High-capacity long-circulation silicon-based negative electrode material and preparation method and application thereof

Abstract

The application relates to the technical field of lithium ion battery preparation, and discloses a high-capacity long-cycle silicon-based negative electrode material and a preparation method and application thereof. One-dimensional / two-dimensional conductive materials are introduced in situ during a metal silicon alloy melting stage, uniform dispersion is realized through strong mechanical stirring, and after atomization powdering and selective acid dissolution, composite porous silicon microspheres with a three-dimensional network of conductive materials are obtained. Subsequently, carbon coating is performed on the outer surface of the porous silicon microspheres through a liquid phase method, a rivet structure formed from the silicon fibers and embedded in the carbon coating layer is formed by using the conductive materials, in the composite structure, the radial silicon fiber skeleton provides a short-range lithium ion diffusion path, the internal pore buffer volume is expanded, the three-dimensional network of the conductive materials realizes fast electron transmission and skeleton locking, the rivet structure ensures that the carbon layer does not peel off in long-term cycles, and the four are combined to realize the unity of high capacity, long cycle and excellent rate performance.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery anode material technology, and in particular to a high-capacity, long-cycle silicon-based anode material, its preparation method, and its application. Background Technology

[0002] Lithium-ion batteries, due to their high energy density, long cycle life, and environmental friendliness, have been widely used in consumer electronics, electric vehicles, and large-scale energy storage. However, with the increasing demands for driving range in electric vehicles and the stringent requirements for cycle life in grid-scale energy storage, traditional graphite anode materials (theoretical specific capacity 372 mAh / g) are no longer sufficient to meet the dual requirements of high energy density and long cycle life. Silicon, on the other hand, boasts a theoretical specific capacity as high as 4200 mAh / g (corresponding to Li...). 22 Si5 alloy phase) and lower lithium intercalation potential (approximately 0.4V vs. Li / Li). + It is considered the most promising anode material for next-generation high-energy-density lithium-ion batteries.

[0003] However, silicon anode materials face two major challenges in practical applications. First, silicon undergoes a massive volume change (approximately 300%) during charge and discharge, leading to particle pulverization, electrode structure damage, and repeated formation and rupture of the solid electrolyte interphase (SEI) film, resulting in irreversible capacity growth and rapid capacity decay. Second, silicon has a low intrinsic electronic conductivity (approximately 10⁻⁶). -3 Its rate capability (S / cm) severely limits its rate performance, making it difficult to meet the needs of fast charging applications.

[0004] Currently, the mainstream strategies for addressing these issues include silicon nanostructuring, porous structure design, and composite with carbon materials. Among these, embedding nano-silicon into a porous carbon framework and then coating it with carbon has proven to be one of the most effective comprehensive solutions. The carbon coating layer can effectively isolate silicon from the electrolyte, suppressing irreversible side reactions; the porous carbon framework can provide a buffer for the volume expansion of silicon. However, existing silicon-carbon anode materials still generally suffer from insufficient interfacial bonding between the carbon coating layer and the internal silicon particles, leading to cracking and detachment of the carbon coating layer during long-term cycling. Furthermore, the porous silicon framework itself has limited mechanical strength, and the framework structure is prone to fatigue collapse during repeated expansion and contraction.

[0005] One-dimensional and two-dimensional conductive materials (including single-walled carbon nanotubes (SWCNTs), multi-walled carbon nanotubes (MWCNTs), carbon nanofibers (CNFs), graphene, etc.) possess excellent mechanical properties and electronic conductivity. Taking SWCNTs as an example, they exhibit tensile strength >50 GPa, elastic modulus ~1 TPa, and axial conductivity ~10⁻⁶. 4S / cm. In the field of silicon-carbon anodes, these materials are usually introduced into electrode slurries as conductive additives through mechanical mixing, but their conductive function is only utilized, failing to realize their potential for mechanical enhancement and structural bridging. Although some studies have attempted to grow carbon nanotubes on the surface of silicon particles using CVD, problems such as uneven dispersion, weak interfacial bonding with the silicon matrix, and limited enhancement of the carbon coating layer exist. Summary of the Invention

[0006] This invention provides a high-capacity, long-cycle silicon-based anode material, its preparation method, and its application, with the aim of solving the aforementioned problems in the background art.

[0007] To achieve the above objectives, embodiments of the present invention provide a high-capacity, long-cycle silicon-based anode material, its preparation method, and its application. The present invention introduces one-dimensional / two-dimensional conductive materials in situ during the melting stage of a metallic silicon alloy. Uniform dispersion is achieved through vigorous mechanical stirring. After atomization powdering and selective acid dissolution, composite porous silicon microspheres with a three-dimensional network of conductive materials are obtained. Subsequently, carbon coating is applied only to the outer surface of the porous silicon microspheres using a liquid-phase method. A rivet structure is formed by the conductive material extending from silicon fibers and embedded in the carbon coating layer, achieving a strong bond between the carbon coating layer and the silicon microspheres, significantly improving structural stability and cycle life.

[0008] One aspect of the present invention provides a high-capacity, long-cycle silicon-based anode material, the silicon-based anode material comprising a porous silicon microsphere core and a carbon coating shell covering the surface of the porous silicon microspheres; The porous silicon microspheres have a three-dimensional porous radial silicon fiber skeleton structure; the carbon coating layer only coats the surface of the porous silicon microspheres; the gaps between the silicon fibers inside the porous silicon microspheres are not filled with carbon. The porous silicon microspheres are internally composited with a three-dimensional network of conductive materials. One end of the conductive material is anchored in the silicon fiber phase, and the other end is embedded in the carbon coating matrix, forming a rivet structure connecting the silicon fiber phase and the carbon coating layer. In the rivet structure, the proportion of conductive material to the total amount of conductive material is not less than 30%; The embedding depth of the conductive material in the carbon coating layer is 30% to 90% of the thickness of the carbon coating layer; The areal density of the rivet structure at the interface between the carbon coating layer and the porous silicon microspheres is not less than 3 rivets / μm. 2 .

[0009] Preferably, the distribution morphology of the conductive material in the silicon-based anode material further includes: type (a) completely embedded inside the silicon fiber phase; type (b) one end embedded inside the silicon fiber phase and the other end extending into the void; type (c) bridging type that penetrates at least two silicon fiber phases and / or voids.

[0010] Preferably, the porous silicon microspheres have a particle size D50 of 1~20 μm, a porosity of 35%~70%, and a pore size of 20~400 nm; the carbon coating layer has a thickness of 5~50 nm; the total mass content of the carbon coating layer is 3%~20%; the silicon fiber has a diameter of 50~500 nm and a length of 0.5~5 μm; the ratio of the length of the conductive material to the diameter of the silicon fiber is 5:1~100:1, to ensure that the conductive material has sufficient suspended sections after extending from the silicon fiber phase and is embedded in the carbon coating layer to form a rivet structure.

[0011] Preferably, the carbon coating layer contains a uniformly dispersed conductive material as a reinforcing phase; the three-dimensional network of the conductive material forms a continuous electron transport channel inside the particles, thereby increasing the overall electronic conductivity of the silicon-based anode material by 1 to 3 orders of magnitude compared to porous silicon-carbon anode materials without conductive materials.

[0012] Preferably, the conductive material includes one-dimensional conductive materials and / or two-dimensional conductive materials; the total mass content of the conductive material is 0.5% to 10%, preferably 1% to 5%.

[0013] More preferably, the one-dimensional conductive material includes at least one of single-walled carbon nanotubes (SWCNTs) and their derivatives, multi-walled carbon nanotubes (MWCNTs) and their derivatives, and carbon nanofibers (CNFs) and their derivatives; the diameter of the one-dimensional conductive material is 0.8–50 nm, and the length is 0.5–30 μm. More preferably, the diameter of SWCNTs is 0.8–2.5 nm, and the diameter of MWCNTs is 5–50 nm.

[0014] More preferably, the two-dimensional conductive material includes at least one of graphene and its derivatives; the thickness of the two-dimensional conductive material is 0.3~5 nm and the sheet diameter is 0.5~10 μm.

[0015] Preferably, the interfacial shear strength between the carbon coating shell and the porous silicon microsphere core is 50~200 MPa, which is at least 80% higher than that of silicon-based anode materials without conductive bridging (whose interfacial shear strength is usually less than 30 MPa).

[0016] Preferably, after the silicon-based anode material is cycled 100 times at a rate of 0.5C, the integrity retention rate of the carbon coating layer is not less than 90%; after 300 cycles, the integrity retention rate of the carbon coating layer is not less than 85%.

[0017] An embodiment of the present invention also provides a method for preparing the above-mentioned high-capacity, long-cycle silicon-based anode material, comprising the following steps: S1: Silicon and the first metal M1 are heated to a molten state under an inert atmosphere in proportion to obtain M1-Si alloy melt; conductive material is added to M1-Si alloy melt, and the conductive material is uniformly dispersed and embedded in M1-Si alloy melt under mechanical stirring. Then, conductive material composite M1-Si alloy powder is prepared by atomization method. S2: The conductive material composite M1-Si alloy powder is placed in an acidic solution and stirred to dissolve. Taking advantage of the difference in selective dissolution rates between the metal phase and the silicon phase in the acidic solution, the M1 metal phase is selectively dissolved and removed, so that the space originally occupied by the M1 metal forms a void, and conductive material composite porous silicon microspheres are obtained. S3: The conductive material composite porous silicon microspheres are dispersed in an organic carbon source solution, stirred and allowed to stand. By controlling the concentration and viscosity of the organic carbon source solution, the organic carbon source solution is spread and coated only on the outer surface of the porous silicon microspheres without penetrating into the internal pores. At the same time, the suspended segments of the conductive material extending from the silicon fiber phase to the outside of the porous silicon microspheres are fully mixed and contacted with the organic carbon source solution. Then, the solvent is removed by drying to obtain an intermediate product. S4: The intermediate product is subjected to high-temperature pyrolysis under an inert atmosphere. The organic carbon source is carbonized to form a carbon coating layer. The conductive material extending into the carbon coating layer is solidified and embedded in the carbon matrix to form a carbon coating shell reinforced by the conductive material. It is then connected to the silicon fiber phase through the conductive material to form an integrated structure. The voids inside the porous silicon microspheres remain carbon-free, thus obtaining the silicon-based anode material.

[0018] Preferably, in step S1, the first metal M1 is selected from at least one of Al, Zn, Mg, and Sn; the mass ratio of silicon to M1 is 1:1 to 1:8; the melting temperature is 400 to 1500°C (the specific temperature depends on the eutectic point of the selected M1 metal and silicon); the stirring speed is 50 to 3000 rpm, and the stirring time is 10 to 120 minutes; the atomization method is gas atomization or centrifugal atomization; the atomization medium is high-purity argon or nitrogen, and the atomization pressure is 1 to 10 MPa; the particle size D50 of the M1-Si alloy powder is 1 to 200 μm; the conductive material further includes a pretreatment process. More preferably, the pretreatment process includes carboxyl functionalization of the conductive material surface.

[0019] Preferably, in step S2, the acidic solution is at least one of hydrochloric acid, sulfuric acid, phosphoric acid, or nitric acid; the concentration of the acidic solution is 0.5~5 mol / L; the acid dissolution temperature is 20~80℃; and the acid dissolution time is 1~24 hours.

[0020] Preferably, in step S3, the organic carbon source is selected from at least one of phenolic resin, asphalt, polyacrylonitrile (PAN), polyvinyl alcohol (PVA), sucrose, glucose, or citric acid; the concentration of the organic carbon source solution is 5% to 40%, and the viscosity is 10 to 1500 mPa·s.

[0021] Preferably, in step S4, the pyrolysis temperature is 500~1000℃; the heating rate is 1~10℃ / min; the holding time is 1~6 hours; and the inert protective atmosphere is high-purity argon or nitrogen.

[0022] An embodiment of the present invention also provides the application of the high-capacity, long-cycle silicon-based anode material described above or the high-capacity, long-cycle silicon-based anode material prepared by the preparation method described in any one of claims 5-9 in a secondary battery.

[0023] The above-described solution of the present invention has the following beneficial effects: (1) Rivet-type interface reinforcement of conductive materials: Some conductive materials extend from the silicon fiber phase and are embedded in the outer carbon coating layer to form a nanoscale rivet structure connecting the silicon fiber phase and the carbon coating layer, which greatly improves the interfacial bonding strength between the carbon coating layer and the internal silicon microspheres. The carbon coating layer is not easy to crack and fall off during long-term cycling.

[0024] (2) Mechanical enhancement of carbon coating layer itself: The conductive material is composited in the carbon coating layer matrix as a nano-reinforcing phase, which significantly improves the tensile strength and fracture toughness of the carbon coating layer itself.

[0025] (3) The porous structure inside provides expansion space: The abundant pores inside the porous silicon microspheres provide sufficient buffer space for the volume expansion of silicon, and the internal voids are not filled with carbon. The silicon fiber has a high degree of freedom in expansion and contraction, and the overall size of the particles remains basically unchanged.

[0026] (4) Multiple functions of three-dimensional network of conductive material: The conductive material forms a three-dimensional conductive network that runs through multiple silicon fiber phases and voids inside the particle, which significantly improves the rate performance of silicon-based anode material. At the same time, like a nano-mesh, it firmly locks the structural units of porous silicon microspheres.

[0027] (5) The preparation process is highly compatible and the material selection is flexible: the process of this invention is highly compatible with the existing industrial route of metal silicon alloy atomization-acid dissolution-carbon coating, and the modification cost is low; the type of conductive material can be flexibly selected (SWCNT, MWCNT, CNF, graphene, etc.), and can be flexibly adjusted according to cost and performance requirements. Attached Figure Description

[0028] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0029] Figure 1 This is a schematic diagram of the structure of a high-capacity, long-cycle silicon-based anode material according to the present invention. Detailed Implementation

[0030] To make the technical problems, technical solutions and advantages of the present invention clearer, a detailed description will be given below in conjunction with the accompanying drawings and specific embodiments.

[0031] 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.

[0032] 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.

[0033] This invention addresses existing problems by providing a high-capacity, long-cycle silicon-based anode material, its preparation method, and its applications.

[0034] The following description is provided through specific embodiments and comparative examples. Example 1 This embodiment provides a method for preparing a high-capacity, long-cycle silicon-based anode material, which specifically includes the following steps: (1) Silicon powder (purity 99.9%, D50=5 μm) and aluminum powder (purity 99.9%, D50=10 μm) were mixed at a mass ratio of 1:3 and heated to a molten state at 800℃ under argon protection to obtain Al-Si alloy melt. SWCNTs (diameter 1.2~1.8 nm, length 5~15 μm, pre-dispersed in ethanol for 30 minutes and dried) were added to the Al-Si alloy melt at 2% of the total alloy mass and mechanically stirred vigorously at 1200 rpm for 40 minutes. Subsequently, SWCNT composite Al-Si alloy powder was prepared by argon atomization (atomization pressure 3.5 MPa), and the powder D50 was about 10 μm.

[0035] (2) The SWCNT composite Al-Si alloy powder was placed in a 2 mol / L hydrochloric acid solution and stirred at 35°C for 6 hours to dissolve it. The aluminum phase was selectively dissolved and removed. After the reaction was completed, the mixture was filtered, washed with deionized water until neutral, and dried under vacuum at 80°C to obtain SWCNT composite porous silicon microspheres. The diameter of the silicon fibers was about 80~250 nm, the porosity was about 55%, and the SWCNT retention rate was about 90%.

[0036] (3) Dissolve phenolic resin in ethanol to prepare a 15% organic carbon source solution (viscosity approximately 80 mPa·s). Immerse SWCNT composite porous silica microspheres in the organic carbon source solution at a phenolic resin to porous silica microsphere mass ratio of 0.25:1, stir slowly for 10 minutes, and let stand for 5 minutes. After removal, vacuum dry at 60℃ to remove the solvent to obtain the intermediate product.

[0037] (4) The intermediate product was placed in a tube furnace and heated to 850°C at 5°C / min under an argon atmosphere, and held at that temperature for 3 hours for pyrolysis and carbonization. After natural cooling to room temperature, the final product, namely the silicon-based anode material, was obtained. The total carbon content was approximately 10%, the SWCNT content was approximately 1.8%, and the carbon coating thickness was approximately 15~25 nm. The rivet structure surface density in the obtained silicon-based anode material was approximately 6 rivets / μm. 2 .

[0038] Example 2 The difference between this embodiment and Example 1 is that: multi-walled carbon nanotubes (MWCNTs, outer diameter 8~15 nm, length 10~20 μm) are used instead of SWCNTs, and the amount added is 5% of the total mass of the alloy; the acid dissolution temperature is 45℃, the time is 4 hours, the acid solution is 1.5 mol / L sulfuric acid; the organic carbon source is pitch (dissolved in NMP, concentration 20%); the pyrolysis temperature is 900℃, and the holding time is 2 hours.

[0039] The larger diameter of MWCNTs gives them better structure retention in the melt.

[0040] Example 3 The difference between this embodiment and Example 1 is that the mass ratio of silicon to M1 metal is 1:5, zinc (Zn) is used instead of aluminum as M1 metal, the melting temperature is 680℃, 3 mol / L phosphoric acid solution is used for acid dissolution at 50℃ for 3 hours, the organic carbon source is polyacrylonitrile (PAN, dissolved in DMF, concentration 12%), the pyrolysis temperature is 800℃, and the holding time is 4 hours.

[0041] Zinc's low melting point helps reduce process energy consumption.

[0042] Example 4 The difference between this embodiment and Embodiment 1 is that: an aluminum-zinc alloy (Al:Zn mass ratio 4:1) is used as the M1 metal, with a melting temperature of 650°C; the conductive material is a mixture of SWCNT and graphene (mass ratio 2:1, with a total addition amount of 3% of the alloy mass); and a mixed acid solution of 2 mol / L hydrochloric acid and 0.5 mol / L nitric acid is used for acid dissolution at 40°C for 5 hours.

[0043] The one-dimensional bridging effect of SWCNT and the two-dimensional surface contact effect of graphene synergistically enhance the mechanical properties and electrical conductivity of the carbon coating.

[0044] Example 5 The difference between this embodiment and Example 1 is as follows: magnesium (Mg) is used as the M1 metal, the silicon-magnesium mass ratio is 1:3, and the melting temperature is 750℃; SWCNT is first ultrasonically treated with mixed acid (concentrated sulfuric acid: concentrated nitric acid volume ratio 3:1) for 30 minutes before addition to perform surface carboxyl functionalization; the organic carbon source is a glucose aqueous solution (concentration 25%, viscosity about 40 mPa·s); the pyrolysis temperature is 850℃, and the holding time is 3 hours.

[0045] Comparative Example 1 The same metal-silicon alloy atomization and acid dissolution process as in Example 1 was used, but without the addition of any conductive material, to obtain pure porous silicon microspheres. Subsequent carbon coating and pyrolysis processes were the same as in Example 1. The resulting material is a conventional carbon-coated porous silicon anode material without conductive material reinforcement.

[0046] Comparative Example 2 Pure porous silicon microspheres were obtained using the same metal-silicon alloy atomization and complete acid dissolution process as in Example 1 (without adding conductive materials). These microspheres were then mixed with SWCNTs (2% of the porous silicon microsphere mass) by mechanical ball milling (300 rpm for 2 hours), followed by carbon coating and pyrolysis treatment as in Example 1.

[0047] SWCNTs mainly exist on the surface of the carbon coating or in the interparticle gaps as external attachments, and fail to embed inside the silicon fiber phase to form a bridging structure.

[0048] Comparative Example 3 The same process as in Example 1 was used, but the concentration of the organic carbon source solution in step (3) was reduced to 5% (viscosity about 5 mPa·s).

[0049] Reducing viscosity and concentration allows a large amount of organic carbon source solution to penetrate into the internal pores of porous silicon microspheres. After carbonization, carbon fills the internal pores between silicon fibers.

[0050] Comparative Example 4 The same process as in Example 1 was used, but in step (1), the amount of SWCNT added was only 0.3% of the total mass of the alloy (15% of the amount used in Example 1), and the other conditions were the same as in Example 1.

[0051] The surface density of the rivet structure in the obtained silicon-based anode material is only about 0.8 rivets / μm. 2 This is significantly lower than the approximately 6 / μm in Example 1. 2 Most of the carbon coating area lacks rivet anchoring, and the interfacial bonding between the carbon coating and the silicon microspheres mainly relies on the van der Waals forces between the carbon layer and the silicon surface.

[0052] Comparative Example 5 The same process as in Example 1 was used, but short-cut SWCNTs (0.2~0.5 μm in length, aspect ratio of about 3:1~8:1, obtained by ball milling and shearing of commercially available long SWCNTs) were added in the same amount as in Example 1 (2% of the total mass of the alloy).

[0053] Due to the insufficient length of carbon nanotubes, most SWCNTs are completely embedded inside the silicon fiber after acid dissolution (distribution pattern as described in type (a)). The suspended segments extending to the outside of the silicon fiber are extremely short (usually <10 nm), which cannot be effectively embedded in the carbon coating layer to form a rivet structure. There is a lack of bridging and anchoring between the carbon coating layer and the silicon microspheres.

[0054] Electrochemical performance testing The silicon-based anode materials prepared in Examples 1-5 and Comparative Examples 1-3 were mixed with conductive agent Super-P and sodium alginate binder at a mass ratio of 8:1:1 to form slurries. These slurries were then coated onto copper foil to prepare electrode sheets. A lithium metal sheet was used as the counter electrode, and a 1M LiPF6 EC / DMC / EMC solution (volume ratio 1:1:1) (containing 5% FEC additive) was used as the electrolyte. CR2032 coin cells were assembled and tested. The voltage range was 0.01~1.5V, and 1C = 3000 mA / g. The actual specific capacity of silicon in the composite material was calculated as 3300 mAh / g (based on the high utilization rate of the nanoporous structure).

[0055] I. Initial Charge-Discharge Performance and Coulombic Efficiency Analysis Example 1 showed an initial reversible specific capacity of 2700 mAh / g and an initial coulombic efficiency (ICE) of 89.0% at 0.1C. The high reversible capacity is attributed to the nanoporous structure of the silicon fibers—the nanoscale silicon fibers (80-250 nm in diameter) effectively shorten the lithium-ion diffusion distance, and the open pore structure of the radial silicon fiber skeleton from the center to the surface ensures sufficient electrolyte wetting, resulting in a silicon active material utilization rate of approximately 92% (actual silicon utilization is approximately 3300 mAh / g, multiplied by a silicon content of approximately 88% and a utilization rate of approximately 92%, with the composite material layer at approximately 2700 mAh / g). The 89.0% initial coulombic efficiency is attributed to two factors: first, the uniform and dense outer carbon coating layer effectively isolates the silicon from direct contact with the electrolyte, significantly reducing irreversible consumption of the SEI film; second, the internal pores are not filled with carbon, and the SEI film mainly forms on the outer surface of the carbon coating layer rather than the silicon surface, reducing active lithium loss.

[0056] Example 2 (MWCNT replacing SWCNT, 5% addition): The initial reversible specific capacity was 2500 mAh / g, and the initial coulombic efficiency was 87.8%. The addition of MWCNT was relatively high (5%), which reduced the silicon content in the silicon-based anode material (approximately 83%). The larger specific surface area of ​​MWCNT resulted in a slightly higher initial irreversible capacity. However, the multilayer tube wall structure of MWCNT maintained good structural integrity in the high-temperature melt.

[0057] Example 3 (Zn replacing Al as the M1 metal) showed an initial reversible specific capacity of 2720 mAh / g and an initial coulombic efficiency of 88.8%. The lower melting point of zinc (approximately 420°C) and the milder acid dissolution process resulted in a more uniform and regular pore structure in the porous silicon framework, a more concentrated silicon fiber diameter distribution (100–200 nm), and the highest silicon utilization rate (approximately 94%) among all examples, thus leading to the highest reversible capacity.

[0058] Example 4 (SWCNT + graphene mixture, total addition 3%) showed an initial reversible specific capacity of 2610 mAh / g and an initial coulombic efficiency of 88.2%. The two-dimensional sheets of graphene enhanced the density and in-plane conductivity of the carbon coating, but the partial stacking of graphene slightly reduced the silicon utilization (approximately 90%), resulting in an initial reversible specific capacity slightly lower than that of the pure SWCNT system.

[0059] Example 5 (Mg system + functionalized SWCNT) showed an initial reversible specific capacity of 2720 mAh / g and an initial coulombic efficiency of 89.5%. The carboxyl functionalization of SWCNT enhanced its wettability with the silicon melt and its dispersion uniformity in the alloy, resulting in a more complete conductive reinforcement network. The carbon coating layer exhibited the best density and uniformity, and the initial coulombic efficiency was the highest among all examples.

[0060] Comparative Example 1 (without conductive material) showed an initial reversible specific capacity of 2460 mAh / g and an initial coulombic efficiency of 86.0%. The lack of a conductive reinforcement network reduced the effective utilization of silicon to approximately 82%, and a large number of silicon fibers failed to fully participate in the electrochemical reaction due to poor electron conduction. Furthermore, the carbon coating layer lacked rivet reinforcement at the interface with the silicon microspheres, resulting in poor uniformity of the carbon coating layer and significant irreversible capacity loss.

[0061] Comparative Example 2 (mechanically mixed SWCNTs) showed an initial reversible specific capacity of 2520 mAh / g and an initial coulombic efficiency of 87.1%. SWCNTs only adhered to the outside of the particles and could not build an effective conductive network inside the particles. Although the utilization rate of silicon inside the particles (about 84%) was better than that of Comparative Example 1, it was still much lower than that of Example 1 (92%). Furthermore, SWCNTs failed to embed into the carbon coating layer to form a rivet structure, resulting in limited interface enhancement.

[0062] Comparative Example 3 (carbon-filled pores) showed an initial reversible specific capacity of only 2110 mAh / g and an initial coulombic efficiency of 87.5%. After the internal pores were filled with carbon, the silicon content of the silicon-based anode material decreased to about 80%. The carbon filler occupied a large volume but contributed a limited capacity (the theoretical capacity of carbon is about 372 mAh / g). Furthermore, due to the loss of expansion buffer space and some electrolyte channels, the utilization rate of the silicon fibers further decreased to about 78%. Overall, the initial reversible specific capacity was significantly lower than that of Example 1 (reduced by about 22%).

[0063] Comparative Example 4 (low rivet density) showed an initial reversible specific capacity of 2520 mAh / g and an ICE of 87.5%. Insufficient rivet density led to localized micro-debonding of the carbon layer, and exposure of silicon fibers caused an irreversible increase in SEI.

[0064] Comparative Example 5 (short SWCNTs) had an initial capacity of 2650 mAh / g and an ICE of 88.5%. The internal short SWCNTs effectively enhanced conductivity and mechanical properties, but the carbon layer was partially peeled off due to the lack of rivet anchoring.

[0065] II. Rate Performance and Conductive Network Mechanism Analysis Example 1 exhibits a reversible specific capacity of 1755 mAh / g at 5C (65.0% retention) and still reaches 1215 mAh / g (45.0%) at 10C. This excellent rate capability stems from the multi-level electron transport network constructed by the conductive material: type (a) provides nanoscale conductive channels along the silicon fiber axis, type (c) bridges adjacent silicon fibers and voids to form a three-dimensional continuous conductive network, and the rivet structure ensures low-resistance contact between the carbon coating and the silicon fiber interface. Example 2 shows a 5C capacity of 1620 mAh / g (64.8% retention). The larger diameter of MWCNTs results in slightly lower conductivity than SWCNTs, and the narrow pore density limits their penetration density.

[0066] The 5C capacity of Example 2 was 1620 mAh / g (64.8% retention). The large diameter (8~15 nm) of MWCNTs makes them less prone to breakage during melting, but electron scattering between the multilayer tube walls makes their intrinsic conductivity slightly lower than that of SWCNTs, and the large radius of curvature of MWCNTs limits their penetration density in narrow pores.

[0067] Example 3 has a 5C capacity of 1810 mAh / g (66.5% retention), which is the best among all examples. This is due to the uniform pore structure formed by zinc acid dissolution, which shortens the diffusion path of lithium ions in the electrolyte and reduces concentration polarization.

[0068] The 5C capacity of Example 4 was 1675 mAh / g (64.2% retention). Graphene improved the in-plane conductivity of the carbon coating, but the vertical contact resistance between the two-dimensional layers limited further improvement in the three-dimensional conductivity.

[0069] The 5C capacity of Example 5 is 1795 mAh / g (66.0% retention), and the uniform dispersion of functionalized SWCNTs makes the conductive network more dense and complete.

[0070] Comparative Example 1 exhibits a 5C capacity of only 880 mAh / g (35.8% retention) and is almost unable to discharge at 10C. Without a conductive reinforcement network, relying solely on silicon-silicon point contacts and carbon layer conduction results in severe ohmic polarization under high current, with a large number of silicon fibers in an electrochemically deactivated state.

[0071] Comparative Example 2 showed a 5C capacity of 1245 mAh / g (49.4%). External mixing of SWCNTs only improved macroscopic conduction between particles, with limited improvement in internal microscopic electron transport.

[0072] The 5C capacity of Comparative Example 3 was 1245 mAh / g (59.0%). Although carbon filling is conductive, it hinders electrolyte penetration, making lithium-ion transport a bottleneck for rate capability.

[0073] The 5C capacity of Comparative Example 4 was 1135 mAh / g (42.0%). The low SWCNT content resulted in a sparse conductive network and partial peeling of the carbon layer due to missing rivets.

[0074] Comparative Example 5 has a 5C capacity of 1295 mAh / g (48.0%). The internal short SWCNTs form an effective conductive network, but the lack of rivet anchoring in the carbon layer leads to interface slippage and debonding under high current, and the rate of increase is still significantly lower than that of Example 1.

[0075] III. Mechanism Analysis of Long-Cycle Performance and Structural Stability Example 1 showed a capacity retention of 91.8% after 300 cycles at 0.5C (relative to the 3rd cycle) and 85.2% after 500 cycles. The carbon coating integrity was maintained at approximately 94% after cycling, and the overall morphology of the porous silicon microspheres remained good. The excellent long-term cycling stability is due to a triple synergistic mechanism: (1) the internal pores (porosity of approximately 55%) provide a buffer for silicon volume expansion, with a macroscopic particle size change of <5%, avoiding repeated thickening of the SEI; (2) the three-dimensional network of conductive materials firmly locks each structural unit, suppressing fatigue collapse of the skeleton; (3) the rivet anchoring allows the carbon coating to deform synchronously with the silicon fiber without peeling off, ensuring continuous protection of the silicon surface.

[0076] Example 2 showed a retention rate of 89.8% after 300 cycles. The large diameter (8~15 nm) of MWCNTs imparts high mechanical strength, but the narrow pores restrict penetration, and local degradation occurs in the micropore region.

[0077] Example 3 has a yield of 91.0%. The uniform porosity allows for synchronized expansion and contraction, reducing local stress concentration.

[0078] Example 4 showed a success rate of 88.5%, indicating that the two-dimensional rigidity of graphene was slightly inferior in terms of fatigue resistance, and a small number of microcracks appeared in the carbon layer.

[0079] Example 5 showed a yield of 92.1%, with the chemical interface bonding (carboxyl-silyl hydroxyl condensation) of functionalized SWCNTs resulting in the highest degree of integration and optimal cycle stability.

[0080] The retention rate of Comparative Example 1 was only 72.5% after 300 cycles, and about 58% after 500 cycles. The porous silicon skeleton without conductive reinforcement network lock exhibited typical fatigue failure: microcracks initiated in the first 100 cycles (retention rate ~92%), crack propagation led to fiber breakage and pore collapse in the 100-200 cycles (reduced to ~82%), and large-area skeleton collapse occurred in the 200-300 cycles, with the carbon layer falling off over a large area due to lack of anchorage, resulting in a sharp decrease in capacity.

[0081] Comparative Example 2 showed a retention rate of 81.2% after 300 cycles. The externally mixed SWCNTs could not embed into the silicon fiber to share the stress, and the internal pores collapsed significantly. However, the carbon layer was more intact than that of Comparative Example 1 due to the external SWCNT wrapping, indicating that rivet anchoring is the determining factor for the integrity of the carbon layer.

[0082] Comparative Example 3 showed a retention rate of 83.5% after 300 cycles, exhibiting a stable-then-declining pattern: the carbon filling constraint was effective in the first 50 cycles (retention rate ~97%), microcracks appeared in the carbon filler from 50 to 150 cycles (retention rate decreased to ~90%), and from 150 to 300 cycles, the cracks penetrated, causing simultaneous damage to both carbon and silicon fibers. Compared to the stable decay in Example 1, this reveals the crucial role of pre-reserved carbon-free pores in long-term cycling—carbon filling deprives silicon of its expansion freedom, thus accelerating long-term failure.

[0083] Comparative Example 4 showed a 300-cycle retention rate of 78.0%. The rivet density was below the critical value, leading to large-area peeling of the carbon layer and irreversible damage to the exposed silicon fibers, similar to Comparative Example 1 (72.5%). This indicates that the stability of the carbon layer depends on the rivets rather than the conductive material itself. Comparative Example 5 showed a 300-cycle retention rate of 80.5%. Although short SWCNTs enhanced the fiber's fracture resistance, the carbon layer gradually peeled off due to lack of anchoring. Both examples reveal that the lack of rivet anchoring (80.5%) and insufficient rivet density (78.0%) were significantly worse than Example 1 (91.8%), verifying that a rivet surface density ≥3 rivets / μm is necessary. 2 Critical parameters.

[0084] In summary, this invention constructs a three-dimensional continuous conductive reinforcement network spanning the silicon phase, voids, and carbon coating by introducing conductive materials in situ during the melting stage of the silicon alloy. The actual specific capacity of silicon reaches 3300 mAh / g (approximately 2700 mAh / g for the composite material layer), achieving multiple synergistic effects of interface bonding enhancement, carbon coating mechanical enhancement, three-dimensional conductive network construction, and framework locking. The riveting bridging mechanism is the core of cycling stability—it not only firmly anchors the carbon coating to the silicon fiber surface but also disperses the cyclic stress concentrated at the carbon / silicon interface into the three-dimensional conductive network, fundamentally eliminating the failure chain of traditional carbon-coated porous silicon materials: carbon layer peeling-silicon exposure-capacity avalanche decay. Furthermore, this invention is applicable to various conductive materials such as SWCNT (~2700 mAh / g), MWCNT (~2500 mAh / g), and SWCNT / graphene hybrids (~2610 mAh / g), as well as various alloy systems such as Al, Zn, Mg, and Sn, providing ample flexibility for industrial applications. Comparative Examples 4 and 5 were obtained from the lower limit of rivet surface density (<3 rivets / μm). 2 The critical conditions for the formation of the rivet structure were verified by two dimensions: the lower limit of the aspect ratio of the conductive material (<5:1). Together with Comparative Examples 1 to 3, they constitute a complete parameter boundary demonstration system.

[0085] Table 1. Comparison of electrochemical performance of silicon-based anode materials in each embodiment and comparative example.

[0086] Note: 1C = 3000 mA / g; 5C capacity retention is the percentage of capacity relative to 0.1C; 300-cycle retention is the percentage of capacity relative to the 3rd cycle.

[0087] like Figure 1As shown, this invention features a unique single-particle, multi-level composite structure. The porous silicon microsphere core is composed of a radially arranged nanofiber framework (50-500 nm in diameter) of silicon fibers, forming an open three-dimensional porous framework (porosity 35%-70%, pore size 20-400 nm) between the silicon fibers, providing ample buffer space for the volume expansion of silicon. The conductive material (SWCNT / MWCNT / graphene, etc.) is distributed in three forms: type (a) completely embedded inside the silicon fibers to enhance mechanical properties; type (b) embedded at one end of the silicon fiber and extending into the voids at the other end; type (c) penetrating multiple fibers and voids to form a bridging network. The carbon coating layer (5-50 nm thick) only coats the outer surface of the microsphere, leaving the voids inside the silicon microsphere unfilled with carbon. The conductive material extending from the silicon fibers is embedded in the carbon coating layer to form a rivet structure, firmly anchoring the carbon layer to the silicon surface, while simultaneously constructing a multi-level continuous conductive pathway from silicon fiber → conductive material → carbon coating layer → external current collector. In this composite structure, the radial silicon fiber skeleton provides a short-range lithium-ion diffusion path, the internal pores buffer volume expansion, the three-dimensional network of conductive materials enables rapid electron transport and skeleton locking, and the rivet structure ensures that the carbon layer does not peel off during long-term cycling. The four elements work together to achieve a combination of high capacity, long cycle life, and excellent rate performance.

[0088] The above description represents the preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A high-capacity, long-cycle silicon-based anode material, characterized in that, It includes a porous silicon microsphere core and a carbon coating shell covering the surface of the porous silicon microsphere; The porous silicon microspheres have a three-dimensional porous radial silicon fiber skeleton structure; the carbon coating layer only coats the surface of the porous silicon microspheres; the gaps between the silicon fibers inside the porous silicon microspheres are not filled with carbon. The porous silicon microspheres are internally composited with a three-dimensional network of conductive materials. One end of the conductive material is anchored in the silicon fiber phase, and the other end is embedded in the carbon coating matrix, forming a rivet structure connecting the silicon fiber phase and the carbon coating layer. In the rivet structure, the proportion of conductive material to the total amount of conductive material is not less than 30%; The embedding depth of the conductive material in the carbon coating layer is 30% to 90% of the thickness of the carbon coating layer; The areal density of the rivet structure at the interface between the carbon coating layer and the porous silicon microspheres is not less than 3 rivets / μm. 2 .

2. The high-capacity, long-cycle silicon-based anode material according to claim 1, characterized in that, The distribution morphology of the conductive material in the silicon-based anode material also includes: type (a) completely embedded in the silicon fiber phase; type (b) one end embedded in the silicon fiber phase and the other end extending into the void; type (c) bridging type that penetrates at least two silicon fiber phases and / or voids. And / or, The porous silicon microspheres have a particle size D50 of 1-20 μm, a porosity of 35%-70%, and a pore size of 20-400 nm; the carbon coating layer has a thickness of 5-50 nm; the total mass content of the carbon coating layer is 3%-20%; the total mass content of the conductive material is 0.5%-10%; the silicon fibers have a diameter of 50-500 nm and a length of 0.5-5 μm; the ratio of the length of the conductive material to the diameter of the silicon fiber is 5:1-100:

1. And / or, The carbon coating contains a uniformly dispersed conductive material as a reinforcing phase; the three-dimensional network of the conductive material forms a continuous electron transport channel inside the particles.

3. The high-capacity, long-cycle silicon-based anode material according to claim 1, characterized in that, The conductive material includes one-dimensional conductive materials and / or two-dimensional conductive materials; the total mass content of the conductive material is 0.5% to 10%. And / or, The one-dimensional conductive material includes at least one of single-walled carbon nanotubes and their derivatives, multi-walled carbon nanotubes and their derivatives, and carbon nanofibers and their derivatives; the diameter of the one-dimensional conductive material is 0.8~50 nm and the length is 0.5~30 μm. And / or, The two-dimensional conductive material includes at least one of graphene and its derivatives; the thickness of the two-dimensional conductive material is 0.3~5 nm and the sheet diameter is 0.5~10 μm.

4. The high-capacity, long-cycle silicon-based anode material according to claim 1, characterized in that, The interfacial shear strength between the carbon coating shell and the porous silicon microsphere core is 50~200 MPa; And / or, After the silicon-based anode material is cycled 100 times at a rate of 0.5C, the integrity retention rate of the carbon coating layer is not less than 90%; after 300 cycles, the integrity retention rate of the carbon coating layer is not less than 85%.

5. The method for preparing the high-capacity, long-cycle silicon-based anode material according to any one of claims 1-4, characterized in that, Includes the following steps: S1: Silicon and the first metal M1 are heated to a molten state under an inert atmosphere in proportion to obtain M1-Si alloy melt; conductive material is added to M1-Si alloy melt, and the conductive material is uniformly dispersed and embedded in M1-Si alloy melt under mechanical stirring. Then, conductive material composite M1-Si alloy powder is prepared by atomization method. S2: The conductive material composite M1-Si alloy powder is placed in an acidic solution and stirred to dissolve it, thereby obtaining conductive material composite porous silicon microspheres; S3: The conductive material composite porous silicon microspheres are dispersed in an organic carbon source solution, stirred and allowed to stand. By controlling the concentration and viscosity of the organic carbon source solution, the organic carbon source solution is spread and coated only on the outer surface of the porous silicon microspheres without penetrating into the internal pores. Then, the solvent is removed by drying to obtain an intermediate product. S4: The intermediate product is subjected to high-temperature pyrolysis under an inert atmosphere to obtain the silicon-based anode material.

6. The method for preparing a high-capacity, long-cycle silicon-based anode material according to claim 5, characterized in that, In step S1, the first metal M1 is selected from at least one of Al, Zn, Mg, and Sn; the mass ratio of silicon to M1 is 1:1 to 1:8; the melting temperature is 400 to 1500℃; the stirring speed is 50 to 3000 rpm, and the stirring time is 10 to 120 minutes; the atomization method is gas atomization or centrifugal atomization; the atomization medium is high-purity argon or nitrogen, and the atomization pressure is 1 to 10 MPa; the particle size D50 of the M1-Si alloy powder is 1 to 200 μm; the conductive material also includes a pretreatment process.

7. The method for preparing a high-capacity, long-cycle silicon-based anode material according to claim 5, characterized in that, In step S2, the acidic solution is at least one of hydrochloric acid, sulfuric acid, phosphoric acid, or nitric acid solution; the concentration of the acidic solution is 0.5~5 mol / L; the acid dissolution temperature is 20~80℃; and the acid dissolution time is 1~24 hours.

8. The method for preparing a high-capacity, long-cycle silicon-based anode material according to claim 5, characterized in that, In step S3, the organic carbon source is selected from at least one of phenolic resin, asphalt, polyacrylonitrile, polyvinyl alcohol, sucrose, glucose or citric acid; the concentration of the organic carbon source solution is 5% to 40%, and the viscosity is 10 to 1500 mPa·s.

9. The method for preparing a high-capacity, long-cycle silicon-based anode material according to claim 5, characterized in that, In step S4, the pyrolysis temperature is 500~1000℃; the heating rate is 1~10℃ / min; the holding time is 1~6 hours; and the inert protective atmosphere is high-purity argon or nitrogen.

10. The application of a high-capacity, long-cycle silicon-based anode material as described in any one of claims 1 to 4, or a high-capacity, long-cycle silicon-based anode material prepared by the preparation method described in any one of claims 5 to 9, in a secondary battery.

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