Ionic liquid with excellent thermal stability for lithium battery and preparation method of ionic liquid

Abstract

The invention relates to the field of lithium batteries, in particular to an ionic liquid with excellent thermal stability for a lithium battery and a preparation method of the ionic liquid, and aims to solve the problem that the performance and the safety of the lithium ion battery are influenced due to the fact that the thermal stability of the traditional ionic liquid is reduced because the traditional ionic liquid is easy to decompose at a high temperature. The ionic liquid is composed of a large number of imidazole cations and hexafluorophosphoric acid anions, rapid charging and discharging of a lithium battery are achieved, the ionic liquid is of a high-crosslinking-degree polymer structure, after a benzene ring and a large number of phosphorus elements are introduced into the ionic liquid, the thermal stability of the ionic liquid can be improved, the ionic liquid is not prone to decomposition at high temperature, and the service life of the ionic liquid is prolonged. The high-temperature cycling stability of the lithium battery is further ensured, so that the risks of short circuit and thermal runaway of the lithium battery are avoided, the safety of the lithium battery is improved, the service life of the lithium battery is prolonged, and the preparation method is simple in operation, easy in raw material obtaining, low in cost and suitable for large-scale industrial production.

Description

Technical Field

[0001] The present invention relates to the field of lithium batteries, and in particular to an ionic liquid with excellent thermal stability for lithium batteries and a preparation method thereof. Background Art

[0002] With the increasing energy crisis and environmental pollution, the development of new high-performance energy storage devices has become a hot topic in current research. As a new type of energy storage device, lithium-ion batteries have the advantages of high energy density, long cycle life, and no memory effect. They have been widely used in electric vehicles, mobile electronic devices and other fields. However, traditional organic solvents have poor thermal stability and safety in high temperature environments, and are prone to decomposition and combustion. As a result, lithium-ion batteries generate a lot of heat during use, causing the battery temperature to rise, thereby affecting the performance and safety of the battery. Therefore, improving the thermal stability of lithium-ion batteries has become one of the important directions of current lithium-ion battery research.

[0003] Ionic liquids are salt substances composed of anions and cations that are liquid at room temperature or near room temperature. They have the advantages of low vapor pressure, good thermal stability, and a wide electrochemical window, and have been widely used in lithium-ion batteries. However, traditional ionic liquids are easily decomposed at high temperatures, resulting in a decrease in their thermal stability, which affects the performance and safety of lithium-ion batteries. Therefore, the development of an ionic liquid with excellent thermal stability is of great significance for improving the performance and safety of lithium-ion batteries. Summary of the invention

[0004] In order to overcome the above-mentioned technical problems, the purpose of the present invention is to provide an ionic liquid with excellent thermal stability for lithium batteries and a preparation method thereof, which solves the problem that traditional ionic liquids are easily decomposed at high temperatures, resulting in a decrease in their thermal stability, thereby affecting the performance and safety of lithium-ion batteries.

[0005] The purpose of the present invention can be achieved through the following technical solutions:

[0006] A method for preparing an ionic liquid with excellent thermal stability for a lithium battery comprises the following steps:

[0007] Step 1: neopentyl glycol and chloroform are added to a four-necked flask equipped with a stirrer, a thermometer, an air guide tube, a constant pressure dropping funnel and a reflux condenser, and nitrogen is introduced for protection. The mixture is stirred for reaction for 20-30 minutes at a temperature of 25-30° C. and a stirring rate of 300-400 r / min, and then phosphorus oxychloride is added dropwise while stirring, and the dropping rate is controlled to be 1-2 drops / s. After the addition is completed, the mixture is heated to 50-55° C. and the stirring reaction is continued for 2-3 hours, and then the mixture is heated to reflux and the stirring reaction is continued for 6-8 hours. After the reaction is completed, the reaction product is cooled to room temperature, and then the solvent is removed by rotary evaporation, and then the mixture is washed with distilled water 2-3 times, and then placed in a vacuum drying oven and dried at a temperature of 60-65° C. for 2-3 hours to obtain intermediate 1;

[0008] Step 2: Add intermediate 1, 1-(1H-imidazol-1-yl)propan-2-ol, triethylamine and anhydrous acetonitrile to a three-necked flask equipped with a stirrer, a thermometer and a gas guide tube, introduce nitrogen protection, stir the reaction at a temperature of 25-30°C and a stirring rate of 300-400r / min for 1-1.5h, then heat to 80-85°C and continue stirring the reaction for 10-12h. After the reaction is completed, cool the reaction product to room temperature, then rotary evaporate to remove the solvent, then pour into ice water, then extract with chloroform 2-3 times, combine the extracts and rotary evaporate to remove the solvent to obtain intermediate 2;

[0009] Step 3: Add the intermediate 2, 3-bromo-1-propylene, anhydrous potassium carbonate, hydroquinone and anhydrous ether to a three-necked flask equipped with a stirrer, a thermometer, an air guide tube and a reflux condenser, introduce nitrogen protection, stir the reaction for 15-20 minutes at a temperature of 25-30°C and a stirring rate of 300-400r / min, then heat to reflux and continue stirring the reaction for 4-5 hours. After the reaction is completed, the reaction product is cooled to room temperature, and then the solvent is removed by rotary evaporation, and then washed with saturated brine 2-3 times, and then placed in a vacuum drying oven, and dried at a temperature of 50-55°C for 3-4 hours to obtain a phosphorus-containing imidazole monomer;

[0010] Step 4: 1-vinylimidazole, styrene, phosphorus-containing imidazole monomer, azobisisobutyronitrile, anhydrous ethanol, deionized water and ethyl acetate are added to a three-necked flask equipped with a stirrer, a thermometer, an air guide tube and a reflux condenser, and nitrogen is introduced for protection. The mixture is stirred for reaction at a temperature of 25-30° C. and a stirring rate of 300-400 r / min for 8-10 minutes, and then the mixture is heated to reflux and stirred for reaction for 20-25 hours. After the reaction is completed, the reaction product is cooled to room temperature, and then vacuum filtered. The filter cake is washed with anhydrous methanol for 2-3 times, and then placed in a vacuum drying oven and dried at a temperature of 50-55° C. for 2-3 hours to obtain phosphorus-containing phenyl polyimidazole;

[0011] Step 5: Add phosphorus-containing phenyl polyimidazole, 1,6-dibromohexane, anhydrous potassium carbonate and anhydrous acetone to a three-necked flask equipped with a stirrer, a thermometer and an air guide tube, introduce nitrogen protection, stir the reaction at a temperature of -5-0°C and a stirring rate of 300-400r / min for 20-30min, then heat to 50-55°C and continue stirring the reaction for 5-6h. After the reaction is completed, the reaction product is cooled to room temperature, and then the solvent is removed by rotary evaporation, and then poured into n-hexane, and then centrifuged. The precipitate is placed in a vacuum drying oven and dried at a temperature of 70-75°C for 4-5h to obtain a cationic polyimidazole;

[0012] Step six: Add cationic polyimidazole, ammonium hexafluorophosphate, deionized water and anhydrous ethanol to a three-necked flask equipped with an agitator, a thermometer and an air duct, introduce nitrogen protection, stir the reaction at a temperature of 25-30°C and a stirring rate of 300-400r / min for 1-2h, then heat the temperature to 65-70°C and continue stirring the reaction for 20-25h. After the reaction is completed, the reaction product is cooled to room temperature, then vacuum filtered, and the filtrate is extracted with anhydrous acetonitrile 2-3 times. The extracts are combined and rotary evaporated to remove the solvent, and then placed in a vacuum drying oven and dried at a temperature of 60-65°C for 10-15h to obtain an ionic liquid with excellent thermal stability for lithium batteries.

[0013] As a further solution of the present invention: the usage ratio of the neopentyl glycol, chloroform and phosphorus oxychloride in step 1 is 0.1 mol: 50-55 mL: 0.1 mol.

[0014] As a further scheme of the present invention: the usage ratio of the intermediate 1, 1-(1H-imidazol-1-yl)propan-2-ol, triethylamine and anhydrous acetonitrile in step 2 is 30 mmol: 30 mmol: 2.5-3.5 mL: 40-50 mL.

[0015] As a further scheme of the present invention: the usage ratio of the intermediate 2,3-bromo-1-propylene, anhydrous potassium carbonate, hydroquinone and anhydrous ether in step 3 is 20mmol:22-25mmol:25-30mmol:0.01-0.05g:50-60mL.

[0016] As a further scheme of the present invention: the usage ratio of the 1-vinylimidazole, styrene, phosphorus-containing imidazole monomer, azobisisobutyronitrile, anhydrous ethanol, deionized water and ethyl acetate in step 4 is 10mmol: 5-9mmol: 3-13mmol: 2-2.6g: 5-8mL: 5-8mL: 25-35mL.

[0017] As a further solution of the present invention: the usage ratio of the phosphorus-containing phenyl polyimidazole, 1,6-dibromohexane, anhydrous potassium carbonate and anhydrous acetone in step five is 5g:30-50mmol:35-55mmol:100-120mL.

[0018] As a further solution of the present invention: the usage ratio of the cationic polyimidazole, ammonium hexafluorophosphate, deionized water and anhydrous ethanol in step six is ​​5g:3.6-9.4g:50-60mL:70-80mL.

[0019] As a further solution of the present invention: an ionic liquid with excellent thermal stability for lithium batteries, wherein the ionic liquid with excellent thermal stability for lithium batteries is prepared according to the preparation method of the ionic liquid with excellent thermal stability for lithium batteries.

[0020] Beneficial effects of the present invention:

[0021] The invention discloses an ionic liquid with excellent thermal stability for lithium batteries and a preparation method thereof. The invention comprises the following steps: reacting neopentyl glycol and phosphorus oxychloride, wherein two hydroxyl groups on the neopentyl glycol and phosphorus oxychloride react with two chlorine atoms on the phosphorus oxychloride to obtain an intermediate 1, then reacting the intermediate 1 and 1-(1H-imidazole-1-yl)propan-2-ol, wherein the chlorine atoms on the intermediate 1 react with the hydroxyl groups on the 1-(1H-imidazole-1-yl)propan-2-ol to obtain an intermediate 2, then reacting the intermediate 2 and 3-bromo-1-propylene, wherein the imidazoles on the intermediate 2 react with the 3-bromo-1-propylene. The azole ring reacts with the bromine atom on 3-bromo-1-propylene to form an imidazole cation to obtain a phosphorus-containing imidazole monomer, and then 1-vinyl imidazole, styrene, and the phosphorus-containing imidazole monomer are used as polymerization monomers to obtain phosphorus-containing phenyl polyimidazole, and then the phosphorus-containing phenyl polyimidazole and 1,6-dibromohexane react, and the imidazole ring on the phosphorus-containing phenyl polyimidazole reacts with the bromine atom on 1,6-dibromohexane to form an imidazole cation, and at the same time, the polymer molecular chain of the phosphorus-containing phenyl polyimidazole is cross-linked to obtain a cationic polyimidazole, and finally the cationic polyimidazole, The invention relates to an ionic liquid having excellent thermal stability for lithium batteries, wherein the ionic liquid is composed of a large number of imidazole cations and hexafluorophosphate anions. Under the action of an electric field, the cations and anions in the ionic liquid migrate, and due to the high ion concentration, the ionic liquid has a high ion conductivity, thereby realizing rapid charging and discharging of the lithium battery. Moreover, the ionic liquid is a polymer structure with a high cross-linking degree, so that the molecular chains in the ionic liquid are more compact, thereby improving the thermal stability of the ionic liquid, making the ionic liquid difficult to decompose at high temperatures. After the benzene ring and a large number of phosphorus elements are introduced into the ionic liquid, the thermal stability and flame retardant performance can be further improved, thereby ensuring the high-temperature cycle stability of the lithium battery, thereby avoiding the risks of short circuit and thermal runaway of the lithium battery, thereby improving the safety of the lithium battery and extending the service life of the lithium battery, so that the ionic liquid has broad application prospects in the field of lithium batteries. Moreover, the preparation method is simple to operate, the raw materials are easily available, the cost is low, and it is suitable for large-scale industrial production. DETAILED DESCRIPTION

[0022] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0023] Embodiment 1:

[0024] This embodiment is a method for preparing an ionic liquid with excellent thermal stability for lithium batteries, comprising the following steps:

[0025] Step 1: 0.1 mol of neopentyl glycol and 50 mL of chloroform are added to a four-necked flask equipped with a stirrer, a thermometer, an air guide tube, a constant pressure dropping funnel and a reflux condenser, and nitrogen is introduced for protection. The mixture is stirred for reaction at a temperature of 25° C. and a stirring rate of 300 r / min for 20 min, and then 0.1 mol of phosphorus oxychloride is added dropwise while stirring, and the dropping rate is controlled to be 1 drop / s. After the addition is completed, the mixture is heated to 50° C. and the stirring reaction is continued for 2 h, and then the mixture is heated to reflux and the stirring reaction is continued for 6 h. After the reaction is completed, the reaction product is cooled to room temperature, and then the solvent is removed by rotary evaporation, and then the mixture is washed twice with distilled water, and then placed in a vacuum drying oven and dried at a temperature of 60° C. for 2 h to obtain intermediate 1;

[0026] Step 2: 30 mmol of intermediate 1, 30 mmol of 1-(1H-imidazol-1-yl)propan-2-ol, 2.5 mL of triethylamine and 40 mL of anhydrous acetonitrile were added to a three-necked flask equipped with a stirrer, a thermometer and a gas guide tube, and nitrogen was introduced for protection. The mixture was stirred at 25°C and a stirring rate of 300 r / min for 1 hour, and then the mixture was heated to 80°C and stirred for 10 hours. After the reaction, the reaction product was cooled to room temperature, and then the solvent was removed by rotary evaporation. The mixture was then poured into ice water, and then extracted twice with chloroform. The extracts were combined and rotary evaporated to remove the solvent to obtain intermediate 2;

[0027] Step 3: 20mmol of intermediate 2, 22mmol of 3-bromo-1-propylene, 25mmol of anhydrous potassium carbonate, 0.01g of hydroquinone and 50mL of anhydrous ether were added to a three-necked flask equipped with a stirrer, a thermometer, a gas duct and a reflux condenser, and nitrogen was introduced for protection. The mixture was stirred for reaction at a temperature of 25°C and a stirring rate of 300r / min for 15min, and then the mixture was heated to reflux and continued to stir for 4h. After the reaction was completed, the reaction product was cooled to room temperature, and then the solvent was removed by rotary evaporation, and then the mixture was washed twice with saturated brine, and then placed in a vacuum drying oven and dried at a temperature of 50°C for 3h to obtain a phosphorus-containing imidazole monomer;

[0028] Step 4: 10mmol 1-vinyl imidazole, 5mmol styrene, 3mmol phosphorus-containing imidazole monomer, 2g azobisisobutyronitrile, 5mL anhydrous ethanol, 5mL deionized water and 25mL ethyl acetate were added to a three-necked flask equipped with a stirrer, a thermometer, a gas guide tube and a reflux condenser, and nitrogen was introduced for protection. The reaction was stirred for 8min at a temperature of 25°C and a stirring rate of 300r / min, and then the temperature was raised to reflux and the stirring reaction was continued for 20h. After the reaction was completed, the reaction product was cooled to room temperature, and then vacuum filtered. The filter cake was washed twice with anhydrous methanol, and then placed in a vacuum drying oven and dried at a temperature of 50°C for 2h to obtain phosphorus-containing phenyl polyimidazole;

[0029] Step 5: Add 5g of phosphorus-containing phenyl polyimidazole, 30mmol 1,6-dibromohexane, 35mmol anhydrous potassium carbonate and 100mL anhydrous acetone to a three-necked flask equipped with a stirrer, a thermometer and an air guide tube, introduce nitrogen protection, stir and react for 20min at a temperature of -5°C and a stirring rate of 300r / min, then heat to 50°C and continue stirring and reacting for 5h. After the reaction is completed, the reaction product is cooled to room temperature, and then the solvent is removed by rotary evaporation, and then poured into n-hexane, and then centrifuged. The precipitate is placed in a vacuum drying oven and dried at a temperature of 70°C for 4h to obtain a cationic polyimidazole;

[0030] Step six: Add 5g of cationic polyimidazole, 3.6g of ammonium hexafluorophosphate, 50mL of deionized water and 70mL of anhydrous ethanol to a three-necked flask equipped with a stirrer, a thermometer and an air duct, introduce nitrogen protection, stir the reaction at a temperature of 25°C and a stirring rate of 300r / min for 1h, then heat the temperature to 65°C and continue stirring the reaction for 20h. After the reaction, the reaction product is cooled to room temperature, then vacuum filtered, and the filtrate is extracted twice with anhydrous acetonitrile. The extracts are combined and rotary evaporated to remove the solvent, and then placed in a vacuum drying oven and dried at a temperature of 60°C for 10h to obtain an ionic liquid with excellent thermal stability for lithium batteries.

[0031] Embodiment 2:

[0032] This embodiment is a method for preparing an ionic liquid with excellent thermal stability for lithium batteries, comprising the following steps:

[0033] Step 1: 0.1 mol of neopentyl glycol and 52 mL of chloroform were added to a four-necked flask equipped with a stirrer, a thermometer, an air guide tube, a constant pressure dropping funnel and a reflux condenser, and nitrogen was introduced for protection. The mixture was stirred for 25 min at a temperature of 28 ° C and a stirring rate of 350 r / min, and then 0.1 mol of phosphorus oxychloride was added dropwise while stirring, and the dropping rate was controlled to be 1 drop / s. After the addition was completed, the mixture was heated to 52 ° C and continued to stir for 2.5 h, and then heated to reflux and continued to stir for 7 h. After the reaction was completed, the reaction product was cooled to room temperature, and then the solvent was removed by rotary evaporation, and then washed twice with distilled water, and then placed in a vacuum drying oven and dried at a temperature of 62 ° C for 2.5 h to obtain intermediate 1;

[0034] Step 2: 30 mmol of intermediate 1, 30 mmol of 1-(1H-imidazol-1-yl)propan-2-ol, 3 mL of triethylamine and 45 mL of anhydrous acetonitrile were added to a three-necked flask equipped with a stirrer, a thermometer and a gas guide tube, and nitrogen was introduced for protection. The reaction was stirred at 28°C and a stirring rate of 350 r / min for 1.2 h, and then the temperature was raised to 82°C and the stirring reaction was continued for 11 h. After the reaction was completed, the reaction product was cooled to room temperature, and then the solvent was removed by rotary evaporation, and then poured into ice water, and then extracted twice with chloroform, and the extracts were combined and rotary evaporated to remove the solvent to obtain intermediate 2;

[0035] Step 3: 20mmol of intermediate 2, 24mmol of 3-bromo-1-propylene, 28mmol of anhydrous potassium carbonate, 0.03g of hydroquinone and 55mL of anhydrous ether were added to a three-necked flask equipped with a stirrer, a thermometer, a gas guide tube and a reflux condenser, and nitrogen was introduced for protection. The reaction was stirred for 18min at a temperature of 28°C and a stirring rate of 350r / min, and then the temperature was raised to reflux and the stirring reaction was continued for 4.5h. After the reaction was completed, the reaction product was cooled to room temperature, and then the solvent was removed by rotary evaporation, and then washed twice with saturated brine, and then placed in a vacuum drying oven and dried at a temperature of 52°C for 3.5h to obtain a phosphorus-containing imidazole monomer;

[0036] Step 4: 10mmol 1-vinyl imidazole, 7mmol styrene, 8mmol phosphorus-containing imidazole monomer, 2.3g azobisisobutyronitrile, 7mL anhydrous ethanol, 7mL deionized water and 30mL ethyl acetate were added to a three-necked flask equipped with a stirrer, a thermometer, a gas guide tube and a reflux condenser, and nitrogen was introduced for protection. The reaction was stirred at a temperature of 28°C and a stirring rate of 350r / min for 9min, and then the temperature was raised to reflux and the stirring reaction was continued for 22h. After the reaction was completed, the reaction product was cooled to room temperature, and then vacuum filtered. The filter cake was washed twice with anhydrous methanol, and then placed in a vacuum drying oven and dried at a temperature of 52°C for 2.5h to obtain phosphorus-containing phenyl polyimidazole;

[0037] Step 5: Add 5g of phosphorus-containing phenyl polyimidazole, 40mmol 1,6-dibromohexane, 45mmol anhydrous potassium carbonate and 110mL anhydrous acetone to a three-necked flask equipped with a stirrer, a thermometer and an air duct, introduce nitrogen protection, stir and react for 25min at a temperature of -3°C and a stirring rate of 350r / min, then heat to 52°C and continue stirring and reacting for 5.5h. After the reaction is completed, the reaction product is cooled to room temperature, and then the solvent is removed by rotary evaporation, and then poured into n-hexane, and then centrifuged. The precipitate is placed in a vacuum drying oven and dried at a temperature of 72°C for 4.5h to obtain a cationic polyimidazole;

[0038] Step six: Add 5g of cationic polyimidazole, 6.5g of ammonium hexafluorophosphate, 55mL of deionized water and 75mL of anhydrous ethanol to a three-necked flask equipped with a stirrer, a thermometer and an air duct, introduce nitrogen protection, stir the reaction at a temperature of 28°C and a stirring rate of 350r / min for 1.5h, then heat the temperature to 68°C and continue stirring the reaction for 22h. After the reaction, the reaction product is cooled to room temperature, then vacuum filtered, and the filtrate is extracted twice with anhydrous acetonitrile. The extracts are combined and rotary evaporated to remove the solvent, and then placed in a vacuum drying oven and dried at a temperature of 62°C for 12h to obtain an ionic liquid with excellent thermal stability for lithium batteries.

[0039] Embodiment 3:

[0040] This embodiment is a method for preparing an ionic liquid with excellent thermal stability for lithium batteries, comprising the following steps:

[0041] Step 1: 0.1 mol of neopentyl glycol and 55 mL of chloroform were added to a four-necked flask equipped with a stirrer, a thermometer, an air guide tube, a constant pressure dropping funnel and a reflux condenser, and nitrogen was introduced for protection. The mixture was stirred for 30 min at a temperature of 30 ° C and a stirring rate of 400 r / min, and then 0.1 mol of phosphorus oxychloride was added dropwise while stirring, and the dropping rate was controlled to be 2 drops / s. After the addition was completed, the mixture was heated to 55 ° C and continued to stir for 3 h, and then heated to reflux and continued to stir for 8 h. After the reaction was completed, the reaction product was cooled to room temperature, and then the solvent was removed by rotary evaporation, and then washed with distilled water 3 times, and then placed in a vacuum drying oven and dried at a temperature of 65 ° C for 3 h to obtain intermediate 1;

[0042] Step 2: 30 mmol of intermediate 1, 30 mmol of 1-(1H-imidazol-1-yl)propan-2-ol, 3.5 mL of triethylamine and 50 mL of anhydrous acetonitrile were added to a three-necked flask equipped with a stirrer, a thermometer and a gas guide tube, and nitrogen was introduced for protection. The reaction was stirred at a temperature of 30°C and a stirring rate of 400 r / min for 1.5 hours, and then the temperature was raised to 85°C and the stirring reaction was continued for 12 hours. After the reaction was completed, the reaction product was cooled to room temperature, and then the solvent was removed by rotary evaporation, and then poured into ice water, and then extracted with chloroform for 3 times, and the extracts were combined and rotary evaporated to remove the solvent to obtain intermediate 2;

[0043] Step 3: 20mmol of intermediate 2, 25mmol of 3-bromo-1-propylene, 30mmol of anhydrous potassium carbonate, 0.05g of hydroquinone and 60mL of anhydrous ether were added to a three-necked flask equipped with a stirrer, a thermometer, a gas guide tube and a reflux condenser, and nitrogen was introduced for protection. The mixture was stirred for reaction at a temperature of 30°C and a stirring rate of 400r / min for 20min, and then the temperature was raised to reflux and the stirring reaction was continued for 5h. After the reaction was completed, the reaction product was cooled to room temperature, and then the solvent was removed by rotary evaporation, and then washed with saturated brine 3 times, and then placed in a vacuum drying oven and dried at a temperature of 55°C for 4h to obtain a phosphorus-containing imidazole monomer;

[0044] Step 4: 10mmol 1-vinyl imidazole, 9mmol styrene, 13mmol phosphorus-containing imidazole monomer, 2.6g azobisisobutyronitrile, 8mL anhydrous ethanol, 8mL deionized water and 35mL ethyl acetate were added to a three-necked flask equipped with a stirrer, a thermometer, an air guide tube and a reflux condenser, and nitrogen was introduced for protection. The reaction was stirred for 10min at a temperature of 30°C and a stirring rate of 400r / min, and then the temperature was raised to reflux and the stirring reaction was continued for 25h. After the reaction was completed, the reaction product was cooled to room temperature, and then vacuum filtered. The filter cake was washed 3 times with anhydrous methanol, and then placed in a vacuum drying oven and dried at a temperature of 55°C for 3h to obtain phosphorus-containing phenyl polyimidazole;

[0045] Step 5: Add 5g of phosphorus-containing phenyl polyimidazole, 50mmol 1,6-dibromohexane, 55mmol anhydrous potassium carbonate and 120mL anhydrous acetone to a three-necked flask equipped with a stirrer, a thermometer and an air guide tube, introduce nitrogen protection, stir the reaction at a temperature of 0°C and a stirring rate of 400r / min for 30min, then heat the temperature to 55°C and continue stirring the reaction for 6h. After the reaction is completed, the reaction product is cooled to room temperature, and then the solvent is removed by rotary evaporation, and then poured into n-hexane, and then centrifuged. The precipitate is placed in a vacuum drying oven and dried at a temperature of 75°C for 5h to obtain a cationic polyimidazole;

[0046] Step six: Add 5g of cationic polyimidazole, 9.4g of ammonium hexafluorophosphate, 60mL of deionized water and 80mL of anhydrous ethanol to a three-necked flask equipped with a stirrer, a thermometer and an air duct, introduce nitrogen protection, stir the reaction at a temperature of 30°C and a stirring rate of 400r / min for 2h, then heat the temperature to 70°C and continue stirring the reaction for 25h. After the reaction, the reaction product is cooled to room temperature, then vacuum filtered, and the filtrate is extracted 3 times with anhydrous acetonitrile. The extracts are combined and rotary evaporated to remove the solvent, and then placed in a vacuum drying oven and dried at a temperature of 65°C for 15h to obtain an ionic liquid with excellent thermal stability for lithium batteries.

[0047] Comparative Example 1:

[0048] This comparative example is a method for preparing an ionic liquid with excellent thermal stability for lithium batteries, comprising the following steps:

[0049] Step S11: 5 g of 1-vinylimidazole, 50 mmol of 1,6-dibromohexane, 55 mmol of anhydrous potassium carbonate and 120 mL of anhydrous acetone were added to a three-necked flask equipped with a stirrer, a thermometer and an air duct, and nitrogen was introduced for protection. The mixture was stirred at 0° C. and a stirring rate of 400 r / min for 30 min, and then the mixture was heated to 55° C. and the stirring reaction was continued for 6 h. After the reaction was completed, the reaction product was cooled to room temperature, and then the solvent was removed by rotary evaporation, and then poured into n-hexane, and then centrifuged. The precipitate was placed in a vacuum drying oven and dried at 75° C. for 5 h to obtain a cationic polyimidazole;

[0050] Step S12: Add 5g of cationic polyimidazole, 9.4g of ammonium hexafluorophosphate, 60mL of deionized water and 80mL of anhydrous ethanol to a three-necked flask equipped with an agitator, a thermometer and an air duct, introduce nitrogen protection, stir the reaction at a temperature of 30°C and a stirring rate of 400r / min for 2h, then heat the temperature to 70°C and continue stirring the reaction for 25h. After the reaction, the reaction product is cooled to room temperature, then vacuum filtered, and the filtrate is extracted 3 times with anhydrous acetonitrile. The extracts are combined and rotary evaporated to remove the solvent, and then placed in a vacuum drying oven and dried at a temperature of 65°C for 15h to obtain an ionic liquid with excellent thermal stability for lithium batteries.

[0051] Comparative Example 2:

[0052] This comparative example is a method for preparing an ionic liquid with excellent thermal stability for lithium batteries, comprising the following steps:

[0053] Step S21: 10 mmol 1-vinyl imidazole, 2.6 g azobisisobutyronitrile, 8 mL anhydrous ethanol, 8 mL deionized water and 35 mL ethyl acetate were added to a three-necked flask equipped with a stirrer, a thermometer, an air guide tube and a reflux condenser, and nitrogen was introduced for protection. The mixture was stirred for reaction at a temperature of 30° C. and a stirring rate of 400 r / min for 10 min, and then the temperature was raised to reflux and the stirring reaction was continued for 25 h. After the reaction was completed, the reaction product was cooled to room temperature, and then vacuum filtered. The filter cake was washed 3 times with anhydrous methanol, and then placed in a vacuum drying oven and dried at a temperature of 55° C. for 3 h to obtain polyimidazole;

[0054] Step S22: 5 g of polyimidazole, 50 mmol of 1,6-dibromohexane, 55 mmol of anhydrous potassium carbonate and 120 mL of anhydrous acetone are added to a three-necked flask equipped with a stirrer, a thermometer and an air duct, and nitrogen is introduced for protection. The mixture is stirred for reaction at a temperature of 0° C. and a stirring rate of 400 r / min for 30 min, and then the mixture is heated to 55° C. and the stirring reaction is continued for 6 h. After the reaction is completed, the reaction product is cooled to room temperature, and then the solvent is removed by rotary evaporation, and then poured into n-hexane, and then centrifuged. The precipitate is placed in a vacuum drying oven and dried at a temperature of 75° C. for 5 h to obtain a cationic polyimidazole;

[0055] Step S23: Add 5g of cationic polyimidazole, 9.4g of ammonium hexafluorophosphate, 60mL of deionized water and 80mL of anhydrous ethanol to a three-necked flask equipped with an agitator, a thermometer and an air duct, introduce nitrogen protection, stir the reaction at a temperature of 30°C and a stirring rate of 400r / min for 2h, then heat the temperature to 70°C and continue stirring the reaction for 25h. After the reaction, the reaction product is cooled to room temperature, then vacuum filtered, and the filtrate is extracted 3 times with anhydrous acetonitrile. The extracts are combined and rotary evaporated to remove the solvent, then placed in a vacuum drying oven and dried at a temperature of 65°C for 15h to obtain an ionic liquid with excellent thermal stability for lithium batteries.

[0056] Comparative Example 3:

[0057] This comparative example is a method for preparing an ionic liquid with excellent thermal stability for lithium batteries, comprising the following steps:

[0058] Step S31: 10 mmol 1-vinyl imidazole, 9 mmol styrene, 2.6 g azobisisobutyronitrile, 8 mL anhydrous ethanol, 8 mL deionized water and 35 mL ethyl acetate were added to a three-necked flask equipped with a stirrer, a thermometer, an air guide tube and a reflux condenser, and nitrogen was introduced for protection. The mixture was stirred for reaction at a temperature of 30° C. and a stirring rate of 400 r / min for 10 min, and then the temperature was raised to reflux and the stirring reaction was continued for 25 h. After the reaction was completed, the reaction product was cooled to room temperature, and then vacuum filtered. The filter cake was washed 3 times with anhydrous methanol, and then placed in a vacuum drying oven and dried at a temperature of 55° C. for 3 h to obtain phenylpolyimidazole;

[0059] Step S32: 5 g of phosphorus-containing phenyl polyimidazole, 50 mmol of 1,6-dibromohexane, 55 mmol of anhydrous potassium carbonate and 120 mL of anhydrous acetone were added to a three-necked flask equipped with a stirrer, a thermometer and an air duct, and nitrogen was introduced for protection. The mixture was stirred for reaction at a temperature of 0° C. and a stirring rate of 400 r / min for 30 min, and then the mixture was heated to 55° C. and continued to stir for reaction for 6 h. After the reaction was completed, the reaction product was cooled to room temperature, and then the solvent was removed by rotary evaporation, and then poured into n-hexane, and then centrifuged. The precipitate was placed in a vacuum drying oven and dried at a temperature of 75° C. for 5 h to obtain a cationic polyimidazole;

[0060] Step S33: Add 5g of cationic polyimidazole, 9.4g of ammonium hexafluorophosphate, 60mL of deionized water and 80mL of anhydrous ethanol to a three-necked flask equipped with an agitator, a thermometer and an air duct, introduce nitrogen protection, stir the reaction at a temperature of 30°C and a stirring rate of 400r / min for 2h, then heat the temperature to 70°C and continue stirring the reaction for 25h. After the reaction, the reaction product is cooled to room temperature, then vacuum filtered, and the filtrate is extracted 3 times with anhydrous acetonitrile. The extracts are combined and rotary evaporated to remove the solvent, then placed in a vacuum drying oven and dried at a temperature of 65°C for 15h to obtain an ionic liquid with excellent thermal stability for lithium batteries.

[0061] Comparative Example 4:

[0062] This comparative example is a method for preparing an ionic liquid with excellent thermal stability for lithium batteries, comprising the following steps:

[0063] Step S41: 0.1 mol of neopentyl glycol and 55 mL of chloroform are added to a four-necked flask equipped with a stirrer, a thermometer, an air guide tube, a constant pressure dropping funnel and a reflux condenser, and nitrogen is introduced for protection. The mixture is stirred and reacted for 30 min at a temperature of 30° C. and a stirring rate of 400 r / min. Then, 0.1 mol of phosphorus oxychloride is added dropwise while stirring, and the dropping rate is controlled to be 2 drops / s. After the addition is completed, the mixture is heated to 55° C. and the stirring reaction is continued for 3 h. Then, the mixture is heated to reflux and the stirring reaction is continued for 8 h. After the reaction is completed, the reaction product is cooled to room temperature, and then the solvent is removed by rotary evaporation. Then, the mixture is washed with distilled water 3 times, and then placed in a vacuum drying oven and dried at a temperature of 65° C. for 3 h to obtain intermediate 1;

[0064] Step S42: 30 mmol of intermediate 1, 30 mmol of 1-(1H-imidazol-1-yl)propan-2-ol, 3.5 mL of triethylamine and 50 mL of anhydrous acetonitrile were added to a three-necked flask equipped with a stirrer, a thermometer and a gas guide tube, and nitrogen was introduced for protection. The mixture was stirred at 30° C. and a stirring rate of 400 r / min for 1.5 h, and then the mixture was heated to 85° C. and stirred for 12 h. After the reaction, the reaction product was cooled to room temperature, and then the solvent was removed by rotary evaporation. The mixture was then poured into ice water, and then extracted with chloroform for 3 times. The extracts were combined and rotary evaporated to remove the solvent to obtain intermediate 2;

[0065] Step S43: 20 mmol of intermediate 2, 25 mmol of 3-bromo-1-propylene, 30 mmol of anhydrous potassium carbonate, 0.05 g of hydroquinone and 60 mL of anhydrous ether were added to a three-necked flask equipped with a stirrer, a thermometer, a gas duct and a reflux condenser, and nitrogen was introduced for protection. The mixture was stirred for reaction at a temperature of 30° C. and a stirring rate of 400 r / min for 20 min, and then the temperature was raised to reflux and the stirring reaction was continued for 5 h. After the reaction was completed, the reaction product was cooled to room temperature, and then the solvent was removed by rotary evaporation, and then the mixture was washed with saturated brine for 3 times, and then placed in a vacuum drying oven and dried at a temperature of 55° C. for 4 h to obtain a phosphorus-containing imidazole monomer;

[0066] Step S44: 10 mmol 1-vinyl imidazole, 13 mmol phosphorus-containing imidazole monomer, 2.6 g azobisisobutyronitrile, 8 mL anhydrous ethanol, 8 mL deionized water and 35 mL ethyl acetate were added to a three-necked flask equipped with a stirrer, a thermometer, an air guide tube and a reflux condenser, and nitrogen was introduced for protection. The mixture was stirred for reaction at a temperature of 30° C. and a stirring rate of 400 r / min for 10 min, and then the temperature was raised to reflux and the stirring reaction was continued for 25 h. After the reaction was completed, the reaction product was cooled to room temperature, and then vacuum filtered. The filter cake was washed 3 times with anhydrous methanol, and then placed in a vacuum drying oven and dried at a temperature of 55° C. for 3 h to obtain phosphorus-containing polyimidazole;

[0067] Step S45: 5 g of phosphorus-containing polyimidazole, 50 mmol of 1,6-dibromohexane, 55 mmol of anhydrous potassium carbonate and 120 mL of anhydrous acetone are added to a three-necked flask equipped with a stirrer, a thermometer and an air duct, and nitrogen is introduced for protection. The mixture is stirred for reaction at a temperature of 0° C. and a stirring rate of 400 r / min for 30 min, and then the mixture is heated to 55° C. and stirred for reaction for 6 h. After the reaction is completed, the reaction product is cooled to room temperature, and then the solvent is removed by rotary evaporation, and then poured into n-hexane, and then centrifuged. The precipitate is placed in a vacuum drying oven and dried at a temperature of 75° C. for 5 h to obtain a cationic polyimidazole;

[0068] Step S46: Add 5g of cationic polyimidazole, 9.4g of ammonium hexafluorophosphate, 60mL of deionized water and 80mL of anhydrous ethanol to a three-necked flask equipped with an agitator, a thermometer and an air duct, introduce nitrogen protection, stir the reaction at a temperature of 30°C and a stirring rate of 400r / min for 2h, then heat the temperature to 70°C and continue stirring the reaction for 25h. After the reaction, the reaction product is cooled to room temperature, then vacuum filtered, and the filtrate is extracted 3 times with anhydrous acetonitrile. The extracts are combined and rotary evaporated to remove the solvent, and then placed in a vacuum drying oven and dried at a temperature of 65°C for 15h to obtain an ionic liquid with excellent thermal stability for lithium batteries.

[0069] The thermal stability of the ionic liquids with excellent thermal stability for lithium batteries of Examples 1-3 and Comparative Examples 1-4 was tested, and the test results are shown in Table 1:

[0070]

[0071] Referring to the data in the above table, based on the comparison between Examples 1-3 and Comparative Examples 1-4, it can be seen that the ionic liquid of the present application has excellent thermal stability.

[0072] In the description of this specification, the description with reference to the terms "one embodiment", "example", "specific example", etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0073] The above contents are merely examples and explanations of the present invention. Those skilled in the art may make various modifications or additions to the specific embodiments described or replace them in a similar manner. As long as they do not deviate from the invention or exceed the scope defined in this application, they shall all fall within the protection scope of the present invention.

Claims

1. A method for preparing an ionic liquid with excellent thermal stability for lithium batteries, characterized in that: The following steps are involved: Step 1: stirring neopentyl glycol and chloroform to react, then adding phosphorus oxychloride dropwise while stirring, and continuing to stir the reaction after the addition is complete. After the reaction is completed, the reaction product is cooled, then rotary evaporated, and then washed and dried to obtain intermediate 1; Step 2: Stir and react the intermediate 1, 1-(1H-imidazol-1-yl)propan-2-ol, triethylamine and anhydrous acetonitrile. After the reaction, cool the reaction product, then rotary evaporate it, then pour it into ice water, extract it, and rotary evaporate the extract to obtain the intermediate 2; Step 3: Stir and react the intermediate 2,3-bromo-1-propylene, anhydrous potassium carbonate, hydroquinone and anhydrous ether. After the reaction is completed, cool the reaction product, then rotary evaporate, wash and dry to obtain a phosphorus-containing imidazole monomer; Step 4: stirring 1-vinylimidazole, styrene, phosphorus-containing imidazole monomer, azobisisobutyronitrile, anhydrous ethanol, deionized water and ethyl acetate for reaction, cooling the reaction product after the reaction is completed, and then vacuum filtering, washing and drying the filter cake to obtain phosphorus-containing phenyl polyimidazole; Step 5: Stirring phosphorus-containing phenyl polyimidazole, 1,6-dibromohexane, anhydrous potassium carbonate and anhydrous acetone for reaction, cooling the reaction product after the reaction is completed, then rotary evaporating, then pouring into n-hexane, then centrifuging, and drying the precipitate to obtain cationic polyimidazole; Step 6: Stir the cationic polyimidazole, ammonium hexafluorophosphate, deionized water and anhydrous ethanol for reaction. After the reaction is completed, cool the reaction product, then vacuum filter it, extract the filtrate, rotary evaporate the extract, and then dry it to obtain an ionic liquid with excellent thermal stability for lithium batteries.

2. The method for preparing an ionic liquid with excellent thermal stability for lithium batteries according to claim 1, characterized in that: The usage ratio of the neopentyl glycol, chloroform and phosphorus oxychloride in step 1 is 0.1 mol: 50-55 mL: 0.1 mol.

3. The method for preparing an ionic liquid with excellent thermal stability for lithium batteries according to claim 1, characterized in that: The usage ratio of the intermediate 1, 1-(1H-imidazol-1-yl)propan-2-ol, triethylamine and anhydrous acetonitrile in step 2 is 30 mmol: 30 mmol: 2.5-3.5 mL: 40-50 mL.

4. The method for preparing an ionic liquid with excellent thermal stability for lithium batteries according to claim 1, characterized in that: The usage ratio of the intermediate 2, 3-bromo-1-propylene, anhydrous potassium carbonate, hydroquinone and anhydrous ether in step 3 is 20 mmol: 22-25 mmol: 25-30 mmol: 0.01-0.05 g: 50-60 mL.

5. The method for preparing an ionic liquid with excellent thermal stability for lithium batteries according to claim 1, characterized in that: The usage ratio of the 1-vinylimidazole, styrene, phosphorus-containing imidazole monomer, azobisisobutyronitrile, anhydrous ethanol, deionized water and ethyl acetate in step 4 is 10 mmol: 5-9 mmol: 3-13 mmol: 2-2.6 g: 5-8 mL: 5-8 mL: 25-35 mL.

6. The method for preparing an ionic liquid with excellent thermal stability for lithium batteries according to claim 1, characterized in that: The usage ratio of the phosphorus-containing phenyl polyimidazole, 1,6-dibromohexane, anhydrous potassium carbonate and anhydrous acetone in step 5 is 5g:30-50mmol:35-55mmol:100-120mL.

7. The method for preparing an ionic liquid with excellent thermal stability for lithium batteries according to claim 1, characterized in that: The usage ratio of the cationic polyimidazole, ammonium hexafluorophosphate, deionized water and anhydrous ethanol in step six is ​​5g:3.6-9.4g:50-60mL:70-80mL.

8. An ionic liquid with excellent thermal stability for lithium batteries, characterized in that: The ionic liquid with excellent thermal stability for lithium batteries is prepared according to the method for preparing an ionic liquid with excellent thermal stability for lithium batteries according to any one of claims 1 to 7.

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