A positive electrode composite material of a solid-state battery and a preparation method and application thereof

Abstract

The application discloses a kind of positive composite material of solid-state battery and its preparation method and application, belong to battery processing technical field, for solving the technical problems that the conductivity and cycle stability of positive composite material of solid-state battery in prior art need to be further improved, specifically including the following raw materials by weight parts: 5-10 parts of modified binder, 3-6 parts of deionized water, 80-100 parts of modified polycrystalline powder and 5-10 parts of modified conductive agent;The application is mixed into mixed slurry by modified polycrystalline powder, modified binder, modified conductive agent and deionized water, is coated on aluminum foil by doctor blade, is scraped flat, is dried, obtains positive composite material, not only improves the conductivity and cycle stability of solid-state battery prepared by positive composite material, also improves its rate performance.

Description

Technical Field

[0001] This invention relates to the field of battery processing technology, specifically to a positive electrode composite material for solid-state batteries, its preparation method, and its application. Background Technology

[0002] In recent years, solid-state batteries, as the next generation of high-performance battery technology, have attracted widespread attention due to their high safety and energy density. As one of the key components of solid-state batteries, cathode composite materials have been developing rapidly.

[0003] Traditional liquid batteries mainly use composite materials such as lithium cobalt oxide and nickel cobalt manganese as cathode materials, while solid-state batteries place more emphasis on the stability and conductivity of materials. Therefore, researchers have achieved certain results by optimizing the microstructure and surface modification of cathode composite materials to improve their compatibility with solid electrolytes.

[0004] Currently, some solid-state battery cathode materials with excellent cycle performance and high energy density have emerged in the market. However, how to further improve their stability and conductivity remains a research hotspot.

[0005] In existing technologies, the conductivity and cycle stability of the cathode composite material in solid-state batteries still need improvement. Especially under high load and rapid charge-discharge conditions, the material is prone to structural changes, leading to a decline in battery performance. Secondly, the interface between the cathode material and the solid electrolyte is unstable, and the problem of side reactions has not been effectively solved. Moreover, the interface impedance is high, which limits the overall efficiency and cycle life of the battery. At the same time, the bonding strength between the conductive agent and the cathode material is insufficient, and it is easy to fall off due to the accumulation of mechanical stress during long-term cycling. The cathode composite material also generates lattice stress accumulation during cycling, which leads to the formation of micro-cracks between the active material and the solid electrolyte, affecting the integrity of the electron conduction network. As the conductive channels are damaged, the electronic conductivity of the battery gradually decreases, resulting in battery capacity degradation. Summary of the Invention

[0006] The purpose of this invention is to provide a positive electrode composite material for solid-state batteries, its preparation method, and its application, in order to solve the technical problem that the conductivity and cycle stability of the positive electrode composite material for solid-state batteries in the prior art need to be further improved.

[0007] The objective of this invention can be achieved through the following technical solution: a positive electrode composite material for a solid-state battery, comprising the following raw materials by weight: 5-10 parts modified binder, 3-6 parts deionized water, 80-100 parts modified polycrystalline powder and 5-10 parts modified conductive agent;

[0008] The modified polycrystalline powder is prepared by the following steps:

[0009] A1. Place dihydrodiamine and ethanol in a reaction vessel and stir for 1-5 min. Add NCM811 and stir for 5-15 min to obtain crude modified polycrystalline powder.

[0010] A2. After ball milling the crude modified polycrystalline powder for 10-12 hours, it is calcined to obtain the modified polycrystalline powder.

[0011] The reaction principle for preparing modified polycrystalline powder is as follows:

[0012] During the reaction, the NCM811 surface contains abundant oxygen atoms and lithium ions. Dihydrodiamine molecules are adsorbed onto the NCM811 surface through van der Waals forces and hydrogen bonds. Ball milling breaks down the NCM811 particles, increasing their specific surface area and exposing more active surfaces, promoting uniform mixing of dihydrodiamine molecules with NCM811. During calcination, ethanol evaporates, and dihydrodiamine adheres to the NCM811 surface in a molecularly dispersed state, forming a uniform precursor layer. Under argon protection, the dihydrodiamine molecules undergo deamination polymerization to form triazine ring structural units. These triazine rings are stacked into a two-dimensional layered g-C3N4 structure through van der Waals forces. 2 Hybridized CN atoms form a highly delocalized π-conjugated system, and the terminal amino group of g-C3N4 forms NOC bonds with oxygen atoms on the NCM811 surface, achieving a strong bond between the coating layer and the substrate, generating a graphitic silicon carbide coating layer, and obtaining modified polycrystalline powder.

[0013] Further, in step A1, the ratio of dihydrodiamine, ethanol, and NCM811 is 0.05-0.10g:50-70mL:3-5g; in step A2, the ball milling media is composed of zirconium dioxide with a particle size of 1-5mm, the ball-to-powder ratio is 10:1, the rotation speed is set to 100r / min, and the calcination operation steps include: placing the ball-milled product in an oven under nitrogen atmosphere protection, heating to 75-85℃, drying for 9-11h, transferring it to a tube furnace at 450-550℃ for calcination for 0.5-1.5h, cooling to room temperature, grinding, and passing through a 200-mesh sieve to obtain modified polycrystalline powder.

[0014] Furthermore, the modified adhesive is prepared by the following steps:

[0015] B1. Place 2-acrylamido-2-methylpropanesulfonic acid, ethanol and deionized water in a reaction vessel, stir for 1-5 min, slowly add lithium hydroxide monohydrate, heat to 20-30℃, keep the temperature for 3-4 h, and then process to obtain the modified lithium salt monomer.

[0016] The reaction principle for the preparation of modified lithium salt monomers is as follows:

[0017] During the reaction, the sulfonic acid group in the 2-acrylamido-2-methylpropanesulfonic acid molecule releases a proton, which combines with the hydroxide ion in lithium hydroxide monohydrate to generate water. The released proton is replaced by lithium ions to generate lithium sulfonate group, thus obtaining the modified lithium salt monomer.

[0018] B2. The modified lithium salt monomer, lithium acrylate, n-butyl acrylate, ammonium persulfate, N,N-dimethylformamide and acrylonitrile are placed in a reaction vessel, heated to 70-80℃, and kept at this temperature for 7-8 hours. The modified binder is then obtained through post-treatment.

[0019] The preparation reaction formula for the modified adhesive is:

[0020]

[0021] The preparation reaction principle of the modified adhesive is as follows:

[0022] During the reaction, under the initiation of ammonium persulfate, the modified lithium salt monomer, lithium acrylate, n-butyl acrylate and acrylonitrile undergo free radical polymerization to obtain the modified binder.

[0023] Further, in step B1, the ratio of 2-acrylamido-2-methylpropanesulfonic acid, ethanol, deionized water, and lithium hydroxide monohydrate is 3-4g:5-10mL:35-45mL:0.5-1g. The post-processing step includes: after the reaction is complete, heating to 95-100℃ and distilling under reduced pressure until no liquid is collected, to obtain the modified lithium salt monomer; in step B2, the ratio of the modified lithium salt monomer, lithium acrylate, n-butyl acrylate, ammonium persulfate, N,N-dimethylformamide, and acrylonitrile is 1-2g:2-4g:4-6g:0.5-1.5g:200-250mL:2-4g. The post-processing step includes: after the reaction is complete, heating to 150-160℃ and distilling under reduced pressure until no liquid is collected, to obtain the modified binder.

[0024] Furthermore, the modified conductive agent is prepared by placing carbon nanotubes in a tube furnace under nitrogen protection, heating to 600-700℃, introducing sulfur dioxide gas, maintaining the temperature for 0.5-1.5h, and then performing post-treatment to obtain the modified conductive agent.

[0025] The preparation reaction principle of modified conductive agents is as follows:

[0026] During the reaction, under the high temperature environment of the tube furnace, sulfur dioxide gas undergoes thermal decomposition, and the sulfur atoms produced covalently bond with the edge carbon atoms on the surface of carbon nanotubes. The sulfur atoms replace some carbon atoms to form a CSC structure, which is embedded in the carbon skeleton to obtain a modified conductive agent.

[0027] Furthermore, the flow rate of the sulfur dioxide gas is 300 sccm, and the post-processing steps include: after the reaction is completed, cooling at room temperature, grinding, and passing through a 200-mesh sieve to obtain the modified conductive agent.

[0028] This invention also proposes a method for preparing a positive electrode composite material for solid-state batteries, comprising the following steps:

[0029] S1. Mix the modified polycrystalline powder, modified binder, modified conductive agent and deionized water evenly to obtain a mixed slurry;

[0030] S2. Apply the mixed slurry onto an aluminum foil sheet using a scraper, smooth it out, and dry it to obtain the positive electrode composite material.

[0031] Furthermore, in step S2, the coating thickness is 50-200 μm, and the drying operation includes: transferring the leveled product to a drying oven protected by a nitrogen atmosphere, heating it to 90-100℃, and drying it for 0.5-1.5 h to obtain the positive electrode composite material.

[0032] This invention also proposes an application of a positive electrode composite material for solid-state batteries, wherein the positive electrode composite material prepared by the above-mentioned method for solid-state batteries is applied to new energy batteries.

[0033] The present invention has the following beneficial effects:

[0034] 1. This invention involves coating a layer of graphitic silicon carbide onto the surface of NCM811 to obtain modified polycrystalline powder. Then, 2-acrylamido-2-methylpropanesulfonic acid is neutralized with lithium hydroxide monohydrate to obtain modified lithium salt monomers. A modified binder is prepared through further free radical copolymerization. A modified conductive agent is prepared by high-temperature calcination using sulfur dioxide gas as a sulfur source. A mixed slurry of the modified polycrystalline powder, modified binder, modified conductive agent, and deionized water is coated onto an aluminum foil sheet using a scraper, smoothed, and dried to obtain a positive electrode composite material. This invention utilizes high temperature to calcine carbon nanotubes under a nitrogen atmosphere. Sulfur-doped carbon nanotubes are modified by calcination under a nitrogen atmosphere, which protects the graphitized structure in the carbon nanotubes and avoids the risk of structural collapse of the electrode during cycling. This alters the electron cloud distribution of carbon in the carbon nanotubes, reduces resistivity, and improves the overall conductivity of the cathode composite material, further enhancing the charge-discharge rate and rate performance of the solid-state battery. Moreover, carbon nanotubes themselves possess excellent mechanical strength and structural stability. Under high-rate charge-discharge conditions, the structural strength of sulfur-doped carbon nanotubes helps prevent the cathode material from falling off or breaking, mitigating the expansion or contraction of the battery during charge-discharge, thereby improving the cycle stability of the solid-state battery.

[0035] 2. In this invention, NCM811 and dihydrodiamine are mixed evenly, and after calcination, a graphitic silicon carbide coating is formed on the surface of NCM811 to obtain modified polycrystalline powder. This modified polycrystalline powder is used as the main active material in the cathode composite material of solid-state batteries. The inert protective layer formed on the surface of NCM811 effectively enhances the surface stability of the cathode composite material, suppresses side reactions between the NCM811 interface and the solid electrolyte, reduces lattice oxygen loss and transition metal dissolution, thereby delaying capacity decay and improving the cycle stability of solid-state batteries. Simultaneously, the high thermal conductivity and mechanical strength of the graphitic silicon carbide can alleviate volume expansion during charging and discharging. Stress is reduced, decreasing the probability of intergranular microcracks and improving the long-cycle stability of the cathode material. The graphite-phase silicon carbide coating provides a stable lithium-ion diffusion channel. At the same time, the graphite-phase silicon carbide coating on the surface of NCM811 particles forms a continuous and dense conductive coating layer, constructing a stable electron conduction network and reducing the migration resistance of electrons in the cathode material, thereby improving the overall conductivity. The defect sites introduced by sulfur doping and the semiconductor properties of graphite-phase silicon carbide synergistically optimize the electron transport path and improve the charge transfer efficiency under high current density. Meanwhile, the high thermal conductivity of graphite-phase silicon carbide helps the modified binder dissipate heat and improves the cycle stability of solid-state batteries.

[0036] 3. This invention involves preparing 2-acrylamido-2-methylpropanesulfonate neutralized with lithium hydroxide monohydrate, and further reacting it with lithium acrylate, n-butyl acrylate, and acrylonitrile via free radical reaction to obtain a modified binder. The lithium ions in the modified lithium salt monomer can form strong ionic bonds with the oxygen anions on the surface of the modified polycrystalline powder, improving the interfacial bonding strength. The cross-linked network structure formed by the free radical reaction can effectively fix the lithium salt, providing continuous ion transport channels, improving the ion mobility of the cathode composite material, and further enhancing the high-rate discharge performance of the solid-state battery. The introduction of acrylonitrile monomer enhances the rigidity of the binder, and its synergistic effect with the flexible segments of lithium acrylate endows the cathode composite material with excellent crack resistance, effectively alleviating stress concentration caused by volume changes during charging and discharging, thereby preventing particle breakage, structural collapse, and other phenomena, maintaining the integrity of the modified polycrystalline powder structure, avoiding capacity decay, and significantly extending the cycle life of the battery. Detailed Implementation

[0037] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0038] The NCM811 used in this invention was purchased from Dongguan Kelude New Energy Technology Co., Ltd., with a particle size of 5-30μm. The product type is polycrystalline nickel cobalt manganese oxide NCM811, the brand is Kelude, and the product standard is the national standard.

[0039] The lithium electrode used in this invention was purchased from Changsha Xinkang New Materials Co., Ltd., and its thickness is 0.05mm.

[0040] The solid electrolyte used in this invention was purchased from Shenzhen Liyou New Energy Technology Co., Ltd., and its model is TOB-LLZO.

[0041] The gasket used in this invention was purchased from Langfang Zhongyang Technology Co., Ltd., and its model is graphite sealing ring;

[0042] The spring sheet used in this invention was purchased from Dongguan Heju Precision Electronics Technology Co., Ltd., and its specifications are 30x20.91mm.

[0043] Example 1

[0044] This embodiment provides a method for preparing a positive electrode composite material for a solid-state battery, including the following steps:

[0045] S1. Preparation of modified polycrystalline powder

[0046] Weigh out 0.5 g of dihydrodiamine and 500 mL of ethanol and place them in a reaction vessel. Stir for 1 min, add 30 g of NCM811, and stir for 5 min to obtain crude modified polycrystalline powder.

[0047] Weighing: After ball milling the crude modified polycrystalline powder for 10 hours, transfer it to an oven under nitrogen atmosphere protection, heat it to 75°C, dry it for 9 hours, transfer it to a tube furnace at 450°C for 0.5 hours, cool it at room temperature, grind it, and pass it through a 200-mesh sieve to obtain the modified polycrystalline powder.

[0048] S2, Preparation of modified adhesive

[0049] Weigh 30g of 2-acrylamido-2-methylpropanesulfonic acid, 50mL of ethanol and 350mL of deionized water and place them in a reaction vessel. Stir for 1 minute, slowly add 5g of lithium hydroxide monohydrate, heat to 20℃, keep the temperature for 3 hours, and after the reaction is complete, heat to 95℃ and distill under reduced pressure until no liquid is collected to obtain the modified lithium salt monomer.

[0050] Weigh out 10g of modified lithium salt monomer, 20g of lithium acrylate, 40g of n-butyl acrylate, 5g of ammonium persulfate, 2000mL of N,N-dimethylformamide and 20g of acrylonitrile and place them in a reaction vessel. Heat to 70℃ and keep the temperature for 7h. After the reaction is complete, heat to 150℃ and distill under reduced pressure until no liquid is collected to obtain the modified binder.

[0051] S3, Preparation of modified conductive agent

[0052] Weigh out: Place carbon nanotubes in a tube furnace under nitrogen protection, heat to 600℃, introduce sulfur dioxide gas at a flow rate of 300 sccm, keep the reaction at this temperature for 0.5 h, cool to room temperature after the reaction is complete, grind, and pass through a 200-mesh sieve to obtain the modified conductive agent.

[0053] S4. Preparation of positive electrode composite materials

[0054] Weigh out the following by weight: 5 parts modified binder, 3 parts deionized water, 80 parts modified polycrystalline powder and 5 parts modified conductive agent, mix them evenly to obtain a mixed slurry;

[0055] The mixed slurry was coated onto an aluminum foil sheet with a scraper and smoothed to a thickness of 50 μm. The smoothed product was then transferred to a drying oven under nitrogen atmosphere protection, heated to 90 °C, and dried for 0.5 h to obtain the positive electrode composite material.

[0056] S5, Fabrication of coin solid-state batteries

[0057] Under a nitrogen atmosphere, the positive electrode composite material is placed in a tablet press and flattened to obtain a positive electrode sheet;

[0058] Under a nitrogen atmosphere, lithium negative electrode, positive electrode, solid electrolyte, pad, and spring sheet are placed in sequence in a coin cell case to encapsulate a coin cell solid-state battery.

[0059] Example 2

[0060] This embodiment provides a method for preparing a positive electrode composite material for a solid-state battery, including the following steps:

[0061] S1. Preparation of modified polycrystalline powder

[0062] Weigh out 0.07 g of dihydrodiamine and 600 mL of ethanol and place them in a reaction vessel. Stir for 3 min, add 40 g of NCM811, and stir for 10 min to obtain crude modified polycrystalline powder.

[0063] Weighing: After ball milling the crude modified polycrystalline powder for 11 hours, transfer it to an oven under nitrogen atmosphere protection, heat it to 80℃, dry it for 10 hours, transfer it to a tube furnace at 500℃ for calcination for 1 hour, cool it at room temperature, grind it, and pass it through a 200-mesh sieve to obtain the modified polycrystalline powder.

[0064] S2, Preparation of modified adhesive

[0065] Weigh 35g of 2-acrylamido-2-methylpropanesulfonic acid, 70mL of ethanol and 400mL of deionized water and place them in a reaction vessel. Stir for 3 minutes, slowly add 7g of lithium hydroxide monohydrate, heat to 25℃, and keep the temperature for 3.5h. After the reaction is complete, heat to 97℃ and distill under reduced pressure until no liquid is collected to obtain the modified lithium salt monomer.

[0066] Weigh out 15g of modified lithium salt monomer, 30g of lithium acrylate, 50g of n-butyl acrylate, 10g of ammonium persulfate, 2250mL of N,N-dimethylformamide and 30g of acrylonitrile and place them in a reaction vessel. Heat to 75℃ and keep the temperature for 7.5h. After the reaction is complete, heat to 155℃ and distill under reduced pressure until no liquid is collected to obtain the modified binder.

[0067] S3, Preparation of modified conductive agent

[0068] Weigh out: Place carbon nanotubes in a tube furnace under nitrogen protection, heat to 650℃, introduce sulfur dioxide gas at a flow rate of 300 sccm, keep the reaction at this temperature for 1 hour, cool to room temperature after the reaction is complete, grind, and pass through a 200-mesh sieve to obtain the modified conductive agent.

[0069] S4. Preparation of positive electrode composite materials

[0070] Weigh out the following by weight: 7 parts modified binder, 5 parts deionized water, 90 parts modified polycrystalline powder and 7 parts modified conductive agent, mix them evenly to obtain a mixed slurry;

[0071] The mixed slurry was coated onto an aluminum foil sheet with a scraper and smoothed to a thickness of 100 μm. The smoothed product was then transferred to a drying oven under nitrogen atmosphere protection, heated to 95 °C, and dried for 1 hour to obtain the positive electrode composite material.

[0072] S5, Fabrication of coin solid-state batteries

[0073] Under a nitrogen atmosphere, the positive electrode composite material is placed in a tablet press and flattened to obtain a positive electrode sheet;

[0074] Under a nitrogen atmosphere, lithium negative electrode, positive electrode, solid electrolyte, pad, and spring sheet are placed in sequence in a coin cell case to encapsulate a coin cell solid-state battery.

[0075] Example 3

[0076] This embodiment provides a method for preparing a positive electrode composite material for a solid-state battery, including the following steps:

[0077] S1. Preparation of modified polycrystalline powder

[0078] Weigh out 1g of dihydrodiamine and 700mL of ethanol and place them in a reaction vessel. Stir for 5 minutes, add 150g of NCM81 and stir for 15 minutes to obtain crude modified polycrystalline powder.

[0079] Weighing: After ball milling the crude modified polycrystalline powder for 12 hours, transfer it to an oven under nitrogen atmosphere protection, heat it to 85°C, dry it for 11 hours, transfer it to a tube furnace at 550°C for calcination for 1.5 hours, cool it at room temperature, grind it, and pass it through a 200-mesh sieve to obtain the modified polycrystalline powder.

[0080] S2, Preparation of modified adhesive

[0081] Weigh 40g of 2-acrylamido-2-methylpropanesulfonic acid, 100mL of ethanol and 450mL of deionized water and place them in a reaction vessel. Stir for 5 minutes, slowly add 10g of lithium hydroxide monohydrate, heat to 30℃, keep the temperature for 4 hours, and after the reaction is complete, heat to 100℃ and distill under reduced pressure until no liquid is collected to obtain the modified lithium salt monomer.

[0082] Weigh out 20g of modified lithium salt monomer, 40g of lithium acrylate, 60g of n-butyl acrylate, 15g of ammonium persulfate, 2500mL of N,N-dimethylformamide and 40g of acrylonitrile and place them in a reaction vessel. Heat to 80℃ and keep the temperature for 8h. After the reaction is complete, heat to 160℃ and distill under reduced pressure until no liquid is collected to obtain the modified binder.

[0083] S3, Preparation of modified conductive agent

[0084] Weigh out: Place carbon nanotubes in a tube furnace under nitrogen protection, heat to 700℃, introduce sulfur dioxide gas at a flow rate of 300 sccm, keep the reaction at this temperature for 1.5 h, cool to room temperature after the reaction is complete, grind, and pass through a 200-mesh sieve to obtain the modified conductive agent.

[0085] S4. Preparation of positive electrode composite materials

[0086] Weigh out the following by weight: 10 parts modified binder, 6 parts deionized water, 100 parts modified polycrystalline powder and 10 parts modified conductive agent, mix them evenly to obtain a mixed slurry;

[0087] The mixed slurry was coated onto an aluminum foil sheet with a scraper and smoothed out to a thickness of 50-200 μm. The smoothed product was then transferred to a drying oven under nitrogen atmosphere protection, heated to 100℃, and dried for 1.5 h to obtain the positive electrode composite material.

[0088] S5, Fabrication of coin solid-state batteries

[0089] Under a nitrogen atmosphere, the positive electrode composite material is placed in a tablet press and flattened to obtain a positive electrode sheet;

[0090] Under a nitrogen atmosphere, lithium negative electrode, positive electrode, solid electrolyte, pad, and spring sheet are placed in sequence in a coin cell case to encapsulate a coin cell solid-state battery.

[0091] Comparative Example 1

[0092] The difference between this comparative example and Example 2 is that, in step S4, when preparing the cathode composite material, an equal amount of modified polycrystalline powder crude product is used instead of modified polycrystalline powder.

[0093] Comparative Example 2

[0094] The difference between this comparative example and Example 2 is that the modified binder is omitted in step S4 when preparing the positive electrode composite material.

[0095] Comparative Example 3

[0096] The difference between this comparative example and Example 2 is that, in step S4, when preparing the positive electrode composite material, carbon nanotubes are used in an equal amount to replace the modified conductive agent.

[0097] Performance testing:

[0098] The first charge-discharge efficiency, rate performance and specific capacity of the coin-type solid-state batteries prepared using positive electrode composite materials in Examples 1-3 and Comparative Examples 1-3 were tested in accordance with the standard SJ / T 11793-2022 "Test Method for Electrochemical Performance of Electrode Materials for Lithium-ion Batteries".

[0099] The conductivity of coin-type solid-state batteries prepared using positive electrode composite materials in Examples 1-3 and Comparative Examples 1-3 was tested in accordance with the standard SJ / T 11792-2022 "Test Method for Conductivity of Electrode Materials for Lithium-ion Batteries".

[0100] The method for cycle performance testing is as follows: charge to 4.1V at 0.5C, then charge at 4.1V with a constant voltage cutoff current of 0.02C, and discharge to 3.0V at 0.5C. The discharge capacity is used as the cycle discharge capacity for comparison, and the highest discharge capacity in the first three cycles is set as 100%.

[0101] Table 1. Test results of the samples

[0102]

[0103] Data Analysis:

[0104] Analysis of the data in Table 1 reveals that the conductivity of the coin cell solid-state battery prepared using the cathode composite material obtained in this experiment is 0.012 S·cm. -1 The initial charging efficiency is 91.5%, the capacity retention rate after 100 cycles is 95.3%, and the rate performance is 91.6%.

[0105] Comparative analysis of the data from Example 2 and Comparative Example 1 reveals that the conductivity, initial charge efficiency, and capacity retention after 100 cycles of Comparative Example 1 are significantly lower. This indicates that the present invention, by uniformly mixing NCM811 and dihydrodiamine and calcining it to form a graphite-phase silicon carbide coating on the surface of NCM811, obtains modified polycrystalline powder. Using this modified polycrystalline powder as the main active material in the cathode composite material of a solid-state battery, the inert protective layer formed on the NCM811 surface effectively enhances the surface stability of the cathode composite material, suppresses side reactions between the NCM811 interface and the solid electrolyte, reduces lattice oxygen loss and transition metal dissolution, thereby delaying capacity decay and improving the cycle stability of the solid-state battery. Simultaneously, the graphite... The high thermal conductivity and mechanical strength of graphitic silicon carbide can alleviate volume expansion stress during charging and discharging, reduce the probability of intergranular microcracks, and improve the long-cycle stability of cathode materials. The graphitic silicon carbide coating provides a stable lithium-ion diffusion channel. At the same time, the graphitic silicon carbide coating on the surface of NCM811 particles forms a continuous and dense conductive coating layer, constructing a stable electronic conduction network, reducing the migration resistance of electrons in the cathode material, thereby improving the overall electronic conductivity. The defect sites introduced by sulfur doping and the semiconductor properties of graphitic silicon carbide synergistically optimize the electron transport path and improve the charge transfer efficiency under high current density. Meanwhile, the high thermal conductivity of graphitic silicon carbide helps the modified binder dissipate heat and improve the cycle stability of solid-state batteries.

[0106] Comparative analysis of the data from Example 2 and Comparative Example 2 revealed a significant decrease in conductivity, initial charge efficiency, capacity retention after 100 cycles, and rate performance of Comparative Example 2. This indicates that the present invention, through the preparation of 2-acrylamido-2-methylpropanesulfonate neutralized with lithium hydroxide monohydrate, further reacts with lithium acrylate, n-butyl acrylate, and acrylonitrile via free radical reaction to obtain a modified binder. The lithium ions in the modified lithium salt monomer can form strong ionic bonds with the oxygen anions on the surface of the modified polycrystalline powder, enhancing the interfacial bonding strength. The cross-linked network structure formed by the free radical reaction can effectively fix the lithium salt, providing continuous ion transport channels, improving the ion mobility of the cathode composite material, and further enhancing the high-rate discharge performance of the solid-state battery. The introduction of acrylonitrile monomer enhances the rigidity of the binder, and its synergistic effect with the flexible segments of lithium acrylate endows the cathode composite material with excellent crack resistance, effectively alleviating stress concentration caused by volume changes during charging and discharging, thereby preventing particle breakage, structural collapse, and other phenomena, maintaining the integrity of the modified polycrystalline powder structure, avoiding capacity decay, and significantly extending the cycle life of the battery.

[0107] Comparative analysis of the data from Example 2 and Comparative Example 3 reveals that the conductivity, initial charge efficiency, capacity retention after 100 cycles, and rate performance of Comparative Example 3 are significantly reduced. This invention, through high-temperature sulfur doping of carbon nanotubes under a nitrogen atmosphere, and calcination under nitrogen atmosphere, protects the graphitized structure in the carbon nanotubes, avoiding the risk of structural collapse of the electrode during cycling. It also alters the electron cloud distribution of carbon in the carbon nanotubes, reducing resistivity and improving the overall conductivity of the cathode composite material, further enhancing the charge / discharge rate and rate performance of the solid-state battery. Furthermore, carbon nanotubes themselves possess excellent mechanical strength and structural stability. Under high-rate charge / discharge conditions, the structural strength of sulfur-doped carbon nanotubes helps prevent the cathode material from detaching or breaking, mitigating battery expansion or contraction during charge / discharge, thereby improving the cycle stability of the solid-state battery.

[0108] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to specific implementations. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention. The invention is limited only by the claims and their full scope and equivalents.

Claims

1. A positive electrode composite material for a solid-state battery, characterized in that, It includes the following raw materials by weight: 5-10 parts modified binder, 3-6 parts deionized water, 80-100 parts modified polycrystalline powder and 5-10 parts modified conductive agent; The modified polycrystalline powder is prepared by the following steps: A1. Place dicyandiamine and ethanol in a reaction vessel and stir for 1-5 min. Add NCM811 and stir for 5-15 min to obtain crude modified polycrystalline powder. A2. After ball milling the crude modified polycrystalline powder for 10-12 hours, calcination and post-treatment are performed to obtain the modified polycrystalline powder. The modified adhesive is prepared by the following steps: B1. Place 2-acrylamido-2-methylpropanesulfonic acid, ethanol and deionized water in a reaction vessel, stir for 1-5 min, slowly add lithium hydroxide monohydrate, heat to 20-30℃, keep the temperature for 3-4 h, and then process to obtain the modified lithium salt monomer. B2. The modified lithium salt monomer, lithium acrylate, n-butyl acrylate, ammonium persulfate, N,N-dimethylformamide and acrylonitrile are placed in a reaction vessel, heated to 70-80℃, and reacted for 7-8 hours. The modified binder is then obtained after post-treatment. The modified conductive agent is prepared by placing carbon nanotubes in a tube furnace under nitrogen protection, heating to 600-700℃, introducing sulfur dioxide gas, maintaining the temperature for 0.5-1.5h, and then processing to obtain the modified conductive agent.

2. The positive electrode composite material for a solid-state battery according to claim 1, characterized in that, In step A1, the ratio of dicyandiamine, ethanol and NCM811 is 0.05-0.10g:50-70mL:3-5g; in step A2, the ball milling media is composed of zirconium dioxide with a particle size of 1-5mm, the ball-to-powder ratio is 10:1, and the rotation speed is set to 100r / min.

3. The positive electrode composite material for a solid-state battery according to claim 1, characterized in that, In step B1, the ratio of 2-acrylamido-2-methylpropanesulfonic acid, ethanol, deionized water, and lithium hydroxide monohydrate is 3-4g:5-10mL:35-45mL:0.5-1g; in step B2, the ratio of modified lithium salt monomer, lithium acrylate, n-butyl acrylate, ammonium persulfate, N,N-dimethylformamide, and acrylonitrile is 1-2g:2-4g:4-6g:0.5-1.5g:200-250mL:2-4g.

4. The positive electrode composite material for a solid-state battery according to claim 1, characterized in that, The flow rate of the sulfur dioxide gas is 300 sccm.

5. A method for preparing a positive electrode composite material for a solid-state battery as described in any one of claims 1-4, characterized in that, Includes the following steps: S1. Mix the modified polycrystalline powder, modified binder, modified conductive agent and deionized water evenly to obtain a mixed slurry; S2. Apply the mixed slurry onto an aluminum foil sheet using a scraper, smooth it out, and dry it to obtain the positive electrode composite material.

6. The method for preparing a positive electrode composite material for a solid-state battery according to claim 5, characterized in that, In step S2, the coating thickness is 50-200 μm.

7. An application of a positive electrode composite material for solid-state batteries, characterized in that, The cathode composite material prepared by the method for preparing a solid-state battery cathode composite material according to claim 5 is applied to new energy batteries.

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