Dispersion medium composition of perfluoropolyether lithium salt electrolyte and application of dispersion medium composition

Abstract

The invention discloses a dispersion medium composition of a perfluoropolyether lithium salt electrolyte. The dispersion medium composition comprises a carbonate solvent, fluorinated ether modified multi-branched carbonate, a cosolvent and fluorobenzene modified carbonate. The dispersion medium composition of the perfluoropolyether lithium salt electrolyte is jointly formed by the substances, so that the temperature range of the electrolyte can be widened, the cold and hot safety boundary of a lithium battery is improved, and the high temperature (gt; 70 DEG C) and low temperature (lt; the out-of-control risk at-40 DEG C is reduced, the state or phase change of the battery in the use and storage process is reduced, the long-term stability is improved, and the flame-retardant safety is realized.

Description

Technical Field

[0001] This invention relates to the field of electrolyte modification technology, specifically to a dispersion medium composition for a perfluoropolyether lithium salt electrolyte and its application. Background Technology

[0002] Lithium-ion batteries have advantages such as high operating voltage (3.6 V, 3 times that of nickel, cadmium, hydrogen, and nickel batteries), small size (30% smaller than hydrogen and nickel batteries), light weight (50% lighter than hydrogen and nickel batteries), high specific energy (140 Wh / kg, 2-3 times that of nickel and cadmium batteries, and 1-2 times that of hydrogen and nickel batteries), wide operating temperature range (-25~45 ℃), no memory effect, low pollution, low self-discharge, and long cycle life. In today's face of energy shortages and environmental degradation, lithium-ion batteries, as green, high-energy rechargeable batteries, have become the focus of attention.

[0003] Electrolyte, as a crucial component of a battery, plays a vital role in charge transfer between the positive and negative electrodes, significantly influencing the battery's specific capacity, operating temperature range, cycle efficiency, and safety performance. Lithium-ion battery electrolytes consist of organic solvents, lithium salts, and necessary additives. The solvent is a core component, primarily responsible for dissolving the lithium salt and creating a conductive ionic environment. These solvents not only affect the electrolyte's electrochemical performance but also determine its physical properties such as operating temperature range, viscosity, and vapor pressure. For example, chain carbonates, cyclic carbonates, and phosphate esters are typically mixed solvents, mainly used to adjust viscosity to ensure a high dielectric constant and provide high ionic conductivity.

[0004] In recent years, researchers have begun to focus on novel solvent systems, such as fluorinated solvents and non-flammable / safe solvents, to improve battery safety and cycle life. Furthermore, weakly solvated electrolytes have attracted widespread attention due to their ability to modulate the solvation structure of lithium ions, thereby improving battery performance. In practical applications, the selection of electrolyte solvents must also consider cost, scalability, environmental friendliness, and wide-temperature operating capability.

[0005] Safety is a key issue restricting the development of high-capacity and high-power lithium-ion batteries. While non-fluorinated electrolytes offer superior electrochemical performance, their low flash point and flammability make them highly susceptible to ignition and even explosion under overcharging and overheating conditions. Furthermore, internal electrochemical decomposition during use severely shortens battery life. Therefore, the solubility of lithium salt electrolytes in fluorinated solvents presents the greatest challenge.

[0006] In summary, an electrolyte solvent needs to have the following characteristics: (1) low viscosity and high solvation capability to ensure rapid ion migration capability; (2) wide liquidus line and high flash point to ensure operation under different conditions without affecting performance or safety; (3) wide electrochemical window or good interface compatibility to be compatible with high energy density lithium metal anodes, etc.; (4) light weight and good wettability to minimize its weight and form good interface contact with all components of the battery; (5) low cost and environmentally friendly, etc.

[0007] Battery use under special conditions is also a critical technological barrier. For example, in harsh environments such as extremely cold regions or winter, the conductivity, lithium-ion transport capacity, and lithium-ion transport capacity at the battery-electrolyte interface decrease significantly at low temperatures, which is difficult to solve and affects usability.

[0008] Chinese patent document CN115986211A discloses a low-temperature electrolyte for lithium batteries and a lithium battery. The electrolyte includes an organic solvent, a lithium salt, and electrolyte additives. The organic solvent is a mixed solvent composed of a basic organic solvent with a high dielectric constant, a low viscosity solvent, and a low melting point solvent. The electrolyte can still have excellent ionic conductivity at -40 °C.

[0009] Chinese patent document CN120149558A discloses a low-temperature electrolyte for lithium batteries and a lithium-ion battery. By introducing a co-solvent, the mass concentration of conventional lithium salts is reduced (<13.5%), and positive / negative electrode film-forming additives, low-resistance lithium salt additives, and functional additives are used in conjunction. By selecting common low-melting-point and low-viscosity carboxylic esters as co-solvents and reducing the lithium salt concentration, the viscosity of the electrolyte at low temperatures is reduced and the ionic conductivity is improved. Low-resistance lithium salt additives are introduced, and conventional positive / negative electrode film-forming additives such as vinylene carbonate and fluoroethylene carbonate are used to construct a stable low-resistance positive / negative electrode interface film. Furthermore, the introduction of lithium salt additive anions regulates the solvation structure of the electrolyte, promoting the desolvation process of lithium ions at low temperatures. This improves the low-temperature performance of the lithium battery while ensuring a long cycle life of the electrolyte at room temperature.

[0010] In summary, existing technologies have not fundamentally solved the problems of electrolyte viscosity and lithium-ion transport capacity at low temperatures, nor the safety of use in medium and high temperature environments, and cannot simultaneously meet the needs of both high and low temperature operating environments. Summary of the Invention

[0011] To address the aforementioned technical problems, this invention provides a dispersion medium composition for a perfluoropolyether lithium salt electrolyte, which broadens the temperature range of the electrolyte, improves the thermal safety boundary of the lithium battery, mitigates the risk of runaway at high temperatures (>70 ℃) and low temperatures (<-40 ℃), reduces state or phase changes during battery use and storage, improves long-term stability, and has flame-retardant safety.

[0012] A dispersion medium composition for a perfluoropolyether lithium salt electrolyte includes a carbonate solvent, a fluorinated ether-modified branched carbonate, a co-solvent, and a fluorobenzene-modified carbonate. The structure of the fluorinated ether modified branched carbonate is shown below: R f -C n H n+3 O n-1 (R a ) k Where n = 4 or 5, k = 2 or 3; R f It is A-(C3F6O) q -CF(CF3)CO-, where A is CF3CF2O- or CF3O-, and q is an integer from 1 to 3; R a It is CH3(CH2) x O-CO-, where x = an integer from 0 to 2.

[0013] In this invention, the fluorinated ether modified multibranched carbonate is a compound with a multibranched structure composed of fluorinated ether segments and non-fluorinated segments, wherein R f As a medium-to-short chain perfluorinated polyether segment, the high electronegativity of fluorine leads to the formation of strongly polarized CF bonds, thereby altering the polar characteristics of the fluorinated molecules. Partially fluorinated molecules exhibit greater polarity than non-fluorinated molecules, and the higher ionization energy and lower polarizability of F result in weaker intermolecular forces among perfluorinated molecules. The energy of the CF bonds typically ensures high chemical and thermal stability of this structure, thus improving the high-temperature stability and flame retardancy of the dispersion medium composition. Furthermore, its multi-branched structure mitigates the incompatibility between fluorinated and non-fluorinated segments, significantly reducing the low-temperature viscosity of the solution system and ensuring lithium-ion transport and charge / discharge capacity retention.

[0014] In this invention, fluorinated flexible segments are introduced into the multi-branched carbonate modified with fluorinated ethers. Combined with carbonate solvents, co-solvents, and fluorobenzene-modified carbonates, these segments serve as a dispersion medium for lithium salt electrolytes. At room temperature, the system exhibits good lithium salt solubility and a relatively suitable system viscosity. The fluorinated multi-branched structure of the fluorinated ether-modified carbonate exhibits weak solvation at low temperatures, significantly reducing the capacity required for lithium-ion desolvation, thus ensuring lithium-ion migration. Simultaneously, the fluorinated end structure reduces the surface tension of the system, allowing for more uniform lithium-ion deposition on the negative electrode surface, thereby preventing dendrite formation and improving capacity retention and safety at low temperatures.

[0015] The above-mentioned dispersion medium composition broadens the temperature range of the electrolyte, improves the cold and hot safety boundary of the lithium battery, mitigates the risk of runaway at high temperature (>70 ℃) and low temperature (<-40 ℃), reduces the state or phase changes of the lithium battery during use and storage, improves long-term stability, and reduces the possibility of spontaneous combustion and improves flame retardant performance during use.

[0016] In this invention, the fluorinated ether modified multibranched carbonate can be selected from any of the following structures: , , .

[0017] Preferably, the carbonate solvent is one or more of dimethyl carbonate, diethyl carbonate, dipropyl carbonate, methyl ethyl carbonate, ethylene carbonate, and propylene carbonate.

[0018] In this invention, the use of the aforementioned carbonate solvent ensures the solubility of the electrolyte lithium salt and its ability to migrate particles under normal use.

[0019] Preferably, the co-solvent is methyl 2,2,3,3-tetrafluoro-3-methoxypropionate or methyl-2-methoxytetrafluoropropionate.

[0020] In this invention, the cosolvent with the above-mentioned structure has a high boiling point and good stability, as well as a relatively high flash point, which ensures the safety and high-temperature stability of the electrolyte. The addition of the cosolvent can significantly prevent the stripping of the graphite electrode. Its low freezing point, together with the fluorinated ether modified multibranched carbonate component in the composition, can reduce the freezing point of the electrolyte at low temperatures, ensuring a certain viscosity and fluidity at low temperatures, thereby promoting the lithium-ion transport capability.

[0021] More preferably, the mass ratio of the co-solvent to the carbonate solvent is 5~10:77~89.

[0022] Preferably, the structure of the fluorobenzene-modified carbonate is as follows: R b -OR c , Among them, R b for , , , , R c It is CH3-(CH2) s -OCO-, where s = integers from 0 to 2.

[0023] In this invention, the fluorobenzene-modified carbonate with the above-mentioned structure can overcome the flammability defects of the complete aliphatic chain segment, and has stronger electrochemical stability and interaction with alkali metals, and better solubility. In addition, the addition of fluorine can reduce the flammability of the dispersion medium by capturing H free radicals with F free radicals.

[0024] Preferably, in the dispersion medium composition of the perfluoropolyether lithium salt electrolyte, the mass ratio of carbonate solvent, fluorinated ether modified multibranched carbonate, and fluorobenzene modified carbonate is 77~89:5~8:1~5.

[0025] The present invention also provides a method for preparing the dispersion medium composition of the above-mentioned perfluoropolyether lithium salt electrolyte, comprising the following steps: Add carbonate solvent to a sealed, dehydrated container, and slowly add fluorinated ether modified multibranched carbonate and fluorobenzene modified carbonate while stirring. Then add a co-solvent and continue stirring until a uniform dispersion medium composition of perfluoropolyether lithium salt electrolyte is obtained.

[0026] Preferably, the preparation method of the fluorinated ether modified multibranched carbonate includes the following steps: R f -F reacts with glycerol or pentaerythritol in the presence of triethylamine to give an intermediate of terminally branched alcohol, followed by the slow addition of R. a -Cl and triethylamine yield fluorinated ether-modified branched carbonate.

[0027] In this invention, glycerol can be 1,2,4-butanetriol.

[0028] The specific reaction formula is shown below:

[0029] Among them, R f It is A-(C3F6O) q CO-, where A is CF3CF2O- or CF3O-, a = 2 or 3, q ​​= integers from 1 to 3; R a It is CH3(CH2) x O-CO-, where x = an integer from 0 to 2.

[0030] In this invention, R f -F raw materials can be prepared according to the methods in Chinese patent documents with publication number CN116925153A or CN117624255A.

[0031] Preferably, the fluorobenzene-modified carbonate is produced by fluorophenol (i.e., R... b -OH) and chlorinated carbonates (i.e., R c The product is prepared by nucleophilic substitution reaction of -Cl under alkaline conditions.

[0032] The present invention also provides the application of the above-mentioned dispersion medium composition of perfluoropolyether lithium salt electrolyte in the preparation of lithium salt electrolyte.

[0033] Preferably, the lithium salt electrolyte comprises a lithium salt and a dispersion medium composition of the above-mentioned perfluoropolyether lithium salt electrolyte.

[0034] Preferably, the lithium salt is lithium hexafluorophosphate.

[0035] A lithium battery includes a positive electrode, a negative electrode, a separator disposed between the positive electrode and the negative electrode, and an electrolyte, wherein the electrolyte is the lithium salt electrolyte described above.

[0036] Preferably, the lithium battery has a conductivity of ≥7 mS·cm at -40 ℃ and a capacity retention rate of ≥98% after 500 charge-discharge cycles.

[0037] Compared with the prior art, the beneficial effects of the present invention are as follows: In this invention, by combining carbonate solvent, fluorinated ether modified multibranched carbonate, co-solvent, and fluorobenzene modified carbonate to form a dispersion medium composition for a perfluoropolyether lithium salt electrolyte, the temperature range of the electrolyte can be broadened, the cold and hot safety boundaries of the lithium battery can be improved, the risk of runaway at high temperatures (>70 ℃) and low temperatures (<-40 ℃) can be mitigated, the state or phase changes during battery use and storage can be reduced, long-term stability can be improved, and flame retardant safety can be provided. Attached Figure Description

[0038] Figure 1 The image shows the infrared spectrum of compound B1 obtained in Example 2.

[0039] Figure 2 The image shows the infrared spectrum of compound D1 obtained in Example 1. Detailed Implementation

[0040] The present invention will be further described in detail below with reference to the embodiments, but the implementation of the present invention is not limited to the following embodiments.

[0041] All raw materials used in this invention are commercially available.

[0042] Example 1 (1) Preparation of fluorinated ether modified multibranched carbonate (compound B1)

[0043] 1,2,4-Butanetriol (0.10 mol) and 50 g of HFE-7200, along with triethylamine (0.105 mol), were added to a cold-insulated, sealed reactor. Then, CF3CF2-O-(CF2CF2O)2-CFCF3-COF (0.1 mol) was slowly added dropwise over 1 h while maintaining the room temperature at 25 ℃. After the reaction was maintained at this temperature for 4 h, ethyl chlorocarbonate (0.24 mol) and triethylamine (0.25 mol) were slowly added dropwise. The reaction was then maintained at this temperature for 8 h. After filtration, the low-boiling point was distilled off to obtain compound B1, with a yield of 73%.

[0044] Figure 1 The image shows the infrared spectrum of compound B1. As can be seen from the image, the typical hydroxyl peak of the 1,2,4-butanetriol structure has completely disappeared, and the methyl peak comes from the methyl group of the chloroacetic acid ester, indicating that the first and second steps of the reaction are complete.

[0045] (2) Preparation of fluorobenzene-modified carbonate (compound D1)

[0046] 4-Fluorophenol (0.10 mol), 30 g of dichloromethane, and 0.105 mol of triethylamine were added to a cold-insulated, sealed reactor. Then, methyl chlorocarbonate (0.1 mol) was slowly added dropwise at room temperature (25 °C) over 1 h. The reaction was then maintained at this temperature for 4 h. The mixture was washed with water to separate the layers, and the lower layer was removed. The low-boiling-point substances were then distilled off to obtain compound D1 with a yield of 88%.

[0047] Figure 2 The image shows the infrared spectrum of compound D1 in Example 1. As can be seen from the image, the typical hydroxyl peak of the phenolic hydroxyl structure has completely disappeared, indicating that the reaction was complete. The methyl peak originates from the methyl group of the chloroformate, and the vibrational peak of the CF of the benzene ring indicates that the fluorobenzene ring has reacted.

[0048] (3) By weight, 77 parts of ethylene carbonate were added to a sealed, dehydrated container, and 8 parts of compound B1 obtained in step (1) and 5 parts of compound D1 obtained in step (2) were added slowly with stirring. Then, 10 parts of methyl 2,2,3,3-tetrafluoro-3-methoxypropionate were added, and stirring was continued until a uniform dispersion medium composition of perfluoropolyether lithium salt electrolyte was obtained.

[0049] Example 2 Preparation of fluorinated ether-modified branched carbonates (compound B3)

[0050] In a cold-insulated, sealed reactor, pentaerythritol (0.10 mol), HFE-7200 50 g, and triethylamine (0.105 mol) were added. Then, CF3-O-(CFCF3CF2O)2-CFCF3-COF (0.1 mol) was slowly added dropwise over 1 h while maintaining the room temperature at 25 ℃. After the reaction was maintained at this temperature for 4 h, methyl chlorocarbonate (0.35 mol) and triethylamine (0.36 mol) were slowly added dropwise. The reaction was then maintained at this temperature for 8 h. After filtration, the low-boiling-point substances were distilled off to obtain compound B3, with a yield of 76%.

[0051] (2) Preparation of fluorobenzene-modified carbonate (compound D2)

[0052] Compound D2 was prepared according to the preparation method in Example 1, with a yield of 90%.

[0053] (3) By weight, 89 parts of ethyl methyl carbonate were added slowly with stirring to a sealed, dehydrated container, along with 5 parts of compound B3 obtained in step (1) and 1 part of compound D2 obtained in step (2), and then 5 parts of methyl-2-methoxytetrafluoropropionate were added. Stirring was continued until a uniform dispersion medium composition of perfluoropolyether lithium salt electrolyte was obtained.

[0054] Example 3 (1) Preparation of fluorinated ether modified multibranched carbonate (compound B2)

[0055] In a cold-insulated, sealed reactor, pentaerythritol (0.10 mol), HFE-7200 50 g, and triethylamine (0.105 mol) were added. Then, CF3CF2-O-(CFCF3CF2O)3-CFCF3-COF (0.1 mol) was slowly added dropwise over 1 h while maintaining the room temperature at 25 ℃. After the reaction was maintained at this temperature for 4 h, propyl chloride carbonate (0.35 mol) and triethylamine (0.36 mol) were slowly added dropwise. The reaction was then maintained at this temperature for 8 h. After filtration, the low-boiling point was distilled off to obtain compound B2, with a yield of 75%.

[0056] (2) Preparation of fluorobenzene-modified carbonate (compound D3)

[0057] Compound D3 was prepared according to the preparation method in Example 1, with a yield of 88%.

[0058] (3) By weight, 82 parts of a mixture of ethylene carbonate, ethyl methyl carbonate and propylene carbonate in a sealed, dehydrated container, wherein the mass ratio of ethylene carbonate, ethyl methyl carbonate and propylene carbonate in the mixture is 6:3:1, 7 parts of compound B2 obtained in step (1) and 3 parts of compound D3 obtained in step (2) are slowly added while stirring, and then 8 parts of methyl 2,2,3,3-tetrafluoro-3-methoxypropionate are added, and stirring is continued until a uniform dispersion medium composition of perfluoropolyether lithium salt electrolyte is obtained.

[0059] Comparative Example 1 (1) Preparation of perfluorinated branched carbonate (compound B4)

[0060] Pentaerythritol (0.10 mol) was added to a cold-insulated, sealed reactor, followed by the dropwise addition of methyl chlorocarbonate (0.35 mol) and triethylamine (0.36 mol). The reaction was maintained at the temperature for 8 h, then filtered, and the low-boiling-point substances were distilled off to obtain compound B4 with a yield of 83%.

[0061] (2) Preparation of benzene-modified carbonate (compound D4)

[0062] Compound D4 was prepared according to the preparation method in Example 1, with a yield of 85%.

[0063] (3) By weight, 82 parts of a mixture of ethylene carbonate, methyl ethyl carbonate and propylene carbonate in a sealed, dehydrated container, wherein the mass ratio of ethylene carbonate, methyl ethyl carbonate and propylene carbonate in the mixture is 6:3:1, 7 parts of compound B4 obtained in step (1) and 3 parts of compound D4 obtained in step (2) are slowly added while stirring, and then 8 parts of methyl 2,2,3,3-tetrafluoro-3-methoxypropionate are added, and stirring is continued until a uniform dispersion medium composition is obtained.

[0064] Comparative Example 2 By weight, 82 parts of a mixture of ethylene carbonate, ethyl methyl carbonate, and propylene carbonate, wherein the mass ratio of ethylene carbonate, ethyl methyl carbonate, and propylene carbonate in the mixture is 6:3:1, are slowly added to the mixture under stirring along with 7 parts of compound B2 obtained in Example 3 and 3 parts of compound D4 obtained in Comparative Example 1, followed by 8 parts of methyl 2,2,3,3-tetrafluoro-3-methoxypropionate. The mixture is stirred until a homogeneous dispersion is obtained.

[0065] Comparative Example 3 The preparation method is the same as in Example 3, except that compound B2 was not added.

[0066] Comparative Example 4 The preparation method is the same as in Example 3, except that compound D3 was not added.

[0067] Sample Analysis The dispersion media compositions obtained in Examples 1-3 and Comparative Examples 1-4 were slowly mixed with lithium hexafluorophosphate and dispersed until fully dissolved to prepare an electrolyte with a concentration of 1 mol / kg. The electrolyte was stored anhydrous for later use.

[0068] I. Thermal Shock Test The prepared electrolyte test solution was placed in a refrigerator (-40 ℃) for 4 hours, then immediately placed in a constant temperature and humidity chamber at 70 ℃ for 4 hours. This constitutes one cycle. After 500 cycles, the temperature was maintained at room temperature (25 ℃), and the state of the electrolyte was observed. A uniform electrolyte with almost no change is classified as A; a cloudy electrolyte without precipitation is classified as B; and an electrolyte with lumps or particles precipitated is classified as C.

[0069] II. Conductivity Test The electrolyte prepared above was tested for conductivity using a Leici DDSJ-308A conductivity meter at ambient pressure and temperatures of 25 ℃ and -40 ℃, respectively.

[0070] III. Low-Temperature Charge-Discharge Test Lithium-ion batteries were prepared using the electrolytes from the above examples and comparative examples. The positive electrode material was lithium iron phosphate, and the negative electrode material was graphite. Low-temperature cycling experiments were conducted. The test method was as follows: the batteries were placed in a -40 °C freezer and cycled at a 1C rate for 500 charge-discharge cycles. The capacity retention rate was then calculated. The conductivity at -40 °C, without further testing, was also used as the unit for 0 cycles at low temperature (i.e., 0 cycles = 100%).

[0071] IV. Flame Retardancy Test The flammability of the above-mentioned electrolyte was tested in a self-made combustion performance test chamber, and the self-ex-tinguishing time (SET) was used to indicate the flame retardant effect. The SET measurement method is as follows: Glass wool balls with a diameter of 5 mm were made from glass wool and placed on a nickel wire mesh. Electrolyte (0.1~0.11 g) was injected onto the glass wool using a needle syringe (5 mL), and quickly ignited. The time from when the ignition device was removed until the flame automatically extinguished was recorded; this time is the self-ex-tinguishing time. The flammability of the above-mentioned electrolyte was compared using the self-ex-tinguishing time per unit mass of electrolyte (i.e., s / g) as the standard.

[0072] Table 3 shows the test results of the electrolytes in Examples 1-3 and Comparative Examples 1-5.

[0073] As shown in the table above, the dispersion medium composition using the perfluorinated polyether lithium salt electrolyte described in this invention exhibits stable conductivity, good conductivity even at low temperatures, excellent flame retardancy, and a charge / discharge capacity retention rate exceeding 98%. Comparative Example 1, with its fluorinated ether-modified branched carbonate, uses perfluorinated modified segments. The excessively high fluorine content leads to poor compatibility with the system, and the system's stability is compromised after high and low temperature shocks, especially at low temperatures, where its compatibility is even worse; after 500 low-temperature charge / discharge cycles, only 63% of the capacity retention rate remains. Comparative Example 2, with its benzene-modified carbonate, lacks fluorination modification, and its compatibility and room-temperature conductivity are unaffected, but its low-temperature conductivity and charge / discharge capacity retention rate are both poor. Comparative Example 3, lacking compound B2, is affected in terms of low-temperature conductivity, flame retardancy, and charge / discharge capacity retention rate. Comparative Example 4, lacking compound D3, also affects its low-temperature performance.

[0074] In summary, the soluble compositions of the present invention form a synergistic and unified whole. The absence of any component will affect the overall performance of the composition, which also proves that the components of the composition of the present invention have an interactive and mutually supportive relationship, and none of them can be omitted.

[0075] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A dispersion medium composition for a perfluoropolyether lithium salt electrolyte, characterized in that, The dispersion medium composition includes a carbonate solvent, a fluorinated ether-modified branched carbonate, a co-solvent, and a fluorobenzene-modified carbonate; The structure of the fluorinated ether modified branched carbonate is shown below: R f -C n H n+3 O n-1 (R a ) k Where n = 4 or 5, k = 2 or 3; R f It is A-(C3F6O) q -CF(CF3)CO-, where A is CF3CF2O- or CF3O-, and q is an integer from 1 to 3; R a It is CH3(CH2) x O-CO-, where x = an integer from 0 to 2.

2. The dispersion medium composition for the perfluoropolyether lithium salt electrolyte according to claim 1, characterized in that, The carbonate solvent is one or more of dimethyl carbonate, diethyl carbonate, dipropyl carbonate, methyl ethyl carbonate, ethylene carbonate, and propylene carbonate.

3. The dispersion medium composition for the perfluoropolyether lithium salt electrolyte according to claim 1, characterized in that, The co-solvent is methyl 2,2,3,3-tetrafluoro-3-methoxypropionate or methyl-2-methoxytetrafluoropropionate.

4. The dispersion medium composition for the perfluoropolyether lithium salt electrolyte according to claim 3, characterized in that, The mass ratio of the co-solvent to the carbonate solvent is 5~10:77~89.

5. The dispersion medium composition for the perfluoropolyether lithium salt electrolyte according to claim 1, characterized in that, The structure of the fluorobenzene-modified carbonate is shown below: R b -O-R c , Among them, R b for , , , , R c It is CH3-(CH2) s O-CO-, where s = integers from 0 to 2.

6. The dispersion medium composition for the perfluoropolyether lithium salt electrolyte according to claim 1, characterized in that, In the dispersion medium composition of the perfluoropolyether lithium salt electrolyte, the mass ratio of ester solvent, fluorinated ether modified multibranched carbonate and fluorobenzene modified carbonate is 77~89:5~8:1~5.

7. The dispersion medium composition for the perfluoropolyether lithium salt electrolyte according to claim 1, characterized in that, The method for preparing the fluorinated ether-modified branched carbonate includes the following steps: R f -F reacts with glycerol or pentaerythritol in the presence of triethylamine to give an intermediate of terminally branched alcohol, followed by the slow addition of R. a -Cl and triethylamine yield fluorinated ether-modified branched carbonate.

8. A lithium salt electrolyte, characterized in that, The lithium salt electrolyte comprises a lithium salt and a dispersion medium composition of the perfluoropolyether lithium salt electrolyte according to any one of claims 1 to 7.

9. A lithium battery, comprising a positive electrode, a negative electrode, a separator disposed between the positive electrode and the negative electrode, and an electrolyte, characterized in that, The electrolyte is the lithium salt electrolyte as described in claim 8.

10. The lithium battery according to claim 9, characterized in that, The lithium battery has a conductivity of ≥7mS·cm at -40 ℃ and a capacity retention of ≥98% after 500 charge-discharge cycles.

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