Preparation method of lithium ion battery electrolyte

Abstract

The invention discloses a preparation method of a lithium ion battery electrolyte, and relates to the technical field of lithium ion battery electrolytes.The preparation method comprises the following steps that S1, single organic solvents, namely diethyl fluoromalonate, fluoroethylene carbonate and dimethyl carbonate are taken and mixed in proportion, and a mixed organic solvent is prepared; s2, preparing a composite lithium salt; and S3, the mixed organic solvent, the composite lithium salt and an additive are taken in proportion and mixed, the lithium ion battery electrolyte is prepared, and the additive is a sulfonate compound and a fluorine-containing sulfonamide compound. According to the invention, by adding the sulfonate compound and the fluorine-containing sulfonamide compound additive, a stable, uniform and thin interfacial film can be formed, the stability of CEI and SEI films can be improved, and the positive and negative electrode materials of the battery can be protected; and the freezing point of the organic solvent is reduced while the ionic conductivity under the high-temperature condition is improved, so that the low-temperature effect of the electrolyte is improved, and the lithium ion battery electrolyte has a wider temperature range.

Description

Technical Field

[0001] The invention relates to the technical field of lithium battery electrolyte, and in particular to a method for preparing a lithium ion battery electrolyte. Background Art

[0002] Electrolyte is one of the key materials of lithium-ion batteries. It has the function of isolating the positive and negative electrodes to prevent battery short circuit and provide lithium ion transmission. The main components of the electrolyte are lithium salt, organic solvent and some functional additives. However, the temperature adaptability of existing electrolytes is poor. When the battery is used under high temperature conditions, the thermal decomposition of its lithium salt is serious, which reduces the high-temperature cycle effect of the battery. When the battery is used in a low temperature environment, the electrolyte is easy to solidify, which reduces the transfer speed of ions and interface charges, thereby reducing the ionic conductivity of the electrolyte.

[0003] The defects of existing lithium battery electrolytes are: The patent document JP2016129106A mainly considers the inhibition of the reaction between Li ions and electrode active materials caused by glycol diester, but does not consider how to improve the applicable temperature range of the electrolyte, thereby improving the high temperature cycle performance of the motor and the ion conductivity under low temperature conditions; The patent document US20130216916A1 mainly considers how to make the solvated polymer in the electrolyte form a continuous network, but does not consider the problem that a single lithium salt dissolves in heat and decomposes to produce corrosive substances, which in turn causes corrosion to the positive and negative electrode materials of the battery; Patent document CN113410518B mainly considers how to reduce the gas production and the impedance of the passivation film, but does not consider how to improve the performance of the electrolyte under low temperature conditions. Summary of the invention

[0004] The object of the present invention is to provide a method for preparing a lithium ion battery electrolyte to solve the problems raised in the above background technology.

[0005] To achieve the above object, the present invention provides the following technical solution: a method for preparing a lithium ion battery electrolyte, comprising the following steps: S1, taking a single type of organic solvent and mixing them in proportion to prepare a mixed organic solvent; S2, preparing composite lithium salt; S3, mixing a mixed organic solvent, a composite lithium salt and an additive in proportion to prepare a lithium-ion battery electrolyte; The additives are sulfonate compounds and fluorine-containing sulfonamide compounds, and the sulfonate compounds include cyclic sulfonate compounds and / or chain sulfonate compounds; The single organic solvent comprises diethyl fluoromalonate, fluoroethylene carbonate and dimethyl carbonate, and the mass ratio of diethyl fluoromalonate, fluoroethylene carbonate and dimethyl carbonate is (4-6):1:(4-6); The sulfonate compound additive is selected from at least one of the following structural formulas: Compound 1 to Compound 6, and the fluorinated sulfonamide compound additive is selected from at least one of the following structural formulas: Compound 7 to Compound 9. Compound 1, Compound 2, Compound 3, Compound 4, Compound 5, Compound 6, Compound 7, Compound 8, Compound 9.

[0006] Preferably, the composite lithium salt comprises lithium hexafluorophosphate, lithium bis(oxalatoborate) and lithium bis(trifluoromethanesulfonyl imide), and the mass ratio of lithium hexafluorophosphate, lithium bis(fluorosulfonyl imide) and lithium bis(trifluoromethanesulfonyl imide) is (1-8):(1-3):(1-3).

[0007] Preferably, the additives also include an overcharge protector, a flame retardant and a neutralizer.

[0008] Preferably, the overcharge protection agent includes one or more of phenylcyclohexane, thiophene and its derivatives and polypyridine complexes.

[0009] Preferably, the flame retardant includes one or more of dimethyl methylphosphonate, pentafluorocyclotriphosphazene and trimethyl phosphate.

[0010] Preferably, the neutralizing agent includes one or more of aluminum oxide, trifluoroethylphosphite, hexafluoromethylamide and cyclopentyl isocyanate.

[0011] Preferably, in S2, the following step is further included: lithium hexafluorophosphate, lithium bis(oxalatoborate) and lithium bis(trifluoromethanesulfonylimide) are mixed with ethylene glycol dimethyl ether solvent in proportion, and a chelating reaction is performed to obtain a composite lithium salt.

[0012] Preferably, in S3, the following steps are further included: in a glove box filled with argon, a solvent is measured in proportion, a composite lithium salt and an additive are weighed, and they are slowly added to the solvent and stirred, and the environmental conditions in the glove box are (H2O< (0.2-0.3) mg / m 3 , O2<(0.4—0.6)mg / m 3), stirring speed is 50-80r / min.

[0013] Compared with the prior art, the present invention has the following beneficial effects: 1. The present invention can form a stable, uniform and thin interface film by adding sulfonate compounds and fluorinated sulfonamide compound additives during the preparation of the electrolyte, and improve the stability of the CEI and SEI films to protect the positive and negative electrode materials of the battery. By using a mixed organic solution to replace single ethylene carbonate or propylene carbonate, the ionic conductivity under high temperature conditions is improved while the freezing point of the organic solvent is reduced, thereby improving the low-temperature effect of the electrolyte, so that the lithium-ion battery electrolyte has a wider temperature range of use.

[0014] 2. The present invention reduces the sensitivity of lithium salt to water and the generation of HF and corrosive substances by using composite lithium salt, thereby avoiding corrosion to the positive and negative electrode materials of the battery, which is beneficial to improving the service life of the lithium-ion battery. In addition, the chelating reaction between ethylene glycol dimethyl ether and lithium salt is used to improve the fusion effect of single lithium salt.

[0015] 3. The present invention uses a mixed organic solvent in the electrolyte preparation process, which is beneficial to reducing the impedance of the electrolyte, facilitating the movement of lithium ions, and passivating the metal negative electrode, thereby inhibiting the production of lithium dendrites and improving ion activity and ion conductivity.

[0016] 4. The present invention adds a neutralizing agent as an additive during the preparation of the electrolyte, utilizes the isocyanate group of cyclopentyl isocyanate and hexafluoromethylamide to reduce the content of water and hydrogen fluoride in the electrolyte, thereby reducing the thermal decomposition of lithium hexafluorophosphate in the composite lithium salt, which is beneficial to improving the stability of the electrolyte, and forms a stable CEI film by oxidizing the neutralizing agent, which is beneficial to improving the interface stability of the electrolyte. DETAILED DESCRIPTION

[0017] The following will be combined with the specific embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments 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 creative work are within the scope of protection of the present invention.

[0018] The present invention discloses a method for preparing a lithium ion battery electrolyte, comprising the following steps: S1, taking a single type of organic solvent and mixing them in proportion to prepare a mixed organic solvent; Furthermore, the single organic solvent includes diethyl fluoromalonate, fluoroethylene carbonate and dimethyl carbonate, and the mass ratio of diethyl fluoromalonate, fluoroethylene carbonate and dimethyl carbonate is (4-6):1:(4-6).

[0019] Furthermore, the electrolyte disclosed in the present invention contains a mixed organic solvent, the freezing point of the electrolyte is lowered by diethyl fluoromalonate, and dimethyl carbonate with low viscosity and low freezing point is added to reduce the viscosity of the electrolyte, so that lithium ions can move forward smoothly under low temperature conditions, thereby improving the low-temperature dynamics of the electrolyte. The addition of fluoroethylene carbonate is beneficial to improving the compactness of SEI, thereby improving the high-temperature interface stability and high-temperature resistance of the electrolyte, which is beneficial to broadening the applicable temperature range of lithium-ion battery electrolytes.

[0020] S2, preparing composite lithium salt; The composite lithium salt includes lithium hexafluorophosphate, lithium bis(oxalatoborate) and lithium bis(trifluoromethanesulfonyl imide), and the mass ratio of lithium hexafluorophosphate, lithium bis(fluorosulfonyl imide) and lithium bis(trifluoromethanesulfonyl imide) is (1-8): (1-3): (1-3); In S2, the following steps are also included: lithium hexafluorophosphate, lithium bis(oxalatoborate) and lithium bis(trifluoromethanesulfonylimide) are mixed with ethylene glycol dimethyl ether solvent in proportion, and a chelating reaction is performed to obtain a composite lithium salt.

[0021] Furthermore, by mixing lithium bis(oxalatoborate) and lithium bis(trifluoromethanesulfonylimide) with lithium hexafluorophosphate, the moisture sensitivity of the composite lithium salt is reduced and the thermal stability is improved, the thermal stability of the electrolyte itself is improved, and the generation of HF is reduced, thereby preventing it from corroding the electrode, which is beneficial to extending the service life of the lithium-ion battery. In addition, by adding lithium bis(trifluoromethanesulfonylimide), inorganic components are introduced into SRI, the SEI thickness is reduced, and the transfer and transportation of lithium ions is beneficial.

[0022] S3, mixing a mixed organic solvent, a composite lithium salt and an additive in proportion to prepare a lithium-ion battery electrolyte; The additives are sulfonate compounds and fluorine-containing sulfonamide compounds, and the sulfonate compounds include cyclic sulfonate compounds and / or chain sulfonate compounds.

[0023] The sulfonate compound additive is selected from at least one of the following structural formulas: Compound 1 to Compound 6, and the fluorinated sulfonamide compound additive is selected from at least one of the following structural formulas: Compound 7 to Compound 9. Compound 1, Compound 2, Compound 3, Compound 4, Compound 5, Compound 6, Compound 7, Compound 8, Compound 9.

[0024] In S3, the following steps are also included: in a glove box filled with argon, a solvent is taken in proportion, a composite lithium salt and an additive are weighed, and they are slowly added to the solvent and stirred. The environmental conditions in the glove box are (H2O< (0.2-0.3) mg / m 3 , O2<(0.4—0.6)mg / m 3 ), stirring speed is 50-80r / min; Additives also include overcharge protectants, flame retardants and neutralizers.

[0025] Further, the overcharge protection agent includes one or more of phenylcyclohexane, thiophene and its derivatives and polypyridine complexes; When the battery charging voltage is too high, the overcharge protection agent alternately enters and exits oxidation reaction and reduction reaction on the surface of the positive electrode and the surface of the negative electrode, forming a closed loop between the positive and negative electrodes in the electrolyte, preventing charge accumulation on the electrode surface, maintaining a stable state of charge on the electrode surface, avoiding damage to the electrode, and thereby extending the service life of the lithium-ion battery.

[0026] Further, the flame retardant includes one or more of dimethyl methylphosphonate, pentafluorocyclotriphosphazene and trimethyl phosphate; Further, the neutralizing agent includes one or more of aluminum oxide, trifluoroethylphosphite, hexafluoromethylamide and cyclopentyl isocyanate.

[0027] Example 1 This embodiment provides a method for preparing a lithium ion battery electrolyte, comprising the following steps: S1, mixing a single organic solvent of diethyl fluoromalonate, fluoroethylene carbonate and dimethyl carbonate, wherein the mass ratio of diethyl fluoromalonate, fluoroethylene carbonate and dimethyl carbonate is 4:1:4; S2. Prepare a composite lithium salt, mix lithium hexafluorophosphate, lithium bis(oxalatoborate) and lithium bis(trifluoromethanesulfonylimide) with ethylene glycol dimethyl ether solvent, perform a chelating reaction, and dry the reaction product under a nitrogen environment to obtain a composite lithium salt, wherein the mass ratio of lithium hexafluorophosphate, lithium bis(oxalatoborate) and lithium bis(trifluoromethanesulfonylimide is 6:1:1, and the volume ratio of the three lithium salt mixture to ethylene glycol dimethyl ether is 1:1; S3, mixing a mixed organic solvent, a composite lithium salt and an additive in proportion, wherein the additive comprises a sulfonate compound and a fluorinated sulfonamide compound, wherein the mass ratio of the sulfonic acid terpene compound to the fluorinated sulfonamide compound is 4:1, and the sulfonate compound is selected from Compound 2 and Compound 3, Compound 2, Compound 3, The mass ratio of compound 2 to compound 3 is 3:1, and the fluorinated sulfonamide compound is compound 7. Compound 7, Sulfonate compounds and fluorinated sulfonamide compound additives are recorded as first-category additives, and the additives also include overcharge protection agents, flame retardants and neutralizers, and the overcharge protection agents, flame retardants and neutralizers are recorded as second-category additives, wherein the overcharge protection agent is phenylcyclohexane, the flame retardant is dimethyl methyl phosphate, the neutralizer includes cyclopentyl isocyanate and hexafluoromethylamide, and the mass ratio of cyclopentyl isocyanate to hexafluoromethylamide is 1:2, and the percentages of organic solvents, composite lithium salts, first-category additives and second-category additives in the electrolyte are 83.5%: 11.8%: 4.1%: 0.6%; S3 also includes the following steps: in a glove box filled with argon, a mixed organic solvent is measured in proportion, a composite lithium salt, a first type additive and a second additive are weighed, and the mixed organic solvent is slowly added and stirred, and the environmental condition in the glove box is H2O<0.22mg / m 3 , O2<0.43mg / m 3 .

[0028] Example 2 This embodiment provides a method for preparing a lithium ion battery electrolyte, comprising the following steps: S1, mixing a single organic solvent of diethyl fluoromalonate, fluoroethylene carbonate and dimethyl carbonate, wherein the mass ratio of diethyl fluoromalonate, fluoroethylene carbonate and dimethyl carbonate is 4:1:4; S2. Prepare a composite lithium salt, mix lithium hexafluorophosphate, lithium bis(oxalatoborate) and lithium bis(trifluoromethanesulfonylimide) with ethylene glycol dimethyl ether solvent, perform a chelating reaction, and dry the reaction product under a nitrogen environment to obtain a composite lithium salt, wherein the mass ratio of lithium hexafluorophosphate, lithium bis(oxalatoborate) and lithium bis(trifluoromethanesulfonylimide is 6:1:1, and the volume ratio of the three lithium salt mixture to ethylene glycol dimethyl ether is 1:1; S3, mixing a mixed organic solvent, a composite lithium salt and an additive in proportion, wherein the additive comprises a sulfonate compound and a fluorinated sulfonamide compound, wherein the mass ratio of the sulfonate compound to the fluorinated sulfonamide compound is 4:1, and the sulfonate compound is compound 1, Compound 1, The fluorinated sulfonamide compound is compound 7, Compound 7, Sulfonate compounds and fluorinated sulfonamide compound additives are recorded as first-category additives, and the additives also include overcharge protection agents, flame retardants and neutralizers, and the overcharge protection agents, flame retardants and neutralizers are recorded as second-category additives, wherein the overcharge protection agent is phenylcyclohexane, the flame retardant is pentafluorocyclotriphosphazene, the neutralizer includes cyclopentyl isocyanate and hexafluoromethylamide, and the mass ratio of cyclopentyl isocyanate to hexafluoromethylamide is 1:2, and the percentages of organic solvents, composite lithium salts, first-category additives and second-category additives in the electrolyte are 83.5%: 11.8%: 4.1%: 0.6%; S3 also includes the following steps: in a glove box filled with argon, a mixed organic solvent is measured in proportion, a composite lithium salt, a first type additive and a second additive are weighed, and the mixed organic solvent is slowly added and stirred, and the environmental condition in the glove box is H2O<0.22mg / m 3 , O2<0.43mg / m 3 .

[0029] Example 3 This embodiment provides a method for preparing a lithium ion battery electrolyte, comprising the following steps: S1, mixing a single organic solvent of diethyl fluoromalonate, fluoroethylene carbonate and dimethyl carbonate, wherein the mass ratio of diethyl fluoromalonate, fluoroethylene carbonate and dimethyl carbonate is 4:1:4; S2. Prepare a composite lithium salt, mix lithium hexafluorophosphate, lithium bis(oxalatoborate) and lithium bis(trifluoromethanesulfonylimide) with ethylene glycol dimethyl ether solvent, perform a chelating reaction, and dry the reaction product under a nitrogen environment to obtain a composite lithium salt, wherein the mass ratio of lithium hexafluorophosphate, lithium bis(oxalatoborate) and lithium bis(trifluoromethanesulfonylimide is 6:1:1, and the volume ratio of the three lithium salt mixture to ethylene glycol dimethyl ether is 1:1; S3, mixing a mixed organic solvent, a composite lithium salt and an additive in proportion, wherein the additive comprises a sulfonate compound and a fluorinated sulfonamide compound, wherein the mass ratio of the sulfonate compound to the fluorinated sulfonamide compound is 4:1, and the sulfonate compound is selected from Compound 2 and Compound 4, Compound 2, Compound 4, The mass ratio of compound 2 to compound 4 is 3:1, and the fluorinated sulfonamide compound is compound 7. Compound 7, Sulfonate compounds and fluorinated sulfonamide compound additives are recorded as first-category additives, and the additives also include overcharge protection agents, flame retardants and neutralizers, and the overcharge protection agents, flame retardants and neutralizers are recorded as second-category additives, wherein the overcharge protection agent is phenylcyclohexane, the flame retardant is dimethyl methyl phosphate, the neutralizer includes cyclopentyl isocyanate and hexafluoromethylamide, and the mass ratio of cyclopentyl isocyanate to hexafluoromethylamide is 1:2, and the percentages of organic solvents, composite lithium salts, first-category additives and second-category additives in the electrolyte are 83.5%: 11.8%: 4.1%: 0.6%; S3 also includes the following steps: in a glove box filled with argon, a mixed organic solvent is measured in proportion, a composite lithium salt, a first type additive and a second additive are weighed, and the mixed organic solvent is slowly added and stirred, and the environmental condition in the glove box is H2O<0.22mg / m 3 , O2<0.43mg / m 3 ; By selecting five-membered cyclic sulfonate compounds as additives, which have a lower LUMO energy level, it is beneficial to form uniform and dense CEI and SEI films during the use of the battery, preventing the electrolyte from reacting with the positive and negative electrode surfaces, which is beneficial to improving the high-temperature cycle performance of the battery. At the same time, the bromide ions in the additives coordinate with the lithium ions in the lithium salt, which is beneficial to inhibit the growth of lithium dendrites, thereby improving the performance of the electrolyte.

[0030] Example 4 This embodiment provides a method for preparing a lithium ion battery electrolyte, comprising the following steps: S1, taking a single organic solvent diethyl fluoromalonate, fluoroethylene carbonate and dimethyl carbonate and mixing them, and the mass ratio of diethyl fluoromalonate, fluoroethylene carbonate and dimethyl carbonate is 5:1:5; S2. Prepare a composite lithium salt, mix lithium hexafluorophosphate, lithium bis(oxalatoborate) and lithium bis(trifluoromethanesulfonylimide) with ethylene glycol dimethyl ether solvent, perform a chelating reaction, and dry the reaction product under a nitrogen environment to obtain a composite lithium salt, wherein the mass ratio of lithium hexafluorophosphate, lithium bis(oxalatoborate) and lithium bis(trifluoromethanesulfonylimide is 6:1:1, and the volume ratio of the three lithium salt mixture to ethylene glycol dimethyl ether is 1.5:1; S3, mixing a mixed organic solvent, a composite lithium salt and an additive in proportion, wherein the additive comprises a sulfonate compound and a fluorinated sulfonamide compound, wherein the mass ratio of the sulfonate compound to the fluorinated sulfonamide compound is 4:1, and the sulfonate compound is selected from Compound 2 and Compound 4, Compound 2, Compound 4, The mass ratio of compound 2 to compound 4 is 3:1, and the fluorinated sulfonamide compound is compound 7. Compound 7, Sulfonate compounds and fluorinated sulfonamide compound additives are recorded as first-category additives, and the additives also include overcharge protection agents, flame retardants and neutralizers, and the overcharge protection agents, flame retardants and neutralizers are recorded as second-category additives, wherein the overcharge protection agent is phenylcyclohexane, the flame retardant is dimethyl methyl phosphate, the neutralizer includes cyclopentyl isocyanate and hexafluoromethylamide, and the mass ratio of cyclopentyl isocyanate to hexafluoromethylamide is 1:2, and the percentages of organic solvents, composite lithium salts, first-category additives and second-category additives in the electrolyte are 83.5%: 11.8%: 4.1%: 0.6%; S3 also includes the following steps: in a glove box filled with argon, a mixed organic solvent is measured in proportion, a composite lithium salt, a first type additive and a second additive are weighed, and the mixed organic solvent is slowly added and stirred, and the environmental condition in the glove box is H2O<0.22mg / m 3 , O2<0.43mg / m 3 .

[0031] Example 5 This embodiment provides a method for preparing a lithium ion battery electrolyte, comprising the following steps: S1, mixing a single organic solvent of diethyl fluoromalonate, fluoroethylene carbonate and dimethyl carbonate, wherein the mass ratio of diethyl fluoromalonate, fluoroethylene carbonate and dimethyl carbonate is 4:1:4; S2. Prepare a composite lithium salt, mix lithium hexafluorophosphate, lithium bis(oxalatoborate) and lithium bis(trifluoromethanesulfonylimide) with ethylene glycol dimethyl ether solvent, perform a chelating reaction, and dry the reaction product under a nitrogen environment to obtain a composite lithium salt, wherein the mass ratio of lithium hexafluorophosphate, lithium bis(oxalatoborate) and lithium bis(trifluoromethanesulfonylimide is 6:1:1, and the volume ratio of the three lithium salt mixture to ethylene glycol dimethyl ether is 1:1; S3, mixing a mixed organic solvent, a composite lithium salt and an additive in proportion, wherein the additive comprises a sulfonate compound and a fluorinated sulfonamide compound, wherein the mass ratio of the sulfonate compound to the fluorinated sulfonamide compound is 4:1, and the sulfonate compound is selected from Compound 5 and Compound 6, Compound 5, Compound 6, The mass ratio of compound 5 to compound 6 is 3.5:1, and the fluorinated sulfonamide compound is compound 7. Compound 7, Sulfonate compounds and fluorinated sulfonamide compound additives are recorded as first-category additives, and the additives also include overcharge protection agents, flame retardants and neutralizers, and the overcharge protection agents, flame retardants and neutralizers are recorded as second-category additives, wherein the overcharge protection agent is phenylcyclohexane, the flame retardant is trimethyl phosphate, the neutralizer includes cyclopentyl isocyanate and trifluoroethyl phosphite, and the mass ratio of cyclopentyl isocyanate to trifluoroethyl phosphite is 1:2, and the percentages of organic solvents, composite lithium salts, first-category additives and second-category additives in the electrolyte are 81.5%: 12.8%: 4.6%: 1.1%; S3 also includes the following steps: in a glove box filled with argon, a mixed organic solvent is measured in proportion, a composite lithium salt, a first type additive and a second additive are weighed, and the mixed organic solvent is slowly added and stirred, and the environmental condition in the glove box is H2O<0.22mg / m 3 , O2<0.43mg / m 3 .

[0032] Example 6 This embodiment provides a method for preparing a lithium ion battery electrolyte, comprising the following steps: S1, mixing a single organic solvent of diethyl fluoromalonate, fluoroethylene carbonate and dimethyl carbonate, wherein the mass ratio of diethyl fluoromalonate, fluoroethylene carbonate and dimethyl carbonate is 4:1:4; S2. Prepare a composite lithium salt, mix lithium hexafluorophosphate, lithium bis(oxalatoborate) and lithium bis(trifluoromethanesulfonylimide) with ethylene glycol dimethyl ether solvent, perform a chelating reaction, and dry the reaction product under a nitrogen environment to obtain a composite lithium salt, wherein the mass ratio of lithium hexafluorophosphate, lithium bis(oxalatoborate) and lithium bis(trifluoromethanesulfonylimide is 6:2:1.5, and the volume ratio of the three lithium salt mixture to ethylene glycol dimethyl ether is 1:1; S3, mixing a mixed organic solvent, a composite lithium salt and an additive in proportion, wherein the additive comprises a sulfonate compound and a fluorinated sulfonamide compound, wherein the mass ratio of the sulfonate compound to the fluorinated sulfonamide compound is 4:1, and the sulfonate compound is selected from Compound 2 and Compound 4, Compound 2, Compound 4, The mass ratio of compound 2 to compound 4 is 3:1, and the fluorinated sulfonamide compound is compound 7. Compound 7, Sulfonate compounds and fluorinated sulfonamide compound additives are recorded as first-category additives, and the additives also include overcharge protection agents, flame retardants and neutralizers, and the overcharge protection agents, flame retardants and neutralizers are recorded as second-category additives, wherein the overcharge protection agent is phenylcyclohexane, the flame retardant is dimethyl methyl phosphate, the neutralizer includes cyclopentyl isocyanate and hexafluoromethylamide, and the mass ratio of cyclopentyl isocyanate to hexafluoromethylamide is 1:2, and the percentages of organic solvents, composite lithium salts, first-category additives and second-category additives in the electrolyte are 83.5%: 11.8%: 4.1%: 0.6%; S3 also includes the following steps: in a glove box filled with argon, a mixed organic solvent is measured in proportion, a composite lithium salt, a first type additive and a second additive are weighed, and the mixed organic solvent is slowly added and stirred, and the environmental condition in the glove box is H2O<0.22mg / m 3 , O2<0.43mg / m 3 .

[0033] Comparative Example 1, This embodiment provides a method for preparing a lithium ion battery electrolyte, comprising the following steps: S1. Mixing single organic solvents ethylene carbonate and propylene carbonate to prepare a mixed organic solvent, wherein the mass ratio of ethylene carbonate to propylene carbonate is 1:1; S2, taking lithium hexafluorophosphate electrolyte lithium salt; S3, mixing a mixed organic solvent, an electrolyte lithium salt and an additive in proportion, wherein the additive comprises a flame retardant and a sulfonate compound, wherein the flame retardant is dimethyl methyl phosphate, and the sulfonate compound is compound 2, Compound 2, The percentages of organic solvent, composite lithium salt and additive in the electrolyte are 83.5%:11.8%:4.7%; S3 also includes the following steps: in a glove box filled with argon, a mixed organic solvent is measured in proportion, a composite lithium salt, a first type additive and a second additive are weighed, and the mixed organic solvent is slowly added and stirred, and the environmental condition in the glove box is H2O<0.22mg / m 3 , O2<0.43mg / m 3 .

[0034] Take the same amount of lithium ion battery electrolyte in the above embodiment and comparative example, and select the same positive and negative electrode materials, inject the electrolyte into the outer packaging, and prepare the lithium ion battery after vacuum packaging and other steps. The prepared battery is subjected to high and low temperature performance charge and discharge tests, including taking the lithium ion battery prepared by each group of the electrolyte of the embodiment and comparative example: The battery was placed at room temperature for constant current charge and discharge, and cycled for 200 cycles at 30°C and 0.5C discharge regime, and the battery capacity retention rate was calculated; Place the battery in an electric drying oven, set the temperature to 65°C, cycle it for 200 cycles under a 0.5C discharge regime, and calculate the battery capacity retention rate; The battery was first tested at room temperature of 30°C with a 0.5C charge-discharge cycle. After the room temperature test, the battery was charged to 3.6V at 0.5C. The test chamber temperature was set to -30°C. Under the 0.5C discharge system, the battery was cycled for 200 cycles and the battery capacity retention rate was calculated. The initial internal resistance of the battery was tested, and the internal resistance of the battery was measured after storage at 65℃ and -30℃ for 72h. The test results are as follows:

[0035] According to the test results of Examples 1-6 and Comparative Example 1, it can be seen that the electrolyte obtained by adding sulfonic acid ester compounds and fluorinated sulfonic acid amine compounds in the preparation process of the electrolyte is compared with the electrolyte obtained by adding only sulfonic acid ester compounds as additives in the preparation process. When it is used in a lithium ion battery, the room temperature cycle capacity retention rate of the lithium ion battery is improved, and the cycle capacity retention rate of the battery under high temperature and low temperature conditions is reduced compared with the change range of the cycle capacity retention rate under normal temperature. According to the test results of Examples 3 and 5, it can be seen that the lithium battery electrolyte prepared by using cyclic sulfonic acid ester compounds as additives is compared with the lithium battery electrolyte prepared by using chain sulfonic acid ester compounds as additives. When it is used in a lithium ion battery, the battery capacity retention rate under normal temperature-high temperature and normal temperature-low temperature conditions is improved. The degree of change is small, indicating that the use of sulfonic acid ester compounds and fluorinated sulfonic acid amine compounds as additives is beneficial to improving the stability of the electrolyte, and when the sulfonic acid ester compound is a cyclic sulfonic acid ester compound, the performance of the lithium ion battery is more stable. According to the experimental results, it can be seen that compared with a single organic solvent, the use of a mixed organic solvent to prepare the electrolyte is beneficial to reducing the internal resistance of the lithium ion battery and facilitating the transmission or transfer of ions. According to Examples 3 and 4, it can be seen that by increasing the proportion of fluoroethylene carbonate in the mixed organic solution, it is beneficial to reduce the internal resistance of the lithium battery and improve the capacity retention rate of the lithium ion battery under low temperature conditions, thereby improving the low-temperature cycle performance of the lithium ion battery, so that the lithium ion battery electrolyte has a wider temperature range of use.

[0036] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above and that the present invention can be implemented in other specific forms without departing from the spirit or essential features of the present invention. Therefore, the embodiments should be considered exemplary and non-restrictive in all respects, and the scope of the present invention is defined by the appended claims rather than the above description, and it is intended that all changes falling within the meaning and scope of the equivalent elements of the claims be included in the present invention.

Claims

1. A method for preparing a lithium ion battery electrolyte, characterized in that: The steps include: S1, taking a single type of organic solvent and mixing them in proportion to prepare a mixed organic solvent; S2, preparing composite lithium salt; S3, mixing a mixed organic solvent, a composite lithium salt and an additive in proportion to prepare a lithium-ion battery electrolyte; The additives are sulfonate compounds and fluorine-containing sulfonamide compounds, and the sulfonate compounds include cyclic sulfonate compounds and / or chain sulfonate compounds; The single organic solvent comprises diethyl fluoromalonate, fluoroethylene carbonate and dimethyl carbonate, and the mass ratio of diethyl fluoromalonate, fluoroethylene carbonate and dimethyl carbonate is (4-6):1:(4-6); The sulfonate compound additive is selected from at least one of the following structural formulas: Compound 1 to Compound 6, and the fluorinated sulfonamide compound additive is selected from at least one of the following structural formulas: Compound 7 to Compound 9. Compound 1, Compound 2, Compound 3, Compound 4, Compound 5, Compound 6, Compound 7, Compound 8, Compound 9.

2. The method for preparing a lithium ion battery electrolyte according to claim 1, characterized in that: The composite lithium salt comprises lithium hexafluorophosphate, lithium bis(oxalatoborate) and lithium bis(trifluoromethanesulfonyl imide), and the mass ratio of lithium hexafluorophosphate, lithium bis(fluorosulfonyl imide) and lithium bis(trifluoromethanesulfonyl imide) is (1-8): (1-3): (1-3).

3. The method for preparing a lithium ion battery electrolyte according to claim 1, characterized in that: The additives also include an overcharge protector, a flame retardant and a neutralizer.

4. The method for preparing a lithium ion battery electrolyte according to claim 3, characterized in that: The overcharge protection agent includes one or more of phenylcyclohexane, thiophene and its derivatives and polypyridine complexes.

5. The method for preparing a lithium ion battery electrolyte according to claim 3, characterized in that: The flame retardant includes one or more of dimethyl methylphosphonate, pentafluorocyclotriphosphazene and trimethyl phosphate.

6. The method for preparing a lithium ion battery electrolyte according to claim 3, characterized in that: The neutralizing agent includes one or more of aluminum oxide, trifluoroethylphosphite, hexafluoromethylamide and cyclopentyl isocyanate.

7. The method for preparing a lithium ion battery electrolyte according to claim 2, characterized in that: In S2, the following steps are also included: lithium hexafluorophosphate, lithium bis(oxalatoborate) and lithium bis(trifluoromethanesulfonylimide) are mixed with ethylene glycol dimethyl ether solvent in proportion, and a chelating reaction is performed to obtain a composite lithium salt.

8. The method for preparing a lithium ion battery electrolyte according to claim 1, characterized in that: In S3, the following steps are also included: in a glove box filled with argon, a solvent is taken in proportion, a composite lithium salt and an additive are weighed, and they are slowly added to the solvent and stirred. The environmental conditions in the glove box are (H2O< (0.2-0.3) mg / m 3 , O2<(0.4—0.6)mg / m 3 ), stirring speed is 50-80r / min.

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