An efficient preparation process for lithium-ion battery anode materials

Abstract

This invention discloses an efficient preparation process for lithium-ion battery anode materials, relating to the field of electrochemical energy storage materials technology. The process involves dispersing micron- or submicron-sized elemental silicon powder, a siloxane-containing precursor, a carbon source compound, and a dispersing agent in a high-boiling-point aprotic solvent to form a homogeneous suspension. The homogeneous suspension is then atomized and dried using a continuous spray dryer to obtain a primary composite powder with a porous microsphere morphology. The primary composite powder is placed in a tube furnace and subjected to multi-stage heat treatment under an inert atmosphere with programmed temperature control. The heat-treated product is then subjected to airflow pulverization and sieving. This invention, through continuous spray drying and gradient pyrolysis, constructs in-situ a triple structure with silicon as the core, silicon dioxide as the buffer shell, and a three-dimensional carbon network as the conductive framework. The resulting material exhibits high specific capacity, excellent cycle stability, and rate performance. Furthermore, the process is concise, scalable, and suitable for mass production of power batteries.

Description

Technical Field

[0001] This invention belongs to the field of electrochemical energy storage materials technology, and more specifically, relates to an efficient preparation process for lithium-ion battery anode materials. Background Technology

[0002] Against the backdrop of the current global energy structure's accelerated transition towards cleaner and electric power, lithium-ion batteries, as the core energy carrier for new energy vehicles and large-scale energy storage systems, directly determine the end-product's range, safety, reliability, and economic feasibility. Anode materials, as a key component of lithium-ion batteries, have a decisive impact on the overall system performance due to their specific capacity, cycle stability, and rate capability. While traditional graphite-based anodes possess good cycle performance and a mature industrial foundation, their theoretical specific capacity ceiling is only 372 mAh / g, which is insufficient to meet the ever-increasing technological demands of high-energy-density batteries. Driven by this, silicon-based anode materials, with their theoretical specific capacity of up to 4200 mAh / g, have become a promising alternative and are considered a key path to breaking through existing energy density bottlenecks. However, silicon undergoes a severe volume expansion effect during lithiation and delithiation, with an expansion rate exceeding 300%. This triggers a series of chain reactions, including particle breakage, repeated rupture and regeneration of the solid electrolyte interface film, and conductive network disconnection, ultimately leading to rapid capacity decay and significantly shortened cycle life, severely restricting its practical application.

[0003] In recent years, researchers have generally adopted strategies such as coating, compositing, and microstructure regulation to modify silicon-based materials. Patent CN115425180B proposes a three-layer composite structure design, using nanosheet silicon as the core, introducing a metal layer or metal particles in the middle to enhance electron conductivity, and then applying carbon coating on the outer layer to suppress electrolyte side reactions and stabilize the solid electrolyte interface film. This scheme, in principle, achieves physical constraint on volume expansion, optimization of electron transport paths, and improvement of interfacial chemical stability through multi-level functional partitioning, exhibiting superior electrochemical performance at the laboratory scale. Another patent, CN110492062B, focuses on interfacial chemical regulation. By coating the surface of silicon particles with a specific nitrogen-containing polymer containing pyridine and imidazole rings, its flexible framework buffers volume changes, and the lone pair electrons of nitrogen atoms participate in the coordination and transport of lithium ions, thereby improving interfacial dynamics. This method constructs a protective layer with ion selectivity and mechanical adaptability at the molecular level, and also alleviates structural degradation during cycling to some extent.

[0004] However, multi-step processes not only significantly extend the production cycle and increase energy consumption, but also make it difficult to maintain high uniformity in morphology, thickness and composition distribution between batches of products due to the uncertainty of interface coupling between each step. This affects the uniformity of electrode coating and the consistency between battery cells. Although the introduction of metal elements can improve conductivity, they may form thermodynamically unstable interface phases with silicon or electrolyte, which can induce side reactions in long-term cycling and weaken the overall stability.

[0005] On the other hand, while the coating strategy based on specific polymers avoids the interface complexity of inorganic multilayer structures, it shifts the process difficulty to the organic synthesis and precise coating process. In essence, while pursuing the optimization of material performance, the existing technology has failed to fully consider the process compatibility and structural robustness of each link in the complete manufacturing chain from powder synthesis to electrode forming, thus falling into the dilemma of "excellent performance in the laboratory but poor performance in the production line".

[0006] Therefore, how to construct a negative electrode material preparation route that combines structural stability, interface compatibility, and simplified process while retaining the high specific capacity advantage of silicon-based materials, so that it can achieve uniform composition, controllable morphology, low cost, and easy large-scale scaling in a single or few-step continuous process, has become a key challenge and a technical problem that needs to be solved by those skilled in the art. Summary of the Invention

[0007] This invention provides an efficient preparation process for lithium-ion battery anode materials, aiming to solve the technical problems of structural instability, frequent interfacial side reactions, and complex manufacturing processes caused by volume expansion effect in existing silicon-based anode materials under the advantage of high specific capacity.

[0008] To solve the above-mentioned technical problems, the present invention provides the following technical solution:

[0009] An efficient preparation process for a lithium-ion battery anode material includes:

[0010] Step S1: Disperse micron- or submicron-sized elemental silicon powder, siloxane precursor, carbon source compound and dispersing agent together in a high-boiling-point aprotic solvent to form a homogeneous suspension;

[0011] Step S2: The homogeneous suspension is introduced into a continuous spray drying device and atomized and dried under a set temperature gradient and airflow rate, so that the droplets undergo solvent evaporation, precursor condensation and preliminary carbonization during flight to obtain a primary composite powder with a porous microsphere morphology.

[0012] Step S3: Place the primary composite powder in a tube furnace and, under the protection of an inert atmosphere, sequentially undergo a low-temperature crosslinking stage, a medium-temperature carbonization stage, and a high-temperature graphitization stage in a programmed temperature control manner.

[0013] Step S4: The heat-treated product is subjected to air jet milling and sieving to obtain target anode material powder with a D50 particle size of 10 to 14 micrometers, a D90 of no more than 20 micrometers, and a particle size distribution span index of less than 1.3;

[0014] The resulting anode material has a core-shell-network triple structure: silicon is the core, accounting for 65% to 80% of the total mass, with a particle size of 0.5 to 3 micrometers; silicon dioxide is the buffer shell, uniformly coating the silicon surface without cracks or pores, with a Young's modulus of 65 to 75 gigapascals; a three-dimensional interpenetrating carbon network runs through the entire microsphere, with a specific surface area of ​​120 to 180 square meters per gram and a pore size distribution concentrated in the range of 2 to 10 nanometers.

[0015] Furthermore, the primary composite powder is placed under an inert atmosphere and undergoes the following three heat treatment stages in sequence:

[0016] Low-temperature crosslinking stage: The temperature is raised to 150°C to 250°C at a heating rate of 2°C / min and held for 2 hours to allow the siloxane-containing precursor to condense on the surface of silicon particles to form a silicon dioxide shell with a thickness of 8 to 15 nanometers.

[0017] Medium-temperature carbonization stage: The temperature is increased to 500℃ to 700℃ at a heating rate of 3℃ / min and held for 3 hours to cause the carbon source compound to decompose and generate an amorphous carbon phase, which penetrates into the interior of the silica shell to form a carbon-silica interpenetrating structure.

[0018] High-temperature graphitization stage: The temperature is increased to 900℃ to 1100℃ at a heating rate of 5℃ / min and held for 1.5 hours to cause local graphitization of some carbon phases. At the same time, the silica shell is densified and retains 18% to 25% porosity. Finally, the shell thickness is stabilized at 12 to 20 nanometers.

[0019] Furthermore, the elemental silicon powder is pretreated with acid washing before dispersion. The acid washing solution is a 5% hydrofluoric acid solution, and the treatment time is 10 minutes. Then, it is washed with deionized water until neutral and vacuum dried so that the hydroxyl density on the silicon surface is not less than 4.5 per square nanometer.

[0020] Furthermore, the siloxane precursor is an organosilicon compound with the general formula R1R2Si(OR3)2, wherein R1 and R2 are independently selected from methyl, ethyl or phenyl, and R3 is methyl or ethyl. It has moderate hydrolytic condensation activity and can react with trace amounts of moisture during spray drying to form a local cross-linking network, which can coat the surface of silicon particles without causing violent agglomeration.

[0021] The carbon source compound is one of phenolic resin, asphalt or sucrose, which undergoes controlled pyrolysis in the temperature range of 300°C to 600°C to generate an amorphous carbon phase. This carbon phase compensates for the volume change stress of silicon particles during cycling, and its softening point is not lower than 120°C and the residual carbon rate is not lower than 55%.

[0022] Furthermore, the high-boiling-point aprotic solvent is one of N-methylpyrrolidone, dimethyl sulfoxide, or γ-butyrolactone, with a boiling point higher than 180°C and a dielectric constant greater than 30.

[0023] Furthermore, the continuous spray drying device employs concentric dual-fluid atomizing nozzles with an inlet temperature of 220°C to 260°C, an outlet temperature of 90°C to 110°C, a feed rate of 80 to 120 ml per minute, and nitrogen as the carrier gas with a flow rate of 1.5 to 2.5 cubic meters per hour. The residence time of droplets in the drying tower is 0.5 to 1.2 seconds. During solvent evaporation, capillary force drives the siloxane precursor and carbon source compound to migrate to the particle surface, forming a shell enrichment structure.

[0024] Furthermore, the working pressure of the airflow pulverizer is 0.6 to 0.8 MPa, and the speed of the classifying wheel is 8000 to 12000 rpm; the screening adopts a 325 mesh vibrating screen, and the mass fraction of the residue is less than 0.5%.

[0025] Furthermore, the dispersing agent is polyvinylpyrrolidone, added at an amount of 0.8% to 1.5% of the silica powder mass, to improve the colloidal stability of the suspension and make its absolute zeta potential greater than 35 millivolts.

[0026] Furthermore, the homogeneous suspension has a solid content of 35% to 42% and a viscosity of 150 to 220 mPa·s (25°C), and no visible agglomerates are observed after high-speed shearing and ultrasonic synergistic dispersion treatment.

[0027] Furthermore, the target negative electrode material is directly mixed with sodium carboxymethyl cellulose, styrene-butadiene rubber and conductive carbon black in a mass ratio of 92:3:3:2 during electrode preparation, and a slurry with a solid content of 65% is prepared using deionized water as a solvent. After being coated on copper foil, it is vacuum dried at 120°C for 12 hours and rolled to a compaction density of 1.45 g / cm³, without the need for additional interface modifiers or adhesive reinforcing agents.

[0028] Compared with the prior art, the beneficial technical effects of the present invention are as follows:

[0029] This invention requires no introduction of metal elements, no multi-step deposition operations, and no complex organic synthesis. All reactions are completed continuously in a closed system, the material residence time is controllable, energy consumption is significantly reduced compared to traditional multi-step methods, and the product composition deviation coefficient is less than 3%, with batch-to-batch electrochemical performance fluctuations of less than 5%. It is suitable for scale-up of production lines with a capacity of tens of thousands of tons.

[0030] In the triple structure of this invention, the silicon core has a particle size of 0.5 to 3 micrometers, accounting for 65% to 80% of the total mass of the composite material; the silicon dioxide shell uniformly coats the silicon surface without cracks or pores, and its Young's modulus is 65 to 75 gigapascals, providing rigid constraint and effectively limiting the radial expansion of silicon particles during lithiation; the three-dimensional interpenetrating carbon network runs through the entire microsphere particle, forming interconnected channels, with a specific surface area of ​​120 to 180 square meters per gram and a pore size distribution concentrated in the range of 2 to 10 nanometers, providing both a fast electron transport path and a lithium-ion diffusion channel, while also resisting high shear forces during electrode slurry preparation and maintaining structural integrity.

[0031] This invention fundamentally abandons the traditional "superimposed" multi-layered construction paradigm. Through molecular design and thermodynamic regulation, it achieves in-situ integration of functional structures in a single continuous process, solving the disconnect between laboratory performance and production line performance. In the triple structure, the silica shell provides rigid buffering and interface passivation, while the carbon network provides flexible support and conductive pathways. The two work synergistically to form a "rigid-flexible" stress dissipation mechanism, effectively suppressing silicon particle breakage and SEI film regeneration, while ensuring efficient lithium-ion and electron transport. The entire process consists of only four defined steps: dispersion, spray drying, gradient pyrolysis, and pulverization and sieving. The equipment is highly versatile, has a wide parameter window, and is easy to automate and scale up, significantly outperforming the complex paths of existing technologies that rely on physical vapor deposition, chemical reduction, or multi-step coating.

[0032] All raw materials used in the process of this invention are industrial-grade chemicals, which are inexpensive and do not contain precious metals or highly toxic reagents. Waste liquid can be discharged in compliance with standards after simple distillation to recover the solvent, which is in line with the principle of green manufacturing. The resulting negative electrode material has a capacity retention rate of no less than 85% after 1000 cycles at 1C rate in a full battery test at 25°C, and an average calendar life decay rate of less than 0.02% per day, which meets the 8-year service life requirement of electric vehicle power batteries.

[0033] In summary, this invention innovatively integrates in-situ self-assembly and gradient pyrolysis technologies to construct a silicon-carbon composite anode material preparation path with a well-defined structure, stable performance, and simplified process. This comprehensively overcomes the inherent defects of existing technologies in terms of structural stability, interface compatibility, and manufacturing economy, providing a practical and feasible technical solution for the industrial application of high-energy-density lithium-ion batteries. Attached Figure Description

[0034] Figure 1 This is a schematic diagram of the core-shell-network triple structure of the lithium-ion battery anode material described in this invention;

[0035] Figure 2 This is a schematic diagram of the efficient preparation process of the present invention. Detailed Implementation

[0036] The features and exemplary embodiments of various aspects of the present invention will now be described in detail. To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are merely intended to explain the present invention and not to limit the present invention. For those skilled in the art, the present invention can be practiced without some of these specific details. The following description of the embodiments is merely to provide a better understanding of the present invention by illustrating examples of the invention.

[0037] It should be noted that, in this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising..." does not exclude the presence of additional identical elements in the process, method, article, or apparatus that includes said element.

[0038] In the embodiments of the present invention, the same reference numerals denote the same components, and for the sake of brevity, detailed descriptions of the same components are omitted in different embodiments. It should be understood that the thickness, length, width, and other dimensions of various components in the embodiments of the present invention shown in the accompanying drawings, as well as the overall thickness, length, width, and other dimensions of the integrated device, are merely illustrative and should not constitute any limitation on the present invention; the term "multiple" in the present invention refers to two or more (including two).

[0039] While existing polymer-based coating strategies avoid the interfacial complexity of inorganic multilayer structures, they shift the technological challenges to the organic synthesis and precise coating stages. The preparation of heterocyclic polymers typically involves multiple organic reactions, requiring high raw material purity, resulting in low synthesis yields and difficult separation of byproducts. Furthermore, their molecular weight and functional group density are highly sensitive to coating effectiveness. During coating, solvent selection, reaction temperature, stirring rate, and post-treatment conditions must be strictly controlled; even slight deviations can lead to uneven coating, polymer degradation, or silicon particle agglomeration. More critically, such flexible coating layers face severe challenges in subsequent slurry preparation: in high-solids, high-shear stirring environments, the polymer layer is prone to localized peeling or plastic deformation, failing to effectively maintain the original structural integrity of the silicon particles; and during electrode coating and drying, capillary forces caused by solvent evaporation can also disrupt the continuity of the coating layer, leading to increased interparticle contact resistance, obstructed lithium-ion diffusion paths, and ultimately, fluctuations in electrode areal density, uneven porosity, and increased battery performance dispersion. Ultimately, while pursuing the optimization of material properties, existing technologies have failed to fully consider the process compatibility and structural robustness of each link in the complete manufacturing chain, from powder synthesis to electrode forming.

[0040] This invention provides an efficient preparation process for lithium-ion battery anode materials. Its core lies in constructing a silicon-carbon composite anode material with a core-shell-network triple-functional integrated structure in a single continuous process through the synergistic effect of in-situ self-assembly and gradient pyrolysis.

[0041] Please refer to Figure 1 The lithium-ion battery anode material prepared by this invention fundamentally abandons the traditional "stacked" multilayer construction paradigm. Through molecular design and thermodynamic regulation, it achieves in-situ integration of functional structures in a single continuous process, solving the problem of the disconnect between laboratory performance and production line performance. In the triple structure, the silicon dioxide shell provides rigid buffering and interface passivation, while the carbon network provides flexible support and conductive pathways. The two work synergistically to form a "rigid-flexible" stress dissipation mechanism, effectively suppressing silicon particle breakage and SEI film regeneration, while ensuring efficient lithium-ion and electron transport.

[0042] Please refer to Figure 2The efficient preparation process of lithium-ion battery anode materials includes the following steps: First, micron- or submicron-sized elemental silicon powder is co-dispersed with a siloxane precursor with a specific molecular structure, a carbon source compound, and a dispersing agent in a high-boiling-point aprotic solvent to form a homogeneous suspension; second, the suspension is introduced into a continuous spray drying device and atomized under a set temperature gradient and airflow rate conditions, causing solvent evaporation, precursor condensation, and preliminary carbonization of the droplets during flight to obtain a primary composite powder with a porous microsphere morphology; subsequently, the primary composite powder is placed in a tube furnace under an inert atmosphere... The material undergoes a series of stages in a programmed temperature-controlled manner: a low-temperature crosslinking stage, a medium-temperature carbonization stage, and a high-temperature graphitization stage. The heating rate, holding temperature, and holding time for each stage are precisely controlled to ensure that the siloxane precursor undergoes directional condensation on the surface of silicon particles to form a dense silica interlayer. Simultaneously, the carbon source compound decomposes to generate a continuous conductive carbon network that is embedded inside the silica layer, ultimately forming a triple structure with silicon as the core, silica as the buffer shell, and a three-dimensional interpenetrating carbon network as the outer framework. Finally, the obtained product is mechanically pulverized and sieved to obtain target anode material powder with a particle size distribution concentrated in the range of 5 to 20 micrometers.

[0043] The entire process consists of only four defined steps: dispersion, spray drying, gradient pyrolysis, and crushing and sieving. The equipment is highly versatile, has a wide parameter window, and is easy to automate and scale up production, which is significantly superior to the complex paths in existing technologies that rely on physical vapor deposition, chemical reduction, or multi-step coating.

[0044] The following will provide a detailed, complete and reproducible engineering description of the technical solution of the present invention in conjunction with several specific embodiments.

[0045] First, the configuration of the raw material system is fundamental to achieving the technical effects of this invention. In a typical implementation, elemental silicon powder with a particle size distribution D50 of 1.8 micrometers and a specific surface area of ​​4.2 square meters per gram is selected as the active core component. This silicon powder undergoes acid washing pretreatment before use.

[0046] The silica powder was immersed in a 5% (w / w) aqueous solution of hydrofluoric acid and stirred at room temperature for 10 minutes to effectively remove the natural oxide layer and trace metal impurities on the surface. It was then repeatedly washed with deionized water until the pH of the filtrate stabilized between 6.8 and 7.2, and dried in a vacuum drying oven at 80°C for 12 hours to obtain clean silica powder with a surface hydroxyl density of 4.7 hydroxyl groups per square nanometer. This pretreatment step ensured the subsequent directional adsorption and controlled condensation of siloxane precursors on its surface.

[0047] As a key component for coating and buffering functions, the siloxane precursor is methyltriethoxysilane (CH3Si(OC2H5)3). One methyl group in its molecular structure imparts moderate hydrophobicity, while the two ethoxy groups provide controllable hydrolytic condensation activity. The carbon source compound is thermoplastic phenolic resin (Novolac resin), with a softening point of 135℃ and a residual carbon content of 58.3% as determined by thermogravimetric analysis (TGA) (nitrogen atmosphere, heating rate 10℃ / min, final temperature 800℃). The dispersant is polyvinylpyrrolidone (PVP-K30), added at 1.2% of the silica powder mass. The high-boiling-point aprotic solvent is N-methylpyrrolidone (NMP), with a boiling point of 202℃ and a dielectric constant of 32.2, which can fully dissolve the phenolic resin and effectively stabilize the suspended silica particles.

[0048] The above components were added to a planetary stirred tank in the following mass ratio: 72.0 wt% silica powder, 9.5 wt% methyltriethoxysilane, 15.0 wt% phenolic resin, 0.9 wt% PVP, and the balance being NMP solvent, to control the solid content at 38.5 wt%. Under a nitrogen protective atmosphere, the components were first initially wetted by stirring at 500 rpm for 30 minutes, then the speed was increased to 2000 rpm for high-speed shear dispersion for 2 hours. Finally, the mixture was treated in an ultrasonic disperser (frequency 40 kHz, power 300 W) for 45 minutes, resulting in a homogeneous suspension with a viscosity of 185 mPa·s (25℃) and no visible agglomerates. The absolute value of the zeta potential of this suspension was greater than 35 mV, indicating that it has good colloidal stability and can meet the requirements of continuous feeding.

[0049] Subsequently, the suspension is pumped into a continuous spray dryer. This device is equipped with concentric dual-fluid atomizing nozzles; the suspension is introduced into the inner tube, and compressed nitrogen is introduced into the outer tube as the atomizing carrier gas. The feed rate is set to 100 mL / min, the inlet hot air temperature to 240℃, and the outlet material temperature is precisely controlled at 100℃ by adjusting the hot air flow rate. The total flow rate of the carrier gas (nitrogen) is 2.0 m³ / min. 3 / h. Under this operating window, the average residence time of the droplets in the drying tower is 0.85 seconds. During this short period, the solvent evaporates rapidly, and capillary force drives methyltriethoxysilane and phenolic resin to migrate towards the outer edge of the droplets, forming a shell-enriched structure. Simultaneously, the phenolic resin undergoes preliminary cross-linking and mild carbonization at localized high temperatures, endowing the primary microspheres with sufficient mechanical strength to resist structural collapse during subsequent heat treatment. The resulting primary composite powder exhibits a regular microspherical morphology. Scanning electron microscopy (SEM) observation shows that its D50 is 18.5 μm, sphericity is greater than 0.92, and it displays a porous network structure with a BET specific surface area of ​​85 m². 2 / g, with pore sizes mainly distributed in the range of 10–50 nm.

[0050] Next, the primary composite powder was transferred to a horizontal tube furnace for programmed temperature-controlled heat treatment. The entire process was carried out under the protection of high-purity argon gas (purity ≥99.999%), with the gas flow rate maintained at 150 mL / min. The heat treatment was performed in three stages sequentially:

[0051] The first stage is the low-temperature crosslinking stage: the temperature is increased from room temperature to 200℃ at a rate of 2℃ / min, and held at this temperature for 2 hours. In this stage, the ethoxy group in the methyltriethoxysilane molecule undergoes a de-alcoholization condensation reaction with the hydroxyl groups on the surface of the silicon powder and trace amounts of ambient moisture, generating a three-dimensional Si–O–Si network that uniformly coats the surface of each silicon particle, forming an initial silica shell. Transmission electron microscopy (TEM) cross-sectional analysis shows that the shell formed in this stage is approximately 10 nm thick and is continuous without cracks.

[0052] The second stage is the intermediate-temperature carbonization stage: the temperature is increased to 600℃ at a rate of 3℃ / min and held for 3 hours. In this temperature range, the phenolic resin undergoes deep pyrolysis, releasing small molecule volatiles (such as H2O, CH4, CO, etc.). The residual carbon phase precipitates in an amorphous structure. Since there are already porous channels formed by spray drying inside the primary microspheres, the pyrolyzed carbon phase can penetrate into the silica shell along these channels to form a carbon-silica interpenetrating structure. Raman spectroscopy shows that the ID / IG ratio of the product in this stage is 1.35, indicating that the carbon phase is highly disordered but has good flexibility. Simultaneous X-ray photoelectron spectroscopy (XPS) depth analysis confirms that the Si 2p peak is significantly enhanced in the shell region, while the C 1s signal runs through the entire microsphere, verifying the formation of the interpenetrating network.

[0053] The third stage is the high-temperature graphitization stage: the temperature is increased to 1000℃ at a heating rate of 5℃ / min and held for 1.5 hours. At this high temperature, some amorphous carbon undergoes localized ordering, the ID / IG ratio decreases to 1.12, and the electronic conductivity increases to 85 S / cm (measured by the four-probe method). At the same time, the silica shell undergoes slight densification, but retains sufficient porosity to accommodate the volume expansion of silicon during lithiation. The final product has a shell thickness of 16±2 nm, a porosity of 21.5% as determined by mercury porosimetry, and a Young's modulus of 70.3 GPa as determined by nanoindentation testing.

[0054] After heat treatment, the product was cooled to room temperature and then transferred to an air jet mill for particle size control. The mill's operating pressure was set to 0.7 MPa, and the classifier wheel speed was 10,000 rpm. After this treatment, the product's D50 particle size was 12.1 μm, D90 was 19.3 μm, and the particle size distribution span index ((D90–D10) / D50) was 1.24, meeting the stringent requirements for powder flowability in electrode coating. Subsequently, it was sieved through a 325-mesh (45 μm aperture) stainless steel vibrating screen, with a residue mass fraction of 0.38%, conforming to industrial-grade product standards.

[0055] The obtained target anode material powder has a distinct core-shell-network triple structure: the silicon core has a particle size of 0.5–3.0 μm, accounting for 72% of the total mass; the silica shell is uniformly coated with a thickness of 12–20 nm and has no macroscopic defects; the three-dimensional interpenetrating carbon network runs through the entire microsphere and has a specific surface area of ​​152 m². 2 / g, with pore sizes concentrated in 2–10 nm, forming a highly efficient dual channel for electron conduction and lithium-ion diffusion.

[0056] To verify the repeatability and performance advantages of the process of the present invention, the following embodiments and comparative examples were designed for systematic comparison.

[0057] Example 1

[0058] The anode material was prepared according to the complete process described above, wherein the silicon powder was not subjected to acid washing pretreatment, and the other parameters were the same as the aforementioned preferred conditions. The resulting material had an initial discharge specific capacity of 2080 mAh / g at a rate of 0.1C (1C = 2000 mA / g), an initial coulombic efficiency of 86.2%, and a capacity retention of 87.5% after 500 cycles.

[0059] Example 2

[0060] The silicon powder was pretreated by acid washing. The siloxane precursor was replaced with phenyltrimethoxysilane (C6H5Si(OCH3)3), the carbon source was replaced with petroleum pitch (softening point 145℃, residual carbon content 61.2%), and the solvent was replaced with dimethyl sulfoxide (DMSO). The spray drying inlet temperature was 250℃, the outlet temperature was 105℃, and the three-stage heat treatment temperatures were 220℃, 650℃, and 1050℃, respectively. The resulting material had an initial discharge specific capacity of 2110 mAh / g at 0.1C, an initial coulombic efficiency of 88.1%, and a capacity retention of 89.7% after 500 cycles.

[0061] Example 3 (Preferred Embodiment of the Invention)

[0062] Silicon powder was pretreated by acid washing, with methyltriethoxysilane as a precursor, phenolic resin as a carbon source, and NMP as a solvent. Spray drying was performed at an inlet temperature of 240℃ and an outlet temperature of 100℃, followed by heat treatment at 200℃ / 2h → 600℃ / 3h → 1000℃ / 1.5h. The resulting material exhibited optimal properties.

[0063] Comparative Example 1

[0064] A traditional physical mixing + high-temperature carbon coating method was used: silicon powder and phenolic resin were dry-mixed and then directly heat-treated in an inert atmosphere at 1000℃ for 4 hours. The resulting material had severe particle agglomeration, with D50 > 40 μm, an initial discharge specific capacity of only 1650 mAh / g at 0.1C, an initial coulombic efficiency of 82.3%, and a capacity retention of less than 60% after 100 cycles.

[0065] Comparative Example 2

[0066] A two-step method was employed: first, silicon dioxide was coated onto the silicon surface using a sol-gel method, followed by carbon layer deposition via CVD. The process was complex, taking up to 24 hours, and resulted in poor batch-to-batch consistency (composition deviation coefficient > 8%). The initial discharge specific capacity at 0.1C was 2050 mAh / g, but the capacity retention rate after 500 cycles was only 78.4%.

[0067] Comparative Example 3

[0068] The spray drying step was omitted, and the suspension was directly dried and then subjected to gradient heat treatment. The resulting product was in block form and could not be used directly for electrode preparation. It required additional high-intensity ball milling, which led to silicon particle breakage. The initial discharge specific capacity at 0.1C was 1920 mAh / g, and the cycle performance was significantly degraded.

[0069] Coin cell half-cells were prepared using the same electrode formulation for each of the above examples and electrochemical tests were conducted: active material: sodium carboxymethyl cellulose (CMC): styrene-butadiene rubber (SBR): conductive carbon black = 92:3:3:2, solid content 65%, coated on 10 μm copper foil, vacuum dried at 120℃ for 12 h, and rolled to a compaction density of 1.45 g / cm³. 3 The electrolyte is 1M LiPF6 in EC / DEC / EMC (1:1:1 vol%) + 2% FEC, and the counter electrode is a lithium metal sheet.

[0070] The test results are summarized in the table below:

[0071] ;

[0072] Furthermore, the material obtained in Example 3 was matched with an NCM811 cathode and assembled into a 2.8 Ah pouch cell, using the same electrolyte. Long-term cycling tests were conducted at 25°C and a 1C rate. After 1000 cycles, the capacity retention was 86.7%, with an average decay of 0.0133% per cycle. This translates to a calendar life decay rate of less than 0.02% / day (assuming one cycle per day), fully meeting the design requirement of an 8-year lifespan for electric vehicle power batteries.

[0073] Throughout the entire preparation process, the total material residence time is approximately 8.5 hours (2.5 h dispersion + 0.1 h spray drying + 6.5 h heat treatment + 0.4 h pulverization and sieving). The calculated energy consumption is 3.2 kWh / kg of product, a 44.8% reduction compared to the two-step method in Comparative Example 2 (5.8 kWh / kg). All raw materials are commercially available industrial-grade chemicals, free of precious metals or highly toxic substances. The waste liquid mainly consists of NMP containing trace amounts of organic matter, which can be recovered at a rate exceeding 95% through simple distillation. The residual COD value is below 200 mg / L, meeting the Class III standard of the Integrated Wastewater Discharge Standard (GB 8978-1996).

[0074] In a modified embodiment of the present invention, the carbon source compound can be replaced with sucrose. Specifically, sucrose is pre-dissolved in deionized water, mixed with NMP at a volume ratio of 1:4, and then blended with other components. Since sucrose begins to caramelize at 160°C, the spray drying inlet temperature needs to be adjusted to 200°C and the outlet temperature to 85°C to avoid premature carbonization and nozzle clogging. The temperature of the second stage of heat treatment is correspondingly lowered to 550°C. The resulting material has a 0.1C initial discharge specific capacity of 2090 mAh / g, an initial coulombic efficiency of 87.8%, and a capacity retention of 90.1% after 500 cycles. While its performance is slightly inferior to the phenolic resin system, it is still significantly better than the comparative example.

[0075] Another variation involves adjusting the silicon powder particle size. When using nano-silicon with a D50 of 0.6 micrometers, the amount of siloxane precursor needs to be increased to 12.0 wt% to ensure complete coating; simultaneously, the spray drying feed rate is reduced to 70 mL / min to prevent excessive viscosity due to increased specific surface area. The resulting material achieves a 0.1C initial discharge specific capacity of 2350 mAh / g, but the initial coulombic efficiency decreases to 85.3%, and the cycle stability also slightly decreases (89.2% retention after 500 cycles), indicating that micron / submicron silicon has a better overall performance balance in the system of this invention.

[0076] Regarding equipment compatibility, the continuous spray drying device described in this invention can be seamlessly integrated with similar equipment in existing lithium iron phosphate or ternary material production lines, requiring only adjustments to temperature and airflow parameters. The tube furnace is also standard industrial equipment and requires no customization. The entire process comprises only four defined steps: dispersion, spray drying, gradient pyrolysis, and pulverization and sieving, without any intermediate separation, washing, or vacuum operations, greatly simplifying production management and quality control logic.

[0077] In summary, this invention achieves nanoscale confinement of silicon particles, in-situ construction of the conductive framework, and gradient formation of the interface stabilization layer in a single continuous process by precisely controlling the molecular structure of raw materials, the rheological properties of the suspension, the spray drying kinetics, and the gradient pyrolysis thermodynamic path. This ultimately yields a silicon-carbon composite anode material with a well-defined structure, excellent performance, controllable cost, and easy scalability. All technical parameters have been extensively verified through experiments, demonstrating a wide operating window and robust process robustness, fully meeting the engineering requirements of a 10,000-ton-level power battery material production line.

[0078] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Therefore, all equivalent changes made in accordance with the structure, shape, and principle of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A process for the efficient preparation of a lithium-ion battery anode material, characterized in that, Includes the following steps: Step S1: Disperse micron- or submicron-sized elemental silicon powder, siloxane precursor, carbon source compound and dispersing agent together in a high-boiling-point aprotic solvent to form a homogeneous suspension; Step S2: The homogeneous suspension is introduced into a continuous spray drying device and atomized and dried under a set temperature gradient and airflow rate, so that the droplets undergo solvent evaporation, precursor condensation and preliminary carbonization during flight to obtain a primary composite powder with a porous microsphere morphology. The continuous spray drying device uses concentric dual-fluid atomizing nozzles with an inlet temperature of 220°C to 260°C, an outlet temperature of 90°C to 110°C, a feed rate of 80 to 120 ml per minute, and nitrogen as the carrier gas with a flow rate of 1.5 to 2.5 cubic meters per hour. The residence time of droplets in the drying tower is 0.5 to 1.2 seconds. During the solvent evaporation process, capillary force drives the siloxane precursor and carbon source compound to migrate to the particle surface, forming a shell enrichment structure. Step S3: Place the primary composite powder in a tube furnace and, under the protection of an inert atmosphere, sequentially undergo a low-temperature crosslinking stage, a medium-temperature carbonization stage, and a high-temperature graphitization stage in a programmed temperature control manner. The primary composite powder is placed under an inert atmosphere and undergoes the following three heat treatment stages in sequence: Low-temperature crosslinking stage: The temperature is raised to 150°C to 250°C at a heating rate of 2°C / min and held for 2 hours to allow the siloxane-containing precursor to condense on the surface of silicon particles to form a silicon dioxide shell with a thickness of 8 to 15 nanometers. Medium-temperature carbonization stage: The temperature is increased to 500℃ to 700℃ at a heating rate of 3℃ / min and held for 3 hours to cause the carbon source compound to decompose and generate an amorphous carbon phase, which penetrates into the interior of the silica shell to form a carbon-silica interpenetrating structure. High-temperature graphitization stage: The temperature is increased to 900℃ to 1100℃ at a heating rate of 5℃ / min and held for 1.5 hours to cause local graphitization of some carbon phases. At the same time, the silica shell is densified and retains 18% to 25% porosity. Finally, the shell thickness is stabilized at 12 to 20 nanometers. Step S4: The heat-treated product is subjected to air jet milling and sieving to obtain target anode material powder with a D50 particle size of 10 to 14 micrometers, a D90 of no more than 20 micrometers, and a particle size distribution span index of less than 1.3; The resulting anode material has a core-shell-network triple structure: silicon is the core, accounting for 65% to 80% of the total mass, with a particle size of 0.5 to 3 micrometers; silicon dioxide is the buffer shell, uniformly coated on the silicon surface without cracks or pores, with a Young's modulus of 65 to 75 gigapascals; a three-dimensional interpenetrating carbon network runs through the entire microsphere, with a specific surface area of ​​120 to 180 square meters per gram and a pore size distribution concentrated in the range of 2 to 10 nanometers.

2. The process as claimed in claim 1, wherein the process is characterized by: The elemental silicon powder is pretreated by acid washing before dispersion. The acid washing solution is a 5% hydrofluoric acid solution, and the treatment time is 10 minutes. Then it is washed with deionized water until neutral and vacuum dried so that the hydroxyl density on the silicon surface is not less than 4.5 per square nanometer.

3. The process as claimed in claim 1, wherein the process is characterized by: The siloxane precursor is an organosilicon compound with the general formula R1R2Si(OR3)2, wherein R1 and R2 are independently selected from methyl, ethyl or phenyl, and R3 is methyl or ethyl. It has moderate hydrolytic condensation activity and can react with trace amounts of moisture during spray drying to form a local cross-linking network, which can coat the surface of silicon particles without causing violent agglomeration. The carbon source compound is one of phenolic resin, asphalt or sucrose, which undergoes controlled pyrolysis in the temperature range of 300°C to 600°C to generate an amorphous carbon phase. This carbon phase compensates for the volume change stress of silicon particles during cycling, and its softening point is not lower than 120°C and the residual carbon rate is not lower than 55%.

4. The process as claimed in claim 1, wherein the process is characterized by: The high-boiling-point aprotic solvent is one of N-methylpyrrolidone, dimethyl sulfoxide, or γ-butyrolactone, with a boiling point above 180°C and a dielectric constant greater than 30.

5. The process as claimed in claim 1, wherein the process is characterized by: The working pressure of the airflow pulverizer is 0.6 to 0.8 MPa, and the speed of the classifying wheel is 8000 to 12000 rpm; the screening adopts a 325 mesh vibrating screen, and the mass fraction of the residue is less than 0.5%.

6. The process as claimed in claim 1, wherein the process is characterized by: The dispersing agent is polyvinylpyrrolidone, added at an amount of 0.8% to 1.5% of the silica powder mass, to improve the colloidal stability of the suspension and make its absolute zeta potential greater than 35 millivolts.

7. The efficient preparation process of a lithium-ion battery anode material according to claim 1, characterized in that: The homogeneous suspension has a solid content of 35% to 42% and a viscosity of 150 to 220 mPa·s at 25°C. After high-speed shearing and ultrasonic synergistic dispersion treatment, no visible agglomerates are observed.

8. The efficient preparation process of a lithium-ion battery anode material according to claim 1, characterized in that: The target negative electrode material is directly mixed with sodium carboxymethyl cellulose, styrene-butadiene rubber and conductive carbon black in a mass ratio of 92:3:3:2 during electrode preparation. A slurry with a solid content of 65% is prepared using deionized water as a solvent. After being coated onto copper foil, it is vacuum dried at 120°C for 12 hours and then rolled to a compaction density of 1.45 g / cm³. No additional interface modifier or bonding reinforcement is required.

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