Lithium ion battery low-temperature electrolyte and application thereof
By using low viscosity, low melting point main solvent and high dielectric constant secondary solvent in lithium battery electrolyte, combined with specific lithium salts, the problem of poor energy density and circulation performance of lithium batteries in low temperature environments is solved, and the extreme cold conditions are achieved Excellent charge and discharge cycle performance and high cycle life.
Patent Information
- Application Number
- CN202411298038.1
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-09-18
- Publication Date
- 2024-12-13
AI Technical Summary
Lithium batteries exhibit reduced energy density, poor circulation performance and safety hazards in low temperature environments, which limit their application scenarios. The prior art is difficult to provide long-term charge and discharge cycle performance under extreme cold conditions.
Using low viscosity, low melting point main solvent and high dielectric constant sub-solvent, combined with specific lithium salts such as lithium difluoroxalate borate, the low temperature ion mobility and liquid phase range of the electrolyte are optimized to form a stable solid electrolyte interface and reduce the Electrode interface impedance.
Under normal temperature and extremely cold conditions at -40°C, the electrolyte exhibits excellent circulation performance and capacity retention, broadening the liquid phase range, improving the low-temperature energy density and cycle life of lithium batteries, and reducing the risk of lithium deposition.
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Figure CN119133598A_ABST
Abstract
Description
Technical Field
[0001] The invention belongs to the field of lithium battery electrolyte and relates to a lithium ion battery low-temperature electrolyte and application thereof. Background Art
[0002] Lithium-ion batteries have the advantages of high energy density, long cycle life, wide voltage window and high safety. They have great application value in the fields of electronic products, electric vehicles, rail transportation, communications and military industry. However, with the advancement of science and technology, higher and higher requirements are also put forward for energy storage products. For example, in low temperature environment, lithium batteries will lose their original advantages due to lower lithium ion mobility and higher desolvation energy, including reduced energy density, decreased cycle performance and poor rate performance, which seriously limits the application scenarios of lithium batteries.
[0003] When the ambient temperature is above 0°C, commercial lithium batteries can barely meet working requirements, but when it drops below -20°C, the ionic conductivity of the electrolyte will drop sharply. In addition, lithium batteries also exhibit slow desolvation behavior, while weakening the speed of lithium ions passing through the solid electrolyte interface and the diffusion speed in the electrode material, limiting the release and embedding of lithium ions, thereby increasing the overall resistance, leading to inevitable active lithium deposition, and even safety hazards. It is urgent to develop electrolytes that can adapt to extreme low temperature environments and work for a long time.
[0004] In order to improve the energy density of lithium batteries in low temperature environments, there are also some studies such as:
[0005] The Chinese patent application number CN202310033894.3 discloses an electrolyte suitable for low-temperature fast charging of lithium iron phosphate power batteries. The electrolyte lithium salt adopts a mixture of lithium hexafluorophosphate, lithium tetrafluoroborate, and lithium bis(fluorosulfonyl)imide; the solvent adopts one or more of ethylene carbonate, ethyl methyl carbonate, dimethyl carbonate, propylene carbonate, ethyl acetate, and propyl acetate; the additive adopts one or more of vinylene carbonate, fluoroethylene carbonate, dimethyl sulfite and diethyl sulfite, and N,N-dimethyltrifluoroacetamide. Although the electrolyte has good performance at a low temperature of -20°C, the capacity retention rate at room temperature is low.
[0006] And, the Chinese patent with application number CN202111199766.3 discloses a low-temperature electrolyte for lithium batteries and a lithium battery; the electrolyte includes an organic solvent, a lithium salt and an electrolyte additive; 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 lithium salt includes a mixture of one or more of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium tetrafluoroborate, bis(trifluoromethanesulfonyl)imide, lithium perchlorate, lithium fluoride, lithium bis(oxalate)borate, lithium difluoroborate and bis(pentafluoroethylsulfonyl)imide; the electrolyte additive is a mixed additive composed of a low-temperature additive and a film-forming additive. This patent application slows down the attenuation of battery capacity at low temperatures by increasing the degree of salt dissociation, the migration rate of lithium ions, the low-temperature ion conductivity and the low-impedance solid electrolyte interface film. This technology has indeed achieved excellent results in improving discharge capacity, but it also has certain shortcomings. This technology mainly improves low-temperature discharge performance, not charging in a low-temperature environment. The actual operating scenario of lithium batteries is long-term charging and discharging cycles at low temperatures.
[0007] Therefore, developing a low-temperature electrolyte for lithium-ion batteries with a long cycle life is a technical problem that urgently needs to be solved in the field of lithium batteries. Summary of the invention
[0008] The purpose of the present invention is to provide a low-temperature electrolyte for lithium-ion batteries and its application. When the electrolyte is applied to lithium batteries, it has good rate performance and cycle performance at room temperature, and still has excellent charge and discharge energy and cycle life under extremely cold conditions of -40°C.
[0009] To achieve the above object, the present invention adopts the following technical solutions:
[0010] A low-temperature electrolyte for a lithium-ion battery. The electrolyte comprises a lithium salt and a solvent. The solvent comprises a main solvent and a secondary solvent. The main solvent comprises ethyl methyl carbonate and / or isobutyl formate, and the secondary solvent comprises dimethyl sulfite and / or propylene trifluorocarbonate.
[0011] The technical concept of the present invention is that the carbonate optimizes the low-temperature ion mobility and liquid phase range of the electrolyte with extremely low viscosity and melting point, and at the same time, the advantage of low binding energy with lithium ions can also significantly reduce the desolvation energy of cations. The secondary solvents dimethyl sulfite and / or trifluoropropylene carbonate have high dielectric constants and can fully dissolve lithium salts. In particular, dimethyl sulfite with a melting point of -125°C also ensures the low-temperature potential of the electrolyte.
[0012] The lithium salt is selected from one or more of lithium difluorooxalatoborate, lithium bis(fluorosulfonyl)imide, lithium hexafluorophosphate, lithium bis(trifluoromethanesulfonyl)imide or lithium tetrafluoroborate.
[0013] The concentration of the lithium salt in the electrolyte is 0.5 mol / L to 1.5 mol / L.
[0014] The lithium salt is selected from lithium difluorooxalatoborate, and the concentration of the lithium salt in the electrolyte is 0.75 mol / L to 1.25 mol / L.
[0015] When the selected lithium salt is lithium difluorooxalatoborate, it can cooperate with the fluorinated solvent propylene trifluorocarbonate to provide a stable, dense and inorganically rich solid electrolyte interface, effectively reducing the electrode interface impedance. Its high stability also reduces the risk of lithium deposition and can reduce the probability of safety accidents.
[0016] The volume percentage of the main solvent in the solvent is 60-75 vt%, and the volume percentage of the secondary solvent in the solvent is 25-40 vt%.
[0017] Preferably, the volume percentage of ethyl methyl carbonate in the solvent is 33.3-37.5 vt%, the volume percentage of isobutyl formate is 33.3-37.5 vt%, the volume percentage of dimethyl sulfite is 12.5-16.7 vt%, and the volume percentage of propylene trifluorocarbonate is 12.5-16.7 vt%; or,
[0018] Preferably, the volume percentage of ethyl methyl carbonate in the solvent is 37.5 vt%, the volume percentage of isobutyl formate is 37.5 vt%; and the volume percentage of dimethyl sulfite is 25 vt%.
[0019] The above electrolyte shows better cycle performance and capacity retention rate at room temperature and at a low temperature of -20°C.
[0020] Preferably, the volume percentage of ethyl methyl carbonate in the solvent is 37.5vt%, the volume percentage of isobutyl formate is 37.5vt%; the volume percentage of dimethyl sulfite is 12.5%, and the volume percentage of propylene trifluorocarbonate is 12.5vt%; the lithium salt is lithium difluorooxalatoborate, and the concentration of the lithium salt in the electrolyte is 0.75mol / L to 1mol / L.
[0021] The above electrolyte exhibits better cycle performance and capacity retention rate in a low temperature environment of -40°C.
[0022] The present invention also provides an application of the above-mentioned lithium ion battery low-temperature electrolyte in a lithium ion battery.
[0023] Preferably, the lithium-ion battery is a lithium sheet||lithium cobalt oxide half-cell, comprising a positive electrode material, a negative electrode material, a current collector, a separator and an electrolyte; the positive electrode material comprises lithium cobalt oxide, conductive carbon black and polyvinylidene fluoride, the negative electrode material is a lithium sheet, the current collector is aluminum foil, and the separator is a glass fiber separator.
[0024] Furthermore, the lithium-ion battery is a CR2032 button cell, the positive electrode material is slurried with lithium cobalt oxide, conductive carbon black and polyvinylidene fluoride in a ratio of 8:1:1, vacuum dried at 120° C. for 8 hours, and then cut into 11 mm pole pieces.
[0025] Preferably, the charge and discharge voltage range of the half-cell is 3.0 to 4.5 V, and the charge and discharge cycle is carried out in a high and low temperature box with an operating temperature of -40 to 25°C.
[0026] Compared with the prior art, the present invention has the following beneficial effects:
[0027] The present invention aims to solve the serious problems existing in traditional electrolytes of lithium batteries, including the highly solvated structure of lithium ions, the solid electrolyte interface lacking inorganic components, the small lithium ion conductivity and diffusion coefficient, as well as the low energy density and poor cycle performance under low temperature and extreme cold conditions. The present invention proposes to use a weak solvent with low viscosity and low melting point as the main solvent, combined with a secondary solvent with a high dielectric constant, which significantly improves the low temperature performance of the lithium battery.
[0028] The electrolyte provided by the present invention, through the synergistic effect of lithium borate salt and strong and weak organic solvents, enables the lithium battery to exhibit excellent cycle performance and capacity retention rate not only at room temperature and low temperature environment, but also in the following aspects: the rate performance and cycle performance are good at room temperature of 25°C, and the charge and discharge energy and cycle life are still excellent under extremely cold conditions of -40°C; the liquid phase range is broadened, and a higher energy density is achieved at a low temperature of -40°C. BRIEF DESCRIPTION OF THE DRAWINGS
[0029] Figure 1 It is the long cycle test result of the lithium ion battery assembled with the electrolyte provided in Example 1 and Comparative Example 1 at 25°C and 1C;
[0030] Figure 2 It is the long cycle test result of the lithium ion battery assembled with the electrolyte provided in Example 1 and Comparative Example 1 at -20°C and 1 / 3C;
[0031] Figure 3 It is the long cycle test result of the lithium ion battery assembled with the electrolyte provided in Examples 1, 5 and 6 at -40°C and 0.1C;
[0032] Figure 4 The results of the comparative test of the rate performance of lithium-ion batteries assembled with the electrolytes provided in Example 1 and Comparative Example 1 at 25°C;
[0033] Figure 5 The results are comparative test results of rate performance of lithium-ion batteries assembled with the electrolytes provided in Example 1 and Comparative Example 1 at -20°C. DETAILED DESCRIPTION
[0034] In order to explain the technical solutions and advantages of the present invention, the present invention will be further described in detail below in combination with the embodiments and drawings. The embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.
[0035] Example 1
[0036] The lithium ion battery low temperature electrolyte provided in this embodiment includes a lithium salt, a main solvent with low viscosity and low melting point, and a secondary solvent with a high dielectric constant. The solvent includes a main solvent of ethyl methyl carbonate, isobutyl formate, and a secondary solvent of dimethyl sulfite and trifluoropropylene carbonate. The volume percentage of ethyl methyl carbonate in the solvent is 37.5vt%, the volume percentage of isobutyl formate is 37.5vt%, the volume percentage of dimethyl sulfite is 12.5vt%, and the volume percentage of trifluoropropylene carbonate is 12.5vt%. The lithium salt is lithium difluorooxalate borate, and the lithium salt concentration is 1mol / L.
[0037] The electrolyte of this embodiment is prepared in a glove box filled with argon atmosphere (H2O≤0.01ppm, O2≤0.01ppm). A certain amount of lithium salt is weighed with an electronic balance and added to a sample bottle. An organic solvent is then added and stirred for 30 minutes until the lithium salt is completely dissolved.
[0038] The electrolyte of this embodiment is applied to lithium-ion batteries. CR2032 button batteries are assembled in a glove box filled with argon atmosphere. The positive electrode material is lithium cobalt oxide, the negative electrode material is lithium foil, the diaphragm is a glass fiber diaphragm, and the electrolyte is the electrolyte of this embodiment.
[0039] Example 2
[0040] The lithium ion battery low temperature electrolyte provided in this embodiment includes a lithium salt, a main solvent with low viscosity and low melting point, and a secondary solvent with a high dielectric constant. The solvent includes a main solvent of ethyl methyl carbonate, isobutyl formate, and a secondary solvent of dimethyl sulfite and trifluoropropylene carbonate. The volume percentage of ethyl methyl carbonate in the solvent is 37.5vt%, the volume percentage of isobutyl formate is 37.5vt%, the volume percentage of dimethyl sulfite is 12.5vt%, and the volume percentage of trifluoropropylene carbonate is 12.5vt%. The lithium salt is lithium difluorooxalate borate, and the lithium salt concentration is 0.75mol / L.
[0041] The electrolyte of this embodiment is prepared in a glove box filled with argon atmosphere (H2O≤0.01ppm, O2≤0.01ppm). A certain amount of lithium salt is weighed with an electronic balance and added to a sample bottle. An organic solvent is then added and stirred for 30 minutes until the lithium salt is completely dissolved.
[0042] The electrolyte of this embodiment is applied to lithium-ion batteries. CR2032 button batteries are assembled in a glove box filled with argon atmosphere. The positive electrode material is lithium cobalt oxide, the negative electrode material is lithium foil, the diaphragm is a glass fiber diaphragm, and the electrolyte is the electrolyte of this embodiment.
[0043] Example 3
[0044] The lithium ion battery low temperature electrolyte provided in this embodiment includes a lithium salt, a main solvent with low viscosity and low melting point, and a secondary solvent with a high dielectric constant. The solvent includes a main solvent of ethyl methyl carbonate, isobutyl formate, and a secondary solvent of dimethyl sulfite and trifluoropropylene carbonate. The volume percentage of ethyl methyl carbonate in the solvent is 37.5vt%, the volume percentage of isobutyl formate is 37.5vt%, the volume percentage of dimethyl sulfite is 12.5vt%, and the volume percentage of trifluoropropylene carbonate is 12.5vt%. The lithium salt is lithium difluorooxalate borate, and the lithium salt concentration is 1.25mol / L.
[0045] The electrolyte of this embodiment is prepared in a glove box filled with argon atmosphere (H2O≤0.01ppm, O2≤0.01ppm). A certain amount of lithium salt is weighed with an electronic balance and added to a sample bottle. An organic solvent is then added and stirred for 30 minutes until the lithium salt is completely dissolved.
[0046] The electrolyte of this embodiment is applied to lithium-ion batteries. CR2032 button batteries are assembled in a glove box filled with argon atmosphere. The positive electrode material is lithium cobalt oxide, the negative electrode material is lithium foil, the diaphragm is a glass fiber diaphragm, and the electrolyte is the electrolyte of this embodiment.
[0047] Example 4
[0048] The lithium ion battery low temperature electrolyte provided in this embodiment includes a lithium salt, a main solvent with low viscosity and low melting point, and a secondary solvent with a high dielectric constant. The solvent includes a main solvent ethyl methyl carbonate and secondary solvents dimethyl sulfite and trifluoropropylene carbonate, wherein the volume percentage of ethyl methyl carbonate in the solvent is 60vt%, the volume percentage of dimethyl sulfite is 20vt%, and the volume percentage of trifluoropropylene carbonate is 20vt%. The lithium salt is lithium difluorooxalate borate, and the lithium salt concentration is 1mol / L.
[0049] The electrolyte of this embodiment is prepared in a glove box filled with argon atmosphere (H2O≤0.01ppm, O2≤0.01ppm). A certain amount of lithium salt is weighed with an electronic balance and added to a sample bottle. An organic solvent is then added and stirred for 30 minutes until the lithium salt is completely dissolved.
[0050] The electrolyte of this embodiment is applied to lithium-ion batteries. CR2032 button batteries are assembled in a glove box filled with argon atmosphere. The positive electrode material is lithium cobalt oxide, the negative electrode material is lithium foil, the diaphragm is a glass fiber diaphragm, and the electrolyte is the electrolyte of this embodiment.
[0051] Example 5
[0052] The lithium-ion battery low-temperature electrolyte provided in this embodiment includes a lithium salt, a main solvent with low viscosity and low melting point, and a secondary solvent with a high dielectric constant. The solvent includes a main solvent of ethyl methyl carbonate, isobutyl formate, and a secondary solvent of dimethyl sulfite and propylene trifluorocarbonate. The volume percentage of ethyl methyl carbonate in the solvent is 37.5vt%, the volume percentage of isobutyl formate is 37.5vt%, and the volume percentage of dimethyl sulfite is 25vt%. The lithium salt is lithium difluorooxalate borate, and the lithium salt concentration is 1mol / L.
[0053] The electrolyte of this embodiment is prepared in a glove box filled with argon atmosphere (H2O≤0.01ppm, O2≤0.01ppm). A certain amount of lithium salt is weighed with an electronic balance and added to a sample bottle. An organic solvent is then added and stirred for 30 minutes until the lithium salt is completely dissolved.
[0054] The electrolyte of this embodiment is applied to lithium-ion batteries. CR2032 button batteries are assembled in a glove box filled with argon atmosphere. The positive electrode material is lithium cobalt oxide, the negative electrode material is lithium foil, the diaphragm is a glass fiber diaphragm, and the electrolyte is the electrolyte of this embodiment.
[0055] Example 6
[0056] The lithium ion battery low temperature electrolyte provided in this embodiment includes a lithium salt, a main solvent with low viscosity and low melting point, and a secondary solvent with a high dielectric constant. The solvent includes a main solvent of ethyl methyl carbonate, isobutyl formate, and a secondary solvent of dimethyl sulfite and trifluoropropylene carbonate. The volume percentage of ethyl methyl carbonate in the solvent is 33.3vt%, the volume percentage of isobutyl formate is 33.3vt%, the volume percentage of dimethyl sulfite is 16.7vt%, and the volume percentage of trifluoropropylene carbonate is 16.7vt%. The lithium salt is lithium difluorooxalate borate, and the lithium salt concentration is 1mol / L.
[0057] The electrolyte of this embodiment is prepared in a glove box filled with argon atmosphere (H2O≤0.01ppm, O2≤0.01ppm). A certain amount of lithium salt is weighed with an electronic balance and added to a sample bottle. An organic solvent is then added and stirred for 30 minutes until the lithium salt is completely dissolved.
[0058] The electrolyte of this embodiment is applied to lithium-ion batteries. CR2032 button batteries are assembled in a glove box filled with argon atmosphere. The positive electrode material is lithium cobalt oxide, the negative electrode material is lithium foil, the diaphragm is a glass fiber diaphragm, and the electrolyte is the electrolyte of this embodiment.
[0059] Comparative Example 1
[0060] The lithium ion battery low temperature electrolyte provided in this comparative example comprises a lithium salt, a main solvent with low viscosity and low melting point, and a secondary solvent with a high dielectric constant. The solvent comprises a main solvent of dimethyl carbonate and a secondary solvent of ethylene carbonate, wherein the volume percentage of dimethyl carbonate in the solvent is 50vt%, and the volume percentage of ethylene carbonate is 50vt%. The lithium salt is lithium hexafluorophosphate, and the concentration of the lithium salt is 1 mol / L.
[0061] The electrolyte of this comparative example was prepared in a glove box filled with argon atmosphere (H2O≤0.01ppm, O2≤0.01ppm). A certain amount of lithium salt was weighed with an electronic balance and added to a sample bottle. An organic solvent was then added and stirred for 30 minutes until the lithium salt was completely dissolved.
[0062] The electrolyte of this comparative example is applied to lithium-ion batteries. CR2032 button batteries are assembled in a glove box filled with argon atmosphere. The positive electrode material is lithium cobalt oxide, the negative electrode material is lithium foil, the diaphragm is a glass fiber diaphragm, and the electrolyte is the electrolyte of this comparative example.
[0063] Electrochemical performance test
[0064] The electrochemical performance of the lithium sheet||lithium cobalt oxide half-cell prepared by the electrolyte of the above embodiment was tested using a blue battery test instrument. First, other experiments were carried out after 3 cycles of activation at 0.1C at room temperature (25°C). For the low-temperature experiment, the half-cell needed to be placed in a high and low temperature test box for 3 hours to allow the battery as a whole to reach the preset temperature before testing. At room temperature, the activated button was first charged to 4.5V at a constant current of 1C, and then discharged to 3V at a constant current of 1C; at -20°C and -40°C, the activated button was first charged to 4.5V at a constant current of 1 / 3C and 0.1C, and then discharged to 3V at a constant current of 1 / 3C and 0.1C. The discharge specific capacity at different temperatures was recorded and compared with the room temperature capacity. The results are shown in Table 1.
[0065] Table 1 Discharge specific capacity of batteries at different temperatures in different embodiments and comparative examples
[0066]
[0067]
[0068] From the capacity comparison of Examples 1-6 and Comparative Example 1, it can be seen that the button battery assembled with the electrolyte provided in Example 1 has a higher capacity retention rate at -20°C and -40°C than at room temperature, and still has 86.7% of the room temperature capacity at -20°C and 1 / 3C charge and discharge, indicating that it can still work normally in most low temperature scenarios; combined with Figure 1-3 It can be found that the button battery assembled with the electrolyte provided in Example 1 has a high capacity retention rate regardless of room temperature or low temperature environment. After 1200 cycles at 25°C and 1C, the capacity retention rate is still above 90% compared with the first cycle; after 120 cycles at -20°C and 1 / 3C, the discharge specific capacity is 123.5mAh / g, which is more than 75% compared with the capacity retention rate at room temperature; after 80 cycles at -40°C and 0.1C, the discharge specific capacity is 115mAh / g, which is more than 70% compared with the capacity retention rate at room temperature. Figure 4 , Figure 5 It is a rate performance comparison chart of Example 1 and Comparative Example 1. At 25°C, the rate performance of Example 1 is slightly better than that of Comparative Example 1. The discharge capacity at 0.2C current is 177.6 mAh / g, and the capacity is still 99 mAh / g when the current increases to 10C, with a retention rate of more than 50%. When the temperature drops to -20°C and the current exceeds 0.5C, the discharge capacity of Comparative Example 1 decays significantly, while the discharge capacity of Example 1 at 1C current reaches 109 mAh / g, and the retention rate is nearly 70% compared to 0.1C. Obviously, Example 1 is superior to Comparative Example 1 in rate performance at both room temperature and low temperature.
[0069] The above electrochemical test results show that the electrolyte provided by the present invention not only improves the cycle performance at room temperature, but also greatly improves the low-temperature capacity and cycle characteristics of the lithium battery. By adding a low-viscosity, low-melting-point main solvent, the melting point and low-temperature viscosity of the electrolyte are reduced, so that it remains liquid in a wide temperature range, and it also plays a greater role in the solvation structure, reducing the desolvation energy of the electrolyte; adjusting the proportion of the high dielectric constant secondary solvent allows the electrolyte to have a relatively high conductivity at the same time, increasing the transmission efficiency of lithium ions; the addition of lithium salt lithium difluorooxalate borate helps to form a dense, low-impedance solid electrolyte interface film, enhance the stability of the battery, and improve the cycle life and rate performance. In summary, the present invention utilizes the respective advantages of a low-viscosity, low-melting-point main solvent, a high dielectric constant secondary solvent, and a lithium salt with good film-forming properties, and achieves an excellent synergistic effect of the electrolyte with the best ratio, significantly improving the stability and rate performance of the lithium battery in a wide temperature range, especially at a low temperature of -40°C, it can still perform high-capacity charge and discharge cycles, providing technical support for lithium batteries to work under ultra-low temperature conditions.
[0070] Finally, it should be noted that the above is only the best embodiment of the present invention, and the protection scope of the present invention is not limited to the above embodiment. All technical solutions under the concept of the present invention belong to the protection scope of the present invention. Ordinary technicians in this field should understand that they can still modify the technical solutions recorded in the above embodiments, or replace some of the technical features therein with equivalents; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.
Claims
1. A low-temperature electrolyte for lithium-ion batteries, characterized in that: The electrolyte includes a lithium salt and a solvent. The solvent includes a main solvent and a secondary solvent. The main solvent includes ethyl methyl carbonate and / or isobutyl formate. The secondary solvent includes dimethyl sulfite and / or propylene trifluorocarbonate.
2. The low-temperature electrolyte for lithium-ion batteries according to claim 1, characterized in that: The lithium salt is selected from one or more of lithium difluorooxalatoborate, lithium bis(fluorosulfonyl)imide, lithium hexafluorophosphate, lithium bis(trifluoromethanesulfonyl)imide or lithium tetrafluoroborate.
3. The ion battery electrolyte according to claim 1, characterized in that The concentration of the lithium salt in the electrolyte is 0.5 mol / L to 1.5 mol / L.
4. The low-temperature electrolyte for lithium-ion batteries according to claim 1, characterized in that: The lithium salt is selected from lithium difluorooxalatoborate, and the concentration of the lithium salt in the electrolyte is 0.75 mol / L to 1.25 mol / L.
5. The low-temperature electrolyte for lithium-ion batteries according to claim 1, characterized in that: The volume percentage of the main solvent in the solvent is 60-75 vt%, and the volume percentage of the secondary solvent in the solvent is 25-40 vt%.
6. The low-temperature electrolyte for lithium-ion batteries according to claim 1, characterized in that: The volume percentage of ethyl methyl carbonate in the solvent is 33.3-37.5vt%, the volume percentage of isobutyl formate is 33.3-37.5vt%, the volume percentage of dimethyl sulfite is 12.5-16.7vt%, and the volume percentage of propylene trifluorocarbonate is 12.5-16.7vt%; or, The volume percentage of ethyl methyl carbonate in the solvent is 37.5 vt%, the volume percentage of isobutyl formate is 37.5 vt%, and the volume percentage of dimethyl sulfite is 25 vt%.
7. The low-temperature electrolyte for lithium-ion batteries according to claim 1, characterized in that: The volume percentage of ethyl methyl carbonate in the solvent is 37.5vt%, the volume percentage of isobutyl formate is 37.5vt%; the volume percentage of dimethyl sulfite is 12.5%, and the volume percentage of propylene trifluorocarbonate is 12.5vt%; the lithium salt is lithium difluorooxalatoborate, and the concentration of the lithium salt in the electrolyte is 0.75mol / L~1mol / L.
8. Use of the low-temperature electrolyte for lithium-ion batteries according to any one of claims 1 to 7 in lithium-ion batteries.
9. The use according to claim 8, characterized in that The lithium-ion battery is a lithium sheet||lithium cobalt oxide half-cell, including a positive electrode material, a negative electrode material, a current collector, a separator and an electrolyte; the positive electrode material includes lithium cobalt oxide, conductive carbon black and polyvinylidene fluoride, the negative electrode material is a lithium sheet, the current collector is aluminum foil, and the separator is a glass fiber separator.
10. The use according to claim 8, characterized in that The charge and discharge voltage range of the half-cell is 3.0 to 4.5 V, and the charge and discharge cycle is carried out in a high and low temperature box with an operating temperature of -40 to 25°C.