Coated modified silicon-carbon negative electrode material and preparation method and application thereof

Abstract

This invention belongs to the field of battery materials and discloses a coated and modified silicon-carbon anode material, its preparation method, and its application. The silicon-carbon anode material includes a porous carbon framework, silicon, and a coating layer. The silicon is distributed in the pores of the porous carbon framework, and the coating layer at least covers a portion of the surface of the particles formed by the porous carbon framework and the silicon. The coating layer includes polyacrylic acid, polygalacturonic acid, and Cu. 2+ and Li + The carboxyl groups and Cu of the polyacrylic acid 2+ Coordination crosslinking, the carboxyl group on the polygalacturonic acid and Li + Through ionic crosslinking, the polyacrylic acid and the polygalacturonic acid are interconnected through any one or two of physical crosslinking and chemical bonding. The silicon-carbon anode material provided by this invention constructs a rigid-flexible protective system through a bimetallic ion crosslinking coating layer, comprehensively solving the core technical problems of silicon-carbon anodes such as volume expansion, SEI film instability, high interfacial impedance, and low initial efficiency.

Description

Technical Field

[0001] This invention belongs to the field of battery materials, and relates to an anode material, specifically a coated and modified silicon-carbon anode material and its preparation method and application. Background Technology

[0002] Currently, graphite is the primary anode material for lithium-ion batteries, but its specific capacity is approaching its theoretical upper limit of 372 mAh / g, making it difficult to meet the demands of high-energy-density devices. While silicon boasts a high theoretical specific capacity of 4200 mAh / g, its application as an anode presents several pressing technical challenges: during charge and discharge, the dramatic volume expansion (exceeding 300%) of silicon easily leads to electrode structure pulverization and repeated rupture and regeneration of the solid electrolyte interphase (SEI) film, severely shortening the battery's cycle life. To address these issues, existing technologies, in addition to employing silicon-carbon composite solutions, further introduce surface coating modification strategies to optimize the electrochemical performance of silicon-carbon materials.

[0003] Coating modification methods for silicon-carbon anodes are mainly divided into several categories, including carbon coating, polymer coating, and oxide coating. However, these methods all have certain limitations: although carbon coating can improve conductivity to a certain extent, conventional carbon coatings (such as amorphous carbon) are relatively rigid and lack mechanical toughness, making it difficult to maintain structural integrity during the repeated and drastic volume expansion and contraction of silicon. This can easily lead to cracks or even rupture, resulting in repeated reconstruction of the SEI film, extremely poor stability, and continuous consumption of lithium ions. While polymer or oxide coatings have a certain degree of flexible buffering capacity, their poor ionic and electronic conductivity significantly increases the electrode interface impedance, hindering lithium ion transport. Furthermore, existing coating modification methods generally suffer from weak interfacial bonding between the coating layer and the silicon-carbon matrix, making the coating layer prone to peeling off during cycling, further exacerbating irreversible capacity loss. These defects collectively lead to the core challenges of low initial coulombic efficiency and poor cycling stability in silicon-carbon anodes, restricting their practical application. Summary of the Invention

[0004] In view of the defects and deficiencies of the existing technology, the present invention provides, in a first aspect, a coated modified silicon-carbon anode material; in a second aspect, a method for preparing the coated modified silicon-carbon anode material; in a third aspect, an anode sheet; and in a fourth aspect, a battery.

[0005] In a first aspect, the present invention provides a coated modified silicon-carbon anode material, comprising a porous carbon framework, silicon and a coating layer, wherein the silicon is distributed in the channels of the porous carbon framework, and the coating layer covers at least a portion of the surface of the particles formed by the porous carbon framework and the silicon. The coating layer includes polyacrylic acid, polygalacturonic acid, and Cu. 2+ and Li+ The carboxyl groups and Cu of the polyacrylic acid 2+ Coordination crosslinking; the carboxyl group and Li on the polygalacturonic acid + Through ionic crosslinking, the polyacrylic acid and the polygalacturonic acid are interconnected by any one or two of the following methods: physical crosslinking and chemical bonding.

[0006] Preferably, the coating layer comprises polyacrylic acid-Cu 2+ The inner region formed and composed of polygalacturonic acid-Li + The outer region that is formed.

[0007] Preferably, the mass ratio of polyacrylic acid to polygalacturonic acid in the coating layer is (0.03~0.6):1.

[0008] Preferably, the porous carbon framework and the silicon form intermediate particles, the D50 of the intermediate particles is 3~15μm, and the silicon content of the intermediate particles is 30wt%~70wt%.

[0009] Preferably, the mass percentage of the coating layer in the modified silicon-carbon anode material is 1 wt% to 5 wt%.

[0010] Preferably, the thickness of the coating layer is 20~200nm.

[0011] Secondly, the present invention provides a method for preparing a coated and modified silicon-carbon anode material, comprising the following steps: Step 1: Add polyacrylic acid and copper source to water and stir to obtain material A; add polygalacturonic acid and lithium source to water and stir to obtain material B; Step 2: Add the intermediate particles to material A, stir and react to obtain a slurry; Step 3: Add material B to the slurry, stir and react, then filter, wash and dry in sequence to obtain the intermediate product; Step 4: The intermediate product is heated and cured under a protective atmosphere to obtain the coated and modified silicon-carbon anode material; The intermediate particles consist of a porous carbon framework and silicon, with silicon distributed in the pores of the porous carbon framework.

[0012] Preferably, in step 1, the lithium source is any one or more of lithium acetate, lithium hydroxide, lithium citrate, and lithium acrylate; and the copper source is any one or more of copper nitrate, copper acetate, and copper chloride.

[0013] Preferably, in step 1, the mass ratio of polygalacturonic acid to lithium source is 1: (0.3~0.8).

[0014] Preferably, in step 1, the mass ratio of polyacrylic acid to copper source is 1: (0.1~0.5).

[0015] Preferably, in step 1, the content of polyacrylic acid in material A is 0.01wt%~0.2wt%; and the content of polygalacturonic acid in material B is 0.5wt%~2wt%.

[0016] Preferably, in step 1, the stirring rate of polyacrylic acid and copper source is 400~600 rpm, and the stirring time is 2~4 h.

[0017] Preferably, in step 1, the stirring rate of polygalacturonic acid and lithium source is 600~800 rpm, and the stirring time is 8~12 h.

[0018] Preferably, in steps 2 and 3, the mass ratio of intermediate particles, polyacrylic acid in material A, and polygalacturonic acid in material B is 100:(0.1~0.3):(0.5~3) based on the proportion of raw materials.

[0019] Preferably, in step 2, the stirring speed is 400~600 rpm and the stirring time is 1~2 hours.

[0020] Preferably, in step 3, the stirring speed is 400~600 rpm and the stirring time is 0.5~1h.

[0021] Preferably, in step 3, the product is washed 2-3 times with pure water.

[0022] Preferably, in step 3, the product is dried at 60-80°C in an air atmosphere for 6-12 hours.

[0023] Preferably, in step 4, the curing temperature is 150~180℃ and the curing time is 2~4h.

[0024] Thirdly, the present invention provides a negative electrode sheet, comprising the silicon-carbon negative electrode material described in the first aspect or the silicon-carbon negative electrode material prepared by the preparation method described in the second aspect, a binder, and a conductive agent.

[0025] Fourthly, the present invention provides a battery comprising the negative electrode sheet described in the third aspect.

[0026] Compared with the prior art, one or more technical solutions provided by the present invention have at least one of the following beneficial effects: (1) In the coated and modified silicon-carbon anode material provided by the present invention, PAA and Cu 2+ Coordination crosslinking forms a network with electronic conductivity, improving the insulation properties of traditional polymer coatings by utilizing copper ions and their coordination structures; polygalacturonic acid is linked through Li... +The ion bridge constructs a continuous and efficient lithium-ion transport channel, enhancing adhesion to silicon particles while reserving expansion space. It also utilizes its affinity with the electrolyte to reduce interfacial charge transfer impedance and alleviate concentration polarization. The outer bimetallic ion cross-linking coating layer constructs a rigid-flexible protection system, comprehensively solving core technical challenges such as volume expansion of silicon-carbon anodes, SEI film instability, high interfacial impedance, and low initial efficiency.

[0027] (2) The rigid-flexible composite structure of the coating layer can effectively buffer the volume expansion of silicon during charging and discharging, suppress electrode cracking and pulverization, prevent the active material from detaching from the conductive network, and maintain a stable electron / ion transport pathway in the long term. In addition, the composite coating layer can form a stable artificial interface, reduce the direct contact between the electrolyte and the silicon-carbon matrix, suppress side reactions and the continuous rise of interface impedance, thereby comprehensively reducing ohmic polarization, concentration polarization and interface polarization during charging and discharging, and significantly improving the structural stability of silicon-carbon anode during cycling.

[0028] (3) The coating layer can form a complete and thin three-dimensional cross-linked network coating film on the surface of silicon carbon particles, which can give full play to the functions of bimetallic cross-linking, buffering expansion and stabilizing the interface, while taking into account the cycle stability and high first coulombic efficiency of silicon carbon anode. Attached Figure Description

[0029] Figure 1 Here is a SEM image of the coated and modified silicon-carbon anode material prepared in Example 1; Figure 2 This is a TEM image of the coated and modified silicon-carbon anode material prepared in Example 1; Figure 3 This is a TEM image of the silicon-carbon anode material prepared in Example 5. Detailed Implementation

[0030] The present invention provides the following specific technical solutions.

[0031] In a first aspect, the present invention provides a coated modified silicon-carbon anode material, comprising a porous carbon framework, silicon, and a coating layer, wherein the silicon is distributed in the channels of the porous carbon framework, and the silicon and the porous carbon framework are composite to form intermediate particles; the coating layer at least covers a portion of the surface of the intermediate particles. The coating layer includes polyacrylic acid, polygalacturonic acid, and Cu. 2+ and Li + The carboxyl groups and Cu of the polyacrylic acid 2+ Coordination crosslinking; the carboxyl group and Li on the polygalacturonic acid + Through ionic crosslinking, the polyacrylic acid and the polygalacturonic acid are interconnected by any one or two of the following methods: physical crosslinking and chemical bonding.

[0032] Research has revealed that this coated modified silicon-carbon anode material has significant structural advantages. Through a multifunctional integrated core-shell structure design, it achieves synergistic improvement in multiple performance aspects: it uses silicon-carbon composite particles as the core, with porous carbon skeleton channels uniformly dispersing silicon and providing basic support, and an outer bimetallic ion cross-linking coating layer to construct a rigid-flexible protective system. This comprehensively solves the core technical challenges of silicon-carbon anode volume expansion, SEI film instability, high interface impedance, and low initial efficiency.

[0033] First, polyacrylic acid (PAA) and Cu 2+ The coordination crosslinking forms a supporting structure, suppressing the huge volume expansion of silicon, and works in conjunction with polygalacturonic acid (PGA) and Li + The framework constructed via ion bridges adheres well to silicon particles while allowing for expansion space; secondly, polygalacturonic acid not only improves the water solubility of polysaccharides but also provides lithium-ion transport channels, effectively enhancing the battery's initial efficiency; while Li + / Cu 2+ The synergistic effect of the bimetallic ion cross-linking network, both through Li + First, an ion transport channel is constructed, and then an efficient electronic conduction pathway is built relying on the coordinated copper ions, achieving dual ion-electron conduction and significantly reducing interfacial impedance. Second, the PAA-Cu network and the PGA-Li network associate with each other through intermolecular hydrogen bonds, lithium ion bridging, and weak interactions between a small number of copper ions and carboxyl groups at the interface, further improving the uniformity and mechanical strength of the coating layer. The uniformly coated three-dimensional network forms a stable core-shell structure, which not only avoids the direct growth of the SEI film on the silicon surface and inhibits its repeated breakage and reconstruction, but also strengthens the bonding stability of the two cross-linked networks through multiple interfacial interactions such as intermolecular hydrogen bonds, lithium ion bridging, and copper ion-carboxyl group coordination.

[0034] Preferably, the coating layer comprises polyacrylic acid-Cu 2+ The inner region formed and composed of polygalacturonic acid-Li + The outer region that is formed.

[0035] Research has shown that using PAA-Cu as the inner coating layer can rely on Cu 2+ Coordination and cross-linking construct a robust framework, tightly anchoring it to the surface of silicon-carbon particles and enhancing matrix bonding stability; Li-PGA, as the outer layer component, can bind to Li through intermolecular hydrogen bonds. + The ion bridging effect allows for efficient and tight bonding with the inner PAA-Cu network, while preventing Li-PGA from directly contacting the silicon-based surface and causing interfacial side reactions that could lead to decreased interfacial stability.

[0036] Preferably, the mass ratio of polyacrylic acid to polygalacturonic acid in the coating layer is (0.03~0.6):1.

[0037] Research has shown that using a smaller amount of polyacrylic acid avoids excessive rigidity and ion channel blockage caused by over-crosslinking. Under the optimized ratio described above, a precise match between rigid and flexible structures and synergistic optimization of dual-network performance can be achieved. The balanced ratio further enhances the performance of Li. + / Cu 2+ The bimetallic cross-linked network improves stability, optimizes interface contact, accelerates ion and electron transport, and synergistically improves the cycle life and first efficiency of the negative electrode.

[0038] Preferably, the porous carbon framework and the silicon form intermediate particles, the D50 of the intermediate particles is 3~15μm, and the silicon content of the intermediate particles is 30wt%~70wt%.

[0039] In actual production, intermediate particles (silicon-carbon materials) can be purchased commercially or prepared in-house. The preparation process involves carbonizing and activating a carbon source precursor under a protective atmosphere to create a porous carbon framework. Then, silicon is deposited into the pores of the porous carbon framework using a vapor deposition process. By controlling the D50 of the prepared intermediate particles to be 3~15μm and the silicon content to be 30wt%~70wt%, it can be made to possess both high specific capacity and good processing fluidity and structural stability, making it suitable for subsequent coating modification and negative electrode coating processes.

[0040] Preferably, the mass percentage of the coating layer in the modified silicon-carbon anode material is 1 wt% to 5 wt%.

[0041] Research has shown that, under the above-mentioned preferred ratio, the coating layer can form a complete and thin three-dimensional cross-linked network coating film on the surface of silicon-carbon particles. This can fully utilize the functions of bimetallic cross-linking, buffering expansion, and stabilizing the interface, while avoiding problems such as ion transport obstruction, increased overall material impedance, and reduced compaction density caused by excessively thick coating layers. It also balances the electrochemical performance of silicon-carbon anodes in terms of cycle stability and first coulombic efficiency.

[0042] Preferably, the thickness of the coating layer is 20~200nm.

[0043] Secondly, the present invention provides a method for preparing a coated and modified silicon-carbon anode material, comprising the following steps: Step 1: Add polyacrylic acid and copper source to water and stir to obtain material A; add polygalacturonic acid and lithium source to water and stir to obtain material B; Step 2: Add the intermediate particles to material A, stir and react to obtain a slurry; Step 3: Then add material B to the slurry, stir and react, then filter, wash and dry in sequence to obtain the intermediate product; Step 4: Place the intermediate product under a protective atmosphere and heat it to solidify, which is the coated and modified silicon-carbon anode material. The intermediate particles consist of a porous carbon framework and silicon, with silicon distributed in the channels of the porous carbon framework.

[0044] Research has shown that a stepwise coating process, first forming an inner layer with PAA and then introducing rigid PGA, allows for the formation of an inner and outer double-rigid or interpenetrating network structure through hydrogen bonding and other interactions. This enables the construction of a dense coating layer with high mechanical strength on the particle surface. This coating layer effectively inhibits excessive SEI film growth and constrains silicon volume expansion, while lithium PGA carboxylate provides lithium-ion transport channels. Stepwise feeding avoids pre-crosslinking and agglomeration of polymers in solution, facilitating the acquisition of well-dispersed powder particles.

[0045] Preferably, in step 1, the lithium source is any one or more of lithium acetate, lithium hydroxide, lithium citrate, and lithium acrylate; and the copper source is any one or more of copper nitrate, copper acetate, and copper chloride.

[0046] Preferably, in step 1, the mass ratio of polygalacturonic acid to lithium source is 1: (0.3~0.8).

[0047] Research has shown that the optimal range of the above-mentioned lithium source can control the degree of lithiation of polygalacturonic acid, accurately match the system structure regulation requirements, and effectively improve the first charge and discharge efficiency of the battery; at the same time, it can maintain the stability of the material skeleton structure, mildly suppress interfacial side reactions, and synergistically improve the initial cycle performance and overall electrochemical performance of the battery.

[0048] Preferably, in step 1, the mass ratio of polyacrylic acid to copper source is 1: (0.1~0.5).

[0049] Research has shown that the optimal amount of copper source described above can construct a cross-linked network structure with moderate density and a balance of rigidity and flexibility. This structure not only forms a stable structural support system, effectively buffering the volume expansion deformation of silicon-based materials during charging and discharging, and maintaining particle integrity, but also constructs a continuous and uniform conductive pathway, optimizing the material's conductivity and reducing powder resistivity. Simultaneously, it enables uniform complexation and fixation of copper ions, optimizing the electrode interface environment, reducing interfacial side reactions, and synergistically improving the material's initial coulombic efficiency and long-term cycling stability.

[0050] Preferably, in step 1, the content of polyacrylic acid in material A is 0.01wt%~0.2wt%; and the content of polygalacturonic acid in material B is 0.5wt%~2wt%.

[0051] Preferably, in step 1, the stirring rate of polyacrylic acid and copper source is 400~600 rpm, and the stirring time is 2~4 h.

[0052] Preferably, in step 1, the stirring rate of polygalacturonic acid and lithium source is 600~800 rpm, and the stirring time is 8~12 h.

[0053] Preferably, in steps 2 and 3, the mass ratio of intermediate particles, polyacrylic acid in material A, and polygalacturonic acid in material B is 100:(0.1~0.3):(0.5~3) based on the proportion of raw materials.

[0054] Research has shown that the optimal amount of polyacrylic acid can form a uniform, complete, and appropriately thick coating layer on the surface of intermediate particles. While ensuring the integrity of the coating and the structural binding effect, it effectively balances the material's specific capacity and initial coulombic efficiency, thus optimizing the basic electrochemical performance. When combined with an appropriate amount of polygalacturonic acid, a composite modified coating system can be synergistically constructed to further stabilize the material's microstructure, adapt to the volume change characteristics of silicon-carbon anodes, and help to simultaneously improve the overall cycle performance and interface stability.

[0055] Preferably, in step 2, the stirring speed is 400~600 rpm and the stirring time is 1~2 hours.

[0056] Preferably, in step 3, the stirring speed is 400~600 rpm and the stirring time is 0.5~1h.

[0057] Preferably, in step 3, the product is washed 2-3 times with pure water.

[0058] Preferably, in step 3, the product is dried at 60-80°C in an air atmosphere for 6-12 hours.

[0059] Preferably, in step 4, the curing temperature is 150~180℃ and the curing time is 2~4h.

[0060] Thirdly, the present invention provides a negative electrode sheet, comprising the silicon-carbon negative electrode material described in the first aspect or the silicon-carbon negative electrode material prepared by the preparation method described in the second aspect, a binder, and a conductive agent.

[0061] In practical applications, the binder is any one or more of sodium carboxymethyl cellulose, styrene-butadiene rubber, polyimide, and sodium alginate; the conductive agent is any one or more of conductive carbon black, single-walled carbon nanotubes, multi-walled carbon nanotubes, graphene, and conductive graphite. The negative electrode sheet, by weight percentage, comprises: silicon-carbon negative electrode material 85wt%~95wt%, binder 1.5wt%~3.0wt%, and conductive agent 3.5wt%~5.0wt%.

[0062] The preparation process of the negative electrode sheet is as follows: silicon-carbon negative electrode material, conductive agent and binder are added to solvent according to the ratio and stirred evenly to obtain slurry; the slurry is coated on copper foil current collector, dried, rolled and cut into sheets to obtain the negative electrode sheet.

[0063] Fourthly, the present invention provides a battery comprising the negative electrode sheet described in the third aspect.

[0064] To make the technical problems, technical solutions and technical advantages of the present invention clearer, a detailed description will be given below with reference to specific examples. However, the scope of protection of the present invention is not limited to the following specific embodiments.

[0065] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0066] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.

[0067] In the specific embodiments and comparative examples of this invention, the intermediate particles are spherical silicon-carbon materials with a D50 of 10 μm and a silicon content of 50 wt%; the solid content of polyacrylic acid is 10 wt%; and polygalacturonic acid is a powder solid.

[0068] Example 1: A method for preparing a coated and modified silicon-carbon anode material includes the following steps: Step 1: Add 1g of polyacrylic acid to 400mL of pure water and stir to dissolve, preparing a PAA solution. Add 0.5g of copper nitrate to the PAA solution and stir at 400rpm for 3 hours at room temperature, allowing the Cu to... 2+ It undergoes ionic cross-linking with PAA to form a PAA-Cu complex, denoted as material A.

[0069] Dissolve 0.1 g of lithium acetate in 100 mL of pure water and stir until completely dissolved to obtain a lithium acetate solution. Add 0.94 g of polygalacturonic acid to the lithium acetate solution and stir at 600 rpm for 12 hours at room temperature to allow the carboxyl groups (-COOH) on the PGA molecular chain to react with the Li. + The reaction produces a lithium carboxylic acid group (-COOLi), yielding a PGA-Li solution, denoted as material B.

[0070] Step 2: Add 100g of spherical silicon carbide material to material A obtained in Step 1, and stir at 500rpm for 1 hour at room temperature. Then, pour all of material B obtained in Step 1 into the reaction system and continue stirring at 500rpm for 1 hour to obtain a slurry, allowing the Li-PGA and PAA-Cu networks to bond through hydrogen bonds and Li... + Ion bridging recombination to form Li + / Cu 2+ Bimetallic ion cross-linked three-dimensional network coating layer.

[0071] Step 3: The slurry obtained in Step 2 is filtered, then washed three times with pure water to remove unreacted free ions and byproducts. It is then dried in a forced-air drying oven at 80°C for 10 hours to ensure thorough drying, yielding the intermediate product.

[0072] Step 4: The intermediate product obtained in Step 3 is placed under a N2 atmosphere and heated to 150°C for 3 hours for curing treatment, so that the hydrogen bonding and ionic crosslinking between PAA and Li-PGA are fully established, while Cu... 2+ The modified silicon-carbon anode material with a coating thickness of 30 nm is obtained by maintaining a stable ionic cross-linking structure with PAA.

[0073] Figure 1 The image shows a SEM image of the coated and modified silicon-carbon anode material prepared in Example 1. Figure 1 It can be seen that a uniform, dense and complete three-dimensional network coating layer is formed on the surface of silicon-carbon particles. The particles maintain a regular spherical morphology and there are no obvious cracks, damages or agglomerations. The coating layer has a uniform thickness and no exposed matrix on the surface. This indicates that the preparation process provided by the present invention has successfully achieved the uniform growth and complete coating of the bimetallic ion crosslinking network on the surface of silicon-carbon particles, providing a stable interface protection structure for silicon-carbon anodes.

[0074] Figure 2 This is a TEM image of the coated and modified silicon-carbon anode material prepared in Example 1. Figure 2 In the middle, the darker area in the upper right corner is silicon-carbon material, and the brighter strip in the middle is the coating layer. Figure 2 It can be seen that the coating layer and the silicon-carbon material interface are tightly bonded with no obvious gaps or peeling, and the internal structure is uniform and free of pores. This proves that the stepwise coating process of this invention has successfully constructed a Li layer with uniform thickness and complete structure on the surface of silicon-carbon particles. + / Cu 2+ The bimetallic ion cross-linked three-dimensional network coating layer can effectively provide stable interface protection for silicon-carbon anodes.

[0075] Example 2: A method for preparing a coated and modified silicon-carbon anode material differs from Example 1 in that, in step 1, 0.14 g of lithium acetate is dissolved in 100 mL of pure water and stirred until completely dissolved to obtain a lithium acetate solution. 0.94 g of polygalacturonic acid is added to the above solution, and the mixture is stirred at 600 rpm for 12 hours at room temperature to obtain material B. Material A is the same as in Example 1.

[0076] Steps 2 through 4 are the same as in Example 1.

[0077] Example 3: A method for preparing a coated and modified silicon-carbon anode material differs from Example 1 in that, in step 1, 0.18 g of lithium acetate is dissolved in 100 mL of pure water and stirred until completely dissolved to obtain a lithium acetate solution. 0.94 g of polygalacturonic acid is added to the above solution, and the mixture is stirred at 600 rpm for 12 hours at room temperature to obtain material B. Material A is the same as in Example 1.

[0078] Steps 2 through 4 are the same as in Example 1.

[0079] Example 4: A method for preparing a coated and modified silicon-carbon anode material differs from Example 1 in that, in step 1, 1g of polyacrylic acid is added to 400mL of pure water, stirred and dissolved to prepare a PAA solution, and 0.25g of copper nitrate is added to the PAA solution. The mixture is stirred at 400rpm for 3 hours at room temperature to obtain material A. Material B is the same as in Example 1.

[0080] Steps 2 to 4 are the same as in Example 1, and the final coating thickness of the modified silicon-carbon anode material is 25 nm.

[0081] Example 5: A method for preparing a coated and modified silicon-carbon anode material includes the following steps: Step 1: Add 2g of polyacrylic acid to 400mL of pure water and stir to dissolve, preparing a PAA solution. Add 0.25g of copper nitrate to the PAA solution and stir at 500rpm for 2 hours at room temperature to obtain material A.

[0082] Dissolve 0.1 g of lithium acetate in 100 mL of pure water and stir until completely dissolved to obtain a lithium hydroxide solution. Add 0.5 g of polygalacturonic acid to the above solution and stir at 700 rpm for 8 hours at room temperature to obtain material B.

[0083] Step 2: Add 100g of spherical silicon carbide material to material A obtained in step 1, and stir at 400rpm for 2 hours at room temperature. Then, pour all of material B obtained in step 1 into the reaction system and stir at 400rpm for 4 hours to obtain a slurry.

[0084] Step 3: Filter the slurry obtained in Step 2, wash it three times with pure water, and then dry it in a forced-air drying oven at 60°C for 12 hours to ensure thorough drying and obtain the intermediate product.

[0085] Step 4: The intermediate product obtained in step 3 is placed in a nitrogen atmosphere and heated to 160°C for 4 hours to cure, thereby obtaining the coated and modified silicon-carbon anode material with a coating thickness of 15 nm.

[0086] Figure 3This is a TEM image of the silicon-carbon anode material prepared in Example 5. Figure 3 It can be seen that a continuous and dense coating layer with a thickness of about 15nm is uniformly grown on the surface of the spherical silicon-carbon material (the darker area on the left) (the brighter band in the middle). The coating layer is tightly bonded to the substrate interface without obvious gaps or peeling, and the internal structure is uniform without pores.

[0087] Example 6: A method for preparing a coated and modified silicon-carbon anode material includes the following steps: Step 1: Add 3g of polyacrylic acid to 400mL of pure water and stir to dissolve, preparing a PAA solution. Add 0.5g of copper nitrate to the PAA solution and stir at 600rpm for 2 hours at room temperature to obtain material A.

[0088] Dissolve 0.18 g of lithium acetate in 100 mL of pure water and stir until completely dissolved to obtain a lithium acetate solution. Add 3 g of polygalacturonic acid to the above solution and stir at 800 rpm for 8 hours at room temperature to obtain material B.

[0089] Step 2: Add 100g of spherical silicon carbide material to material A obtained in step 1, and stir at 600rpm for 2 hours at room temperature. Then, pour all of material B obtained in step 1 into the reaction system and stir at 600rpm for 0.5 hours to obtain a slurry.

[0090] Step 3: Filter the slurry obtained in Step 2, wash it three times with pure water, and then dry it in a forced-air drying oven at 70°C for 10 hours to ensure thorough drying and obtain the intermediate product.

[0091] Step 4: The intermediate product obtained in step 3 is placed in a nitrogen atmosphere and heated to 180°C for 2 hours to cure, thereby obtaining the coated and modified silicon-carbon anode material with a coating thickness of 60 nm.

[0092] Comparative Example 1: A method for preparing a coated and modified silicon-carbon anode material, which differs from Example 1 in that material A is used to coat spherical silicon-carbon material alone, and the preparation steps are as follows: Step 1: Material A was prepared in the same manner as in Example 1, but material B was not prepared.

[0093] Step 2: Add 100g of spherical silicon carbide material to material A obtained in step 1, and stir at 500rpm for 2 hours at room temperature to obtain a slurry.

[0094] Steps 3 to 4 are the same as in Example 1.

[0095] Comparative Example 2: A method for preparing a coated and modified silicon-carbon anode material, which differs from Example 1 in that material B is used to coat spherical silicon-carbon material alone. Step 1: Material B is prepared in the same manner as in Example 1, but material A is not prepared.

[0096] Step 2: Add 100g of spherical silicon carbide material to material B obtained in step 1, and stir at 500rpm for 2 hours at room temperature to obtain a slurry.

[0097] Steps 3 to 4 are the same as in Example 1.

[0098] Comparative Example 3: A method for preparing a coated and modified silicon-carbon anode material, which differs from Example 1 in that PGA is not added to coat the spherical silicon-carbon material, and the preparation steps are as follows: Step 1: Prepare material A in the same way as in Example 1; dissolve 0.1g of lithium acetate in 100mL of pure water and stir until completely dissolved to obtain a lithium acetate solution, which is material B.

[0099] Step 2: Add 100g of spherical silicon carbide material to material A obtained in step 1, and stir at 500rpm for 1 hour at room temperature. Then pour all of material B obtained in step 1 into the reaction system and continue stirring at 500rpm for 1 hour to obtain a slurry.

[0100] Steps 3 to 4 are the same as in the example.

[0101] Comparative Example 4: A method for preparing a coated and modified silicon-carbon anode material, which differs from Example 1 in that PAA is not added to coat the spherical silicon-carbon material, and the preparation steps are as follows: Step 1: Add 0.5g of copper nitrate to 400mL of pure water and stir at 400rpm for 1 hour at room temperature to obtain material A; the preparation of material B is the same as in Example 1.

[0102] Step 2: Add 100g of spherical silicon carbide material to material A obtained in step 1, and stir at 500rpm for 1 hour at room temperature. Then add all of material B obtained in step 1 to the reaction system and continue stirring at 500rpm for 1 hour to obtain a slurry.

[0103] Steps 3 to 4 are the same as in the example.

[0104] Comparative Example 5: A method for preparing a coated modified silicon-carbon anode material differs from Example 1 in that the PGA is not pre-lithiated. Specifically, in step 1, 0.94 g of polygalacturonic acid is added to 100 mL of pure water and stirred at 500 rpm for 12 hours at room temperature to obtain material B.

[0105] Steps 2 through 4 are the same as in Example 1.

[0106] Comparative Example 6: A method for preparing a coated and modified silicon-carbon anode material differs from Example 1 in that copper nitrate is not added to treat PAA. In step 1, 1g of polyacrylic acid (10% solid content) is added to 400mL of pure water, stirred and dissolved to prepare a PAA solution, which is material A.

[0107] Steps 2 through 4 are the same as in Example 1.

[0108] Comparative Example 7: A method for preparing a coated and modified silicon-carbon anode material differs from Example 1 in that copper nitrate is not added to treat the PAA, and lithium acetate is not added to treat the PGA. Specifically, in step 1, 1g of polyacrylic acid is added to 400mL of pure water and stirred to dissolve, preparing a PAA solution, which is material A. 0.94g of polygalacturonic acid is added to 100mL of pure water and stirred at 500rpm for 12 hours at room temperature until completely dispersed, preparing a PGA solution, which is material B.

[0109] Steps 2 through 4 are the same as in Example 1.

[0110] Comparative Example 8: A method for preparing a coated and modified silicon-carbon anode material includes the following steps: Step 1 is the same as in Example 1.

[0111] Step 2: Add 100g of spherical silicon carbide material to material B obtained in step 1, and stir at 500rpm for 1 hour at room temperature. Then pour all of material A obtained in step 1 into the reaction system and continue stirring at 500rpm for 1 hour to obtain a slurry.

[0112] Steps 3 to 4 are the same as in Example 1.

[0113] Comparative Example 9: A method for preparing a coated and modified silicon-carbon anode material includes the following steps: Step 1 is the same as in Example 1.

[0114] Step 2: Mix material A and material B, then stir at 500 rpm for 1 hour at room temperature. Then add 100g of spherical silicon carbide material to the mixed solution of material A and material B, and continue stirring at 500 rpm for 1 hour to obtain a slurry.

[0115] Steps 3 to 4 are the same as in Example 1.

[0116] Comparative Example 10: The spherical silicon-carbon material used in step 2 of Example 1 was used as a baseline control group, without any other treatment.

[0117] The negative electrode materials obtained in Examples 1-6 and Comparative Examples 1-10 were used to prepare electrodes and half-cells by the following methods, and their electrochemical performance was tested.

[0118] Using the silicon-based composite materials prepared in the examples and comparative examples as negative electrode active materials, negative electrode sheets were prepared respectively. The composition of the negative electrode sheets was: 90 wt% of active material, 5 wt% of binder SBR, 4.9 wt% of conductive agent SP, and 0.1 wt% of SWCNT.

[0119] The above negative electrode sheets were assembled into a half-cell: CR2032 coin cells were assembled in a glove box, using a lithium metal sheet as the counter electrode, a polypropylene microporous membrane as the separator, a mixture of PAA and CMC as the binder, and LiPF6 dissolved in a mixture of ethyl carbonate (EC) and diethyl carbonate (DEC) (volume ratio EC∶DEC=1∶1), with a LiPF6 concentration of 1 mol / L. The cells were charged and discharged at a rate of 0.1C between 0.05V and 1.5V using a LAND battery testing system.

[0120] The negative electrode sheet is prepared using conventional methods for CR2032 coin cells. After drying, the positive and negative electrode sheets, separator, battery casing, spring contacts, and gaskets are transferred to a glove box. The assembly sequence of the coin cell is as follows: positive electrode casing - positive electrode sheet - separator - lithium sheet - gasket - spring contact - negative electrode casing, stacked centrally from bottom to top. After pressure is applied by a sealing machine, a sealed standard coin cell is assembled.

[0121] The cycle capacity and initial efficiency tests were conducted as follows: After the CR2032 coin cell was left to stand for 6 hours, it was discharged at 0.1C to 0.005V, and the capacity was recorded as Q1; then it was discharged at a constant current of 0.02C to 0.005V as the cutoff point, and the capacity was recorded as Q2; after standing for 5 minutes, it was charged at a constant current of 0.1C to 1.5V, and the capacity was recorded as Q3 (initial lithium removal capacity); after standing for 5 minutes, it was discharged at a constant current of 1C to 0.05V, and the capacity was recorded as Q4. The initial coulombic efficiency at 1.5V = Q3 / (Q1+Q2)×100%; Capacity retention test: Three cells were taken, allowed to stand for 5 minutes, then discharged at 0.1C constant current and constant voltage to 0.005V, allowed to stand for 5 minutes, discharged at 0.02C to 0.005V, and charged at 0.1C constant current and constant voltage to 1.5V; allowed to stand for 5 minutes, then discharged at 0.25C to 0.005V; allowed to stand for 5 minutes, then charged at 0.25C constant current to 1.5V, and cycled 50 times at a rate of 0.25C. The specific capacity of the 50th cycle / the charging capacity of the 1st cycle × 100% was used to calculate the specific capacity retention rate. Powder resistivity test: After compacting the porous carbon material with a pressure of 4.0 MPa, the powder resistivity tester was used with ST2722-SD four-terminal method. Compacted density test: The test is conducted under 5T pressure. The weighed powder is loaded into the mold, and after holding the pressure at 5T for a period of time, the thickness of the compact is measured. Finally, the compacted density is calculated based on the mass, cross-sectional area and thickness. Trace element testing: Metal content was tested using ICP-OES.

[0122] Table 1. Performance of the negative electrode materials prepared in Examples 1-6 and Comparative Examples 1-10, and electrochemical performance of the batteries composed of them. As shown in Table 1, the Li obtained in Examples 1-6 + / Cu 2+ The silicon-carbon anode material coated with a three-dimensional network reinforced by bimetallic ion crosslinking exhibits high initial charge-discharge efficiency, capacity retention, and superior resistivity and compressive strength. In the lithium-ion battery test system, the initial reversible capacity of Example 1 reached over 1920.5 mA·h / g, and the initial coulombic efficiency reached 94%. The coating layers in Examples 1-6 can quickly compensate for the lithium ions consumed by the SEI film during the initial lithium insertion, reducing irreversible capacity loss. The synergistic effect of PGA and PAA also improves the compressive strength of the material itself and enhances cycle performance. Among them, Cu... 2+ The introduction of [a specific component] enhances electronic conductivity, compensating for the insufficient conductivity of PAA in the structure.

[0123] Comparing Example 1 and Comparative Example 1, Comparative Example 1 only uses PAA-Cu single-layer network coating without Li-PGA outer layer composite modification. The resistivity of the sample powder is slightly lower than that of Example 1. Its initial delithiation specific capacity, initial coulombic efficiency and 50-cycle capacity retention are all weaker than those of Example 1. This indicates that without the outer ion transport network of Li-PGA, the single coating layer has limited buffering capacity for expansion, and the electrode structure is prone to degradation during long cycles. This fully demonstrates the key role of Li-PGA composite coating in improving initial efficiency and cycle stability.

[0124] Comparing Example 1 and Comparative Example 2, Comparative Example 2 only used Li-PGA single coating and did not construct a PAA-Cu cross-linked framework; lacking the support structure formed by copper ion coordination, the coating layer could not effectively restrain the volume expansion of silicon carbon, the ion-electron synergistic conduction system was missing, and the delithiation specific capacity, cycle retention rate and structural stability were significantly different from Example 1, verifying the irreplaceable nature of the inner PAA-Cu network anchoring support.

[0125] Comparative Examples 1-2 show that a single PAA-Cu or Li-PGA coating layer cannot simultaneously meet the requirements of high conductivity and long-term cycling stability.

[0126] Comparing Example 1 and Comparative Example 3, Comparative Example 3 only added free lithium acetate solution and did not introduce PGA, so it could not construct a complete outer cross-linked network. Although it contained a certain amount of lithium, it lacked ion transport channels and hydrogen bond binding sites constructed by PGA, and the bimetallic synergistic cross-linked structure was missing. The specific capacity and capacity retention rate after 50 cycles of delithiation decreased significantly, proving that the PGA polymer framework is the core component for maintaining the multilayer network composite and stabilizing the electrode interface. The addition of lithium salt alone cannot achieve the multifunctional modification effect.

[0127] Comparing Example 1 and Comparative Example 4, Comparative Example 4 did not add PAA polymer, relying solely on the complexation of copper ions and Li-PGA, lacking the adhesion of PAA segments and sufficient carboxyl crosslinking sites; the sample powder resistivity was high, the electronic conduction network was incomplete, and the capacity retention rate after 50 cycles was only 51.3%, indicating significant attenuation. This suggests that PAA is not only a Cu... 2+ Coordination crosslinking provides reaction sites and can also adapt to silicon-based volume deformation, making it an important component of the synergistic coating system.

[0128] Example 1 was compared with Comparative Examples 5 and 6, respectively. Comparative Example 5 did not involve lithiation of PGA, and Comparative Example 6 did not involve Cu deposition of PAA. 2+ Coordination crosslinking. As shown in Table 1, Comparative Example 5 lacks Li... + The constructed ion transport channel exhibited a powder resistivity increased to 45.6 Ω·m, but its initial coulombic efficiency and cycle stability were significantly lower than those of Example 1. Comparative Example 6, lacking Cu... 2+ The cross-linked network, with insufficient mechanical strength of the coating layer, is prone to loosening and breakage, and its 50-turn capacity retention rate (65.4%) is far lower than that of Example 1 (74.9%). This indicates that Li alone... + Ion conduction network or Cu 2+ Cross-linked networks cannot achieve a synergistic improvement in overall performance. Only when both exist simultaneously and form a functionally complementary dual-network structure can the synergistic modification effect of ion-electron dual conduction be fully utilized.

[0129] Comparing Example 1 and Comparative Example 7, Comparative Example 7 did not undergo copper ion crosslinking or PGA pre-lithiation modification; it was simply a mixture of pure PAA and pure PGA for coating; it completely lacked Li. + / Cu 2+ The bimetallic crosslinking process resulted in a loose network structure and poor interfacial bonding, with a powder resistivity of 75.4 Ω·m. The first-effect, reversible capacity, and long-cycle stability were all significantly degraded, demonstrating that bimetallic synergistic crosslinking is the core key to achieving multifunctional integrated modification.

[0130] Comparing Example 1 and Comparative Example 8, Comparative Example 8 reversed the coating order, coating Li-PGA first and then composited with PAA-Cu solution. Changing the coating order alters the contact sequence with the electrolyte, resulting in some irreversible capacity loss and initial efficiency reduction. The carboxyl groups in the PAA-Cu network interact with Cu... 2+ After coordination, Li + Jumping migration along the polymer chain is suppressed, and its ionic conductivity is significantly lower than that of the Li-PGA network. When PAA-Cu is used as the outer layer, Li + After entering the coating layer from the electrolyte, the electrolyte must first pass through the low ionic conductivity PAA-Cu region before reaching the high ionic conductivity Li-PGA region, forming a bottleneck in ion transport and leading to increased polarization, decreased reversible capacity, and reduced cycle stability. However, when PAA-Cu is used as the inner layer and Li-PGA as the outer layer (Example 1), Li… + It can directly enter the Li-PGA network with high ionic conductivity to achieve rapid transport, while the PAA-Cu inner layer focuses on electron conduction and support functions. The two work together to improve the electrochemical performance of the battery.

[0131] Comparing Example 1 and Comparative Example 9, Comparative Example 9 mixed Material A and Material B before overall coating, causing disordered cross-linking of the two polymers and bimetallic ions in the liquid phase, which easily leads to gel aggregation and particle adhesion. The coating layer was uneven in thickness, ion transport channels were blocked, the three-dimensional network regularity was destroyed, and the mechanical properties and electrochemical stability of the sample decreased. The comparison proved that stepwise sequential coating can avoid the defects of premature cross-linking in the liquid phase and ensure uniform coating of single particles.

[0132] Comparative examples 7-9 further demonstrate that only when Cu 2+ With Li + Only by employing a specific stepwise process—PAA-Cu followed by Li-PGA—can a three-dimensional network structure with excellent ionic / electronic conductivity, structural stability, and high first-pass efficiency be constructed.

[0133] Comparing Example 1 and Comparative Example 10, Comparative Example 10 is a pristine spherical silicon-carbon material without any modification, with a powder resistivity as high as 125Ω. m, poor conductivity; low initial coulombic efficiency, with a capacity retention of only 37.6% after 50 cycles; high compressive strength, much higher than Example 1, with a high compaction density. However, this is due to the brittle breakage and rigid stacking of particles without a coating layer for buffering. The specific capacity after 50 cycles shows that Comparative Example 10 exhibits significant silicon volume expansion in actual cycling. Due to the lack of buffer space provided by the coating layer, the structure cannot suppress its repeated volume changes, leading to continuous rupture and regeneration of the SEI film and rapid capacity decay.

[0134] The above-described embodiments are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the technical scope of the present invention, based on the technical solution and concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A coated modified silicon-carbon negative electrode material, characterized in that, It includes a porous carbon framework, silicon, and a coating layer, wherein the silicon is distributed in the channels of the porous carbon framework, and the coating layer covers at least a portion of the surface of the particles formed by the porous carbon framework and the silicon. The coating layer comprises polyacrylic acid, polygalacturonic acid, Cu 2+ and Li + ; the carboxyl group of the polyacrylic acid and Cu 2+ are coordination cross-linked; the carboxyl group on the polygalacturonic acid and Li + are ionically cross-linked; the polyacrylic acid and the polygalacturonic acid are connected to each other by any one or both of physical cross-linking and chemical bonding.

2. The coating-modified silicon-carbon anode material of claim 1, wherein, The coating layer includes an inner region formed of polyacrylic acid-Cu 2+ and an outer region formed of polygalacturonic acid-Li + .

3. The coating-modified silicon-carbon anode material of claim 1 or 2, wherein The mass ratio of polyacrylic acid to polygalacturonic acid in the coating layer is (0.03~0.6):

1.

4. The coating-modified silicon-carbon anode material of claim 1, wherein, The coating layer in the modified silicon-carbon anode material has a mass percentage of 1wt% to 5wt% and a thickness of 20 to 200 nm.

5. The coating-modified silicon-carbon anode material of claim 1 or 2, wherein The porous carbon framework and the silicon form intermediate particles, the D50 of which is 3~15μm and the silicon content of which is 30wt%~70wt%.

6. A method for preparing a coated modified silicon-carbon negative electrode material, characterized in that, Includes the following steps: Step 1: Add polyacrylic acid and copper source to water and stir to obtain material A; add polygalacturonic acid and lithium source to water and stir to obtain material B; Step 2: Add intermediate particles to material A, stir and react to obtain slurry; Step 3: Add material B to the slurry, stir and react, then filter, wash and dry in sequence to obtain the intermediate product; Step 4: The intermediate product is heated and cured under a protective atmosphere to obtain the coated and modified silicon-carbon anode material; The intermediate particles consist of a porous carbon framework and silicon, with silicon distributed in the channels of the porous carbon framework.

7. The method for preparing the coated and modified silicon-carbon anode material as described in claim 6, characterized in that, In step 1, the lithium source is any one or more of lithium acetate, lithium hydroxide, lithium citrate, and lithium acrylate; the copper source is any one or more of copper nitrate, copper acetate, and copper chloride. The mass ratio of polyacrylic acid to copper source is 1:(0.1~0.5); the stirring speed of polyacrylic acid and copper source is 400~600 rpm; the stirring time is 2~4 h; The mass ratio of polygalacturonic acid to lithium source is 1:(0.3~0.8); the stirring rate of polygalacturonic acid and lithium source is 600~800 rpm, and the stirring time is 8~12 h; Material A contains 0.01wt% to 0.2wt% polyacrylic acid; Material B contains 0.5wt% to 2wt% polygalacturonic acid.

8. The method for preparing the coated and modified silicon-carbon anode material as described in claim 6 or 7, characterized in that, In steps 2 and 3, based on the proportion of raw materials, the mass ratio of intermediate particles, polyacrylic acid in material A, and polygalacturonic acid in material B is 100:(0.1~0.3):(0.5~3); the stirring speed is 400~600 rpm, and the stirring time is 1~2 hours. In step 3, the stirring speed is 400~600 rpm; the stirring time is 0.5~1 h; In step 4, the curing temperature is 150~180℃; the curing time is 2~4h.

9. A negative electrode sheet, characterized in that, It includes the silicon-carbon anode material as described in any one of claims 1 to 5, or the silicon-carbon anode material prepared by the preparation method described in any one of claims 6 to 8, a binder, and a conductive agent.

10. A battery, characterized in that, Includes the negative electrode sheet as described in claim 9.

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