage of this example remains unchanged and Compound 1 is replaced by Compound 2;

[0082] The preparation method specifically includes the following steps: in a glove box filled with argon, ethylene carbonate (EC) and ethyl methyl carbonate (EMC) are mixed in a mass ratio of 3:7, and then 1.0M lithium hexafluorophosphate (LiPF6) is added. After the lithium salt is completely dissolved, 0.5wt% of vinylene carbonate, 1.0wt% of vinyl sulfate and 0.8wt% of lithium difluorooxalatoborate are added based on the total mass of the electrolyte, and then 1.5wt% of N-(4-aminophenyl)maleimide and 1.5wt% of compound 2 are added, and the electrolyte is obtained after stirring evenly.

[0083] Example 8

[0084] The difference from Example 1 is that the dosage of this example remains unchanged and Compound 1 is replaced by Compound 3;

[0085] The preparation method specifically includes the following steps: in a glove box filled with argon, ethylene carbonate (EC) and ethyl methyl carbonate (EMC) are mixed in a mass ratio of 3:7, and then 1.0M lithium hexafluorophosphate (LiPF6) is added. After the lithium salt is completely dissolved, 0.5wt% of vinylene carbonate, 1.0wt% of vinyl sulfate and 0.8wt% of lithium difluorooxalatoborate are added based on the total mass of the electrolyte, and then 1.5wt% of N-(4-aminophenyl)maleimide and 1.5wt% of compound 3 are added, and the electrolyte is obtained after stirring evenly.

[0086] Example 9

[0087] The difference from Example 1 is that the dosage of this example remains unchanged and Compound 1 is replaced by Compound 4;

[0088] The preparation method specifically includes the following steps: in a glove box filled with argon, ethylene carbonate (EC) and ethyl methyl carbonate (EMC) are mixed in a mass ratio of 3:7, and then 1.0M lithium hexafluorophosphate (LiPF6) is added. After the lithium salt is completely dissolved, 0.5wt% of vinylene carbonate, 1.0wt% of vinyl sulfate, and 0.8wt% of lithium difluorooxalatoborate are added based on the total mass of the electrolyte, and then 1.5wt% of N-(4-aminophenyl)maleimide and 1.5wt% of compound 4 are added, and the electrolyte is obtained after stirring evenly.

[0089] Example 10

[0090] The difference from Example 1 is that in this example, the lithium salt is adjusted to 0.8M lithium hexafluorophosphate (LiPF6) and 0.2M lithium bis(fluorosulfonyl)imide (LiFSI);

[0091] The preparation method specifically includes the following steps: in a glove box filled with argon, ethylene carbonate (EC) and ethyl methyl carbonate (EMC) are mixed in a mass ratio of 3:7, and then 0.8M lithium hexafluorophosphate (LiPF6) and 0.2M lithium bis(fluorosulfonyl)imide (LiFSI) are added. After the lithium salt is completely dissolved, 0.5wt% of vinylene carbonate, 1.0wt% of vinyl sulfate and 0.8wt% of lithium difluorooxalatoborate are added based on the total mass of the electrolyte, and then 1.5wt% of N-(4-aminophenyl)maleimide and 1.5% of compound 1 are added, and the electrolyte is obtained after stirring evenly.

[0092] Example 11

[0093] The difference from Example 1 is that the functional additives in this example are adjusted to 1.0 wt% of fluoroethylene carbonate, 0.8 wt% of methylene methanedisulfonate, and 0.5 wt% of lithium difluorophosphate;

[0094] The preparation method specifically includes the following steps: in a glove box filled with argon, ethylene carbonate (EC) and ethyl methyl carbonate (EMC) are mixed in a mass ratio of 3:7, and then 1.0M lithium hexafluorophosphate (LiPF6) is added. After the lithium salt is completely dissolved, 1.0wt% of fluoroethylene carbonate, 0.8wt% of methylene disulfonate and 0.5wt% of lithium difluorophosphate are added based on the total mass of the electrolyte, and then 1.5wt% of N-(4-aminophenyl)maleimide and 1.5wt% of compound 1 are added, and the mixture is stirred evenly to obtain an electrolyte.

[0095] Example 12

[0096] The difference from Example 1 is that in this example, the amount of N-(4-aminophenyl)maleimide is adjusted to 3.5 wt %, and the amount of Compound 1 is adjusted to 0.1 wt %.

[0097] The preparation method specifically includes the following steps: in a glove box filled with argon, ethylene carbonate (EC) and ethyl methyl carbonate (EMC) are mixed in a mass ratio of 3:7, and then 1.0M lithium hexafluorophosphate (LiPF6) is added. After the lithium salt is completely dissolved, 0.5wt% of vinylene carbonate, 1.0wt% of vinyl sulfate and 0.8wt% of lithium difluorooxalatoborate are added based on the total mass of the electrolyte, and then 3.5wt% of N-(4-aminophenyl)maleimide and 0.1wt% of compound 1 are added, and the electrolyte is obtained after stirring evenly.

[0098] Example 13

[0099] The difference from Example 1 is that in this example, the amount of N-(4-aminophenyl)maleimide is adjusted to 0.1 wt %, and the amount of Compound 1 is adjusted to 3.5 wt %.

[0100] The preparation method specifically includes the following steps: in a glove box filled with argon, ethylene carbonate (EC) and ethyl methyl carbonate (EMC) are mixed in a mass ratio of 3:7, and then 1.0M lithium hexafluorophosphate (LiPF6) is added. After the lithium salt is completely dissolved, 0.5wt% of vinylene carbonate, 1.0wt% of vinyl sulfate and 0.8wt% of lithium difluorooxalatoborate are added based on the total mass of the electrolyte, and then 0.1wt% of N-(4-aminophenyl)maleimide and 3.5wt% of compound 1 are added, and the electrolyte is obtained after stirring evenly.

[0101] Example 14

[0102] The difference from Example 1 is that the dosage of this example remains unchanged and Compound 1 is replaced by Compound 5;

[0103] The preparation method specifically includes the following steps: in a glove box filled with argon, ethylene carbonate (EC) and ethyl methyl carbonate (EMC) are mixed in a mass ratio of 3:7, and then 1.0M lithium hexafluorophosphate (LiPF6) is added. After the lithium salt is completely dissolved, 0.5wt% of vinylene carbonate, 1.0wt% of vinyl sulfate and 0.8wt% of lithium difluorooxalatoborate are added based on the total mass of the electrolyte, and then 1.5wt% of N-(4-aminophenyl)maleimide and 1.5wt% of compound 5 are added, and the electrolyte is obtained after stirring evenly.

[0104] Example 15

[0105] The difference from Example 1 is that the dosage of this example remains unchanged, and Compound 1 is replaced by Compound 6;

[0106] The preparation method specifically includes the following steps: in a glove box filled with argon, ethylene carbonate (EC) and ethyl methyl carbonate (EMC) are mixed in a mass ratio of 3:7, and then 1.0M lithium hexafluorophosphate (LiPF6) is added. After the lithium salt is completely dissolved, 0.5wt% of vinylene carbonate, 1.0wt% of vinyl sulfate and 0.8wt% of lithium difluorooxalatoborate are added based on the total mass of the electrolyte, and then 1.5wt% of N-(4-aminophenyl)maleimide and 1.5wt% of compound 6 are added, and the electrolyte is obtained after stirring evenly.

[0107] Example 16

[0108] The difference from Example 1 is that the dosage of this example remains unchanged and Compound 1 is replaced by Compound 7;

[0109] The preparation method specifically includes the following steps: in a glove box filled with argon, ethylene carbonate (EC) and ethyl methyl carbonate (EMC) are mixed in a mass ratio of 3:7, and then 1.0M lithium hexafluorophosphate (LiPF6) is added. After the lithium salt is completely dissolved, 0.5wt% of vinylene carbonate, 1.0wt% of vinyl sulfate and 0.8wt% of lithium difluorooxalatoborate are added based on the total mass of the electrolyte, and then 1.5wt% of N-(4-aminophenyl)maleimide and 1.5wt% of compound 7 are added, and the electrolyte is obtained after stirring evenly.

[0110] Example 17

[0111] The difference from Example 1 is that the dosage of this example remains unchanged, and Compound 1 is replaced by Compound 8;

[0112] The preparation method specifically includes the following steps: in a glove box filled with argon, ethylene carbonate (EC) and ethyl methyl carbonate (EMC) are mixed in a mass ratio of 3:7, and then 1.0M lithium hexafluorophosphate (LiPF6) is added. After the lithium salt is completely dissolved, 0.5wt% of vinylene carbonate, 1.0wt% of vinyl sulfate and 0.8wt% of lithium difluorooxalatoborate are added based on the total mass of the electrolyte, and then 1.5wt% of N-(4-aminophenyl)maleimide and 1.5wt% of compound 8 are added, and the electrolyte is obtained after stirring evenly.

[0113] Comparative Example 1

[0114] The difference from Example 1 is that Compound 1 is not added in this comparative example, and the amount of N-(4-aminophenyl)maleimide is adjusted to 3.0 wt %.

[0115] The preparation method specifically includes the following steps: in a glove box filled with argon, ethylene carbonate (EC) and ethyl methyl carbonate (EMC) are mixed in a mass ratio of 3:7, and then 1.0M lithium hexafluorophosphate (LiPF6) is added. After the lithium salt is completely dissolved, 0.5wt% of vinylene carbonate, 1.0wt% of vinyl sulfate and 0.8wt% of lithium difluorooxalatoborate are added based on the total mass of the electrolyte, and then 3.0wt% of N-(4-aminophenyl)maleimide is added, and the electrolyte is obtained after stirring evenly.

[0116] Comparative Example 2

[0117] The difference from Example 1 is that N-(4-aminophenyl)maleimide is not added in this comparative example, and the amount of compound 1 is adjusted to 3.0 wt %.

[0118] The preparation method specifically includes the following steps: in a glove box filled with argon, ethylene carbonate (EC) and ethyl methyl carbonate (EMC) are mixed in a mass ratio of 3:7, and then 1.0M lithium hexafluorophosphate (LiPF6) is added. After the lithium salt is completely dissolved, 0.5wt% of vinylene carbonate, 1.0wt% of vinyl sulfate and 0.8wt% of lithium difluorooxalatoborate are added based on the total mass of the electrolyte, and then 3.0wt% of compound 1 is added, and the electrolyte is obtained after stirring evenly.

[0119] Comparative Example 3

[0120] The difference from Example 1 is that N-(4-aminophenyl)maleimide and Compound 1 are not added in this comparative example.

[0121] The preparation method specifically includes the following steps: in a glove box filled with argon, ethylene carbonate (EC) and ethyl methyl carbonate (EMC) are mixed in a mass ratio of 3:7, and then 1.0M lithium hexafluorophosphate (LiPF6) is added. After the lithium salt is completely dissolved, 0.5wt% of vinylene carbonate, 1.0wt% of vinyl sulfate and 0.8wt% of lithium difluorooxalatoborate are added based on the total mass of the electrolyte, and the electrolyte is obtained after stirring evenly.

[0122] Comparative Example 4

[0123] The difference from Example 10 is that N-(4-aminophenyl)maleimide and Compound 1 are not added in this comparative example.

[0124] The preparation method specifically includes the following steps: in a glove box filled with argon, ethylene carbonate (EC) and ethyl methyl carbonate (EMC) are mixed in a mass ratio of 3:7, and then 0.8M lithium hexafluorophosphate (LiPF6) and 0.2M lithium bis(fluorosulfonyl)imide (LiFSI) are added. After the lithium salt is completely dissolved, 0.5wt% of vinylene carbonate, 1.0wt% of vinyl sulfate and 0.8wt% of lithium difluorooxalatoborate are added based on the total mass of the electrolyte, and the electrolyte is obtained after stirring evenly.

[0125] Comparative Example 5

[0126] The difference from Example 11 is that N-(4-aminophenyl)maleimide and Compound 1 are not added in this comparative example.

[0127] The preparation method specifically includes the following steps: in a glove box filled with argon, ethylene carbonate (EC) and ethyl methyl carbonate (EMC) are mixed in a mass ratio of 3:7, and then 1.0M lithium hexafluorophosphate (LiPF6) is added. After the lithium salt is completely dissolved, 1.0wt% of fluoroethylene carbonate, 0.8wt% of methylene methanedisulfonate and 0.5wt% of lithium difluorophosphate are added based on the total mass of the electrolyte, and the electrolyte is obtained after stirring evenly.

[0128] Comparative Example 6

[0129] The difference from Example 1 is that in this example, the amount of N-(4-aminophenyl)maleimide is adjusted to 0.05 wt %, and the amount of Compound 1 is adjusted to 3.55 wt %.

[0130] The preparation method specifically includes the following steps: in a glove box filled with argon, ethylene carbonate (EC) and ethyl methyl carbonate (EMC) are mixed in a mass ratio of 3:7, and then 1.0M lithium hexafluorophosphate (LiPF6) is added. After the lithium salt is completely dissolved, 0.5wt% of vinylene carbonate, 1.0wt% of vinyl sulfate and 0.8wt% of lithium difluorooxalatoborate are added based on the total mass of the electrolyte, and then 0.05wt% of N-(4-aminophenyl)maleimide and 3.55wt% of compound 1 are added, and the electrolyte is obtained after stirring evenly.

[0131] Comparative Example 7

[0132] The difference from Example 1 is that in this example, the amount of N-(4-aminophenyl)maleimide is adjusted to 3.55 wt %, and the amount of Compound 1 is adjusted to 0.05 wt %.

[0133] The preparation method specifically includes the following steps: in a glove box filled with argon, ethylene carbonate (EC) and ethyl methyl carbonate (EMC) are mixed in a mass ratio of 3:7, and then 1.0M lithium hexafluorophosphate (LiPF6) is added. After the lithium salt is completely dissolved, 0.5wt% of vinylene carbonate, 1.0wt% of vinyl sulfate and 0.8wt% of lithium difluorooxalatoborate are added based on the total mass of the electrolyte, and then 3.55wt% of N-(4-aminophenyl)maleimide and 0.05wt% of compound 1 are added, and the electrolyte is obtained after stirring evenly.

[0134] Test Example 1

[0135] The electrolytes provided in the above examples and comparative examples were assembled into lithium-ion batteries, and high-voltage room-temperature cycle performance tests and high-voltage high-temperature cycle performance tests were performed. The results are shown in Table 2.

[0136] Preparation of positive electrode: LiNi 0.7 Co 0.1 Mn 0.2 O2, conductive agent Super P (conductive carbon black), adhesive PVDF (polyvinylidene fluoride) and carbon nanotubes (CNT) are mixed uniformly in a mass ratio of 97.5:0.5:1:1 to form a lithium-ion battery positive electrode slurry, which is coated on the aluminum foil used for the current collector. The coating amount is 360g / m 2 , dried at 85°C and then cold pressed; then striped and sliced, and then baked at 85°C in vacuum for 4 hours to make lithium-ion battery positive electrodes that meet the requirements.

[0137] Preparation of negative electrode sheet: Artificial graphite is mixed with conductive agent Super P, thickener CMC, and adhesive SBR (styrene-butadiene rubber emulsion) in a mass ratio of 95:1.5:1.0:2.5 to make a slurry, mix them evenly, and apply the mixed slurry on both sides of the copper foil. After drying and roller pressing, the negative electrode sheet is obtained, and then it is baked at 85°C in a vacuum for 4 hours to make a lithium-ion battery negative electrode sheet that meets the requirements.

[0138] Preparation of lithium-ion batteries: The positive electrode sheet, negative electrode sheet and separator (polyethylene film coated ceramic separator) prepared according to the above process are laminated to form a lithium-ion battery with a thickness of 0.5 mm, a width of 8 mm and a length of 10 mm, with a capacity of 3 Ah. The battery is vacuum-baked at 85°C for 48 hours, and the above-mentioned electrolyte is injected. The 3 Ah soft-pack lithium-ion battery is completed through the processes of packaging, shelving, formation, aging, secondary packaging and capacity division.

[0139] High voltage room temperature cycle test: In a 25°C incubator, discharge at 1C to 2.8V, charge at 1C constant current to 4.45V, and then charge at constant voltage to 0.05C. This is counted as one cycle. The average cycle discharge capacity of the 1st to 5th cycles is taken as the initial discharge capacity. When the cycle reaches 1000 cycles, the 1000th cycle discharge capacity is calculated and compared with the initial discharge capacity to calculate the capacity retention rate.

[0140] Calculation formula: 1000th cycle capacity retention rate = (1000th cycle discharge capacity / initial discharge capacity) × 100%

[0141] High voltage and high temperature cycle test: In a 45°C incubator, discharge at 1C to 2.8V, charge at 1C constant current to 4.45V, and charge at constant voltage to 0.05C. This is counted as one cycle. The discharge capacity of the 1st to 5th cycle is taken as the initial discharge capacity. When the cycle reaches 700 cycles, the discharge capacity of the 700th cycle is calculated and compared with the initial discharge capacity to calculate the capacity retention rate.

[0142] Calculation formula: 700th cycle capacity retention rate = (700th cycle discharge capacity / initial discharge capacity) × 100%

[0143] For each test, three batteries assembled in the embodiment / comparative example were tested in parallel, and the average test results were listed in Table 2.

[0144] Table 2

[0145]

[0146]

[0147] As can be seen from the results in Table 2, in the present invention, N-(4-aminophenyl)maleimide and trifluorotoluene compounds are used in combination (Examples 1-17), and the mass ratio of the two is (1 to 35): (1 to 35). The electrolyte prepared in this way has excellent room temperature cycle stability and high temperature cycle stability under high voltage. After 1000 cycles at room temperature of 25°C, the battery capacity retention rate reaches 83.74% to 88.80%, and after 700 cycles at high temperature of 45°C, the battery capacity retention rate reaches 81.37% to 85.27%.

[0148] Compared with Examples 1-17, if only N-(4-aminophenyl)maleimide (Comparative Example 1) or only trifluorotoluene compounds (Comparative Example 2) are used, the battery capacity retention rate of the prepared 3Ah soft-pack lithium-ion battery after 1000 cycles at room temperature and 25°C under high voltage and 700 cycles at high temperature and 45°C is reduced, indicating that its room temperature cycle performance or high temperature cycle performance under high voltage is poor.

[0149] Compared with Examples 1-17, if N-(4-aminophenyl)maleimide and trifluorotoluene compounds are not added (Comparative Examples 3-5), the prepared 3Ah soft-pack lithium-ion batteries have a battery capacity retention rate after 1000 cycles at room temperature under high voltage and a battery capacity retention rate after 700 cycles at high temperature, both of which are less than 80%, indicating that their room temperature cycle performance or high temperature cycle performance at high voltage is significantly reduced.

[0150] Compared with Examples 1-17, if the mass ratio of N-(4-aminophenyl)maleimide and trifluorotoluene compounds is too large or too small (Comparative Examples 6-7), the prepared 3Ah soft-pack lithium-ion battery has a significantly reduced battery capacity retention rate after 1000 cycles of room temperature cycling at high voltage and a significantly reduced battery capacity retention rate after 700 cycles of high temperature cycling, indicating that its room temperature cycling performance or high temperature cycling performance at high voltage is significantly reduced.

[0151] In summary, by comparing the test results of the batteries of Examples 1-17 and Comparative Examples 1-7, it can be observed that under the conditions of 2.8 to 4.45 V, the electrolyte prepared by using N-(4-aminophenyl)maleimide and trifluorotoluene compounds in a mass ratio of (1 to 35): (1 to 35) has good voltage resistance and cycle stability, and can significantly improve the cycle performance at room temperature and high temperature under high voltage.

[0152] Compared with other conventional additives, the electrolyte additive in the present invention can significantly improve the cycle performance of lithium-ion batteries when operating at high voltage (4.45V), and has broad application prospects in high-voltage systems.

[0153] From the above description, it can be seen that the above embodiments of the present invention achieve the following technical effects:

[0154] The electrolyte additive provided by the present application, by introducing trifluorotoluene compounds and N- (4-aminophenyl) maleimide, utilizes the trifluoromethyl (-CF3) in trifluorotoluene compounds to undergo oxidation reaction under high voltage conditions, and produces a synergistic effect with the amide group (-CONH2) of N- (4-aminophenyl) maleimide on the positive electrode sheet, thereby constructing a stable and dense cathode electrolyte interface layer (CEI) on the surface of the positive electrode sheet. The CEI layer effectively suppresses the decomposition reaction of the electrolyte under high voltage, and effectively blocks the direct contact between the electrolyte and the positive electrode material, suppresses the dissolution of transition metal ions in the positive electrode material, thereby enhancing the structural stability of the positive electrode material. In addition, the CEI layer also has excellent ionic conductivity and can serve as a high-speed lithium ion conduction channel to accelerate the embedding and deintercalation process of lithium ions in the positive electrode material. Through the above-mentioned synergistic effect, the cycle stability of the lithium-ion battery at high voltage is significantly improved, the service life of the lithium-ion battery is extended, and an effective solution is provided for the performance improvement of the lithium-ion battery under high voltage conditions.

[0155] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. An electrolyte additive, characterized in that The invention comprises a trifluorotoluene compound and N-(4-aminophenyl)maleimide, and the mass ratio of the two is (1-35):(1-35); The trifluorotoluene compound has a structure shown in formula (I): wherein n is any integer from 0 to 5, and R is selected from substituted or unsubstituted C1-C 10 Alkyl, substituted or unsubstituted C2-C 10 Alkenyl, substituted or unsubstituted C2-C 10 Alkynyl, halogen, substituted or unsubstituted C1-C 10 Carboxyl, substituted or unsubstituted C1-C 10 of cyano.

2. The electrolyte additive according to claim 1, characterized in that Said n is 1 or 2, and said R is selected from substituted or unsubstituted C1-C4 alkyl, substituted or unsubstituted C2-C4 alkenyl, substituted or unsubstituted C2-C4 alkynyl, halogen, substituted or unsubstituted C1-C4 carboxyl, substituted or unsubstituted C1-C4 cyano.

3. The electrolyte additive according to claim 1, characterized in that R is selected from *CH3, *CH2-CH3, *CH2-CH2-CH3, *CH-(CH3)2, *CH2-CH2-CH2-CH3, *CH2-CH-(CH3)2, *C(CH3)3, *F, *CF3, *CH2-CF3, *CH2-CH2-CF3, *CH-(CF3)2, *CH2-CH2-CH2-CF3, *CH2-CH-(CF3)2, *C(CF3)3, *CF2-CF3, *CF2 -CF2-CF3, *CF2-CF2-CF2-CF3, *CH=CH2, *CH=CH-CH3, *CH2-CH=CH2, *CH2-CH=CH-CH3, *CH=CH-CF3, *CF2-CH =CH2, *CH=CH-CH2-CF3, *C≡CH, *C≡C-CH3, *CH2-C≡CH, *CH2-C≡C-CH3, *C≡C-CF3, *CF2-C≡CH, *CH2-C≡C-CF3.

4. The electrolyte additive according to claim 1, characterized in that The trifluorotoluene compounds include At least one of .

5. An electrolyte, characterized in that include: An organic solvent, a lithium salt and an electrolyte additive, wherein the electrolyte additive is the electrolyte additive according to any one of claims 1 to 4.

6. The electrolyte according to claim 5, characterized in that Based on the total mass of the electrolyte, the mass content of the trifluorotoluene compound is 0.1% to 3.5%, preferably 0.8% to 2.5%; And / or, based on the total mass of the electrolyte, the mass content of the N-(4-aminophenyl)maleimide is 0.1% to 3.5%, preferably 0.5% to 2.2%; And / or, the mass ratio of the N-(4-aminophenyl)maleimide to the trifluorotoluene compound is (5 to 22): (8～25)。 7. The electrolyte according to claim 5 or 6, characterized in that The organic solvent includes at least one of ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, fluoroethylene carbonate, 1,4-butyrolactone, methyl formate, ethyl acetate, methyl propionate, ethyl propionate, propyl propionate, butyl propionate, and ethyl butyrate.

8. The electrolyte according to claim 5 or 6, characterized in that The lithium salt includes at least one of lithium hexafluorophosphate, lithium difluorobisoxalatophosphate, lithium tetrafluorooxalatophosphate, lithium difluorophosphate, lithium oxalatephosphate, lithium bisoxalatoborate, lithium difluorooxalatoborate, lithium tetrafluoroborate, lithium bisfluorosulfonyl imide salt and lithium bisfluorosulfonyl imide; Preferably, the concentration of the lithium salt is 0.5M to 1.5M.

9. The electrolyte according to claim 5 or 6, characterized in that The electrolyte further includes a functional additive; and Based on the total mass of the electrolyte, the mass content of the functional additive is 0.1 to 5%; Preferably, the functional additive includes at least one of vinylene carbonate, fluoroethylene carbonate, vinyl sulfate, tris(trimethylsilyl)phosphate, 1,3-propane sultone, methylene disulfonate, 1,3,6-hexanetrinitrile, tris(pentafluorophenyl)borane, lithium difluorophosphate, 3-hexylthiophene, hexafluorocyclotriphosphazene, and tris(hexafluoroisopropyl)phosphate; Preferably, based on the total mass of the electrolyte, the total mass content of the electrolyte additive and the functional additive is 0.3-12%.

10. A lithium ion battery, characterized in that: include: A positive electrode sheet, a negative electrode sheet, a separator and an electrolyte; wherein the electrolyte is the electrolyte according to any one of claims 5 to 9.

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