Isosxazole derivative-based solvent for low-temperature organic electrolyte and application thereof

Abstract

The application provides a low-temperature organic electrolyte based on an isoxazole derivative solvent and application thereof. The low-temperature organic electrolyte comprises a lithium salt, a base solvent and a cosolvent; the base solvent is an isoxazole derivative; and the structural formula of the isoxazole derivative is shown as formula I. Compared with a conventional electrolyte, the low-temperature electrolyte provided by the application still exhibits higher ionic conductivity at a lower temperature (-60 DEG C). The selected specific isoxazole derivative base solvent has lower desolvation energy with metal cations, promotes the desolvation process at low temperature, in addition, the isoxazole derivative also participates in the film forming reaction in the electrochemical process, promotes the ion transmission at the interface, optimizes the electrode interface, inhibits the precipitation of lithium dendrites at low temperature, and the synergistic effect of the two improves the cycle performance of the battery at low temperature.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery technology and relates to a low-temperature organic electrolyte based on isoxazole derivatives as the base solvent and its application. Background Technology

[0002] Lithium-ion batteries have been widely used in consumer electronics, new energy vehicles, and energy storage due to their advantages such as high energy density, long cycle life, wide operating temperature range, and environmental friendliness. As the application areas of lithium-ion batteries continue to expand, they are increasingly being used in military, aerospace, and new energy vehicle fields. This necessitates that batteries not only possess high capacity, high energy density, and long cycle life, but also place new demands on battery safety and low-temperature performance. Traditional lithium-ion batteries typically operate within a temperature range of -20 to 55°C. Below -20°C, the performance of lithium-ion batteries deteriorates sharply. However, in aerospace, new energy vehicle, and other fields, batteries are required to function normally at -40°C. Therefore, improving the low-temperature performance of lithium-ion batteries is of great significance.

[0003] Lithium-ion batteries, when used in low-temperature environments, exhibit lithium plating and lithium insertion / extraction imbalances, leading to capacity decay, reduced rate performance, and decreased cycle life, severely limiting battery performance and lifespan. The electrolyte is a crucial factor affecting the low-temperature performance of lithium-ion batteries. At low temperatures, the physicochemical properties of the electrolyte are significantly impacted, resulting in slower ion conduction, a mismatch in electron migration speeds in the external circuit, a marked increase in charge transfer resistance, and severe polarization, ultimately causing a sharp decrease in battery capacity. Therefore, improving the electrolyte is key to enhancing the low-temperature performance of lithium-ion batteries. In recent years, many scientists have conducted extensive research and achieved considerable results. However, the electrolyte formulation currently used in traditional lithium-ion batteries is primarily lithium hexafluorophosphate (LiPF6) / ethylene carbonate (EC) + co-solvent. This electrolyte possesses high conductivity and a wide electrochemical window, but the lithium salt LiPF6 used is sensitive to moisture and easily decomposes; while EC has a high melting point (37°C) and remains solid at low temperatures, limiting the application of lithium-ion batteries at low temperatures.

[0004] Faced with the challenge of low energy density in batteries at low temperatures, which prevents them from fully utilizing their room-temperature performance, finding a novel electrolyte with low melting point, wide temperature range, low solvation energy, and the ability to participate in interfacial film formation is an important direction for improving the performance of low-temperature batteries. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a low-temperature organic electrolyte based on isoxazole derivatives as the base solvent and its applications.

[0006] The technical solution of the present invention is as follows:

[0007] A low-temperature organic electrolyte with an isoxazole derivative as the base solvent includes a lithium salt, a base solvent, and a co-solvent; the base solvent is an isoxazole derivative; the structural formula of the isoxazole derivative is shown in Formula I:

[0008]

[0009] In Formula I, R1 is H, methyl, isopropyl or phenyl; R2 is H or phenyl; R3 is methyl, isopropyl, amino, carboxyl, nitro or sulfonic acid, and R1 and R3 are not both methyl.

[0010] According to a preferred embodiment of the present invention, the isoxazole derivative is one or a combination of two or more of 3-isopropylisooxazole-5-amine, isoxazole-5-carboxylic acid, and 5-methyl-3,4-diphenylisooxazole; the structural formulas of the 3-isopropylisooxazole-5-amine, isoxazole-5-carboxylic acid, and 5-methyl-3,4-diphenylisooxazole are shown below:

[0011]

[0012] According to a preferred embodiment of the present invention, the lithium salt is selected from one or more of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium tetrafluoroborate, lithium bis(trifluoromethanesulfonyl)imide, lithium perchlorate, lithium difluorobis(oxalato)phosphate, and lithium difluorooxalatoborate; the concentration of the lithium salt in the electrolyte is 0.5 to 1.5 mol / L.

[0013] According to a preferred embodiment of the present invention, the co-solvent is a carbonate solvent and / or an ether solvent; the carbonate solvent is one or more of dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, ethyl acetate, methyl formate, and ethyl carbonate; the ether solvent is one or more of ethylene glycol dimethyl ether, tetrahydrofuran, dioxapentane, and dimethoxymethane; the volume of the co-solvent is 0-50% of the total volume of the co-solvent and the base solvent, more preferably 20-40%; the addition of a specific amount of co-solvent in the present invention can lower the freezing point of the solvent, increase the ionic conductivity of the electrolyte, and promote the dissolution of lithium salt.

[0014] According to the present invention, the preparation method of the low-temperature organic electrolyte based on isox derivatives as the solvent can be carried out by conventional physical mixing in a glove box.

[0015] The present invention also provides a lithium-ion battery comprising the above-mentioned low-temperature organic electrolyte based on isoxazole derivatives as a solvent.

[0016] According to the present invention, the positive electrode material and the negative electrode material of the lithium-ion battery can be materials commonly used in the art; preferably, the positive electrode material of the lithium-ion battery can be lithium manganese oxide (LMO), ternary lithium nickel cobalt manganese oxide (NMC), lithium iron phosphate (LiFePO4) or graphite (Gr); the negative electrode material is lithium metal (Li) or graphite (Gr).

[0017] The technical features and beneficial effects of this invention are as follows:

[0018] 1. The low-temperature electrolyte provided by this invention exhibits higher ionic conductivity at a lower temperature (-60℃) compared to traditional electrolytes. The specific isoxazole derivative base solvent and metal cations selected have low desolvation energy, promoting the desolvation process at low temperatures. In addition, the isoxazole derivative also participates in the film-forming reaction during the electrochemical process, promoting ion transport at the interface, optimizing the electrode interface, and inhibiting the precipitation of lithium dendrites at low temperatures. The synergistic effect of these two factors improves the cycle performance of the battery at low temperatures. Compared with electrolytes prepared from other types of isoxazole derivatives other than those of this invention, the electrolyte of this invention can effectively improve the cycle performance of the battery at low temperatures.

[0019] 2. The low-temperature electrolyte provided by this invention uses lithium salt molecules with small radii, which can be effectively dissolved at low temperatures. Furthermore, a specific proportion of co-solvent is added to the electrolyte of this invention. The addition of the co-solvent can lower the freezing point of the solvent, increase the ionic conductivity of the electrolyte, and promote the dissolution of lithium salt. However, if the proportion of co-solvent is too high, it will lead to a decrease in the conductivity of the electrolyte, affecting the lithium ion transport rate and reducing battery performance. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0021] Example 1

[0022] A low-temperature organic electrolyte with isoxazole derivative as the base solvent includes a lithium salt and a base solvent; the lithium salt is lithium difluorosulfonylimide, and the concentration of the lithium salt in the electrolyte is 1 mol / L; the base solvent is 3-isopropylisooxazole-5-amine.

[0023] The electrolyte was prepared as follows: under anhydrous and oxygen-free conditions, lithium difluorosulfonylimide was dissolved in 3-isopropylisoxazole-5-amine at a concentration of 1 mol / L. The resulting electrolyte had a temperature range below -80℃.

[0024] Example 2

[0025] A low-temperature organic electrolyte with an isoxazole derivative as the base solvent includes a lithium salt, a base solvent, and a co-solvent; the lithium salt is lithium difluorosulfonylimide, and the concentration of the lithium salt in the electrolyte is 1 mol / L; the base solvent is 3-isopropylisooxazole-5-amine, and the co-solvent is ethyl acetate; based on the volume of the base solvent and the co-solvent being 100%, the volume percentage of the base solvent is 70%, and the volume percentage of the co-solvent is 30%.

[0026] The electrolyte is prepared as follows: Under anhydrous and oxygen-free conditions, a base solvent and a co-solvent are mixed, and lithium bis(fluorosulfonyl)imide is dissolved in the mixture at a concentration of 1 mol / L. The resulting electrolyte has a temperature range below -80℃.

[0027] Comparative Example 1

[0028] An organic electrolyte includes a lithium salt and a base solvent; the lithium salt is lithium bis(fluorosulfonyl)imide, and the concentration of the lithium salt in the electrolyte is 1 mol / L; the base solvent is isoxazole.

[0029] The electrolyte is prepared as follows: under anhydrous and oxygen-free conditions, lithium difluorosulfonylimide is dissolved in isoxazole at a concentration of 1 mol / L.

[0030] Comparative Example 2

[0031] An organic electrolyte includes a lithium salt and a base solvent; the lithium salt is lithium bis(fluorosulfonyl)imide, and the concentration of the lithium salt in the electrolyte is 1 mol / L; the base solvent is 3-isopropylisoxazole.

[0032] The electrolyte is prepared as follows: under anhydrous and oxygen-free conditions, lithium difluorosulfonylimide is dissolved in 3-isopropylisoxazole at a concentration of 1 mol / L.

[0033] Comparative Example 3

[0034] An organic electrolyte comprises a lithium salt, a base solvent, and a co-solvent; wherein the lithium salt is lithium bis(fluorosulfonyl)imide, and the concentration of the lithium salt in the electrolyte is 1 mol / L; the base solvent is isoxazole, and the co-solvent is ethyl acetate, wherein the volume percentage of the base solvent is 70% and the volume percentage of the co-solvent is 30% based on the total volume of the base solvent and the co-solvent being 100%.

[0035] The electrolyte is prepared as follows: under anhydrous and oxygen-free conditions, the base solvent and co-solvent are mixed, and lithium difluorosulfonylimide is dissolved in the mixture at a concentration of 1 mol / L.

[0036] Comparative Example 4

[0037] An organic electrolyte comprises a lithium salt, a base solvent, and a co-solvent; wherein the lithium salt is lithium bis(fluorosulfonyl)imide, and the concentration of the lithium salt in the electrolyte is 1 mol / L; the base solvent is 3-isopropylisoxazole, and the co-solvent is ethyl acetate, wherein the volume percentage of the base solvent is 70% and the volume percentage of the co-solvent is 30% based on the total volume of the base solvent and the co-solvent being 100%.

[0038] The electrolyte is prepared as follows: under anhydrous and oxygen-free conditions, the base solvent and co-solvent are mixed, and lithium difluorosulfonylimide is dissolved in the mixture at a concentration of 1 mol / L.

[0039] Experimental Example 1

[0040] Using the organic electrolytes of the examples and comparative examples as electrolytes, the following lithium-ion batteries were assembled and their battery capacity was tested.

[0041] (1) Lithium manganese oxide (LMO) was used as the positive electrode material, and lithium metal was used as the negative electrode material. The battery casing used was model CR2025. In the glove box, the positive electrode casing was placed flat in the center of the worktable. The LMO was placed in the center of the positive electrode casing with tweezers. The separator was placed over the electrode, and electrolyte was added. The lithium sheet and the pad were pressed into a whole and placed in the center of the separator. The spring clip was then placed on top of the pad, and the negative electrode casing was placed on the positive electrode casing for sealing. Finally, the sealed battery was taken out of the glove box and left to stand at room temperature for 12 hours to ensure that the electrolyte was fully impregnated. After that, the assembled battery was charged and discharged at a rate of 0.1C on a blue electric tester.

[0042] (2) Ternary lithium nickel cobalt manganese oxide (NMC) was used as the positive electrode material, and lithium metal as the negative electrode material. The battery casing used was model CR2025. In the glove box, the positive electrode casing was placed flat in the center of the worktable. The NMC was placed in the center of the positive electrode casing with tweezers. The separator was placed over the electrode, and electrolyte was added. The lithium sheet and the pad were pressed into a whole and placed in the center of the separator. The spring clip was then placed on top of the pad, and the negative electrode casing was placed on the positive electrode casing for sealing. Finally, the sealed battery was removed from the glove box and left to stand at room temperature for 12 hours to ensure that the electrolyte was fully impregnated. The assembled battery was then cycled at a rate of 0.1C on a blue battery tester.

[0043] (3) Using lithium iron phosphate (LiFePO4) as the positive electrode material and lithium metal as the negative electrode material, the battery casing model used is CR2025. In the glove box, the positive electrode casing is placed flat in the center of the worktable. LiFePO4 is placed in the center of the positive electrode casing using tweezers. The separator is placed over the electrode, and electrolyte is added. The lithium sheet and gasket are pressed together and placed in the center of the separator. A spring clip is then placed over the gasket, and the negative electrode casing is placed on top of the positive electrode casing for sealing. Finally, the sealed battery is removed from the glove box and left to stand at room temperature for 12 hours to ensure sufficient electrolyte wetting. The assembled battery is then cycled at a 0.1C rate using a blue battery tester.

[0044] (4) Assemble a half-cell using graphite (Gr) to lithium metal. The battery case used is model CR2025. In the glove box, place the positive electrode case flat in the center of the worktable. Use tweezers to place the Gr in the center of the positive electrode case. Cover the electrode with the separator, add electrolyte, press the lithium sheet and the pad into a whole and place it in the center of the separator. Then place the spring clip on top of the pad, and finally put the negative electrode case on the positive electrode case for sealing. Finally, remove the sealed battery from the glove box and let it stand at room temperature for 12 hours to ensure that the electrolyte is fully wetted. Then, cycle the assembled battery at a 1C rate using a blue electric shock tester.

[0045] (5) Using lithium nickel manganese cobalt oxide (NMC) as the positive electrode material and graphite (Gr) as the negative electrode material, the battery casing model used was CR2025. In a glove box, the positive electrode casing was placed flat in the center of the worktable. Using tweezers, the NMC was placed in the center of the positive electrode casing. The separator was placed over the electrode, and electrolyte was added. The Gr was then placed in the center of the separator, followed by the gasket and spring sheet placed on top of the Gr. The negative electrode casing was then placed on top of the positive electrode casing for sealing. Finally, the sealed battery was removed from the glove box and allowed to stand at room temperature for 12 hours to ensure sufficient electrolyte wetting. The assembled coin cell was then cycled at a rate of 0.05C using a blue electrode tester. The results are shown in Table 1.

[0046] Table 1

[0047]

[0048]

[0049]

[0050] Table 1 shows the electrochemical performance tests conducted using different solvent systems and different types of lithium-ion batteries to demonstrate the universality of the selected solvent systems. The test data demonstrates that the electrochemical performance is significantly improved when isoxazole, a solvent specific to this invention, is used. Furthermore, the electrochemical performance is further enhanced upon the addition of a co-solvent, proving the superiority of the designed low-temperature electrolyte system.

[0051] The above description of the embodiments is only for the purpose of helping to understand the method and core ideas of the present invention. It should be noted that those skilled in the art can make several improvements and modifications to the present invention without departing from the principles of the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

Claims

1. A low-temperature organic electrolyte with isoxazole derivatives as the base solvent, characterized in that, The low-temperature organic electrolyte comprises a lithium salt, a base solvent, and a co-solvent; the base solvent is an isoxazole derivative, which is one or a combination of two of 3-isopropylisooxazole-5-amine and 5-methyl-3,4-diphenylisooxazole. The lithium salt is selected from one or more of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium tetrafluoroborate, lithium bis(trifluoromethanesulfonyl)imide, lithium perchlorate, lithium difluorobis(oxalato)phosphate, and lithium difluorooxalatoborate. The co-solvent is one or more of dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, ethyl acetate, methyl acetate, methyl formate, ethylene glycol dimethyl ether, tetrahydrofuran, dioxapentane, and dimethoxymethane; the volume of the co-solvent is 0 to 50% of the total volume of the co-solvent and the base solvent.

2. The low-temperature organic electrolyte based on isoxazole derivatives as the base solvent according to claim 1, characterized in that, The concentration of lithium salt in the electrolyte is 0.5~1.5 mol / L.

3. The low-temperature organic electrolyte based on isoxazole derivatives as the base solvent according to claim 1, characterized in that, The volume of the co-solvent is 20-40% of the total volume of the co-solvent and the base solvent.

4. A lithium-ion battery, characterized in that, The low-temperature organic electrolyte based on isoxazole derivatives as a solvent, as described in any one of claims 1-3.

5. The lithium-ion battery according to claim 4, characterized in that, The positive electrode material of the lithium-ion battery is lithium manganese oxide, ternary lithium nickel cobalt manganese oxide, lithium iron phosphate, or graphite; the negative electrode material is lithium metal or graphite.

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