Lithium ion battery electrolyte with high ion conductivity and preparation method thereof

Abstract

This invention discloses a lithium-ion battery electrolyte with high ionic conductivity and its preparation method, belonging to the field of lithium-ion battery material technology. First, an amino-cerium-based MOF is synthesized via a solvothermal method. Then, sulfonic acid groups are grafted through an amidation coupling reaction. An ionic liquid is then loaded into the pores of the MOF using an impregnation method to obtain a composite additive. Finally, this composite additive, lithium bis(fluorosulfonyl)imide, ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate are mixed under an inert atmosphere to obtain a lithium-ion battery electrolyte with high ionic conductivity. This invention combines the confined ion transport of the MOF, the dissociation-promoting properties of the sulfonic acid groups, and the low-temperature fluidity of the ionic liquid to synergistically improve the ionic conductivity and interfacial stability of the electrolyte at low temperatures. This solves the problems of low low-temperature ionic conductivity and rapid capacity decay of traditional electrolytes, meeting the urgent need for high-performance, long-life lithium-ion batteries under extreme low-temperature conditions.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery material technology, specifically a lithium-ion battery electrolyte with high ion conductivity and its preparation method. Background Technology

[0002] Lithium-ion batteries have become the core power source for portable electronic devices, electric vehicles, and large-scale energy storage systems due to their advantages such as high energy density, long cycle life, and no memory effect. With the expansion of application fields, especially in cold regions and extreme working conditions, developing lithium-ion batteries that can maintain excellent performance at low temperatures (such as below -20°C) has become one of the key challenges in the industry. As the "blood" of the battery, the electrolyte's ionic conductivity and interface stability are the core factors that determine the battery's low-temperature performance.

[0003] Currently, commercial lithium-ion batteries generally use carbonate electrolytes based on lithium hexafluorophosphate (LiPF6). However, these electrolytes face two major bottlenecks at low temperatures: First, conventional carbonate solvents (such as ethylene carbonate EC) have high melting points and high viscosity. When the temperature drops below 0°C, the ionic conductivity of the electrolyte system drops sharply, leading to increased internal resistance and severely limited power output and capacity. Second, LiPF6 salts decompose to produce hydrogen fluoride (HF) in the presence of trace amounts of water in the electrolyte. This not only corrodes the electrode materials but also damages the stability of the solid electrolyte interphase (SEI) film on the negative electrode, exacerbating the loss of active lithium and capacity decay during low-temperature cycling.

[0004] Chinese patent application CN114530632A discloses a lithium-ion battery electrolyte and a lithium-ion battery. The solution aims to use low-viscosity carboxylic acid ester solvents to replace traditional carbonates to lower the freezing point, and to combine high-concentration lithium salts and film-forming additives to improve interface stability.

[0005] However, high-concentration lithium salts pose a risk of crystallization at low temperatures. Carboxylic acid ester solvents have limited solubility for lithium salts (especially LiPF6), and their solubility decreases sharply as the temperature decreases. When the ambient temperature drops below 0°C, supersaturated lithium salts in the electrolyte may precipitate in crystal form. This not only disrupts the physical homogeneity of the electrolyte and causes local ion concentration imbalance, but also forms an insulating deposition layer at the interface between the separator and the electrode, severely hindering lithium ion transport. Summary of the Invention

[0006] The purpose of this invention is to provide a lithium-ion battery electrolyte with high ionic conductivity and its preparation method. By combining the confined ion transport of MOF, the dissociation promotion of sulfonic acid groups, and the low-temperature fluidity of ionic liquids, the ionic conductivity and interfacial stability of the electrolyte in low-temperature environments are synergistically improved. This solves the problems of low low-temperature ionic conductivity and rapid capacity decay of traditional electrolytes, and meets the urgent need for high-performance and long-life lithium-ion batteries in extreme low-temperature environments.

[0007] The objective of this invention can be achieved through the following technical solutions: A method for preparing a lithium-ion battery electrolyte with high ionic conductivity includes the following steps: Step 1: Using cerium salt and 2-aminoterephthalic acid as raw materials, amino-cerium-based MOFs are synthesized by a solvothermal method.

[0008] Step 2: Using an amidation coupling reaction, sulfonic acid groups are grafted onto the MOF framework, and then 1-ethyl-3-methylimidazolium difluorosulfonylimide salt ionic liquid is loaded into the MOF channels by an impregnation method to obtain a low-temperature ionic liquid-cerium-sulfonic acid composite additive.

[0009] Step 3: Mix the low-temperature ionic liquid-cerium-sulfonic acid composite additive, lithium difluorosulfonyl imide, ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate under an inert atmosphere to obtain a lithium-ion battery electrolyte with high ionic conductivity.

[0010] Furthermore, the mass ratio of ethylene carbonate, dimethyl carbonate, ethyl methyl carbonate, lithium bis(fluorosulfonyl)imide, and low-temperature ionic liquid-cerium-sulfonic acid composite additive in the high ionic conductivity lithium-ion battery electrolyte is 24-26:32-35:24-26:15-16.5:1.2-1.8.

[0011] Furthermore, the specific preparation steps of the low-temperature ionic liquid-cerium-sulfonic acid composite additive are as follows: Under an argon atmosphere, 1-ethyl-3-methylimidazolium difluorosulfonylimide salt ionic liquid and anhydrous acetonitrile were added to a reaction vessel and sonicated until completely dispersed. Sulfonic acid functionalized amino-cerium MOF powder was added to the reaction vessel, and the mixture was stirred at room temperature for 22-26 hours. After centrifugation at 10000 r / min for 10 min, the mixture was washed and dried to obtain a low-temperature ionic liquid-cerium-sulfonic acid composite additive.

[0012] Furthermore, the ratio of 1-ethyl-3-methylimidazolium difluorosulfonylimide salt ionic liquid, anhydrous acetonitrile, and sulfonic acid-functionalized amino-cerium MOF powder is 0.6-0.9 g : 30-40 mL : 1.2-1.8 g.

[0013] Furthermore, the specific preparation steps of sulfonic acid-functionalized amino-cerium MOF powder are as follows: Amino-cerium MOF powder and PBS buffer (pH 7.35) were added to the reaction vessel. While maintaining the rotation speed, the activation solution was slowly added dropwise to the reaction vessel. The pH of the system was adjusted to 7.2. The reaction was carried out at room temperature and a rotation speed of 250-350 r / min for 2.5-3.5 h. After the reaction was completed, the solid product was collected by centrifugation and washed successively with anhydrous methanol and acetone. Finally, it was vacuum dried at 60 °C for 12 h to obtain sulfonic acid functionalized amino-cerium MOF powder.

[0014] Furthermore, the ratio of amino-cerium MOF powder, PBS buffer, and activation solution is 1.8-2.2g: 35-45mL: 75-85mL.

[0015] Furthermore, the activation solution is prepared by mixing p-aminobenzenesulfonic acid, MES buffer at pH 5.5, 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride and N-hydroxysuccinimide in a ratio of 0.7-0.9g:75-85mL:3.4-3.8g:2-2.4g.

[0016] Furthermore, the specific preparation steps of amino-cerium-based MOF powder are as follows: 2-Aminoterephthalic acid, N,N-dimethylformamide, and methanol were added to a reaction vessel and stirred at 400-600 r / min until dissolved. Then, cerium nitrate solution was added dropwise to the reaction vessel over 30 min, and the reaction was continued for 0.5-1.5 h. The resulting mixture was transferred to a polytetrafluoroethylene reaction vessel, heated to 150 °C at a rate of 2 °C / min, and reacted at this temperature for 46-50 h. After the reaction was completed, the mixture was cooled to room temperature, and the product was collected by centrifugation. It was washed with N,N-dimethylformamide and methanol, respectively, and then vacuum dried at 60 °C for 8 h. After grinding and passing through a 200-mesh sieve, amino-cerium-based MOF powder was obtained.

[0017] Furthermore, the ratio of 2-aminoterephthalic acid, N,N-dimethylformamide, methanol, and cerium nitrate solution is 5-5.8 g: 85-95 mL: 8-12 mL: 8-12 mL.

[0018] Furthermore, the cerium nitrate solution is prepared by mixing cerium nitrate hexahydrate and N,N-dimethylformamide in a ratio of 4-4.5g:8-12mL.

[0019] The beneficial effects of this invention are: 1. This invention constructs and introduces a low-temperature ionic liquid-cerium-sulfonic acid composite additive as a functional component, which is then compounded with conventional concentrations of lithium difluorosulfonylimide and carbonate (EC / DMC / EMC) base solvents to form an electrolyte system. This system helps to improve the crystallization risk that traditional high-concentration lithium salt strategies may face in low-temperature applications, and has a positive effect on improving the ion conduction performance of the electrolyte under low-temperature conditions, thus helping to promote the performance improvement of lithium-ion batteries in low-temperature application scenarios.

[0020] 2. In this invention, an amino-cerium-based MOF synthesized via a solvothermal method constructs a stable three-dimensional porous crystal framework. This structure can accommodate lithium ions (Li... + This provides nanoscale transport channels, physically reducing its migration resistance, while cerium ions (Ce) in the framework... 4+ The Lewis acidity exhibited by the electrolyte helps to preferentially bind FSI in the electrolyte through electrostatic interactions. - The restriction of anions can effectively increase the transport number of lithium ions without significantly increasing the viscosity of the system, thereby optimizing the electrolyte from the perspective of transport mechanism, especially the ionic conductivity at low temperatures.

[0021] 3. This invention grafts sulfonic acid groups onto the MOF backbone via an amidation coupling reaction. These strongly acidic groups can efficiently anchor the subsequently loaded ionic liquid through electrostatic interaction, preventing it from falling off during cycling. On the other hand, the sulfonic acid groups and the amino groups on the MOF backbone can serve as active sites, preferentially capturing trace amounts of water molecules in the electrolyte and hydrofluoric acid (HF) generated from the hydrolysis of lithium salt, forming stable complexes. This inhibits the corrosion of electrode materials by HF and improves the cycle stability of the battery.

[0022] 4. In this invention, [EMIm][FSI] ionic liquid is loaded into the MOF pores by impregnation. The ionic liquid itself has an extremely low freezing point and excellent low-temperature fluidity. Loading it into the MOF pores avoids the side reactions that may be caused by directly adding ionic liquid, and can form a high-speed ion transport micro-region inside the pores that is not affected by the external low temperature, ensuring that lithium ions can still migrate rapidly at extreme low temperatures.

[0023] 5. During battery cycling, the cerium element in the MOF framework of this invention can dissolve in trace amounts and migrate to the electrode interface. These redox-active cerium ions can participate in and catalyze interfacial reactions, promoting the formation of a dense solid electrolyte interphase (SEI) film rich in lithium fluoride (LiF). In addition, the variable valence characteristics of cerium ions enable them to dynamically respond to microcracks generated in the SEI film during cycling, repairing the damaged areas through local redox reactions, thus endowing the battery interface with a certain self-healing ability. This helps maintain the long-term integrity of the interface and significantly extends the battery cycle life. Detailed Implementation

[0024] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. 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 of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0025] Example 1: A lithium-ion battery electrolyte with high ionic conductivity and its preparation method, comprising the following steps: S1: Dissolve 4.3g of cerium nitrate hexahydrate in 10mL of N,N-dimethylformamide and sonicate until completely dissolved to obtain a cerium nitrate solution. Add 5.4g of 2-aminoterephthalic acid, 90mL of N,N-dimethylformamide and 10mL of methanol to a reaction vessel and stir at 500r / min until dissolved. Then, add 10mL of cerium nitrate solution dropwise to the reaction vessel over 30min and continue the reaction for 1h. Transfer the resulting mixture to a polytetrafluoroethylene reaction vessel and heat it to 150℃ at a rate of 2℃ / min and react at this temperature for 48h. After the reaction is completed, cool to room temperature, collect the product by centrifugation, wash with N,N-dimethylformamide and methanol respectively, and then vacuum dry at 60℃ for 8h. After grinding and passing through a 200-mesh sieve, amino-cerium-based MOF powder is obtained.

[0026] A solvothermal method was employed, using cerium nitrate hexahydrate as the metal source and 2-aminoterephthalic acid as the organic ligand, in an N,N-dimethylformamide / methanol mixed solvent system under high temperature and high pressure conditions of 150°C to promote the ionization of cerium metal ions (Ce). 3+ The amino-cerium-based MOF powder undergoes a coordination self-assembly reaction with the carboxyl group (-COOH) on the ligand, forming a stable three-dimensional network framework through the interweaving of coordination bonds. At the same time, by taking advantage of the molecular structure characteristics of the ligand itself, the amino (-NH2) functional group is anchored in situ and uniformly in the MOF framework, which not only does not destroy the integrity of its porous structure, but also endows the material surface with abundant active sites, and finally obtains an amino-cerium-based MOF powder with both structural stability and functional specificity.

[0027] S2: Add 0.8g of p-aminobenzenesulfonic acid and 80mL of MES buffer (0.01M) with a pH of 5.5 to the reaction vessel. Stir at room temperature and 300r / min to disperse the mixture evenly. Then, add 3.6g of 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride and 2.2g of N-hydroxysuccinimide to the vessel in sequence. Continue stirring until completely dissolved. Adjust the pH of the mixture to 5.5 and maintain the stirring speed and room temperature for 30min to obtain the activated solution. 2g of amino-cerium MOF powder and 40mL of PBS buffer (pH 7.35) were added to the reaction vessel. While maintaining the rotation speed, 80mL of activation solution was slowly added dropwise to the reaction vessel. The pH of the system was adjusted to 7.2. The reaction was carried out at room temperature and a rotation speed of 300r / min for 3h. After the reaction was completed, the solid product was collected by centrifugation and washed successively with anhydrous methanol and acetone. Finally, it was vacuum dried at 60℃ for 12h to obtain sulfonic acid functionalized amino-cerium MOF powder.

[0028] An amidation coupling reaction was employed, using p-aminobenzenesulfonic acid as the sulfonic acid group donor and 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride and N-hydroxysuccinimide as activators to activate the sulfonic acid group in MES buffer. Subsequently, in PBS buffer, the activated sulfonic acid group underwent a specific coupling reaction with the amino group (-NH2) on the surface of the amino-cerium MOF, and the sulfonic acid group (-SO3H) was firmly grafted onto the MOF backbone surface through amide bonds, finally yielding sulfonic acid-functionalized amino-cerium MOF powder.

[0029] S3: Under an argon atmosphere, 0.75 g of 1-ethyl-3-methylimidazolium difluorosulfonylimide salt ([EMIm][FSI]) ionic liquid and 35 mL of anhydrous acetonitrile were added to a reaction vessel and sonicated until completely dispersed. 1.5 g of sulfonic acid-functionalized amino-cerium MOF powder was added to the reaction vessel and stirred at room temperature for 24 h to allow the ionic liquid to fully enter the MOF channels and interact with the sulfonic acid groups. The mixture was centrifuged at 10000 r / min for 10 min, the supernatant was discarded, and the precipitate was washed with anhydrous acetonitrile to remove excess ionic liquid physically adsorbed on the MOF surface. Finally, it was vacuum dried at 60 °C for 12 h to obtain a low-temperature ionic liquid-cerium-sulfonic acid composite additive.

[0030] An impregnation method was used to mix ionic liquid with sulfonic acid-functionalized amino-cerium MOF powder in anhydrous acetonitrile. The confinement effect of MOF channels and the electrostatic attraction of sulfonic acid groups on the surface were utilized to fix the ionic liquid inside the MOF channels, forming a structurally stable low-temperature ionic liquid-cerium-sulfonic acid composite additive.

[0031] S4: In an argon atmosphere glove box with water and oxygen content both <1ppm, 25.3g of ethylene carbonate (EC), 33.7g of dimethyl carbonate (DMC) and 25.3g of ethyl methyl carbonate (EMC) were mixed evenly. Then, 15.7g of lithium difluorosulfonyl imide (LiFSI) was added to the mixed solvent and stirred continuously until completely dissolved. Then, 1.5g of low-temperature ionic liquid-cerium-sulfonic acid composite additive was added. The mixture was first ultrasonically dispersed for 30min and then stirred at 300r / min for 2h to obtain a lithium-ion battery electrolyte with high ionic conductivity.

[0032] Example 2: A lithium-ion battery electrolyte with high ionic conductivity and its preparation method, comprising the following steps: S1: Dissolve 4g of cerium nitrate hexahydrate in 8mL of N,N-dimethylformamide and sonicate until completely dissolved to obtain a cerium nitrate solution. Add 5g of 2-aminoterephthalic acid, 85mL of N,N-dimethylformamide and 8mL of methanol to a reaction vessel and stir at 400r / min until dissolved. Then, add 8mL of cerium nitrate solution dropwise to the reaction vessel over 30min and continue the reaction for 0.5h. Transfer the resulting mixture to a polytetrafluoroethylene reaction vessel and heat it to 150℃ at a rate of 2℃ / min and react at this temperature for 46h. After the reaction is completed, cool to room temperature, collect the product by centrifugation, wash with N,N-dimethylformamide and methanol respectively, and then vacuum dry at 60℃ for 8h. After grinding and passing through a 200-mesh sieve, amino-cerium-based MOF powder is obtained.

[0033] S2: Add 0.7g of p-aminobenzenesulfonic acid and 75mL of MES buffer (0.01M) with a pH of 5.5 to the reaction vessel. Stir at room temperature and 250r / min to disperse the mixture evenly. Then, add 3.4g of 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride and 2g of N-hydroxysuccinimide to the vessel in sequence. Continue stirring until completely dissolved. Adjust the pH of the mixture to 5.5 and maintain the stirring speed and room temperature for 25min to obtain the activated solution. 1.8 g of amino-cerium MOF powder and 35 mL of PBS buffer (pH 7.35) were added to the reaction vessel. While maintaining the rotation speed, 75 mL of activation solution was slowly added dropwise to the reaction vessel. The pH of the system was adjusted to 7.2. The reaction was carried out at room temperature and a rotation speed of 250 r / min for 2.5 h. After the reaction was completed, the solid product was collected by centrifugation and washed successively with anhydrous methanol and acetone. Finally, it was vacuum dried at 60 °C for 12 h to obtain sulfonic acid functionalized amino-cerium MOF powder.

[0034] S3: Under an argon atmosphere, 0.6 g of 1-ethyl-3-methylimidazolium difluorosulfonylimide salt ([EMIm][FSI]) ionic liquid and 30 mL of anhydrous acetonitrile were added to a reaction vessel and sonicated until completely dispersed. 1.2 g of sulfonic acid-functionalized amino-cerium MOF powder was added to the reaction vessel and stirred at room temperature for 22 h to allow the ionic liquid to fully enter the MOF channels and interact with the sulfonic acid groups. The mixture was centrifuged at 10000 r / min for 10 min, the supernatant was discarded, and the precipitate was washed with anhydrous acetonitrile to remove excess ionic liquid physically adsorbed on the MOF surface. Finally, it was vacuum dried at 60 °C for 12 h to obtain a low-temperature ionic liquid-cerium-sulfonic acid composite additive.

[0035] S4: In an argon atmosphere glove box with water and oxygen content both <1ppm, 24g of ethylene carbonate (EC), 32g of dimethyl carbonate (DMC) and 24g of ethyl methyl carbonate (EMC) were mixed evenly. Then, 15g of lithium difluorosulfonyl imide (LiFSI) was added to the mixed solvent and stirred continuously until completely dissolved. Then, 1.2g of low-temperature ionic liquid-cerium-sulfonic acid composite additive was added. The mixture was first ultrasonically dispersed for 25min and then stirred at 250r / min for 1.5h to obtain a lithium-ion battery electrolyte with high ionic conductivity.

[0036] Example 3: A lithium-ion battery electrolyte with high ionic conductivity and its preparation method, comprising the following steps: S1: Dissolve 4.5g of cerium nitrate hexahydrate in 12mL of N,N-dimethylformamide and sonicate until completely dissolved to obtain a cerium nitrate solution. Add 5.8g of 2-aminoterephthalic acid, 95mL of N,N-dimethylformamide and 12mL of methanol to a reaction vessel and stir until dissolved at 600r / min. Then, add 12mL of cerium nitrate solution dropwise to the reaction vessel over 30min and continue the reaction for 1.5h. Transfer the resulting mixture to a polytetrafluoroethylene reaction vessel and heat it to 150℃ at a rate of 2℃ / min and react at this temperature for 50h. After the reaction is completed, cool to room temperature, collect the product by centrifugation, wash with N,N-dimethylformamide and methanol respectively, and then vacuum dry at 60℃ for 8h. After grinding and passing through a 200-mesh sieve, amino-cerium-based MOF powder is obtained.

[0037] S2: Add 0.9g of p-aminobenzenesulfonic acid and 85mL of MES buffer (pH 5.5) to the reaction vessel and stir at room temperature and 350r / min to disperse it evenly. Then, add 3.8g of 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride and 2.4g of N-hydroxysuccinimide to the vessel in sequence, and continue stirring until completely dissolved. Adjust the pH of the mixture to 5.5 and maintain the stirring speed and room temperature for 35min to obtain the activated solution. 2.2 g of amino-cerium MOF powder and 45 mL of PBS buffer (pH 7.35) were added to the reaction vessel. While maintaining the rotation speed, 85 mL of activation solution was slowly added dropwise to the reaction vessel. The pH of the system was adjusted to 7.2. The reaction was carried out at room temperature and a rotation speed of 350 r / min for 3.5 h. After the reaction was completed, the solid product was collected by centrifugation and washed successively with anhydrous methanol and acetone. Finally, it was vacuum dried at 60 °C for 12 h to obtain sulfonic acid functionalized amino-cerium MOF powder.

[0038] S3: Under an argon atmosphere, 0.9 g of 1-ethyl-3-methylimidazolium difluorosulfonylimide salt ([EMIm][FSI]) ionic liquid and 40 mL of anhydrous acetonitrile were added to a reaction vessel and sonicated until completely dispersed. 1.8 g of sulfonic acid-functionalized amino-cerium MOF powder was added to the reaction vessel and stirred at room temperature for 26 h to allow the ionic liquid to fully enter the MOF channels and interact with the sulfonic acid groups. The mixture was centrifuged at 10000 r / min for 10 min, the supernatant was discarded, and the precipitate was washed with anhydrous acetonitrile to remove excess ionic liquid physically adsorbed on the MOF surface. Finally, it was vacuum dried at 60 °C for 12 h to obtain a low-temperature ionic liquid-cerium-sulfonic acid composite additive.

[0039] S4: In an argon atmosphere glove box with water and oxygen content both <1ppm, 26g of ethylene carbonate (EC), 35g of dimethyl carbonate (DMC) and 26g of ethyl methyl carbonate (EMC) were mixed evenly. Then, 16.5g of lithium difluorosulfonyl imide (LiFSI) was added to the mixed solvent and stirred continuously until completely dissolved. Then, 1.8g of low-temperature ionic liquid-cerium-sulfonic acid composite additive was added. The mixture was first ultrasonically dispersed for 35min and then stirred at 350r / min for 2.5h to obtain a lithium-ion battery electrolyte with high ionic conductivity.

[0040] Comparative Example 1: Based on Example 1, step S3, the preparation of the low-temperature ionic liquid-cerium-sulfonic acid composite additive, was omitted. In step S4, the composite additive was not added. All other steps and parameters remained unchanged to obtain the lithium-ion battery electrolyte.

[0041] Comparative Example 2: Based on Example 1, step S3, the preparation of the low-temperature ionic liquid-cerium-sulfonic acid composite additive, was omitted. In step S4, 1.5g of sulfonic acid-functionalized amino-cerium MOF powder and 0.75g of [EMIm][FSI] ionic liquid were directly added by physical mixing. All other steps and parameters remained unchanged to obtain the lithium-ion battery electrolyte.

[0042] Comparative Example 3: Based on Example 1, step S2, the preparation of sulfonic acid functionalized amino-cerium MOF powder, was omitted. In step S3, the amino-cerium MOF powder produced in step S1 was directly used for ionic liquid impregnation. All other steps and parameters remained unchanged to obtain the lithium-ion battery electrolyte.

[0043] The ionic conductivity of the lithium-ion battery electrolytes prepared in Examples 1-3 and Comparative Examples 1-3 was tested using a precision conductivity meter equipped with a constant-temperature conductivity cell. The lithium-ion battery electrolyte samples prepared in Examples 1-3 and Comparative Examples 1-3 were placed in dry, clean sample bottles, and the conductivity cell was placed in a constant-temperature bath. The temperatures were set to 50℃, 25℃, 0℃, -20℃, -40℃, and -50℃, respectively. After the temperature stabilized, the electrolyte samples were injected into the conductivity cell. After the instrument reading stabilized, the ionic conductivity values ​​of each sample at each temperature were recorded. Each sample was measured three times at each temperature point, and the average value was taken as the final ionic conductivity of the sample. The results are shown in Table 1. As shown in Table 1, the lithium-ion battery electrolytes prepared in Examples 1-3 of this invention exhibit excellent ionic conductivity over a wide temperature range. Under both room temperature and high temperature conditions, the examples and comparative examples maintain high conductivity levels, indicating that the electrolyte system of this invention possesses good basic conductivity. Under low temperature conditions (0℃ to -50℃), the examples show significantly better low-temperature conductivity than the comparative examples. In the extremely low temperature range, the conductivity of the examples remains at a high level, and even shows an increase in conductivity as the temperature decreases. This proves that the electrolyte of this invention has excellent low-temperature fluidity and ion transport capabilities.

[0044] Comparative Example 1, without the composite additive described in this invention, showed in its performance test results that although the conductivity was acceptable at room temperature, it dropped sharply at low temperatures, especially at lower temperatures where the conductivity had decreased significantly and could not be effectively measured at even lower temperatures. This may be because the lack of composite additive leads to a sharp increase in the viscosity of the electrolyte at low temperatures and hinders ion migration. This indicates that constructing a specific ionic liquid-cerium-sulfonic acid composite additive system is indispensable for maintaining the ion transport stability of the electrolyte at extreme low temperatures and is a prerequisite for the electrolyte to function effectively.

[0045] Comparative Example 2 uses a physical mixing method to add the auxiliary components. Its performance test results show that although its low-temperature conductivity is slightly better than that of Comparative Example 1, it is still significantly lower than that of all examples. This indicates that simple physical mixing cannot achieve effective synergy between the auxiliary components, resulting in limited conductivity promotion effect under low-temperature conditions. In contrast, the present invention constructs a more efficient ion transport channel and optimizes the ion migration environment through a specific composite auxiliary system.

[0046] Comparative Example 3 used MOF powder without sulfonation treatment to prepare the additive. The low-temperature conductivity of the resulting electrolyte was significantly deteriorated. The conductivity was greatly reduced at lower temperatures and it was basically ineffective at extremely low temperatures. This result indicates that under the same process conditions, the lack of sulfonation treatment leads to insufficient active sites on the surface of the additive and deterioration of ion migration kinetics. This further proves the key role of the sulfonation treatment described in this invention in achieving high low-temperature conductivity of the electrolyte.

[0047] It should be noted that, in this document, terms such as “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.

[0048] 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.

Claims

1. A method for preparing a lithium-ion battery electrolyte with high ionic conductivity, characterized in that, Includes the following steps: Step 1: Using cerium salt and 2-aminoterephthalic acid as raw materials, amino-cerium-based MOFs are synthesized by a solvothermal method; Step 2: Using an amidation coupling reaction, sulfonic acid groups are grafted onto the MOF framework, and then 1-ethyl-3-methylimidazolium difluorosulfonylimide salt ionic liquid is loaded into the MOF channels by an impregnation method to obtain a low-temperature ionic liquid-cerium-sulfonic acid composite additive. Step 3: Mix the low-temperature ionic liquid-cerium-sulfonic acid composite additive, lithium difluorosulfonyl imide, ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate under an inert atmosphere to obtain a lithium-ion battery electrolyte with high ionic conductivity.

2. The method for preparing a lithium-ion battery electrolyte with high ionic conductivity according to claim 1, characterized in that, The mass ratio of ethylene carbonate, dimethyl carbonate, ethyl methyl carbonate, lithium bis(fluorosulfonyl)imide, and low-temperature ionic liquid-cerium-sulfonic acid composite additive in the high ionic conductivity lithium-ion battery electrolyte is 24-26:32-35:24-26:15-16.5:1.2-1.

8.

3. The method for preparing a lithium-ion battery electrolyte with high ionic conductivity according to claim 1, characterized in that, The specific preparation steps of the low-temperature ionic liquid-cerium-sulfonic acid composite additive are as follows: Under an argon atmosphere, 1-ethyl-3-methylimidazolium difluorosulfonylimide salt ionic liquid and anhydrous acetonitrile were added to a reaction vessel and sonicated until completely dispersed. Sulfonic acid functionalized amino-cerium MOF powder was added to the reaction vessel, and the mixture was stirred at room temperature for 22-26 hours. After centrifugation at 10000 r / min for 10 min, the mixture was washed and dried to obtain a low-temperature ionic liquid-cerium-sulfonic acid composite additive.

4. The method for preparing a lithium-ion battery electrolyte with high ionic conductivity according to claim 3, characterized in that, The ratio of the 1-ethyl-3-methylimidazolium difluorosulfonylimide salt ionic liquid, anhydrous acetonitrile, and sulfonic acid-functionalized amino-cerium MOF powder is 0.6-0.9 g : 30-40 mL : 1.2-1.8 g.

5. The method for preparing a lithium-ion battery electrolyte with high ionic conductivity according to claim 3, characterized in that, The specific preparation steps of the sulfonic acid-functionalized amino-cerium-based MOF powder are as follows: Amino-cerium MOF powder and PBS buffer (pH 7.35) were added to the reaction vessel. While maintaining the rotation speed, the activation solution was slowly added dropwise to the reaction vessel. The pH of the system was adjusted to 7.

2. The reaction was carried out at room temperature and a rotation speed of 250-350 r / min for 2.5-3.5 h. After the reaction was completed, the solid product was collected by centrifugation and washed successively with anhydrous methanol and acetone. Finally, it was vacuum dried at 60 °C for 12 h to obtain sulfonic acid functionalized amino-cerium MOF powder.

6. The method for preparing a lithium-ion battery electrolyte with high ionic conductivity according to claim 5, characterized in that, The ratio of amino-cerium MOF powder, PBS buffer, and activation solution is 1.8-2.2g: 35-45mL: 75-85mL.

7. The method for preparing a lithium-ion battery electrolyte with high ionic conductivity according to claim 5, characterized in that, The activation solution is prepared by mixing p-aminobenzenesulfonic acid, MES buffer with pH 5.5, 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride and N-hydroxysuccinimide in a ratio of 0.7-0.9g:75-85mL:3.4-3.8g:2-2.4g.

8. The method for preparing a lithium-ion battery electrolyte with high ionic conductivity according to claim 5, characterized in that, The specific preparation steps of the amino-cerium-based MOF powder are as follows: 2-Aminoterephthalic acid, N,N-dimethylformamide, and methanol were added to a reaction vessel and stirred at 400-600 r / min until dissolved. Then, cerium nitrate solution was added dropwise to the reaction vessel over 30 min, and the reaction was continued for 0.5-1.5 h. The resulting mixture was transferred to a polytetrafluoroethylene reaction vessel, heated to 150 °C at a rate of 2 °C / min, and reacted for 46-50 h. After the reaction was completed, the mixture was cooled to room temperature, and the product was collected by centrifugation. It was washed with N,N-dimethylformamide and methanol, respectively, and then vacuum dried at 60 °C for 8 h. After grinding and passing through a 200-mesh sieve, amino-cerium-based MOF powder was obtained. The ratio of the amounts of 2-aminoterephthalic acid, N,N-dimethylformamide, methanol, and cerium nitrate solution is 5-5.8 g: 85-95 mL: 8-12 mL: 8-12 mL.

9. The method for preparing a lithium-ion battery electrolyte with high ionic conductivity according to claim 8, characterized in that, The cerium nitrate solution is prepared by mixing cerium nitrate hexahydrate and N,N-dimethylformamide in a ratio of 4-4.5g:8-12mL.

10. A lithium-ion battery electrolyte with high ionic conductivity, prepared according to any one of claims 1-9.

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