Silicon-carbon composite negative electrode material for constructing confinement structure based on multi-step calcination and preparation method of silicon-carbon composite negative electrode material

Abstract

The invention discloses a silicon-carbon composite negative electrode material for constructing a confinement structure based on multi-step calcination and a preparation method of the silicon-carbon composite negative electrode material, and belongs to the technical field of lithium ion batteries. The core of the invention lies in that a carbon source with structure construction capability is combined with a multi-step calcination process. The method comprises the following steps: mixing nano silicon with a specific carbon source (such as asphalt, phenolic resin, lignin and the like) to prepare a precursor; then performing three-step heat treatment on the precursor in an inert atmosphere: firstly, performing structure curing at 200-350 DEG C, so that a carbon source is crosslinked to form a stable skeleton; then carrying out preliminary carbonization at 400-550 DEG C to form an amorphous carbon matrix with buffering capability; and finally, performing interface strengthening at 600-950 DEG C to promote the combination between carbon and silicon particles and enhance the graphitization degree and conductivity of a carbon layer. According to the preparation method disclosed by the invention, a plurality of carbon-based confinement structures which are hard outside, tough inside and firm in interface are constructed in situ outside silicon particles by cooperatively regulating and controlling a carbon structure and a calcining process, and the volume expansion of silicon can be effectively inhibited, so that the silicon-carbon composite negative electrode material with high capacity and excellent cycling stability is prepared.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery anode material technology, specifically relating to a silicon-carbon composite anode material based on a confined structure constructed by multi-step calcination and its preparation method. Background Technology

[0002] Silicon, with its theoretical specific capacity of up to 4200 mAh / g (approximately ten times that of traditional graphite anodes), is considered an ideal anode material for next-generation high-energy-density lithium-ion batteries. However, silicon experiences volume expansion exceeding 300% during charge and discharge, easily leading to electrode structure pulverization, electrical contact failure between the active material and the current collector, and repeated rupture and regeneration of the solid electrolyte interphase (SEI) film. These problems collectively cause rapid capacity decay and shortened cycle life, severely restricting the practical application of silicon anodes. To address these challenges, current research often employs a "nano-sizing + carbon coating" strategy: by nano-sizing silicon materials to alleviate the stress caused by volume changes, and then combining it with carbon materials, utilizing their good conductivity and mechanical toughness to construct a conductive network and buffer expansion. Currently, common methods often use a single carbon source (such as glucose, pitch, or polymer) mixed with nano-silicon followed by a one-step high-temperature treatment to achieve coating. However, a single carbon source is difficult to simultaneously meet multiple performance requirements: for example, the porous carbon formed after glucose carbonization has good buffering capacity but poor density; pitch-derived carbon layers have excellent conductivity but insufficient toughness and are prone to cracking when silicon expands. Furthermore, one-step high-temperature sintering makes it difficult to precisely control the carbon layer formation process, and it is impossible to achieve the "stepwise construction" of the carbon structure and the "in-situ strengthening" of the silicon-carbon interface. This results in an unsatisfactory coating structure and weak bonding, which limits the improvement of the material's overall performance. Summary of the Invention

[0003] This invention addresses the shortcomings of existing technologies by providing a silicon-carbon composite anode material with a confined structure based on multi-step calcination and its preparation method. This method involves introducing carbon sources with different functions in stages for secondary composite formation, combined with a three-step calcination process. The aim is to construct a composite carbon shell around the nano-silicon core, characterized by ample internal buffer space, dense external encapsulation, and strong bonding with the silicon core interface, thereby simultaneously achieving high specific capacity, high initial coulombic efficiency, and ultra-long cycle life.

[0004] The specific preparation steps of this invention are as follows:

[0005] (1) Preparation of blend: The nano-silicon material and the first carbon source were weighed at a mass ratio of 1:1 to 5:1 and dispersed together in an aqueous solvent (the mass ratio of nano-silicon powder to aqueous solvent was 1:100 to 1:800). The mixture was thoroughly and uniformly mixed by mechanical stirring and ultrasonic treatment. Subsequently, the mixture was centrifuged (5000-12000 r / min, 2-10 minutes), the supernatant was discarded, and the resulting precipitate was dried at 80-120℃ for 6-12 hours to obtain the blend of nano-silicon and the first carbon source.

[0006] (2) Construction of core-shell precursor: Add a second carbon source to the blend obtained in step (1), place it in a planetary ball mill for dry ball milling, and mechanically dry mix at a speed of 300~400 r / min for 2-10h to obtain Si-C composite precursor. The mass ratio of the amount of the second carbon source added to the blend is 1:2~1:10. Stir to make the second carbon source evenly distributed in the blend;

[0007] (3) Structural solidification treatment: The core-shell precursor obtained in step (2) is placed in a tube furnace or atmosphere sintering furnace, and heated to 200-350℃ at a rate of 1-8℃ / min under an inert protective atmosphere (such as argon or nitrogen), and held for 1-5h.

[0008] (4) Primary carbonization treatment: After completing step (3), continue to heat to 400-550℃ at a rate of 3-14℃ / min under an inert atmosphere and keep warm for 2-9h;

[0009] (5) Interface strengthening and graphitization treatment: After completing step (4), continue to heat to 600-950℃ at a rate of 5-13℃ / min under an inert atmosphere and keep it at that temperature for 2-8 hours. Then, cool it naturally to room temperature to obtain the final silicon-carbon composite anode material.

[0010] The beneficial effects of this invention are:

[0011] By introducing carbon sources with different functions in stages, an ideal configuration of "inner buffer and outer encapsulation" is achieved. The first carbon source is responsible for constructing a flexible matrix to accommodate volume expansion, while the second carbon source is responsible for providing a dense and robust protective shell and conductive network. The two work together to overcome the shortcomings of single carbon source performance. Simultaneously, multi-step calcination achieves precise control of different carbon structures through three key stages: "structural solidification treatment," "primary carbonization treatment," and "interface strengthening and graphitization treatment." This method not only constructs an ideal silicon-carbon configuration but also achieves chemical bonding at the interface by constructing a confined structure through multi-step calcination, solving the core problem of easy coating layer detachment. The silicon-carbon composite material prepared by this invention has sufficient internal buffer space, a robust and dense external conductive shell, and strong silicon-carbon interface bonding, exhibiting high reversible capacity, initial coulombic efficiency, and excellent cycle stability. Therefore, this invention, from the perspective of silicon-carbon composite anode material structure construction, utilizes multiple carbon sources combined with multi-step calcination to construct a confined structure, efficiently synthesizing a silicon-carbon composite anode material with uniform particle size, high bonding strength, and no wear. The material produced by this invention has high reversible capacity (>2700 mAh / g), high first-efficiency (86.5%), and excellent cycling stability (capacity retention of 88% after 100 cycles). Structurally, it achieves a "buffer-density" double coating, solving industry problems such as easy carbon layer detachment and silicon particle pulverization. The process is universal and applicable to a variety of carbon source combinations, and has industrialization potential. Attached Figure Description

[0012] Figure 1 This is a scanning electron microscope image of the silicon-carbon composite anode material with a confined structure prepared by multi-step calcination in Example 1 of this invention;

[0013] Figure 2 This is a scanning electron microscope image of the silicon-carbon composite anode material with a confined structure prepared by multi-step calcination in Example 2 of this invention;

[0014] Figure 3 This is a cycle performance diagram of the silicon-carbon composite anode material with a confined structure prepared by multi-step calcination in Example 3 of the present invention;

[0015] Figure 4 This is a charge-discharge rate diagram of the silicon-carbon composite anode material with a confined structure prepared by multi-step calcination in Example 4 of this invention;

[0016] Figure 5 This is a charge-discharge curve of the silicon-carbon composite anode material with a confined structure prepared by multi-step calcination in Example 5 of the present invention. Detailed Implementation

[0017] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments, but the scope of protection of the present invention is not limited to the content described.

[0018] A method for preparing silicon-carbon composite anode materials with confined structures based on multi-step calcination is described below:

[0019] (1) The nano-silicon material and the first carbon source are mixed in an aqueous solvent and dispersed by mechanical stirring and ultrasound to form a uniform suspension. Then, the mixture is centrifuged and dried to obtain a Si-C blend.

[0020] (2) Add a second carbon source to the blend obtained in step (1), place it in a planetary ball mill for dry ball milling, and perform mechanical dry mixing at a speed of 300~400 r / min for 2-10 h to obtain the Si-C composite precursor;

[0021] (3) The Si-C composite precursor obtained in step (2) is heated to 200-350℃ at a rate of 1-8℃ / min under an inert atmosphere and kept at that temperature for 1-5h to carry out structural curing treatment.

[0022] (4) After completing step (3), continue to heat to 400-550℃ at a rate of 3-14℃ / min under an inert atmosphere and keep at that temperature for 2-9 hours to complete the primary carbonization process.

[0023] (5) After completing step (4), continue to heat to 600-950℃ at a rate of 5-13℃ / min under an inert atmosphere, and keep at the temperature for 2-8h to carry out interface strengthening and partial graphitization treatment, and then cool naturally to room temperature to obtain the final Si-C composite anode material.

[0024] The nano-silicon material mentioned in step (1) is one or more of the following: nano-silicon particles, nano-silicon spheres, porous nano-silicon, silicon nanowires, and silicon nanotubes; the particle size range of the nano-silicon is 10~800nm; the aqueous solvent is deionized water, ethanol, or a mixture of the two, and the mass ratio of nano-silicon to aqueous solvent is 1:100~1:800.

[0025] In step (1), the first carbon source is one or more of ordered mesoporous carbon, biomass porous carbon, resin-based carbon, and graphitized porous carbon, and the mass ratio of nano-silicon to the first carbon source is 1:1 to 5:1.

[0026] The second carbon source in step (2) is one or more of glucose, sucrose, petroleum asphalt, coal tar pitch, and phenolic resin. The ratio of the amount of the second carbon source added to the mass of the Si-C blend is 1:2 to 1:10.

[0027] The process of solidification treatment of the structure in step (3) is as follows: the heating rate is 3-6℃ / min, the sintering temperature is 250-300℃, and the holding time is 4-8h.

[0028] The process parameters for the primary carbonization treatment in step (4) are: heating to 450-500℃ at 5-10℃ / min and holding for 3-6 hours.

[0029] The process parameters for the interface strengthening and graphitization treatment in step (5) are: heating to 750-850℃ at 6-9℃ / min and holding for 4-7h.

[0030] Example 1

[0031] A method for preparing silicon-carbon composite anode materials based on dual-carbon-source dry composite and three-step calcination, the specific steps of which are as follows:

[0032] (1) Weigh nano-silicon particles and ordered mesoporous carbon at a mass ratio of 5:4 to 5:1, and add them together to deionized water (the mass ratio of nano-silicon powder to deionized water is 1:150 to 1:250). Stir magnetically for 4 to 6 hours and then use ultrasonic dispersion for 1 to 2 hours to ensure thorough mixing. Then, centrifuge to separate the mixture, discard the supernatant, and place the resulting precipitate in a vacuum oven to dry at 80 to 120°C for 8 to 12 hours to obtain the Si-C blend.

[0033] (2) The dried Si-C blend powder obtained in step (1) is placed together with sucrose in a planetary ball mill at a mass ratio of 2:1 to 5:1 and mechanically dry-mixed at a speed of 300 to 400 r / min for 2 to 4 h to ensure that the sucrose is uniformly coated on the surface of the blend to obtain the Si-C composite precursor.

[0034] (3) The Si-C composite precursor obtained in step (2) is heated to 250-300℃ at a rate of 2-6℃ / min under argon protection and kept at the temperature for 1-1.5 h to carry out structural curing treatment;

[0035] (4) After completing step (3), continue to raise the temperature to 450-500℃ at a rate of 3-5℃ / min under argon protection, and keep it at that temperature for 3-6 h to complete the primary carbonization process;

[0036] (5) After completing step (4), continue to heat to 800-850°C at a rate of 3-5°C / min under argon protection, and keep at the temperature for 5-8 hours to carry out interface strengthening and graphitization treatment. Then, cool naturally to room temperature to obtain the final silicon-carbon composite anode material.

[0037] Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) analyses of the silicon-carbon composite anode material prepared in this embodiment show that the material exhibits relatively uniform, near-spherical particles. TEM images clearly reveal a typical core-shell structure: the core is composed of nanocrystalline silicon, and the outermost layer is a dense, graphitized carbon layer derived from pitch, with a uniform thickness of approximately 3–5 nm. Between the core and outer layer, a light-contrast amorphous porous carbon buffer layer derived from glucose is visible. This dual-carbon-layer structure, formed through dry composite and three-step calcination, effectively avoids direct contact between the nanocrystalline silicon particles and the electrolyte, reducing side reactions and loss of active materials. Simultaneously, the dense outer carbon layer provides an excellent electron conduction pathway.

[0038] Example 2

[0039] A method for preparing silicon-carbon composite anode materials based on dual-carbon-source dry composite and three-step calcination, the specific steps of which are as follows:

[0040] (1) Weigh silicon nanowires and biomass porous carbon at a mass ratio of 1:1 to 5:3 and add them together to ethanol (the mass ratio of nano-silicon powder to ethanol is 1:300 to 1:600). Stir magnetically for 5 to 8 hours to ensure thorough mixing and dispersion. Then, centrifuge to separate the mixture, discard the supernatant, and place the resulting precipitate in a vacuum oven to dry at 80 to 100°C for 10 to 14 hours to obtain a Si-C blend.

[0041] (2) The dried Si-C blend powder obtained in step (1) is placed together with petroleum asphalt powder in a high-efficiency mixer at a mass ratio of 10:3 to 10:1 and dry mechanically fused for 1 to 3 hours to ensure that the petroleum asphalt is uniformly coated on the surface of the blend, thus obtaining the Si-C composite precursor.

[0042] (3) The Si-C composite precursor obtained in step (2) is heated to 250-300℃ at a rate of 3-5℃ / min under argon protection and kept at the temperature for 1-6 h to carry out structural curing treatment;

[0043] (4) After completing step (3), continue to raise the temperature to 480-520℃ at a rate of 3-8℃ / min under argon protection, and keep it at that temperature for 3-5 h to complete the primary carbonization treatment;

[0044] (5) After completing step (4), continue to heat to 700-800℃ at a rate of 2-5℃ / min under argon protection, and keep at the temperature for 2-6 h to carry out interface strengthening and graphitization treatment, and then cool naturally to room temperature to obtain the final silicon-carbon composite anode material.

[0045] Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) analyses of the silicon-carbon composite anode material prepared in this embodiment show that the material exhibits good dispersibility and its core-shell structure is clearly visible. The core is silicon crystal, the middle layer is high-strength glassy carbon formed by carbonization of phenolic resin, and the outer layer is amorphous carbon produced by pyrolysis of sucrose. The outer carbon shell has a uniform thickness of approximately 4–6 nm and is tightly bonded to the inner layer.

[0046] Example 3

[0047] A method for preparing silicon-carbon composite anode materials based on dual-carbon-source dry composite and three-step calcination, the specific steps of which are as follows:

[0048] (1) Weigh out nano-silicon spheres and resin-based carbon at a mass ratio of 5:3 to 1:1, and add them together to deionized water (the mass ratio of nano-silicon powder to deionized water is 1:250 to 1:400). Stir magnetically for 5 to 8 hours to ensure thorough mixing and dispersion. Then, centrifuge to separate the mixture, discard the supernatant, and place the resulting precipitate in a vacuum oven to dry at 80 to 100°C for 10 to 14 hours to obtain the Si-C blend.

[0049] (2) The dried Si-C blend powder obtained in step (1) is placed together with glucose powder in a planetary ball mill at a mass ratio of 5:2 to 5:1 and mechanically dry-mixed at a speed of 300 to 400 r / min for 2 to 4 h to ensure that glucose is uniformly coated on the surface of the blend, thus obtaining the Si-C composite precursor.

[0050] (3) The Si-C composite precursor obtained in step (2) is heated to 250-300℃ at a rate of 1-3℃ / min under argon protection and held for 1-2 h to carry out structural curing treatment;

[0051] (4) After completing step (3), continue to heat to 480-520℃ at a rate of 2-4℃ / min under argon protection, and keep at the temperature for 2-3 h to complete the primary carbonization treatment;

[0052] (5) After completing step (4), continue to heat to 700-800℃ at a rate of 5-7℃ / min under argon protection, and keep at the temperature for 2-4 h to carry out interface strengthening and graphitization treatment, and then cool naturally to room temperature to obtain the final silicon-carbon composite anode material.

[0053] Weigh 0.14g of the composite material prepared in this example, 0.04g of acetylene black, and 0.02g of sodium alginate (SA), put them into a mortar, mix and grind for 80min, then add 2mL of deionized water and continue grinding for 40min. Coat the viscous mixture evenly onto the copper foil, then pre-dry it at 80℃ for 30min, and then dry it in a vacuum oven at 60℃ for 12h. Cut the coated copper foil into a disc with a diameter of 14mm as the working electrode (active material loading is 1.3±0.1mg / cm²).

[0054] In an argon-filled glove box (O2 content <1ppm, H2O content <1ppm), electrodes, separators, lithium sheets, and nickel foam mesh were assembled into CR2032 coin cells using conventional methods. The battery's electrochemical performance was then tested using a constant current charge-discharge system. The charge-discharge curves are shown below. Figure 3 As shown in the figure, the material prepared in this example exhibits excellent lithium storage capacity and cycle stability as a negative electrode material for lithium-ion batteries. Under constant current discharge-charge testing at a current density of 1 A / g, between 0.01 and 2.0 V, its initial reversible capacity reached 2710 mAh / g, with an initial coulombic efficiency of 86.5%. After 100 cycles, the capacity retention rate remained as high as 88%, indicating that the synergistic effect of the dual carbon sources of phenolic resin and pitch, combined with the "buffered-dense" dual carbon coating structure formed by the three-step calcination process, effectively suppresses the volume expansion of silicon, maintains the integrity of the electrode structure, and thus achieves stable long-cycle performance.

[0055] Example 4

[0056] A method for preparing silicon-carbon composite anode materials based on dual-carbon-source dry composite and three-step calcination, the specific steps of which are as follows:

[0057] (1) Weigh silicon nanotubes and graphitized porous carbon at a mass ratio of 5:4 to 2:1 and add them together to deionized water (the mass ratio of nano-silicon powder to deionized water is 1:150 to 1:250). Stir magnetically for 4 to 6 hours and then use ultrasonic dispersion for 1 to 2 hours to ensure thorough mixing. Then, centrifuge to separate the mixture, discard the supernatant, and place the resulting precipitate in a vacuum oven to dry at 80 to 120°C for 8 to 12 hours to obtain the Si-C blend.

[0058] (2) The dried Si-C blend powder obtained in step (1) is placed together with phenolic resin powder in a planetary ball mill at a mass ratio of 10:3 to 10:1 and mechanically dry-mixed at a speed of 300 to 400 r / min for 2 to 4 h to ensure that the phenolic resin is uniformly coated on the surface of the blend to obtain the Si-C composite precursor.

[0059] (3) The Si-C composite precursor obtained in step (2) is heated to 250-300℃ at a rate of 3-5℃ / min under argon protection and kept at the temperature for 1-2 h to carry out structural curing treatment;

[0060] (4) After completing step (3), continue to raise the temperature to 480~520℃ at a rate of 3~5℃ / min under argon protection, and keep it at that temperature for 1~2 h to complete the primary carbonization treatment;

[0061] (5) After completing step (4), continue to heat to 700-800℃ at a rate of 3-5℃ / min under argon protection, and keep at the temperature for 2-4 h to carry out interface strengthening and graphitization treatment, and then cool naturally to room temperature to obtain the final silicon-carbon composite anode material.

[0062] Weigh 0.14g of the composite material prepared in this example, 0.04g of acetylene black, and 0.02g of sodium alginate (SA), put them into a mortar, mix and grind for 30min, then add 2mL of deionized water and continue grinding for 30min. Coat the viscous mixture evenly onto the copper foil, then pre-dry it at 80℃ for 15min, and then dry it in a vacuum oven at 60℃ for 12h. Cut the coated copper foil into a disc with a diameter of 14mm as the working electrode (active material loading is 1.3±0.1mg / cm²).

[0063] In an argon-filled glove box (O2 content <1ppm, H2O content <1ppm), electrodes, separators, lithium sheets, and nickel foam mesh were assembled into CR2032 coin cells using conventional methods. The battery electrochemical performance was then tested using a constant current charge-discharge system. Cycle performance graphs are shown below. Figure 5 As shown in the figure, the silicon-carbon composite material prepared by the dual-carbon-source dry composite and three-step calcination process exhibits excellent and stable electrochemical performance. After 200 cycles at a current density of 1 A / g, this anode material still retains a reversible capacity of 1250 mAh / g, with a capacity retention rate exceeding 85%. Under the same conditions, the silicon-carbon material prepared by a single glucose carbon source has a discharge specific capacity of 680 mAh / g after 200 cycles, while the silicon-carbon material prepared by mechanical ball milling has a discharge capacity of only 520 mAh / g after 200 cycles. The cycling performance of the material prepared in this embodiment is significantly better than the comparative sample, which fully demonstrates that the synergistic effect of the dual-carbon-source design and the three-step calcination process can effectively construct a stable composite structure and significantly improve the cycling stability of the silicon-carbon anode.

[0064] Example 5

[0065] A method for preparing silicon-carbon composite anode materials based on dual-carbon-source dry composite and three-step calcination, the specific steps of which are as follows:

[0066] (1) Weigh porous nano-silicon and biomass porous carbon at a mass ratio of 5:4 to 2:1 and add them together to deionized water (the mass ratio of nano-silicon powder to deionized water is 1:400 to 1:800). Stir magnetically for 4 to 6 hours and then use ultrasonic dispersion for 1 to 2 hours to ensure thorough mixing. Then, centrifuge to separate the mixture, discard the supernatant, and place the resulting precipitate in a vacuum oven to dry at 80 to 120°C for 8 to 12 hours to obtain the Si-C blend.

[0067] (2) The dried Si-C blend powder obtained in step (1) is placed together with coal tar powder in a planetary ball mill at a mass ratio of 10:3 to 10:1 and mechanically dry-mixed at a speed of 300 to 400 r / min for 2 to 4 h to ensure that sucrose is uniformly coated on the surface of the blend to obtain the Si-C composite precursor.

[0068] (3) The Si-C composite precursor obtained in step (2) is heated to 250-300℃ at a rate of 3-5℃ / min under argon protection and kept at the temperature for 1-2 h to carry out structural curing treatment;

[0069] (4) After completing step (3), continue to raise the temperature to 480~520℃ at a rate of 3~5℃ / min under argon protection, and keep it at that temperature for 1~2 h to complete the primary carbonization treatment;

[0070] (5) After completing step (4), continue to heat to 700-800℃ at a rate of 3-5℃ / min under argon protection, and keep at the temperature for 2-4 h to carry out interface strengthening and graphitization treatment, and then cool naturally to room temperature to obtain the final silicon-carbon composite anode material.

[0071] Weigh 0.14g of the composite material prepared in this example, 0.04g of acetylene black, and 0.02g of sodium alginate (SA), put them into a mortar, mix and grind for 30min, then add 2mL of deionized water and continue grinding for 30min. Coat the viscous mixture evenly onto the copper foil, then pre-dry it at 80℃ for 15min, and then dry it in a vacuum oven at 60℃ for 12h. Cut the coated copper foil into a disc with a diameter of 14mm as the working electrode (active material loading is 1.3±0.1mg / cm²).

[0072] In an argon-filled glove box (O2 content <1ppm, H2O content <1ppm), electrodes, separators, lithium sheets, and nickel foam mesh were assembled into CR2032 coin cells using conventional methods. The battery electrochemical performance was then tested using a constant current charge-discharge system. Cycle performance graphs are shown below. Figure 5As shown in the figure, the silicon-carbon composite material prepared by the dual-carbon-source dry composite and three-step calcination process exhibits excellent and stable electrochemical performance. After 200 cycles at a current density of 1 A / g, this anode material still retains a reversible capacity of 1250 mAh / g, with a capacity retention rate exceeding 85%. Under the same conditions, the silicon-carbon material prepared by a single glucose carbon source has a discharge specific capacity of 680 mAh / g after 200 cycles, while the silicon-carbon material prepared by mechanical ball milling has a discharge capacity of only 520 mAh / g after 200 cycles. The cycling performance of the material prepared in this embodiment is significantly better than the comparative sample, which fully demonstrates that the synergistic effect of the dual-carbon-source design and the three-step calcination process can effectively construct a stable composite structure and significantly improve the cycling stability of the silicon-carbon anode.

[0073] This invention details the specific implementation scheme for preparing high-performance silicon-carbon composite anode materials based on a dual-carbon source synergistic strategy and a three-step calcination precision process through Examples 1 to 5. Each example demonstrates that this technical solution achieves complementary advantages in structure and function between the two carbon sources by constructing a "blend" and a "core-shell precursor" in stages. The first carbon source (such as glucose or phenolic resin) mainly constructs the internal buffer layer, effectively accommodating the volume expansion of the silicon core; the second carbon source (such as pitch or sucrose) forms the external sealing coating layer, ensuring structural integrity and improving electronic conductivity. More importantly, the three-step calcination process (structural solidification → primary carbonization → interface strengthening and graphitization) is not a simple temperature segmentation, but rather a precise control of the physicochemical changes at different stages during the pyrolysis of the composite precursor. This process ensures the controllable formation of the carbon layer from nothing to something, from loose to dense, and from physical adsorption to chemical bonding, ultimately successfully constructing an ideal coating structure that is "strong on the outside and tough on the inside, with a firm interface." Therefore, this invention not only provides a specific and feasible preparation method, but also offers a set of innovative and universally applicable technical ideas and process blueprints for solving the industry problem of volume expansion of silicon-based anodes, which has significant industrial application value.

Claims

1. A method for preparing silicon-carbon composite anode materials with confined structures based on multi-step calcination, characterized in that... The specific steps are as follows: (1) The nano-silicon material and the first carbon source are mixed in an aqueous solvent and dispersed by mechanical stirring and ultrasound to form a uniform suspension. Then, the mixture is centrifuged and dried to obtain a Si-C blend. (2) Add a second carbon source to the blend obtained in step (1), place it in a planetary ball mill for dry ball milling, and perform mechanical dry mixing at a speed of 300~400 r / min for 2-10 h to obtain the Si-C composite precursor; (3) The Si-C composite precursor obtained in step (2) is heated to 200-350℃ at a rate of 1-8℃ / min under an inert atmosphere and kept at that temperature for 1-5h to carry out structural curing treatment. (4) After completing step (3), continue to heat to 400-550℃ at a rate of 3-14℃ / min under an inert atmosphere and keep at that temperature for 2-9 hours to complete the primary carbonization process. (5) After completing step (4), continue to heat to 600-950℃ at a rate of 5-13℃ / min under an inert atmosphere, and keep at the temperature for 2-8h to carry out interface strengthening and partial graphitization treatment, and then cool naturally to room temperature to obtain the final Si-C composite anode material.

2. The method for preparing a silicon-carbon composite anode material based on a multi-step calcination process to construct a confined structure according to claim 1, characterized in that: The nano-silicon material mentioned in step (1) is one or more of the following: nano-silicon particles, nano-silicon spheres, porous nano-silicon, silicon nanowires, and silicon nanotubes; the particle size range of the nano-silicon is 10~800nm; the aqueous solvent is deionized water, ethanol, or a mixture of the two, and the mass ratio of nano-silicon to aqueous solvent is 1:100~1:

800.

3. The method for preparing a silicon-carbon composite anode material based on a multi-step calcination process to construct a confined structure according to claim 1, characterized in that: In step (1), the first carbon source is one or more of ordered mesoporous carbon, biomass porous carbon, resin-based carbon, and graphitized porous carbon, and the mass ratio of nano-silicon to the first carbon source is 1:1 to 5:

1.

4. The method for preparing a silicon-carbon composite anode material based on a multi-step calcination process to construct a confined structure according to claim 1, characterized in that: The second carbon source in step (2) is one or more of glucose, sucrose, petroleum asphalt, coal tar pitch, and phenolic resin. The ratio of the amount of the second carbon source added to the mass of the Si-C blend is 1:2 to 1:

10.

5. The method for preparing a silicon-carbon composite anode material based on a multi-step calcination process to construct a confined structure according to claim 1, characterized in that: The process of solidification treatment of the structure in step (3) is as follows: the heating rate is 3-6℃ / min, the sintering temperature is 250-300℃, and the holding time is 4-8h.

6. The method for preparing a silicon-carbon composite anode material based on a multi-step calcination process to construct a confined structure according to claim 1, characterized in that: The process parameters for the primary carbonization treatment in step (4) are: heating to 450-500℃ at 5-10℃ / min and holding for 3-6 hours.

7. The method for preparing a silicon-carbon composite anode material based on a multi-step calcination process to construct a confined structure according to claim 1, characterized in that: The process parameters for the interface strengthening and graphitization treatment in step (5) are: heating to 750-850℃ at 6-9℃ / min and holding for 4-7h.

8. A silicon-carbon composite anode material prepared by the preparation method according to any one of claims 1-7.

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