Modified silicon-based negative electrode material and preparation method thereof, negative electrode plate and lithium ion battery

Abstract

The invention belongs to the technical field of lithium ion batteries, and particularly relates to a modified silicon-based negative electrode material, a preparation method thereof, a negative electrode plate and a lithium ion battery. Comprising a silicon-based inner core, a stress response buffer layer and a rigid mechanical protection layer from inside to outside in sequence, specifically, the stress response buffer layer wraps the surface of the silicon-based inner core, and the stress response buffer layer comprises a high-elasticity polymer matrix, a stress release functional unit and a conductive agent; and the rigid mechanical protection layer is coated on the surface of the stress response buffer layer. By constructing a three-layer core-shell structure of the silicon-based core / stress response buffer layer / rigid mechanical protection layer, repeated rupture of an SEI film caused by volume expansion of silicon particles is effectively inhibited without depending on an internal volume buffer space, and meanwhile, the SEI film has a self-repairing function, so that the cycling stability and the first-circle coulombic efficiency are remarkably improved.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery technology, and particularly relates to a modified silicon-based anode material and its preparation method, anode sheet and lithium-ion battery. Background Technology

[0002] Silicon, with a theoretical specific capacity of approximately 4200 mAh / g, is one of the most promising anode materials for next-generation high-energy-density lithium-ion batteries. However, during lithium insertion / extraction, silicon undergoes a volume change of over 300%, leading to problems such as particle pulverization, loss of electrical contacts, and repeated rupture and regeneration of the SEI film. This results in continuous electrolyte consumption, increased battery internal resistance, and a sharp decline in cycle life, severely limiting the practical application of silicon anodes.

[0003] To alleviate the aforementioned problems, various improvement methods have been proposed in existing technologies, such as constructing porous silicon structures, yolk-shell hollow structures, and using elastic binders. These methods, by reserving volume buffer space or introducing flexible components, reduce the mechanical stress caused by volume expansion to some extent, but often significantly reduce the electrode tap density, making it difficult to meet the volumetric energy density requirements of the battery. Meanwhile, traditional artificial SEI films mostly focus on the initial film formation process, improving the chemical stability of the SEI film by constructing inorganic / organic coatings. However, these artificial SEI films lack the ability to actively "sensitize" and "self-repair" interface cracks during cycling. Once the outer coating is torn or peeled off due to silicon volume expansion, the interface integrity is difficult to restore quickly, failing to fundamentally solve the cycling stability problem.

[0004] Therefore, developing an artificial SEI film structure that combines battery volumetric energy density with the ability to effectively adapt to silicon volume expansion and has reliable "self-healing" capability is key to realizing the practical application of high-capacity silicon anodes. Summary of the Invention

[0005] This invention provides a modified silicon-based anode material, its preparation method, an anode sheet, and a lithium-ion battery. By constructing a three-layer core-shell structure consisting of a silicon-based core, a stress-response buffer layer, and a rigid mechanical protective layer, the SEI film repeatedly ruptures due to silicon particle volume expansion without relying on internal volume buffer space, thereby significantly improving cycle stability and first-cycle coulombic efficiency. Furthermore, the invention incorporates scalable spray drying, solvent evaporation, and CVD / ALD processes, ensuring a controllable preparation process and enabling large-scale production.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] In a first aspect, this application provides a modified silicon-based anode material, comprising, from the inside out, a silicon-based core, a stress-response buffer layer, and a rigid mechanical protective layer, specifically:

[0008] The stress-response buffer layer is coated on the surface of the silicon-based core;

[0009] The rigid mechanical protective layer covers the surface of the stress-response buffer layer;

[0010] The Young's modulus E of the rigid mechanical protective layer shell With respect to the Young's modulus E of the stress-response buffer layer buffer Satisfying relation: E shell ≥10×E buffer .

[0011] It should be noted that the above Young's modulus relationship can form a mechanical gradient structure of "hard outer shell - soft inner layer", which on the one hand inhibits the overall breakage of particles, and on the other hand avoids interface debonding caused by direct contact between the overly hard coating and brittle silicon.

[0012] The stress-response buffer layer is a buffer layer with a nano-microcapsule structure or a supramolecular polymer network buffer layer with dynamic reversible bonds.

[0013] Preferably, the buffer layer with the nanocapsule structure comprises a highly elastic polymer matrix, nanocapsules, and a first conductive agent; preferably, the mass percentage of the highly elastic polymer matrix: nanocapsules: first conductive agent is 60-80:15-30:5-10.

[0014] It should be noted that the highly elastic polymer matrix of this application is a polymer capable of withstanding strain and maintaining structural integrity during cycling. The advantage of the nanocapsule structure is that, during cycling, when the local stress of the particles accumulates to the shell strength limit, the nanocapsule shell ruptures, and the internal repair agent is released near the crack and participates in in-situ film formation, rebuilding a stable SEI film.

[0015] Preferably, the supramolecular polymer network buffer layer with dynamic reversible bonds includes a dual-network DN monomer structure and a second conductive agent. Preferably, the mass ratio of the dual-network DN monomer to the second conductive agent is (10-15):1.

[0016] Preferably, the nanocapsules comprise an outer shell material and an inner encapsulated repair agent, and the nanocapsules have a particle size of 50-100 nm.

[0017] Preferably, the shell material is selected from one or more of urea-formaldehyde resin (UF), melamine-formaldehyde resin (MF), polyurethane, or polymethyl methacrylate, and the critical stress threshold for shell rupture is set to 0.5-2.0 GPa.

[0018] Preferably, the repair agent is selected from at least one of fluoroethylene carbonate (FEC), vinylene carbonate (VC), or hexamethyldisilazane (HMDS);

[0019] Preferably, the method for preparing the nanocapsules is as follows:

[0020] 1) Emulsification: The repair agent and emulsifier are added to deionized water and processed under a high-speed shear emulsifier to form a water-in-oil emulsion;

[0021] 2) Polymerization: The prepolymer of the shell material is added dropwise to the emulsion described in step 1), the pH value is adjusted, the temperature is raised to a certain temperature, and the mixture is stirred for a certain time.

[0022] 3) Purification: The product obtained in step 2) is washed with anhydrous ethanol 3-5 times, centrifuged, and dried in a vacuum drying oven to obtain nanocapsules.

[0023] Preferably, the supramolecular polymer network comprises dynamic reversible covalent bonds and / or reversible physical crosslinking bonds;

[0024] Preferably, the dynamically reversible covalent bond is selected from one or more of the following: disulfide bond -SS-, borate ester bond BO, or Diels-Alder addition bond;

[0025] Preferably, the reversible physical crosslinking bond is selected from hydrogen bonds or ionic bonds;

[0026] The dual-network DN monomer structure is polymerized from dual-network monomers, preferably a combination of acrylamide AM / sodium alginate SA, agar AG / gelatin, sodium alginate SA / polyvinyl alcohol PVA, and sodium alginate SA / agar AG.

[0027] It should be noted that when the silicon core generates stress during lithium insertion / extraction, its volume will repeatedly expand and contract. When the silicon core generates stress due to volume changes, the "dynamic reversible bonds" inside the material are mainly covalent bonds, supplemented by physical cross-linking bonds, which will actively "break or rearrange" to "dissipate" the energy brought by the stress. After the stress is eliminated (for example, after the charge-discharge cycle ends and the volume of the silicon core returns to stability), these broken bonds will reconnect and re-form a complete network structure, allowing the material to restore its original shape and properties.

[0028] Preferably, the highly elastic polymer matrix is ​​one or more of polyacrylic acid (PAA), lithium polyacrylate, sodium polyacrylate, polyacrylamide, and alginate.

[0029] Both the first conductive agent and the second conductive agent are conductive carbon black SuperP, carbon nanotubes (CNTs), or conductive carbon fibers, used to maintain the electron transport network inside the stress response buffer layer.

[0030] Preferably, the silicon-based core is one or more of nano-silicon, silicon suboxide, or silicon carbon composite particles, with a preferred particle size of 50nm-500nm.

[0031] Preferably, the rigid mechanical protective layer is composed of dense inorganic materials or high-modulus carbon materials;

[0032] Preferably, the high-modulus carbon material is amorphous carbon.

[0033] Preferably, the dense inorganic material is at least one selected from TiO2, Al2O3, LiF, Li3PO4, or ZrO2.

[0034] Preferably, the thickness of the rigid mechanical protective layer is 5-50 nm.

[0035] It should be noted that the rigid mechanical protective layer of this application has lattice defects or micropore channels that allow lithium ions to penetrate.

[0036] A second aspect of this application provides a method for preparing the modified silicon-based anode material described above, comprising the following steps:

[0037] Step 1, Buffer layer coating:

[0038] 1.1 The buffer layer with the nanocapsule structure was prepared in the following manner:

[0039] S1. Slurry preparation: Dissolve the highly elastic polymer matrix, nanocapsules, and first conductive agent with the silicon-based core material in deionized water;

[0040] S2. Dispersion: The mixture is processed using an ultrasonic cell disruptor and then dispersed in a planetary mixer to obtain a homogeneous slurry;

[0041] S3. Spray drying: The slurry described in step S2 is fed into a spray dryer with an inlet air temperature of 150-200℃ and an outlet air temperature of 60-100℃. A buffer layer with a silicon-based core nanocapsule structure is collected.

[0042] 1.2 The supramolecular polymer network buffer layer with dynamic reversible bonds was prepared using the following method:

[0043] S11. Dual-network DN precursor configuration

[0044] First, dissolve monomer A in water to obtain solution A; then dissolve monomer B in water together with the crosslinking agent and initiator to obtain solution B; finally, mix solution A and solution B at a volume ratio of 1:1 and stir until homogeneous to obtain a mixed solution.

[0045] S12. In-situ coating and crosslinking

[0046] S12.1 Introduction of silicon particles: The silicon-based core material is added to the mixed solution, and a second conductive agent is added simultaneously, followed by ultrasonic dispersion;

[0047] S12.2 First stage crosslinking: Stir the reaction at 50-70℃ for 1-4 hours to form a flexible network system containing –S–S– dynamic crosslinking points under the action of the disulfide bond crosslinking agent in step S12.1;

[0048] S12.3 Second stage crosslinking: Add an aqueous solution containing metal cations dropwise to the system in step S12.2 and coordinate crosslinking occurs to construct an "egg-box" rigid ionic network, which interpenetrates with the network in step S12.2 to form a double-network stress-response buffer layer, followed by drying treatment;

[0049] Step 2. Rigid layer construction: A rigid mechanical protective layer is deposited on the surface of the precursor using chemical vapor deposition (CVD) or atomic layer deposition (ALD) processes to obtain a core-shell structure silicon-based anode material with stress buffering, self-healing functions, and rigid mechanical protection.

[0050] A third aspect of this application provides a negative electrode sheet comprising the modified silicon-based negative electrode material described above. A fourth aspect of this application provides a lithium-ion battery comprising the negative electrode sheet described above.

[0051] Compared with the prior art, the beneficial effects of the present invention are:

[0052] The modified silicon-based anode material of this application achieves the dual functions of stress buffering and self-healing, as well as rigid mechanical protection, through a gradient core-shell structure design of "silicon-based core - stress-response buffer layer - rigid mechanical protection layer". Specifically: the stress-response buffer layer (inner layer) is similar to a "shock-absorbing airbag" or "repair glue". The rigid mechanical protection layer (outer layer) is similar to "armor", providing mechanical support and preventing electrolyte molecules from directly contacting the internal silicon, thus preventing continuous side reactions.

[0053] (1) By constructing a three-layer core-shell structure consisting of a stress response buffer layer and a rigid mechanical protection layer outside the silicon-based core, stress concentration caused by volume expansion is effectively reduced without adopting a large-volume buffer hollow structure, while taking into account both high tap density and high cycle stability.

[0054] (2) The introduction of nanocapsule repair units and / or supramolecular polymers with dynamic reversible bonds into the stress response buffer layer enables adaptive response to interface damage during cycling: when the local stress exceeds the set threshold, the nanocapsules rupture and release the repair agent, and rebuild the SEI film in situ at the crack; the dynamic reversible covalent bonds and reversible physical crosslinking bonds break or rearrange under stress and rebond after unloading, realizing the self-healing and energy dissipation of the buffer layer structure.

[0055] (3) The Young's modulus of the rigid mechanical protective layer is significantly higher than that of the buffer layer, forming an external "mechanical skeleton" that supports and constrains the inner structure during electrochemical cycling, preventing the overall pulverization of silicon particles and excessive wetting of electrolyte. At the same time, it ensures the reversible migration of lithium ions through lattice defects or micropore channels.

[0056] The core of the above structural design is to replace or strengthen the natural SEI film with a composite layer that combines flexible buffering and rigid protection. The middle stress-response buffer layer can absorb the volume expansion stress during silicon lithium intercalation, and at the same time, it has a self-healing function. The outer rigid mechanical protective layer can maintain structural stability. The two work together to suppress repeated rupture of the SEI film without relying on the internal large-volume buffer structure, thus ensuring volumetric energy density while improving cycle stability and first-cycle coulombic efficiency.

[0057] On the other hand, this application utilizes scalable processes such as spray drying, solvent evaporation, and CVD / ALD to prepare controllable, uniformly coated particles, achieving a composite core-shell silicon-based anode material with uniform structure and repeatable performance, suitable for large-scale production. Attached Figure Description

[0058] Figure 1 The following is a schematic diagram of the structure of the modified silicon-based anode material prepared in the embodiments of the present invention, showing the core-shell structure of the silicon-based core, stress response buffer layer and rigid mechanical protective layer;

[0059] Figure 2 : Schematic diagram of stress release and self-healing mechanism in charge-discharge cycle of an embodiment of the present invention;

[0060] Figure 3 : Comparison of cyclic performance between the embodiments and comparative examples in this invention;

[0061] Figure 4 Comparison of electrochemical impedance spectroscopy (EIS) evolution at different cycle numbers in the embodiments of this invention. Detailed Implementation

[0062] To enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings and preferred embodiments.

[0063] 1. Preparation of raw materials and equipment

[0064] The raw materials used in this application are: silicon-based cores made of nano-silicon powder (D50 = 100nm, purity 99.9%, provided by Shanghai Aladdin Biochemical Technology Co., Ltd.);

[0065] Nanocapsules: The shell is made of melamine-formaldehyde resin MF prepolymer (70% solid content, self-made);

[0066] Repair agent: Fluorinated ethylene carbonate (FEC, battery grade, purity ≥99.95%, Guangzhou Tinci Materials);

[0067] The dual-network DN monomers are acrylamide (AM) and sodium alginate (SA, low viscosity), which are polymerized to form polyacrylamide (PAM), and then combined with SA through ionic crosslinking to construct an "AM-SA" dual-network composite matrix.

[0068] Rigid layer precursors: trimethylaluminum (TMA) and titanium tetrachloride (TiCl4), wherein trimethylaluminum (TMA) is adapted to Al2O3 rigid layer and titanium tetrachloride (TiCl4) is adapted to TiO2 rigid layer.

[0069] The testing equipment used in this application includes: an electrochemical workstation (Solartron 1260A), a scanning electron microscope (Hitachi S-4800), and a nanoindenter (Hysitron TI 980).

[0070] Example 1: Microencapsulated stress-buffered composite silicon anode (Si@Capsule@TiO2)

[0071] S1. Synthesis of self-healing microcapsules

[0072] 1) Emulsification: Add 5.0g of repair agent FEC and 0.5g of emulsifier (sodium dodecylbenzenesulfonate) to 50mL of deionized water and treat for 10min at 10000rpm high-speed shear emulsifier to form a stable water-in-oil emulsion with an average particle size of 80nm.

[0073] 2) Polymerization: Add 10g of melamine-formaldehyde resin prepolymer dropwise to the above emulsion, adjust the pH value to 3.5 (using citric acid), and heat to 60℃ and stir for 4h.

[0074] 3) Purification: The product was washed three times with anhydrous ethanol, centrifuged, and dried in a vacuum drying oven at 40℃ for 12 hours to obtain nanocapsules containing FEC (MF-FEC). SEM showed that they were spherical with an average wall thickness of 10 nm.

[0075] S2. Buffer layer covering (constructing an inner soft layer)

[0076] 1) Slurry preparation: Dissolve 20g of nano-silica powder, 3.0g of MF-FEC nanocapsules, 1.0g of conductive carbon black SuperP, and 8.0g of polyacrylic acid (PAA, Mw≈450,000) in 150mL of deionized water. Based on the solid portion of the buffer layer (PAA, nanocapsules, and conductive agent), the mass ratio of PAA:nanocapsules:conductive agent = 4:1.5:0.5, corresponding to approximately 66.7wt%, 25wt%, and 8.3wt% respectively.

[0077] 2) Dispersion: The mixture was treated with an ultrasonic cell disruptor (600W) for 30 minutes, and then dispersed in a planetary mixer at 2000 rpm for 1 hour to obtain a uniform slurry.

[0078] 3) Spray drying: The slurry is fed into a spray dryer with an inlet air temperature of 180℃ and an outlet air temperature of 80℃, and Si@PAA-Capsule precursor powder is collected. The surface of the silicon particles is coated with a stress-response buffer layer composed of PAA matrix, MF-FEC microcapsules and conductive agent.

[0079] S3. Rigid shell construction (building an outer hard layer)

[0080] 1) ALD deposition: The Si@PAA-Capsule precursor was placed in the fluidized bed ALD reaction chamber at a reaction temperature of 100℃. TiCl4 and H2O were introduced sequentially. Each ALD cycle included: TiCl4 pulse for 0.5s / N2 purging for 20s / H2O pulse for 0.5s / N2 purging for 20s.

[0081] 2) Thickness control: Execute 100 ALD cycles to grow a dense, amorphous TiO2 rigid layer approximately 10 nm thick on the surface of the precursor particles, forming a Si@Capsule@TiO2 composite silicon-based anode material, where Si is the silicon-based core, Capsule is the stress-response buffer layer, and TiO2 is the rigid mechanical protection layer. For example... Figure 1 The diagram shows the structure of the modified silicon-based anode material. A schematic diagram illustrating the stress release and self-healing mechanism during charge-discharge cycles is shown below. Figure 2 As shown.

[0082] 3) Modulus determination: The buffer layer and TiO2 layer were tested separately using a nanoindenter. The results showed that E shell Approximately 5–10 GPa, E buffer Approximately 50–100 MPa, satisfying E shell ≥10×E buffer The relationship.

[0083] The modified silicon-based anode material prepared above is used to make anode sheets, which are then assembled with cathode sheets, separators, and electrolytes to form a lithium-ion battery.

[0084] Example 2: Dual-network self-healing composite silicon anode (Si@DN-Gel@Al2O3)

[0085] S1. Dual Network (DN) Precursor Configuration

[0086] 1) Solution A: Dissolve 2g of sodium alginate SA in 100mL of water to form a rigid ionic network framework.

[0087] 2) Solution B: Dissolve 5g of acrylamide AM monomer, 0.05g of N,N'-methylenebisacrylamide MBAA (crosslinking agent) and 0.01g of ammonium persulfate (initiator) in 50mL of water to form a flexible dynamic covalent network precursor.

[0088] 3) Mixing: Mix solution A and solution B at a volume ratio of 1:1 and stir until homogeneous.

[0089] S2. In-situ coating and crosslinking

[0090] 1) Introduction of silicon particles: Add 10g of nano-silicon powder to the above mixed solution, and add 0.6g of carbon nanotubes (CNTs) as a conductive agent. Disperse the mixture by ultrasonication for 30min to make the silicon particles uniformly suspended and surrounded by monomers / polymers.

[0091] 2) First stage crosslinking: The reaction is stirred at 60°C for 2 hours to initiate AM polymerization and form a PAM flexible network with –S–S– dynamic crosslinking points under the action of MBAA and disulfide crosslinking agent. This network tightly encapsulates the silicon particles.

[0092] 3) Second stage crosslinking: Add a 2wt% CaCl2 aqueous solution to the system dropwise. 2+ It coordinates and crosslinks with the carboxyl groups on SA to construct an "egg-box" type rigid ionic network, which interpenetrates with the PAM network to form a dual-network stress-response buffer layer.

[0093] 4) Drying treatment: The obtained gel system was freeze-dried for 24 hours to obtain Si@DN particles with a double network stress response buffer layer.

[0094] S3. External rigid carbon layer

[0095] 1) Low-temperature ALD coating: To avoid damaging the internal organic double network structure at high temperatures, a low-temperature atomic layer deposition (ALD) process is used. Si@DN particles are placed in a reaction chamber, and the temperature is set to 100℃.

[0096] 2) Precursors: Trimethylaluminum (TMA) and water (H2O) were used as precursors. Deposition: 80 cycles were performed to form a dense, rigid Al2O3 layer with a thickness of approximately 8 nm on the gel surface.

[0097] 3) Finished product: Si@DN-Gel@Al2O3 composite silicon-based anode material is obtained, wherein: Si is the silicon-based core, DN-Gel is the stress response buffer layer, and Al2O3 is the rigid mechanical protection layer.

[0098] Comparative Example 1 (lacking buffer layer): "Hard carbon coated silicon"

[0099] Preparation difference: Compared with Example 1, step S2 is omitted, and carbon is directly coated on the nano-silicon particles by CVD deposition in step S3 to form a closely contacted Si@C structure without internal buffer space.

[0100] Comparative Example 2 (lacking rigid layer): "Soft-coated silicon"

[0101] Preparation difference: Compared with Example 1, only steps S1 and S2 are performed to prepare Si@PAA-Capsule. The ALD deposition process in step S3 is omitted, and the material is used directly as the negative electrode.

[0102] Comparative Example 3 (non-core-shell structure, simple blending): "Traditional homogenization process"

[0103] Preparation difference: Compared with Example 1, spray drying granulation was not performed. Nano-silicon, nano-microcapsules, PAA binder, and conductive agent were directly physically mixed in a mixing tank to prepare the electrode slurry. The nano-microcapsules were randomly distributed within the electrode sheet, non-directionally coated on the surface of the silicon particles.

[0104] Comparative Example 4 (Standard buffer layer, no repair function):

[0105] Preparation difference: Compared with Example 1, in step S1, solid polystyrene (PS) nanospheres are used instead of "nanocapsules containing repair agents," while the remaining steps are the same as in Example 1. That is, it only provides physical buffering and has no chemical repair capability.

[0106] 2. Performance Testing:

[0107] Performance tests were conducted on the above embodiments and comparative examples, and the test results are shown in Table 1. The cycle performance comparison is shown below. Figure 3 As shown, the evolution of electrochemical impedance spectroscopy (EIS) under different cycle numbers is compared to... Figure 4 As shown.

[0108] Table 1. Performance Comparison of Examples and Comparative Examples

[0109]

[0110]

[0111] 3. Data Conclusion Analysis:

[0112] As can be seen from Table 1, the first-cycle coulombic efficiency and capacity retention of Examples 1 and 2 of the present invention are significantly better than those of the comparative examples, and the electrode thickness expansion rate is the lowest. SEI The growth rate was also significantly lower than that of the control group, indicating that the synergistic effect of the stress response buffer layer and the rigid mechanical protection layer can effectively suppress repeated rupture and ineffective thickening of the SEI film, and significantly improve the cycle stability of the silicon-based anode.

[0113] Comparative Example 1 shows that relying solely on the outer rigid shell cannot adequately mitigate the large volume expansion of silicon, and stress concentration easily leads to shell cracking and silicon particle pulverization. Comparative Example 2 shows that although the flexible buffer layer can partially buffer stress, the SEI continues to thicken and the electrode expansion rate is high due to the lack of mechanical constraints and electrolyte shielding. Comparative Example 3 shows that the non-core-shell simple blend structure is difficult to achieve stress management at the particle scale, and stress concentration and conductive network breakage are more severe. The comparison between Comparative Example 4 and Example 1 shows that, while maintaining similar buffering capacity, the introduction of microcapsules containing repair agents can significantly reduce the increase in interfacial impedance and improve the cycle retention rate, demonstrating the key role of self-healing function.

[0114] In summary, the modified silicon-based anode material of this application constructs a three-layer core-shell structure consisting of a stress-responsive buffer layer and a rigid mechanical protective layer outside the silicon-based core. In Example 1, the stress-responsive buffer layer is a buffer layer with a nano-microcapsule structure. The shell can cope with deformation and disperse stress. When the local stress of the particles accumulates to the shell's strength limit, the nano-microcapsule shell ruptures, and the internal repair agent is released near the crack and participates in in-situ film formation, rebuilding a stable SEI film. In Example 2, the stress-responsive buffer layer is a dual-network DN structure. Covalent cross-linking bonds are formed through polymerization between the dual-network monomers, resulting in a rigid-flexible interpenetrating network structure. When the silicon-based core generates stress due to volume changes, the "dynamically reversible bonds" inside the material are mainly covalent bonds, supplemented by physical cross-linking bonds, which actively "break or rearrange" to "dissipate" the energy brought by the stress. After the stress is eliminated, these broken bonds reconnect, reforming a complete network structure, allowing the material to restore its original shape and performance. The rigid mechanical protective layer has a higher Young's modulus than the stress-response buffer layer, used to maintain the overall morphological integrity of the particles, provide mechanical support, and prevent electrolyte molecules from directly contacting the internal silicon, thus preventing continuous side reactions. In the above embodiments, after 100 cycles at 0.5C, the volume expansion rate is no more than 20%, the coulombic efficiency in the first cycle is approximately 88–90%, the capacity retention after 100 cycles exceeds 90%, and the electrochemical impedance spectroscopy R0... SEI The growth rate is no greater than 0.005Ω / cycle, exhibiting excellent structural and interface stability.

[0115] The above description is merely an example of the embodiments of this application. It should be noted that, for those skilled in the art, various equivalent substitutions or modifications can be made to this invention without departing from the spirit and essence of this invention, and such equivalent substitutions or modifications should all fall within the protection scope of the claims of this invention.

Claims

1. A modified silicon-based anode material, characterized in that: It consists of, from the inside out, a silicon-based core, a stress-response buffer layer, and a rigid mechanical protective layer, specifically: The stress-response buffer layer is coated on the surface of the silicon-based core; The rigid mechanical protective layer covers the surface of the stress-response buffer layer; Young's modulus E of the rigid mechanical protective layer shell Young's modulus E of the stress-responsive buffer layer buffer satisfies the relationship: E shell ≥ 10 x E buffer .

2. The modified silicon-based anode material of claim 1, wherein, The stress-response buffer layer is a buffer layer with a nano-microcapsule structure or a supramolecular polymer network buffer layer with dynamic reversible bonds. Preferably, the buffer layer with the nanocapsule structure comprises a highly elastic polymer matrix, nanocapsules, and a first conductive agent; preferably, the mass percentage of the highly elastic polymer matrix: nanocapsules: first conductive agent is 60-80:15-30:5-10. Preferably, the supramolecular polymer network buffer layer with dynamic reversible bonds includes a dual-network DN monomer structure and a second conductive agent. Preferably, the mass ratio of the dual-network DN monomer to the second conductive agent is (10-15):

1.

3. The modified silicon-based anode material of claim 2, wherein, The nanocapsules comprise an outer shell material and an inner encapsulated repair agent, and the nanocapsule particle size is 50-100 nm. Preferably, the shell material is selected from one or more of urea-formaldehyde resin (UF), melamine-formaldehyde resin (MF), polyurethane, or polymethyl methacrylate, and the critical stress threshold for shell rupture is set to 0.5-2.0 GPa. Preferably, the repair agent is selected from at least one of fluoroethylene carbonate (FEC), vinylene carbonate (VC), or hexamethyldisilazane (HMDS); Preferably, the method for preparing the nanocapsules is as follows: 1) Emulsification: The repair agent and emulsifier are added to deionized water and processed under a high-speed shear emulsifier to form a water-in-oil emulsion; 2) Polymerization: The prepolymer of the shell material is added dropwise to the emulsion described in step 1), the pH value is adjusted, the temperature is raised to a certain temperature, and the mixture is stirred for a certain time. 3) Purification: The product obtained in step 2) is washed with anhydrous ethanol 3-5 times, centrifuged, and dried in a vacuum drying oven to obtain nanocapsules.

4. The modified silicon-based anode material of claim 2, wherein the carbon-based material is selected from the group consisting of graphite, graphene, carbon nanotubes, carbon nanoribbons, and combinations thereof. The supramolecular polymer network comprises dynamic reversible covalent bonds and / or reversible physical crosslinking bonds; Preferably, the dynamically reversible covalent bond is selected from one or more of the following: disulfide bond -SS-, borate ester bond BO, or Diels-Alder addition bond; Preferably, the reversible physical crosslinking bond is selected from hydrogen bonds or ionic bonds; The dual-network DN monomer structure is polymerized from dual-network monomers, preferably a combination of acrylamide AM / sodium alginate SA, agar AG / gelatin, sodium alginate SA / polyvinyl alcohol PVA, and sodium alginate SA / agar AG.

5. The modified silicon-based anode material according to claim 2, characterized in that, The highly elastic polymer matrix is ​​one or more of polyacrylic acid (PAA), lithium polyacrylate, sodium polyacrylate, polyacrylamide, and alginate. Both the first conductive agent and the second conductive agent are conductive carbon black SuperP, carbon nanotubes (CNTs), or conductive carbon fibers, used to maintain the electron transport network inside the stress response buffer layer.

6. The modified silicon-based anode material according to claim 1, characterized in that: The silicon-based core is one or more of nano-silicon, silicon suboxide, or silicon carbide composite particles, preferably with a particle size of 50nm-500nm.

7. The modified silicon-based anode material according to claim 1, characterized in that, The rigid mechanical protective layer is composed of dense inorganic materials or high-modulus carbon materials; Preferably, the high-modulus carbon material is amorphous carbon; Preferably, the dense inorganic material is at least one of TiO2, Al2O3, LiF, Li3PO4 or ZrO2; Preferably, the thickness of the rigid mechanical protective layer is 5-50 nm.

8. A method for preparing the modified silicon-based anode material according to any one of claims 1-7, comprising the following steps: Step 1: Buffer layer coating 1.1 The buffer layer with the nanocapsule structure was prepared in the following manner: S1. Slurry preparation: Dissolve the highly elastic polymer matrix, nanocapsules, and first conductive agent with the silicon-based core material in deionized water; S2. Dispersion: The mixture is processed using an ultrasonic cell disruptor and then dispersed in a planetary mixer to obtain a homogeneous slurry; S3. Spray drying: The slurry described in step S2 is fed into a spray dryer with an inlet air temperature of 150-200℃ and an outlet air temperature of 60-100℃. A buffer layer with a silicon-based core nanocapsule structure is collected. 1.2 The supramolecular polymer network buffer layer with dynamic reversible bonds was prepared using the following method: S11. Dual-network DN precursor configuration First, dissolve monomer A in water to obtain solution A; then dissolve monomer B in water together with the crosslinking agent and initiator to obtain solution B; finally, mix solution A and solution B at a volume ratio of 1:1 and stir until homogeneous to obtain a mixed solution. S12. In-situ coating and crosslinking S12.1 Introduction of silicon particles: The silicon-based core material is added to the mixed solution, and a second conductive agent is added simultaneously, followed by ultrasonic dispersion; S12.2 First stage crosslinking: Stir the reaction at 50-70℃ for 1-4 hours to form a flexible network system containing –S–S– dynamic crosslinking points under the action of the disulfide bond crosslinking agent in step S12.1; S12.3 Second stage crosslinking: Add an aqueous solution containing metal cations dropwise to the system in step S12.2 and coordinate crosslinking occurs to construct an "egg-box" rigid ionic network, which interpenetrates with the network in step S12.2 to form a double network stress response buffer layer, followed by drying treatment; Step 2: Construction of Rigid Layers A rigid mechanical protective layer is deposited on the surface of the precursor using chemical vapor deposition (CVD) or atomic layer deposition (ALD) processes to obtain a core-shell structure silicon-based anode material with stress buffering, self-healing functions, and rigid mechanical protection.

9. A negative electrode sheet, characterized in that, Includes the modified silicon-based anode material as described in any one of claims 1-7.

10. A lithium-ion battery comprising the negative electrode sheet as described in claim 9.

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