Porous carbon material, preparation method thereof and lithium ion battery

Abstract

The invention belongs to the field of battery materials, and discloses a porous carbon material with a lotus-leaf-like structure. The preparation method comprises the following steps: mixing biomass powder with water, and carrying out microwave-assisted hydrothermal reaction to obtain a carbon nanodot suspension; placing the carbon nanodot suspension in rotary freezing equipment for rotary freezing to obtain a porous carbon precursor with a lotus-leaf-like structure; calcining the porous carbon precursor in a tubular furnace, and then pickling to obtain the porous carbon material with the lotus-leaf-like structure. The porous carbon material disclosed by the invention has a lotus-leaf-like structure, and the unique structure is connected through a micro-nano porous network and chemical bonds, so that the porous carbon material has the characteristics of a lotus leaf part, such as good stress dispersion capacity; the unique structure provides a buffer space for volume expansion of silicon particles in the charging process, stress can be effectively dispersed, mechanical damage caused by volume expansion is reduced, and the cycling stability of the material is improved.

Description

Technical Field

[0001] The present invention belongs to the field of lithium-ion battery materials, and particularly relates to a porous carbon material, a preparation method thereof, and a lithium-ion battery. Background Art

[0002] In recent years, with the rapid development of fields such as electric vehicles and smart grids, higher requirements have been put forward for the energy density, power density, and cycle life of lithium-ion batteries. Although traditional graphite anode materials have advantages such as low cost and mature processes, their theoretical specific capacity is only 372 mAh / g, making it difficult to meet the requirements of the next generation of high-energy-density lithium-ion batteries.

[0003] Silicon-based anode materials have attracted much attention due to their extremely high theoretical specific capacity (4200 mAh / g) and are regarded as one of the ideal anode materials for the next generation of high-energy-density lithium-ion batteries. However, silicon materials have poor intrinsic conductivity and a large volume expansion (~300%) during the charging process, resulting in poor cycle stability and severely limiting their practical applications. In contrast, carbon materials have good electrical conductivity and structural stability. By compounding silicon with carbon materials, the advantages of both can be fully integrated, effectively alleviating the volume expansion of silicon during charging, while significantly improving the electrical conductivity and cycle stability of the composite material.

[0004] The specific surface area and microporosity of materials play an important role in their electrochemical performance. Some studies have shown that, firstly, a high specific surface area provides an ideal site for the deposition of silicon, which can promote the uniform distribution of silicon and avoid the aggregation of silicon particles; secondly, a high microporosity provides a buffer space for the volume expansion of silicon during the lithium intercalation process, effectively alleviating stress concentration and reducing the damage to the electrode structure caused by volume expansion. At the same time, it can reduce the direct contact between silicon and the electrolyte, reduce the occurrence of irreversible side reactions, and thus improve the electrochemical performance of the material.

[0005] The electrical conductivity of materials plays an important role in their electrochemical performance. Some studies have shown that a porous carbon framework with high electrical conductivity provides a good electron conduction path for silicon particles, reduces internal resistance, improves the overall electrical conductivity of the electrode, and improves the efficiency of electrochemical reactions.

[0006] At the same time, a porous carbon with high electrical conductivity can maintain the integrity of the conductive network during cycling. Even if the silicon particles undergo volume changes, the electron transport path can still be maintained, improving the cycle stability.

[0007] However, among the current modification methods, silicon-carbon negative electrode materials prepared based on the fluidized bed method have great advantages. Nano-scale silicon materials are uniformly deposited in porous carbon materials with high specific surface area, microporosity and conductivity. First, the high specific surface area and high microporosity provide a buffer space for the volume expansion of silicon during lithium insertion, effectively relieve stress concentration, reduce the breakage and shedding of silicon particles, and thus significantly improve the cycle stability. Secondly, the excellent conductivity of the porous carbon material itself constructs a continuous conductive network, improves the overall conductivity of the electrode, and promotes the rapid transmission of electrons. At present, the preparation methods of porous carbon are mainly divided into physical activation and chemical activation. Physical activation (such as CO2 or water vapor activation) requires high temperature and long time, high energy consumption, and the activation process is difficult to accurately control, which easily leads to pore collapse and affects the microporosity and specific surface area of ​​the material. Although chemical activation (such as KOH) can increase the porosity, its strong corrosiveness may cause the pore wall to be too thin or even collapse, which reduces the microporosity. Moreover, the porous carbon prepared by the above-mentioned traditional methods usually has a low degree of graphitization and less sp² hybridized carbon structure, resulting in weak electron transmission ability and low conductivity. Therefore, how to effectively improve the specific surface area, microporosity and conductivity of porous carbon is a technical problem that needs to be solved urgently. Summary of the invention

[0008] The technical problem to be solved by the present invention is to overcome the deficiencies and defects mentioned in the above background technology and provide a porous carbon material and a preparation method thereof and a lithium ion battery.

[0009] In order to solve the above technical problems, the technical solution proposed by the present invention is: A porous carbon material has a lotus leaf-like structure.

[0010] The porous carbon material mentioned above preferably has a specific surface area of ​​not less than 3000 m 2 / g, microporosity not less than 90%, and electrical conductivity not less than 4S / mm. As a general inventive concept, the present invention also provides a method for preparing a porous carbon material having a lotus leaf-like structure, comprising the following steps: (1) mixing biomass powder with water and subjecting it to microwave-assisted hydrothermal reaction to obtain a carbon nanodot suspension; (2) placing the carbon nanodot suspension in a rotary freezing machine for rotary freezing to obtain a porous carbon precursor with a lotus leaf-like structure; (3) The porous carbon precursor obtained in step (2) is calcined in a tubular furnace, and then acid-washed to obtain a porous carbon material having a lotus leaf-like structure. For the above preparation method, preferably, in step (1), the microwave-assisted hydrothermal reaction is carried out in a microwave reactor. The power of the microwave-assisted hydrothermal reaction is 300 - 800 W, the reaction temperature is 120 - 200 °C, and the reaction time is 60 - 180 min. The temperature and power of the microwave-assisted hydrothermal reaction need to be controlled within the scope of the present invention. Otherwise, if the reaction temperature is higher than 200 °C, it will cause excessive growth or aggregation of carbon nanodots, destroying their uniform size distribution; if the reaction temperature is <120 °C, the energy of the reaction system is insufficient, which may lead to incomplete hydrolysis and degradation of the organic components in the biomass, incomplete reaction, and a significant reduction in the generation efficiency of carbon nanodots. If the power of the reaction is too high, the heating rate of the reaction system will be too fast, and the reaction process will be difficult to precisely control, which may lead to overreaction in some areas and damage the structure of carbon nanodots; if the power of the reaction is too low, some areas may not reach the required reaction temperature, resulting in uneven size distribution of carbon nanodots and reduced crystallinity, affecting the performance of the material. For the above preparation method, preferably, in step (1), the particle size of the biomass powder is 100 - 500 mesh, and the mass-volume ratio of the biomass powder to water is 1:10 - 1:50, with the ratio unit being g / mL.

[0011] For the above preparation method, preferably, in step (2), the rotation speed of the rotary freezing is 100 - 500 rpm, the temperature is -20 °C to -80 °C, and the freezing time is 2 - 12 h. The rotation speed of the rotary freezing needs to be controlled within the scope of the present invention. Otherwise, if the rotation speed is too high, the centrifugal force field will be too strong, which may cause excessive compression of ice crystals, and the pore structure will be squeezed or even collapsed, destroying the integrity of the lotus-leaf-like structure; if the rotation speed is too low, the centrifugal force field is not sufficient to guide the directional growth of ice crystals, and the ice crystals may grow randomly, resulting in a disordered pore structure and unable to form a continuous three-dimensional microporous network.

[0012] For the above preparation method, preferably, in step (3), the calcination is carried out in a nitrogen atmosphere. The temperature of the calcination is 600 - 800 °C, the heating rate is 5 - 8 °C / min, and the calcination time is 2 - 4 h.

[0013] For the above preparation method, preferably, in step (3), the pickling refers to stirring and washing in a hydrochloric acid solution with a concentration of 1 - 5 mol / L for 1 - 5 h.

[0014] For the above preparation method, preferably, the biomass powder is obtained by cleaning, crushing, and sieving the biomass, and the biomass powder is any one of coconut shells, walnut shells, moso bamboo, or reeds. As a general inventive concept, the present invention also provides a lithium-ion battery, including the above porous carbon material or a lithium-ion battery prepared by the above preparation method.

[0015] For the above-mentioned lithium-ion battery, preferably, when the current density is 0.5 A / g, the reversible capacity of the lithium-ion battery is not less than 1800 mAh / g, and the retention rate after 300 cycles of cyclic stability test is not less than 85%.

[0016] The invention mechanism of the present invention includes: first, using microwave radiation to uniformly transfer energy to the reaction system through the dielectric heating effect, causing the polar molecules (such as water molecules) inside the biomass to vibrate and rub violently, generating a local high-temperature and high-pressure environment, thereby accelerating the hydrolysis and degradation of macromolecular structures such as cellulose, hemicellulose, and lignin in the biomass, and generating intermediate products such as small-molecule sugars, organic acids, and phenolic compounds. Subsequently, these intermediate products undergo dehydration, condensation, and aromatization reactions under high-temperature and high-pressure conditions, not only retaining abundant surface functional groups, providing abundant chemical reaction sites for their subsequent applications, but also gradually forming aromatic polycyclic compounds with sp² hybrid carbon structures, and further polymerizing into carbon nuclei, and gradually growing, finally forming carbon nanodots with high crystallinity, uniform size, and good dispersibility; then, during the rotary freezing process, the carbon nanodot suspension is directionally frozen along the radial direction under the combined action of the centrifugal force field and the low-temperature environment. Due to the anisotropic growth of ice crystals, water molecules preferentially crystallize along the direction perpendicular to the temperature gradient (i.e., the radial direction), forming a radially arranged ice crystal template. At the same time, the action of the centrifugal force field causes the carbon nanodots to migrate and accumulate towards the ice crystal interface, and through the interaction between their surface functional groups and the ice crystal interface, an ice crystal-carbon nanodot composite structure is formed. Under the action of the ice crystal growth pressure, the carbon nanodots are directly repelled to the ice crystal interface and arranged directionally, and finally self-assembled into a lotus-leaf-like porous structure. In addition, the mutual connection between carbon nanodots and the subsequent removal of the ice crystal template further form a continuous three-dimensional microporous network, significantly increasing the microporosity and specific surface area of the material; and through mutual connection, an efficient conductive network is constructed, reducing the resistance of electron transport, thereby improving the overall conductivity of the material. Compared with the prior art, the beneficial effects of the present invention are as follows: (1) The porous carbon material of the present invention has a lotus-leaf-like structure. This unique lotus-leaf-like structure is connected by a micro-nano porous network and chemical bonds, and has some characteristics of a lotus leaf, such as good stress dispersion ability; this unique structure provides a buffer space for the volume expansion of silicon particles during the charging process, can effectively disperse stress, reduce mechanical damage caused by volume expansion, and improve the cyclic stability of the material. (2) The present invention utilizes the rapid heating and uniform heating characteristics of microwave-assisted hydrothermal treatment, enabling the prepared carbon nanodots to have a more uniform size distribution and higher crystallinity. In addition, the carbon nanodots synthesized by microwave-assisted hydrothermal treatment are rich in more C=C and C=O double bonds on the surface, which can enhance their ability to provide stronger chemical bonding during the subsequent self-assembly process. Combined with the rotary freezing technique, taking advantage of the anisotropy of ice crystal growth and the directional effect of the centrifugal force field, a template is provided for the self-assembly of carbon nanodots, enabling them to align along a specific direction and further guiding the distribution of carbon nanodots, and finally self-assembling into a lotus leaf-like structure.

[0017] (3) The method for preparing the porous carbon material with a lotus leaf-like structure in the present invention does not require additional template materials, reducing the template removal step and avoiding the damage to the lotus leaf-like structure caused by template removal.

[0018] (4) In the preparation method of the present invention, the rotary freezing technique is introduced. Under the condition of applying directional rotary freezing, by regulating the directional pore structure constructed by the ice crystal template and the densification structure of the centrifugal force field, the defects inside the material are reduced, and the resistance of electron transport is lowered, thereby improving the electrical conductivity of the material.

[0019] (5) Under the condition of applying directional rotary freezing in the preparation method of the present invention, by adjusting the freezing rotation speed, carbon nanodots with uniform size and high crystallinity are evenly distributed on the surface of the ice crystal template. The C=C and C=O double bonds on their surface can serve as nucleation sites to promote the directional growth of ice crystals, and then form a highly ordered porous structure, enabling it to form a porous carbon material with high microporosity and specific surface area during the subsequent carbonization and pickling processes, avoiding the problem of low specific surface area and microporosity caused by carbon nanodot aggregation in the traditional method.

[0020] (6) When the lotus leaf-like porous carbon material prepared by the present invention is used as the electrode material of a lithium-ion battery, the lithium-ion battery has good electrochemical performance.

[0021] (7) The preparation process of the present invention is simple, convenient to operate and controllable. Description of the Drawings

[0022] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the following drawings are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0023] Figure 1 SEM image of the lotus leaf-like porous carbon material obtained in Example 1 of the present invention; Figure 2 SEM image of the layered porous carbon material obtained in Comparative Example 1 of the present invention; Figure 3 SEM image of the flaky porous carbon material obtained in Comparative Example 2 of the present invention; Figure 4 BET diagram of the lotus leaf-like porous carbon material obtained in Example 1 of the present invention; Figure 5 Cyclic test diagram of the lotus leaf-like porous carbon material obtained in Example 1 of the present invention at 0.5 A / g. Detailed implementation manners

[0024] To facilitate the understanding of the present invention, the following will describe the present invention more comprehensively and meticulously in conjunction with the accompanying drawings of the specification and preferred embodiments. However, the protection scope of the present invention is not limited to the following specific embodiments.

[0025] Unless otherwise defined, all professional terms used hereinafter have the same meaning as commonly understood by those skilled in the art. The professional terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the protection scope of the present invention.

[0026] Unless otherwise specifically stated, various raw materials, reagents, instruments, and equipment used in the present invention can be obtained through market purchases or can be prepared by existing methods.

[0027] Example 1: A porous carbon material of the present invention has a lotus leaf-like structure, with a specific surface area of 3672 m 2 / g, a microporosity of 94%, and an electrical conductivity of 5.25 S / mm.

[0028] The preparation method of the porous carbon material with a lotus leaf-like structure in this example includes the following steps: (1) After cleaning the moso bamboo, it is pulverized into powder and sieved through a 200-mesh sieve to obtain bamboo powder with uniform particle size; (2) The mass-volume ratio of bamboo powder to deionized water is stirred evenly at a ratio of 1 g:10 mL, placed in a microwave reactor, and subjected to microwave-assisted hydrothermal reaction at a power of 500 W and a temperature of 160 °C for 1 h. After the reaction, it is cooled to room temperature, centrifuged, and the supernatant is collected to obtain a carbon nanodot suspension; (3) Pour the carbon nanodot suspension into a mold, place the mold in a rotary freezer, and rotate and freeze at a speed of 300 rpm and a temperature of -20 °C for 6 h. After freezing, a porous carbon material precursor with a lotus leaf-like structure is obtained; (4) The precursor was placed in a tube furnace and calcined at 600 °C for 2 h under a nitrogen atmosphere with a heating rate of 5 °C / min. Finally, it was stirred and washed in a 3 mol / L hydrochloric acid solution for 3 h, dried, and a porous carbon material (BPC-6-600) was obtained. Its SEM is as Figure 1 shown. It can be seen from Figure 1 that the porous carbon material (BPC-6-600) of this example has a lotus leaf-like structure.

[0029] The nitrogen adsorption / desorption test was carried out on the porous carbon material (BPC-6-600) of this example. The test results are as Figure 4 and Table 1 shown. It can be known from Figure 4 and Table 1 that the specific surface area of BPC-6-600 is 3672 m 2 / g, and the microporosity is 94%. According to GB / T 24525-2009: "Determination Method of Resistivity of Carbon Materials", the conductivity test was carried out on the porous carbon material (BPC-6-600) of this example, and its conductivity is 5.25 S / mm.

[0030] Silane / acetylene was deposited on the porous carbon material of this example by chemical vapor deposition to prepare a silicon-carbon negative electrode material (BPC-6-600 / Si / C) with a silicon content of 51%. Then, a battery was assembled to conduct a constant current charge-discharge test to evaluate its electrochemical performance. The specific method of assembling the battery is as follows: The silicon-carbon negative electrode material (BPC-6-600 / Si / C), carbon black, and CMC binder were prepared into a negative electrode slurry in a ratio of 8:1:1. Then, it was coated on a copper foil with a scraper and vacuum dried at 60 °C for 24 h, and cut into circular electrode sheets with a diameter of 12 mm. The positive electrode used a lithium metal sheet (diameter 12 mm, thickness 0.5 mm), the separator was glass fiber (Whatman, 20 mm), and the electrolyte was 1 M LiPF6 (dissolved in a mixed solvent of EC:DMC = 1:1). The battery was assembled in the order of negative electrode sheet, electrolyte, separator, electrolyte, and lithium metal sheet to form a CR2032 battery.

[0031] The electrochemical performance of the CR2032 battery was tested. When the current density was 0.5 A / g, the initial discharge capacity was 2312 mAh / g, the initial Coulomb efficiency was 94%, and the retention rate after 300 cycles of stability test was 92.1%, as Figure 5 shown.

[0032] Example 2: The difference between this example and Example 1 is only that: in step (3), the rotational freezing speed was 400 rpm, and the prepared material was labeled as BPC-400.

[0033] The specific surface area of the porous carbon material (BPC-400) in this example is 3559 m 2 / g, the microporosity is 93%, and the electrical conductivity is 4.75 S / mm.

[0034] Assemble the battery in the same way as in Example 1, and perform constant current charge and discharge tests to evaluate its electrochemical performance. When the current density is 0.5 A / g, the reversible capacity is 2156 mAh / g, the initial Coulomb efficiency is 92%, and the retention rate after 300 cycles of stability test is 90.4%.

[0035] Example 3: The difference between this example and Example 1 is only that: in step (3), the rotational freezing speed is 500 rpm, and the prepared material is marked as BPC-500.

[0036] The specific surface area of the porous carbon material (BPC-500) in this example is 3376 m 2 / g, the microporosity is 92%, and the electrical conductivity is 4.32 S / mm.

[0037] Assemble the battery in the same way as in Example 1, and perform constant current charge and discharge tests to evaluate its electrochemical performance. When the current density is 0.5 A / g, the reversible capacity is 2001 mAh / g, the initial Coulomb efficiency is 92%, and the retention rate after 300 cycles of stability test is 89.9%. By comparing Example 1, Example 2 and Example 3, it can be seen that the rotational freezing speed is a key parameter. An overly long rotational freezing speed may cause the ice crystal spacing to become smaller, the pore structure to become denser, resulting in the pores being compressed or blocked, a significant reduction in the specific surface area and microporosity, and it will also hinder the electron transport in the material and increase the internal resistance.

[0038] Example 4: The difference between this example and Example 1 is only that: in step (4), the calcination temperature is 700 °C, and the prepared material is marked as BPC-6-700.

[0039] The specific surface area of the porous carbon material (BPC-6-700) in this example is 3320 m 2 / g, the microporosity is 92%, and the electrical conductivity is 4.67 S / mm.

[0040] Perform constant current charge and discharge tests in the same way as in Example 1 to evaluate its electrochemical performance. When the current density is 0.5 A / g, the reversible capacity is 2121 mAh / g, the initial Coulomb efficiency is 91%, and the retention rate after 300 cycles of stability test is 89.4%. Example 5: The difference between this example and Example 1 is only that: in step (4), the calcination temperature is 800 °C, and the prepared material is marked as BPC-6-800.

[0041] The specific surface area of the porous carbon material (BPC-6-800) in this example is 3282 m 2 / g, the microporosity is 91%, and the conductivity is 4.41 S / mm.

[0042] The constant current charge-discharge test was carried out in the same way as in Example 1 to evaluate its electrochemical performance. When the current density is 0.5 A / g, the reversible capacity is 1989 mAh / g, the first Coulomb efficiency is 90%, and the retention rate after 300 cycles of stability test is 87.5%. By comparing Example 1, Example 4 and Example 5, it can be seen that the pyrolysis temperature also has a great influence on the electrochemical performance, specific surface area, microporosity and conductivity of the material.

[0043] Comparative Example 1: The difference between this comparative example and Example 1 is only that: step (2) is not passed, that is, microwave-assisted hydrothermal reaction is not used, and the prepared material is marked as BC-1.

[0044] The specific surface area of the carbon material BC-1 in this comparative example is 1235 m 2 / g, the microporosity is 70%, and the conductivity of BC-1 is 1.72 S / mm. Its SEM is as Figure 2 shown, from Figure 2 it can be seen that the porous carbon material (BC-1) in this comparative example is a layered structure, not a lotus leaf-like structure.

[0045] The constant current charge-discharge test was carried out in the same way as in Example 1 to evaluate its electrochemical performance. When the current density is 0.5 A / g, the reversible capacity is 1174 mAh / g, the first Coulomb efficiency is 79%, and the retention rate after 300 cycles of stability test is 75%.

[0046] Comparative Example 2: The difference between this comparative example and Example 1 is only that: step (3) is not passed, that is, directional rotation freezing is not used, and the prepared material is marked as BC-2.

[0047] The specific surface area of the carbon material BC-2 in this comparative example is 899 m 2 / g, the microporosity is 65%, and the conductivity is 1.11 S / mm. Its SEM is as Figure 3 shown, from Figure 3 it can be seen that the porous carbon material (BC-2) in this comparative example is a flake structure, not a lotus leaf-like structure.

[0048] The constant current charge-discharge test was carried out in the same way as in Example 1 to evaluate its electrochemical performance. When the current density was 0.5 A / g, the reversible capacity was 747 mAh / g, the first Coulombic efficiency was 72%, and the retention rate after 300 cycles of stability test was 60%.

[0049] By comparing Example 1, Comparative Example 1 and Comparative Example 2, it can be seen that the specific preparation process has a great influence on the structure of the material.

[0050] Table 1: Performance data of porous carbon materials in examples and comparative examples

[0051] It should be noted that the above examples are only used to illustrate the technical solutions of the present invention, rather than limiting it; although the present invention has been described in detail with reference to the foregoing examples, those of ordinary skill in the art should understand that they can still modify the technical solutions recorded in the foregoing examples, or perform equivalent replacements for some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A porous carbon material, characterized in that: The porous carbon material has a lotus leaf-like structure.

2. The porous carbon material according to claim 1, characterized in that The specific surface area of ​​the porous carbon material is not less than 3000 m 2 / g, microporosity not less than 90%, and electrical conductivity not less than 4S / mm.

3. A method for preparing a porous carbon material having a lotus leaf-like structure, characterized in that: The following steps are involved: (1) mixing biomass powder with water and subjecting it to microwave-assisted hydrothermal reaction to obtain a carbon nanodot suspension; (2) placing the carbon nanodot suspension in a rotary freezing device for rotary freezing to obtain a porous carbon precursor with a lotus leaf-like structure; (3) The porous carbon precursor obtained in step (2) is calcined in a tubular furnace, and then acid-washed to obtain a porous carbon material having a lotus leaf-like structure.

4. The preparation method according to claim 3, characterized in that: In step (1), the microwave-assisted hydrothermal reaction is carried out in a microwave reactor, the power of the microwave-assisted hydrothermal reaction is 300-800 W, the reaction temperature is 120-200° C., and the reaction time is 60-180 min.

5. The preparation method according to claim 3, characterized in that: In step (1), the particle size of the biomass powder is 100-500 mesh, and the mass volume ratio of the biomass powder to water is 1:10-1:50, and the ratio unit is g / mL.

6. The preparation method according to claim 3, characterized in that: In step (2), the rotation speed of the rotary freezer is 100-500 rpm, the temperature is -20°C to -80°C, and the freezing time is 2-12 hours.

7. The preparation method according to claim 3, characterized in that: In step (3), the calcination is carried out in a nitrogen atmosphere, the calcination temperature is 600-800°C, the heating rate is 5-8°C / min, and the calcination time is 2-4h.

8. The preparation method according to claim 3, characterized in that: In step (3), the acid washing refers to stirring and washing in a hydrochloric acid solution with a concentration of 1-5 mol / L for 1-5 hours.

9. The preparation method according to claim 1, characterized in that: The biomass powder is obtained by cleaning, crushing and sieving the biomass, and the biomass powder is any one of coconut shell, walnut shell, bamboo or reed.

10. A lithium ion battery, characterized in that: A lithium ion battery comprising the porous carbon material as claimed in claim 1 or 2 or prepared by the preparation method as claimed in any one of claims 3 to 9.

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