A silicon-carbon based composite material, a preparation method thereof, and applications thereof in lithium ion batteries

Abstract

The present invention relates to the technical field of lithium-ion batteries, and specifically discloses a silicon-carbon composite material, a preparation method thereof, and an application in lithium-ion batteries. In the present invention, silicon-carbon particles with different silicon content distributions are obtained by controlling the concentration of silicon particle deposition. An amorphous carbon layer and a silicon-carbon composite layer are sequentially deposited on the surface of the silicon-carbon particles, and the silicon in the silicon-carbon composite layer is etched away to obtain a porous carbon layer. Finally, a porous polymer composite solid electrolyte layer is coated. The amorphous carbon layer has a relatively dense structure, which can effectively inhibit the volume change of silicon particles during charge and discharge, and prevent the silicon particles from breaking and falling off during the cycle; the porous carbon layer effectively increases the specific surface area of the material, opening up more paths for lithium-ion storage and transmission; the outermost porous polymer composite solid electrolyte layer can not only uniformly coat the silicon-carbon particles, but also its porous structure can improve its compatibility with the electrolyte, thereby significantly improving the high-temperature, fast-charging and cycle stability of the material.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium - ion batteries, and particularly to a silicon - carbon - based composite material, a preparation method thereof, and an application 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, due to their ultra - high theoretical specific capacity of up to 4200 mAh / g, show great potential as the next - generation anode materials for lithium - ion batteries and have become a hot research direction in recent years. However, silicon anode materials face severe challenges in practical applications. During charge - discharge processes, silicon anodes will experience extremely significant volume expansion phenomena, and their volume expansion rate can exceed 300%. Such a large - scale 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, leading to 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 charge - discharge processes 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, with its unique advantages, has become the most commonly used method for preparing silicon - carbon composite materials at present. 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 - discharge, thus significantly improving the overall performance of the battery.

[0005] 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 for current such materials. For example, the expansion is still large, the cycle performance is not good, and the rate performance needs to be improved, etc. It is difficult to meet the requirements of high capacity, fast charging, long cycle life, and low expansion simultaneously. Therefore, developing a new - structure silicon - carbon anode material to overcome the above problems has become a technical problem that needs to be urgently solved by those skilled in the art. Summary of the Invention

[0006] In view of 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 lithium-ion batteries. By sequentially coating a carbon isolation layer and a porous polymer composite solid electrolyte layer outside the silicon-carbon material with a specific structure, the silicon-carbon composite material of the present invention 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.

[0007] To solve the above technical problems, the technical solution provided by the present invention is:

[0008] In the first aspect, the present invention provides a silicon-carbon-based composite material, comprising a silicon-carbon particle layer, and a carbon isolation layer and a porous polymer composite solid electrolyte layer that are sequentially coated on the surface of the silicon-carbon particles from the inside to the outside;

[0009] Among them, 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;

[0010] The carbon isolation layer includes a non-porous carbon layer and a porous carbon layer from the inside to the outside.

[0011] Compared with the prior art, in the silicon-carbon-based composite material provided by the present invention, the content of the 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 enhance the performance of the silicon-carbon material. When the silicon-carbon particles exhibit 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, enabling the lithium ions captured in the middle region to be quickly transferred to the external circuit, reducing the resistance of charge transmission, and greatly improving the overall charging speed.

[0012] If it is a structure with 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 improve 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.

[0013] 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.

[0014] 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.

[0015] 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.

[0016] Furthermore, the silicon-carbon particles include at least one of the particles having the following structures:

[0017] 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;

[0018] 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;

[0019] 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.

[0020] It should be noted that when the above-mentioned various silicon-carbon particles are used in combination, the compounding ratio can be adjusted according to specific performance requirements. The specific ratio can be obtained through conventional tests, and the present invention does not make special limitations.

[0021] Furthermore, 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.

[0022] Furthermore, 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.

[0023] Furthermore, 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.

[0024] Furthermore, the solid electrolyte in the porous polymer composite solid electrolyte is selected from at least one of lithium lanthanum titanium oxide (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).

[0025] 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.

[0026] In a second aspect, the present invention provides a method for preparing a silicon-carbon-based composite material, comprising the following steps:

[0027] Step a, depositing silicon particles onto the surface and / or pores of the porous carbon substrate according to a preset content by chemical vapor deposition to obtain silicon-carbon particles;

[0028] 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;

[0029] 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 a silicon-carbon-based composite material.

[0030] Specifically, in step b, after the silicon carbide particles are coated with a carbon source gas, they are further coated with a silicon-carbon composite coating using a carbon source gas and a silane gas. Then, the obtained material is placed in a strong alkali solution to etch away the silicon in the silicon-carbon composite coating, resulting in a porous carbon-coated material.

[0031] Specifically, in step c, the dispersion liquid is coated on the surface of the porous carbon-coated material by spray drying.

[0032] 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 the silicon in the silicon-carbon composite layer is further etched away with an 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 cycling process, 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 cycling 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, having excellent structural stability, but also its porous structure can increase the contact area between the silicon-carbon particles and the electrolyte, improving its compatibility with the electrolyte, thus significantly improving the high-temperature, fast-charging and cycling stability of the material.

[0033] The present invention significantly improves the capacity, cycling stability and fast-charging performance of the silicon-carbon material by coating the silicon-carbon particles with a specific three-layer structure, showing broad application prospects in the field of lithium-ion batteries.

[0034] As a specific embodiment of the present invention, the preparation method of the silicon-carbon-based composite material specifically includes the following steps:

[0035] In step a, the porous carbon is placed in a chemical vapor deposition silicon device, an inert gas is introduced to discharge the oxygen in the device, the temperature is raised to 450°C to 500°C, and a silane gas is introduced. The concentration of the silane gas during deposition is controlled according to the set silicon content to complete the preparation of the silicon-carbon particles.

[0036] Step b: Introduce a carbon source gas into the chemical vapor deposition silicon device. Control the temperature at 520°C - 620°C. After reacting for 2 h - 3 h, stop introducing the carbon source gas. After stabilizing for 0.5 h - 2 h, introduce the carbon source gas and silane gas simultaneously. After reacting for 1 h - 3 h, stop the gas supply and cool down to room temperature. Add the obtained material to a strong alkali solution for etching and washing to obtain silicon-carbon particles coated with porous carbon.

[0037] Step c: Add a solid electrolyte to an aqueous polymer solution and disperse it evenly to obtain a slurry. Spray-coat the slurry on the surface of the silicon-carbon particles coated with porous carbon and dry to obtain a silicon-carbon-based composite material.

[0038] Further, in step a, control the concentration of silane gas to gradually decrease from an initial 10% - 30% to 0 to obtain silicon-carbon particles A1. Among them, the concentration of silane gas decreases by 2% - 6% every 0.5 h - 1.5 h and decreases to 0 after 4 h - 6 h. The total flow rate of silane gas and carrier gas is 10 L / min - 30 L / min.

[0039] Further, control the concentration of silane gas to gradually increase from an initial 2% - 6% to 10% - 30% to obtain silicon-carbon particles A2. Among them, the concentration of silane gas increases by 2% - 6% every 0.5 h - 1.5 h and increases to 10% - 30% after 4 h - 6 h. The total flow rate of silane gas and carrier gas is 10 L / min - 30 L / min.

[0040] Further, control the concentration of silane gas to be constant at 5% - 15% during the deposition process and react for 4 h - 6 h to obtain silicon-carbon particles A3. The total flow rate of silane gas and carrier gas is 10 L / min - 30 L / min.

[0041] Further, in step a, the inert gas is one or more of nitrogen, argon, helium, or carbon dioxide.

[0042] Further, in step a, the silane gas is one or more of silane, disilane, dichlorosilane, or trichlorosilane.

[0043] Preferably, in step a, the silane gas is silane or disilane.

[0044] 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.

[0045] Further, in step b, the carbon source gas is one or more of methane, ethane, propane, butane, ethylene, propylene, acetylene, or propyne.

[0046] Preferably, in step b, the carbon source gas is ethylene or acetylene.

[0047] Further, in step b, the flow rate of the carbon source gas is 1 L / min to 3 L / min.

[0048] Further, in step b, the flow rate of the silane gas is 0.3 L / min to 0.7 L / min.

[0049] Further, in step b, the strong base solution is a sodium hydroxide solution with a concentration of 0.3 mol / L to 1 mol / L.

[0050] Further, in step c, the solid content of the polymer aqueous solution is 1% to 3%.

[0051] Further, in step c, the solid content of the slurry is 35% to 45%.

[0052] Further, in step c, the mass ratio of the polymer to the solid electrolyte is (5% to 80%):(95% to 20%), and the sum of the masses of the polymer and the solid electrolyte is 100%.

[0053] Further, in step c, the temperature of the spray is 90°C to 100°C.

[0054] Further, in step c, the temperature of the drying is 150°C to 300°C, and the drying time is 0.5 h to 4 h.

[0055] Thirdly, the present invention also provides a negative electrode comprising the silicon-carbon based composite material described above.

[0056] Fourthly, the present invention also provides the use of the above-mentioned silicon-carbon based composite material or the above-mentioned negative electrode in the preparation of a lithium-ion battery.

[0057] Fifthly, the present invention also provides a lithium-ion battery comprising the above-mentioned silicon-carbon based composite material or the above-mentioned negative electrode.

[0058] Sixthly, the present invention also provides a battery module comprising the above-mentioned lithium-ion battery.

[0059] 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-mentioned 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 relying 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. Description of the Drawings

[0060] Figure 1TEM image of the silicon-carbon composite material prepared in Example 1 of the present invention;

[0061] Figure 2 TEM image of the silicon-carbon composite material prepared in Example 4 of the present invention;

[0062] Figure 3 TEM image of the silicon-carbon composite material prepared in Example 7 of the present invention;

[0063] Figure 4 Schematic structural diagrams of different silicon-carbon particles A1, A2, and A3 prepared by the present invention. Detailed implementation manners

[0064] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to 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.

[0065] To better illustrate the present invention, further examples are given below by way of embodiments.

[0066] 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.

[0067] Example 1

[0068] This example provides a preparation method of a silicon-carbon composite material, which specifically includes the following steps:

[0069] 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, introduce a mixed gas of nitrogen and silane, the total flow rate is 20 L / min, the initial concentration of silane is 20%, reduce it by 4% every 1 h, and make it 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, introduce acetylene (2 L / min) and silane (0.5 L / min) simultaneously, 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 with water until the washing liquid is neutral, and dry it under vacuum to obtain porous carbon-coated silicon-carbon particles;

[0070] Step b: Dissolve the 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 liquid with a solid content of 40%;

[0071] Mix the polymer solution and the lithium lanthanum titanium oxide dispersion evenly, where the mass ratio of polyethylene oxide polymer to lithium lanthanum titanium oxide is 40:60. 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.

[0072] Example 2

[0073] This example provides a method for preparing a silicon-carbon-based composite material, which specifically includes the following steps:

[0074] 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 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 and an initial silane concentration of 30%. Reduce it by 6% every 1 h until it 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, simultaneously introduce acetylene (3 L / min) and silane (0.7 L / min) for 1 h. Stop ventilation and naturally cool to room temperature. Add the obtained material to a 1 mol / L sodium hydroxide solution and etch 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.

[0075] 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%.

[0076] Mix the polymer solution and the lithium aluminum titanium phosphate dispersion evenly, where 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 for 4 h to obtain the silicon-carbon-based composite material.

[0077] Example 3

[0078] This example provides a method for preparing a silicon-carbon-based composite material, which specifically includes the following steps:

[0079] 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 a 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;

[0080] 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%;

[0081] Mix the polymer solution and the lithium aluminum germanium phosphate dispersion evenly. 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 it for 0.5 h to obtain a silicon-carbon-based composite material.

[0082] Example 4

[0083] This example provides a method for preparing a silicon-carbon-based composite material, which specifically includes the following steps:

[0084] 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 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. The initial concentration of silane is 4%, which increases by 4% every 1 h and becomes 20% after 5 h. Stop introducing silane. Heat it to 550 °C and introduce acetylene with a flow rate of 2 L / min for 2.5 h. Stop introducing acetylene. After stabilizing for 0.5 h, introduce acetylene (2 L / min) and silane (0.5 L / min) simultaneously for 2 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 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;

[0085] 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%;

[0086] Mix the polymer solution and the lithium lanthanum titanium oxide dispersion evenly. Among them, the mass ratio of polyurethane to lithium lanthanum titanium oxide is 80:20. Spray and 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 a silicon-carbon-based composite material.

[0087] Example 5

[0088] This example provides a method for preparing a silicon-carbon-based composite material, which specifically includes the following steps:

[0089] 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 480 °C at a rate of 8 °C / min. Pass in a mixed gas of nitrogen and silane. The total flow rate is 30 L / min. The initial concentration of silane is 2%. Increase it by 6% every 1 h and reach 20% after 4 h. Stop passing in silane. Heat it to 520 °C. Pass in acetylene. The flow rate of acetylene is 1 L / min and the passing time is 3 h. Stop passing in acetylene. After stabilizing for 2 h, simultaneously pass in acetylene (2 L / min) and silane (0.3 L / min). The passing 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 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;

[0090] 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%;

[0091] 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 and 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 for 4 h to obtain a silicon-carbon-based composite material.

[0092] Example 6

[0093] This example provides a method for preparing a silicon-carbon-based composite material, which specifically includes the following steps:

[0094] 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 and an initial silane concentration of 6%. Increase the concentration by 2% every 1 h until it reaches 18% after 6 h. Stop introducing silane, heat up to 620 °C, introduce acetylene with a flow rate of 3 L / min for 2 h. Stop introducing acetylene. After stabilizing for 1 h, simultaneously introduce acetylene (3 L / min) and silane (0.7 L / min) for 1 h. Stop gas introduction and let it cool naturally to room temperature. Add the obtained material to 1.0 mol / L sodium hydroxide solution for etching for 6 h, wash with water until the washing liquid is neutral, and dry under vacuum to obtain porous carbon-coated silicon-carbon particles;

[0095] 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%;

[0096] Mix the polymer solution and the lithium germanium phosphorus sulfide dispersion evenly. 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 a silicon-carbon-based composite material.

[0097] Example 7

[0098] This example provides a method for preparing a silicon-carbon-based composite material, which specifically includes the following steps:

[0099] 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 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 a silane concentration of 10%. React for 5 h. Stop introducing silane, heat up to 550 °C, introduce acetylene with a flow rate of 2 L / min for 2.5 h. Stop introducing acetylene. After stabilizing for 0.5 h, simultaneously introduce acetylene (2 L / min) and silane (0.5 L / min) for 2 h. Stop gas introduction and let it cool naturally to room temperature. Add the obtained material to 0.5 mol / L sodium hydroxide solution for etching for 8 h, wash with water until the washing liquid is neutral, and dry under vacuum to obtain porous carbon-coated silicon-carbon particles;

[0100] Step b: Dissolve polymethyl methacrylate in ethyl acetate 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%;

[0101] Mix the polymer solution and the lithium lanthanum titanium oxide dispersion evenly, where the mass ratio of polymethyl methacrylate to lithium lanthanum titanium oxide 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.

[0102] Example 8

[0103] This example provides a method for preparing a silicon-carbon-based composite material, which specifically includes the following steps:

[0104] 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 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 and a silane concentration of 5%. React for 6 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, simultaneously introduce acetylene (1 L / min) and silane (0.7 L / min) for 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 then dry it under vacuum to obtain porous carbon-coated silicon-carbon particles.

[0105] Step b: Dissolve phenolic resin in water at 80°C to obtain a polymer solution with a solid content of 1%; ultrasonically disperse lithium phosphorus oxynitride in water to obtain a lithium phosphorus oxynitride dispersion with a solid content of 45%.

[0106] Mix the polymer solution and the lithium phosphorus oxynitride dispersion evenly, where the mass ratio of phenolic resin to lithium phosphorus oxynitride 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 for 4 h to obtain the silicon-carbon-based composite material.

[0107] Example 9

[0108] This example provides a method for preparing a silicon-carbon-based composite material, which specifically includes the following steps:

[0109] Step a: Transfer the dry and water-free porous carbon to the fluidized bed of a gas-phase deposition silicon equipment with air exhausted. 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 an acetylene 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 gas introduction, and naturally cool to room temperature. Add the obtained material to 1 mol / L sodium hydroxide solution for etching for 6 h, wash with water until the washing liquid is neutral, and dry in vacuum to obtain porous carbon-coated silicon-carbon particles;

[0110] 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%;

[0111] 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-coat the prepared slurry on the surface of the above-mentioned porous carbon-coated silicon-carbon particles, with a spray temperature of 100 °C, and transfer it to an oven at 300 °C for drying for 0.5 h after drying to obtain a silicon-carbon-based composite material.

[0112] Comparative Example 1

[0113] This comparative example provides a silicon-carbon-based composite material. The only difference from Example 1 is that the outermost coating is only lithium lanthanum titanium oxide and no polymer is compounded. The specific steps are as follows:

[0114] Step a: It is exactly the same as that in Example 1;

[0115] Step b: Ultrasonically disperse lithium lanthanum titanium oxide in water to obtain a lithium lanthanum titanium oxide dispersion with a solid content of 40%; spray-coat the prepared lithium lanthanum titanium oxide dispersion on the surface of the above-mentioned porous carbon-coated silicon-carbon particles, with a spray temperature of 95 °C, and transfer it to an oven at 200 °C for drying for 2 h after drying to obtain a silicon-carbon-based composite material

[0116] Comparative Example 2

[0117] This comparative example provides a silicon-carbon-based composite material. The only difference from Example 1 is that the outermost coating is only polymer and no oxide is compounded. The specific steps are as follows:

[0118] Step a: It is exactly the same as that in Example 1;

[0119] Step b: Dissolve the 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.

[0120] Comparative Example 3

[0121] This comparative example provides a silicon-carbon-based composite material. The only difference from Example 1 is that the coating of the polymer composite solid electrolyte is not carried out. The specific steps are as follows:

[0122] Transfer the dried 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. Introduce a mixed gas of nitrogen and silane. The total flow rate is 20 L / min. The initial concentration of silane is 20%. Every 1 h, it is reduced by 4%. After 5 h, it becomes 0%. Stop introducing silane. Heat it to 550 °C. Introduce acetylene. The flow rate of acetylene is 2 L / min. 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). The introduction time is 2 h. Stop ventilation. Naturally cool 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. Dry it in vacuum to obtain the silicon-carbon-based composite material.

[0123] Application Example

[0124] 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:

[0125] (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 in 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. The coating surface density is 1 - 2 mg / cm 2 , and then dry it at 105 °C, roll it, cut it into a round sheet with a diameter of 14 mm, and weigh it for use.

[0126] (2) Assembly of lithium-ion batteries: A metallic lithium sheet with a diameter of 15.8 mm and a thickness of 100 μm was used as the counter electrode, Celgard 2400 with a diameter of 16 mm and a thickness of 25 μm was used as the separator, and the prepared 14-mm negative electrode sheet was used as the working electrode. A solution of 1 mol / L LiPF6 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 six groups of data were tested. After removing the highest and lowest data, the average value of the remaining four groups of data was taken as the battery performance data.

[0127] (3) The specific test conditions for the performance of button cells are 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 and cycled three times. 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 is 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 time is the 0.1 C discharge capacity retention rate.

[0128] Further, 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 and cycled five times. 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.

[0129] Table 1

[0130]

[0131] It can be seen from the results that the discharge specific capacity, first Coulomb efficiency, capacity retention rate, and full-charge expansion rate in the first week of the lithium-ion batteries with the silicon-carbon-based composite materials prepared in Examples 1 to 9 of the present invention are all superior to 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.

[0132] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modification, equivalent replacement, or improvement 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 includes a silicon-carbon particle layer, a carbon isolation layer coated on the surface of the silicon-carbon particles in sequence from the inside to the outside, and a porous polymer composite solid electrolyte layer; Among them, 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 shows a gradient distribution 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.

2. The silicon-carbon-based composite material according to claim 1, wherein The silicon-carbon particles include at least one of the particles with 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.

3. The silicon-carbon-based composite material according to claim 1 or 2, characterized in that, 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; and / or 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.

4. The silicon-carbon based composite material according to claim 1, wherein 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 titanate, lithium aluminum titanium phosphate, lithium aluminum germanium phosphate, lithium lanthanum zirconium oxide, lithium germanium phosphorus sulfide, lithium phosphorus oxynitride, or lithium phosphate.

5. The preparation method of the silicon-carbon-based composite material according to any one of claims 1 to 4, characterized in that, It includes 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 a silicon-carbon-based composite material.

6. The preparation method of the silicon-carbon-based composite material according to claim 5, wherein, In step a, controlling the concentration of silane gas to decrease in a gradient from an initial 10% to 30% to 0 to obtain silicon-carbon particle A1; among them, the concentration of silane gas decreases by 2% to 6% every 0.5 h to 1.5 h, and the concentration decreases to 0 in 4 h to 6 h; the total flow rate of the silane gas and the carrier gas is 10 L / min to 30 L / min; Controlling the concentration of silane gas to increase in a gradient from an initial 2% to 6% to 10% to 30% to obtain silicon-carbon particle A2; among them, the concentration of silane gas increases by 2% to 6% every 0.5 h to 1.5 h, and the concentration increases to 10% to 30% in 4 h to 6 h; the total flow rate of the silane gas and the carrier gas is 10 L / min to 30 L / min; During the deposition process, the concentration of silane gas is kept constant at 5% - 15% to obtain silicon-carbon particles A3; the total flow rate of silane gas and carrier gas is 10 L / min - 30 L / min.

7. A negative electrode, characterized in that, Comprising the silicon-carbon based composite material according to 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, Comprising 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, Comprising the lithium-ion battery according to claim 9.

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