Negative electrode material, negative electrode plate and electrochemical device
By covalently grafting a polyurethane polymer layer onto the surface of a silicon-carbon composite matrix, the problem of fragile interfacial bonding in silicon-based anode materials during charge and discharge is solved, improving electrode structural stability and cycle performance, simplifying electrode fabrication process, and increasing battery energy density.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-12-26
- Publication Date
- 2026-03-27
AI Technical Summary
Silicon-based anode materials suffer from weak interfacial bonding and degraded cycle performance due to volume expansion during charging and discharging. Existing physical mixing and coating strategies cannot effectively solve the problem of insufficient interfacial bonding.
By chemically grafting a polyurethane polymer layer onto the surface of a silicon-carbon composite matrix with covalent bonds, the interfacial bonding force is enhanced, volume expansion is buffered, and the initial coulombic efficiency and cycle stability of the negative electrode are improved.
It improves the material's tolerance to volume expansion, enhances the stability and cycle performance of the electrode structure, reduces the amount of binder used, simplifies the electrode fabrication process, and increases the battery energy density.
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Abstract
Description
Technical Field
[0001] This application relates to the field of battery anode material technology, and in particular to an anode material, anode sheet, and an electrochemical device. Background Technology
[0002] As a next-generation energy storage device, the performance of lithium-ion batteries is highly dependent on the anode material. Silicon-based materials (such as elemental silicon and silicon suboxide) are considered to be highly promising next-generation high-energy-density anode materials due to their theoretical specific capacity of up to 4200 mAh / g. However, silicon-based materials exhibit a huge volume expansion of approximately 300% during charge and discharge, low intrinsic conductivity, and an unstable solid electrolyte interphase (SEI) film, leading to electrode pulverization, active material shedding, and rapid capacity decay, which seriously hinders their commercial application.
[0003] To overcome these shortcomings, related technologies mainly revolve around physical mixing and structural coating, but both have inherent defects. First, the physical mixing strategy involves physically blending silicon or silicon-carbon composite materials, conductive agents (such as carbon black), and polymer binders (such as polyacrylic acid PAA and polyvinylidene fluoride PVDF). In this method, the components are mainly bonded by weak van der Waals forces or hydrogen bonds. Under the enormous shear stress generated by the volume expansion of silicon, the interfaces are prone to failure, ultimately leading to electrode structure collapse and capacity degradation. Second, the physical coating strategy involves coating the surface of silicon particles with carbon or polymer layers through vapor deposition or solution impregnation. Although this strategy can buffer volume expansion to some extent, the bonding between the coating layer and the core is mainly physical adsorption, resulting in weak adhesion. Under long-term drastic volume changes, the coating layer is still prone to peeling. Crucially, for example, using polyurethane as a carbon precursor and carbonizing it at high temperatures can form a carbon coating layer, but it completely loses the inherent high elasticity and excellent bonding properties of the polyurethane polymer itself. Summary of the Invention
[0004] This application aims to address the problems of fragile interfacial bonding and degraded cycle performance in existing silicon-based anode materials caused by physical mixing or coating, by providing a modified silicon anode material and its preparation method. This material utilizes a polyurethane polymer layer covalently grafted onto the surface of a silicon-carbon composite matrix, which helps to enhance interfacial bonding and buffer volume expansion, thereby improving the initial coulombic efficiency and cycle stability of the anode.
[0005] On the other hand, this application also provides a negative electrode and an electrochemical device.
[0006] To achieve the above objectives, in a first aspect, this application provides a modified silicon anode material, comprising a core and a shell, wherein the core comprises silicon anode particles and a carbon material layer coating the surface of the silicon anode particles, and the shell is a polyurethane polymer layer, wherein the polyurethane polymer layer is chemically grafted onto the surface of the carbon material layer via covalent bonds.
[0007] Based on the first aspect, in some embodiments of this application, the covalent bond is formed by the reaction of hydroxyl or amino groups on the surface of the carbon material layer with isocyanate groups at the ends of the polyurethane polymer chains.
[0008] Based on the first aspect, in some embodiments of this application, the material of the silicon anode particles includes silicon material, which is selected from at least one of pure silicon, silicon-carbon material or silicon-oxygen material; the carbon material layer is composed of carbon material, which is selected from at least one of graphite, amorphous carbon, graphene or carbon nanotubes; and / or, the silicon anode particles are porous silicon.
[0009] Based on the first aspect, in some embodiments of this application, the polyurethane polymer layer is a linear structure, a cross-linked network structure, or a functionalized structure containing polyoxyethylene segments.
[0010] Secondly, this application provides a method for preparing the modified silicon anode material, comprising the following steps: An initial core is provided, comprising silicon anode particles and a carbon material layer coating the surface of the silicon anode particles; The surface of the carbon material layer of the initial core is activated to generate hydroxyl or amino groups on the surface of the carbon material layer, thus obtaining a surface-activated core; The surface-activated core is reacted with a diisocyanate compound, and the hydroxyl or amino group reacts with the isocyanate group of the diisocyanate compound to obtain a grafting intermediate with isocyanate groups on its surface. The grafting intermediate is polymerized with a polyol compound and a chain extender to grow and graft the polyurethane polymer layer in situ on the surface of the carbon material layer, thereby obtaining the modified silicon anode material.
[0011] Based on the second aspect, in some embodiments of this application, the activation treatment includes refluxing the initial kernel in a hydrogen peroxide solution; and / or, The diisocyanate is isophorone diisocyanate.
[0012] Based on the second aspect, in some embodiments of this application, when the activation treatment is performed, the mass fraction of the hydrogen peroxide solution is 10% to 50%; The solid-liquid ratio of the initial kernel to the hydrogen peroxide solution is 1g:(20-100)ml.
[0013] Based on the second aspect, in some embodiments of this application, the molar ratio of the diisocyanate compound to the active group is not less than 3:1; The volume-to-mass ratio of the diisocyanate compound to the initial core is 0.5 ml to 5 ml: 1 g.
[0014] Based on the second aspect, in some embodiments of this application, the diisocyanate compound includes at least one of isophorone diisocyanate, hexamethylene diisocyanate, toluene diisocyanate, and diphenylmethane diisocyanate; The polyol includes at least one selected from polytetrahydrofuran ether diol, polycaprolactone diol, or polyethylene oxide-polytetrahydrofuran-polyethylene oxide triblock copolymer diol; and / or The chain extender includes at least one of 1,4-butanediol, ethylenediamine, or trimethylolpropane.
[0015] Based on the second aspect, in some embodiments of this application, the diisocyanate compound is isophorone diisocyanate, and the mass ratio of the diisocyanate compound to the silicon carbide material is 2 ml: 1 g.
[0016] Based on the second aspect, in some embodiments of this application, after the polymerization reaction is completed, a polymer binder is added to the reaction product containing the modified silicon anode material, wherein the mass of the polymer binder is m; the mass of the modified silicon anode material is M; and the following condition is met: m ≤ 0.03M.
[0017] Thirdly, this application provides a negative electrode sheet, including a negative electrode current collector and a negative electrode layer disposed on the negative electrode current collector, wherein the negative electrode layer comprises the aforementioned modified silicon negative electrode material or a negative electrode sheet prepared by the aforementioned method for preparing the modified silicon negative electrode material.
[0018] Fourthly, this application provides an electrochemical device, such as a battery, comprising the aforementioned negative electrode.
[0019] Compared with related technologies, the modified silicon anode material provided in this application shows improvements in interfacial bonding, expansion suppression, and electrochemical performance. Compared to coating layers relying on physical adsorption or binder systems based on physical mixing, this application chemically grafts a polyurethane polymer layer onto the surface of the silicon-carbon material via covalent bonds, forming a more robust interfacial bond. This chemically bonded interfacial structure can more effectively transfer and disperse stress, thereby improving the material's tolerance to the volume expansion of silicon during charging and discharging, and enhancing the structural stability of the electrode during cycling. This inherently strengthened integrated structure can directly and efficiently convert the volume expansion stress of silicon into elastic deformation of the polymer chains, thus fundamentally solving the core problems of electrode structure damage and rapid capacity decay.
[0020] The polyurethane graft layer buffers mechanical stress through the elastic deformation of polymer segments, while its polar groups help improve electrolyte wettability and lithium-ion transport kinetics at the interface. Simultaneously, the adhesive effect of the polyurethane layer helps maintain the continuity of electrical contact between the active material and the conductive agent, supporting the stability of the internal conductive network during long-term cycling. The uniformly coated polyurethane layer can form a physical barrier with a certain degree of isolation on the silicon-carbon material surface. By reducing direct contact between the electrolyte and the highly active silicon-carbon core, it inhibits side reactions and excessive growth of the solid electrolyte interfacial film, thereby helping to improve the initial coulombic efficiency and long-term cycle capacity retention of the negative electrode. Furthermore, in terms of electrode preparation, the polyurethane layer grafted onto the surface of the silicon negative electrode particles itself has adhesive properties. Its polymer segments can entangle with each other to form a self-supporting network during electrode drying, thus reducing the amount of external binder used in traditional slurry formulations. This characteristic not only simplifies the electrode formulation and preparation process but also increases the proportion of active material in the electrode, making it possible to improve battery energy density. Detailed Implementation
[0021] The technical solutions in the embodiments of this application will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.
[0022] This application provides a modified silicon anode material that can be used as the anode in lithium-ion batteries. The electrochemical device described in this application can be used in electric vehicles, power tools, mobile power supplies, energy storage systems, electronic products, aerospace, weaponry, robotics, medical devices, and military equipment.
[0023] In a first aspect, this application provides a modified silicon anode material, comprising a core and a shell. The core comprises silicon anode particles and a carbon material layer coating the surface of the silicon anode particles. The shell is a polyurethane polymer layer, which is chemically grafted onto the surface of the carbon material layer via covalent bonds.
[0024] Based on the above technical solutions, the modified silicon anode material provided in this application shows improvements in interfacial bonding, expansion suppression, and electrochemical performance. Compared to coating layers that rely on physical adsorption or binder systems that rely on physical mixing, this application chemically grafts a polyurethane polymer layer onto the surface of silicon-carbon material via covalent bonds, forming a more robust interfacial bond. This chemically bonded interfacial structure can more effectively transfer and disperse stress, thereby improving the material's tolerance to volume expansion of silicon during charging and discharging, and improving the structural stability of the electrode during cycling.
[0025] The polyurethane graft layer buffers mechanical stress through the elastic deformation of polymer segments, and its polar groups help improve electrolyte wettability and lithium-ion transport kinetics at the interface. Simultaneously, the adhesive effect of the polyurethane layer helps maintain the continuity of electrical contact between the active material and the conductive agent, supporting the stability of the internal conductive network of the electrode during long-term cycling. The uniformly coated polyurethane layer can form a physical barrier with a certain degree of isolation on the surface of silicon-carbon materials. By reducing the direct contact between the electrolyte and the highly active silicon-carbon core, it inhibits side reactions and excessive growth of the solid electrolyte interfacial film, thereby helping to improve the initial coulombic efficiency and long-term cycle capacity retention of the negative electrode. Furthermore, in terms of electrode preparation, the polyurethane layer grafted onto the surface of the silicon negative electrode particles itself has adhesive properties; its polymer segments can entangle with each other to form a self-supporting network during electrode drying, thus reducing the amount of external binder used in traditional slurry formulations. This characteristic not only simplifies the electrode formulation and preparation process but also increases the proportion of active material in the electrode, making it possible to improve battery energy density.
[0026] In some embodiments, the covalent bond is formed by the reaction of hydroxyl or amino groups on the surface of the carbon material layer with isocyanate groups at the ends of the polyurethane polymer chain.
[0027] Based on the above technical solution, this application employs a structural design that uses a polyurethane polymer layer to covalently graft a silicon-carbon composite core with hydroxyl or amino groups on the surface of a carbon material layer and their terminal isocyanate groups. This design achieves interface strengthening and functional synergy. The covalent bond helps transfer and disperse volume expansion stress within the polymer chain segments, thus maintaining interface integrity during charging and discharging. The flexibility and extension properties of the polyurethane polymer chains allow them to buffer the mechanical strain generated by silicon anode particles during lithium insertion / extraction through chain segment movement. Simultaneously, the polar groups in the polymer layer facilitate electrolyte wetting and lithium-ion transport. The intertwining of the chain segments within the electrode forms a network, which acts as a binder phase to fix active particles and construct conductive pathways, collectively maintaining the stability of the electrode structure. This integrated structure enables the material to achieve stress buffering while simultaneously ensuring interfacial adhesion and ion conduction, thereby improving the initial coulombic efficiency and cycle capacity retention of the silicon anode.
[0028] In some embodiments, the silicon anode particles are made of silicon material, which is selected from at least one of pure silicon, silicon-carbon material, or silicon-oxygen material; the carbon material layer is composed of carbon material, which is selected from at least one of graphite, amorphous carbon, graphene, or carbon nanotubes; and / or, the silicon anode particles are porous silicon.
[0029] In some embodiments, the polyurethane polymer layer is a linear structure, a cross-linked network structure, or a functionalized structure containing polyoxyethylene segments.
[0030] Secondly, this application provides a method for preparing a modified silicon anode material, comprising the following steps: Step S1: Provide an initial core consisting of silicon anode particles and a carbon material layer coating the surface of the silicon anode particles.
[0031] Step S2: Activate the surface of the carbon material layer of the initial core to generate hydroxyl or amino groups on the surface of the carbon material layer, thus obtaining a surface-activated core.
[0032] Step S3: React the surface-activated core with a diisocyanate compound to react the hydroxyl or amino groups with the isocyanate groups of the diisocyanate compound, thereby obtaining a grafting intermediate containing isocyanate groups on its surface.
[0033] Step S4: The grafting intermediate is polymerized with a polyol compound and a chain extender to grow and graft a polyurethane polymer layer on the surface of the carbon material layer in situ, thereby obtaining a modified silicon anode material.
[0034] Based on the above preparation method, this application provides a modified silicon anode material that achieves functional integration through covalent bonds. Specifically, a polyurethane polymer layer is grafted in situ onto the surface of the carbon material layer within a silicon-carbon core, forming an interface structure bonded by chemical bonds. This grafting structure helps enhance the interfacial bonding between the active material particles and the polymer layer, improves the material's tolerance to volume expansion of silicon during charge and discharge, and maintains the overall stability of the electrode structure during cycling. Simultaneously, the polar groups and elastic segments in the grafted polyurethane layer can simultaneously improve the wettability of the electrolyte and the interfacial transport characteristics of lithium ions, and provide a certain buffering effect for mechanical stress during volume changes. Furthermore, the uniformly coated polyurethane layer, by appropriately limiting the direct contact between the electrolyte and the silicon-carbon core, facilitates the formation of a relatively more stable solid electrolyte interface film, thereby positively impacting the initial coulombic efficiency and long-term cycle capacity retention performance of the anode material. In the electrode fabrication process, the inherent bonding function of this grafted material can correspondingly reduce the proportion of external binders used, simplify the slurry preparation process, and support increasing the mass ratio of active material in the electrode.
[0035] In some embodiments, step S1 provides an initial core comprising silicon anode particles and a carbon material layer coating the surface of the silicon anode particles, including at least one of the following: (1) Directly purchase commercial silicon-carbon composite materials; or (2) First, silicon particles are prepared, and then the carbon material layer is formed on the surface of the silicon particles by chemical vapor deposition, liquid phase coating carbonization, or physical composite methods; or (3) Prepare a three-dimensional composite of silicon and carbon materials, wherein the carbon material at least partially coats the silicon particles.
[0036] In some embodiments, the activation treatment includes refluxing the initial kernel in an aqueous hydrogen peroxide solution; and / or, the diisocyanate is isophorone diisocyanate.
[0037] In some embodiments, the mass fraction of the hydrogen peroxide solution is 10% to 50% during the activation treatment; In some embodiments, the hydrogen peroxide solution has a mass fraction of 10% to 50% when the activation treatment is performed.
[0038] In some embodiments, the solid-liquid ratio of the initial kernel to the hydrogen peroxide solution is 1 g:(20-100) ml.
[0039] As an example, the solid-liquid ratio can be 1g:20ml, 1g:40ml, 1g:60ml, 1g:80ml, 1g:100ml, or any value within the range of any two of the above values. It should be noted that "gram" and "milliliters" here are merely exemplary units and are not intended to limit the amount of material used in the technical solution of this application. In actual implementation, those skilled in the art can proportionally increase or decrease the solid-liquid ratio according to specific process requirements and equipment scale, as long as the relative proportions between the components remain within the corresponding range, the technical effect of this application can be achieved.
[0040] In some embodiments, the molar ratio of the diisocyanate compound to the active group is not less than 3:1; the volume-to-mass ratio of the diisocyanate compound to the initial core is 0.5 ml to 5 ml: 1 g. As an example, the volume-to-mass ratio of the diisocyanate compound to the initial core can be 0.5 ml / g, 1 ml / g, 2 ml / g, 3 ml / g, 4 ml / g, 5 ml / g, or any value within the range of any two of the above values.
[0041] In some embodiments, the diisocyanate compound includes at least one of isophorone diisocyanate, hexamethylene diisocyanate, toluene diisocyanate, and diphenylmethane diisocyanate; the polyol includes at least one of polytetrahydrofuran ether diol, polycaprolactone diol, or polyethylene oxide-polytetrahydrofuran-polyethylene oxide triblock copolymer diol; and / or, the chain extender includes at least one of 1,4-butanediol, ethylenediamine, or trimethylolpropane.
[0042] In some embodiments, the diisocyanate compound is isophorone diisocyanate, and the mass ratio of the diisocyanate compound to the silicon carbide material is 2 ml: 1 g.
[0043] In some embodiments, after the polymerization reaction is completed, a polymer binder is added to the reaction product containing the modified silicon anode material, wherein the mass of the polymer binder is m; the mass of the modified silicon anode material is M; and the following condition is met: m ≤ 0.03M.
[0044] As an example, m can be 0.03M, 0.02M, 0.01M, 0.005M, or 0, or any value within the range of any two of the above values. As an example, the polymer binder is selected from at least one of polyacrylic acid, polyimide, sodium alginate, sodium carboxymethyl cellulose, styrene-butadiene rubber, and polyvinylidene fluoride. Since the modified silicon anode material itself possesses effective bonding capabilities through chemical grafting, the amount of added polymer binder can be controlled at a low level. When the mass m of the added polymer binder and the mass M of the modified silicon anode material are set to satisfy m≤0.03M, this electrode system can reduce the proportion of traditional binders while ensuring the integrity of the electrode structure and cycle stability. A lower binder content helps increase the proportion of active materials in the electrode, thereby supporting the improvement of the battery's energy density; simultaneously, reducing the amount of binder can correspondingly reduce the interfacial impedance of the electrode, which is beneficial for improving the ion and electron transport characteristics of the electrode; furthermore, this formulation system can still maintain the processing performance of the electrode slurry and the structural integrity of the electrode sheet, simplifying the electrode preparation process while maintaining the structural stability of the electrode during long-term cycling. Therefore, the modified silicon anode material provided in this application can reduce the use of traditional binders in practical applications, and achieve a balance between material system and process optimization while maintaining electrode performance.
[0045] Thirdly, this application provides a negative electrode sheet, including a negative electrode current collector and a negative electrode layer disposed on the negative electrode current collector. The negative electrode layer includes a modified silicon negative electrode material as described in the first aspect or a modified silicon negative electrode material prepared by the preparation method of the modified silicon negative electrode material as described in the second aspect, a conductive agent, and a polymer binder.
[0046] In some embodiments, the mass ratio of modified silicon anode material to conductive agent is (85 to 99): (1 to 15).
[0047] As an example, the mass ratio of modified silicon anode material to conductive agent can be 85:15, 90:10, 95:5, 99:1, or any value within the range of any two of the above values.
[0048] In some embodiments, the mass ratio of the modified silicon anode material to the conductive agent is (92 to 97):(3 to 8).
[0049] In some embodiments, the mass ratio of modified silicon anode material to conductive agent is 95:5.
[0050] In some embodiments, the polymer binder is selected from at least one of polyacrylic acid, polyimide, carboxymethyl cellulose and its salts, styrene-butadiene rubber, and polyvinylidene fluoride.
[0051] In some embodiments, the conductive agent is selected from at least one of carbon black, acetylene black, Ketjen black, carbon nanotubes, graphene, and carbon fiber.
[0052] In some embodiments, the negative current collector can be copper foil, porous copper foil, copper foil alloy, copper-plated metal foil, or polymer-based conductive foil.
[0053] Fourthly, this application provides an electrochemical device comprising the aforementioned negative electrode. The electrochemical device includes, but is not limited to, a battery.
[0054] This application achieves a "three-in-one" functional integration of active material, binder, and conductive network by chemically grafting a polyurethane adhesive onto the surface of silicon-carbon material in a covalent bond manner. Specifically, the grafted polyurethane layer acts as a "molecular spring," effectively buffering the volume expansion stress of silicon during charging and discharging through the reversible extension and retraction of its polymer chain segments. The covalent bond connection ensures that this buffering effect directly acts on the surface of the active particles, helping to maintain the integrity of the electrode structure and inhibiting particle breakage and detachment. Simultaneously, the polar groups in the polyurethane layer are beneficial for electrolyte wetting and lithium-ion transport, and its polymer network structure can also adhere to and bridge the active material and conductive agent, forming a stable electron conduction path, thereby improving both the ion and electron transport characteristics of the electrode. Furthermore, the uniformly coated polyurethane layer can moderately reduce the direct contact between the electrolyte and the silicon-carbon core, helping to inhibit the excessive growth and repeated rupture of the solid electrolyte interface film, thus positively impacting the initial coulombic efficiency and cycle life. The material itself has a bonding function, which can reduce or even eliminate the use of external adhesives. This not only simplifies the electrode preparation process, but also helps to increase the proportion of active materials in the electrode, thus supporting the improvement of battery energy density.
[0055] The foregoing embodiments of this application will be described below through specific examples.
[0056] Example 1: This example provides a porous silicon@carbon core-shell material surface grafted with linear polyurethane, including the following steps: Step 1: Preparation of porous silicon@carbon: (1.1) Preparation of porous silicon by magnesothermic reduction method: 1g of silica nanospheres (300nm) were uniformly mixed with 1.2g of magnesium powder, and heated to 700℃ at 1℃ / min under argon atmosphere, and held at that temperature for 5 hours. After cooling, the product was etched with 1MHCl solution for 24 hours to remove the byproduct MgO. After washing and drying, porous silicon was obtained.
[0057] (1.2) Chemical vapor deposition method for coating carbon layer: Porous silicon is placed in a tube furnace and reacted at 650°C for 2 hours under argon / ethylene mixed gas to form a uniform carbon shell with a thickness of about 10 nm, thus obtaining porous silicon@carbon.
[0058] Step 2: Surface grafting of linear polyurethane: (2.1) Surface hydroxylation: 0.5g of porous silicon@carbon was dispersed in 40ml of 30% hydrogen peroxide solution, refluxed at 80℃ for 6 hours, and centrifuged and washed to obtain a matrix with a surface rich in -OH.
[0059] (2.2) Isocyanation: The hydroxylated material was dispersed in 50 ml of anhydrous toluene, and 2 ml of isophorone diisocyanate and 2 drops of dibutyltin dilaurate catalyst were added. The reaction was carried out at 85 °C for 8 hours under nitrogen protection. After centrifugation and washing with toluene, porous silicon@carbon-NCO was obtained.
[0060] (2.3) Polyurethane grafting: Disperse all the above porous silicon@carbon-NCO in 50 ml of anhydrous DMF. Separately dissolve 2.0 g of polytetrahydrofuran ether diol and 0.22 g of 1,4-butanediol (molar ratio [NCO]:[OH]=1.05:1.0) in 20 ml of DMF and add them to the reaction system. React at 70 °C for 24 hours under nitrogen protection.
[0061] (2.4) After the reaction is complete, the product is poured into a large amount of ethanol to precipitate, centrifuged, washed three times with ethanol, and dried under vacuum at 60°C for 48 hours to obtain a modified silicon anode material with linear polyurethane grafted onto the surface of a porous silicon@carbon core-shell material.
[0062] Example 2: This example provides a cross-linked polyurethane network grafted onto the surface of a silicon suboxide carbon composite material. The preparation method is as follows: Step 1: Raw material preparation.
[0063] Prepare commercial SiOx / C materials, where x≈1.0 and carbon content is 15wt%; isophorone diisocyanate; polycaprolactone diol; 1,4-butanediol; trimethylolpropane.
[0064] Step 2: Surface grafting of cross-linked polyurethane network.
[0065] (2.1) Surface hydroxylation: 1.0 g of commercial SiOx / C powder was dispersed in 40 ml of 30% hydrogen peroxide solution and refluxed at 80 °C for 6 hours. After the reaction was completed, the powder was centrifuged, washed until neutral, and vacuum dried at 60 °C to obtain acidified SiOx / C with a surface rich in hydroxyl groups.
[0066] (2.2) Isocyanation: The acidified-SiOx / C obtained in step (2.1) was dispersed in 50 ml of anhydrous toluene, and 2.0 ml of isophorone diisocyanate and 2 drops of dibutyltin dilaurate catalyst were added. The reaction was carried out at 85 °C for 8 hours under nitrogen protection. After the reaction was completed, the mixture was centrifuged and washed three times with anhydrous toluene to obtain the intermediate SiOx / C-NCO with isocyanate groups modified on its surface.
[0067] (2.3) Crosslinking network grafting: Disperse 1.0g SiOx / C-NCO in 50ml anhydrous N,N-dimethylformamide. Separately dissolve 1.8g polycaprolactone diol, 0.15g 1,4-butanediol and 0.05g trimethylolpropane (the molar ratio of the total hydroxyl groups of the three to the NCO groups in step (2.2) is 0.95:1) in 20ml DMF, mix well and then add to the above dispersion system.
[0068] (2.4) Add an appropriate amount of catalyst and stir the reaction at 75°C for 18 hours under nitrogen protection. Due to the trifunctionality of trimethylolpropane, a cross-linked network polyurethane graft layer will be formed on the surface of the material.
[0069] (2.5) After the reaction is complete, the reaction solution is poured into a large amount of anhydrous ethanol to precipitate. After centrifugation and washing with ethanol three times, the precipitate is dried under vacuum at 60°C for 48 hours to obtain the surface-modified silicon anode material.
[0070] Example 3: This example provides a polyurethane with ion-transporting groups grafted onto the surface of a nano-silicon / graphene composite material. The preparation method is as follows: Step 1: Preparation of nano-silicon / graphene composite: (1.1) Aqueous dispersion of graphene oxide (2 mg / ml) was prepared using the modified Hummers method.
[0071] (1.2) Mix 0.1g of nano-silicon (100nm) with 100ml of GO dispersion and sonicate for 2 hours.
[0072] (1.3) Add 0.5g ascorbic acid, reduce at 95℃ for 6 hours, filter and wash to obtain a silicon / graphene composite with a three-dimensional network structure.
[0073] Step 2: Grafting polyurethane containing PEO segments: (2.1) Pretreatment with silane coupling agent using defects and residual oxygen-containing groups on the graphene surface: The composite is dispersed in ethanol, 3-aminopropyltriethoxysilane is added, and the mixture is refluxed for 8 hours to introduce the silane coupling agent. .
[0074] (2.2) The above material is reacted with excess IPDI to obtain an intermediate with -NCO on the surface.
[0075] (2.3) Using polyethylene oxide-polytetrahydrofuran-polyethylene oxide triblock copolymer diol as the soft segment, reacting with ethylenediamine chain extender, and grafting polyurethane rich in ether oxygen bonds onto the surface; (2.4) After the reaction is complete, the product is poured into a large amount of ethanol to precipitate, centrifuged, washed three times with ethanol, and dried under vacuum at 60°C for 48 hours to obtain the modified silicon anode material.
[0076] Example 4: This example provides a polyurethane grafted onto the surface of a silicon-carbon material based on recycled silicon waste. The preparation method is as follows: Step 1: Preparation of recycled silicon-carbon materials.
[0077] (1.1) Purification of silicon waste: Collect silicon wafer cutting waste slurry, soak it in 1M hydrochloric acid solution for 12 hours to remove metal impurities, then wash it with deionized water until neutral, and dry it to obtain purified silicon powder.
[0078] (1.2) Carbon coating: The purified silica powder and pitch were mixed evenly at a mass ratio of 9:1 and placed in a tube furnace. Under an argon atmosphere, the temperature was increased to 1000℃ at a rate of 5℃ / min and carbonized at this temperature for 4 hours.
[0079] (1.3) After cooling, the product is ball-milled for 2 hours and passed through a 400-mesh sieve to obtain the recovered silicon-carbon composite powder, denoted as r-Si / C.
[0080] Step 2: Surface grafting with conventional polyurethane.
[0081] (2.1) Surface hydroxylation: 1.0 g of recycled silicon-carbon material r-Si / C was dispersed in 40 ml of 30% hydrogen peroxide solution and refluxed at 80 °C for 6 hours. After the reaction was completed, the material was centrifuged, washed and dried to obtain hydroxylated r-Si / C-OH.
[0082] (2.2) Isocyanation: r-Si / C-OH was dispersed in 50 ml of anhydrous toluene, and 2.0 ml of isophorone diisocyanate and 2 drops of catalyst were added. The reaction was carried out at 85 °C for 8 hours under nitrogen protection. After centrifugation and washing with toluene, the intermediate r-Si / C-NCO was obtained.
[0083] (2.3) Polyurethane grafting: Disperse all r-Si / C-NCO in 50 ml of anhydrous DMF. Separately dissolve 2.0 g of poly(1,4-butanediol adipate) and 0.22 g of 1,4-butanediol (molar ratio [NCO]:[OH]=1.05:1.0) in 20 ml of DMF and add them to the reaction system.
[0084] (2.4) Under nitrogen protection, react at 70°C for 24 hours.
[0085] (2.5) After the reaction is complete, the product is poured into ethanol to precipitate, centrifuged and washed three times with ethanol, and then vacuum dried at 60°C for 48 hours to obtain the modified silicon anode material.
[0086] [Preparation of Secondary Batteries] CR2032 coin cells were prepared using the modified silicon anode materials obtained in Examples 1 to 4; specifically as follows: Step 1: Mix the modified silicon anode material with conductive carbon black at a weight ratio of 95:5, and add an appropriate amount of N-methylpyrrolidone (NMP) to prepare a slurry (without adding any additional binder). Coat the slurry evenly onto copper foil, vacuum dry at 120°C for 12 hours, and then punch the sheet to obtain the anode sheet.
[0087] Step 2: Assemble CR2032 coin cells using lithium metal sheets as the counter electrode in an argon-filled glove box. The electrolyte is 1M LiPF6 in EC / DMC (1:1 vol%), containing 10% FEC additive.
[0088] Comparative Example 1: This comparative example provides a physical mixture of commercial silicon carbide material and polyacrylic acid (PAA) adhesive, specifically as follows: Step 1: Raw Materials and Proportions Active material: Commercial silicon suboxide / carbon composite material, with specifications of SiOx / C (x≈1.0, carbon content ~15wt%), particle size D50=5μm, 80 parts by weight.
[0089] Conductive agent: Conductive carbon black, 10 parts by weight.
[0090] Adhesive: Polyacrylic acid, average molecular weight ~500,000, 10 parts by weight.
[0091] Solvent: Deionized water, solid content controlled at 40wt%.
[0092] Step 2: Electrode preparation method: (2.1) Dissolve the PAA adhesive in part of the deionized water and stir magnetically until completely dissolved to form a homogeneous adhesive solution.
[0093] (2.2) Premix the SiOx / C active material and conductive carbon black in a Thinky planetary mixer for 5 minutes.
[0094] (2.3) Add the premixed dry powder to the PAA adhesive solution and stir at 2000 rpm for 30 minutes in a Thinky mixer to form a uniform slurry.
[0095] (2.4) Use a 100μm doctor blade to coat the slurry onto a 10μm thick copper foil and place it in an 80℃ forced-air oven for initial drying for 2 hours.
[0096] (2.5) The final product is mixed with conductive carbon black at a weight ratio of 95:5, and an appropriate amount of N-methylpyrrolidone (NMP) is added to prepare a slurry (without any additional binder). The slurry is uniformly coated on copper foil, vacuum dried at 120°C for 12 hours, and then punched to obtain the negative electrode sheet.
[0097] (2.6) Roll the electrode sheets using a roller press under 3 tons of pressure to achieve a compaction density of approximately 1.2 g / cm³, and finally punch them into round sheets with a diameter of 12 mm. f. Assemble CR2032 coin cells using lithium metal sheets as the counter electrode in an argon glove box. The electrolyte is 1M LiPF6 in EC / DMC (1:1 vol%), containing 10% FEC additive.
[0098] (2.7) Using lithium metal sheets as the counter electrode, CR2032 coin cells were assembled in an argon glove box. The electrolyte was 1M LiPF6 in EC / DMC (1:1 vol%), containing 10% FEC additive.
[0099] Comparative Example 2: This comparative example provides a silicon-carbon material surface physically coated with a polyurethane layer, specifically as follows: Step 1: Raw Materials and Proportions Matrix material: 1.0 g of commercial SiOx / C, same as Comparative Example 1.
[0100] Coated polymer: thermoplastic polyurethane granules, model 1185A, 0.2 g (target coating rate 20 wt%).
[0101] Solvent: N,N-dimethylformamide, 100 ml.
[0102] Step Two: Physical Coating Method (2.1) Dissolve 0.2 g of polyurethane particles completely in 100 mL of DMF to form a 0.2 wt% transparent solution.
[0103] (2.2) Slowly add 1.0 g of SiOx / C powder to the above solution and ultrasonically disperse it at room temperature for 1 hour to fully wet the particles.
[0104] (2.3) Place the mixture on a magnetic stirrer and stir continuously at 60°C for 12 hours to allow the polyurethane molecules to be fully adsorbed onto the silicon carbon surface.
[0105] (2.4) Use a rotary evaporator to remove most of the DMF solvent at 80°C.
[0106] (2.5) The obtained viscous material was dried in a vacuum oven at 120°C for 24 hours to obtain physically coated SiOx / C@PU powder.
[0107] (2.6) Using the powder as the active material, mix it with conductive carbon black and PAA binder at a ratio of 80:10:10 as in Comparative Example 1 to prepare the electrode sheet. Note: PAA still needs to be added here because the physically coated PU layer does not have a stable chemical cross-linking network and cannot perform the bonding function alone.
[0108] (2.7) Using lithium metal sheets as the counter electrode, CR2032 coin cells were assembled in an argon glove box. The electrolyte was 1M LiPF6 in EC / DMC (1:1 vol%), containing 10% FEC additive.
[0109] Experimental testing: (1) Initial Coulomb efficiency: Electrochemical testing: The specifics are as follows: Instruments: Battery testing systems such as Landon and Xinwei are used.
[0110] Test mode: Constant current charge and discharge.
[0111] Specific steps: (a) First charge (lithium intercalation): Discharge the battery from the open circuit voltage to 0.01V with a constant small current (usually 0.1C or 100mA / g current density) (cutoff condition: voltage drops to 0.01V and current drops to 0.01C or similar setting).
[0112] (b) Let stand: After charging is complete, let stand for 5-10 minutes.
[0113] (c) First discharge (lithiation removal): Charge the battery from 0.01V to 1.5V at the same current density (cutoff conditions are the same as above).
[0114] (d) Data recording and calculation: The first charge capacity (Q_charge,1) and the first discharge capacity (Q_discharge,1) are read directly from the test equipment software.
[0115] (e) Initial coulombic efficiency = (initial discharge capacity / initial charge capacity) × 100%.
[0116] (f) 200-cycle capacity retention (0.5C): After the first charge-discharge test is completed, a long-cycle test is performed at a constant current density of 0.5C under the same voltage window (0.01-1.5 V). The discharge capacity of each cycle is recorded and the capacity retention rate is calculated until 200 cycles are completed.
[0117] (g) 100-cycle negative electrode expansion: The negative electrodes obtained in the examples and comparative examples were used to make batteries, which were cycled for 100 cycles at a current density of 0.5C within a voltage range of 0.01V to 1.5V. After discharging to 0.01V in the 100th cycle, the batteries were disassembled in an argon glove box, and the electrodes were removed, cleaned and dried by DMC, and the thickness was measured using a digital micrometer. The electrode expansion rate was calculated using the formula (thickness after cycling - initial thickness) / initial thickness × 100%.
[0118] The experimental test results of the secondary batteries prepared by Examples 1 to 4 and Comparative Examples 1 to 2 are shown in Table 1 below.
[0119] Table 1
[0120] Results Analysis: Based on the comparative analysis of the preparation processes and technical effects of Examples 1-4 and Comparative Examples 1-2, the technical solution provided by this application demonstrates advantages in the following aspects: Firstly, regarding interfacial bonding and structural stability, Examples 1-4 established a chemically bonded interface by directly grafting polyurethane onto the surface of silicon-carbon material via covalent bonds. This robust connection helps improve the material's tolerance to silicon volume expansion, thereby maintaining the stability of the electrode structure during cycling. In contrast, Comparative Example 1 used a physical mixing method, resulting in weaker interfacial bonding between the components; Comparative Example 2, by physically adsorbing and coating a polyurethane layer, improved the interfacial bonding to some extent, but still did not reach the stability level of chemical bonding.
[0121] Secondly, regarding electrochemical performance, the materials prepared in Examples 1-4 exhibited improved initial coulombic efficiency and cycling stability. This demonstrates that the grafted polyurethane layer, while maintaining the integrity of the electrode structure, contributes to improving electrolyte wettability and lithium-ion transport kinetics with its polar groups, while its polymer network structure helps maintain the continuity of the electron conduction pathway.
[0122] In particular, regarding the electrode fabrication process, the materials in Examples 1-4 inherently possess binding properties, thus eliminating the need for additional binders during electrode slurry preparation. This not only simplifies the fabrication process but also helps to increase the proportion of active material in the electrode. In contrast, Comparative Example 1 requires the addition of a considerable proportion of PAA binder, and although Comparative Example 2 uses polyurethane coating, it still requires the addition of PAA binder to maintain the electrode structure. Therefore, it is evident that the chemically grafted polyurethane material provided in this application has a significant advantage in achieving the integrated functionality of "active material-binder-conductive network".
[0123] In summary, this application, through the design of covalently grafted polyurethane, can achieve the functional integration of active material, binder and conductive network. While improving the cycle stability and electrochemical performance of silicon anode materials, it can also simplify the electrode preparation process, providing a feasible technical path for improving battery energy density.
[0124] The above description is merely an exemplary embodiment of this application and does not limit the patent scope of this application. Any equivalent structural transformations made using the technical concept of this application or direct / indirect applications in other related technical fields are included within the patent protection scope of this application.
Claims
1. A modified silicon anode material, characterized in that, It includes a core and a shell. The core includes silicon anode particles and a carbon material layer covering the surface of the silicon anode particles. The shell is a polyurethane polymer layer, which is chemically grafted onto the surface of the carbon material layer via covalent bonds.
2. The modified silicon anode material according to claim 1, characterized in that, The covalent bond is formed by the reaction of hydroxyl or amino groups on the surface of the carbon material layer with isocyanate groups at the ends of the polyurethane polymer chain.
3. The modified silicon anode material according to any one of claims 1 to 2, characterized in that, The silicon anode particles are made of silicon material, which is selected from at least one of pure silicon, silicon-carbon material or silicon-oxygen material. The carbon material layer is composed of a carbon material selected from at least one of graphite, amorphous carbon, graphene, or carbon nanotubes; and / or, The silicon anode particles are porous silicon.
4. The modified silicon anode material according to any one of claims 1 to 2, characterized in that, The polyurethane polymer layer is a linear structure, a cross-linked network structure, or a functionalized structure containing polyoxyethylene segments.
5. A method for preparing the modified silicon anode material according to any one of claims 1 to 4, characterized in that, Includes the following steps: An initial core is provided, comprising silicon anode particles and a carbon material layer coating the surface of the silicon anode particles; The surface of the carbon material layer of the initial core is activated to generate active groups on the surface of the carbon material layer, thus obtaining a surface-activated core; the active groups are hydroxyl or amino groups. The surface-activated core is reacted with a diisocyanate compound, and the hydroxyl or amino group reacts with the isocyanate group of the diisocyanate compound to obtain a grafting intermediate with isocyanate groups on its surface. The grafting intermediate is polymerized with a polyol compound and a chain extender to grow and graft the polyurethane polymer layer in situ on the surface of the carbon material layer, thereby obtaining the modified silicon anode material.
6. The method for preparing the modified silicon anode material according to claim 5, characterized in that, The activation treatment includes refluxing the initial kernel in a hydrogen peroxide solution; and / or, The diisocyanate is isophorone diisocyanate.
7. The method for preparing the modified silicon anode material according to claim 6, characterized in that, During the activation treatment, the hydrogen peroxide aqueous solution has a mass fraction of 10% to 50%. The solid-liquid ratio of the initial kernel to the hydrogen peroxide solution is 1g:(20-100)ml.
8. The method for preparing the modified silicon anode material according to claim 5, characterized in that, The molar ratio of the diisocyanate compound to the active group is not less than 3:1; The volume-to-mass ratio of the diisocyanate compound to the initial core is 0.5 ml to 5 ml: 1 g.
9. The method for preparing the modified silicon anode material according to claim 5, characterized in that, The diisocyanate compound includes at least one of isophorone diisocyanate, hexamethylene diisocyanate, toluene diisocyanate, and diphenylmethane diisocyanate; The polyol includes at least one selected from polytetrahydrofuran ether diol, polycaprolactone diol, or polyethylene oxide-polytetrahydrofuran-polyethylene oxide triblock copolymer diol; and / or The chain extender includes at least one of 1,4-butanediol, ethylenediamine, or trimethylolpropane.
10. The method for preparing the modified silicon anode material according to claim 5, characterized in that, The method further includes: After the polymerization reaction is completed, a polymer binder is added to the reaction product containing the modified silicon anode material, wherein the mass of the polymer binder is m; the mass of the modified silicon anode material is M; and the following condition is met: m ≤ 0.03M.
11. A negative electrode sheet, characterized in that, It includes a negative electrode current collector and a negative electrode layer disposed on the negative electrode current collector, wherein the negative electrode layer comprises a modified silicon negative electrode material as described in any one of claims 1 to 4 or a negative electrode sheet prepared by the preparation method of the modified silicon negative electrode material as described in any one of claims 5 to 10.
12. An electrochemical device, characterized in that, It includes the negative electrode sheet as described in claim 11.