Lithium ion battery repair liquid and preparation method thereof

Abstract

The invention discloses a lithium ion battery repair liquid and a preparation method thereof in the field of electrochemical battery repair. The repair liquid comprises a carbonic ester solvent, lithium hexafluorophosphate, a film-forming additive and a key nitrogen-phosphorus co-doped porous carbon nanosphere grafted polyethylene oxide interface stabilizer according to a specific ratio. The preparation method mainly comprises the following steps: sequentially dissolving the components in an inert atmosphere and uniformly dispersing the functional additive. The interface stabilizer is prepared by synthesizing nitrogen and phosphorus co-doped carbon nanospheres through a template method, then carrying out acid oxidation and acyl chloride activation, and grafting with polyethylene oxide. The repairing liquid can effectively infiltrate an aged battery electrode, and functional components of the repairing liquid can repair a damaged solid electrolyte interface film and reconstruct a conductive network, so that the capacity and the cycle performance of the battery are remarkably recovered, and the service life of the battery is prolonged. The method is simple in process and suitable for repairing and regenerating aged lithium ion batteries of various systems.

Description

Technical Field

[0001] This invention relates to the field of electrochemical battery repair technology, specifically to a lithium-ion battery repair solution and its preparation method. Background Technology

[0002] Lithium-ion batteries, as the core of contemporary energy storage technology, face significant bottlenecks in performance degradation and lifespan limitations, hindering the further development of electric vehicles, large-scale energy storage, and portable electronic devices. After long-term cycling, the irreversible capacity loss of batteries stems primarily from two aspects: first, the continuous consumption of active lithium during the formation and repair of the solid electrolyte interface film; and second, the continuous damage and thickening of electrode materials, especially the interface film on the negative electrode surface, as well as the degradation of the conductive network caused by microcracks in the electrode structure. These two factors are interconnected, jointly exacerbating the increase in battery internal resistance and the decrease in effective capacity. To address these issues, existing technologies have primarily explored two repair pathways: one is "lithium replenishment" technology, which directly supplements active materials, such as adding lithium-rich compounds during manufacturing or injecting lithium-containing reagents into failed batteries. These methods focus on replenishing the lithium source but have limited improvement on the deterioration of electron-ion transport caused by physical structural damage; the other is "repair" technology targeting the electrode interface, aiming to stabilize or rebuild more efficient ion transport channels, such as adding film-forming additives to the electrolyte to optimize the interface film composition. However, these traditional interface additives are mostly small molecules or homopolymers, and their effects on complex electrode surfaces are relatively limited, lacking the ability to physically repair and maintain the electrode microstructure over a long period of time.

[0003] In the field of interface repair, carbon-based nanomaterials have attracted attention due to their excellent conductivity and chemical stability. Researchers have attempted to introduce carbon nanotubes, graphene, and other materials as functional additives into battery systems to improve electrode conductivity. However, unmodified carbon materials have strong surface inertness, poor interfacial compatibility with electrolytes and electrode active materials, and are prone to aggregation, making it difficult to uniformly disperse and form a stable, dense repair layer on the electrode surface. More importantly, simple physical doping cannot achieve a strong bond with the electrode structure and is prone to failure during the volume changes of long-term battery cycling. On the other hand, polymers with flexibility and lithium-ion conductivity, such as polyethylene oxide, have been studied for coating electrode materials to buffer volume effects and promote lithium-ion transport. However, simple polymer coatings often lack sufficient mechanical strength, have poor electronic conductivity, and weak bonding with the electrode. Therefore, current technologies lack a solution that can deeply integrate the structural support and electronically conductive network repair capabilities of carbon materials with the interfacial compatibility, ion conduction, and volume adaptability of polymers through stable chemical bonding.

[0004] In summary, significant technological gaps remain in the current repair of aging lithium-ion batteries, particularly in the synergistic regeneration of the complex system of electrode interfaces and conductive networks. An ideal repair material should possess multiple composite functions: it should be able to precisely repair physical cracks in electrode materials at the nanoscale, rebuilding efficient electron conduction pathways; and it should be able to construct a stable ion transport layer on the electrode surface through good interfacial wettability and flexibility, thereby simultaneously addressing the physical and chemical causes of battery degradation. However, the controllable and robust chemical integration of highly conductive doped carbon nanostructures with long-chain ion-conducting polymers, and the resulting dispersibility and interfacial activity suitable for the complex electrolyte environment of batteries, remains a challenge that has not been adequately addressed. This hinders the development of efficient, long-lasting, and universal battery repair technologies. Against this backdrop, this invention aims to propose a novel interfacial functional material design and its application in battery repair solutions to overcome these limitations. Summary of the Invention

[0005] The purpose of this invention is to provide a lithium-ion battery repair solution and its preparation method, which solves the technical problem that existing lithium-ion battery repair technologies have limited functionality and cannot simultaneously and effectively repair the deteriorated electrode interface and the degraded conductive network in aged batteries, resulting in incomplete repair and short-lasting effects.

[0006] The present invention achieves the above objectives through the following technical solutions: A method for preparing a lithium-ion battery repair solution, comprising the following steps: S1. In an argon-filled glove box, ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate are added to a dry, sealed glass container and stirred at 24-26°C to obtain a mixed solvent; lithium hexafluorophosphate is added and stirred continuously in a constant temperature water bath at 34-36°C to obtain a basic electrolyte. S2. Add fluoroethylene carbonate and ethylene sulfate to the basic electrolyte and stir at 24-26℃; add nitrogen and phosphorus co-doped porous carbon nanospheres grafted with polyethylene oxide interface stabilizer, sonicate, and allow to stand for aging.

[0007] In this invention, nitrogen-phosphorus co-doped porous carbon nanospheres grafted with polyethylene oxide interface stabilizers are incorporated into the lithium-ion battery repair solution formulation. Their repair mechanism on aged batteries manifests as a multi-layered physicochemical synergy. When the repair solution is introduced into the aged battery system, the interface stabilizer, with its nanoscale and surface properties, can effectively disperse and penetrate deep into the electrode structure where microcracks have formed due to long-term cycling. Its rigid nitrogen-phosphorus co-doped carbon nanosphere core can embed between active material particles, bridging the electron conduction paths broken due to volume expansion and contraction, directly repairing and enhancing the electronic conductivity network of the electrode. This physical repair effect cannot be achieved by simple liquid additives or polymers. Meanwhile, the surface-grafted polyethylene oxide (PEO) long chains play multiple key roles: on the one hand, the PEO segments possess excellent lithium-ion solvation ability and chain mobility, forming a dynamic interface layer with excellent ionic conductivity on the surface of the carbon spheres and electrode materials, significantly promoting uniform and rapid lithium-ion transport at the interface and reducing charge transfer impedance; on the other hand, this flexible long chain, through entropic elastic steric hindrance effect, can effectively adapt to the volume changes of the electrode materials during charging and discharging, buffering stress and preventing mechanical damage to the newly formed interface film. More importantly, this structure can produce a synergistic effect with other film-forming additives in the repair solution. Components such as fluoroethylene carbonate and ethylene sulfate in the repair solution are preferentially reduced on the electrode surface, constructing a dense and stable solid electrolyte interface film foundation; while this stabilizer, on this basis, through the physical reinforcement of its carbon core and the optimization and dynamic buffering of ion transport in the PEO shell, jointly constructs a more robust, stable, and self-adaptive composite interface layer. This composite layer effectively suppresses side reactions such as the continuous decomposition of the electrolyte and the shuttle effect of transition metal ions, thereby fundamentally blocking the chain reaction of battery performance degradation and achieving efficient recovery of capacity and cycle life. This mechanism breaks through the limitations of traditional repair technologies that only focus on chemical lithium replenishment or single interface modification, and realizes integrated synergistic repair of the electrode interface and the bulk conductive network.

[0008] According to a preferred embodiment of the present invention, in step S1, the stirring time is 30-60 min at 24-26°C.

[0009] According to a preferred embodiment of the present invention, in step S2, the stirring time is 4-6 hours at 18-20°C.

[0010] According to a preferred embodiment of the present invention, the preparation method of the nitrogen-phosphorus co-doped porous carbon nanospheres grafted with polyethylene oxide interface stabilizer includes: A1. Mesoporous silica nanospheres were dispersed in a water-ethanol mixed solution containing melamine and phytic acid, and ultrasonically treated to obtain a mixture. The mixture was transferred to a hydrothermal reactor and reacted at 175-185℃ to obtain a nitrogen-phosphorus polymer-coated composite precursor. The nitrogen-phosphorus polymer-coated composite precursor was centrifuged, washed, and dried, and then carbonized in a tube furnace under an argon atmosphere with programmed temperature rise. After carbonization, it was etched with hydrofluoric acid aqueous solution, centrifuged, washed with water until neutral, and freeze-dried to obtain nitrogen-phosphorus co-doped porous carbon nanospheres. A2. Nitrogen-phosphorus co-doped porous carbon nanospheres were dispersed in a mixed acid solution of concentrated nitric acid and concentrated sulfuric acid, and ultrasonically oxidized at 60-80℃. After centrifugation and washing with water until neutral, they were dried to obtain nitrogen-phosphorus co-doped porous carbon nanospheres with carboxyl groups on the surface. A3. Disperse nitrogen and phosphorus oxide co-doped porous carbon nanospheres with carboxyl groups on the surface in anhydrous N,N-dimethylformamide, add thionyl chloride, and reflux at 68-72℃ to obtain a reaction mixture. Distill the reaction mixture under reduced pressure to obtain activated carbon nanospheres with acyl chloride groups on the surface. A4. Activated carbon spheres with acyl chloride groups on their surface are redispersed in anhydrous toluene. Monomethoxy-terminated polyethylene oxide and triethylamine are added, and the mixture is refluxed at 80-100°C under argon protection to obtain a mixture. The mixture is cooled to room temperature, and the product is separated by centrifugation. The product is washed repeatedly with toluene and methanol in sequence, and finally dried under vacuum at 38-42°C.

[0011] According to a preferred embodiment of the present invention, the preparation steps of the monomethoxyl-terminated polyethylene oxide include: First, under nitrogen protection, 200 mL of anhydrous tetrahydrofuran is added to a strictly dried 500 mL three-necked flask, followed by 1.2 g of potassium metal. Then, 3.2 g of anhydrous methanol is slowly added dropwise under ice bath cooling, controlling the dropping temperature at 20°C. After the addition is complete, the reaction is continued at 25°C with stirring for 6 h to obtain a potassium methoxide initiator solution. Next, all the above solutions are transferred to a 2 L high-pressure reactor. The reaction system is evacuated to 5 Pa and cooled. Then, 220 g of purified gaseous ethylene oxide monomer is precisely introduced. The reactor is placed in a 70°C oil bath and the reaction is continuously stirred at 300 rpm for 48 h. After the reaction is completed, the system is cooled to 5°C, and after depressurization, 2 mL of glacial acetic acid is added to terminate the reaction. The resulting reaction solution was concentrated under reduced pressure at 45°C to remove the solvent. The crude product was dissolved in 500 mL of dichloromethane and washed three times with 200 mL of deionized water to thoroughly remove water-soluble impurities such as potassium acetate. The organic phase was dried over anhydrous magnesium sulfate, filtered, and the filtrate was concentrated to approximately 100 mL. This filtrate was then slowly added dropwise to 2000 mL of cold diethyl ether under vigorous stirring to induce precipitation. The white solid was collected by filtration, washed with 3 × 100 mL of cold diethyl ether, and finally dried in a vacuum drying oven at 40°C for 24 h to obtain the target product, a white waxy solid with monomethoxyl-terminated polyethylene oxide. The entire process must be carried out under a strictly dehydrated inert atmosphere to ensure product purity and the expected molecular weight.

[0012] In this invention, the preparation process of nitrogen-phosphorus co-doped porous carbon nanospheres grafted with polyethylene oxide interface stabilizers embodies a chemical reaction logic of progressively constructing a "rigid-flexible" heterostructure. The entire preparation begins with mesoporous silica nanospheres as a hard template, whose uniform pores provide precise shape and size control for the precursor. Melamine and phytic acid are hydrothermally polymerized and subsequently carbonized on their surface. Essentially, melamine provides the nitrogen source and constructs the carbon framework, while phytic acid acts as both a phosphorus source and a crosslinking agent, synergistically transforming into a nitrogen-phosphorus co-doped graphitized carbon layer at high temperature. After etching to remove the template, porous carbon nanospheres with high conductivity, doped active sites, and replication from the template are obtained. Subsequently, they are subjected to ultrasonic oxidation treatment with a mixture of concentrated nitric acid and concentrated sulfuric acid, a key surface functionalization step: the strong oxidizing acid attacks the defects and edges of the carbon sphere surface, introducing a large number of carboxyl functional groups, thereby transforming the originally chemically inert carbon surface into a platform rich in active reaction sites. Next, under anhydrous conditions, thionyl chloride is reacted with these carboxyl groups in a classic acyl chloride process. The hydroxyl groups in the carboxyl groups are replaced by chlorine atoms, generating highly reactive acyl chloride groups. This step transforms the surface of the carbon spheres into an "activated" state, readily undergoing nucleophilic substitution reactions. Finally, in the presence of the basic reagent triethylamine, the activated carbon spheres with acyl chloride groups on their surface undergo a nucleophilic substitution reaction with the terminal hydroxyl groups of the monomethoxyl-terminated polyethylene oxide, generating covalent ester bonds. This permanently grafts the flexible polyethylene oxide long chain onto the rigid carbon nanosphere core via chemical grafting. Thus, a core functional material with a conductive porous carbon core and a flexible ionic conductor shell is synthesized, its structure ensuring an organic combination of electronic and ionic conductivity.

[0013] According to a preferred embodiment of the present invention, in step A1, the reaction time is 12-14 h at 175-185°C.

[0014] According to a preferred embodiment of the present invention, in step A2, the ultrasonic oxidation treatment at 60-80°C is carried out for 2-4 hours.

[0015] According to a preferred embodiment of the present invention, in step A3, the reflux reaction time at 68-72°C is 12-14 hours.

[0016] According to a preferred embodiment of the present invention, in step A4, the reflux reaction at 80-100°C takes 24-36 hours.

[0017] The present invention also provides a lithium-ion battery repair solution prepared by the method described above, comprising the following raw materials in parts by weight: 20-35 parts by weight of ethylene carbonate; 20-35 parts by weight of dimethyl carbonate; 20-35 parts by weight of ethyl methyl carbonate; 8-15 parts by weight of lithium hexafluorophosphate; 1-5 parts by weight of fluoroethylene carbonate; 0.5-2 parts by weight of ethylene sulfate; and 0.5-3 parts by weight of nitrogen-phosphorus co-doped porous carbon nanospheres grafted with polyethylene oxide interface stabilizer.

[0018] The beneficial effects of this invention are as follows: The lithium-ion battery repair solution and its preparation method provided by this invention can bring significant and multifaceted performance recovery and improvement to aged lithium-ion batteries. Its technical effects are mainly reflected in three aspects: the synergy of the repair mechanism, the comprehensive improvement of battery performance, and the superiority of the technology application.

[0019] First, this repair solution achieves a dual repair mechanism combining physical and chemical approaches by grafting a polyoxyethylene (PEE) interface stabilizer onto nitrogen-phosphorus co-doped porous carbon nanospheres. This stabilizer possesses a unique heterogeneous structure: its core consists of nitrogen-phosphorus co-doped porous carbon nanospheres with high specific surface area, excellent electronic conductivity, and structural rigidity; its outer shell is composed of flexible long chains of PEE grafted through stable chemical bonds. When the repair solution is injected into an aged battery, this component effectively disperses and penetrates into the electrode material, especially the microcracks and pores on the negative electrode surface. The carbon nanosphere core bridges broken active material particles, rebuilding an efficient electronic conductivity network and directly reducing the ohmic impedance of the electrode. Simultaneously, the long chains of PEE in the outer shell, due to their excellent lithium-ion solvation capability and flexibility, form a well-conducting interface layer between the carbon nanospheres and the electrode material surface, promoting uniform lithium-ion deposition and deintercalation, and buffering volumetric stress during cycling. This structural design simultaneously repairs the critical interfaces of battery degradation through both electron and ion transport pathways.

[0020] Secondly, based on the aforementioned synergistic repair mechanism, aged batteries treated with this repair solution exhibit comprehensive improvements in several key electrochemical performance aspects. The most direct effect is a significant recovery of the battery's reversible capacity, due to the restored lithium-ion intercalation / deintercalation active sites and lower reaction impedance in the repaired electrodes. The battery's rate performance is also enhanced, as the reconstructed conductive network and optimized interface greatly improve charge transfer kinetics. Cycle stability is fundamentally improved, partly due to the robust carbon core support and the buffering effect of the flexible polymer chains, which jointly stabilize the electrode structure and inhibit the pulverization and peeling of active materials; and partly due to the dense and stable novel interface layer, which effectively reduces continuous side reactions in the electrolyte and prevents excessive thickening of the solid electrolyte interfacial film. Therefore, the repaired battery not only recovers its capacity but also significantly slows down its degradation rate, achieving an effective extension of its lifespan.

[0021] Finally, this invention possesses significant advantages in both technical implementation and application. The entire preparation process of the repair solution is mild and simple, using all commonly available raw materials, making large-scale preparation easy. The designed synthetic route for the interface stabilizer is logically clear, ensuring the precision of the product structure and the reliability of its performance through stepwise oxidation, activation, and grafting reactions. This repair solution is applicable to various mainstream lithium-ion battery systems, demonstrating excellent repair effects on multiple interface failure modes caused by long-term cycling, over-discharge, or storage aging, exhibiting strong versatility. Compared to physical repairs requiring battery disassembly or single additives offering only short-term improvements, this invention provides a highly efficient, long-lasting, and easily implemented in-situ chemical repair solution, offering a reliable technical means for the recycling and value regeneration of lithium-ion batteries, and possessing significant economic and environmental value. Detailed Implementation

[0022] The following detailed embodiments are only used to further illustrate this application and should not be construed as limiting the scope of protection of this application. Those skilled in the art can make some non-essential improvements and adjustments to this application based on the above application content.

[0023] Preparation Example 1 This preparation example provides a method for preparing monomethoxyl-terminated polyethylene oxide, comprising the following steps: First, under nitrogen protection, 200 mL of anhydrous tetrahydrofuran is added to a strictly dried 500 mL three-necked flask, followed by 1.2 g of potassium metal. Then, 3.2 g of anhydrous methanol is slowly added dropwise under ice bath cooling, controlling the dropping temperature at 20 °C. After the addition is complete, the reaction is continued at 25 °C with stirring for 6 h to obtain a potassium methoxide initiator solution. Next, all the above solutions are transferred to a 2 L high-pressure reactor. The reaction system is evacuated to 5 Pa and cooled. Then, 220 g of purified gaseous ethylene oxide monomer is precisely introduced. The reactor is placed in a 70 °C oil bath and the reaction is continuously stirred at 300 rpm for 48 h. After the reaction is completed, the system is cooled to 5 °C, and after depressurization, 2 mL of glacial acetic acid is added to terminate the reaction. The resulting reaction solution was concentrated under reduced pressure at 45°C to remove the solvent. The crude product was dissolved in 500 mL of dichloromethane and washed three times with 200 mL of deionized water to thoroughly remove water-soluble impurities such as potassium acetate. The organic phase was dried over anhydrous magnesium sulfate, filtered, and the filtrate was concentrated to approximately 100 mL. This filtrate was then slowly added dropwise to 2000 mL of cold diethyl ether under vigorous stirring to induce precipitation. The white solid was collected by filtration, washed with 3 × 100 mL of cold diethyl ether, and finally dried in a vacuum drying oven at 40°C for 24 h to obtain the target product, a white waxy solid with monomethoxyl-terminated polyethylene oxide. The entire process must be carried out under a strictly dehydrated inert atmosphere to ensure product purity and the expected molecular weight.

[0024] Example 1: Preparation of nitrogen-phosphorus co-doped porous carbon nanospheres grafted with polyethylene oxide interface stabilizer: Preparation of carbon nanosphere precursor. 1.0 g of mesoporous silica nanospheres were added to a 50 mL mixed solvent containing 0.5 g of melamine and 0.5 g of phytic acid. The mixed solvent consisted of 25 mL of deionized water and 25 mL of anhydrous ethanol. The system was sonicated at room temperature for 30 minutes to obtain a uniformly dispersed mixture. Subsequently, the mixture was transferred to a 100 mL polytetrafluoroethylene-lined hydrothermal reactor, sealed, and placed in an oven at 180 °C for 13 hours. After the reaction, the mixture was allowed to cool naturally to room temperature. The resulting product was separated by centrifugation and washed three times each with deionized water and anhydrous ethanol, each centrifugation at 8000 rpm for 10 minutes. The washed solid was dried in a vacuum drying oven at 80 °C for 12 hours to obtain a nitrogen-phosphorus polymer-coated silica composite precursor. Carbonization and template removal. The dried precursor was placed in a quartz boat in a tube furnace and subjected to programmed temperature carbonization under a continuously flowing argon atmosphere. The specific temperature program was as follows: the temperature was increased from room temperature to 350°C at a rate of 2°C / min and held at that temperature for 1 hour; then, the temperature was further increased to 800°C at a rate of 5°C / min and held at that temperature for 2 hours. After carbonization, the mixture was naturally cooled to room temperature in an argon flow to obtain a silicon-carbon composite. This composite was immersed in 50 mL of a 5% (w / w) aqueous solution of hydrofluoric acid and stirred at room temperature for 24 hours to thoroughly etch the silica template. The etched product was collected by centrifugation and washed with a large amount of deionized water until the pH of the supernatant was neutral. Finally, the product was freeze-dried to obtain black nitrogen-phosphorus co-doped porous carbon nanospheres, denoted as NPCNS. Surface oxidation introduced carboxyl groups. 0.5 g of the above NPCNS was dispersed in 80 mL of a mixed acid solution, which was prepared by pre-mixing 20 mL of concentrated nitric acid and 60 mL of concentrated sulfuric acid and cooling to room temperature. The dispersion was subjected to ultrasonic oxidation treatment at 70°C for 3 hours using a 250W ultrasonic cell disruptor (2 seconds of sonication followed by a 3-second interval). After treatment, the reaction solution was quenched in 500 mL of ice water, and the solid was collected by centrifugation and repeatedly washed with deionized water until neutral. The washed solid was dried in a vacuum drying oven at 70°C for 12 hours to obtain nitrogen oxide phosphorus co-doped porous carbon nanospheres with carboxyl groups on the surface, denoted as O-NPCNS. Surface acyl chloride activation was then performed. 0.4 g of dried O-NPCNS was dispersed in 50 mL of anhydrous N,N-dimethylformamide, and 2.0 mL of thionyl chloride was slowly added. The mixture was heated to 70°C under argon protection and refluxed at this temperature for 13 hours. After the reaction, the reaction apparatus was connected to a rotary evaporator, and the mixture was distilled under reduced pressure in a 40°C water bath to remove excess thionyl chloride and most of the solvent, yielding activated carbon nanosphere wet solids with acyl chloride groups on the surface. This intermediate must be kept anhydrous and used immediately in the next reaction. Polyethylene oxide grafting.The activated carbon sphere intermediates obtained in the previous step were rapidly redispersed in 50 mL of anhydrous toluene dried with metallic sodium. 2.0 g of monomethoxylated terminal polyethylene oxide and 0.2 mL of triethylamine were added to the suspension. Under argon protection, the mixture was heated to 90 °C and refluxed for 30 hours. After the reaction was complete, the mixture was cooled to room temperature, transferred to a centrifuge tube, and centrifuged at 10,000 rpm for 15 minutes to separate the product. The resulting solid was washed three times each with anhydrous toluene and anhydrous methanol to thoroughly remove physically adsorbed polymers and reagents. Finally, the product was placed in a vacuum drying oven and dried at 40 °C for 24 hours to obtain the final product, a nitrogen-phosphorus co-doped porous carbon nanosphere grafted polyethylene oxide interface stabilizer, denoted as NPCNS-g-PEO.

[0025] Preparation of Lithium-ion Battery Repair Solution: The operation was carried out in a glove box filled with argon gas, where the water and oxygen content were both below 0.1 ppm. Preparation of the basic electrolyte: In a dry 500 mL sealed glass reaction flask, accurately weigh and add 25 g of ethylene carbonate, 30 g of dimethyl carbonate, and 25 g of ethyl methyl carbonate sequentially. Place the reaction flask on a magnetic stirrer and stir at 300 rpm for 45 minutes at 25°C to form a homogeneous and transparent mixed solvent. While continuously stirring, slowly add 12 g of lithium hexafluorophosphate in batches to the mixed solvent, controlling the addition rate to prevent local overheating. After all the lithium salt has been added, increase the stirring speed to 500 rpm and transfer the reaction flask to a constant temperature water bath at 35°C, stirring continuously for 12 hours until a completely clear basic electrolyte without any suspended matter is obtained. Addition of conventional additives: While maintaining the system at 25°C and under stirring, add 3 g of fluoroethylene carbonate and 1 g of ethylene sulfate sequentially to the basic electrolyte. After addition, the reaction was continued for 2 hours at 25°C and 300 rpm with stirring. A functional interface stabilizer was added and dispersed. 1.5 g of the prepared NPCNS-g-PEO was added to the electrolyte. To ensure uniform dispersion, the mixture was placed in an ice-water bath and ultrasonically dispersed for 1 hour using a 200W ultrasonic cell disruptor with a 2-second working, 3-second intermittent pulse mode to prevent overheating. After ultrasonication, the repair solution was allowed to stand in a glove box for 24 hours to age. Finally, the aged repair solution was pressure filtered using a 0.22 μm polytetrafluoroethylene microporous membrane, and the filtrate was collected in a well-sealed glass bottle to obtain the final lithium-ion battery repair solution. In this example, the monomethoxy-terminated polyoxyethylene was the material obtained in Preparation Example 1. Example 2 is implemented in the same manner as Example 1, except that the preparation of nitrogen-phosphorus co-doped porous carbon nanospheres grafted with polyethylene oxide interface stabilizers is as follows: Preparation of carbon nanosphere precursor. 1.0 g of mesoporous silica nanospheres were added to a 50 mL mixed solvent containing 0.6 g of melamine and 0.4 g of phytic acid. The mixed solvent consisted of 25 mL of deionized water and 25 mL of anhydrous ethanol. The system was ultrasonically treated at room temperature for 30 minutes. The mixture was transferred to a 100 mL hydrothermal reactor and reacted at 180 °C for 13 hours. The product was centrifuged, washed with water and alcohol, and then vacuum dried at 80 °C for 12 hours. Carbonization and template removal. The dried precursor was carbonized under argon atmosphere with a programmed temperature increase: increasing to 350 °C at 2 °C / min and holding for 1 hour, then increasing to 800 °C at 5 °C / min and holding for 2 hours. After carbonization, the product was etched with a 5% hydrofluoric acid aqueous solution for 24 hours. After washing with water until neutral, the product was freeze-dried to obtain NPCNS. Surface oxidation introduced carboxyl groups. 0.6 g of NPCNS was dispersed in 80 mL of a mixed acid consisting of 20 mL of concentrated nitric acid and 60 mL of concentrated sulfuric acid, and ultrasonically oxidized at 70 °C for 3 hours. The reaction solution was quenched in ice water, the solid was collected by centrifugation, washed with water until neutral, and then vacuum-dried at 70 °C for 12 hours to obtain O-NPCNS. Surface acyl chloride activation. 0.5 g of dried O-NPCNS was dispersed in 50 mL of anhydrous N,N-dimethylformamide, and 2.2 mL of thionyl chloride was added. The mixture was refluxed at 70 °C for 13 hours. After the reaction, the reagents were removed by vacuum distillation to obtain the activated carbon sphere intermediate. Polyethylene oxide grafting. The intermediate was dispersed in 50 mL of anhydrous toluene, and 1.5 g of monomethoxy-terminated polyethylene oxide and 0.18 mL of triethylamine were added. The mixture was refluxed at 90 °C for 30 hours under argon protection. After the reaction, the mixture was centrifuged, washed three times each with toluene and methanol, and finally dried under vacuum at 40 °C for 24 hours to obtain NPCNS-g-PEO.

[0026] Preparation of lithium-ion battery repair solution: In a glove box, 20g of ethylene carbonate, 35g of dimethyl carbonate, and 20g of ethyl methyl carbonate were added to a dry 500mL sealed glass reaction flask. The mixture was stirred at 300rpm for 60 minutes at 25℃. 15g of lithium hexafluorophosphate was slowly added while stirring. After the addition was complete, the stirring speed was increased to 500rpm, and the reaction flask was transferred to a 34℃ constant temperature water bath and stirred continuously for 15 hours to obtain the basic electrolyte. Maintaining the system at 24℃, 1g of fluoroethylene carbonate and 0.5g of ethylene sulfate were added sequentially, and stirring continued for 1 hour. Finally, 0.5g of NPCNS-g-PEO was added, and the mixture was ultrasonically dispersed at 200W for 50 minutes in an ice bath. Afterward, the mixture was allowed to stand for 20 hours and then filtered through a 0.22μm filter membrane to obtain the repair solution.

[0027] Example 3 is implemented in the same way as Example 1, except for the preparation of nitrogen-phosphorus co-doped porous carbon nanospheres grafted with polyethylene oxide interface stabilizer: Preparation of carbon nanosphere precursor. 1.0 g of mesoporous silica nanospheres were added to a 50 mL mixed solvent containing 0.4 g of melamine and 0.6 g of phytic acid. The mixed solvent consisted of 25 mL of deionized water and 25 mL of anhydrous ethanol. The system was sonicated at room temperature for 30 minutes. The mixture was transferred to a 100 mL hydrothermal reactor and reacted at 180 °C for 13 hours. The product was centrifuged, washed with water and alcohol, and then vacuum dried at 80 °C for 12 hours. Carbonization and template removal. The dried precursor was carbonized under argon atmosphere with a programmed temperature rise: increasing to 350 °C at 2 °C / min and holding for 1 hour, then increasing to 800 °C at 5 °C / min and holding for 2 hours. After carbonization, the product was etched with a 5% hydrofluoric acid aqueous solution for 24 hours. After washing with water until neutral, the product was freeze-dried to obtain NPCNS. Surface oxidation introduced carboxyl groups. 0.3 g of NPCNS was dispersed in 80 mL of a mixed acid consisting of 20 mL of concentrated nitric acid and 60 mL of concentrated sulfuric acid, and ultrasonically oxidized at 70 °C for 3 hours. The reaction solution was quenched in ice water, the solid was collected by centrifugation, washed with water until neutral, and then vacuum-dried at 70 °C for 12 hours to obtain O-NPCNS. Surface acyl chloride activation. 0.25 g of dried O-NPCNS was dispersed in 50 mL of anhydrous N,N-dimethylformamide, and 1.5 mL of thionyl chloride was added. The mixture was refluxed at 70 °C for 13 hours. After the reaction, the reagents were removed by vacuum distillation to obtain the activated carbon sphere intermediate. Polyethylene oxide grafting. The intermediate was dispersed in 50 mL of anhydrous toluene, and 3.0 g of monomethoxy-terminated polyethylene oxide and 0.25 mL of triethylamine were added. The mixture was refluxed at 90 °C for 30 hours under argon protection. After the reaction, the mixture was centrifuged, washed three times each with toluene and methanol, and finally dried under vacuum at 40 °C for 24 hours to obtain NPCNS-g-PEO.

[0028] Preparation of lithium-ion battery repair solution: In a glove box, 35g of ethylene carbonate, 20g of dimethyl carbonate, and 35g of ethyl methyl carbonate were added to a dry 500mL sealed glass reaction flask. The mixture was stirred at 300rpm for 30 minutes at 26℃. 8g of lithium hexafluorophosphate was slowly added while stirring. After the addition was complete, the stirring speed was increased to 500rpm, and the reaction flask was transferred to a 36℃ constant temperature water bath and stirred continuously for 10 hours to obtain the basic electrolyte. Maintaining the system at 26℃, 5g of fluoroethylene carbonate and 2g of ethylene sulfate were added sequentially, and stirring continued for 3 hours. Finally, 3g of NPCNS-g-PEO was added, and the mixture was ultrasonically dispersed at 200W for 70 minutes in an ice bath. Afterward, the mixture was allowed to stand for 30 hours and then filtered through a 0.22μm filter membrane to obtain the repair solution.

[0029] Comparative Example 1 The specific implementation method is the same as in Example 1, except for the preparation of the lithium-ion battery repair solution: In a glove box, 25g of ethylene carbonate, 30g of dimethyl carbonate, and 25g of ethyl methyl carbonate were added to a dry 500mL sealed glass reaction flask, and stirred at 300rpm for 45 minutes at 25°C. 12g of lithium hexafluorophosphate was slowly added while stirring. After the addition was complete, the stirring speed was increased to 500rpm, and the reaction flask was transferred to a 35°C constant temperature water bath and stirred continuously for 12 hours to obtain the basic electrolyte. Maintaining the system at 25°C, 3g of fluoroethylene carbonate and 1g of ethylene sulfate were added sequentially, and stirring continued for 2 hours. The mixture was then allowed to stand for 24 hours and filtered through a 0.22μm filter membrane to obtain the repair solution. This comparative example does not contain any nitrogen-phosphorus co-doped porous carbon nanospheres grafted with polyethylene oxide interface stabilizers.

[0030] Comparative Example 2 The specific implementation method is the same as in Example 1, except that the preparation steps for nitrogen-phosphorus co-doped porous carbon nanospheres are exactly the same as in Example 1, resulting in untreated and ungrafted raw NPCNS powder. The preparation steps for the lithium-ion battery repair solution are exactly the same as in Example 1, except that 1.5g of the above-mentioned unmodified raw NPCNS is used instead of an equal mass of NPCNS-g-PEO in the base electrolyte, and the same ultrasonic dispersion, static aging, and filtration operations are performed.

[0031] Comparative Example 3 The specific implementation method is the same as in Example 1, except for the preparation of the physical mixture: NPCNS is prepared in the same manner as in Example 1, and the same monomethoxy-terminated polyethylene oxide raw material is used. 0.4g of NPCNS powder and 2.0g of monomethoxy-terminated polyethylene oxide are weighed and physically ground and mixed in an agate mortar for 10 minutes to obtain a simple physical mixture. Preparation of the lithium-ion battery repair solution: The preparation steps of the repair solution are exactly the same as those in Example 1, except that 1.5g of the above physical mixture is used to replace an equal mass of NPCNS-g-PEO in the basic electrolyte, and the same ultrasonic dispersion, static aging, and filtration operations are performed.

[0032] Performance testing The performance of Examples 1-3 and Comparative Examples 1-3 was tested according to the following method, which included the following steps: Commercial 18650 lithium iron phosphate / graphite system lithium-ion batteries with a rated capacity of 2000mAh and a capacity decay to 65% of their initial capacity after 500 standard charge-discharge cycles were selected as the objects to be repaired. The precise initial capacity decay of each battery was recorded before testing. In an argon-filled glove box, a precision syringe was used to inject the test repair solution, equivalent to 5% of the total mass of the original electrolyte, into each battery through the original injection port. After injection, the batteries were resealed and placed in a 45°C constant temperature chamber for 24 hours of immersion. Subsequently, the batteries were connected to a Xinwei or Landian brand battery testing system, and electrochemical testing was conducted in a 25°C constant temperature environment. The testing procedure was as follows: First, repair activation was performed, i.e., the battery was subjected to three complete charge-discharge cycles at a low current rate of 0.05C. After activation, a capacity recovery test was performed. The initial post-repair discharge capacity was measured and recorded at a 0.5C rate, and the recovery rate relative to the original rated capacity was calculated. Next, a long-cycle life test was conducted. The battery was continuously charged and discharged at a 0.5C rate within a 2.5V-3.65V voltage window, with the discharge capacity recorded every 50 cycles until the battery capacity dropped to 80% of its initial post-repair capacity. The total number of cycles was recorded. Rate performance testing was performed on the 10th cycle after repair, discharging sequentially at different rates of 0.2C, 0.5C, 1C, and 2C, with 5 cycles at each rate. The average discharge capacity retention rate at each rate was recorded. Finally, after battery repair and after the long-cycle test, electrochemical impedance spectroscopy (EIS) was performed using an electrochemical workstation. The test frequency range was 0.01Hz to 100kHz, and the amplitude was 5mV. The ohmic internal resistance and charge transfer resistance of the battery were obtained through fitting analysis.

[0033] Test results: Table 1: Test results of each embodiment and comparative example ; As shown in Table 1, the superior performance of Examples 1-3 compared to Comparative Examples 1-3 fully demonstrates that the present invention, by introducing nitrogen-phosphorus co-doped porous carbon nanospheres with a specific chemical structure grafted with a polyethylene oxide interface stabilizer, successfully solves the core problems of existing repair technologies, namely, limited functionality and incomplete repair. Specifically, Comparative Example 1, without the addition of the stabilizer, showed a battery capacity recovery rate of only 68.1% and a cycle life of only 135 cycles after repair, with a charge transfer impedance as high as 89.7 ohms. This clearly indicates that relying solely on conventional electrolyte components has negligible repair effects on severely aged batteries and cannot address interface deterioration and conductive network degradation. Comparative Example 2, with the addition of unmodified original nitrogen-phosphorus co-doped carbon nanospheres, showed a slightly improved repair effect (capacity recovery rate of 72.3% and cycle life of 210 cycles) compared to Comparative Example 1, proving that rigid carbon cores play a certain role in repairing the conductive network and providing electronic pathways. However, its charge transfer impedance remained as high as 75.6 ohms, and the improvement in cycle life was limited. This indicates that simple carbon materials cannot effectively repair and stabilize ion transport interfaces, and their function remains limited. Comparative Example 3, using a physically mixed carbon nanosphere and polyethylene oxide, outperformed Comparative Example 2 in performance (capacity recovery rate of 75.6% and cycle life of 305 cycles), confirming the auxiliary value of flexible PEO segments in improving ion transport. However, its effect was still far inferior to any of the examples, especially in terms of cycle life, which was less than one-third of that of Example 1. This crucially demonstrates that physical mixing cannot achieve a stable synergy of "rigidity and flexibility," and the PEO chains are prone to detachment during cycling, failing to sustainably perform their interface stabilization function. In contrast, Examples 1-3, especially the optimal Example 1, achieved a high capacity recovery rate of 94.2%, a durable cycle life of over 1000 cycles, and a low charge transfer impedance of only 25.4 ohms. This is collectively attributed to the dual synergistic repair mechanism generated by its chemical grafting structure: the core carbon nanospheres are embedded in the electrode, effectively repairing the deteriorating electronic conductivity network; simultaneously, the flexible PEO long chains, firmly covalently bonded to its surface, construct an efficient and stable ion transport layer at the electrode interface, which can also buffer volumetric stress. This integrated "conductive network repair" and "electrode interface reshaping" function, achieved through chemical design, is something that no single component or physical mixture in the comparison can achieve. This conclusively proves that the present invention can simultaneously, effectively, and persistently solve the dual degradation problem of aging batteries, achieving unexpected technical results.

[0034] The embodiments described above are merely examples of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention.

Claims

1. A method for preparing a lithium-ion battery repair solution, characterized in that the steps include... include: S1. In an argon-filled glove box, ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate are added to a dry, sealed glass container and stirred at 24-26°C to obtain a mixed solvent; lithium hexafluorophosphate is added and stirred continuously in a constant temperature water bath at 34-36°C to obtain a basic electrolyte. S2. Add fluoroethylene carbonate and ethylene sulfate to the basic electrolyte and stir at 24-26℃; add nitrogen and phosphorus co-doped porous carbon nanospheres grafted with polyethylene oxide interface stabilizer, sonicate, and allow to stand for aging.

2. The method for preparing the lithium-ion battery repair solution according to claim 1, characterized in that, In step S1, the stirring time is 30-60 minutes at 24-26℃.

3. The method for preparing the lithium-ion battery repair solution according to claim 1, characterized in that, In step S2, the stirring time is 4-6 hours at 18-20℃.

4. The method for preparing the lithium-ion battery repair solution according to claim 1, characterized in that, The preparation method of the nitrogen-phosphorus co-doped porous carbon nanospheres grafted with polyethylene oxide interface stabilizer includes: A1. Mesoporous silica nanospheres were dispersed in a water-ethanol mixed solution containing melamine and phytic acid, and ultrasonically treated to obtain a mixture. The mixture was transferred to a hydrothermal reactor and reacted at 175-185℃ to obtain a nitrogen-phosphorus polymer-coated composite precursor. The nitrogen-phosphorus polymer-coated composite precursor was centrifuged, washed, and dried, and then carbonized in a tube furnace under an argon atmosphere with programmed temperature rise. After carbonization, it was etched with hydrofluoric acid aqueous solution, centrifuged, washed with water until neutral, and freeze-dried to obtain nitrogen-phosphorus co-doped porous carbon nanospheres. A2. Nitrogen-phosphorus co-doped porous carbon nanospheres were dispersed in a mixed acid solution of concentrated nitric acid and concentrated sulfuric acid, and ultrasonically oxidized at 60-80℃. After centrifugation and washing with water until neutral, they were dried to obtain nitrogen-phosphorus co-doped porous carbon nanospheres with carboxyl groups on the surface. A3. Disperse nitrogen and phosphorus oxide co-doped porous carbon nanospheres with carboxyl groups on the surface in anhydrous N,N-dimethylformamide, add thionyl chloride, and reflux at 68-72℃ to obtain a reaction mixture. Distill the reaction mixture under reduced pressure to obtain activated carbon nanospheres with acyl chloride groups on the surface. A4. Activated carbon spheres with acyl chloride groups on their surface are redispersed in anhydrous toluene. Monomethoxy-terminated polyethylene oxide and triethylamine are added, and the mixture is refluxed at 80-100°C under argon protection to obtain a mixture. The mixture is cooled to room temperature, and the product is separated by centrifugation. The product is washed repeatedly with toluene and methanol in sequence, and finally dried under vacuum at 38-42°C.

5. The method for preparing the lithium-ion battery repair solution according to claim 4, characterized in that, In step A1, the reaction time is 12-14 hours at 175-185℃.

6. The method for preparing the lithium-ion battery repair solution according to claim 4, characterized in that, In step A2, the ultrasonic oxidation treatment at 60-80℃ takes 2-4 hours.

7. The method for preparing the lithium-ion battery repair solution according to claim 4, characterized in that, In step A3, the reflux reaction is carried out at 68-72℃ for 12-14 hours.

8. The method for preparing the lithium-ion battery repair solution according to claim 4, characterized in that, In step A4, the reflux reaction at 80-100℃ takes 24-36 hours.

9. A lithium-ion battery repair solution prepared by the method according to any one of claims 1-8, characterized in that, The raw materials include the following parts by weight: 20-35 parts by weight of ethylene carbonate; 20-35 parts by weight of dimethyl carbonate; 20-35 parts by weight of methyl ethyl carbonate; 8-15 parts by weight of lithium hexafluorophosphate; 1-5 parts by weight of fluoroethylene carbonate; 0.5-2 parts by weight of ethylene sulfate; and 0.5-3 parts by weight of nitrogen-phosphorus co-doped porous carbon nanospheres grafted with polyethylene oxide interface stabilizer.