Composite binder and preparation method thereof, silicon-based negative electrode sheet and preparation method thereof, and all-solid-state lithium ion battery

Abstract

The application provides a composite binder and a preparation method thereof, a silicon-based negative electrode sheet and a preparation method thereof, and a full-solid-state lithium ion battery. The composite binder comprises a main chain polymer and a hyperbranched polymer grafted on the main chain polymer by a grafting monomer; the main chain polymer is a hydrogenated styrene-butadiene-styrene block copolymer or a hydrogenated styrene-isoprene-styrene block copolymer; the terminal of the hyperbranched polymer has a first functional group; and the first functional group is selected from one of a hydroxyl group, an amino group, a carboxyl group, a mercapto group and an epoxy group. The composite binder has excellent adhesion, elastic deformation capacity and self-repairing capacity, can effectively buffer the volume change of the modified silicon-based material in the battery charging and discharging process and improve the interface stability, thereby improving the structural stability and interface stability of the silicon-based negative electrode sheet.

Description

Technical Field

[0001] This application relates to the field of solid-state battery technology, specifically to a composite binder and its preparation method, a silicon-based anode sheet and its preparation method, and an all-solid-state lithium-ion battery. Background Technology

[0002] Silicon-based anode materials, with their theoretical specific capacity of up to 4200 mAh / g, have become ideal anode materials for high-energy-density solid-state batteries. However, silicon-based materials undergo volume expansion and contraction exceeding 300% during battery charging and discharging. This drastic mechanical strain leads to problems such as active material pulverization, desorption of active material from the current collector, and failure of the interface between the solid electrolyte and the anode. Furthermore, this drastic volume change continuously consumes the active lithium source, causing lithium ions to form an unstable solid electrolyte interphase (SEI) film on the anode surface. This not only increases the battery's internal resistance but also leads to rapid capacity decay, severely limiting the lifespan of silicon-based anodes in all-solid-state lithium-ion batteries.

[0003] Chemical vapor deposition (CVD) technology can achieve uniform silicon-carbon composites at the atomic scale through gas-phase reactions, forming a core-shell structure with nano-silicon as the core and a dense carbon layer as the shell, which can effectively buffer the volume expansion of silicon. However, in practical applications, CVD silicon-carbon materials are highly dependent on the stable bonding formed between them and the binder, as well as the integrity of the entire electrode-electrolyte interface. In all-solid-state lithium-ion batteries, the binder must not only have good adhesion but also be compatible with sulfide solid electrolytes, suppressing side reactions of the sulfide solid electrolytes during processing that could damage the electrode structure and lead to decreased electrode interface stability and electrochemical performance.

[0004] In recent years, researchers have developed a variety of novel binders, such as self-healing binders based on dynamic covalent bonds, ion-conducting polymer binders, and natural polymer-based binders. However, these binders typically focus on solving only a single problem and struggle to meet the stringent requirements of all-solid-state lithium-ion batteries regarding binder adhesion, mechanical properties, electrochemical performance, and interfacial stability. Furthermore, due to the strong surface chemical inertness of commercial silicon-carbon materials (such as CVD silicon-carbon materials prepared by chemical vapor deposition), their interaction with binders is weak. This not only accelerates the desorption of active materials from the current collector but also further reduces the interfacial stability between the sulfide solid electrolyte and the negative electrode. However, existing binders have failed to provide effective solutions to these problems.

[0005] Therefore, researching and developing a composite binder with excellent adhesion, mechanical properties and interfacial stability and its preparation method is of great significance for improving the structural stability and interfacial stability of silicon-based anode sheets, as well as improving the rate performance and cycle stability of all-solid-state lithium-ion batteries. Summary of the Invention

[0006] The main objective of this application is to provide a composite binder and its preparation method, a silicon-based anode sheet and its preparation method, and an all-solid-state lithium-ion battery, so as to solve the problem that the binder in the prior art is difficult to achieve excellent adhesion, mechanical properties, electrochemical performance and interface stability at the same time, and the resulting poor structural stability and interface stability of the anode sheet and poor rate performance and cycle performance of the all-solid-state lithium-ion battery.

[0007] To achieve the above objectives, this application provides a composite adhesive comprising a main-chain polymer and a hyperbranched polymer grafted onto the main-chain polymer by grafting monomers; the main-chain polymer is a hydrogenated styrene-butadiene-styrene block copolymer or a hydrogenated styrene-isoprene-styrene block copolymer; the hyperbranched polymer has a first functional group at its end; the first functional group is selected from hydroxyl, amino, carboxyl, mercapto, and epoxy groups.

[0008] Furthermore, the grafting monomer is a compound having a carbon-carbon double bond, a second functional group, and a third functional group; the second functional group and the third functional group are each independently selected from one of carboxyl, hydroxyl, epoxy, amino, isocyanate, anhydride, phosphate, furan, and maleimide groups; the carbon-carbon double bond in the grafting monomer is connected to the unsaturated double bond in the main chain polymer; the second functional group or the third functional group in the grafting monomer is connected to the first functional group in the hyperbranched polymer.

[0009] Furthermore, the weight ratio of the grafted monomer to the main chain polymer is (2-15):100.

[0010] Furthermore, in the grafted monomer, the second functional group is selected from one of carboxyl, acid anhydride, and phosphate ester groups; the third functional group is selected from one of epoxy, acid anhydride, isocyanate, and furan groups.

[0011] Further, the grafting monomer is selected from one or more of the group consisting of acid anhydride compounds having carbon-carbon double bonds, acrylate compounds having a second or third functional group, and olefin derivatives having a second and third functional group; preferably, the grafting monomer is selected from one or more of the group consisting of maleic anhydride, glycidyl methacrylate, acrylic acid, 2-hydroxyethyl methacrylate phosphate, N-(2-hydroxyethyl)maleimide, itaconic acid, allyl glycidyl ether, and itaconic anhydride.

[0012] Furthermore, the content of unsaturated double bonds in the main chain polymer is 0.5 to 3 wt%; preferably, the number average molecular weight of the main chain polymer is 50,000 to 500,000 g / mol, more preferably 100,000 to 300,000 g / mol.

[0013] Furthermore, the degree of hydrogenation of the hydrogenated styrene-butadiene-styrene block copolymer is 90-99%; the degree of hydrogenation of the hydrogenated styrene-isoprene-styrene block copolymer is 90-99%.

[0014] Furthermore, the main chain polymer includes a first segment and a second segment, wherein the first segment is a polystyrene segment and the second segment is a hydrogenated polybutadiene segment or a hydrogenated isoprene segment; the content of the first segment is 20-80 wt%, preferably 30-50 wt%; and the content of the second segment is 20-80 wt%.

[0015] Furthermore, in the composite adhesive, the grafting rate of the hyperbranched polymer is 5-30 wt%; preferably, the degree of branching of the hyperbranched polymer is 0.4-0.7; preferably, the number average molecular weight of the hyperbranched polymer is 1000-50000 g / mol, more preferably 2000-10000 g / mol.

[0016] Furthermore, the first functional group accounts for 10 to 40% of the weight percentage of the hyperbranched polymer.

[0017] Further, the hyperbranched polymer is selected from one or more of the group consisting of hydroxyl-terminated hyperbranched polyester, amino-terminated hyperbranched polyethyleneimine, carboxyl-terminated hyperbranched polyester, hyperbranched polysiloxane, mercapto-terminated hyperbranched polyglycidyl ether, and epoxy-terminated hyperbranched polyester; preferably, the hyperbranched polymer may also optionally include conductive polymer modification segments; the conductive polymer modification segments are selected from one or more of the group consisting of thiophene conductive polymers, pyrrole conductive polymers, and aniline conductive polymers.

[0018] To achieve the above objectives, another aspect of this application provides a method for preparing the composite adhesive provided in this application. The method includes: step N1, in which the main chain polymer and the grafted monomer undergo a first grafting reaction in a first organic solvent in the presence of an initiator, followed by a first drying to obtain an intermediate product; and step N2, in which the intermediate product and the hyperbranched polymer undergo a second grafting reaction in a second organic solvent under the catalysis of a catalyst, followed by a second drying to obtain the composite adhesive.

[0019] Furthermore, in step N1, the temperature of the first grafting reaction is 110–140°C, and the time is 2–6 h.

[0020] Further, the weight ratio of the main chain polymer to the grafted monomer is 100:(2-15); preferably, the weight ratio of the initiator to the grafted monomer is (0.5-2):100; preferably, the weight ratio of the main chain polymer to the first organic solvent is (5-15):100.

[0021] Further, the initiator is selected from one or more of the group consisting of dicumyl peroxide, benzoyl peroxide, and azobisisobutyronitrile; preferably, the first organic solvent is selected from one or more of the group consisting of toluene, xylene, cyclohexane, butyl butyrate, and anisole.

[0022] Furthermore, the first drying temperature is 60–80°C, and the time is 6–12 hours.

[0023] Furthermore, in step N2, the temperature of the second grafting reaction is 60–90°C, and the time is 12–24 h.

[0024] Further, the weight ratio of the intermediate product to the hyperbranched polymer is 100:(5-40); preferably, the weight ratio of the catalyst to the intermediate product is (0.1-2):100; preferably, the weight ratio of the intermediate product to the second organic solvent is (8-20):100.

[0025] Further, the catalyst is selected from one or more of the group consisting of p-toluenesulfonic acid, 4-dimethylaminopyridine, N,N-dicyclohexylcarbodiimide, 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride and triethylamine; preferably, the second organic solvent is selected from one or more of the group consisting of toluene, xylene and tetrahydrofuran.

[0026] Furthermore, the second drying temperature is 50–70°C, and the time is 12–24 hours.

[0027] Another aspect of this application provides a silicon-based negative electrode sheet, comprising a negative electrode current collector and a negative electrode active material layer disposed on at least one side of the sheet, wherein the negative electrode active material layer comprises a modified silicon-based material, a binder, a solid electrolyte, and a conductive agent; the modified silicon-based material is a silicon-based material having a fourth functional group on its surface; the fourth functional group is selected from hydroxyl, carboxyl, carbonyl, and amino groups; the binder is the composite binder provided in this application.

[0028] The fourth aspect of this application also provides a method for preparing the silicon-based negative electrode sheet provided in this application. The method includes: step S1, modifying the surface of a silicon-based material by introducing a fourth functional group on the surface of the silicon-based material to obtain a modified silicon-based material; step S2, mixing the modified silicon-based material, a composite binder, a solid electrolyte, a conductive agent, and a third organic solvent to obtain a negative electrode slurry; and step S3, coating the negative electrode slurry onto at least one side of the surface of a negative electrode current collector and drying it to obtain a silicon-based negative electrode sheet.

[0029] Further, in step S1, the surface modification method includes: mixing a silicon-based material with an oxidant, and sequentially subjecting it to a first heat treatment and a fourth drying to obtain a modified silicon-based material; or, placing the silicon-based material in an ozone or air atmosphere and subjecting it to a second heat treatment to obtain a modified silicon-based material; or, subjecting the silicon-based material to oxygen plasma treatment or ammonia plasma treatment to obtain a modified silicon-based material.

[0030] Furthermore, the fourth functional group accounts for 0.1% to 2% of the weight of the modified silicon-based material.

[0031] Further, the weight ratio of silicon-based material to oxidant is 100:(1-20); preferably, the oxidant is selected from one or more of the group consisting of concentrated nitric acid, a mixed solution of concentrated sulfuric acid and hydrogen peroxide, potassium permanganate solution, ammonium persulfate solution and nitric acid.

[0032] Furthermore, the temperature of the first heat treatment is 60–120°C, and the time is 0.5–6 h; the temperature of the fourth drying is 80–120°C, and the time is 6–24 h.

[0033] Furthermore, the second heat treatment is carried out at a temperature of 300–500°C for a time of 1–4 hours.

[0034] Further, in step S2, the weight ratio of the modified silicon-based material, composite binder, solid electrolyte and conductive agent is (50-80):(1.5-5):(10-35):(1-3); the weight ratio of the third organic solvent and the modified silicon-based material is 100:(30-60).

[0035] Furthermore, the relative permittivity of the third organic solvent is ≤30, preferably one or more of the group consisting of p-xylene, anisole, phenethyl ether, tetrahydronaphthalene, n-heptane, 1,2-dibromomethane, butyl butyrate and isobutyl isobutyrate.

[0036] Furthermore, in step S3, the coating amount of the negative electrode slurry on the surface of the negative electrode current collector is 3–20 mg / cm². 2 .

[0037] Furthermore, in step S3, the temperature of the third drying is 50–160°C, and the time is 2–12 hours.

[0038] The fifth aspect of this application also provides an all-solid-state lithium-ion battery, including a positive electrode, a negative electrode, and a solid electrolyte layer disposed between the positive electrode and the negative electrode, wherein the negative electrode is the silicon-based negative electrode provided in this application.

[0039] The present application provides a composite binder in which the main-chain polymer is a linear block copolymer of the aforementioned specific type. This copolymer not only provides structural support and enhances the mechanical properties of the composite binder, but also imparts excellent flexibility and stress buffering capacity. This effectively buffers the significant volume changes of the modified silicon-based material during battery charging and discharging, and suppresses the pulverization and detachment of the negative electrode active material layer. Graft monomers can connect the main-chain polymer and the hyperbranched polymer to form the composite binder. Hyperbranched polymers form dynamic and reversible covalent or hydrogen bonds with grafted monomers through their terminal first functional groups. These dynamic bonds can dissipate energy through breakage under external forces and can recombine after stress relief. This gives the composite binder excellent self-healing capabilities, effectively coping with the stress generated by the volume expansion of modified silicon-based materials and improving the structural stability of silicon-based anode sheets. The presence of the terminal first functional groups of hyperbranched polymers can enhance the interaction force between the composite binder and silicon-based materials, especially suitable for silicon-based materials with oxygen-containing or nitrogen-containing groups on the surface, significantly improving the bonding strength. On the other hand, it can also improve the compatibility of the composite binder with solid electrolytes, thereby improving interfacial stability and promoting electron and lithium-ion conduction. In addition, the highly branched structure of hyperbranched polymers can reduce the entanglement of composite binder molecular chains, improving the flowability and processability of the composite binder.

[0040] In summary, the composite binder provided in this application possesses excellent adhesion, elastic deformation capability, and self-healing ability, effectively buffering the significant volume changes of modified silicon-based materials during battery charging and discharging and improving interfacial stability. Applying this composite binder to silicon-based anode sheets can improve the bonding strength of the anode active material layer and its adhesion to the anode current collector, while also maintaining the electron and lithium-ion transport paths within the silicon-based anode sheet. This enhances the structural and interfacial stability of the silicon-based anode sheet, thereby significantly improving the rate performance and cycle stability of silicon-based all-solid-state lithium-ion batteries. Detailed Implementation

[0041] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The present application will now be described in detail with reference to the embodiments.

[0042] As described in the background section, existing binders for silicon-based anodes suffer from difficulties in simultaneously achieving excellent adhesion, mechanical properties, electrochemical performance, and interfacial stability. This results in poor structural and interfacial stability of the anode sheet and poor rate and cycle performance of all-solid-state lithium-ion batteries. To address these technical problems, a first aspect of this application provides a composite binder comprising a main-chain polymer and a hyperbranched polymer grafted onto the main-chain polymer via grafted monomers. The main-chain polymer is a hydrogenated styrene-butadiene-styrene block copolymer or a hydrogenated styrene-isoprene-styrene block copolymer. The hyperbranched polymer has a first functional group at its end, selected from hydroxyl, amino, carboxyl, mercapto, and epoxy groups.

[0043] This application provides a composite binder in which the main-chain polymer is a specific type of linear block copolymer, which not only provides structural support and enhances the mechanical properties of the composite binder, but also endows it with excellent flexibility and stress buffering capacity. This effectively buffers the significant volume changes of the modified silicon-based material during battery charging and discharging, and suppresses the pulverization and detachment of the negative electrode active material layer. Graft monomers can connect the main-chain polymer and the hyperbranched polymer to form the composite binder. Hyperbranched polymers form dynamic and reversible covalent or hydrogen bonds with grafted monomers through their terminal first functional groups. These dynamic bonds can dissipate energy through breakage under external forces and can recombine after stress relief. This gives the composite binder excellent self-healing capabilities, effectively coping with the stress generated by the volume expansion of modified silicon-based materials and improving the structural stability of silicon-based anode sheets. The presence of the terminal first functional groups of hyperbranched polymers can enhance the interaction force between the composite binder and silicon-based materials, especially suitable for silicon-based materials with oxygen-containing or nitrogen-containing groups on the surface, significantly improving the bonding strength. On the other hand, it can also improve the compatibility of the composite binder with solid electrolytes, thereby improving interfacial stability and promoting electron and lithium-ion conduction. In addition, the highly branched structure of hyperbranched polymers can reduce the entanglement of composite binder molecular chains, improving the flowability and processability of the composite binder.

[0044] In summary, the composite binder provided in this application possesses excellent adhesion, elastic deformation capability, and self-healing ability, effectively buffering the significant volume changes of modified silicon-based materials during battery charging and discharging and improving interfacial stability. Applying this composite binder to silicon-based anode sheets can improve the bonding strength of the anode active material layer and its adhesion to the anode current collector, while also maintaining the electron and lithium-ion transport paths within the silicon-based anode sheet. This enhances the structural and interfacial stability of the silicon-based anode sheet, thereby significantly improving the rate performance and cycle stability of silicon-based all-solid-state lithium-ion batteries.

[0045] In a preferred embodiment, the grafting monomer is a compound having carbon-carbon double bonds, a second functional group, and a third functional group; the second and third functional groups are each independently including, but not limited to, one of carboxyl, hydroxyl, epoxy, amino, isocyanate, anhydride, phosphate, furan, and maleimide groups; the carbon-carbon double bond in the grafting monomer is connected to the unsaturated double bond in the main chain polymer; the second or third functional group in the grafting monomer is connected to the first functional group in the hyperbranched polymer. The grafting monomer can connect the main chain polymer and the hyperbranched polymer to form a composite binder, and the aforementioned specific types of second or third functional groups can form hydrogen bonds with functional groups on the surface of silicon-based materials (especially silicon-based materials with oxygen-containing or nitrogen-containing groups on the surface) or form covalent bonds during the drying process of the silicon-based negative electrode sheet, thereby improving the interaction force between the silicon-based material and the composite binder, and improving the adhesion strength of the negative electrode active material layer and its adhesion to the negative electrode current collector.

[0046] It should be noted that in the composite adhesive described above in this application, when the second functional group in the grafting unit is used to graft hyperbranched polymer, its unreacted third functional group is used to interact with the functional groups on the surface of the silicon-based material; when the third functional group in the grafting unit is used to graft hyperbranched polymer, its unreacted second functional group is used to interact with the functional groups on the surface of the silicon-based material.

[0047] In order to improve the mechanical strength and adhesion of the composite adhesive, and to better serve as a bridge, a more suitable amount of hyperbranched polymer is introduced. In a preferred embodiment, the weight ratio of graft monomer to main chain polymer is (2-15):100.

[0048] In a preferred embodiment, the second functional group in the grafted monomer includes, but is not limited to, one of a carboxyl group, an anhydride group, and a phosphate ester group; the third functional group includes, but is not limited to, one of an epoxy group, an anhydride group, an isocyanate group, and a furan group. Compared with other types, using the above-mentioned second and third functional groups is beneficial to improving the structural stability, stress buffering capacity, and self-healing ability of the composite binder. It also helps to improve the interaction between the composite binder and the silicon-based material, enhancing their bonding strength. This, in turn, helps to improve the bonding strength of the negative electrode active material layer and its adhesion to the negative electrode current collector, thereby improving the structural stability and interfacial stability of the silicon-based negative electrode sheet.

[0049] To further improve the structural stability, stress buffering capacity, and self-healing ability of the composite binder, further enhance the interaction between the composite binder and the silicon-based material, and strengthen its bonding strength, thereby further improving the bonding strength of the negative electrode active material layer and its adhesion to the negative electrode current collector, and further improving the structural stability and interface stability of the silicon-based negative electrode sheet, preferably, the grafting monomer includes, but is not limited to, one or more of the following groups: acid anhydride compounds with carbon-carbon double bonds, acrylate compounds with second or third functional groups, and olefin derivatives with second and third functional groups.

[0050] In a preferred embodiment, the grafting monomers include, but are not limited to, one or more of the group consisting of maleic anhydride, glycidyl methacrylate, acrylic acid, 2-hydroxyethyl methacrylate phosphate, N-(2-hydroxyethyl)maleimide, itaconic acid, allyl glycidyl ether, and itaconic anhydride. Compared to other types, using the above-mentioned grafting monomers is beneficial for improving the structural stability, stress buffering capacity, and self-healing ability of the composite binder. It also helps to improve the interaction between the composite binder and the silicon-based material, enhancing their bonding strength. This, in turn, improves the bonding strength of the negative electrode active material layer and its adhesion to the negative electrode current collector, thereby improving the structural and interfacial stability of the silicon-based negative electrode sheet.

[0051] In order to retain an appropriate amount of unsaturated double bonds in the main chain polymer, thereby providing more active sites for grafting monomers and obtaining a composite adhesive with better performance, in a preferred embodiment, the content of unsaturated double bonds in the main chain polymer is 0.5 to 3 wt%.

[0052] In order to improve the mechanical strength and processing performance of the composite binder and enhance its compatibility with other components, in a preferred embodiment, the number-average molecular weight (Mn) of the main chain polymer is 50,000 to 500,000 g / mol.

[0053] To further improve the mechanical strength and processing performance of the composite adhesive, and to further improve its compatibility with other components, preferably, the number average molecular weight of the main chain polymer is 100,000 to 300,000 g / mol.

[0054] In a preferred embodiment, the degree of hydrogenation of the hydrogenated styrene-butadiene-styrene block copolymer is 90-99%; the degree of hydrogenation of the hydrogenated styrene-isoprene-styrene block copolymer is 90-99%. Compared to other ranges, using hydrogenated styrene-butadiene-styrene block copolymers or hydrogenated styrene-isoprene-styrene block copolymers with the above-mentioned specific degrees of hydrogenation is beneficial for retaining an appropriate amount of unsaturated double bonds in the main chain polymer, thereby providing more active sites for grafting the above-mentioned graft monomers of this application, resulting in a composite adhesive with superior performance.

[0055] It should be noted that, in this application, the degree of hydrogenation of the hydrogenated styrene-butadiene-styrene block copolymer refers to the percentage of unsaturated carbon-carbon double bonds in the polybutadiene segments that are converted into saturated bonds by hydrogen addition; the degree of hydrogenation of the hydrogenated styrene-isoprene-styrene block copolymer refers to the percentage of unsaturated carbon-carbon double bonds in the isoprene segments that are converted into saturated bonds by hydrogen addition.

[0056] In a preferred embodiment, the main chain polymer includes a first segment and a second segment. The first segment is a polystyrene segment (i.e., a hard segment), and the second segment is a hydrogenated polybutadiene segment or a hydrogenated isoprene segment (i.e., a soft segment). The content of the first segment is 20–80 wt%, and the content of the second segment is 20–80 wt%. In the main chain polymer, the hard segment (first segment) provides structural rigidity and cohesive strength, while the soft segment (second segment) provides elasticity and flexibility. Compared to other ranges, limiting the content of the first and second segments in the main chain polymer to the above range is beneficial to improving the mechanical strength and elastic deformation capability of the composite binder. This helps to buffer the huge volume changes of silicon-based materials during battery charging and discharging, suppresses the pulverization and shedding of the negative electrode active material layer, and thus helps to improve the structural stability of the prepared silicon-based negative electrode sheet.

[0057] To further improve the mechanical strength and elastic deformation capability of the composite binder, and to further improve the structural stability of the prepared silicon-based anode sheet, preferably, the content of the first segment in the main chain polymer is 30-50 wt%.

[0058] In a preferred embodiment, the grafting rate of the hyperbranched polymer in the composite binder is 5 to 30 wt%. Compared to other ranges, limiting the grafting rate of the hyperbranched polymer to the above range is beneficial to improving the interfacial stability of the composite binder and its interaction with the modified silicon-based material, thereby improving the bonding strength of the negative electrode active material layer and its adhesion to the negative electrode current collector, and improving the structural stability of the silicon-based negative electrode sheet.

[0059] In a preferred embodiment, the degree of branching of the hyperbranched polymer is 0.4–0.7; the number-average molecular weight of the hyperbranched polymer is 1000–50000 g / mol. The degree of branching and number-average molecular weight of the hyperbranched polymer include, but are not limited to, the above ranges. Limiting them to these ranges is beneficial for improving the dispersion uniformity of the hyperbranched polymer in the composite binder, for improving the compatibility of the composite binder with the solid electrolyte, and for promoting the transport of electrons and lithium ions, thereby improving the structural stability and interfacial stability of the prepared silicon-based anode sheet.

[0060] To further improve the dispersion uniformity of hyperbranched polymers in composite binders, further improve the compatibility of composite binders with solid electrolytes, and thus further improve the electron and lithium ion transport efficiency, preferably, the number average molecular weight of the hyperbranched polymer is 2000-10000 g / mol.

[0061] In order to provide enough reaction sites to react with the grafted monomers, construct dynamic and reversible linkages, improve the stress buffering capacity and self-healing capacity of the composite binder, and further improve the compatibility of the composite binder with the solid electrolyte and improve the interfacial stability of the prepared modified silicon-carbon anode, in a preferred embodiment, the first functional group accounts for 10 to 40% of the weight percentage of the hyperbranched polymer.

[0062] In a preferred embodiment, the hyperbranched polymer includes, but is not limited to, one or more of the following groups: hydroxyl-terminated hyperbranched polyester, amino-terminated hyperbranched polyethyleneimine, carboxyl-terminated hyperbranched polyester, hyperbranched polysiloxane, mercapto-terminated hyperbranched polyglycidyl ether, and epoxy-terminated hyperbranched polyester. Compared to other types, using the above-mentioned hyperbranched polymers is beneficial for improving the adhesion, stress buffering capacity, self-healing ability, and processability of the composite binder. It also helps improve the compatibility of the composite binder with the solid electrolyte, promotes electron and lithium-ion transport, and thus improves the structural and interfacial stability of the prepared silicon-based anode sheet.

[0063] To further promote electron and lithium-ion transport and further improve the structural and interfacial stability of the prepared silicon-based anode sheet, preferably, the hyperbranched polymer may also optionally include conductive polymer modification segments; the conductive polymer modification segments include, but are not limited to, one or more of the group consisting of thiophene conductive polymers, pyrrole conductive polymers and aniline conductive polymers.

[0064] The second aspect of this application provides a method for preparing the composite adhesive provided in this application. The method includes: step N1, in which the main chain polymer and the grafted monomer undergo a first grafting reaction in a first organic solvent in the presence of an initiator, followed by a first drying to obtain an intermediate product; and step N2, in which the intermediate product and the hyperbranched polymer undergo a second grafting reaction in a second organic solvent under the catalysis of a catalyst, followed by a second drying to obtain the composite adhesive.

[0065] In step N1, the carbon-carbon double bond in the grafting unit undergoes a first grafting reaction with the unsaturated double bond in the second segment of the main polymer chain under the initiation of an initiator, thereby grafting the grafting unit onto the main polymer chain to obtain an intermediate product. In step N2, the first functional group at the end of the hyperbranched polymer can undergo a second grafting reaction with the unreacted second or third functional group of the grafting unit in the intermediate product under the catalysis of a catalyst, thereby grafting the hyperbranched polymer onto the grafting unit in the intermediate product to obtain a composite binder.

[0066] Compared to other methods, the composite binder prepared by the above method exhibits excellent adhesion, elastic deformation capability, and self-healing ability. It can effectively buffer the significant volume changes of modified silicon-based materials during battery charging and discharging and improve interfacial stability. Applying this composite binder to silicon-based anode sheets can improve the bonding strength of the anode active material layer and its adhesion to the anode current collector. Simultaneously, it can maintain the electron and lithium-ion transport paths within the silicon-based anode sheet, thereby improving the structural and interfacial stability of the silicon-based anode sheet. This, in turn, can significantly enhance the rate performance and cycle stability of silicon-based all-solid-state lithium-ion batteries.

[0067] In order to improve the reaction efficiency of the first grafting reaction, reduce the occurrence of side reactions, promote the uniform distribution of grafting units, and further improve the purity and consistency of the obtained composite adhesive, in a preferred embodiment, the temperature of the first grafting reaction in step N1 is 110-140°C and the time is 2-6 hours.

[0068] In a preferred embodiment, the weight ratio of the main-chain polymer to the grafted monomer is 100:(2-15). The weight ratio of the main-chain polymer to the grafted monomer includes, but is not limited to, the range described above; limiting it to this range is beneficial for improving the mechanical properties and adhesion of the resulting composite adhesive.

[0069] In order to initiate the first grafting reaction, further improve the reaction efficiency of the first grafting reaction and regulate its reaction rate, and further reduce the occurrence of side reactions, thereby further improving the purity and consistency of the obtained composite adhesive, in a preferred embodiment, the weight ratio of initiator to grafting monomer is (0.5~2):100.

[0070] The initiator can be selected from commonly used initiators in the art. In a preferred embodiment, the initiator includes, but is not limited to, one or more of the group consisting of dicumyl peroxide, benzoyl peroxide, and azobisisobutyronitrile. Using the above-mentioned types of initiators is beneficial to further improve the reaction efficiency of the first grafting reaction and control its reaction rate.

[0071] In a preferred embodiment, the weight ratio of the main-chain polymer to the first organic solvent is (5-15):100. The weight ratio of the main-chain polymer to the first organic solvent includes, but is not limited to, the above range. Limiting it to this range is beneficial for improving the dispersibility of the main-chain polymer and the grafted monomer, thereby improving the reaction efficiency of the first grafting reaction.

[0072] To further improve the dispersibility of the main-chain polymer and the grafted monomer, and to further improve the reaction efficiency of the first grafting reaction, preferably, the first organic solvent includes, but is not limited to, one or more of the group consisting of toluene, xylene, cyclohexane, butyl butyrate and anisole.

[0073] In order to remove the first organic solvent and improve the purity of the intermediate product, thereby facilitating the subsequent second grafting reaction, in a preferred embodiment, the first drying temperature is 60-80°C and the time is 6-12 hours.

[0074] In a preferred embodiment, in step N2, the temperature of the second grafting reaction is 60–90°C, and the time is 12–24 h. The temperature and time of the second grafting reaction include, but are not limited to, the above-mentioned ranges. Limiting them to the above-mentioned ranges is beneficial to improving the reaction efficiency of the second grafting reaction, reducing the occurrence of side reactions, promoting the uniform distribution of hyperbranched polymers, and thus improving the purity and consistency of the obtained composite binder.

[0075] In a preferred embodiment, the weight ratio of the intermediate product to the hyperbranched polymer is 100:(5-40). The weight ratio of the intermediate product to the hyperbranched polymer includes, but is not limited to, the above range. Limiting it to the above range is beneficial to improving the adhesion and self-healing ability of the obtained composite adhesive, and also beneficial to improving the compatibility of the obtained composite adhesive with the solid electrolyte.

[0076] In order to catalyze the second grafting reaction, further improve the reaction efficiency of the second grafting reaction and regulate its reaction rate, and further reduce the occurrence of side reactions, thereby further improving the purity and consistency of the obtained composite binder, in a preferred embodiment, the weight ratio of catalyst to intermediate product is (0.1-2):100.

[0077] In a preferred embodiment, the catalyst includes, but is not limited to, one or more of the group consisting of p-toluenesulfonic acid, 4-dimethylaminopyridine, N,N-dicyclohexylcarbodiimide, 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride, and triethylamine. Compared to other types, using the above-mentioned catalysts is beneficial for improving the reaction efficiency of the second grafting reaction and reducing the occurrence of side reactions.

[0078] In a preferred embodiment, the weight ratio of the intermediate product to the second organic solvent is (8-20):100. The weight ratio of the intermediate product to the second organic solvent includes, but is not limited to, the above range. Limiting it to this range is beneficial for improving the dispersibility of the intermediate product and the hyperbranched polymer, thereby improving the reaction efficiency of the second grafting reaction.

[0079] To further improve the dispersibility of intermediate products and hyperbranched polymers, and to further improve the reaction efficiency of the second grafting reaction, in a preferred embodiment, the second organic solvent includes, but is not limited to, one or more of the group consisting of toluene, xylene, and tetrahydrofuran.

[0080] In order to remove the second organic solvent and improve the purity of the obtained composite adhesive, in a preferred embodiment, the second drying temperature is 50-70°C and the time is 12-24 hours.

[0081] A third aspect of this application also provides a silicon-based negative electrode sheet, comprising a negative electrode current collector and a negative electrode active material layer disposed on at least one side surface thereon, wherein the negative electrode active material layer comprises a modified silicon-based material, a binder, a solid electrolyte, and a conductive agent; the modified silicon-based material is a silicon-based material having a fourth functional group on its surface; the fourth functional group is selected from one of hydroxyl, carboxyl, carbonyl, and amino groups; the binder is the composite binder provided in this application.

[0082] The silicon-based anode sheet provided in this application comprises a modified silicon-based material, a solid electrolyte, a conductive agent, and a composite binder in its negative electrode active material layer. The surface of the modified silicon-based material has a specific type of fourth functional group, which can form hydrogen bonds or chemical bonds with the functional groups in the composite binder. This significantly improves the interaction force between the modified silicon-based material and the composite binder, increases the bonding strength, and effectively suppresses the pulverization and detachment of the negative electrode active material layer, thereby improving the structural and interfacial stability of the silicon-based anode sheet. The composite binder provided in this application has excellent adhesion, elastic deformation ability, and self-healing ability, effectively buffering the large volume changes of the modified silicon-based material during battery charging and discharging and improving interfacial stability. Simultaneously, through the interaction with the modified silicon-based material, it can further improve the bonding strength of the negative electrode active material layer and its adhesion to the negative electrode current collector, improving the structural stability of the silicon-based anode sheet. Furthermore, the specific structure of the composite binder can also stabilize the electron and lithium ion transport paths within the silicon-based anode sheet. Applying the silicon-based anode sheet provided in this application to all-solid-state lithium-ion batteries can significantly improve their rate performance and cycle stability.

[0083] The fourth aspect of this application also provides a method for preparing the silicon-based negative electrode sheet provided in this application. The method includes: step S1, modifying the surface of a silicon-based material by introducing a fourth functional group on the surface of the silicon-based material to obtain a modified silicon-based material; step S2, mixing the modified silicon-based material, a composite binder, a solid electrolyte, a conductive agent, and a third organic solvent to obtain a negative electrode slurry; and step S3, coating the negative electrode slurry onto at least one side of the surface of a negative electrode current collector and drying it to obtain a silicon-based negative electrode sheet.

[0084] In step S1 of the above preparation method, by surface modification of the silicon-based material, a specific type of fourth functional group can be introduced onto the surface of the silicon-based material to obtain a modified silicon-based material. This allows the modified silicon-based material to form hydrogen bonds or chemical bonds with the second or third functional groups in the grafted units of the composite binder during the subsequent preparation of the negative electrode slurry. This improves the interaction force between the modified silicon-based material and the composite binder, increases the bonding strength, and effectively inhibits the pulverization and detachment of the negative electrode active material layer, thereby improving the structural and interfacial stability of the silicon-based negative electrode sheet. In step S2, mixing the modified silicon-based material, the composite binder provided in this application, the solid electrolyte, the conductive agent, and the third organic solvent yields a stable, uniform negative electrode slurry with good flowability, facilitating subsequent coating. The composite binder provided in this application possesses excellent adhesion, elastic deformation capability, and self-healing ability. When applied to the preparation of silicon-based anode sheets, it effectively buffers the significant volume changes of modified silicon-based materials during battery charging and discharging, and improves interfacial stability. Simultaneously, through the interaction between the composite binder and the modified silicon-based material, the bonding strength of the anode active material layer and its adhesion to the anode current collector are further enhanced, improving the structural stability of the resulting silicon-based anode sheet. Furthermore, the specific structure of the composite binder can improve the electron and lithium-ion transport paths within the silicon-based anode sheet, increasing electron and lithium-ion transport efficiency. In step S3, the aforementioned anode slurry is coated onto at least one side of the anode current collector, and after a third drying process, a silicon-based anode sheet is obtained.

[0085] In summary, the silicon-based anode sheet prepared by the above-mentioned preparation method provided in this application has excellent structural stability and interface stability. Its application in all-solid-state lithium-ion batteries can significantly improve the rate performance and cycle stability of all-solid-state lithium-ion batteries.

[0086] The solid electrolyte in this application can be any type of solid electrolyte commonly used in the art, and the conductive agent can be any type of conductive agent commonly used in the art, both of which can achieve the effects of this application. For example, the solid electrolyte includes, but is not limited to, sulfide solid electrolyte, halide solid electrolyte, oxide solid electrolyte, or polymer solid electrolyte; the conductive agent includes, but is not limited to, one or more of conductive carbon black, conductive graphite, carbon fiber, and carbon nanotubes.

[0087] The silicon-based material used in the preparation method of the silicon-based negative electrode in this application can be any commercially available silicon-based material in the art, and all of them can achieve the effect of this application. For example, the silicon-based material in this application includes, but is not limited to, silicon-oxygen materials, silicon-carbon materials or pure silicon.

[0088] In order to introduce a fourth functional group on the surface of a silicon-based material, thereby enhancing the interaction between the obtained modified silicon-based material and the composite binder, in a preferred embodiment, the surface modification method in step S1 includes: mixing the silicon-based material with an oxidant, and sequentially subjecting it to a first heat treatment and a fourth drying to obtain a modified silicon-based material; or, placing the silicon-based material in an ozone or air atmosphere and subjecting it to a second heat treatment to obtain a modified silicon-based material; or, subjecting the silicon-based material to oxygen plasma treatment or ammonia plasma treatment to obtain a modified silicon-based material.

[0089] It should be noted that in the above-mentioned surface modification methods, by mixing silicon-based materials with oxidants and preparing modified silicon-based materials using liquid-phase oxidation, hydroxyl (-OH) and carboxyl (-COOH) groups can be introduced onto the surface of silicon-based materials; by placing silicon-based materials in an ozone or air atmosphere and preparing modified silicon-based materials using gas-phase oxidation, hydroxyl (-OH) and carbonyl (-C=O) groups can be introduced onto the surface of silicon-based materials; and by subjecting silicon-based materials to oxygen plasma treatment or ammonia plasma treatment, oxygen-containing functional groups (such as -OH) and amino (-NH2) groups can be introduced onto the surface of silicon-based materials.

[0090] In a preferred embodiment, the fourth functional group accounts for 0.1% to 2% of the weight of the modified silicon-based material. Compared to other ranges, limiting the content of the fourth functional group within the above range is beneficial to improving the interaction between the modified silicon-based material and the composite binder, enhancing the bonding strength of the negative electrode active material layer and its adhesion to the negative electrode current collector, thereby improving the structural stability and interface stability of the silicon-based negative electrode sheet.

[0091] In a preferred embodiment, the weight ratio of silicon-based material to oxidant is 100:(1-20). The weight ratio of silicon-based material to oxidant includes, but is not limited to, the above range. Limiting it to the above range is beneficial to improving the surface modification effect of silicon-based material and to introducing an appropriate amount of first functional groups on the surface of silicon-based material.

[0092] To further improve the surface modification effect of silicon-based materials, preferably, the oxidant includes, but is not limited to, one or more of the following groups: concentrated nitric acid, a mixed solution of concentrated sulfuric acid and hydrogen peroxide, potassium permanganate solution, ammonium persulfate solution, and nitric acid.

[0093] In a preferred embodiment, the temperature of the first heat treatment is 60–120°C, and the time is 0.5–6 hours. The temperature and time of the first heat treatment include, but are not limited to, the above ranges. Limiting them to the above ranges is beneficial to improving the surface modification effect of the silicon-based material and to improving the bonding stability between the first functional group and the surface of the silicon-based material.

[0094] In order to improve the removal efficiency of solvent components in modified silicon-based materials and further improve the purity of the obtained modified silicon-based materials, in a preferred embodiment, the fourth drying temperature is 80-120°C and the time is 6-24 hours.

[0095] In a preferred embodiment, the temperature of the second heat treatment is 300–500°C, and the time is 1–4 hours. The temperature and time of the second heat treatment include, but are not limited to, the above-mentioned ranges. Limiting them to the above-mentioned ranges is beneficial to improving the surface modification effect of silicon-based materials and to improving the bonding stability between the first functional group and the surface of silicon-based materials.

[0096] In order to further improve the surface modification effect of silicon-based materials and further improve the bonding stability between the first functional group and the surface of silicon-based materials, in a preferred embodiment, the oxygen plasma treatment and ammonia plasma treatment times are each independently 30s to 10min.

[0097] In order to further improve the interaction between the components and further improve the structural stability and interface stability of the prepared silicon-based anode sheet, in a preferred embodiment, in step S2, the weight ratio of modified silicon-based material, composite binder, solid electrolyte and conductive agent is (50-80):(1.5-5):(10-35):(1-3).

[0098] In order to improve the dispersibility of each component in the negative electrode slurry and to obtain a negative electrode slurry with uniform dispersion and better processing performance, in a preferred embodiment, the weight ratio of the third organic solvent to the modified silicon-based material is 100:(30-60).

[0099] To further improve the dispersibility of the composite binder in the negative electrode slurry, in a preferred embodiment, the relative permittivity (ε) of the third organic solvent at 25°C is ≤30; preferably, the third organic solvent includes, but is not limited to, one or more of the group consisting of p-xylene, anisole, phenethyl ether, tetrahydronaphthalene, n-heptane, 1,2-dibromomethane, butyl butyrate and isobutyl isobutyrate.

[0100] In a preferred embodiment, in step S3, the amount of negative electrode slurry coated on the surface of the negative electrode current collector is 3–20 mg / cm². 2 The amount of negative electrode slurry coated on the surface of the negative electrode current collector includes, but is not limited to, the range mentioned above. Limiting it to the range mentioned above is beneficial to improving the continuity and uniformity of the negative electrode slurry coating, which is beneficial to improving the energy density of the prepared silicon-based negative electrode sheet, thereby improving the rate performance and cycle stability of the all-solid-state lithium-ion battery.

[0101] In order to remove the residual solvent components in the electrode to be dried, further improve the bonding strength of each component in the negative electrode active material layer, further improve the peel strength between the negative electrode active material layer and the negative electrode current collector, and thus further improve the structural stability of the prepared silicon-based negative electrode, in a preferred embodiment, in step S3, the temperature of the third drying is 50-160°C and the time is 2-12 hours.

[0102] A fifth aspect of this application also provides an all-solid-state lithium-ion battery, comprising a positive electrode, a negative electrode, and a solid electrolyte layer disposed between the positive and negative electrode, wherein the negative electrode is the silicon-based negative electrode provided in this application. The silicon-based negative electrode provided in this application comprises the modified silicon-based material and composite binder provided in this application. Through the interaction between the two, the bonding strength of the negative electrode active material layer and its adhesion to the negative electrode current collector can be effectively improved, thereby improving the structural stability and interfacial stability of the silicon-based negative electrode. Applying this silicon-based negative electrode to an all-solid-state lithium-ion battery can significantly improve the rate performance and cycle stability of the all-solid-state lithium-ion battery.

[0103] The present application will be further described in detail below with reference to specific embodiments, which should not be construed as limiting the scope of protection claimed in the present application.

[0104] Preparation Example 1

[0105] A method for preparing a composite adhesive specifically includes the following steps:

[0106] (1) 100g of main chain polymer A-1, 6g of maleic anhydride, 0.06g of dicumyl peroxide (DCP) and 1200g of toluene were mixed to obtain a mixture; wherein, the main chain polymer A-1 is a hydrogenated styrene-butadiene-styrene block copolymer (SEBS), with a Mn of 150,000 g / mol, an unsaturated double bond content of 1wt%, a hydrogenation degree of 96%, a polystyrene segment content of 30wt%, and a hydrogenated polybutadiene segment content of 70wt%; the mixture was subjected to the first grafting reaction for 4h under a nitrogen atmosphere and at 120℃. After the reaction was completed, the reaction solution was poured into 5000mL of acetone to obtain a precipitate. After filtration, the precipitate was washed three times with acetone and then vacuum dried at 60℃ and -0.095MPa for 12h to obtain 98.5g of intermediate product;

[0107] (2) Mix 50g of the intermediate product obtained in step (1), 16.9g of terminal hydroxyl hyperbranched polyester (branching degree of 0.5, Mn of 2100g / mol, hydroxyl content of 16.3wt%), 0.5g of p-toluenesulfonic acid (PTSA) and 500g of toluene, and carry out the second grafting reaction at 80℃ for 18h. After the reaction is completed, pour the reaction solution into 5000mL of methanol to obtain a precipitate. After filtration, wash with methanol 3 times, and then vacuum dry at 60℃ and -0.095MPa for 24h to obtain 58.5g of composite adhesive.

[0108] In the composite adhesive prepared in Example 1, the weight ratio of grafted monomer to main chain polymer was 6:100, and the grafting rate of hyperbranched polymer was 20wt%.

[0109] Preparation Example 2

[0110] The difference from Preparation Example 1 is as follows: In step (1), an equal weight of main chain polymer A-2 is used to replace the main chain polymer A-1 in Preparation Example 1; the main chain polymer A-2 is a hydrogenated styrene-isoprene-styrene block copolymer (SEPS), with a Mn of 250,000 g / mol, an unsaturated double bond content of 1.5 wt%, a hydrogenation degree of 95%, a polystyrene segment content of 50 wt%, and a hydrogenated polyisoprene segment content of 50 wt%; at the same time, an equal weight of glycidyl methacrylate is used to replace maleic anhydride in Preparation Example 1; in step (2), an equal weight of terminal amino hyperbranched polyethyleneimine (branching degree of 0.45, Mn of 10,000 g / mol, amino content of 18 wt%) is used to replace the terminal hydroxyl hyperbranched polyester in Preparation Example 1; the remaining steps are the same as in Preparation Example 1.

[0111] In the composite adhesive prepared in Example 2, the weight ratio of grafted monomer to main chain polymer was 6:100, and the grafting rate of hyperbranched polymer was 20wt%.

[0112] Preparation Example 3

[0113] The difference from Preparation Example 1 is as follows: In step (1), an equal weight of main chain polymer A-3 is used to replace the main chain polymer A-1 in Preparation Example 1; the main chain polymer A-3 is hydrogenated styrene-butadiene-styrene block copolymer (SEBS), with a Mn of 180,000 g / mol, an unsaturated double bond content of 1.2 wt%, a hydrogenation degree of 97%, a polystyrene segment content of 35 wt%, and a hydrogenated polybutadiene segment content of 65 wt%; at the same time, an equal weight of a mixture of acrylic acid and 2-hydroxyethyl methacrylate phosphate is used to replace the maleic anhydride in Preparation Example 1, wherein the weight ratio of acrylic acid to 2-hydroxyethyl methacrylate phosphate is 8:2; in step (2), an equal weight of terminal carboxyl hyperbranched polyester (branching degree of 0.6, Mn of 3500 g / mol, and carboxyl content of 10 wt%) is used to replace the terminal hydroxyl hyperbranched polyester in Preparation Example 1; the remaining steps are the same as in Preparation Example 1.

[0114] In the composite adhesive prepared in Example 3, the weight ratio of grafted monomer to main chain polymer was 6:100, and the grafting rate of hyperbranched polymer was 20wt%.

[0115] Preparation Example 4

[0116] The difference from Preparation Example 1 is that: in step (1), glycidyl methacrylate of equal weight is used to replace maleic anhydride in Preparation Example 1; in step (2), hydroxyl-terminated hyperbranched polyethyleneimine (branching degree of 0.45, Mn of 10000 g / mol, amino content of 18 wt%) of equal weight is used to replace hydroxyl-terminated hyperbranched polyester in Preparation Example 1; the remaining steps are the same as in Preparation Example 1.

[0117] In the composite adhesive prepared in Example 4, the weight ratio of grafted monomer to main chain polymer was 6:100, and the grafting rate of hyperbranched polymer was 20wt%.

[0118] Preparation Example 5

[0119] The difference from Preparation Example 1 is as follows: In step (1), an equal weight of main chain polymer A-4 is used to replace the main chain polymer A-1 in Preparation Example 1; the main chain polymer A-4 is a hydrogenated styrene-isoprene-styrene block copolymer (SEPS), with a Mn of 200,000 g / mol, an unsaturated double bond content of 2 wt%, a hydrogenation degree of 94%, a polystyrene segment content of 40 wt%, and a hydrogenated polyisoprene segment content of 60 wt%; at the same time, an equal weight of N-(2-hydroxyethyl)maleimide is used to replace the maleic anhydride in Preparation Example 1; in step (2), an equal weight of terminal thiol hyperbranched polyglycidyl ether (HPG-SH, branching degree of 0.5, Mn of 6000 g / mol, thiol content of 15 wt%) is used to replace the terminal hydroxyl hyperbranched polyester in Preparation Example 1; the remaining steps are the same as in Preparation Example 1.

[0120] In the composite adhesive prepared in Example 5, the weight ratio of grafted monomer to main chain polymer was 6:100, and the grafting rate of hyperbranched polymer was 20wt%.

[0121] Preparation Example 6

[0122] The difference from Preparation Example 1 is that an equal weight of poly(3,4-ethylenedioxythiophene)-modified terminal amino hyperbranched polyethyleneimine (HBP-PEI-PEDOT) is used instead of the terminal hydroxyl hyperbranched polyester in Preparation Example 1. The preparation method of HBP-PEI-PEDOT is as follows: 10g of terminal amino hyperbranched polyethyleneimine is dispersed in 200mL of water, and 2g of 3,4-ethylenedioxythiophene monomer, 0.3g of sodium polystyrene sulfonate and 5g of ammonium persulfate (ammonium sulfate dissolved in 50mL of water is added at 0℃) are added. The mixture is then reacted at 0℃ for 24h, purified by dialysis and freeze-dried to obtain the final product. The PEDOT modification amount is 25wt%. The remaining steps are the same as in Preparation Example 1.

[0123] Preparation Example 7

[0124] The difference from Preparation Example 1 is that in step (1), the amount of maleic anhydride is adjusted to 2g so that the weight ratio of grafted monomer to main chain polymer in the obtained composite binder is 2:100; the remaining steps are the same as those in Preparation Example 1.

[0125] Preparation Example 8

[0126] The difference from Preparation Example 1 is that in step (1), the amount of maleic anhydride is adjusted to 15g so that the weight ratio of grafted monomer to main chain polymer in the obtained composite binder is 15:100; the remaining steps are the same as in Preparation Example 1.

[0127] Preparation Example 9

[0128] The difference from Preparation Example 1 is that in step (1), the amount of maleic anhydride is adjusted to 18g so that the weight ratio of grafted monomer to main chain polymer in the obtained composite binder is 18:100; the remaining steps are the same as in Preparation Example 1.

[0129] Preparation Example 10

[0130] The difference from Preparation Example 1 is that in step (2), the amount of hydroxyl-terminated hyperbranched polyester is adjusted to 4.2g, so that the grafting rate of hyperbranched polymer in the obtained composite adhesive is 5wt%; the remaining steps are the same as those in Preparation Example 1.

[0131] Preparation Example 11

[0132] The difference from Preparation Example 1 is that in step (2), the amount of hydroxyl-terminated hyperbranched polyester is adjusted to 21.4g, so that the grafting rate of hyperbranched polymer in the prepared composite adhesive is 30wt%; the remaining steps are the same as those in Preparation Example 1.

[0133] Preparation Example 12

[0134] The difference from Preparation Example 1 is that in step (2), the amount of hydroxyl-terminated hyperbranched polyester is adjusted to 1g, so that the grafting rate of hyperbranched polymer in the obtained composite adhesive is 2wt%; the remaining steps are the same as those in Preparation Example 1.

[0135] Preparation Example 13

[0136] The difference from Preparation Example 1 is that in step (2), the amount of hydroxyl-terminated hyperbranched polyester is adjusted to 25.7g, so that the grafting rate of hyperbranched polymer in the obtained composite adhesive is 35wt%; the remaining steps are the same as those in Preparation Example 1.

[0137] Preparation of Comparative Example 1

[0138] The difference from Preparation Example 1 is that the main chain polymer A-1 (the same as the main chain polymer A-1 in Preparation Example 1) is used as the binder.

[0139] Preparation of Comparative Example 2

[0140] The difference from Preparation Example 1 is that step (2) is omitted, and the intermediate product obtained in step (1) is used as the binder; the remaining steps are the same as those in Preparation Example 1.

[0141] The binder prepared in Comparative Example 2 comprises a main-chain polymer and graft monomers grafted onto the main-chain polymer (the weight ratio of graft monomers to main-chain polymer is 6:100), and the binder does not contain grafted hyperbranched polymers.

[0142] Application Examples 1 to 13

[0143] A method for preparing a silicon-based negative electrode sheet specifically includes the following steps:

[0144] (1) Surface modification of silicon-carbon material (silicon deposition amount of about 50wt%) is carried out by introducing hydroxyl groups (-OH) on the surface of the silicon-carbon material to obtain modified silicon-carbon material. The hydroxyl group accounts for 0.8% of the weight of the modified silicon-carbon material. The surface modification method is: place the silicon-carbon material in an oxygen plasma cleaner and treat it at 200W power for 5min.

[0145] (2) The modified silicon carbon material, composite binder, solid electrolyte Li6PS5Cl and conductive agent vapor-grown carbon fiber (VGCF) obtained in step (1) are mixed in a weight ratio of 65:3:30:2 to obtain a mixture. Then, a mixed solvent of butyl butyrate and toluene (the weight ratio of butyl butyrate and toluene is 1:1) is added. The weight ratio of the mixed solvent to the mixture is 1:1. After mixing evenly, a negative electrode slurry is obtained. The composite binder is the composite binder prepared in the preparation examples 1 to 13 above.

[0146] (3) The negative electrode slurry obtained in step (2) is mixed with 5 mg / cm³. 2 The coating amount was applied to one side of a carbon-coated copper foil with a thickness of 10 μm, and then vacuum dried at 100 °C for 12 h to obtain a silicon-based negative electrode.

[0147] Application Example 14

[0148] The difference from Application Example 1 is that the content of the fourth functional group in the modified silicon-carbon material obtained in step (1) is 0.1 wt%; the remaining steps are the same as in Application Example 1.

[0149] Application Example 15

[0150] The difference from Application Example 1 is that the content of the fourth functional group in the modified silicon-carbon material obtained in step (1) is 2wt%; the remaining steps are the same as in Application Example 1.

[0151] Application Example 16

[0152] The difference from Application Example 1 is that the content of the fourth functional group in the modified silicon-carbon material obtained in step (1) is 0.05 wt%; the remaining steps are the same as in Application Example 1.

[0153] Application Example 17

[0154] The difference from Application Example 1 is that in step (2), the weight ratio of modified silicon carbon material, composite binder, solid electrolyte and conductive agent is adjusted to 63:5:30:2; the remaining steps are the same as in Application Example 1.

[0155] Application Example 18

[0156] The difference from Application Example 1 is that in step (2), the weight ratio of modified silicon carbon material, composite binder, solid electrolyte and conductive agent is adjusted to 66.5:1.5:30:2; the remaining steps are the same as in Application Example 1.

[0157] Application Example 19

[0158] The difference from Application Example 1 is that in step (2), the weight ratio of modified silicon carbon material, composite binder, solid electrolyte and conductive agent is adjusted to 67:1:30:2; the remaining steps are the same as in Application Example 1.

[0159] Application of Comparative Examples 1 and 2

[0160] The difference from Application Example 1 is that in step (2), the adhesives prepared by Comparative Examples 1 and 2 are used to replace the composite adhesive in Application Example 1; the remaining steps are the same as in Application Example 1.

[0161] Application Comparative Example 3

[0162] The difference from Application Example 1 is that step (1) is omitted and the silicon-carbon material is not surface modified; in step (2), the negative electrode slurry is prepared using silicon-carbon material without surface modification; the remaining steps are the same as in Application Example 1.

[0163] Assemble an all-solid-state lithium-ion battery as follows: (1) Prepare the positive electrode sheet: Mix the positive electrode active material NCM811, the binder hydrogenated SEBS (weight average molecular weight of 120,000 g / mol, unsaturated double bond content of 1.2 wt%, hydrogenation degree of 95%, polystyrene segment content of 30 wt%, hydrogenated polybutadiene segment content of 70 wt%), the solid electrolyte Li6PS5Cl and the conductive agent vapor-grown carbon fiber (VGCF) in a weight ratio of 86.5:2:10:1.5, then add isobutyl isobutyrate, and mix evenly to obtain a positive electrode slurry with a solid content of 70 wt%; the positive electrode slurry is then mixed with 18 mg / cm³ of water. 2 The coating amount was coated on one side of a 12μm thick carbon-coated aluminum foil and vacuum dried at 100℃ for 12h to obtain a positive electrode sheet; (2) Preparation of solid electrolyte layer: solid electrolyte powder Li6PS5Cl was mixed with binder polyisobutylene (PIB) at a weight ratio of 96:4, and then xylene solvent was added. After mixing evenly, an electrolyte slurry with a solid content of 50wt% was obtained; the electrolyte slurry was then coated with 2.5mg / cm 2The coating was applied to one side of the prepared positive electrode and negative electrode (the silicon-based negative electrode prepared by all the above application examples and application comparison examples of this application, respectively), and dried at 80°C for 6 hours to obtain a positive electrode coated with a solid electrolyte layer and a negative electrode coated with a solid electrolyte layer; (3) Assemble the all-solid-state lithium-ion battery: the positive electrode coated with a solid electrolyte layer and the negative electrode coated with a solid electrolyte layer were stacked in sequence, and pressure treated at 550MPa for 30 minutes, and then packaged to assemble the all-solid-state lithium-ion battery.

[0164] Rate performance and cycle performance tests were conducted on all solid-state lithium-ion batteries assembled using the above-described application embodiments and comparative examples of this application. The rate performance test conditions were as follows: constant current discharge was performed at 25°C and a voltage range of 2.5–4.2V at 1C and 2C rates, respectively. The discharge capacity was recorded, and the ratio of the discharge capacity at 2C rate to the discharge capacity at 1C was calculated, which is the 2C / 1C discharge capacity retention rate. The cycle performance test conditions were as follows: 300 cycles were performed at 25°C, 1C rate, and a voltage range of 2.5–4.2V, and the capacity retention rate after 300 cycles was recorded. The test results are shown in Table 1.

[0165] Table 1

[0166]

[0167] As can be seen from the above description, the embodiments of this application achieve the following technical effects:

[0168] Comparing Application Examples 1 to 6 with Comparative Examples 1 and 2, the binder in Comparative Example 1 is a main-chain polymer without grafted monomers or hyperbranched polymers, while the binder in Comparative Example 2 is a main-chain polymer grafted with grafted monomers without hyperbranched polymers. Based on the data in Table 1, it can be seen that the rate performance and cycle capacity retention of Application Examples 1 to 6 are significantly better than those of Comparative Examples 1 and 2. Therefore, the specific composite binder provided in this application, by introducing a hyperbranched polymer with a first functional group, strengthens the interaction between the composite binder and the modified silicon-based material, thereby improving the bonding strength of the negative electrode active material layer and its adhesion to the negative electrode current collector, and enhancing the structural stability of the silicon-based negative electrode sheet. Simultaneously, the specific structure of the composite binder in this application can also stabilize the electron and lithium-ion transport paths within the silicon-based negative electrode sheet, thus significantly improving the rate performance and cycle stability of the fabricated all-solid-state lithium-ion battery.

[0169] Comparing Application Example 1 and Application Comparative Example 3, compared with the use of unmodified silicon-carbon material (Application Comparative Example 5), the use of modified silicon-based material with the fourth functional group of the specific type mentioned above in this application can significantly improve the interaction force between the modified silicon-based material and the composite binder, improve the bonding strength, effectively suppress the pulverization and detachment of the negative electrode active material layer, improve the structural stability and interface stability of the silicon-based negative electrode sheet, and thus improve the rate performance and cycle stability of the prepared all-solid-state lithium-ion battery.

[0170] Comparing Application Example 1 and Application Examples 7 to 9, and referring to the data in Table 1, it can be seen that, compared to other ranges, limiting the weight ratio of the grafted monomer to the main chain polymer within the preferred range described above in this application is beneficial to improving the mechanical strength and adhesion of the composite binder, thereby improving the structural stability and interface stability of the silicon-based anode sheet, and further improving the rate performance and cycle stability of the prepared all-solid-state lithium-ion battery.

[0171] Comparing Application Example 1 and Application Examples 10 to 13, and referring to the data in Table 1, it can be seen that, compared to other ranges, limiting the grafting rate of the hyperbranched polymer to the preferred range described above in this application is beneficial to enhancing the interaction between the composite binder and the modified silicon-based material, improving the bonding strength of the negative electrode active material layer and its adhesion to the negative electrode current collector, and improving the structural stability of the silicon-based negative electrode sheet; at the same time, it is also beneficial to stabilize the electron and lithium ion transport paths inside the silicon-based negative electrode sheet, thereby improving the rate performance and cycle stability of the prepared all-solid-state lithium-ion battery.

[0172] Comparing Application Example 1 and Application Examples 14 to 16, and referring to the data in Table 1, it can be seen that, compared to other ranges, limiting the weight percentage of the fourth functional group in the modified silicon-based material to the preferred range described above in this application is beneficial to improving the interaction between the modified silicon-based material and the composite binder, enhancing the bonding strength of the negative electrode active material layer and its adhesion to the negative electrode current collector, thereby improving the structural stability and interface stability of the silicon-based negative electrode sheet, and further improving the rate performance and cycle stability of the prepared all-solid-state lithium-ion battery.

[0173] Comparing Application Example 1 with Application Examples 17 to 19, and referring to the data in Table 1, it can be seen that, compared to other ranges, limiting the weight ratio of modified silicon-based material, composite binder, solid electrolyte, and conductive agent to the preferred range described above in this application is beneficial to improving the interaction between the components, thereby improving the structural stability and interface stability of the prepared silicon-based anode sheet, and further improving the rate performance and cycle stability of the prepared all-solid-state lithium-ion battery.

[0174] It should be noted that the terms "first," "second," etc., used in the specification and claims of this application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such terms can be used interchangeably where appropriate so that the embodiments of this application described herein can be implemented, for example, in a sequence other than those described herein.

[0175] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A composite adhesive, characterized in that, The composite binder comprises a main-chain polymer and a hyperbranched polymer grafted onto the main-chain polymer by grafting monomers; the main-chain polymer is a hydrogenated styrene-butadiene-styrene block copolymer or a hydrogenated styrene-isoprene-styrene block copolymer; the hyperbranched polymer has a first functional group at its end; the first functional group is selected from hydroxyl, amino, carboxyl, mercapto, and epoxy groups.

2. The composite adhesive according to claim 1, characterized in that, The grafting monomer is a compound having a carbon-carbon double bond, a second functional group, and a third functional group; the second functional group and the third functional group are each independently selected from one of carboxyl, hydroxyl, epoxy, amino, isocyanate, anhydride, phosphate, furan, and maleimide groups; the carbon-carbon double bond in the grafting monomer is connected to an unsaturated double bond in the main chain polymer; the second functional group or the third functional group in the grafting monomer is connected to the first functional group in the hyperbranched polymer; Preferably, the weight ratio of the grafted monomer to the main chain polymer is (2-15):100; Preferably, in the grafted monomer, the second functional group is selected from one of carboxyl, acid anhydride, and phosphate ester groups; and / or, the third functional group is selected from one of epoxy, acid anhydride, isocyanate, and furan groups; Preferably, the grafting monomer is selected from one or more of the group consisting of acid anhydride compounds having carbon-carbon double bonds, acrylate compounds having the second functional group or the third functional group, and olefin derivatives having the second functional group and the third functional group; More preferably, the grafting monomer is selected from one or more of the group consisting of maleic anhydride, glycidyl methacrylate, acrylic acid, 2-hydroxyethyl methacrylate phosphate, N-(2-hydroxyethyl)maleimide, itaconic acid, allyl glycidyl ether, and itaconic anhydride.

3. The composite adhesive according to claim 1 or 2, characterized in that, The main chain polymer contains 0.5–3 wt% unsaturated double bonds. Preferably, the number-average molecular weight of the main-chain polymer is 50,000 to 500,000 g / mol, more preferably 100,000 to 300,000 g / mol; Preferably, the degree of hydrogenation of the hydrogenated styrene-butadiene-styrene block copolymer is 90-99%; the degree of hydrogenation of the hydrogenated styrene-isoprene-styrene block copolymer is 90-99%. Preferably, the main chain polymer comprises a first segment and a second segment, wherein the first segment is a polystyrene segment, and the second segment is a hydrogenated polybutadiene segment or a hydrogenated isoprene segment; the content of the first segment is 20–80 wt%, more preferably 30–50 wt%; and the content of the second segment is 20–80 wt%. Preferably, in the composite adhesive, the grafting rate of the hyperbranched polymer is 5-30 wt%; Preferably, the degree of branching of the hyperbranched polymer is 0.4 to 0.7; the number average molecular weight of the hyperbranched polymer is 1000 to 50000 g / mol, more preferably 2000 to 10000 g / mol; Preferably, the first functional group accounts for 10-40% by weight of the hyperbranched polymer; Preferably, the hyperbranched polymer is selected from one or more of the group consisting of hydroxyl-terminated hyperbranched polyester, amino-terminated hyperbranched polyethyleneimine, carboxyl-terminated hyperbranched polyester, hyperbranched polysiloxane, mercapto-terminated hyperbranched polyglycidyl ether, and epoxy-terminated hyperbranched polyester; more preferably, the hyperbranched polymer may optionally include conductive polymer modification segments; the conductive polymer modification segments are selected from one or more of the group consisting of thiophene conductive polymers, pyrrole conductive polymers, and aniline conductive polymers.

4. A method for preparing a composite adhesive according to any one of claims 1 to 3, characterized in that, The method for preparing the composite adhesive includes: Step N1 involves subjecting the main-chain polymer and the grafted monomer to a first grafting reaction in a first organic solvent in the presence of an initiator, followed by a first drying process to obtain an intermediate product. Step N2 involves subjecting the intermediate product and the hyperbranched polymer to a second grafting reaction in a second organic solvent under the catalysis of a catalyst, followed by a second drying process to obtain the composite binder.

5. The method for preparing the composite adhesive according to claim 4, characterized in that, In step N1, the temperature of the first grafting reaction is 110-140°C, and the time is 2-6 hours. Preferably, the weight ratio of the main chain polymer to the grafted monomer is 100:(2-15). Preferably, the weight ratio of the initiator to the grafted monomer is (0.5-2):100; Preferably, the initiator is selected from one or more of the group consisting of dicumyl peroxide, benzoyl peroxide, and azobisisobutyronitrile; Preferably, the weight ratio of the main chain polymer to the first organic solvent is (5-15):100; Preferably, the first organic solvent is selected from one or more of the group consisting of toluene, xylene, cyclohexane, butyl butyrate, and anisole; Preferably, the temperature of the first drying is 60-80°C and the time is 6-12 hours.

6. The method for preparing the composite adhesive according to claim 4 or 5, characterized in that, In step N2, the temperature of the second grafting reaction is 60–90°C, and the time is 12–24 h. Preferably, the weight ratio of the intermediate product to the hyperbranched polymer is 100:(5-40). Preferably, the weight ratio of the catalyst to the intermediate product is (0.1-2):100; Preferably, the catalyst is selected from one or more of the group consisting of p-toluenesulfonic acid, 4-dimethylaminopyridine, N,N-dicyclohexylcarbodiimide, 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride and triethylamine; Preferably, the weight ratio of the intermediate product to the second organic solvent is (8-20):100; Preferably, the second organic solvent is selected from one or more of the group consisting of toluene, xylene, and tetrahydrofuran; Preferably, the second drying temperature is 50–70°C and the time is 12–24 hours.

7. A silicon-based negative electrode sheet, comprising a negative electrode current collector and a negative electrode active material layer disposed on at least one surface thereon, characterized in that, The negative electrode active material layer comprises a modified silicon-based material, a binder, a solid electrolyte, and a conductive agent; the modified silicon-based material is a silicon-based material with a fourth functional group on its surface; the fourth functional group is selected from one of hydroxyl, carboxyl, carbonyl, and amino groups; the binder is a composite binder as described in any one of claims 1 to 3.

8. A method for preparing a silicon-based negative electrode sheet according to claim 7, characterized in that, The preparation method includes: Step S1: Surface modification of silicon-based material is performed by introducing a fourth functional group on the surface of the silicon-based material to obtain a modified silicon-based material; Step S2: Mix the modified silicon-based material, the composite binder, the solid electrolyte, the conductive agent, and the third organic solvent to obtain the negative electrode slurry; Step S3: The negative electrode slurry is coated on at least one side of the negative electrode current collector, and then dried in a third step to obtain the silicon-based negative electrode sheet.

9. The method for preparing a silicon-based negative electrode according to claim 8, characterized in that, In step S1, the surface modification method includes: mixing the silicon-based material with an oxidant, and sequentially subjecting it to a first heat treatment and a fourth drying to obtain the modified silicon-based material; or, placing the silicon-based material in an ozone or air atmosphere and subjecting it to a second heat treatment to obtain the modified silicon-based material; or, subjecting the silicon-based material to oxygen plasma treatment or ammonia plasma treatment to obtain the modified silicon-based material. Preferably, the fourth functional group accounts for 0.1% to 2% of the weight of the modified silicon-based material; Preferably, the weight ratio of the silicon-based material to the oxidant is 100:(1-20); more preferably, the oxidant is selected from one or more of the group consisting of concentrated nitric acid, a mixed solution of concentrated sulfuric acid and hydrogen peroxide, potassium permanganate solution, ammonium persulfate solution, and nitric acid. Preferably, the temperature of the first heat treatment is 60–120°C and the time is 0.5–6 h; and / or, the temperature of the fourth drying is 80–120°C and the time is 6–24 h. Preferably, the temperature of the second heat treatment is 300–500°C, and the time is 1–4 hours; Preferably, in step S2, the weight ratio of the modified silicon-based material, the composite binder, the solid electrolyte, and the conductive agent is (50-80):(1.5-5):(10-35):(1-3); and the weight ratio of the third organic solvent to the modified silicon-based material is 100:(30-60). Preferably, the relative permittivity of the third organic solvent is ≤30; more preferably, it is one or more of the group consisting of p-xylene, anisole, phenethyl ether, tetrahydronaphthalene, n-heptane, 1,2-dibromomethane, butyl butyrate and isobutyl isobutyrate. Preferably, in step S3, the amount of the negative electrode slurry coated on the surface of the negative electrode current collector is 3–20 mg / cm². 2 ; Preferably, in step S3, the temperature of the third drying is 50-160°C, and the time is 2-12 hours.

10. An all-solid-state lithium-ion battery, comprising a positive electrode, a negative electrode, and a solid electrolyte layer disposed between the positive electrode and the negative electrode, characterized in that, The negative electrode is the silicon-based negative electrode as described in claim 7.

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