Coating modification method of negative electrode material, negative electrode material and application thereof

Abstract

The present application relates to the technical field of lithium ion battery negative electrode material, and particularly relates to a coating modification method of negative electrode material, the negative electrode material and application thereof, the negative electrode material comprising, from inside to outside, a silicon core, a gradient interface layer, a self-repairing elastic layer and a multi-stage pore carbon framework; the gradient interface layer is coated on the surface of the silicon core and comprises, from inside to outside, an amino silane coupling agent modification layer and a conductive polymer layer; the self-repairing elastic layer is coated on the outside of the gradient interface layer and contains a dynamic covalent bond crosslinking network; and the multi-stage pore carbon framework is coated on the outside of the self-repairing elastic layer, and through hydroxylation, amino silane coupling and in-situ polymerization of a conductive polymer, a strong bonding gradient interface layer is first constructed on the silicon core, then a reversible crosslinking network is formed outside the gradient interface layer based on Diels-Alder dynamic covalent bonds, in-situ crack repair is realized, and finally, biomass carbon and CVD carbon nanotubes are compounded to form a micropore / mesopore synergistic conductive buffer structure outside the reversible crosslinking network, thereby improving the cycle stability of the battery.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium ion battery negative electrode materials, in particular to a coating modification method of negative electrode materials, negative electrode materials and applications thereof. BACKGROUND

[0002] Silicon-based materials are considered as ideal negative electrode materials for the next generation of high-energy-density lithium ion batteries due to their high theoretical specific capacity (4200 mAh / g), but their volume expansion (>300%) during charging and discharging leads to particle pulverization, repeated rupture of the SEI film, and other problems. Existing carbon coating technologies (such as graphene, carbon nanotubes, etc.) can alleviate expansion, but have problems such as easy cracking of the coating layer and insufficient interfacial bonding between the coating layer and the silicon matrix.

[0003] For example, the Chinese patent application No. 202410352158.9 applied by Zhuhai Guanyu, specifically discloses "a silicon-carbon composite material, a negative electrode sheet, and a battery", which disperses silicon nanoparticles in the pore channels of a hierarchical porous carbon material and coats an amorphous carbon layer on the surface of the hierarchical porous carbon material to inhibit the aggregation of silicon nanoparticles through the pore structure. However, this patent technology still cannot achieve self-repair of the cracking of the coating layer.

[0004] Furthermore, the Chinese patent application No. 201910918320.8 applied by Bettery New Material Group Co., Ltd., specifically discloses "a composite negative electrode material, a preparation method thereof, and a lithium ion battery", which coats a carbon material layer on the silicon-containing material core to improve the cycle capacity retention rate and other performances. This is also a surface coating technology, but it cannot achieve self-repair of the cracking of the coating layer.

[0005] In addition, the Chinese patent application No. 202411153164.8 applied by Wanxiang 123 Company, specifically discloses "a metal nitride and porous carbon coated silicon negative electrode material, a preparation method and applications thereof", which mixes nano-silicon particles and a high-molecular compound carbon source, grinds and carbonizes to obtain a metal nitride and porous carbon coated silicon negative electrode material. This also cannot achieve self-repair of the cracking of the coating layer.

[0006] Therefore, there is an urgent need for a negative electrode material that can achieve self-repair of the cracking of the coating layer, thereby improving the cycle stability of the battery. SUMMARY

[0007] To solve the above problems, the application provides a coating modification method of a negative electrode material, the negative electrode material and application thereof, a strong combined gradient interface layer is first constructed on a silicon core through hydroxylation, amino silane coupling and in-situ polymerization of a conductive polymer, then a reversible cross-linking network is formed outside the gradient interface layer based on a Diels-Alder dynamic covalent bond, in-situ crack repair is realized, finally, a micro-porous / mesoporous synergistic conductive buffer structure is formed outside the reversible cross-linking network by using biomass carbon and CVD carbon nanotube compounding, and the cycle stability of the battery is further improved.

[0008] To achieve the above object, the application provides the following technical scheme.

[0009] A negative electrode material sequentially comprises, from inside to outside:

[0010] A silicon core, a gradient interface layer, a self-repairing elastic layer and a multi-level pore carbon framework.

[0011] The silicon core is a nano-silicon particle with a particle size of 50-200 nm.

[0012] The gradient interface layer is coated on the surface of the silicon core and sequentially comprises, from inside to outside, an amino silane coupling agent modification layer and a conductive polymer layer.

[0013] The self-repairing elastic layer is coated on the outside of the gradient interface layer and contains a dynamic covalent bond cross-linking network.

[0014] The multi-level pore carbon framework is coated on the outside of the self-repairing elastic layer and is composed of biomass carbon and gas-phase deposition carbon nanotube compounding, and the porosity is 50-70%.

[0015] Gradient interface layer: a gradient interface layer is constructed on the surface of the silicon particle through multi-step chemical modification to enhance the bonding force between the silicon and the carbon layer.

[0016] Self-repairing elastic layer: a polymer elastic layer containing a dynamic covalent bond is introduced to repair cracks through thermal or electrochemical stimulation in the cycle process.

[0017] Multi-level pore carbon framework: biomass-derived carbon and gas-phase deposition carbon are combined to form a multi-level pore structure, adapt to the volume expansion of silicon and improve the ion / electron transmission efficiency.

[0018] The total thickness of the gradient interface layer is 10-30 nm, the thickness of the amino silane modification layer is 2-5 nm, and the conductive polymer layer is polypyrrole with a thickness of 5-15 nm.

[0019] If the total thickness of the gradient interface layer is less than 10 mm, the gradient interface layer will be too thin to effectively transfer and disperse the mechanical stress generated by the expansion of silicon, which is easy to cause the cracking of the coating layer or the direct exposure of the silicon particles, and thus the repeated rupture of the SEI film.

[0020] The total thickness of the gradient interface layer is greater than 30 mm, which causes the gradient interface layer to be too thick, prolongs the lithium ion diffusion path, significantly increases the internal resistance, causes the rate performance to decrease, the thick interface layer increases the rigidity, reduces the adaptability to the silicon expansion, and instead accelerates the failure due to stress concentration.

[0021] The minimum thickness of the amino silane modification layer is 2 nm, which ensures that the silicon surface hydroxyl (-OH) and the amino silane (such as KH550) are fully reacted to form a dense Si-O-Si covalent bond network with a coverage of ≥95%;

[0022] If the thickness is less than 2 nm, the surface modification is incomplete, the interfacial binding energy decreases, and the measured shear strength decreases from 50 MPa to 30 MPa;

[0023] The maximum thickness is 5 nm, and the length of the amino silane molecular chain is about 1-2 nm. Multiple layer stacking may cause the molecular arrangement to be loose, thereby reducing the bonding strength, and a too thick amino silane layer will hinder the uniformity of the subsequent in-situ polymerization of the conductive polymer (PPy).

[0024] The minimum thickness of the conductive polymer layer is 5 nm, which forms a continuous conductive network, and the electronic conductivity of the silicon particle surface is increased from <10 -5 S / cm to ≥10² S / cm (four-probe test). If the thickness is less than 5 nm, the conductive path is discontinuous, which causes the polarization to increase (EIS shows that the charge transfer resistance Rct increases from 25 Ω to 50 Ω);

[0025] The maximum thickness is 15 nm, and the flexibility of PPy can buffer the initial stress of silicon expansion (the elastic modulus is about 1 GPa), but a too thick layer will reduce the elasticity of the overall interface layer and occupy too much thickness budget (the total thickness needs to be ≤30 nm).

[0026] In addition, the dynamic covalent bond is a reversible crosslinking structure formed by Diels-Alder reaction, which is composed of a polyurethane prepolymer containing furan groups and a bismaleimide crosslinking agent, and the distance between the crosslinking points is 2-5 nm. The furan group (Dienes) acts as an electron donor (such as the furan side group in the polyurethane segment), and the maleimide group (Dienophiles) acts as an electron acceptor (such as the bismaleimide crosslinking agent).

[0027] Reversibility of Diels-Alder reaction

[0028] 1. Forward reaction (low temperature):

[0029] At a lower temperature (<60°C), the furan group (diene) and the maleimide group (dienophile) undergo DA addition reaction to form a six-membered ring covalent bond (DA adduct), which constructs a crosslinking network.

[0030] Chemical formula: Furan + Maleimide DA Adduct

[0031] 2. Reverse reaction (high temperature):

[0032] When the temperature rises to 60-100℃, the DA adduct undergoes a retro-DA reaction, the covalent bond breaks, and the cross-linked network temporarily dissociates, and the material exhibits fluidity.

[0033] Chemical formula: DA Adduct Furan + Maleimide

[0034] Specifically, silicon expands in volume during charging and discharging (such as lithium intercalation expansion), causing local stress concentration in the elastic layer and generating microcracks. Internal heat is generated during battery cycling (40-60℃), and the local temperature reaches the threshold of the retro-DA reaction (such as 60℃). The DA adduct at the crack site dissociates, the cross-linking point temporarily breaks, the material fluidity increases, the broken molecular chains (containing furan / maleimide groups) diffuse to the crack area driven by heat, filling the crack gap, and the temperature slightly drops (such as the temperature falls to <60℃ after stopping charging and discharging), and the DA reaction occurs again, forming new covalent bonds at the crack interface, achieving in-situ repair.

[0035] The self-repairing elastic layer is preferably 20-50 nm thick. The self-repairing elastic layer needs to absorb expansion stress through deformation to prevent stress from being transmitted to the outer carbon skeleton, causing cracking. The elastic modulus (about 0.5-1 GPa) and thickness work together. If the thickness is too thin (<20 nm), the modulus is insufficient and is easily broken by silicon expansion; if the thickness is too thick (>50 nm), the rigidity increases and the cushioning ability is lost.

[0036] Moreover, when the self-repairing elastic layer is less than 20 nm thick, the dynamic bond density is insufficient (the cross-linking point spacing is greater than 5 nm), and the repair efficiency is significantly reduced (<70%); when the thickness is greater than or equal to 20 nm, the cross-linking point spacing is less than or equal to 5 nm, and the repair efficiency is greater than or equal to 90%.

[0037] If the self-repairing elastic layer is too thick (>50 nm), it will prolong the Li⁺ diffusion path, causing the ionic conductivity to decrease (from 10 -4 S / cm to 10 -5 S / cm) and the internal resistance to increase (Rct from 25Ω to 60Ω).

[0038] In addition, in the multi-level pore carbon skeleton, the biomass carbon is a porous carbon formed by carbonization of sodium lignosulfonate, with micropores of <2 nm and mesopores of 2-50 nm; the length of the vapor-deposited carbon nanotubes is 1-5 μm, and the density is ≥104 tubes / μm².

[0039] Biomass carbon is porous carbon formed by the carbonization of sodium lignosulfonate. Micropores buffer expansion, mesopores promote electrolyte wetting and ion transport, and vapor-deposited carbon nanotubes form a continuous conductive network, reducing the internal resistance of the electrode.

[0040] The present invention also provides a method for modifying the above-described negative electrode material by coating, comprising the following steps:

[0041] Step a, Gradient interface treatment of silicon particles:

[0042] a1. Hydroxylating silicon particles in a mixture of concentrated sulfuric acid and hydrogen peroxide enhances the dispersibility of silicon particles, prevents agglomeration, and lays a chemical foundation for subsequent silane coupling agent modification.

[0043] a2. Modification in an ethanol solution of an aminosilane coupling agent forms an amino functional layer, which enhances the interfacial bonding energy and inhibits the peeling of silicon and carbon layers due to expansion stress. At the same time, amino groups can serve as polymerization initiation sites for conductive polymers (such as polypyrrole).

[0044] a3. By in-situ polymerization to coat the silicon surface with a polypyrrole layer, the conductivity of PPy (approximately 100 S / cm) improves the electron transport efficiency of silicon particles, and its flexibility buffers part of the volume expansion stress.

[0045] Step b, self-healing elastic layer coating:

[0046] b1. A polyurethane prepolymer containing furan groups is mixed with a bismaleimide crosslinking agent, and a dynamic covalent elastomer is prepared by Diels-Alder reaction. The dynamic covalent elastomer can spontaneously repair cracks at the battery operating temperature (40-60℃), maintain the integrity of the coating layer, and avoid continuous decomposition of the electrolyte.

[0047] b2. Spin-coating the elastomer solution onto the surface of silicon particles after gradient interface treatment, and curing to form a 20-50 nm thick self-healing elastic layer. The self-healing elastic layer (20-50 nm thick) provides mechanical buffering, disperses silicon expansion stress to the carbon skeleton, and inhibits particle pulverization.

[0048] Step c, Construction of a multi-level porous carbon framework:

[0049] c1. Silicon particles coated with an elastic layer are mixed with a sodium lignosulfonate solution and spray-dried to form a precursor. The porosity (50-70%) of the biomass carbon provides a buffer space for volume expansion, while its surface functional groups (such as -SO3) - Enhance electrolyte wettability;

[0050] c2. Carbonization is carried out in an argon atmosphere with a gradient temperature increase to 800℃ to form a porous carbon framework. The conductivity of the carbon framework is approximately 10. 2Simultaneous improvement in S / m and mechanical strength (elastic modulus of approximately 10 GPa), nitrogen doping enhances lithium-ion diffusion kinetics;

[0051] c3. Carbon nanotube networks (CNTs) are grown on the surface of a carbon framework by chemical vapor deposition (CVD). The CNT network (1-5 μm in length) reduces the internal resistance of the electrode and improves the capacity retention to ≥80% at 5C rate.

[0052] In step a, the hydroxylation treatment uses a mixture of concentrated sulfuric acid and hydrogen peroxide in a volume ratio of 3:1, and is ultrasonically treated for 30-60 minutes. The mixture of concentrated sulfuric acid (H2SO4) and hydrogen peroxide (H2O2) (such as piranha solution) has strong oxidizing properties and can oxidize the silicon surface to generate Si-OH bonds, forming a hydrophilic surface.

[0053] Furthermore, in step b, the spin coating process has a rotation speed of 2000-5000 rpm, a curing temperature of 60-80℃, and a curing time of 1-2 hours.

[0054] In addition, in step c, the carbon source for chemical vapor deposition is acetylene, the deposition temperature is 600-800℃, and the deposition time is 10-30 minutes.

[0055] The present invention also provides an application of the above-described negative electrode material, which is used as a negative electrode active material in a lithium-ion battery.

[0056] The beneficial effects of this invention are as follows:

[0057] (1) The present invention enhances the bonding force between silicon and carbon layers through gradient interface design, and the self-healing elastic layer (Diels-Alder dynamic covalent bond) can spontaneously repair cracks at the battery operating temperature (40-60℃), with a crack closure rate ≥90% and a mechanical recovery rate ≥85%;

[0058] (2) This invention significantly improves the cycle stability (capacity retention ≥ 90% after 500 cycles under 1C charge-discharge conditions) and rate performance (5C capacity ≥ 2500 mAh / g) of silicon-based anodes through the synergistic effect of gradient interface design (hydroxylation → aminosilane coupling → conductive polymer), self-healing elastic layer (Diels-Alder dynamic covalent bond) and multi-level porous carbon skeleton (biomass carbon + CVD-CNT).

[0059] In summary, this invention offers advantages such as a synergistic solution to silicon expansion from the atomic-level interface to the macroscopic structure, while also considering conductivity and cycle life, demonstrating significant technological breakthroughs. It is particularly suitable for the field of coating modification technology for anode materials. Attached Figure Description

[0060] Figure 1This is a SEM image of the negative electrode material in Embodiment 1 of the invention;

[0061] Figure 2 This is a schematic diagram of the modification method in Embodiment 2 of the present invention;

[0062] Figure 3 SEM image of the negative electrode material before repair in Example 1 of this invention;

[0063] Figure 4 Here is a SEM image of the anode material after repair in Example 1 of this invention;

[0064] Figure 5 SEM images of the anode material prepared in Example 3 of this invention before repair;

[0065] Figure 6 SEM images of the three negative electrode materials prepared in this invention after repair;

[0066] Figure 7 SEM image of the negative electrode material before repair in Example 6 of this invention;

[0067] Figure 8 SEM image of the negative electrode material after repair in Example 6 of this invention. Detailed Implementation

[0068] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0069] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," and "counterclockwise," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0070] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0071] Example 1:

[0072] like Figure 1 As shown, a negative electrode material comprises, from the inside out:

[0073] Silicon core, gradient interface layer, self-healing elastic layer and multi-level porous carbon skeleton;

[0074] The silicon core consists of nano-sized silicon particles with a diameter of 50-200 nm;

[0075] A gradient interface layer is coated on the surface of the silicon core, consisting of an aminosilane coupling agent modification layer and a conductive polymer layer from the inside out.

[0076] A self-healing elastic layer is coated on the outside of the gradient interface layer, containing a dynamic covalent bond cross-linking network;

[0077] A multi-level porous carbon framework is coated on the outside of the self-healing elastic layer. It is composed of biomass carbon and vapor-deposited carbon nanotubes, with a porosity of 50-70%.

[0078] The gradient interface layer has a total thickness of 10-30 nm, the aminosilane modified layer has a thickness of 2-5 nm, and the conductive polymer layer is polypyrrole with a thickness of 5-15 nm.

[0079] Furthermore, the dynamic covalent bond is a reversible cross-linked structure formed by the Diels-Alder reaction, consisting of a polyurethane prepolymer containing furan groups and a bismaleimide cross-linking agent, with a cross-linking point spacing of 2-5 nm.

[0080] Furthermore, in the hierarchical porous carbon framework, the biomass carbon is porous carbon formed by the carbonization of sodium lignosulfonate, with a pore size distribution of micropores <2nm and mesopores 2-50nm; the vapor-deposited carbon nanotubes have a length of 1-5μm and a density ≥10. 4 With tubes / μm², lignin replaces traditional graphite, reducing raw material costs by more than 30% and carbon emissions by 50%.

[0081] First and foremost, it is worth emphasizing that the -NH2 group of aminosilane forms hydrogen bonds with the furan group in the elastic layer, enhancing the adhesion between the elastic layer and the silicon core and forming an interface anchor. At the same time, the flexible-rigid gradient transition of the gradient interface layer (PPy + coupling agent) prevents the elastic layer from failing prematurely due to stress concentration, achieving a synergistic effect where the interface peeling area is reduced from 30% to <5% after 500 battery cycles.

[0082] Furthermore, it is important to emphasize that the elastic layer repairs microcracks, prevents cracks from propagating to the carbon skeleton, and maintains the integrity of the pore structure. At the same time, the flexibility of the elastic layer complements the rigidity of the carbon skeleton, forming a "rigid-flexible" composite structure (the overall elastic modulus is about 5 GPa), achieving a synergistic effect of improving the porosity utilization of the carbon skeleton and increasing the 5C capacity by 40% (compared to the design without an elastic layer).

[0083] Furthermore, it should be emphasized that the CNT network connects to the PPy conductive layer, forming a "point-line-surface" conductive path that runs through the electrode, increasing the electronic conductivity from 10. -5 S / cm increased to 10 2 S / cm, and the hierarchical channels shorten the Li⁺ diffusion path, increasing the ion diffusion coefficient from 10 -14 cm² / s increased to 10 -12 The efficiency is cm² / s, achieving a synergistic effect of reduced electrode polarization (ΔV≤0.1 V) and increased coulombic efficiency to ≥99.5%.

[0084] Example 2:

[0085] like Figure 2 As shown, a method for modifying the negative electrode material described in Example 1 by coating includes the following steps:

[0086] Step a, Gradient interface treatment of silicon particles:

[0087] a1. Hydroxylating silicon particles in a mixture of concentrated sulfuric acid and hydrogen peroxide;

[0088] a2. Modification in an ethanol solution of an aminosilane coupling agent to form an amino functional layer;

[0089] a3. Coating a polypyrrole layer onto the silicon surface via in-situ polymerization;

[0090] Step b, self-healing elastic layer coating:

[0091] b1. A dynamic covalent elastomer is prepared by mixing a polyurethane prepolymer containing furan groups with a bismaleimide crosslinking agent and then reacting the mixture via a Diels-Alder reaction.

[0092] b2. Spin-coat the elastomer solution onto the surface of silicon particles after gradient interface treatment, and cure to form a self-healing elastic layer.

[0093] Step c, Construction of a multi-level porous carbon framework:

[0094] c1. Mix the silicon particles coated with the elastic layer with a sodium lignosulfonate solution and spray dry to form a precursor;

[0095] c2. Carbonization is carried out in an argon atmosphere by gradient heating to 800℃ to form a porous carbon framework.

[0096] c3. Carbon nanotube networks are grown on the surface of a carbon framework by chemical vapor deposition.

[0097] In step a, the hydroxylation treatment uses a mixture of concentrated sulfuric acid and hydrogen peroxide in a volume ratio of 3:1, and is ultrasonically treated for 30-60 minutes.

[0098] The -Si-OH introduced by hydroxylation on the silicon core surface forms Si-O-Si covalent bonds with aminosilanes (such as KH550) (bond energy is about 450 kJ / mol), increasing the interfacial bonding strength to ≥50 MPa (compared to only about 5 MPa for traditional physical adsorption). At the same time, the amino group (-NH2) serves as the polymerization initiation site for the conductive polymer (PPy), ensuring continuous coating of the PPy layer. Furthermore, the dispersibility of the hydroxylated silicon particles in solution is improved, avoiding local stress concentration caused by agglomeration.

[0099] Furthermore, in step b, the spin coating process has a rotation speed of 2000-5000 rpm, a curing temperature of 60-80℃, and a curing time of 1-2 hours.

[0100] Based on Diels-Alder dynamic covalent bonds, a crack closure rate of ≥90% is achieved at 40-80℃, suppressing repeated rupture of the SEI film; the elastic modulus (approximately 0.5-1 GPa) matches the silicon expansion stress, dispersing mechanical impact; and the self-healing temperature window overlaps with the battery operating temperature (40-60℃), requiring no external intervention.

[0101] In addition, in step c, the carbon source for chemical vapor deposition is acetylene, the deposition temperature is 600-800℃, and the deposition time is 10-30 minutes.

[0102] The micropores (<2nm) and mesopores (2-50nm) of biomass carbon provide hierarchical buffer space, reducing the expansion rate from 300% to ≤120%; CVD-CNTs (density ≥10 4 The tubes / μm² reduce the internal resistance of the electrode (Rct≤25 Ω) and improve the rate performance (5C capacity≥2500mAh / g); the carbon skeleton has an elastic modulus≥10GPa to support silicon particles and prevent pulverization.

[0103] Example 3:

[0104] An application of the negative electrode material described in Example 1, wherein the negative electrode material is used as a negative electrode active material in a lithium-ion battery.

[0105] The prepared lithium battery exhibits a capacity retention rate of ≥90% after 500 cycles under 1C charge-discharge conditions, which is +28% higher than that of traditional silicon materials. The silicon volume expansion rate is ≤120%, the 5C rate capacity is ≥2500 mAh / g, the self-healing efficiency is ≥90%, and the interface bonding strength is ≥50 MPa.

[0106] Preparation Example 1:

[0107] Using 100 nm diameter silicon nanoparticles as the silicon core, and following the preparation method of Example 2, an interface layer with a total thickness of 10 nm (PPy 7 nm + aminosilane modification layer 3 nm), a self-healing elastic layer with a thickness of 30 nm, a crosslinking point spacing of 3 nm, a multi-level porous carbon framework with a porosity of 60%, and a CNT density of 1.2 × 10⁻⁶ was prepared. 4 Anode material with tubes / μm².

[0108] Preparation Example 2:

[0109] Using 50 nm silicon nanoparticles as the silicon core, and following the preparation method of Example 2, an interface layer with a total thickness of 7 nm (PPy 5 nm + aminosilane modification layer 2 nm), a self-healing elastic layer with a thickness of 20 nm, a crosslinking point spacing of 2 nm, a multi-level porous carbon framework with a porosity of 70%, and a CNT density of 1.5 × 10⁻⁶ was prepared. 4 Anode material with tubes / μm².

[0110] Preparation Example 3:

[0111] Using 200 nm diameter silicon nanoparticles as the silicon core, and following the preparation method of Example 2, an interface layer with a total thickness of 20 nm (PPy 15 nm + aminosilane modification layer 5 nm), a self-healing elastic layer with a thickness of 50 nm, a crosslinking point spacing of 5 nm, a multi-level porous carbon framework with a porosity of 50%, and a CNT density of 1.0 × 10⁻⁶ was prepared. 4 Anode material with tubes / μm².

[0112] Preparation Example 4:

[0113] Using 150 nm diameter silicon nanoparticles as the silicon core, and following the preparation method of Example 2, an interface layer with a total thickness of 15 nm (PPy 11 nm + aminosilane modification layer 4 nm), a self-healing elastic layer with a thickness of 40 nm, a crosslinking point spacing of 4 nm, a multi-level porous carbon framework with a porosity of 65%, and a CNT density of 1.3 × 10⁻⁶ was prepared. 4 Anode material with tubes / μm².

[0114] Preparation Example 5:

[0115] Using 80 nm silicon nanoparticles as the silicon core, and following the preparation method of Example 2, an interface layer with a total thickness of 12 nm (PPy 9 nm + aminosilane modification layer 3 nm), a self-healing elastic layer with a thickness of 25 nm, a crosslinking point spacing of 3 nm, a multi-level porous carbon framework with a porosity of 55%, and a CNT density of 1.1 × 10⁻⁶ was prepared. 4 Anode material with tubes / μm².

[0116] Preparation Example 6:

[0117] Using 50 nm diameter silicon nanoparticles as the silicon core, and following the preparation method of Example 2, an interface layer with a total thickness of 7 nm (PPy 5 nm + aminosilane modification layer 2 nm), a self-healing elastic layer with a thickness of 20 nm, a crosslinking point spacing of 2 nm, a multi-level porous carbon framework with a porosity of 70%, and a CNT density of 2.0 × 10⁻⁶ was prepared. 4 Anode material with tubes / μm².

[0118] Preparation Example 7:

[0119] Using 200 nm diameter silicon nanoparticles as the silicon core, and following the preparation method of Example 2, an interface layer with a total thickness of 20 nm (PPy 15 nm + aminosilane modification layer 5 nm), a self-healing elastic layer with a thickness of 50 nm, a crosslinking point spacing of 5 nm, a multi-level porous carbon framework with a porosity of 50%, and a CNT density of 2.0 × 10⁻⁶ was prepared. 4 Anode material with tubes / μm².

[0120] Comparative Example 1:

[0121] Using 100 nm diameter silicon nanoparticles as the silicon core, and following the preparation method of Example 2, a 15 nm PPy layer without amino silane modification, a 30 nm thick self-healing elastic layer, a hierarchical porous carbon framework with a porosity of 60%, and a CNT density of 1.2 × 10⁻⁶ were prepared. 4 Anode material with tubes / μm².

[0122] Comparative Example 2:

[0123] Using 50 nm diameter silicon nanoparticles as the silicon core, and following the preparation method of Example 2, an interface layer with a total thickness of 7 nm, no self-healing elastic layer thickness, a hierarchical porous carbon framework with a porosity of 70%, and a CNT density of 2.0 × 10⁻⁶ was prepared. 4 Anode material with tubes / μm².

[0124] Comparative Example 3:

[0125] Using 200 nm diameter silicon nanoparticles as the silicon core, and following the preparation method of Example 2, an interface layer with a total thickness of 20 nm (PPy 15 nm + aminosilane modification layer 5 nm), a self-healing elastic layer with a thickness of 50 nm, a crosslinking point spacing of 5 nm, a multi-level porous carbon framework with a porosity of 40%, and a CNT density of 0.5 × 10⁻⁶ was prepared. 4 Anode material with tubes / μm².

[0126] For Preparation Examples 1-7 and Comparative Examples 1-3, the capacity retention rate after 500 cycles under 1C charge-discharge conditions was tested sequentially using existing electrode fabrication, battery assembly, and battery testing methods. The test results are shown in Table 1 below:

[0127] Table 1

[0128]

[0129] By comparing the preparation examples 1-7 with the comparative examples 1-3, it can be seen that the capacity retention rates of examples 1-7 are significantly higher than those of the comparative examples, reflecting the synergistic effect of the gradient interface layer, elastic layer and carbon skeleton. Among them, example 6 has the best capacity retention performance due to the high porosity and high CNT density compensating thin interface layer; comparative example 2 has the worst performance due to the lack of self-healing mechanism.

[0130] The expansion rates of Examples 1-7 were ≤115%, while those of the comparative examples were ≥200%, demonstrating the synergistic buffering effect of the multi-level carbon skeleton (porosity ≥50%) and the elastic layer. Examples 2 (85%) and 6 (80%) showed the best expansion suppression due to their high porosity and small particle size silicon.

[0131] Examples 1-7 exhibit a 5C capacity ≥2200mAh / g, significantly higher than the comparative examples (≤1800mAh / g), thanks to the CNT network (density ≥10). 4 The synergy of the CNT density ( / μm²) and the PPy conductive layer, in particular, Example 6 (2900 mAh / g) is due to its ultra-high CNT density (2×10⁻⁶ / μm²). 4 Achieve optimal rate performance ( / μm²).

[0132] like Figures 3 to 8 As shown, the repair efficiency of Examples 1-7 is ≥82%, while Comparative Example 1 cannot trigger repair due to interface peeling, Comparative Example 2 has no repair capability, and Example 6 (96%) achieves the ultimate repair efficiency due to high dynamic bond density (crosslinking spacing 2 nm).

[0133] In summary, the problems of interface delamination and electron transport are solved by chemical bonding (Si-O-Si) and conductive networks (PPy). Dynamic covalent bonds (DA reaction) enable in-situ crack repair, buffer expansion stress, micropores buffer expansion, mesopores accelerate ion transport, and CNTs enhance conductivity. Furthermore, Example 6 demonstrates that structural optimization (high porosity + high CNT density) can overcome thickness limitations and achieve optimal performance. Even with parameter degradation as in Example 7, it is still significantly superior to traditional silicon-carbon materials (compared to Example 3). Moreover, compared to Example 1, interface delamination leads to a precipitous drop in capacity, proving the necessity of chemical bonding. Compared to Example 2, uncontrolled crack propagation highlights the core role of dynamic bonds. Compared to Example 3, stress concentration and poor conductivity verify the irreplaceable nature of the multi-level structure.

[0134] Therefore, this technical solution successfully solves the three major problems of volume expansion, interface peeling and poor conductivity of silicon-based anodes through the synergistic innovative design of gradient interface layer, self-healing elastic layer and multi-level carbon skeleton, fully verifying the creativity, novelty and practicality of the solution, and providing technical support for the industrialization of high energy density lithium-ion batteries.

[0135] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A negative electrode material, characterized in that, From the inside out, the following are included: Silicon core, gradient interface layer, self-healing elastic layer and multi-level porous carbon skeleton; The silicon core consists of nano-sized silicon particles with a diameter of 50-200 nm; A gradient interface layer is coated on the surface of the silicon core, consisting of an aminosilane coupling agent modification layer and a conductive polymer layer from the inside out. The self-healing elastic layer is coated on the outside of the gradient interface layer and contains a dynamic covalent cross-linking network. The dynamic covalent bond is a reversible cross-linking structure formed by the Diels-Alder reaction. It is composed of a polyurethane prepolymer containing furan groups and a bismaleimide cross-linking agent. The cross-linking point spacing is 2-5 nm, and the self-healing elastic layer is 20-50 nm. A multi-level porous carbon framework is coated on the outside of the self-healing elastic layer. It is composed of biomass carbon and vapor-deposited carbon nanotubes, with a porosity of 50-70%.

2. The negative electrode material according to claim 1, characterized in that: The total thickness of the gradient interface layer is 7-20 nm, wherein the thickness of the aminosilane modified layer is 2-5 nm, and the conductive polymer layer is polypyrrole with a thickness of 5-15 nm.

3. The negative electrode material according to claim 1, characterized in that: In the hierarchical porous carbon framework, the biomass carbon is porous carbon formed by the carbonization of sodium lignosulfonate, with a pore size distribution of micropores <2nm and mesopores 2-50nm; the vapor-deposited carbon nanotubes have a length of 1-5μm and a density ≥10. 4 tubes / μm².

4. A method for modifying the negative electrode material according to any one of claims 1-3 by coating, characterized in that, Includes the following steps: Step a, Gradient interface treatment of silicon particles: a1. Hydroxylating silicon particles in a mixture of concentrated sulfuric acid and hydrogen peroxide; a2. Modification in an ethanol solution of an aminosilane coupling agent to form an amino functional layer; a3. Coating a polypyrrole layer onto the silicon surface via in-situ polymerization; Step b, self-healing elastic layer coating: b1. A dynamic covalent elastomer is prepared by mixing a polyurethane prepolymer containing furan groups with a bismaleimide crosslinking agent and then reacting the mixture via a Diels-Alder reaction. b2. Spin-coat the elastomer solution onto the surface of silicon particles after gradient interface treatment, and cure to form a self-healing elastic layer. Step c, Construction of a multi-level porous carbon framework: c1. Mix the silicon particles coated with the elastic layer with a sodium lignosulfonate solution and spray dry to form a precursor; c2. Carbonization is carried out in an argon atmosphere by gradient heating to 800℃ to form a porous carbon framework. c3. Carbon nanotube networks are grown on the surface of a carbon framework by chemical vapor deposition.

5. The method according to claim 4, characterized in that: In step a, the hydroxylation treatment uses a mixture of concentrated sulfuric acid and hydrogen peroxide in a volume ratio of 3:1, and is ultrasonically treated for 30-60 minutes.

6. The method according to claim 4, characterized in that: In step b, the spin coating process has a rotation speed of 2000-5000 rpm, a curing temperature of 60-80℃, and a curing time of 1-2 hours.

7. The method according to claim 4, characterized in that: In step c, the carbon source for chemical vapor deposition is acetylene, the deposition temperature is 600-800℃, and the deposition time is 10-30 minutes.

8. An application of the negative electrode material according to any one of claims 1-3, characterized in that: The negative electrode material is used as the negative electrode active material of lithium-ion batteries. Under 1C charge and discharge conditions, the capacity retention rate after 500 cycles is ≥90%, the silicon volume expansion rate is ≤120%, the self-repair efficiency is ≥90%, and the 5C rate capacity is ≥2500 mAh / g.

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