Ionic liquid functionalized conductive agent and preparation method and application thereof

Abstract

The invention discloses an ionic liquid functionalized conductive agent as well as a preparation method and application thereof, and relates to the technical field of solid-state batteries. The ionic liquid functionalized conductive agent provided by the invention comprises a modified carbon-based conductive agent core and an ionic liquid which is grafted on the surface of the core and contains an amino functional group, the modified carbon-based conductive agent is a carbon-based conductive agent bonded with carboxyl functional groups on the surface. The ionic liquid group is introduced to the surface of the conductive agent, and the ionic liquid is grafted to the surface of the conductive agent through amidation reaction, so that the interface impedance between the conductive agent and the solid electrolyte can be reduced, and the interface ion transmission capability is enhanced; after grafting, a continuous ion transmission channel can be formed on the surface of the conductive agent, and the ion migration rate is increased.

Description

Technical Field

[0001] This invention relates to the field of solid-state battery technology, and more specifically, to an ionic liquid functionalized conductive agent, its preparation method, and its application. Background Technology

[0002] Lithium-ion batteries have become core energy storage devices in portable electronic devices, electric vehicles, and aerospace due to their significant advantages such as high power density, high operating voltage, environmental friendliness, and low self-discharge rate. With continuously increasing technological demands, developing next-generation lithium-ion batteries that combine high quality, high performance, and high safety has become an industry consensus. Among these, all-solid-state lithium-ion batteries have become a current research hotspot because they completely eliminate the leakage and combustion risks associated with liquid electrolytes and promise to achieve higher energy densities.

[0003] However, the commercial application of solid-state batteries still faces severe challenges. One of the core bottlenecks lies in the poor solid-solid interface contact within the electrode, resulting in high interfacial impedance between the conductive carbon and the solid electrolyte, which severely restricts efficient ion transport. To improve the interface problem, existing technologies attempt to introduce ionic liquids into conductive carbon, but simple physical mixing suffers from weak bonding and easy phase separation and detachment. In-situ polymerization can improve compatibility, but its process is complex and lacks controllability. In contrast, chemical grafting can firmly bond ionic liquid groups to the surface of conductive carbon through stable covalent bonds, providing a highly promising solution for constructing a stable interface. However, the successful implementation of this technology depends heavily on how to efficiently introduce sufficient active sites onto the conductive carbon and achieve precise control over the grafting density, which remains a key technical challenge that needs to be overcome.

[0004] In view of this, the present invention is proposed. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide an ionic liquid functionalized conductive agent, its preparation method, and its applications. By introducing ionic liquid groups onto the surface of a conductive agent and grafting the ionic liquid onto the conductive agent surface via an amidation reaction, the interfacial impedance between the conductive agent and the solid electrolyte can be reduced, enhancing the interfacial ion transport capability. Furthermore, the ionic liquid, acting as an ion conduction medium, can form continuous ion transport channels on the conductive agent surface after grafting, accelerating ion migration rates. The preparation method involves oxidizing a carbon-based conductive agent to introduce carboxyl groups, followed by an amidation reaction to graft an amino-containing ionic liquid onto the conductive agent surface, ultimately forming an ionic liquid functionalized conductive agent with a core-shell structure.

[0006] This invention is implemented as follows: In a first aspect, the present invention provides an ionic liquid functionalized conductive agent, comprising a modified carbon-based conductive agent core and an ionic liquid containing amino functional groups grafted onto the surface of the core. The modified carbon-based conductive agent is a carbon-based conductive agent with carboxyl functional groups bonded to its surface.

[0007] In some preferred embodiments, the carbon-based conductive agent includes at least one of acetylene black, multi-walled carbon nanotubes, graphene, or single-walled carbon nanotubes. The amino-functionalized ionic liquid includes at least one of 1-aminopropyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, 1-aminoethyl-3-methylimidazolium tetrafluoroborate, or 1-aminobutyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide.

[0008] Secondly, the present invention provides a method for preparing an ionic liquid functionalized conductive agent, comprising the following steps: dispersing a carbon-based conductive agent in water to form a uniform suspension, subjecting it to ultrasonic treatment, adding an oxidant to carry out an oxidation reaction, and centrifuging and drying the solution after the reaction to generate a modified carbon-based conductive agent; adding an activating reagent to the modified carbon-based conductive agent suspension to carry out a carboxyl activation reaction, and then adding an ionic liquid containing an amino functional group to carry out an amidation reaction; and finally purifying and drying the solution after the reaction to obtain the ionic liquid functionalized conductive agent.

[0009] In some preferred embodiments, the ultrasonic treatment has a power of 300-500W, a frequency of 30-50Hz, a duration of 30-50min, and a temperature of 30-50℃.

[0010] In some preferred embodiments, the oxidant is a mixed acid formed by mixing sulfuric acid and nitric acid in a volume ratio of (3-5):1, and the oxidation reaction is carried out by stirring at 55-75°C for 6-12 hours.

[0011] In some preferred embodiments, the activating agent is 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide and N-hydroxysuccinimide; the molar ratio of the carboxyl groups of the 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide to the modified carbon-based conductive agent is (1.5-2):1; the molar ratio of the carboxyl groups of the N-hydroxysuccinimide to the modified carbon-based conductive agent is (1-2):1.

[0012] In some preferred embodiments, the carboxyl activation reaction is carried out at 15-30°C for 2-4 hours under an inert atmosphere.

[0013] In some preferred embodiments, the molar ratio of the amino-functionalized ionic liquid to the carboxyl groups of the modified carbon-based conductive agent is (1.2-2):1; the amidation reaction is carried out at 60-70°C for at least 24 hours under an inert atmosphere; and the grafting rate of the amino-functionalized ionic liquid and the modified carbon-based conductive agent is 10%-30%.

[0014] In some preferred embodiments, the purification and drying process includes the following steps: washing sequentially with anhydrous N,N-dimethylformamide and anhydrous ethanol at 8000-10000 rpm for 10-15 min, washing 3-5 times, and then vacuum drying at 50-70°C for at least 12 h.

[0015] Thirdly, the present invention provides an application of ionic liquid functionalized conductive agents in solid-state batteries.

[0016] The present invention has the following beneficial effects: (1) The present invention provides an ionic liquid functionalized conductive agent in which an amino-containing ionic liquid is grafted onto a carbon-based conductive agent. The ionic liquid, as an ion conduction medium, can form a continuous ion transport channel on the surface of the conductive agent after grafting, thereby accelerating the ion migration rate.

[0017] (2) The core-shell structure formed by the amino-containing ionic liquid and the modified conductive agent in the ionic liquid functionalized conductive agent provided by the present invention can improve the structural stability of the conductive agent in the solid-state battery and reduce the impact of volume change on battery performance during charging and discharging.

[0018] (3) In the ionic liquid functionalized conductive agent provided by the present invention, the conductive agent surface is functionalized, which can better combine with other electrode materials to form a more complete conductive network and reduce electron transport resistance. Attached Figure Description

[0019] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 This is a schematic diagram of the preparation process of an ionic liquid functionalized conductive agent provided by the present invention. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0022] The following provides a detailed description of an ionic liquid functionalized conductive agent proposed in this application, its preparation method, and its application.

[0023] In a first aspect, the present invention provides an ionic liquid functionalized conductive agent, comprising a modified carbon-based conductive agent core and an ionic liquid containing amino functional groups grafted onto the surface of the core. The modified carbon-based conductive agent is a carbon-based conductive agent with carboxyl functional groups bonded to its surface.

[0024] In an optional embodiment, the carbon-based conductive agent includes at least one of acetylene black, multi-walled carbon nanotubes, graphene, or single-walled carbon nanotubes. Preferably, it is at least one of acetylene black or multi-walled carbon nanotubes; The amino-functionalized ionic liquid includes at least one of 1-aminopropyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, 1-aminoethyl-3-methylimidazolium tetrafluoroborate, or 1-aminobutyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide. Preferably, it is one of 1-aminopropyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt or 1-aminoethyl-3-methylimidazolium tetrafluoroborate.

[0025] This invention constructs a novel composite conductive material by chemically modifying the surface of a conductive agent with ionic liquid groups (such as imidazole, pyrrolidone, etc.). First, a carbon-based conductive agent is oxidized to introduce carboxyl groups. Then, an amino-containing ionic liquid is grafted onto the conductive agent surface via an amidation reaction, ultimately forming an ionic liquid-functionalized conductive agent with a core-shell structure. This design enables the material to possess both an electronically conductive framework and ion transport channels. Its key feature lies in the strong covalent bond between the ionic liquid groups and the conductive agent.

[0026] First, ionic liquid groups spontaneously form a nanoscale composite conductive layer at the electrode / electrolyte interface, suppressing side reactions between the solid electrolyte (such as LLZO, LGPS) and the electrode material through electrostatic shielding. Second, the flexible chain structure of the ionic liquid enhances the physical contact between the electrode and the electrolyte, increasing the interfacial contact area, especially at high areal capacities (>3 mAh / cm²). 2 Under these conditions, it maintains a stable lithium-ion flux. Third, the covalently grafted ionic liquid groups have high thermal stability, which improves the cycle capacity retention of the electrode at high temperatures compared to the traditional PVDF binder system. Furthermore, this conductive agent modulates the anion type of the ionic liquid group (such as TFSI). - BF4 - This allows for optimized chemical compatibility with different solid-state electrolytes. For example, using FSI... - When anions are used, it promotes uniform deposition of lithium ions in the sulfide electrolyte, enabling lithium metal batteries to exceed 1000 cycles. Synchrotron radiation XAS characterization confirmed that this design effectively eliminates the space charge layer at the interface, reducing the lithium-ion migration barrier from 0.75 eV to 0.45 eV. This molecular-level interface engineering strategy provides an innovative solution for developing high-energy-density, long-life solid-state batteries.

[0027] Secondly, the present invention provides a method for preparing an ionic liquid functionalized conductive agent, the process flow diagram of which is shown below. Figure 1 As shown, it includes the following steps: S1. Disperse the carbon-based conductive agent in water to form a uniform suspension. After ultrasonic treatment, add an oxidant to carry out an oxidation reaction. After the reaction is completed, centrifuge and dry to generate a modified carbon-based conductive agent. The oxidant is a mixed acid formed by mixing sulfuric acid and nitric acid in a volume ratio of (3-5):1. Preferably, the volume ratio of sulfuric acid to nitric acid is 3:1, and the amount of the mixed acid is controlled so that the final concentration of sulfuric acid in the reaction system is not less than 60 wt%. The oxidation reaction is carried out by stirring at 55-75°C for 6-12 hours.

[0028] In an optional embodiment, the concentration of the carbon-based conductive agent suspension is 1-2 mg / mL, and the water is preferably deionized water to avoid adverse effects from ions in the water.

[0029] In some preferred embodiments, the ultrasonic treatment has a power of 300-500W, a frequency of 30-50Hz, a duration of 30-50min, and a temperature of 30-50℃, which can effectively break up agglomerates and ensure that the particles are fully dispersed.

[0030] The core function of introducing active sites through oxidation pretreatment in carbon-based conductive agents is to introduce a large number of carboxyl groups (-COOH) onto the surface of the carbon-based conductive agent through acid oxidation. These carboxyl groups will serve as active reaction sites for subsequent chemical grafting, laying the foundation for the stable binding of ionic liquids.

[0031] S2. Add an activating reagent to the modified carbon-based conductive agent suspension to carry out a carboxyl activation reaction, and then add an ionic liquid containing an amino functional group to carry out an amidation reaction.

[0032] In an optional embodiment, the modified carbon-based conductive agent suspension is prepared by redispersing the modified carbon-based conductive agent in anhydrous dimethylformamide (DMF) at a concentration of 1-10 mg / mL.

[0033] In some preferred embodiments, the activating agent is 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide (EDC) and N-hydroxysuccinimide (NHS); the molar ratio of the carboxyl groups of the 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide to the modified carbon-based conductive agent is (1.5-2):1; the molar ratio of the carboxyl groups of the N-hydroxysuccinimide to the modified carbon-based conductive agent is (1-2):1; EDC and NHS can activate the carboxyl groups to form highly reactive ester intermediates, significantly improving their reaction efficiency with amino groups.

[0034] The carboxyl activation reaction is carried out at 15-30°C for 2-4 hours under an inert atmosphere, preferably nitrogen.

[0035] In some preferred embodiments, the molar ratio of the amino-functionalized ionic liquid to the carboxyl groups of the modified carbon-based conductive agent is (1.2-2):1, preferably 1.2:1; the amidation reaction is carried out under an inert atmosphere, preferably nitrogen, at 60-70°C for at least 24 hours; during this time, the amino group (-NH2) in the ionic liquid molecule undergoes an amidation reaction with the activated carboxyl group (-COOH + -NH2 → -CONH- + H2O). The ionic liquid is stably grafted onto the surface of the conductive agent through covalent bonds, and the grafting rate between the amino-functionalized ionic liquid and the modified carbon-based conductive agent is 10%-30%.

[0036] S3. After the reaction is complete, the ionic liquid functionalized conductive agent is obtained by purification and drying.

[0037] In some preferred embodiments, the purification and drying process includes the following steps: washing with anhydrous N,N-dimethylformamide (DMF) and anhydrous ethanol at 8000-10000 rpm for 10-15 min, washing 3-5 times, and then vacuum drying at 50-70°C for at least 12 h.

[0038] DMF can effectively remove unreacted activating agents and residual ionic liquid monomers, while ethanol further washes away residual DMF and physically adsorbed ionic liquids, ensuring that only functionalized components grafted by covalent bonds are retained in the product. Drying can completely remove residual solvents.

[0039] It should be noted that the concentration of anhydrous ethanol is ≥99.5%.

[0040] The entire preparation process of this invention involves the steps of "oxidation to introduce active groups → activation to enhance reactivity → amidation covalent grafting → purification and drying," which achieves a stable combination of ionic liquid and carbon-based conductive agent. This endows the material with a core-shell structure that combines conductivity with the functional properties of ionic liquids (such as high ionic conductivity and chemical stability), meeting the needs of functionalized conductive materials in fields such as energy storage and catalysis.

[0041] Thirdly, the present invention provides an application of ionic liquid functionalized conductive agents in solid-state batteries.

[0042] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0043] Example 1 This embodiment provides an ionic liquid functionalized conductive agent, the preparation method of which includes the following steps: S1. Disperse 1.0 g of carbon-based conductive agent Super P in 1000 mL of deionized water and sonicate for 30 minutes (400 W) to fully deagglomerate. Slowly add 200 mL of mixed acid (concentrated HNO3:concentrated H2SO4 = 1:3, v / v) and stir at 60 °C for 8 hours. After the reaction is complete, centrifuge to collect the solid, wash with water until neutral, and dry under vacuum at 60 °C to obtain modified Super P (COOH-Super P).

[0044] S2. Redisperse 0.5 g of COOH-Super P in 500 mL of anhydrous DMF, add 2.0 times the molar amount of EDC and 1.0 times the molar amount of NHS of COOH-Super P carboxyl groups, and react at room temperature for 2 hours under nitrogen protection. Add 1.2 times the molar amount of 1-aminopropyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt of COOH-Super P, and react at 60°C under a nitrogen atmosphere for 24 hours.

[0045] S3. The reaction solution was centrifuged (10,000 rpm, 10 min), washed three times each with DMF and anhydrous ethanol, and dried under vacuum at 60°C for 24 hours to obtain ionic liquid functionalized Super P (IL-Super P).

[0046] Example 2 This embodiment provides an ionic liquid functionalized conductive agent, the preparation method of which includes the following steps: S1. Multi-walled carbon nanotubes (MWCNTs) were added to a mixed acid (concentrated HNO3:concentrated H2SO4 = 1:3 v / v) and ultrasonically dispersed for 30 minutes (300 W power) to initially deagglomerate. The mixture was refluxed and condensed in an oil bath for 4 hours at a controlled temperature of 80-90℃. After the reaction was completed, the mixture was cooled to room temperature, diluted to neutral with deionized water, and filtered through a 0.22 μm polytetrafluoroethylene (PTFE) membrane. The filter cake was washed three times with ethanol and vacuum dried at 60℃ for 12 hours to obtain modified MWCNTs (COOH-MWCNTs).

[0047] S2. Disperse COOH-MWCNTs in DMF and sonicate for 30 minutes to form a homogeneous suspension with a concentration of approximately 10 mg / mL. Add EDC and NHS, and stir at room temperature for 2 hours under nitrogen protection. Add 10 mL of a DMF solution of ionic liquid [AEIM][BF4] dropwise, heat to 80°C, and continue the reaction for 12 hours (magnetically stirred at 500 rpm). After the reaction is complete, cool to room temperature.

[0048] S3. Transfer the reaction solution to a centrifuge tube and centrifuge at 10,000 rpm for 15 minutes, discarding the supernatant. Wash the precipitate three times each with DMF, ethanol, and deionized water, sonicating for 5 minutes each time to help remove the physically adsorbed ionic liquid. Dry the final product in a vacuum drying oven at 60°C for 24 hours to obtain ionic liquid modified MWCNTs (IL-MWCNTs).

[0049] Example 3 This embodiment provides an ionic liquid functionalized conductive agent, the preparation method of which includes the following steps: S1. 1.0 g of multi-walled carbon nanotubes (MWCNTs) were dispersed in 1000 mL of deionized water and sonicated for 30 minutes (400 W) to fully deagglomerate. 200 mL of a mixed acid (concentrated HNO3:concentrated H2SO4 = 1:3, v / v) was slowly added, and the mixture was stirred at 60 °C for 8 hours. After the reaction was completed, the solid was collected by centrifugation, washed with water until neutral, and dried under vacuum at 60 °C to obtain modified MWCNTs (COOH-MWCNTs).

[0050] S2. 0.5 g of COOH-MWCNTs were redispersed in 500 mL of anhydrous DMF. EDC (2.0 times the molar amount of the carboxyl group of COOH-MWCNTs) and NHS (1.0 times the molar amount of the carboxyl group of COOH-MWCNTs) were added. The reaction was carried out at room temperature for 2 hours under nitrogen protection. Then, 1.2 times the molar amount of 1-aminopropyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt was added, and the reaction was carried out at 60°C under a nitrogen atmosphere for 24 hours.

[0051] S3. The reaction solution was centrifuged (10,000 rpm, 10 min), washed three times each with DMF and anhydrous ethanol, and dried under vacuum at 60°C for 24 hours to obtain ionic liquid-modified MWCNTs conductive agents.

[0052] Example 4 This embodiment provides an ionic liquid functionalized conductive agent, the preparation method of which includes the following steps: S1. Take a certain amount of acetylene black and place it in a three-necked flask. Add a mixed solution of H2O2 (30%) and concentrated H2SO4 with a volume ratio of about 1:1. Stir well and place the flask in an oil bath at 80°C. Stir magnetically for 8 hours to generate carboxyl groups (-COOH) on the surface of acetylene black. After the reaction is complete, cool the mixture to room temperature, dilute it with deionized water and centrifuge. Wash repeatedly until the supernatant is neutral (pH=6-7) to remove residual acid and impurities. Place the product in a vacuum drying oven at 60°C and dry for 12 hours to obtain modified acetylene black.

[0053] S2. Disperse carboxylated acetylene black in anhydrous DMF and sonicate for 30 minutes to form a uniform suspension. Separately weigh 1-aminopropyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt (diamino ionic liquid), calculate the amount to be used according to the grafting amount of 18wt% (the molar ratio of amino to carboxyl is about 1.5:1, excess ensures sufficient reaction), and dissolve it in a small amount of anhydrous DMF. Slowly add the ionic liquid solution dropwise to the acetylene black suspension, purge with nitrogen to remove air, and stir the reaction in an oil bath at 100℃ for 15 hours to achieve grafting through the amidation reaction of carboxyl and amino groups.

[0054] S3. After the reaction, the solid is collected by centrifugation and washed 3-4 times alternately with anhydrous ethanol and deionized water to remove unreacted ionic liquid and DMF. The mixture is then vacuum dried at 60℃ for 12 hours to obtain the acetylene black composite material grafted with the diamino ionic liquid.

[0055] Example 5 This embodiment provides an ionic liquid functionalized conductive agent, the preparation method of which includes the following steps: S1. Disperse 1.0 g of carbon-based conductive agent Super P in 1000 mL of deionized water and sonicate for 30 minutes (400 W) to fully deagglomerate. Slowly add 200 mL of mixed acid (concentrated HNO3:concentrated H2SO4 = 1:3, v / v) and stir at 60 °C for 8 hours. After the reaction is complete, centrifuge to collect the solid, wash with water until neutral, and dry under vacuum at 60 °C to obtain oxidized Super P (COOH-Super P).

[0056] S2. Weigh a certain amount of carboxyl-containing Super P (COOH-Super P) and 1-methyl-3-(pyrenebutyric acid) imidazole hexafluorophosphate (non-covalent modifier). Add COOH-Super P to an appropriate amount of N,N-dimethylformamide (DMF) and ultrasonically disperse for 15 minutes until initially uniform. Then add 1-methyl-3-(pyrenebutyric acid) imidazole hexafluorophosphate and continue ultrasonic treatment for 2 hours. Non-covalent adsorption modification is achieved by utilizing the π-π stacking effect between the pyrene group and the carbon material.

[0057] S3. Centrifuge and collect the mixed product, wash it 2-3 times with a small amount of solvent to remove the unadsorbed free modifier, and dry it under vacuum at 60℃ for later use; redisperse the non-covalently modified COOH-Super P in anhydrous DMF and sonicate for 30 minutes to form a uniform suspension; weigh 1-aminopropyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt, calculate the amount to be used according to the molar ratio of amino to carboxyl group in COOH-Super P of 1.2-1.5:1, and dissolve it in a small amount of anhydrous DMF.

[0058] S4. Add an appropriate amount of condensing agent (such as 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide, EDC) and catalyst (such as 4-dimethylaminopyridine, DMAP) to the COOH-Super P suspension, stir for 10 minutes to activate the carboxyl group; then slowly add a DMF solution of 1-aminopropyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt, and stir the reaction at 60-70℃ for 12-24 hours.

[0059] S5. After the reaction is complete, the solid product is separated by centrifugation and washed 3-4 times alternately with anhydrous ethanol and deionized water to remove unreacted ionic liquid, condensing agent and solvent. After vacuum drying at 60°C, the final modified product is obtained.

[0060] Comparative Example 1 This comparative example uses pristine multi-walled carbon nanotubes as the conductive agent, without carboxylation or ionic liquid modification.

[0061] Comparative Example 2 This comparative example provides a modified carbon-based conductive agent, the steps of which are the same as those in Example 2, except that only the carbon-based conductive agent is oxidized and no ionic liquid modification is performed.

[0062] Comparative Example 3 This comparative example provides an ionic liquid functionalized conductive agent, the steps of which are the same as those in Example 1, the only difference being that: the carbon-based conductive agent is not oxidized, but the carbon-based conductive agent is directly grafted with the ionic liquid.

[0063] Comparative Example 4 This comparative example provides an ionic liquid functionalized conductive agent, the steps of which are the same as those in Example 1, except that EDC / NHS is not added for carboxyl activation reaction.

[0064] Comparative Example 5 This comparative example provides an ionic liquid functionalized conductive agent, the steps of which are the same as those in Example 1, the only difference being that: a single concentrated nitric acid is used instead of a mixed acid as the oxidant.

[0065] Comparative Example 6 This comparative example provides an ionic liquid functionalized conductive agent, the steps of which are the same as those in Example 1, except that: 1-aminopropyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt is added at a molar amount of 0.5 times that of the carboxyl group in the modified carbon-based conductive agent.

[0066] Comparative Example 7 This comparative example provides an ionic liquid functionalized conductive agent, the steps of which are the same as those in Example 1, the only difference being that the amidation reaction temperature is 25°C.

[0067] Comparative Example 8 This comparative example provides an ionic liquid functionalized conductive agent, the steps of which are the same as those in Example 1, the only difference being that the carboxyl activation reaction and amidation reaction are both carried out in an air atmosphere.

[0068] Comparative Example 9 This comparative example provides an ionic liquid functionalized conductive agent, the preparation method of which includes the following steps: S1. Weigh 1.0 g of MWCNTs into a 500 mL round-bottom flask, add 100 mL of 4 M nitric acid solution (prepared by diluting with 65% concentrated nitric acid), and sonicate; preheat in an oil bath to 120 °C, react for 12 hours, and dry under vacuum at 60 °C for 24 hours to obtain COOH-MWCNTs.

[0069] S2. Take 500 mg COOH-MWCNTs into a dry Schlenk flask, add 20 mL of freshly distilled SOCl2 (it is recommended to add 1 drop of DMF for catalysis), reflux at 70 °C for 6 hours (a tail gas absorption device needs to be installed), cool and remove excess SOCl2 by vacuum distillation, and wash 3 times with anhydrous THF (10 mL each time).

[0070] After S3, COOH-MWCNTs reacted with SOCl2, they were reacted with 1-aminobutyl-3-methylimidazolium hexafluorophosphate (0.6 g) in THF at 60 °C for 10 hours to obtain ionic liquid functionalized MWCNTs.

[0071] Comparative Example 10 This comparative example provides an ionic liquid functionalized conductive agent, the preparation method of which includes the following steps: S1. Disperse 1.0 g of carbon-based conductive agent Super P in 1000 mL of deionized water and sonicate for 30 minutes (400 W) to fully deagglomerate. Slowly add 200 mL of mixed acid (concentrated HNO3:concentrated H2SO4 = 1:3, v / v) and stir at 60 °C for 8 hours. After the reaction is complete, centrifuge to collect the solid, wash with water until neutral, and dry under vacuum at 60 °C to obtain modified Super P (COOH-Super P).

[0072] S2. Disperse 0.5 g COOH-Super P in 50 mL SOCl2, add 1 drop of DMF as a catalyst, reflux at 70 °C for 6 hours, remove excess SOCl2 by evaporation to obtain acyl chloride Super P, react the acyl chloride product with 1-aminopropyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt (1.2 times the molar amount of carboxyl group) in DMF at 80 °C for 12 hours.

[0073] S3. The reaction solution was centrifuged (10,000 rpm, 10 min), washed three times each with DMF and anhydrous ethanol, and dried under vacuum at 60°C for 24 hours to obtain IL-Super P.

[0074] Experimental Example 1 The ionic liquid functionalized conductive agents prepared in the various embodiments and comparative examples were combined with positive electrode active materials and binders to form a positive electrode slurry, which was then coated onto aluminum foil. After drying and rolling, the slurry was punched into a positive electrode sheet. The negative electrode was made of lithium metal foil or a corresponding material. The solid electrolyte was coated or pre-pressed into a film according to its type. The positive electrode, solid electrolyte, and negative electrode were stacked in sequence and then hot-pressed into shape. The solid electrolyte was then encapsulated in an inert atmosphere using an aluminum-plastic film or a metal shell. The cycle performance of the all-solid-state battery was tested using the Blue Battery Testing System. The test voltage range was 2.5-4.25V. Before the test, the all-solid-state battery was placed at the test temperature for 12 hours to reach a stable state. The battery was first activated by performing 5 cycles of charge-discharge at a low rate of 0.1C. Then, 100 cycles of charge-discharge were performed at a rate of 0.5C. The capacity retention rate was recorded, and the data are shown in Table 1.

[0075] Table 1. Ionic conductivity and capacity retention of each embodiment and comparative example

[0076] Based on the experimental results above, the ionic liquid functionalized conductive agents prepared in Examples 1 to 5 all exhibit excellent electrochemical performance in all-solid-state batteries. Their ionic conductivity is generally in the range of 4.8–6.3 mS / cm, and the capacity retention after 100 cycles exceeds 91%, significantly better than all comparative examples. The dismal performance of Comparative Example 1 (capacity retention of 72.6%) of the original MWCNTs indicates that conductive agents lacking interface modification cannot work effectively in solid-state systems. Comparative Example 2, which only uses mixed acid oxidation, shows improvement but is still insufficient, indicating that simple carboxylation, while providing hydrophilicity, fails to solve the fundamental bottleneck of ion transport. The success of these examples lies in the preservation of the electronic conduction framework of the conductive agent itself, while the grafted ionic liquid layer forms a highly efficient ion conduction pathway on its surface. This construction of a dual-continuous "electron-ion" channel ensures that the electrode reaction proceeds efficiently and uniformly in three-dimensional space, which is the physical basis for improving battery rate performance and cycle stability.

[0077] Furthermore, every step in the preparation process is crucial; the omission or weakening of any step will lead to a decline in performance. First, the performance of Comparative Example 3 (omitted oxidation) and Comparative Example 5 (oxidation with concentrated nitric acid alone) was significantly lower than that of Example 1, indicating that mixed acid oxidation is key to the efficient introduction of carboxyl functional groups. H2SO4 plays a role in dehydration and promotes the nitration reaction of HNO3, creating more and more uniform grafting sites on the carbon material surface. Insufficient grafting sites directly lead to a decrease in the final ionic liquid coverage and imperfect ion channels. Second, the performance degradation of Comparative Example 4 (omitted activation) indicates that the direct amidation reaction between carboxyl and amino groups is inefficient. EDC / NHS, as a highly efficient carboxyl activator, can convert carboxyl groups into mediators that are more readily reacted with amino groups, significantly improving the grafting rate and reaction specificity. Omitting this step results in a large number of carboxyl groups failing to participate in the reaction, leading to insufficient grafting of the ionic liquid. Finally, the performance degradation of Comparative Example 6 (reduced ionic liquid amount), Comparative Example 7 (lower reaction temperature), and Comparative Example 8 (no nitrogen protection) collectively points to the importance of reaction kinetics and side reaction control. Sufficient reactant concentration and suitable temperature are necessary conditions to ensure a high grafting rate; however, the lack of nitrogen protection may cause some active components (such as activated carboxyl groups) to be destroyed by oxygen or moisture in the air, or trigger unnecessary side reactions.

[0078] Furthermore, Comparative Examples 9 and 10 employed the conventional SOCI2 acyl chloride method for grafting. While their performance was superior to the incompletely treated comparative examples, it still failed to reach the level of Example 1. This is likely because the SOCI2 method involves harsh reaction conditions (requiring complete anhydrousness and generating corrosive gases), which may cause some damage to the structure of the carbon material. Alternatively, the grafting process may not be as gentle and precise as the EDC / NHS method, resulting in a slightly inferior final interface layer quality.

[0079] By introducing sufficient carboxyl sites through "mixed acid oxidation pretreatment," followed by "EDC / NHS activation" to achieve efficient and controllable covalent grafting, and then reacting with ionic liquids under optimized reaction conditions, this is one of the most effective ways to prepare high-performance ionic liquid functionalized conductive agents. This strategy successfully solves the problem of ion transport inside solid-state battery electrodes, providing a key material foundation for the development of long-life, high-safety all-solid-state batteries.

[0080] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. An ionic liquid functionalized conductive agent, characterized in that, It includes a modified carbon-based conductive agent core and an ionic liquid containing amino functional groups grafted onto the surface of the core; The modified carbon-based conductive agent is a carbon-based conductive agent with carboxyl functional groups bonded to its surface.

2. The ionic liquid functionalized conductive agent according to claim 1, characterized in that, The carbon-based conductive agent includes at least one of acetylene black, multi-walled carbon nanotubes, graphene, or single-walled carbon nanotubes. The amino-functionalized ionic liquid includes at least one of 1-aminopropyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, 1-aminoethyl-3-methylimidazolium tetrafluoroborate, or 1-aminobutyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide.

3. A method for preparing an ionic liquid functionalized conductive agent as described in claim 1 or 2, characterized in that, Includes the following steps: A carbon-based conductive agent is dispersed in water to form a uniform suspension. After ultrasonic treatment, an oxidant is added to carry out an oxidation reaction. After the reaction is completed, the agent is centrifuged and dried to generate a modified carbon-based conductive agent. An activating reagent was added to a suspension of modified carbon-based conductive agent to carry out a carboxyl activation reaction. Then, an ionic liquid containing an amino functional group was added to carry out an amidation reaction. After the reaction was completed, the ionic liquid functionalized conductive agent was obtained by purification and drying.

4. The method for preparing an ionic liquid functionalized conductive agent according to claim 3, characterized in that, The ultrasonic treatment has a power of 300-500W, a frequency of 30-50Hz, a duration of 30-50min, and a temperature of 30-50℃.

5. The method for preparing an ionic liquid functionalized conductive agent according to claim 3, characterized in that, The oxidant is a mixed acid formed by mixing sulfuric acid and nitric acid in a volume ratio of (3-5):1, and the oxidation reaction is carried out by stirring at 55-75°C for 6-12 hours.

6. The method for preparing an ionic liquid functionalized conductive agent according to claim 3, characterized in that, The activating agent is 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide and N-hydroxysuccinimide; the molar ratio of the carboxyl groups of the 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide and the modified carbon-based conductive agent is (1.5-2):1; the molar ratio of the carboxyl groups of the N-hydroxysuccinimide and the modified carbon-based conductive agent is (1-2):

1.

7. The method for preparing an ionic liquid functionalized conductive agent according to claim 3, characterized in that, The carboxyl activation reaction is carried out under an inert atmosphere at 15-30°C for 2-4 hours.

8. The method for preparing an ionic liquid functionalized conductive agent according to claim 3, characterized in that, The molar ratio of the amino-functionalized ionic liquid to the carboxyl groups of the modified carbon-based conductive agent is (1.2-2):1; the amidation reaction is carried out at 60-70°C for at least 24 hours under an inert atmosphere; the grafting rate of the amino-functionalized ionic liquid and the modified carbon-based conductive agent is 10%-30%.

9. The method for preparing an ionic liquid functionalized conductive agent according to claim 3, characterized in that, The purification and drying process includes the following steps: washing with anhydrous N,N-dimethylformamide and anhydrous ethanol at 8000-10000 rpm for 10-15 min, washing 3-5 times, and then vacuum drying at 50-70 ℃ for at least 12 h.

10. The application of an ionic liquid functionalized conductive agent as described in claim 1 or 2 in a solid-state battery.

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