High-performance silicon-carbon negative electrode porous carbon material and preparation method thereof

Abstract

The application discloses a kind of high-performance silicon-carbon negative electrode porous carbon material and preparation method thereof, belong to lithium ion battery negative material technical field.The application uses natural, non-toxic, renewable coconut shell as carbon precursor to prepare porous carbon, after pre-carbonization of coconut shell powder, then mixed with single-crystal zinc oxide doping, water vapor, carbon dioxide is passed in and activated, to obtain porous carbon, again pass in silane gas containing germanium and deposit, finally CVD carbon coating is obtained.The process of the application realizes the specific surface area of porous carbon material more than 1700 m 2 / g by regulating the pore structure of porous carbon, pore volume is not less than 0.85 cm 3 / g, micropore ratio is not less than 83%, which can effectively improve the specific capacity and cycle stability of lithium ion battery, realize low-cost, continuous, large-scale production of high-quality porous carbon.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery anode material technology, specifically relating to a high-performance silicon-carbon anode porous carbon material and its preparation method. Background Technology

[0002] The technological breakthroughs and industrial applications of new energy storage batteries will help improve my country's energy efficiency, reduce dependence on traditional energy sources, and promote the development and upgrading of my country's new energy industry. Lithium-ion batteries, due to their excellent performance, have been widely used in portable consumer electronics, power tools, and electric vehicles. Currently, commercially available lithium-ion batteries mainly use graphite as the anode material, but the theoretical specific capacity of traditional graphite is only 372 mAh / g. With the increasing demand for battery energy density in various fields, developing lithium-ion batteries with higher energy density has become an urgent task. Silicon materials have a specific capacity of up to 4200 mAh / g, far exceeding that of graphite. Silicon materials are environmentally friendly, abundant, and low-cost, but they suffer from problems such as low cycle life, large volume changes, and continuous formation of SEI films. Silicon-carbon anode materials can effectively improve these problems and are a key focus for future anode material development. The performance of silicon-carbon anodes mainly depends on the structural properties of the porous carbon framework; therefore, developing porous carbon with high structural performance is of paramount importance in the development of silicon-carbon anodes.

[0003] Porous carbon is a carbon material with highly developed pores, composed of randomly arranged graphite-like microcrystals. It possesses significant advantages such as high specific surface area, tunable pore and surface chemical structures, and stable physical and chemical properties, making it widely used in environmental protection, medicine, food, chemical industry, and military fields. Porous carbon plays a crucial role in silicon-carbon anode materials, serving not only as a conductive framework to improve electron transport rates but also mitigating the significant volume expansion of silicon during charging and discharging. However, while existing porous carbon materials can ensure high pore volume, they generally suffer from low micropore ratios and small specific surface areas, resulting in a reduction in lithium-ion storage sites and severely impacting battery capacity and cycle stability. Therefore, it is of great significance to regulate the pore structure of porous carbon and research and prepare a high-performance silicon-carbon anode porous carbon material with a large specific surface area and high micropore ratio. Summary of the Invention

[0004] In view of the content mentioned in the background art, the purpose of this invention is to provide a high-performance silicon-carbon anode porous carbon material and its preparation method. By doping single-crystal zinc and germanium to construct a special porous structure, the specific surface area and micropore ratio of the obtained silicon-carbon anode porous carbon material are significantly improved, which can meet the application requirements of high-performance lithium-ion batteries.

[0005] To achieve the above objectives, the present invention specifically adopts the following technical solution: This invention provides a method for preparing high-performance silicon-carbon anode porous carbon materials, comprising the following steps: Step 1: Crush the coconut shells, wash, dry, and pulverize them to obtain coconut shell powder as a carbon precursor; Step 2: Under a protective gas atmosphere, the carbon precursor is pre-carbonized by heating and then ground to obtain a black powder. Step 3: Take single crystal zinc oxide and add solvent to prepare impregnation solution. Add black powder to impregnation solution, stir and mix thoroughly, take it out, dry and grind to obtain doped powder; Step 4: The obtained doped powder is heated in a fluidized bed and activated by an activation gas under a protective gas to obtain porous carbon; then silane gas containing germanium is introduced for deposition, followed by carbon coating to obtain silicon-carbon anode porous carbon material.

[0006] In a preferred embodiment, the particle size of the coconut shell powder in step one is 50-200 μm.

[0007] In a preferred embodiment, the pre-carbonization temperature in step two is 490-520℃, the heating rate is 2-4℃ / min, and the holding time is 2-3 h.

[0008] In a preferred embodiment, the solvent in step three is anhydrous ethanol, and the mass ratio of black powder to single-crystal zinc oxide in the impregnation solution is 10:(2.5-4); the single-crystal zinc oxide is prepared by polystyrene template method.

[0009] As a preferred embodiment, the specific steps for preparing single-crystal zinc oxide using the polystyrene template method are as follows: zinc nitrate hexahydrate is dissolved in methanol to obtain a zinc source precursor solution, which is then filled into the interstices of the polystyrene template. The template surface is washed to remove residual zinc, and ammonia is added to generate zinc hydroxide nanosheets in the template interstices. The template is then removed, washed, and dried. Finally, heat treatment is performed to convert the nanosheets into single-crystal zinc oxide. This invention uses single-crystal zinc oxide for doping, which inherently possesses high carrier mobility. When its highly ordered crystal structure is uniformly dispersed in a porous carbon matrix, it can more effectively form continuous, high-speed electron transport channels. Under long-term operating conditions, it can maintain structural stability and exhibit slower performance degradation, thereby effectively improving the battery's cycle stability.

[0010] In a preferred embodiment, the fluidized bed heating rate in step four is 5-7℃ / min, the temperature is raised to 850-950℃, and then held for 30-50 min after reaching the temperature.

[0011] In a preferred embodiment, the activation gas in step four consists of water vapor and carbon dioxide in a volume ratio of (7-8):(3-2), and the activation time is 6-10 h. The combined activation gas of this invention works synergistically; water vapor rapidly opens and widens the pores, while carbon dioxide slowly and precisely etches the pore walls, contributing to the development of micropores and fine mesopores. A suitable hierarchical pore structure is crucial for high-performance silicon-carbon anodes, providing space for silicon particle deposition and volume expansion. Abundant micropores effectively store lithium ions, contributing to the formation of a stable solid electrolyte interface film.

[0012] In a preferred embodiment, the germanium-containing silane gas in step four is methanesilane / germanium hydride, with a volume ratio of 10:(0.1-0.25). The germanium doping in this invention is beneficial because germanium itself has a high specific capacity, and introducing germanium can improve the energy density to a certain extent. Furthermore, by doping germanium, the lattice structure of the silicon-based material is modulated, reducing the lithium-ion insertion / extraction resistance. Due to its extremely high lithium-ion diffusion rate, it can promote the rapid transport of lithium ions and electrons, thereby improving the charge / discharge rate. In this invention, the single-crystal zinc and germanium can form a beneficial conductive network, which not only has a stress buffering effect, suppressing the expansion and pulverization of the silicon-carbon matrix, but also helps maintain the integrity of the porous carbon structure during cycling, further improving cycle stability.

[0013] The present invention also provides a silicon-carbon anode porous carbon material obtained by the above preparation method.

[0014] In a preferred embodiment, the specific surface area of ​​the silicon-carbon anode porous carbon material is ≥1700 m². 2 / g, pore volume ≥0.85 cm³ 3 / g, micropores account for ≥83%.

[0015] Compared with the prior art, the beneficial effects of the present invention are: This invention uses natural, non-toxic, and renewable coconut shells to prepare carbonized materials as precursors, achieving the recycling of waste resources and reducing environmental pollution. By controlling raw material and process parameters, the pore size, channel shape, and pore distribution of the porous carbon are optimized. The porous carbon obtained by this invention has a large specific surface area and a high proportion of micropores, providing abundant lithium storage active sites, promoting rapid ion transport and storage, and laying the foundation for high capacity. At the same time, the rich pore structure can buffer volume changes during charge and discharge, resulting in low mechanical stress in the carbon skeleton and excellent cycle stability. The silicon-carbon anode porous carbon material of this invention can significantly improve electrochemical performance and can be used as a high-performance anode material in the field of high-end lithium-ion batteries. Detailed Implementation

[0016] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below in conjunction with embodiments. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0017] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. The terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to limit the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0018] Example 1 A method for preparing a high-performance silicon-carbon anode porous carbon material includes the following steps: 1. Take high-quality coconut shells, crush them, wash and dry them, and pulverize them to obtain coconut shell powder (50-200 μm) for use as a carbon precursor. Transfer the carbon precursor powder into an atmosphere furnace, and under nitrogen protection, heat it to 505℃ at a rate of 3℃ / min and hold it for 2.5 h for pre-carbonization. Then grind it to obtain a black powder for use.

[0019] 2. Dissolve zinc nitrate hexahydrate in an appropriate amount of methanol to obtain a zinc source precursor solution. Then, immerse the polystyrene template in the zinc source precursor solution for 1 hour, wash and dry to obtain a zinc-filled polystyrene template. Then, transfer it to an ammonia-methanol solution (water to methanol volume ratio 1:1, methanol mass fraction 20%) and immerse it overnight. Wash and dry to remove the polystyrene template. Finally, transfer it to a furnace and heat it at 550℃ for 1.5 hours. After natural cooling, obtain single crystal zinc oxide for later use.

[0020] 3. Weigh out black powder and single-crystal zinc oxide at a mass ratio of 10:3.3; add single-crystal zinc oxide to an appropriate amount of anhydrous ethanol to prepare an impregnation solution, then add black powder, stir magnetically for 6 hours, take out, dry, and grind to obtain doped powder.

[0021] 4. Add the doped powder to a fluidized bed, introduce nitrogen gas (20 L / min) while simultaneously heating to 910℃ at a rate of 6℃ / min, and hold at that temperature for 40 min. Adjust the gas flow to: nitrogen (10 L / min) / water vapor (7.5 L / min) / carbon dioxide (2.5 L / min), and perform high-temperature activation treatment for 8 h to obtain porous carbon. Then, transfer the porous carbon to a chemical vapor deposition chamber, heat to 540℃, introduce silane gas (6 L / min, nitrogen, silane, germanium hydride volume ratio of 19.8:10:0.2), and deposit silicon for 5 h. Subsequently, control the temperature at 525℃ and introduce acetylene (4 L / min) for CVD carbon coating for 2 h to obtain the silicon-carbon anode porous carbon material.

[0022] Example 2 A method for preparing a high-performance silicon-carbon anode porous carbon material includes the following steps: 1. Take high-quality coconut shells, crush them, wash and dry them, and pulverize them to obtain coconut shell powder (50-200 μm) for use as a carbon precursor. Transfer the carbon precursor powder into an atmosphere furnace, and under nitrogen protection, heat it to 490℃ at a rate of 2℃ / min and hold it for 3 hours for pre-carbonization. Then grind it to obtain a black powder for use.

[0023] 2. Dissolve zinc nitrate hexahydrate in an appropriate amount of methanol to obtain a zinc source precursor solution. Then, immerse the polystyrene template in the zinc source precursor solution for 1 hour, wash and dry to obtain a zinc-filled polystyrene template. Then, transfer it to an ammonia-methanol solution (water and methanol volume ratio 1:1, methanol mass fraction 20%) and immerse it overnight. Wash and dry to remove the polystyrene template. Finally, transfer it to a furnace and heat it at 500℃ for 2 hours. After natural cooling, obtain single crystal zinc oxide for later use.

[0024] 3. Weigh out black powder and single-crystal zinc oxide at a mass ratio of 10:2.5; add single-crystal zinc oxide to an appropriate amount of anhydrous ethanol to prepare an impregnation solution, then add black powder, stir magnetically for 6 hours, take out, dry, and grind to obtain doped powder.

[0025] 4. Add the doped powder to a fluidized bed, introduce nitrogen gas (20 L / min) and simultaneously heat to 850℃ at a rate of 5℃ / min, hold at the temperature for 50 min after reaching the target temperature; adjust the gas flow to: nitrogen (10 L / min) / water vapor (7 L / min) / carbon dioxide (3 L / min), and perform high-temperature activation treatment for 10 h to obtain porous carbon; then transfer the porous carbon to a chemical vapor deposition chamber, heat to 540℃, introduce silane gas (6 L / min, nitrogen, silane, germanium hydride volume ratio of 19.9:10:0.1), and deposit silicon for 5 h; subsequently, control the temperature at 525℃ and introduce acetylene (4 L / min), and perform CVD carbon coating for 2 h to obtain silicon-carbon anode porous carbon material.

[0026] Example 3 A method for preparing a high-performance silicon-carbon anode porous carbon material includes the following steps: 1. Take high-quality coconut shells, crush them, wash and dry them, and pulverize them to obtain coconut shell powder (50-200 μm) for use as a carbon precursor. Transfer the carbon precursor powder into an atmosphere furnace, and under nitrogen protection, heat it to 520℃ at a rate of 4℃ / min and hold it for 2 hours for pre-carbonization. Then grind it to obtain a black powder for use.

[0027] 2. Dissolve zinc nitrate hexahydrate in an appropriate amount of methanol to obtain a zinc source precursor solution. Then, immerse the polystyrene template in the zinc source precursor solution for 1 hour, wash and dry to obtain a zinc-filled polystyrene template. Then, transfer it to an ammonia-methanol solution (water and methanol volume ratio 1:1, methanol mass fraction 20%) and immerse it overnight. Wash and dry to remove the polystyrene template. Finally, transfer it to a furnace and heat it at 530℃ for 1.5 hours. After natural cooling, obtain single crystal zinc oxide for later use.

[0028] 3. Weigh out black powder and single-crystal zinc oxide at a mass ratio of 10:4; add single-crystal zinc oxide to an appropriate amount of anhydrous ethanol to prepare an impregnation solution, then add black powder, stir magnetically for 6 hours, take out, dry, and grind to obtain doped powder.

[0029] 4. Add the doped powder to a fluidized bed, introduce nitrogen gas (20 L / min) while simultaneously heating to 950℃ at a rate of 7℃ / min, and hold at that temperature for 30 min. Adjust the gas flow to: nitrogen (10 L / min) / water vapor (8 L / min) / carbon dioxide (2 L / min), and perform high-temperature activation treatment for 6 h to obtain porous carbon. Then, transfer the porous carbon to a chemical vapor deposition chamber, heat to 540℃, introduce silane gas (6 L / min, nitrogen, silane, germanium hydride volume ratio of 19.75:10:0.25), and deposit silicon for 5 h. Subsequently, control the temperature at 525℃ and introduce acetylene (4 L / min) for CVD carbon coating for 2 h to obtain the silicon-carbon anode porous carbon material.

[0030] Comparative Example 1 Referring to the steps and parameters of Embodiment 1 of the present invention, the only difference is that commercially available ordinary zinc oxide is used instead of the single-crystal zinc oxide prepared in step 2.

[0031] Comparative Example 2 Referring to the step parameters of Embodiment 1 of the present invention, the only difference is that germanium hydrogen is not introduced in step 4 silicon deposition, that is, the silane gas is composed of nitrogen and methane in a volume ratio of 19.8:10.

[0032] Comparative Example 3 Referring to the steps and parameters of Embodiment 1 of the present invention, the only difference is that the composition of the activation gas is adjusted to: nitrogen (10 L / min) / water vapor (10 L / min).

[0033] Test case The performance of the silicon-carbon anode porous carbon material samples prepared in the above embodiments and comparative examples was tested, and the results are shown in Table 1 (testing was conducted according to GB / T 19587-2017).

[0034] Table 1. Detection results of porous carbon samples for silicon-carbon anodes

[0035] According to the sample test results in Table 1, the porous carbon material prepared by the process of this invention has a specific surface area of ​​not less than 1700 m². 2 / g, pore volume up to 0.85 cm³ 3 The micropore content is above / g, not less than 83%, which is a significant improvement compared to traditional microporous and mesoporous porous carbon materials. Comparison of data from Comparative Example 1 shows that the pore volume and micropore effect of commercially available ordinary polycrystalline zinc doping are significantly reduced compared to monocrystalline zinc; comparison of data from Comparative Example 2 shows that the specific surface area of ​​monocrystalline zinc doped with only one type is also significantly reduced, proving that monocrystalline zinc and germanium have a certain synergistic effect; comparison of data from Comparative Example 3 shows that the combination and ratio of activation gases also have a key influence on the porous carbon structure.

[0036] Half-cell tests were conducted on the silicon-carbon anode porous carbon material samples prepared in the above embodiments and comparative examples. The slurry ratio was: silicon-carbon anode porous carbon material:CNTs:CMC:SBR=85:7:8:5. A PE separator was placed between the copper foil of the test electrode and the lithium sheet of the counter electrode. The test voltage was 0.005-2 V, and the rate was 1 C. The test results are shown in Table 2. Table 2 Half-cell test results

[0037] According to the sample test results in Table 2, corresponding to the aforementioned porous carbon pore structure, the porous carbon material of the present invention can significantly improve the specific capacity and cycle stability of the battery.

[0038] The embodiments described above are merely preferred embodiments of the present invention, and while the descriptions are specific and detailed, they are not intended to limit the present invention. It should be noted that various changes and modifications can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the concept and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a high-performance silicon-carbon anode porous carbon material, characterized in that, Includes the following steps: Step 1: Crush the coconut shells, wash, dry, and pulverize them to obtain coconut shell powder as a carbon precursor; Step 2: Under a protective gas atmosphere, the carbon precursor is pre-carbonized by heating and then ground to obtain a black powder. Step 3: Take single crystal zinc oxide and add solvent to prepare impregnation solution. Add black powder to impregnation solution, stir and mix thoroughly, take it out, dry and grind to obtain doped powder; Step 4: The obtained doped powder is heated in a fluidized bed and activated by an activation gas under a protective gas to obtain porous carbon; then silane gas containing germanium is introduced for deposition, followed by carbon coating to obtain silicon-carbon anode porous carbon material. The activation gas consists of water vapor and carbon dioxide in a volume ratio of (7-8):(3-2), and the activation time is 6-10 h; the germanium-containing silane gas is methanesilane / germanium hydrogen, and the volume ratio of the two is 10:(0.1-0.25).

2. The method for preparing a high-performance silicon-carbon anode porous carbon material according to claim 1, characterized in that, The particle size of the coconut shell powder mentioned in step one is 50-200 μm.

3. The method for preparing a high-performance silicon-carbon anode porous carbon material according to claim 1, characterized in that, The pre-carbonization temperature in step two is 490-520℃, the heating rate is 2-4℃ / min, and the holding time is 2-3 h.

4. The method for preparing a high-performance silicon-carbon anode porous carbon material according to claim 1, characterized in that, The solvent in step three is anhydrous ethanol, and the mass ratio of black powder to single-crystal zinc oxide in the impregnation solution is 10:(2.5-4); the single-crystal zinc oxide is prepared by polystyrene template method.

5. The method for preparing a high-performance silicon-carbon anode porous carbon material according to claim 4, characterized in that, The specific steps for preparing single-crystal zinc oxide by polystyrene template method are as follows: zinc nitrate hexahydrate is dissolved in methanol to obtain a zinc source precursor solution, which is then filled into the gaps of the polystyrene template. The zinc residue on the template surface is washed away, and ammonia is added to generate zinc hydroxide nanosheets in the template gaps. The template is removed, washed, and dried. Finally, heat treatment is performed to convert the nanosheets into single-crystal zinc oxide.

6. The method for preparing a high-performance silicon-carbon anode porous carbon material according to claim 1, characterized in that, In step four, the fluidized bed heating rate is 5-7℃ / min, and the temperature is raised to 850-950℃. After reaching the temperature, it is held for 30-50 minutes.

7. The silicon-carbon anode porous carbon material obtained by the preparation method according to any one of claims 1-6.

8. The silicon-carbon anode porous carbon material according to claim 7, characterized in that, The specific surface area of ​​the silicon-carbon anode porous carbon material is ≥1700 m². 2 / g, pore volume ≥0.85 cm³ 3 / g, micropores account for ≥83%.

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