High-compaction-density silicon-carbon-graphite composite negative electrode material and preparation method and application thereof

Abstract

The invention discloses a high-compaction-density silicon-carbon-graphite composite negative electrode material as well as a preparation method and application thereof, and belongs to the technical field of lithium ion battery materials. The method comprises the following steps: grinding and dispersing nano silicon powder, carbon nanotubes and a dispersing agent in a solvent to obtain nano silicon slurry; adding a micron-sized artificial graphite framework material and a water-soluble polymer carbon source, and dispersing at a high speed to obtain mixed precursor slurry; carrying out spray drying granulation on the slurry to obtain a spherical precursor; and finally, performing high-temperature carbonization treatment in an inert atmosphere to obtain the silicon-carbon-graphite composite negative electrode material. The micron-sized graphite is introduced as a framework support, so that the compaction density of the material is effectively improved; a long-range conductive network is constructed by using the carbon nanotubes, and in-situ carbonization coating is matched, so that the problems of volume expansion and poor conductivity of a silicon-based material are solved. The process flow is short, secondary granulation is not needed, the cost is low, and the method is suitable for large-scale industrial production.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery material technology, specifically relating to a high-density silicon-carbon-graphite composite anode material, its preparation method, and its application. Background Technology

[0002] With the rapid development of new energy vehicles and portable electronic devices, higher demands are being placed on the energy density of lithium-ion batteries. The theoretical specific capacity of traditional graphite anode materials is only 372 mAh / g, approaching their performance limit. Silicon-based anode materials, due to their ultra-high theoretical specific capacity (4200 mAh / g), are considered the most promising next-generation anode materials. However, silicon undergoes dramatic volume expansion (>300%) during charging and discharging, leading to particle pulverization, conductive agent shedding, and repeated SEI film rupture and regeneration, ultimately causing rapid capacity decay. Current silicon-carbon composite materials mainly suffer from the following problems: complex processes and high costs: many technologies employ CVD vapor deposition or multi-step granulation and sintering, requiring sophisticated equipment and consuming significant energy. Low compaction density: traditional nano-silicon / porous carbon composite materials have excessive internal pores, resulting in low electrode compaction density (typically <1.0 g / cm³). 3 This limits the volumetric energy density of the battery. Maintaining conductivity is difficult: the simple carbon coating is prone to breakage after silicon expansion, leading to an interruption of internal conductivity.

[0003] Chinese patent application CN107342411B discloses a method for preparing graphene-silicon-carbon lithium-ion battery anode materials. The method employs a multi-step process involving "nano-silicon, graphene coating, pitch carbon coating, and carbonization" to prepare the graphene-silicon-carbon composite material. Nano-silicon is dispersed between graphene sheets, providing mechanical support and a conductive network. Pitch carbon coating further forms carbon microspheres, preventing direct contact between silicon and the electrolyte and improving cycle stability. However, this method involves multiple steps, including graphene coating, spray drying, heat treatment, carbon microsphere growth, and carbonization, resulting in a long process and high energy consumption. With graphene and carbon microspheres as the main structure, the numerous internal pores lead to a low compaction density (the highest in the examples is only 1.48 g / cm³). 3 This limits the improvement of volumetric energy density. Insufficient flexibility and the potential for conductive contact failure due to silicon volume expansion during long-term cycling are also limitations. Chinese patent application CN108736007B discloses a method for preparing high-density silicon-carbon anode materials for lithium-ion batteries. It employs a "nano-silicon + porous natural graphite + carbon source coating" strategy, embedding nano-silicon into the pores of porous graphite through ball milling, followed by carbon source coating and carbonization granulation to obtain high-density silicon-carbon materials (compact density reaching 1.65–1.75 g / cm³). 3However, this requires the use of special porous natural graphite as a carrier, which limits the availability of raw materials and increases costs. It also necessitates the separate preparation of nano-silicon and porous graphite, followed by multiple rounds of ball milling, coating, and carbonization, a complex process. Furthermore, it relies heavily on the conductivity of graphite itself, lacking a flexible, long-range conductive network, and contact failure still easily occurs after silicon expansion.

[0004] Therefore, the industry urgently needs to develop a method for preparing silicon-based anode materials that is simple to process, low in cost, and can achieve high capacity, high real density, and long cycle life. Summary of the Invention

[0005] In order to overcome the shortcomings of the prior art, the present invention aims to provide a high-density silicon-carbon-graphite composite anode material, its preparation method and application, so as to solve the technical problems of complex preparation process, high cost and difficulty in achieving both high density and long cycle performance of existing silicon-carbon anode materials.

[0006] To achieve the above objectives, the present invention employs the following technical solution: This invention discloses a method for preparing a high-density silicon-carbon-graphite composite anode material, comprising: Nanoscale silicon powder, conductive carbon nanotubes, and a dispersant are added to deionized water and dispersed by grinding to obtain a nano-slurry. Micron-sized graphite framework material and water-soluble polymeric carbon source are added to the nano-slurry and mixed evenly to obtain a mixed precursor slurry. The mixed precursor slurry is granulated by spray drying to obtain a spherical composite precursor. The spherical composite precursor is subjected to high-temperature carbonization under an inert atmosphere to obtain a high-density silicon-carbon-graphite composite anode material.

[0007] Preferably, the mass ratio of nano-silicon powder, conductive carbon nanotubes, dispersant and deionized water is (5-20):(0.1-2):(0.1-1):(70-90).

[0008] Preferably, the D50 particle size of the nano-silicon powder is 80-200 nm; the conductive carbon nanotubes are single-walled carbon nanotubes or multi-walled carbon nanotubes with a diameter of 2-20 nm and a length of 5-50 μm.

[0009] Preferably, the micron-sized graphite framework material is one or more of artificial graphite, natural graphite, and mesophase carbon microspheres; the D50 particle size of the micron-sized graphite framework material is 5-15 μm; and the mass ratio of nano-silicon powder to micron-sized graphite framework material is 1:(3-9).

[0010] Preferably, the water-soluble polymeric carbon source is selected from one or more of polyacrylic acid, sodium alginate, sodium carboxymethyl cellulose, polyvinyl alcohol, waterborne asphalt emulsion, and waterborne phenolic resin; the amount of water-soluble polymeric carbon source added is 5%-15% of the total mass of solid raw materials; and the solid content of the mixed precursor slurry is 20%-40%.

[0011] Preferably, the spray drying is centrifugal spray drying, with an inlet air temperature of 180-250℃ and an outlet air temperature of 80-110℃; the D50 particle size of the resulting spherical composite precursor is 15-25μm.

[0012] Preferably, the conditions for high-temperature carbonization are: heating to 700-1000°C at a heating rate of 3-10°C / min in a nitrogen or argon atmosphere, and holding at that temperature for 2-6 hours; after the carbonization treatment, the material is further subjected to surface vapor deposition treatment, and the carbon source for deposition is selected from methane, acetylene or ethylene.

[0013] This invention discloses a high-density silicon-carbon-graphite composite anode material, which is prepared by the above-mentioned method for preparing high-density silicon-carbon-graphite composite anode materials.

[0014] Preferably, the compaction density of the high-density silicon-carbon-graphite composite anode material is ≥1.4 g / cm³. 3 Specific surface area ≤ 5 m² 2 / g; The structure of the high-density silicon-carbon-graphite composite anode material is a microsphere structure in which nano-silicon and carbon nanotubes are uniformly embedded in the gaps between micron-sized graphite particles and coated with amorphous carbon.

[0015] This invention discloses the application of the above-mentioned high-density silicon-carbon-graphite composite anode material in the preparation of lithium-ion batteries.

[0016] Compared with the prior art, the present invention has the following beneficial effects: This invention discloses a method for preparing a high-density silicon-carbon-graphite composite anode material. The dispersion of nano-silicon, its composite with a conductive agent, its integration with the framework material, and preliminary granulation are all completed in a single spray drying step. Compared to the prior art processes requiring multiple coating steps, heat treatment, or special porous raw materials, this method significantly shortens the process, reduces equipment requirements, and facilitates large-scale production, achieving low-cost one-step preparation. Spray drying forces nano-silicon and carbon nanotubes to tightly bond with graphite particles in the droplets and dry to form a dense precursor structure with graphite as the core and nano-active materials filling the gaps. Subsequent carbonization transforms the polymeric carbon source into amorphous carbon, welding the components into a single unit. This structure lays the foundation for simultaneously achieving high density and good cycling performance from the source.

[0017] This invention discloses a high-density silicon-carbon-graphite composite anode material. Conventional, dense micron-sized graphite is used instead of expensive or special porous materials as the main structural component, forming a high-density matrix. The gaps between the matrix serve as spaces to accommodate active materials; in the embodiments, the density reaches 1.25-1.48 g / cm³. 3 The compaction density of this material fundamentally solves the problem of low compaction density in traditional silicon-carbon materials due to the high porosity of the porous carbon matrix (Comparative Example 1: only 0.65 g / cm³). 3 This addresses the problem of confining high-capacity nano-silicon within the limited space between graphite particles, rather than loosely adhering or forming a separate phase. This allows the silicon to be constrained and buffered by the surrounding rigid graphite sheets during charge and discharge, dispersing the expansion force and preventing the pulverization of macroscopic particles or the collapse of the electrode structure. The sharp deterioration in cycle performance compared to Example 1 (using micron-sized silicon) or Comparative Example 1 (without a framework) demonstrates the decisive role of this structural design. While achieving high reversible capacity (620-1105 mAh / g), it significantly mitigates cycle decay caused by volume expansion. High aspect ratio and flexibility of carbon nanotubes are introduced as structural conductive agents. During spray drying, the carbon nanotubes are uniformly distributed with the slurry. After drying, they overlap inside the microspheres, encapsulating silicon particles and bridging graphite to form a through-hole flexible conductive network. This network is fundamentally different from traditional point-contact conductive carbon black, providing channels for electron transport and improving rate performance. When silicon particles repeatedly expand and contract, this network deforms accordingly without breaking, maintaining electrical contact throughout. This ensures the stability of the conductive network during long-term cycling, resulting in high cycle retention (as per actual value). Example 1 achieves a structural guarantee of 92.5%; utilizing the integrated effect of a water-soluble polymeric carbon source, which acts as both a granulation binder and the final carbon source, after high-temperature carbonization, this carbon source transforms into a continuous layer of amorphous carbon, acting as a protective shell to tightly weld graphite, silicon, and carbon nanotubes into a mechanical whole from the outside, and covering surface defects; this strengthens the structural integrity of the particles, enabling them to withstand electrode rolling pressure and cyclic stress; it reduces the specific surface area of ​​the material, effectively reducing side reactions between the electrolyte and the active material, which is the direct reason for obtaining a high initial coulombic efficiency. Example 4 further enhances this effect by adding additional carbon through CVD, increasing the initial efficiency to 90.5% and the cycle retention rate to 94.8%. It achieves a synergistic improvement in high compaction density (derived from a dense graphite skeleton), high initial efficiency (derived from carbon coating reducing side reactions), and long cycle life (derived from the flexible network of carbon nanotubes and the buffering effect of graphite).

[0018] This invention discloses the application of a high-density silicon-carbon-graphite composite anode material in the preparation of lithium-ion batteries. Lithium-ion batteries prepared using this material inherit and amplify its core advantages: 1) Higher energy density: The high density of the material (≥1.4 g / cm³) allows for more active material to be filled within a limited electrode volume, directly increasing the volumetric energy density of the battery; combined with the material's high reversible capacity (620-1105 mAh / g in Examples 1-5), the gravimetric energy density can be simultaneously improved. 2) Better cycle life and safety: The material's excellent cycle retention rate (generally >85% in examples) directly translates into a longer battery life. Simultaneously, the graphite framework and carbon coating structure effectively suppress electrode pulverization caused by silicon expansion, reducing abnormal internal resistance growth and the risk of thermal runaway, thus improving the overall safety of the battery. 3) Potential fast-charging capability: The three-dimensional conductive network constructed from carbon nanotubes within the material provides extremely high electron conduction rates, which helps reduce battery polarization during high-current charging, thereby supporting faster charging speeds. Therefore, this claim protects the high-performance lithium-ion battery powered by this advanced material, clarifying the ultimate industrial value and market application of the invention. Attached Figure Description

[0019] Figure 1 This is a flowchart of the preparation method of the high-density silicon-carbon-graphite composite anode material disclosed in this invention. Detailed Implementation

[0020] The technical solution of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, 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.

[0021] Unless otherwise specified, all embodiments and preferred embodiments mentioned herein can be combined to form new technical solutions.

[0022] Unless otherwise specified, all the technical features and preferred features mentioned herein can be combined to form new technical solutions.

[0023] In this invention, unless otherwise specified, percentage (%) or parts refer to weight percentage or parts relative to the composition.

[0024] Unless otherwise specified, the components or preferred components involved in this invention can be combined with each other to form new technical solutions.

[0025] In this invention, unless otherwise specified, the numerical range "a~b" represents a shortened representation of any combination of real numbers between a and b, where a and b are both real numbers. For example, the numerical range "6~22" indicates that all real numbers between "6~22" have been listed in this document, and "6~22" is simply a shortened representation of these numerical combinations.

[0026] The "scope" disclosed in this invention can be in the form of a lower limit and an upper limit, and can be one or more lower limits and one or more upper limits, respectively.

[0027] In this invention, the term "and / or" as used herein refers to any combination of one or more of the associated listed items, as well as all possible combinations, and includes such combinations.

[0028] In this invention, unless otherwise stated, the various reactions or operation steps may be performed sequentially or in a particular order. Preferably, the reaction methods described herein are performed sequentially.

[0029] Unless otherwise stated, the technical and scientific terms used herein have the same meanings as those familiar to those skilled in the art. Furthermore, any methods or materials similar to or equivalent to those described herein may also be used in this invention.

[0030] This invention employs a ternary composite strategy of "nano-silicon + carbon nanotubes + graphite framework" and achieves engineered preparation through a one-step spray drying and carbonization process.

[0031] This invention provides a method for preparing a high-density silicon-carbon-graphite composite anode material, comprising the following steps: 1) Place nano-silicon powder, carbon nanotubes and dispersant in a medium and grind and disperse to obtain a stable nano-slurry; 2) Add micron-sized graphite as a framework support material and add a water-soluble polymer resin with good film-forming properties as a carbon source binder, and mix evenly; 3) The slurry is atomized and dried using a spray drying process to form a dense spherical precursor with graphite as the core, nano-silicon and CNTs filling the gaps and bonded by resin; 4) High-temperature carbonization causes the resin to decompose into amorphous carbon, which tightly locks in all components, resulting in the final product.

[0032] The beneficial effects of this invention are as follows: High compaction density: By introducing micron-sized dense graphite as a framework, the pores of the nano-silicon aggregates are significantly filled, resulting in a significant increase in compaction density compared to pure silicon-carbon materials (reaching 1.4-1.6 g / cm³). 3 ).

[0033] Three-dimensional conductive network: Carbon nanotubes construct a long-range conductive network inside the microspheres. Even if the silicon particles expand and contract, the flexible CNTs can still maintain contact, reducing the internal resistance of the material.

[0034] Low-cost one-step process: Compared with complex dual granulation or vapor deposition, this invention only requires one spraying and one sintering, with a short process flow and easy to achieve large-scale mass production.

[0035] This invention provides a method for preparing a high-density silicon-carbon-graphite composite anode material, which specifically includes the following steps: 1) Preparation of Nanoscale Dispersion: Nanoscale silicon powder, conductive carbon nanotubes (CNTs), and a dispersant are added to deionized water and dispersed by grinding in a sand mill to obtain a uniformly dispersed nanoscale conductive slurry. The D50 of the nanoscale silicon powder is controlled between 80-200 nm. The mass ratio of nanoscale silicon powder, carbon nanotubes, dispersant, and deionized water is (5-20):(0.1-2):(0.1-1):(70-90). The carbon nanotubes are single-walled or multi-walled carbon nanotubes with a diameter of 2-20 nm and a length of 5-50 μm.

[0036] 2) Preparation of composite slurry: Add micron-sized graphite framework material and water-soluble polymeric carbon source to the slurry obtained in step 1), perform high-speed shear dispersion, and adjust the solid content to 20%-40% to obtain a mixed precursor slurry. The micron-sized graphite framework material is one or more of artificial graphite, natural graphite, or mesophase carbon microspheres with a particle size D50 of 5-15 μm; the mass ratio of nano-silica powder to micron-sized graphite framework material is 1:(3-9). The water-soluble polymeric carbon source is one or more of polyacrylic acid, sodium alginate, sodium carboxymethyl cellulose, polyvinyl alcohol, waterborne asphalt emulsion, and waterborne phenolic resin; the amount of polymeric carbon source added is 5%-15% of the total mass of solid raw materials.

[0037] 3) One-step spray granulation: The mixed precursor slurry from step 2) is granulated using a centrifugal spray drying tower, with the inlet air temperature controlled at 180-250℃ and the outlet air temperature at 80-110℃, to obtain a spherical composite precursor with a micro-nano embedded structure. The particle size D50 of the spherical composite precursor obtained by spray drying is controlled at 15-25 μm.

[0038] 4) High-temperature carbonization: The spherical composite precursor is placed in a rotary kiln or pusher furnace under an inert atmosphere and heated to 700-1000℃ at a heating rate of 3-10℃ / min. It is held at this temperature for 2-6 hours, allowed to cool naturally, and then sieved to obtain the high-density silicon-carbon-graphite composite anode material. The inert atmosphere is nitrogen or argon. After carbonization, a surface vapor deposition (CVD) process is performed on the material, with methane, acetylene, or ethylene as the carbon source.

[0039] Furthermore, by optimizing the solid-liquid system, the full and stable dispersion of nano-silicon powder and carbon nanotubes in the medium was ensured. If the nano-silicon content is too low, its capacity contribution is limited; if it is too high, it is prone to agglomeration, affecting dispersion and subsequent composite uniformity. A carbon nanotube ratio within this range (0.1-2) effectively constructs a continuous three-dimensional conductive network while avoiding a sharp increase in slurry viscosity or cost due to excessive amounts.

[0040] Furthermore, limiting the D50 of nano-silicon to 80-200 nm is key to mitigating the absolute volume expansion stress of silicon during lithium intercalation by utilizing the nanosize effect. Excessively large sizes (e.g., micrometer-level) lead to stress concentration and particle breakage; excessively small sizes result in excessively large surface areas, exacerbating side reactions and reducing first-cycle efficiency. A comparison of data from Example 3 (high silicon content) and Comparative Example 1 (no framework) confirms the importance of nano-composite structures for maintaining cycling performance. Limiting carbon nanotubes to single-walled or multi-walled structures and controlling their diameter (2-20 nm) and length (5-50 μm) aims to utilize their high aspect ratio and excellent mechanical properties. Inside the microspheres formed by spray granulation, these carbon nanotubes can overlap, encapsulating silicon particles and connecting to the graphite framework, forming a continuous, flexible three-dimensional conductive network. This network is not easily broken during repeated expansion and contraction of silicon particles, maintaining good electronic conductivity, thereby significantly reducing electrode polarization and improving rate performance and cycling stability.

[0041] Furthermore, dense artificial graphite and natural graphite with a D50 of 5-15 μm are used as the framework, which inherently possesses a high tap density. Using this as the core of the composite particles effectively fills the excess pores created by nano-silicon and carbon nanotubes, fundamentally improving the compaction density of the composite powder. The compaction densities of Examples 1-5 are 1.25-1.48 g / cm³. 3 The concentration was significantly higher than that of pure silicon-carbon material in Comparative Example 1 (0.65 g / cm³). 3 This directly demonstrates the contribution of the graphite framework. Maintaining a mass ratio of nano-silicon to graphite of 1:(3-9) means that silicon is diluted and confined within the limited space between graphite particles. Graphite not only serves as the conductive substrate, but its rigid, layered structure also mechanically restricts and buffers the expansion of silicon, inhibiting overall particle pulverization and electrode structure collapse, thereby improving cycle retention (e.g., 92.5% in Example 1).

[0042] Furthermore, the selected water-soluble polymers, such as polyacrylic acid and sodium alginate, play an excellent role in binding and film formation during the slurry stage, ensuring the formation of structurally complete spherical particles during spray drying. During the carbonization stage, they can pyrolyze to generate an amorphous carbon layer, further coating and fixing the internal nano-silicon and graphite, enhancing structural integrity, compensating for defects on the graphite surface, reducing electrolyte side reactions, and thus improving the initial coulombic efficiency (generally >86% in the examples). The amount of polymeric carbon source is controlled at 5%-15% of the total solid mass, and the slurry solid content is adjusted to 20%-40%, ensuring that the slurry has good rheological properties, suitable for high-speed dispersion and pumping, and meeting the process requirements of spray drying to form precursors with uniform particle size and good sphericity.

[0043] Furthermore, centrifugal spray drying is employed, with the inlet air temperature controlled at 180-250℃ and the outlet air temperature at 80-110℃. This ensures rapid and uniform solvent evaporation, preventing localized overheating that could lead to component segregation or particle adhesion. The resulting D50 is a spherical composite precursor with a diameter of 15-25 μm, exhibiting good flowability, bulk density, and a consistent microstructure (graphite core with silicon and CNTs embedded). This provides an excellent raw material foundation for subsequent electrode processing (coating uniformity, compaction). By directly converting the solution dispersion system into a solid powder with a pre-defined composite structure, the uniform composite and preliminary shaping of various nanoscale and microscale materials are efficiently achieved.

[0044] Furthermore, carbonization at 700-1000℃ under an inert atmosphere with a specific heating program (3-10℃ / min) allows the polymeric carbon source to be stably and fully converted into amorphous carbon. This carbon phase, like a gel, firmly binds nano-silicon, carbon nanotubes, and the graphite framework into a single mechanical unit, greatly enhancing the structural rigidity of the composite particles. This, in turn, resists volume change stress during long-term cycling and improves capacity retention. Selective surface vapor deposition (CVD) treatment, using carbon sources such as methane and acetylene to deposit a dense, highly conductive graphitized carbon layer on the surface of the carbonized material, can further reduce the specific surface area of ​​the material (e.g., reduced to 2.5 μm in Example 4). 2 / g), reducing irreversible capacity loss in the first week and improving first-efficiency (90.5% in Example 4); at the same time, this more robust coating layer can more effectively isolate the electrolyte and significantly improve cycle life (94.8% retention rate in Example 4).

[0045] This invention provides a high-density silicon-carbon-graphite composite anode material prepared by the above method, exhibiting a microsphere structure in which nano-silicon and carbon nanotubes are uniformly embedded in the gaps between micron-sized graphite particles and coated with amorphous carbon. The powder compaction density of the high-density silicon-carbon-graphite composite anode material is ≥1.4 g / cm³. 3 Specific surface area ≤ 5 m² 2 / g. Powder compaction density ≥1.4 g / cm³ 3 This solves the problem of the generally low compaction density of silicon-carbon materials (typically <1.60 g / cm³) mentioned in the background technology. 3 Comparative Example 1 was even only 0.65 g / cm³. 3 Addressing the industry pain points of [missing information] is a prerequisite for achieving high volumetric energy density batteries; specific surface area ≤ 5 m² 2 The / g value strictly controls the contact area between the material and the electrolyte, which is a key structural parameter for achieving high initial coulombic efficiency (generally >86% in examples) and reducing ongoing side reactions. Micron-sized graphite particles serve as the framework and matrix, providing high density and physical support; nano-silicon embedded in its gaps contributes high capacity while its expansion is limited and buffered by the surrounding graphite space; the uniform distribution of carbon nanotubes constructs a flexible three-dimensional conductive highway that runs through the microspheres, ensuring high rate performance and the durability of the conductive network during cycling; the outer layer of amorphous carbon acts as a structural adhesive and protective shell, binding the components together and reducing surface defects.

[0046] This invention provides a lithium-ion battery comprising the aforementioned high-density silicon-carbon-graphite composite anode material. Lithium-ion batteries manufactured using the composite anode material provided by this invention will inherit all the advantages of the material: namely, significantly improved energy density (thanks to high density and high reversible capacity), cycle life (thanks to the stable composite structure), and potential fast-charging performance (thanks to the three-dimensional conductive network).

[0047] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, 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, not all, of the embodiments of the present invention. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0048] Example 1 A method for preparing a high-density silicon-carbon-graphite composite anode material includes the following steps: 1) Add 100g of silicon nanoparticles with a particle size D50 of 150nm, 5g of single-walled carbon nanotubes, and 2g of PVP dispersant to 1000ml of deionized water and grind them in a sand mill for 2 hours to obtain a nano dispersion.

[0049] 2) Add 800g of artificial graphite fine powder with a particle size D50 of 8μm and 100g of water-based asphalt emulsion with a solid content to the above dispersion, stir for 2 hours using a high-speed disperser, and adjust the solid content of the slurry to 35%.

[0050] 3) Pump the slurry into a centrifugal spray dryer with an inlet temperature of 220°C, an outlet temperature of 100°C, and a centrifugal disc speed of 15000 rpm to obtain spherical precursor powder.

[0051] 4) The precursor was placed in a tube furnace and heated to 900℃ at a rate of 5℃ / min under nitrogen protection, and held at that temperature for 4 hours. After natural cooling, it was sieved to obtain silicon-carbon graphite composite material A1.

[0052] Tests showed that material A1 has a D50 of 18.5 μm and a powder compaction density of 1.45 g / cm³. 3 It has a reversible specific capacity of 620mAh / g and an initial coulombic efficiency of 89.2%.

[0053] Example 2 A method for preparing a high-density silicon-carbon-graphite composite anode material includes the following steps: 1) Add 150g of nano-silicon powder with a particle size D50 of 100nm, 8g of multi-walled carbon nanotubes, and 3g of sodium carboxymethyl cellulose (CMC) to water and disperse by sand milling.

[0054] 2) Add 700g of natural graphite modified powder with a particle size D50 of 12μm and 150g of sucrose as a carbon source, and stir evenly.

[0055] 3) The spray drying conditions were the same as in Example 1 to obtain the precursor.

[0056] 4) Carbonize at 800℃ for 5 hours under an argon atmosphere to obtain composite material A2.

[0057] The reversible specific capacity of material A2 was tested to be 750 mAh / g, the initial coulombic efficiency was 87.5%, and the compaction density was 1.38 g / cm³. 3 .

[0058] Example 3 A method for preparing a high-density silicon-carbon-graphite composite anode material, designed for high capacity, includes the following steps: 1) Disperse 300g of nano-silicon powder with a particle size D50 of 80nm and 10g of single-walled carbon nanotubes in water.

[0059] 2) Add 500g of artificial graphite (D50=6μm) and 200g of waterborne phenolic resin as a high residual carbon source.

[0060] 3) After spray granulation, carbonize at 1000℃ for 3 hours.

[0061] Composite material A3 was obtained. Due to its high silicon content, this material achieves a reversible specific capacity of 1100 mAh / g, making it suitable for high-energy-density pouch cells, with a compaction density of 1.25 g / cm³. 3 .

[0062] Example 4 A method for preparing a high-density silicon-carbon-graphite composite anode material, which is a CVD-enhanced version, includes the following steps: The precursor was prepared by repeating steps (1)-(3) of Example 1. In step (4), carbonization was first carried out at 900°C, followed by CVD vapor deposition treatment with acetylene gas for 30 minutes, and then cooled and removed from the furnace.

[0063] Composite material A4 was obtained. Compared to Example 1, the specific surface area of ​​A4 was further reduced to 2.5 m². 2 / g, cycle life increased by 15%, first-efficacy rate increased to 90.5%.

[0064] Example 5 A method for preparing a high-density silicon-carbon-graphite composite anode material, using different binder systems, includes the following steps: 1) The nano-silicon dispersion is the same as in Example 1.

[0065] 2) Add an artificial graphite skeleton and replace the binder with sodium alginate (100g), taking advantage of its rich carboxyl group content to form hydrogen bonds with the silicon surface.

[0066] 3) Spray drying and carbonization at 900℃.

[0067] Composite material A5 was obtained. This material exhibits the best performance in slurry dispersion stability, and the prepared electrodes have high peel strength and excellent cycle stability.

[0068] Example 6 A method for preparing a high-density silicon-carbon-graphite composite anode material includes the following steps: 1) Add 50g of nano-silicon powder with a particle size D50 of 200nm, 1g (content 0.1) of multi-walled carbon nanotubes (tube diameter 5nm, length 10μm) and 5g of PVP dispersant to 700g of deionized water, and grind with a sand mill for 2 hours to obtain a nano-dispersion.

[0069] 2) Add 150g of mesophase carbon microspheres with a particle size D50 of 5μm and 10.25g of polyacrylic acid (about 5% of the total solid mass) to the above dispersion, stir using a high-speed disperser, and adjust the solid content of the slurry to 20%.

[0070] 3) Pump the slurry into a centrifugal spray dryer with an inlet temperature of 180°C and an outlet temperature of 80°C to obtain spherical precursor powder.

[0071] 4) The precursor was placed in a tube furnace and heated to 700°C at a rate of 3°C / min under nitrogen protection, and held at that temperature for 2 hours. After natural cooling, it was sieved to obtain silicon-carbon graphite composite material A6.

[0072] Example 7 A method for preparing a high-density silicon-carbon-graphite composite anode material includes the following steps: 1) Add 200g of nano-silicon powder with a particle size D50 of 100nm, 20g of single-walled carbon nanotubes (tube diameter 15nm, length 30μm) and 10g of sodium carboxymethyl cellulose to 900g of deionized water and grind and disperse them.

[0073] 2) Add 1800g of artificial graphite with a particle size D50 of 15μm to the above dispersion, mix well, and adjust the slurry solid content to 40%.

[0074] 3) Pump the slurry into a centrifugal spray dryer with an inlet temperature of 250°C and an outlet temperature of 110°C to obtain spherical precursor powder.

[0075] 4) The precursor was heated to 900℃ at 10℃ / min under argon protection and held for 6 hours. Then, methane gas was introduced for CVD vapor deposition for 30 minutes, and the mixture was cooled and removed from the furnace to obtain composite material A7.

[0076] Example 8 A method for preparing a high-density silicon-carbon-graphite composite anode material includes the following steps: 1) Add 120g of nano-silicon powder with a particle size D50 of 120nm, 6g of multi-walled carbon nanotubes, and 6g of polyvinyl alcohol to 800g of deionized water and grind and disperse them.

[0077] 2) Add 600g of natural graphite with a particle size D50 of 10μm to the above dispersion, mix well, and adjust the slurry solid content to 30%.

[0078] 3) Spray dry the slurry (inlet 200℃, outlet 95℃) to obtain the precursor.

[0079] 4) After carbonizing the precursor under nitrogen protection (800℃, heat preservation for 4h), ethylene gas was introduced for short-time CVD treatment to obtain composite material A8.

[0080] Comparative Example 1 Simply mix 100g of nano-silica powder and 100g of water-based asphalt, spray granulate and carbonize, without adding graphite skeletons and carbon nanotubes.

[0081] The resulting material B1 is a pure silicon-carbon material. Although it has a high capacity (~2000 mAh / g), its compaction density is only 0.65 g / cm³. 3 Furthermore, the capacity retention rate was less than 50% after 50 cycles, indicating that the lack of graphite framework and CNT network seriously affected the engineering practicality of the material.

[0082] Figure 1 This is a flowchart illustrating the preparation method of the high-density silicon-carbon-graphite composite anode material disclosed in this invention. As can be seen from the diagram, this invention simplifies the complex multi-scale material composite and structural construction process into a one-step continuous process through a simple path of nano-dispersion, composite formulation, spray granulation, and high-temperature carbonization. From a uniform nano-dispersion to a slurry embedded with a micron-sized graphite framework, and finally through spray drying and carbonization consolidation, a unique product with a microsphere structure and an internal conductive network is directionally constructed. This achieves in-situ optimized composite of active materials, conductive agents, and structural frameworks, thereby simultaneously overcoming the fundamental challenge of balancing compaction density, initial efficiency, and cycle life in silicon-carbon anodes.

[0083] Performance test results The negative electrode materials prepared in Examples 1-5 and Comparative Example 1 were assembled into coin cells for testing (0.01-1.5V, 0.1C charge and discharge).

[0084] Table 1. Performance Comparison of Batteries Fabricated from High-Density Silicon-Carbon-Graphite Composite Anode Materials in the Examples and Comparative Examples

[0085] Table 1 compares the performance of batteries made from the high-density silicon-carbon-graphite composite anode materials disclosed in the examples and comparative examples. As shown in the table, although Comparative Example 1 (pure silicon-carbon, without graphite framework and CNTs) achieved an extremely high initial discharge capacity (2010.5 mAh / g), its compaction density (0.65 g / cm³) was low. 3 The initial coulombic efficiency (78.5%) and 100-cycle retention (45.2%) were both extremely low. Examples 1-5 successfully achieved high compaction density (1.25-1.48 g / cm³). 3 An excellent balance is achieved between high initial efficiency (86.1-90.5%) and excellent cycling stability (85.4-94.8% retention). The compacted density of all embodiments is ≥1.4 g / cm³. 3(Except for Example 3, which has a value of 1.25), far exceeding Comparative Example 1, directly demonstrating the decisive role of the micron-scale graphite framework in filling pores and increasing material density. The first-cycle efficiency of the examples is generally above 87%, reaching a maximum of 90.5% (Example 4). This is mainly due to the amorphous carbon coating layer formed by the carbonization of the water-soluble polymeric carbon source, which effectively reduces the specific surface area of ​​the material and reduces irreversible electrolyte decomposition side reactions in the first cycle. Example 4 further deposits a dense carbon layer via CVD, maximizing the first-cycle efficiency and confirming this. The 100-cycle retention rate of the examples all exceeds 85%, with Examples 4 and 5 exceeding 93%. This is because the graphite framework physically constrains and buffers the volume expansion of silicon; the flexible conductive network constructed by carbon nanotubes maintains the integrity of the electron pathway during cycling; and the amorphous carbon coating layer stabilizes the overall structure. The synergistic effect of these three factors effectively suppresses capacity decay. Example 3, by increasing the silicon content (300g) and using a high residual carbon resin, achieved the highest initial discharge capacity (1105.4 mAh / g), suitable for applications requiring high energy density. Its compaction density (1.25 g / cm³) was also achieved. 3 Although the silicon / graphite ratio and cycle retention rate (85.4%) decreased, they remained at an acceptable high level. Examples 1, 2, 4, and 5, by controlling the silicon / graphite ratio and optimizing the carbon source, maintained a high compaction density (1.38-1.48 g / cm³). 3 While exhibiting excellent cycling performance (retention rate >90%), this invention provides a reversible capacity of 620-750 mAh / g, meeting the requirements for high volumetric energy density and long lifetime. By introducing a one-step granulation process using a graphite framework and CNTs, this invention significantly improves the compaction density and cycling stability of the material, possessing extremely high industrialization value.

[0086] In summary, this invention discloses a high-compact-density silicon-carbon-graphite composite anode material, its preparation method, and its application. The process involves grinding and dispersing nano-silicon powder, carbon nanotubes, and a dispersant in a solvent to obtain a nano-silicon slurry. Micron-sized artificial graphite framework material and a water-soluble polymeric carbon source are then added and dispersed at high speed to obtain a mixed precursor slurry. The slurry is then spray-dried and granulated to obtain spherical precursors. Finally, high-temperature carbonization is performed under an inert atmosphere to obtain the silicon-carbon-graphite composite anode material. This invention effectively improves the compaction density of the material by introducing micron-sized graphite as a framework support. The use of carbon nanotubes to construct a long-range conductive network, combined with in-situ carbonization coating, solves the problems of volume expansion and poor conductivity in silicon-based materials. This process is short, requires no secondary granulation, and is low-cost, making it suitable for large-scale industrial production.

[0087] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a high-density silicon-carbon-graphite composite anode material, characterized in that, include: Nano-silicon powder, conductive carbon nanotubes and dispersant are added to deionized water and dispersed by grinding to obtain a nano slurry; Micron-sized graphite framework material and water-soluble polymeric carbon source are added to nano-slurry and mixed evenly to obtain a mixed precursor slurry. The mixed precursor slurry is granulated by spray drying to obtain a spherical composite precursor. The spherical composite precursor is then subjected to high-temperature carbonization under an inert atmosphere to obtain a high-pressure, solid-density silicon-carbon-graphite composite anode material.

2. The method for preparing the high-density silicon-carbon-graphite composite anode material according to claim 1, characterized in that, The mass ratio of the nano-silicon powder, conductive carbon nanotubes, dispersant and deionized water is (5-20):(0.1-2):(0.1-1):(70-90).

3. The method for preparing the high-density silicon-carbon-graphite composite anode material according to claim 1, characterized in that, The D50 particle size of the nano-silicon powder is 80-200nm; the conductive carbon nanotubes are single-walled carbon nanotubes or multi-walled carbon nanotubes with a diameter of 2-20nm and a length of 5-50μm.

4. The method for preparing the high-density silicon-carbon-graphite composite anode material according to claim 1, characterized in that, The micron-sized graphite framework material is one or more of artificial graphite, natural graphite, and mesophase carbon microspheres; the D50 particle size of the micron-sized graphite framework material is 5-15 μm; the mass ratio of the nano-silicon powder to the micron-sized graphite framework material is 1:(3-9).

5. The method for preparing the high-density silicon-carbon-graphite composite anode material according to claim 1, characterized in that, The water-soluble polymeric carbon source is selected from one or more of polyacrylic acid, sodium alginate, sodium carboxymethyl cellulose, polyvinyl alcohol, waterborne asphalt emulsion, and waterborne phenolic resin; the amount of water-soluble polymeric carbon source added is 5%-15% of the total mass of solid raw materials; the solid content of the mixed precursor slurry is 20%-40%.

6. The method for preparing the high-density silicon-carbon-graphite composite anode material according to claim 1, characterized in that, The spray drying is centrifugal spray drying, with an inlet air temperature of 180-250℃ and an outlet air temperature of 80-110℃; the D50 particle size of the resulting spherical composite precursor is 15-25μm.

7. The method for preparing the high-density silicon-carbon-graphite composite anode material according to claim 1, characterized in that, The conditions for high-temperature carbonization are as follows: in a nitrogen or argon atmosphere, the temperature is increased to 700-1000℃ at a heating rate of 3-10℃ / min and held for 2-6 hours; after the carbonization treatment, the material is subjected to surface vapor deposition treatment, and the carbon source for deposition is selected from methane, acetylene or ethylene.

8. A high-density silicon-carbon-graphite composite anode material, characterized in that, The high-density silicon-carbon-graphite composite anode material was prepared using the preparation method described in any one of claims 1-7.

9. The high-density silicon-carbon-graphite composite anode material according to claim 8, characterized in that, The high-density silicon-carbon-graphite composite anode material has a powder compaction density ≥ 1.4 g / cm³. 3 Specific surface area ≤ 5 m² 2 / g; The high-density silicon-carbon-graphite composite anode material has a microsphere structure in which nano-silicon and carbon nanotubes are uniformly embedded in the gaps between micron-sized graphite particles and coated with amorphous carbon.

10. The application of the high-density silicon-carbon-graphite composite anode material as described in claim 8 or 9 in the preparation of lithium-ion batteries.

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