A high-rate lithium battery electrolyte based on the synergistic effect of borate ester and phosphate ester and its preparation method

Abstract

The present invention provides a high-rate lithium battery electrolyte based on the synergistic effect of borate ester and phosphate ester and a preparation method thereof, belonging to the field of lithium metal batteries. By introducing allyl groups into tris(trimethylsilyl) phosphate, the solvation ability thereof is effectively enhanced while maintaining the low-viscosity characteristic; secondly, trimethylsilyl groups are introduced to modify tris(2,2,2-trifluoroethyl) borate, enhancing the mechanical strength and uniformity of the interfacial film and inhibiting the growth of lithium dendrites; ethylene carbonate is modified by fluorination and etherification to improve its low-temperature fluidity and the mechanical strength of the interfacial film; finally, 1,4-butyrolactone is modified by introducing amino groups and sulfonic acid groups, improving the toughness and mechanical strength of the interfacial film and enhancing its stability under high voltage, thereby effectively reducing the occurrence of side reactions; through the modification of the electrolyte components, the performance of the lithium battery is optimized, and the rate performance, safety and service life of the battery are improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium metal batteries, and relates to a high-rate lithium battery electrolyte based on the synergistic effect of borate ester and phosphate ester and a preparation method thereof. Background Art

[0002] As an important part of modern energy storage technology, lithium batteries are widely used in fields such as electric vehicles, portable electronic devices, and renewable energy storage. The performance and reliability of the battery largely depend on the characteristics of its electrolyte. As the core part of the battery, the main function of the electrolyte is to provide a conductive medium for lithium ions to ensure efficient conduction of ions during the charge and discharge process of the battery. In addition to ionic conductivity, the electrolyte also needs to have good chemical stability and thermal stability to ensure the long-term safe operation of the battery. In electric vehicles and other high-power applications, the battery needs to quickly release electrical energy during high-rate discharge, which poses higher requirements for the conductivity of the electrolyte. During the fast charge and discharge process, lithium ions need to quickly migrate through the electrolyte between the negative and positive electrodes of the battery. If the ionic conductivity of the electrolyte is insufficient, it will lead to an increase in the internal resistance of the battery, thereby affecting the output power and energy efficiency of the battery.

[0003] Currently, the widely used lithium battery electrolyte is based on lithium salts dissolved in organic solvents such as carbonate solvents. These traditional electrolytes meet the application requirements of lithium batteries to a certain extent, but there are still some obvious deficiencies: traditional electrolytes are prone to form lithium dendrites during high-rate charge and discharge, resulting in short circuits and capacity degradation; at the same time, the deposition and stripping of the lithium metal negative electrode will cause large volume changes, increasing the mechanical stress of the interface film and affecting the battery stability. Summary of the Invention

[0004] In view of the above problems, the purpose of the present invention is to provide a high-rate lithium battery electrolyte based on the synergistic effect of borate and phosphate and a preparation method thereof. The present invention improves the performance and safety of lithium batteries by modifying various electrolyte components. First, allyl groups are used to modify tris(trimethylsilyl) phosphate to enhance its solvation ability and improve its interaction with lithium ions, while retaining the low-viscosity property. Secondly, trimethylsilyl groups are introduced to modify tris(2,2,2-trifluoroethyl) borate to enhance the flexibility and mechanical strength of the interface film, thereby inhibiting the growth of lithium dendrites and improving the battery cycle stability. Ethylene carbonate is modified by fluorination and etherification to enhance its low-temperature fluidity and the mechanical strength of the interface film, and further improve the migration rate of lithium ions. 1,4-Butyrolactone is modified by introducing amino and sulfonic acid groups to enhance the toughness and mechanical strength of the interface film and improve its stability under high-voltage conditions. In summary, the present invention effectively improves the ion migration, interface stability, high-voltage and low-temperature performance of the electrolyte through chemical structure modification, and significantly improves the rate performance, safety and service life of lithium batteries.

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

[0006] In the first aspect, the present invention provides a preparation method of a high-rate lithium battery electrolyte based on the synergistic effect of borate and phosphate. The preparation method of the high-rate lithium battery electrolyte based on the synergistic effect of borate and phosphate includes:

[0007] S1: Add tris(trimethylsilyl) phosphate and allyl alcohol into tetrahydrofuran, stir at room temperature to obtain reaction solution A, cool reaction solution A in an ice bath and dropwise add a tetrahydrofuran solution of potassium tert-butoxide to obtain reaction solution B, react at a constant temperature, perform reduced-pressure distillation and column chromatography to obtain modified tris(trimethylsilyl) phosphate;

[0008] S2: Add tris(2,2,2-trifluoroethyl) borate and trimethylchlorosilane into dichloromethane under nitrogen protection to obtain reaction solution C, dropwise add triethylamine at a constant temperature, then raise the temperature to room temperature for reaction, filter, wash, and perform reduced-pressure distillation to obtain silyl-modified tris(2,2,2-trifluoroethyl) borate;

[0009] S3: Mix ethylene carbonate and a selective fluorinating agent in acetonitrile to obtain reaction solution D, stir and react in an ice bath under nitrogen protection to obtain reaction solution E, perform reduced-pressure distillation and column chromatography to obtain fluorinated ethylene carbonate; Prepare a methanol dispersion of fluorinated ethylene carbonate, add sodium methoxide to obtain reaction solution F, stir and react at room temperature to obtain reaction solution G, adjust the pH with dilute hydrochloric acid, perform reduced-pressure distillation and column chromatography to obtain ether-based fluorinated ethylene carbonate;

[0010] S4: Add 1,4 - butyrolactone and dimethylamine into methanol to obtain reaction solution H. Stir the reaction at room temperature under nitrogen protection to obtain reaction solution I. Then, perform vacuum distillation and column chromatography to obtain amino - butyrolactone. Prepare a dichloromethane solution of amino - butyrolactone, and dropwise add a dichloromethane solution of chlorosulfonic acid to it under an ice bath to obtain reaction solution J. After stirring under the ice bath, raise the temperature to room temperature and continue stirring the reaction to obtain a pretreated reaction solution. Add ice - water to quench the reaction, followed by filtration, washing, vacuum distillation, and column chromatography to obtain amino - sulfonated butyrolactone;

[0011] S5: Add dimethyl carbonate and ethyl methyl carbonate into ether - fluorinated ethylene carbonate and stir to obtain a solvent. Then, sequentially add amino - sulfonated butyrolactone, modified tris(trimethylsilyl) phosphate, and tris(2,2,2 - trifluoroethyl) silane - modified borate. After stirring, add lithium hexafluorophosphate to obtain reaction solution K. Continue stirring, and after standing, filter through a PTFE membrane to obtain a high - rate lithium battery electrolyte based on the synergistic effect of borate and phosphate.

[0012] As a preferred technical solution of the present invention, in step S1, the molar ratio of tris(trimethylsilyl) phosphate to allyl alcohol is 1:1.2 - 1.5. For example, it can be 1:1.2, 1:1.23, 1:1.26, 1:1.29, 1:1.32, 1:1.35, 1:1.38, 1:1.41, 1:1.44, 1:1.47, or 1:1.5. However, it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0013] In some alternative embodiments, the volume ratio of tris(trimethylsilyl) phosphate to tetrahydrofuran is 1:3 - 4. For example, it can be 1:3, 1:3.1, 1:3.2, 1:3.3, 1:3.4, 1:3.5, 1:3.6, 1:3.7, 1:3.8, 1:3.9, or 1:4. However, it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0014] In some alternative embodiments, the molar ratio of tris(trimethylsilyl) phosphate to potassium tert - butoxide is 1:1.1 - 1.3. For example, it can be 1:1.1, 1:1.12, 1:1.14, 1:1.16, 1:1.18, 1:1.2, 1:1.22, 1:1.24, 1:1.26, 1:1.28, or 1:1.3. However, it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0015] In some alternative embodiments, the concentration of the potassium tert-butoxide solution in tetrahydrofuran is 0.8 - 1.2 M. For example, it can be 0.8 M, 0.84 M, 0.88 M, 0.92 M, 0.96 M, 1.0 M, 1.04 M, 1.08 M, 1.12 M, 1.16 M, or 1.2 M. However, it is not limited to the listed values, and other unlisted values within this range are equally applicable.

[0016] In some alternative embodiments, the temperature for the constant-temperature reaction of the reaction solution B is 50 - 60 °C. For example, it can be 50 °C, 51 °C, 52 °C, 53 °C, 54 °C, 55 °C, 56 °C, 57 °C, 58 °C, 59 °C, or 60 °C. However, it is not limited to the listed values, and other unlisted values within this range are equally applicable.

[0017] In some alternative embodiments, the time for the constant-temperature reaction of the reaction solution B is 8 - 10 h. For example, it can be 8 h, 8.2 h, 8.4 h, 8.6 h, 8.8 h, 9 h, 9.2 h, 9.4 h, 9.6 h, 9.8 h, or 10 h. However, it is not limited to the listed values, and other unlisted values within this range are equally applicable.

[0018] As a preferred technical solution of the present invention, in step S2, the molar ratio of tris(2,2,2-trifluoroethyl) borate to trimethylchlorosilane is 1:1.2 - 1.3. For example, it can be 1:1.2, 1:1.21, 1:1.22, 1:1.23, 1:1.24, 1:1.25, 1:1.26, 1:1.27, 1:1.28, 1:1.29, or 1:1.3. However, it is not limited to the listed values, and other unlisted values within this range are equally applicable.

[0019] In some alternative embodiments, the volume ratio of tris(2,2,2-trifluoroethyl) borate to dichloromethane is 1:3 - 4. For example, it can be 1:3, 1:3.1, 1:3.2, 1:3.3, 1:3.4, 1:3.5, 1:3.6, 1:3.7, 1:3.8, 1:3.9, or 1:4. However, it is not limited to the listed values, and other unlisted values within this range are equally applicable.

[0020] In some alternative embodiments, the temperature for dropping triethylamine into the reaction solution C is 0 - 5 °C. For example, it can be 0 °C, 0.5 °C, 1 °C, 1.5 °C, 2 °C, 2.5 °C, 3 °C, 3.5 °C, 4 °C, 4.5 °C, or 5 °C. However, it is not limited to the listed values, and other unlisted values within this range are equally applicable.

[0021] In some alternative embodiments, the molar ratio of tris(2,2,2-trifluoroethyl) borate to triethylamine is 1:1 - 1.5. For example, it can be 1:1, 1:1.05, 1:1.1, 1:1.15, 1:1.2, 1:1.25, 1:1.3, 1:1.35, 1:1.4, 1:1.45, or 1:1.5. However, it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0022] In some alternative embodiments, the reaction is carried out at room temperature for 4 - 6 h. For example, it can be 4 h, 4.2 h, 4.4 h, 4.6 h, 4.8 h, 5 h, 5.2 h, 5.4 h, 5.6 h, 5.8 h, or 6 h. However, it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0023] As a preferred technical solution of the present invention, in step S3, the molar ratio of ethylene carbonate to the selective fluorinating agent is 1:0.8 - 1.2. For example, it can be 1:0.8, 1:0.84, 1:0.88, 1:0.92, 1:0.96, 1:1, 1:1.04, 1:1.08, 1:1.12, 1:1.16, or 1:1.2. However, it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0024] In some alternative embodiments, the volume ratio of ethylene carbonate to acetonitrile is 1:3 - 4. For example, it can be 1:3, 1:3.1, 1:3.2, 1:3.3, 1:3.4, 1:3.5, 1:3.6, 1:3.7, 1:3.8, 1:3.9, or 1:4. However, it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0025] In some alternative embodiments, the stirring speed of the reaction solution D during the ice bath stirring reaction under nitrogen protection is 500 - 600 rpm. For example, it can be 500 rpm, 510 rpm, 520 rpm, 530 rpm, 540 rpm, 550 rpm, 560 rpm, 570 rpm, 580 rpm, 590 rpm, or 600 rpm. However, it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0026] In some alternative embodiments, the reaction time of the reaction solution D during the ice bath stirring reaction under nitrogen protection is 3 - 5 h. For example, it can be 3 h, 3.2 h, 3.4 h, 3.6 h, 3.8 h, 4 h, 4.2 h, 4.4 h, 4.6 h, 4.8 h, or 5 h. However, it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0027] In some alternative embodiments, the volume ratio of fluorinated ethylene carbonate to methanol in the fluorinated ethylene carbonate methanol dispersion is 1:1.5 - 2.5. For example, it can be 1:1.5, 1:1.6, 1:1.7, 1:1.8, 1:1.9, 1:2, 1:2.1, 1:2.2, 1:2.3, 1:2.4, or 1:2.5. However, it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0028] In some alternative embodiments, the molar ratio of fluorinated ethylene carbonate to sodium methoxide is 1:0.9 - 1.1. For example, it can be 1:0.9, 1:0.92, 1:0.94, 1:0.96, 1:0.98, 1:1, 1:1.02, 1:1.04, 1:1.06, 1:1.08, or 1:1.1. However, it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0029] In some alternative embodiments, the stirring speed of the reaction solution F during stirring reaction at room temperature is 400 - 600 rpm. For example, it can be 400 rpm, 420 rpm, 440 rpm, 460 rpm, 480 rpm, 500 rpm, 520 rpm, 540 rpm, 560 rpm, 580 rpm, or 600 rpm. However, it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0030] In some alternative embodiments, the stirring reaction time of the reaction solution F at room temperature is 5 - 7 h. For example, it can be 5 h, 5.2 h, 5.4 h, 5.6 h, 5.8 h, 6 h, 6.2 h, 6.4 h, 6.6 h, 6.8 h, or 7 h. However, it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0031] In some alternative embodiments, the concentration of the dilute hydrochloric acid is 0.5 - 1.5 M. For example, it can be 0.5 M, 0.6 M, 0.7 M, 0.8 M, 0.9 M, 1 M, 1.1 M, 1.2 M, 1.3 M, 1.4 M, or 1.5 M. However, it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0032] In some alternative embodiments, the pH of the reaction solution G is adjusted to 6.5 - 7.5 with dilute hydrochloric acid. For example, it can be 6.5, 6.6, 6.7, 6.8, 6.9, 7, 7.1, 7.2, 7.3, 7.4, or 7.5. However, it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0033] As a preferred technical solution of the present invention, in step S4, the molar ratio of 1,4-butyrolactone to dimethylamine is 1:0.8 - 1.2. For example, it can be 1:0.8, 1:0.84, 1:0.88, 1:0.92, 1:0.96, 1:1, 1:1.04, 1:1.08, 1:1.12, 1:1.16 or 1:1.2. However, it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0034] In some alternative embodiments, the volume ratio of 1,4-butyrolactone to methanol is 1:3 - 4. For example, it can be 1:3, 1:3.1, 1:3.2, 1:3.3, 1:3.4, 1:3.5, 1:3.6, 1:3.7, 1:3.8, 1:3.9 or 1:4. However, it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0035] In some alternative embodiments, the reaction solution H is stirred at room temperature for 6 - 8 h under nitrogen protection. For example, it can be 6 h, 6.2 h, 6.4 h, 6.6 h, 6.8 h, 7 h, 7.2 h, 7.4 h, 7.6 h, 7.8 h or 8 h. However, it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0036] In some alternative embodiments, the volume ratio of aminobutyrolactone to dichloromethane in the dichloromethane solution of aminobutyrolactone is 1:4 - 6. For example, it can be 1:4, 1:4.2, 1:4.4, 1:4.6, 1:4.8, 1:5, 1:5.2, 1:5.4, 1:5.6, 1:5.8 or 1:6. However, it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0037] In some alternative embodiments, the molar ratio of aminobutyrolactone to chlorosulfonic acid is 1:0.9 - 1.1. For example, it can be 1:0.9, 1:0.92, 1:0.94, 1:0.96, 1:0.98, 1:1, 1:1.02, 1:1.04, 1:1.06, 1:1.08 or 1:1.1. However, it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0038] In some alternative embodiments, the concentration of the dichloromethane solution of chlorosulfonic acid is 0.8 - 1.0 M. For example, it can be 0.8 M, 0.82 M, 0.84 M, 0.86 M, 0.88 M, 0.9 M, 0.92 M, 0.94 M, 0.96 M, 0.98 M or 1.0 M. However, it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0039] In some alternative embodiments, the reaction solution J is stirred in an ice bath for 2 - 3 h. For example, it can be 2.0 h, 2.1 h, 2.2 h, 2.3 h, 2.4 h, 2.5 h, 2.6 h, 2.7 h, 2.8 h, 2.9 h, or 3.0 h. However, it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0040] In some alternative embodiments, the time for continued stirring of the reaction at room temperature is 4 - 5 h. For example, it can be 4.0 h, 4.1 h, 4.2 h, 4.3 h, 4.4 h, 4.5 h, 4.6 h, 4.7 h, 4.8 h, 4.9 h, or 5.0 h. However, it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0041] In some alternative embodiments, the volume ratio of the pretreated reaction solution to ice water is 1:2 - 3. For example, it can be 1:2.0, 1:2.1, 1:2.2, 1:2.3, 1:2.4, 1:2.5, 1:2.6, 1:2.7, 1:2.8, 1:2.9, or 1:3.0. However, it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0042] As a preferred technical solution of the present invention, in step S5, the rotation speed of adding dimethyl carbonate and ethyl methyl carbonate to ether-based fluorinated ethylene carbonate and stirring is 500 - 600 rpm. For example, it can be 500 rpm, 510 rpm, 520 rpm, 530 rpm, 540 rpm, 550 rpm, 560 rpm, 570 rpm, 580 rpm, 590 rpm, or 600 rpm. However, it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0043] In some alternative embodiments, the time for adding dimethyl carbonate and ethyl methyl carbonate to ether-based fluorinated ethylene carbonate and stirring is 30 - 40 min. For example, it can be 30 min, 31 min, 32 min, 33 min, 34 min, 35 min, 36 min, 37 min, 38 min, 39 min, or 40 min. However, it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0044] In some alternative embodiments, the time for continued stirring of the reaction solution K is 2 - 3 h. For example, it can be 2.0 h, 2.1 h, 2.2 h, 2.3 h, 2.4 h, 2.5 h, 2.6 h, 2.7 h, 2.8 h, 2.9 h, or 3.0 h. However, it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0045] In some alternative embodiments, the standing time is 12 - 18h, for example, it can be 12.0h, 12.6h, 13.2h, 13.8h, 14.4h, 15.0h, 15.6h, 16.2h, 16.8h, 17.4h or 18.0h, but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0046] In a second aspect, the present invention provides a high-rate lithium battery electrolyte based on the synergistic effect of borate and phosphate. The high-rate lithium battery electrolyte based on the synergistic effect of borate and phosphate includes modified tris(trimethylsilyl) phosphate, silicon-based modified tris(2,2,2-trifluoroethyl) borate, ether-based fluorinated ethylene carbonate, dimethyl carbonate, ethyl methyl carbonate, amino-sulfonated butyrolactone, and lithium hexafluorophosphate.

[0047] The present invention selects tris(trimethylsilyl) phosphate. Tris(trimethylsilyl) phosphate is an organosilicon compound containing a phosphate group and has good electrochemical stability. Its phosphate group can form an ion pair with the lithium salt and form a stable interfacial film on the surface of the negative electrode through decomposition, effectively inhibiting the growth of lithium dendrites; however, the methylsilyl group in tris(trimethylsilyl) phosphate has a certain degree of hydrophobicity, which to a certain extent reduces its compatibility with polar solvents, resulting in limited solvation ability. Therefore, although it can indirectly reduce the viscosity of the electrolyte, its effect on directly improving the lithium ion mobility is limited.

[0048] In order to enhance the solvation ability of tris(trimethylsilyl) phosphate while retaining its low viscosity advantage, the present invention modifies tris(trimethylsilyl) phosphate by introducing an allyl group. By reacting with allyl alcohol, some of the methylsilyl groups are replaced with allyl groups. The allyl group has a certain degree of polarity and flexibility, which can improve the polarity of the tris(trimethylsilyl) phosphate molecule to a certain extent and enhance its interaction with lithium ions. In addition, the flexibility of the allyl group helps to improve the compatibility of tris(trimethylsilyl) phosphate with carbonate solvents and enables it to exhibit more excellent ion migration kinetics performance under high-rate charge and discharge conditions of lithium batteries. Due to the small molecular volume of the allyl group, the modified tris(trimethylsilyl) phosphate can still maintain low viscosity characteristics and avoid significantly increasing the viscous resistance of the system.

[0049] In the present invention, tris(2,2,2-trifluoroethyl) borate is selected. Tris(2,2,2-trifluoroethyl) borate is a boron-containing organic compound. In its structure, the central boron atom is connected to the trifluoroethyl groups through three B-O bonds respectively, forming a trigonal pyramidal structure. The boron atom in the borate skeleton exhibits obvious Lewis acidity and can have a weak coordination interaction with anions in the solution, thereby optimizing the ionic environment of the electrolyte; while the three fluorine atoms in its trifluoroethyl group produce an electron attraction effect through strong electronegativity, reducing its tendency to react with other chemical substances and enhancing its chemical stability under high voltage conditions; the trifluoroethyl group makes the whole molecule have a certain hydrophobicity, which helps to reduce the interaction with polar solvents, thereby reducing the overall viscosity of the electrolyte and contributing to improving the ionic mobility of the electrolyte; in addition, the trifluoroethyl group has a relatively large volume, which can provide a certain steric hindrance effect to inhibit the polymerization reaction or side reaction between molecules, thereby improving the stability of the electrolyte. After tris(2,2,2-trifluoroethyl) borate decomposes on the surface of the lithium battery negative electrode, compounds containing B-F bonds and B-O bonds can be formed. These compounds can form a dense and chemically stable interfacial film on the surface of the lithium metal negative electrode. This film has high chemical stability and thermal stability, which helps to effectively protect the lithium metal negative electrode and inhibit the growth of lithium dendrites.

[0050] Although the interfacial film formed by the decomposition of tris(2,2,2-trifluoroethyl) borate has high chemical stability, its mechanical strength is relatively weak and it is easily affected by mechanical stress especially under high current density and high rate charge-discharge conditions. The volume change (such as deposition and stripping) on the surface of the lithium metal will exert a large mechanical stress on the interfacial film, which will in turn cause the film to rupture or peel off, thereby exposing the surface of the lithium metal and accelerating the occurrence of side reactions. In addition, due to the relatively strong molecular rigidity of the interfacial film, its distribution on the surface of the lithium metal may be uneven. Especially when the microscopic morphology of the lithium metal surface is uneven, this unevenness may promote the growth of lithium dendrites in local areas.

[0051] Therefore, in the present invention, trimethylchlorosilane is used to introduce trimethylsilyl groups for modification. The trimethylsilyl group is a group with a certain structural flexibility. Its introduction can form a silicon-containing network structure in the decomposition products. This structure, in cooperation with the original B-F bonds and B-O bonds, significantly enhances the flexibility and mechanical strength of the interfacial film. In addition, the silicon-based modification can effectively disperse local stress and relieve the stress concentration phenomenon by forming a silicon-oxygen network in the film, thereby reducing the risk of film rupture. The interfacial film formed by the decomposition of tris(2,2,2-trifluoroethyl) borate after silicon-based modification shows higher mechanical strength and anti-peeling ability under high-rate charge and discharge conditions due to the enhanced silicon-oxygen network structure, thus improving the cycle stability of lithium batteries. In addition, the silicon oxide generated by the decomposition of tris(2,2,2-trifluoroethyl) borate molecules after silicon-based modification has high surface activity and can form a stronger chemical bonding force with the lithium metal surface, which helps to fill surface microdefects and enhance the stability of the interfacial film. The flexible structure of the modified molecule helps to form a more continuous and uniform interfacial film on the lithium metal surface, reducing the areas with too high local current density, further improving the uniformity and bonding force of the interfacial film, thereby effectively inhibiting the growth of lithium dendrites and improving the safety and service life of lithium batteries.

[0052] Ethylene carbonate is introduced in the present invention. Ethylene carbonate is a common organic carbonate solvent, and its molecular structure consists of a carbonate group and a vinyl structure. Ethylene carbonate has a high dielectric constant and can effectively dissolve high-concentration lithium salts to form a uniform electrolyte solution, thereby providing a high ionic conductivity and improving the electrochemical performance of the battery. During the electrochemical reaction process, ethylene carbonate molecules will decompose preferentially to generate a series of products, which help to form a dense solid electrolyte interface film on the negative electrode surface, thereby ensuring the cycle stability of the battery. The ethylene carbonate molecule contains stable ester bonds and a cyclic ether structure, which can form a strong coordination interaction with lithium ions, significantly enhancing the solvation ability and making lithium ions more easily migrate in the electrolyte. However, at extremely low temperatures, ethylene carbonate may have a reduced fluidity in the electrolyte due to the enhanced intermolecular forces, thus affecting the migration performance of lithium ions, which limits its use in low-temperature environments; at the same time, due to the strong intermolecular forces, it will result in a high viscosity in the electrolyte, and this high viscosity limits the migration rate of lithium ions in the electrolyte, especially under high-rate charge and discharge conditions, which is likely to cause battery polarization. In addition, the interfacial film formed by the decomposition of ethylene carbonate mainly consists of inorganic carbonates and polycarbonates. Although these products have good chemical stability, their mechanical strength is low. Especially during the volume change (such as deposition and stripping) of the lithium metal negative electrode, the interfacial film is prone to rupture or peeling, thus exacerbating side reactions.

[0053] Based on the above deficiencies, the present invention uses a selective fluorinating reagent and sodium methoxide to modify ethylene carbonate. Through the fluorination and etherification of ethylene carbonate, the introduction of the C-F bond enhances the hydrophobicity of the molecule, helps improve the low-temperature fluidity, and reduces the intermolecular hydrogen bonding effect, making it easier to maintain a liquid state and enhancing the low-temperature fluidity. The flexible structure of the ether group further reduces the intermolecular interaction force, enabling the electrolyte to maintain a high ion migration rate under low-temperature conditions. Secondly, by introducing F atoms, the decomposition behavior of ethylene carbonate can be optimized, and the generated LiF forms an inorganic product with high mechanical strength in the interfacial film. LiF is an inorganic substance with extremely high chemical and thermal stability, and its high mechanical strength and hydrophobicity can significantly enhance the anti-peeling ability of the interfacial film, thereby improving the mechanical properties of the interfacial film. The organic polymer generated by the decomposition of the ether group endows the interfacial film with certain flexibility, enabling it to better adapt to the volume change of lithium metal. The interfacial film generated by the decomposition of the modified ethylene carbonate has both high mechanical strength and certain flexibility, which can effectively inhibit the growth of lithium dendrites and reduce side reactions. In addition, by introducing an ether group structure, the intermolecular interaction force of ethylene carbonate molecules is reduced, and at the same time, the modified molecules are more likely to form a homogeneous mixed electrolyte with other low-viscosity solvents. The introduction of the ether group structure effectively reduces the viscosity of the system, improves the migration rate of lithium ions, and the modified electrolyte has lower viscosity and higher ionic conductivity, thereby enhancing the rate performance of lithium batteries.

[0054] The present invention introduces 1,4-butyrolactone. The 1,4-butyrolactone molecule contains an ester group and a lactone ring structure. Its low molecular weight and weak intermolecular interaction force result in low viscosity, which helps reduce the overall viscosity of the electrolyte and improve the migration rate of lithium ions. At the same time, it has high polarity, can effectively dissolve lithium salts, and is miscible with other carbonate solvents, improving the ionic conductivity of the electrolyte. Secondly, 1,4-butyrolactone has good low-temperature performance and can still maintain high fluidity and conductivity in a low-temperature environment, which helps improve the performance of the electrolyte under low-temperature conditions, thereby enhancing the capacity retention rate and rate performance of lithium batteries in a low-temperature environment. In addition, the ester group in the 1,4-butyrolactone molecule has high chemical stability and can maintain good redox stability within a wide voltage window. During the decomposition of the electrolyte, 1,4-butyrolactone can form a solid electrolyte interface film on the negative electrode surface, which helps inhibit side reactions and improve the cycle stability of the battery.

[0055] However, the interfacial film formed by the decomposition of 1,4-butyrolactone has relatively low mechanical strength. At the same time, its oxidation decomposition temperature is relatively low, and it is prone to oxidation decomposition under high-voltage conditions, resulting in side reactions and affecting the stability of the electrolyte. Therefore, it is modified by introducing amino groups and sulfonic acid groups. The introduction of amino groups increases the polarity of the molecule and promotes the formation of nitrogen-containing polymers during the reduction decomposition process. These polymers can significantly enhance the toughness of the interfacial film. The introduction of sulfonic acid groups can promote the decomposition of butyrolactone to generate lithium sulfite or other sulfate compounds. These products have relatively high mechanical strength and chemical stability and can enhance the structure of the interfacial film. The interfacial film formed by the modified butyrolactone has both relatively high mechanical strength and certain flexibility, can effectively adapt to the dynamic volume change of the lithium metal anode, inhibit the growth of lithium dendrites, and thus improve the cycle performance of the battery. In addition, as a strong electron-withdrawing group, the introduction of sulfonic acid groups reduces the electron cloud density of 1,4-butyrolactone molecules, thereby increasing its oxidation decomposition potential and reducing the risk of side reactions under high-voltage conditions, significantly improving its stability under high voltage.

[0056] There is also a synergistic enhancement effect in the present invention: Both tris(trimethylsilyl) phosphate and tris(2,2,2-trifluoroethyl) borate have relatively high polarity and can effectively dissolve lithium salts. The phosphate group in tris(trimethylsilyl) phosphate provides solvation ability, while the trifluoroethyl group in tris(2,2,2-trifluoroethyl) borate can effectively enhance its stability under high voltage. When these two substances are combined, their polarities are complementary, which can enhance the dissolution ability of the electrolyte and improve the ionic conductivity of the lithium battery. Secondly, the phosphate structure of tris(trimethylsilyl) phosphate and the trifluoroethyl group in tris(2,2,2-trifluoroethyl) borate work together to improve the electrochemical stability of the electrolyte, especially under high-voltage conditions. Tris(trimethylsilyl) phosphate itself has good electrochemical stability, and the fluorine element in tris(2,2,2-trifluoroethyl) borate enhances the chemical stability of the electrolyte, making the overall system not easily decompose under high voltage. The combination of the two ensures the stable operation of the battery under high voltage. The combined action of tris(trimethylsilyl) phosphate and tris(2,2,2-trifluoroethyl) borate in the electrolyte not only improves the dissolution ability and ionic conductivity but also optimizes the stability of the electrolyte and reduces the occurrence of side reactions, especially under high voltage and high temperature conditions.

[0057] Ethylene carbonate, as a commonly used solvent, has a high dissolving capacity and moderate polarity. However, its molecular structure is relatively rigid, and it may exhibit a high viscosity at low temperatures. The introduction of tris(trimethylsilyl) phosphate not only increases the polarity of the electrolyte but also reduces the intermolecular hydrogen bonding, enabling it to have good fluidity at low temperatures. After the two are combined, tris(trimethylsilyl) phosphate can improve the fluidity of ethylene carbonate, ensuring that the electrolyte still maintains a low viscosity under low-temperature conditions, thereby enhancing the migration rate of lithium ions; there is a certain interaction between the phosphate group of tris(trimethylsilyl) phosphate and the ester group in ethylene carbonate, which can enhance the stability of the electrolyte, especially under high-temperature and high-voltage conditions. As a substance with strong electrochemical stability, tris(trimethylsilyl) phosphate helps improve the performance of ethylene carbonate under these extreme conditions; the combination of the two enhances the low-temperature performance, fluidity, and conductivity of the electrolyte, ensuring that the battery can operate stably under different environmental conditions. Especially under high-voltage and low-temperature environments, the combination of tris(trimethylsilyl) phosphate and ethylene carbonate optimizes the performance of the electrolyte, enhancing the rate performance and cycle life of the battery.

[0058] Ethylene carbonate and tris(2,2,2-trifluoroethyl) borate exhibit different stabilities under high voltages. Ethylene carbonate is prone to oxidative decomposition under high voltages, but it has a strong dissolving capacity. Tris(2,2,2-trifluoroethyl) borate has high oxidative stability, and its trifluoroethyl groups enhance the stability under high voltages. The introduction of tris(2,2,2-trifluoroethyl) borate can inhibit the decomposition reaction of ethylene carbonate under high voltages, improving the stability of the electrolyte under high-voltage conditions; ethylene carbonate has a high polarity and can effectively dissolve lithium salts, while the polarity and dissolving capacity of tris(2,2,2-trifluoroethyl) borate have a stronger effect on the stability under high voltages. The synergistic effect of the two ensures the stability of the electrolyte under high voltages and simultaneously enhances the ionic conductivity of the electrolyte; after the two are combined, they can effectively inhibit side reactions in a high-voltage environment, enhance the dissolving capacity and ionic conductivity of the electrolyte, and improve the electrochemical performance and safety of the battery.

[0059] After the decomposition of 1,4-butyrolactone, an interfacial film can be formed, and the introduction of tris(trimethylsilyl) phosphate can enhance the chemical stability and mechanical strength of the interfacial film. The interfacial film formed by 1,4-butyrolactone has good flexibility, and the phosphate structure of tris(trimethylsilyl) phosphate can further improve the mechanical strength of the interfacial film. The two interact with each other to improve the stability and anti-peeling ability of the interfacial film; 1,4-butyrolactone itself has good solvation ability, which can improve the migration rate of lithium ions. The phosphate groups introduced by tris(trimethylsilyl) phosphate can further enhance the solvation ability to ensure the smooth migration of lithium ions in the electrolyte. After the two are combined, they can jointly improve the ionic conductivity of the electrolyte and enhance the rate performance of the battery.

[0060] The interfacial film formed by 1,4-butyrolactone is relatively soft, but it has strong chemical corrosion resistance. Tris(2,2,2-trifluoroethyl) borate enhances the chemical stability of the interfacial film through the introduction of trifluoroethyl groups, especially under high voltage and high temperature conditions. The combination of the two enables the interfacial film to have strong chemical stability while providing flexibility to adapt to the volume change of the lithium metal anode; the flexible interfacial film formed by 1,4-butyrolactone may be easily damaged during cycling, and the introduction of tris(2,2,2-trifluoroethyl) borate can prevent peeling, reduce side reactions, and improve the cycle stability of the battery by increasing the mechanical strength of the interfacial film.

[0061] 1,4-Butyrolactone has good low-temperature performance, while ethylene carbonate has poor fluidity at low temperatures. The introduction of 1,4-butyrolactone can improve the fluidity of the electrolyte at low temperatures, while ethylene carbonate provides good solubility and polarity for the electrolyte. The combination of the two enables the electrolyte to maintain good fluidity and ionic conductivity in a low-temperature environment. The combination of 1,4-butyrolactone and ethylene carbonate helps to form a uniform and stable solvent environment in the electrolyte, thereby promoting the stability of the interfacial film and the smooth migration of lithium ions.

[0062] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0063] (1) Allyl groups are introduced to modify tris(trimethylsilyl) phosphate, replacing some methylsilyl groups, improving the compatibility with carbonate solvents, improving ion migration performance, and at the same time retaining its advantage of low viscosity;

[0064] (2) Tris(2,2,2-trifluoroethyl) borate is introduced and modified with trimethylchlorosilane. The silicon-oxygen network enhances the flexibility and mechanical strength of the interfacial film, helps to relieve local stress, reduces the risk of interfacial film rupture, and at the same time improves the uniformity and adhesion of the interfacial film, effectively inhibiting the growth of lithium dendrites;

[0065] (3) Fluorinate and etherify ethylene carbonate: Fluorination enhances the molecular hydrophobicity, improves the low-temperature fluidity, and reduces the intermolecular hydrogen bond interaction; etherification reduces the intermolecular interaction force and maintains a high ion migration rate;

[0066] (4) Introduce amino groups to increase the polarity of 1,4-butyrolactone, promote the formation of nitrogen-containing polymers, and enhance the toughness of the interfacial film; introduce sulfonic acid groups to generate lithium sulfite or other sulfate compounds, and improve the mechanical strength and stability of the interfacial film;

[0067] (5) The synergistic effect among the components effectively improves the ion migration rate and stability of the electrolyte, and enhances the performance and stability of the electrolyte under conditions such as low temperature, high voltage, and high-rate charge and discharge. Description of the Drawings

[0068] Figure 1 It is a flowchart of the preparation method of a high-rate lithium battery electrolyte based on the synergistic effect of borate and phosphate provided in Embodiment 1 of the present invention. Detailed Embodiments

[0069] The technical solution of the present invention will be described in detail below in conjunction with specific embodiments and their accompanying drawings. The embodiments described herein are specific specific embodiments of the present invention and are used to illustrate the concept of the present invention; these descriptions are all explanatory and exemplary, and should not be construed as limiting the embodiments of the present invention and the protection scope of the present invention. Except for the embodiments described herein, those skilled in the art can also adopt other obvious technical solutions based on the content disclosed in the claims and the specification of the present application. These technical solutions include technical solutions that make any obvious substitutions and modifications to the embodiments described herein.

[0070] The chemical reagents used in the embodiments and comparative examples of the present invention are all commercially available products and have not been further purified or processed.

[0071] Embodiment 1

[0072] As Figure 1 shown, this embodiment provides a high-rate lithium battery electrolyte based on the synergistic effect of borate and phosphate and its preparation method. The preparation method specifically includes the following steps:

[0073] S1: Add tris(trimethylsilyl) phosphate and allyl alcohol into tetrahydrofuran, where the molar ratio of tris(trimethylsilyl) phosphate to allyl alcohol is 1:1.2, and the volume ratio of tris(trimethylsilyl) phosphate to tetrahydrofuran is 1:3.5. Stir at room temperature to obtain reaction solution A. Ice-bath reaction solution A and dropwise add a tetrahydrofuran solution of potassium tert-butoxide with a concentration of 0.8 M to obtain reaction solution B, where the molar ratio of tris(trimethylsilyl) phosphate to potassium tert-butoxide is 1:1.2. React at a constant temperature of 55 °C for 9 h, perform vacuum distillation and column chromatography to obtain modified tris(trimethylsilyl) phosphate;

[0074] S2: Add tris(2,2,2-trifluoroethyl) borate and trimethylchlorosilane into dichloromethane with a molar ratio of 1:1.28 under nitrogen protection to obtain reaction solution C, where the volume ratio of tris(2,2,2-trifluoroethyl) borate to dichloromethane is 1:3.4. Dropwise add triethylamine at a constant temperature of 0 °C, where the molar ratio of tris(2,2,2-trifluoroethyl) borate to triethylamine is 1:1. Then raise the temperature to room temperature and react for 4 h. Filter, wash, and perform vacuum distillation to obtain silicon-based modified tris(2,2,2-trifluoroethyl) borate;

[0075] S3: Mix ethylene carbonate and a selective fluorinating agent in acetonitrile with a molar ratio of 1:0.8 to obtain reaction solution D, where the volume ratio of ethylene carbonate to acetonitrile is 1:3.6. Stir the reaction under nitrogen protection in an ice bath to obtain reaction solution E, where the stirring speed is 550 rpm and the time is 4 h. Perform vacuum distillation and column chromatography to obtain fluorinated ethylene carbonate. Prepare a methanol dispersion of fluorinated ethylene carbonate, where the volume ratio of fluorinated ethylene carbonate to methanol in the dispersion is 1:2.5. Add sodium methoxide to obtain reaction solution F, where the molar ratio of fluorinated ethylene carbonate to sodium methoxide is 1:1. Stir and react at room temperature to obtain reaction solution G, where the stirring speed is 600 rpm and the time is 6 h. Adjust the pH to 7.2 with dilute hydrochloric acid with a concentration of 0.5 M, perform vacuum distillation and column chromatography to obtain ether-based fluorinated ethylene carbonate;

[0076] S4: Add 1,4 - butyrolactone and dimethylamine into methanol to obtain reaction solution H, where the molar ratio of 1,4 - butyrolactone to dimethylamine is 1:0.8, and the volume ratio of 1,4 - butyrolactone to methanol is 1:3. Stir the reaction at room temperature for 6.6 h under nitrogen protection to obtain reaction solution I. After vacuum distillation and column chromatography, amino - butyrolactone is obtained. Prepare a dichloromethane solution of amino - butyrolactone, where the volume ratio of amino - butyrolactone to dichloromethane in the dichloromethane solution of amino - butyrolactone is 1:6. Dropwise add a dichloromethane solution of chlorosulfonic acid with a concentration of 1 M to the reaction solution under ice - bath to obtain reaction solution J, where the molar ratio of amino - butyrolactone to chlorosulfonic acid is 1:0.9. Stir for 2 h under ice - bath and then raise the temperature to room temperature and continue to stir the reaction for 5 h to obtain a pretreatment reaction solution. Add ice - water to quench the reaction, where the volume ratio of the pretreatment reaction solution to ice - water is 1:2. Filter, wash, vacuum distill, and perform column chromatography to obtain amino - sulfonated butyrolactone;

[0077] S5: Add dimethyl carbonate and ethyl methyl carbonate into ether - fluorinated ethylene carbonate and stir at a speed of 550 rpm for 30 min to obtain a solvent, where the volume ratio of dimethyl carbonate, ethyl methyl carbonate, and ether - fluorinated ethylene carbonate is 32:33:35. Sequentially add amino - sulfonated butyrolactone with a feeding amount of 0.5% of the solvent mass, modified tris(trimethylsilyl) phosphate with a feeding amount of 1.5% of the solvent mass, and tris(2,2,2 - trifluoroethyl) borate modified by silicon group with a feeding amount of 1.2% of the solvent mass. After stirring, add lithium hexafluorophosphate to obtain reaction solution K, where the concentration of lithium hexafluorophosphate in the solvent is 1.2 M. Continue to stir for 2 h, let it stand for 12 h, and then filter through a PTFE membrane to obtain a high - rate lithium - battery electrolyte based on the synergistic effect of borate and phosphate.

[0078] Example 2

[0079] This example provides a high - rate lithium - battery electrolyte based on the synergistic effect of borate and phosphate and its preparation method. The preparation method specifically includes the following steps:

[0080] S1: Add tris(trimethylsilyl) phosphate and allyl alcohol into tetrahydrofuran, where the molar ratio of tris(trimethylsilyl) phosphate to allyl alcohol is 1:1.4, and the volume ratio of tris(trimethylsilyl) phosphate to tetrahydrofuran is 1:3. Stir at room temperature to obtain reaction solution A. Ice - bath reaction solution A and dropwise add a tetrahydrofuran solution of potassium tert - butoxide with a concentration of 1.2 M to obtain reaction solution B, where the molar ratio of tris(trimethylsilyl) phosphate to potassium tert - butoxide is 1:1.26. React at a constant temperature of 50 °C for 10 h. After vacuum distillation and column chromatography, modified tris(trimethylsilyl) phosphate is obtained;

[0081] S2: Tris(2,2,2-trifluoroethyl) borate and trimethylchlorosilane were added to dichloromethane at a molar ratio of 1:1.3 under nitrogen protection to obtain reaction solution C, where the volume ratio of tris(2,2,2-trifluoroethyl) borate to dichloromethane was 1:3.8. Triethylamine was added dropwise at a constant temperature of 2 °C, where the molar ratio of tris(2,2,2-trifluoroethyl) borate to triethylamine was 1:1.4. Subsequently, the temperature was raised to room temperature and the reaction was carried out for 5 h. After filtration, washing, and vacuum distillation, silicon-based modified tris(2,2,2-trifluoroethyl) borate was obtained;

[0082] S3: Ethylene carbonate and a selective fluorinating reagent were mixed in acetonitrile at a molar ratio of 1:1.2 to obtain reaction solution D, where the volume ratio of ethylene carbonate to acetonitrile was 1:3.2. Under nitrogen protection, the reaction was stirred in an ice bath to obtain reaction solution E, where the stirring speed was 570 rpm and the time was 3 h. After vacuum distillation and column chromatography, fluorinated ethylene carbonate was obtained; A methanol dispersion of fluorinated ethylene carbonate was prepared, where the volume ratio of fluorinated ethylene carbonate to methanol in the dispersion was 1:2. Sodium methoxide was added to obtain reaction solution F, where the molar ratio of fluorinated ethylene carbonate to sodium methoxide was 1:1.1. After stirring at room temperature, reaction solution G was obtained, where the stirring speed was 550 rpm and the time was 7 h. The pH was adjusted to 6.5 with 1.5 M dilute hydrochloric acid. After vacuum distillation and column chromatography, ether-based fluorinated ethylene carbonate was obtained;

[0083] S4: 1,4-Butyrolactone and dimethylamine were added to methanol to obtain reaction solution H, where the molar ratio of 1,4-butyrolactone to dimethylamine was 1:1.1 and the volume ratio of 1,4-butyrolactone to methanol was 1:3.5. Under nitrogen protection, the reaction was stirred at room temperature for 8 h to obtain reaction solution I. After vacuum distillation and column chromatography, aminoated butyrolactone was obtained; A dichloromethane solution of aminoated butyrolactone was prepared, where the volume ratio of aminoated butyrolactone to dichloromethane in the dichloromethane solution of aminoated butyrolactone was 1:5. A dichloromethane solution of chlorosulfonic acid with a concentration of 0.9 M was added dropwise in an ice bath to obtain reaction solution J, where the molar ratio of aminoated butyrolactone to chlorosulfonic acid was 1:1.0. After stirring in an ice bath for 2.5 h, the temperature was raised to room temperature and the reaction was continued for 4.5 h to obtain a pretreatment reaction solution. Ice water was added to quench the reaction, where the volume ratio of the pretreatment reaction solution to ice water was 1:3. After filtration, washing, vacuum distillation, and column chromatography, amino-sulfonated butyrolactone was obtained;

[0084] S5: Add dimethyl carbonate and ethyl methyl carbonate to fluoroethyl ethylene carbonate ether and stir at 500 rpm for 40 min to obtain a solvent, where the volume ratio of dimethyl carbonate, ethyl methyl carbonate, and fluoroethyl ethylene carbonate ether is 30:30:40. Sequentially add 0.8% by mass of the solvent of amino-sulfonated butyrolactone, 1.3% by mass of the solvent of modified tris(trimethylsilyl) phosphate, and 1% by mass of the solvent of tris(2,2,2-trifluoroethyl) borate modified with silicon group. After stirring, add lithium hexafluorophosphate to obtain reaction solution K, where the concentration of lithium hexafluorophosphate in the solvent is 1 M. Continue to stir for 2.8 h, let it stand for 14 h, and then filter through a PTFE membrane to obtain a high-rate lithium battery electrolyte based on the synergistic effect of borate and phosphate.

[0085] Example 3

[0086] This example provides a high-rate lithium battery electrolyte based on the synergistic effect of borate and phosphate and its preparation method. The preparation method specifically includes the following steps:

[0087] S1: Add tris(trimethylsilyl) phosphate and allyl alcohol to tetrahydrofuran, where the molar ratio of tris(trimethylsilyl) phosphate to allyl alcohol is 1:1.5, and the volume ratio of tris(trimethylsilyl) phosphate to tetrahydrofuran is 1:4. Stir at room temperature to obtain reaction solution A. Ice-bath reaction solution A and dropwise add a tetrahydrofuran solution of potassium tert-butoxide with a concentration of 1.1 M to obtain reaction solution B, where the molar ratio of tris(trimethylsilyl) phosphate to potassium tert-butoxide is 1:1.1. React at a constant temperature of 60 °C for 8 h, carry out vacuum distillation and column chromatography to obtain modified tris(trimethylsilyl) phosphate;

[0088] S2: Add tris(2,2,2-trifluoroethyl) borate and trimethylchlorosilane to dichloromethane under nitrogen protection with a molar ratio of 1:1.25, where the volume ratio of tris(2,2,2-trifluoroethyl) borate to dichloromethane is 1:4. Dropwise add triethylamine at a constant temperature of 4 °C, where the molar ratio of tris(2,2,2-trifluoroethyl) borate to triethylamine is 1:1.3. Then raise the temperature to room temperature and react for 5.5 h. Filter, wash, and carry out vacuum distillation to obtain tris(2,2,2-trifluoroethyl) borate modified with silicon group;

[0089] S3: Mix ethylene carbonate and a selective fluorinating reagent in acetonitrile at a molar ratio of 1:1.0 to obtain reaction solution D, where the volume ratio of ethylene carbonate to acetonitrile is 1:3. Stir the reaction under ice bath with nitrogen protection to obtain reaction solution E, with a stirring speed of 500 rpm and a reaction time of 5 h. After vacuum distillation and column chromatography, fluorinated ethylene carbonate is obtained. Prepare a methanol dispersion of fluorinated ethylene carbonate, where the volume ratio of fluorinated ethylene carbonate to methanol in the dispersion is 1:1.5. Add sodium methoxide to obtain reaction solution F, where the molar ratio of fluorinated ethylene carbonate to sodium methoxide is 1:0.9. Stir the reaction at room temperature to obtain reaction solution G, with a stirring speed of 500 rpm and a reaction time of 6.6 h. Adjust the pH to 7 with 1 M dilute hydrochloric acid, and after vacuum distillation and column chromatography, ether-based fluorinated ethylene carbonate is obtained.

[0090] S4: Add 1,4-butyrolactone and dimethylamine to methanol to obtain reaction solution H, where the molar ratio of 1,4-butyrolactone to dimethylamine is 1:1 and the volume ratio of 1,4-butyrolactone to methanol is 1:3.8. Stir the reaction at room temperature under nitrogen protection for 7 h to obtain reaction solution I. After vacuum distillation and column chromatography, amino-functionalized butyrolactone is obtained. Prepare a dichloromethane solution of amino-functionalized butyrolactone, where the volume ratio of amino-functionalized butyrolactone to dichloromethane in the dichloromethane solution of amino-functionalized butyrolactone is 1:4. Dropwise add a dichloromethane solution of chlorosulfonic acid with a concentration of 0.8 M under ice bath to obtain reaction solution J, where the molar ratio of amino-functionalized butyrolactone to chlorosulfonic acid is 1:1.1. Stir for 3 h under ice bath and then continue to stir the reaction at room temperature for 4.8 h to obtain a pretreated reaction solution. Add ice water to quench the reaction, where the volume ratio of the pretreated reaction solution to ice water is 1:2.5. After filtration, washing, vacuum distillation, and column chromatography, amino-sulfonated butyrolactone is obtained.

[0091] S5: Add dimethyl carbonate and ethyl methyl carbonate to ether-based fluorinated ethylene carbonate and stir at a speed of 590 rpm for 33 min to obtain a solvent, where the volume ratio of dimethyl carbonate, ethyl methyl carbonate, and ether-based fluorinated ethylene carbonate is 31:31:38. Sequentially add amino-sulfonated butyrolactone with a dosage of 0.6% of the solvent mass, modified tris(trimethylsilyl) phosphate with a dosage of 1.2% of the solvent mass, and tris(2,2,2-trifluoroethyl) silane-modified boric acid with a dosage of 1.1% of the solvent mass. After stirring, add lithium hexafluorophosphate to obtain reaction solution K, where the concentration of lithium hexafluorophosphate in the solvent is 1.1 M. Continue to stir for 2.4 h, let stand for 18 h, and then filter through a PTFE membrane to obtain a high-rate lithium battery electrolyte based on the synergistic effect of borate and phosphate.

[0092] Example 4

[0093] This example provides a high-rate lithium battery electrolyte based on the synergistic effect of borate and phosphate and its preparation method. The preparation method specifically includes the following steps:

[0094] S1: Add tris(trimethylsilyl) phosphate and allyl alcohol into tetrahydrofuran, where the molar ratio of tris(trimethylsilyl) phosphate to allyl alcohol is 1:1.3, and the volume ratio of tris(trimethylsilyl) phosphate to tetrahydrofuran is 1:3.8. Stir at room temperature to obtain reaction solution A. Ice-bath reaction solution A and dropwise add a tetrahydrofuran solution of potassium tert-butoxide with a concentration of 1.0 M to obtain reaction solution B, where the molar ratio of tris(trimethylsilyl) phosphate to potassium tert-butoxide is 1:1.3. React at a constant temperature of 57 °C for 9.4 h, perform vacuum distillation and column chromatography to obtain modified tris(trimethylsilyl) phosphate;

[0095] S2: Add tris(2,2,2-trifluoroethyl) borate and trimethylchlorosilane into dichloromethane with a molar ratio of 1:1.2 under nitrogen protection to obtain reaction solution C, where the volume ratio of tris(2,2,2-trifluoroethyl) borate to dichloromethane is 1:3. Dropwise add triethylamine at a constant temperature of 5 °C, where the molar ratio of tris(2,2,2-trifluoroethyl) borate to triethylamine is 1:1.5. Then raise the temperature to room temperature and react for 6 h. Filter, wash, and perform vacuum distillation to obtain silyl-modified tris(2,2,2-trifluoroethyl) borate;

[0096] S3: Mix ethylene carbonate and a selective fluorinating reagent in acetonitrile with a molar ratio of 1:1.1 to obtain reaction solution D, where the volume ratio of ethylene carbonate to acetonitrile is 1:4. Stir and react under nitrogen protection in an ice bath to obtain reaction solution E, where the stirring speed is 600 rpm and the time is 4.4 h. Perform vacuum distillation and column chromatography to obtain fluorinated ethylene carbonate. Prepare a methanol dispersion of fluorinated ethylene carbonate, where the volume ratio of fluorinated ethylene carbonate to methanol in the dispersion is 1:2.2. Add sodium methoxide to obtain reaction solution F, where the molar ratio of fluorinated ethylene carbonate to sodium methoxide is 1:1.06. Stir and react at room temperature to obtain reaction solution G, where the stirring speed is 400 rpm and the time is 5 h. Adjust the pH to 7.5 with dilute hydrochloric acid with a concentration of 1.2 M, perform vacuum distillation and column chromatography to obtain ether-based fluorinated ethylene carbonate;

[0097] S4: Add 1,4 - butyrolactone and dimethylamine into methanol to obtain reaction solution H, where the molar ratio of 1,4 - butyrolactone to dimethylamine is 1:1.2, and the volume ratio of 1,4 - butyrolactone to methanol is 1:4. Stir the reaction at room temperature for 6 h under nitrogen protection to obtain reaction solution I. Then, perform vacuum distillation and column chromatography to obtain amino - butyrolactone. Prepare a dichloromethane solution of amino - butyrolactone, where the volume ratio of amino - butyrolactone to dichloromethane in the dichloromethane solution of amino - butyrolactone is 1:4.6. Dropwise add a dichloromethane solution of chlorosulfonic acid with a concentration of 0.95 M under an ice bath to obtain reaction solution J, where the molar ratio of amino - butyrolactone to chlorosulfonic acid is 1:1.06. Stir for 2.8 h under an ice bath and then raise the temperature to room temperature and continue stirring the reaction for 4 h to obtain a pretreatment reaction solution. Add ice - water to quench the reaction, where the volume ratio of the pretreatment reaction solution to ice - water is 1:2.7. Filter, wash, perform vacuum distillation, and column chromatography to obtain amino - sulfonated butyrolactone;

[0098] S5: Add dimethyl carbonate and ethyl methyl carbonate into ether - fluorinated ethylene carbonate and stir at a speed of 600 rpm for 38 min to obtain a solvent, where the volume ratio of dimethyl carbonate, ethyl methyl carbonate, and ether - fluorinated ethylene carbonate is 35:35:30. Sequentially add amino - sulfonated butyrolactone with a feed amount of 0.7% of the solvent mass, modified tris(trimethylsilyl) phosphate with a feed amount of 1% of the solvent mass, and tris(2,2,2 - trifluoroethyl) silane - modified boric acid with a feed amount of 0.8% of the solvent mass. After stirring, add lithium hexafluorophosphate to obtain reaction solution K, where the concentration of lithium hexafluorophosphate in the solvent is 1.18 M. Continue stirring for 3 h, let it stand for 16 h, and then filter through a PTFE membrane to obtain a high - rate lithium battery electrolyte based on the synergistic effect of borate and phosphate.

[0099] Comparative Example 1

[0100] This comparative example provides a high - rate lithium battery electrolyte based on the synergistic effect of borate and phosphate. The difference from Example 1 is that in step S3, the molar ratio of ethylene carbonate to the selective fluorinating agent is 1:2, and other operation steps and process parameters are exactly the same as those in Example 1.

[0101] Comparative Example 2

[0102] This comparative example provides a high - rate lithium battery electrolyte based on the synergistic effect of borate and phosphate. The difference from Example 1 is that in step S3, the molar ratio of ethylene carbonate to the selective fluorinating agent is 1:0.1, and other operation steps and process parameters are exactly the same as those in Example 1.

[0103] Comparative Example 3

[0104] This comparative example provides a high-rate lithium battery electrolyte based on the synergistic effect of borate and phosphate. The difference from Example 1 is that in step S5, modified tris(trimethylsilyl) phosphate is not added, and other operation steps and process parameters are exactly the same as those in Example 1.

[0105] Comparative Example 4

[0106] This comparative example provides a high-rate lithium battery electrolyte based on the synergistic effect of borate and phosphate. The difference from Example 1 is that in step S5, tris(2,2,2-trifluoroethyl) borate modified with silicon is not added, and other operation steps and process parameters are exactly the same as those in Example 1.

[0107] Perform performance tests on the high-rate lithium battery electrolytes based on the synergistic effect of borate and phosphate in the above Examples 1-4 and Comparative Examples 1-4. The specific process is as follows:

[0108] Measure the conductivity of the electrolyte using a DJS-307 conductivity meter.

[0109] Stack the positive electrode sheet (NCM811), separator, and negative electrode (lithium metal) sheet in sequence, with the separator placed between the positive and negative electrode sheets to play an isolation role. After winding, place it in an outer packaging foil, inject the prepared electrolyte, and then go through processes such as vacuum packaging, standing, forming, and shaping to obtain a lithium metal battery.

[0110] At 25°C, first charge the lithium metal battery at a constant current of 1C to 4.3V, then charge it at a constant voltage of 4.3V until the current is 0.025C, and then discharge it at a constant current of 1C to 3.0V. This is one charge-discharge cycle process, and the discharge capacity at this time is the discharge capacity of the first cycle. Perform multiple cycle charge-discharge tests on the lithium metal battery in the above manner, and detect the discharge capacity of the 500th cycle.

[0111] The capacity retention rate (%) of the lithium metal battery after 500 cycles = [discharge capacity of the 500th cycle / discharge capacity of the first cycle] × 100%.

[0112] High-rate performance test:

[0113] At 25°C, charge the lithium metal battery at a constant current of 1C rate to 4.3V, and then charge it at a constant voltage of 4.3V until the current is 0.025C. Subsequently, discharge it at a high rate (5C, 10C, 20C) at a constant current to 3.0V, and record the discharge capacity under different rate conditions.

[0114] The high-rate capacity retention rate of the lithium metal battery = [discharge capacity at high rate / discharge capacity at 1C rate] × 100%.

[0115] The test results are shown in Table 1.

[0116] Table 1: Test Results of High-rate Lithium Battery Electrolytes and Corresponding Lithium Metal Batteries for Examples 1-4 and Comparative Examples 1-4

[0117]

[0118]

[0119] From the test results of Example 1 and Comparative Examples 1 and 2, it can be seen that an excessive amount of selective fluorinating reagent will cause excessive fluorination of ethylene carbonate, resulting in a high fluoride content in the electrolyte, a decrease in the conductivity of the electrolyte, and excessive fluorination will inhibit the stable migration of lithium ions at the electrode / electrolyte interface, thus leading to capacity decay of the battery; when the dosage of the selective fluorinating reagent is too small, the fluorination of ethylene carbonate is incomplete and the expected modification effect cannot be achieved, resulting in insufficient electrochemical stability of ethylene carbonate; and the interfacial film formed by the decomposition of incompletely fluorinated ethylene carbonate has insufficient mechanical strength and cannot effectively inhibit the growth of lithium dendrites and reduce the occurrence of by-products.

[0120] From the test results of Example 1 and Comparative Example 3, it can be seen that the modified tris(trimethylsilyl) phosphate mainly enhances the solvation ability of the electrolyte and improves the interaction with lithium ions, thereby increasing the ion migration rate of the electrolyte. Without adding it, the solvation effect and lithium ion conduction ability of the electrolyte will be poor, and the conductivity will decrease; at the same time, the modified tris(trimethylsilyl) phosphate helps to improve the interfacial stability of the electrolyte, reduce the growth of lithium dendrites, and enhance the cycle stability and capacity retention rate of the battery. If the modified phosphate is not added, the stability of the interfacial film may be poor, resulting in uneven deposition of lithium ions on the electrode surface, thereby affecting the capacity retention.

[0121] From the test results of Example 1 and Comparative Example 4, it can be seen that the role of tris(2,2,2-trifluoroethyl) borate modified with silicon is to improve the cycle stability of the battery, especially by preventing the growth of lithium dendrites. Without adding this component, the protective effect of the interfacial film will be weakened, easily leading to the growth of lithium dendrites, thereby affecting the cycle performance of the battery and resulting in a decrease in the capacity retention rate; the influence on the conductivity of the electrolyte is relatively small.

[0122] The above are only specific embodiments 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 preparation method of a high-rate lithium battery electrolyte based on the synergistic effect of borate and phosphate, characterized in that, The preparation method includes: S1: Add tris(trimethylsilyl) phosphate and allyl alcohol into tetrahydrofuran, stir at room temperature to obtain reaction solution A. Cool reaction solution A in an ice bath and dropwise add a tetrahydrofuran solution of potassium tert-butoxide to obtain reaction solution B. React at a constant temperature to obtain modified tris(trimethylsilyl) phosphate; S2: Add tris(2,2,2-trifluoroethyl) borate and trimethylchlorosilane into dichloromethane under nitrogen protection to obtain reaction solution C. Dropwise add triethylamine at a constant temperature and then heat up to room temperature to react to obtain silyl-modified tris(2,2,2-trifluoroethyl) borate; S3: Mix ethylene carbonate and a selective fluorinating agent in acetonitrile to obtain reaction solution D. Stir and react in an ice bath under nitrogen protection to obtain reaction solution E, and treat to obtain fluorinated ethylene carbonate. Add the fluorinated ethylene carbonate methanol dispersion to sodium methoxide to obtain reaction solution F. Stir and react at room temperature to obtain reaction solution G. Adjust the pH with dilute hydrochloric acid and treat to obtain ether-based fluorinated ethylene carbonate; S4: Add 1,4-butyrolactone and dimethylamine into methanol to obtain reaction solution H. Stir and react at room temperature under nitrogen protection to obtain reaction solution I, and treat to obtain amino-functionalized butyrolactone. Dropwise add a dichloromethane solution of chlorosulfonic acid to the dichloromethane solution of amino-functionalized butyrolactone in an ice bath to obtain reaction solution J. Stir in an ice bath and then raise the temperature to room temperature and continue to stir and react. Add ice water to quench the reaction and treat to obtain amino-sulfonated butyrolactone; S5: Add dimethyl carbonate and ethyl methyl carbonate into ether-based fluorinated ethylene carbonate and stir to obtain a solvent. Sequentially add amino-sulfonated butyrolactone, modified tris(trimethylsilyl) phosphate, and silyl-modified tris(2,2,2-trifluoroethyl) borate. Stir and then add lithium hexafluorophosphate to obtain reaction solution K. Continue to stir, let stand, and then filter through a PTFE membrane to obtain a high-rate lithium battery electrolyte based on the synergistic effect of borate and phosphate.

2. The preparation method of a high-rate lithium battery electrolyte based on the synergistic effect of borate ester and phosphate ester according to claim 1, wherein In S1: The molar ratio of the tris(trimethylsilyl) phosphate to the allyl alcohol is 1:1.2 - 1.5; The volume ratio of the tris(trimethylsilyl) phosphate to the tetrahydrofuran is 1:3 - 4; The molar ratio of the tris(trimethylsilyl) phosphate to the potassium tert-butoxide is 1:1.1 - 1.3; The concentration of the tetrahydrofuran solution of the potassium tert-butoxide is 0.8 - 1.2 M; The temperature for the constant-temperature reaction of the reaction solution B is 50 - 60 °C; The time for the constant-temperature reaction of the reaction solution B is 8 - 10 h.

3. The preparation method of a high-rate lithium battery electrolyte based on the synergistic effect of borate ester and phosphate ester according to claim 1, characterized in that, In S2: The molar ratio of the tris(2,2,2-trifluoroethyl) borate to the trimethylchlorosilane is 1:1.2 - 1.3; The volume ratio of the tris(2,2,2-trifluoroethyl) borate to the dichloromethane is 1:3 - 4; The temperature for dropping the triethylamine into the reaction solution C is 0 - 5 °C; The molar ratio of the tris(2,2,2-trifluoroethyl) borate to the triethylamine is 1:1 - 1.5; React at room temperature for 4 - 6 h.

4. A method for preparing a high-rate lithium battery electrolyte based on the synergistic effect of borate ester and phosphate ester according to claim 1, characterized in that, In S3: The molar ratio of the ethylene carbonate to the selective fluorinating agent is 1:0.8 - 1.2; The volume ratio of the ethylene carbonate to the acetonitrile is 1:3 - 4; The stirring speed for the reaction solution D to stir and react in an ice bath under nitrogen protection is 500 - 600 rpm; The reaction solution D is stirred and reacted in an ice bath under nitrogen protection for 3 - 5 h.

5. The preparation method of a high-rate lithium battery electrolyte based on the synergistic effect of borate ester and phosphate ester according to claim 1, characterized in that, In S3: In the fluorinated ethylene carbonate methanol dispersion liquid, the volume ratio of fluorinated ethylene carbonate to methanol is 1:1.5 - 2.5; The molar ratio of fluorinated ethylene carbonate to sodium methoxide is 1:0.9 - 1.1; The stirring speed of the reaction solution F during stirring and reaction at room temperature is 400 - 600 rpm; The reaction solution F is stirred and reacted at room temperature for 5 - 7 h.

6. The preparation method of a high-rate lithium battery electrolyte based on the synergistic effect of borate and phosphate according to claim 1, characterized in that, In S3: The concentration of the dilute hydrochloric acid is 0.5 - 1.5 M; The pH of the reaction solution G is adjusted to 6.5 - 7.5 with dilute hydrochloric acid.

7. The preparation method of a high-rate lithium battery electrolyte based on the synergistic effect of borate ester and phosphate ester according to claim 1, characterized in that, In S4: The molar ratio of 1,4 - butyrolactone to dimethylamine is 1:0.8 - 1.2; The volume ratio of 1,4 - butyrolactone to methanol is 1:3 - 4; The reaction solution H is stirred and reacted at room temperature under nitrogen protection for 6 - 8 h.

8. The preparation method of a high-rate lithium battery electrolyte based on the synergistic effect of borate ester and phosphate ester according to claim 1, characterized in that, In S4: In the dichloromethane solution of amino - sulfonated butyrolactone, the volume ratio of amino - sulfonated butyrolactone to dichloromethane is 1:4 - 6; The molar ratio of amino - sulfonated butyrolactone to chlorosulfonic acid is 1:0.9 - 1.1; The concentration of the chlorosulfonic acid dichloromethane solution is 0.8 - 1.0 M; The reaction solution J is stirred in an ice bath for 2 - 3 h; The time for continuing stirring and reaction after rising to room temperature is 4 - 5 h; The volume ratio of the pretreated reaction solution to ice water is 1:2 - 3.

9. The preparation method of a high-rate lithium battery electrolyte based on the synergistic effect of borate ester and phosphate ester according to claim 1, characterized in that, In S5: The stirring speed for adding dimethyl carbonate and ethyl methyl carbonate into ether - fluorinated ethylene carbonate is 500 - 600 rpm; The time for adding dimethyl carbonate and ethyl methyl carbonate into ether - fluorinated ethylene carbonate and stirring is 30 - 40 min; The reaction solution K continues to be stirred for 2 - 3 h; The standing time is 12 - 18 h.

10. A high-rate lithium battery electrolyte based on the synergistic effect of borate ester and phosphate ester, prepared by the preparation method according to any one of claims 1-9, characterized in that, In the high - rate lithium battery electrolyte based on the synergistic effect of borate and phosphate: In the solvent, the volume ratio of dimethyl carbonate, ethyl methyl carbonate and ether - fluorinated ethylene carbonate is (30 - 35):(30 - 35):(30 - 40); The feeding amount of amino - sulfonated butyrolactone is 0.5 - 0.8% of the solvent mass; The feeding amount of modified tris(trimethylsilyl) phosphate is 1 - 1.5% of the solvent mass; The feeding amount of tris(2,2,2 - trifluoroethyl) borate modified with silicon is 0.8 - 1.2% of the solvent mass; The concentration of lithium hexafluorophosphate in the solvent is 1 - 1.2 M.

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