Functional ionic liquid additive, electrolyte and high-voltage lithium-ion battery

Abstract

The present invention belongs to the field of battery technology, and in particular relates to a functional ionic liquid additive, an electrolyte and a high-voltage lithium-ion battery. The structure of the functional ionic liquid additive is composed of cations and anions. Both the anions and the anions have large ionic radii and are easy to dissociate. The smaller radius of Li + It is easier to combine with anions, thus changing the solvation structure of the electrolyte. More functional anions participate in the solvation sheath, which can achieve more anions participating in the solvation configuration coordination at conventional concentrations, thereby ultimately inducing the formation of anion-derived SEI film, which contains more LiF with high Young's modulus, so it is thin and strong, and not easy to break during the cycle. At the same time, the functional groups contained in the cationic groups can alleviate the damage of the free acid in the electrolyte to the positive and negative electrode interface films, further improving the interface stability, thereby intuitively improving the high-temperature cycle performance of the battery.

Description

Technical Field

[0001] The present invention belongs to the technical field of batteries, and in particular relates to a functional ionic liquid additive, an electrolyte and a high-voltage lithium-ion battery. Background Art

[0002] As battery energy density increases, the voltage of cathode materials continues to rise, pushing the electrochemical window of electrolytes to a wider range. As a result, the electrochemical window of conventional electrolytes can no longer meet the requirements of high-voltage materials. For example, the voltage platform of lithium nickel manganese oxide is 4.7V, while conventional electrolytes begin to oxidatively decompose at 4.3V, degrading the cathode interface and failing to fully utilize the advantages of high-voltage materials. Furthermore, conventional electrolytes also present a series of issues such as volatility, flammability, and environmental impact. To overcome these issues, ionic liquids have been introduced as an alternative electrolyte or additive. Due to their low volatility, high chemical stability, and wide electrochemical window, they have attracted considerable attention in the field of high-voltage electrolytes. Furthermore, the formation of a stable SEI film is crucial. An unstable SEI film will break down during battery cycling, consuming a large amount of active lithium. Furthermore, the accumulation of the SEI film increases the energy barrier for ion transport, leading to slow interfacial kinetics. Therefore, it is essential to fine-tune the interfacial reactions and generate a uniform, stable, and robust SEI film. In recent years, anion-derived SEI has shown great advantages in improving the electrochemical performance of batteries due to its high mechanical strength, high ionic conductivity, and fast ion diffusion.

[0003] At present, the commonly used cations in electrolytes are imidazolium cations, piperidinium cations, pyrrole cations, quaternary ammonium cations, etc., and the anions are PF 6- , BF 4- , bis(fluorosulfonyl)imide anion (FSI - ), bis(trifluoromethanesulfonyl imide) anion (TFSI - ) etc. However, existing ionic liquid electrolytes still have some challenges, including high viscosity and less than ideal anion thermal stability and high-voltage stability. Although most ionic liquid anions can form a stable SEI film on the negative electrode surface, the protection of the positive electrode is weaker than that of the negative electrode. In addition, the solvation ability of the anion is the key to the formation of anion-derived SEI film, which is highly dependent on the competitive coordination between solvent-cation and anion-cation. By introducing weakly solvating solvents or anions with strong coordination ability, more anions can be achieved to participate in the solvation configuration coordination at conventional concentrations, thereby changing the solvation structure of the electrolyte.

[0004] Therefore, it is necessary to develop a new type of ionic liquid with low viscosity, high oxidation potential, and not easy to decompose under high pressure. The anion can form an effective passivation film at the positive electrode, effectively reducing the phase change and interfacial side reactions of the positive electrode material under high pressure, thereby meeting the long cycle requirements of high-voltage system batteries. Summary of the Invention

[0005] In view of this, the technical problem to be solved by the present invention is to provide a functional ionic liquid additive, an electrolyte and a high-voltage lithium-ion battery; the structure of the functional ionic liquid additive is composed of cations and anions, both of which have large ionic radius and are easy to dissociate, and the smaller radius Li + It is easier to combine with anions, thus changing the solvation structure of the electrolyte. More functional anions participate in the solvation sheath, which can achieve more anions participating in the solvation configuration coordination at conventional concentrations, thereby ultimately inducing the formation of anion-derived SEI film, which contains more LiF with high Young's modulus, so it is thin and strong, and not easy to break during the cycle. At the same time, the functional groups contained in the cationic groups can alleviate the damage of the free acid in the electrolyte to the positive and negative electrode interface films, further improving the interface stability, thereby intuitively improving the high-temperature cycle performance of the battery.

[0006] The present invention provides a functional ionic liquid additive having a structure shown in Formula B:

[0007]

[0008] wherein m and n are each independently an integer from 1 to 5;

[0009] R1 is selected from hydrogen, C1-C5 alkyl, C2-C5 alkenyl or C2-C5 alkynyl;

[0010] R2 to R5 are each independently selected from hydrogen, a C1 to C5 alkyl group, a C2 to C5 alkenyl group, a C2 to C5 alkynyl group, a halogen atom or a C1 to C5 nitrile group;

[0011] R6 is selected from C1 to C5 alkyl groups.

[0012] Preferably, it has the structure shown in structural formula A:

[0013]

[0014] wherein R1 is selected from hydrogen, C1-C5 alkyl, C2-C5 alkenyl or C2-C5 alkynyl;

[0015] R2 to R5 are each independently selected from hydrogen, a C1-C5 alkyl group, a C2-C5 alkenyl group, a C2-C5 alkynyl group, a halogen atom or a C1-C5 nitrile group.

[0016] Preferably, R1 is selected from hydrogen, methyl, ethyl, vinyl, ethynyl or propynyl;

[0017] R2 to R5 are each independently selected from hydrogen, vinyl, ethynyl, fluorine or acetonitrile.

[0018] Preferably, the functional ionic liquid additive has at least one of the structures shown in formula (I) to formula (VI):

[0019]

[0020] The present invention also provides a method for preparing a functional ionic liquid additive, comprising the following steps:

[0021] reacting the lithium borate salt represented by formula (VII) with the compound represented by formula (VIII) to obtain a functional ionic liquid additive having a structure represented by formula B;

[0022]

[0023] wherein m and n are each independently an integer from 1 to 5;

[0024] R1 is selected from hydrogen, C1-C5 alkyl, C2-C5 alkenyl or C2-C5 alkynyl;

[0025] R2 to R5 are each independently selected from hydrogen, a C1 to C5 alkyl group, a C2 to C5 alkenyl group, a C2 to C5 alkynyl group, a halogen atom or a C1 to C5 nitrile group;

[0026] R6 is selected from C1 to C5 alkyl groups.

[0027] The present invention also provides a non-aqueous electrolyte comprising the above-mentioned functional ionic liquid additive.

[0028] Preferably, the mass of the functional ionic liquid additive is 0.5% to 3% of the mass of the non-aqueous electrolyte.

[0029] Preferably, the non-aqueous electrolyte further comprises a lithium salt, a non-aqueous solvent and an auxiliary electrolyte additive;

[0030] The mass of the lithium salt is 14% to 16% of the mass of the non-aqueous electrolyte;

[0031] The mass of the non-aqueous solvent is 79% to 81.5% of the mass of the non-aqueous electrolyte;

[0032] The mass of the auxiliary electrolyte additive is 2% to 3.8% of the mass of the non-aqueous electrolyte.

[0033] Preferably, the lithium salt is selected from one or more of lithium hexafluorophosphate, lithium perchlorate, lithium tetrafluoroborate, lithium bis(trifluoromethylsulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium bis(oxalatoborate), lithium difluorooxalatoborate and lithium difluorobis(oxalatophosphate);

[0034] The non-aqueous solvent is selected from organic esters and / or ether solvents; the organic esters are selected from one or more of ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, ethyl formate, ethyl acetate, propyl acetate, propyl propionate, methyl trifluoroethyl carbonate, fluoroethylene carbonate and bis(2,2,2-trifluoroethyl) carbonate; the ether solvents are selected from one or more of dimethyl ether, diethyl ether, methyl ethyl ether, ethylene glycol dimethyl ether, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether and 1H,1H,5H-octafluoropentyl-1,1,2,2-tetrafluoroethyl ether;

[0035] The auxiliary electrolyte additive is selected from one or more of unsaturated cyclic carbonate compounds, fluorinated carbonate compounds, sulfate compounds, sulfonate compounds, sulfonimide compounds, phosphate compounds, silane compounds, trimethylsilyl ester compounds, isocyanate compounds, nitrile compounds and lithium salt additives.

[0036] The present invention also provides a high-voltage lithium-ion battery comprising the above-mentioned non-aqueous electrolyte.

[0037] Compared with the prior art, the present invention has the following beneficial effects:

[0038] (1) The novel functional ionic liquid compound proposed in the present invention is used as an electrolyte additive in lithium-ion batteries and has the advantages of low vapor pressure and wide electrochemical window of ionic liquids. At the same time, compared with traditional pyrrole ionic liquids, the anion and cation molecular structure of this ionic liquid is relatively small, the intermolecular force is weak, and the viscosity is low. In addition, the introduction of trimethylsilane into the pyrrole cation increases the polarity of the ionic liquid, reduces the intermolecular force, and further reduces the viscosity of the ionic liquid.

[0039] (2) The novel functional ionic liquid compound proposed in the present invention has a structure in which both anions and cations have large ionic radii, resulting in weak complexing ability and easy dissociation. The smaller radius of Li+ makes it easier for anions to bind to anions, thereby changing the solvation structure of the electrolyte. More functional anions participate in the solvation sheath, enabling more anions to participate in solvation configuration coordination at conventional concentrations, thereby forming an anion-derived high-stability SEI film. At the same time, the special functional groups contained in the anion and cation structures can also play a role in scavenging free acids in the electrolyte and complexing and stabilizing high-valent transition metals, thereby further improving the electrochemical performance of high-voltage lithium-ion batteries. DETAILED DESCRIPTION

[0040] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0041] The present invention provides a functional ionic liquid additive, characterized in that it has a structure shown in Formula B:

[0042]

[0043] Here, m and n are each independently an integer of 1 to 5, preferably an integer of 1 to 4, more preferably an integer of 1 to 3, and most preferably 1 or 2.

[0044] R1 is hydrogen, C1-C5 alkyl, C2-C5 alkenyl or C2-C5 alkynyl, preferably hydrogen, C1-C3 alkyl, C2-C3 alkenyl or C2-C3 alkynyl, more preferably hydrogen, methyl, ethyl, vinyl, ethynyl or propynyl.

[0045] R2 to R5 are each independently hydrogen, C1 to C5 alkyl, C2 to C5 alkenyl, C2 to C5 alkynyl, halogen atom or C1 to C5 nitrile group, preferably hydrogen, C1 to C4 alkyl, C2 to C4 alkenyl, C2 to C4 alkynyl, halogen atom or C1 to C4 nitrile group, more preferably hydrogen, C1 to C3 alkyl, C2 to C3 alkenyl, C2 to C3 alkynyl, halogen atom or C1 to C3 nitrile group, further preferably hydrogen, vinyl, ethynyl, fluorine atom or acetonitrile group.

[0046] Further preferably, at least one of R1, R2 to R5 is an unsaturated group or a halogen atom; the halogen atom is any halogen atom well known to those skilled in the art without any particular limitation, and specifically can be fluorine, chlorine or bromine, more preferably a fluorine atom.

[0047] R6 is a C1-C5 alkyl group, preferably a C1-C4 alkyl group, more preferably a C1-C3 alkyl group, and even more preferably a methyl group or an ethyl group.

[0048] In a specific embodiment provided by the present invention, the functional ionic liquid additive has a structure shown in structural formula A:

[0049]

[0050] Here, m and n are each independently an integer of 1 to 5, preferably an integer of 1 to 4, more preferably an integer of 1 to 3, and most preferably 1 or 2.

[0051] R1 is hydrogen, C1-C5 alkyl, C2-C5 alkenyl or C2-C5 alkynyl, preferably hydrogen, C1-C3 alkyl, C2-C3 alkenyl or C2-C3 alkynyl, more preferably hydrogen, methyl, ethyl, vinyl, ethynyl or propynyl.

[0052] R2 to R5 are each independently hydrogen, C1 to C5 alkyl, C2 to C5 alkenyl, C2 to C5 alkynyl, halogen atom or C1 to C5 nitrile group, preferably hydrogen, C1 to C4 alkyl, C2 to C4 alkenyl, C2 to C4 alkynyl, halogen atom or C1 to C4 nitrile group, more preferably hydrogen, C1 to C3 alkyl, C2 to C3 alkenyl, C2 to C3 alkynyl, halogen atom or C1 to C3 nitrile group, further preferably hydrogen, vinyl, ethynyl, fluorine atom or acetonitrile group.

[0053] Further preferably, at least one of R1, R2 to R5 is an unsaturated group or a halogen atom; the halogen atom is any halogen atom well known to those skilled in the art without any particular limitation, and specifically can be fluorine, chlorine or bromine, more preferably a fluorine atom.

[0054] R6 is a C1-C5 alkyl group, preferably a C1-C4 alkyl group, more preferably a C1-C3 alkyl group, and even more preferably a methyl group or an ethyl group.

[0055] In another specific embodiment provided by the present invention, the functional ionic liquid additive has at least one of the structures shown in Formula (I) to Formula (VI):

[0056]

[0057] The structure of the functional ionic liquid additive provided by the present invention is composed of cations and anions. Both cations and anions have large ionic radii, so their complexing ability is weak and they are easy to dissociate. + It is easier to combine with anions, thus changing the solvation structure of the electrolyte. More functional anions participate in the solvation sheath, which can achieve more anions participating in the solvation configuration coordination at normal concentrations, thus forming a highly stable anion-derived SEI film. At the same time, the special functional groups contained in the anion and cation structures can also play a role in scavenging free acids in the electrolyte and complexing and stabilizing high-valent transition metals, thereby further improving the electrochemical performance of high-voltage lithium-ion batteries.

[0058] The present invention also provides a method for preparing a functional ionic liquid additive, comprising the following steps: reacting a lithium borate salt represented by formula (VII) with a compound represented by formula (VIII) to obtain a functional ionic liquid additive having a structure represented by formula B;

[0059]

[0060]

[0061] wherein m and n are each independently an integer of 1 to 5; R1 is hydrogen, a C1 to C5 alkyl group, a C2 to C5 alkenyl group or a C2 to C5 alkynyl group; R2 to R5 are each independently hydrogen, a C1 to C5 alkyl group, a C2 to C5 alkenyl group, a C2 to C5 alkynyl group, a halogen atom or a C1 to C5 nitrile group; and R6 is a C1 to C5 alkyl group.

[0062] The present invention has no particular limitation on the sources of all raw materials, which may be commercially available or homemade. The m, n, R1, R2 to R5 and R6 are the same as those described above and will not be repeated here.

[0063] According to the present invention, the lithium borate salt represented by formula (VII) is preferably prepared according to the following method: reacting the compound represented by formula (IX) with lithium tetrafluoroborate to obtain the lithium borate salt represented by formula (VII); the molar ratio of the compound represented by formula (IX) to lithium tetrafluoroborate is preferably 2 to 2.5:1, more preferably 2.2:1; the reaction temperature is preferably 50°C to 70°C, more preferably 55°C to 65°C, and even more preferably 60°C; the reaction time is preferably 6 to 8 hours.

[0064]

[0065] In a specific embodiment provided by the present invention, the compound represented by formula (IX) is reacted with lithium tetrafluoroborate preferably in a protective atmosphere; the protective atmosphere is preferably nitrogen.

[0066] In a specific embodiment provided by the present invention, the compound represented by formula (IX) reacts with lithium tetrafluoroborate in the presence of silicon tetrachloride; the molar ratio of the compound represented by formula (IX) to silicon tetrachloride is preferably 1:0.5-0.8, more preferably 1:0.6-0.7; the reaction is preferably carried out in an organic solvent; the organic solvent is an organic solvent well known to those skilled in the art and is not particularly limited. In the present invention, ultra-dry dichloromethane is preferred.

[0067] In a specific embodiment provided by the present invention, lithium tetrafluoroborate, silicon tetrachloride and an organic solvent are preferably first mixed and heated, and then an organic solution containing the compound represented by formula (IX) is added dropwise. After the addition is complete, the heating reaction is continued to obtain a lithium borate salt represented by formula (VII); the temperature of the mixed heating is preferably 50°C to 70°C, more preferably 55°C to 65°C, and more preferably 60°C; the concentration of the compound represented by formula (IX) in the organic solution containing the compound represented by formula (IX) is preferably 3 to 5 mol / L, more preferably 4 to 5 mol / L, and more preferably 4.4 to 4.5 mol / L; the organic solution containing the compound represented by formula (IX) is preferably added dropwise within 1 hour; the temperature of the heating reaction is preferably 50°C to 70°C, more preferably 55°C to 65°C, and more preferably 60°C; the heating reaction time is preferably 6 to 8 hours, and more preferably 7 hours.

[0068] After the reaction is completed, it is preferably cooled to room temperature, saturated sodium bicarbonate solution and water are added, and then extracted with an organic solvent. The organic layer is collected, washed with saturated brine and dried with a desiccant, and then concentrated under reduced pressure. The residue is washed with a mixed solution of dichloromethane and petroleum ether, and dried to obtain a lithium borate salt represented by formula (VII); the organic solvent is preferably dichloromethane; the volume ratio of dichloromethane to petroleum ether in the mixed solution of dichloromethane and petroleum ether is preferably (1-2): (9-8), more preferably 1:9.

[0069] According to the present invention, the compound represented by formula (VIII) is preferably prepared according to the following method: the compound represented by formula (X) is reacted with the compound represented by formula (XI) to obtain the compound represented by formula (VIII); the molar ratio of the compound represented by formula (X) to the compound represented by formula (XI) is preferably 1:(1-1.3), more preferably 1:1.1; the reaction temperature is preferably 70°C to 90°C, more preferably 75°C to 85°C, and even more preferably 80°C; the reaction time is preferably 20-30h, more preferably 24h.

[0070]

[0071] In a specific embodiment provided by the present invention, the compound represented by formula (X) and the compound represented by formula (XI) are preferably reacted in a protective atmosphere; the protective atmosphere is preferably nitrogen.

[0072] In a specific embodiment provided by the present invention, the compound represented by formula (X) and the compound represented by formula (XI) are preferably reacted in an organic solvent; the organic solvent is an organic solvent well known to those skilled in the art and is not particularly limited. In the present invention, N,N-dimethylformamide (DMF) is preferred.

[0073] After the reaction is completed, the solvent is preferably removed, and the residue is washed with anhydrous ether and then dried to obtain the compound represented by formula (VIII).

[0074] The lithium borate salt represented by formula (VII) is reacted with the compound represented by formula (VIII); the molar ratio of the lithium borate salt represented by formula (VII) to the compound represented by formula (VIII) is preferably 1:1; the reaction is preferably carried out in water, more preferably in deionized water; the reaction is preferably carried out under stirring conditions; the reaction time is preferably 2 to 4 hours, more preferably 2.5 to 3.5 hours, and more preferably 3 hours.

[0075] After the reaction is completed, the solvent is preferably removed, washed with dichloromethane, and concentrated and dried to obtain a functional ionic liquid additive having a structure represented by Formula B; the method for removing the solvent is a method well known to those skilled in the art and is not particularly limited. In the present invention, it is preferably concentrated under reduced pressure; the number of dichloromethane washings is preferably 2 to 4 times, more preferably 3 times.

[0076] In a specific embodiment provided by the present invention, the functional ionic liquid additive is synthesized according to the following route:

[0077]

[0078] The present invention also provides a non-aqueous electrolyte comprising the above-mentioned functional ionic liquid additive.

[0079] According to the present invention, the mass of the ionic liquid additive is preferably 0.1% to 0.3% of the mass of the non-aqueous electrolyte, more preferably 0.5% to 3%, more preferably 1% to 3%, more preferably 1.5% to 2.5%, and most preferably 2%.

[0080] According to the present invention, the non-aqueous electrolyte preferably further includes a lithium salt; the lithium salt is any lithium salt well known to those skilled in the art and is not particularly limited. In the present invention, it is preferably one or more of lithium hexafluorophosphate (LiPF6), lithium perchlorate (LiClO4), lithium tetrafluoroborate (LiBF4), lithium bistrifluoromethylsulfonyl imide (LiTFSI), lithium bisfluorosulfonyl imide (LiFSI), lithium bisoxalatoborate (LiBOB), lithium difluorooxalatoborate (LiODFB) and lithium difluorobisoxalatophosphate (LiDODFP); the mass of the lithium salt is preferably 14% to 16% of the mass of the non-aqueous electrolyte.

[0081] According to the present invention, the non-aqueous electrolyte preferably further includes a non-aqueous solvent; the non-aqueous solvent is any non-aqueous solvent well known to those skilled in the art and is not particularly limited. In the present invention, it is preferably an organic ester and / or ether solvent; the organic ester is preferably ethylene carbonate, propylene carbonate (PC), butylene carbonate, dimethyl carbonate (DMC), diethyl carbonate, dipropyl carbonate, ethyl methyl carbonate (EMC), methyl propyl carbonate, ethyl propyl carbonate, ethyl formate, ethyl acetate, propyl acetate, propyl propionate, methyl trifluoroethyl carbonate (FEMC), fluoroethylene carbonate (FEC) and bis(2,2,2-trifluoroethyl) carbonate (TFEC) One or more; the ether solvent is preferably dimethyl ether, diethyl ether, methyl ethyl ether, ethylene glycol dimethyl ether, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether and 1H,1H,5H- One or more of octafluoropentyl-1,1,2,2-tetrafluoroethyl ether; in the embodiments provided by the present invention, propylene carbonate (PC), fluoroethylene carbonate (FEC), methyl trifluoroethyl carbonate (FEMC), dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC) are specifically used as non-aqueous solvents for illustration; the mass ratio of propylene carbonate (PC), fluoroethylene carbonate (FEC), methyl trifluoroethyl carbonate (FEMC), dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC) is preferably 5: (5-15): (5-15): (30-50): (30-40), more preferably 5: (5-15): (5-15): (35-45): (30-40), and further preferably 5: 10: 10: 40: 35; the mass of the non-aqueous solvent is preferably 79% to 81.5% of the mass of the non-aqueous electrolyte.

[0082] According to the present invention, the non-aqueous electrolyte preferably further includes an auxiliary electrolyte additive; the auxiliary electrolyte additive is preferably one or more of unsaturated cyclic carbonate compounds, fluorocarbonate compounds, sulfate compounds, sulfonate compounds, sulfonimide compounds, phosphate compounds, silane compounds, trimethylsilyl ester compounds, isocyanate compounds, lithium salt additives and nitrile compounds; the unsaturated cyclic carbonate compound is preferably vinylene carbonate (VC) and / or vinyl ethylene carbonate (VEC); The fluorocarbonate compound is preferably fluoroethylene carbonate (FEC); the sulfate compound is preferably one or more of vinyl sulfate, vinyl bissulfate, propylene sulfate and propylene bissulfate; the sulfonate compound is preferably one or more of 1,3-propane sultone, 1,3-propylene sultone, 1,4-butane sultone, 2,4-butane sultone, phenyl methanesulfonate and methylene methanedisulfonate; the sulfonimide compound is preferably N-phenylbis(trifluoromethanesulfonyl)imide; the phosphate compound is preferably trifluoromethanesulfonyl imide. One or more of allyl phosphate, tris(trimethylsilyl)phosphate, trimethyl phosphite, triphenyl phosphite, tetramethylmethylene diphosphate and propargyl phosphate; the silane compound is preferably (2-allylphenoxy)trimethylsilane; the trimethylsilyl ester compound is preferably tris(trimethylsilyl)borate; the isocyanate compound is preferably one or more of 1,3,5-triallyl isocyanurate, isocyanoethyl methacrylate, hexamethylene diisocyanate, p-phenylene diisocyanate and 2,4-toluene diisocyanate; The lithium salt additive is any lithium salt additive well known to those skilled in the art and is not particularly limited. In the present invention, it is preferably one or more of lithium difluorodioxalatophosphate (LiDODFP), lithium tetrafluorophosphate oxalate, lithium tetrafluorooxalatoborate phosphate, and lithium difluorophosphate; the nitrile compound is preferably one or more of adiponitrile, succinonitrile, glutaronitrile, 1,3,6-hexanetrinitrile, and 1,2-bis(cyanoethoxy)ethane; the mass of the auxiliary electrolyte additive is preferably 2% to 5% of the mass of the non-aqueous electrolyte, more preferably 2% to 3.8%.

[0083] The present invention also provides a high-voltage lithium-ion battery and the above-mentioned non-aqueous electrolyte.

[0084] Specifically, the high-voltage lithium-ion battery includes a positive electrode, a separator, a negative electrode and the above-mentioned non-aqueous electrolyte.

[0085] More specifically, the positive electrode includes a positive electrode active material; the positive electrode active material is preferably one or more of lithium cobalt oxide, lithium manganese oxide, ternary nickel cobalt manganese lithium, lithium nickel manganese oxide, lithium iron phosphate and lithium manganese iron phosphate, more preferably lithium nickel manganese oxide.

[0086] More specifically, the negative electrode includes a negative electrode active material; the negative electrode active material is preferably one or more of artificial graphite, natural graphite, lithium titanate, metallic lithium, silicon-carbon composite material and silicon oxide, more preferably artificial graphite.

[0087] More specifically, the diaphragm is preferably polypropylene, polyethylene diaphragm, or polyethylene diaphragm coated with aluminum oxide on one side, more preferably polyethylene diaphragm coated with aluminum oxide on one side.

[0088] The lithium ion battery made with the non-aqueous electrolyte of the present invention has better electrochemical performance, specifically, the electrochemical performance of the prepared lithium nickel manganese oxide lithium ion battery in the voltage range of 3.0 to 4.8V at room temperature and high temperature is greatly improved.

[0089] To further illustrate the present invention, a functional ionic liquid additive, an electrolyte, and a high-voltage lithium-ion battery provided by the present invention are described in detail below with reference to examples.

[0090] The reagents used in the following examples are all commercially available.

[0091] Example 1

[0092] Preparation of compound (I), the specific steps are as follows:

[0093]

[0094] Under nitrogen, add 200 mL of ultra-dry dichloromethane to a clean, dry 500 mL three-necked flask equipped with a magnetic rotor, then add lithium tetrafluoroborate (9.40 g, 100.00 mmol) and silicon tetrachloride (11.20 g, 66.67 mmol). Then, start stirring and heating. After the system temperature reaches the set temperature of 60°C, slowly add 50 mL of ultra-dry dichloromethane solution containing 3-hydroxypropionitrile (15.63 g, 220.00 mmol) to the reaction system through a constant pressure dropping funnel. The dropwise addition is controlled within 1 hour. The reaction system is then heated and stirred for 7 hours. After the reaction was completed, the mixture was cooled to room temperature and saturated sodium bicarbonate solution (150 mL) was added to the reaction mixture. 100 mL of deionized water was then added, and the mixed solution was extracted three times with 100 mL of dichloromethane. The organic layers were collected and combined, washed with saturated saline solution, dried over anhydrous sodium sulfate, and concentrated under reduced pressure. The residue was washed three times with 50 mL of a dichloromethane / petroleum ether mixture (volume ratio 10:90) and dried to obtain the desired product, lithium difluorodicyanoethoxyborate, with a yield of 82.2%. HRMS (m / z): calcd. for C6H8O2N2F2B - :189.07,found189.18.

[0095]

[0096] Under nitrogen, 100 mL of ultra-dry N,N-dimethylformamide (DMF) was added to a clean, dry 250 mL three-necked flask equipped with a magnetic rotor, followed by N-vinylpyrrolidine (9.71 g, 100.00 mmol) and chloromethyltrimethylsilane (13.42 g, 110 mmol). Stirring and heating were then initiated, and the reaction was incubated at 80°C for 24 h. After completion of the reaction, the solvent was removed by distillation under reduced pressure, and the product was washed with 100 mL of anhydrous ether and concentrated under reduced pressure to remove the solvent, affording Intermediate 1 with a yield of 82.5%. Intermediate 1 (10.96 g, 50.00 mmol), lithium difluorodicyanoethoxyborate (9.80 g, 50.00 mmol), and 100 mL of deionized water were then added to a clean, dry 250 mL three-necked flask equipped with a magnetic rotor. The reaction was stirred for 3 h before stopping. The solvent was removed by distillation under reduced pressure, and then washed three times with 50 mL of dichloromethane. Finally, the target ionic liquid compound (I) was obtained after concentration and drying with a yield of 76.4%. HRMS (m / z): calcd.for C 16 H 30 O2N3F2BSi:373.22, found 373.31.

[0097] Prepare the electrolyte 1 sample as follows:

[0098] In an argon glove box with a water and oxygen content of ≤0.1ppm, propylene carbonate (PC), fluoroethylene carbonate (FEC), methyl trifluoroethyl carbonate (FEMC), dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC) were uniformly mixed in a mass ratio of 5:10:10:40:35 to obtain an organic solvent. Subsequently, lithium salts LiPF6 and lithium difluorobis(oxaloyl)phosphate (LiDODFP) were slowly added to the organic solvent. After complete dissolution, 1,3-propane sultone (PS), vinyl sulfate (DTD) and ionic liquid compound (I) were added, and the mixture was stirred evenly to obtain electrolyte 1, wherein the amounts of LiPF6, LiDODFP, organic solvent, PS, DTD and ionic liquid compound (I) used were 10%, 5%, 80%, 2%, 1% and 2% of the total mass of the electrolyte, respectively.

[0099] Prepare the experimental battery 1 sample, the specific steps are as follows:

[0100] Preparation of positive electrode sheet: the positive electrode material lithium nickel manganese oxide LiNi 0.5 Mn 1.5O4 (LNMO), conductive agent carbon black (SuperP), carbon nanotubes (CNT, NMP solution with a content of 5% by mass) and binder polyvinylidene fluoride (PVDF, NMP solution with a content of 5% by mass) were weighed and mixed in a mass ratio of 97:0.7:0.8:1.5. After mixing, an appropriate amount of NMP was added to control the theoretical solid content to 65%. A planetary homogenizer was used to homogenize the positive electrode slurry, and the positive electrode slurry was evenly coated on a 12 μm thick aluminum foil with a double-sided coating surface density of 350 g / m 2 , compacted density is 3.0g / cm 3 After drying, rolling and cutting, 50mm×70mm positive electrode sheets are obtained.

[0101] Preparation of diaphragm: A polyethylene diaphragm coated with aluminum oxide on one side was used as the isolation membrane and was placed in a drying room with a dew point of -35°C for 72 hours before use.

[0102] Preparation of negative electrode sheet: artificial graphite (capacity 355mAh g) -1 ), conductive agent SuperP, thickener sodium carboxymethyl cellulose (CMC, deionized water solution with a solid content of 1.5%), and binder styrene-butadiene rubber (SBR, deionized water solution with a solid content of 48%) were mixed in a mass ratio of 95:1:1.5:2.5. After mixing, deionized water was added to control the theoretical solid content to 52%. A planetary homogenizer was used to homogenize the negative electrode slurry, and the negative electrode slurry was evenly coated on a copper foil with a thickness of 6 μm. After drying, rolling, and double-sided coating, the surface density was 126 g / m 2 , compacted density is 1.65g / cm 3 After cutting, a 52mm×72mm negative electrode sheet was obtained. The N / P ratio of the positive and negative electrodes was 1.1.

[0103] Preparation of battery: The battery was made in a dry room with an ambient dew point of ≤-35°C. The separator was folded in a Z shape, and the positive and negative electrodes were placed on each side. There were 18 layers of positive electrode sheets and 19 layers of negative electrode sheets. The positive electrode, separator, and negative electrode were aligned and stacked in order. The separator was coated with alumina to face the positive electrode to obtain an electrode group. The electrode group was fixed with polyimide tape and then the tabs were welded. The battery was then placed in an aluminum-plastic film and vacuum-baked at 90°C for 12 hours. After cooling, the electrolyte 1 prepared above was injected. Finally, the battery was vacuum-packaged, soaked at 45°C, hot-pressed at 45°C (pressure coefficient 6 kg / cm 2 After high-temperature aging at 45°C, secondary sealing, and capacity separation, an experimental battery 1 with a capacity of approximately 2.5Ah was obtained. The formation conditions were: charging to 4.0V at 0.02C, stabilizing for 5 minutes, then charging to 4.8V at 0.05C, aging at 45°C for 24 hours, secondary sealing, and capacity separation at a rate of 0.1C.

[0104] Example 2

[0105] Preparation of compound (II), the specific steps are as follows:

[0106]

[0107] Under nitrogen, 100 mL of ultra-dry N,N-dimethylformamide (DMF) was added to a clean, dry 250 mL three-necked flask equipped with a magnetic rotor, followed by N-propynylpyrrolidine (10.91 g, 100.00 mmol) and chloromethyltrimethylsilane (13.42 g, 110 mmol). Stirring and heating were then initiated, and the reaction was incubated at 80°C for 24 h. After completion of the reaction, the solvent was removed by distillation under reduced pressure, and the product was washed with 100 mL of anhydrous ether and concentrated under reduced pressure to obtain intermediate 2 with a yield of 80.7%. Subsequently, intermediate 2 (11.56 g, 50.00 mmol), lithium difluorodicyanoethoxyborate (9.80 g, 50.00 mmol), and 100 mL of deionized water were added to a clean, dry 250 mL three-necked flask equipped with a magnetic rotor. The reaction was stirred for 3 h before stopping. The solvent was removed by distillation under reduced pressure, and then washed three times with 50 mL of dichloromethane. Finally, the product was concentrated and dried to obtain the target ionic liquid compound (II) with a yield of 75.3%. HRMS (m / z): calcd.for C 17 H 30 O2N3F2BSi:385.22, found 385.14.

[0108] Electrolyte 2 and experimental battery 2 were prepared according to the method of Example 1, except that the functional ionic liquid additive added to electrolyte 2 was compound (II), wherein the usage amounts of LiPF6, LiDODFP, organic solvent, PS, DTD, and ionic liquid compound (II) were 10%, 5%, 80%, 2%, 1%, and 2% of the total mass of the electrolyte, respectively.

[0109] Example 3

[0110] Preparation of compound (III), the specific steps are as follows:

[0111]

[0112] Under nitrogen, 100 mL of ultra-dry N,N-dimethylformamide (DMF) was added to a clean, dry 250 mL three-necked flask equipped with a magnetic rotor, followed by 1-methyl-3-vinylpyrrolidine (11.11 g, 100.00 mmol) and chloromethyltrimethylsilane (13.42 g, 110 mmol). Stirring and heating were then initiated, and the reaction was incubated at 80°C for 24 h. After completion of the reaction, the solvent was removed by distillation under reduced pressure, and the product was washed with 100 mL of anhydrous ether and concentrated under reduced pressure to obtain intermediate 3 with a yield of 83.8%. Subsequently, intermediate 2 (11.66 g, 50.00 mmol), lithium difluorodicyanoethoxyborate (9.80 g, 50.00 mmol), and 100 mL of deionized water were added to a clean, dry 250 mL three-necked flask equipped with a magnetic rotor. The reaction was stirred for 3 h before stopping. The solvent was removed by distillation under reduced pressure, and then washed three times with 50 mL of dichloromethane. Finally, the target ionic liquid compound (III) was obtained after concentration and drying with a yield of 77.1%. HRMS (m / z): calcd.for C 17 H 32 O2N3F2BSi:387.23,found387.29.

[0113] Electrolyte 3 and experimental battery 3 were prepared according to the method of Example 1, except that the solvent in electrolyte 3 was propylene carbonate (PC), fluoroethylene carbonate (FEC), bis(2,2,2-trifluoroethyl) carbonate (TFEC), ethyl methyl carbonate (EMC) and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (HFE) in a mass ratio of 5:10:10:40:35, and the functional ionic liquid additive added was compound (III), wherein the usage amounts of LiPF6, LiDODFP, organic solvent, PS, DTD and ionic liquid compound (III) were 10%, 6%, 80%, 1%, 1% and 2% of the total mass of the electrolyte, respectively.

[0114] Example 4

[0115] Preparation of compound (IV), the specific steps are as follows:

[0116]

[0117] Under nitrogen, 100 mL of ultra-dry N,N-dimethylformamide (DMF) was added to a clean, dry 250 mL three-necked flask equipped with a magnetic rotor, followed by 3-ethynyl-1-methylpyrrolidine (10.91 g, 100.00 mmol) and chloromethyltrimethylsilane (13.42 g, 110 mmol). Stirring and heating were then initiated, and the reaction was incubated at 80°C for 24 h. After completion of the reaction, the solvent was removed by distillation under reduced pressure, and the product was washed with 100 mL of anhydrous ether and concentrated under reduced pressure to obtain intermediate 4 with a yield of 81.9%. Subsequently, intermediate 4 (11.56 g, 50.00 mmol), lithium difluorodicyanoethoxyborate (9.80 g, 50.00 mmol), and 100 mL of deionized water were added to a clean, dry 250 mL three-necked flask equipped with a magnetic rotor. The reaction was stirred for 3 h before stopping. The solvent was removed by distillation under reduced pressure, and then washed three times with 50 mL of dichloromethane. Finally, the product was concentrated and dried to obtain the target ionic liquid compound (IV) with a yield of 76.9%. HRMS (m / z): calcd.for C 17 H 30 O2N3F2BSi:385.22,found385.31.

[0118] Electrolyte 4 and experimental battery 4 were prepared according to the method of Example 1, except that the lithium salts added to electrolyte 4 were LiPF6 and lithium tetrafluoroborate (LiBF4), and the additives were PS, tris(trimethylsilyl) phosphate (TMSP) and ionic liquid compound (IV), wherein the amounts of LiPF6, LiBF4, organic solvent, PS, TMSP and ionic liquid compound (IV) used were 10%, 4%, 80.7%, 3%, 0.3% and 2% of the total mass of the electrolyte, respectively.

[0119] Example 5

[0120] Preparation of compound (V), the specific steps are as follows:

[0121]

[0122] Under nitrogen, 100 mL of ultra-dry N,N-dimethylformamide (DMF) was added to a clean, dry 250 mL three-necked flask equipped with a magnetic rotor. 1-Methyl-2,5-dicyanopyrrolidine (13.52 g, 100.00 mmol) and chloromethyltrimethylsilane (13.42 g, 110 mmol) were then added. Stirring and heating were then initiated, and the reaction was incubated at 80°C for 24 h. After completion of the reaction, the solvent was removed by distillation under reduced pressure, and the product was washed with 100 mL of anhydrous ether and concentrated under reduced pressure to obtain Intermediate 5 with a yield of 76.2%. Intermediate 5 (12.86 g, 50.00 mmol), lithium difluorodicyanoethoxyborate (9.80 g, 50.00 mmol), and 100 mL of deionized water were then added to a clean, dry 250 mL three-necked flask equipped with a magnetic rotor. The reaction was stirred for 3 h before stopping. The solvent was removed by distillation under reduced pressure, and then washed three times with 50 mL of dichloromethane. Finally, the target ionic liquid compound (V) was obtained after concentration and drying with a yield of 75.7%. HRMS (m / z): calcd.for C 17 H 28 O2N5F2BSi:411.21,found411.35.

[0123] Electrolyte 5 and experimental battery 5 were prepared according to the method of Example 1, except that the lithium salts added to electrolyte 5 were LiPF6 and lithium difluorooxalatoborate (LiODFB), and the additives were PS, DTD, hexamethylene diisocyanate (HDMI) and ionic liquid compound (V), wherein the usage amounts of LiPF6, LiODFB, organic solvent, PS, DTD, HDMI and ionic liquid compound (V) were 10%, 5%, 79.5%, 2%, 1%, 0.5% and 2% of the total mass of the electrolyte, respectively.

[0124] Example 6

[0125] Preparation of compound (VI), the specific steps are as follows:

[0126]

[0127] Under nitrogen, 100 mL of ultra-dry N,N-dimethylformamide (DMF) was added to a clean, dry 250 mL three-necked flask equipped with a magnetic rotor, followed by 1-methyl-3,4-difluoropyrrolidine (12.11 g, 100.00 mmol) and chloromethyltrimethylsilane (13.42 g, 110 mmol). Stirring and heating were then initiated, and the reaction was incubated at 80°C for 24 h. After completion of the reaction, the solvent was removed by distillation under reduced pressure, and the product was washed with 100 mL of anhydrous ether and concentrated under reduced pressure to obtain intermediate 6 with a yield of 75.9%. Subsequently, intermediate 6 (12.16 g, 50.00 mmol), lithium difluorodicyanoethoxyborate (9.80 g, 50.00 mmol), and 100 mL of deionized water were added to a clean, dry 250 mL three-necked flask equipped with a magnetic rotor. The reaction was stirred for 3 h before stopping. The solvent was removed by distillation under reduced pressure, and then washed three times with 50 mL of dichloromethane. Finally, the product was concentrated and dried to obtain the target ionic liquid compound (VI) with a yield of 74.4%. HRMS (m / z): calcd.for C 15 H 28 O2N3F4BSi:397.20,found397.32.

[0128] Electrolyte 6 and experimental battery 6 were prepared according to the method of Example 1, except that the lithium salts added to electrolyte 6 were LiPF6, lithium bis(fluorosulfonyl)imide (LiFSI) and lithium bis(oxalatoborate) (LiBOB), and the additives were PS, DTD, lithium difluorophosphate (LiPO2F2) and ionic liquid compound (VI), wherein the usage amounts of LiPF6, LiFSI, LiBOB, organic solvent, PS, DTD, LiPO2F2 and ionic liquid compound (VI) were 10%, 3%, 2%, 79.2%, 2%, 1%, 0.8% and 2% of the total mass of the electrolyte, respectively.

[0129] Example 7

[0130] Electrolyte 7 and experimental battery 7 were prepared according to the method of Example 1, except that the additives added to electrolyte 7 were PS, succinonitrile (ADN) and ionic liquid compound (VI), wherein the usage amounts of LiPF6, LiDODFP, organic solvent, PS, ADN and ionic liquid compound (VI) were 10%, 5%, 81.5%, 2%, 1% and 0.5% of the total mass of the electrolyte, respectively.

[0131] Example 8

[0132] Electrolyte 8 and experimental battery 8 were prepared according to the method of Example 1, except that the functional ionic liquid additive added to electrolyte 8 was compound (VI), wherein the usage amounts of LiPF6, LiDODFP, organic solvent, PS, DTD, and ionic liquid compound (VI) were 10%, 5%, 79%, 2%, 1%, and 3% of the total mass of the electrolyte, respectively.

[0133] Comparative Example 1

[0134] Electrolyte 9 and experimental battery 9 were prepared according to the method of Example 1, except that the usage amounts of LiPF6, LiDODFP, organic solvent, PS and DTD were 10%, 5%, 82%, 2% and 1% of the total mass of the electrolyte, respectively.

[0135] Comparative Example 2

[0136] An electrolyte 10 and an experimental battery 10 were prepared according to the method of Example 1, except that the additives added to the electrolyte 10 were PS, DTD, and N-methyl-N-butyl-piperidinium-bistrifluoromethylsulfonamide (PP14TFSI), wherein the usage amounts of LiPF6, LiDODFP, organic solvent, PS, DTD, and PP14TFSI were 10%, 5%, 80%, 2%, 1%, and 2% of the total mass of the electrolyte, respectively.

[0137] Comparative Example 3

[0138] An electrolyte 11 and an experimental battery 11 were prepared according to the method of Example 1, except that the additives added to the electrolyte 11 were PS, DTD and 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMIMTFSI), wherein the amounts of LiPF6, LiDODFP, organic solvent, PS, DTD and EMIMTFSI were 10%, 5%, 80%, 2%, 1% and 2% of the total mass of the electrolyte, respectively.

[0139] The electrolyte compositions and contents of Examples 1 to 8 and Comparative Examples 1 to 3 are shown in Table 1.

[0140] The lithium-ion batteries prepared in Examples 1 to 8 and Comparative Examples 1 to 3 were subjected to room temperature cycle performance tests, high temperature cycle tests, and low temperature discharge performance tests, respectively. The results are shown in Table 1, where the test conditions are as follows:

[0141] Battery room temperature cycle test

[0142] The prepared lithium-ion battery was placed in a constant temperature room at an ambient temperature of 25°C, charged at a current of 0.5C and a voltage of 4.8V under constant current and constant voltage until the cutoff current reached 0.05C. It was then discharged at a constant current of 0.5C to a voltage of 3V. This cycle was repeated 500 times, and the capacity retention rate was recorded: capacity retention rate at the nth cycle (%) = (discharge capacity at the nth cycle / discharge capacity at the first cycle) × 100%.

[0143] Battery high temperature cycle test

[0144] Before the test, use an internal resistance tester to measure the internal resistance of the battery, and use the drainage method to measure the battery volume. Then, place the prepared lithium-ion battery in a high and low temperature box at a temperature of 45°C for 2 hours to stabilize the temperature inside and outside the battery. Charge with a constant current and constant voltage at a current of 0.5C and a voltage of 4.8V until the cutoff current is 0.05C, then discharge with a constant current of 0.5C to a voltage of 3V, cycle 500 weeks, and record the capacity retention rate. The capacity retention rate of the nth cycle (%) = (nth cycle discharge capacity / first cycle discharge capacity) × 100%. After the test is completed, use the internal resistance tester to measure the internal resistance of the battery again, and use the drainage method to measure the battery volume.

[0145] DC resistance (DCR) test

[0146] The prepared battery was fully charged after 500 cycles, and then discharged at a constant current of 1C for 30 minutes, adjusting the SOC to 50%. After standing for 2 hours, the voltage value V0 was recorded. Then, the battery was discharged at a constant current of 3C (the actual value is recorded as I0) for 10 seconds, and the voltage value V1 and DCR were recorded. (3C,10s) =(V0-V1) / I0.

[0147] Table 1. Electrolyte compositions and corresponding battery performances of various examples and comparative examples

[0148]

[0149]

[0150]

[0151] From the performance test results of lithium ion batteries prepared using the electrolytes prepared in Examples 1 to 8 and Comparative Examples 1 to 3 in Table 1, it can be seen that the functional ionic liquid provided by the present invention has a larger anion and cation radius than the traditional ionic liquid, which changes the solvation structure of the electrolyte, allowing more anions to participate in the formation of a highly stable SEI film, thereby improving the high-voltage and high-temperature tolerance of the positive and negative electrode interfaces, and greatly improving the high-voltage cycle performance of the battery.

[0152] This is because, compared with Comparative Examples 2 and 3, the functional ionic liquids provided by the present invention in Examples 1 to 6 have relatively small anion and cation molecular structures, weak intermolecular forces, and low viscosity. In addition, the introduction of trimethylsilane into the pyrrole cation increases the polarity of the ionic liquid, reduces the intermolecular forces, further reduces the viscosity of the ionic liquid, and optimizes the SEI film composition, thereby reducing impedance and improving the low-temperature discharge performance of the battery.

[0153] Moreover, compared with Comparative Examples 2 and 3, the special functional groups contained in the anion and cation structures of Examples 1 to 8, namely trimethylsilyl and cyano, can also play the role of removing free acids in the electrolyte, complexing and stabilizing high-valent transition metals, etc., reducing the continuous side reactions during high-voltage cycling, and reducing the DCIR of the battery, thereby further improving the high-temperature electrochemical performance of the high-voltage lithium-ion battery.

[0154] Compared with Examples 6, 7, and 8, the optimal addition of functional ionic liquid is 2%. If the addition amount is too small, the performance improvement will be small. If the addition amount is too large, the membrane impedance will increase, the battery DCIR will increase, and the cycle performance will deteriorate.

[0155] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A functional ionic liquid additive, characterized in that: It has the structure shown in formula B: wherein m and n are each independently an integer from 1 to 5; R1 is selected from hydrogen, C1-C5 alkyl, C2-C5 alkenyl or C2-C5 alkynyl; R2 to R5 are each independently selected from hydrogen, a C1 to C5 alkyl group, a C2 to C5 alkenyl group, a C2 to C5 alkynyl group, a halogen atom or a C1 to C5 nitrile group; R6 is selected from C1 to C5 alkyl groups.

2. The functional ionic liquid additive according to claim 1, characterized in that It has the structure shown in structural formula A: wherein R1 is selected from hydrogen, C1-C5 alkyl, C2-C5 alkenyl or C2-C5 alkynyl; R2 to R5 are each independently selected from hydrogen, a C1-C5 alkyl group, a C2-C5 alkenyl group, a C2-C5 alkynyl group, a halogen atom or a C1-C5 nitrile group.

3. The functional ionic liquid additive according to claim 2, characterized in that Said R1 is selected from hydrogen, methyl, ethyl, vinyl, ethynyl or propynyl; R2 to R5 are each independently selected from hydrogen, vinyl, ethynyl, fluorine or acetonitrile.

4. The functional ionic liquid additive according to claim 1, characterized in that The functional ionic liquid additive has at least one of the structures shown in formula (I) to formula (VI):

5. A method for preparing a functional ionic liquid additive, characterized in that: The following steps are involved: reacting the lithium borate salt represented by formula (VII) with the compound represented by formula (VIII) to obtain a functional ionic liquid additive having a structure represented by formula B; wherein m and n are each independently an integer from 1 to 5; R1 is selected from hydrogen, C1-C5 alkyl, C2-C5 alkenyl or C2-C5 alkynyl; R2 to R5 are each independently selected from hydrogen, a C1 to C5 alkyl group, a C2 to C5 alkenyl group, a C2 to C5 alkynyl group, a halogen atom or a C1 to C5 nitrile group; R6 is selected from C1 to C5 alkyl groups.

6. A non-aqueous electrolyte, characterized in that The invention comprises the functional ionic liquid additive according to any one of claims 1 to 4 or the functional ionic liquid additive prepared by the preparation method according to claim 5.

7. The non-aqueous electrolyte according to claim 6, characterized in that The mass of the functional ionic liquid additive is 0.5% to 3% of the mass of the non-aqueous electrolyte.

8. The non-aqueous electrolyte according to claim 6, characterized in that The non-aqueous electrolyte further comprises a lithium salt, a non-aqueous solvent and an auxiliary electrolyte additive; The mass of the lithium salt is 14% to 16% of the mass of the non-aqueous electrolyte; The mass of the non-aqueous solvent is 79% to 81.5% of the mass of the non-aqueous electrolyte; The mass of the auxiliary electrolyte additive is 2% to 3.8% of the mass of the non-aqueous electrolyte.

9. The non-aqueous electrolyte according to claim 8, characterized in that The lithium salt is selected from one or more of lithium hexafluorophosphate, lithium perchlorate, lithium tetrafluoroborate, lithium bis(trifluoromethylsulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium bis(oxalatoborate), lithium difluorooxalatoborate and lithium difluorobis(oxalatophosphate); The non-aqueous solvent is selected from organic esters and / or ether solvents; the organic esters are selected from one or more of ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, ethyl formate, ethyl acetate, propyl acetate, propyl propionate, methyl trifluoroethyl carbonate, fluoroethylene carbonate and bis(2,2,2-trifluoroethyl) carbonate; the ether solvents are selected from one or more of dimethyl ether, diethyl ether, methyl ethyl ether, ethylene glycol dimethyl ether, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether and 1H,1H,5H-octafluoropentyl-1,1,2,2-tetrafluoroethyl ether; The auxiliary electrolyte additive is selected from one or more of unsaturated cyclic carbonate compounds, fluorinated carbonate compounds, sulfate compounds, sulfonate compounds, sulfonimide compounds, phosphate compounds, silane compounds, trimethylsilyl ester compounds, isocyanate compounds, nitrile compounds and lithium salt additives.

10. A high-voltage lithium-ion battery, characterized in that: The non-aqueous electrolyte comprises the non-aqueous electrolyte according to any one of claims 6 to 9.

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