Low-temperature lithium-ion battery electrolyte, its manufacturing method, and lithium-ion battery

Abstract

The present invention relates to the technical field of lithium ion batteries, and in particular to a low-temperature type lithium ion battery electrolyte and its manufacturing method, and a lithium ion battery. The low-temperature type lithium ion battery electrolyte of the present invention includes an electrolyte salt and an organic solvent, and the organic solvent includes a fluorocarboxylic acid ester, a fluorocarbonic acid ester, and 1,3-dioxane. The fluorocarboxylic acid ester has a low freezing point and is suitable as a low-temperature electrolyte solvent, and the fluorocarbonic acid ester is mixed with the fluorocarboxylic acid ester as a co-solvent to adjust the low-temperature performance and film-forming property of the electrolyte, and the introduction of 1,3-dioxane with a low freezing point and low viscosity obviously reduces the impedance of the battery. The low-temperature type lithium ion battery electrolyte of the present invention can effectively improve the low-temperature lithium ion conductivity, which is advantageous for the low-temperature capacity of a lithium ion battery, and can especially improve the discharge specific capacity and capacity retention rate of a lithium iron phosphate lithium ion battery under low-temperature conditions.

Description

[Technical Field]

[0001] (CROSS-REFERENCE TO RELATED APPLICATIONS) This application claims priority from a Chinese invention patent application, application number 202211016568.3, filed on August 24, 2022, entitled "Low-temperature lithium-ion battery electrolyte and manufacturing method thereof, and lithium-ion battery," the disclosure of which is incorporated herein by reference.

[0002] The present invention relates to the technical field of lithium ion batteries, and more particularly to a low-temperature lithium ion battery electrolyte, a manufacturing method thereof, and a lithium ion battery. [Background technology]

[0003] As the range of applications of lithium-ion batteries (LIBs) expands, especially in electric vehicles, aerospace, and defense industries, there are increasing demands for their low-temperature charge-discharge performance. However, there are still many technical challenges to overcome in improving the low-temperature energy storage performance and cycle stability of LIBs. In particular, the tendency of commercial carbonate-based electrolytes to solidify at low temperatures and their high impedance limit the further application of LIBs in low-temperature EVs.

[0004] Therefore, optimizing electrolytes has become one of the research focuses for improving the low-temperature performance of lithium-ion batteries. Among the many cathode materials, lithium iron phosphate is widely used in the electric vehicle field due to its high safety performance and low cost, but its low conductivity means that its low-temperature performance needs to be improved. Therefore, lithium iron phosphate is used as a lithium-ion cathode, and research into modifying low-temperature electrolytes to improve its suitability has been conducted, which has certain market potential.

[0005] Patent 202111011044.0 discloses a low-temperature lithium-ion battery electrolyte for a high-nickel ternary positive electrode, specifically comprising lithium difluorooxalate borate (LiDFOB) and a mixed solvent, where the concentration of lithium difluorooxalate borate (LiDFOB) is 0.8-1.5 mol / L, and the mixed solvent is a linear carbonate, a cyclic carbonate, and gamma-butyrolactone.

[0006] This technical solution lowers the melting point of the electrolyte by adding gamma-butyrolactone, a low-melting organic solvent, to the basic solvent, carbonate, thereby improving the low-temperature performance of lithium-ion batteries and enhancing the electrochemical performance of lithium-ion batteries under low-temperature conditions. However, there is still room for improvement in the low-temperature resistance of lithium-ion batteries.

[0007] The present invention has been made in view of these points. Summary of the Invention [Problem to be solved by the invention]

[0008] A first object of the present invention is to provide a low-temperature lithium-ion battery electrolyte that can effectively improve the discharge specific capacity and capacity retention rate of a lithium-ion battery under low-temperature conditions.

[0009] The second object of the present invention is to provide a method for preparing the above low-temperature lithium ion battery electrolyte, which has simple steps, is easy to operate, and is convenient for practical popularization and large-scale application.

[0010] A third object of the present invention is to provide a lithium ion battery containing the above low-temperature lithium ion battery electrolyte and having excellent electrochemical performance under low-temperature conditions. [Means for solving the problem]

[0011] In order to achieve the above object of the present invention, the following technical solutions are particularly adopted.

[0012] The present invention provides a low-temperature lithium-ion battery electrolyte, comprising an electrolyte salt and an organic solvent, The organic solvent includes a fluorocarboxylic acid ester, a fluorocarbonic acid ester, and 1,3-dioxane.

[0013] Further, the fluorocarboxylic acid ester includes diethyl fluoromalonate.

[0014] Furthermore, the fluorocarbonate includes fluoroethylene carbonate.

[0015] Furthermore, the electrolyte salt includes lithium bis(trifluoromethanesulfonyl)imide and / or lithium trifluoromethanesulfonylimide.

[0016] Preferably, the electrolyte salt comprises lithium bis(trifluoromethanesulfonyl)imide.

[0017] Furthermore, in the low-temperature lithium-ion battery electrolyte, the volume percentage of the fluorocarboxylic acid ester is greater than 40%.

[0018] Preferably, in the low-temperature lithium-ion battery electrolyte, the volume percentage of the fluorocarboxylic acid ester is 50% to 70%.

[0019] Furthermore, the volume ratio of the fluorocarboxylic acid ester, the fluorocarbonic acid ester, and the 1,3-dioxane is 90-40:5-50:5-30.

[0020] Preferably, the volume ratio of the fluorocarboxylic acid ester, the fluorocarbonic acid ester, and the 1,3-dioxane is 55-65:15-25:15-25.

[0021] Furthermore, in the low-temperature lithium-ion battery electrolyte, the concentration of the electrolyte salt is 1.0 to 5.0 mol / L.

[0022] Preferably, in the low-temperature lithium-ion battery electrolyte, the concentration of the electrolyte salt is 1.5 to 2.5 mol / L.

[0023] The present invention further provides a method for preparing the above-mentioned low-temperature lithium ion battery electrolyte, in which the low-temperature lithium ion battery electrolyte is obtained after uniformly mixing an organic solvent and an electrolyte salt.

[0024] The present invention further provides a lithium-ion battery comprising the low-temperature lithium-ion battery electrolyte as described above.

[0025] Furthermore, the positive electrode material of the lithium ion battery is lithium iron phosphate. [Effects of the Invention]

[0026] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0027] (1) The low-temperature lithium-ion battery electrolyte of the present invention uses a fluorocarboxylic acid ester as a main solvent, a fluorocarbonic acid ester and 1,3-dioxane as co-solvents, and is combined with lithium bis(trifluoromethanesulfonyl)imide, thereby significantly improving low-temperature lithium ion conductivity and being advantageous for enabling lithium-ion batteries to exhibit their capacity at low temperatures.

[0028] (2) The low-temperature lithium-ion battery electrolyte of the present invention uses lithium bis(trifluoromethanesulfonyl)imide as an electrolyte salt, which allows the formation of a stable inorganic component interfacial phase at the positive electrode, and fluoroethylene carbonate as an electrolyte salt, which allows the formation of a stable inorganic component interfacial phase at the negative electrode, thereby significantly improving the cycle stability of the battery at low temperatures (-30°C).

[0029] (3) The low-temperature lithium-ion battery electrolyte of the present invention can significantly improve the discharge specific capacity and capacity retention rate of a lithium iron phosphate lithium-ion battery under low-temperature conditions. A LiFePO4 / Li battery assembled using the electrolyte can achieve a 0.2C discharge specific capacity of 90 mAh / g in a low-temperature environment of -30°C. [Brief explanation of the drawings]

[0030] In the following, in order to more clearly explain the specific embodiments of the present invention or the technical solutions in the prior art, drawings required for the description of the specific embodiments or the prior art will be briefly introduced. It is obvious that the drawings in the following description are some embodiments of the present invention, and those skilled in the art can derive other drawings based on these drawings without any creative efforts. [Figure 1] 1 is a graph comparing the charge / discharge voltages at 2.7 to 4.2 V and the discharge specific capacity at −30° C. of batteries fabricated using the low-temperature lithium ion battery electrolyte of Example 7 of the present invention and the lithium ion battery electrolyte of Comparative Example 5. DETAILED DESCRIPTION OF THE INVENTION

[0031] The technical solutions of the present invention will be described below clearly and completely with reference to the drawings and specific embodiments. Those skilled in the art will understand that the examples described below are only some of the examples of the present invention, not all of the examples, and are intended to merely illustrate the present invention and should not be construed as limiting the scope of the present invention.

[0032] Based on the examples of the present invention, all other examples that can be made by those skilled in the art without creative effort fall within the scope of the present invention. Unless specific conditions are specified in the examples, the usual conditions or the conditions recommended by the manufacturer are followed. Unless the manufacturer is specified, the reagents and equipment used are all ordinary commercially available products.

[0033] Hereinafter, a low-temperature lithium-ion battery electrolyte, a method for producing the same, and a lithium-ion battery according to examples of the present invention will be specifically described.

[0034] In some embodiments of the present invention, a low-temperature lithium-ion battery electrolyte is provided, the low-temperature lithium-ion battery electrolyte comprising an electrolyte salt and an organic solvent, The organic solvent includes a fluorocarboxylic acid ester, a fluorocarbonic acid ester, and 1,3-dioxane.

[0035] The low-temperature lithium-ion battery electrolyte of the present invention uses a fluorocarboxylic acid ester as a main solvent and a fluorocarbonic acid ester and 1,3-dioxane as co-solvents, thereby effectively improving low-temperature lithium ion conductivity and being advantageous for enabling lithium-ion batteries to exhibit their capacity at low temperatures.

[0036] Fluorocarboxylic acid esters have a low melting point, and the freezing point of the carboxylic acid ester can be further lowered by the fluorine. The low melting point of the fluorocarboxylic acid ester lowers the freezing point of the electrolyte itself, improving the ionic conductivity of the electrolyte at low temperatures, thereby improving the low-temperature performance of the battery. The introduction of fluorine element is also advantageous in improving interfacial performance.

[0037] Since fluorocarboxylic acid esters have poor film-forming properties, fluorocarbonic acid esters are selected as co-solvents and mixed with the fluorocarboxylic acid esters to adjust the film-forming properties of the electrolyte solution.

[0038] The addition of 1,3-dioxane (DOL), which has a low freezing point and low viscosity, significantly reduces the impedance of lithium-ion batteries, thereby improving the discharge specific capacity and capacity retention rate of lithium-ion batteries, especially lithium iron phosphate batteries, under low-temperature conditions.

[0039] In some embodiments of the present invention, the fluorocarboxylic acid ester comprises diethyl fluoromalonate.

[0040] Diethyl fluoromalonate (DEFM) is used as a solvent for the electrolyte solution. The bond energy between diethyl fluoromalonate and lithium ions is low, which is advantageous for the lithium ion intercalation and deintercalation process at low temperatures.

[0041] In some embodiments of the present invention, the fluorocarbonate comprises fluoroethylene carbonate (4-Fluoro-1,3-dioxolan-2-one, FEC).

[0042] In some embodiments of the present invention, the electrolyte salt comprises lithium bis(trifluoromethanesulfonyl)imide and / or lithium trifluoromethanesulfonylimide, preferably, the electrolyte salt comprises lithium bis(trifluoromethanesulfonyl)imide (LiTFSI).

[0043] Lithium bis(trifluoromethanesulfonyl)imide can be dissolved in solvents at high concentrations and has a high HOMO level and a low LUMO level. During the first charge, it decomposes at the cathode / anode-electrolyte interface, forming an interfacial film with a high inorganic component content, significantly improving the cycle stability of the battery at low temperatures (-30°C). Lithium bis(trifluoromethanesulfonyl)imide at an appropriate concentration can provide a stable fluorine-containing interfacial film with high ionic conductivity.

[0044] The HOMO is the highest occupied molecular orbital, and the higher the HOMO level, the more likely a substance is to lose electrons. For electrolytes, the HOMO level can be used to determine the order in which each component decomposes during charging. Components with higher HOMO levels are more likely to be oxidized and form a film at the positive electrode / electrolyte interface, preventing direct contact between other components and the electrolyte during subsequent charging and discharging, and suppressing side reactions at the positive electrode / electrolyte interface.

[0045] The LUMO level is the lowest unoccupied molecular orbital, and the lower the LUMO level, the easier it is for a substance to gain electrons. For electrolytes, the LUMO level can be used to determine the order of decomposition of each component during the discharge process. Components with lower LUMO levels are more likely to be reduced and form a film at the anode-electrolyte interface, which prevents direct contact between the electrode and the electrolyte during subsequent charge and discharge processes and suppresses side reactions at the interface.

[0046] The organic solvents used in the low-temperature lithium-ion battery electrolyte of the present invention are fluorocarboxylic acid ester, fluoroethylene carbonate, and 1,3-dioxane. The fluorocarboxylic acid ester and fluorocarbonate have low melting points, which lower the melting point of the electrolyte and improve the ionic conductivity of the electrolyte at low temperatures. The high HOMO level of LiFSI allows it to decompose preferentially onto the surface of the positive electrode of a lithium-ion battery to form a film, improving the stability of the positive electrode-electrolyte interface.

[0047] The LUMO level of fluoroethylene carbonate is low, and it can be preferentially decomposed to form a film on the surface of the negative electrode of a lithium ion battery, improving the stability of the negative electrode-electrolyte interface. Therefore, the electrolyte of the present invention can improve the discharge specific capacity and capacity retention rate of a lithium ion battery at low temperatures (-30°C).

[0048] In some implementations of the present invention, the low temperature lithium ion battery electrolyte includes lithium bis(trifluoromethanesulfonyl)imide, diethyl fluoromalonate, fluoroethylene carbonate, and 1,3-dioxane.

[0049] In some implementations of the present invention, the volume percentage of fluorocarboxylic acid ester in the low temperature lithium ion battery electrolyte is >40%.

[0050] In some embodiments of the present invention, the volume percentage of the fluorocarboxylic acid ester in the low-temperature lithium-ion battery electrolyte is 50% to 70%. Typical but non-limiting examples of the volume percentage of the fluorocarboxylic acid ester in the low-temperature lithium-ion battery electrolyte include 50%, 51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59%, 60%, 61%, 62%, 63%, 64%, 65%, 66%, 67%, 68%, 69%, and 70%. Preferably, the volume percentage of the fluorocarboxylic acid ester in the low-temperature lithium-ion battery electrolyte is 55% to 65%, and more preferably 58% to 62%.

[0051] In some embodiments of the present invention, the volume ratio of the fluorocarboxylic acid ester, the fluorocarbonate ester, and the 1,3-dioxane is 90 to 40:10 to 50:1 to 30, and typical but non-limiting examples include the volume ratio of the fluorocarboxylic acid ester, the fluorocarbonate ester, and the 1,3-dioxane is 80:10:10, 70:15:15, 60:20:20, 50:25:25, 40:30:30, 80:10:5, 70:30:10, 60:10:5, 50:10:20, etc., and preferably the volume ratio of the fluorocarboxylic acid ester, the fluorocarbonate ester, and the 1,3-dioxane is 55 to 65:15 to 25:15 to 25, and more preferably the volume ratio of the fluorocarbonate ester to the 1,3-dioxane is 1:1.

[0052] In some embodiments of the present invention, the low-temperature lithium-ion battery electrolyte has an electrolyte salt concentration of 1.0 to 5.0 mol / L, and typically, but not limited to, for example, the low-temperature lithium-ion battery electrolyte has an electrolyte salt concentration of 1.0 mol / L, 1.5 mol / L, 2.0 mol / L, 2.5 mol / L, 3.0 mol / L, 3.5 mol / L, 4.0 mol / L, 4.5 mol / L, or 5.0 mol / L, and preferably, the low-temperature lithium-ion battery electrolyte has an electrolyte salt concentration of 1.5 to 2.5 mol / L.

[0053] In some embodiments of the present invention, a method for preparing the low-temperature lithium ion battery electrolyte is further provided, in which the low-temperature lithium ion battery electrolyte is obtained after uniformly mixing the organic solvent and the electrolyte salt.

[0054] In some embodiments of the present invention, the organic solvent is an anhydrous organic solvent, and the method for producing the anhydrous organic solvent includes adding a dehydrating agent to the organic solvent and allowing the organic solvent to stand for 2 to 4 days. Preferably, the dehydrating agent is a molecular sieve having a type number of 3 Å, 4 Å, or 5 Å.

[0055] In some embodiments of the present invention, a lithium ion battery is further provided, comprising the low temperature lithium ion battery electrolyte described above.

[0056] In some embodiments of the present invention, the positive electrode material of the lithium ion battery is lithium iron phosphate.

[0057] In some embodiments of the present invention, a lithium ion battery includes a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte; Here, the positive electrode sheet is mainly made of a positive electrode active material, a conductive agent, a binder, and a dispersant, and the positive electrode active material is LiFePO4, The negative electrode sheet is a lithium sheet, The electrolyte is the low-temperature lithium-ion battery electrolyte.

[0058] In some embodiments of the present invention, the conductive agent comprises conductive carbon black.

[0059] In some embodiments of the present invention, the binder comprises polyvinylidene fluoride.

[0060] In some embodiments of the present invention, the conductive agent comprises N-methyl-2-pyrrolidone.In some embodiments of the present invention, the separator comprises a polypropylene microporous film.

[0061] The LiFePO4 / Li battery assembled using the low-temperature lithium ion battery electrolyte of the present invention has a 0.2C discharge specific capacity of 90mAh / g in a low-temperature environment of -30°C, and can maintain stable cycles.

[0062] Examples 1 to 12 The manufacturing method of the low-temperature lithium-ion battery electrolyte in each example is the same, and the only differences are the volume ratio of the solvents DEFM, FEC, and DOL used in the low-temperature lithium-ion battery electrolyte and the concentration of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI). The volume ratio of the solvents and the concentration of LiTFSI in each example are shown in Table 1.

[0063] [Table 1]

[0064] A method for producing a low-temperature lithium-ion battery electrolyte includes the following steps: In an inert gas-protected glove box, diethyl fluoromalonate (DEFM), fluorocarbon ester (FEC), and 1,3-dioxane (DOL) were mixed in a volumetric ratio. After mixing, 3Å molecular sieve desiccant was added and allowed to stand for two days. Lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) was then added, controlling the LiTFSI concentration. The mixture was stirred until clear and homogeneous, yielding a low-temperature lithium-ion battery electrolyte. The moisture content in the glove box was less than 0.1 ppm, and the oxygen content was less than 0.1 ppm. The 3Å molecular sieve desiccant was Alfa L05335-250g.

[0065] (Comparative Examples 1 to 5) The manufacturing method of the lithium ion battery electrolyte in each comparative example is the same, and the only differences are the type of organic solvent used in the lithium ion battery electrolyte, the volume ratio, and the type and concentration of the electrolyte salt, as shown in Table 2.

[0066] [Table 2]

[0067] Here, EC is ethylene carbonate and DEC is diethyl carbonate.

[0068] A method for preparing a lithium-ion battery electrolyte includes the steps of: The organic solvents were mixed in a volumetric ratio in an inert gas-protected glove box. After mixing, 3Å molecular sieve desiccant was added and allowed to stand for two days. The electrolyte salt was then added and stirred evenly to control the concentration of the electrolyte salt. After stirring evenly, a lithium-ion electrolyte solution was obtained. The moisture content in the glove box was less than 0.1 ppm, and the oxygen content was less than 0.1 ppm. The 3Å molecular sieve desiccant was Alfa L05335-250g.

[0069] (Test Example 1) Batteries were assembled using the low-temperature lithium ion battery electrolytes of Examples 1 to 12 and the lithium ion battery electrolytes of Comparative Examples 1 to 5, along with a lithium iron phosphate positive electrode and a lithium negative electrode, and electrochemical tests were performed using the following test methods.

[0070] First, a positive electrode sheet was prepared. The positive electrode active material was LiFePO4, the conductive agent was conductive carbon black (SuperP, Timcal Ltd.), the binder was polyvinylidene fluoride (PVDF, HSV900, Arkema), and the dispersant was N-methyl-2-pyrrolidone (NMP). These were mixed and polished in a mass ratio of LiFePO4:Super P:PVDF = 7:2:1, and then coated on aluminum foil. After drying, roll pressing, and dicing, an electrode sheet was prepared. The active material on the electrode surface was 2 to 4 mg / cm2. 2 Then, button batteries were fabricated in a glove box filled with argon gas, with a lithium sheet as the negative electrode and a microporous polypropylene film as the separator, and different electrolyte solutions were used to obtain different batteries and conduct tests.

[0071] Electrochemical performance tests were performed using a Neware electrochemical tester. The batteries were activated by two cycles at room temperature at 0.2 C, then left at -30°C for 2 hours and then subjected to low-temperature cycles at a current density of 0.2 C. The charge / discharge voltage range was 2.7 to 4.2 V, and the test results are shown in Table 3. Figure 1 compares the charge / discharge voltages of the lithium-ion battery electrolyte of Example 1 and the lithium-ion battery electrolyte of Comparative Example 5 at 2.7 to 4.2 V and the discharge specific capacity at -30°C. Here, the lithium-ion battery electrolyte of Comparative Example 5 is referred to as "Baseline," and the low-temperature lithium-ion battery electrolyte of Example 7 is referred to as "LT-Electrolyte."

[0072] [Table 3]

[0073] As can be seen from FIG. 1, at a low temperature of −30° C., 0.2C multiplication factor, and 50 cycles, the discharge specific capacity and cycle stability of the battery assembled using the low-temperature lithium ion battery electrolyte of the present invention are significantly superior to those of the lithium ion battery electrolyte of Comparative Example 5.

[0074] As can be seen from Table 1, the highest discharge specific capacity was obtained when the electrolyte solvent was a mixture of diethyl fluoromalonate (DEFM), fluorocarbonate (FEC), and 1,3-dioxane (DOL) and the lithium salt was lithium bis(trifluoromethanesulfonyl)imide (LiTFSI).

[0075] Comparing Examples 1 to 12, it can be seen that Example 7 has the greatest effect. At a low temperature of -30°C, the discharge specific capacity of the LiFePO4 / Li battery is 90mAh / g, and the capacity retention rate at 50 cycles is close to 100%, which is far higher than that of the other comparative examples.

[0076] As can be seen from a comparison of Examples 1 to 12, when the solvent component is a mixed solvent of diethyl fluoromalonate (DEFM), fluoroethylene carbonate (FEC), and 1,3-dioxane (DOL), the discharge specific capacity is highest when the occupancy rate of fluoroethylene carbonate is 20% and the occupancy rate of 1,3-dioxane is 20%. This is thought to be because FEC is advantageous for forming a LiF-rich inorganic interface at the negative electrode and is more stable at low temperatures, and the low viscosity of DOL is advantageous for reducing the ionic conductivity of the electrolyte at low temperatures.

[0077] As can be seen from a comparison between Examples 1 to 12 and Comparative Examples 1 to 4, the performance was best when the lithium salt was LiTFSI and the concentration was 2M. This is thought to be because LiTFSI preferentially decomposes to form an inorganic component interfacial film containing F, which is more stable, and the electrolyte solution has optimal viscosity and conductivity when the concentration is 2M.

[0078] As can be seen from Comparative Examples 1 to 4, when LiTFSI is not included, the solvent components diethyl fluoromalonate (DEFM), fluoroethylene carbonate (FEC), and 1,3-dioxane (DOL) have a superior effect to ordinary carbonate (base electrolyte), which is believed to be because the mixed solvent has superior low-temperature conductivity and superior film-forming properties.

[0079] From the above, it can be seen from the comparison that, compared to Comparative Example 5, an electrolyte solution using lithium bis(trifluoromethanesulfonyl)imide as the electrolyte salt and diethyl fluoromalonate (DEFM), fluoroethylene carbonate (FEC), and 1,3-dioxane (DOL) as the solvent can significantly improve the discharge specific capacity and capacity retention rate of a LiFePO4 / Li battery in a low-temperature environment of -30°C. Here, the discharge specific capacity and cycle stability of the battery are best when the DEFM:FEC:DOL ratio is 60:20:20 and the LiTFSI concentration is 2M.

[0080] The discharge specific capacity of the assembled LiFePO4 / Li battery at -30℃ is 90mAh / g, which is more stable.

[0081] Finally, it should be noted that the above embodiments are only used to explain the technical solutions of the present invention, and are not intended to limit the technical solutions of the present invention. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art may still modify the technical solutions described in the above embodiments or equally replace some or all of the technical features thereof, and it should be understood that these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. an electrolyte salt and an organic solvent; the electrolyte salt includes lithium bis(trifluoromethanesulfonyl)imide; The organic solvent comprises diethyl fluoromalonate, a fluorocarbonate, and 1,3-dioxane. Low-temperature lithium-ion battery electrolyte.

2. The fluorocarbonate ester includes fluoroethylene carbonate. The low-temperature lithium-ion battery electrolyte according to claim 1.

3. In the low-temperature lithium-ion battery electrolyte, the volume percentage of diethyl fluoromalonate is greater than 40%; The low-temperature lithium-ion battery electrolyte according to claim 1.

4. In the low-temperature lithium-ion battery electrolyte, the volume percentage of diethyl fluoromalonate is 50% to 70%. The low-temperature lithium-ion battery electrolyte according to claim 3.

5. the volume ratio of the diethyl fluoromalonate, the fluorocarbonate, and the 1,3-dioxane is 90 to 40:5 to 50:5 to 30; The low-temperature lithium-ion battery electrolyte according to claim 1.

6. the volume ratio of the diethyl fluoromalonate, the fluorocarbonate, and the 1,3-dioxane is 55 to 65:15 to 25:15 to 25; The low-temperature lithium-ion battery electrolyte according to claim 5.

7. In the low-temperature lithium-ion battery electrolyte, the concentration of the electrolyte salt is 1.0 mol / L to 5.0 mol / L. The low-temperature lithium-ion battery electrolyte according to claim 1.

8. In the low-temperature lithium-ion battery electrolyte, the concentration of the electrolyte salt is 1.5 mol / L to 2.5 mol / L. The low-temperature lithium-ion battery electrolyte according to claim 7.

9. A low-temperature lithium-ion battery comprising the electrolyte solution according to any one of claims 1 to 8. Lithium-ion battery.

10. The positive electrode material of the lithium ion battery is lithium iron phosphate. The lithium ion battery of claim 9.

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