Positive electrode composite material of solid-state battery as well as preparation method and application of positive electrode composite material

Abstract

The invention discloses a positive electrode composite material of a solid-state battery as well as a preparation method and application thereof, belongs to the technical field of battery processing, and is used for solving the technical problem that the conductivity and the cycling stability of the positive electrode composite material of the solid-state battery in the prior art need to be further improved. The conductive coating specifically comprises the following raw materials in parts by weight: 5-10 parts of a modified binder, 3-6 parts of deionized water, 80-100 parts of modified polycrystalline powder and 5-10 parts of a modified conductive agent, modified polycrystalline powder, a modified binder, a modified conductive agent and deionized water are mixed into mixed slurry, an aluminum foil sheet is coated with the mixed slurry through a scraper, the aluminum foil sheet is scraped to be flat and dried, the positive electrode composite material is obtained, the conductivity and cycling stability of a solid-state battery prepared from the positive electrode composite material are improved, and the rate capability of the solid-state battery is also improved.

Description

Technical Field

[0001] The present invention relates to the technical field of battery processing, and in particular to a positive electrode composite material for a solid-state battery, a preparation method thereof, and applications thereof. Background Art

[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. The positive electrode composite materials of solid-state batteries, as one of their key components, have developed rapidly.

[0003] The positive electrode materials used in traditional liquid batteries are mainly composite materials such as lithium cobalt oxide and nickel cobalt manganese, while solid-state batteries pay more attention to the stability and conductivity of the materials. Therefore, researchers have achieved certain results by optimizing the microstructure and surface modification of the positive electrode composite materials and improving their compatibility with solid-state electrolytes.

[0004] At present, some solid-state battery positive electrode materials with excellent cycle performance and high energy density have emerged on the market. However, how to further improve their stability and conductivity is still a research hotspot.

[0005] In the existing technology, the conductivity and cycle stability of the positive electrode composite materials of solid-state batteries still need to be improved, especially under high load and rapid charge and discharge conditions, the material is prone to structural changes, resulting in a decline in battery performance. Secondly, the interface between the positive electrode material and the solid electrolyte is unstable, and the problem of prone to side reactions has not been effectively solved, and 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 positive electrode material is insufficient, and it is easy to fall off due to accumulated mechanical stress during long-term circulation. The positive electrode composite material will also produce lattice stress accumulation during the cycle, resulting in the formation of microcracks between the active material and the solid electrolyte, affecting the integrity of the electronic conduction network. As the conductive channel is destroyed, the electronic conductivity of the battery gradually decreases, resulting in battery capacity decline. Summary of the Invention

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

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

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

[0009] A1. Place dihydrogen diamine and ethanol in a reaction kettle, stir for 1-5 minutes, add NCM811, and stir for 5-15 minutes to obtain a crude modified polycrystalline powder;

[0010] A2. Ball-mill the crude modified polycrystalline powder for 10-12 hours and then calcine to obtain the modified polycrystalline powder.

[0011] The preparation reaction principle of modified polycrystalline powder is:

[0012] During the reaction, the surface of NCM811 contains abundant oxygen atoms and lithium ions. Dihydrogen diamine molecules are adsorbed on the surface of NCM811 through van der Waals forces and hydrogen bonds. Ball milling breaks up the NCM811 particles, increases their specific surface area, exposes more active surfaces, and promotes the uniform mixing of dihydrogen diamine molecules and NCM811. During calcination, ethanol evaporates, and dihydrogen diamine is attached to the surface of NCM811 in a molecularly dispersed state, forming a uniform precursor layer. Under argon protection, dihydrogen diamine molecules undergo deamination polymerization to form triazine ring structural units. The triazine rings are stacked into two-dimensional layered g-C3N4 through van der Waals forces. The sp in its structure 2 The hybridized CN atoms form a highly delocalized π-conjugated system, and the terminal amino group of g-C3N4 forms an NOC bond with the oxygen atoms on the surface of NCM811, achieving a firm bond between the coating layer and the substrate, generating a graphite phase silicon carbide coating layer and obtaining a modified polycrystalline powder.

[0013] Furthermore, in step A1, the amount ratio of dihydrogen diamine, ethanol and NCM811 is 0.05-0.10g:50-70mL:3-5g; in step A2, the ball milling medium 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 protected by a nitrogen atmosphere, heating to 75-85°C, drying for 9-11h, transferring to a tubular furnace at a temperature of 450-550°C and calcining for 0.5-1.5h, cooling at room temperature, grinding, and passing through a 200-mesh sieve to obtain a modified polycrystalline powder.

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

[0015] B1. Place 2-acrylamido-2-methylpropanesulfonic acid, ethanol, and deionized water in a reaction kettle, stir for 1-5 minutes, slowly add lithium hydroxide monohydrate, raise the temperature to 20-30° C., keep the temperature for reaction for 3-4 hours, and post-treat to obtain a modified lithium salt monomer;

[0016] The preparation reaction principle of modified lithium salt monomer is:

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

[0018] B2. Place the modified lithium salt monomer, lithium acrylate, n-butyl acrylate, ammonium persulfate, N,N-dimethylformamide and acrylonitrile in a reactor, heat to 70-80° C., keep the temperature for 7-8 hours, and post-treat to obtain a modified binder.

[0019] The preparation reaction formula of the modified binder is:

[0020]

[0021] The preparation reaction principle of the modified binder is:

[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 a modified binder.

[0023] Furthermore, in step B1, the amount ratio of the 2-acrylamido-2-methylpropanesulfonic acid, ethanol, deionized water and lithium hydroxide monohydrate is 3-4g:5-10mL:35-45mL:0.5-1g, and the post-treatment step includes: after the reaction is completed, heating to 95-100°C, and distilling under reduced pressure until no liquid is produced to obtain a modified lithium salt monomer; in step B2, the amount 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, and the post-treatment step includes: after the reaction is completed, heating to 150-160°C, and distilling under reduced pressure until no liquid is produced to obtain a modified binder.

[0024] Furthermore, the preparation method of the modified conductive agent is: placing carbon nanotubes in a nitrogen-protected tubular furnace, heating to 600-700° C., introducing sulfur dioxide gas, keeping the temperature for reaction for 0.5-1.5 hours, and post-treating to obtain the modified conductive agent.

[0025] The preparation reaction principle of the modified conductive agent is:

[0026] During the reaction, sulfur dioxide gas undergoes thermal decomposition in the high-temperature environment of the tubular furnace, and the generated sulfur atoms covalently bond with the edge carbon atoms on the surface of the carbon nanotubes. The sulfur atoms replace some carbon atoms to form a CSC structure and embed into 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 step includes: after the reaction is completed, cooling to room temperature, grinding, and passing through a 200-mesh sieve to obtain a modified conductive agent.

[0028] The present invention also provides a method for preparing a positive electrode composite material for a solid-state battery, comprising the following steps:

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

[0030] S2. Coat the mixed slurry on an aluminum foil with a scraper, flatten it, and dry it to obtain a positive electrode composite material.

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

[0032] The present invention also proposes an application of a positive electrode composite material for a solid-state battery. The positive electrode composite material prepared by the above-mentioned preparation method of the positive electrode composite material for a solid-state battery is applied to a new energy battery.

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

[0034] 1. The present invention is to coat a layer of graphite phase silicon carbide on the surface of NCM811 to obtain a modified polycrystalline powder, then neutralize 2-acrylamido-2-methylpropanesulfonic acid with lithium hydroxide monohydrate to obtain a modified lithium salt monomer, prepare a modified binder through further free radical copolymerization, use sulfur dioxide gas as a sulfur source, and prepare a modified conductive agent through high-temperature calcination, and mix the modified polycrystalline powder, modified binder, modified conductive agent and deionized water to form a mixed slurry, which is coated on an aluminum foil with a scraper, flattened, and dried to obtain a positive electrode composite material; the present invention uses high temperature to calcine the carbon nanotubes under a nitrogen atmosphere. The carbon nanotubes are modified by sulfur doping and calcination under a nitrogen atmosphere to protect the graphitized structure in the carbon nanotubes, avoid the risk of structural collapse of the electrode during the cycle, change the electron cloud distribution of carbon in the carbon nanotubes, reduce resistivity, and improve the overall conductivity of the positive electrode composite material, further improving the charge and discharge rate and rate performance of the solid-state battery. The carbon nanotubes themselves have excellent mechanical strength and structural stability. Under high-rate charge and discharge conditions, the structural strength of the sulfur-doped carbon nanotubes helps prevent the positive electrode material from falling off or breaking, and alleviates the expansion or contraction of the battery during the charge and discharge process, thereby improving the cyclic stability of the solid-state battery.

[0035] 2. The present invention also mixes NCM811 and dihydrogen diamine evenly, forms a graphite phase silicon carbide coating on the surface of NCM811 after calcination, and obtains a modified polycrystalline powder. The modified polycrystalline powder is used as the main active material of the positive electrode composite material of the solid-state battery. The inert protective layer formed on the surface of NCM811 can effectively enhance the surface stability of the positive electrode composite material, inhibit the side reaction between the surface interface of NCM811 and the solid electrolyte, reduce the loss of lattice oxygen and the dissolution of transition metals, thereby delaying capacity decay and improving the cycle stability of the solid-state battery. At the same time, the high thermal conductivity and mechanical strength of graphite phase silicon carbide can alleviate the volume expansion during the charge and discharge process. Stress, reduce the probability of intercrystalline microcracks, improve the long cycle stability of the positive electrode material, the graphite phase silicon carbide coating provides a stable lithium ion diffusion channel, and at the same time, the graphite phase silicon carbide is coated on the surface of the NCM811 particles to form a continuous and dense conductive coating layer, build a stable electron conduction network, reduce the migration resistance of electrons in the positive electrode 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 transmission path, improve the charge transfer efficiency under high current density, and at the same time, the high thermal conductivity of graphite phase silicon carbide helps to modify the heat dissipation of the adhesive and improve the cycle stability of the solid-state battery.

[0036] 3. The present invention prepares 2-acrylamido-2-methylpropanesulfonate neutralized with lithium hydroxide monohydrate, and further reacts the 2-acrylamido-2-methylpropanesulfonate with lithium acrylate, n-butyl acrylate and acrylonitrile through free radical reaction to obtain a modified adhesive. 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, thereby improving the interfacial bonding strength. The cross-linked network structure formed by the free radical reaction can effectively fix the lithium salt, provide a continuous ion transport channel, improve the ion mobility of the positive electrode composite material, and further improve the high-rate discharge performance of the solid-state battery. The introduction of acrylonitrile monomer enhances the rigidity of the adhesive, and synergizes with the flexible chain segment of lithium acrylate to give the positive electrode composite material excellent anti-cracking performance, effectively alleviating the stress concentration caused by volume change of the positive electrode during charging and discharging, thereby preventing particle breakage, structural collapse and the like, maintaining the integrity of the modified polycrystalline powder structure, avoiding capacity decay, and significantly extending the cycle life of the battery. DETAILED DESCRIPTION

[0037] The technical solutions of the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

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

[0039] The lithium sheet electrode used in the present invention was purchased from Changsha Xinkang New Materials Co., Ltd. and has a thickness of 0.05 mm.

[0040] The solid electrolyte used in the present invention is purchased from Shenzhen Liyou New Energy Technology Co., Ltd., model number is TOB-LLZO;

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

[0042] The spring sheet used in the present invention is purchased from Dongguan Heju Precision Electronic Technology Co., Ltd., with a specification of 30x20.91mm.

[0043] Example 1

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

[0045] S1. Preparation of modified polycrystalline powder

[0046] Weigh: 0.5 g of dihydrogen diamine and 500 mL of ethanol were placed in a reactor, stirred for 1 min, and then 130 g of NCM811 was added and stirred for 5 min to obtain a crude modified polycrystalline powder;

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

[0048] S2. Preparation of modified binder

[0049] Weigh: 30 g of 2-acrylamido-2-methylpropanesulfonic acid, 50 mL of ethanol, and 350 mL of deionized water into a reactor, stir for 1 min, slowly add 5 g of lithium hydroxide monohydrate, raise the temperature to 20°C, and keep the temperature to react for 3 h. After the reaction is completed, raise the temperature to 95°C and distill under reduced pressure until no liquid is recovered to obtain a modified lithium salt monomer;

[0050] Weigh: 10 g of modified lithium salt monomer, 20 g of lithium acrylate, 40 g of n-butyl acrylate, 5 g of ammonium persulfate, 2000 mL of N,N-dimethylformamide and 20 g of acrylonitrile, place them in a reactor, heat to 70°C, and keep warm for 7 hours. After the reaction is completed, heat to 150°C and distill under reduced pressure until no liquid is produced to obtain a modified binder.

[0051] S3. Preparation of modified conductive agent

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

[0053] S4. Preparation of positive electrode composite materials

[0054] Weigh 5 parts by mass of the modified binder, 3 parts by mass of deionized water, 80 parts by mass of the modified polycrystalline powder, and 5 parts by mass of the modified conductive agent, and mix them evenly to obtain a mixed slurry.

[0055] The mixed slurry was coated on an aluminum foil with a scraper and flattened to a thickness of 50 μm. The flattened product was transferred to a drying oven protected by a nitrogen atmosphere, heated to 90° C., and dried for 0.5 h to obtain a positive electrode composite material.

[0056] S5. Preparation of button-type solid-state batteries

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

[0058] Under a nitrogen atmosphere, the lithium sheet negative electrode, positive electrode sheet, solid electrolyte, gasket and spring sheet are placed in a button battery shell in sequence and encapsulated to obtain a button solid-state battery.

[0059] Example 2

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

[0061] S1. Preparation of modified polycrystalline powder

[0062] Weigh: 0.07 g of dihydrogen diamine and 600 mL of ethanol into a reactor, stir for 3 minutes, add 140 g of NCM81, and stir for 10 minutes to obtain a crude modified polycrystalline powder;

[0063] Weigh: After ball milling the crude modified polycrystalline powder for 11 hours, transfer it to an oven protected by a nitrogen atmosphere, heat it to 80°C, dry it for 10 hours, transfer it to a tube furnace at a temperature of 500°C and calcine it for 1 hour, cool it to room temperature, grind it, and pass it through a 200-mesh sieve to obtain a modified polycrystalline powder.

[0064] S2. Preparation of modified binder

[0065] Weigh: 35 g of 2-acrylamido-2-methylpropanesulfonic acid, 70 mL of ethanol, and 400 mL of deionized water into a reactor, stir for 3 minutes, slowly add 7 g of lithium hydroxide monohydrate, raise the temperature to 25°C, and keep the temperature to react for 3.5 hours. After the reaction is completed, raise the temperature to 97°C and distill under reduced pressure until no liquid is recovered to obtain a modified lithium salt monomer;

[0066] Weigh: 15 g of modified lithium salt monomer, 30 g of lithium acrylate, 50 g of n-butyl acrylate, 10 g of ammonium persulfate, 2250 mL of N,N-dimethylformamide and 30 g of acrylonitrile, place them in a reactor, heat to 75°C, keep warm and react for 7.5 hours. After the reaction is completed, heat to 155°C and distill under reduced pressure until no liquid is produced to obtain a modified binder.

[0067] S3. Preparation of modified conductive agent

[0068] Weigh: Place carbon nanotubes in a nitrogen-protected tube furnace, heat to 650°C, introduce sulfur dioxide gas at a flow rate of 300 sccm, and keep reacting for 1 hour. After the reaction is completed, cool to room temperature, grind, and pass through a 200-mesh sieve to obtain a modified conductive agent.

[0069] S4. Preparation of positive electrode composite materials

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

[0071] The mixed slurry was coated on an aluminum foil with a scraper and flattened to a thickness of 100 μm. The flattened product was transferred to a drying oven protected by a nitrogen atmosphere, heated to 95° C., and dried for 1 h to obtain a positive electrode composite material.

[0072] S5. Preparation of button-type solid-state batteries

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

[0074] Under a nitrogen atmosphere, the lithium sheet negative electrode, positive electrode sheet, solid electrolyte, gasket and spring sheet are placed in a button battery shell in sequence and encapsulated to obtain a button solid-state battery.

[0075] Example 3

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

[0077] S1. Preparation of modified polycrystalline powder

[0078] Weigh: 1 g of dihydrogen diamine and 700 mL of ethanol are placed in a reactor, stirred for 5 minutes, and then 150 g of NCM81 is added and stirred for 15 minutes to obtain a crude modified polycrystalline powder;

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

[0080] S2. Preparation of modified binder

[0081] Weigh: 40 g of 2-acrylamido-2-methylpropanesulfonic acid, 100 mL of ethanol, and 450 mL of deionized water are placed in a reactor and stirred for 5 minutes. Slowly add 10 g of lithium hydroxide monohydrate, raise the temperature to 30°C, and keep the temperature to react for 4 hours. After the reaction is completed, raise the temperature to 100°C and distill under reduced pressure until no liquid is recovered to obtain a modified lithium salt monomer;

[0082] Weigh: 20 g of modified lithium salt monomer, 40 g of lithium acrylate, 60 g of n-butyl acrylate, 15 g of ammonium persulfate, 2500 mL of N,N-dimethylformamide and 40 g of acrylonitrile, place them in a reactor, heat to 80°C, and keep warm for 8 hours. After the reaction is completed, heat to 160°C and distill under reduced pressure until no liquid is produced to obtain a modified binder.

[0083] S3. Preparation of modified conductive agent

[0084] Weigh: Place carbon nanotubes in a nitrogen-protected tube furnace, heat to 700°C, introduce sulfur dioxide gas at a flow rate of 300 sccm, and keep reacting for 1.5 hours. After the reaction is completed, cool to room temperature, grind, and pass through a 200-mesh sieve to obtain a modified conductive agent.

[0085] S4. Preparation of positive electrode composite materials

[0086] Weigh 10 parts by mass of the modified binder, 6 parts by mass of deionized water, 100 parts by mass of the modified polycrystalline powder, and 10 parts by mass of the modified conductive agent, and mix them evenly to obtain a mixed slurry.

[0087] The mixed slurry was coated on an aluminum foil with a scraper and flattened to a thickness of 50-200 μm. The flattened product was transferred to a drying oven protected by a nitrogen atmosphere, heated to 100° C., and dried for 1.5 h to obtain a positive electrode composite material.

[0088] S5. Preparation of button-type solid-state batteries

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

[0090] Under a nitrogen atmosphere, the lithium sheet negative electrode, positive electrode sheet, solid electrolyte, gasket and spring sheet are placed in a button battery shell in sequence and encapsulated to obtain a button solid-state battery.

[0091] Comparative Example 1

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

[0093] Comparative Example 2

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

[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, an equal amount of carbon nanotubes is used to replace the modified conductive agent.

[0097] Performance testing:

[0098] The first charge and discharge efficiency, rate performance, and specific capacity of the button-type solid-state batteries prepared using the positive electrode composite materials in Examples 1-3 and Comparative Examples 1-3 were tested with reference to the standard SJ / T 11793-2022 "Test Methods for Electrochemical Properties of Lithium-ion Battery Electrode Materials";

[0099] The conductive properties of the button-type solid-state batteries prepared using the positive electrode composite materials in Examples 1-3 and Comparative Examples 1-3 were tested in accordance with the standard SJ / T 11792-2022 "Test method for conductivity of lithium-ion battery electrode materials";

[0100] The method for the cycle performance test is: charge to 4.1V at 0.5C, then charge at 4.1V constant voltage with a cut-off 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 among the first three cycle discharge capacities is set as 100%.

[0101] Table 1. Test results of samples

[0102]

[0103] Data Analysis:

[0104] By analyzing the data in Table 1, it can be found that the conductivity of the button-type solid-state battery prepared by using the positive electrode composite material prepared in this experiment is 0.012S·cm -1 , the first charge efficiency is 91.5%, the capacity retention rate after 100 cycles is 95.3% and the rate performance is 91.6%;

[0105] By comparing and analyzing the data of Example 2 and Comparative Example 1, it can be found that the conductivity, first charge efficiency and capacity retention rate of Comparative Example 1 are significantly reduced, indicating that the present invention obtains modified polycrystalline powder by uniformly mixing NCM811 and dihydrogen diamine, forming a graphite phase silicon carbide coating on the surface of NCM811 after calcination, and using the modified polycrystalline powder as the main active material of the positive electrode composite material of the solid-state battery. The inert protective layer formed on the surface of NCM811 can effectively enhance the surface stability of the positive electrode composite material, inhibit the side reaction between the surface interface of NCM811 and the solid electrolyte, reduce the loss of lattice oxygen and the dissolution of transition metals, thereby delaying capacity decay and improving the cycle stability of the solid-state battery. At the same time, the graphite phase silicon carbide coating can effectively enhance the surface stability of the positive electrode composite material, inhibit the side reaction between the surface interface of NCM811 and the solid electrolyte, reduce the loss of lattice oxygen and the dissolution of transition metals, thereby delaying capacity decay and improving the cycle stability of the solid-state battery. The high thermal conductivity and mechanical strength of graphite phase silicon carbide can alleviate the volume expansion stress during the charge and discharge process, reduce the probability of intercrystalline microcracks, and improve the long-cycle stability of the positive electrode material. The graphite phase silicon carbide coating provides a stable lithium ion diffusion channel. At the same time, the graphite phase silicon carbide is coated on the surface of the NCM811 particles to form a continuous and dense conductive coating layer, building a stable electron conduction network, reducing the migration resistance of electrons in the positive electrode material, thereby improving the overall electronic conductivity. The defect sites introduced by sulfur doping and the semiconductor properties of graphite phase silicon carbide synergistically optimize the electron transmission path, improving the charge transfer efficiency under high current density. At the same time, the high thermal conductivity of graphite phase silicon carbide helps to modify the heat dissipation of the adhesive and improve the cycle stability of the solid-state battery.

[0106] By comparing and analyzing the data of Example 2 and Comparative Example 2, it can be found that the conductivity, first charge efficiency, capacity retention rate after 100 cycles and rate performance of Comparative Example 2 are significantly reduced, indicating that the present invention prepares 2-acrylamido-2-methylpropanesulfonate neutralized by lithium hydroxide monohydrate, and further reacts with lithium acrylate, n-butyl acrylate and acrylonitrile to obtain a modified adhesive through a free radical reaction. 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, thereby improving the interfacial bonding strength. The cross-linked network structure formed by the free radical reaction can effectively fix the lithium salt, provide a continuous ion transport channel, improve the ion mobility of the positive electrode composite material, and further improve the high-rate discharge performance of the solid-state battery. The introduction of acrylonitrile monomer enhances the rigidity of the adhesive, and synergizes with the flexible chain segment of lithium acrylate to give the positive electrode composite material excellent anti-cracking performance, effectively alleviating the stress concentration caused by volume change of the positive electrode during charging and discharging, thereby preventing particle breakage, structural collapse and the like, maintaining the integrity of the modified polycrystalline powder structure, avoiding capacity decay, and significantly extending the cycle life of the battery;

[0107] By comparing and analyzing the data of Example 2 and Comparative Example 3, it can be found that the conductivity, first charge efficiency, capacity retention rate after 100 cycles and rate performance of Comparative Example 3 are significantly reduced. The present invention uses high temperature to sulfur-dope the carbon nanotubes in a nitrogen atmosphere. The calcination in the nitrogen atmosphere protects the graphitized structure in the carbon nanotubes, avoids the risk of structural collapse of the electrode during the cycle, changes the electron cloud distribution of the carbon in the carbon nanotubes, reduces the resistivity, and improves the overall conductivity of the positive electrode composite material, further improving the charge and discharge rate and rate performance of the solid-state battery. The carbon nanotubes themselves have excellent mechanical strength and structural stability. Under high-rate charge and discharge conditions, the structural strength of the sulfur-doped carbon nanotubes helps to prevent the positive electrode material from falling off or breaking, and alleviates the expansion or contraction of the battery during the charge and discharge process, thereby improving the cyclic stability of the solid-state battery.

[0108] The preferred embodiments of the present invention disclosed above are intended only to help illustrate the present invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the present invention to specific embodiments. Obviously, many modifications and variations are possible based on the contents of this specification. These embodiments are selected and described in detail in this specification to better explain the principles and practical applications of the present invention, thereby enabling those skilled in the art to better understand and utilize the present invention. The present 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: The invention comprises the following raw materials in parts by weight: 5-10 parts of a modified binder, 3-6 parts of deionized water, 80-100 parts of a modified polycrystalline powder and 5-10 parts of a modified conductive agent; The modified polycrystalline powder is prepared by the following steps: A1. Place dihydrogen diamine and ethanol in a reaction kettle, stir for 1-5 minutes, add NCM811, and stir for 5-15 minutes to obtain a crude modified polycrystalline powder; A2. The crude modified polycrystalline powder is ball-milled for 10-12 hours, calcined, and post-treated to obtain the modified polycrystalline powder.

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

3. The positive electrode composite material for a solid-state battery according to claim 1, characterized in that: The modified binder is prepared by the following steps: B1. Place 2-acrylamido-2-methylpropanesulfonic acid, ethanol, and deionized water in a reaction kettle, stir for 1-5 minutes, slowly add lithium hydroxide monohydrate, raise the temperature to 20-30° C., keep the temperature for reaction for 3-4 hours, and post-treat to obtain a modified lithium salt monomer; B2. Place the modified lithium salt monomer, lithium acrylate, n-butyl acrylate, ammonium persulfate, N,N-dimethylformamide and acrylonitrile in a reactor, heat to 70-80° C., keep the temperature for 7-8 hours, and post-treat to obtain a modified binder.

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

5. The positive electrode composite material for a solid-state battery according to claim 1, characterized in that: The preparation method of the modified conductive agent comprises the following steps: placing carbon nanotubes in a nitrogen-protected tubular furnace, heating to 600-700° C., introducing sulfur dioxide gas, keeping the temperature for reaction for 0.5-1.5 hours, and performing post-processing to obtain the modified conductive agent.

6. The positive electrode composite material for a solid-state battery according to claim 6, characterized in that: The flow rate of the sulfur dioxide gas is 300 sccm.

7. A method for preparing a positive electrode composite material for a solid-state battery according to any one of claims 1 to 6, characterized in that: The following steps are involved: S1. Evenly mixing the modified polycrystalline powder, the modified binder, the modified conductive agent and deionized water to obtain a mixed slurry; S2. Coat the mixed slurry on an aluminum foil with a scraper, flatten it, and dry it to obtain a positive electrode composite material.

8. The method for preparing a positive electrode composite material for a solid-state battery according to claim 7, characterized in that: In step S2, the coating thickness is 50-200 μm.

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

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