Preparation method of low-temperature-resistant and high-voltage-resistant electrolyte

Abstract

The invention discloses a preparation method of a low-temperature-resistant and high-voltage electrolyte in the technical field of high-performance electrolyte of a secondary battery, which is characterized in that the electrolyte with low melting point, low viscosity and wide electrochemical stability window is prepared by creating a pressure environment, taking halogenated hydrocarbon, dimethyl ether and lithium salt as raw materials and increasing the number of freely movable Li < + > of the electrolyte; the process is stable, the safety is high, the melting point of the prepared electrolyte is lower than-60 DEG C, the electrochemical stability window is 4.5-4.8 V, the electrolyte is suitable for low-temperature and high-voltage lithium ion batteries, the core energy storage requirements in the fields of consumer electronics, new energy automobiles, energy storage equipment and the like can be met, the electrolyte is suitable for low-temperature scenes such as cold regions and high-altitude operation, and the electrolyte is suitable for industrial production and has wide application prospects. And a new thought is provided for the battery to adapt to requirements in an extreme environment.

Description

Technical Field

[0001] This invention relates to the field of high-performance electrolysis technology for secondary batteries, and in particular to a method for preparing an electrolyte. Background Technology

[0002] To meet the core energy storage needs of consumer electronics, new energy vehicles, and energy storage equipment, developing lithium-ion batteries with high energy density and long cycle life is crucial. As application areas continue to expand, the adaptability of batteries to extreme environments, such as low temperatures and high pressures, is increasingly important. Currently used electrolytes mostly use esters and ethers as organic solvents. These solvents have strong intermolecular forces, high viscosity, and melting points above room temperature. In environments below -20°C, the ionic conductivity of the electrolyte decreases significantly, leading to a substantial drop in battery capacity and cycle performance, making it difficult to adapt to low-temperature scenarios such as cold regions and high-altitude operations. Furthermore, traditional electrolytes have a narrow electrochemical stability window and are prone to decomposition under high voltage systems, which also limits further improvements in battery energy density.

[0003] While some existing technologies attempt to improve low-temperature performance by adding low-temperature additives or optimizing solvent ratios (Chen Chen, Liu Yang. Methods for improving the low-temperature performance of lithium-ion batteries [J]. Electronic Engineering Album, 2021), they often suffer from limited low-temperature effects, poor compatibility with high-voltage systems, and complex preparation processes (PING L, CHENG FY, et al. Modulating interfacial solvation via ion dipole interactions for low-temperature and high-voltage lithium batteries [J]. Angewandte Chemie International Edition, 2025.). Furthermore, existing electrolyte preparation methods are mostly designed for conventional solvent systems, with insufficient research on preparation processes for special media such as hydrofluoroolefins. Therefore, developing a stable preparation method that can produce electrolytes with both -60°C low-temperature resistance and a wide electrochemical stability window has become a pressing technical challenge in this field. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a method for preparing a low-temperature, high-pressure electrolyte. By introducing hydrofluoroolefins into a pressure environment, an electrolyte with a low melting point, low viscosity, and a wide electrochemical stability window can be stably prepared. The process is simple, safe, and suitable for industrial production.

[0005] The objective of this invention is achieved as follows: a method for preparing a low-temperature, high-voltage resistant electrolyte, comprising the following steps: Step (1) Select hydrofluoroolefins, dimethyl ether, and lithium salt as raw materials, wherein the hydrofluoroolefins are selected from one or more of 2,3,3,3-tetrafluoropropene (HFO-1234yf), 1,3,3,3-tetrafluoropropene (HFO-1234ze, including E-type and Z-type isomers), 2,3,3,3-tetrafluoro-1-propene (HFO-1233zd), 1,2,3,3,3-pentafluoropropene (HFO-1224yd), and 1,1,1,2,3,3,3-heptafluoropropene (HFO-1216); and the lithium salt is selected from one or more of lithium hexafluorophosphate (LiPF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium tetrafluoroborate (LiBF4), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonylimide, lithium nitrate (LiNO3), and lithium perchlorate (LiClO4). Step (2) Under the protection of an inert gas, the hydrofluoroolefin and dimethyl ether are added to a sealed pressure vessel, the system pressure is adjusted to 0.3-0.8 MPa, and the mixture is stirred until a homogeneous and transparent mixed solvent is formed. Step (3) The lithium salt is added to the mixed solvent in batches, the system pressure is kept stable at 0.3 to 0.8 MPa, and the mixture is stirred until the lithium salt is completely dissolved to obtain a colorless and transparent electrolyte, wherein the total concentration of lithium salt is 0.8 to 3.0 mol / L.

[0006] Furthermore, in step (1), the lithium salt is ground to a particle size ≤ 50 μm for later use, in order to improve the dissolution rate and uniformity of the lithium salt.

[0007] Furthermore, the hydrofluoroolefin is a composite hydrofluoroolefin, which is premixed from two or more hydrofluoroolefins in a mass ratio of 0.5:1 to 6:1 to enhance the low melting point and low viscosity characteristics of the solvent; preferably, it is a mixture of HFO-1234yf and HFO-1234ze in a mass ratio of 0.5 to 4:1, or a mixture of HFO-1233zd and HFO-1216 in a mass ratio of 1 to 6:1 to optimize the low temperature resistance of the electrolyte down to -60 °C.

[0008] Furthermore, the lithium salt is a composite lithium salt, which is formed by pre-mixing two or more lithium salts in a molar ratio of 0.5:1 to 4:1 in a dry environment with a water oxygen content of less than 0.1 ppm to improve ionic conductivity and electrochemical stability; preferably, it is a mixture of LiFSI and LiPF6 in a molar ratio of 0.5 to 4:1, or a mixture of LiTFSI and LiBF4 in a molar ratio of 0.5 to 4:1, to form a stable solvation structure.

[0009] Furthermore, the mass ratio of the hydrofluoroolefin to the dimethyl ether is 0.5:1 to 6:1, and the total mass is 10 to 35 g, in order to achieve low viscosity and a wide electrochemical window.

[0010] Furthermore, the pressure vessel is made of corrosion-resistant alloy material, including Hastelloy or Monel alloy, and the inner wall is passivated; before step (2), the inside of the vessel is replaced with high-purity inert gas at least 3 times to ensure that the water oxygen content is less than 0.1 ppm, so as to prevent the introduction of impurities and reaction byproducts.

[0011] Furthermore, in step (2), the hydrofluoroolefin and dimethyl ether are added at a flow rate of 0.5 to 0.9 g / min and stirred for 30 to 60 min to ensure the uniformity and transparency of the mixed solvent.

[0012] Furthermore, the lithium salt is added in batches of 2 to 3 times, with each addition being 1 / 3 to 1 / 2 of the total amount, with an interval of 30 to 60 minutes. During the addition process, an inert gas protection is maintained to prevent air from entering. The mixture is stirred for a total of 2 to 4 hours, thereby improving the dissolution efficiency of high-concentration lithium salt and reducing the risk of precipitation.

[0013] Furthermore, before step (3), the lithium salt is dried at 100-120 °C for 10-12 h to remove surface adsorbed water and improve the purity and stability of the electrolyte. The preparation method is carried out at room temperature, and the system pressure is monitored in real time throughout the process to ensure that the fluctuation range is controlled within ±0.02 MPa in order to maintain the stability and safety of the reaction system.

[0014] Furthermore, the electrolyte has an electrochemical window of 0–4.8 V, and lithium ions are efficiently transported through a vehicle-type transport mechanism, thereby maintaining stability and ionic conductivity at low temperatures of -60 °C and high voltages greater than 0.5 MPa, making it suitable for high-performance applications of lithium-ion batteries.

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows: The electrolyte of the present invention has an electrochemical window exceeding 4.3V, which is suitable for the working requirements of high-voltage full batteries. Furthermore, the full battery with this electrolyte exhibits significant advantages in cycle stability, high-rate performance, and low-temperature adaptability. Existing conventional electrolytes with low electrochemical windows are prone to rapid capacity decay due to electrolyte decomposition at high voltages, limiting high-rate performance, and they fail directly at -40℃ (Qin M, Zeng Z, Wu Q, et al. Microsolvating competition in Li +Solvation structure affording PC-based electrolyte with fast kinetics for lithium-ion batteries[J]. Advanced Functional Materials, 2024, 34(35):2406357), and the electrolyte of this invention, when used with a full battery, has a better overall electrochemical performance than existing similar products. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0017] Figure 1 The electrochemical window test results are for the electrolyte prepared in Example 1 of this invention.

[0018] Figure 2 The impedance spectrum test results of the electrolyte prepared in Example 2 of this invention at different temperatures are shown. Detailed Implementation

[0019] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0020] In the following embodiments: Raw material specifications: Hydrofluoroolefins (HFO-1234yf, HFO-1234ze, HFO-1233zd, HFO-1216) all have a purity of 99.8%, dimethyl ether has a purity of 99.7%, and lithium salts (LiFSI, LiPF6, LiTFSI, LiBF4) all have a purity of 99.95%. Pressure vessel: made of Hastelloy alloy, with passivated inner wall, 5L volume. Example 1

[0021] Step 1: Select HFO-1234yf (99.8% purity), dimethyl ether (99.7% purity), and LiFSI and LiPF6 (99.95% purity) as raw materials. Mix LiFSI and LiPF6 in a dry glove box (water and oxygen content <0.1ppm) at a molar ratio of 4:1 to obtain a composite lithium salt for later use. Simultaneously, check the sealing of the pressure vessel (Hastelloy alloy material, passivated inner wall, 5L volume) to ensure the valves, pressure gauge, and stirring device are functioning properly. Purge the inside of the vessel three times with high-purity argon to remove air and moisture.

[0022] Step 2: At room temperature (25°C), place 30g of HFO-1234yf and 5g of dimethyl ether in a sealed pressure vessel and slowly add them at a flow rate of 0.9g / min. After all raw materials have been added, close the feed valve, adjust the system pressure to 0.5MPa, start the stirring device, and stir continuously for 60 minutes. Monitor the system pressure in real time to ensure that its fluctuation range is controlled within ±0.02MPa until the mixture is homogeneous and transparent.

[0023] Step 3: Calculate the total amount of the prepared composite lithium salt based on a total concentration of 3.0 mol / L. Add it in batches to the mixed solvent in two portions, each time adding half of the total amount, with a 40-minute interval between each addition. After the first addition of lithium salt, maintain the pressure inside the container at 0.5 MPa and stir. After the interval, open the inlet and quickly add the remaining lithium salt (maintain argon protection during the feeding process to prevent air from entering), and continue stirring at the same rate. The total stirring time is 3 hours, until the lithium salt is completely dissolved, resulting in a colorless and transparent electrolyte that is resistant to low temperatures and high pressures.

[0024] In the reduction limiting potential test, copper foil was used as the working electrode and aluminum foil as the counter electrode. In the oxidation limiting potential test, aluminum foil was used as the working electrode and copper foil as the counter electrode. The electrochemical window range of the two-phase electrolyte was measured to be 0~4.8V. Figure 1 ), while commercial mainstream carbonate electrolytes undergo significant oxidative decomposition at 4.3V, with an electrochemical window of only 3.0~4.3V (Lv H, Li X, Wang Y, et al. Fluorinated Electrolyte Additives for High‐Voltage Lithium‐Ion Batteries[J]. Langmuir, 2013, 29(30):9342-9349). Example 2

[0025] Step 1: Select HFO-1234ze (Type E) and HFO-1234yf (99.8% purity), dimethyl ether (99.7% purity), and LiTFSI and LiBF4 (99.95% purity) as raw materials. Mix HFO-1234ze (Type E) and HFO-1234yf uniformly at a mass ratio of 1:4 to obtain a composite hydrofluoroolefin. Mix LiTFSI and LiBF4 uniformly in a dry glove box at a molar ratio of 4:1 to obtain a composite lithium salt for later use. Check the sealing of the 5L Hastelloy pressure vessel by purging the internal air three times with high-purity argon to ensure that the water and oxygen content is <0.1ppm.

[0026] Step 2: At room temperature (25°C), place 15g of the complex hydrofluoroolefin and 5g of dimethyl ether in a sealed pressure vessel and slowly add them at a flow rate of 0.6g / min. After all raw materials have been added, close the feed valve, adjust the system pressure to 0.4MPa, start the stirring device, and stir continuously for 40 minutes. Monitor the system pressure in real time to ensure that its fluctuation range is controlled within ±0.02MPa until the mixture is homogeneous and transparent.

[0027] Step 3: Calculate the total amount of the prepared composite lithium salt based on a total concentration of 1.0 mol / L. Add it to the mixed solvent in three batches, each time adding 1 / 3 of the total amount, with a 30-minute interval between each addition. After the first addition of lithium salt, maintain the pressure inside the container at 0.4 MPa and stir. After the interval, open the inlet and quickly add the remaining lithium salt (maintain argon protection during the feeding process to prevent air from entering), and continue stirring at the same rate. The total stirring time is 3 hours, until the lithium salt is completely dissolved, resulting in a colorless and transparent electrolyte that is resistant to low temperatures and high pressures.

[0028] The prepared electrolyte has Li + Impedance spectroscopy tests were performed on the material at different temperatures using a "vehicle-type transmission" mechanism. Figure 2 ). Example 3

[0029] Step 1: Select HFO-1233zd and HFO-1216 with a purity of 99.8%, dimethyl ether with a purity of 99.7%, and LiFSI with a purity of 99.95% as raw materials. Mix HFO-1233zd and HFO-1216 in a mass ratio of 6:1 beforehand to obtain a composite hydrofluoroolefin for later use. Check the sealing performance of the 5L Hastelloy pressure vessel by purging the internal air three times with high-purity argon to ensure that the water and oxygen content is <0.1ppm; simultaneously, place the LiFSI in a drying oven and dry it at 120°C for 12 hours to remove surface adsorbed water.

[0030] Step 2: At room temperature (25°C), place 5g of the complex hydrofluoroolefin and 10g of dimethyl ether in a sealed pressure vessel and slowly add them at a flow rate of 0.5g / min. After all raw materials have been added, close the feed valve, adjust the system pressure to 0.6MPa, start the stirring device, and stir continuously for 30 minutes. Monitor the system pressure in real time to ensure that its fluctuation range is controlled within ±0.02MPa until the mixture is homogeneous and transparent.

[0031] Step 3: Calculate the total amount of dried LiFSI to be used at a concentration of 0.8 mol / L. Add it in two batches to the mixed solvent, each time adding half of the total amount, with a 50-minute interval between each addition. After the first addition of LiFSI, maintain the pressure inside the container at 0.6 MPa and stir. After the interval, quickly add the remaining LiFSI (maintain argon protection during the feeding process to prevent air from entering), and continue stirring at the same rate. The total stirring time is 3.5 hours, until the LiFSI is completely dissolved, resulting in a colorless and transparent electrolyte that is resistant to low temperatures and high pressures. Example 4

[0032] Step 1: Select HFO-1234yf with a purity of 99.8%, dimethyl ether with a purity of 99.7%, and LiPF6 with a purity of 99.95% as raw materials. Check the sealing performance of the pressure vessel (Hastelloy alloy material, passivated inner wall, 5L volume) to ensure that the valves, pressure gauges, and stirring devices are operating normally. Then, purge the inside of the vessel three times with high-purity argon gas to remove air and moisture.

[0033] Step 2: At room temperature (25°C), place 20g of HFO-1234yf and 5g of dimethyl ether in a sealed pressure vessel and slowly add them at a flow rate of 0.7g / min. After all raw materials have been added, close the feed valve, adjust the system pressure to 0.5MPa, start the stirring device, and stir continuously for 50 minutes. Monitor the system pressure in real time to ensure that its fluctuation range is controlled within ±0.02MPa until the mixture is homogeneous and transparent.

[0034] Step 3: Calculate the total amount of lithium salt to be used based on a total concentration of 1.5 mol / L. Add the lithium salt in two batches to the mixed solvent, each batch containing half the total amount, with a 40-minute interval between each addition. After the first addition of lithium salt, maintain the pressure inside the container at 0.5 MPa and stir. After the interval, open the inlet and quickly add the remaining lithium salt (maintaining argon protection during the feeding process to prevent air from entering), and continue stirring at the same rate. The total stirring time is 3 hours, until the lithium salt is completely dissolved, resulting in a colorless and transparent electrolyte that is resistant to low temperatures and high pressures. Example 5

[0035] Step 1: Select HFO-1224yd (99.8% purity), dimethyl ether (99.7% purity), and LiPF6 (99.95% purity) as raw materials. Check the sealing of the 5L Hastelloy pressure vessel, and replace the internal air three times with high-purity argon to ensure that the water and oxygen content is <0.1ppm. Simultaneously, place the LiPF6 in a drying oven and dry it at 100°C for 10 hours to remove surface adsorbed water for later use.

[0036] Step 2: At room temperature (25°C), place 10g of HFO-1224yd and 10g of dimethyl ether in a sealed pressure vessel and slowly add them at a flow rate of 0.6g / min. After all raw materials have been added, close the feed valve, adjust the system pressure to 0.3MPa, start the stirring device, and stir continuously for 50 minutes. Monitor the system pressure in real time to ensure that its fluctuation range is controlled within ±0.02MPa until the mixture is homogeneous and transparent.

[0037] Step 3: Calculate the total amount of dried LiPF6 to be used at a concentration of 2.0 mol / L. Add it in two batches to the mixed solvent, each time adding half of the total amount, with a 60-minute interval between each addition. After the first addition of LiPF6, maintain the pressure inside the container at 0.3 MPa and stir. After the interval, open the inlet and quickly add the remaining LiPF6 (maintain argon protection during the feeding process to prevent air from entering), and continue stirring at the same rate. The total stirring time is 4 hours, until the LiPF6 is completely dissolved, resulting in a colorless and transparent electrolyte that is resistant to low temperatures and high pressures.

[0038] The above description of the embodiments is only for the purpose of helping to understand the method and core ideas of the present invention. It should be noted that those skilled in the art can make several improvements and modifications to the present invention without departing from the principles of the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

Claims

1. A method for preparing a low-temperature, high-voltage resistant electrolyte, characterized in that, Includes the following steps: Step (1) Select hydrofluoroolefins, dimethyl ether, and lithium salts as raw materials, wherein the hydrofluoroolefins are selected from one or more of 2,3,3,3-tetrafluoropropene, 1,3,3,3-tetrafluoropropene, 2,3,3,3-tetrafluoro-1-propene, 1,2,3,3,3-pentafluoropropene, and 1,1,1,2,3,3,3-heptafluoropropene; and the lithium salts are selected from one or more of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium tetrafluoroborate, lithium bis(trifluoromethyl)sulfonylimide, lithium trifluoromethanesulfonylimide, lithium nitrate, and lithium perchlorate. Step (2) Under the protection of an inert gas, the hydrofluoroolefin and dimethyl ether are added to a sealed pressure vessel, the system pressure is adjusted to 0.3-0.8 MPa, and the mixture is stirred until a homogeneous and transparent mixed solvent is formed. Step (3) The lithium salt is added to the mixed solvent in batches, the system pressure is kept stable at 0.3 to 0.8 MPa, and the mixture is stirred until the lithium salt is completely dissolved to obtain a colorless and transparent electrolyte, wherein the total concentration of lithium salt is 0.8 to 3.0 mol / L.

2. The preparation method according to claim 1, characterized in that, In step (1), the lithium salt is ground to a particle size ≤50 μm for later use, in order to improve the dissolution rate and uniformity of the lithium salt.

3. The preparation method according to claim 1, characterized in that, The hydrofluoroolefin is a composite hydrofluoroolefin, which is formed by pre-mixing two or more hydrofluoroolefins in a mass ratio of 0.5:1 to 6:1 to enhance the low melting point and low viscosity characteristics of the solvent.

4. The preparation method according to claim 1, characterized in that, The lithium salt is a composite lithium salt, which is prepared by pre-mixing two or more lithium salts in a molar ratio of 0.5:1 to 4:1 in a dry environment with a water oxygen content of less than 0.1 ppm, in order to improve ionic conductivity and electrochemical stability.

5. The preparation method according to claim 1, characterized in that, The mass ratio of the hydrofluoroolefin to the dimethyl ether is 0.5:1 to 6:1, and the total mass is 10 to 35 g, in order to achieve low viscosity and a wide electrochemical window.

6. The preparation method according to claim 1, characterized in that, The pressure vessel is made of corrosion-resistant alloy material, including Hastelloy or Monel alloy, and the inner wall is passivated. Before step (2), the inside of the vessel is replaced with high-purity inert gas at least 3 times to ensure that the water oxygen content is less than 0.1 ppm, so as to prevent the introduction of impurities and reaction byproducts.

7. The preparation method according to claim 1, characterized in that, In step (2), the hydrofluoroolefin and dimethyl ether are added at a flow rate of 0.5 to 0.9 g / min and stirred for 30 to 60 min to ensure the homogeneity and transparency of the mixed solvent.

8. The preparation method according to claim 1, characterized in that, In step (3), the lithium salt is added in batches of 2 to 3 times, each time adding 1 / 3 to 1 / 2 of the total amount, with an interval of 30 to 60 minutes. During the addition process, an inert gas protection is maintained to prevent air from entering. The mixture is stirred for a total of 2 to 4 hours, thereby improving the dissolution efficiency of high-concentration lithium salt and reducing the risk of precipitation.

9. The preparation method according to claim 1, characterized in that, Before step (3), the lithium salt is dried at 100-120°C for 10-12 h to remove surface adsorbed water and improve the purity and stability of the electrolyte. The preparation method is carried out at room temperature, and the system pressure is monitored in real time throughout the process to ensure that the fluctuation range is controlled within ±0.02 MPa in order to maintain the stability and safety of the reaction system.

10. The preparation method according to any one of claims 1 to 9, characterized in that, The electrolyte has an electrochemical window of 0–4.8 V, and lithium ions are efficiently transported through a vehicle-type transport mechanism, thereby maintaining stability and ionic conductivity at low temperatures of -60 °C and high voltages of greater than 0.5 MPa, making it suitable for high-performance applications of lithium-ion batteries.

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