Biomass-derived porous carbon material, preparation method therefor, and use thereof

Abstract

Embodiments of the present invention relate to a biomass-derived porous carbon material, a preparation method therefor, and a use thereof. The biomass-derived porous carbon material is composed of graphite-like carbon microcrystallites. The biomass-derived porous carbon material has a degree of ordering η of 20000-80000, an equivalent number of atomic layers ηa of carbon atoms periodically arranged along the a-axis direction is 30-50, and a number of atomic layers ηc of carbon atoms periodically arranged along the c-axis direction is 20-40. In an X-ray diffraction pattern of the biomass-derived porous carbon material, the (002) crystal plane has a diffraction angle 2θ ranging from 24.5° to 26.2°, the graphite-like carbon microcrystallites has a carbon interlayer spacing of 0.340 nm to 0.365 nm, and the (002) crystal-plane diffraction peak has a full width at half maximum β002 of 0.5 rad to1.5 rad. In the present invention, the degree of ordering and the interlayer spacing of carbon atomic layers in the graphite‑like carbon microcrystallites enable the biomass-derived porous carbon material to have sufficient strength and electrical conductivity, so that the material does not undergo mechanical fracture or deformation during repeated charge-discharge processes, thereby effectively suppressing volume expansion of nano-silicon particles, improving the initial coulombic efficiency and rate performance of the battery, and prolonging the cycle life and service life of the battery under high-rate conditions.

Description

A biomass porous carbon material, its preparation method and application

[0001] This application claims priority to Chinese Patent Application No. 202411904611.9, filed on December 23, 2024, entitled "A Biomass Porous Carbon Material and Its Preparation Method and Application". Technical Field

[0002] This invention relates to the field of materials, and more particularly to a biomass porous carbon material, its preparation method, and its application. Background Technology

[0003] Lithium-ion batteries are widely used in consumer electronics, new energy vehicles, and other fields due to their high energy density and long cycle life. Currently, the anode materials for lithium-ion batteries mainly use graphite-based materials, with a theoretical specific capacity of 372 mAh / g, which limits further improvements in battery energy density and hinders the development of industries such as portable electronics and electric aircraft. Silicon (Si)-based anode materials have a theoretical specific capacity of 4200 mAh / g, showing a significant advantage over graphite-based materials. However, silicon undergoes a volume change exceeding 300% during charge and discharge, leading to rapid performance degradation and severely restricting its widespread application. Nanoconfining technology can significantly alleviate the performance degradation caused by the volume change of lithium insertion / extraction in nano-silicon anodes, but it cannot fundamentally change the problem caused by the expansion of nano-silicon. Because the strength of porous carbon in biomass is insufficient, its effect on suppressing the volume expansion of nano-silicon particles is relatively poor. Therefore, in the battery manufacturing process, the silicon-carbon anode materials prepared by this method suffer from silicon-carbon particle breakage after the electrode is rolled, resulting in a very low coulombic efficiency in the first cycle and a short cycle life.

[0004] Furthermore, existing biomass porous carbon is amorphous carbon, composed of numerous short-range ordered and long-range disordered graphite-like carbon microcrystals. The random stacking of these carbon microcrystals forms the pores, becoming a fundamental characteristic of biomass porous carbon. This typically refers to the arrangement of carbon atoms in biomass porous carbon materials in a graphite-like structure. As shown in Figure 1, graphite is a layered structure composed of carbon atoms arranged in a hexagonal pattern, with each layer interacting through van der Waals forces. Where d 002 denoted as the interlayer spacing of the graphite carbon, La as the average size of the graphite crystals along the a-axis, and Lc as the thickness of the graphite flakes stacked along the c-axis perpendicular to it.

[0005] In biomass porous carbon materials, these graphite-like carbon crystallites are not perfect graphite structures, but they possess some characteristics of graphite, such as the layered structure of carbon atoms and a certain degree of crystal order. These ordered carbon crystallites exhibit sp2-sp2 orbital hybridization, which can serve as channels for electron transfer. Therefore, the electrical conductivity of the material can be improved by controlling the structure of the graphite-like carbon crystallites. The disordered stacking of graphite-like carbon crystallites gives biomass porous carbon materials a certain porosity, resulting in a large specific surface area. The size and arrangement of the graphite-like carbon crystallites also affect many properties of biomass porous carbon materials, such as physical properties like specific surface area, pore size, pore size distribution, pore volume, and strength, as well as chemical properties like electrical conductivity and thermal stability.

[0006] However, existing technologies generally use graphitization degree to describe the crystal structure of porous carbon in biomass. As mentioned above, porous carbon in biomass is not graphite, and the concept and method of graphitization degree are no longer suitable for evaluating the microstructure of porous carbon materials in biomass. Specifically:

[0007] X-ray diffraction (XRD) method for determining graphitization degree first involves determining the interlayer spacing d of graphite (002) crystal planes. 002 Then substitute the formula into the Mering-Maire formula (also known as the Franklin formula) to calculate:

[0008] G=(0.3440–d 002 ) / (0.3440–0.3354)×100%

[0009] Where: G is the degree of graphitization; 0.3440 is the interlayer spacing of non-graphitized carbon; 0.3354 is the interlayer spacing of ideal graphite crystals, which is also 1 / 2 of the c-axis lattice constant of hexagonal graphite; d 002 denoted as the interlayer spacing of the (002) crystal plane of carbon material.

[0010] As can be seen from the above formula, it essentially compares the interlayer spacing of amorphous (non-graphitized carbon) carbon (the lower limit of interlayer spacing for amorphous carbon) of 0.3440 nm with that of ideal graphite. However, the actual interlayer spacing d of amorphous carbon... 002 Since none of them are less than 0.3440 nm, the calculated degree of graphitization is negative and has no physical meaning. Therefore, the degree of graphitization cannot quantitatively describe the structural characteristics of porous carbon in biomass, and thus cannot be used to regulate the preparation conditions of porous carbon in biomass to achieve the required electrochemical performance. Summary of the Invention

[0011] The purpose of this invention is to address the deficiencies of existing technologies by providing a biomass porous carbon material, its preparation method, and its application. This biomass porous carbon material has a suitable degree of order, resulting in strong mechanical properties and high electrical conductivity.

[0012] To achieve the above objectives, in a first aspect, the present invention provides a biomass porous carbon material, wherein the biomass porous carbon material is composed of graphite-like carbon microcrystals;

[0013] The degree of order η of the biomass porous carbon material is 20,000-80,000, and the equivalent number of atomic layers η of carbon atoms periodically arranged along the a-axis direction is... a The number of atomic layers η, where carbon atoms are periodically arranged along the c-axis, is 30-50. c The range is 20-40; in the X-ray diffraction pattern of the biomass porous carbon material, the diffraction angle 2θ of the (002) crystal plane ranges from 24.5° to 26.2°, and the carbon interlayer spacing of the graphite-like carbon microcrystals is 0.340 nm to 0.365 nm; the full width at half maximum (FWHM) of the (002) crystal plane diffraction peak is β. 002 It is 0.5 rad - 1.5 rad.

[0014] Preferably, the specific surface area of ​​the biomass porous carbon material is 800 m². 2 / g-2800m 2 / g, pore volume is 0.4ml / g-1.8ml / g, pore size is 1.5nm-5.0nm, particle size D50 is 0.5μm-50μm; the degree of order η is preferably 20000-70000.

[0015] In a second aspect, the present invention provides a method for preparing the biomass porous carbon material according to any one of the first aspects, the preparation method comprising:

[0016] The biomass porous carbon raw material is subjected to heat treatment to carbonize it and generate carbonization products; the heat treatment temperature is 550℃-750℃ and the time is 2 hours-6 hours.

[0017] The carbonized product is subjected to physical activation treatment to generate a first activated product; the temperature of the physical activation treatment is 800℃-950℃ and the time is 4 hours-10 hours.

[0018] The first activated product is subjected to chemical activation treatment to generate a second activated product; the temperature of the chemical activation treatment is 700℃-1100℃ and the time is 4 hours-8 hours.

[0019] The second activated product is washed and dried to obtain the biomass porous carbon material.

[0020] Preferably, the activator for the physical activation treatment is water vapor and / or carbon dioxide.

[0021] Preferably, the activator for the chemical activation treatment is one or more of KOH, NaOH, K2CO3, and Na2CO3.

[0022] Preferably, the mass ratio of the chemical activator to the first activation product in the chemical activation treatment is 2.5-4.5.

[0023] Preferably, the washing process specifically involves placing the second activated product in an acid solution, soaking it at a certain temperature for a period of time, and then centrifuging and washing it with water.

[0024] Thirdly, the present invention provides a silicon-carbon anode material, the silicon-carbon anode material comprising the biomass porous carbon material described in any of the first aspects or the biomass porous carbon material prepared by any of the preparation methods described in any of the second aspects, and nano-silicon particles deposited in the pores of the biomass porous carbon material.

[0025] Fourthly, the present invention provides a negative electrode sheet, the negative electrode sheet comprising the silicon-carbon negative electrode material described in the third aspect.

[0026] Fifthly, the present invention provides a lithium-ion battery, the lithium-ion battery comprising the negative electrode sheet described in the fourth aspect.

[0027] The biomass porous carbon material provided in this invention has sufficient strength and electrical conductivity due to its high degree of order and the carbon layer spacing of graphite-like carbon microcrystals. When applied to battery anode materials, it will not undergo mechanical breakage or deformation during repeated charging and discharging, effectively suppressing the volume expansion of nano-silicon particles, improving the battery's first-cycle coulombic efficiency and rate performance, and extending the battery's cycle life and service life at high rates. Attached Figure Description

[0028] Figure 1 is an analysis diagram of the graphite structure provided by the prior art in the embodiments of the present invention;

[0029] Figure 2 is a flowchart of the preparation method of biomass porous carbon material provided in the embodiment of the present invention;

[0030] Figure 3 is the XRD pattern of the biomass porous carbon material provided in Example 1 of the present invention;

[0031] Figure 4 is the XRD pattern of the biomass porous carbon material provided in Comparative Example 1 of the present invention;

[0032] Figure 5-a is one of the SEM images of the biomass porous carbon material provided in Example 1 of the present invention;

[0033] Figure 5-b is a second SEM image of the biomass porous carbon material provided in Example 1 of the present invention;

[0034] Figure 6-a is one of the SEM images of the biomass porous carbon material provided in Comparative Example 1 of the present invention;

[0035] Figure 6-b is a second SEM image of the biomass porous carbon material provided in Comparative Example 1 of the present invention. Detailed Implementation

[0036] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0037] The present invention provides a biomass porous carbon material composed of graphite-like carbon microcrystals, wherein the degree of order η of the biomass porous carbon material is 20000-80000, preferably 20000-70000.

[0038] The equivalent number of atomic layers η of carbon atoms arranged periodically along the a-axis. a The number of atomic layers η, where carbon atoms are periodically arranged along the c-axis, is 30-50. c The range of the diffraction angle 2θ of the (002) crystal plane is 24.5°-26.2°, and the interlayer spacing of the graphite-like carbon microcrystals is 0.340nm-0.365nm. The full width at half maximum (FWHM) of the (002) crystal plane diffraction peak is β. 002 It is 0.5 rad - 1.5 rad.

[0039] Because biomass porous carbon materials are generally composed of graphite-like carbon microcrystals and amorphous regions, and the arrangement of carbon atoms in the graphite-like carbon microcrystals still exhibits some graphite-like characteristics, such as layered structure and a certain degree of crystal order, this application does not use the degree of graphitization but rather the degree of order to describe the crystal structure of biomass porous carbon materials. The specific calculations are as follows:

[0040] η = η a *η a *η c ;

[0041] η a =(La / d 002 +1);

[0042] η c =(Lc / d 002 +1).

[0043] In the formula, La=1.84λ / (β) 100 *cosθ 100), where Lc is the average size of the graphite-like carbon microcrystals along the a-axis, in nm; Lc = 0.89λ / (β 002 *cosθ 002 ), where d is the stacking thickness of graphite-like carbon microcrystals along the c-axis, in nm. 002 β is the interlayer spacing of graphite-like microcrystalline carbon, measured in nm; 100 The full width at half maximum (FWHM) of the (100) peak is expressed in rad; β 002 The full width at half maximum (FWHM) of peak (002) is given by rad, λ is the X-ray wavelength of 0.15406 nm, and θ is the peak width of peak (002). 100 The Bragg angle of the (100) peak is in rad; θ 002 The Bragg angle of peak (002) is expressed in rad; η c η represents the number of atomic layers in which carbon atoms are periodically arranged along the c-axis in graphitic carbon microcrystals. a η represents the equivalent atomic layer number of carbon atoms periodically arranged along the a-axis in graphite-like microcrystals, and η represents the degree of order of porous carbon in biomass, that is, the degree of order in the periodic arrangement of carbon atoms in space in graphite-like carbon microcrystals.

[0044] The ordered nature of biomass porous carbon and the interlayer spacing of graphite-like carbon microcrystalline carbon give biomass porous carbon materials sufficient strength and electrical conductivity. When applied to battery anode materials, they do not undergo mechanical breakage or deformation during repeated charge and discharge processes. This effectively suppresses the volume expansion of nano-silicon particles, improves the battery's first-cycle coulombic efficiency and rate performance, and extends the battery's cycle life and service life at high rates.

[0045] The specific surface area of ​​biomass porous carbon material is 800 m². 2 / g-2800m 2 / g, pore volume is 0.4ml / g-1.8ml / g, pore size is 1.5nm-5.0nm, and particle size D50 is 0.5μm-50μm.

[0046] This invention also provides a method for preparing biomass porous carbon materials, the process of which is shown in Figure 2 and includes the following steps:

[0047] Step 110: Heat-treat the biomass porous carbon raw material to carbonize it and generate carbonization products.

[0048] Specifically, biomass porous carbon raw materials may include at least one of the following: coconut shell, birch, poplar, lychee wood, apple wood, walnut wood, pea wood, balsa wood, bamboo, walnut shell, palm shell, rice husk, or straw.

[0049] The heat treatment atmosphere is nitrogen and / or argon, the temperature can be 550℃-750℃, preferably 650℃-750℃, and the time can be 2 hours-6 hours, preferably 2 hours-4 hours.

[0050] The main purpose of heat treatment is to decompose the organic matter in the biomass porous carbon raw material into carbon structure, forming a large number of graphite-like microcrystals and a certain amount of pores. However, the specific surface area, pore volume and pore size of the material are relatively small.

[0051] Step 120: Physically activate the carbonized product to generate the first activated product;

[0052] Specifically, the activator for physical activation treatment can be water vapor and / or carbon dioxide, preferably water vapor. The temperature for physical activation treatment can be 800℃-950℃, preferably 850℃-900℃, and the time can be 4 hours-10 hours, preferably 6 hours-8 hours.

[0053] During the physical activation process, the activation gas reacts with carbon to further form pores, which to some extent expands the specific surface area, pore volume and pore size of the material; at the same time, the graphite-like carbon microcrystals will be reduced or disordered due to etching, thereby adjusting the structure of the graphite-like carbon microcrystals.

[0054] Step 130: The first activated product is chemically activated to generate the second activated product;

[0055] Specifically, the activator for chemical activation is one or more of KOH, NaOH, K2CO3, and Na2CO3, with KOH being preferred. The mass ratio of the chemical activator to the first activation product can be 2.5-4.5. The temperature for chemical activation can be 700℃-1100℃, preferably 800℃-1100℃, and the time can be 2 hours-8 hours, preferably 3 hours-6.5 hours.

[0056] In chemical activation, the reaction between the chemical reagent and the first activation product mainly plays a role in continuing pore formation and promoting the growth and adjustment of carbon atoms in graphite-like carbon microcrystals. Specifically, on the one hand, the chemical activator reacts with carbon to form alkali metal atoms, which can embed into the carbon atom layers, creating more pores in the biomass porous carbon, resulting in a higher specific surface area, pore volume, and suitable pore size. On the other hand, the embedding of alkali metal ions with carbon atoms can form carbides. At the chemical activation temperature, the chemical activator is in a molten state, which is conducive to the movement of carbon and alkali metal atoms and promotes the growth of alkali metal carbide microcrystals. When the temperature reaches a certain value, the alkali metal atoms volatilize, carbon precipitates, and carbon microcrystals are continuously formed or reshaped. By changing the carbon raw material, the type of activator, the ratio of activator, the mixing (contact) method of activator and carbon, the reaction temperature, and the time, the carbon microcrystals can be regulated, thereby affecting the degree of order in the biomass porous carbon.

[0057] Step 140: Wash the second activated product and dry it to obtain biomass porous carbon material.

[0058] Specifically, the washing process is as follows: the second activated product is placed in an acid solution and soaked at a certain temperature for a period of time, followed by centrifugation and washing with water. The acid solution can be one or more of sulfuric acid, hydrochloric acid, and nitric acid. The concentration of the acid solution can be 70%. The washing temperature can be 80℃, and the time can be 24 hours. The centrifugation speed can be 8000 r / min, and the time can be 5 min. The standard for water washing is that the supernatant after centrifugation is neutral, for example, pH 6-7. Drying can be carried out in an oven at 100℃ for 12 hours.

[0059] This invention provides a method for preparing porous biomass carbon materials. By carbonizing, physically activating, and chemically activating the biomass porous carbon raw material, and by controlling the temperature and time of each step, the spatial arrangement of carbon atoms in the graphite-like carbon microcrystals in the biomass porous carbon is adjusted, thereby changing the size and arrangement of the graphite-like microcrystals, controlling the pore structure and the interlayer spacing of the graphite-like carbon microcrystals, and thus changing the degree of order of the biomass porous carbon, so that the biomass porous carbon has sufficient mechanical strength and electrical conductivity.

[0060] This invention also provides a silicon-carbon anode material, which includes the biomass porous carbon material provided in this application or the biomass porous carbon material prepared by the preparation method of this application, as well as nano-silicon particles deposited in the pores of the biomass porous carbon material.

[0061] The biomass porous carbon material provided by this invention can be applied to electrode materials of energy storage devices such as supercapacitors, lithium-ion batteries, lithium-air batteries, and dye-sensitized batteries, as well as catalyst carriers, gas adsorption materials, and water treatment.

[0062] To better understand the technical solution provided by the present invention, the following uses several specific examples to illustrate the specific process of preparing biomass porous carbon materials using the method provided in the above embodiments of the present invention, as well as the electrochemical characteristics of the prepared biomass porous carbon materials.

[0063] Example 1

[0064] Step 1: After drying and crushing 20 kg of coconut shells, place them in a high-temperature furnace under a nitrogen atmosphere and heat-treat them at 550°C for 6 hours to carbonize the coconut shells and obtain carbonized products.

[0065] Step 2: Place the carbonized product in a water vapor atmosphere and perform physical activation treatment at 850°C for 10 hours to obtain the first activated product.

[0066] Step 3: Mix KOH and the first activation product at a mass ratio of 2.5:1, then place the mixture in an activation furnace and treat it at 700°C for 6 hours to obtain the second activation product.

[0067] Step 4: Place the second activated product in 70% nitric acid and soak it at 80°C for 24 hours. Then, centrifuge at 8000 r / min for 5 min to remove the supernatant. Wash with deionized water until the supernatant is neutral. Finally, bake in an oven at 100°C for 12 hours to obtain biomass porous carbon material.

[0068] Subsequently, the biomass porous carbon material prepared above was subjected to the following tests:

[0069] First, electrochemical performance testing.

[0070] First, silicon-carbon anode material was prepared. The prepared biomass porous carbon material was placed in a vapor deposition furnace. Nitrogen gas was introduced into the vapor deposition furnace at a gas flow rate of 8 L / min for protection. The temperature of the vapor deposition furnace was increased to 540℃ at a heating rate of 4℃ / min and held for 30 min. Then, silane and nitrogen gas were introduced into the vapor deposition furnace at a flow rate ratio of 10 L / min:10 L / min, and the temperature was maintained for another 6 hours to deposit nano-silicon particles. After deposition, the gas was switched to nitrogen gas at a flow rate of 8 L / min and held for 1 hour. Then, the temperature was increased to 580℃, and a mixture of nitrogen and acetylene gas was introduced at a flow rate ratio of 10 L / min:10 L / min and held for 10 hours to perform carbon coating, thus obtaining the silicon-carbon anode material.

[0071] Secondly, the preparation of the electrode sheets. The aforementioned silicon-carbon anode material, conductive agent Super P, and binder sodium carboxymethyl cellulose (CMC) were added to a mortar and initially ground in a mass ratio of 8:1:1. Then, deionized water was added, and the mixture was transferred to a pulping machine to form a slurry. The obtained slurry was coated onto a copper foil current collector and baked in a vacuum oven at 80°C for 12 hours. After drying, the electrode sheets were rolled once at a pressure of 14 MPa. The rolled electrode sheets were then cut into circular pieces with a diameter of 14 mm to serve as the electrode sheets for the coin cell.

[0072] Next, the coin cell was assembled. The electrodes were assembled into a coin cell in an argon-filled glove box. The electrolyte used in the coin cell was a non-aqueous electrolyte; the lithium salt was 1 mol / L lithium hexafluorophosphate (LiPF6), and the solvents were ethylene carbonate (EC), dimethyl carbonate (DMC), and diethyl carbonate (DEC), with a volume ratio of EC, DEC, and DMC of 1:1:1. The counter electrode was a lithium sheet.

[0073] Finally, the assembled button cells were tested: the first-week coulombic efficiency, cycle capacity retention, and 2C capacity retention were tested on the Blue Battery Testing System.

[0074] The test temperature was 25℃, the test voltage window was 0.005V-2V, and the discharge was carried out in a stepped discharge manner. First, the voltage was discharged to 0.005V at a rate of 0.2C, and after resting for 5 minutes, it was discharged to 0.005V at a rate of 0.1C, and after resting for 5 minutes, it was discharged to 0.005V at a rate of 0.05C, and after resting for 5 minutes, it was discharged to 0.005V at a rate of 0.02C, and after resting for 5 minutes, it was discharged to 0.005V at a rate of 0.01C. Then, it was charged using a constant current charging method with a charging rate of 0.1C and a cycle count of 100 cycles.

[0075] First-week coulombic efficiency: The ratio of charging specific capacity to discharging specific capacity is the first-week coulombic efficiency; test data is detailed in Table 2. Cycle capacity retention: The ratio of charging specific capacity after 100 cycles to the charging specific capacity in the first week is the capacity retention; test data is detailed in Table 2. 2C capacity retention: Rate performance testing is measured by the ratio of the specific capacity at 2C charging rate to that at 0.1C charging rate. The rate test is consistent with the first-week coulombic efficiency and cycle test, except that the charging rate used is 2C.

[0076] Second, specific surface area, pore volume, and average pore size were tested.

[0077] The surface area was analyzed using a Micromeritics ASAP2460 analyzer. Biomass porous carbon material was used as the sample, and it was sieved using a 200-mesh sieve. The sample was placed in a vacuum and degassed at 200℃ for 6 hours. Nitrogen gas was introduced at a constant temperature of -196℃, and the nitrogen pressure was controlled to allow the sample to adsorb and desorb at different pressures, obtaining isothermal adsorption-desorption curves. Based on the isothermal adsorption-desorption curves, the specific surface area was calculated using BET fitting, and the average pore size and pore volume were calculated using a t-plot model.

[0078] Third, X-ray diffraction pattern testing and order calculation.

[0079] X-ray powder diffractometer (model: BRUKER D8 Advance) was used for testing: Biomass porous carbon material was taken as the sample to be tested. After sieving through a 200-mesh sieve, the sample was placed into the sample cell, the surface was flattened, and excess powder was removed from the periphery. Then, the sample was placed in the X-ray powder diffractometer for testing, and XRD patterns were acquired. The degree of order was then calculated using the XRD patterns.

[0080] Fourth, conductivity testing.

[0081] The conductivity of biomass porous carbon material powder was tested using a powder conductivity meter (model MCP-PD51) based on the four-probe testing principle. 2.0g of biomass porous carbon material powder was placed in a dedicated powder sample testing mold, and pressure was slowly applied while simultaneously measuring the conductivity value until the pressure reached 63MPa. The conductivity of the biomass porous carbon material at this pressure was then obtained.

[0082] Table 1 lists the differences between Examples 2-12 and Comparative Examples 1-4 and Example 1. The remaining steps and testing procedures are the same as in Example 1.

[0083] Table 1

[0084] Table 2 summarizes the test data for Examples 1-12 and Comparative Examples 1-4.

[0085] Table 2

[0086] As shown in Table 2, Examples 1-12, by adjusting the activation conditions, maintained a suitable degree of order in the carbon atoms of the biomass porous carbon materials. This improved the strength and suitable electrical conductivity of the biomass porous carbon materials, effectively suppressed the volume expansion of silicon nanoparticles, and also exhibited excellent compressive strength. Consequently, high first-cycle coulombic efficiency and rate performance were achieved, resulting in excellent electrochemical properties. In contrast, the biomass porous carbon materials in Comparative Examples 1, 3, and 4 had lower degree of order, insufficient strength, poor compressive strength, or weaker performance in suppressing silicon expansion, leading to poorer first-cycle coulombic efficiency and cycle life; furthermore, they had lower electrical conductivity and poorer rate performance. In Comparative Example 2, the biomass porous carbon material has excessive order, resulting in smaller carbon interlayer spacing and reduced ion transport rate in the biomass porous carbon matrix. Furthermore, due to the larger carbon crystallite size, the resulting pores are larger and more susceptible to deformation under pressure, exposing the nano-silicon particles. This leads to lower coulombic efficiency in the first cycle and a poorer cycle life. Although the electrical conductivity is high, the ion transport rate is mismatched, and the rate performance is not outstanding.

[0087] Figure 3 shows the XRD pattern of the biomass porous carbon material provided in Example 1 of this invention. It can be seen that the (002) crystal plane diffraction peak of the biomass porous carbon material is relatively strong and the half-width at half-maximum (WHM) is relatively narrow. This corresponds to a relatively moderate carbon interlayer spacing and degree of order in the biomass porous carbon, resulting in excellent electrochemical performance of the silicon-carbon anode material prepared from it. Figure 4 shows the XRD pattern of the biomass porous carbon material provided in Comparative Example 1 of this invention. It can be seen that its (002) crystal plane diffraction peak is relatively weak and the WHM is relatively wide. The carbon interlayer spacing of the biomass porous carbon is relatively large and the degree of order is relatively small, resulting in poor electrochemical performance of the silicon-carbon anode material prepared from it.

[0088] SEM images of the biomass porous carbon material prepared in Example 1 of this invention are shown in Figures 5-a and 5-b.

[0089] The SEM images of the biomass porous carbon material prepared in Comparative Example 1 of this invention are shown in Figures 6-a and 6-b.

[0090] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A biomass porous carbon material, characterized in that, The biomass porous carbon material is composed of graphite-like carbon microcrystals; wherein, the degree of order η of the biomass porous carbon material is 20000-80000, and the equivalent number of atomic layers η in which carbon atoms are periodically arranged along the a-axis direction. a The number of atomic layers η, where carbon atoms are periodically arranged along the c-axis, is 30-50. c The range is 20-40; in the X-ray diffraction pattern of the biomass porous carbon material, the diffraction angle 2θ of the (002) crystal plane ranges from 24.5° to 26.2°, and the carbon interlayer spacing of the graphite-like carbon microcrystals is 0.340 nm to 0.365 nm; the full width at half maximum (FWHM) of the (002) crystal plane diffraction peak is β. 002 It is 0.5 rad - 1.5 rad.

2. The biomass porous carbon material according to claim 1, characterized in that, The specific surface area of ​​the biomass porous carbon material is 800 m². 2 / g-2800m 2 / g, pore volume is 0.4ml / g-1.8ml / g, pore size is 1.5nm-5.0nm, particle size D50 is 0.5μm-50μm; the degree of order η is preferably 20000-70000.

3. A method for preparing a biomass porous carbon material according to any one of claims 1-2, characterized in that, The preparation method includes: The biomass porous carbon raw material is subjected to heat treatment to carbonize the biomass porous carbon raw material and generate carbonization products; the heat treatment temperature is 550℃-750℃ and the time is 2 hours-6 hours. The carbonized product is subjected to physical activation treatment to generate a first activated product; the temperature of the physical activation treatment is 800℃-950℃ and the time is 4 hours-10 hours. The first activated product is subjected to chemical activation treatment to generate a second activated product; the temperature of the chemical activation treatment is 700℃-1100℃ and the time is 4 hours-8 hours. The second activated product is washed and dried to obtain the biomass porous carbon material.

4. The preparation method according to claim 3, characterized in that, The activator for the physical activation treatment is water vapor and / or carbon dioxide.

5. The preparation method according to claim 3, characterized in that, The activator for the chemical activation treatment is one or more of KOH, NaOH, K2CO3, and Na2CO3.

6. The preparation method according to claim 3, characterized in that, The mass ratio of the chemical activator to the first activated product in the chemical activation treatment is 2.5-4.

5.

7. The preparation method according to claim 3, characterized in that, The washing process specifically involves placing the second activated product in an acid solution, soaking it at a certain temperature for a period of time, and then centrifuging and washing it with water.

8. A silicon-carbon anode material, characterized in that, The silicon-carbon anode material includes the biomass porous carbon material according to any one of claims 1-2 or the biomass porous carbon material prepared by any one of claims 3-7, as well as nano-silicon particles deposited in the pores of the biomass porous carbon material.

9. A negative electrode sheet, characterized in that, The negative electrode sheet comprises the silicon-carbon negative electrode material as described in claim 8.

10. A lithium-ion battery, characterized in that, The lithium-ion battery includes the negative electrode sheet as described in claim 9.

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