Porous carbon material, preparation method thereof and silicon-carbon negative electrode material

Abstract

The invention relates to a porous carbon material, a preparation method thereof and a silicon-carbon negative electrode material, and belongs to the technical field of battery negative electrode materials. The invention relates to a porous carbon material, the porous carbon material has a plurality of pores, the pore diameter in the pores is 2-10 nm, the pore diameter of the pores is 0.5-2 nm, and the pore volume is 0.5-1.6 cm < 3 > / g; and the particle size of the porous carbon material is 3-19 microns. The pore of the porous carbon material is of a structure with a small pore opening and a large pore cavity, and the structural design with the small pore opening and the large pore cavity can reduce the expansion overflow amount of the nano silicon under the condition of improving the deposition amount of the nano silicon, effectively inhibit the expansion of the silicon-carbon negative electrode material in the charge-discharge process, reduce the volume change of the silicon-carbon negative electrode material in the charge-discharge process, and improve the charge-discharge performance of the silicon-carbon negative electrode material. Therefore, the cycle stability and the service life of the silicon-carbon negative electrode material are improved.

Description

Technical Field

[0001] This application relates to the technical field of battery anode materials, and particularly to a porous carbon material, a preparation method thereof, and a silicon-carbon anode material. Background Art

[0002] Currently, the commonly used graphite anode is limited by its low theoretical capacity (372 mA h g -1 ), making it difficult to meet the growing demand for high capacity. Silicon, due to its low potential, low cost, and extremely high lithium storage capacity (4200 mAh g -1 ), is considered the most likely material to replace graphite anodes or other carbon anodes. However, during the lithium intercalation / deintercalation process, the formation of lithium-silicon alloys leads to a large volume expansion (300%) of the silicon anode, and the repeated growth of the SEI during cyclic charge and discharge, resulting in a large loss of active lithium during the first cycle, leading to a large irreversible capacity and poor cycling performance. Therefore, silicon-based anode materials such as silicon-carbon composite anode materials have received extensive attention. Currently, after extensive verification in the industry, the comprehensive performance of vapor-deposited silicon-carbon is superior to that of silicon-oxygen anodes and silicon-carbon prepared by the sanding method. However, vapor-deposited silicon-carbon still has problems of large expansion and high cost, making it difficult to meet the requirements of high-end power batteries. The main reasons are as follows: First, there is a bottleneck in the macroscale amplification of silane cracking deposition equipment; second, for the porous carbon substrate used for nano-silicon deposition, the pore channels are generally straight pore structures, and it is difficult to change the pore structure morphology and the uniformity of the pore size distribution through existing template methods, alkali activation, and gas activation methods; third, when nano-silicon is deposited into the pore channels of the straight-pore porous carbon material, after lithium intercalation in the nano-silicon, it is easy to expand along the depth direction of the pore and overflow outside the pore, thereby damaging the carbon layer coated on the surface by gas phase; fourth, the currently used porous carbon substrates are basically micropores. When increasing the nano-silicon deposition amount, it is easy to have floating silicon, which in turn leads to deterioration of expansion. Summary of the Invention

[0003] Aiming at the deficiencies of the prior art, the objectives of the embodiments of this application include providing a porous carbon material, a preparation method thereof, and a silicon-carbon anode material to effectively inhibit the expansion of the silicon-carbon anode material during charge and discharge, thereby improving the cycling performance of the silicon-carbon anode material.

[0004] The embodiments of this application are implemented as follows:

[0005] In a first aspect, the embodiments of this application provide a porous carbon material. The porous carbon material has a plurality of pores. The pore diameter inside the pores is 2 - 10 nm, the pore diameter at the pore mouth is 0.5 - 2 nm, and the pore volume is 0.5 - 1.6 cm 3 / g; the particle size of the porous carbon material is 3 - 19 μm.

[0006] The pores of the porous carbon material of the present application have a structure of "small pore orifice and large pore cavity"; among them, the design of the small pore orifice, when subsequently applied to the preparation of a silicon-carbon negative electrode material, nano-silicon is deposited into the pores of the porous carbon material. After the nano-silicon is lithiated, due to the small diameter of the pore orifice, the nano-silicon is not easily spilled out of the pores to cause floating silicon, which in turn leads to swelling deterioration and destroys the carbon layer coated on the surface of the silicon-carbon negative electrode material; that is to say, the small pore orifice diameter is beneficial to reducing the spillage of nano-silicon during charge and discharge, maintaining the integrity of the electrode structure, reducing interfacial reactions, and thus improving the long-term stability of the electrode; while the design of the large pore cavity can accommodate more nano-silicon when subsequently preparing the silicon-carbon negative electrode material, increasing the deposition amount of nano-silicon, thereby improving the specific capacity and electrochemical performance of the battery. Therefore, this structural design of "small pore orifice and large pore cavity" can reduce the swelling and spillage amount of nano-silicon while increasing the deposition amount of nano-silicon, and can also effectively inhibit the swelling of the silicon-carbon negative electrode material during charge and discharge, reducing its volume change during charge and discharge, thereby enhancing the cycle stability and lifespan of the silicon-carbon negative electrode material.

[0007] In a second aspect, an embodiment of the present application provides a method for preparing the above-mentioned porous carbon material, including: dispersing a porous carbon matrix and an organic coating material in a solvent to obtain a mixed solution, and drying to remove the solvent to obtain a coated material; the pore diameter of the porous carbon matrix is 2 - 10 nm, the specific surface area is 600 - 2000 m 2 / g, and the particle size is 2 - 15 μm; carbonizing the coated material to obtain the porous carbon material.

[0008] Currently, the pore diameter of the commonly used porous carbon matrix is 5 - 10 nm, and the pore diameter from the pore orifice to the inside of the pore is basically the same. In the present application, the porous carbon matrix material is first coated with the organic coating material on the porous carbon matrix, that is, a coating layer containing the above-mentioned organic coating material is formed on the surface of the porous carbon matrix, and then through carbonization treatment, since there is air in the pore cavity of the porous carbon matrix, when carbonization is carried out, as the temperature rises, the air pressure increases, which will promote the opening of small holes above the main pores of the porous carbon matrix, and then multiple nano-scale holes are generated in the coating layer. The nano-scale holes are connected to the pore cavity of the main pores of the porous carbon matrix. Therefore, the finally prepared porous carbon material has multiple pores, and the pores have a structure of "small pore orifice and large pore cavity". The small pore orifice diameter can effectively inhibit the floating silicon phenomenon caused by nano-silicon spillage when this porous carbon material is subsequently applied to the preparation of a silicon-carbon negative electrode material, and the large pore cavity can increase the accommodation capacity of nano-silicon. Therefore, this structural design of "small pore orifice and large pore cavity" can effectively control the swelling of nano-silicon, reduce its volume change during charge and discharge, and thus enhance the cycle stability and lifespan of the silicon-carbon negative electrode material.

[0009] In some embodiments of the present application, the organic coating material includes one or more of asphalt, phenolic resin, epoxy resin, polystyrene, and polyacrylonitrile.

[0010] After carbonization of the above-mentioned organic coating materials, the mechanical strength of the porous carbon material can be effectively enhanced, providing better protection for the porous carbon matrix and reducing structural damage during charge and discharge, thereby improving the cycle stability and service life of the electrode material.

[0011] In some embodiments of the present application, the solvent includes one or more of absolute ethanol, water, N-methylpyrrolidone, toluene, and n-hexane.

[0012] The above solvents can disperse the porous carbon matrix and the organic coating material well and can be removed by heating.

[0013] In some embodiments of the present application, the mass ratio of the organic coating material to the porous carbon matrix is 1-10%.

[0014] Having the mass ratio of the organic coating material to the porous carbon matrix be 1-10% is beneficial for forming a more appropriate coating layer thickness, providing sufficient protection for the porous carbon matrix, reducing structural damage caused by volume changes during charge and discharge, and thus improving the cycle life; a suitable thickness is more conducive to ion transport, thereby improving the electrochemical performance of the porous carbon material.

[0015] In some embodiments of the present application, the mass ratio of the organic coating material to the porous carbon matrix is 5-8%.

[0016] Within the above ratio range, it is more beneficial to improve the electrochemical performance of the porous carbon material and provide better protection for the porous carbon matrix.

[0017] In some embodiments of the present application, the temperature of the carbonization treatment is 300-1000 °C, and the time of the carbonization treatment is 3-10 h.

[0018] By controlling the temperature and time of carbonization within the above ranges, the pore size of the pore orifice can be adjusted to form appropriate nano-scale pores, obtaining a structure of "small pore orifice and large pore cavity", thereby effectively suppressing the expansion rate of the silicon-carbon negative electrode material during charge and discharge and significantly improving the cycle life.

[0019] In some embodiments of the present application, the temperature of the carbonization treatment is 500-700 °C.

[0020] By controlling the temperature of carbonization to be 500-700 °C, it is more beneficial to obtain pores with appropriate pore orifice sizes.

[0021] In some embodiments of the present application, the thickness of the organic coating material on the surface of the porous carbon matrix is 0.5-2 μm.

[0022] The porous carbon material prepared by the preparation method provided by this application includes a porous carbon matrix, and a coating layer is provided on the surface of the porous carbon matrix. The thickness of the organic coating material on the surface of the porous carbon matrix is the thickness of the coating layer. A coating layer with a thickness of 0.5 - 2 μm is provided on the surface of the porous carbon matrix. On the one hand, it is beneficial to form better protection for the porous carbon matrix. On the other hand, it is beneficial to the rapid transport of ions in the material, enhance the electrochemical performance, and improve the charge and discharge efficiency of the lithium-ion battery.

[0023] In some embodiments of this application, after the carbonization treatment, a fusion treatment is further included, and the fusion treatment is carried out in a fusion coater; wherein, the rotation speed of the fusion treatment is 500 - 3000 r / min, and the time of the fusion treatment is 1 - 4 h.

[0024] Through the fusion treatment, the organic coating material can be coated more uniformly on the porous carbon matrix, forming a coating layer with a uniform thickness. After such a fusion treatment, the sizes of the small holes formed on the surface of the porous carbon matrix are more uniform and consistent. Furthermore, a porous carbon material with a uniform surface pore size distribution and basically the same size is obtained. In addition, if there are some defects on the surface of the coating layer of the prepared porous carbon material, such as cracks and uneven pores, through the fusion treatment, these surface defects can be improved or reduced. When used for preparing the silicon-carbon anode material subsequently, it can reduce the adsorption of gases such as silane on these defects of the porous carbon material, resulting in cracking during subsequent heat treatment or reaction processes and forming undesirable deposits.

[0025] In a third aspect, an embodiment of this application provides a silicon-carbon anode material, including any of the above-mentioned porous carbon materials and a carbon layer coated on the surface of the porous carbon material, and a plurality of nano-silicon particles are attached in the pores of the porous carbon material.

[0026] Benefiting from the structural design of the "small pore orifice and large pore cavity" of the porous carbon material of this application, when preparing this silicon-carbon anode material, the large pore cavity means that more nano-silicon can be accommodated, improving the nano-silicon deposition amount, and further improving the specific capacity and electrochemical performance of the battery. Due to the smaller pore orifice diameter of the porous carbon material, the amount of nano-silicon expansion and overflow is reduced, and it is compounded with the carbon layer coating the nano-silicon, thereby effectively suppressing the expansion of the silicon-carbon anode material during charge and discharge, reducing its volume change during charge and discharge, and thus improving the cycle stability and lifespan of the silicon-carbon anode material. Description of the Drawings

[0027] To more clearly illustrate the technical solutions of the embodiments of the present application, the accompanying drawings required for the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present application and should not be regarded as limiting the scope. For those of ordinary skill in the art, without creative efforts, other related drawings can also be obtained based on these drawings.

[0028] Figure 1 TEM image of the porous carbon material prepared in Example 1 of the present application;

[0029] Figure 2 SEM image of the silicon-carbon anode material prepared in Example 1 of the present application. Detailed implementation manners

[0030] To make the objectives, technical solutions, and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be clearly and completely described below. For those not specified in the embodiments, they are carried out according to conventional conditions or conditions recommended by the manufacturer. For reagents or instruments not specified by the manufacturer, they are all conventional products that can be obtained through commercial purchase.

[0031] A porous carbon material, its preparation method, and a silicon-carbon anode material in the embodiments of the present application will be specifically described below.

[0032] The embodiments of the present application provide a porous carbon material. The porous carbon material has a plurality of pores. The pore diameter inside the pores is 2 - 10 nm, the pore diameter at the pore opening is 0.5 - 2 nm, and the pore volume is 0.5 - 1.6 cm 3 / g; the particle size of the porous carbon material is 3 - 19 μm.

[0033] The porous carbon material of the present application has a plurality of pores, and the pore diameter at the pore opening is smaller than the pore diameter inside the pores, 0.5 - 1.6 cm 3The pore volume per gram shows a relatively large pore cavity. Therefore, the pores of the porous carbon material of this application have a structure of "small pore orifice and large pore cavity". The small pore orifice can reduce the overflow of nano-silicon during charge and discharge, maintain the integrity of the electrode structure, reduce interfacial reactions, and thus improve the long-term stability of the electrode. The large pore cavity can accommodate more nano-silicon, increase the deposition amount of nano-silicon. Increasing the deposition amount of nano-silicon means that the active material in the battery increases relatively, thereby enhancing the energy density of the lithium-ion battery. This enables the battery to store more energy under the same volume or weight, improving its overall performance. Moreover, nano-silicon has a higher theoretical specific capacity than graphite. Increasing its deposition amount will directly increase the specific capacity of the battery and improve the charge and discharge performance of the battery. Therefore, this structural design of "small pore orifice and large pore cavity" can reduce the swelling and overflow amount of nano-silicon while increasing the deposition amount of nano-silicon, and can also effectively inhibit the swelling of the silicon-carbon negative electrode material during charge and discharge, reduce its volume change during charge and discharge, thereby enhancing the cycle stability and lifespan of the silicon-carbon negative electrode material.

[0034] The preparation method of the porous carbon material of this application will be described below.

[0035] A preparation method of a porous carbon material includes the following steps:

[0036] S1. Dispersing a porous carbon matrix and an organic coating material in a solvent to obtain a mixed solution, and drying to remove the solvent to obtain a coated material. Among them, the pore diameter of the porous carbon matrix is 2 - 10 nm, the specific surface area is 600 - 2000 m 2 / g, and the particle size is 2 - 15 μm.

[0037] As another method, in the above step S1, the porous carbon matrix and the organic coating material are respectively dispersed in a first solvent and a second solvent, and ultrasonic vibration stirring is used to obtain a first dispersion liquid containing the porous carbon matrix and a second dispersion liquid containing the organic coating material; then the first dispersion liquid and the second dispersion liquid are mixed evenly to obtain a mixed solution; the mixed solution is heated to remove the first solvent and the second solvent to obtain the coated material in the above step S1. Among them, the first solvent and the second solvent can be the same or different, and are each selected from one or more of anhydrous ethanol, water, N-methylpyrrolidone, toluene, and n-hexane.

[0038] Among them, the organic coating material includes but is not limited to one or more of asphalt, phenolic resin, epoxy resin, polystyrene, and polyacrylonitrile.

[0039] Different organic coating materials have their own unique physical and chemical properties. For example, asphalt has good adhesion and impact resistance and can form a strong protective layer; while phenolic resin and epoxy resin can provide high thermal stability and plasticity. Appropriate organic coating materials can be selected according to specific application requirements to optimize the material properties.

[0040] Among them, the mass ratio of the organic coating material to the porous carbon matrix is 1-10%. Exemplarily, the mass ratio of the organic coating material to the porous carbon matrix includes but is not limited to 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%.

[0041] Among them, the thickness of the organic coating material on the surface of the porous carbon matrix is 0.5-2 μm. The surface of the porous carbon matrix has a coating layer, and the thickness of the organic coating material on the surface of the above porous carbon matrix is the thickness of this coating layer. Exemplarily, the thickness of the coating layer includes but is not limited to 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1.0 μm, 1.1 μm, 1.2 μm, 1.3 μm, 1.4 μm, 1.5 μm, 1.6 μm, 1.7 μm, 1.8 μm, 1.9 μm, 2.0 μm.

[0042] S2. Carbonize the coating material prepared in step S1 to obtain a porous carbon material.

[0043] In the above steps, the carbonization treatment includes: placing the coating material obtained in step S1 in a corundum crucible, then placing this corundum crucible in a tube furnace, introducing nitrogen, and keeping the nitrogen flow rate at 0.5 L / min; at this time, start heating the tube furnace, with a heating rate of 5 °C / min, and heating to 300-1000 °C and maintaining for 3-10 h.

[0044] As another method, after the above carbonization treatment, a fusion treatment is also included, and the fusion treatment is carried out in a fusion coater; among them, the rotation speed of the fusion treatment is 500-3000 r / min, and the time of the fusion treatment is 1-4 h.

[0045] Through the above fusion treatment, the defects on the surface of the coating layer of the porous carbon material can be reduced, avoiding the adsorption of gases such as silane on the surface of the porous carbon material particles and the occurrence of cracking to form undesirable deposits during the subsequent preparation of the silicon-carbon negative electrode material.

[0046] The embodiment of the present application also provides a silicon-carbon negative electrode material, including any of the above porous carbon materials, and its preparation method includes continuing the following steps after the above step S2:

[0047] S3. Nano - silicon chemical vapor deposition: Load the porous carbon material obtained in step S2 into a rotary furnace. Introduce nitrogen protective gas into the rotary furnace at a flow rate of 5 L / min, and purge the furnace body for 10 min to ensure an inert atmosphere inside the rotary furnace. Heat the rotary furnace to 400 - 700 °C at a rate of 5 °C / min and keep it constant. At this time, introduce gas into the rotary furnace according to the ratio of silane : nitrogen = (0.5 - 2) : (8 - 10), and control the total flow rate at 3 L / min. React for 0.5 - 10 h. After the reaction is completed, close the outlet valve, start natural cooling to room temperature, and slowly introduce nitrogen (the flow rate is kept at 0.01 - 0.5 sccm). Open the furnace cavity cover and take out the obtained intermediate product.

[0048] Through nano - silicon chemical vapor deposition, silane gas is cracked at high temperature to produce nano - silicon, which is deposited in the pores of the porous carbon material.

[0049] S4. Gas - phase carbon coating: Clean the rotary furnace cavity with nitrogen, and then heat the rotary furnace to 400 - 1000 °C (carbon coating temperature) at a rate of 5 °C / min and keep it. According to the gas flow ratio of nitrogen : acetylene = 1 : 1, introduce the mixed gas at a total flow rate of 1 L / min, and ventilate for 1 - 10 h. After the reaction is complete, an amorphous carbon layer is formed on the surface of the intermediate product in step S3 to obtain the final product, the silicon - carbon anode material.

[0050] By using high - temperature cracking of carbon - source gas to produce carbon atoms deposited on the surface of the target material, where the carbon - source gas includes but is not limited to one or several mixtures of acetylene, ethylene, methane, and ethane.

[0051] Exemplarily, the carbon coating temperature includes but is not limited to 400 °C, 450 °C, 500 °C, 550 °C, 600 °C, 650 °C, 700 °C, 750 °C, 800 °C, 850 °C, 900 °C, 950 °C, 1000 °C.

[0052] Among them, the carbon coating amount is 3 - 5%; the ventilation rate of the carbon - source gas is 50 - 150 mL / min. The specific surface area of the silicon - carbon anode material is 1.0 - 10 m 2 / g, and the particle size is 2 - 15 μm.

[0053] Exemplarily, the carbon coating amount includes but is not limited to 3%, 3.5%, 4%, 4.5%, 5%.

[0054] In summary, this application selects a porous carbon matrix, conducts surface coating on the porous carbon matrix by a liquid - phase method, then performs high - temperature carbonization in an inert atmosphere, and then uses a fusion device to process the surface defects that are easy to adsorb gas. Finally, a porous carbon material with "small pore openings and large pore cavities" is prepared; subsequently, through nano - silicon chemical vapor deposition and carbon coating in sequence, a silicon - carbon anode material with excellent performance is prepared.

[0055] The features and performance of the present application will be further described in detail below in conjunction with embodiments.

[0056] Embodiment 1

[0057] This embodiment provides a porous carbon material and a silicon-carbon negative electrode material prepared from the porous carbon material. The preparation method includes the following steps:

[0058] S1. Liquid-phase carbon coating: Weigh 4 g of pitch and disperse it in 200 g of absolute ethanol, and use ultrasonic oscillation to stir for 0.5 h to obtain suspension A; then disperse 100 g of porous carbon matrix in 200 g of absolute ethanol, and use ultrasonic oscillation to stir for 0.5 h to obtain suspension B; then mix suspension A and suspension B evenly and pour them into a water bath together. Control the temperature of the water bath at 80 °C, stir until the absolute ethanol solvent evaporates completely, and then through cooling and grinding, obtain a pitch-coated porous carbon powder material.

[0059] S2. Carbonization treatment: Place the pitch-coated porous carbon powder material obtained in step S1 in a corundum crucible, and then place the corundum crucible in a tubular furnace, and introduce nitrogen, and keep the nitrogen flow rate at 0.5 L / min. At this time, start to heat the tubular furnace, and the heating rate is 5 °C / min, and heat up to 1000 °C and keep it for 6 h.

[0060] S3. Fusion treatment: Pour the porous carbon powder material after high-temperature carbonization treatment in step S2 into a small VS-3 fusion device, adjust the rotation speed parameter of the device to 1500 r / min, and the fusion time is 10 min, then a porous carbon material with a smooth surface and fewer defects, "small holes at the pore mouth and large cavities", can be obtained.

[0061] S4. Nano-silicon chemical vapor deposition: Load the porous carbon material in step S3 into a rotary furnace, introduce nitrogen protective gas into the rotary furnace at a flow rate of 5 L / min, and purge the furnace body for 10 min to ensure an inert atmosphere in the rotary furnace; heat the rotary furnace to 550 °C at a rate of 5 °C / min and keep it constant; at this time, introduce gas into the rotary furnace according to the gas flow ratio of silane:nitrogen = 2:8, and control the total flow rate at 3 L / min, and react at a constant temperature of 550 °C for 4 h; after the reaction is completed, close the outlet valve, start to cool naturally to room temperature, slowly introduce nitrogen (the flow rate is kept at 0.01 - 0.5 sccm), open the furnace chamber cover, and take out the prepared intermediate product.

[0062] S5. Gas-phase carbon coating: Clean the rotary furnace chamber with nitrogen, then heat the rotary furnace to 850 °C at a rate of 5 °C / min and keep it. According to the gas flow ratio of nitrogen:acetylene = 1:1, introduce the mixed gas at a total flow rate of 1 L / min, and ventilate for 1.5 h. After the reaction is complete, an amorphous carbon layer is formed on the surface of the intermediate product in step S4 to obtain the final product, the silicon-carbon negative electrode material.

[0063] Example 2

[0064] This example provides a porous carbon material and a silicon-carbon negative electrode material prepared from the porous carbon material. The preparation method includes the following steps:

[0065] S1. Liquid-phase carbon coating: Weigh 4 g of asphalt and disperse it in 200 g of absolute ethanol. Use ultrasonic oscillation to stir for 0.5 h to obtain suspension A; then disperse 100 g of porous carbon matrix in 200 g of absolute ethanol and use ultrasonic oscillation to stir for 0.5 h to obtain suspension B; then mix suspension A and suspension B evenly and pour them into a water bath together. Control the temperature of the water bath at 80 °C and stir until the absolute ethanol solvent completely evaporates. Then, after cooling and grinding, obtain the porous carbon powder material coated with asphalt.

[0066] S2. Carbonization treatment: Place the porous carbon powder material coated with asphalt obtained in step S1 in a corundum crucible, and then place the corundum crucible in a tube furnace. Introduce nitrogen, and keep the nitrogen flow rate at 0.5 L / min. At this time, start to heat the tube furnace, with a heating rate of 5 °C / min, and heat up to 1100 °C and hold for 6 h.

[0067] The remaining steps S3 - S5 are the same as those in Example 1.

[0068] Example 3

[0069] This example provides a porous carbon material and a silicon-carbon negative electrode material prepared from the porous carbon material. The preparation method includes the following steps:

[0070] S1. Liquid-phase carbon coating: Weigh 4 g of asphalt and disperse it in 200 g of absolute ethanol. Use ultrasonic oscillation to stir for 0.5 h to obtain suspension A; then disperse 100 g of porous carbon matrix in 200 g of absolute ethanol and use ultrasonic oscillation to stir for 0.5 h to obtain suspension B; then mix suspension A and suspension B evenly and pour them into a water bath together. Control the temperature of the water bath at 80 °C and stir until the absolute ethanol solvent completely evaporates. Then, after cooling and grinding, obtain the porous carbon powder material coated with asphalt.

[0071] S2. Carbonization treatment: Place the porous carbon powder material coated with asphalt obtained in step S1 in a corundum crucible, and then place the corundum crucible in a tube furnace. Introduce nitrogen, and keep the nitrogen flow rate at 0.5 L / min. At this time, start to heat the tube furnace, with a heating rate of 5 °C / min, and heat up to 800 °C and hold for 6 h.

[0072] The remaining steps S3 - S5 are the same as those in Example 1.

[0073] Example 4

[0074] This embodiment provides a porous carbon material and a silicon-carbon negative electrode material prepared from the porous carbon material. The preparation method includes the following steps:

[0075] S1. Liquid-phase carbon coating: Weigh 4 g of pitch and disperse it in 200 g of absolute ethanol. Use ultrasonic oscillation to stir for 0.5 h to obtain suspension A. Then disperse 100 g of porous carbon matrix in 200 g of absolute ethanol and use ultrasonic oscillation to stir for 0.5 h to obtain suspension B. After that, mix suspension A and suspension B evenly and pour them into a water bath together. Control the temperature of the water bath at 80 °C and stir until the absolute ethanol solvent completely evaporates. Then, after cooling and grinding, a pitch-coated porous carbon powder material is obtained.

[0076] S2. Carbonization treatment: Place the pitch-coated porous carbon powder material obtained in step S1 in a corundum crucible, and then place the corundum crucible in a tubular furnace. Introduce nitrogen, and keep the nitrogen flow rate at 0.5 L / min. At this time, start heating the tubular furnace, with a heating rate of 5 °C / min. Heat up to 500 °C and hold for 6 h.

[0077] The remaining steps S3 - S5 are the same as those in Example 1.

[0078] Example 5

[0079] This embodiment provides a porous carbon material and a silicon-carbon negative electrode material prepared from the porous carbon material. The preparation method includes the following steps:

[0080] S1. Liquid-phase carbon coating: Weigh 4 g of phenolic resin and disperse it in 200 g of absolute ethanol. Use ultrasonic oscillation to stir for 0.5 h to obtain suspension A. Then disperse 100 g of porous carbon matrix in 200 g of absolute ethanol and use ultrasonic oscillation to stir for 0.5 h to obtain suspension B. After that, mix suspension A and suspension B evenly and pour them into a water bath together. Control the temperature of the water bath at 80 °C and stir until the absolute ethanol solvent completely evaporates. Then, after cooling and grinding, a pitch-coated porous carbon powder material is obtained.

[0081] The remaining steps S2 - S5 are the same as those in Example 1.

[0082] Comparative Example 1

[0083] This comparative example provides a silicon-carbon negative electrode material. The preparation method includes the following steps:

[0084] S21. Use commercial microporous carbon material as the carbon substrate for depositing nano-silicon.

[0085] S22. Nano - silicon chemical vapor deposition: Load the microporous carbon material in step S21 into a rotary furnace, introduce nitrogen protective gas into the rotary furnace at a flow rate of 5 L / min, purge the furnace body for 10 min to ensure an inert atmosphere in the rotary furnace; heat the rotary furnace to 550 °C at a rate of 5 °C / min and keep it constant; at this time, introduce gas into the rotary furnace according to the gas flow ratio of silane:nitrogen = 2:8, control the total flow rate at 3 L / min, and react at a constant temperature of 550 °C for 4 h; after the reaction is completed, close the outlet valve, start natural cooling to room temperature, slowly introduce nitrogen (the flow rate is kept at 0.2 sccm), open the furnace chamber cover, and take out the obtained intermediate product.

[0086] S5. Gas - phase carbon coating: Clean the rotary furnace chamber with nitrogen, then heat the rotary furnace to 850 °C at a rate of 5 °C / min and keep it. According to the gas flow ratio of nitrogen:acetylene = 1:1, introduce the mixed gas at a total flow rate of 1 L / min, and introduce the gas for 1.5 h. After the reaction is complete, form an amorphous carbon layer on the surface of the intermediate product in step S4 to obtain the final product, the silicon - carbon anode material.

[0087] Comparative Example 2

[0088] This comparative example provides a silicon - carbon anode material, and its preparation method includes the following steps:

[0089] S21. Use the raw material in Example 1 - the porous carbon matrix as the carbon substrate for nano - silicon deposition.

[0090] S22. Nano - silicon chemical vapor deposition: Load the porous carbon matrix in step S21 into a rotary furnace, introduce nitrogen protective gas into the rotary furnace at a flow rate of 5 L / min, purge the furnace body for 10 min to ensure an inert atmosphere in the rotary furnace; heat the rotary furnace to 550 °C at a rate of 5 °C / min and keep it constant; at this time, introduce gas into the rotary furnace according to the gas flow ratio of silane:nitrogen = 2:8, control the total flow rate at 3 L / min, and react at a constant temperature of 550 °C for 4 h; after the reaction is completed, close the outlet valve, start natural cooling to room temperature, slowly introduce nitrogen (the flow rate is kept at 0.2 sccm), open the furnace chamber cover, and take out the obtained intermediate product.

[0091] S5. Gas - phase carbon coating: Clean the rotary furnace chamber with nitrogen, then heat the rotary furnace to 850 °C at a rate of 5 °C / min and keep it. According to the gas flow ratio of nitrogen:acetylene = 1:1, introduce the mixed gas at a total flow rate of 1 L / min, and introduce the gas for 1.5 h. After the reaction is complete, form an amorphous carbon layer on the surface of the intermediate product in step S4 to obtain the final product, the silicon - carbon anode material.

[0092] For some parameters of the above - mentioned examples and comparative examples, please refer to Table 1 for details.

[0093] Table 1

[0094] Group Coating material Carbonization temperature Nanocrystalline silicon deposited carbon substrate Example 1 Pitch 1000℃ Porous carbon material obtained in step S3 Example 2 Pitch 1100℃ Porous carbon material obtained in step S3 Example 3 Pitch 800℃ Porous carbon material obtained in step S3 Example 4 Pitch 500℃ Porous carbon material obtained in step S3 Example 5 Phenolic resin 1000℃ Porous carbon material obtained in step S3 Comparative example 1 / / Commercial microporous carbon material Comparative example 2 / / Raw material in Example 1 - Porous carbon matrix

[0095] Test Example 1

[0096] In this test example, the porous carbon material obtained in Example 1 of this application and the silicon-carbon negative electrode material prepared from the porous carbon material will be subjected to morphological characterization. The morphological structure diagrams are as shown in Figure 1 and Figure 2 . Figure 1 is the TEM image of the porous carbon material obtained in Example 1 of this application, and Figure 2 is the SEM image of the silicon-carbon negative electrode material obtained in Example 1 of this application. Please refer to Figure 1 and Figure 2 .

[0097] It can be seen from Figure 1 that the pore diameter of the carbon pore substrate is in the range of 1-2 nm, belonging to the microporous structure. The interfaces between the particles are clear and arranged in an orderly manner. It is speculated that the pore connectivity of the material is good, which is helpful for the diffusion of lithium ions. From the high-magnification TEM (the dark area in the figure shows), the nano-silicon particles are evenly embedded inside the porous carbon. From the light-colored outer edge of the surface layer, the continuous and crack-free carbon coating layer completely covers the nano-silicon particles, and the thickness is between 5-15 nm, effectively preventing the increase of side reactions of the electrolyte.

[0098] It can be seen from Figure 2 that the particle size of the porous carbon material is between 2-15 μm. No obvious floating silicon is found on the surface of the material. The pitch carbon is coated on the surface of the porous carbon-silicon material, forming a uniform coating layer (dark transparent coating layer). The surface of the particles is dense, which can effectively isolate the side reactions of the electrolyte, improve the first charge-discharge efficiency of the material, and improve the structural stability of the electrode material.

[0099] Test Example 2

[0100] In this test example, the pore diameter and pore volume of the porous carbon materials in Examples 1-5 and Comparative Examples 1-2 of this application will be measured, and the silicon-carbon negative electrode materials prepared from the porous carbon materials will be used to prepare batteries, and the electrochemical performance of the batteries will be measured, including the specific capacity, the first-cycle Coulombic efficiency, the pole piece expansion rate, and the capacity retention rate.

[0101] The preparation method of the battery includes the following steps:

[0102] First, the assembly is carried out in a glove box with the water concentration controlled at <0.01 ppm and the oxygen concentration also controlled at <0.01 ppm. Then, a lithium sheet is used as the counter electrode, and a nickel foam sheet is placed below it as a buffer gasket. The negative electrode plate is prepared using the silicon-carbon negative electrode material obtained in this application. The silicon-carbon negative electrode material: sp (conductive carbon black): cmc (carboxymethyl cellulose): paa (polyacrylic acid): swcnt (single-walled carbon nanotube) = 96:0.85:1.8:1.2:0.15 are mixed in proportion to make each component evenly dispersed. Finally, 1M LiPF6 is selected as the electrolyte and dissolved in organic solvents of ethylene carbonate (EC) and dimethyl carbonate (DMC) to complete the preparation of the electrolyte. After the above steps are completed, all components are assembled into a button-type half cell (CR2016).

[0103] The measurement of the battery cycle performance is carried out on a Blue Electric test device, and the test regime is as follows: constant current discharge at 0.1C to 0.005V, constant current charge at 0.1C to 1.5V, and the above steps are repeated in cycles. The measurement results of the above test items are shown in Table 2 and Table 3 for details.

[0104] Table 2

[0105]

[0106] Table 3

[0107]

[0108] It can be seen from the data in Table 2 that the pore volume of the porous carbon materials prepared in Examples 1-5 of this application remains basically unchanged, the average pore diameter is significantly reduced to the micropore level, the number of nano-silicon accommodated by the porous carbon materials prepared by the preparation method of this application on the surface remains basically unchanged, and it is speculated that the pore cavity diameter and depth remain basically unchanged. However, the average pore diameter at the pore mouth is significantly reduced, indicating that a porous carbon material with a "small pore mouth and large pore cavity" has been successfully prepared.

[0109] Combining the data in Table 2 and Table 3, it can be seen that the silicon-carbon negative electrode material prepared with the "small pore mouth and large pore cavity" porous carbon material of this application as the substrate has a higher specific capacity, a lower electrode plate expansion rate, and significantly improved cycle performance.

[0110] The embodiments described above are some, but not all, of the embodiments of this application. The detailed description of the embodiments of this application is not intended to limit the scope of this application claimed, but merely represents the selected embodiments of this application. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in this application without creative efforts fall within the scope of protection of this application.

Claims

1. A porous carbon material, characterized in that, The porous carbon material has a plurality of pores. The pore diameter inside the pores is 2 - 10 nm, the pore diameter at the pore opening is 0.5 - 2 nm, and the pore volume is 0.5 - 1.6 cm 3 / g; The particle size of the porous carbon material is 3 - 19 μm.

2. A method for preparing a porous carbon material as described in claim 1, characterized in that, Comprising: Disperse a porous carbon matrix and an organic coating material in a solvent to obtain a mixed solution, and dry to remove the solvent to obtain a coating material; The pore size of the porous carbon matrix is 2 - 10 nm, the specific surface area is 600 - 2000 m 2 / g, and the particle size is 2 - 15 μm; Perform carbonization treatment on the coating material to obtain the porous carbon material.

3. The preparation method according to claim 2, wherein The organic coating material includes one or more of pitch, phenolic resin, epoxy resin, polystyrene, and polyacrylonitrile; Optionally, the solvent includes one or more of absolute ethanol, water, N-methylpyrrolidone, toluene, and n-hexane.

4. The preparation method according to claim 2, characterized in that, The mass ratio of the organic coating material to the porous carbon matrix is 1-10%.

5. The preparation method according to claim 4, wherein The mass ratio of the organic coating material to the porous carbon matrix is 5-8%.

6. The preparation method according to any one of claims 2-5, characterized in that, The temperature of the carbonization treatment is 300-1000 °C, and the time of the carbonization treatment is 3-10 h.

7. The preparation method according to claim 6, characterized in that, The temperature of the carbonization treatment is 500-700 °C.

8. The preparation method according to any one of claims 2-5, characterized in that, The thickness of the organic coating material on the surface of the porous carbon matrix is 0.5-2 μm.

9. The preparation method according to any one of claims 2-5, characterized in that, After the carbonization treatment, a fusion treatment is further included, and the fusion treatment is carried out in a fusion coater; Wherein, the rotation speed of the fusion treatment is 500-3000 r / min, and the time of the fusion treatment is 1-4 h.

10. A silicon-carbon anode material, characterized in that, Comprising the porous carbon material according to claim 1 or 2 and a carbon layer coated on the surface of the porous carbon material, and a plurality of nano-silicon particles are attached in the pores of the porous carbon material.

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