Preparation method of wide-temperature electrolyte

Abstract

This invention discloses a method for preparing a wide-temperature electrolyte, belonging to the field of electrolyte preparation technology. Using 1M LiPF6 / EC:EMC (3:7) as the base electrolyte, the method includes the following steps: Step S1, placing the 1M LiPF6 / EC:EMC (3:7) base electrolyte in a tetrafluoroethylene bottle; Step S2, adding at least one organic reagent to the 1M LiPF6 / EC:EMC (3:7) base electrolyte to obtain a multi-component co-solvent system electrolyte; Step S3, adding at least one lithium salt to the multi-component co-solvent system electrolyte to obtain a composite lithium salt electrolyte; Step S4, adding at least one functional additive to the composite lithium salt electrolyte and stirring evenly under an inert gas protective atmosphere, then sealing and allowing it to stand for 22-26 hours to obtain a wide-temperature electrolyte; Step S5, testing the wide-temperature electrolyte. This invention solves the problems of poor stability, insufficient fast ion conductivity, and safety hazards of existing electrolytes over a wide temperature range, which limit the working temperature range of the electrolyte and seriously affect the applicability of the battery.

Description

Technical Field

[0001] This invention belongs to the field of electrolyte preparation technology, and particularly relates to a method for preparing a wide-temperature electrolyte. Background Technology

[0002] Electrolyte is an indispensable and important component of a battery. It plays a key role in conducting ions between the positive and negative electrodes, directly affecting the battery's performance, including charge and discharge efficiency, cycle life, and safety. Its performance is crucial to whether the battery can work stably and efficiently under various environmental conditions.

[0003] However, existing electrolytes generally suffer from the following problems over a wide temperature range: 1. Poor stability makes it difficult to maintain good performance, which affects the reliability of the battery under extreme temperature conditions.

[0004] 2. Insufficient fast ion conductivity limits the battery's charging and discharging speed, making it unsuitable for some application scenarios that require fast charging and high power output.

[0005] 3. It poses safety hazards and cannot adequately meet safety requirements in different environments. Summary of the Invention

[0006] To address the problems existing in the prior art, this invention provides a method for preparing a wide-temperature electrolyte, which has the advantages of effectively improving the stability, fast ion conductivity and safety of the electrolyte. It solves the problems of poor stability, insufficient fast ion conductivity and safety hazards of existing electrolytes over a wide temperature range, which limit the working temperature range of the electrolyte and seriously affect the applicability of the battery.

[0007] This invention is achieved as follows: a method for preparing a wide-temperature-range electrolyte, using 1M LiPF6 / EC:EMC (3:7) as the base electrolyte, includes the following steps: Step S1: Place the 1M LiPF6 / EC:EMC (3:7) basic electrolyte into a tetrafluoroethylene bottle. The tetrafluoroethylene bottle must be vacuum dried at a temperature of 80-100℃ for 4-6 hours to remove residual moisture from the bottle. Step S2: Add at least one organic reagent to the 1M LiPF6 / EC:EMC (3:7) basic electrolyte and stir evenly in a constant temperature water bath at 25-35℃. The stirring rate is 300-500 r / min and the stirring time is 30-60 minutes to obtain the multi-component co-solvent system electrolyte. Step S3: Add at least one lithium salt to the multi-component co-solvent electrolyte system by constant pressure dropping at a rate of 1-2 drops / second. After the dropping is completed, adjust the electrolyte concentration to 1.0-1.5 mol / L to obtain a composite lithium salt electrolyte. Step S4: Add at least one functional additive to the composite lithium salt electrolyte and stir evenly under an inert gas protective atmosphere. The stirring rate is 200-300 r / min and the stirring time is 20-40 minutes. Then seal and let stand for 22-26 hours to obtain a wide-temperature electrolyte. Step S5: Test the wide-temperature electrolyte.

[0008] As a preferred embodiment of the present invention, in step S2, the organic reagents include, but are not limited to, propylene carbonate (PC), diethyl carbonate (DEC), ethyl acetate (EA), and γ-butyrolactone (GBL), and the amount of the organic reagents added accounts for 5%-15% of the mass of the 1MLiPF6 / EC:EMC (3:7) base electrolyte. When multiple organic reagents are added at the same time, the mass ratio of each organic reagent needs to be adjusted according to the low-temperature performance requirements of the target electrolyte.

[0009] As a preferred embodiment of the present invention, in step S3, the lithium salt includes, but is not limited to, lithium difluorooxalate borate (LiODFB) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI). The amount of lithium salt added should be such that the total lithium concentration in the composite lithium salt electrolyte meets the requirement of 1.0-1.5 mol / L. Before addition, the lithium salt needs to be vacuum dried at a temperature of 120-150°C for 8-10 hours to reduce the moisture content in the lithium salt to below 50 ppm.

[0010] In a preferred embodiment of the present invention, in step S4, the functional additives include, but are not limited to, film-forming additives and positive electrode protection additives. The film-forming additives include, but are not limited to, vinylene carbonate (VC) and fluoroethylene carbonate (FEC). The amount of the film-forming additives added accounts for 1%-5% of the mass of the composite lithium salt electrolyte. The positive electrode protection additives include, but are not limited to, trimethyl phosphate (TMP) and triethyl phosphate (TEP). The amount of the positive electrode protection additives added accounts for 0.5%-2% of the mass of the composite lithium salt electrolyte. When adding the functional additives, they must first be filtered through a 0.22 μm polytetrafluoroethylene filter membrane to remove impurity particles.

[0011] As a preferred embodiment of the present invention, in step S4, the electrolyte is allowed to stand for 24 hours, and the ambient temperature is controlled at 20-25°C and the relative humidity is ≤30%.

[0012] As a preferred embodiment of the present invention, the detection content in step S5 includes, but is not limited to, the following items: Conductivity testing: The conductivity of the electrolyte was measured every 10℃ in the temperature range of -60℃ to 80℃ using a conductivity meter. The conductivity was required to be ≥1mS / cm at -40℃ and ≥10mS / cm at 60℃. Moisture content detection: The moisture content of the electrolyte was determined using a Karl-Fisher coulometric moisture analyzer, and the moisture content was required to be ≤20ppm; Viscosity testing: The viscosity of the electrolyte was measured at three temperature points: -40℃, 25℃, and 60℃ using a rotational viscometer. The viscosity was required to be ≤200 mPa·s at -40℃ and ≤10 mPa·s at 60℃. Electrochemical stability testing: The oxidation potential of the electrolyte was tested using linear sweep voltammetry (LSV), requiring an oxidation potential ≥ 4.5V (vs. Li). + / Li), the reduction stability of the electrolyte was tested by cyclic voltammetry (CV), requiring no obvious side reaction peaks in the range of 2.8-4.3V (with nickel-cobalt-manganese 622 as the positive electrode); Safety testing: Thermogravimetric analysis (TGA) is used to test the mass change of the electrolyte in the range of 100-300℃. The mass loss rate is required to be ≤5% below 200℃. At the same time, the electrolyte combustion test is carried out, and the electrolyte is required to extinguish itself within 3 seconds after being ignited.

[0013] As a preferred embodiment of the present invention, in step S2, in addition to adding the organic reagent to the 1MLiPF6 / EC:EMC (3:7) basic electrolyte, nano-ceramic particles (two or one of Al2O3 and CeO2) can also be added simultaneously. The amount of nano-ceramic particles added accounts for 0.1%-1% of the mass of the 1MLiPF6 / EC:EMC (3:7) basic electrolyte, and after addition, ultrasonic dispersion treatment is required, with an ultrasonic power of 300-500W and an ultrasonic time of 15-30 minutes.

[0014] As a preferred embodiment of the present invention, in step S3, when adjusting the electrolyte concentration, a precision densitometer is used to monitor the electrolyte density in real time, and the amount of lithium salt added is adjusted according to the correspondence between density and concentration to ensure that the control accuracy of the electrolyte concentration is within ±0.05mol / L.

[0015] As a preferred embodiment of the present invention, in step S4, the sealing is performed using a polytetrafluoroethylene sealing plug in conjunction with a stainless steel clamp. Before sealing, a layer of fluororubber sealant needs to be applied to the contact area between the sealing plug and the bottle opening.

[0016] As a preferred embodiment of the present invention, the entire preparation process must be carried out in a glove box, and the water and oxygen content in the glove box is controlled to be below 0.1 ppm.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention uses 1MLiPF6 / EC:EMC (3:7) as the base electrolyte, introduces specific reagent molecules (such as low melting point reagents and flame retardant reagents), and designs a multi-component co-solvent system. The components of the SEI film-forming additive and the positive electrode protection additive can improve the high and low temperature conductivity of the electrolyte, enhance the high temperature cycle stability of the SEI film, reduce the lithium ion transport impedance, and prevent the oxidative decomposition of the electrolyte at high temperatures.

[0018] Nanoceramic particles such as Al2O3 and CeO2 possess high modulus and high hardness. When uniformly dispersed in the electrolyte and adsorbed on the electrode surface (especially the negative electrode), they can act as a physical barrier, inhibiting the growth of lithium dendrites. Furthermore, their Lewis acid or base properties allow them to efficiently adsorb and neutralize HF generated from the reaction of LiPF6 and water in the electrolyte, significantly reducing the acidity of the electrolyte and improving its chemical stability at high temperatures and voltages, thus protecting the integrity of the positive and negative electrode materials. Finally, they can also suppress the oxidative decomposition and gas generation of the electrolyte at high temperatures; in cases of localized overheating, their high thermal conductivity helps dissipate heat, slowing down the heat spread process to some extent.

[0019] The synergistic effect of specific reagent molecules and nano-ceramic particles solves the problems of poor stability, insufficient fast ion conductivity, and safety hazards of existing electrolytes over a wide temperature range. Attached Figure Description

[0020] Figure 1 This is a flowchart illustrating the preparation process of a wide-temperature electrolyte according to an embodiment of the present invention; Figure 2 This is a flowchart illustrating the preparation process of a wide-temperature electrolyte containing nano-ceramic particles, as provided in an embodiment of the present invention. Figure 3 These are the LSV curves comparing the electrolyte system of Example 4 of this invention with the basic electrolyte; Figure 4 This is a CV curve comparing the electrolyte system of Example 4 of the present invention with the basic electrolyte. Detailed Implementation

[0021] To further understand the invention's content, features, and effects, the following embodiments are provided, and detailed descriptions are given in conjunction with the accompanying drawings.

[0022] The structure of the present invention will now be described in detail with reference to the accompanying drawings.

[0023] refer to Figure 1 and Figure 2 The present invention provides a method for preparing a wide-temperature electrolyte, using 1M LiPF6 / EC:EMC (3:7) as the base electrolyte, comprising the following steps: Step S1: Place the 1M LiPF6 / EC:EMC (3:7) basic electrolyte into a tetrafluoroethylene bottle. The tetrafluoroethylene bottle must be vacuum dried at a temperature of 80-100℃ for 4-6 hours to remove residual moisture from the bottle. Step S2: Add at least one organic reagent to the 1M LiPF6 / EC:EMC (3:7) basic electrolyte and stir evenly in a constant temperature water bath at 25-35℃. The stirring rate is 300-500 r / min and the stirring time is 30-60 minutes to obtain the multi-component co-solvent system electrolyte. Step S3: Add at least one lithium salt to the multi-component co-solvent electrolyte system by constant pressure dropping at a rate of 1-2 drops / second. After the dropping is completed, adjust the electrolyte concentration to 1.0-1.5 mol / L to obtain a composite lithium salt electrolyte. Step S4: Add at least one functional additive to the composite lithium salt electrolyte and stir evenly under an inert gas protective atmosphere. The stirring rate is 200-300 r / min and the stirring time is 20-40 minutes. Then seal and let stand for 22-26 hours to obtain a wide-temperature electrolyte. Step S5: Test the wide-temperature electrolyte.

[0024] Further, in step S2, the organic reagents include, but are not limited to, propylene carbonate (PC), diethyl carbonate (DEC), ethyl acetate (EA), and γ-butyrolactone (GBL), and the amount of the organic reagents added accounts for 5%-15% of the mass of the 1M LiPF6 / EC:EMC (3:7) base electrolyte. When multiple organic reagents are added simultaneously, the mass ratio of each organic reagent needs to be adjusted according to the low-temperature performance requirements of the target electrolyte. Among them, when the mass ratio of propylene carbonate (PC) to γ-butyrolactone (GBL) is 1:1-3:1, the conductivity improvement effect of the electrolyte at -40℃ is optimal.

[0025] Further, in step S3, the lithium salt includes, but is not limited to, lithium difluorooxalate borate (LiODFB) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI). The amount of lithium salt added should be such that the total lithium concentration in the composite lithium salt electrolyte meets the requirement of 1.0-1.5 mol / L. Before addition, the lithium salt needs to be vacuum dried at a temperature of 120-150°C for 8-10 hours to reduce the moisture content in the lithium salt to below 50 ppm.

[0026] Further, in step S4, the functional additives include, but are not limited to, film-forming additives and positive electrode protection additives. The film-forming additives include, but are not limited to, vinylene carbonate (VC) and fluoroethylene carbonate (FEC). The amount of film-forming additives added accounts for 1%-5% of the mass of the composite lithium salt electrolyte. The positive electrode protection additives include, but are not limited to, trimethyl phosphate (TMP) and triethyl phosphate (TEP). The amount of positive electrode protection additives added accounts for 0.5%-2% of the mass of the composite lithium salt electrolyte. When adding the functional additives, they must first be filtered through a 0.22μm polytetrafluoroethylene filter membrane to remove impurity particles.

[0027] Furthermore, in step S4, the electrolyte is allowed to stand for 24 hours, and the ambient temperature is controlled at 20-25℃ with a relative humidity of ≤30% to avoid the environmental humidity affecting the performance of the electrolyte.

[0028] Furthermore, in step S5, the detection content includes, but is not limited to, the following items: Conductivity testing: The conductivity of the electrolyte was measured every 10℃ in the temperature range of -60℃ to 80℃ using a conductivity meter. The conductivity was required to be ≥1mS / cm at -40℃ and ≥10mS / cm at 60℃. Moisture content detection: The moisture content of the electrolyte was determined using a Karl-Fisher coulometric moisture analyzer, and the moisture content was required to be ≤20ppm; Viscosity testing: The viscosity of the electrolyte was measured at three temperature points: -40℃, 25℃, and 60℃ using a rotational viscometer. The viscosity was required to be ≤200 mPa·s at -40℃ and ≤10 mPa·s at 60℃. Electrochemical stability testing: The oxidation potential of the electrolyte was tested using linear sweep voltammetry (LSV), requiring an oxidation potential ≥ 4.5V (vs. Li). + / Li), the reduction stability of the electrolyte was tested by cyclic voltammetry (CV), requiring no obvious side reaction peaks in the range of 2.8-4.3V (with nickel-cobalt-manganese 622 as the positive electrode); Safety testing: Thermogravimetric analysis (TGA) is used to test the mass change of the electrolyte in the range of 100-300℃. The mass loss rate is required to be ≤5% below 200℃. At the same time, the electrolyte combustion test is carried out, and the electrolyte is required to extinguish itself within 3 seconds after being ignited.

[0029] Furthermore, in step S2, in addition to adding the organic reagent to the 1M LiPF6 / EC:EMC (3:7) basic electrolyte, nano-ceramic particles can also be added simultaneously. The amount of nano-ceramic particles added accounts for 0.1%-1% of the mass of the 1M LiPF6 / EC:EMC (3:7) basic electrolyte, and after addition, ultrasonic dispersion treatment is required. The ultrasonic power is 300-500W and the ultrasonic time is 15-30 minutes to make the nano-ceramic particles uniformly dispersed in the electrolyte, so as to improve the thermal stability and mechanical strength of the electrolyte.

[0030] Furthermore, in step S3, when adjusting the electrolyte concentration, a precision densitometer is used to monitor the electrolyte density in real time, and the amount of lithium salt added is adjusted according to the correspondence between density and concentration to ensure that the control accuracy of the electrolyte concentration is within ±0.05 mol / L.

[0031] Furthermore, in step S4, the sealing is achieved by using a polytetrafluoroethylene sealing plug in conjunction with a stainless steel clamp. Before sealing, a layer of fluororubber sealant is applied to the contact area between the sealing plug and the bottle opening to enhance the sealing performance and prevent air and moisture from entering the electrolyte during the standing process.

[0032] Furthermore, the entire preparation process must be carried out in a glove box, where the water and oxygen content is controlled below 0.1 ppm to ensure that the electrolyte does not react with air and moisture during preparation, thus guaranteeing the stability of the electrolyte's performance.

[0033] It should be noted that organic reagents, lithium salts, and functional additives can be designed and selected based on their specific physicochemical properties (such as melting point, saturation, flash point, viscosity, dielectric constant, electrochemical window, etc.) to enable the electrolyte to meet different application requirements.

[0034] Example 1: Preparation of a wide-temperature electrolyte containing a single organic reagent and a film-forming additive Step S1: Select 1M LiPF6 / EC:EMC (3:7) as the basic electrolyte. Place the tetrafluoroethylene bottle in an 80℃ vacuum drying oven for 6 hours to remove residual moisture. After drying, transfer 500mL of the basic electrolyte into the dried tetrafluoroethylene bottle in a glove box (water and oxygen content ≤0.1ppm).

[0035] Step S2: Add 25g of propylene carbonate (PC, accounting for 5% of the mass of the basic electrolyte) to the basic electrolyte, place the tetrafluoroethylene bottle in a constant temperature water bath at 25℃, and stir at a rate of 300r / min for 60 minutes. After stirring, the multi-component co-solvent system electrolyte is obtained.

[0036] Step S3: Lithium difluorooxalate borate (LiODFB) is dried in a vacuum drying oven at 120℃ for 10 hours. After cooling, it is added to the multi-component co-solvent electrolyte system in a glove box using a constant pressure dropping method (dropping rate 1 drop / second). During the process, the electrolyte density is monitored in real time using a precision densitometer. The amount of lithium difluorooxalate borate (LiODFB) added is adjusted according to the density-concentration correspondence. Finally, the electrolyte concentration is controlled to 1.0 mol / L to obtain the composite lithium salt electrolyte.

[0037] Step S4: After filtering vinylene carbonate (VC) through a 0.22μm polytetrafluoroethylene (PTFE) filter membrane, add it to the composite lithium salt electrolyte under an argon protective atmosphere (VC addition accounts for 1% of the mass of the composite lithium salt electrolyte). Stir at a rate of 200r / min for 40 minutes. After stirring, seal the bottle with a PTFE sealing plug and a stainless steel clamp. Apply fluororubber sealing grease to the contact area between the sealing plug and the bottle mouth. Then let it stand for 24 hours in an environment of 20℃ and relative humidity ≤30% to obtain a wide-temperature electrolyte.

[0038] Step S5, the detection results are as follows: Conductivity: Measured every 10℃ within the range of -60℃ to 80℃. The conductivity is 1.2 mS / cm at -40℃ and 11.5 mS / cm at 60℃, which meets the requirements.

[0039] Moisture content: 15 ppm as determined by Karl-Fisher coulometric method, which meets the standard of ≤20 ppm.

[0040] Viscosity: The viscosity is 180 mPa·s at -40℃, 8 mPa·s at 25℃, and 8.5 mPa·s at 60℃, all within the specified range.

[0041] Electrochemical stability: Linear sweep voltammetry (LSV) testing showed an oxidation potential of 4.6 V (vs. Li). + / Li), cyclic voltammetry (CV) tests showed no obvious side reaction peaks in the range of 2.8-4.3 V (with nickel-cobalt-manganese 622 as the positive electrode).

[0042] Safety: Thermogravimetric analysis (TGA) showed a mass loss rate of 3% below 200°C, and the electrolyte self-extinguished within 2 seconds after ignition in the combustion test, meeting the safety standards.

[0043] Example 2: Preparation of a wide-temperature electrolyte containing various organic reagents and positive electrode protection additives Step S1: Select 1M LiPF6 / EC:EMC (3:7) as the basic electrolyte. Place the tetrafluoroethylene bottle in a vacuum drying oven at 100℃ and dry for 4 hours to remove residual moisture. After drying, transfer 600mL of the basic electrolyte into the dried tetrafluoroethylene bottle in a glove box (water and oxygen content ≤0.1ppm).

[0044] Step S2: Add 36g of propylene carbonate (PC) and 18g of γ-butyrolactone (GBL) to the basic electrolyte (PC to GBL mass ratio 2:1, total addition amount accounts for 9% of the mass of the basic electrolyte). Place the tetrafluoroethylene bottle in a constant temperature water bath at 35℃ and stir at a rate of 500r / min for 30 minutes. After stirring, the multi-component co-solvent system electrolyte is obtained.

[0045] In step S3, lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) was dried in a vacuum drying oven at 150°C for 8 hours. After cooling, it was added to the multi-component co-solvent electrolyte system in a glove box using a constant pressure dropping method (dropping rate of 2 drops / second). During the process, the electrolyte density was monitored in real time using a precision densitometer. The amount of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) added was adjusted according to the density-concentration correspondence. Finally, the electrolyte concentration was adjusted to 1.5 mol / L to obtain the composite lithium salt electrolyte.

[0046] Step S4: Vinyl carbonate (VC) and trimethyl phosphate (TMP) are filtered through a 0.22 μm polytetrafluoroethylene (PTFE) filter membrane and added to the composite lithium salt electrolyte under a nitrogen protective atmosphere (VC accounts for 5% of the mass of the composite lithium salt electrolyte, and TMP accounts for 0.5%). The mixture is stirred at 300 r / min for 20 minutes. After stirring, the mixture is sealed with a PTFE stopper and a stainless steel clamp. Fluororubber sealant is applied to the contact area between the stopper and the bottle mouth. The mixture is then allowed to stand for 24 hours at 25°C and relative humidity ≤30% to obtain a wide-temperature electrolyte.

[0047] Step S5, the detection results are as follows: Conductivity: Measured every 10℃ within the range of -60℃ to 80℃. The conductivity is 1.5mS / cm at -40℃ and 13mS / cm at 60℃, which meets the requirements.

[0048] Moisture content: 12 ppm as determined by Karl-Fisher coulometric method, which meets the standard of ≤20 ppm.

[0049] Viscosity: The viscosity is 160 mPa·s at -40℃, 7 mPa·s at 25℃, and 7.8 mPa·s at 60℃, all within the specified range.

[0050] Electrochemical stability: Linear sweep voltammetry (LSV) testing showed an oxidation potential of 4.7 V (vs. Li). + / Li), cyclic voltammetry (CV) tests showed no obvious side reaction peaks in the range of 2.8-4.3 V (with nickel-cobalt-manganese 622 as the positive electrode).

[0051] Safety: Thermogravimetric analysis (TGA) showed a mass loss rate of 2.5% below 200℃, and the electrolyte self-extinguished within 1.5 seconds after ignition in the combustion test, meeting the safety standards.

[0052] Example 3: Preparation of a wide-temperature electrolyte containing nano-ceramic particles Step S1: Select 1M LiPF6 / EC:EMC (3:7) as the basic electrolyte. Place the tetrafluoroethylene bottle in a vacuum drying oven at 90℃ and dry for 5 hours to remove residual moisture. After drying, transfer 400mL of the basic electrolyte into the dried tetrafluoroethylene bottle in a glove box (water and oxygen content ≤0.1ppm).

[0053] In step S2, 24g of diethyl carbonate (DEC, accounting for 6% of the mass of the basic electrolyte) and 0.4g of nano-ceramic particles (particle size 10-50nm, accounting for 0.1% of the mass of the basic electrolyte) are added to the basic electrolyte. The mixture is first ultrasonically dispersed at 300W for 30 minutes, and then the tetrafluoroethylene bottle is placed in a constant temperature water bath at 30℃ and stirred at a rate of 400r / min for 45 minutes to obtain a multi-component co-solvent electrolyte system containing nanoparticles.

[0054] In step S3, lithium difluorooxalate borate (LiODFB) was dried in a vacuum drying oven at 130°C for 9 hours. After cooling, it was added to the multi-component co-solvent electrolyte in a glove box using a constant pressure dropping method (dropping rate of 1.5 drops / second). During the process, the electrolyte density was monitored in real time using a precision densitometer. The amount of lithium difluorooxalate borate (LiODFB) added was adjusted according to the density-concentration correspondence. Finally, the electrolyte concentration was adjusted to 1.2 mol / L to obtain the composite lithium salt electrolyte.

[0055] Step S4: Fluoroethylene carbonate (FEC) is filtered through a 0.22 μm polytetrafluoroethylene (PTFE) filter membrane and then added to the composite lithium salt electrolyte under an argon protective atmosphere (the amount of FEC added accounts for 3% of the mass of the composite lithium salt electrolyte). The mixture is stirred at a rate of 250 r / min for 30 minutes. After stirring, the mixture is sealed with a PTFE stopper and a stainless steel clamp. Fluororubber sealant is applied to the contact area between the stopper and the bottle mouth. The mixture is then allowed to stand for 24 hours at 22°C and relative humidity ≤30% to obtain a wide-temperature electrolyte.

[0056] Step S5, the detection results are as follows: Electrical conductivity: Measured every 10℃ within the range of -60℃ to 80℃. The conductivity is 1.3 mS / cm at -40℃ and 12 mS / cm at 60℃, which meets the requirements.

[0057] Moisture content: 13 ppm as determined by Karl-Fisher coulometric method, which meets the standard of ≤20 ppm.

[0058] Viscosity: The viscosity is 170 mPa·s at -40℃, 7.5 mPa·s at 25℃, and 8.2 mPa·s at 60℃, all within the specified range.

[0059] Electrochemical stability: Linear sweep voltammetry (LSV) testing showed an oxidation potential of 4.65 V (vs. Li). + / Li), cyclic voltammetry (CV) tests showed no obvious side reaction peaks in the range of 2.8-4.3 V (with nickel-cobalt-manganese 622 as the positive electrode).

[0060] Safety: Thermogravimetric analysis (TGA) showed a mass loss rate of 2.8% below 200℃. In the combustion test, the electrolyte self-extinguished within 2 seconds after ignition, meeting the safety standards, and the thermal stability of the electrolyte was significantly improved.

[0061] Example 4: Preparation of a wide-temperature electrolyte with high-concentration lithium salt and composite functional additives Step S1: Select 1M LiPF6 / EC:EMC (3:7) as the basic electrolyte. Place the tetrafluoroethylene bottle in a vacuum drying oven at 95℃ and dry for 4.5 hours to remove residual moisture. After drying, transfer 500mL of the basic electrolyte into the dried tetrafluoroethylene bottle in a glove box (water and oxygen content ≤0.1ppm).

[0062] Step S2: Add 37.5g ethyl acetate (EA, accounting for 7.5% of the mass of the basic electrolyte) and 12.5g γ-butyrolactone (GBL, accounting for 2.5% of the mass of the basic electrolyte) and 0.4g nano-ceramic particles (particle size 10-50nm, accounting for 0.1% of the mass of the basic electrolyte) to the basic electrolyte. First, ultrasonically disperse the particles at 300W for 30 minutes. Then, place the tetrafluoroethylene bottle in a constant temperature water bath at 32℃ and stir at a rate of 450r / min for 50 minutes. After stirring, a multi-component co-solvent electrolyte system containing nanoparticles is obtained.

[0063] In step S3, lithium difluorooxalate borate (LiODFB) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) are mixed at a mass ratio of 1:1 and dried in a vacuum drying oven at 140°C for 8.5 hours. After cooling, the mixture is added to the multi-component co-solvent electrolyte system in a glove box using a constant pressure dropping method (dropping rate of 1.2 drops / second). During the process, the electrolyte density is monitored in real time using a precision densitometer. The amount of lithium difluorooxalate borate (LiODFB) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) mixture is adjusted according to the density-concentration correspondence. Finally, the electrolyte concentration is controlled to 1.4 mol / L to obtain the composite lithium salt electrolyte.

[0064] Step S4: Vinyl carbonate (VC, accounting for 2% of the mass of the composite lithium salt electrolyte) and triethyl phosphate (TEP, accounting for 2% of the mass of the composite lithium salt electrolyte) are filtered through a 0.22μm polytetrafluoroethylene (PTFE) filter membrane, respectively, and added to the composite lithium salt electrolyte under nitrogen protection. The mixture is stirred at a rate of 280 r / min for 25 minutes. After stirring, the mixture is sealed with a PTFE stopper and a stainless steel clamp. Fluororubber sealant is applied to the contact area between the stopper and the bottle mouth. The mixture is then allowed to stand for 24 hours at 23℃ and relative humidity ≤30% to obtain a wide-temperature electrolyte.

[0065] Step S5, the detection results are as follows: Conductivity: Measured every 10℃ within the range of -60℃ to 80℃. The conductivity is 1.4 mS / cm at -40℃ and 12.5 mS / cm at 60℃, which meets the requirements.

[0066] Moisture content: 11 ppm as determined by Karl-Fisher coulometric method, which meets the standard of ≤20 ppm.

[0067] Viscosity: The viscosity is 165 mPa·s at -40℃, 7.2 mPa·s at 25℃, and 8.0 mPa·s at 60℃, all within the specified range.

[0068] Electrochemical stability: Linear sweep voltammetry (LSV) testing showed that the oxidation potential of Example 4 was lower than that of the base electrolyte. Figure 3 Its oxidation potential is 4.6V (vs. Li). + / Li), indicating that lithium salts and composite functional additives can reduce the oxidation level of the electrolyte under high voltage. Furthermore, cyclic voltammetry (CV) tests showed no significant side reaction peaks in the range of 2.8–4.3 V (using Nickel-Cobalt-Manganese 622 as the positive electrode). Figure 4 Furthermore, the potential difference between the redox peaks decreased from 0.8 V to 0.49 V compared to the basic electrolyte. The synergistic effect of high-concentration lithium salt and composite functional additives can reduce the polarity of the cathode material during electrochemical processes and improve reversibility.

[0069] Safety: Thermogravimetric analysis (TGA) showed a mass loss rate of 2.2% below 200℃. In the combustion test, the electrolyte self-extinguished within 1.8 seconds after ignition, meeting safety standards. The high concentration of lithium salt and composite functional additives synergistically improved the overall performance of the electrolyte.

[0070] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0071] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a wide-temperature-range electrolyte, characterized in that, Using 1M LiPF6 / EC:EMC (3:7) as the base electrolyte, the following steps are included: Step S1: Place the 1M LiPF6 / EC:EMC (3:7) basic electrolyte into a tetrafluoroethylene bottle. The tetrafluoroethylene bottle must be vacuum dried at a temperature of 80-100 ℃ for 4-6 hours to remove residual moisture from the bottle. Step S2: Add at least one organic reagent to the 1M LiPF6 / EC:EMC (3:7) basic electrolyte and stir evenly in a constant temperature water bath at 25-35℃. The stirring rate is 300-500 r / min and the stirring time is 30-60 minutes to obtain the multi-component co-solvent system electrolyte. Step S3: Add at least one lithium salt to the multi-component co-solvent electrolyte system by constant pressure dropping at a rate of 1-2 drops / second. After the dropping is completed, adjust the electrolyte concentration to 1.0-1.5 mol / L to obtain a composite lithium salt electrolyte. Step S4: Add at least one functional additive to the composite lithium salt electrolyte and stir evenly under an inert gas protective atmosphere. The stirring rate is 200-300 r / min and the stirring time is 20-40 minutes. Then seal and let stand for 22-26 hours to obtain a wide-temperature electrolyte. Step S5: Test the wide-temperature electrolyte.

2. The method for preparing a wide-temperature electrolyte as described in claim 1, characterized in that: In step S2, the organic reagents include, but are not limited to, propylene carbonate (PC), diethyl carbonate (DEC), ethyl acetate (EA), and γ-butyrolactone (GBL), and the amount of the organic reagents added accounts for 5%-15% of the mass of the 1MLiPF6 / EC:EMC (3:7) base electrolyte. When multiple organic reagents are added at the same time, the mass ratio of each organic reagent needs to be adjusted according to the low-temperature performance requirements of the target electrolyte.

3. The method for preparing a wide-temperature electrolyte as described in claim 1, characterized in that: In step S3, the lithium salt includes, but is not limited to, lithium difluorooxalate borate (LiODFB) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI). The amount of lithium salt added should be such that the total lithium concentration in the composite lithium salt electrolyte meets the requirement of 1.0-1.5 mol / L. Before addition, the lithium salt needs to be vacuum dried at a temperature of 120-150°C for 8-10 hours to reduce the moisture content in the lithium salt to below 50 ppm.

4. The method for preparing a wide-temperature electrolyte as described in claim 1, characterized in that: In step S4, the functional additives include, but are not limited to, film-forming additives and positive electrode protection additives. The film-forming additives include, but are not limited to, vinylene carbonate (VC) and fluoroethylene carbonate (FEC). The amount of film-forming additives added accounts for 1%-5% of the mass of the composite lithium salt electrolyte. The positive electrode protection additives include, but are not limited to, trimethyl phosphate (TMP) and triethyl phosphate (TEP). The amount of positive electrode protection additives added accounts for 0.5%-2% of the mass of the composite lithium salt electrolyte. The functional additives must be filtered through a 0.22μm polytetrafluoroethylene filter membrane before being added to remove impurity particles.

5. The method for preparing a wide-temperature electrolyte as described in claim 1, characterized in that: In step S4, the electrolyte is allowed to stand for 24 hours, and the ambient temperature is controlled at 20-25℃ and the relative humidity is ≤30%.

6. The method for preparing a wide-temperature electrolyte as described in claim 1, characterized in that: In step S5, the detection content includes, but is not limited to, the following items: Conductivity testing: The conductivity of the electrolyte was measured every 10℃ in the temperature range of -60℃ to 80℃ using a conductivity meter. The conductivity was required to be ≥1mS / cm at -40℃ and ≥10mS / cm at 60℃. Moisture content detection: The moisture content of the electrolyte was determined using a Karl-Fisher coulometric moisture analyzer, and the moisture content was required to be ≤20ppm; Viscosity testing: The viscosity of the electrolyte was measured at three temperature points: -40℃, 25℃, and 60℃ using a rotational viscometer. The viscosity was required to be ≤200 mPa·s at -40℃ and ≤10 mPa·s at 60℃. Electrochemical stability testing: The oxidation potential of the electrolyte was tested using linear sweep voltammetry (LSV), requiring an oxidation potential ≥ 4.5V (vs. Li). + / Li), the reduction stability of the electrolyte was tested by cyclic voltammetry (CV), requiring no obvious side reaction peaks in the range of 2.8-4.3 V (with nickel-cobalt-manganese 622 as the positive electrode); Safety testing: Thermogravimetric analysis (TGA) is used to test the mass change of the electrolyte in the range of 100-300℃. The mass loss rate is required to be ≤5% below 200℃. At the same time, the electrolyte combustion test is carried out, and the electrolyte is required to extinguish itself within 3 seconds after being ignited.

7. The method for preparing a wide-temperature electrolyte as described in claim 1, characterized in that: In step S2, in addition to adding the organic reagent to the 1M LiPF6 / EC:EMC (3:7) basic electrolyte, nano-ceramic particles (two or one of Al2O3 and CeO2) can also be added simultaneously. The amount of nano-ceramic particles added accounts for 0.1%-1% of the mass of the 1M LiPF6 / EC:EMC (3:7) basic electrolyte, and after addition, ultrasonic dispersion treatment is required. The ultrasonic power is 300-500W and the ultrasonic time is 15-30 minutes.

8. The method for preparing a wide-temperature electrolyte as described in claim 1, characterized in that: In step S3, when adjusting the electrolyte concentration, a precision densitometer is used to monitor the electrolyte density in real time. The amount of lithium salt added is adjusted according to the relationship between density and concentration to ensure that the control accuracy of the electrolyte concentration is within ±0.05 mol / L.

9. The method for preparing a wide-temperature electrolyte as described in claim 1, characterized in that: In step S4, the sealing is achieved by using a polytetrafluoroethylene (PTFE) sealing plug in conjunction with a stainless steel clamp. Before sealing, a layer of fluororubber sealant must be applied to the contact area between the sealing plug and the bottle opening.

10. The method for preparing a wide-temperature electrolyte as described in claim 1, characterized in that: The entire preparation process must be carried out in a glove box, where the water and oxygen content is controlled to be below 0.1 ppm.

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