High-rate lithium battery electrolyte based on synergistic effect of boric acid ester and phosphate ester and preparation method of high-rate lithium battery electrolyte

Abstract

The invention provides a high-rate lithium battery electrolyte based on a synergistic effect of boric acid ester and phosphate ester and a preparation method thereof, and belongs to the field of lithium metal batteries. According to the invention, an allyl group is introduced into tris (trimethylsilane) phosphate, so that the solvating ability of tris (trimethylsilane) phosphate is effectively enhanced, and the characteristic of low viscosity is maintained; secondly, trimethylsilyl groups are introduced to modify tris (2, 2, 2-trifluoroethyl) borate, so that the mechanical strength and uniformity of an interfacial film are enhanced, and the growth of lithium dendrites is inhibited; ethylene carbonate is subjected to fluorination and etherification modification, so that the low-temperature fluidity of ethylene carbonate and the mechanical strength of an interfacial film are improved; finally, 1, 4-butyrolactone is modified by introducing amino groups and sulfonic groups, so that the toughness and mechanical strength of an interfacial film are improved, and the stability of the interfacial film under high voltage is enhanced, thereby effectively reducing the occurrence of side reactions; by modifying the electrolyte components, the performance of the lithium battery is optimized, the rate capability and safety of the battery are improved, and the service life of the battery is prolonged.

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 electric vehicles, portable electronic devices and renewable energy storage. The performance and reliability of batteries depend largely on the characteristics of their electrolytes. As the core part of the battery, the main function of the electrolyte is to provide a conductive medium for lithium ions and ensure that the ions are efficiently conducted during the battery charging and discharging process. In addition to ionic conductivity, the electrolyte must also 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 release electrical energy quickly when discharged at a high rate, which puts higher requirements on the conductivity of the electrolyte. During the rapid charging and discharging process, lithium ions need to quickly migrate between the negative and positive electrodes of the battery through the electrolyte. If the ionic conductivity of the electrolyte is insufficient, the internal resistance of the battery will increase, which will in turn affect the output power and energy efficiency of the battery.

[0003] At present, the widely used lithium battery electrolyte is based on lithium salt 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 shortcomings: traditional electrolytes are prone to form lithium dendrites during high-rate charge and discharge, leading to short circuits and capacity degradation; at the same time, the deposition and stripping of the metal lithium negative electrode will lead to large volume changes, increase the mechanical stress of the interface film, and affect the stability of the battery. Summary of the invention

[0004] In view of the above problems, the object of the present invention is to provide a high-rate lithium battery electrolyte based on the synergistic effect of borate esters and phosphates and a preparation method thereof. The present invention improves the performance and safety of lithium batteries by modifying a variety of electrolyte components. First, tris(trimethylsilyl)phosphate is modified by an allyl group to enhance its solvation ability and improve its interaction with lithium ions while retaining the low viscosity characteristics. Secondly, tris(2,2,2-trifluoroethyl) borate is modified by introducing a trimethylsilyl group 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 improve low-temperature fluidity and enhance the mechanical strength of the interface film, further improving 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, while improving 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 the lithium battery.

[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-rate lithium battery electrolyte based on the synergistic effect of borate ester and phosphate ester, the method for preparing a high-rate lithium battery electrolyte based on the synergistic effect of borate ester and phosphate ester comprising:

[0007] S1: adding tri(trimethylsilyl)phosphate and allyl alcohol to tetrahydrofuran, stirring at room temperature to obtain reaction solution A, placing the reaction solution A in an ice bath and adding dropwise a tetrahydrofuran solution of potassium tert-butoxide to obtain reaction solution B, reacting at a constant temperature, and performing reduced pressure distillation and column chromatography to obtain modified tri(trimethylsilyl)phosphate;

[0008] S2: adding tri(2,2,2-trifluoroethyl) borate and trimethylsilyl chloride to dichloromethane under nitrogen protection to obtain reaction solution C, adding triethylamine dropwise at a constant temperature, then heating to room temperature for reaction, filtering, washing, and distilling under reduced pressure to obtain silicon-modified tri(2,2,2-trifluoroethyl) borate;

[0009] S3: mixing ethylene carbonate and a selective fluorine reagent in acetonitrile to obtain a reaction solution D, stirring the mixture in an ice bath under nitrogen protection to obtain a reaction solution E, distilling the mixture under reduced pressure and performing column chromatography to obtain fluorinated ethylene carbonate; preparing a methanol dispersion of fluorinated ethylene carbonate, adding sodium methoxide to obtain a reaction solution F, stirring the mixture at room temperature to obtain a reaction solution G, adjusting the pH with dilute hydrochloric acid, distilling the mixture under reduced pressure and performing column chromatography to obtain ether-fluorinated ethylene carbonate;

[0010] S4: 1,4-butyrolactone and dimethylamine are added to methanol to obtain a reaction solution H, and the reaction is stirred at room temperature under nitrogen protection to obtain a reaction solution I, and the amino-butyrolactone is obtained by vacuum distillation and column chromatography; a dichloromethane solution of the amino-butyrolactone is prepared, and a dichloromethane solution of chlorosulfonic acid is added dropwise under an ice bath to obtain a reaction solution J, and the reaction is stirred under an ice bath and then heated to room temperature and continued to stir to obtain a pre-treated reaction solution, and ice water is added to quench the reaction, and the reaction is filtered, washed, vacuum distilled, and column chromatographed to obtain amino-sulfonated butyrolactone;

[0011] S5: Add dimethyl carbonate and ethyl methyl carbonate to ether-fluorinated vinyl carbonate and stir to obtain a solvent, add amino-sulfonated butyrolactone, modified tris(trimethylsilyl) phosphate and silicon-modified tris(2,2,2-trifluoroethyl) borate in sequence, stir and add lithium hexafluorophosphate to obtain a reaction solution K, continue stirring, let stand and filter through a PTFE filter membrane to obtain a high-rate lithium battery electrolyte based on the synergistic effect of borate ester and phosphate ester.

[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, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0013] In some optional 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, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0014] In some optional 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, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0015] In some optional embodiments, the concentration of the tetrahydrofuran solution of potassium tert-butoxide 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, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0016] In some optional embodiments, the temperature of the constant temperature reaction of the reaction liquid 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, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0017] In some optional embodiments, the isothermal reaction time of the reaction liquid 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, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also 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, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0019] In some optional embodiments, the volume ratio of tris(2,2,2-trifluoroethyl) borate to dichloromethane is 1:3-4, for example, 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, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0020] In some optional embodiments, the temperature for adding triethylamine to the reaction solution C is 0-5°C, for example, 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, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0021] In some optional embodiments, the molar ratio of tris(2,2,2-trifluoroethyl) borate to triethylamine is 1:1-1.5, for example, 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, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

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

[0023] As a preferred technical solution of the present invention, in step S3, the molar ratio of ethylene carbonate to the selective fluorine reagent 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, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0024] In some optional 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, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0025] In some optional embodiments, the stirring speed of the reaction liquid D in an 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, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0026] In some optional embodiments, the reaction time of the reaction liquid D in an ice bath with stirring under nitrogen protection is 3-5 hours, for example, it can be 3 hours, 3.2 hours, 3.4 hours, 3.6 hours, 3.8 hours, 4 hours, 4.2 hours, 4.4 hours, 4.6 hours, 4.8 hours or 5 hours, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0027] In some optional 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, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0028] In some optional embodiments, the molar ratio of the 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, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0029] In some optional embodiments, the stirring speed of the reaction liquid F during the 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, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

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

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

[0032] In some optional 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, 7M, 7.1, 7.2, 7.3, 7.4 or 7.5, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also 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, but it is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0034] In some optional 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, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

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

[0036] In some optional 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, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0037] In some optional embodiments, the molar ratio of the 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, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

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

[0039] In some optional embodiments, the reaction solution J is stirred in an ice bath for 2-3 h, for example, 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, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0040] In some optional embodiments, the time for continuing to stir the reaction after warming to room temperature is 4-5h, for example, it can be 4.0h, 4.1h, 4.2h, 4.3h, 4.4h, 4.5h, 4.6h, 4.7h, 4.8h, 4.9h or 5.0h, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0041] In some optional embodiments, the volume ratio of the pretreatment reaction liquid 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, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0042] As a preferred technical solution of the present invention, in step S5, the speed of stirring when dimethyl carbonate and ethyl methyl carbonate are added to ether-fluorinated vinyl carbonate 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, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0043] In some optional embodiments, the time for stirring dimethyl carbonate and ethyl methyl carbonate in ether-fluorinated vinyl carbonate 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, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0044] In some optional embodiments, the reaction liquid K is stirred for 2-3 hours, for example, 2.0 hours, 2.1 hours, 2.2 hours, 2.3 hours, 2.4 hours, 2.5 hours, 2.6 hours, 2.7 hours, 2.8 hours, 2.9 hours or 3.0 hours, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

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

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

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

[0048] In order to enhance the solvation ability of tris(trimethylsilyl)phosphate while retaining its advantage of low viscosity, the present invention adopts the introduction of allyl groups to modify tris(trimethylsilyl)phosphate. By reacting with allyl alcohol, some methylsilyl groups are replaced with allyl groups. The allyl group has certain polarity and flexibility, which can improve the polarity of tris(trimethylsilyl)phosphate molecules 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 can also make it show more excellent ion migration kinetics 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 a relatively low viscosity characteristic, avoiding a significant increase in the viscous resistance of the system.

[0049] In the present invention, tri(2,2,2-trifluoroethyl) borate is selected. Tri(2,2,2-trifluoroethyl) borate is a boron-containing organic compound, in which the central boron atom is connected to the trifluoroethyl group through three BO bonds to form a trigonal pyramid structure. The boron atom in the borate skeleton exhibits obvious Lewis acidity and can have a weak coordination effect with the anions in the solution, thereby optimizing the ionic environment of the electrolyte; and 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 improving its chemical stability under high voltage conditions; the trifluoroethyl group makes the molecule as a whole have a certain hydrophobicity, which helps to reduce the interaction with polar solvents, thereby reducing the overall viscosity of the electrolyte and helping to improve the ion mobility of the electrolyte; in addition, the trifluoroethyl group has a large volume and can provide a certain steric hindrance to inhibit the polymerization reaction or side reaction between molecules, thereby improving the stability of the electrolyte. After tri(2,2,2-trifluoroethyl) borate decomposes on the surface of the negative electrode of a lithium battery, it can generate compounds containing BF bonds and BO bonds. 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 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 generated by the decomposition of tri(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 and discharge conditions. Volume changes on the lithium metal surface (such as deposition and stripping) will exert greater mechanical stress on the interfacial film, which will lead to rupture or peeling of the film, thereby exposing the lithium metal surface and accelerating the occurrence of side reactions. In addition, due to the strong molecular rigidity of the interfacial film, its distribution on the lithium metal surface 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, trimethylsilyl chloride is used to introduce trimethylsilyl groups to modify them. The trimethylsilyl group is a group with certain structural flexibility, and its introduction can form a silicon-containing network structure in the decomposition product. This structure synergizes with the original BF bond and BO bond to significantly enhance the flexibility and mechanical strength of the interface film. In addition, silicon-based modification can effectively disperse local stress and alleviate stress concentration by forming a silicon-oxygen network in the film, thereby reducing the risk of film rupture. The interface film generated by the decomposition of tri(2,2,2-trifluoroethyl) borate after silicon-based modification exhibits higher mechanical strength and anti-peeling ability under high-rate charge and discharge conditions, relying on the enhanced silicon-oxygen network structure, thereby improving the cycle stability of the lithium battery. In addition, the silicon oxide generated by the decomposition of tri(2,2,2-trifluoroethyl) borate molecules after silicon-based modification has a high surface activity and can form a stronger chemical bonding force with the lithium metal surface, which helps to fill the surface microscopic defects and enhance the stability of the interface film. The flexible structure of the modified molecules helps to form a more continuous and uniform interface film on the surface of lithium metal, reduce areas with excessively high local current density, and further improve the uniformity and bonding strength of the interface film, thereby effectively inhibiting the growth of lithium dendrites and improving the safety and service life of lithium batteries.

[0052] Ethylene carbonate is introduced into the present invention. Ethylene carbonate is a common organic carbonate solvent, and its molecular structure is composed 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, thereby providing a higher ionic conductivity and improving the electrochemical performance of the battery. During the electrochemical reaction, the ethylene carbonate molecules will preferentially decompose to generate a series of products, which help to form a dense solid electrolyte interface film on the surface of the negative electrode, thereby ensuring the cycle stability of the battery. Ethylene carbonate molecules contain stable ester bonds and cyclic ether structures, which can form a strong coordination effect with lithium ions, significantly enhance the solvation ability, and make lithium ions easier to migrate in the electrolyte. However, in extremely low temperature environments, the mobility of ethylene carbonate in the electrolyte may be reduced due to the enhanced intermolecular forces, thereby 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 lead to a higher viscosity in the electrolyte. This high viscosity limits the migration rate of lithium ions in the electrolyte, especially under high-rate charge and discharge conditions, which is easy to cause battery polarization. In addition, the interfacial film generated by the decomposition of ethylene carbonate is mainly composed of inorganic carbonates and polycarbonates. Although these products have good chemical stability, they have low mechanical strength. Especially during the volume change of the lithium metal negative electrode (such as deposition and stripping), the interfacial film is easy to break or peel off, thereby exacerbating side reactions.

[0053] Based on the above shortcomings, the present invention uses a selective fluorine reagent and sodium methoxide to modify ethylene carbonate. By fluorinating and etherifying ethylene carbonate, the introduction of CF bonds enhances the hydrophobicity of the molecule and helps to improve low-temperature fluidity, while reducing the effect of intermolecular hydrogen bonds, making it easier to maintain a liquid state and improving low-temperature fluidity; the flexible structure of the ether group further reduces the interaction force between molecules, so that the electrolyte maintains 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 interface 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-stripping ability of the interface film, thereby improving the mechanical properties of the interface film. The organic polymer generated by the decomposition of the ether group gives the interface film a certain flexibility, so that it can better adapt to the volume change of lithium metal. The interface 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 the ether structure, the interaction force between ethylene carbonate molecules is reduced, and the modified molecules are easier to form a uniform mixed electrolyte with other low-viscosity solvents. The introduction of the ether structure effectively reduces the viscosity of the system and improves the migration rate of lithium ions. The modified electrolyte has lower viscosity and higher ionic conductivity, thereby improving 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 lower molecular weight and weaker intermolecular forces make it have a lower viscosity, which helps to reduce the overall viscosity of the electrolyte and improve the migration rate of lithium ions; at the same time, it has a higher polarity, can effectively dissolve lithium salts, and is well 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 to improve the performance of the electrolyte under low-temperature conditions, thereby improving 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 a higher chemical stability and can maintain good redox stability within a wider voltage window. During the decomposition of the electrolyte, 1,4-butyrolactone can form a layer of solid electrolyte interface film on the surface of the negative electrode, which helps to inhibit side reactions and improve the cycle stability of the battery.

[0055] However, the interfacial film generated by the decomposition of 1,4-butyrolactone has low mechanical strength. At the same time, its oxidative decomposition temperature is low, and it is easy to undergo oxidative decomposition under high voltage conditions, resulting in side reactions and affecting the stability of the electrolyte. Therefore, it is modified by introducing amino 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 high mechanical strength and chemical stability and can enhance the structure of the interfacial film. The interfacial film generated by the modified butyrolactone has both high mechanical strength and certain flexibility, which can effectively adapt to the dynamic volume changes of the lithium metal negative electrode, inhibit the growth of lithium dendrites, and thus improve the cycle performance of the battery; in addition, the sulfonic acid group is a strong electron-attracting group, and its introduction reduces the electron cloud density of the 1,4-butyrolactone molecule, thereby increasing its oxidative decomposition potential, thereby reducing the risk of side reactions under high voltage conditions and significantly improving its stability under high voltage.

[0056] There is also a synergistic enhancement effect in the present invention: tri(trimethylsilane) phosphate and tri(2,2,2-trifluoroethyl) borate both have high polarity and can effectively dissolve lithium salts. The phosphate group in tri(trimethylsilane) phosphate provides solvation ability, and the trifluoroethyl group in tri(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 tri(trimethylsilane) phosphate and the trifluoroethyl group in tri(2,2,2-trifluoroethyl) borate work together to improve the electrochemical stability of the electrolyte, especially under high voltage conditions. Tri(trimethylsilane) phosphate itself has good electrochemical stability, and the fluorine element in tri(2,2,2-trifluoroethyl) borate enhances the chemical stability of the electrolyte, so that the overall system will not easily decompose under high voltage. The combination of the two ensures that the battery can still operate stably at high voltage; the combined effect of tri(trimethylsilyl) phosphate and tri(2,2,2-trifluoroethyl) borate in the electrolyte not only improves the solubility 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] As a commonly used solvent, ethylene carbonate has high solubility and moderate polarity, but its molecular structure is relatively rigid and may show high viscosity at low temperatures. The introduction of tris(trimethylsilyl) phosphate not only improves the polarity of the electrolyte, but also reduces the hydrogen bonding between molecules, making it have better 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 increasing the migration rate of lithium ions; the phosphate group of tris(trimethylsilyl) phosphate and the ester group in ethylene carbonate have a certain interaction, 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 to improve the performance of ethylene carbonate under these extreme conditions; the combination of the two improves 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 environment, the combination of tri(trimethylsilyl)phosphate and ethylene carbonate optimizes the performance of the electrolyte and enhances the rate performance and cycle life of the battery.

[0058] Ethylene carbonate and tri(2,2,2-trifluoroethyl) borate have different stability performances under high voltage. Ethylene carbonate is prone to oxidative decomposition under high voltage, but its solubility is strong. Tri(2,2,2-trifluoroethyl) borate has high oxidative stability, and its trifluoroethyl group enhances its stability under high voltage. The introduction of tri(2,2,2-trifluoroethyl) borate can inhibit the decomposition reaction of ethylene carbonate under high voltage and improve 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 solubility of tri(2,2,2-trifluoroethyl) borate have a stronger effect on stability under high voltage. The synergistic effect of the two ensures the stability of the electrolyte under high voltage and improves the ionic conductivity of the electrolyte; the combination of the two can effectively inhibit side reactions under high voltage environment, enhance the solubility and ionic conductivity of the electrolyte, and improve the electrochemical performance and safety of the battery.

[0059] After decomposition, 1,4-butyrolactone can form an interfacial film, and the introduction of tris(trimethylsilyl)phosphate can enhance the chemical stability and mechanical strength of the interfacial film. The interfacial film generated by 1,4-butyrolactone has good flexibility, and the phosphate structure of tris(trimethylsilyl)phosphate can further enhance 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 and can increase the migration rate of lithium ions. The phosphate group introduced by tris(trimethylsilyl)phosphate can further enhance the solvation ability and ensure the smooth migration of lithium ions in the electrolyte. When combined, the two can jointly improve the ionic conductivity of the electrolyte and improve the rate performance of the battery.

[0060] The interfacial film generated by 1,4-butyrolactone is relatively soft, but it has strong resistance to chemical corrosion. The introduction of tri(2,2,2-trifluoroethyl) borate enhances the chemical stability of the interfacial film by introducing trifluoroethyl groups, especially under high voltage and high temperature conditions. The combination of the two allows the interfacial film to provide flexibility to adapt to the volume changes of the lithium metal negative electrode while also having strong chemical stability; the flexible interfacial film generated by 1,4-butyrolactone may be easily damaged during the cycle, while the introduction of tri(2,2,2-trifluoroethyl) borate can improve the mechanical strength of the interfacial film, prevent peeling, reduce side reactions, and improve the cycle stability of the battery.

[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 the electrolyte with better solubility and polarity. The combination of the two enables the electrolyte to maintain good fluidity and ion conductivity in low-temperature environments. 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 interface film and the smooth migration of lithium ions.

[0062] Compared with the prior art, the present invention has the following beneficial effects:

[0063] (1) Introducing allyl groups to modify tris(trimethylsilyl) phosphate and replace part of the methylsilane groups, thereby improving the compatibility with carbonate solvents and the ion migration performance while retaining its advantage of low viscosity;

[0064] (2) The introduction of tri(2,2,2-trifluoroethyl) borate and the use of trimethylchlorosilane for modification, the silicon-oxygen network enhances the flexibility and mechanical strength of the interface film, helps to relieve local stress, reduces the risk of interface film rupture, and at the same time improves the uniformity and bonding strength of the interface film, effectively inhibiting the growth of lithium dendrites;

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

[0066] (4) Introducing 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; introducing sulfonic acid groups to generate lithium sulfite or other sulfate compounds to improve the mechanical strength and stability of the interfacial film;

[0067] (5) The synergistic effect between the various components effectively improves the ion migration rate and stability of the electrolyte, and improves the performance and stability of the electrolyte under conditions of low temperature, high voltage, and high rate charge and discharge. BRIEF DESCRIPTION OF THE DRAWINGS

[0068] Figure 1 This is a flow chart of a method for preparing a high-rate lithium battery electrolyte based on the synergistic effect of borate esters and phosphate esters provided in Example 1 of the present invention. DETAILED DESCRIPTION

[0069] 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.

[0070] The chemical reagents used in the examples and comparative examples of the present invention are all commercially available products without further purification or treatment.

[0071] Example 1

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

[0073] S1: adding tri(trimethylsilyl)phosphate and allyl alcohol to tetrahydrofuran, wherein the molar ratio of tri(trimethylsilyl)phosphate to allyl alcohol is 1:1.2, and the volume ratio of tri(trimethylsilyl)phosphate to tetrahydrofuran is 1:3.5, stirring at room temperature to obtain reaction solution A, placing the reaction solution A in an ice bath and dropwise adding a 0.8M tetrahydrofuran solution of potassium tert-butoxide to obtain reaction solution B, wherein the molar ratio of tri(trimethylsilyl)phosphate to potassium tert-butoxide is 1:1.2, reacting at a constant temperature of 55° C. for 9 h, and performing reduced pressure distillation and column chromatography to obtain modified tri(trimethylsilyl)phosphate;

[0074] S2: adding tri(2,2,2-trifluoroethyl) borate and trimethylsilyl chloride in a molar ratio of 1:1.28 to dichloromethane under nitrogen protection to obtain reaction solution C, wherein the volume ratio of tri(2,2,2-trifluoroethyl) borate to dichloromethane is 1:3.4, adding triethylamine dropwise at a constant temperature of 0°C, wherein the molar ratio of tri(2,2,2-trifluoroethyl) borate to triethylamine is 1:1, then heating to room temperature to react for 4 hours, filtering, washing, and distilling under reduced pressure to obtain silicon-modified tri(2,2,2-trifluoroethyl) borate;

[0075] S3: mixing ethylene carbonate and a selective fluorine reagent in acetonitrile at a molar ratio of 1:0.8 to obtain a reaction solution D, wherein the volume ratio of ethylene carbonate to acetonitrile is 1:3.6, reacting in an ice bath under nitrogen protection with stirring to obtain a reaction solution E, wherein the stirring speed is 550 rpm and the time is 4 hours, and performing reduced pressure distillation and column chromatography to obtain fluorinated ethylene carbonate; preparing a fluorinated ethylene carbonate methanol dispersion, wherein the volume ratio of fluorinated ethylene carbonate to methanol in the dispersion is 1:2.5, adding sodium methoxide to obtain a reaction solution F, wherein the molar ratio of fluorinated ethylene carbonate to sodium methoxide is 1:1, reacting under stirring at room temperature to obtain a reaction solution G, wherein the stirring speed is 600 rpm and the time is 6 hours, adjusting the pH to 7.2 with 0.5 M dilute hydrochloric acid, and performing reduced pressure distillation and column chromatography to obtain ether-fluorinated ethylene carbonate;

[0076] S4: adding 1,4-butyrolactone and dimethylamine to methanol to obtain reaction solution H, wherein 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, stirring at room temperature under nitrogen protection for 6.6 hours to obtain reaction solution I, distilling under reduced pressure and column chromatography to obtain aminobutyrolactone; preparing a dichloromethane solution of aminobutyrolactone, wherein the volume ratio of aminobutyrolactone to dichloromethane in the dichloromethane solution of aminobutyrolactone is 1:6, adding dropwise a dichloromethane solution of 1M chlorosulfonic acid under ice bath to obtain reaction solution J, wherein the molar ratio of aminobutyrolactone to chlorosulfonic acid is 1:0.9, stirring under ice bath for 2 hours, then warming to room temperature and continuing stirring for 5 hours to obtain a pre-treated reaction solution, adding ice water to quench the reaction, wherein the volume ratio of the pre-treated reaction solution to ice water is 1:2, filtering, washing, distilling under reduced pressure and column chromatography to obtain amino-sulfonated butyrolactone;

[0077] S5: Dimethyl carbonate and ethyl methyl carbonate are added to ether-fluorinated vinyl carbonate and stirred at a speed of 550 rpm for 30 minutes to obtain a solvent, wherein the volume ratio of dimethyl carbonate, ethyl methyl carbonate and ether-fluorinated vinyl carbonate is 32:33:35, and amino-sulfonated butyrolactone in an amount of 0.5% of the mass of the solvent, modified tris(trimethylsilyl) phosphate in an amount of 1.5% of the mass of the solvent and silicon-modified tri(2,2,2-trifluoroethyl) borate in an amount of 1.2% of the mass of the solvent are added in sequence, and lithium hexafluorophosphate is added after stirring to obtain a reaction solution K, wherein the concentration of lithium hexafluorophosphate in the solvent is 1.2 M, and stirring is continued for 2 hours. After standing for 12 hours, the mixture is filtered through a PTFE filter membrane to obtain a high-rate lithium battery electrolyte based on the synergistic effect of borate ester and phosphate ester.

[0078] Example 2

[0079] This embodiment provides a high-rate lithium battery electrolyte based on the synergistic effect of borate ester and phosphate ester and a preparation method thereof, the preparation method specifically comprising the following steps:

[0080] S1: adding tri(trimethylsilyl)phosphate and allyl alcohol to tetrahydrofuran, wherein the molar ratio of tri(trimethylsilyl)phosphate to allyl alcohol is 1:1.4, and the volume ratio of tri(trimethylsilyl)phosphate to tetrahydrofuran is 1:3, stirring at room temperature to obtain reaction solution A, placing the reaction solution A in an ice bath and dropwise adding a 1.2M tetrahydrofuran solution of potassium tert-butoxide to obtain reaction solution B, wherein the molar ratio of tri(trimethylsilyl)phosphate to potassium tert-butoxide is 1:1.26, reacting at a constant temperature of 50° C. for 10 h, and performing reduced pressure distillation and column chromatography to obtain modified tri(trimethylsilyl)phosphate;

[0081] S2: adding tri(2,2,2-trifluoroethyl) borate and trimethylsilyl chloride in a molar ratio of 1:1.3 to dichloromethane under nitrogen protection to obtain reaction solution C, wherein the volume ratio of tri(2,2,2-trifluoroethyl) borate to dichloromethane is 1:3.8, adding triethylamine dropwise at a constant temperature of 2°C, wherein the molar ratio of tri(2,2,2-trifluoroethyl) borate to triethylamine is 1:1.4, then heating to room temperature to react for 5 hours, filtering, washing, and distilling under reduced pressure to obtain silicon-modified tri(2,2,2-trifluoroethyl) borate;

[0082] S3: Mixing ethylene carbonate and a selective fluorine reagent in acetonitrile at a molar ratio of 1:1.2 to obtain a reaction solution D, wherein the volume ratio of ethylene carbonate to acetonitrile is 1:3.2, and reacting in an ice bath under nitrogen protection with stirring to obtain a reaction solution E, wherein the stirring speed is 570 rpm and the time is 3 hours, and performing reduced pressure distillation and column chromatography to obtain fluorinated ethylene carbonate; preparing a fluorinated ethylene carbonate methanol dispersion, wherein the volume ratio of fluorinated ethylene carbonate to methanol in the dispersion is 1:2, and adding sodium methoxide to obtain a reaction solution F, wherein the molar ratio of fluorinated ethylene carbonate to sodium methoxide is 1:1.1, and reacting under stirring at room temperature to obtain a reaction solution G, wherein the stirring speed is 550 rpm and the time is 7 hours, and adjusting the pH to 6.5 with 1.5M dilute hydrochloric acid, and performing reduced pressure distillation and column chromatography to obtain ether-fluorinated ethylene carbonate;

[0083] S4: adding 1,4-butyrolactone and dimethylamine to methanol to obtain a reaction solution H, wherein the molar ratio of 1,4-butyrolactone to dimethylamine is 1:1.1, and the volume ratio of 1,4-butyrolactone to methanol is 1:3.5, stirring at room temperature for 8 hours under nitrogen protection to obtain a reaction solution I, and performing reduced pressure distillation and column chromatography to obtain aminobutyrolactone; preparing a dichloromethane solution of aminobutyrolactone, wherein the dichloromethane solution of aminobutyrolactone contains aminobutyrolactone and dichloromethane. The volume ratio of methane is 1:5, and a dichloromethane solution of 0.9M chlorosulfonic acid is added dropwise under ice bath to obtain reaction solution J, wherein the molar ratio of aminobutyrolactone to chlorosulfonic acid is 1:1.0, and the mixture is stirred under ice bath for 2.5 hours, then warmed to room temperature and continued to stir and react for 4.5 hours to obtain a pre-treated reaction solution, and ice water is added to quench the reaction, wherein the volume ratio of the pre-treated reaction solution to ice water is 1:3, filtered, washed, distilled under reduced pressure, and subjected to column chromatography to obtain amino-sulfonated butyrolactone;

[0084] S5: Dimethyl carbonate and ethyl methyl carbonate are added to ether-fluorinated vinyl carbonate and stirred at a speed of 500 rpm for 40 minutes to obtain a solvent, wherein the volume ratio of dimethyl carbonate, ethyl methyl carbonate and ether-fluorinated vinyl carbonate is 30:30:40, and amino-sulfonated butyrolactone in an amount of 0.8% of the mass of the solvent, modified tris(trimethylsilyl) phosphate in an amount of 1.3% of the mass of the solvent and silicon-modified tri(2,2,2-trifluoroethyl) borate in an amount of 1% of the mass of the solvent are added in sequence, and lithium hexafluorophosphate is added after stirring to obtain a reaction solution K, wherein the concentration of lithium hexafluorophosphate in the solvent is 1M, and stirring is continued for 2.8 hours. After standing for 14 hours, the mixture is filtered through a PTFE filter membrane to obtain a high-rate lithium battery electrolyte based on the synergistic effect of borate ester and phosphate ester.

[0085] Example 3

[0086] This embodiment provides a high-rate lithium battery electrolyte based on the synergistic effect of borate ester and phosphate ester and a preparation method thereof, the preparation method specifically comprising the following steps:

[0087] S1: adding tri(trimethylsilyl)phosphate and allyl alcohol to tetrahydrofuran, wherein the molar ratio of tri(trimethylsilyl)phosphate to allyl alcohol is 1:1.5, and the volume ratio of tri(trimethylsilyl)phosphate to tetrahydrofuran is 1:4, stirring at room temperature to obtain reaction solution A, placing the reaction solution A in an ice bath and dropwise adding a 1.1M tetrahydrofuran solution of potassium tert-butoxide to obtain reaction solution B, wherein the molar ratio of tri(trimethylsilyl)phosphate to potassium tert-butoxide is 1:1.1, reacting at a constant temperature of 60° C. for 8 h, and performing reduced pressure distillation and column chromatography to obtain modified tri(trimethylsilyl)phosphate;

[0088] S2: Add tri(2,2,2-trifluoroethyl) borate and trimethylsilyl chloride in a molar ratio of 1:1.25 to dichloromethane under nitrogen protection to obtain reaction solution C, wherein the volume ratio of tri(2,2,2-trifluoroethyl) borate to dichloromethane is 1:4, and triethylamine is added dropwise at a constant temperature of 4°C, wherein the molar ratio of tri(2,2,2-trifluoroethyl) borate to triethylamine is 1:1.3, then the temperature is raised to room temperature for reaction for 5.5 hours, filtered, washed, and distilled under reduced pressure to obtain silicon-modified tri(2,2,2-trifluoroethyl) borate;

[0089] S3: Mixing ethylene carbonate and a selective fluorine reagent in acetonitrile at a molar ratio of 1:1.0 to obtain a reaction solution D, wherein the volume ratio of ethylene carbonate to acetonitrile is 1:3, stirring in an ice bath under nitrogen protection to obtain a reaction solution E, wherein the stirring speed is 500 rpm and the time is 5 hours, and vacuum distillation and column chromatography are performed to obtain fluorinated ethylene carbonate; preparing a fluorinated ethylene carbonate methanol dispersion, wherein the volume ratio of fluorinated ethylene carbonate to methanol in the dispersion is 1:1.5, adding sodium methoxide to obtain a reaction solution F, wherein the molar ratio of fluorinated ethylene carbonate to sodium methoxide is 1:0.9, stirring at room temperature to obtain a reaction solution G, wherein the stirring speed is 500 rpm and the time is 6.6 hours, adjusting the pH to 7 with 1M dilute hydrochloric acid, and vacuum distillation and column chromatography are performed to obtain ether-fluorinated ethylene carbonate;

[0090] S4: adding 1,4-butyrolactone and dimethylamine to methanol to obtain a reaction solution H, wherein 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, stirring at room temperature under nitrogen protection for 7 hours to obtain a reaction solution I, and performing reduced pressure distillation and column chromatography to obtain aminobutyrolactone; preparing a dichloromethane solution of aminobutyrolactone, wherein the dichloromethane solution of aminobutyrolactone contains aminobutyrolactone and dichloromethane. The volume ratio of the pretreatment reaction liquid to the alkane is 1:4, and a dichloromethane solution of 0.8M chlorosulfonic acid is added dropwise under ice bath to obtain reaction liquid J, wherein the molar ratio of aminobutyrolactone to chlorosulfonic acid is 1:1.1, and the mixture is stirred under ice bath for 3 hours, then warmed to room temperature and continued to stir and react for 4.8 hours to obtain a pretreatment reaction liquid, and ice water is added to quench the reaction, wherein the volume ratio of the pretreatment reaction liquid to ice water is 1:2.5, and the reaction is filtered, washed, distilled under reduced pressure, and subjected to column chromatography to obtain amino-sulfonated butyrolactone;

[0091] S5: Dimethyl carbonate and ethyl methyl carbonate are added to ether-fluorinated vinyl carbonate and stirred at a speed of 590 rpm for 33 minutes to obtain a solvent, wherein the volume ratio of dimethyl carbonate, ethyl methyl carbonate and ether-fluorinated vinyl carbonate is 31:31:38, and amino-sulfonated butyrolactone in an amount of 0.6% of the mass of the solvent, modified tris(trimethylsilyl) phosphate in an amount of 1.2% of the mass of the solvent and silicon-modified tri(2,2,2-trifluoroethyl) borate in an amount of 1.1% of the mass of the solvent are added in sequence, and lithium hexafluorophosphate is added after stirring to obtain a reaction solution K, wherein the concentration of lithium hexafluorophosphate in the solvent is 1.1 M, and stirring is continued for 2.4 hours. After standing for 18 hours, the mixture is filtered through a PTFE filter membrane to obtain a high-rate lithium battery electrolyte based on the synergistic effect of borate ester and phosphate ester.

[0092] Example 4

[0093] This embodiment provides a high-rate lithium battery electrolyte based on the synergistic effect of borate ester and phosphate ester and a preparation method thereof, the preparation method specifically comprising the following steps:

[0094] S1: adding tri(trimethylsilyl)phosphate and allyl alcohol to tetrahydrofuran, wherein the molar ratio of tri(trimethylsilyl)phosphate to allyl alcohol is 1:1.3, and the volume ratio of tri(trimethylsilyl)phosphate to tetrahydrofuran is 1:3.8, stirring at room temperature to obtain reaction solution A, placing reaction solution A in an ice bath and adding dropwise a 1.0M solution of potassium tert-butoxide in tetrahydrofuran to obtain reaction solution B, wherein the molar ratio of tri(trimethylsilyl)phosphate to potassium tert-butoxide is 1:1.3, reacting at a constant temperature of 57° C. for 9.4 h, and performing reduced pressure distillation and column chromatography to obtain modified tri(trimethylsilyl)phosphate;

[0095] S2: adding tri(2,2,2-trifluoroethyl) borate and trimethylsilyl chloride in a molar ratio of 1:1.2 to dichloromethane under nitrogen protection to obtain reaction solution C, wherein the volume ratio of tri(2,2,2-trifluoroethyl) borate to dichloromethane is 1:3, adding triethylamine dropwise at a constant temperature of 5°C, wherein the molar ratio of tri(2,2,2-trifluoroethyl) borate to triethylamine is 1:1.5, then heating to room temperature to react for 6 hours, filtering, washing, and distilling under reduced pressure to obtain silicon-modified tri(2,2,2-trifluoroethyl) borate;

[0096] S3: Mixing ethylene carbonate and a selective fluorine reagent in acetonitrile at a molar ratio of 1:1.1 to obtain a reaction solution D, wherein the volume ratio of ethylene carbonate to acetonitrile is 1:4, stirring in an ice bath under nitrogen protection to obtain a reaction solution E, wherein the stirring speed is 600 rpm and the time is 4.4 hours, and vacuum distillation and column chromatography to obtain fluorinated ethylene carbonate; preparing a fluorinated ethylene carbonate methanol dispersion, wherein the volume ratio of fluorinated ethylene carbonate to methanol in the dispersion is 1:2.2, adding sodium methoxide to obtain a reaction solution F, wherein the molar ratio of fluorinated ethylene carbonate to sodium methoxide is 1:1.06, stirring at room temperature to obtain a reaction solution G, wherein the stirring speed is 400 rpm and the time is 5 hours, adjusting the pH to 7.5 with 1.2M dilute hydrochloric acid, and vacuum distillation and column chromatography to obtain ether-fluorinated ethylene carbonate;

[0097] S4: adding 1,4-butyrolactone and dimethylamine to methanol to obtain a reaction solution H, wherein 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, stirring at room temperature for 6 hours under nitrogen protection to obtain a reaction solution I, and performing reduced pressure distillation and column chromatography to obtain aminobutyrolactone; preparing a dichloromethane solution of aminobutyrolactone, wherein the molar ratio of aminobutyrolactone to dimethylamine is 1:1.2, and the volume ratio of 1,4-butyrolactone to methanol is 1:4. The volume ratio is 1:4.6, and a dichloromethane solution of 0.95M chlorosulfonic acid is added dropwise under an ice bath to obtain a reaction solution J, wherein the molar ratio of aminobutyrolactone to chlorosulfonic acid is 1:1.06, and the mixture is stirred under an ice bath for 2.8 hours, then warmed to room temperature and continued to stir and react for 4 hours to obtain a pre-treated reaction solution, and ice water is added to quench the reaction, wherein the volume ratio of the pre-treated reaction solution to ice water is 1:2.7, filtered, washed, distilled under reduced pressure, and subjected to column chromatography to obtain amino-sulfonated butyrolactone;

[0098] S5: Dimethyl carbonate and ethyl methyl carbonate are added to ether-fluorinated vinyl carbonate and stirred at a speed of 600 rpm for 38 minutes to obtain a solvent, wherein the volume ratio of dimethyl carbonate, ethyl methyl carbonate and ether-fluorinated vinyl carbonate is 35:35:30, and amino-sulfonated butyrolactone in an amount of 0.7% of the mass of the solvent, modified tris(trimethylsilyl) phosphate in an amount of 1% of the mass of the solvent and silicon-modified tri(2,2,2-trifluoroethyl) borate in an amount of 0.8% of the mass of the solvent are added in sequence, and lithium hexafluorophosphate is added after stirring to obtain a reaction solution K, wherein the concentration of lithium hexafluorophosphate in the solvent is 1.18 M, and stirring is continued for 3 hours. After standing for 16 hours, the mixture is filtered through a PTFE filter membrane to obtain a high-rate lithium battery electrolyte based on the synergistic effect of borate ester and phosphate ester.

[0099] Comparative Example 1

[0100] This comparative example provides a high-rate lithium battery electrolyte based on the synergistic effect of borate ester and phosphate ester. The difference from Example 1 is that in step S3, the molar ratio of ethylene carbonate to the selective fluorine reagent is 1:2, and the other operating 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 ester and phosphate ester. The difference from Example 1 is that in step S3, the molar ratio of ethylene carbonate to the selective fluorine reagent is 1:0.1, and the other operating 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 ester and phosphate ester. The difference from Example 1 is that in step S5, modified tris(trimethylsilyl) phosphate is not added, and the other operating 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 esters and phosphate esters. The difference from Example 1 is that in step S5, silicon-modified tri(2,2,2-trifluoroethyl) borate is not added, and the other operating steps and process parameters are exactly the same as those in Example 1.

[0107] The performance test of the high-rate lithium battery electrolyte based on the synergistic effect of borate ester and phosphate ester in the above Examples 1-4 and Comparative Examples 1-4 was carried out, and the specific process is as follows:

[0108] The conductivity test of the electrolyte was measured using a DJS-307 conductivity meter;

[0109] The positive electrode sheet (NCM811), the separator, and the negative electrode (metal lithium) sheet are stacked in order, so that the separator is between the positive and negative electrode sheets to play a role of isolation, and then wound and placed in an outer packaging foil, and the prepared electrolyte is injected, and then vacuum packaging, standing, forming, shaping and other processes are carried out to obtain a lithium metal battery;

[0110] At 25°C, the lithium metal battery is first charged to 4.3V at a constant current of 1C, then further charged to a current of 0.025C at a constant voltage of 4.3V, and then discharged to 3.0V at a constant current of 1C. This is a charge and discharge cycle process, and the discharge capacity this time is the discharge capacity of the first cycle. The lithium metal battery is subjected to multiple cycle charge and discharge tests in the above manner, and the discharge capacity of the 500th cycle is detected;

[0111] The capacity retention rate (%) of the lithium metal battery after 500 cycles = [discharge capacity at the 500th cycle / discharge capacity at the 1st cycle] × 100%.

[0112] High rate performance test:

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

[0114] High rate capacity retention rate of 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: Performance test results of high-rate lithium battery electrolytes and corresponding lithium metal batteries of Examples 1-4 and Comparative Examples 1-4

[0117]

[0118]

[0119] It can be seen from the test results of Example 1 and Comparative Examples 1 and 2 that excessive selective fluorine reagent will lead to excessive fluorination of ethylene carbonate, resulting in a high fluoride content in the electrolyte, which reduces the conductivity of the electrolyte. Excessive fluorination will inhibit the stable migration of lithium ions at the interface between the electrode and the electrolyte, thereby causing the capacity of the battery to decay; when the amount of selective fluorine reagent added 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 produced 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 improving the ion migration rate of the electrolyte. If it is not added, the solvation effect and lithium ion conductivity of the electrolyte will be poor, and the conductivity will decrease; at the same time, the modified tris(trimethylsilyl)phosphate helps to improve the interface stability of the electrolyte, reduce the growth of lithium dendrites, and improve the cycle stability and capacity retention rate of the battery. If the modified phosphate is not added, the stability of the interface film may be poor, resulting in uneven deposition of lithium ions on the electrode surface, thereby affecting the retention of capacity.

[0121] From the test results of Example 1 and Comparative Example 4, it can be seen that the role of silicon-modified tri(2,2,2-trifluoroethyl) borate is to improve the cycle stability of the battery, especially by preventing the growth of lithium dendrites. If this component is not added, the protective effect of the interface film will be weakened, which will easily lead to the growth of lithium dendrites, thereby affecting the cycle performance of the battery and reducing the capacity retention rate; the effect on the conductivity of the electrolyte is relatively small.

[0122] 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-rate lithium battery electrolyte based on the synergistic effect of borate esters and phosphate esters, characterized in that: The preparation method comprises: S1: adding tri(trimethylsilyl)phosphate and allyl alcohol to tetrahydrofuran, stirring at room temperature to obtain reaction solution A, placing the reaction solution A in an ice bath and adding dropwise a tetrahydrofuran solution of potassium tert-butoxide to obtain reaction solution B, and reacting at a constant temperature to obtain modified tri(trimethylsilyl)phosphate; S2: adding tri(2,2,2-trifluoroethyl) borate and trimethylsilyl chloride into dichloromethane under nitrogen protection to obtain reaction solution C, adding triethylamine dropwise at a constant temperature, and then heating to room temperature to react to obtain silicon-modified tri(2,2,2-trifluoroethyl) borate; S3: mixing ethylene carbonate and a selective fluorine reagent in acetonitrile to obtain a reaction solution D, stirring the mixture in an ice bath under nitrogen protection to obtain a reaction solution E, and treating the mixture to obtain fluorinated ethylene carbonate; adding sodium methoxide to a methanol dispersion of fluorinated ethylene carbonate to obtain a reaction solution F, stirring the mixture at room temperature to obtain a reaction solution G, adjusting the pH with dilute hydrochloric acid, and treating the mixture to obtain ether-fluorinated ethylene carbonate; S4: adding 1,4-butyrolactone and dimethylamine to methanol to obtain a reaction solution H, stirring the reaction at room temperature under nitrogen protection to obtain a reaction solution I, and treating the reaction solution to obtain amino-butyrolactone; adding a dichloromethane solution of chlorosulfonic acid dropwise to the dichloromethane solution of amino-butyrolactone under an ice bath to obtain a reaction solution J, stirring the reaction solution under an ice bath, then heating the reaction solution to room temperature and continuing to stir the reaction to obtain a pre-treated reaction solution, adding ice water to quench the reaction, and treating the reaction solution to obtain amino-sulfonated butyrolactone; S5: Add dimethyl carbonate and ethyl methyl carbonate to ether-fluorinated vinyl carbonate and stir to obtain a solvent, add amino-sulfonated butyrolactone, modified tris(trimethylsilyl) phosphate and silicon-modified tris(2,2,2-trifluoroethyl) borate in sequence, stir and add lithium hexafluorophosphate to obtain a reaction solution K, continue stirring, let stand and filter through a PTFE filter membrane to obtain a high-rate lithium battery electrolyte based on the synergistic effect of borate ester and phosphate ester.

2. The 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 S1: The molar ratio of tris(trimethylsilyl)phosphate to allyl alcohol is 1:1.2-1.5; The volume ratio of tris(trimethylsilyl)phosphate to tetrahydrofuran is 1:3-4; The molar ratio of tris(trimethylsilyl)phosphate to potassium tert-butoxide is 1:1.1-1.3; The concentration of the tetrahydrofuran solution of potassium tert-butoxide is 0.8-1.2M; The temperature of the constant temperature reaction of the reaction solution B is 50-60°C; The constant temperature reaction time of the reaction solution B is 8-10 hours.

3. The 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 S2: The molar ratio of tris(2,2,2-trifluoroethyl) borate to trimethylsilyl chloride is 1:1.2-1.3; The volume ratio of tris(2,2,2-trifluoroethyl) borate to dichloromethane is 1:3-4; The temperature of adding triethylamine to the reaction solution C is 0-5°C; The molar ratio of tri(2,2,2-trifluoroethyl) borate to triethylamine is 1:1-1.5; The reaction is carried out at room temperature for 4-6 hours.

4. The 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 ethylene carbonate to the selective fluorine reagent is 1:0.8-1.2; The volume ratio of ethylene carbonate to acetonitrile is 1:3-4; The reaction solution D was stirred in an ice bath under nitrogen protection at a stirring speed of 500-600 rpm; The reaction solution D is stirred in an ice bath under nitrogen protection for 3-5 hours.

5. The 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 volume ratio of fluorinated ethylene carbonate to methanol in the fluorinated ethylene carbonate methanol dispersion is 1:1.5-2.5; The molar ratio of the fluorinated ethylene carbonate to sodium methoxide is 1:0.9-1.1; The stirring speed of the reaction solution F at room temperature is 400-600 rpm; The reaction solution F is stirred at room temperature for 5-7 hours.

6. The 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 concentration of the dilute hydrochloric acid is 0.5-1.5M; The pH of the reaction solution G is adjusted to 6.5-7.5 with dilute hydrochloric acid.

7. The 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 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 was stirred at room temperature for 6-8 hours under nitrogen protection.

8. The 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 S4: The volume ratio of the aminobutyrolactone to dichloromethane in the dichloromethane solution of the aminobutyrolactone is 1:4-6; The molar ratio of the aminobutyrolactone to chlorosulfonic acid is 1:0.9-1.1; The concentration of the dichloromethane solution of chlorosulfonic acid is 0.8-1.0M; The reaction solution J is stirred in an ice bath for 2-3 hours; The time of heating to room temperature and continuing stirring the reaction is 4-5 hours; The volume ratio of the pretreatment reaction liquid to ice water is 1:2-3.

9. The 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 S5: The stirring speed of adding dimethyl carbonate and ethyl methyl carbonate into ether-fluorinated vinyl carbonate is 500-600 rpm; The stirring time of adding dimethyl carbonate and ethyl methyl carbonate into ether-fluorinated vinyl carbonate is 30-40 minutes; The reaction solution K is stirred for 2-3 hours; The standing time is 12-18 hours.

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

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