A boron-doped porous carbon gas-phase silicon-carbon composite negative electrode material and a preparation method thereof

Abstract

The present application relates to a new type of negative electrode material for lithium ion batteries, and particularly relates to a boron-doped porous carbon gas-phase silicon-carbon composite negative electrode material and a preparation method thereof. The boron-doped porous carbon gas-phase silicon-carbon composite negative electrode material is prepared by mixing a resin with a template agent, doping a boron source, adding a spheroidizing agent and an initiator for spheroidization polymerization, removing impurities and drying, and then performing gas-phase etching to form pores. Silicon is deposited in the pores of the porous carbon and a carbon layer is deposited on the surface of the silicon-carbon precursor by twice chemical vapor deposition, so as to obtain the boron-doped porous carbon gas-phase silicon-carbon composite negative electrode material. The boron element is doped to optimize the electronic conductivity, the spheroidized porous carbon structure is improved to improve the lithium ion transmission channel and enhance the substrate stiffness, and the material has excellent performance of high rate, low expansion and long cycle, so as to solve the problems of insufficient rate performance, low substrate strength and blocked lithium ion transmission of the existing gas-phase silicon-carbon composite negative electrode material in the prior art.

Description

Technical Field

[0001] This invention relates to the field of novel anode technology for lithium-ion batteries, and in particular to a boron-doped porous carbon vapor-phase silicon-carbon composite anode material and its preparation method. Background Technology

[0002] With the continuous development of lithium-ion battery technology, graphite materials, due to their low capacity, can no longer meet the requirements of high energy density systems. The ultra-high capacity micron-sized silicon anode (Si) results in enormous volume expansion during battery charging and discharging, making it impractical in engineering. Therefore, silicon suboxide (SiO2) is being considered as a next-generation alternative. x SiO₂ was proposed as an alternative. However, SiO₂... x Due to its extremely high specific surface area, the side reactions generated during charging and discharging result in significant electrolyte consumption, thus reducing battery life. Therefore, researchers are studying SiO₂... x Pre-lithiation treatment is performed, followed by secondary coating to reduce its specific surface area, resulting in a pre-lithiated silicon-oxygen anode (Pre-SiO2). x (x~1), in improving SiO x While improving stability, it also makes it more feasible for engineering. However, Pre-SiO x There are gas-generating side reactions that affect the long-cycle performance of the battery.

[0003] To address the aforementioned issues, researchers used biomass-based materials (such as coconut shells, rice husks, and petroleum coke) and employed physical and chemical methods to obtain biomass porous carbon materials. They then used chemical vapor deposition to deposit nano-Si into the pores of the porous carbon, forming amorphous floating Si. After a secondary coating of the porous carbon with the floating Si deposited, a novel vapor-phase silicon-carbon composite anode material was obtained.

[0004] Vapor-phase silicon-carbon composite anode materials (Si / C, 1800~2000 mAh / g) exhibit excellent initial efficiency and 1C charge-discharge cycle performance when used as anodes in lithium-ion batteries. However, when applied in the 3C digital field, their fast-charging and fast-discharging performance is limited by the poor performance of porous carbon precursors. This is because biomass porous carbon is prepared by vapor etching, resulting in uneven pore size and uncontrollable pore curvature. This leads to the formation of Si-Si crystals rather than amorphous silicon during nano-silicon deposition, reducing the actual lithium storage capacity. Simultaneously, surface tension in some pores hinders the entry of silane gas, causing silicon to deposit only on the carbon material surface, further affecting performance. Furthermore, during charge and discharge, the pore size and pore curvature of the porous carbon prevent lithium ions from quickly passing through the tortuous channels, resulting in electrochemical hysteresis relaxation, leading to poor rate performance of the Si / C anode, even significantly lower than that of traditional graphite anodes. Additionally, biomass carbon materials are typically in bulk particles with low mechanical strength, making them unable to resist the expansion of Si during cycling.

[0005] Therefore, there is an urgent need to develop a Si / C anode material that combines high lithium-ion conductivity, high matrix stiffness, and excellent rate performance. Summary of the Invention

[0006] The purpose of this invention is to provide a boron-doped porous carbon vapor-phase silicon-carbon composite anode material and its preparation method. By doping with boron, the electronic conductivity is optimized, and the spheroidized porous carbon structure improves the lithium-ion transport channel and enhances the matrix stiffness, thereby achieving excellent performance of high rate capability, low expansion, and long cycle life. This solves the problems of insufficient rate capability, low matrix strength, and hindered lithium-ion transport in existing vapor-phase silicon-carbon composite anode materials.

[0007] To achieve the above objectives, the present invention provides a method for preparing a boron-doped porous carbon fumed silicon-carbon composite anode material, comprising the following steps:

[0008] S1. Dissolve the resin in an organic solvent, add the template agent and stir at room temperature, then add the boron source, heat and stir to obtain a boron-containing prepolymer precursor;

[0009] S2. Add a spheroidizing agent and an initiator to the boron-containing prepolymer precursor of S1 to carry out a spheroidization polymerization reaction. After washing and drying, the boronized resin porous spheres are obtained.

[0010] S3. The boronized resin porous spheres from S2 are etched in a CVD tube furnace to create pores, and then purified and dried to obtain boron-doped spherical porous carbon.

[0011] S4. Using ammonia as a carrier, silane gas is introduced to deposit silicon in the boron-doped spherical porous carbon pores obtained in S3, thus obtaining a boron-doped porous carbon silicon-carbon precursor.

[0012] S5. Under an inert gas atmosphere, a secondary chemical vapor deposition is performed using an activated carbon source to deposit a carbon layer on the surface of the boron-doped porous carbon silicon-carbon precursor obtained in S4, thereby obtaining a boron-doped porous carbon vapor-phase silicon-carbon composite anode material.

[0013] Preferably, in S1, the resin is one or more of phenolic resin, furfural resin, epoxy resin, polyurethane resin, polystyrene resin, polyester resin, polyethylene terephthalate resin, and polyvinyl chloride resin; the organic solvent is toluene or xylene, and the mass ratio of resin to organic solvent is 0.4~0.6:1.5~2.

[0014] Preferably, in S1, the template agent is one or more of polyvinyl alcohol, polystyrene, and polyacrylonitrile, the amount of template agent added is 1.5-2.5 times the mass of the resin, the stirring speed at room temperature is 500-700 r / min, and the stirring time is 1-2 h.

[0015] Preferably, in S1, the boron source is one or more of boric acid, sodium borate, sodium borohydride, silicon borate, and boron trifluoride ethylamine. The amount of boron source added is 4-6% of the resin mass. The heating and stirring temperature is 40-50℃, the rotation speed is 1500-2000 r / min, and the stirring time is 2-4 h.

[0016] Preferably, in S2, the spheroidizing agent is one or more of cetyltrimethylammonium bromide, polyvinyl alcohol, sodium alginate, N-methylpyrrolidone, and polyvinylpyrrolidone, and the amount of spheroidizing agent added is 2-3% of the resin mass; the initiator is one or more of benzoyl peroxide, diethylamine, and azobisisobutyronitrile, and the amount of initiator added is 2-3% of the resin mass.

[0017] Preferably, in S2, the temperature of the spheroidization polymerization reaction is 60~80℃, the stirring speed of the pre-spheroidization in the spheroidization polymerization reaction is 1800r / min, and the stirring speed of the polymerization reaction is 800-1000r / min.

[0018] Preferably, in S3, the gas used for vapor phase etching to create holes is one or more of boric acid, borate, sodium borohydride, and boron trifluoride ethylamine, the CVD tube furnace temperature is 150~200℃, and the etching time is 11-13h.

[0019] Preferably, in S4, the flow ratio of ammonia to silane is 1:1-1.2, and the deposition temperature is 540-560℃.

[0020] Preferably, in S5, the active carbon source is one or more of methane, ethane, ethylene, acetylene, and propyne, and the temperature of the secondary chemical vapor deposition is 600~1000℃.

[0021] The present invention also provides a boron-doped porous carbon vapor phase silicon-carbon composite anode material, which is prepared by the above-mentioned preparation method of the boron-doped porous carbon vapor phase silicon-carbon composite anode material.

[0022] Mechanism of the invention:

[0023] This invention involves in-situ polymerization of a boron source and resin material, doping the porous carbon material before its preparation to obtain intrinsically boron-doped porous carbon. Furthermore, a secondary etching process using a boron-containing gas is employed to re-etch boron into the pores and channels, creating holes in the carbon matrix and enhancing electronic conductivity, thereby optimizing lithium-ion transport within the porous carbon channels. The resin-based carbon material is then spheroidized and polymerized using a spheroidizing agent, followed by washing away the template agent with an organic solvent to create pores. After impurity removal, silicon vapor deposition is performed to obtain a vapor-phase silicon-carbon composite anode material based on porous spherical carbon. The spherical structure of the porous carbon shortens the lithium-ion transport path, the uniform pore size ensures uniform silicon deposition, and the vapor-phase etching further enhances channel connectivity and reduces ion diffusion resistance. The resin-based spherical carbon matrix buffers silicon volume expansion, and the secondary carbon coating isolates the electrolyte, strengthens the silicon-carbon bond, and reduces side reactions and structural damage.

[0024] Therefore, the present invention employs the above-mentioned boron-doped porous carbon fumed silicon-carbon composite anode material and its preparation method, which have the following beneficial effects:

[0025] (1) This invention uses raw materials containing boron sources, which are fully mixed with resin and template agent under the shearing and stirring action of a high-speed homogenizer. Spheroidization polymerization is carried out under the action of spheroidizing agent and initiator. After impurity removal, silicon-carbon vapor deposition is performed and then secondary coating is performed to obtain boron-doped porous carbon vapor phase silicon-carbon composite anode material (Si / C@B material). The lithium-ion transport capability is optimized, and a Si / C@B material with high lithium-ion flux is prepared. Compared with ordinary biomass Si / C material, the battery assembled with Si / C@B material has good rate performance at 3C rate and good cycle stability at 2C charging / 1C discharging, providing a better fast-charging anode for 3C digital products such as drones, mobile phones, and laptops.

[0026] (2) The boron-doped porous carbon vapor phase silicon-carbon composite anode material prepared by the present invention has outstanding high rate performance, which meets the fast charging requirements of 3C digital devices; high lithium-ion diffusion efficiency, taking into account both high rate and high capacity; extended cycle life, low electrode expansion rate and stable structure; balanced first efficiency and capacity, and excellent performance when matched with high nickel cathode; simple and controllable process, suitable for industrial production.

[0027] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0028] Figure 1 This is a SEM characterization image of the Si / C@B material prepared in Example 1 of this invention;

[0029] Figure 2 These are XPS characterization images of the Si / C@B material prepared in Example 1 of this invention. Figure 2(a) in the diagram is the silicon 2P orbital energy level spectrum. Figure 2 (b) in the diagram is the orbital spectrum of the boron 1s level;

[0030] Figure 3 This is a comparison diagram of the lithium diffusion coefficients of CR2016 batteries assembled from Si / C@B material in Example 1 and Si / C material in Comparative Example 1.

[0031] Figure 4 This is a comparison chart of the rate performance of CR2016 batteries assembled with Si / C@B material in Example 1 and Si / C material in Comparative Example 1.

[0032] Figure 5 The Si / C@B material in Example 1 and the Si / C material in Comparative Example 1 are compared with LiNi. 0.9 Co 0.04 Mn 0.06 Comparison chart of rate performance of CR2016 type batteries assembled with O2;

[0033] Figure 6 The Si / C@B material in Example 1 and the Si / C material in Comparative Example 1 are respectively used with LiNi 0.9 Co 0.04 Mn 0.06 First-efficiency comparison of CR2016 type batteries assembled with O2;

[0034] Figure 7 The Si / C@B anode in Example 1 and the Si / C anode in Comparative Example 1 are respectively reacted with LiNi 0.9 Co 0.04 Mn 0.06 Comparison of cycle performance of 1Ah soft-pack battery cells assembled with O2;

[0035] Figure 8 The Si / C@B anode in Example 1 and the Si / C anode in Comparative Example 1 are respectively reacted with LiNi 0.9 Co 0.04 Mn 0.06 Comparison of the expansion performance of the electrode plates when fully charged in a 1Ah soft-pack battery assembled with O2. Detailed Implementation

[0036] The present invention will be further described below with reference to the accompanying drawings and embodiments. Unless otherwise defined, the technical or scientific terms used in this invention should be understood in their ordinary sense by those skilled in the art. The features mentioned above or in the specific examples mentioned in this invention can be combined arbitrarily, and these specific embodiments are only used to illustrate the invention and are not intended to limit the scope of the invention.

[0037] This invention provides a method for preparing a boron-doped porous carbon fumed silicon-carbon composite anode material, comprising the following steps:

[0038] S1. Dissolve the resin in an organic solvent, add the template agent and stir at room temperature, then add the boron source, heat and stir to obtain a boron-containing prepolymer precursor;

[0039] S2. Add a spheroidizing agent and an initiator to the boron-containing prepolymer precursor of S1 to carry out a spheroidization polymerization reaction. After washing and drying, the boronized resin porous spheres are obtained.

[0040] S3. The boronized resin porous spheres from S2 are etched in a CVD tube furnace to create pores, and then purified and dried to obtain boron-doped spherical porous carbon.

[0041] S4. Using ammonia as a carrier, silane gas is introduced to deposit silicon in the boron-doped spherical porous carbon pores obtained in S3, thus obtaining a boron-doped porous carbon silicon-carbon precursor.

[0042] S5. Under an inert gas atmosphere, a secondary chemical vapor deposition is performed using an activated carbon source to deposit a carbon layer on the surface of the boron-doped porous carbon silicon-carbon precursor obtained in S4, thereby obtaining a boron-doped porous carbon vapor-phase silicon-carbon composite anode material.

[0043] This invention is based on resin-based porous carbon spheres, and introduces a boron source during the preparation of the resin-based porous spheres. Boron, as a P-type dopant, can introduce holes to enhance the electronic conductivity of silicon-carbon composite anode materials, thereby improving the electron conduction capability. This makes the synergistic effect between electrons and lithium ions more efficient during charging and discharging, thus helping to improve the overall rate performance and charge-discharge efficiency of the battery.

[0044] Preferably, in S1, the resin is one or more of phenolic resin, furfural resin, epoxy resin, polyurethane resin, polystyrene resin, polyester resin, polyethylene terephthalate resin, and polyvinyl chloride resin; the organic solvent is toluene or xylene, and the mass ratio of resin to organic solvent is 0.4~0.6:1.5~2.

[0045] Preferably, in S1, the template agent is one or more of polyvinyl alcohol, polystyrene, and polyacrylonitrile, the amount of template agent added is 1.5-2.5 times the mass of the resin, the stirring speed at room temperature is 500-700 r / min, and the stirring time is 1-2 h.

[0046] The present invention controls the amount of template agent within the above range to obtain porous spherical carbon with a pore size distribution range of about 2~10nm.

[0047] Preferably, in S1, the boron source is one or more of boric acid, sodium borate, sodium borohydride, silicon borate, and boron trifluoride ethylamine. The amount of boron source added is 4-6% of the resin mass. The heating and stirring temperature is 40-50℃, the rotation speed is 1500-2000 r / min, and the stirring time is 2-4 h.

[0048] This invention controls the amount of boron source within the above-mentioned range to obtain a carbon substrate with fast lithium-ion conduction properties.

[0049] Preferably, in S2, the spheroidizing agent is one or more of cetyltrimethylammonium bromide, polyvinyl alcohol, sodium alginate, N-methylpyrrolidone, and polyvinylpyrrolidone, and the amount of spheroidizing agent added is 2-3% of the resin mass; the initiator is one or more of benzoyl peroxide, diethylamine, and azobisisobutyronitrile, and the amount of initiator added is 2-3% of the resin mass.

[0050] The present invention controls the amounts of spheroidizing agent and initiator within the above-mentioned range to obtain positively spherical porous carbon with high spheroidization rate.

[0051] Preferably, in S2, the temperature of the spheroidization polymerization reaction is 60~80℃, the stirring speed of the pre-spheroidization in the spheroidization polymerization reaction is 1800r / min, and the stirring speed of the polymerization reaction is 800-1000r / min.

[0052] In a further preferred embodiment, in step S2, after adding the spheroidizing agent, the mixture is sheared and mixed in a high-speed homogenizer before the initiator is added to initiate the spheroidization polymerization reaction. The high-speed homogenizer operates at a speed of 1800 r / min, and the shearing and mixing time is 5 hours. This invention uses high-speed shearing to form a spherical structure in the material, optimizing the subsequent pore distribution.

[0053] In a further preferred embodiment, in step S2, washing involves sequentially washing with an isopropanol aqueous solution and deionized water until the solution pH value is close to 7; drying is performed under vacuum at 60-70°C for 12 hours. This invention removes residual impurities and unreacted components through washing.

[0054] More preferably, the volume concentration of the isopropanol aqueous solution in S2 is 40%.

[0055] Preferably, in S3, the gas used for vapor phase etching to create holes is one or more of boric acid, borate, sodium borohydride, and boron trifluoride ethylamine, the CVD tube furnace temperature is 150~200℃, and the etching time is 11-13h;

[0056] This invention further optimizes the pore structure by creating pores through vapor phase etching and achieves secondary doping of boron within the pores.

[0057] In an even more preferred embodiment, in S3, impurity removal is performed using an isopropanol aqueous solution, and the drying method is vacuum drying at 60-70℃ for 12 hours.

[0058] More preferably, the volume concentration of the isopropanol aqueous solution in S3 is 20%. This invention uses an isopropanol aqueous solution for deep impurity removal, eliminating impurities generated during the etching process.

[0059] Preferably, in S4, the flow ratio of ammonia to silane is 1:1-1.2, and the deposition temperature is 540-560℃.

[0060] In this invention, the first chemical vapor deposition is performed in S4. Silane gas is cracked and deposited into amorphous silicon in the pores of boron-doped spherical porous carbon. Ammonia gas is used as a carrier to ensure uniform diffusion of silane gas, so that amorphous silicon is uniformly deposited in the pores, avoiding performance degradation caused by surface deposition.

[0061] Preferably, in S5, the active carbon source is one or more of methane, ethane, ethylene, acetylene, and propyne, and the temperature of the secondary chemical vapor deposition is 600~1000℃.

[0062] In this invention, a secondary chemical vapor deposition is performed in S5 to deposit an amorphous soft carbon layer on the surface of a boron-doped porous carbon silicon-carbon precursor. The deposited carbon layer can suppress direct contact between the electrolyte and silicon, reduce side reactions, and enhance the conductivity and structural stability of the material.

[0063] This invention also provides a boron-doped porous carbon fumed silicon-carbon composite anode material, prepared by the aforementioned method for preparing boron-doped porous carbon fumed silicon-carbon composite anode material. The synergistic effect of the double boron doping and the spherical porous carbon structure in this invention significantly improves electronic conductivity and lithium-ion diffusion capability through boron doping, optimizes channel transport efficiency and enhances matrix stiffness through the spherical structure, and further enhances structural stability through secondary carbon coating.

[0064] Example 1

[0065] This invention provides a boron-doped porous carbon fumed silicon-carbon composite anode material, the preparation method of which includes the following steps:

[0066] S1. Weigh 50g of polystyrene resin and add it to 200g of xylene. Then add 100g of polystyrene as a template agent and place it in a mixer. Stir at 600r / min for 1 hour to form a homogeneous resin-based mixture. Then add 2.5g of sodium borate to the resin-based mixture, transfer it to a water bath, heat it to 45℃, and stir at 1800r / min for 3 hours to obtain a boron-containing prepolymer precursor.

[0067] S2. Add 1.5g of polyvinyl alcohol as a spheroidizing agent to the boron-containing prepolymer precursor obtained in S1, and transfer it to a high-speed homogenizer for shear mixing and stirring at 1800r / min for 5h to complete pre-spheroidization. Then transfer it to a water bath device, add 1.5g of diethylamine as an initiator, set the water bath temperature to 70℃ and the stirring speed to 900r / min, and heat and stir for 1.5h to initiate polymerization, obtaining boronized resin balls. Add the boronized resin balls to 250g of a 40% isopropanol aqueous solution, stir at room temperature for 1h, let stand for 10min, remove the supernatant, transfer to a forced-air oven to dry at 60℃ for 2h, then wash repeatedly with deionized water until the solution pH is close to 7, and finally vacuum dry at 60℃ for 12h to obtain positive spherical boronized resin porous balls.

[0068] S3. The boronized resin porous spheres from S2 were transferred to a CVD tube furnace, and a gas-phase etching gas containing sodium borate was introduced. The gas flow rate was controlled at 150 mL / min, and the temperature was raised to 180 °C for etching for 12 hours to obtain a boron-doped porous sphere precursor. After passing through a 200-mesh sieve, 250 g of a 20% isopropanol aqueous solution was added for impurity removal. Subsequently, the precursor was vacuum dried at 65 °C for 12 hours to obtain boron-doped spherical porous carbon.

[0069] S4. In the CVD tube furnace of S3, ammonia gas (flow rate 150 mL / min) is introduced as a deposition carrier, and silane gas (flow rate 150 mL / min) is introduced at the same time. The temperature is raised to 550℃ for the first chemical vapor deposition, which lasts for 5 hours to obtain a boron-doped porous carbon silicon-carbon precursor.

[0070] S5. In the CVD tube furnace of S4, under inert gas protection, a carbon source (nitrogen, flow rate 500 mL / min; carbon source: ethane, flow rate 150 mL / min) is introduced, and the furnace temperature is raised to 800℃. Secondary chemical vapor deposition is performed for 3 hours to deposit a carbon layer on the surface of the boron-doped porous carbon silicon-carbon precursor obtained in S4. After cooling with the furnace, a boron-doped porous carbon vapor-phase silicon-carbon composite anode material (Si / C@B material) is obtained.

[0071] Example 2

[0072] This invention provides a boron-doped porous carbon fumed silicon-carbon composite anode material, the preparation method of which includes the following steps:

[0073] S1. Weigh 50g of phenolic resin and add it to 170g of toluene, then add 75g of polyvinyl alcohol as a template agent. Place the mixture in a mixer and stir at 500r / min for 1 hour to form a homogeneous resin-based mixture. Then add 2g of boric acid to the resin-based mixture, transfer it to a water bath, heat it to 40℃, and stir at 1500r / min for 3 hours to obtain a boron-containing prepolymer precursor.

[0074] S2. Add 1g of hexadecyltrimethylammonium bromide as a spheroidizing agent to the boron-containing prepolymer precursor obtained in S1, and transfer it to a high-speed homogenizer for shear mixing and stirring at 1800r / min for 5h to complete pre-spheroidization. Then transfer it to a water bath device, add 1g of benzoyl peroxide as an initiator, set the water bath temperature to 60℃ and the stirring speed to 800r / min, and heat and stir for 1h to initiate polymerization to obtain boronized resin balls. Add the boronized resin balls to 250g of a 40% isopropanol aqueous solution, stir at room temperature for 1h, let stand for 10min, remove the supernatant, transfer to a forced-air oven to dry at 60℃ for 2h, then wash repeatedly with deionized water until the pH value of the solution is close to 7, and finally vacuum dry at 60℃ for 12h to obtain positive spherical porous boronized resin balls.

[0075] S3. The boronized resin porous spheres from S2 were transferred to a CVD tube furnace, and a boric acid-containing gas phase etching gas was introduced. The gas flow rate was controlled at 150 mL / min, and the temperature was raised to 150 °C for etching for 11 hours to obtain a boron-doped porous sphere precursor. After passing through a 200-mesh sieve, 250 g of a 20% isopropanol aqueous solution was added for impurity removal. Subsequently, the precursor was vacuum dried at 60 °C for 20 hours to obtain boron-doped spherical porous carbon.

[0076] S4. In the CVD tube furnace of S3, ammonia gas (flow rate 150 mL / min) is introduced as a deposition carrier, and silane gas (flow rate 150 mL / min) is introduced at the same time. The temperature is raised to 540℃ for the first chemical vapor deposition, which lasts for 5 hours to obtain a boron-doped porous carbon silicon-carbon precursor.

[0077] S5. In the CVD tube furnace of S4, under inert gas protection, a carbon source (nitrogen, flow rate 500 mL / min; carbon source: methane, flow rate 150 mL / min) is introduced, and the furnace temperature is raised to 600℃. Secondary chemical vapor deposition is performed for 3 hours to deposit a carbon layer on the surface of the boron-doped porous carbon silicon-carbon precursor obtained in S4. After cooling with the furnace, a boron-doped porous carbon vapor-phase silicon-carbon composite anode material (Si / C@B material) is obtained.

[0078] Example 3

[0079] This invention provides a boron-doped porous carbon fumed silicon-carbon composite anode material, the preparation method of which includes the following steps:

[0080] S1. Weigh 50g of polyethylene terephthalate resin and add it to 185g of toluene. Then add 125g of polyacrylonitrile as a template agent. Place the mixture in a mixer and stir at 700r / min for 2 hours to form a homogeneous resin-based mixture. Then add 3g of sodium borohydride to the resin-based mixture, transfer it to a water bath, heat it to 50℃, and stir at 2000r / min for 4 hours to obtain a boron-containing prepolymer precursor.

[0081] S2. Add 1.5g of N-methylpyrrolidone as a spheroidizing agent to the boron-containing prepolymer precursor obtained in S1, and transfer it to a high-speed homogenizer for shear mixing and stirring at 1800r / min for 5h to complete pre-spheroidization. Then, transfer the material to a water bath, add 1.5g of azobisisobutyronitrile as an initiator, set the water bath temperature to 80℃ and the stirring speed to 1000r / min, and heat and stir for 2h to initiate polymerization, obtaining boronized resin balls. Add the boronized resin balls to 250g of a 40% isopropanol aqueous solution, stir at room temperature for 1h, let stand for 10min, remove the supernatant, transfer to a forced-air oven to dry at 60℃ for 2h, then wash repeatedly with deionized water until the solution pH is close to 7, and finally vacuum dry at 70℃ for 12h to obtain positive spherical boronized resin porous balls.

[0082] S3. The boronized resin porous spheres from S2 were transferred to a CVD tube furnace, and a gas-phase etching gas containing sodium borohydride was introduced. The gas flow rate was controlled at 150 mL / min, and the temperature was raised to 200 °C for etching for 13 hours to obtain a boron-doped porous sphere precursor. After passing through a 200-mesh sieve, 250 g of a 20% isopropanol aqueous solution was added for impurity removal. Subsequently, the precursor was vacuum dried at 70 °C for 12 hours to obtain boron-doped spherical porous carbon.

[0083] S4. In the CVD tube furnace of S3, ammonia gas (flow rate 150 mL / min) is introduced as a deposition carrier, and silane gas (flow rate 150 mL / min) is introduced at the same time. The temperature is raised to 560℃ for the first chemical vapor deposition, which lasts for 5 hours to obtain a boron-doped porous carbon silicon-carbon precursor.

[0084] S5. In the CVD tube furnace of S4, under inert gas protection, a carbon source (nitrogen, flow rate 500 mL / min; carbon source: propyne, flow rate 150 mL / min) is introduced, and the furnace temperature is raised to 1000℃. Secondary chemical vapor deposition is performed for 3 hours to deposit a carbon layer on the surface of the boron-doped porous carbon silicon-carbon precursor obtained in S4. After cooling with the furnace, a boron-doped porous carbon vapor-phase silicon-carbon composite anode material (Si / C@B material) is obtained.

[0085] Comparative Example 1

[0086] Biomass-based Si / C materials.

[0087] Performance testing

[0088] The Si / C@B anode material of Example 1 and the biomass-based Si / C material of Comparative Example 1 were assembled into half-cells or full-cells for performance testing.

[0089] Half-cell assembly: The Si / C@B material of Example 1 or the biomass-based Si / C material of Comparative Example 1, conductive agent (SuperP-Li), dispersant (CMC-Na), binder (SBR, PAA), and single-walled carbon nanotubes were ground into a slurry in a ratio of 80:10:3:3.9:0.1. After uniformly mixing in a high-speed homogenizer at 2000 r / min for 1 h, the slurry was coated onto copper foil to form the negative electrode half-cell electrode. The electrode was dried in a vacuum drying oven at 60℃ for 12 h, then cut into 12 mm diameter discs. The counter electrode was a Li metal sheet, and the separator was PE. The electrodes were then assembled into CR2016 coin cells.

[0090] Full cell assembly: The Si / C@B material (580 mAh / g) of Example 1 (doped with graphite) or the biomass-based Si / C material (580 mAh / g) of Comparative Example 1 (doped with graphite), conductive agent (SuperP-Li), dispersant (CMC-Na), binder (SBR, PAA), and single-walled carbon nanotubes were ground into a slurry in a ratio of 92.9:3:1:1.4:0.1. This slurry was then uniformly mixed in a high-speed homogenizer at 2000 r / min for 1 hour. The mixture was then coated onto copper foil to form the negative electrode for the full cell. The negative electrode was then punched into pre-drilled tabs using commercially available machinery. The negative electrode contained 84% graphite, and the positive electrode used was LiNi. 0.9 Co 0.04 Mn 0.06 O2, conductive agent (SuperP-Li), and binder (PVDF) are ground into a slurry in a ratio of 92.9:3:4.1. This slurry is then uniformly mixed at 2000 rpm for 0.5 hours in a high-speed homogenizer. The mixture is then coated onto aluminum foil to form the positive electrode for the full cell. Commercially available machines are used to punch out the positive electrode with pre-reserved tabs. The NP ratio of the positive and negative electrodes is selected as 1.1.

[0091] The Si / C@B material prepared in Example 1 of this invention was characterized by SEM, and the results are as follows: Figure 1 As shown, the particles of Si / C@B material are standard spherical.

[0092] The Si / C@B material prepared in Example 1 of this invention was characterized by XPS, and the results are as follows: Figure 2 As shown, XPS results confirmed the presence of the Si / C@B element prepared in Example 1.

[0093] Lithium diffusion coefficient (GITT) tests were performed on CR2016 coin cells assembled from the Si / C@B material of Example 1 and the biomass-based Si / C material of Comparative Example 1. Figure 3As shown, the Si / C@B material in Example 1 has a higher lithium-ion diffusion coefficient, indicating that its lithium-ion transport efficiency is better. This is because the P-type doping formed by boron accelerates the diffusion and transport of lithium ions and reduces the inhibition of lithium ions caused by relaxation.

[0094] The Si / C@B material from Example 1 and the biomass-based Si / C material from Comparative Example 1 were assembled into half-cell electrodes, and CR2016 coin cells were assembled for rate performance testing. Constant current charge-discharge tests were performed at currents of 0.1 / 0.2 / 0.5 / 1 / 2 / 3 / 5C, respectively. The results are as follows: Figure 4 As shown, the Si / C@B material in Example 1 has a much higher reversible capacity (i.e. specific capacity) at 3C and 5C rates than the Si / C material in Example 1. This indicates that Example 1 can perform stable fast charging and discharging at high current. This is because boron doping of porous carbon forms P-type doping, which improves electronic conductivity and allows lithium ions to be adsorbed and migrate rapidly in a directional manner, thus improving the charge and discharge performance under high current.

[0095] The Si / C@B material of Example 1 and the biomass-based Si / C material of Comparative Example 1 were assembled into negative electrode sheets, respectively using LiNi 0.9 Co 0.04 Mn 0.06 Using O2 as the positive electrode, CR2016 coin cell full cells were assembled and their rate performance was tested. Constant current charge-discharge tests were performed at currents of 0.1 / 0.2 / 0.5 / 1 / 2 / 3 / 5C. The results are as follows: Figure 5 As shown, the specific capacity of the Si / C@B material in Example 1 is 147 mAh / g at 3C rate and 118 mAh / g at 5C rate, which is much higher than the 136 mAh / g and 105 mAh / g of the Si / C material in Example 1. This indicates that after being assembled into a full battery with a matching positive electrode, Example 1 can still perform stable fast charging and discharging at high current.

[0096] The negative electrode sheets of the full cell made from the Si / C@B material of Example 1 and the biomass-based Si / C material of Comparative Example 1 were respectively coated with LiNi 0.9 Co 0.04 Mn 0.06 The positive electrode sheet of the full cell, made of O2, was punched into a 12mm diameter disc and then assembled into a CR2016 coin cell. The separator was made of PE. Initial charge-discharge performance tests were conducted at 0.1C charging and 0.1C discharging rates, with a voltage range of 2.0V to 4.25V. The initial efficiency and initial reversible capacity of two different negative electrode materials matched with a high-nickel positive electrode were compared. Figure 6As shown, Example 1 has a higher initial efficiency of 87.4% and a capacity of 217.97 mAh / g (Comparative Example 1 has an initial efficiency of 85.2% and a capacity of 205.25 mAh / g). This is because Example 1, after being doped with boron, has higher electronic conductivity, which reduces the obstacles encountered by lithium ions during transport and reduces the consumption of active lithium ions when forming SEI. Therefore, Example 1 has higher initial efficiency and capacity.

[0097] The full-cell negative electrode assembly of the Si / C@B material of Example 1, the biomass-based Si / C material of Comparative Example 1, and the LiNi-based negative electrode assembly were compared. 0.9 Co 0.04 Mn 0.06 O2-based positive electrode sheets were used to fabricate 1.0Ah pouch cells for cycle performance testing. The first cycle employed a 0.05C charge-discharge formation process to activate the battery's active materials. Cycle testing was conducted at 0.5C charge and 1C discharge rates. The capacity retention and coulombic efficiency stability of pouch cells with two different negative electrode materials matched with high-nickel positive electrodes were compared during long-term cycling. Figure 7 As shown, the initial specific capacity of Example 1 was 189 mAh / g, and the specific capacity after 600 cycles was 163 mAh / g. The initial specific capacity of Comparative Example 1 was 183 mAh / g, and the specific capacity after 600 cycles was 151 mAh / g. Example 1 had a longer cycle life than Comparative Example 1. The capacity retention rate of Example 1 after 753 cycles was 80%, while that of Comparative Example 1 was 80% after 642 cycles. Example 1 has better cycle stability and capacity retention, indicating that the anode doped with boron has higher electronic conductivity, a thinner SEI layer is formed on the anode, and the electrolyte consumption is lower than that of Comparative Example 1. Therefore, the cycle performance and capacity retention rate are better than those of Comparative Example 1.

[0098] The full-cell negative electrode assembly of the Si / C@B material of Example 1, the biomass-based Si / C material of Comparative Example 1, and the LiNi-based negative electrode assembly were compared. 0.9 Co 0.04 Mn 0.06 The positive electrode of the full battery, made from O2, was used to manufacture a 1.0Ah soft-pack cell. The expansion performance of the electrode was tested upon disassembly during full charging. Figure 8 As shown, the cells of Comparative Example 1 and Example 1 were disassembled after 200 / 400 / 600 cycles respectively. The thickness of the electrode was measured using a micrometer. The expansion of the electrode compared to that when it was wetted with electrolyte but not cyclic was calculated. The results showed that Example 1 had a lower electrode expansion rate. This is because the porous carbon doped with boron has strong rigidity, which can suppress the mechanical expansion of silicon during cycling.

[0099] Therefore, this invention employs the aforementioned boron-doped porous carbon vapor-phase silicon-carbon composite anode material and its preparation method. Boron doping not only improves the lithium diffusion capability but also relatively reduces its bulk charge transfer impedance, thereby enhancing the lithium conductivity of the Si / C anode material and reducing its bulk impedance. Simultaneously, the resin-based spherical carbon skeleton effectively prevents electrode expansion, improving the cycle life of the cell. The prepared anode sheet has many advantages such as low expansion, high lithium diffusion coefficient, and high initial efficiency. The assembled battery exhibits better cycle stability and capacity retention, and can be applied to high-rate, high-energy-density lithium-ion batteries.

[0100] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for preparing a boron-doped porous carbon fumed silicon-carbon composite anode material, characterized in that: Includes the following steps: S1. Dissolve the resin in an organic solvent, add the template agent and stir at room temperature, then add the boron source, heat and stir to obtain a boron-containing prepolymer precursor; S2. Add a spheroidizing agent and an initiator to the boron-containing prepolymer precursor of S1 to carry out a spheroidization polymerization reaction. After washing and drying, the boronized resin porous spheres are obtained. S3. The boronized resin porous spheres from S2 are subjected to vapor phase etching in a CVD tube furnace to create pores. After impurity removal and drying, boron-doped spherical porous carbon is obtained. The gas used for vapor phase etching is one or more of boric acid, borate, sodium borohydride, and boron ethylamine trifluoride. The temperature of the CVD tube furnace is 150~200℃, and the etching time is 11-13h. S4. Using ammonia as a carrier, silane gas is introduced to deposit silicon in the boron-doped spherical porous carbon pores obtained in S3, thus obtaining a boron-doped porous carbon silicon-carbon precursor. S5. Under an inert gas atmosphere, a secondary chemical vapor deposition is performed using an activated carbon source to deposit a carbon layer on the surface of the boron-doped porous carbon silicon-carbon precursor obtained in S4, thereby obtaining a boron-doped porous carbon vapor-phase silicon-carbon composite anode material.

2. The method for preparing a boron-doped porous carbon fumed silicon-carbon composite anode material according to claim 1, characterized in that: In S1, the resin is one or more of phenolic resin, furfural resin, epoxy resin, polyurethane resin, polystyrene resin, polyester resin, polyethylene terephthalate resin, and polyvinyl chloride resin; the organic solvent is toluene or xylene, and the mass ratio of resin to organic solvent is 0.4~0.6:1.5~2.

3. The method for preparing a boron-doped porous carbon fumed silicon-carbon composite anode material according to claim 1, characterized in that: In S1, the template agent is one or more of polyvinyl alcohol, polystyrene, and polyacrylonitrile. The amount of template agent added is 1.5-2.5 times the mass of the resin. The stirring speed at room temperature is 500-700 r / min, and the stirring time is 1-2 h.

4. The method for preparing a boron-doped porous carbon fumed silicon-carbon composite anode material according to claim 1, characterized in that: In S1, the boron source is one or more of boric acid, sodium borate, sodium borohydride, silicon borate, and boron trifluoride ethylamine. The amount of boron source added is 4-6% of the resin mass. The heating and stirring temperature is 40-50℃, the rotation speed is 1500-2000 r / min, and the stirring time is 2-4 h.

5. The method for preparing a boron-doped porous carbon fumed silicon-carbon composite anode material according to claim 1, characterized in that: In S2, the spheroidizing agent is one or more of cetyltrimethylammonium bromide, polyvinyl alcohol, sodium alginate, N-methylpyrrolidone, and polyvinylpyrrolidone, and the amount of spheroidizing agent added is 2-3% of the resin mass; the initiator is one or more of benzoyl peroxide, diethylamine, and azobisisobutyronitrile, and the amount of initiator added is 2-3% of the resin mass.

6. The method for preparing a boron-doped porous carbon fumed silicon-carbon composite anode material according to claim 1, characterized in that: In S2, the temperature of the spheroidization polymerization reaction is 60~80℃, the stirring speed of the pre-spheroidization reaction is 1800r / min, and the stirring speed of the polymerization reaction is 800-1000r / min.

7. The method for preparing a boron-doped porous carbon fumed silicon-carbon composite anode material according to claim 1, characterized in that: In S4, the flow ratio of ammonia to silane is 1:1-1.2, and the deposition temperature is 540-560℃.

8. The method for preparing a boron-doped porous carbon fumed silicon-carbon composite anode material according to claim 1, characterized in that: In S5, the active carbon source is one or more of methane, ethane, ethylene, acetylene, and propyne, and the temperature of the secondary chemical vapor deposition is 600~1000℃.

9. A boron-doped porous carbon fumed silicon-carbon composite anode material, characterized in that: It is prepared by the method for preparing boron-doped porous carbon gas-phase silicon-carbon composite anode material according to any one of claims 1-8.

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