Spherical artificial graphite composite particle and spray drying preparation method and application thereof

Abstract

The invention relates to the technical field of battery negative electrode materials, and discloses a spherical artificial graphite composite particle and a spray drying preparation method and application thereof.The composite particle is prepared from artificial graphite, a silicon-based active material, a conductive agent and a liquid-phase binder system and is of a spherical structure with a compact shell and communicating pores inside. The aperture distribution of micron-sized pores in the particles is 0.5-3 [mu] m, the micron-sized pores account for more than 50% of the total pore volume, and the content of the amorphous carbon coating is 1-5 wt%. The preparation method comprises the following steps: preparing emulsion slurry containing a dispersing agent and a carbon source precursor, carrying out three-temperature-zone gradient spray drying to carry out rapid shell forming, phase separation pore forming and curing shaping, and finally carrying out high-temperature carbonization treatment. According to the invention, the problems of volume expansion and interface side reaction of the silicon-based negative electrode are solved, an effective buffer space is provided while high tap density is ensured, and the cycling stability and volume energy density of the lithium ion battery are improved.

Description

Technical Field

[0001] This invention relates to the field of battery anode material technology, specifically to a spherical artificial graphite composite particle and its spray drying preparation method and application. Background Technology

[0002] With the rapid development of new energy vehicles and portable electronic devices, the market has placed higher demands on the energy density and cycle life of lithium-ion batteries. As the current mainstream commercial anode material, artificial graphite's theoretical specific capacity limits further improvements in battery energy density. Silicon-based materials, with their much higher theoretical specific capacity than graphite, are considered an important development direction for next-generation high-energy-density anode materials. Silicon-carbon composite materials, combining the high capacity of silicon with the conductivity and stability of carbon materials, have become a current research hotspot.

[0003] However, silicon-based materials still face significant challenges in practical applications. Silicon undergoes substantial volume expansion during lithium intercalation, and these repeated volume changes lead to the pulverization and breakage of active material particles, causing them to peel off from current collectors or conductive networks, resulting in rapid capacity decay. To address this issue, existing technologies typically employ strategies such as nanostructuring, porous structures, or carbon coating. While constructing porous structures can provide some buffering space for silicon volume expansion, existing porous silicon-carbon materials often struggle to balance buffering effectiveness with volumetric energy density.

[0004] Conventional porous structures typically contain numerous open nanoscale micropores, resulting in an excessively large specific surface area. This larger surface area increases the contact area between the negative electrode material and the electrolyte, leading to excessive consumption of active lithium during the formation of the solid electrolyte interphase (SEI) film during the initial charge-discharge cycle, thus reducing the battery's initial coulombic efficiency. Furthermore, an overly porous structure results in a low tap density, making it difficult to meet the electrode compaction requirements of high-volume-density batteries. On the other hand, simple surface coating modification struggles to maintain structural integrity when internal silicon particles undergo drastic expansion. Once the coating layer ruptures, the exposed fresh surface continuously reacts with the electrolyte, causing the SEI film to thicken and its impedance to increase. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides spherical artificial graphite composite particles, their spray drying preparation method, and their applications. This solves the problems of poor cycle stability caused by the drastic volume expansion during charging and discharging of existing silicon-based anode materials, and low initial coulombic efficiency and insufficient volumetric energy density caused by the large specific surface area and low tap density of conventional porous buffer structures.

[0006] In a first aspect, the present invention provides spherical artificial graphite composite particles, employing the following technical solution:

[0007] A spherical artificial graphite composite particle, the composite particle having a dense outer shell and an internally interconnected pore structure, is made from raw materials comprising the following parts by weight: 88 to 95 parts artificial graphite, 3 to 10 parts silicon-based active material, 1 to 5 parts conductive agent, and a liquid phase binder system; the liquid phase binder system comprises a solvent, a dispersant, and a carbon source precursor, the amount of carbon source precursor added such that the content of the amorphous carbon coating in the final composite particle is 1 wt% to 5 wt%; the composite particle has micron-sized pores with a pore size distribution in the range of 0.5 μm to 3 μm, and the pore volume of the micron-sized pores accounts for more than 50% of the total pore volume.

[0008] By adopting the above technical solution, the overall performance of the silicon-carbon anode can be improved through a structural design combining a specific pore distribution with a dense outer shell, and by constructing an amorphous carbon conductive network in situ using a carbon source precursor in a liquid phase system. Its specific mechanism of action is as follows:

[0009] A gradient structure with a dense outer layer and a porous inner layer is constructed. The dense outer layer effectively reduces the direct contact area between the composite particles and the electrolyte, suppressing side reactions and reducing irreversible capacity loss; the interconnected micron-sized pore structure inside provides ample buffer space for the volume expansion of the silicon-based material. Compared to conventional nanopores, the dominant micron-sized pores in this scheme are better able to accommodate the expansion of micron-sized aggregates of silicon-based particles in the lithium-intercalated state, preventing the overall particle breakage.

[0010] The liquid-phase binder system synergistically enhances the in-situ curing effect of the carbon source precursor. During the preparation process, the solvent, dispersant, and carbon source precursor form a homogeneous system, uniformly encapsulating the artificial graphite and silicon-based materials. The carbon source precursor undergoes cross-linking, curing, and carbonization reactions during high-temperature treatment, transforming in-situ into a continuously distributed amorphous carbon coating. This amorphous carbon coating not only acts as a physical binder, firmly anchoring silicon and graphite and preventing silicon particles from detaching, but also serves as a conductive bridge, ensuring that the silicon particles maintain electrical contact with the graphite matrix even during volume changes.

[0011] Control of the proportion of micron-sized pores. By limiting pores from 0.5μm to 3μm to account for more than 50% of the total pore volume, it is ensured that the interior of the particles mainly consists of effective pores for buffering expansion, rather than ineffective dead pores or nanopores that would result in excessively large specific surface areas. This structure alleviates volume expansion stress while maintaining a high tap density, thereby improving the volumetric energy density of the material.

[0012] Preferably, the artificial graphite is primary particles with a median particle size D50 between 8 micrometers and 12 micrometers; the silicon-based active material is selected from nano-silicon powder or silicon monoxide, with a median particle size D50 between 80 nanometers and 3 micrometers; the conductive agent is selected from multi-walled carbon nanotubes, vapor-grown carbon fibers and conductive carbon black.

[0013] By adopting the above technical solution, artificial graphite primary particles with a median particle size (D50) of 8 to 12 micrometers are selected as the skeleton, which can provide good mechanical support and prevent secondary particles from breaking under high pressure compaction. Combined with nano- or micron-sized silicon-based materials with matching particle size, effective filling of silicon particles in the gaps between graphite particles is achieved. Multi-walled carbon nanotubes and vapor-grown carbon fibers serve as long-range conductive agents, constructing a three-dimensional conductive network of points, lines, and surfaces with conductive carbon black, improving the electron transport capability within the composite particles and reducing polarization impedance.

[0014] Preferably, the carbon source precursor is selected from phenolic resin, polyacrylonitrile, sucrose, asphalt or epoxy resin; the solvent is selected from water, anhydrous ethanol, methanol, acetone, dimethylformamide or N-methylpyrrolidone; and the dispersant is selected from polyvinylpyrrolidone or sodium alginate.

[0015] By employing the above technical solutions, the aforementioned carbon source precursors exhibit high carbon residue and good film-forming properties. For example, phenolic resin and polyacrylonitrile, after carbonization, can form a high-strength hard carbon framework, which not only provides conductivity but also limits the excessive outward expansion of silicon particles. Polyvinylpyrrolidone or sodium alginate, as dispersants, utilize the polar groups on their molecular chains to form non-covalent bonds with the silicon and graphite surfaces, preventing slurry sedimentation and ensuring uniform distribution of components at the microscale.

[0016] Preferably, the tap density of the composite particles is 1.20 g / cm³. 3 Up to 1.32 g / cm 3 The specific surface area of ​​BET is 2.0 m². 2 / g to 4.0m 2 / g, with a total specific pore volume ranging from 0.20 mL / g to 0.35 mL / g.

[0017] By adopting the above technical solution, the specific surface area of ​​BET is controlled at 2.0m². 2 / g to 4.0m 2 Within the lower range of / g, the consumption of active lithium by SEI film formation during the first charge-discharge process is reduced, thereby improving the first coulombic efficiency. Meanwhile, 1.20 g / cm³ 3 The above tap density ensures the electrode compaction density, meeting the design requirements of high-energy-density lithium-ion batteries. The total specific pore volume of 0.20 mL / g to 0.35 mL / g, combined with the aforementioned micron-sized pore distribution, achieves an optimal balance between buffer space and volumetric density.

[0018] Secondly, the present invention provides a spray drying method for preparing spherical artificial graphite composite particles, employing the following technical solution:

[0019] A spray drying method for preparing spherical artificial graphite composite particles includes the following steps: First, an aqueous solution containing a water-soluble polymeric dispersant and an oil solution containing an organic solvent are prepared, and a carbon source precursor is dissolved in the aqueous or oil solution; second, artificial graphite, silicon-based active materials, and conductive agents are dispersed in the aqueous or oil solution to form a solid-liquid suspension, and then another phase solution is added under shear conditions to emulsify and form an oil-in-water or water-in-oil emulsion slurry; next, the emulsion slurry is fed into a pressure spray drying tower with three independent temperature zones for granulation to obtain a spherical precursor, wherein the three independent temperature zones, from top to bottom, are a high-temperature rapid forming zone, a middle-layer phase separation and pore formation zone, and a lower-layer curing and shaping zone; finally, the spherical precursor is placed in an inert atmosphere furnace for high-temperature carbonization treatment to obtain spherical artificial graphite composite particles.

[0020] By employing the above technical solution, this method utilizes a multiphase emulsion system combined with gradient temperature-controlled spray drying technology. Through the synergistic effect of physical phase separation and chemical cross-linking, it achieves precise control over the microstructure of particles. Its specific forming mechanism is as follows:

[0021] Step 1, Emulsion Template Construction: Utilizing the immiscibility of the aqueous and oil phases and the interfacial activity of the polymeric dispersant, a stable emulsion system is formed under shear force. Graphite and silicon-based particles are encapsulated and suspended in the continuous phase by the dispersant, while the discontinuous phase droplets act as the initial physical pore-forming template.

[0022] Step 2, gradient thermal field molding: In the high-temperature rapid molding zone, the solvent on the droplet surface evaporates rapidly upon heating, the polymer concentration on the droplet surface increases sharply and forms a film, creating a dense semi-solid shell, thus defining the spherical outline of the particle; entering the middle layer phase separation and pore formation zone, the internal solvent is heated to generate vapor pressure, while the dispersed phase droplets in the emulsion undergo phase separation, aggregation, and migration, leaving interconnected micron-level channels in situ inside the particle; in the lower layer curing and shaping zone, the remaining solvent is removed, and the carbon source precursor undergoes a preliminary thermal crosslinking reaction, curing and shaping the above porous framework structure.

[0023] Step 3, high-temperature carbonization fixation: The organic precursor is converted into amorphous carbon through high-temperature treatment, permanently locking the relative positions of graphite and silicon-based materials, and finally obtaining a composite structure with a dense outer shell and interconnected porous interior.

[0024] Preferably, the inlet air temperature of the high-temperature rapid prototyping zone is set to 200°C to 260°C, the temperature of the middle layer phase separation and channel formation zone is set to 120°C to 180°C, and the outlet air temperature of the lower layer curing and shaping zone is set to 80°C to 120°C; the shearing speed of the shearing conditions is 4000 rpm to 6000 rpm, and the shearing time is 30 minutes to 60 minutes.

[0025] By adopting the above technical solutions, strictly controlling the temperature gradient and shear conditions in each temperature zone is the key to forming a specific pore structure.

[0026] In the high-temperature range of 200 to 260 degrees Celsius, it can ensure that the polymer on the droplet surface forms a film instantly, forming a dense protective layer to prevent the internal silicon particles from being directly exposed to the electrolyte during subsequent battery cycle expansion.

[0027] In the medium temperature range of 120°C to 180°C, the solvent evaporation rate reaches equilibrium with the internal gas pressure, which promotes the dispersed phase to stably occupy the space and form micron-sized pores of 0.5 microns to 3 microns, thus avoiding particle shattering due to excessively rapid evaporation or structural collapse due to excessively slow evaporation.

[0028] With a shear rate of 4000 to 6000 rpm, the size of the dispersed phase droplets can be controlled at the micrometer level, which directly determines the final pore size distribution range, thus ensuring that the effective pore volume ratio exceeds 50%.

[0029] Preferably, the high-temperature carbonization process includes two stages: the first stage is to raise the temperature to 300°C to 450°C and hold it for 2 to 4 hours; the second stage is to raise the temperature to 800°C to 1200°C and hold it for 4 to 8 hours.

[0030] By adopting the above technical solution, the segmented heat treatment mechanism ensures the integrity of the structure and the electrochemical performance of the material.

[0031] The first stage (300°C to 450°C) mainly involves the debinding reaction and thermal cross-linking and curing of the precursor (such as phenolic resin or polyacrylonitrile). During this stage, low molecular weight volatiles are released slowly to prevent the spherical particles from breaking due to rapid gas release. At the same time, pre-oxidation or pre-cross-linking is completed, and the carbon skeleton is initially shaped.

[0032] The second stage (800°C to 1200°C) mainly involves carbonization and graphitization reactions. Within this temperature range, the precursor undergoes complete dehydrogenation and deoxygenation, transforming into a highly conductive amorphous carbon network. Simultaneously, some lattice defects are eliminated, improving the overall conductivity and structural strength of the material, enabling it to withstand the mechanical pressure during electrode compaction.

[0033] Preferably, the aqueous phase solution is an aqueous solution of polyvinylpyrrolidone or an aqueous solution of sodium alginate, and the oil phase solution is an ethanol solution of phenolic resin or a mixed solution of dimethylformamide and acetone of polyacrylonitrile; polymethyl methacrylate microspheres are added to the oil phase solution during the preparation of the liquid phase system or the preparation of the emulsion slurry.

[0034] By employing the above technical solution, a specific solvent and polymer combination exhibits a suitable surface tension difference, which is beneficial for forming a stable emulsion interface. Polymethyl methacrylate microspheres are added as sacrificial pore-forming agents; these microspheres undergo pyrolysis and vaporization during subsequent high-temperature carbonization treatment.

[0035] The reaction process is as follows: polymethyl methacrylate microspheres undergo depolymerization in the temperature range of 300℃ to 400℃, breaking down to generate gaseous methyl methacrylate monomers, which are then discharged from the system, leaving spherical cavities in situ. These cavities are interconnected with the pores formed by the separation of the emulsion phase, improving the connectivity and pore volume ratio of the micron-sized pores. This provides more ample directional release space for the volume expansion of the silicon-based anode material, preventing the overall pulverization of the particles.

[0036] This invention provides spherical artificial graphite composite particles, their spray drying preparation method, and their applications. It offers the following advantages:

[0037] 1. This invention effectively resolves the contradiction between volume expansion and interfacial side reactions in silicon-based anode materials by constructing a spherical structure with a dense outer shell and interconnected pores inside. Specifically, the dense outer shell significantly reduces the specific surface area of ​​the particles, minimizing direct contact between the electrolyte and the active material, thereby inhibiting excessive growth of the solid electrolyte interphase (SEI) film and improving the initial coulombic efficiency. Simultaneously, the micron-sized pores, distributed between 0.5 and 3 micrometers and accounting for over 50% of the total pore volume, provide ample and effective buffer space for the volume expansion of the silicon-based material, preventing particle pulverization or breakage due to localized stress concentration and improving the material's cycle stability.

[0038] 2. This invention utilizes in-situ carbonization technology with a liquid-phase binder system and carbon source precursor to construct a high-strength three-dimensional conductive network within the composite particles. The amorphous carbon coating, with a content of 1wt% to 5wt%, not only acts as a physical binder to firmly anchor nano-silicon or silicon monoxide onto the surface of the artificial graphite skeleton, preventing the active material from detaching during repeated charge-discharge cycles, but also works synergistically with the added conductive agent to ensure that even when the silicon particles undergo volume changes, a stable electron transport channel is maintained within the particles, effectively reducing the polarization impedance of the electrodes and improving rate performance.

[0039] 3. The gradient temperature spray drying process employed in this invention achieves precise control over the microstructure of the composite particles, balancing high porosity and high tap density. Through segmented control of high-temperature rapid molding, mid-temperature phase separation for pore formation, and low-temperature curing and shaping, the resulting composite particles retain internal buffer pores while exhibiting regular sphericity and high tap density. This structural feature helps maintain particle integrity during electrode rolling, thereby improving the volumetric energy density of lithium-ion batteries and meeting the application requirements of high-energy-density batteries. Attached Figure Description

[0040] Figure 1 This is a schematic diagram of the preparation method of the present invention;

[0041] Figure 2 This is a SEM image of the artificial graphite composite particles of the present invention.

[0042] Figure 3 This is a comparison chart of the charging performance of the present invention at different rates;

[0043] Figure 4 This is a comparison chart of the long-cycle stability of the present invention. Detailed Implementation

[0044] The raw material content defined in the claims of this invention is in parts by weight. In the following specific embodiments, for ease of weighing and experimental operation, parts by weight are specified in grams (g). For example, 88-95 parts of artificial graphite as described in the claims are represented in the embodiments as 880g to 950g of artificial graphite (i.e., scaled up to a ratio of 10 parts to 100g). This specification of units is only to illustrate the mass ratio between the components. All mass units (such as kg, ton, etc.) that conform to the weight ratio described in the claims are acceptable.

[0045] Figure 1 A flowchart of the spray drying preparation method for spherical artificial graphite composite particles is provided, demonstrating how the spherical artificial graphite composite particles are obtained by combining emulsion template method with gradient spray drying technology.

[0046] Figure 2 The image shows a SEM image of the artificial graphite composite particles, which visually demonstrates the opening of these pores on the particle surface and the overall spherical secondary granulation morphology. The non-dense, slightly loose texture on the particle surface is the physical trace left by the controlled escape of solvent and pore-forming agent during the gradient temperature control process. If gradient temperature control is not used (such as the solid structure in Comparative Example 1), the particle surface will usually be overly dense or appear as a dense block; if the temperature is out of control (such as in Comparative Example 2), large cracks are likely to appear on the particle surface.

[0047] Figure 3 The comparison chart of charging performance by rate verifies the ion transport efficiency; as the charging rate increases from 0.2C to 6C, the capacity retention rate of Example 1 is higher than that of the comparative example (86.4% is still maintained at 6C).

[0048] Comparative analysis: Comparative Example 1 (solid structure) shows a sharp drop in capacity above 3C, indicating that the lack of internal pores leads to an excessively long ion diffusion path and severe polarization at high rates.

[0049] Figure 4The comparison chart of long-cycle stability verifies the expansion buffer mechanism; after 500 cycles, Example 1 still maintains a high capacity of 89.4%, and the decay curve is gentle. This verifies that the internal micron-sized pores act as a breathing airbag, effectively absorbing about 10% of the volume expansion of graphite during lithium intercalation, and preventing the particles from pulverizing and peeling off due to excessive internal stress.

[0050] Failure analysis: The rapid decay of Comparative Example 1 (with a retention rate of only 52.3%) corresponds to the phenomenon that dense solid particles are prone to mechanical cracking during repeated expansion and contraction, leading to repeated rupture and regeneration of the SEI film and consumption of active lithium.

[0051] Preparation Examples 1-3:

[0052] Preparation Example 1:

[0053] This preparation example provides a method for preparing a modified phenolic resin precursor solution for constructing an oil-phase system, comprising the following steps:

[0054] Add 800g of anhydrous ethanol to a three-necked flask equipped with a reflux condenser and a mechanical stirrer, and heat to 45°C;

[0055] While stirring, add 200g of thermosetting linear phenolic resin in batches and continue stirring for 60min until the resin is completely dissolved to obtain a pale yellow transparent solution.

[0056] Add 10g of hexamethylenetetramine (HMTA) to the above solution as a curing agent, and continue stirring for 30 minutes to dissolve it;

[0057] The solution was naturally cooled to room temperature and then filtered through a 1000-mesh filter to remove insoluble impurities, yielding a phenolic resin ethanol solution with a solid content of 21 wt%. The solution was then sealed and stored for later use.

[0058] Preparation Example 2:

[0059] This preparation example provides a method for preparing a monodisperse nano-silicon predispersed slurry, including the following steps:

[0060] Preparation of dispersion medium: Dissolve 5g of polyvinylpyrrolidone in 845g of deionized water and stir until completely dissolved;

[0061] Premixing: Slowly add 150g of nano-silicon powder (primary particle size D50 of 80nm) to the above dispersion medium while simultaneously performing high-speed mechanical stirring (1000rpm) for 30min to form a coarse suspension;

[0062] Ultrasonic dispersion: The coarse suspension was placed in an ultrasonic disperser and treated at 400W power for 30 minutes;

[0063] Sand milling: The ultrasonically treated suspension was pumped into a laboratory horizontal sand mill, using 0.3mm zirconia beads as the grinding medium, and circulated for 90 minutes, controlling the temperature of the discharged slurry to be below 40℃.

[0064] The final nano-silicon slurry had a solid content of 15wt%, and its D50 was 95nm and D90 was 160nm as measured by a laser particle size analyzer.

[0065] Preparation Example 3:

[0066] This preparation example provides a method for preparing a polymethyl methacrylate (PMMA) microsphere dispersion, including the following steps:

[0067] Add 160g of methanol and 40g of deionized water to a four-necked flask equipped with a nitrogen inlet tube, a stirrer and a condenser, and stir until well mixed.

[0068] Add 6g of polyvinylpyrrolidone as a dispersant and stabilizer, and stir to dissolve at room temperature;

[0069] Add 30g of methyl methacrylate (MMA) monomer and 0.3g of azobisisobutyronitrile (AIBN) initiator, and purge with high-purity nitrogen for 30 minutes to remove oxygen;

[0070] Under nitrogen protection, the mixture was stirred at 200 rpm and heated to 70°C, and the reaction was carried out at a constant temperature for 24 hours.

[0071] After the reaction was completed, the product was cooled to room temperature, centrifuged, and washed three times with anhydrous ethanol to remove unreacted monomers and excess PVP.

[0072] The washed PMMA microspheres were redispersed in anhydrous acetone and ultrasonically dispersed to obtain a PMMA microsphere dispersion with a solid content of 20 wt%. SEM testing showed that the average particle size of the microspheres was 1.2 μm.

[0073] Reference Figures 1-4 Examples 1-6:

[0074] Example 1:

[0075] This embodiment provides a method for preparing spherical artificial graphite composite particles using an oil-in-water system, including the following steps:

[0076] Preparation of the liquid phase system: Dissolve 30 g of polyvinylpyrrolidone K30 in 600 g of deionized water and stir until clear to obtain the aqueous continuous phase; take another 150 g of the phenolic resin ethanol solution obtained in Example 1 as the oil phase dispersion.

[0077] Preparation of solid-phase mixture: Weigh 920g of artificial graphite primary particles with a median particle size D50 of 8 micrometers; 50g of nano-silicon powder with a median particle size D50 of 80 nanometers; 15g of multi-walled carbon nanotubes and 15g of vapor-grown carbon fibers; premix the above solid-phase materials in a high-speed mixer for 30 minutes.

[0078] Preparation of emulsion slurry: The premixed solid phase mixture is added to the aqueous continuous phase and mechanically dispersed for 60 minutes to form a suspension; then, under high-speed shearing conditions of 4000 rpm, the oil phase dispersion is slowly added and shearing is continued for 30 minutes to form a stable oil-in-water Pickering emulsion slurry.

[0079] Spray drying: The emulsion slurry is pumped into a three-temperature zone pressure spray drying tower. The inlet air temperature of the upper high-temperature rapid molding zone is set at 240 degrees Celsius, the temperature of the middle phase separation and pore formation zone is set at 160 degrees Celsius, the outlet air temperature of the lower curing and shaping zone is set at 100 degrees Celsius, and the atomization pressure is 2.0 MPa. Spherical precursor powder is collected.

[0080] Heat treatment and shaping: The spherical precursor is placed in a nitrogen atmosphere furnace and heated to 400 degrees Celsius at a rate of 2 degrees Celsius per minute and held for 3 hours for debinding. Then, it is heated to 1000 degrees Celsius at a rate of 4 degrees Celsius per minute and held for 4 hours for carbonization. After natural cooling, the material is shaped by an air jet mill and screened through a 325-mesh sieve to obtain the final product.

[0081] Example 2:

[0082] This embodiment provides a method for preparing spherical artificial graphite composite particles using a water-in-oil system, including the following steps:

[0083] Preparation of the liquid phase system: Take 500g of the phenolic resin ethanol solution obtained in Preparation Example 1 as the oil phase continuous phase; and dissolve 10g of sodium alginate in 200g of deionized water as the aqueous phase dispersion phase.

[0084] Preparation of solid-phase mixture: Weigh 880 grams of artificial graphite primary particles with a D50 of 12 micrometers; 100 grams of silica powder with a D50 of 3 micrometers; and 20 grams of carbon nanotubes; mix evenly and set aside.

[0085] Preparation of emulsion slurry: The solid phase mixture is dispersed in the oil phase continuous phase and stirred evenly; then the aqueous phase dispersion is added dropwise at a shear speed of 6000 rpm, and emulsification is carried out for 40 minutes to form a water-in-oil emulsion slurry.

[0086] Spray drying: The slurry is fed into a drying tower, and the upper layer temperature is set to 220 degrees Celsius, the middle layer temperature to 140 degrees Celsius, and the lower layer temperature to 90 degrees Celsius for drying and granulation.

[0087] Heat treatment and shaping: Under argon protection, the first heat treatment was held at 350 degrees Celsius for 2 hours, and the second heat treatment was held at 1100 degrees Celsius for 5 hours; the subsequent shaping steps were the same as in Example 1.

[0088] Example 3:

[0089] This embodiment provides a spherical artificial graphite composite particle with an introduced solid pore-forming agent and its preparation method, including the following steps:

[0090] Preparation of the mixed liquid phase: Take 400g of a 5% (w / w) polyvinylpyrrolidone aqueous solution as the aqueous phase; take 100g of the polymethyl methacrylate microsphere dispersion obtained in Preparation Example 3 and mix it evenly with 50g of the phenolic resin ethanol solution obtained in Preparation Example 1 as the oil phase.

[0091] Solid phase ingredients: 930 grams of artificial graphite primary particles, 40 grams of the dry powder equivalent of the nano-silicon slurry obtained in Preparation Example 2, and 30 grams of carbon nanotubes were selected.

[0092] Emulsification granulation: The solid phase is dispersed in the aqueous phase, and then the oil phase is added for shear emulsification at 5000 rpm; the spray drying conditions are set to 250 degrees Celsius for the upper layer, 170 degrees Celsius for the middle layer, and 110 degrees Celsius for the lower layer.

[0093] Carbonization treatment: Under a nitrogen atmosphere, the polymethyl methacrylate microspheres are first heated to 450 degrees Celsius for 3 hours to fully decompose them and create pores. Then, the temperature is raised to 1050 degrees Celsius for carbonization for 4 hours to finally obtain the finished product.

[0094] Example 4:

[0095] This embodiment provides spherical artificial graphite composite particles using different carbon sources and conductive agents, and a method for preparing the same, including the following steps:

[0096] Preparation of the liquid phase system: Dissolve 20 g of sucrose in 500 g of water to form an aqueous phase; dissolve 15 g of polyacrylonitrile in a mixed solvent of 150 g of dimethylformamide and acetone to form an oil phase.

[0097] Solid phase composition: 950g of primary artificial graphite particles, 30g of nano-silicon and 20g of vapor-grown carbon fiber.

[0098] Preparation and drying: The solid phase was mixed into the aqueous phase for dispersion, and then the oil phase was added for emulsification; the spray drying temperature was set to 230 degrees Celsius for the upper layer, 150 degrees Celsius for the middle layer, and 100 degrees Celsius for the lower layer.

[0099] Heat treatment: The temperature is slowly increased to 300 degrees Celsius in nitrogen at a rate of 1 degree Celsius per minute and held for 4 hours, then increased to 900 degrees Celsius and held for 6 hours to complete carbonization and shaping.

[0100] Example 5:

[0101] This embodiment provides a method for preparing spherical artificial graphite composite particles under the lower limit of process parameters, including the following steps:

[0102] Raw material preparation: The same solid-phase formulation as in Example 1 was used; in the liquid-phase system, the aqueous phase was an aqueous solution of polyvinylpyrrolidone, and the oil phase was a 10% (w / w) phenolic resin ethanol solution.

[0103] Spray drying: The drying tower parameters were adjusted to 200 degrees Celsius for the upper layer, 120 degrees Celsius for the middle layer, and 80 degrees Celsius for the lower layer. The feed rate was reduced by 20% compared to Example 1.

[0104] Heat treatment: The maximum carbonization temperature is set at 800 degrees Celsius, and the holding time is extended to 8 hours to ensure the stability of the structure under low-temperature carbonization conditions.

[0105] Example 6:

[0106] This embodiment provides a method for preparing spherical artificial graphite composite particles under the upper limit of process parameters, including the following steps:

[0107] Raw material preparation: The same formulation system as in Example 1 was used.

[0108] Spray drying: Adjust the drying tower parameters to 260 degrees Celsius for the upper layer, 180 degrees Celsius for the middle layer, and 120 degrees Celsius for the lower layer, and appropriately increase the feed rate.

[0109] Heat treatment: The maximum carbonization temperature is set at 1200 degrees Celsius, and the holding time is 4 hours, in order to obtain a highly crystalline carbon coating and a high-density shell structure.

[0110] Comparative Examples 1-4:

[0111] Comparative Example 1:

[0112] Compared with Example 1, the difference is that the liquid phase system does not use an incompatible combination of water and oil phases. Instead, polyvinylpyrrolidone and phenolic resin are both dissolved in anhydrous ethanol to form a homogeneous solution. All solid components are directly dispersed in this homogeneous solution for spray drying. No emulsion template is formed. Everything else is the same.

[0113] Comparative Example 2:

[0114] Compared with Example 1, the difference is that the spray drying process does not use multi-stage gradient temperature control. The temperature of the upper, middle and lower layers of the drying tower is set to a constant 200 degrees Celsius, and the rest are the same.

[0115] Comparative Example 3:

[0116] Compared with Example 1, the difference is that no phenolic resin carbon source precursor was added to the oil phase, and only anhydrous ethanol was used as the oil phase dispersion phase. The final product lacks carbon coating. All other aspects are the same.

[0117] Comparative Example 4:

[0118] Compared with Example 1, the difference is that spray drying was not used for granulation. Instead, the prepared solid-liquid mixture was dried in an oven to remove the solvent, then ground into powder and directly subjected to heat treatment and carbonization. All other aspects are the same.

[0119] Test Examples 1-5:

[0120] Test Example 1: Quantitative characterization of internal multi-level porous structure using mercury intrusion porosimetry.

[0121] This test example uses mercury intrusion porosimetry (MIP) to test the internal porosity characteristics of the prepared particles. This method involves injecting a non-wetting liquid (mercury) into the pores of a porous material under external pressure. The Washburn equation is used to correlate pressure with pore size, thereby obtaining porosity, pore volume, and pore size distribution data. This test aims to verify whether a specific micron-scale interconnected pore structure has been successfully constructed within the particles.

[0122] Experimental steps:

[0123] Sampling: Weigh 2.00 g of each of the powder samples prepared in Examples 1 to 3, 5, 6 and Comparative Examples 1 and 2, and place them in sample tubes.

[0124] Pretreatment: Place the sample tube containing the sample in a vacuum drying oven and vacuum dry at 110°C for 4 hours to remove moisture and impurity gases adsorbed on the sample surface and in the pores. Cool to room temperature for later use.

[0125] Low-pressure test: Install the sample tube into the low-pressure station of the fully automated mercury porosimeter. Evacuate to below 50 μmHg, then fill with mercury to perform a low-pressure test, measuring coarse pores and particle packing porosity, and determining the bulk density of the sample.

[0126] High-pressure test: The sample tube was transferred to a high-pressure station, and the pressure was gradually increased to 33,000 psia. The volume of mercury injected under different pressures was recorded. At this point, the mercury will overcome capillary forces and enter the micropores inside the particles (corresponding to a pore size range of approximately 5 nm to 3 μm).

[0127] Data processing: Based on the relationship curve between mercury inlet pressure and mercury inlet volume, the total porosity and total specific pore volume are calculated, and the pore size distribution is differentiated to extract the peak characteristics of different pore size ranges.

[0128] The experimental data are shown in Table 1:

[0129] Table 1 Summary of the structural parameters of the mercury porosimetry test holes for each sample

[0130] Sample number Total porosity (%) Total specific pore volume (mL / g) Peak position of characteristic aperture (μm) Percentage of mercury entering the 0.5-3μm range (%) Average pore size (nm) Example 1 34.21 0.284 1.58 62.4 452 Example 2 31.05 0.256 1.15 58.7 389 Example 3 39.82 0.331 2.04 71.2 840 Example 5 27.64 0.215 0.82 45.3 295 Example 6 29.18 0.233 1.34 51.6 360 Comparative Example 1 14.82 0.112 No obvious peak 12.4 85 Comparative Example 2 43.50 0.389 Disorderly and multi-peaked 35.8 1240

[0131] Results Analysis and Conclusions:

[0132] Based on the data analysis in Table 1, the differences in pore structure parameters between the examples and the comparative examples confirm the regulatory effect of the preparation process on the microstructure.

[0133] The test results of Examples 1 to 3 show that the total porosity of the samples is concentrated between 30% and 40%, with a characteristic peak in the pore size range of 0.5-3 μm, and the mercury ingress rate in this range exceeds 50%. This indicates that the emulsion template method successfully induced phase separation during spray drying, leaving uniform micron-sized pores after the dispersed phase (oil or aqueous phase) inside the droplets evaporates. In particular, Example 3 introduced PMMA microspheres, which further increased the total porosity and average pore size, and the characteristic peak shifted to the right to 2.04 μm, verifying the ability of the solid template agent to control the macroporous structure. These micron-sized pores constitute the main liquid-phase diffusion channel for lithium ions, while providing the necessary buffer space for the volume expansion of silicon-based materials.

[0134] Examples 5 and 6 represent the lower and upper limits of the process window, respectively. Example 5 (low temperature) has a smaller characteristic pore size and slightly lower porosity, which is due to the slower solvent evaporation at low temperatures, resulting in smaller droplet sizes and greater shrinkage during phase separation. Example 6 (high temperature), on the other hand, maintains a better pore structure, demonstrating that the target structure can be effectively constructed within the gradient temperature range defined in the claims.

[0135] In contrast, Comparative Example 1 used a homogeneous solution system with a total porosity of only 14.82%, and the proportion of mercury ingress in the 0.5-3 μm range was extremely low (12.4%), with no obvious characteristic peaks in the pore size distribution. This indicates that in the absence of an emulsion interface and phase separation mechanism, the solvent evaporates uniformly during spray drying, and the solid particles are tightly packed to form solid spheres, making it impossible for a micron-scale pore network conducive to ion transport to spontaneously form.

[0136] Although Comparative Example 2 has a high total porosity (43.50%), its pore size distribution exhibits a chaotic, multi-peaked characteristic, lacking controllability. This is because the absence of gradient temperature control and the use of a single temperature resulted in an imbalance in drying kinetics, potentially leading to premature shell cracking or internal structural collapse, forming numerous unstructured open macropores or cracks. While this disordered structure boasts high porosity, it is typically accompanied by reduced tap density and insufficient mechanical strength, failing to meet the requirements for high energy density.

[0137] Test Example 2: Test on particle shell density and powder engineering properties.

[0138] This test primarily focuses on measuring the specific surface area (BET) and tap density of the prepared powder material. These two indicators are directly related to the volumetric energy density of lithium-ion batteries and the degree of electrolyte side reactions. The test aims to verify whether the programmed gradient drying process of this invention can successfully form a dense particulate shell while constructing an internal porous structure, thereby maintaining a high engineering density and suppressing excessively high specific surface area.

[0139] Experimental steps:

[0140] Specific surface area testing: Specific surface area and porosity were measured using a fully automated specific surface area and porosity analyzer. Accurately weigh 1.5g to 2.0g of sample into a test tube, place it in a degassing station, and degas for 4 hours under vacuum at 200℃ to completely remove surface adsorbed impurities. After degassing, transfer the sample tube to the analysis station for nitrogen adsorption-desorption testing at 77K liquid nitrogen temperature. Adsorption data with relative pressures (P / P0) ranging from 0.05 to 0.30 were selected, and the specific surface area of ​​the sample was calculated using the BET multipoint method equation.

[0141] Tapped density test: A BT-300 powder tapped density tester was used. 50.0 g ± 0.1 g of sample powder was weighed and carefully placed into a clean, dry 100 mL graduated cylinder, and the initial volume was read. The graduated cylinder was fixed to the vibration assembly, and the vibration frequency was set to 250 times / min, the amplitude to 3 mm, and the number of vibrations to 3000. After vibration, the volume of the compressed powder in the graduated cylinder was read horizontally. The tapped density was calculated based on the ratio of the sample mass to the tapped volume. Each group of samples was tested in parallel three times, and the average value was taken.

[0142] The experimental data are shown in Table 2:

[0143] Table 2 Summary of the test results of specific surface area and tap density of each sample

[0144] Sample number <![CDATA[Specific surface area (m 2 / g)]]> <![CDATA[Tap density (g / cm 3 ).]]> Remark Example 1 2.85 1.28 The shell is dense and has a high degree of sphericity. Example 2 3.14 1.26 Slightly rough surface Example 3 3.52 1.23 The high internal porosity leads to a slight decrease in density. Example 5 2.41 1.32 Slower film formation at low temperatures results in a more solid structure. Example 6 3.03 1.25 High temperature rapid setting Comparative Example 1 1.84 1.34 Solid structure, no internal holes Comparative Example 2 6.78 0.94 The particles are severely broken and the outer shell is porous. Comparative Example 4 5.21 0.88 Irregular shape and poor gradation

[0145] Results Analysis and Conclusions:

[0146] The tap density data of Examples 1 to 6 are mainly distributed at 1.23 g / cm³. 3 Up to 1.32 g / cm 3 Between these values, this level is comparable to that of a solid, dense sphere in Comparative Example 1 (1.34 g / cm³). 3The results are very close. Combined with the fact confirmed in Test Example 1 that a large number of micron-sized pores exist inside the embodiment, this demonstrates that the gradient temperature drying process of the present invention rapidly solidifies the surface at a high temperature (200-260°C), forming a robust and dense outer shell. This shell effectively maintains the macroscopic volume stability of the particles, preventing them from collapsing due to internal hollowness during stacking, thus ensuring a volumetric energy density comparable to that of solid particles.

[0147] Meanwhile, the specific surface area of ​​the sample in the example was controlled at 2.41 m². 2 / g to 3.52m 2 The specific surface area is in the lower range of / g. In contrast, Comparative Example 4 (physical mixing / no granulation) has a higher specific surface area of ​​5.21 m². 2 / g, and the tap density is only 0.88g / cm³. 3 This indicates that spray drying spheroidization is crucial for reducing specific surface area and increasing bulk density.

[0148] A more crucial comparison occurs between Example 1 and Comparative Example 2. Comparative Example 2, using isothermal spray drying, exhibited an abnormally high specific surface area of ​​6.78 m². 2 / g, while the tap density drops sharply to 0.94g / cm³. 3 This is because, under constant temperature conditions, the evaporation rates of the solvent inside and outside the droplet are mismatched. The internal pressure buildup causes the outer shell to burst or form open pores during the drying process, exposing the internal structure. This not only prevents the formation of a dense protective layer but also damages the spherical integrity.

[0149] Example 3 introduced a PMMA pore-forming agent, which resulted in a slight increase in specific surface area to 3.52 m². 2 / g, tap density slightly decreased to 1.23g / cm³. 3 However, it is still within the excellent range for industrial applications. Example 5 was prepared at a lower temperature, resulting in the most dense structure due to slow solvent evaporation, but this may sacrifice some internal pore space.

[0150] Test Example 3: Lithium-ion diffusion kinetics and fast charging performance test.

[0151] This test case uses a half-cell system for constant current charge-discharge testing and intermittent titration (GITT) to evaluate the rate performance and lithium-ion diffusion rate in the solid phase of materials prepared using different processes. The core of the test is to verify whether the constructed internal interconnected pore network effectively shortens the ion transport path, thereby improving the fast-charging capability under high current.

[0152] Experimental steps:

[0153] Electrode fabrication and battery assembly: The active material powder, conductive carbon black, sodium carboxymethyl cellulose (CMC), and styrene-butadiene rubber (SBR) prepared in each example and comparative example were mixed at a mass ratio of 92:2:2:4. An appropriate amount of deionized water was added, and the mixture was stirred evenly in a vacuum mixer to form a slurry. The slurry was evenly coated onto a copper foil current collector, dried, and then rolled to control the compaction density at 1.5 g / cm³. 3 Up to 1.6 g / cm 3 Cut into 14mm diameter round slices and dry in a vacuum oven at 110℃ for 12 hours.

[0154] Rate charging performance testing: The battery was tested using a battery testing system (Blue Electric CT2001A). The battery was first activated for three weeks at a 0.1C rate (voltage range 0.01V-1.5V). Subsequently, rate charging tests were performed, with the discharge (lithium desorption) rate fixed at 1C, and the charge (lithium insertion) rates set sequentially to 0.2C, 1C, 3C, and 6C. Each rate was tested for 5 cycles, and the constant current charging specific capacity of the last week at each rate was recorded, and the capacity retention rate relative to 0.2C was calculated.

[0155] Diffusion coefficient determination: GITT tests were performed on the activated batteries. The batteries were charged to 50% state of charge (SOC) and allowed to stand for 2 hours to stabilize the voltage. A 0.1C pulse current was applied for 10 minutes, followed by a 60-minute rest period to eliminate concentration polarization. Voltage changes during the pulse and relaxation processes were recorded to calculate the apparent diffusion coefficient of lithium ions.

[0156] The experimental data are shown in Table 3:

[0157] Table 3. Rate performance and lithium-ion diffusion coefficient test results for each sample.

[0158] Sample number Specific capacity at 0.2C (mAh / g) 1C capacity retention rate (%) 3C Capacity Retention Rate (%) 6C Capacity Retention Rate (%) <![CDATA[Diffusion coefficient at 50% SOC (cm 2 / s)]]> Example 1 358.4 98.2 92.1 86.4 <![CDATA[4.12×10 -9 ]]> Example 2 355.7 97.9 91.5 84.9 <![CDATA[3.85×10 -9 ]]> Example 3 352.1 98.5 93.8 88.2 <![CDATA[5.67×10 -9 ]]> Example 5 360.2 97.1 88.4 79.5 <![CDATA[2.31×10 -9 ]]> Example 6 356.9 98.0 90.7 83.6 <![CDATA[3.55×10 -9 ]]> Comparative Example 1 361.5 94.3 72.8 45.1 <![CDATA[4.82×10 -11 ]]> Comparative Example 2 342.8 91.6 65.4 32.7 <![CDATA[8.94×10 -11 ]]> Comparative Example 4 348.3 89.2 58.9 24.5 <![CDATA[6.51×10 -11 ]]>

[0159] Results Analysis and Conclusions:

[0160] At low rates (0.2C), the specific capacity of the samples did not differ significantly, with Comparative Example 1 even exhibiting a slightly higher specific capacity. This is attributed to its solid, dense structure having a higher proportion of active material. However, as the charging rate increased to 3C and 6C, the capacity retention of Comparative Example 1 dropped sharply, reaching only 72.8% and 45.1%, respectively. This is because in solid particles, lithium ions must rely on slow solid-phase diffusion to traverse the entire particle radius, resulting in severe polarization at high rates, which prevents the capacity from being effectively utilized.

[0161] In contrast, Examples 1 to 3 exhibited excellent stability at high rates. Example 1 maintained a capacity retention of 86.4% at an ultra-high rate of 6C. GITT test results further corroborated its kinetic advantages: the lithium-ion diffusion coefficient of Example 1 was two orders of magnitude higher than that of Comparative Example 1. This improvement directly demonstrates the liquid-phase storage mechanism described in this invention: the micron-sized internal channels formed by phase separation during spray drying allow the electrolyte to penetrate into the particle interior, extending the liquid-phase transport path of ions to the particle core, significantly shortening the limited solid-phase diffusion distance, thereby achieving a breakthrough in fast-charging performance.

[0162] Example 3, due to the introduction of PMMA pore-forming agent, has a richer internal porosity, thus exhibiting the highest retention rate (88.2%) and the highest diffusion coefficient at 6C magnification. However, this is accompanied by a slight decrease in tap density as seen in Test Example 2. Example 5 (prepared at low temperature) has a relatively dense structure, and its high-rate performance (6C retention rate of 79.5%) is slightly lower than that of Example 1, but still superior to all comparative examples.

[0163] Comparative Example 2 (constant temperature drying) and Comparative Example 4 (physical mixing) performed the worst at high magnification, with 6C retention rates both below 35%. Although Comparative Example 2 had high porosity (see Test Example 1), its pore structure was disordered and consisted mostly of dead pores or cracks, resulting in poor electronic contact between particles, increased internal resistance, and failure to form an effective ion-electron dual-conductivity network.

[0164] Test Example 4: Cyclic stability and electrode expansion test.

[0165] This test primarily examines the electrochemical stability and volume change of the material during long-term charge-discharge cycles. Given the significant volume expansion effect of silicon-based anode materials during lithium intercalation, the electrode thickness change rate is a key indicator of whether the particle structure can effectively buffer silicon expansion. This test aims to verify the suppressive effect of the internal porous structure constructed in this invention on the silicon volume effect and the protective effect of the carbon coating layer on structural integrity.

[0166] Experimental steps:

[0167] Cyclic performance testing: The coin cells assembled and activated in Test Example 3 were selected and placed in a constant temperature test chamber (25℃). The charge / discharge voltage range was set to 0.01V to 1.5V, and the charge / discharge regime was set to 1C constant current constant voltage charging (cutoff current 0.05C) and 1C constant current discharging. 500 charge / discharge cycles were performed continuously, and the discharge specific capacity of each cycle was recorded in real time. The capacity retention rate of the 500th cycle relative to the 1st cycle was calculated.

[0168] Electrode Expansion Rate Test: To accurately measure the change in electrode thickness, a set of parallel sample cells was prepared. Before battery assembly, the average thickness of the fresh electrodes (excluding the current collector thickness) was measured and recorded at multiple points using a micrometer. After cycling the batteries for 500 cycles according to the above procedure, the batteries were brought to a fully charged state (i.e., the lithium-intercalated state, where the volume expansion is maximum). The batteries were disassembled in an argon-filled glove box, the electrodes were removed, and the surface residual electrolyte was cleaned with dimethyl carbonate. After natural drying, the electrode thickness was measured again. The electrode volume expansion rate was calculated based on the thickness difference before and after cycling.

[0169] The experimental data are shown in Table 4:

[0170] Table 4. Cycle life and electrode expansion rate test data for each sample

[0171] Sample number Discharge specific capacity in week 1 (mAh / g) 500-week capacity retention rate (%) Fully charged electrode expansion rate (%) Example 1 358.4 89.4 18.5 Example 2 355.7 88.1 19.2 Example 3 352.1 91.2 14.8 Example 5 360.2 85.6 23.4 Example 6 356.9 87.9 20.1 Comparative Example 1 361.5 52.3 68.7 Comparative Example 2 342.8 63.5 42.6 Comparative Example 3 349.4 41.5 55.2

[0172] Results Analysis and Conclusions:

[0173] After 500 cycles of high-intensity cycling, Examples 1 to 3 all maintained a capacity retention rate of over 88%, and the electrode expansion rate was controlled within 20%. Among them, Example 3, due to the introduction of PMMA microspheres to create pores, had the most ample internal space, resulting in the lowest electrode expansion rate (14.8%) and the highest capacity retention rate (91.2%). This directly demonstrates that the micron-sized cavities pre-placed inside the particles using the emulsion template method can effectively accommodate the huge volume deformation of nano-silicon during lithium intercalation. This "internal digestion" expansion mechanism avoids drastic changes in the overall particle outline, thereby ensuring the stability of electrical contact between active material particles and between particles and the current collector.

[0174] In contrast, Comparative Example 1 (homogeneous solid structure) exhibited a catastrophic degradation. Although its initial capacity was high, the retention rate after 500 cycles was only 52.3%, and the electrode expansion rate was as high as 68.7%. This is because the solid structure lacks buffer space, and the expansion stress of the silicon material acts directly on the particle shell and the entire electrode, causing the particles to crack and pulverize. This leads to repeated cracking and regeneration of the solid electrolyte interphase (SEI) film, continuously consuming electrolyte and active lithium, ultimately resulting in battery failure.

[0175] Comparative Example 3 (without carbon coating) showed the lowest cycle retention rate (41.5%). This indicates that without the protection of a conductive carbon layer, silicon particles are highly susceptible to detachment from the conductive network (electrical contact failure) during expansion and contraction. The embodiments of this invention employ an in-situ carbonization process, which forms a continuous conductive carbon coating layer while constructing a porous framework. This not only improves conductivity but also acts as a physical barrier, limiting excessive displacement of silicon particles and providing mechanical confinement.

[0176] The expansion rate (23.4%) of Example 5 (low-temperature process) was slightly higher than that of Example 1, while the retention rate was slightly lower (85.6%). Combined with the data from Test Example 1, this is because the internal porosity formed at low temperatures is relatively low, the buffer space is limited, and some of the silicon expansion is transferred outwards. However, its performance is still far superior to the comparative example.

[0177] Test Example 5: Sensitivity and batch stability analysis of process parameters.

[0178] This test case aims to examine the impact of parameter variations within the gradient temperature process window described in the claims on product quality consistency. By comparing the fluctuations in production yield, morphological integrity, and key performance indicators under optimal process parameters (Example 1), lower limit boundary (Example 5), upper limit boundary (Example 6), and non-gradient isothermal conditions (Comparative Example 2), the robustness of the process method and the necessity of gradient temperature control are verified.

[0179] Experimental steps:

[0180] Continuous batch preparation: Five consecutive batches of pilot-scale preparation experiments were conducted under the process conditions of Examples 1, 5, 6, and Comparative Example 2. The solid feed amount per batch was set at 5.0 kg, and the solid content and feed rate of the slurry were kept constant.

[0181] Yield calculation: After each batch of spray drying is completed, the weight of the powder collected below the cyclone separator is calculated, and the single-pass powder yield is calculated as (collected weight / theoretical total solid weight × 100%). The adhesion to the inner wall of the drying tower is recorded as a qualitative auxiliary evaluation.

[0182] Spherical integrity statistics: Random samples were taken from each batch of products, dispersed, and observed under an optical microscope. The number of particles that maintained a complete spherical shape among 500 particles in the field of view was counted, and the spherical integrity was calculated as (number of complete particles / total number of particles × 100%). Damaged, severely dented, or fragmented particles were all counted as incomplete particles.

[0183] Performance consistency assessment: Perform an initial coulombic efficiency (ICE) test on each batch of finished product (test method is the same as in Test Example 3), calculate the average value and standard deviation of the 5 batches to assess the batch stability of electrochemical performance.

[0184] The experimental data are shown in Table 5:

[0185] Table 5. Statistical data on process parameter sensitivity and batch stability

[0186] Sample number Temperature zones in the drying tower (upper / middle / lower, °C) Powder single-pass yield (%) Adhesion to the tower wall Sphere integrity (%) First coulomb efficiency (%, mean ± standard deviation) Example 1 240 / 160 / 100 94.2 No obvious adhesion to the wall 98.6 91.5±0.12 Example 5 200 / 120 / 80 88.7 Slight adhesion to the wall 96.4 90.8±0.25 Example 6 260 / 180 / 120 92.3 Non-adhesive wall 95.1 91.1±0.18 Comparative Example 2 200 / 200 / 200 65.4 Severe adhesion to the wall 72.8 86.4±1.45

[0187] Results Analysis and Conclusions:

[0188] Example 1, under preferred gradient temperature conditions, achieved the highest single-pass yield (94.2%) and sphericity (98.6%), with minimal fluctuations in the initial coulombic efficiency across the five batches (standard deviation of only 0.12%). This indicates that under these process conditions, the solvent evaporation rate on the droplet surface and the internal solvent diffusion rate are balanced, rapidly forming a strong outer shell to prevent adhesion while avoiding rupture due to excessive internal pressure.

[0189] Example 5 represents the low-temperature process boundary. The data mainly show a slight decrease in yield (88.7%), accompanied by slight wall adhesion. This is because the enthalpy in the low-temperature zone (200°C in the upper column) is insufficient to instantly and completely solidify the droplet surface, causing some semi-dry droplets to adhere upon contact with the column wall. Nevertheless, the sphericity remains at a high level (96.4%), and the electrochemical performance (ICE 90.8%) remains stable and acceptable, demonstrating that the lower temperature limit defined in the claims is industrially feasible.

[0190] Example 6 represents the high-temperature process boundary. Its yield was high (92.3%), but the sphericity was lower than in Example 1 (95.1%). Microscopic observation revealed a small number of donut-shaped collapses or microcracks in the particles. This was due to the instantaneous explosive vaporization of the solvent caused by the excessively high temperature in the upper column (260°C), resulting in internal pressure impacting the incompletely hardened shell. However, these microscopic defects did not affect the uniformity of macroscopic electrochemical performance (standard deviation 0.18%), indicating that the upper temperature limit was still within the safe operating range.

[0191] Comparative Example 2, which employed isothermal control (200℃ throughout), showed significant deterioration in all its performance indicators. The yield was only 65.4%, accompanied by severe wall adhesion, indicating that isothermal control cannot simultaneously meet the conflicting requirements of rapid surface film formation and slow internal drying. The low sphericity (72.8%) suggests that a large number of particles broke or distorted during the drying process. This structural damage is directly reflected in the electrochemical performance; the initial coulombic efficiency was not only low (86.4%) but also exhibited significant batch-to-batch fluctuations (standard deviation 1.45%), demonstrating that the isothermal process cannot guarantee product consistency.

Claims

1. A spherical artificial graphite composite particle, characterized in that, The composite particles have a spherical structure with a dense outer shell and interconnected pores inside, and are made from raw materials comprising the following parts by weight: Artificial graphite: 88-95 parts; Silicon-based active material: 3-10 parts; Conductive agent: 1-5 parts; A liquid-phase binder system comprising a solvent, a dispersant, and a carbon source precursor, wherein the amount of carbon source precursor added results in the content of an amorphous carbon coating in the final composite particles being 1-5 wt%. The composite particles have micron-sized pores with a pore size distribution in the range of 0.5-3μm, and the pore volume of the micron-sized pores accounts for more than 50% of the total pore volume.

2. The spherical artificial graphite composite particle according to claim 1, characterized in that, The artificial graphite is primary particles with a median particle size D50 between 8 micrometers and 12 micrometers; the silicon-based active material is selected from nano-silicon powder or silicon monoxide, with a median particle size D50 between 80 nanometers and 3 micrometers; the conductive agent is selected from multi-walled carbon nanotubes, vapor-grown carbon fibers, and conductive carbon black.

3. The spherical artificial graphite composite particle according to claim 1, characterized in that, The carbon source precursor is selected from phenolic resin, polyacrylonitrile, sucrose, asphalt or epoxy resin; the solvent is selected from water, anhydrous ethanol, methanol, acetone, dimethylformamide or N-methylpyrrolidone; the dispersant is selected from polyvinylpyrrolidone or sodium alginate.

4. The spherical artificial graphite composite particle according to claim 1, characterized in that, The tap density of the composite particles is 1.20 g / cm³. 3 Up to 1.32 g / cm 3 Its specific surface area is 2.0 m². 2 / g to 4.0m 2 / g, with a total specific pore volume ranging from 0.20 mL / g to 0.35 mL / g.

5. A spray drying method for preparing spherical artificial graphite composite particles according to any one of claims 1-4, characterized in that, Includes the following steps: The carbon source precursor is dissolved in the aqueous solution or the oil solution; Artificial graphite, silicon-based active materials and conductive agents are dispersed in the aqueous phase solution or the oil phase solution to form a solid-liquid suspension. Then, another phase solution is added under shear conditions to emulsify and form an oil-in-water or water-in-oil emulsion slurry. The emulsion slurry is fed into a pressure spray drying tower with three independent temperature zones for granulation to obtain spherical precursors. The three independent temperature zones, from top to bottom, are a high-temperature rapid forming zone, a middle phase separation and pore formation zone, and a lower solidification and shaping zone. The spherical precursor is placed in an inert atmosphere furnace for high-temperature carbonization to obtain the spherical artificial graphite composite particles.

6. The spray drying preparation method of spherical artificial graphite composite particles according to claim 5, characterized in that, The inlet air temperature of the high-temperature rapid prototyping zone is set to 200°C to 260°C, the temperature of the middle layer phase separation and pore formation zone is set to 120°C to 180°C, and the outlet air temperature of the lower layer curing and shaping zone is set to 80°C to 120°C.

7. The spray drying preparation method for spherical artificial graphite composite particles according to claim 5, characterized in that, The shearing conditions are defined as follows: shearing speed of 4000 rpm to 6000 rpm, and shearing time of 30 minutes to 60 minutes.

8. The spray drying preparation method of spherical artificial graphite composite particles according to claim 5, characterized in that, The high-temperature carbonization process includes two stages: The first stage involves raising the temperature to 300℃ to 450℃ and holding it at that temperature for 2 to 4 hours. The second stage involves raising the temperature to 800℃ to 1200℃ and holding it at that temperature for 4 to 8 hours.

9. The spray drying preparation method of spherical artificial graphite composite particles according to claim 5, characterized in that, The aqueous phase solution is an aqueous solution of polyvinylpyrrolidone or an aqueous solution of sodium alginate, and the oil phase solution is an ethanol solution of phenolic resin or a mixed solution of dimethylformamide and acetone of polyacrylonitrile.

10. The application of a spherical artificial graphite composite particle according to any one of claims 1-4 in the preparation of a negative electrode sheet for a lithium-ion battery or a lithium-ion battery.

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