Fluoro-carboxylic ester-based high-temperature stable lithium ion battery electrolyte and preparation method thereof

Abstract

The invention belongs to the field of lithium ion battery electrolyte, and provides high-temperature stable lithium ion battery electrolyte based on fluoro-carboxylic ester and a preparation method of the high-temperature stable lithium ion battery electrolyte. The preparation method comprises the following steps: firstly, carrying out copolymerization reaction on methyl methacrylate, trifluoroethyl methacrylate and methacrylic acid, and then reacting with lithium bis (fluorosulfonyl) imide, fluoropropyl carbonate and a boron trifluoride diethyl etherate complex to obtain a lithium bis (fluorosulfonyl) imide compound; the preparation method comprises the following steps: reacting triethyl phosphate, glutathione and ethylene glycol to prepare a phosphorus-sulfur compound; the preparation method comprises the following steps: reacting methyl difluorophosphate with ethylene glycol and triethylamine to prepare fluorophosphate, reacting glyceryl borate with triethoxyborane to prepare boric acid ester, and finally compounding the fluorophosphate with the boric acid ester under the action of ethylene glycol and triethylamine to obtain the fluorophosphate-boric acid ester compound. The electrolyte can form a stable solid electrolyte interface film under a high-temperature condition, so that the high-temperature stability of the lithium ion battery is improved.

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 fluorinated carboxylic acid ester 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 environmental protection characteristics. However, with the rapid development of lithium-ion batteries in the direction of high energy density and high power output, their working environment and performance requirements are also constantly improving, especially the stability in high temperature environment has become one of the key and difficult points of research. Conventional lithium-ion battery electrolytes are easily decomposed under high temperature conditions, and their chemical stability and electrochemical performance are significantly reduced, which leads to battery 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, lithium hexafluorophosphate is easily decomposed to produce byproducts such as HF under high temperature conditions, which accelerates the decomposition of the electrolyte and corrodes the electrode material. In addition, the 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. A 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 object of the present invention is 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 using methyl methacrylate, trifluoroethyl methacrylate and methacrylic acid, and then 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 lithium salts, 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 to coordinate with lithium ions and optimize ion migration behavior. The cross-linking of ethylene glycol generates a molecular network to enhance the thermal stability and mechanical strength of the complex. Fluorinated phosphates containing polar groups are prepared by the ester reaction of methyl difluorophosphate and ethylene glycol. Boric acid glyceride reacts with triethoxyborane to generate borate esters, which are then compounded with fluorophosphate to obtain fluorophosphate-borate ester complexes. The multifunctional complexes work 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 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, cooled to room temperature after sufficient reaction, washed and rotary evaporated to obtain a precursor A, lithium bis(fluorosulfonyl)imide is dispersed in anhydrous acetonitrile, fluoropropyl carbonate and precursor A are added in sequence, boron trifluoride ether complex is added, the temperature is raised to a second temperature under an argon atmosphere, the reaction is sufficient, 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 evaporating to obtain a phosphorus-sulfur complex, and then dispersing the phosphorus-sulfur complex in anhydrous ethanol, adding ethylene glycol, 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 distilling to obtain fluorophosphate, then dispersing boric acid glyceride and triethoxyborane in anhydrous ethanol, stirring and reacting at room temperature, and distilling under reduced pressure to obtain boric ester, under an argon atmosphere, dispersing fluorophosphate and boric 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 distilling to obtain a fluorophosphate-borate complex;

[0010] Step S2, dispersing lithium salt in ethyl trifluoroacetate, and then sequentially adding organic solvent, tri(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 into free radicals, which react with the double bonds of methyl methacrylate to form new free radical centers. The polymer chain forms a copolymer chain by gradually adding methyl methacrylate, trifluoroethyl methacrylate and methacrylic acid. Fluoropropyl carbonate is a cyclic carbonate with strong polarity and high chemical stability. During the reaction, the carboxyl group of the methacrylic acid unit in the precursor A undergoes 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 under the catalysis of boron trifluoride ether complex, and reacts with the carboxyl or hydroxyl group of the 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 are easy to form coordination bonds with polar groups (such as ester groups and C=O in carboxyl groups). TFSI- has a dispersed charge and a flexible structure, which makes the electrostatic interaction between it and lithium ions weak, 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 be distributed 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 thiol group (-SH). The sulfur atom in the thiol 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 thiol group. The reaction product is a phosphorus-sulfur complex. The phosphorus-sulfur complex contains both an active phosphate structure (P=O, PS bond) and the multifunctional groups of glutathione (-COOH, -NH2), which provides the possibility 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 induce 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 phosphate esters to generate new phosphate ester 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 -OH groups introduced by P=O, PS and 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 the 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 and limit the disordered diffusion of anions. The -OH groups of P=O, PS and ethylene glycol in the phosphorus-sulfur complex can form a hydrogen bond network 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 to attack the phosphorus atom in methyl difluorophosphate. This process causes one of the methoxy groups to be replaced by the hydroxyl group of ethylene glycol, and an ester exchange reaction occurs to generate a fluorophosphate containing an ethylene glycol fragment. 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 PF bond has high chemical stability and weak polarity, which can enhance the binding force between molecules. The presence of the PF bond and the P=O bond in the fluorophosphate improves the resistance of the molecule to heat and chemical environments. The ethoxy group in triethoxyborane undergoes a partial ester exchange reaction with the ester group in boric acid glyceride. During the reaction, the boron atoms may form a bridge structure through oxygen atoms to generate a borate ester complex with a network structure. The borate ester complex contains multiple boron oxygen bonds, which have high chemical stability. Through the boron oxygen bridge bond and ester exchange, the borate ester complex forms a molecular structure with three-dimensional network characteristics, and this network structure can improve the thermal stability of the complex. Under the combined action of ethylene glycol and triethylamine, fluorophosphate and borate are combined through weak intermolecular interactions (such as hydrogen bonds, polar effects and electrostatic effects) to form a stable complex. The P=O group and PF bond in fluorophosphate can be combined with the BO bond or ester group in borate through hydrogen bonds. The dihydroxyl group of ethylene glycol may also connect fluorophosphate and borate molecules through hydrogen bonds. Electrostatic attraction may occur between the polar PF bond in fluorophosphate and the polar BO bond in borate, thereby enhancing the intermolecular binding force. The chemical stability of PF bond and BO bond enables the complex to maintain structural integrity under high temperature environment, and the three-dimensional network structure further increases the thermal decomposition temperature of the complex; P=O and PF groups in fluorophosphate can form coordination with lithium ions to increase the dissociation degree of lithium salts, and the flexible network structure of borate provides a channel for ion migration, promoting the rapid conduction of ions in 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 increasing 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 coordinate competitively 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 effects, 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 the 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 the operation of the battery, LiF generated by the decomposition of lithium bis(fluorosulfonyl)imide is deposited on the surface of the negative electrode to form a dense and stable inorganic protective layer to prevent the negative electrode from directly contacting 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 precursor A. The fluorosulfonyl anions can bind to the carboxylic acid groups in 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. Fluorinated phosphates decompose under high voltage environments to generate CO3 2- The ions are deposited on the positive electrode surface and react with the transition metal oxide on the positive electrode surface 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- Ions - can form weak interactions with the carboxyl groups in 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, resulting in 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, and reduces the direct contact between the positive electrode material surface and the electrolyte, thereby inhibiting the occurrence of side reactions; lithium sulfide is an inorganic component with high mechanical strength and chemical inertness and has excellent thermal stability. Together with lithium thiophosphate, it forms a composite protective film to provide mechanical support and 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. The phosphorus-sulfur complex replaces some solvent molecules through weak interactions with the phosphite and thiol groups in its molecular structure, deconstructs the solvation shell of lithium ions, reduces the solvation energy of lithium ions, and improves the ionic conductivity of the electrolyte and the lithium ion migration number.

[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 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 instances, 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 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 instances, 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 the range are also applicable.

[0037] In some optional instances, the fourth temperature is 40-45°C, for example, it may 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 10-11h, for example, it can be 10.0h, 10.1h, 10.2h, 10.3h, 10.4h, 10.5h, 10.6h, 10.7h, 10.8h, 10.9h or 11.0h, 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, tri(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 to form a dense and stable inorganic protective layer to prevent the negative electrode from directly contacting 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, generate sulfur-rich compounds (Li3PS4 and Li2S), form a sulfur-rich protective film on the positive electrode surface, and improve 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, which forms 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 This is a flow chart of the method for preparing a high-temperature stable lithium-ion battery electrolyte based on fluorocarboxylic acid ester provided in Examples 1-4 of the present invention. DETAILED DESCRIPTION

[0057] The technical solution of the present invention is described in detail below in conjunction with specific embodiments and their accompanying drawings. The embodiments recorded herein are specific embodiments of the present invention, which are used to illustrate the concept of the present invention; these descriptions are explanatory and exemplary and should not be construed as limitations on the embodiments of the present invention and the scope of protection of the present invention. In addition to the embodiments recorded 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 recorded herein.

[0058] The chemical reagents used in the examples and comparative examples of the present invention are all commercially available products without 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 fluorinated carboxylic acid ester, such as Figure 1 As shown, the preparation method specifically comprises the following steps:

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

[0062] Step A2, dispersing 10 g of triethyl phosphate and 15 g of glutathione in 100 mL of anhydrous ethanol, stirring and reacting at room temperature for 6.4 h, and after the reaction, rotary evaporation to obtain a phosphorus-sulfur complex, and then dispersing 20 g of the phosphorus-sulfur complex in 100 mL of anhydrous ethanol, adding 3 g of ethylene glycol, and stirring and reacting 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, 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 10.3 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 rotary evaporation was performed to obtain a fluorophosphate-borate complex;

[0064] Step S2, dispersing 15g of lithium hexafluorophosphate and lithium tetrafluoroborate in 55g of ethyl trifluoroacetate, and then adding 22g of ethylene carbonate / dimethyl carbonate, 7.3g of tri-2,2,2-trifluoroethyl phosphate, 3.6g of trifluoropropionitrile, 5.7g of lithium bis(fluorosulfonyl)imide complex, 3.6g of fluorophosphate-borate complex and 3.9g of phosphorus-sulfur complex 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 fluorinated carboxylic acid ester, such as Figure 1 As shown, the preparation method specifically comprises the following steps:

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

[0068] Step A2, dispersing 10 g of triethyl phosphate and 15 g of glutathione in 100 mL of anhydrous ethanol, stirring and reacting at room temperature for 6.1 h, and after the reaction, rotary evaporation to obtain a phosphorus-sulfur complex, and then dispersing 20 g of the phosphorus-sulfur complex in 100 mL of anhydrous ethanol, adding 3 g of ethylene glycol, and stirring and reacting 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 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 51°C, the reaction was fully reacted for 10.8 h, and then rotary evaporation was performed to obtain a fluorophosphate-borate complex;

[0070] Step S2, dispersing 11g of lithium hexafluorophosphate and lithium tetrafluoroborate in 51g of ethyl trifluoroacetate, and then adding 28g of ethylene carbonate / dimethyl carbonate, 5.4g of tri-2,2,2-trifluoroethyl phosphate, 4.8g of trifluoropropionitrile, 9.4g of lithium bis(fluorosulfonyl)imide complex, 4.2g of fluorophosphate-borate complex and 3.1g of phosphorus-sulfur complex 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 fluorinated carboxylic acid ester, such as Figure 1 As shown, the preparation method specifically comprises the following steps:

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

[0074] Step A2, dispersing 10 g of triethyl phosphate and 15 g of glutathione in 100 mL of anhydrous ethanol, stirring and reacting at room temperature for 6.9 h, and after the reaction, rotary evaporation to obtain a phosphorus-sulfur complex, and then dispersing 20 g of the phosphorus-sulfur complex in 100 mL of anhydrous ethanol, adding 3 g of ethylene glycol, and stirring and reacting 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, 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 11.8 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 rotary evaporation was performed to obtain a fluorophosphate-borate complex;

[0076] Step S2, dispersing 12g of lithium hexafluorophosphate and lithium tetrafluoroborate in 58g of ethyl trifluoroacetate, and then adding 24g of ethylene carbonate / dimethyl carbonate, 8.9g of tri-2,2,2-trifluoroethyl phosphate, 4.2g of trifluoropropionitrile, 6.3g of lithium bis(fluorosulfonyl)imide complex, 4.8g of fluorophosphate-borate complex and 4.6g of phosphorus-sulfur complex 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 fluorinated carboxylic acid ester, such as Figure 1 As shown, the preparation method specifically comprises the following steps:

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

[0080] Step A2, dispersing 10 g of triethyl phosphate and 15 g of glutathione in 100 mL of anhydrous ethanol, stirring and reacting at room temperature for 6.5 h, and after the reaction, rotary evaporation to obtain a phosphorus-sulfur complex, and then dispersing 20 g of the phosphorus-sulfur complex in 100 mL of anhydrous ethanol, adding 3 g of ethylene glycol, and stirring and reacting 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 hours, 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 hours, 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 54°C, the reaction was fully reacted for 10.6 hours, and then rotary evaporation was performed to obtain a fluorophosphate-borate complex;

[0082] Step S2, dispersing 14g of lithium hexafluorophosphate and lithium tetrafluoroborate in 53g of ethyl trifluoroacetate, and then adding 29g of ethylene carbonate / dimethyl carbonate, 9.1g of tri-2,2,2-trifluoroethyl phosphate, 3.2g of trifluoropropionitrile, 7.8g of lithium bis(fluorosulfonyl)imide complex, 3.3g of fluorophosphate-borate complex and 4.1g of phosphorus-sulfur complex 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, which differs from Example 1 in that the mass of triethyl phosphate in step A2 is 1 g, which is 9 g less than that in Example 1, and 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 fluorocarboxylic acid ester, which differs from Example 1 in that the mass of triethyl phosphate in step A2 is 20 g, which is 10 g more than that in Example 1, and 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, and 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, and the working voltage range was 4.2V to 2.5V. 25°C cycle 300 times capacity retention test standard: At 25°C, charge to 4.2V at 0.4C constant current, then charge to a cut-off current of 0.02C at constant voltage, and then discharge to 2.5V at 1C constant current, measure the first cycle discharge capacity, and after 300 cycles of charge / discharge, measure the 300th cycle discharge capacity. 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 cut-off current of 0.02C, discharge at 0.33C to 2.5V, record the initial discharge capacity of the battery, 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 cut-off 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 discharge capacity at the 300th cycle.

[0092] 60℃ high temperature test standard: At 25℃, charge the battery to 4.2V at 0.33C constant current, charge it to a cut-off current of 0.02C at constant voltage, discharge it to 2.5V at 0.33C, record the discharge capacity of the battery before storage, then charge it to 4.2V at 0.33C constant current, charge it to a cut-off current of 0.02C at constant voltage, use the drainage method to test the volume of the battery before high temperature storage, store the battery in a 60℃ constant temperature box for 7 days, take out the battery after storage, place it at 25℃ for 12h and test the volume after storage; discharge the battery to 2.5V at 0.33C constant current, and record the discharge capacity. 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 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 of Comparative Example 1 is reduced, and the volume expansion rate of 7 days stored at 60°C is increased; the capacity retention rate of 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 of Comparative Example 2 is reduced, and the volume expansion rate of 7 days stored at 60°C is 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 thiol group of glutathione to generate a complex with a stable PS bond. Triethyl phosphate itself has high thermal stability. Its introduction can enhance the anti-decomposition ability of the electrolyte at high temperature and inhibit the occurrence of side reactions. In Comparative Example 1, insufficient use of triethyl phosphate will lead to a decrease in the efficiency of phosphorus-sulfur complex formation, a decrease in the number of PS bonds, a decrease in the polar sites of the complex, and a decrease in the degree of dissociation of the lithium salt, thereby affecting the ionic conductivity. Insufficient use of triethyl phosphate will lead to a decrease in the thermal stability of the electrolyte. At the same time, the electrolyte is more easily decomposed at high temperatures due to the lack of sufficient network structure support. In Comparative Example 2, the excess triethyl phosphate reacts incompletely with the thiol group of glutathione, resulting in an increase in the number of triethyl phosphate molecules that do not participate in the reaction in the complex, making the molecular network of the complex not tight enough, and the incompletely bound triethyl phosphate may react with other electrolyte components (such as lithium salts or solvents) to produce by-products, thereby accelerating the degradation of the electrolyte.

[0096] As shown in Table 1, compared with Example 1, the capacity retention rate of 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 of Comparative Example 3 is reduced, and the volume expansion rate of 7 days stored at 60°C is increased; the capacity retention rate of 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 of Comparative Example 4 is reduced, and the volume expansion rate of 7 days stored at 60°C is increased. The BO bonds in borate esters provide polar sites, which can form weak electrostatic interactions or coordination effects with lithium ions, thereby promoting the dissociation of lithium salts and improving ion conductivity. Borates form a three-dimensional cross-linked network through boron oxygen bridge bonds. This structure can not only stabilize the microenvironment of the electrolyte and optimize the 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. Borates and fluorophosphates form complexes through hydrogen bonds and electrostatic effects. This synergistic effect significantly improves the chemical stability and thermal stability of the complex. In Comparative Example 3, insufficient borate dosage will result in an incomplete three-dimensional network structure of the fluorophosphate-borate complex, insufficient ion migration channels, reduced ion conductivity, affecting the capacity retention rate of the battery, and also making it difficult to resist decomposition caused by high temperature. In Comparative Example 4, the borate is excessive, and the free borate that does not participate in the composite reaction may react with other components in the electrolyte (such as lithium salts or solvents), reducing the chemical stability of the electrolyte. In a high temperature environment, the excess borate may accelerate the generation of free radicals or by-products in the electrolyte and reduce the stability of the electrode interface film (SEI). The excess borate may cause volume expansion due to thermal decomposition or side reactions with the solvent to generate gas.

[0097] The above description is only a specific implementation mode 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 are 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 fluorocarboxylic acid ester, characterized in that: The preparation method is: 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 to react to obtain fluorophosphate, dispersing boric acid glyceride and triethoxyborane in anhydrous ethanol to react to obtain boric acid ester, dispersing fluorophosphate and boric acid ester in anhydrous acetonitrile under an argon atmosphere, adding a second portion of ethylene glycol and a second portion of triethylamine to react to obtain a fluorophosphate-boric acid ester complex; Step S2, dispersing lithium salt in ethyl trifluoroacetate, and then sequentially adding organic solvent, tri(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.

2. The method for preparing a high temperature stable lithium ion battery electrolyte based on fluorocarboxylic acid ester according to claim 1, characterized in that: The preparation method of the lithium bis(fluorosulfonyl)imide complex is as follows: Step A1, methyl methacrylate, trifluoroethyl methacrylate and methacrylic acid are added to anhydrous toluene in sequence, azobisisobutyronitrile is added under a nitrogen atmosphere to react to obtain a precursor A, lithium bis(fluorosulfonyl)imide is dispersed in anhydrous acetonitrile, and fluoropropyl carbonate, the precursor and boron trifluoride ether complex are added to react to obtain a lithium bis(fluorosulfonyl)imide complex.

3. The method for preparing a high temperature stable lithium ion battery electrolyte based on fluorocarboxylic acid ester according to claim 1, characterized in that: The preparation method of the phosphorus-sulfur complex is: Step A2, dispersing triethyl phosphate and glutathione in anhydrous ethanol, reacting to obtain a phosphorus-sulfur complex, and then dispersing the phosphorus-sulfur complex in anhydrous ethanol, adding ethylene glycol, and reacting to obtain a phosphorus-sulfur complex.

4. The method for preparing a high temperature stable lithium ion battery electrolyte based on fluorocarboxylic acid ester according to claim 1, characterized in that: 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; The mass ratio of the fluorophosphate to the borate is 2:

3.

5. The method for preparing a high temperature stable lithium ion battery electrolyte based on fluorocarboxylic acid ester according to claim 1, characterized in that: 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.

6. The method for preparing a high temperature stable lithium ion battery electrolyte based on fluorocarboxylic acid ester according to claim 1, characterized in that: In step S2, The mass ratio of the lithium salt, ethyl trifluoroacetate, organic solvent, tri(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).

7. The method for preparing a high temperature stable lithium ion battery electrolyte based on fluorocarboxylic acid ester according to claim 2, characterized in that: In step A1, 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).

8. The method for preparing a high temperature stable lithium ion battery electrolyte based on fluorocarboxylic acid ester according to claim 3, characterized in that: In step A2, The mass ratio of triethyl phosphate to glutathione is 2:3; The mass volume ratio of the triethyl phosphate to anhydrous ethanol is 1 g:10 mL.

9. The method for preparing a high temperature stable lithium ion battery electrolyte based on fluorocarboxylic acid ester according to claim 3, characterized in that: In step A2, 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. 10 . A high temperature stable lithium ion battery electrolyte based on fluorocarboxylate obtained according to the preparation method according to any one of claims 1 to 9 .

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