Methods for Repairing and Upgrading the Positive Electrode Materials of Waste Power Batteries

Abstract

This invention belongs to the field of electrode repair technology and relates to a method for repairing and improving the performance of cathode materials from spent power batteries. The method involves introducing sulfur into the cathode material of spent power batteries to significantly increase the battery's energy density. A porous carbon matrix is ​​then used to fix the sulfur, suppressing the shuttle effect and delaying capacity decay. Carbon and sulfur form a sulfur-carbon conductive network, increasing the electrochemical reaction rate during fast charging and enabling fast charging. A self-healing polymer is used as a binder. The polymer is made from bis(3-aminopropyl)-terminated polydimethylsiloxane, reacted with hexamethylene diisocyanate and butanediol to obtain a block copolymer network containing siloxane segments, urea bonds, and urethane bonds. Self-repair is achieved through the dynamic chemical bond recombination of urea bonds and the migration of siloxane segments, extending the battery's lifespan.

Description

Technical Field

[0001] This invention belongs to the field of electrode repair technology, and in particular relates to a method for repairing and improving the performance of cathode materials from waste power batteries. Background Technology

[0002] With technological advancements and improved living standards, batteries, as crucial energy storage devices, are widely used in mobile electronic devices, new energy vehicles, and other fields. However, batteries have a limited lifespan: lead-acid batteries last 2-3 years, nickel-metal hydride batteries 3-5 years, and lithium batteries 2-6 years. Coupled with the rapid pace of electronic product upgrades and the increasing market demand for new energy vehicles, the number of discarded batteries is also growing rapidly.

[0003] Used batteries contain large amounts of heavy metals, such as nickel, cobalt, manganese, and mercury, as well as other organic matter. Improper handling can lead to these pollutants entering soil and water sources, damaging ecosystems. Heavy metals are also absorbed by organisms and enter the human food chain through various pathways, accumulating in the human body and threatening human health. Furthermore, lithium, cobalt, and nickel in used batteries are scarce metal resources with high economic value; failure to recycle them results in resource waste.

[0004] Chinese patent application CN 106099236 A discloses a method for recycling cathode materials of lithium-ion batteries. This technical solution involves heat-treating the cathode material of lithium-ion batteries to obtain regenerated cathode material, restoring its initial "superlattice" structure and thus its initial electrochemical performance. This allows for the recycling of waste battery materials, significantly reducing environmental pollution, helping to alleviate environmental and ecological pressures, and also enabling the rational utilization of waste resources.

[0005] Chinese patent application CN 114420921 A discloses a method for microwave regenerating lithium-ion battery cathode materials. This technical solution involves thoroughly mixing the lithium-ion battery cathode material with a solid lithium source and then performing microwave treatment. This reduces energy consumption, enables lithium replenishment of the cathode material, and allows the replenished lithium to penetrate deep into the cathode material, achieving higher capacity recovery while simultaneously restoring the structure of the cathode material.

[0006] In addition to the methods mentioned above for restoring electrode performance using heat treatment and microwave treatment, other methods such as cathode material resynthesis and doping modification are also employed. Among these, cathode material resynthesis enables adjustable battery performance, meets diverse needs, and adapts to different battery systems. Summary of the Invention

[0007] This invention aims to provide a method for repairing and improving the performance of cathode materials in spent power batteries. The method introduces sulfur into the battery cathode to optimize the conductivity, lithium-ion diffusion kinetics, and cycle stability of the cathode material; the infiltration of sulfur into a porous carbon matrix effectively delays the "shuttle effect"; and a self-healing polymer is used as a binder, utilizing dynamic chemical bond recombination and soft segment migration within the polymer structure to achieve electrode self-repair. Compared to ordinary power batteries, batteries assembled using electrodes prepared by this method exhibit higher specific capacity, longer service life, and the ability to achieve fast charging.

[0008] To achieve the above objectives, this invention provides a method for repairing and upgrading the positive electrode material of spent power batteries. The method involves introducing conductive porous carbon and sulfur elements into the positive electrode material of spent batteries, and then assembling it with a self-healing polymer to obtain a high-performance power battery positive electrode material. The structural formula of the self-healing polymer is shown below:

[0009] ,

[0010] Where n is an integer between 10 and 100, and m is an integer between 1 and 10.

[0011] A method for repairing and improving the performance of cathode materials from spent power batteries includes:

[0012] Step S1: Mix the cathode material of the waste battery with the lithium source to obtain lithium-rich cathode material, add acetylene black, ball mill and calcine to obtain carbon-cathode composite.

[0013] Step S2: Mix the carbon-cathode composite and sulfur powder, and heat under vacuum until the sulfur powder melts to obtain the sulfur-carbon-cathode composite.

[0014] Step S3: Dissolve the bis(3-aminopropyl)-terminated polydimethylsiloxane in tetrahydrofuran and stir to obtain a bis(3-aminopropyl)-terminated polydimethylsiloxane solution. Dissolve hexamethylene diisocyanate in tetrahydrofuran to obtain a hexamethylene diisocyanate solution. Add all of the hexamethylene diisocyanate solution to the bis(3-aminopropyl)-terminated polydimethylsiloxane solution and react to obtain a prepolymer.

[0015] Step S4: Disperse ZnO nanoparticles in an ethanol aqueous solution, add silane coupling agent, and stir to obtain amino-modified ZnO nanoparticles. Disperse boron nitride nanosheets in toluene, add silane coupling agent, and react to obtain amino-modified boron nitride nanosheets.

[0016] Step S5: Add amino-modified ZnO nanoparticles and amino-modified boron nitride nanosheets to the prepolymer, stir, then add 1,4-butanediol and catalyst, and react to obtain a self-healing polymer.

[0017] Step S6: Add the self-healing polymer to the sulfur-carbon-positive electrode composite, stir, coat it on aluminum foil, and dry to obtain the positive electrode sheet.

[0018] Preferably, in step S1, the lithium source is lithium carbonate.

[0019] Preferably, in step S1, the calcination temperature is 700~800℃ and the calcination time is 2~4 h.

[0020] Preferably, in step S1, the ball milling speed is 400~800 rpm and the ball milling time is 3~6 h.

[0021] Preferably, in step S1, the mass ratio of the positive electrode material, lithium source, and acetylene black of the waste battery is 1:(0.05~0.2):(0.3~0.5).

[0022] Preferably, in step S2, the temperature of the vacuum heating is 120~150℃.

[0023] Preferably, in step S2, the mass ratio of the carbon-cathode composite to sulfur powder is 1:(0.4~0.6).

[0024] Preferably, in step S3, the stirring time is 15-30 min; the reaction time is 20-24 h.

[0025] Preferably, in step S3, the mass ratio of the bis(3-aminopropyl)-terminated polydimethylsiloxane to tetrahydrofuran is 1:(20~25); and the mass ratio of the hexamethylene diisocyanate to tetrahydrofuran is 1:(700~800).

[0026] Preferably, the silane coupling agent is 3-aminopropyltriethoxysilane.

[0027] Preferably, in step S4, the mass ratio of water to ethanol in the ethanol-water solution is 1:9.

[0028] Preferably, in step S4, the stirring temperature is 50~70℃ and the stirring time is 2~4 h.

[0029] Preferably, in step S4, the mass ratio of the ZnO nanoparticles, the ethanol aqueous solution, and the silane coupling agent is 1:(5~10):(0.01~0.03).

[0030] Preferably, in step S4, the reaction temperature is 80~100℃ and the reaction time is 2~4 h.

[0031] Preferably, in step S4, the mass ratio of the boron nitride nanosheets, toluene, and silane coupling agent is 1:(5~10):(0.02~0.04).

[0032] Preferably, in step S5, the stirring time is 15-30 minutes.

[0033] Preferably, the catalyst is dibutyltin dilaurate.

[0034] Preferably, in step S5, the reaction temperature is 40~60℃ and the reaction time is 2~4 h.

[0035] Preferably, in step S5, the mass ratio of the prepolymer, 1,4-butanediol, catalyst, amino-modified ZnO nanoparticles and amino-modified boron nitride nanosheets is 1:(0.055~0.1):(0.005~0.01):(0.01~0.03):(0.01~0.02).

[0036] Preferably, in step S6, the stirring speed is 300~500 rpm and the stirring time is 1~2 h.

[0037] Preferably, in step S6, the drying temperature is 60~80℃ and the drying time is 2~4 h.

[0038] Preferably, in step S6, the mass ratio of the sulfur-carbon-cathode composite to the self-healing polymer is 1:(0.05~0.07).

[0039] Compared with the prior art, the beneficial effects of the present invention are reflected in:

[0040] (1) The technical solution of this application introduces sulfur into the cathode material of waste power battery. By utilizing the high specific capacity and low density of sulfur, the energy density of the battery is greatly improved, the total weight of the battery is reduced, and the portability is optimized. Sulfur is fixed in a porous carbon matrix. The three-dimensional pore structure of porous carbon is used to uniformly encapsulate sulfur, restricting the dissolution and migration of sulfur in the electrolyte, suppressing the shuttle effect, and thus delaying the decay of battery capacity. Sulfur and carbon form a sulfur-carbon conductive network, shortening the electron transport path. Sulfur is adsorbed in the carbon pores, reducing the lithium ion diffusion distance, increasing the reaction interface area, and improving the electrochemical reaction rate during fast charging, thus achieving fast charging.

[0041] (2) This application synthesizes a self-healing polymer. The polymer uses bis(3-aminopropyl)-terminated polydimethylsiloxane as a starting material, reacting it with hexamethylene diisocyanate and butanediol to prepare a polyurethane-siloxane block copolymer. The amino groups in the bis(3-aminopropyl)-terminated polydimethylsiloxane react with the isocyanate groups in the hexamethylene diisocyanate to form urea bonds (-NH-CO-NH-). The remaining isocyanate groups in the hexamethylene diisocyanate react with the hydroxyl groups in the butanediol to form urethane bonds (-NH-CO-O), ultimately yielding a block copolymer network with siloxane (-Si-O-Si-) as soft segments and urea and urethane bonds as hard segments. The soft segments possess high flexibility and a low glass transition temperature, endowing the material with good chain mobility. The hard segments form physical crosslinking points through hydrogen bonds and van der Waals forces, providing mechanical strength. The repair mechanism of polymers is based on the recombination of dynamic chemical bonds and the migration of soft segments. In urea bonds, NH and C=O can form intermolecular hydrogen bonds. When the material is damaged by external force, the hydrogen bonds break, leading to local network damage. However, after heating or removal of external force, the broken hydrogen bonds can be re-paired through molecular motion. When microcracks are generated in the material, the siloxane soft segments migrate to the crack and fill the defect through segment diffusion induced by thermal activation or mechanical stimulation. At the same time, the hydrogen bonds of urea bonds in the hard segments reform, thus achieving crack healing. Attached Figure Description

[0042] Figure 1 A flowchart for the repair and performance enhancement of cathode materials from spent power batteries.

[0043] Figure 2 This is a schematic diagram of the synthetic route for a self-healing polymer.

[0044] Figure 3 The charge-discharge curves of the battery assembled with the electrode sheets prepared for the examples and comparative examples are shown. Detailed Implementation

[0045] The following embodiments are only used to illustrate the technical solutions of the present invention more clearly, and should not be used to limit the scope of protection of the present invention.

[0046] Unless otherwise specified, all reagents and equipment used in the following examples were purchased from commercial sources.

[0047] Example 1

[0048] like Figure 1 As shown, the methods for repairing and upgrading the positive electrode material of spent power batteries include:

[0049] Step S1: Mix 10 g of cathode material from waste batteries with 0.5 g of lithium carbonate to obtain lithium-rich cathode material, add 3 g of acetylene black, ball mill at 400 rpm for 6 h, and calcine at 700℃ for 4 h to obtain carbon-cathode composite.

[0050] Step S2: Mix 10 g of carbon-cathode composite and 4 g of sulfur powder, and heat under vacuum at 120°C until the sulfur powder melts to obtain sulfur-carbon-cathode composite.

[0051] Step S3: Dissolve 5 g of bis(3-aminopropyl)-terminated polydimethylsiloxane in 100 g of tetrahydrofuran and stir for 15 min to obtain a bis(3-aminopropyl)-terminated polydimethylsiloxane solution; dissolve 30 mg of hexamethylene diisocyanate in 20 g of tetrahydrofuran to obtain a hexamethylene diisocyanate solution, and add all of it to the bis(3-aminopropyl)-terminated polydimethylsiloxane solution. React at room temperature for 20 h to obtain the prepolymer.

[0052] Step S4: Disperse 10 g of ZnO nanoparticles in 50 g of ethanol aqueous solution (5 g of water and 45 g of ethanol), add 0.1 g of 3-aminopropyltriethoxysilane, and stir at 50 °C for 4 h to obtain amino-modified ZnO nanoparticles; disperse 10 g of boron nitride nanosheets in 50 g of toluene, add 0.2 g of 3-aminopropyltriethoxysilane, and react at 80 °C for 4 h to obtain amino-modified boron nitride nanosheets.

[0053] Step S5: Add 0.1 g of amino-modified ZnO nanoparticles and 0.1 g of amino-modified boron nitride nanosheets to 10 g of prepolymer, stir for 15 min, then add 0.55 g of 1,4-butanediol and dibutyltin dilaurate, react at 40 °C for 4 h to obtain the self-healing polymer, as shown below. Figure 2 As shown.

[0054] Step S6: Add 0.5 g of self-healing polymer to 10 g of sulfur-carbon-positive electrode composite, stir at 300 rpm for 2 h, coat on aluminum foil, and dry at 60℃ for 4 h to obtain positive electrode sheet.

[0055] Example 2

[0056] like Figure 1 As shown, the methods for repairing and upgrading the positive electrode material of spent power batteries include:

[0057] Step S1: Mix 10 g of cathode material from waste batteries with 1 g of lithium carbonate to obtain lithium-rich cathode material, add 4 g of acetylene black, ball mill at 500 rpm for 4 h, and calcine at 750℃ for 3 h to obtain carbon-cathode composite.

[0058] Step S2: Mix 10 g of carbon-cathode composite and 5 g of sulfur powder, and heat under vacuum at 135°C until the sulfur powder melts to obtain sulfur-carbon-cathode composite.

[0059] Step S3: Dissolve 5 g of bis(3-aminopropyl)-terminated polydimethylsiloxane in 115 g of tetrahydrofuran and stir for 20 min to obtain a bis(3-aminopropyl)-terminated polydimethylsiloxane solution; dissolve 30 mg of hexamethylene diisocyanate in 23 g of tetrahydrofuran to obtain a hexamethylene diisocyanate solution, and add all of it to the bis(3-aminopropyl)-terminated polydimethylsiloxane solution. React at room temperature for 22 h to obtain the prepolymer.

[0060] Step S4: Disperse 10 g of ZnO nanoparticles in 75 g of ethanol aqueous solution (7.5 g of water and 67.5 g of ethanol), add 0.2 g of 3-aminopropyltriethoxysilane, stir at 60 °C for 3 h to obtain amino-modified ZnO nanoparticles. Disperse 10 g of boron nitride nanosheets in 75 g of toluene, add 0.3 g of 3-aminopropyltriethoxysilane, react at 90 °C for 3 h to obtain amino-modified boron nitride nanosheets.

[0061] Step S5: Add 0.2 g of amino-modified ZnO nanoparticles and 0.15 g of amino-modified boron nitride nanosheets to 10 g of prepolymer, stir for 20 min, then add 0.85 g of 1,4-butanediol and dibutyltin dilaurate, react at 50 °C for 3 h to obtain the self-healing polymer, as shown below. Figure 2 As shown.

[0062] Step S6: Add 0.6 g of self-healing polymer to 10 g of sulfur-carbon-positive electrode composite, stir at 400 rpm for 1.5 h, coat on aluminum foil, and dry at 70 °C for 3 h to obtain positive electrode sheet.

[0063] Example 3

[0064] like Figure 1 As shown, the methods for repairing and upgrading the positive electrode material of spent power batteries include:

[0065] Step S1: Mix 10 g of cathode material from waste batteries with 2 g of lithium carbonate to obtain lithium-rich cathode material, add 5 g of acetylene black, ball mill at 400 rpm for 3 h, and calcine at 800℃ for 2 h to obtain carbon-cathode composite.

[0066] Step S2: Mix 10 g of carbon-cathode composite and 6 g of sulfur powder, and heat under vacuum at 150°C until the sulfur powder melts to obtain sulfur-carbon-cathode composite.

[0067] Step S3: Dissolve 5 g of bis(3-aminopropyl)-terminated polydimethylsiloxane in 125 g of tetrahydrofuran and stir for 30 min to obtain a bis(3-aminopropyl)-terminated polydimethylsiloxane solution; dissolve 30 mg of hexamethylene diisocyanate in 24 g of tetrahydrofuran to obtain a hexamethylene diisocyanate solution, and add all of it to the bis(3-aminopropyl)-terminated polydimethylsiloxane solution. React at room temperature for 24 h to obtain the prepolymer.

[0068] Step S4: Disperse 10 g of ZnO nanoparticles in 100 g of ethanol aqueous solution (10 g of water and 90 g of ethanol), add 0.3 g of 3-aminopropyltriethoxysilane, and stir at 70 °C for 2 h to obtain amino-modified ZnO nanoparticles; disperse 10 g of boron nitride nanosheets in 100 g of toluene, add 0.4 g of 3-aminopropyltriethoxysilane, and react at 100 °C for 2 h to obtain amino-modified boron nitride nanosheets.

[0069] Step S5: Add 0.3 g of amino-modified ZnO nanoparticles and 0.2 g of amino-modified boron nitride nanosheets to 10 g of prepolymer, stir for 30 min, then add 1 g of 1,4-butanediol and dibutyltin dilaurate, react at 60 °C for 2 h to obtain the self-healing polymer, as shown below. Figure 2 As shown.

[0070] Step S6: Add 0.7 g of self-healing polymer to 10 g of sulfur-carbon-positive electrode composite, stir at 500 rpm for 1 h, coat on aluminum foil, and dry at 80℃ for 2 h to obtain positive electrode sheet.

[0071] Comparative Example 1

[0072] The method for repairing and upgrading the positive electrode material of waste power batteries differs from that in Example 3 in that acetylene black is not added in step S1.

[0073] Comparative Example 2

[0074] The method for repairing and upgrading the positive electrode material of waste power batteries differs from that in Example 3 in that sulfur powder is not added in step S2.

[0075] Comparative Example 3

[0076] The method for repairing and upgrading the positive electrode material of spent power batteries differs from that in Example 3 in that self-healing polymers are not used in step S6, and ordinary adhesives are used for assembly.

[0077] Performance testing:

[0078] The recycled cathode materials prepared in the examples and comparative examples were assembled into single-cell batteries and subjected to charge-discharge tests at 25°C and a current of 0.1 C. The first-cycle discharge capacity and cycle performance test results are shown in Table 1 below, and the charge-discharge curves are shown in the figure below. Figure 3 As shown.

[0079] Fast charging performance test: The battery was charged at a current of 1 C. After 5 minutes of charging, the percentage of the total battery capacity charged by each battery was tested. The battery was charged to 4.2 V at different currents, then switched to constant voltage charging to 1 A, and then discharged at constant current to 3.0 V and 20 A. After 1000 cycles, the capacity retention rate (%) of the product was tested. The results are shown in Table 2.

[0080] Table 1 Results of first-week discharge capacity test and cycle performance test

[0081] Sample number <![CDATA[Initial week discharge specific capacity (mAh·g -1 ).]]> 0.1 C-cycle 50-cycle capacity retention rate (%) 0.1 Capacity retention rate after 100 cycles of C (%) Example 1 145.13 93.75 87.05 Example 2 143.87 94.49 87.52 Example 3 145.27 95.05 90.15 Comparative Example 1 125.78 71.85 45.25 Comparative Example 2 110.10 78.16 53.58 Comparative Example 3 123.09 76.13 51.52

[0082] The first-week charge-discharge curves of the battery packs assembled from the positive electrode sheets prepared in Examples 1 to 3 are shown below. Figure 3 As shown in Table 1, the specific capacity of the first week of discharge is 140 mAh·g in Examples 1 to 3. -1 After 50 cycles, the battery capacity retention rate is above 85%, and after 100 cycles, the battery capacity is above 85%.

[0083] The first-week charge-discharge curves of the battery packs assembled from the positive electrode sheets prepared in Comparative Examples 1 to 2 are shown in the figure. Figure 3 As shown in Table 1, the specific capacity of the first-week discharge is 120.78 mAh·g. (Comparative Example 1 has a first-week discharge specific capacity of 120.78 mAh·g) -1 The specific capacity of Comparative Example 2 during the first week of discharge was 110.10 mAh·g. -1 The specific capacity of Comparative Example 3 during the first week of discharge was 123.09 mAh·g. -1 After 50 cycles, the battery capacity retention of Comparative Examples 1 to 3 was below 80%, and after 100 cycles, it was below 60%.

[0084] Experiments have shown that introducing sulfur into the positive electrode material of spent power batteries can significantly improve the battery's energy density. Higher specific capacity means a stronger ability to store electrical energy. Therefore, the first-cycle discharge specific capacity of Comparative Example 2 (without added sulfur powder) was significantly lower than the other groups. Infiltrating sulfur into the porous carbon matrix can delay the shuttle effect, which causes a sharp decline in battery capacity with increasing cycle count, shortening battery life. Comparative Example 1 (without added acetylene black) showed significantly lower capacity retention after 50 cycles compared to the other groups, with a capacity retention of only 32.25% after 100 cycles. Using a self-healing polymer as a binder allows for reversible recombination of dynamic chemical bonds in the self-healing polymer when the discharge electrode cracks due to volume expansion or cyclic stress. This restores the adhesive's bonding strength and maintains the electrode's structural integrity. Traditional binders are prone to mechanical fatigue failure during cycling, leading to the shedding of sulfur and nanoparticles. The self-healing polymer can continuously repair the bonding surface, maintaining contact between active and conductive materials, reducing capacity decay, and extending battery life.

[0085] Table 2 Fast charging performance test results

[0086] Sample number Percentage of charge remaining after 5 minutes (%) Capacity retention rate (%) Example 1 90.58 78.15 Example 2 90.78 76.98 Example 3 92.23 78.86 Comparative Example 1 58.16 40.52 Comparative Example 2 47.58 43.25 Comparative Example 3 70.25 35.12

[0087] According to the data in Table 2, the battery packs assembled with electrode sheets prepared in Examples 1 and 2 had a charging capacity of over 90% after 5 minutes in the fast charging experiment, and a capacity retention rate of over 70% after 1000 cycles. The battery pack assembled with electrode sheets prepared in Comparative Example 1 had a charging capacity of 58.16% after 5 minutes, the battery pack assembled with electrode sheets prepared in Comparative Example 2 had a charging capacity of 37.58% after 5 minutes, and the battery pack assembled with electrode sheets prepared in Comparative Example 3 had a charging capacity of 70.25% after 5 minutes.

[0088] Experiments have shown that the three-dimensional pores of porous carbon provide a highly dispersed carrier for sulfur. The resulting carbon-sulfur conductive network shortens the electron transport path, increases the area of ​​the reaction interface, and enhances the electrochemical reaction rate during fast charging, thus achieving rapid charging. Comparative Examples 1 and 2 lacked one of these substances, therefore their fast charging performance was significantly lower than the other groups. The self-healing polymer, through reversible recombination of dynamic chemical bonds, adaptively buffers stress, thereby alleviating volume expansion stress, preventing electrode cracking or interface detachment, and maintaining the continuity of ion / electron transport channels. Comparative Example 3 did not use a self-healing polymer; although its fast charging performance was better than Comparative Examples 1 and 2, its battery capacity retention rate decreased the fastest.

[0089] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for repairing and upgrading the positive electrode material of spent power batteries, characterized in that, The method involves introducing conductive porous carbon and sulfur elements into the cathode material of spent batteries, and then assembling it with a self-healing polymer to obtain a high-performance power battery cathode material; the structural formula of the self-healing polymer is shown below: ， Where n is an integer between 10 and 100, and m is an integer between 1 and 10; The method includes: Step S1: Mix the cathode material of the waste battery with the lithium source to obtain lithium-rich cathode material, add acetylene black, ball mill and calcine to obtain carbon-cathode composite. Step S2: Mix the carbon-cathode composite and sulfur powder, and heat under vacuum until the sulfur powder melts to obtain the sulfur-carbon-cathode composite. Step S3: Dissolve the bis(3-aminopropyl)-terminated polydimethylsiloxane in tetrahydrofuran and stir to obtain a bis(3-aminopropyl)-terminated polydimethylsiloxane solution. Dissolve hexamethylene diisocyanate in tetrahydrofuran to obtain a hexamethylene diisocyanate solution. Add all of the hexamethylene diisocyanate solution to the bis(3-aminopropyl)-terminated polydimethylsiloxane solution and react to obtain a prepolymer. Step S4: Disperse ZnO nanoparticles in an ethanol aqueous solution, add silane coupling agent, and stir to obtain amino-modified ZnO nanoparticles. Disperse boron nitride nanosheets in toluene, add silane coupling agent, and react to obtain amino-modified boron nitride nanosheets. Step S5: Add amino-modified ZnO nanoparticles and amino-modified boron nitride nanosheets to the prepolymer, stir, then add 1,4-butanediol and catalyst, and react to obtain a self-healing polymer. Step S6: Add the self-healing polymer to the sulfur-carbon-positive electrode composite, stir, coat it on aluminum foil, and dry to obtain the positive electrode sheet.

2. The method for repairing and upgrading the positive electrode material of spent power batteries according to claim 1, characterized in that, In step S1, the lithium source is lithium carbonate; the ball milling speed is 400~800 rpm, and the ball milling time is 3~6 h; the calcination temperature is 700~800℃, and the calcination time is 2~4 h; the mass ratio of the cathode material, lithium source and acetylene black of the waste battery is 1:(0.05~0.2):(0.3~0.5).

3. The method for repairing and upgrading the positive electrode material of spent power batteries according to claim 1, characterized in that, In step S2, the vacuum heating temperature is 120~150℃; the mass ratio of the carbon-cathode composite to sulfur powder is 1:(0.4~0.6).

4. The method for repairing and upgrading the positive electrode material of spent power batteries according to claim 1, characterized in that, In step S3, the stirring time is 15-30 min; the reaction time is 20-24 h; the mass ratio of the bis(3-aminopropyl)-terminated polydimethylsiloxane to tetrahydrofuran is 1:(20-25); and the mass ratio of the hexamethylene diisocyanate to tetrahydrofuran is 1:(700-800).

5. The method for repairing and upgrading the positive electrode material of spent power batteries according to claim 1, characterized in that, The silane coupling agent is 3-aminopropyltriethoxysilane; in step S4, the mass ratio of water to ethanol in the ethanol aqueous solution is 1:9; the stirring temperature is 50~70℃, and the stirring time is 2~4 h; the mass ratio of ZnO nanoparticles, ethanol aqueous solution and silane coupling agent is 1:(5~10):(0.01~0.03).

6. The method for repairing and upgrading the positive electrode material of spent power batteries according to claim 1, characterized in that, In step S4, the reaction temperature is 80~100℃ and the reaction time is 2~4 h; the mass ratio of boron nitride nanosheets, toluene and silane coupling agent is 1:(5~10):(0.02~0.04).

7. The method for repairing and upgrading the positive electrode material of spent power batteries according to claim 1, characterized in that, In step S5, the stirring time is 15-30 min; the reaction temperature is 40-60℃; the reaction time is 2-4 h; and the catalyst is dibutyltin dilaurate.

8. The method for repairing and upgrading the positive electrode material of spent power batteries according to claim 1, characterized in that, In step S5, the mass ratio of the prepolymer, 1,4-butanediol, catalyst, amino-modified ZnO nanoparticles and amino-modified boron nitride nanosheets is 1:(0.055~0.1):(0.005~0.01):(0.01~0.03):(0.01~0.02).

9. The method for repairing and upgrading the positive electrode material of spent power batteries according to claim 1, characterized in that, In step S6, the stirring speed is 300-500 rpm and the stirring time is 1-2 h; the drying temperature is 60-80℃ and the drying time is 2-4 h; the mass ratio of the sulfur-carbon-positive electrode composite to the self-healing polymer is 1:(0.05-0.07).

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