Wide-temperature-range lithium ion battery electrolyte as well as preparation method and application thereof

Abstract

The invention discloses a wide-temperature-range lithium ion battery electrolyte and a preparation method and application thereof, and belongs to the technical field of lithium ion batteries, the wide-temperature-range lithium ion battery electrolyte comprises the following components by mass: 10-12% of a lithium salt, 80-85% of an organic solvent, and 3-5% of an additive. According to the wide-temperature-range lithium ion battery electrolyte as well as the preparation method and the application thereof, the lithium salt, the solvent and the additive system are elaborately designed and optimized, and all the components have a synergistic effect, so that the conduction efficiency of lithium ions is improved, the stability of an electrode-electrolyte interface is enhanced, side reactions at high and low temperatures are inhibited, and the service life of the battery is prolonged. Therefore, the performance more excellent than that of a traditional contrast is realized in a wide temperature range, and a powerful guarantee is provided for efficient, stable and lasting operation of the lithium ion battery under different environmental conditions.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium-ion batteries, and particularly to a wide-temperature-range lithium-ion battery electrolyte and its preparation method and application. Background Art

[0002] In a high-temperature environment, organic solvents in traditional electrolytes, such as carbonate compounds, have poor thermal stability. When the temperature rises, the organic solvents are prone to decomposition reactions, generating gases, which leads to an increase in the internal pressure of the battery. This not only accelerates the attenuation of the battery capacity but may also cause serious safety problems such as battery bulging and even explosion. For example, common ethylene carbonate (EC) decomposes at high temperatures to generate gases such as carbon dioxide, affecting the battery performance.

[0003] High temperature also causes the decomposition of lithium salts, thereby affecting the ionic conductivity of the electrolyte. Taking lithium hexafluorophosphate (LiPF 6 6) as an example, it decomposes at high temperatures to produce harmful hydrogen fluoride (HF) gas, and HF will react with the electrode material, damaging the solid electrolyte interface (SEI) film on the electrode surface. The SEI film is crucial for maintaining the stability and cycling performance of the battery. Once damaged, the electrolyte will continuously undergo side reactions with the electrode material, further reducing the battery performance. Summary of the Invention

[0004] The purpose of the present invention is to provide a wide-temperature-range lithium-ion battery electrolyte and its preparation method and application. Through the careful design and optimization of the lithium salt, solvent, and additive system, the components work synergistically to improve the conduction efficiency of lithium ions, enhance the stability of the electrode-electrolyte interface, and inhibit side reactions at high and low temperatures, thereby achieving more excellent performance than traditional comparative examples in a wide temperature range, providing a strong guarantee for the efficient, stable, and long-lasting operation of lithium-ion batteries under different environmental conditions.

[0005] To achieve the above purpose, the present invention provides a wide-temperature-range lithium-ion battery electrolyte, which includes the following components by mass percentage: 10-12% lithium salt, 80-85% organic solvent, and 3-5% additive.

[0006] Preferably, the lithium salt includes one or more of lithium bis(trifluoromethanesulfonyl)imide, lithium difluoro(oxalato)borate, lithium hexafluorophosphate, and lithium bis(oxalato)borate; The organic solvent includes one or more of ethylene carbonate, diethyl carbonate, ethyl propionate, 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, and a thermotropic liquid crystal-based intelligent responsive solvent additive; The additive includes one or more of vinylene sulfite, diethyl methylmalonate, and biphenyl.

[0007] The preparation method of the above-mentioned wide-temperature-range lithium-ion battery electrolyte comprises the following steps: Step 1: Pretreat the lithium salt, organic solvent and additive; Step 2: Place the organic solvent in a container equipped with a magnetic stirrer and an ultrasonic probe, and slowly add the lithium salt. Stir and sonicate until the lithium salt is completely dissolved. The rotation speed of the magnetic stirrer is 300 - 500 r / min, the ultrasonic power is 200 - 300 W, and the frequency is 40 - 50 kHz. After dissolution, inject the treated organic solvent, lithium salt solution and additive into different inlets of the microfluidic chip respectively for mixing and reaction.

[0008] Preferably, the pretreatment of the lithium salt in Step 1 includes: placing the lithium salt in a drying oven for vacuum drying, dissolving the dried lithium salt in anhydrous acetonitrile, adding a fluoroalkyl halide and a catalyst for reaction. After the reaction, remove the anhydrous acetonitrile by vacuum distillation, wash the product with diethyl ether, and finally dry the product in a drying oven.

[0009] Preferably, the pretreatment of the organic solvent in Step 1 includes: dehydrating the organic solvent, placing the dehydrated organic solvent in a clean container in a dry argon atmosphere glove box, then adding EMIM-TFSI, and then adding a thermotropic liquid crystal intelligent responsive solvent additive, and mixing the components evenly with a magnetic stirrer.

[0010] Preferably, the pretreatment of the additive in Step 1 includes: adding the additive to a reaction vessel, using p-toluenesulfonic acid as a catalyst, and carrying out an esterification reaction in a toluene solution. After the reaction is completed, remove the toluene by vacuum distillation, and recrystallize the product with n-hexane to obtain a self-healing film-forming additive.

[0011] Preferably, in the pretreatment of the lithium salt, the drying temperature is set at 100 - 150 °C, the drying time is 10 - 12 h, the reaction temperature is 50 - 100 °C, and the reaction time is 10 - 12 h.

[0012] Preferably, in the pretreatment of the organic solvent, the organic solvent is filled into a column of 4A molecular sieve for dehydration, and the organic solvent is controlled to pass through the molecular sieve column at a flow rate of 0.3 - 0.5 mL / min, and the operation is repeated three times. The addition amount of EMIM-TFSI is 10 - 12% of the total volume, and the addition amount of the thermotropic liquid crystal intelligent responsive solvent additive is 3 - 5% of the total volume.

[0013] Preferably, in the pretreatment of the additive, the esterification reaction temperature is 100 - 120 °C, and the reaction time is 8 - 10 h.

[0014] The present invention also provides an application of the wide-temperature-range lithium-ion battery electrolyte, applying the above-mentioned wide-temperature-range lithium-ion battery electrolyte to the preparation of lithium-ion batteries.

[0015] Therefore, the present invention adopts the above-mentioned wide-temperature-range lithium-ion battery electrolyte, its preparation method and application, and has the following beneficial effects: (1) Through the synergistic effect of the lithium salt system, the enhanced thermal stability of the ionic liquid and the regulation of the intelligent response additive, the decomposition of the lithium salt, the volatilization and decomposition of the organic solvent are effectively inhibited, and the excessive damage of the SEI film is avoided, enabling the battery to maintain a high charge-discharge capacity and capacity retention rate at high temperatures, and the cycle life is also greatly extended; (2) The conjugated structure in the multifunctional additive will undergo a polymerization reaction on the surface of the positive electrode to form a high-impedance film during high-temperature overcharge, preventing further lithium ion intercalation into the positive electrode and restricting the charging process of the battery. At the same time, the improvement of the overall thermal stability of the electrolyte reduces the risk of thermal runaway of the battery during overcharge.

[0016] (3) The synergistic effect of various additives forms a stable, dense and ion-conductive SEI film on the electrode surface. Especially the self-healing film-forming additive can self-repair when the SEI film is damaged, maintain the integrity of the film, effectively prevent the continuous side reaction between the electrolyte and the electrode material, and thus extend the cycle life of the battery.

[0017] The technical solution of the present invention will be further described in detail below through examples. Specific Embodiments

[0018] The technical solution of the present invention will be further described below through examples.

[0019] Unless otherwise defined, the technical terms or scientific terms used in the present invention shall have the ordinary meanings understood by those of ordinary skill in the field to which the present invention belongs.

[0020] The present invention provides a wide-temperature-range lithium-ion battery electrolyte, which includes the following components by mass percentage: 10-12% lithium salt, 80-85% organic solvent, 3-5% additive.

[0021] Among them, the lithium salt includes one or more of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium difluorooxalate borate (LiDFOB), lithium hexafluorophosphate (LiPF 6 ), lithium bis(oxalato)borate (LiBOB); the organic solvent includes one or more of ethylene carbonate (EC), diethyl carbonate (DEC), ethyl propionate (EP), 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMIM-TFSI) and a thermotropic liquid crystal-based intelligent response solvent additive; the additive includes one or more of ethylene sulfite (ES), diethyl methylmalonate (DM) and biphenyl (BP), and also includes the raw materials for synthesizing the self-healing film-forming additive and the related raw materials for synthesizing the multifunctional integrated additive.

[0022] The preparation method of the above-mentioned wide-temperature-range lithium-ion battery electrolyte includes the following steps: Step 1: Pretreat the lithium salt, organic solvent and additive. The pretreatment of the lithium salt includes: placing the lithium salt in a drying oven for vacuum drying, dissolving the dried lithium salt in anhydrous acetonitrile, adding a fluoroalkyl halide and a catalyst for reaction, removing the anhydrous acetonitrile by vacuum distillation after the reaction, washing the product with ether, and finally drying the product in a drying oven. High-temperature vacuum drying of the lithium salt removes moisture to prevent hydrolysis of the lithium salt and affect its performance; the organic solvent is dehydrated through a 4A molecular sieve column, and the water content is strictly controlled to ensure the conductivity and chemical stability of the electrolyte.

[0023] In the pretreatment of the lithium salt, the drying temperature is set at 100-150°C, the drying time is 10-12h, the reaction temperature is 50-100°C, and the reaction time is 10-12h.

[0024] The main lithium salt LiTFSI has high ionic conductivity and good chemical and thermal stability, constructing an efficient channel for lithium-ion transmission. The auxiliary lithium salt LiDFOB forms a SEI film on the electrode surface at low temperature, inhibits the decomposition of the electrolyte, and ensures lithium-ion conduction. The combination of the two takes into account the high and low temperature performance. Modifying the connection of LiDFOB with a fluoroalkyl chain reduces the crystallinity of the SEI film at low temperature, facilitating the penetration of lithium ions; at high temperature, it enhances the interaction with LiTFSI and stabilizes the SEI film. At the same time, the design of the lithium salt concentration gradient on the electrode surface reduces the concentration polarization of lithium ions during charge and discharge, and improves the charge and discharge rate performance.

[0025] The pretreatment of the organic solvent includes: dehydrating the organic solvent, placing the dehydrated organic solvent in a clean container in a dry argon atmosphere glove box, then adding EMIM-TFSI, and then adding a thermotropic liquid crystal intelligent responsive solvent additive, and mixing the components evenly with a magnetic stirrer.

[0026] In the pretreatment of the organic solvent, the organic solvent is loaded into a column of 4A molecular sieve for dehydration, and the organic solvent is controlled to pass through the molecular sieve column at a flow rate of 0.3-0.5 mL / min, and the process is repeated three times. The addition amount of EMIM-TFSI is 10-12% of the total volume, and the addition amount of the thermotropic liquid crystal intelligent responsive solvent additive is 3-5% of the total volume.

[0027] EC promotes the dissociation of lithium salts with its high dielectric constant, DEC reduces the resistance to ion migration with its low viscosity, and EP expands the low-temperature application range with its low melting point. The three are mixed in a specific ratio (2:3:5) to achieve performance optimization in a wide temperature range. The ionic liquid EMIM-TFSI inhibits the volatilization and decomposition of the electrolyte at high temperatures, and interacts with lithium ions at low temperatures to reconstruct the solvation sheath and improve the lithium ion diffusion coefficient. Thermotropic liquid crystal intelligent responsive solvent additives self-assemble to form ion conduction channels at low temperatures, and disorder the molecular arrangement at high temperatures to reduce internal resistance, thereby realizing intelligent adjustment of electrolyte performance with temperature.

[0028] The pretreatment of the additive includes: adding the additive into a reaction container, using p-toluenesulfonic acid as a catalyst, carrying out an esterification reaction in a toluene solution, removing the toluene by vacuum distillation after the reaction, and using n-hexane to recrystallize the product to obtain a self-healing film-forming additive.

[0029] In the pretreatment of the additive, the esterification reaction temperature is 100-120° C. and the reaction time is 8-10 hours.

[0030] ES forms a stable SEI film on the surface of the negative electrode to prevent further reaction between the electrolyte and the negative electrode. DM lowers the freezing point of the electrolyte and enhances the low-temperature migration ability of lithium ions. When the battery is overcharged, BP oxidatively polymerizes on the surface of the positive electrode to form a high-impedance film to prevent overcharging. The self-healing film-forming additive introduces disulfide bonds on the basis of ES. When the SEI film is damaged, it self-repairs through the dynamic covalent bond exchange reaction of the disulfide bonds, thereby extending the battery cycle life. The multifunctional integrated additive forms a stable SEI film on the negative electrode with its special molecular structure, and polymerizes at the positive electrode to achieve overcharge protection when overcharged at high temperature. At the same time, it lowers the freezing point of the electrolyte, simplifies the additive system, and reduces mutual interference.

[0031] Step 2: Place the organic solvent in a container with a magnetic stirrer and an ultrasonic probe, slowly add the lithium salt, and stir and ultrasonicate until the lithium salt is completely dissolved. The speed of the magnetic stirrer is 300-500r / min, the ultrasonic power is 200-300W, and the frequency is 40-50kHz. After dissolution, the treated organic solvent, lithium salt solution and additive are respectively injected into different inlets of the microfluidic chip for mixing and reaction.

[0032] The present invention also provides an application of a wide temperature range lithium ion battery electrolyte, wherein the wide temperature range lithium ion battery electrolyte is applied to prepare a lithium ion battery.

[0033] Example 1 The present invention provides a wide temperature range lithium ion battery electrolyte, and the preparation method is as follows: S1. Place LiTFSI and LiDFOB in a drying oven for vacuum drying. Set the temperature of the vacuum drying oven to 100 °C and the drying time to 10 h. Under a nitrogen protection atmosphere, dissolve the dried LiDFOB in anhydrous acetonitrile, and add CF 2 CF 3 Br and the catalyst potassium carbonate, and stir and react at a reaction temperature of 50 °C for 10 h. After the reaction, remove anhydrous acetonitrile by vacuum distillation, wash the product with diethyl ether, and finally dry the product in a drying oven.

[0034] S2. Load EC, DEC, and EP into a column filled with 4A molecular sieve for dehydration. Control the organic solvent to pass through the molecular sieve column at a flow rate of 0.3 mL / min, and repeat three times. In a dry argon atmosphere glove box, place the dehydrated EC, DEC, and EP in a clean container according to a ratio of 2:3:5. Then add EMIM-TFSI accounting for 10% of the total volume and a thermotropic liquid crystal intelligent responsive solvent additive accounting for 3% of the total volume, and use a magnetic stirrer to stir to make each component fully mixed and uniform.

[0035] S3. Add ES and dithiodipropionic acid to a reaction vessel, use p-toluenesulfonic acid as a catalyst, and carry out an esterification reaction in a toluene solution at a reaction temperature of 100 °C for 8 h. After the reaction, remove toluene by vacuum distillation, and recrystallize the product with n-hexane to obtain a self-healing film-forming additive.

[0036] S4. Add the treated organic solvent to a container equipped with a magnetic stirrer and an ultrasonic probe. Turn on the magnetic stirrer, set the rotation speed of the magnetic stirrer to 300 r / min, the ultrasonic power to 200 W, and the frequency to 40 kHz. Slowly add the dried LiTFSI and the modified LiDFOB, and continuously stir and ultrasonicate for 4 h until the lithium salt is completely dissolved; After dissolution, inject the preliminarily mixed solution containing lithium salt and organic solvent, conventional additives, the synthesized self-healing film-forming additive, and the multifunctional integrated additive into different inlets of the microfluidic chip through a micro-injection pump at different flow rates. Among them, the flow rate of the solution containing lithium salt and organic solvent is 50 μL / min, the flow rate of ES is 0.75 μL / min, the flow rate of DM is 0.4 μL / min, and the flow rate of BP is 0.5 μL / min. Inside the microfluidic chip, each component realizes rapid and uniform mixing in the microchannel. Utilize the microchannel of the microfluidic chip to achieve rapid heat exchange, and control the temperature of the mixing process to 25 °C ± 2 °C by setting a temperature control device outside the microfluidic chip, and finally prepare a wide-temperature-range lithium-ion battery electrolyte.

[0037] Example 2 The present invention provides an electrolyte for a wide-temperature-range lithium-ion battery, and the preparation method is as follows: S1. Place LiTFSI and LiDFOB in a drying oven for vacuum drying. Set the temperature of the vacuum drying oven to 130 °C and the drying time to 11 h. Under a nitrogen protection atmosphere, dissolve the dried LiDFOB in anhydrous acetonitrile, and add CF 2 CF 3 Br and the catalyst potassium carbonate and stir for reaction. The reaction temperature is 80 °C and the reaction time is 11 h. After the reaction, remove anhydrous acetonitrile by vacuum distillation, wash the product with ether, and finally dry the product in a drying oven.

[0038] S2. Load EC, DEC, and EP into a column filled with 4A molecular sieve for dehydration. Control the organic solvent to pass through the molecular sieve column at a flow rate of 0.4 mL / min, and repeat three times. In a dry argon atmosphere glove box, place the dehydrated EC, DEC, and EP in a clean container according to a ratio of 2:3:5. Then add EMIM-TFSI accounting for 11% of the total volume and a thermotropic liquid crystal intelligent responsive solvent additive accounting for 4% of the total volume, and use a magnetic stirrer to stir to make each component fully mixed and uniform.

[0039] S3. Add ES and dithiodipropionic acid to a reaction vessel, use p-toluenesulfonic acid as a catalyst, and carry out an esterification reaction in a toluene solution. The reaction temperature is 110 °C and the reaction time is 9 h. After the reaction, remove toluene by vacuum distillation, and recrystallize the product with n-hexane to obtain a self-healing film-forming additive.

[0040] S4. Add the treated organic solvent to a container equipped with a magnetic stirrer and an ultrasonic probe. Turn on the magnetic stirrer, set the rotation speed of the magnetic stirrer to 400 r / min, the ultrasonic power to 250 W, and the frequency to 45 kHz. Slowly add the dried LiTFSI and the modified LiDFOB, and continuously stir and ultrasonicate for 4 h until the lithium salt is completely dissolved; After dissolution, inject the preliminarily mixed solution containing lithium salt and organic solvent, conventional additives, the synthesized self-healing film-forming additive, and the multifunctional integrated additive into different inlets of the microfluidic chip through a micro-injection pump at different flow rates. Among them, the flow rate of the solution containing lithium salt and organic solvent is 50 μL / min, the flow rate of ES is 0.75 μL / min, the flow rate of DM is 0.4 μL / min, and the flow rate of BP is 0.5 μL / min. Inside the microfluidic chip, each component realizes rapid and uniform mixing in the microchannel. Utilize the microchannel of the microfluidic chip to achieve rapid heat exchange, and control the temperature of the mixing process at 25 °C ± 2 °C by setting a temperature control device outside the microfluidic chip, and finally prepare the electrolyte for a wide-temperature-range lithium-ion battery.

[0041] Example 3 The present invention provides an electrolyte for a lithium-ion battery with a wide temperature range, and the preparation method is as follows: S1. LiTFSI and LiDFOB are placed in a drying oven for vacuum drying. The temperature of the vacuum drying oven is set to 150 °C, and the drying time is 12 h. Under the protection of a nitrogen atmosphere, the dried LiDFOB is dissolved in anhydrous acetonitrile, and CF 2 CF 3 Br and the catalyst potassium carbonate are stirred and reacted. The reaction temperature is 100 °C, and the reaction time is 12 h. After the reaction, anhydrous acetonitrile is removed by vacuum distillation, and the product is washed with ether. Finally, the product is placed in a drying oven for drying.

[0042] S2. EC, DEC, and EP are loaded into a column filled with 4A molecular sieve for dehydration. The organic solvent is controlled to flow through the molecular sieve column at a flow rate of 0.5 mL / min, and this is repeated three times. In a dry argon atmosphere glove box, the dehydrated EC, DEC, and EP are placed in a clean container in a ratio of 2:3:5. Then, 12% of the total volume of EMIM-TFSI and 5% of the total volume of a thermotropic liquid crystal intelligent responsive solvent additive are added, and a magnetic stirrer is used to stir to fully mix all components evenly.

[0043] S3. ES and dithiodipropionic acid are added to a reaction vessel, and p-toluenesulfonic acid is used as a catalyst for an esterification reaction in a toluene solution. The reaction temperature is 120 °C, and the reaction time is 10 h. After the reaction, toluene is removed by vacuum distillation, and the product is recrystallized with n-hexane to obtain a self-healing film-forming additive.

[0044] S4. The treated organic solvent is added to a container equipped with a magnetic stirrer and an ultrasonic probe. The magnetic stirrer is turned on, and the rotation speed of the magnetic stirrer is set to 500 r / min, the ultrasonic power is 300 W, and the frequency is 50 kHz. The dried LiTFSI and the modified LiDFOB are slowly added, and stirring and ultrasonic treatment are continued for 4 h until the lithium salt is completely dissolved; After dissolution, the preliminarily mixed solution containing the lithium salt and the organic solvent, the conventional additive, the synthesized self-healing film-forming additive, and the multifunctional integrated additive are respectively injected into different inlets of a microfluidic chip through a micro-injection pump at different flow rates. The flow rate of the solution containing the lithium salt and the organic solvent is 50 μL / min, the flow rate of ES is 0.75 μL / min, the flow rate of DM is 0.4 μL / min, and the flow rate of BP is 0.5 μL / min. Inside the microfluidic chip, all components are quickly and evenly mixed in the microchannels. The microchannels of the microfluidic chip are used to achieve rapid heat exchange. By setting a temperature control device outside the microfluidic chip, the temperature of the mixing process is controlled at 25 °C ± 2 °C, and finally, an electrolyte for a lithium-ion battery with a wide temperature range is prepared.

[0045] Comparative Example 1 The only difference between Comparative Example 1 and Example 1 is that lithium hexafluorophosphate is used in Comparative Example 1, and other conditions are the same.

[0046] Performance test: The electrolytes obtained in Examples 1-3 and Comparative Example 1 were applied to the preparation of lithium-ion batteries. According to the conventional battery assembly process, the positive electrode sheet, separator, and negative electrode sheet were assembled in sequence, and the electrolytes obtained in Examples 1-3 and Comparative Example 1 were injected. After sealing the battery, pre-treatment steps such as formation and aging were carried out.

[0047] The batteries obtained above were subjected to 100-cycle charge and discharge tests at a rate of 0.1C under different temperature environments, and the charge and discharge specific capacities and charge and discharge efficiencies of the batteries were recorded.

[0048] Table 1 Charge and discharge capacities and charge and discharge efficiencies of the batteries at different temperatures

[0049] As can be seen from Table 1, compared with Comparative Example 1, the lithium-ion batteries prepared from the electrolytes obtained in Examples 1-3 can still maintain a high capacity after multiple cycles, proving that the electrolytes prepared in Examples 1-3 are more conducive to the efficient operation of lithium-ion batteries.

[0050] Therefore, the present invention adopts the above-mentioned wide-temperature-range lithium-ion battery electrolyte and its preparation method and application. Through the careful design and optimization of the lithium salt, solvent, and additive systems, the components act synergistically, improving the lithium-ion conduction efficiency, enhancing the stability of the electrode-electrolyte interface, and suppressing side reactions at high and low temperatures. Thus, more excellent performance than the traditional comparative example is achieved within a wide temperature range, providing a strong guarantee for the efficient, stable, and durable operation of lithium-ion batteries under different environmental conditions.

[0051] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that they can still modify or equivalently replace the technical solutions of the present invention, and these modifications or equivalent replacements cannot make the modified technical solutions deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A wide temperature range lithium ion battery electrolyte, characterized in that: By mass percentage, it includes the following components: 10-12% lithium salt, 80-85% organic solvent, and 3-5% additives.

2. The wide temperature range lithium ion battery electrolyte according to claim 1, characterized in that: The lithium salt includes one or more of lithium bis(trifluoromethanesulfonyl)imide, lithium difluorooxalatoborate, lithium hexafluorophosphate, and lithium bis(oxalatoborate); The organic solvent includes one or more of ethylene carbonate, diethyl carbonate, ethyl propionate, 1-ethyl-3-methylimidazole bis(trifluoromethylsulfonyl) and a smart responsive solvent additive based on thermotropic liquid crystal; The additive includes one or more of vinyl sulfite, diethyl methylmalonate and biphenyl.

3. A method for preparing a wide temperature range lithium ion battery electrolyte according to any one of claims 1 to 2, characterized in that: The following steps are involved: Step 1, pre-treating lithium salt, organic solvent and additives; Step 2: Place the organic solvent in a container with a magnetic stirrer and an ultrasonic probe, slowly add the lithium salt, and stir and ultrasonicate until the lithium salt is completely dissolved. The speed of the magnetic stirrer is 300-500r / min, the ultrasonic power is 200-300W, and the frequency is 40-50kHz. After dissolution, the treated organic solvent, lithium salt solution and additive are respectively injected into different inlets of the microfluidic chip for mixing and reaction.

4. The method for preparing a wide temperature range lithium-ion battery electrolyte according to claim 3, characterized in that: The pretreatment of the lithium salt in step 1 includes: placing the lithium salt in a drying oven and vacuum drying it, dissolving the dried lithium salt in anhydrous acetonitrile, adding a fluorinated alkyl halide and a catalyst to react, removing the anhydrous acetonitrile by vacuum distillation after the reaction, washing the product with ether, and finally drying the product in a drying oven.

5. The method for preparing a wide temperature range lithium-ion battery electrolyte according to claim 3, characterized in that: The pretreatment of the organic solvent in step 1 includes: dehydrating the organic solvent, placing the dehydrated organic solvent in a clean container in a dry argon atmosphere glove box, then adding EMIM-TFSI, and then adding the intelligent responsive solvent additive of the thermotropic liquid crystal, and using a magnetic stirrer to mix the components evenly.

6. The method for preparing a wide temperature range lithium ion battery electrolyte according to claim 3, characterized in that: The pretreatment of the additive in step 1 includes: adding the additive to a reaction container, using p-toluenesulfonic acid as a catalyst, performing an esterification reaction in a toluene solution, removing the toluene by vacuum distillation after the reaction, and using n-hexane to recrystallize the product to obtain a self-healing film-forming additive.

7. The method for preparing a wide temperature range lithium-ion battery electrolyte according to claim 4, characterized in that: In the pretreatment of lithium salt, the drying temperature is set to 100-150°C, the drying time is set to 10-12h, the reaction temperature is set to 50-100°C, and the reaction time is set to 10-12h.

8. The method for preparing a wide temperature range lithium-ion battery electrolyte according to claim 5, characterized in that: In the pretreatment of the organic solvent, the organic solvent is loaded into a 4A molecular sieve column for dehydration, and the organic solvent is controlled to pass through the molecular sieve column at a flow rate of 0.3-0.5 mL / min. This is repeated three times. The amount of EMIM-TFSI added is 10-12% of the total volume, and the amount of the intelligent responsive solvent additive of the thermotropic liquid crystal added is 3-5% of the total volume.

9. The method for preparing a wide temperature range lithium-ion battery electrolyte according to claim 6, characterized in that: In the pretreatment of the additive, the esterification reaction temperature is 100-120° C. and the reaction time is 8-10 hours.

10. An application of a wide temperature range lithium-ion battery electrolyte, characterized in that: The wide temperature range lithium ion battery electrolyte according to any one of claims 1 to 2 is used to prepare a lithium ion battery.

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