Silicon-carbon-based composite material, preparation method and application of silicon-carbon-based composite material in lithium ion battery

Abstract

The invention relates to the technical field of lithium ion batteries, and particularly discloses a silicon-carbon-based composite material, a preparation method and application of the silicon-carbon-based composite material in a lithium ion battery. Silicon-carbon particles with different silicon content distributions are obtained by controlling the deposition concentration of the silicon particles, a nonporous carbon layer and a silicon-carbon composite layer are sequentially deposited on the surfaces of the silicon-carbon particles, silicon in the silicon-carbon composite layer is etched to obtain a porous carbon layer, and finally the porous polymer composite solid electrolyte layer is coated. The non-porous carbon layer has a compact structure, can effectively inhibit the volume change of silicon particles in the charging and discharging process, and prevents the silicon particles from being broken and falling off in the circulation process; the porous carbon layer effectively increases the specific surface area of the material, and opens up more paths for lithium ion storage and transmission; the outermost porous polymer composite solid electrolyte layer can uniformly coat the silicon carbon particles, and the porous structure can improve the compatibility with the electrolyte, so that the high-temperature, fast-charging and cycling stability of the material is remarkably improved.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium-ion batteries, and particularly to a silicon-carbon composite material, a preparation method thereof, and an application thereof in lithium-ion batteries. Background Art

[0002] For traditional graphite anode materials, their theoretical specific capacity is only 372 mAh / g. Facing the increasingly stringent requirements of the current market for high-energy-density batteries, they have gradually shown limitations and are difficult to fully meet the urgent expectations of long endurance and high-performance power sources in fields such as electric vehicles and portable electronic devices.

[0003] Silicon materials have shown great potential as the next-generation lithium-ion battery anode materials due to their ultra-high theoretical specific capacity of up to 4200 mAh / g, and have become a hot research direction in recent years. However, silicon anode materials face severe challenges in practical applications. During the charge and discharge process, the silicon anode will undergo a very significant volume expansion phenomenon, and its volume expansion rate can exceed 300%. Such a large volume change will cause a series of serious consequences: the internal structure of the electrode is irreversibly damaged, resulting in the active material falling off the electrode surface and gradually pulverizing; at the same time, the solid electrolyte interface (SEI) film is also difficult to maintain a stable state due to the stress of volume expansion, resulting in a sharp decline in the cycle performance of the battery and a significant increase in internal resistance, greatly restricting the wide application of silicon anode materials in actual battery systems.

[0004] To effectively solve the bottleneck problem of silicon material volume expansion, silicon-carbon composite materials have emerged. By compounding silicon with carbon materials, using the buffering characteristics and conductivity of carbon materials, it is possible to buffer the volume change of silicon during the charge and discharge process to a certain extent, thereby improving the cycle stability and rate performance of the battery. Among the many process methods for preparing silicon-carbon composite materials, the chemical vapor deposition (CVD) method has become the most commonly used method for preparing silicon-carbon composite materials due to its unique advantages. This method can achieve uniform compounding of silicon and carbon by depositing silicon on the surface of a porous carbon substrate, and reserve a certain space inside the composite material to accommodate the volume expansion of silicon during charge and discharge, thereby significantly improving the overall performance of the battery. Although the CVD silicon-carbon anode materials based on porous carbon substrates have improved some performance of silicon anodes to a certain extent, there are still many problems to be solved in current such materials. For example, the expansion is still relatively large, the cycle performance is not good, and the rate performance needs to be improved, etc., and it is difficult to meet the requirements of high capacity, fast charging, long cycle life, and low expansion at the same time. Therefore, developing a new structure of silicon-carbon anode material to overcome the above problems has become a technical problem that needs to be solved urgently by those skilled in the art. Summary of the Invention

[0005] Aiming at the problems that it is difficult for existing porous carbon-based CVD silicon-carbon anode materials to simultaneously achieve high capacity, fast charging performance, long cycle life, and low expansion rate, etc., the present invention provides a silicon-carbon-based composite material, a preparation method thereof, and an application in a lithium-ion battery. By sequentially coating a carbon isolation layer and a polymer composite solid electrolyte layer outside the silicon-carbon material with a specific structure, the silicon-carbon composite material has excellent properties such as low expansion, long cycle life, fast charging, and high temperature resistance, showing broad application prospects in the field of lithium-ion batteries.

[0006] To solve the above technical problems, the technical solution provided by the present invention is as follows: In the first aspect, the present invention provides a silicon-carbon-based composite material, including a silicon-carbon particle layer and a carbon isolation layer and a porous polymer composite solid electrolyte layer sequentially coated on the surface of the silicon-carbon particles from the inside to the outside; wherein, the silicon-carbon particles include a porous carbon substrate and silicon particles distributed in the porous carbon substrate; the content of the silicon particles in the porous carbon substrate is uniformly distributed or distributed in a gradient along the radial direction; The carbon isolation layer includes a non-porous carbon layer and a porous carbon layer from the inside to the outside.

[0007] Compared with the prior art, in the silicon-carbon-based composite material provided by the present invention, the content of silicon particles in the porous carbon substrate is uniformly distributed or distributed in a gradient along the radial direction. This flexible distribution method can optimize the contact area and reaction active sites between the silicon particles and the electrolyte, improve the expansion stress, and overall improve the performance of the silicon-carbon material. When the silicon-carbon particles have a structure with a high silicon content in the middle and a low content at the edge, the high-silicon region in the middle can provide a large number of lithium storage sites, while the relatively low silicon content and thicker carbon layer at the edge can provide a certain buffer space while ensuring a certain capacity, alleviating the damage of silicon expansion to the particle structure, thereby improving the cycle stability. At the same time, the relatively low silicon content at the edge makes the transmission paths of electrons and lithium ions more smooth at the particle edge, and can quickly transfer the lithium ions captured in the middle region to the external circuit, reducing the resistance of charge transmission and greatly improving the overall charging speed.

[0008] If the structure has a low silicon content in the middle and a high content at the edge, the abundant silicon particles at the edge can first contact and react with the electrolyte, quickly store lithium ions at the initial stage of charging, and then the silicon in the middle region gradually participates in the reaction to continuously increase the capacity. This lithium-ion transmission mode from the outside to the inside makes full use of the surface and internal space of the silicon-carbon particles, accelerates the overall charging process, and significantly improves the fast charging performance of the battery.

[0009] If the structure has the same silicon content in the middle and at the edge, it can ensure that the entire silicon-carbon particles uniformly store lithium ions, stably contribute to the capacity, and have a relatively balanced contact and reaction with the electrolyte. The volume change during charge and discharge is also relatively uniform, avoiding structural damage caused by local stress concentration, ensuring that the battery can still maintain a high capacity retention rate after multiple cycles, and achieving a long cycle life.

[0010] Furthermore, the present invention coats a carbon isolation layer on the surface of the silicon-carbon particles, providing a certain buffer space for the volume change of silicon during charge and discharge, restricting the volume change of silicon, and also isolating the direct contact between the silicon particles and the electrolyte to a certain extent, reducing the decomposition of the electrolyte and the repeated formation of the SEI film, and improving the initial Coulomb efficiency. Among them, the protective effect of the non-porous carbon layer can prevent the silicon particles from breaking and falling off during the cycle, maintaining the integrity of the electrode structure and enhancing the cycle life of the battery. On the one hand, the porous carbon layer can provide a lithium-ion diffusion channel, reduce the diffusion resistance, and improve the rate performance; on the other hand, it has good conductivity, can form a conductive network, promote electron transport, and improve the conductivity of the electrode.

[0011] Even further, the present invention coats a porous polymer composite solid electrolyte layer outside the carbon isolation layer, which can effectively buffer the volume change of silicon during charge and discharge, reduce the electrode structure damage and SEI film rupture caused by expansion, thereby improving the cycle stability of the battery; at the same time, it can also improve the conductivity of the electrode, provide a uniform lithium-ion diffusion channel, reduce the lithium-ion diffusion resistance, improve the rate performance and fast charging performance; this electrolyte layer can further reduce the contact between the negative electrode and the electrolyte, minimize the occurrence of side reactions, improve the initial Coulomb efficiency, and extend the cycle life of the battery. In addition, this porous polymer composite solid electrolyte layer can also improve the stability of the silicon-carbon material at high temperatures.

[0012] Furthermore, the silicon-carbon particles include at least one of the particles having the following structures: Silicon-carbon particle A1: The content of the silicon particles in the porous carbon substrate decreases in a gradient along the radial direction from the inside to the outside; among them, the silicon content in the range of 0 to r / 2 is 40% to 60% of the mass of the silicon-carbon particles, and the silicon content in the range of r / 2 to r is 30% to 50% of the mass of the silicon-carbon particles; Silicon-carbon particle A2: The content of the silicon particles in the porous carbon substrate increases in a gradient along the radial direction from the inside to the outside; among them, the silicon content in the range of 0 to r / 2 is 30% to 50% of the mass of the silicon-carbon particles, and the silicon content in the range of r / 2 to r is 40% to 60% of the mass of the silicon-carbon particles; Silicon-carbon particle A3: The content of the silicon particles in the porous carbon substrate is uniformly distributed; the silicon content is 30% to 60% of the mass of the silicon-carbon particles.

[0013] It should be noted that when the above-mentioned various silicon-carbon particles are used in combination, the mixing ratio can be adjusted according to specific performance requirements. The specific ratio can be obtained through conventional tests and is not particularly limited in the present invention.

[0014] Further, the thicknesses of the silicon-carbon particle layer, the carbon isolation layer, and the porous polymer composite solid electrolyte layer are all 5 nm to 100 nm.

[0015] Further, the D50 of the porous carbon substrate is 2 μm to 20 μm, the specific surface area is 1000 m 2 / g to 2000 m 2 / g, the average pore diameter is 0.5 nm to 10 nm, and the pore volume is 0.6 mL / g to 1.2 mL / g.

[0016] Further, the polymer in the porous polymer composite solid electrolyte is selected from at least one of phenolic resin, acrylamide, polyethylene, polystyrene, polyvinyl alcohol, polyvinyl chloride, polyether, polyester, polyamide, polyurethane, polysulfide rubber, polymethyl methacrylate, or styrene-butadiene rubber.

[0017] Further, the solid electrolyte in the porous polymer composite solid electrolyte is selected from at least one of lithium lanthanum titanate (LLTO), lithium aluminum titanium phosphate (LATP), lithium aluminum germanium phosphate (LAGP), lithium lanthanum zirconium oxide (LLZO), lithium germanium phosphorus sulfide (LGPS), lithium phosphorus oxynitride (LiPON), or lithium phosphate (LIPO3).

[0018] Using the porous polymer composite solid electrolyte can significantly improve the stability and conductivity of the organic and inorganic artificial solid electrolyte interface film layer, and improve the high-temperature, fast charging, and cycling performance of the silicon-carbon material.

[0019] In a second aspect, the present invention provides a method for preparing a silicon-carbon-based composite material, including the following steps: Step a, depositing silicon particles onto the surface and / or pores of the porous carbon substrate according to a preset content through chemical vapor deposition to obtain silicon-carbon particles; Step b, sequentially performing carbon coating and silicon-carbon composite coating on the silicon-carbon particles, and etching away the silicon in the silicon-carbon composite layer to obtain a carbon-coated material; Step c, dispersing the solid electrolyte in an aqueous polymer solution, and then using the obtained dispersion to perform secondary coating on the carbon-coated material and drying to obtain the silicon-carbon-based composite material.

[0020] Specifically, in step b, after the silicon-carbon particles are coated with a carbon source gas, they are then coated with a silicon-carbon composite using a carbon source gas and a silane gas, and then the obtained material is placed in a strong base solution to etch away the silicon in the silicon-carbon composite coating layer to obtain a porous carbon-coated material.

[0021] Specifically, in step c, the dispersion liquid is coated on the surface of the porous carbon-coated material by spray drying method.

[0022] The preparation method of the silicon-carbon-based composite material provided by the present invention obtains silicon-carbon particles with different silicon content distributions by controlling the concentration of silicon particle deposition. A non-porous carbon layer and a silicon-carbon composite layer are sequentially deposited on the surface of the silicon-carbon particles, and then the silicon in the silicon-carbon composite layer is etched away by alkali to obtain a porous carbon layer. Finally, a porous polymer composite solid electrolyte layer is coated outside the porous carbon layer. Among them, the non-porous carbon layer has a relatively dense structure, which can effectively inhibit the volume change of silicon particles during charge and discharge, avoid the fragmentation and shedding of silicon particles during the cycle, and maintain the integrity of the electrode structure; the porous carbon layer effectively increases the specific surface area of the material, opening up more paths for lithium ion storage and transmission, not only improving the capacity of the material, but also making the migration of lithium ions during charge and discharge more rapid. Moreover, the elasticity and compressibility of the porous carbon layer can effectively buffer the stress through its own structural deformation when the volume of silicon particles expands, further reducing the risk of structural damage and pulverization of silicon particles caused by stress concentration, and significantly improving the cycle stability. The outermost porous polymer composite solid electrolyte layer has both high ionic conductivity and good flexibility. It can not only uniformly coat the silicon-carbon particles, has excellent structural stability, but also its porous structure can increase the contact area between the silicon-carbon particles and the electrolyte, improve its compatibility with the electrolyte, thereby significantly improving the high temperature, fast charge and cycle stability of the material.

[0023] The present invention significantly improves the capacity, cycle stability and fast charge performance of silicon-carbon materials by coating silicon-carbon particles with a specific three-layer structure, showing broad application prospects in the field of lithium-ion batteries.

[0024] As a specific embodiment of the present invention, the preparation method of the silicon-carbon-based composite material specifically includes the following steps: Step a, placing the porous carbon in a vapor deposition silicon device, introducing an inert gas, discharging the oxygen in the device, heating to 450 °C - 500 °C, introducing silane gas, and controlling the concentration of silane gas during deposition according to the set silicon content to complete the preparation of silicon-carbon particles; Step b, introducing a carbon source gas into the vapor deposition silicon device, controlling the temperature at 520 °C - 620 °C, reacting for 2 h - 3 h, then stopping the introduction of the carbon source gas, stabilizing for 0.5 h - 2 h, and then simultaneously introducing the carbon source gas and silane gas, reacting for 1 h - 3 h, then stopping the gas supply, cooling to room temperature, and adding the obtained material to a strong alkali solution for etching and washing to obtain silicon-carbon particles coated with porous carbon; Step c, adding a solid electrolyte to an aqueous polymer solution and dispersing evenly to obtain a slurry; spraying and coating the slurry on the surface of the silicon-carbon particles coated with porous carbon, and drying to obtain a silicon-carbon-based composite material.

[0025] Further, in step a, the concentration of the silane gas is controlled to decrease from an initial 10% - 30% in a gradient to 0, obtaining silicon-carbon particles A1; wherein, every 0.5 h - 1.5 h, the concentration of the silane gas decreases by 2% - 6%, and it decreases to 0 in 4 h - 6 h; the total flow rate of the silane gas and the carrier gas is 10 L / min - 30 L / min.

[0026] Further, the concentration of the silane gas is controlled to increase from an initial 2% - 6% in a gradient to 10% - 30%, obtaining silicon-carbon particles A2; wherein, every 0.5 h - 1.5 h, the concentration of the silane gas increases by 2% - 6%, and it increases to 10% - 30% in 4 h - 6 h; the total flow rate of the silane gas and the carrier gas is 10 L / min - 30 L / min.

[0027] Further, during the deposition process, the concentration of the silane gas is controlled to be constant at 5% - 15% for 4 h - 6 h, obtaining silicon-carbon particles A3; the total flow rate of the silane gas and the carrier gas is 10 L / min - 30 L / min.

[0028] Further, in step a, the inert gas is one or more of nitrogen, argon, helium, or carbon dioxide.

[0029] Further, in step a, the silane gas is one or more of silane, disilane, dichlorosilane, or trichlorosilane.

[0030] Preferably, in step a, the silane gas is silane or disilane.

[0031] Further, in step a, a programmed temperature increase method is adopted, and the heating rate is 2 °C / min - 25 °C / min, preferably 5 °C / min - 10 °C / min.

[0032] Further, in step b, the carbon source gas is one or more of methane, ethane, propane, butane, ethylene, propylene, acetylene, or propyne.

[0033] Preferably, in step b, the carbon source gas is ethylene or acetylene.

[0034] Further, in step b, the flow rate of the carbon source gas is 1 L / min - 3 L / min.

[0035] Further, in step b, the flow rate of the silane gas is 0.3 L / min - 0.7 L / min.

[0036] Further, in step b, the strong base solution is a sodium hydroxide solution with a concentration of 0.3 mol / L - 1 mol / L.

[0037] Further, in step c, the solid content of the polymer aqueous solution is 1% - 3%.

[0038] Further, in step c, the solid content of the slurry is 35% - 45%.

[0039] Further, in step c, the mass ratio of the polymer to the solid electrolyte is (5% - 80%):(95% - 20%), and the sum of the masses of the polymer and the solid electrolyte is 100%.

[0040] Further, in step c, the temperature of the spray is 90°C - 100°C.

[0041] Further, in step c, the temperature of the drying is 150°C - 300°C, and the drying time is 0.5 h - 4 h.

[0042] In a third aspect, the present invention also provides a negative electrode comprising the silicon-carbon-based composite material described above.

[0043] In a fourth aspect, the present invention also provides the use of the above silicon-carbon-based composite material or the above negative electrode in the preparation of a lithium-ion battery.

[0044] In a fifth aspect, the present invention also provides a lithium-ion battery comprising the above silicon-carbon-based composite material or the above negative electrode.

[0045] In a sixth aspect, the present invention also provides a battery module comprising the above lithium-ion battery.

[0046] The silicon-carbon-based composite material prepared by the present invention has a high electrochemical capacity and high conductivity. At the same time, it can maintain the stability of the material during charge and discharge, has good fast-charging performance, and comprehensively optimizes the structure and performance of the material; applying the above silicon-carbon-based composite material to a lithium-ion battery not only helps to promote the upgrading of lithium-ion battery technology, but also brings new development opportunities to many fields that rely on lithium-ion batteries, such as smart grid energy storage, aerospace equipment, etc., and helps various industries achieve a qualitative leap in energy utilization efficiency and equipment performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 It is a TEM image of the silicon-carbon-based composite material prepared in Example 1 of the present invention; Figure 2 It is a TEM image of the silicon-carbon-based composite material prepared in Example 4 of the present invention; Figure 3 It is a TEM image of the silicon-carbon-based composite material prepared in Example 7 of the present invention; Figure 4 It is a schematic structural diagram of different silicon-carbon particles A1, A2, and A3 prepared by the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0048] In order to make the objectives, technical solutions and advantages of the present invention clearer and more understandable, the present invention will be further described in detail below in conjunction with embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0049] To better illustrate the present invention, further examples are given below through embodiments.

[0050] In the following embodiments, the D50 of the porous carbon used is 5 μm to 10 μm, the specific surface area is 1500 m 2 / g to 1700 m 2 / g, the average pore diameter is 0.5 nm to 10 nm, and the pore volume is 0.6 mL / g to 1.2 mL / g.

[0051] Example 1 This embodiment provides a method for preparing a silicon-carbon-based composite material, which specifically includes the following steps: Step a: Transfer the dry water-free porous carbon to the fluidized bed of a gas-phase deposition silicon device that discharges air, heat it to 450 °C at a rate of 5 °C / min, and introduce a mixed gas of nitrogen and silane. The total flow rate is 20 L / min, and the initial concentration of silane is 20%. Every 1 h, it is reduced by 4%, and it becomes 0% after 5 h. Stop introducing silane, heat it to 550 °C, introduce acetylene, the flow rate of acetylene is 2 L / min, and the introduction time is 2.5 h. Stop introducing acetylene. After stabilizing for 0.5 h, simultaneously introduce acetylene (2 L / min) and silane (0.5 L / min), and the introduction time is 2 h. Stop ventilation, and naturally cool to room temperature. Add the obtained material to a 0.5 mol / L sodium hydroxide solution for etching for 8 h, wash it with water until the washing liquid is neutral, and dry it under vacuum to obtain porous carbon-coated silicon-carbon particles; Step b: Dissolve polyethylene oxide polymer in water at 80 °C to obtain a polymer solution with a solid content of 2%; ultrasonically disperse lithium lanthanum titanate in water to obtain a lithium lanthanum titanate dispersion with a solid content of 40%; Mix the polymer solution and the lithium lanthanum titanate dispersion evenly. Among them, the mass ratio of polyethylene oxide polymer to lithium lanthanum titanate is 40:60. Spray the prepared slurry on the surface of the above-mentioned porous carbon-coated silicon-carbon particles. The spraying temperature is 95 °C. After drying, transfer it to an oven at 200 °C and dry it for 2 h to obtain a silicon-carbon-based composite material.

[0052] Example 2 This embodiment provides a method for preparing a silicon-carbon-based composite material, which specifically includes the following steps: Step a: Transfer the dry water-free porous carbon to the fluidized bed of a vapor deposition silicon device with air exhausted. Heat it to 480 °C at a rate of 20 °C / min. Introduce a mixed gas of nitrogen and silane with a total flow rate of 10 L / min. The initial concentration of silane is 30%, which decreases by 6% every 1 h and becomes 0% after 5 h. Stop introducing silane. Heat it to 520 °C and introduce acetylene with a flow rate of 3 L / min for 2 h. Stop introducing acetylene. After stabilizing for 1 h, introduce acetylene (3 L / min) and silane (0.7 L / min) simultaneously for 1 h. Stop ventilation and cool it naturally to room temperature. Add the obtained material to 1 mol / L sodium hydroxide solution for etching for 6 h, wash it with water until the washing liquid is neutral, and dry it under vacuum to obtain porous carbon-coated silicon-carbon particles; Step b: Dissolve polysulfide rubber in ethyl acetate to obtain a polymer solution with a solid content of 3%; ultrasonically disperse lithium aluminum titanium phosphate in water to obtain a lithium aluminum titanium phosphate dispersion with a solid content of 45%; Mix the polymer solution and the lithium aluminum titanium phosphate dispersion evenly. Among them, the mass ratio of polysulfide rubber to lithium aluminum titanium phosphate is 95:5. Spray-coat the prepared slurry on the surface of the above-mentioned porous carbon-coated silicon-carbon particles. The spraying temperature is 90 °C. After drying, transfer it to an oven at 150 °C and dry it for 4 h to obtain a silicon-carbon-based composite material.

[0053] Example 3 This example provides a method for preparing a silicon-carbon-based composite material, which specifically includes the following steps: Step a: Transfer the dry water-free porous carbon to the fluidized bed of a vapor deposition silicon device with air exhausted. Heat it to 500 °C at a rate of 15 °C / min. Introduce a mixed gas of nitrogen and silane with a total flow rate of 30 L / min. The initial concentration of silane is 10%, which decreases by 2% every 1 h and becomes 0% after 5 h. Stop introducing silane. Heat it to 620 °C and introduce acetylene with a flow rate of 1 L / min for 3 h. Stop introducing acetylene. After stabilizing for 2 h, introduce acetylene (1 L / min) and silane (0.3 L / min) simultaneously for 3 h. Stop ventilation and cool it naturally to room temperature. Add the obtained material to 0.3 mol / L sodium hydroxide solution for etching for 10 h, wash it with water until the washing liquid is neutral, and dry it under vacuum to obtain porous carbon-coated silicon-carbon particles; Step b: Dissolve polyvinyl alcohol in water at 80 °C to obtain a polymer solution with a solid content of 1%; ultrasonically disperse lithium aluminum germanium phosphate in water to obtain a lithium aluminum germanium phosphate dispersion with a solid content of 35%; Mix the polymer solution and the lithium aluminum germanium phosphate dispersion evenly, wherein the mass ratio of polyvinyl alcohol to lithium aluminum germanium phosphate is 20:80. Spray-coat the prepared slurry on the surface of the above-mentioned porous carbon-coated silicon-carbon particles. The spraying temperature is 95°C. After drying, transfer it to an oven at 300°C and dry for 0.5 h to obtain the silicon-carbon-based composite material.

[0054] Example 4 This example provides a method for preparing a silicon-carbon-based composite material, which specifically includes the following steps: Step a: Transfer the dry water-free porous carbon to the fluidized bed of a chemical vapor deposition silicon device that discharges air. Heat it to 450°C at a rate of 5°C / min. Introduce a mixed gas of nitrogen and silane, with a total flow rate of 20 L / min and an initial concentration of silane of 4%. Increase it by 4% every 1 h until it becomes 20% after 5 h. Stop introducing silane, heat it to 550°C, introduce acetylene with a flow rate of 2 L / min for 2.5 h. Stop introducing acetylene, and after stabilizing for 0.5 h, introduce acetylene (2 L / min) and silane (0.5 L / min) simultaneously for 2 h. Stop ventilation and let it cool naturally to room temperature. Add the obtained material to a 0.5 mol / L sodium hydroxide solution and etch for 8 h. Wash it with water until the washing liquid is neutral, and then dry it under vacuum to obtain porous carbon-coated silicon-carbon particles. Step b: Dissolve polyurethane in N-methylpyrrolidone to obtain a polymer solution with a solid content of 2%; ultrasonically disperse lithium lanthanum titanium oxide in water to obtain a lithium lanthanum titanium oxide dispersion with a solid content of 40%. Mix the polymer solution and the lithium lanthanum titanium oxide dispersion evenly, wherein the mass ratio of polyurethane to lithium lanthanum titanium oxide is 80:20. Spray-coat the prepared slurry on the surface of the above-mentioned porous carbon-coated silicon-carbon particles. The spraying temperature is 95°C. After drying, transfer it to an oven at 200°C and dry for 2 h to obtain the silicon-carbon-based composite material.

[0055] Example 5 This example provides a method for preparing a silicon-carbon-based composite material, which specifically includes the following steps: Step a: Transfer the dry water-free porous carbon to the fluidized bed of a vapor deposition silicon device with air exhausted. Heat it to 480 °C at a rate of 8 °C / min. Introduce a mixed gas of nitrogen and silane with a total flow rate of 30 L / min. The initial concentration of silane is 2%, and it increases by 6% every 1 h and becomes 20% after 4 h. Stop introducing silane, heat it to 520 °C, introduce acetylene with a flow rate of 1 L / min for 3 h. Stop introducing acetylene. After stabilizing for 2 h, introduce acetylene (2 L / min) and silane (0.3 L / min) simultaneously for 3 h. Stop ventilation and cool it naturally to room temperature. Add the obtained material to a 0.5 mol / L sodium hydroxide solution for etching for 6 h, wash it with water until the washing liquid is neutral, and dry it in vacuum to obtain porous carbon-coated silicon-carbon particles; Step b: Dissolve polyamide in N-methylpyrrolidone to obtain a polymer solution with a solid content of 1%; ultrasonically disperse lithium lanthanum zirconium oxide in water to obtain a lithium lanthanum zirconium oxide dispersion with a solid content of 35%; Mix the polymer solution and the lithium lanthanum zirconium oxide dispersion evenly. Among them, the mass ratio of polyamide to lithium lanthanum zirconium oxide is 95:5. Spray the prepared slurry on the surface of the above-mentioned porous carbon-coated silicon-carbon particles. The spraying temperature is 90 °C. After drying, transfer it to an oven at 150 °C and dry it for 4 h to obtain a silicon-carbon-based composite material.

[0056] Example 6 This example provides a preparation method of a silicon-carbon-based composite material, which specifically includes the following steps: Step a: Transfer the dry water-free porous carbon to the fluidized bed of a vapor deposition silicon device with air exhausted. Heat it to 500 °C at a rate of 10 °C / min. Introduce a mixed gas of nitrogen and silane with a total flow rate of 10 L / min. The initial concentration of silane is 6%, and it increases by 2% every 1 h and becomes 18% after 6 h. Stop introducing silane, heat it to 620 °C, introduce acetylene with a flow rate of 3 L / min for 2 h. Stop introducing acetylene. After stabilizing for 1 h, introduce acetylene (3 L / min) and silane (0.7 L / min) simultaneously for 1 h. Stop ventilation and cool it naturally to room temperature. Add the obtained material to a 1.0 mol / L sodium hydroxide solution for etching for 6 h, wash it with water until the washing liquid is neutral, and dry it in vacuum to obtain porous carbon-coated silicon-carbon particles; Step b: Dissolve polystyrene in ethyl acetate to obtain a polymer solution with a solid content of 3%; ultrasonically disperse lithium germanium phosphorus sulfide in water to obtain a lithium lanthanum titanium oxide dispersion with a solid content of 45%; Mix the polymer solution and the lithium germanium phosphorus sulfide dispersion evenly. Among them, the mass ratio of polystyrene to lithium germanium phosphorus sulfide is 20:80. Spray-coat the prepared slurry on the surface of the above-mentioned porous carbon-coated silicon-carbon particles. The spraying temperature is 100 °C. After drying, transfer it to an oven at 300 °C and dry for 0.5 h to obtain the silicon-carbon-based composite material.

[0057] Example 7 This example provides a method for preparing a silicon-carbon-based composite material, which specifically includes the following steps: Step a, Transfer the dry water-free porous carbon to the fluidized bed of the gas-phase deposition silicon equipment that discharges air. Heat it to 450 °C at a rate of 5 °C / min. Introduce a mixed gas of nitrogen and silane. The total flow rate is 20 L / min, and the silane concentration is 10%. React for 5 h. Stop introducing silane. Heat it to 550 °C. Introduce acetylene. The acetylene flow rate is 2 L / min, and the introduction time is 2.5 h. Stop introducing acetylene. After stabilizing for 0.5 h, simultaneously introduce acetylene (2 L / min) and silane (0.5 L / min), and the introduction time is 2 h. Stop ventilation and naturally cool to room temperature. Add the obtained material to a 0.5 mol / L sodium hydroxide solution and etch for 8 h. Wash with water until the washing liquid is neutral, and dry in vacuum to obtain porous carbon-coated silicon-carbon particles; Step b, Dissolve polymethyl methacrylate in ethyl acetate to obtain a polymer solution with a solid content of 2%; Ultrasonically disperse lithium lanthanum titanate in water to obtain a lithium lanthanum titanate dispersion with a solid content of 40%; Mix the polymer solution and the lithium lanthanum titanate dispersion evenly. Among them, the mass ratio of polymethyl methacrylate to lithium lanthanum titanate is 60:40. Spray-coat the prepared slurry on the surface of the above-mentioned porous carbon-coated silicon-carbon particles. The spraying temperature is 95 °C. After drying, transfer it to an oven at 200 °C and dry for 2 h to obtain the silicon-carbon-based composite material.

[0058] Example 8 This example provides a method for preparing a silicon-carbon-based composite material, which specifically includes the following steps: Step a, Step a, Transfer the dry water-free porous carbon to the fluidized bed of the gas-phase deposition silicon equipment that discharges air. Heat it to 500 °C at a rate of 10 °C / min. Introduce a mixed gas of nitrogen and silane. The total flow rate is 10 L / min, and the silane concentration is 5%. React for 6 h. Stop introducing silane. Heat it to 520 °C. Introduce acetylene. The acetylene flow rate is 1 L / min, and the introduction time is 3 h. Stop introducing acetylene. After stabilizing for 2 h, simultaneously introduce acetylene (1 L / min) and silane (0.7 L / min), and the introduction time is 3 h. Stop ventilation and naturally cool to room temperature. Add the obtained material to a 0.5 mol / L sodium hydroxide solution and etch for 10 h. Wash with water until the washing liquid is neutral, and dry in vacuum to obtain porous carbon-coated silicon-carbon particles; Step b: Dissolve phenolic resin in water at 80 °C to obtain a polymer solution with a solid content of 1%; ultrasonically disperse lithium phosphonitride in water to obtain a lithium phosphonitride dispersion with a solid content of 45%. Mix the polymer solution and the lithium phosphonitride dispersion evenly. Among them, the mass ratio of phenolic resin to lithium phosphonitride is 95:5. Spray the prepared slurry on the surface of the above-mentioned porous carbon-coated silicon-carbon particles. The spraying temperature is 90 °C. After drying, transfer it to an oven at 150 °C and dry for 4 h to obtain a silicon-carbon-based composite material.

[0059] Example 9 This example provides a method for preparing a silicon-carbon-based composite material, which specifically includes the following steps: Step a: Transfer dry water-free porous carbon to the fluidized bed of a chemical vapor deposition silicon device that discharges air. Heat it to 480 °C at a rate of 7 °C / min. Introduce a mixed gas of nitrogen and silane, with a total flow rate of 30 L / min and a silane concentration of 15%. React for 4 h. Stop introducing silane. Heat it to 620 °C. Introduce acetylene with a flow rate of 3 L / min for 2 h. Stop introducing acetylene. After stabilizing for 1 h, introduce acetylene (3 L / min) and silane (0.3 L / min) simultaneously for 1 h. Stop ventilation and naturally cool to room temperature. Add the obtained material to 1 mol / L sodium hydroxide solution for etching for 6 h. Wash it with water until the washing liquid is neutral, and then dry it under vacuum to obtain porous carbon-coated silicon-carbon particles. Step b: Dissolve styrene-butadiene rubber in acetone to obtain a polymer solution with a solid content of 3%; ultrasonically disperse lithium phosphate in water to obtain a lithium phosphate dispersion with a solid content of 35%. Mix the polymer solution and the lithium phosphate dispersion evenly. Among them, the mass ratio of styrene-butadiene rubber to lithium phosphate is 20:80. Spray the prepared slurry on the surface of the above-mentioned porous carbon-coated silicon-carbon particles. The spraying temperature is 100 °C. After drying, transfer it to an oven at 300 °C and dry for 0.5 h to obtain a silicon-carbon-based composite material.

[0060] Comparative Example 1 This comparative example provides a silicon-carbon-based composite material. The only difference from Example 1 is that only lithium lanthanum titanate is coated on the outermost layer, and no polymer is compounded. The specific steps are as follows: Step a: Exactly the same as Example 1. Step b: Ultrasonically disperse lithium lanthanum titanate in water to obtain a lithium lanthanum titanate dispersion with a solid content of 40%; spray the prepared lithium lanthanum titanate dispersion on the surface of the above-mentioned porous carbon-coated silicon-carbon particles. The spraying temperature is 95 °C. After drying, transfer it to an oven at 200 °C and dry for 2 h to obtain a silicon-carbon-based composite material Comparative Example 2 This comparative example provides a silicon-carbon-based composite material. The only difference from Example 1 is that only a polymer is coated on the outermost layer, and no oxide is compounded. The specific steps are as follows: Step a is exactly the same as that in Example 1; Step b: Dissolve polyethylene oxide polymer in water at 80 °C to obtain a polymer solution with a solid content of 2%. Spray-coat the prepared polymer solution on the surface of the above-mentioned porous carbon-coated silicon-carbon particles. The spraying temperature is 95 °C. After drying, transfer it to an oven at 200 °C and dry for 2 h to obtain the silicon-carbon-based composite material.

[0061] Comparative Example 3 This comparative example provides a silicon-carbon-based composite material. The only difference from Example 1 is that no polymer composite solid electrolyte is coated. The specific steps are as follows: Transfer the dry water-free porous carbon to the fluidized bed of a gas-phase deposition silicon device with air exhausted. Heat it to 450 °C at a rate of 5 °C / min. Pass a mixed gas of nitrogen and silane, with a total flow rate of 20 L / min and an initial concentration of silane of 20%. Reduce it by 4% every 1 h and make it 0% after 5 h. Stop passing silane and heat it to 550 °C. Pass acetylene with a flow rate of 2 L / min for 2.5 h. Stop passing acetylene. After stabilizing for 0.5 h, simultaneously pass acetylene (2 L / min) and silane (0.5 L / min) for 2 h. Stop ventilation and cool it naturally to room temperature. Add the obtained material to 0.5 mol / L sodium hydroxide solution and etch for 8 h. Wash it with water until the washing liquid is neutral, and dry it in vacuum to obtain the silicon-carbon-based composite material.

[0062] Application Example Assemble the silicon-carbon-based composite materials prepared in the above Examples 1 to 9 and Comparative Examples 1 to 3 into batteries respectively. The specific steps are as follows: (1) Preparation of the negative electrode sheet: Add the above-prepared silicon-carbon-based composite material, conductive carbon black Super P, and polyvinylidene fluoride to purified water according to a weight ratio of 70%:15%:15% and mix them at high speed to obtain a black viscous slurry with a solid content of 30%. Coat the black viscous slurry evenly on the surface of the copper foil with a doctor blade to form a film, with a coating areal density of 1 - 2 mg / cm 2 , and then dry it at 105 °C, roll it, cut it into a disc with a diameter of 14 mm, and weigh it for later use.

[0063] (2) Assembly of the lithium-ion battery: Use a metal lithium sheet with a diameter of 15.8 mm and a thickness of 100 μm as the counter electrode, Celgard 2400 with a diameter of 16 mm and a thickness of 25 μm as the separator, and the above-prepared 14 mm negative electrode sheet as the working electrode. Use 1 mol / L LiPF 6A solution dissolved in ethylene carbonate and diethyl carbonate (volume ratio 1:1) was used as the electrolyte to assemble 2032 type button cells. Six cells were assembled for each negative electrode material, and a total of 6 groups of data were tested. After removing the highest and lowest data, the average value of the remaining 4 groups of data was taken as the battery performance data.

[0064] (3) The specific test conditions for the performance of the button cells were as follows: at room temperature of 25 °C, using a Blue Power tester, the assembled button cells were discharged to 0.005 V at 0.1 C (1 C corresponds to 1800 mAh / g) to end the discharge process. After standing for 5 min, they were charged to 1.5 V at 0.1 C for three cycles, and the average value of the discharge specific capacity was taken, that is, the 0.1 C discharge capacity. The ratio of the charge specific capacity to the discharge specific capacity was the first Coulomb efficiency at 1.5 V. The ratio of the discharge specific capacity after 100 cycles of this process to the discharge specific capacity of the first cycle was the 0.1 C discharge capacity retention rate.

[0065] Furthermore, the battery was discharged to 0.005 V at 3 C, and after standing for 5 min, it was continuously charged to 1.5 V at 3 C for 5 cycles, and the average value of the discharge capacity was taken, that is, the 3 C discharge capacity. On the other hand, by testing the ratio of the thickness of the electrode sheet after the first cycle of charging (excluding the thickness of the copper foil) to the thickness of the electrode sheet before cycling (excluding the thickness of the copper foil), the full charge expansion rate in the first week was obtained. The results are shown in Table 1.

[0066] Table 1

[0067] It can be seen from the results that the discharge specific capacity, the first Coulomb efficiency, the capacity retention rate, and the full charge expansion rate in the first week of the lithium-ion batteries with the silicon-carbon composite materials prepared in Examples 1 to 9 of the present invention are all better than those of Comparative Examples 1 to 3 under the same variable comparison system, which proves that using the silicon-carbon material prepared with the porous carbon provided by the present invention as the negative electrode material can significantly improve the electrochemical performance and cycle service life of lithium-ion batteries, and is of great significance for the development of lithium-ion batteries.

[0068] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, or improvements made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A silicon-carbon based composite material, characterized in that: It comprises a silicon-carbon particle layer and a carbon isolation layer and a porous polymer composite solid electrolyte layer sequentially coated on the surface of the silicon-carbon particles from the inside to the outside; The silicon-carbon particles include a porous carbon substrate and silicon particles distributed in the porous carbon substrate; the silicon particles are uniformly distributed in the porous carbon substrate or distributed in a gradient along the radial direction; The carbon isolation layer comprises a non-porous carbon layer and a porous carbon layer from inside to outside.

2. The silicon-carbon based composite material according to claim 1, characterized in that: The silicon-carbon particles include at least one of particles having the following structures: Silicon-carbon particles A1: The content of the silicon particles in the porous carbon substrate decreases gradually along the radial direction from the inside to the outside; wherein, the silicon content in the range of 0 to r / 2 is 40% to 60% of the mass of the silicon-carbon particles, and the silicon content in the range of r / 2 to r is 30% to 50% of the mass of the silicon-carbon particles; Silicon-carbon particles A2: The content of the silicon particles in the porous carbon substrate increases gradually from the inside to the outside along the radial direction; wherein the silicon content in the range of 0 to r / 2 is 30% to 50% of the mass of the silicon-carbon particles, and the silicon content in the range of r / 2 to r is 40% to 60% of the mass of the silicon-carbon particles; Silicon-carbon particles A3: The silicon particles are evenly distributed on the porous carbon substrate; the silicon content is 30% to 60% of the mass of the silicon-carbon particles.

3. The silicon-carbon based composite material according to claim 1 or 2, characterized in that: The thickness of the silicon-carbon particle layer, the carbon isolation layer and the porous polymer composite solid electrolyte layer are all 5nm to 100nm; and / or The D50 of the porous carbon substrate is 2 μm to 20 μm, and the specific surface area is 1000 m 2 / g~2000m 2 / g, the average pore size is 0.5nm~10nm, and the pore volume is 0.6mL / g~1.2mL / g.

4. The silicon-carbon-based composite material according to claim 1, characterized in that: The polymer in the porous polymer composite solid electrolyte is selected from at least one of phenolic resin, acrylamide, polyethylene, polystyrene, polyvinyl alcohol, polyvinyl chloride, polyether, polyester, polyamide, polyurethane, polysulfide rubber, polymethyl methacrylate or styrene-butadiene rubber; and / or The solid electrolyte in the porous polymer composite solid electrolyte is selected from at least one of lithium lanthanum titanium oxide, lithium aluminum titanium phosphate, lithium aluminum germanium phosphate, lithium lanthanum zirconium oxide, lithium germanium phosphosulfide, lithium phosphorus oxygen nitrogen or lithium phosphate.

5. A method for preparing the silicon-carbon based composite material according to any one of claims 1 to 4, characterized in that: The steps include: Step a, depositing silicon particles according to a preset content onto the surface and / or pores of the porous carbon substrate by chemical vapor deposition to obtain silicon-carbon particles; Step b, sequentially performing carbon coating and silicon-carbon composite coating on the silicon-carbon particles, etching away silicon in the silicon-carbon composite layer to obtain a carbon-coated material; Step c, dispersing the solid electrolyte in the polymer aqueous solution, and then using the obtained dispersion to perform secondary coating on the carbon coating material, and drying to obtain a silicon-carbon based composite material.

6. The method for preparing the silicon-carbon based composite material according to claim 5, characterized in that: In step a, the concentration of silane gas is controlled to decrease gradually from the initial 10% to 30% to 0, to obtain silicon-carbon particles A1; wherein the concentration of silane gas is decreased by 2% to 6% every 0.5h to 1.5h, and the concentration is decreased to 0 after 4h to 6h; the total flow rate of silane gas and carrier gas is 10L / min to 30L / min; The concentration of silane gas was controlled to increase gradually from the initial 2% to 6% to 10% to 30%, and silicon-carbon particles A2 were obtained; wherein, the concentration of silane gas increased by 2% to 6% every 0.5h to 1.5h, and the concentration increased to 10% to 30% after 4h to 6h; the total flow rate of silane gas and carrier gas was 10L / min to 30L / min; The concentration of silane gas was controlled to be constant at 5% to 15% during the deposition process to obtain silicon-carbon particles A3; the total flow rate of silane gas and carrier gas was 10 L / min to 30 L / min.

7. A negative electrode, characterized in that The invention comprises the silicon-carbon-based composite material as described in any one of claims 1 to 4.

8. Use of the silicon-carbon-based composite material according to any one of claims 1 to 4 or the negative electrode according to claim 7 in the preparation of a lithium-ion battery.

9. A lithium ion battery, characterized in that: It comprises the silicon-carbon-based composite material according to any one of claims 1 to 4 or the negative electrode according to claim 7.

10. A battery module, characterized in that: Includes the lithium ion battery as claimed in claim 9.

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