High-temperature stable lithium-ion battery electrolyte based on fluorinated carboxylate and preparation method thereof

Abstract

The present invention belongs to the field of lithium ion battery electrolytes, and provides a high-temperature stable lithium ion battery electrolyte based on fluorocarboxylic acid esters and a preparation method thereof. First, by copolymerization of methyl methacrylate, trifluoroethyl methacrylate and methacrylic acid, a lithium bis(fluorosulfonyl)imide complex is obtained by reaction with lithium bis(fluorosulfonyl)imide, fluoropropyl carbonate and boron trifluoride ether complex; a phosphorus-sulfur complex is prepared by reaction of triethyl phosphate, glutathione and ethylene glycol; a fluorophosphate is prepared by reaction of methyl difluorophosphate with ethylene glycol and triethylamine, and then a borate is prepared by reaction of boric acid glyceride with triethoxyborane, and finally the fluorophosphate and borate are compounded under the action of ethylene glycol and triethylamine to obtain a fluorophosphate-borate complex. The electrolyte of the present invention can form a stable solid electrolyte interface film under high temperature conditions, thereby improving the high-temperature stability of the lithium ion battery.

Description

Technical Field

[0001] The invention belongs to the field of lithium ion battery electrolytes and relates to a high-temperature stable lithium ion battery electrolyte based on fluorocarboxylate and a preparation method thereof. Background Art

[0002] Lithium-ion batteries are widely used in consumer electronics, electric vehicles, and energy storage devices due to their high energy density, long cycle life, and environmentally friendly properties. However, with the rapid development of lithium-ion batteries towards higher energy density and higher power output, the requirements for their operating environment and performance have also continued to increase. In particular, stability in high-temperature environments has become a key research focus and difficulty. Conventional lithium-ion battery electrolytes are prone to decomposition under high temperature conditions, significantly reducing their chemical stability and electrochemical performance, leading to capacity decay and even safety hazards (such as thermal runaway, fire, or explosion).

[0003] The current lithium-ion battery electrolyte is mainly composed of high-purity carbonate solvents (such as ethylene carbonate, dimethyl carbonate, etc.), lithium salts (such as lithium hexafluorophosphate), functional additives, etc. Although the existing electrolyte system exhibits excellent conductivity and stability at room temperature, under high temperature environment, lithium hexafluorophosphate is easily decomposed to produce by-products such as HF, which accelerates the decomposition of the electrolyte and corrodes the electrode material. In addition, traditional carbonate solvents have poor oxidative stability under high temperature conditions and are prone to cause irreversible decomposition reactions, significantly reducing the cycle life and safety of the battery. The Chinese patent application with publication number CN101834315A discloses a high-temperature electrolyte for lithium-ion batteries, which is composed of lithium salts, organic solvents and ammonium salt additives. The invention uses ammonium salts to hinder the deposition of metal ions on the graphite negative electrode, thereby reducing the decomposition of the electrolyte on the negative electrode and improving the use and storage performance of lithium-ion batteries in high temperature environments. However, the ammonium salt itself will decompose and cannot effectively prevent the occurrence of electrolyte decomposition reactions. Contents of the invention

[0004] In view of the shortcomings of the prior art, the present invention aims to provide a high-temperature stable lithium-ion battery electrolyte based on fluorocarboxylate and a preparation method thereof. First, a precursor A containing polar groups and fluorine-containing groups is prepared by methyl methacrylate, trifluoroethyl methacrylate and methacrylic acid, which is further reacted with lithium bis(fluorosulfonyl)imide, fluoropropyl carbonate and boron trifluoride ether complex to obtain a lithium bis(fluorosulfonyl)imide complex. The polar sites of the precursor A coordinate with lithium ions to enhance the dissociation degree of the lithium salt, and the fluorine-containing groups provide thermal stability and antioxidant properties. A phosphorus-sulfur complex is generated by reacting triethyl phosphate with glutathione, and then By adding ethylene glycol for cross-linking, a phosphorus-sulfur complex is obtained. The phosphate and thiol groups in the phosphorus-sulfur complex provide polar sites, coordinate with lithium ions, and optimize ion migration behavior. The cross-linking of ethylene glycol generates a molecular network, which enhances the thermal stability and mechanical strength of the complex. Fluorophosphate containing polar groups is prepared by the ester reaction of methyl difluorophosphate and ethylene glycol. Boric acid glyceride reacts with triethoxyborane to form borate, which is then compounded with fluorophosphate to obtain a fluorophosphate-borate complex. The multifunctional complex works synergistically to improve the chemical stability, thermal stability and ionic conductivity of the electrolyte, thereby meeting the needs of actual production.

[0005] To achieve this object, the present invention adopts the following technical solutions:

[0006] In a first aspect, the present invention provides a method for preparing a high-temperature stable lithium-ion battery electrolyte based on a fluorocarboxylate, the preparation method comprising:

[0007] Step A1: methyl methacrylate, trifluoroethyl methacrylate, and methacrylic acid are added to anhydrous toluene in sequence, azobisisobutyronitrile is added under a nitrogen atmosphere, the temperature is raised to a first temperature, the reaction is fully completed, and the mixture is cooled to room temperature, washed and rotary evaporated to obtain a precursor A, lithium bis(fluorosulfonyl)imide is dispersed in anhydrous acetonitrile, and fluoropropyl carbonate and precursor A are added in sequence, and boron trifluoride etherate is added. The temperature is raised to a second temperature under an argon atmosphere, the reaction is fully completed, washed and rotary evaporated, and vacuum dried to obtain a lithium bis(fluorosulfonyl)imide complex;

[0008] Step A2: dispersing triethyl phosphate and glutathione in anhydrous ethanol, stirring and reacting at room temperature, and after the reaction, rotary evaporation to obtain a phosphorus-sulfur complex. The phosphorus-sulfur complex is then dispersed in anhydrous ethanol, and ethylene glycol is added, and stirring and reacting to obtain a phosphorus-sulfur complex.

[0009] Step S1: under an argon atmosphere, dispersing methyl difluorophosphate and a first portion of ethylene glycol in anhydrous acetonitrile, adding a first portion of triethylamine, heating to a fourth temperature, fully reacting, and then rotary evaporating to obtain a fluorophosphate ester; then dispersing boric acid glyceride and triethoxyborane in anhydrous ethanol, stirring and reacting at room temperature, and distilling under reduced pressure to obtain a borate ester; under an argon atmosphere, dispersing the fluorophosphate ester and the borate ester in anhydrous acetonitrile, adding a second portion of ethylene glycol and a second portion of triethylamine, heating to a fifth temperature, fully reacting, and then rotary evaporating to obtain a fluorophosphate-borate complex;

[0010] Step S2: dispersing the lithium salt in ethyl trifluoroacetate, and then sequentially adding an organic solvent, tris(2,2,2-trifluoroethyl) phosphate, trifluoropropionitrile, lithium bis(fluorosulfonyl)imide complex, fluorophosphate-borate complex, and phosphorus-sulfur complex to obtain a high-temperature stable lithium-ion battery electrolyte based on fluorocarboxylate.

[0011] Under heating conditions, azobisisobutyronitrile decomposes to produce free radicals, which react with the double bond of methyl methacrylate to form a new free radical center. The polymer chain then gradually adds methyl methacrylate, trifluoroethyl methacrylate, and methacrylic acid to form a copolymer chain. Fluoropropyl carbonate is a cyclic carbonate ester with strong polarity and high chemical stability. During the reaction, the carboxyl group of the methacrylic acid unit in precursor A undergoes an ester exchange with the ester group of fluoropropyl carbonate. This reaction introduces a fluorine-containing group, further improving the electrochemical stability of the precursor. The cyclic carbonic acid structure of fluoropropyl carbonate undergoes a ring-opening reaction catalyzed by a boron trifluoride etherate complex, reacting with the carboxyl or hydroxyl groups of precursor A to form a polymer compound. Lithium bis(fluorosulfonyl)imide (LiTFSI) is a high-performance lithium salt. Due to its small size and high charge density, lithium ions (Li+) have a strong coordination tendency and easily form coordination bonds with polar groups (such as ester groups and C=O in carboxyl groups). TFSI- has a dispersed charge and flexible structure, which makes the electrostatic interaction between it and lithium ions weaker, thereby increasing the dissociation degree of lithium ions. The bis(fluorosulfonyl)imide anion is composed of a central nitrogen atom connected to two symmetrical sulfonyl groups (-SO2F). Each sulfonyl group (-SO2F) contains a sulfur atom connected to two oxygen atoms and a fluorine atom. The sulfur is connected to the coordinated nitrogen atom through a double bond (S=O) and a single bond (SF). The fluorine atom, due to its high electronegativity, reduces the electron cloud density of the sulfur atom, making the sulfur-oxygen double bond (S=O) more polar. The polarization of the sulfur-oxygen double bond (S=O) enhances the coordination ability of the oxygen atom to the outside world. TFS Due to the high electronegativity of the fluorine atom, the fluorinated group in I- may produce a weak repulsive effect with the fluorine atom of the trifluoroethyl group in precursor A between molecules, making the TFSI- anion more inclined to distribute around the molecular skeleton of precursor A and avoid direct coordination with lithium ions. Due to the polarization effect, the sulfur-oxygen double bond in TFSI- can form a weak electrostatic attraction with the ester group or carboxyl group in precursor A. Through the weak interaction between the TFSI- anion and the polar group of precursor A, the electrostatic coupling between lithium ions and TFSI- is weakened, which ensures a high dissociation degree of lithium ions and increases the ion migration number of the electrolyte. In addition, the TFSI- anion reduces the disordered migration of anions through the interaction with the fluorine group or polar group of precursor A, optimizes the migration channel of lithium ions in the system, and thus improves the overall ionic conductivity.

[0012] Glutathione contains an active sulfhydryl group (-SH). The sulfur atom in the sulfhydryl group has a high nucleophilicity. The phosphorus atom in triethyl phosphate has partial electrophilicity due to the formation of a P=O double bond with the oxygen atom, and can be attacked by the sulfhydryl group. The reaction product is a phosphorus-sulfur complex. The phosphorus-sulfur complex contains both an active phosphate structure (P=O, PS bond) and retains the multifunctional groups of glutathione (-COOH, -NH2), providing possibilities for subsequent molecular cross-linking and chemical modification. At the same time, the polar properties of the P=O and PS bonds enable the complex to synergize with other polar substances. On the basis of the phosphorus-sulfur complex, ethylene glycol is added to further trigger chemical interactions to form a more complex phosphorus-sulfur complex. The ethylene glycol molecule contains two hydroxyl groups. The hydroxyl groups in ethylene glycol can undergo weak intermolecular interactions with the P=O or PS bonds in the phosphorus-sulfur complex through hydrogen bonds. The formation of hydrogen bonds not only increases the intermolecular binding force of the system, but also improves the thermal stability of the complex. In addition, the hydroxyl groups of ethylene glycol can undergo ester exchange reactions with phosphates to generate new phosphate derivatives, introduce molecular fragments of ethylene glycol, and form more cross-linking points in the complex. The multifunctional polarity and cross-linked network structure of the phosphorus-sulfur complex enable it to produce synergistic effects with other system components (such as lithium salts, solvents or polar additives). The P=O, PS and -OH groups introduced by ethylene glycol in the phosphorus-sulfur complex can coordinate with lithium ions (Li+) in the lithium salt through lone pairs of electrons. The coordination effect stabilizes the lithium ions and reduces the electrostatic coupling between lithium ions and TFSI-, thereby improving the dissociation degree of the lithium salt and the ionic conductivity of the electrolyte. At the same time, the cross-linked network structure of the phosphorus-sulfur complex can promote the migration of lithium ions in the system while limiting the disordered diffusion of anions. The P=O, PS and -OH groups of ethylene glycol in the phosphorus-sulfur complex can form hydrogen bond networks with polar solvents (such as acetonitrile and carbonate solvents), reducing the volatility of the solvent molecules.

[0013] The oxygen atom in the hydroxyl group of ethylene glycol acts as a nucleophile, attacking the phosphorus atom in methyl difluorophosphate. This process results in the replacement of one of the methoxy groups with the hydroxyl group of ethylene glycol, leading to an ester exchange reaction and the formation of a fluorophosphate containing an ethylene glycol segment. The P=O double bond in the fluorophosphate structure is highly polar and can form hydrogen bonds or electrostatic interactions with other polar substances (such as borate esters). The P=O bond is chemically stable and weakly polar, which can enhance intermolecular bonding. The presence of the P=O bond and the P=O bond in the fluorophosphate enhances the molecule's resistance to thermal and chemical environments. The ethoxy group in triethoxyborane partially transesterifies with the ester group in boric acid glyceride. During the reaction, the boron atoms may form bridge structures through oxygen atoms, forming a borate ester complex with a network-like structure. The borate ester complex contains multiple boron-oxygen bonds, which are highly chemically stable. Through the boron-oxygen bridges and transesterification, the borate ester complex forms a molecular structure with three-dimensional network characteristics, which can improve the thermal stability of the complex. Under the combined action of ethylene glycol and triethylamine, the fluorophosphate and borate bind to each other through weak intermolecular interactions (such as hydrogen bonding, polar interactions, and electrostatic interactions), forming a stable complex. The P=O group and PF bond in the fluorophosphate can hydrogen bond with the BO bond or ester group in the borate. The dihydroxyl groups of ethylene glycol can also hydrogen bond the fluorophosphate and borate molecules. Electrostatic attraction may occur between the polar PF bond in the fluorophosphate and the polar BO bond in the borate, thereby strengthening the intermolecular binding force. The chemical stability of the PF and BO bonds enables the complex to maintain its structural integrity at high temperatures, while the three-dimensional network structure further increases the thermal decomposition temperature of the complex. The P=O and PF groups in the fluorophosphate can coordinate with lithium ions, increasing the dissociation degree of the lithium salt. The flexible network structure of the borate provides channels for ion migration, promoting rapid ion conduction within the complex.

[0014] Fluorophosphate-borate complexes not only provide unique chemical stability and high ionic conductivity in lithium-ion electrolyte systems, but also further optimize the comprehensive performance of the electrolyte through synergistic effects with lithium salts, solvents and additives. The P=O double bond in the fluorophosphate molecule has a strong polarity. Due to the uneven distribution of the positive charge on the phosphorus atom and the negative charge on the oxygen atom, the lone pair of electrons on the oxygen atom can act as a coordination group to form a coordination effect with the lithium ions in the lithium salt. Through this coordination effect, the electrostatic coupling between lithium ions and anions is reduced, thereby improving the dissociation degree of the lithium salt. The BO bond in the borate molecule has a strong polarity, and the lone pair of electrons on the oxygen atom can also coordinate with the lithium ions, further stabilizing the lithium ions. Lithium salts usually exist in the form of ion pairs or ion clusters in electrolytes. The P=O group in fluorophosphates and the BO bond in borate have a strong affinity for lithium ions and can competitively coordinate with lithium ions, weakening the electrostatic attraction between lithium ions and anions, thereby promoting the dissociation of lithium salts. The BO network structure of borate may reduce the freedom of movement of anions through weak electrostatic interactions, further reducing the probability of anions binding to lithium ions. The polar groups in fluorophosphates and borate (such as P=O, PF, BO) can form hydrogen bonds with polar groups in solvent molecules (carbonate solvents). The P=O group interacts with the solvent molecules through hydrogen bonding, enhancing the stability of the solvent molecules and reducing the tendency of the solvent molecules to evaporate. The BO bond of borate can also stabilize the distribution of solvent molecules through hydrogen bonding, especially in high-temperature environments. This effect improves the thermal stability of the system.

[0015] During battery operation, LiF generated by the decomposition of lithium bis(fluorosulfonyl)imide is deposited on the surface of the negative electrode, forming a dense and stable inorganic protective layer to prevent the negative electrode from direct contact with the electrolyte. LiF has extremely low solubility and excellent chemical stability, which can significantly inhibit the decomposition of the SEI layer. The fluorosulfonyl anions generated by the decomposition of lithium bis(fluorosulfonyl)imide can interact with the carboxylic acid groups and fluorinated groups in the precursor A. The fluorosulfonyl anions can combine with the carboxylic acid groups in the precursor A through hydrogen bonding to stabilize the interface chemical environment, and can also form van der Waals forces with the fluorinated groups to further stabilize the interface. Fluorophosphate decomposes under high voltage environment, and the generated CO3 2- The ions are deposited on the surface of the positive electrode and react with the transition metal oxide on the surface of the positive electrode to form an inorganic protective film with good chemical stability, which improves the antioxidant capacity of the positive electrode interface, prevents oxidative decomposition under high voltage, and improves the thermal stability of the positive electrode interface; and the generated CO3 2- Ion-can form a weak interaction with the carboxylate in the precursor A, synergistically improving the chemical stability of the interface. 2- The combination makes the positive electrode protective film more uniform and dense.

[0016] Under high temperature conditions, the positive and negative electrode interfaces of lithium-ion batteries are active areas of electrochemical reactions, and side reactions are prone to occur, leading to decreased cycle performance. Under high pressure conditions, phosphorus-sulfur complexes decompose to form phosphite and thiol groups. These chemical groups further react on the positive electrode surface to form sulfur-rich compounds (such as Li3PS4 and Li2S). Among them, lithium thiophosphate is a chemically stable inorganic solid electrolyte that is deposited on the positive electrode surface to form a sulfur-rich protective film, which improves the antioxidant capacity of the positive electrode interface, prevents the decomposition of electrolyte components under high voltage conditions, reduces direct contact between the positive electrode material surface and the electrolyte, and thus inhibits the occurrence of side reactions; lithium sulfide is a mechanically strong and chemically inert inorganic component with excellent thermal stability. It forms a composite protective film together with lithium thiophosphate, providing mechanical support to prevent the interface film from rupturing under high temperature or high voltage conditions. In lithium-ion batteries, the migration ability of lithium ions directly affects the battery's rate performance and cycle stability. In the electrolyte, Li+ usually forms a tight solvation shell with solvent molecules, which reduces the migration speed of lithium ions. Phosphorus-sulfur complexes replace some solvent molecules through weak interactions with the phosphite and thiol groups in their molecular structure, deconstruct the solvation shell of lithium ions, reduce the solvation energy of lithium ions, and improve the ionic conductivity and lithium ion migration number of the electrolyte.

[0017] As a preferred technical solution of the present invention, in step A1, the mass ratio of methyl methacrylate, trifluoroethyl methacrylate and methacrylic acid is 5:12:2.

[0018] In some optional examples, the mass volume ratio of methyl methacrylate to anhydrous toluene is 1 g:20 mL.

[0019] In some optional examples, the mass of the azobisisobutyronitrile is 1-2% of the mass of methyl methacrylate, for example, it can be 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9% or 2.0%, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0020] In some optional examples, the first temperature is 75-80°C, for example, it can be 75.0°C, 75.5°C, 76.0°C, 76.5°C, 77.0°C, 77.5°C, 78.0°C, 78.5°C, 79.0°C, 79.5°C or 80.0°C, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0021] In some optional examples, the reaction time at the first temperature is 6-7h, for example, it can be 6.0h, 6.1h, 6.2h, 6.3h, 6.4h, 6.5h, 6.6h, 6.7h, 6.8h, 6.9h or 7.0h, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0022] In some optional examples, the mass volume ratio of the lithium bis(fluorosulfonyl)imide to anhydrous acetonitrile is 1 g:20 mL.

[0023] In some optional examples, the mass ratio of the lithium bis(fluorosulfonyl)imide to fluoropropyl carbonate is 5:3.5.

[0024] In some optional examples, the mass ratio of the lithium bis(fluorosulfonyl)imide to the precursor A is 5:0.4.

[0025] In some optional examples, the mass ratio of the lithium bis(fluorosulfonyl)imide to the boron trifluoride diethyl ether complex is 5:(0.4-0.5), for example, it can be 5:0.40, 5:0.41, 5:0.42, 5:0.43, 5:0.44, 5:0.45, 5:0.46, 5:0.47, 5:0.48, 5:0.49 or 5:0.50, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0026] In some optional examples, the second temperature is 60-65°C, for example, it can be 60.0°C, 60.5°C, 61.0°C, 61.5°C, 62.0°C, 62.5°C, 63.0°C, 63.5°C, 64.0°C, 64.5°C or 65.0°C, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0027] In some optional examples, the reaction time at the second temperature is 10-12h, for example, it can be 10.0h, 10.2h, 10.4h, 10.6h, 10.8h, 11.0h, 11.2h, 11.4h, 11.6h, 11.8h or 12.0h, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0028] As a preferred technical solution of the present invention, in step A2, the mass ratio of triethyl phosphate to glutathione is 2:3.

[0029] In some optional examples, the mass volume ratio of the triethyl phosphate to anhydrous ethanol is 1 g:10 mL.

[0030] In some optional examples, the room temperature stirring reaction time is 6-7h, for example, it can be 6.0h, 6.1h, 6.2h, 6.3h, 6.4h, 6.5h, 6.6h, 6.7h, 6.8h, 6.9h or 7.0h, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0031] The mass volume ratio of the phosphorus-sulfur complex to anhydrous ethanol is 1 g:5 mL.

[0032] The mass ratio of the phosphorus-sulfur complex to ethylene glycol is 20:3.

[0033] In some optional examples, the reaction time after adding ethylene glycol is 8-9h, for example, it can be 8.0h, 8.1h, 8.2h, 8.3h, 8.4h, 8.5h, 8.6h, 8.7h, 8.8h, 8.9h or 9.0h, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0034] As a preferred technical solution of the present invention, in step S1, the mass ratio of the methyl difluorophosphate to the first portion of ethylene glycol is 5:2.

[0035] In some optional examples, the mass volume ratio of the methyl difluorophosphate to anhydrous acetonitrile is 1 g:10 mL.

[0036] In some optional examples, the mass of the first portion of triethylamine is 3-5% of the mass of methyl difluorophosphate, for example, it can be 3.0%, 3.2%, 3.4%, 3.6%, 3.8%, 4.0%, 4.2%, 4.4%, 4.6%, 4.8% or 5.0%, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0037] In some optional instances, the fourth temperature is 40-45°C, for example, it can be 40.0°C, 40.5°C, 41.0°C, 41.5°C, 42.0°C, 42.5°C, 43.0°C, 43.5°C, 44.0°C, 44.5°C or 45.0°C, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0038] In some optional examples, the reaction time at the fourth temperature is 8-9h, for example, it can be 8.0h, 8.1h, 8.2h, 8.3h, 8.4h, 8.5h, 8.6h, 8.7h, 8.8h, 8.9h or 9.0h, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0039] In some optional examples, the mass ratio of the boric acid glyceride to triethoxyborane is 2:1.

[0040] In some optional examples, the mass volume of the boric acid glyceride and anhydrous ethanol is 1 g:10 mL.

[0041] In some optional examples, the stirring reaction time at room temperature is 10-12h, for example, it can be 10.0h, 10.2h, 10.4h, 10.6h, 10.8h, 11.0h, 11.2h, 11.4h, 11.6h, 11.8h or 12.0h, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0042] In some optional examples, the mass ratio of the fluorophosphate to the borate is 2:3.

[0043] In some optional examples, the mass volume ratio of the fluorophosphate to anhydrous acetonitrile is 1 g:10 mL.

[0044] In some optional examples, the mass ratio of the fluorophosphate to the second portion of ethylene glycol is 6:1.

[0045] In some optional examples, the mass ratio of the fluorophosphate to the second portion of triethylamine is 60:1.

[0046] In some optional instances, the fifth temperature is 50-55°C, for example, it can be 50.0°C, 50.5°C, 51.0°C, 51.5°C, 52.0°C, 52.5°C, 53.0°C, 53.5°C, 54.0°C, 54.5°C or 55.0°C, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0047] In some optional examples, the reaction time at the fifth temperature is 10-11 hours, for example, it can be 10.0 hours, 10.1 hours, 10.2 hours, 10.3 hours, 10.4 hours, 10.5 hours, 10.6 hours, 10.7 hours, 10.8 hours, 10.9 hours or 11.0 hours, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0048] As a preferred technical solution of the present invention, in step S2, the lithium salt is one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, and lithium trifluoromethanesulfonate.

[0049] In some optional examples, the organic solvent is one or more of ethylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, and propylene carbonate.

[0050] In some optional examples, the mass ratio of the lithium salt, ethyl trifluoroacetate, organic solvent, tris(2,2,2-trifluoroethyl) phosphate, trifluoropropionitrile, lithium bis(fluorosulfonyl)imide complex, fluorophosphate-borate complex and phosphorus-sulfur complex is (10-15):(50-60):(20-30):(5-10):(3-5):(5-10):(3-5):(3-5).

[0051] In a second aspect, the present invention provides a high-temperature stable lithium-ion battery electrolyte based on fluorocarboxylate prepared by the preparation method described in the first aspect.

[0052] Compared with the prior art, the present invention has the following beneficial effects:

[0053] (1) LiF generated by the decomposition of lithium bis(fluorosulfonyl)imide is deposited on the surface of the negative electrode, forming a dense and stable inorganic protective layer to prevent the negative electrode from direct contact with the electrolyte. LiF has extremely low solubility and excellent chemical stability, which can significantly inhibit the decomposition of the SEI layer. The fluorosulfonyl anion carboxylic acid groups generated by the decomposition of lithium bis(fluorosulfonyl)imide are combined through hydrogen bonding to stabilize the interfacial chemical environment.

[0054] (2) The phosphorus-sulfur complex can decompose to generate phosphite and thiol groups, generating sulfur-rich compounds (Li3PS4 and Li2S), forming a sulfur-rich protective film on the surface of the positive electrode, thereby improving the antioxidant capacity of the positive electrode interface; lithium sulfide has excellent thermal stability and together with lithium thiophosphate forms a composite protective film, providing mechanical support to prevent the interface film from rupturing at high temperatures;

[0055] (3) The P=O double bond in the fluorophosphate-borate complex molecule has a strong polarity, forming a coordination effect with the lithium ions in the lithium salt, thereby increasing the dissociation degree of the lithium salt; and the P=O group in the fluorophosphate and the BO bond in the borate can promote the dissociation of the lithium salt. At the same time, the polar groups in the fluorophosphate and borate can form hydrogen bonds with the polar groups in the solvent molecules (carbonate solvents) to enhance the stability of the solvent molecules. The BO bond of the borate can also stabilize the distribution of the solvent molecules through hydrogen bonding, thereby improving the thermal stability of the system under high temperature conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0056] Figure 1 Flowchart of the method for preparing a high-temperature stable lithium-ion battery electrolyte based on fluorocarboxylate provided in Examples 1-4 of the present invention. DETAILED DESCRIPTION

[0057] The technical solutions of the present invention are described in detail below in conjunction with specific embodiments and their accompanying drawings. The embodiments described herein are specific embodiments of the present invention and are used to illustrate the concept of the present invention; these descriptions are explanatory and exemplary and should not be understood as limiting the embodiments of the present invention and the scope of protection of the present invention. In addition to the embodiments described herein, those skilled in the art can also adopt other obvious technical solutions based on the contents disclosed in the claims of this application and its specification, including technical solutions that adopt any obvious replacements and modifications to the embodiments described herein.

[0058] The chemical reagents used in the examples and comparative examples of the present invention are all commercially available products and have not been subjected to any further purification treatment.

[0059] Example 1

[0060] This embodiment provides a method for preparing a high-temperature stable lithium-ion battery electrolyte based on fluorocarboxylate, such as Figure 1 As shown, the preparation method specifically includes the following steps:

[0061] Step A1, 10g of methyl methacrylate, 24g of trifluoroethyl methacrylate and 4g of methacrylic acid were added to 200mL of anhydrous toluene in sequence, 0.15g of azobisisobutyronitrile was added under a nitrogen atmosphere, the temperature was raised to 75°C, and the mixture was fully reacted for 6.1h, then cooled to room temperature, washed and evaporated to obtain precursor A, 5g of lithium bis(fluorosulfonyl)imide was dispersed in 100mL of anhydrous acetonitrile, and 3.5g of fluoropropyl carbonate and 0.4g of precursor A were added in sequence, and 0.41g of boron trifluoride ether complex was added. Under an argon atmosphere, the temperature was raised to 61°C, the mixture was fully reacted for 10.2h, washed and evaporated, and vacuum dried to obtain a lithium bis(fluorosulfonyl)imide complex;

[0062] Step A2: Disperse 10 g of triethyl phosphate and 15 g of glutathione in 100 mL of anhydrous ethanol, stir and react at room temperature for 6.4 h. After the reaction, rotary evaporation is performed to obtain a phosphorus-sulfur complex. Then, disperse 20 g of the phosphorus-sulfur complex in 100 mL of anhydrous ethanol, add 3 g of ethylene glycol, and stir and react for 8.2 h to obtain a phosphorus-sulfur complex.

[0063] Step S1: Under an argon atmosphere, 5 g of methyl difluorophosphate and 2 g of ethylene glycol were dispersed in 50 mL of anhydrous acetonitrile, 0.17 g of triethylamine was added, the temperature was raised to 44 ° C, and the reaction was fully reacted for 8.6 h, and then the fluorophosphate was obtained by rotary evaporation. Then, 6 g of boric acid glyceride and 3 g of triethoxyborane were dispersed in 60 mL of anhydrous ethanol, stirred and reacted at room temperature for 10.3 h, and the borate was obtained after reduced pressure distillation. Under an argon atmosphere, 6 g of fluorophosphate and 9 g of borate were dispersed in 60 mL of anhydrous acetonitrile, 1 g of ethylene glycol and 0.1 g of triethylamine were added, the temperature was raised to 55 ° C, the reaction was fully reacted for 10.2 h, and then the fluorophosphate-borate complex was obtained by rotary evaporation;

[0064] Step S2: 15 g of lithium hexafluorophosphate and lithium tetrafluoroborate are dispersed in 55 g of ethyl trifluoroacetate, and then 22 g of ethylene carbonate / dimethyl carbonate, 7.3 g of tris-2,2,2-trifluoroethyl phosphate, 3.6 g of trifluoropropionitrile, 5.7 g of lithium bis(fluorosulfonyl)imide complex, 3.6 g of fluorophosphate-borate complex and 3.9 g of phosphorus-sulfur complex are added in sequence to obtain a high-temperature stable lithium-ion battery electrolyte based on fluorocarboxylate.

[0065] Example 2

[0066] This embodiment provides a method for preparing a high-temperature stable lithium-ion battery electrolyte based on fluorocarboxylate, such as Figure 1 As shown, the preparation method specifically includes the following steps:

[0067] Step A1, 10g of methyl methacrylate, 24g of trifluoroethyl methacrylate and 4g of methacrylic acid were added to 200mL of anhydrous toluene in sequence, 0.18g of azobisisobutyronitrile was added under a nitrogen atmosphere, the temperature was raised to 79°C, and the mixture was fully reacted for 6.8h, then cooled to room temperature, washed and evaporated to obtain precursor A, 5g of lithium bis(fluorosulfonyl)imide was dispersed in 100mL of anhydrous acetonitrile, and 3.5g of fluoropropyl carbonate and 0.4g of precursor A were added in sequence, and 0.48g of boron trifluoride ether complex was added. Under an argon atmosphere, the temperature was raised to 60°C, the mixture was fully reacted for 11.6h, washed and evaporated, and vacuum dried to obtain a lithium bis(fluorosulfonyl)imide complex;

[0068] Step A2: Disperse 10 g of triethyl phosphate and 15 g of glutathione in 100 mL of anhydrous ethanol, stir and react at room temperature for 6.1 h. After the reaction, rotary evaporation is performed to obtain a phosphorus-sulfur complex. Then, disperse 20 g of the phosphorus-sulfur complex in 100 mL of anhydrous ethanol, add 3 g of ethylene glycol, and stir and react for 8.9 h to obtain a phosphorus-sulfur complex.

[0069] Step S1: Under an argon atmosphere, 5 g of methyl difluorophosphate and 2 g of ethylene glycol were dispersed in 50 mL of anhydrous acetonitrile, 0.24 g of triethylamine was added, the temperature was raised to 40 ° C, and the reaction was fully reacted for 8.1 h, followed by rotary evaporation to obtain fluorophosphate, and then 6 g of boric acid glyceride and 3 g of triethoxyborane were dispersed in 60 mL of anhydrous ethanol, stirred and reacted at room temperature for 10.8 h, and distilled under reduced pressure to obtain borate. Under an argon atmosphere, 6 g of fluorophosphate and 9 g of borate were dispersed in 60 mL of anhydrous acetonitrile, 1 g of ethylene glycol and 0.1 g of triethylamine were added, the temperature was raised to 51 ° C, the reaction was fully reacted for 10.8 h, and then rotary evaporation was obtained to obtain a fluorophosphate-borate complex;

[0070] Step S2: 11 g of lithium hexafluorophosphate and lithium tetrafluoroborate are dispersed in 51 g of ethyl trifluoroacetate, and then 28 g of ethylene carbonate / dimethyl carbonate, 5.4 g of trifluoroethyl phosphate, 4.8 g of trifluoropropionitrile, 9.4 g of lithium bis(fluorosulfonyl)imide complex, 4.2 g of fluorophosphate-borate complex and 3.1 g of phosphorus-sulfur complex are added in sequence to obtain a high-temperature stable lithium-ion battery electrolyte based on fluorocarboxylate.

[0071] Example 3

[0072] This embodiment provides a method for preparing a high-temperature stable lithium-ion battery electrolyte based on fluorocarboxylate, such as Figure 1 As shown, the preparation method specifically includes the following steps:

[0073] Step A1, 10g of methyl methacrylate, 24g of trifluoroethyl methacrylate and 4g of methacrylic acid were added to 200mL of anhydrous toluene in sequence, 0.11g of azobisisobutyronitrile was added under a nitrogen atmosphere, the temperature was raised to 80°C, and the mixture was fully reacted for 7.0h, then cooled to room temperature, washed and evaporated to obtain precursor A, 5g of lithium bis(fluorosulfonyl)imide was dispersed in 100mL of anhydrous acetonitrile, and 3.5g of fluoropropyl carbonate and 0.4g of precursor A were added in sequence, and 0.43g of boron trifluoride ether complex was added. Under an argon atmosphere, the temperature was raised to 65°C, the mixture was fully reacted for 11.9h, washed and evaporated, and vacuum dried to obtain a lithium bis(fluorosulfonyl)imide complex;

[0074] Step A2: Disperse 10 g of triethyl phosphate and 15 g of glutathione in 100 mL of anhydrous ethanol, stir and react at room temperature for 6.9 h. After the reaction, rotary evaporation is performed to obtain a phosphorus-sulfur complex. Then, disperse 20 g of the phosphorus-sulfur complex in 100 mL of anhydrous ethanol, add 3 g of ethylene glycol, and stir and react for 8.6 h to obtain a phosphorus-sulfur complex.

[0075] Step S1: Under an argon atmosphere, 5 g of methyl difluorophosphate and 2 g of ethylene glycol were dispersed in 50 mL of anhydrous acetonitrile, 0.21 g of triethylamine was added, the temperature was raised to 42 ° C, and the reaction was fully reacted for 8.4 h, and then the fluorophosphate was obtained by rotary evaporation. Then, 6 g of boric acid glyceride and 3 g of triethoxyborane were dispersed in 60 mL of anhydrous ethanol, stirred and reacted at room temperature for 11.8 h, and the borate was obtained after reduced pressure distillation. Under an argon atmosphere, 6 g of fluorophosphate and 9 g of borate were dispersed in 60 mL of anhydrous acetonitrile, 1 g of ethylene glycol and 0.1 g of triethylamine were added, the temperature was raised to 53 ° C, the reaction was fully reacted for 10.4 h, and then the fluorophosphate-borate complex was obtained by rotary evaporation;

[0076] Step S2: 12 g of lithium hexafluorophosphate and lithium tetrafluoroborate are dispersed in 58 g of ethyl trifluoroacetate, and then 24 g of ethylene carbonate / dimethyl carbonate, 8.9 g of trifluoroethyl phosphate, 4.2 g of trifluoropropionitrile, 6.3 g of lithium bis(fluorosulfonyl)imide complex, 4.8 g of fluorophosphate-borate complex and 4.6 g of phosphorus-sulfur complex are added in sequence to obtain a high-temperature stable lithium-ion battery electrolyte based on fluorocarboxylate.

[0077] Example 4

[0078] This embodiment provides a method for preparing a high-temperature stable lithium-ion battery electrolyte based on fluorocarboxylate, such as Figure 1 As shown, the preparation method specifically includes the following steps:

[0079] Step A1, 10g of methyl methacrylate, 24g of trifluoroethyl methacrylate and 4g of methacrylic acid were added to 200mL of anhydrous toluene in sequence, 0.20g of azobisisobutyronitrile was added under a nitrogen atmosphere, the temperature was raised to 76°C, and the mixture was fully reacted for 6.4h, then cooled to room temperature, washed and evaporated to obtain precursor A, 5g of lithium bis(fluorosulfonyl)imide was dispersed in 100mL of anhydrous acetonitrile, and 3.5g of fluoropropyl carbonate and 0.4g of precursor A were added in sequence, and 0.49g of boron trifluoride ether complex was added. Under an argon atmosphere, the temperature was raised to 63°C, the mixture was fully reacted for 10.7h, washed and evaporated, and vacuum dried to obtain a lithium bis(fluorosulfonyl)imide complex;

[0080] Step A2: Disperse 10 g of triethyl phosphate and 15 g of glutathione in 100 mL of anhydrous ethanol, stir and react at room temperature for 6.5 h. After the reaction, rotary evaporation is performed to obtain a phosphorus-sulfur complex. Then, disperse 20 g of the phosphorus-sulfur complex in 100 mL of anhydrous ethanol, add 3 g of ethylene glycol, and stir and react for 8.4 h to obtain a phosphorus-sulfur complex.

[0081] Step S1: Under an argon atmosphere, 5 g of methyl difluorophosphate and 2 g of ethylene glycol were dispersed in 50 mL of anhydrous acetonitrile, 0.19 g of triethylamine was added, the temperature was raised to 45 ° C, and the reaction was fully reacted for 8.9 h, followed by rotary evaporation to obtain fluorophosphate, and then 6 g of boric acid glyceride and 3 g of triethoxyborane were dispersed in 60 mL of anhydrous ethanol, stirred and reacted at room temperature for 11.4 h, and distilled under reduced pressure to obtain borate ester. Under an argon atmosphere, 6 g of fluorophosphate and 9 g of borate ester were dispersed in 60 mL of anhydrous acetonitrile, 1 g of ethylene glycol and 0.1 g of triethylamine were added, the temperature was raised to 54 ° C, the reaction was fully reacted for 10.6 h, and then rotary evaporation was obtained to obtain a fluorophosphate-borate complex;

[0082] Step S2: 14 g of lithium hexafluorophosphate and lithium tetrafluoroborate are dispersed in 53 g of ethyl trifluoroacetate, and then 29 g of ethylene carbonate / dimethyl carbonate, 9.1 g of trifluoroethyl phosphate, 3.2 g of trifluoropropionitrile, 7.8 g of lithium bis(fluorosulfonyl)imide complex, 3.3 g of fluorophosphate-borate complex and 4.1 g of phosphorus-sulfur complex are added in sequence to obtain a high-temperature stable lithium-ion battery electrolyte based on fluorocarboxylate.

[0083] Comparative Example 1

[0084] This comparative example provides a method for preparing a high-temperature stable lithium-ion battery electrolyte based on fluorocarboxylic acid ester. The difference between the method and Example 1 is that the mass of triethyl phosphate in step A2 is 1 g, which is 9 g less than that in Example 1. The other process parameters and operating conditions are exactly the same as those in Example 1.

[0085] Comparative Example 2

[0086] This comparative example provides a method for preparing a high-temperature stable lithium-ion battery electrolyte based on fluorocarboxylate. The difference between the method and Example 1 is that the mass of triethyl phosphate in step A2 is 20 g, which is 10 g more than that in Example 1. The other process parameters and operating conditions are exactly the same as those in Example 1.

[0087] Comparative Example 3

[0088] This comparative example provides a method for preparing a high-temperature stable lithium-ion battery electrolyte based on fluorocarboxylic acid ester. The difference between the comparative example and Example 1 is that the mass of the boric acid ester in step S1 is 1 g, which is 8 g less than that in Example 1. The other process parameters and operating conditions are exactly the same as those in Example 1.

[0089] Comparative Example 4

[0090] This comparative example provides a method for preparing a high-temperature stable lithium-ion battery electrolyte based on fluorocarboxylic acid ester. The difference between the comparative example and Example 1 is that the mass of the boric acid ester in step S1 is 20 g, which is 11 g more than that in Example 1. The other process parameters and operating conditions are exactly the same as those in Example 1.

[0091] The electrolytes prepared in Examples 1-4 and Comparative Examples 1-4 of the present invention were injected into unpackaged batteries for testing. The operating voltage range was 4.2V to 2.5V. The capacity retention rate after 300 cycles at 25°C was tested as follows: At 25°C, the battery was charged at a constant current of 0.4C to 4.2V, then charged at a constant voltage to a cutoff current of 0.02C, and then discharged at a constant current of 1C to 2.5V. The discharge capacity of the first cycle was measured. After 300 cycles of charge and discharge, the discharge capacity at the 300th cycle was measured. 50℃ cycle 300 times capacity retention test standard: first at 25℃, charge the initially adjusted battery at a constant current of 0.33C to 4.2V, then charge at a constant voltage to a cutoff current of 0.02C, discharge at 0.33C to 2.5V, record the battery initial discharge capacity, then place the battery in a 50℃ high temperature box, charge at a constant current of 0.33C to 4.2V, then charge at a constant voltage to a cutoff current of 0.02C, discharge at 0.33C to 2.5V, leave it for 5 minutes, cycle charge / discharge for 300 times, and record the 300th cycle discharge capacity.

[0092] 60°C high-temperature test standard: At 25°C, the battery was charged at a constant current of 0.33C to 4.2V, then charged at a constant voltage to a cutoff current of 0.02C, and discharged at 0.33C to 2.5V. The discharge capacity before storage was recorded. The battery was then charged at a constant current of 0.33C to 4.2V, then charged at a constant voltage to a cutoff current of 0.02C. The volume of the battery before high-temperature storage was measured using the water displacement method. The battery was placed in a 60°C constant temperature chamber for 7 days. After storage, the battery was removed and placed at 25°C for 12 hours, and the post-storage volume was measured. The battery was then discharged at a constant current of 0.33C to 2.5V, and the discharge capacity was recorded. The test results are shown in Table 1.

[0093] Table 1 Test results of high temperature stable lithium ion battery electrolytes based on fluorocarboxylate prepared in Examples 1-4 and Comparative Examples 1-4

[0094]

[0095] As shown in Table 1, compared with Example 1, the capacity retention rate of Comparative Example 1 after 300 cycles at 25°C, the capacity retention rate of 300 cycles at 50°C, and the capacity retention rate of 7 days stored at 60°C decreased, and the volume expansion rate of 7 days stored at 60°C increased; the capacity retention rate of Comparative Example 2 after 300 cycles at 25°C, the capacity retention rate of 300 cycles at 50°C, and the capacity retention rate of 7 days stored at 60°C decreased, and the volume expansion rate of 7 days stored at 60°C increased. The P=O double bond in triethyl phosphate is polar and can form a coordination effect with lithium ions, thereby increasing the dissociation degree of lithium salt and enhancing the ionic conductivity of the electrolyte. In the formation of the phosphorus-sulfur complex, triethyl phosphate reacts with the sulfhydryl group of glutathione to form a complex with a stable PS bond. Triethyl phosphate itself has high thermal stability. Its introduction can improve the electrolyte's resistance to decomposition at high temperatures and inhibit the occurrence of side reactions. In Comparative Example 1, insufficient triethyl phosphate resulted in decreased efficiency in phosphorus-sulfur complex formation, a reduced number of PS bonds, fewer polar sites in the complex, and a lower degree of lithium salt dissociation, thus affecting ionic conductivity. Insufficient triethyl phosphate also reduced the thermal stability of the electrolyte. Furthermore, the electrolyte lacked sufficient network support, making it more susceptible to decomposition at high temperatures. In Comparative Example 2, the excess triethyl phosphate reacted incompletely with the sulfhydryl group of glutathione, resulting in an increase in unreacted triethyl phosphate molecules in the complex and a less compact molecular network. Incompletely bound triethyl phosphate may react with other electrolyte components (such as lithium salts or solvents), leading to the formation of byproducts and accelerating electrolyte degradation.

[0096] As shown in Table 1, compared with Example 1, the capacity retention rate of Comparative Example 3 after 300 cycles at 25°C, the capacity retention rate of 300 cycles at 50°C, and the capacity retention rate of 7 days stored at 60°C decreased, while the volume expansion rate of 7 days stored at 60°C increased; the capacity retention rate of Comparative Example 4 after 300 cycles at 25°C, the capacity retention rate of 300 cycles at 50°C, and the capacity retention rate of 7 days stored at 60°C decreased, while the volume expansion rate of 7 days stored at 60°C increased. The BO bonds in borate esters provide polar sites that can form weak electrostatic interactions or coordination effects with lithium ions, thereby promoting the dissociation of lithium salts and improving ionic conductivity. Borate esters form a three-dimensional cross-linked network through boron-oxygen bridge bonds. This structure not only stabilizes the microenvironment of the electrolyte and optimizes ion migration behavior, but also the BO bonds of borate esters can capture free radicals generated in the electrolyte, thereby inhibiting chain side reactions and extending the life of the electrolyte. Borate esters and fluorophosphates form a complex through hydrogen bonds and electrostatic interactions. This synergistic effect significantly improves the chemical stability and thermal stability of the complex. In Comparative Example 3, insufficient borate ester usage results in an imperfect three-dimensional network structure of the fluorophosphate-borate ester complex, insufficient ion migration channels, reduced ionic conductivity, and poor battery capacity retention. The electrolyte also struggles to resist decomposition caused by high temperatures. In Comparative Example 4, an excess of borate ester is present. Free borate ester that does not participate in the complex reaction may react with other components in the electrolyte (such as lithium salts or solvents), reducing the chemical stability of the electrolyte. In high-temperature environments, excess borate ester may accelerate the generation of free radicals or byproducts in the electrolyte and reduce the stability of the electrode interface film (SEI). Excess borate ester may also generate gas due to thermal decomposition or side reactions with the solvent, leading to volume expansion.

[0097] The above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention fall within the protection scope and disclosure scope of the present invention.

Claims

1. A method for preparing a high-temperature stable lithium-ion battery electrolyte based on a fluorocarboxylate, characterized in that: The preparation method is: Step S1: Under an argon atmosphere, methyl difluorophosphate and a first portion of ethylene glycol are dispersed in anhydrous acetonitrile, a first portion of triethylamine is added to react to obtain a fluorophosphate ester, glycerol borate and triethoxyborane are dispersed in anhydrous ethanol to react to obtain a borate ester, and under an argon atmosphere, the fluorophosphate ester and the borate ester are dispersed in anhydrous acetonitrile, a second portion of ethylene glycol and a second portion of triethylamine are added to react to obtain a fluorophosphate-borate complex; Step S2, dispersing the lithium salt in ethyl trifluoroacetate, and then sequentially adding an organic solvent, tris(2,2,2-trifluoroethyl) phosphate, trifluoropropionitrile, lithium bis(fluorosulfonyl)imide complex, fluorophosphate-borate complex, and phosphorus-sulfur complex to obtain a high-temperature stable lithium-ion battery electrolyte based on fluorocarboxylate; The preparation method of the lithium bis(fluorosulfonyl)imide complex comprises: sequentially adding methyl methacrylate, trifluoroethyl methacrylate and methacrylic acid to anhydrous toluene, adding azobisisobutyronitrile under a nitrogen atmosphere to react to obtain a precursor A, dispersing lithium bis(fluorosulfonyl)imide in anhydrous acetonitrile, and then adding fluoropropyl carbonate, the precursor and a boron trifluoride ether complex to react to obtain the lithium bis(fluorosulfonyl)imide complex; The preparation method of the phosphorus-sulfur complex comprises: dispersing triethyl phosphate and glutathione in anhydrous ethanol, reacting to obtain a phosphorus-sulfur complex, then dispersing the phosphorus-sulfur complex in anhydrous ethanol, adding ethylene glycol, and reacting to obtain the phosphorus-sulfur complex; The mass ratio of the fluorophosphate to the borate is 2:3; The mass ratio of the triethyl phosphate to glutathione is 2:

3.

2. The method for preparing a high-temperature stable lithium-ion battery electrolyte based on a fluorocarboxylate according to claim 1, wherein: In step S1, The mass of the first portion of triethylamine is 3-5% of the mass of methyl difluorophosphate; The mass ratio of the boric acid glyceride to triethoxyborane is 2:

1.

3. The method for preparing a high-temperature stable lithium-ion battery electrolyte based on fluorocarboxylate according to claim 1, wherein: In step S2, The lithium salt is one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, and lithium trifluoromethanesulfonate; The organic solvent is one or more of ethylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate and propylene carbonate.

4. The method for preparing a high-temperature stable lithium-ion battery electrolyte based on fluorocarboxylate according to claim 1, wherein: In step S2, The mass ratio of the lithium salt, ethyl trifluoroacetate, organic solvent, tris(2,2,2-trifluoroethyl) phosphate, trifluoropropionitrile, lithium bis(fluorosulfonyl)imide complex, fluorophosphate-borate complex and phosphorus-sulfur complex is (10-15):(50-60):(20-30):(5-10):(3-5):(5-10):(3-5):(3-5).

5. The method for preparing a high-temperature stable lithium-ion battery electrolyte based on fluorocarboxylate according to claim 1, wherein: The mass ratio of methyl methacrylate, trifluoroethyl methacrylate and methacrylic acid is 5:12:2; The mass ratio of lithium bis(fluorosulfonyl)imide to fluoropropyl carbonate is 5:3.5; The mass ratio of the lithium bis(fluorosulfonyl)imide to the precursor A is 5:0.4; The mass ratio of the lithium bis(fluorosulfonyl)imide to the boron trifluoride ether complex is 5:(0.4-0.5).

6. The method for preparing a high-temperature stable lithium-ion battery electrolyte based on fluorocarboxylate according to claim 1, wherein: The mass volume ratio of the triethyl phosphate to anhydrous ethanol is 1 g:10 mL.

7. The method for preparing a high-temperature stable lithium-ion battery electrolyte based on fluorocarboxylate according to claim 1, wherein: The mass volume ratio of the phosphorus-sulfur complex to anhydrous ethanol is 1 g:5 mL; The mass ratio of the phosphorus-sulfur complex to ethylene glycol is 20:

3. 8 . The high-temperature stable lithium-ion battery electrolyte based on fluorocarboxylate obtained by the preparation method according to claim 1 .

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