Silicon-carbon negative electrode composite material, preparation method and application thereof

Abstract

This invention relates to a silicon-carbon anode composite material, its preparation method, and its applications. The silicon-carbon anode composite material comprises: a silicon-carbon composite material, a lithium salt layer coated on the surface of the silicon-carbon composite material, and a carbon coating layer covering the lithium salt layer; the silicon-carbon composite material has a Dv... 50 Its thickness is 5–12 μm, and its specific surface area is 30.0–100.0 m². 2 / g; the specific surface area of ​​the silicon-carbon composite material coated with a lithium salt layer is 20.0–80.0 m². 2 / g; Silicon-carbon anode composite material Dv 50 Its diameter is 6–13 μm, and its specific surface area is 0.3–5.0 m². 2 / g; In the silicon-carbon composite material coated with a lithium salt layer, the mass of silicon accounts for 20% to 60% of the total mass of the silicon-carbon composite material coated with a lithium salt layer; In the lithium salt layer, the general chemical formula of the lithium salt is Li. x M a A b PO4X c M represents a metallic element, A represents a non-metallic element, and X represents a halogen element; 2.5 ≤ x ≤ 3.5, 0 < a ≤ 0.3, 0 < b ≤ 0.3, and 0 < c ≤ 0.3. The silicon-carbon anode composite material of this invention exhibits high first-cycle coulombic efficiency, excellent cycle stability, and good interfacial stability.

Description

Technical Field

[0001] This invention relates to the field of battery anode material technology, and in particular to a silicon-carbon anode composite material, its preparation method, and its application. Background Technology

[0002] With the rapid development of new energy vehicles and energy storage systems, the demand for high-energy-density and high-rate-performance anode materials for lithium-ion batteries is increasing. Silicon, due to its high theoretical specific capacity (approximately 4200 mAh / g), is considered an important candidate material to replace traditional graphite anodes. However, silicon exhibits a volume expansion of up to approximately 300% during charge and discharge, which easily leads to particle pulverization, conductive network breakage, and repeated rupture and regeneration of the solid electrolyte interphase (SEI) film, resulting in low initial coulombic efficiency, poor cycle life, and rate performance degradation. Therefore, constructing a stable silicon-carbon composite structure and effectively controlling its interface has become a key direction for current research and industrial applications.

[0003] In existing technologies, a common approach is to coat the surface of silicon-carbon materials with a lithium salt-based inorganic phase to improve interfacial stability and ion transport performance. For example, the technical solution with publication number CN118039910A proposes coating a silicon-carbon core-shell structure material with a lithium aluminate layer to improve the material's ionic conductivity and rate performance; the technical solution with publication number CN116190622A constructs a composite lithium phosphate-fluorine doped cavity structure carbon double-coated silicon nanocomposite material to enhance interfacial stability and mitigate volume expansion. While these technologies improve the electrochemical performance of the materials to some extent, they still have shortcomings.

[0004] On the one hand, the interfacial bonding between some lithium salt coating systems (such as lithium aluminate) and the silicon-carbon matrix is ​​limited, making them prone to interfacial delamination or structural damage under long-term cyclic stress, affecting cycle stability. On the other hand, some technical solutions employ multi-step synthesis or complex structural designs, resulting in cumbersome processes, difficult production control, and hindering large-scale continuous production. Furthermore, achieving heteroatom-doped carbon structures (such as N, P, S, F, etc.) typically requires processing at high temperatures, leading to high energy consumption, increased costs, and limited yield.

[0005] Meanwhile, while chemical vapor deposition (CVD) can achieve relatively uniform silicon deposition in silicon-carbon composite structures, without effective interface control and structural confinement measures, issues such as insufficient high-rate performance, low first-cycle coulombic efficiency, and lithium salt or functional phase migration, agglomeration, or even detachment during cycling may still exist. Especially when lithium salt particles are large or unevenly dispersed, their stability during electrochemical reactions is difficult to guarantee, thus affecting the overall material performance. Summary of the Invention

[0006] The purpose of this invention is to address the shortcomings of existing technologies by providing a silicon-carbon anode composite material, its preparation method, and its applications. By coating the surface of the silicon-carbon composite material with nanoscale modified lithium salts, a pre-lithiated lithium source can be provided, inducing the formation of a stable SEI film and simultaneously improving ionic conductivity. Two vapor-phase carbon deposition processes are used to immobilize lithium salt particles, suppress silicon volume expansion, prevent excessive reaction between lithium salt and silicon, and improve conductivity. The silicon-carbon anode composite material of this invention exhibits high first-cycle coulombic efficiency, excellent cycle stability, and good interfacial stability.

[0007] To achieve the above objectives, in a first aspect, the present invention provides a silicon-carbon anode composite material, comprising: a silicon-carbon composite material, a lithium salt layer coated on the surface of the silicon-carbon composite material, and a carbon coating layer coated outside the lithium salt layer; The Dv of the silicon-carbon composite material 50 Its thickness is 5–12 μm, and its specific surface area is 30.0–100.0 m². 2 / g; The specific surface area of ​​the silicon-carbon composite material coated with the lithium salt layer is 20.0–80.0 m². 2 / g; Silicon-carbon anode composite material Dv 50 Its diameter is 6–13 μm, and its specific surface area is 0.3–5.0 m². 2 / g; In the silicon-carbon composite material coated with the lithium salt layer, the mass of silicon accounts for 20% to 60% of the total mass of the silicon-carbon composite material coated with the lithium salt layer; In the lithium salt layer, the general chemical formula of the lithium salt is Li. x M a A b PO4X c M is a metallic element, A is a nonmetallic element, X is a halogen element, 2.5≤x≤3.5, 0<a≤0.3, 0≤b≤0.3, 0≤c≤0.3, and b and c are not both 0.

[0008] Preferably, the metallic element M includes one or more of Mg, Al, and Ti, and the non-metallic element A includes one or more of N and S.

[0009] Preferably, 0.05≤a≤0.15, 0.05≤b≤0.15, and 0.05≤c≤0.15.

[0010] Secondly, embodiments of the present invention provide a method for preparing the silicon-carbon anode composite material described in the first aspect above, comprising: According to the target molecular formula Li x M a A b PO4X cAccording to the stoichiometric ratio, a lithium source, a metal element M doping source, a non-metal element A doping source, and a halogen source are mixed and dispersed to obtain a mixed precursor material. The mixed precursor material is then dried and granulated, followed by segmented heat treatment to obtain the lithium salt material Li. x M a A b PO4X c ; The lithium salt material is dispersed in a liquid medium and then subjected to sand milling to obtain a lithium salt slurry with a particle size D50 < 300 nm. In an inert atmosphere, a silicon-carbon composite material is formed by deposition reaction on porous carbon material using a vapor-phase silicon source. The lithium salt slurry is loaded onto the silicon-carbon composite material; A first gaseous carbon source is introduced for thermal decomposition deposition to perform a gaseous carbon deposition process, which is used to fix the lithium salt particles at the interface and construct a conductive connection structure. The material obtained from the first gas phase carbon deposition process is placed in a heat treatment device, and a second gas phase carbon source is introduced under a protective atmosphere to perform a second gas phase carbon deposition process. This process is used to construct a continuous carbon phase on the outermost surface and to confine and fix the lithium salt particles, thereby inhibiting the migration and shedding of the lithium salt particles during the subsequent electrochemical reaction process, thus obtaining the silicon-carbon anode composite material.

[0011] Preferably, the lithium source comprises one or more of lithium carbonate, lithium hydroxide, lithium fluoride, or lithium chloride; preferably, the lithium source is in excess by 5 wt.%-15 wt.%. The metal element M doping source includes one or more of the following: magnesium oxide, magnesium chloride, aluminum oxide, aluminum chloride, titanium oxide, or titanium chloride; The non-metallic element A doping source includes one or more of the following: ammonium dihydrogen phosphate, urea, melamine, thiourea, or lithium sulfide; The halogen source includes one or more of lithium fluoride, ammonium chloride, ammonium fluoride, or aluminum chloride; The liquid medium includes deionized water or an organic solvent; the organic solvent includes alcohol-based organic solvents.

[0012] Preferably, the segmented heat treatment includes: a low-temperature decomposition stage and a high-temperature doping crystallization stage; The low-temperature decomposition stage specifically includes: heating to 400-550 ℃ at a heating rate of 5-15 ℃ / min under an inert atmosphere, and holding at that temperature for 2-5 h; The high-temperature doping crystallization stage specifically includes: continuing to heat to 600-850 ℃ and holding at that temperature for 6-12 h to form the lithium salt material Li. x M a Ab PO4X c .

[0013] Preferably, the deposition reaction on porous carbon material using a vapor-phase silicon source under an inert atmosphere to form a silicon-carbon composite material specifically includes: transferring porous carbon to a fluidized bed, heating it to 400-800 °C in an inert environment, introducing a vapor-phase silicon source, and performing vapor-phase deposition on the porous carbon; wherein the vapor-phase silicon source includes silane or tetramethylsilane. The specific steps of loading the lithium salt slurry onto the silicon-carbon composite material include: pumping the lithium salt slurry into the fluidized bed under a fluidized state maintained by an inert atmosphere, and uniformly loading lithium salt particles onto the surface of the silicon-carbon composite material through atomization and evaporation of the liquid slurry to form the lithium salt layer. The process of introducing a first gaseous carbon source for thermal decomposition deposition specifically includes: introducing a first gaseous carbon source into the fluidized bed, and performing a gaseous carbon deposition process on the lithium salt layer through the thermal decomposition of the first gaseous carbon source; the first gaseous carbon source includes one or more of methane, acetylene, and ethylene. The secondary gas-phase carbon deposition process by introducing a second gas-phase carbon source under a protective atmosphere specifically includes: heating to 500-600°C under a protective atmosphere, introducing a mixed gas formed by a carrier gas and a second gas-phase carbon source at a volume flow rate ratio of [4:1]-[1:1], maintaining the temperature for 0.5-3 h, and further depositing carbon on the material surface through the thermal decomposition of the second gas-phase carbon source to form a uniform carbon coating layer; wherein the carrier gas is nitrogen or argon, and the second gas-phase carbon source includes one or more of methane, acetylene, ethylene, and propylene.

[0014] Preferably, after the secondary vapor-phase carbon deposition treatment, the method further includes: The material is cooled in a protective atmosphere, then broken down, sieved, and demagnetized to obtain the silicon-carbon anode composite material.

[0015] Thirdly, embodiments of the present invention provide a negative electrode, comprising the silicon-carbon negative electrode composite material described in the first aspect above.

[0016] Fourthly, embodiments of the present invention provide a lithium battery, including the negative electrode described in the third aspect above.

[0017] The silicon-carbon anode composite material provided in this invention avoids direct contact between silicon-carbon and electrolyte by coating the surface of the silicon-carbon composite material with nanoscale modified lithium salt, effectively reducing side reactions, optimizing ion transport, improving physical contact and chemical compatibility with the positive / negative electrode active materials, reducing interfacial impedance, and fixing lithium salt particles through two vapor-phase carbon deposition processes, suppressing silicon volume expansion, preventing excessive reaction between lithium salt and silicon, and improving conductivity. Doping the material with halogen atoms, non-metals, and metals effectively enhances the material's conductivity, structural stability, and interfacial compatibility. The resulting silicon-carbon anode composite material forms a uniform and stable SEI film on its surface, exhibiting good ion-electron dual conductivity and effectively mitigating silicon volume expansion. It demonstrates high reversible capacity in lithium-ion batteries, excellent long-cycle stability, and superior rate performance. The silicon-carbon anode composite material of this invention achieves an initial coulombic efficiency greater than 86% at 0.8V, and retains up to 80% capacity after 1000 cycles. Attached Figure Description

[0018] Figure 1 A flowchart illustrating the preparation method of the silicon-carbon anode composite material provided in this embodiment of the invention; Figure 2 The energy dispersive spectroscopy (EDS) image of the silicon-carbon composite material coated with a lithium salt layer provided in Embodiment 1 of the present invention; Figure 3 A scanning electron microscope (SEM) image of the silicon-carbon composite material provided in Embodiment 1 of the present invention; Figure 4 This is a SEM image of the silicon-carbon composite material coated with a lithium salt layer provided in Embodiment 1 of the present invention; Figure 5 This is a SEM image of the silicon-carbon anode composite material with spray-coated modified lithium salt provided in Comparative Example 4 of the present invention. Detailed Implementation

[0019] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0020] This invention provides a silicon-carbon anode composite material, its preparation method, and its application.

[0021] The silicon-carbon anode composite material of the present invention comprises: a silicon-carbon composite material, a lithium salt layer coated on the surface of the silicon-carbon composite material, and a carbon coating layer coated outside the lithium salt layer.

[0022] Among them, Dv, a silicon-carbon composite material used as the core. 50 Its thickness is 5–12 μm, and its specific surface area is 30.0–100.0 m². 2 / g; the specific surface area of ​​the silicon-carbon composite material coated with a lithium salt layer is 20.0–80.0 m². 2 / g; the final silicon-carbon anode composite material with carbon coating layer Dv 50 Its diameter is 6–13 μm, and its specific surface area is 0.3–5.0 m². 2 / g.

[0023] In the silicon-carbon composite material coated with a lithium salt layer, the mass of silicon accounts for 20% to 60% of the total mass of the silicon-carbon composite material coated with the lithium salt layer.

[0024] In the lithium salt layer, the general chemical formula of the lithium salt is Li. x M a A b PO4X c M is a metallic element, preferably including one or more of Mg, Al, and Ti; A is a non-metallic element, preferably including one or more of N and S; X is a halogen element, including one or more of F, Cl, Br, and I, preferably including F or Cl; the ranges of a, b, and c are 2.5≤x≤3.5, 0<a≤0.3, 0≤b≤0.3, 0≤c≤0.3, and b and c are not simultaneously 0, more preferably 0.05≤a≤0.15, 0.05≤b≤0.15, 0.05≤c≤0.15.

[0025] The silicon-carbon anode composite material of the present invention is obtained by the following preparation method. Figure 1 The preparation method of the silicon-carbon anode composite material provided in the embodiments of the present invention is described below in conjunction with... Figure 1 The preparation method of the present invention will be described.

[0026] The method for preparing silicon-carbon anode composite materials proposed in this invention mainly involves optimizing the silicon-carbon composite material by constructing a composite interface of a modified lithium salt layer and a dual vapor-phase carbon deposition structure on its surface. The main preparation steps include: Step 110, according to the target molecular formula Li x M a A b PO4X c By using a stoichiometric ratio, lithium source, metal element M doping source, non-metal element A doping source, and halogen source are mixed and dispersed to obtain a mixed precursor material. This mixed precursor material is then dried and granulated, followed by segmented heat treatment to obtain the lithium salt material Li. x M a A b PO4X c .

[0027] The lithium source includes one or more of lithium carbonate, lithium hydroxide, lithium fluoride, or lithium chloride; preferably, the lithium source is in excess at 5 wt.%-15 wt.%. The metal element M doping source includes one or more of the following: magnesium oxide, magnesium chloride, aluminum oxide, aluminum chloride, titanium oxide, or titanium chloride; The sources of non-metallic element A doping include one or more of the following: ammonium dihydrogen phosphate, urea, melamine, thiourea, or lithium sulfide; Halogen sources include one or more of lithium fluoride, ammonium chloride, ammonium fluoride, or aluminum chloride; Liquid media include: deionized water or organic solvents; organic solvents include alcoholic organic solvents, such as anhydrous ethanol.

[0028] Mixing and dispersion can be achieved by ball milling or mechanical stirring. Various sources are dissolved in a mixed solvent of deionized water and anhydrous ethanol, and then ball milled or mechanically stirred to mix. The mixing time is preferably greater than 1 hour.

[0029] For drying and granulation, a spray dryer or a disc dryer is preferred, and the powder is dried at 80-150℃ for 2-4 hours to obtain a dry powder.

[0030] The segmented heat treatment includes a low-temperature decomposition stage and a high-temperature doping and crystallization stage. Specifically, the low-temperature decomposition stage may include: heating to 400-550℃, preferably 430-550℃, at a heating rate of 5-15℃ / min under an inert atmosphere, and holding at this temperature for 2-5 hours. The high-temperature doping and crystallization stage may include: further heating to 600-850℃ and holding at this temperature for 6-12 hours to form the lithium salt material Li. x M a A b PO4X c .

[0031] During the low-temperature decomposition stage, by controlling the heating rate and holding time, the volatile components and organic residues in the precursor are gradually decomposed and released, while promoting the initial solid-phase reaction of each element to form a uniform amorphous or semi-crystalline intermediate phase, providing a uniform reaction basis for the subsequent crystal structure construction.

[0032] During the high-temperature doping crystallization stage, further heating promotes element diffusion and lattice rearrangement, allowing metallic element M, non-metallic element A, and halogen element X to enter the Li3PO4 crystal structure to form a stable solid solution, thereby improving the crystal order and structural stability.

[0033] The lithium salt material Li formed in this step x M a A b PO4X cBy partially replacing lithium sites or transition metal sites with metal elements M that have high charge and moderate ionic radius, a stable crystal framework is constructed and lattice strain during lithium-ion diffusion is reduced. By partially replacing oxygen sites with non-metal elements A and / or halogen elements X that have higher electronegativity, the stability of PO4 polyhedra is enhanced through inductive effects and the covalentity of metal-oxygen bonds is adjusted, thereby increasing the operating voltage.

[0034] Step 120: Disperse the lithium salt material in a liquid medium and perform sand milling to obtain a lithium salt slurry with a particle size D50 < 300 nm.

[0035] The liquid medium can be deionized water or an organic solvent. Organic solvents are commonly used solvents that can disperse lithium salt materials and can be volatilized or removed under subsequent process conditions, such as alcohol solvents, ketone solvents, ether solvents, or ester solvents.

[0036] Alcohol solvents may include one or more of methanol, ethanol, isopropanol, and n-butanol; ketone solvents may include acetone and methyl ethyl ketone; ether solvents may include diethyl ether and tetrahydrofuran; and ester solvents may include ethyl acetate and dimethyl carbonate.

[0037] In this invention, the lithium salt particles are milled to achieve a particle size (D50) of less than 300 nm. This process aims to obtain a higher specific surface area and better dispersibility, while also making it easier for the lithium salt slurry to form a continuous interface layer when subsequently loaded onto the silicon-carbon composite material. If the particle size is too large, it will be difficult to uniformly cover the surface of the silicon-carbon composite material, making it easier to form dot-like adhesions, resulting in exposed areas at the interface instead of forming a continuous and complete interface coverage, thus leading to uneven SEI.

[0038] Step 130: Under an inert atmosphere, a silicon-carbon composite material is formed by a deposition reaction on a porous carbon material using a vapor-phase silicon source.

[0039] Specifically, porous carbon is transferred to a fluidized bed, heated to 400-800 ℃ in an inert environment, and a gaseous silicon source is introduced to perform vapor deposition on the porous carbon. The deposition time is preferably 5-20 hours. The gaseous silicon source may include silane or tetramethylsilane, etc.

[0040] Steps 110-120 and step 130 above can be performed in any order. That is, the silicon-carbon composite material can be prepared first, followed by the lithium salt slurry, or the lithium salt slurry can be prepared first, followed by the silicon-carbon composite material, as described above. Alternatively, the silicon-carbon composite material and the lithium salt slurry can be prepared separately and simultaneously. The order of execution of the above steps does not constitute a limitation on the technical solution and scope of protection of this invention.

[0041] Step 140: Load the lithium salt slurry onto the silicon-carbon composite material.

[0042] Specifically, under a fluidized state maintained by an inert atmosphere, lithium salt slurry is pumped into a fluidized bed. Through atomization and evaporation of the liquid slurry, lithium salt particles are uniformly loaded onto the surface of the silicon-carbon composite material, forming a lithium salt layer. Preferably, the pumping flow rate is 10-100 mL / min, while nitrogen or argon gas is introduced at a flow rate of 30-100 L / min.

[0043] Step 150: A first gaseous carbon source is introduced for thermal decomposition deposition to perform a gaseous carbon deposition process, which is used to fix the lithium salt particles at the interface and construct a conductive connection structure.

[0044] Specifically, this step is performed in a deposition apparatus. The primary gas-phase carbon deposition process includes: introducing a first gas-phase carbon source into a fluidized bed, and performing a primary gas-phase carbon deposition process on the lithium salt layer through the thermal decomposition of the first gas-phase carbon source; the first gas-phase carbon source includes one or more of methane, acetylene, and ethylene. Preferably, the temperature of the primary gas-phase carbon deposition process is not lower than 500 °C, and the time is not less than 1 hour.

[0045] Step 160: The material obtained from the first gas phase carbon deposition treatment is placed in a heat treatment device, and a second gas phase carbon source is introduced under a protective atmosphere to perform a second gas phase carbon deposition treatment, so as to build a continuous carbon phase on the outermost surface and confine and fix the lithium salt particles, thereby inhibiting the migration and shedding of lithium salt particles in the subsequent electrochemical reaction process, and obtaining silicon-carbon anode composite material.

[0046] The secondary gas phase carbon deposition process specifically includes: heating to 500-600℃, preferably 520-560℃, under a protective atmosphere; introducing a mixed gas formed by carrier gas and second gas phase carbon source at a volume flow rate ratio of [4:1]-[1:1]; maintaining the temperature for 0.5-3 h; and further depositing carbon on the material surface through the thermal decomposition of the second gas phase carbon source to form a uniform carbon coating layer; the carrier gas can be nitrogen or argon, and the second gas phase carbon source includes one or more of methane, acetylene, ethylene, and propylene.

[0047] After secondary vapor-phase carbon deposition, the material is cooled in a protective atmosphere and then dispersed, sieved, and demagnetized to obtain silicon-carbon anode composite material.

[0048] This invention achieves synergistic control over the interface structure and stability of silicon anodes by constructing a multi-level composite structure of modified lithium salt layer-two-stage vapor-phase carbon deposition on the surface of silicon-carbon composite materials. First, nanoscale doped lithium salt Li... x M a A b PO4X cLithium salts are loaded onto the surface of silicon-carbon composite materials. Through the synergistic doping of metallic element M, non-metallic element A, and halogen element X, the crystal structure and local electronic structure of lithium salts are modulated, improving their ion conductivity and structural stability. During charge and discharge, lithium salts can participate in interfacial reactions and promote the formation of a stable and uniform interfacial film structure, thereby reducing the direct contact between silicon materials and the electrolyte and minimizing interfacial side reactions.

[0049] After lithium salt loading is completed, a first vapor-phase carbon deposition process is performed to construct the first conductive carbon phase structure. This improves the continuity of electron transport in the composite system and provides preliminary interface fixation for the lithium salt particles, forming a structural transition and buffer in the interface region, thereby reducing the impact of silicon volume changes during lithium insertion / extraction on the local interface.

[0050] A second vapor-phase carbon deposition process is then performed to further construct a continuous carbon phase structure on the overall outer surface of the composite particles, thereby spatially confining and fixing the nanoscale lithium salt particles, inhibiting their migration, aggregation, or detachment during heat treatment and electrochemical cycling, and enhancing the structural integrity of the composite particles during volume changes.

[0051] Through the synergistic effect of interfacial carbon phase construction by primary vapor-phase carbon deposition and overall carbon phase reinforcement by secondary vapor-phase carbon deposition, a stable multi-scale composite interfacial structure is formed, thereby improving the interfacial stability and recyclability of the material.

[0052] The silicon-carbon anode composite material proposed in this invention can be used as a lithium battery anode and applied in various lithium battery systems, including power batteries, energy storage batteries and consumer electronics batteries.

[0053] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0054] Example 1 S1. Lithium carbonate, alumina, ammonium dihydrogen phosphate, and lithium fluoride were mixed in a molar ratio of 30:1:20:2 and transferred to a ball mill. Anhydrous ethanol was added as a dispersant (liquid-to-solid volume ratio of 1.2:1), and ball milling was performed. The ball milling speed was 300 r / min, the milling time was 4 h, and the forward and reverse rotation intervals were 30 min to ensure that the raw materials were uniformly mixed at the molecular level. The ball-milled slurry was transferred to a spray dryer and dried at 120 ℃ for 3 h to obtain a dried powder. The dried powder was transferred to a kiln and pyrolyzed at 450 ℃ under nitrogen for 3 h, and then the temperature was further increased to 720 ℃ and held for 8 h to obtain lithium salt Li. 3.1 Al 0.1 N 0.1 PO4F 0.1 .

[0055] S2, the lithium salt in S1 is mixed with deionized water at a ratio of 1:30 and milled for 10 h to obtain a lithium salt slurry with D50 < 150 nm.

[0056] S3: Porous carbon was placed in a fluidized bed, and nitrogen gas was introduced into the furnace at a flow rate of 50 L / min for more than 30 min to purge the air. The temperature was raised to 480 °C, and a mixture of nitrogen and silane was introduced at a volumetric flow rate of 80 L / min: 20 L / min. The mixture was held at this temperature for 4 h to deposit silicon on the porous carbon. After the holding period, the material was purged by continuing to hold at this temperature for 0.5 h under nitrogen gas at a flow rate of 50 L / min.

[0057] S4: Take 3 kg of lithium salt slurry prepared in S2 and pump it into the fluidized bed, controlling the flow rate at 50 mL / min, while simultaneously introducing nitrogen gas at a flow rate of 80 L / min. Figure 2 The image shows the energy dispersive spectroscopy (EDS) image of the silicon-carbon composite material coated with a lithium salt layer obtained after step S4 of Example 1 of the present invention.

[0058] S5. The product of S4 is transferred to a deposition furnace, heated to 540°C, and a mixture of nitrogen and acetylene is introduced at a volume flow rate of 40 L / min: 10 L / min. The mixture is kept at this temperature for 1 h to uniformly coat the material surface with the first carbon layer, and then cooled under a protective atmosphere.

[0059] In step S6, the material prepared in step S5 is heated to 560°C in a rotary kiln, and a mixture of nitrogen and acetylene is introduced at a volumetric flow rate of 40 L / min: 10 L / min. The mixture is held at this temperature for 2 hours, resulting in a uniform coating of a second carbon layer on the material surface. After cooling under a protective atmosphere, the material is discharged, and after being dispersed, sieved, and demagnetized, a silicon-carbon composite material is obtained.

[0060] Example 2 S1. Lithium carbonate, magnesium oxide, ammonium dihydrogen phosphate, and lithium fluoride were mixed in a molar ratio of 30:1:20:2 and transferred to a ball mill. Anhydrous ethanol was added as a dispersant (liquid-to-solid volume ratio of 1.2:1), and ball milling was performed. The ball milling speed was 300 r / min, the milling time was 4 h, and the forward and reverse rotation intervals were 30 min to ensure that the raw materials were uniformly mixed at the molecular level. The ball-milled slurry was transferred to a spray dryer and dried at 120 ℃ for 3 h to obtain a dried powder. The dried powder was transferred to a kiln and pyrolyzed at 450 ℃ under nitrogen for 3 h, and then the temperature was further increased to 720 ℃ and held for 8 h to obtain lithium salt Li. 3.2 Mg 0.1 N 0.1 PO4F 0.1 .

[0061] Steps S2-S6 are the same as in Example 1.

[0062] Example 3 S1. Lithium carbonate, titanium dioxide, ammonium dihydrogen phosphate, and lithium fluoride were mixed in a molar ratio of 30:1:20:2 and transferred to a ball mill. Anhydrous ethanol was added as a dispersant (liquid-to-solid volume ratio of 1.2:1), and ball milling was performed. The ball milling speed was 300 r / min, the milling time was 4 h, and the forward and reverse rotation intervals were 30 min to ensure that the raw materials were uniformly mixed at the molecular level. The ball-milled slurry was transferred to a spray dryer and dried at 120 ℃ for 3 h to obtain a dried powder. The dried powder was transferred to a kiln and pyrolyzed at 450 ℃ under nitrogen for 3 h, and then the temperature was further increased to 720 ℃ and held for 8 h to obtain lithium salt Li3Ti. 0.1 N 0.1 PO4F 0.1 .

[0063] Steps S2-S6 are the same as in Example 1.

[0064] Example 4 S1. Lithium carbonate, magnesium chloride, ammonium dihydrogen phosphate, and lithium chloride were mixed in a molar ratio of 30:1:20:2 and transferred to a ball mill. Anhydrous ethanol was added as a dispersant (liquid-to-solid volume ratio of 1.2:1), and ball milling was performed. The ball milling speed was 300 r / min, the milling time was 4 h, and the forward and reverse rotation intervals were 30 min to ensure that the raw materials were uniformly mixed at the molecular level. The ball-milled slurry was transferred to a spray dryer and dried at 120 ℃ for 3 h to obtain a dried powder. The dried powder was transferred to a kiln and pyrolyzed at 450 ℃ under nitrogen for 3 h, and then the temperature was further increased to 720 ℃ and held for 8 h to obtain lithium salt Li. 3.2 Mg 0.1 N 0.1 PO4Cl 0.1 .

[0065] Steps S2-S6 are the same as in Example 1.

[0066] Example 5 S1. Lithium carbonate, aluminum chloride, ammonium dihydrogen phosphate, and lithium chloride were mixed in a molar ratio of 30:1:20:2 and transferred to a ball mill. Anhydrous ethanol was added as a dispersant (liquid-to-solid volume ratio of 1.2:1), and ball milling was performed. The ball milling speed was 300 r / min, the milling time was 4 h, and the forward and reverse rotation intervals were 30 min to ensure that the raw materials were uniformly mixed at the molecular level. The ball-milled slurry was transferred to a spray dryer and dried at 120 ℃ for 3 h to obtain a dried powder. The dried powder was transferred to a kiln and pyrolyzed at 450 ℃ under nitrogen for 3 h, and then the temperature was further increased to 720 ℃ and held for 8 h to obtain lithium salt Li. 3.1 Al 0.1 N 0.1 PO4Cl 0.1 .

[0067] Steps S2-S6 are the same as in Example 1.

[0068] Example 6 S1. Lithium carbonate, titanium chloride, ammonium dihydrogen phosphate, and lithium chloride were mixed in a molar ratio of 30:1:20:2 and transferred to a ball mill. Anhydrous ethanol was added as a dispersant (liquid-to-solid volume ratio of 1.2:1), and ball milling was performed. The ball milling speed was 300 r / min, the milling time was 4 h, and the forward and reverse rotation intervals were 30 min to ensure that the raw materials were uniformly mixed at the molecular level. The ball-milled slurry was transferred to a spray dryer and dried at 120 ℃ for 3 h to obtain a dried powder. The dried powder was transferred to a kiln and pyrolyzed at 450 ℃ under nitrogen for 3 h, and then the temperature was further increased to 720 ℃ and held for 8 h to obtain lithium salt Li3Ti. 0.1 N 0.1 PO4Cl 0.1 .

[0069] Steps S2-S6 are the same as in Example 1.

[0070] Example 7 S1. Lithium carbonate, alumina, ammonium dihydrogen phosphate, and lithium fluoride were mixed in a molar ratio of 30:1:20:6 and transferred to a ball mill. Anhydrous ethanol was added as a dispersant (liquid-to-solid volume ratio of 1.2:1), and ball milling was performed. The ball milling speed was 300 r / min, the milling time was 4 h, and the forward and reverse rotation intervals were 30 min to ensure that the raw materials were uniformly mixed at the molecular level. The ball-milled slurry was transferred to a spray dryer and dried at 120 ℃ for 3 h to obtain a dried powder. The dried powder was transferred to a kiln and pyrolyzed at 450 ℃ under nitrogen for 3 h, and then the temperature was further increased to 720 ℃ and held for 8 h to obtain lithium salt Li. 3.3 Al 0.1N 0.1 PO4F 0.3 .

[0071] Steps S2-S6 are the same as in Example 1.

[0072] Example 8 S1. Lithium carbonate, alumina, ammonium dihydrogen phosphate, and lithium fluoride were mixed in a molar ratio of 30:2:20:2 and transferred to a ball mill. Anhydrous ethanol was added as a dispersant (liquid-to-solid volume ratio of 1.2:1), and ball milling was performed. The ball milling speed was 300 r / min, the milling time was 4 h, and the forward and reverse rotation intervals were 30 min to ensure that the raw materials were uniformly mixed at the molecular level. The ball-milled slurry was transferred to a spray dryer and dried at 120 ℃ for 3 h to obtain a dried powder. The dried powder was transferred to a kiln and pyrolyzed at 450 ℃ under nitrogen for 3 h, and then the temperature was further increased to 720 ℃ and held for 8 h to obtain lithium salt Li. 2.8 Al 0.2 N 0.1 PO4F 0.1 .

[0073] Steps S2-S6 are the same as in Example 1.

[0074] Example 9 Steps S1-S3 and S5-S6 are the same as in Example 1.

[0075] S4: Take 1.5 kg of lithium salt slurry prepared in S2 and pump it into the fluidized bed, controlling the flow rate at 50 mL / min, while simultaneously introducing nitrogen gas at a flow rate of 80 L / min.

[0076] Example 10 Steps S1-S3 and S5-S6 are the same as in Example 1.

[0077] S4: Take 6 kg of lithium salt slurry prepared in S2 and pump it into the fluidized bed, controlling the flow rate at 50 mL / min, while simultaneously introducing nitrogen gas at a flow rate of 80 L / min.

[0078] Comparative Example 1 S1. Lithium carbonate and ammonium dihydrogen phosphate were mixed at a molar ratio of 30:20 and transferred to a ball mill. Anhydrous ethanol was added as a dispersant (liquid-to-solid volume ratio of 1.2:1), and ball milling was performed. The ball milling speed was 300 r / min, the milling time was 4 h, and the forward and reverse rotation intervals were 30 min to ensure that the raw materials were uniformly mixed at the molecular level. The ball-milled slurry was transferred to a spray dryer and dried at 120 ℃ for 3 h to obtain a dried powder. The dried powder was transferred to a kiln and pyrolyzed at 450 ℃ under nitrogen for 3 h, and then the temperature was further increased to 720 ℃ and held for 8 h to obtain lithium salt Li. 3.3 N 0.1PO4.

[0079] Steps S2-S6 are the same as in Example 1.

[0080] Comparative Example 2 Steps S1, S2-S6 are the same as in Example 1.

[0081] S2, the lithium salt in S1 is manually ground with deionized water at a ratio of 1:30 for 10 hours to obtain a lithium salt slurry with D50 > 5 micrometers.

[0082] Comparative Example 3 S1. Porous carbon was placed in a fluidized bed, and nitrogen gas was introduced into the furnace at a flow rate of 50 L / min for more than 30 min to purge the air. The temperature was raised to 480 °C, and a mixture of nitrogen and silane was introduced at a volumetric flow rate of 80 L / min: 20 L / min. The mixture was held at this temperature for 4 h to deposit silicon on the porous carbon. After the holding period, the material was purged by continuing to hold at this temperature for 0.5 h under the condition of introducing nitrogen gas at a flow rate of 50 L / min.

[0083] S2: The product of S1 is transferred to a deposition furnace, heated to 540°C, and a mixture of nitrogen and acetylene is introduced at a volume flow rate of 40 L / min: 10 L / min. The mixture is kept at this temperature for 1 h to uniformly coat the material surface with the first carbon layer, and then cooled under a protective atmosphere.

[0084] In step S3, the material prepared in step S2 is heated to 560°C in a rotary kiln, and a mixture of nitrogen and acetylene is introduced at a volumetric flow rate of 40 L / min: 10 L / min. The mixture is held at this temperature for 2 hours, resulting in a uniform coating of a second carbon layer on the material surface. After cooling under a protective atmosphere, the material is discharged, and after being dispersed, sieved, and demagnetized, a silicon-carbon composite material is obtained.

[0085] Comparative Example 4 Example 1 Steps S1-S2 are the same as in Example 1.

[0086] S3: 10 kg of silicon-carbon composite material was dispersed in deionized water, and 0.1 kg of hexadecyltrimethylammonium bromide (CTAB) was added. The mixture was then stirred with the milled lithium salt slurry for 4 hours. Spray drying was performed with continuous stirring of the slurry during spraying. The inlet temperature was 250°C, the outlet temperature was 160°C, and the atomizer frequency was 220 Hz.

[0087] Porous carbon was placed in a fluidized bed, and nitrogen gas was introduced into the furnace at a flow rate of 50 L / min for more than 30 min to purge the air. The temperature was raised to 480 °C, and a mixture of nitrogen and silane was introduced at a volumetric flow rate of 80 L / min: 20 L / min. The mixture was held at this temperature for 4 h to deposit silicon on the porous carbon. After the holding period, the material was purged by continuing to hold at this temperature for 0.5 h under nitrogen gas at a flow rate of 50 L / min.

[0088] S4. The product of S3 is transferred to a deposition furnace, heated to 540°C, and a mixture of nitrogen and acetylene is introduced at a volume flow rate of 40 L / min: 10 L / min. The mixture is kept at this temperature for 1 h to uniformly coat the material surface with the first carbon layer, and then cooled under a protective atmosphere.

[0089] In step S6, the material prepared in step S5 is heated to 560°C in a rotary kiln, and a mixture of nitrogen and acetylene is introduced at a volumetric flow rate of 40 L / min: 10 L / min. The mixture is held at this temperature for 2 hours, resulting in a uniform coating of a second carbon layer on the material surface. After cooling under a protective atmosphere, the material is discharged, and after being dispersed, sieved, and demagnetized, a silicon-carbon composite material is obtained.

[0090] The silicon-carbon composite material after step S3 in Example 1, the silicon-carbon composite material with lithium salt coating obtained after step S4, and the material after step S3 in Comparative Example 4 were characterized by scanning electron microscopy (HITACHI SU8600). The test results are as follows: Figure 3-5 .

[0091] Figure 3 In the material, the overall structure is a regular spherical shape, the particles are relatively evenly distributed, the surface is relatively smooth, and no obvious agglomeration is observed between the particles. Figure 4 In this study, the silicon-carbon composite particles coated with a lithium salt layer maintained a complete spherical structure, exhibiting good overall dispersion. Figure 3 In contrast, a certain degree of surface roughening or slight particle adhesion can be observed on the particle surface, indicating that the lithium salt layer was successfully deposited on the surface of silicon-carbon particles without destroying the original spherical structure. This demonstrates that the fluidized bed in-situ coating method used in this invention has good uniformity and controllability.

[0092] Figure 5 The material obtained by spray coating, although the particles are still spherical overall, shows uneven adhesion or local agglomeration on the surface of some particles, the interparticle interfaces are more complex, and the surface uniformity is relatively poor. This indicates that a simple spray coating method is difficult to achieve a dense and uniform lithium salt layer deposition.

[0093] In summary, the lithium salt coating layer formed by in-situ fluidized bed deposition in this invention can achieve a more uniform and stable surface modification effect while maintaining the complete spherical structure of silicon-carbon particles, providing a structural basis for subsequent improvement of electrochemical performance.

[0094] Test Example 1 The silicon-carbon composite materials prepared in Examples 1-6 and Comparative Examples 1-4 were mixed with Super P conductive agent, sodium carboxymethyl cellulose, and styrene-butadiene rubber at a mass ratio of 8:2:1:1 to prepare an aqueous negative electrode slurry. The solid content of the slurry was controlled at approximately 45 wt.%, and the slurry was homogenized using a homogenizer. The slurry was coated onto copper foil to a thickness of 100 micrometers. After drying at 80°C, rolling, cutting, and vacuum drying at 110°C for 24 hours, a silicon-carbon negative electrode sheet was obtained. Using lithium metal sheets as the counter electrode and reference electrode, and with a CR2032 matching battery case, a Celgard2500 separator, and a 1 mol / L LiPF6 / ethylene carbonate + dimethyl carbonate (volume ratio v / v = 1:1) electrolyte (with 5.0 vol% fluorocarbonate and 1.0 vol% ethylene carbonate added), the negative electrode half-cell was assembled in a glove box. Six batteries were assembled for each embodiment and comparative example, and constant current charge-discharge tests were simultaneously conducted on the LAND test system at different current densities. The test voltage range was 0.005-2V, and the tests were carried out at 25°C. The batteries were first discharged to 0.005V at 0.1C (1C = 1000mAh / g), allowed to stand for 5 minutes, and then charged to 2V at 0.1C. The specific capacity of each discharge and charge was recorded, and the coulombic efficiency of the first cycle was calculated. The results are shown in Table 1.

[0095] Test Example 2 The silicon-carbon composite materials prepared in Examples 1-6 and Comparative Examples 1-4 were used to prepare silicon-carbon negative electrode sheets using the same method as in Test Example 1, and half-cell electrochemical tests were performed. After 1000 charge-discharge cycles, the charging capacity at 0.8V was recorded, and the capacity retention rate was calculated. The results are shown in Table 1.

[0096] Test Example 3 During the sand milling process of step S2 in each embodiment and comparative examples 1, 2 (manual grinding) and 4, after sand milling for 3 hours, samples were taken every 1 hour thereafter for nano-laser particle size testing to monitor the sand milling process and ensure that each embodiment met the requirement of D50 < 150 nm at the end of sand milling. The results are shown in Table 1.

[0097] Table 1 As can be seen from Table 1, the silicon-carbon composite materials prepared in Examples 1-10 of this invention exhibit excellent electrochemical performance.

[0098] Firstly, regarding the lithium salt particle size, after sand milling in Examples 1-10, the lithium salt Dv50 was controlled below 150 nm (approximately 130-140 nm range), indicating that the nano-sizing effect was stable. In contrast, Comparative Example 2, which was manually milled, achieved a particle size of 6130 nm, significantly larger than the examples, demonstrating that the sand milling process is crucial for obtaining nanoscale lithium salt particles.

[0099] Regarding the initial charging performance, the specific capacity of Examples 1-10 at 2.0V ranged from 1868 to 1912 mAh / g, with initial coulombic efficiencies generally exceeding 91%, reaching 94.3% in Example 1, demonstrating high reversible capacity and good initial efficiency. In contrast, Comparative Example 2, due to its excessively large lithium salt particle size, experienced a decrease in initial coulombic efficiency to 90.5%, indicating that increased particle size is detrimental to interface stability and electrochemical reaction uniformity.

[0100] Regarding cycle stability, the capacity retention rates of Examples 1-10 after 1000 cycles were all between 77.6% and 83.6%, with Example 1 reaching 83.6%, which was significantly better than Comparative Example 3 (75.9%) without lithium salt coating. This indicates that the introduction of a lithium salt layer can effectively improve cycle stability and alleviate structural stress and interfacial side reactions.

[0101] Furthermore, although Comparative Example 1 (without the introduction of metal elements and halogen regulation) had a higher initial cycle capacity, its cycle retention rate was lower than that of the Example system, indicating that the synergistic regulation of metal elements and halogens has a positive effect on structural stability. Comparative Example 4 used a simple mixing method for coating, and although its cycle performance was improved, it was still lower than that of the in-situ fluidized bed deposition method of Example 1, indicating that the in-situ deposition coating process used in this invention is more conducive to the formation of a uniform and dense lithium salt layer.

[0102] In summary, this invention achieves an effective balance between first-cycle efficiency and long-cycle stability in silicon-carbon composite materials through nano-sized lithium salt regulation and in-situ fluidized bed coating process, demonstrating a significant overall performance advantage over the comparative example.

[0103] The silicon-carbon anode composite material provided in this invention avoids direct contact between silicon-carbon and electrolyte by coating the surface of the silicon-carbon composite material with nanoscale modified lithium salt, effectively reducing side reactions, optimizing ion transport, improving physical contact and chemical compatibility with the positive / negative electrode active materials, reducing interfacial impedance, and fixing lithium salt particles through two vapor-phase carbon deposition processes, suppressing silicon volume expansion, preventing excessive reaction between lithium salt and silicon, and improving conductivity. Doping the material with halogen atoms, non-metals, and metals effectively enhances the material's conductivity, structural stability, and interfacial compatibility. The resulting silicon-carbon anode composite material forms a uniform and stable SEI film on its surface, exhibiting good ion-electron dual conductivity and effectively mitigating silicon volume expansion. It demonstrates high reversible capacity in lithium-ion batteries, excellent long-cycle stability, and superior rate performance. The silicon-carbon anode composite material of this invention achieves an initial coulombic efficiency greater than 86% at 0.8V, and retains up to 80% capacity after 1000 cycles.

[0104] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A silicon-carbon anode composite material, characterized in that, The silicon-carbon anode composite material includes: a silicon-carbon composite material, a lithium salt layer covering the surface of the silicon-carbon composite material, and a carbon coating layer covering the lithium salt layer. The Dv of the silicon-carbon composite material 50 Its thickness is 5–12 μm, and its specific surface area is 30.0–100.0 m². 2 / g; The specific surface area of ​​the silicon-carbon composite material coated with the lithium salt layer is 20.0–80.0 m². 2 / g; Silicon-carbon anode composite material Dv 50 Its diameter is 6–13 μm, and its specific surface area is 0.3–5.0 m². 2 / g; In the silicon-carbon composite material coated with the lithium salt layer, the mass of silicon accounts for 20% to 60% of the total mass of the silicon-carbon composite material coated with the lithium salt layer; In the lithium salt layer, the general chemical formula of the lithium salt is Li. x M a A b PO4X c M is a metallic element, A is a nonmetallic element, X is a halogen element, 2.5≤x≤3.5, 0<a≤0.3, 0≤b≤0.3, 0≤c≤0.3, and b and c are not both 0.

2. The silicon-carbon anode composite material according to claim 1, characterized in that, Metallic elements M include one or more of Mg, Al, and Ti, while non-metallic elements A include one or more of N and S.

3. The silicon-carbon anode composite material according to claim 1, characterized in that, 0.05≤a≤0.15, 0.05≤b≤0.15, 0.05≤c≤0.

15.

4. A method for preparing the silicon-carbon anode composite material according to any one of claims 1-3, characterized in that, The preparation method includes: According to the target molecular formula Li x M a A b PO4X c According to the stoichiometric ratio, a lithium source, a metal element M doping source, a non-metal element A doping source, and a halogen source are mixed and dispersed to obtain a mixed precursor material. The mixed precursor material is then dried and granulated, followed by segmented heat treatment to obtain the lithium salt material Li. x M a A b PO4X c 2.5 ≤ x ≤ 3.5, 0 < a ≤ 0.3, 0 < b ≤ 0.3, 0 < c ≤ 0.3; The lithium salt material is dispersed in a liquid medium and then subjected to sand milling to obtain a lithium salt slurry with a particle size D50 < 300 nm. In an inert atmosphere, a silicon-carbon composite material is formed by deposition reaction on porous carbon material using a vapor-phase silicon source. The lithium salt slurry is loaded onto the silicon-carbon composite material; A first gaseous carbon source is introduced for thermal decomposition deposition to perform a gaseous carbon deposition process, which is used to fix the lithium salt particles at the interface and construct a conductive connection structure. The material obtained from the first gas phase carbon deposition process is placed in a heat treatment device, and a second gas phase carbon source is introduced under a protective atmosphere to perform a second gas phase carbon deposition process. This process is used to construct a continuous carbon phase on the outermost surface and to confine and fix the lithium salt particles, thereby inhibiting the migration and shedding of the lithium salt particles during the subsequent electrochemical reaction process, thus obtaining the silicon-carbon anode composite material.

5. The preparation method according to claim 4, characterized in that, The lithium source includes one or more of lithium carbonate, lithium hydroxide, lithium fluoride, or lithium chloride; preferably, the lithium source is in excess by 5 wt.%-15 wt.%. The metal element M doping source includes one or more of the following: magnesium oxide, magnesium chloride, aluminum oxide, aluminum chloride, titanium oxide, or titanium chloride; The non-metallic element A doping source includes one or more of the following: ammonium dihydrogen phosphate, urea, melamine, thiourea, or lithium sulfide; The halogen source includes one or more of lithium fluoride, ammonium chloride, ammonium fluoride, or aluminum chloride; The liquid medium includes deionized water or an organic solvent; the organic solvent includes alcohol-based organic solvents.

6. The preparation method according to claim 4, characterized in that, The segmented heat treatment includes: a low-temperature decomposition stage and a high-temperature doping crystallization stage; The low-temperature decomposition stage specifically includes: heating to 400-550℃ at a heating rate of 5-15℃ / min under an inert atmosphere, and holding at that temperature for 2-5 hours; The high-temperature doping crystallization stage specifically includes: continuing to heat to 600-850 ℃ and holding at that temperature for 6-12 h to form the lithium salt material Li. x M a A b PO4X c .

7. The preparation method according to claim 4, characterized in that, The process of forming a silicon-carbon composite material by deposition reaction on porous carbon material using a gas-phase silicon source under an inert atmosphere specifically includes: transferring porous carbon to a fluidized bed, heating it to 400-800 ℃ in an inert environment, introducing a gas-phase silicon source, and performing gas-phase deposition on the porous carbon; wherein the gas-phase silicon source includes silane or tetramethylsilane. The specific steps of loading the lithium salt slurry onto the silicon-carbon composite material include: pumping the lithium salt slurry into the fluidized bed under a fluidized state maintained by an inert atmosphere, and uniformly loading lithium salt particles onto the surface of the silicon-carbon composite material through atomization and evaporation of the liquid slurry to form the lithium salt layer. The process of introducing a first gaseous carbon source for thermal decomposition deposition specifically includes: introducing a first gaseous carbon source into the fluidized bed, and performing a gaseous carbon deposition process on the lithium salt layer through the thermal decomposition of the first gaseous carbon source; the first gaseous carbon source includes one or more of methane, acetylene, and ethylene. The secondary gas-phase carbon deposition process by introducing a second gas-phase carbon source under a protective atmosphere specifically includes: heating to 500-600°C under a protective atmosphere, introducing a mixed gas formed by a carrier gas and a second gas-phase carbon source at a volume flow rate ratio of [4:1]-[1:1], maintaining the temperature for 0.5-3 h, and further depositing carbon on the material surface through the thermal decomposition of the second gas-phase carbon source to form a uniform carbon coating layer; wherein the carrier gas is nitrogen or argon, and the second gas-phase carbon source includes one or more of methane, acetylene, ethylene, and propylene.

8. The preparation method according to claim 4, characterized in that, Following the secondary vapor-phase carbon deposition process, the method further includes: The material is cooled in a protective atmosphere, then broken down, sieved, and demagnetized to obtain the silicon-carbon anode composite material.

9. A negative electrode, characterized in that, The negative electrode sheet comprises the silicon-carbon negative electrode composite material as described in any one of claims 1-3.

10. A lithium battery, characterized in that, The lithium battery includes the negative electrode as described in claim 9.

Images