Preparation method of biomass porous carbon material for lithium battery

Abstract

The application relates to the field of lithium battery electrode materials, and particularly discloses a preparation method of a biomass porous carbon material for lithium batteries. The preparation method of the biomass porous carbon material for lithium batteries comprises the following steps: biomass is pulverized and mixed with nano-zinc oxide, a precursor is obtained by impregnating the mixture in 0.1-0.5 mol / L phosphoric acid for 2-6 hours; the precursor is pre-carbonized under nitrogen, and then activated at 800-900 DEG C under a nitrogen mixed gas with a water vapor volume fraction of 20-40%; after being cleaned with hydrochloric acid, the precursor is treated with melamine at 60-80 DEG C for 2-4 hours, and then heat-treated at 700-800 DEG C under argon for 1-2 hours; and the precursor is pulverized to D50=5-10 microns. The preparation method of the biomass porous carbon material for lithium batteries solves the problems that the mesopore proportion of the existing biomass porous carbon is low, the pore structure is disordered, the silicon particles are unevenly distributed, and stress is concentrated during charging and discharging.

Description

Technical Field

[0001] This application relates to the field of lithium battery electrode materials, and more specifically, it relates to a method for preparing a biomass porous carbonaceous material for lithium batteries. Background Technology

[0002] Biomass porous carbon materials, as a novel type of carbon material, have shown great application potential in the field of energy storage due to their advantages such as wide availability of raw materials, high renewability, and low cost. Prepared from biomass such as coconut shells, wood chips, and straw through carbonization and activation processes, they not only achieve high-value utilization of agricultural and forestry waste but also effectively reduce the production costs of energy storage devices such as batteries. Aligning with the current concept of green and sustainable development, they have become an ideal alternative to traditional resin-based carbon materials.

[0003] In the field of silicon-carbon anodes for lithium-ion batteries, the pore structure of biomass porous carbon plays a crucial role. An ideal pore network requires a reasonable proportion of mesopores and an ordered pore size distribution to achieve uniform loading of silicon particles and efficient lithium-ion transport. Mesopores act as "reservoirs" for silicon particles, mitigating their volume expansion during charging and discharging; micropores provide abundant specific surface area, enhancing the contact between the electrode and the electrolyte. This structural advantage makes biomass porous carbon a promising candidate for high-quality carriers of silicon-carbon composite materials, driving the development of high-capacity lithium-ion batteries.

[0004] However, existing processes for preparing porous biomass carbon still have significant drawbacks. Due to the complex composition of biomass raw materials, such as lignin and cellulose, it is difficult to form a uniform pore network during carbonization and activation, resulting in a mesopore ratio generally below 35%, and a mixed distribution of micropores, mesopores, and macropores. This disordered structure limits the diffusion efficiency of silane precursors, causing uneven distribution of silicon particles, which in turn leads to stress concentration during charging and discharging, accelerating electrode structure collapse and severely restricting its practical application in silicon-carbon anodes. Summary of the Invention

[0005] To address the aforementioned issues, this application provides a method for preparing biomass porous carbonaceous materials for lithium batteries.

[0006] This application provides a method for preparing a biomass porous carbonaceous material for lithium batteries, which employs the following technical solution:

[0007] A method for preparing a biomass porous carbonaceous material for lithium batteries includes the following steps:

[0008] The biomass raw material was pulverized to D90=50-150μm, mixed with nano zinc oxide template agent at a mass ratio of 1:(0.2-0.6), and impregnated with 0.1-0.5mol / L phosphoric acid solution for 2-6h. After drying, the composite precursor was obtained.

[0009] The composite precursor was pre-carbonized at 400-500℃ for 1-2 hours under nitrogen protection, and then activated at 800-900℃ for 0.5-1.5 hours by switching to a mixture of water vapor and nitrogen, wherein the volume fraction of water vapor was 20-40%.

[0010] After cooling, the activated product is washed with 1-3 mol / L hydrochloric acid solution to remove the zinc oxide template, and then washed with deionized water until neutral. The washed carbon material is then immersed in 0.5-2 mol / L melamine solution and stirred at 60-80℃ for 2-4 hours. After drying, a nitrogen-doped precursor is obtained.

[0011] The nitrogen-doped precursor was heat-treated at 700-800℃ for 1-2 hours in an argon atmosphere and then pulverized by airflow to a D50 of 5-10μm to obtain a biomass porous carbonaceous material.

[0012] By adopting the above technical solution, biomass raw materials are pulverized to a D90 of 50-150 μm. This particle size increases the contact area between the raw materials and the template agent and impregnation solution, ensuring the uniformity of subsequent reactions. Biomass and nano-zinc oxide template agent are mixed at a ratio of 1:(0.2-0.6). Zinc oxide remains stable during carbonization and, after removal by hydrochloric acid, forms pores matching the template particle size, providing a foundation for mesoporous structures. Impregnation with 0.1-0.5 mol / L phosphoric acid can destroy the biomass fiber structure through proton catalysis, promoting the decomposition of lignin and cellulose, creating conditions for subsequent activation and pore formation. The pre-carbonization stage is treated at 400-500℃ under nitrogen protection, which can gradually remove volatiles while retaining the carbon skeleton, avoiding structural collapse caused by direct high-temperature carbonization. During activation with a mixture of water vapor and nitrogen, the 20-40% water vapor volume fraction can precisely control the pore structure through oxidative etching. The temperature range of 800-900℃ can ensure activation efficiency while avoiding excessive etching that damages the skeleton, ultimately significantly increasing the proportion of mesoporous structures. After removing the zinc oxide template by washing with hydrochloric acid, nitrogen doping is achieved by impregnation with melamine solution. The introduction of nitrogen atoms can enhance the conductivity of carbon materials and provide active sites. Stirring at 60-80℃ promotes the uniform distribution of nitrogen. Heat treatment at 700-800℃ under an argon atmosphere further consolidates the carbon skeleton structure. Air jet pulverization to a particle size of D50=5-10μm facilitates silicon particle loading. The final material can effectively alleviate silicon volume expansion and improve lithium-ion transport efficiency.

[0013] Optionally, the biomass raw material is at least one of walnut shells, apricot shells, and coconut shells.

[0014] By adopting the above technical solutions, these shell-based raw materials have a moderate lignin-to-cellulose ratio, which facilitates the formation of a stable carbon skeleton during carbonization. Furthermore, their naturally occurring microporous structure provides a good foundation for subsequent activation and pore expansion. Compared to other biomass materials, these raw materials have low ash content, reducing the impact of impurities on the conductivity of carbon materials. Simultaneously, their dense fibrous structure, after processing, can form a more regular pore network, which is beneficial for increasing the proportion of mesopores and the uniformity of pore size distribution, thus better meeting the structural requirements of silicon-carbon anode carrier materials.

[0015] Optionally, the obtained biomass porous carbonaceous material is further subjected to microwave pore-expansion treatment, which is carried out in a nitrogen atmosphere and involves microwave irradiation at a power of 800-900W for 8-12 minutes.

[0016] By employing the above technical solution, microwave irradiation with a power of 800-900W under a nitrogen atmosphere can generate localized high temperatures inside carbon materials, inducing selective pyrolysis and reorganization of the carbon skeleton, thereby expanding existing pores and opening up closed channels. A processing time of 8-12 minutes avoids structural damage caused by overheating. This treatment further optimizes pore connectivity, increases the synergistic effect between mesopores and macropores, improves the diffusion efficiency of silane precursors and the uniformity of silicon particle loading, while also enhancing electrolyte wettability, improving lithium-ion transport paths, and alleviating stress concentration problems during charging and discharging.

[0017] Optionally, the particle size of the nano zinc oxide template agent is 20-50 nm.

[0018] By employing the above technical solution, zinc oxide particles of 20-50 nm can be uniformly dispersed in a biomass matrix and then removed to form mesopores of comparable size. These mesopores can act as "reservoirs" for silicon particles, precisely accommodating nano-silicon particles (typically 50-200 nm in size) and preventing silicon particle aggregation. Simultaneously, the size of these mesopores balances the number of pores with structural stability, ensuring sufficient specific surface area to enhance electrode-electrolyte contact while maintaining the mechanical strength of the carbon framework, effectively mitigating electrode structure collapse caused by silicon volume expansion (approximately 300%).

[0019] Optionally, pyrolytic polymer microspheres are also added to the nano zinc oxide template agent. The pyrolytic polymer microspheres have a particle size of 200-400 nm, and the biomass raw material: nano zinc oxide: pyrolytic polymer microspheres are in a mass ratio of 1:(0.2-0.4):(0.1-0.3).

[0020] By employing the above technical solution, pyrolytic polymer microspheres of 200-400 nm are added, forming a synergistic effect of a hierarchical porous structure with the nano-zinc oxide template. After biomass raw materials, nano-zinc oxide, and polymer microspheres are mixed in a specific ratio, the polymer microspheres undergo thermal decomposition during the pre-carbonization stage, forming macropores of 200-400 nm. These macropores interconnect with the mesopores formed by the zinc oxide, constructing a three-level network of "micropore-mesopore-macropore". The macropores serve as transport channels for silicon particles, shortening the diffusion path; the mesopores are responsible for loading silicon particles; and the micropores provide additional specific surface area. These three elements synergistically improve the uniformity of silicon particle distribution, reduce stress concentration, and simultaneously accelerate the transport of lithium ions in pores of different scales, thereby improving the battery's rate performance.

[0021] Optionally, the melamine solution is a mixture of nano-silica sol and melamine, wherein the solid content of the nano-silica sol in the nano-silica sol-melamine mixture is 18-22%.

[0022] By employing the above technical solution, nano-silica sol with a solid content of 18-22% can uniformly disperse silicon particles in a melamine solution. During the impregnation process, silicon particles, along with nitrogen, enter the pores of the carbon material, forming a silicon-nitrogen synergistic modification. The silicon particles in the silica sol pre-occupy part of the pores and can subsequently act as a silicon source to combine with external silicon particles, enhancing the interfacial bonding between silicon and the carbon support. Nitrogen, on the other hand, improves conductivity. The synergistic effect of both can reduce the shedding of silicon particles during charge and discharge, improve cycle stability, and simultaneously increase the initial coulombic efficiency of the material.

[0023] Optionally, the pulverized biomass raw material is subjected to laccase-xylanase composite treatment, wherein the enzymatic hydrolysis conditions for the laccase-xylanase composite treatment are pH 4.2-4.8 and 45-50℃ for 6-8 hours.

[0024] By employing the above technical solutions, laccase can degrade aromatic compounds in lignin, and xylanase can decompose xylan in hemicellulose. Under suitable conditions of pH 4.2-4.8 and 45-50℃ for 6-8 hours, non-carbon components in biomass can be selectively removed, preserving a pure cellulose skeleton. This enzymatic hydrolysis reduces the porosity caused by impurity volatilization during carbonization, resulting in more uniform pore formation during subsequent activation. This improves the proportion of mesopores and the orderliness of pore size distribution, creating favorable structural conditions for uniform loading of silicon particles.

[0025] Optionally, based on the quality of the biomass raw material, the amount of laccase added is 20-30 U / g and the amount of xylanase added is 50-60 U / g.

[0026] By adopting the above technical solution, this enzyme dosage ratio can fully degrade lignin and hemicellulose, avoiding incomplete degradation due to insufficient enzyme dosage (resulting in residual impurities affecting the pore structure) or cost waste caused by excessive enzyme dosage. Precise enzyme dosage ensures that the biomass skeleton forms a regular network structure after enzymatic hydrolysis, providing a stable basis for pore regulation in subsequent carbonization and activation processes, ultimately improving the structural uniformity and performance stability of porous carbon materials.

[0027] In summary, this application has the following beneficial effects:

[0028] 1. This application utilizes nano-zinc oxide templates and pyrolytic polymer microspheres for hierarchical pore creation, combined with microwave pore expansion and enzymatic pretreatment, to form a multi-level structure of ordered interconnected "micropores-mesopores-macropores" in biomass porous carbon. This significantly increases the proportion of mesopores and ensures a uniform pore size distribution. This structure provides suitable "storage" space for silicon particles to alleviate volume expansion, shortens the lithium-ion diffusion path, improves the diffusion efficiency of silane precursors and the uniformity of silicon particle loading, and solves the stress concentration problem caused by traditional disordered pores.

[0029] 2. In this application, nitrogen doping and pre-loading with nano-silica sol are preferred to enhance the conductivity of carbon materials and strengthen the interfacial bonding between silicon and carbon support, reducing silicon particle shedding during charging and discharging. Enzymatic hydrolysis and precise activation processes reduce impurity residues and improve the structural stability of the material. Ultimately, this improves the cycle stability of the silicon-carbon anode, enhances the initial coulombic efficiency, and significantly improves the rate performance due to accelerated lithium-ion transport.

[0030] 3. The method of this application, by selecting natural high-carbon biomass raw materials such as walnut shells and combining laccase-xylanase biodegradation technology, realizes the high-value utilization of agricultural and forestry waste and reduces raw material costs; the precise ratio of template agent and activator and the optimization of processes such as microwave assistance reduce reagent consumption and energy consumption while ensuring performance, which is in line with the concept of green manufacturing and provides a feasible path for large-scale production. Detailed Implementation

[0031] The following detailed description of this application is provided in conjunction with the embodiments. It should be noted that: unless otherwise specified, the conditions in the following embodiments are performed under conventional conditions or conditions recommended by the manufacturer. Unless otherwise specified, the raw materials used in the following embodiments are all from commercially available sources.

[0032] Example 1

[0033] A method for preparing biomass porous carbonaceous materials for lithium batteries

[0034] Coconut shells were used as biomass raw material and pulverized to a particle size distribution of D90=100μm (D10=15μm, D50=45μm, D90=100μm). The raw material was weighed according to a mass ratio of biomass raw material: nano-zinc oxide template agent = 1:0.4. The nano-template agent was nano-zinc oxide with a purity >98% and a particle size of 50-100nm. Both were placed in a high-speed mixer and dry-mixed at 800rpm for 30min until homogeneous. A 0.3mol / L phosphoric acid solution was added to the mixture (liquid-solid ratio 5:1, i.e., 5mL solution per gram of solid). The mixture was soaked in a 50℃ constant temperature water bath for 4h, with stirring for 5min every 30min at a stirring rate of 200rpm. After filtration, the mixture was dried in a forced-air drying oven at 80℃ for 12h to obtain the composite precursor.

[0035] The composite precursor was placed in a tube furnace and nitrogen gas with a purity ≥99.99% was introduced at a flow rate of 100 mL / min. The temperature was increased to 450 °C at a rate of 5 °C / min and held for 1.5 h to complete pre-carbonization. The nitrogen gas was then switched to a water vapor-nitrogen mixture with a water vapor volume fraction of 30%, generated by nitrogen bubbling at a total flow rate of 120 mL / min. The temperature was increased to 800 °C at a rate of 10 °C / min and activated for 1 h.

[0036] After naturally cooling to room temperature, the activated product was placed in a 2 mol / L hydrochloric acid solution with a liquid-to-solid ratio of 10:1.

[0037] Wash at 80℃ with stirring for 2 hours at a stirring speed of 300 rpm, repeating the washing process 3 times until the filtrate is free of Zn². + Wash with deionized water until neutral, and dry at 105℃ for 6 hours;

[0038] The washed carbon material was immersed in a 1 mol / L melamine solution with a liquid-to-solid ratio of 8:1; it was stirred at a constant temperature of 70℃ for 3 hours at a stirring speed of 250 rpm; after filtration, it was dried at 80℃ for 10 hours to obtain a nitrogen-doped precursor.

[0039] The nitrogen-doped precursor was placed in an argon-atmosphere tube furnace with an argon flow rate of 50 mL / min; the temperature was increased to 750℃ at a rate of 5℃ / min, held for 1.5 h, and then cooled with the furnace; the precursor was then pulverized using an air jet mill (pressure 0.8 MPa) to a particle size distribution of D50=7.5μm (D10=2.1μm, D50=7.5μm, D90=18μm) to obtain the biomass porous carbonaceous material.

[0040] Example 2

[0041] A method for preparing biomass porous carbonaceous material for lithium batteries differs from Example 1 in that the biomass raw material is pulverized and mixed with nano zinc oxide template agent at a mass ratio of 1:0.2.

[0042] Example 3

[0043] A method for preparing biomass porous carbonaceous material for lithium batteries differs from Example 1 in that the biomass raw material is pulverized and mixed with nano zinc oxide template agent at a mass ratio of 1:0.6.

[0044] Example 4

[0045] A method for preparing a biomass porous carbonaceous material for lithium batteries differs from Example 1 in that it is impregnated with a 0.1 mol / L phosphoric acid solution.

[0046] Example 5

[0047] A method for preparing a biomass porous carbonaceous material for lithium batteries differs from Example 1 in that it is impregnated with a 0.5 mol / L phosphoric acid solution.

[0048] Example 6

[0049] A method for preparing biomass porous carbonaceous material for lithium batteries differs from Example 1 in that the volume fraction of water vapor in the mixture of water vapor and nitrogen is 20%.

[0050] Example 7

[0051] A method for preparing biomass porous carbonaceous material for lithium batteries differs from Example 1 in that the volume fraction of water vapor in the mixture of water vapor and nitrogen is 40%.

[0052] Example 8

[0053] A method for preparing biomass porous carbonaceous material for lithium batteries differs from Example 1 in that the activated product is cooled and then washed with 1 mol / L hydrochloric acid solution to remove the zinc oxide template.

[0054] Example 9

[0055] A method for preparing biomass porous carbonaceous material for lithium batteries differs from Example 1 in that the activated product is cooled and then washed with 3 mol / L hydrochloric acid solution to remove the zinc oxide template.

[0056] Example 10

[0057] A method for preparing biomass porous carbonaceous material for lithium batteries differs from Example 1 in that the washed carbonaceous material is immersed in a 0.5 mol / L melamine solution.

[0058] Example 11

[0059] A method for preparing biomass porous carbonaceous material for lithium batteries differs from Example 1 in that the washed carbonaceous material is immersed in a 2 mol / L melamine solution.

[0060] Example 12

[0061] A method for preparing a biomass porous carbonaceous material for lithium batteries differs from Example 1 in that the biomass raw material is walnut shell.

[0062] Example 13

[0063] A method for preparing a biomass porous carbonaceous material for lithium batteries differs from Example 1 in that the biomass raw material is apricot shells.

[0064] Example 14

[0065] A method for preparing biomass porous carbonaceous material for lithium batteries differs from Example 1 in that the carbonaceous material is irradiated with 850W microwave for 10 minutes under nitrogen after heat treatment, and then naturally cooled after microwave irradiation.

[0066] Example 15

[0067] A method for preparing biomass porous carbonaceous materials for lithium batteries differs from Example 1 in that the particle size of the nano zinc oxide template agent is 20-50 nm.

[0068] Example 16

[0069] A method for preparing biomass porous carbonaceous materials for lithium batteries differs from Example 1 in that pyrolytic polymer microspheres (polystyrene microspheres) are added to the nano zinc oxide template agent, with a particle size of 200-400 nm, and the biomass raw material: nano zinc oxide: pyrolytic polymer microspheres ratio is 1:0.3:0.2 by mass.

[0070] Example 17

[0071] A method for preparing biomass porous carbonaceous material for lithium batteries differs from Example 16 in that the biomass raw material: nano zinc oxide: pyrolytic polymer microspheres are in a mass ratio of 1:0.2:0.3.

[0072] Example 18

[0073] A method for preparing biomass porous carbonaceous material for lithium batteries differs from Example 16 in that the biomass raw material: nano zinc oxide: pyrolytic polymer microspheres are in a mass ratio of 1:0.4:0.1.

[0074] Example 19

[0075] A method for preparing biomass porous carbonaceous material for lithium batteries differs from Example 1 in that the melamine solution used is a mixture of nano-silica sol and melamine, and the solid content of nano-silica sol in the nano-silica sol-melamine mixture is 20%.

[0076] Example 20

[0077] A method for preparing biomass porous carbonaceous materials for lithium batteries differs from Example 1 in that a laccase-xylanase composite treatment step is added after the biomass raw material is pulverized and before it is mixed with nano-zinc oxide. The specific operation is as follows:

[0078] Take biomass raw material pulverized to D90=100μm, prepare an acetate-sodium acetate buffer solution with pH 4.5 and a concentration of 0.1mol / L; add laccase 25U / g (enzyme activity ≥200U / mg, derived from Trametesversicolor) and xylanase 55U / g (enzyme activity ≥5000U / g, derived from Thermomyces lanuginosus) according to the mass of biomass raw material, and form a solid-liquid ratio of 1:10 in the buffer solution;

[0079] The reaction was carried out in a constant temperature shaker at 48°C for 7 hours with a shaking frequency of 150 rpm. After the enzymatic hydrolysis was completed, the solid residue was separated by centrifugation and washed with deionized water at 60°C until the conductivity was <5 μS / cm. The residue was then vacuum dried at 80°C for 12 hours to obtain the enzyme-modified biomass raw material. The subsequent steps were the same as in Example 1.

[0080] Example 21

[0081] A method for preparing a biomass porous carbonaceous material for lithium batteries differs from Example 20 in that the following are added according to the mass of the biomass raw materials: laccase 20 U / g and xylanase 60 U / g.

[0082] Example 22

[0083] A method for preparing a biomass porous carbonaceous material for lithium batteries differs from Example 20 in that the following are added according to the mass of the biomass raw materials: laccase 30 U / g and xylanase 50 U / g.

[0084] Comparative Example 1

[0085] A method for preparing biomass porous carbonaceous materials for lithium batteries differs from Example 1 in that the nano zinc oxide template agent is omitted, and the biomass raw materials are directly impregnated with phosphoric acid after being crushed.

[0086] Comparative Example 2

[0087] A method for preparing biomass porous carbonaceous material for lithium batteries differs from Example 1 in that the phosphoric acid solution is replaced with an equal amount of deionized water for impregnation.

[0088] Comparative Example 3

[0089] A method for preparing biomass porous carbonaceous material for lithium batteries differs from Example 1 in that the water vapor-nitrogen mixture is replaced with pure CO2 gas during the activation stage.

[0090] Performance testing

[0091] The pore structure of porous carbonaceous materials was characterized using a nitrogen adsorption-desorption method, and the specific steps are as follows:

[0092] Sample pretreatment: Take about 0.5g of sample and degas it under vacuum at 150℃ for 6h to remove surface-adsorbed moisture and impurities;

[0093] Test conditions: Nitrogen adsorption-desorption experiments were conducted at 77 K using a surface area and pore size analyzer (such as Micromeritics ASAP2460).

[0094] Data calculation:

[0095] Specific surface area (m² / g): calculated using the BET (Brunauer-Emmett-Teller) method;

[0096] Total pore volume (cm³ / g): Calculated based on the adsorption capacity at a relative pressure P / P0 = 0.99;

[0097] Micropore volume percentage (%): The micropore volume (pore size <2nm) was calculated using the t-plot method and compared with the total pore volume;

[0098] Mesopore volume percentage (%): The mesopore volume (2nm < pore size < 50nm) was calculated using the BJH (Barrett-Joyner-Halenda) method and compared with the total pore volume;

[0099] Macropore volume percentage (%): determined by mercury porosimetry.

[0100] Table 1 Detection Data

[0101] Specific surface area (m² / g) Total pore volume (cm³ / g) Micropore percentage (%) Mesoporous percentage (%) Percentage of large pores (%) Example 1 2150 1.12 35 48 17 Example 2 1980 0.98 37 45 18 Example 3 2260 1.25 38 47 15 Example 4 1850 0.85 37 43 20 Example 5 2320 1.30 33 48 19 Example 6 2020 1.02 37 45 18 Example 7 2280 1.28 32 47 21 Example 8 2100 1.08 36 47 17 Example 9 2180 1.15 34 49 17 Example 10 2130 1.10 36 46 18 Example 11 2160 1.13 37 48 15 Example 12 2100 1.10 35 47 18 Example 13 2080 1.09 39 44 17 Example 14 2200 1.35 24 53 23 Example 15 2300 1.20 34 51 15 Example 16 2180 1.45 22 53 25 Example 17 2150 1.50 24 50 26 Example 18 2220 1.40 27 51 22 Example 19 2050 1.10 30 49 21 Example 20 2250 1.20 31 54 15 Example 21 2230 1.18 33 52 15 Example 22 2260 1.22 32 53 15 Comparative Example 1 1500 0.70 43 37 20 Comparative Example 2 1200 0.50 48 34 18 Comparative Example 3 1800 0.85 35 42 23

[0102] Combining Example 1 and Comparative Example 1 with Table 1, it can be seen that Comparative Example 1, due to the omission of the nano-zinc oxide template agent, has significantly lower specific surface area (1500 m² / g) and total pore volume (0.70 cm³ / g) than Example 1, and its mesoporous proportion (37%) is significantly reduced while its microporous proportion (43%) is increased. This indicates that the addition of the nano-zinc oxide template agent is key to increasing the mesoporous proportion, specific surface area, and total pore volume, effectively providing a foundation for the mesoporous structure.

[0103] Combining Example 1 and Comparative Example 2 with Table 1, it can be seen that in Comparative Example 2, after replacing the phosphoric acid solution with deionized water, the specific surface area (1200 m² / g) and total pore volume (0.50 cm³ / g) decreased significantly, the proportion of mesopores (34%) was lower, and the proportion of micropores (48%) was higher. This indicates that phosphoric acid impregnation, through proton catalysis, disrupts the biomass fiber structure, playing a crucial role in promoting subsequent activation and pore formation, and is a necessary step in improving pore structure parameters.

[0104] Combining Example 1 and Comparative Example 3 with Table 1, it can be seen that Comparative Example 3, activated with pure CO2, has a lower specific surface area (1800 m² / g), lower total pore volume (0.85 cm³ / g), and lower mesopore percentage (42%) than Example 1. This indicates that the water vapor-nitrogen mixture can more precisely control the pore structure compared to pure CO2, which is more conducive to increasing the mesopore percentage and total pore volume, resulting in a better activation effect.

[0105] Combining Examples 1 and 4-5 with Table 1, it can be seen that as the phosphoric acid concentration increases from 0.1 mol / L (Example 4) to 0.5 mol / L (Example 5), the specific surface area, total pore volume, and mesopore ratio of the material all show an increasing trend. Example 5 (0.5 mol / L) exhibits the best performance, followed by Example 1 (0.3 mol / L). This indicates that within the range of 0.1-0.5 mol / L, appropriately increasing the phosphoric acid concentration can enhance the destructive effect on biomass fibers, promote pore formation, and improve pore structure parameters.

[0106] Combining Examples 1, 6-7, and Table 1, it can be seen that as the water vapor ratio increases from 20% (Example 6) to 40% (Example 7), the total pore volume and the proportion of macropores gradually increase, with the macropore proportion reaching 21% in Example 7; while in Example 1 (30%), the mesopore proportion (48%) is the highest. This indicates that increasing the water vapor ratio can promote macropore formation, and at 30%, both mesopore and macropore control can be balanced, with the mesopore proportion being optimal.

[0107] Based on Examples 1, 8-9, and Table 1, it can be seen that when the hydrochloric acid concentration increases from 1 mol / L (Example 8) to 3 mol / L (Example 9), the proportion of mesopores slightly increases (47%→49%), and the specific surface area and total pore volume also increase slightly. This indicates that increasing the hydrochloric acid concentration can more thoroughly remove the zinc oxide template, which is beneficial to the formation of mesoporous structures, and 3 mol / L has the best effect.

[0108] Based on Examples 1, 10-11 and Table 1, it can be seen that when the melamine concentration is in the range of 0.5-2 mol / L, the specific surface area, total pore volume, and pore ratio of the material show little difference, and the mesopore ratio remains stable at 46%-48%. This indicates that within this concentration range, melamine mainly acts as a nitrogen dopant and has little impact on the pore structure, thus meeting the basic requirements.

[0109] As can be seen from Examples 1, 12-13 and Table 1, when walnut shells (Example 12) and apricot shells (Example 13) are used as raw materials, their specific surface area, total pore volume, and pore ratio are similar to those of coconut shells (Example 1). This indicates that these three types of shell biomass all have suitable lignin-to-cellulose ratios and can all be used to prepare high-performance porous carbon materials.

[0110] Combining Examples 1 and 14 with Table 1, it can be seen that after microwave pore-expanding treatment in Example 14, the total pore volume (1.35 cm³ / g) was significantly increased, the proportion of micropores (24%) decreased, and the proportions of mesopores (53%) and macropores (23%) were significantly increased. This indicates that microwave irradiation can effectively expand pores, open up closed channels, optimize pore connectivity, and enhance the synergistic effect of mesopores and macropores.

[0111] Combining Examples 1 and 15 with Table 1, it can be seen that Example 15, using a 20-50 nm nano-zinc oxide template, has a higher specific surface area (2300 m² / g) and mesopore ratio (51%) than Example 1 (50-100 nm template). This indicates that a smaller zinc oxide template can form more mesopores, which is more conducive to increasing the mesopore ratio and specific surface area, thus meeting the silicon particle loading requirements.

[0112] As can be seen from Examples 1, 16-18 and Table 1, the addition of pyrolytic polymer microspheres significantly increased the total pore volume (1.40-1.50 cm³ / g), the proportion of macropores (22%-26%), and the proportion of mesopores (50%-53%). This indicates that the polymer microspheres and zinc oxide template synergistically constructed a three-level network of "micropore-mesopore-macropores," with the optimal mesopore proportion at a ratio of 1:0.3:0.2.

[0113] Combining Examples 1 and 19 with Table 1, it can be seen that in Example 19, after using the nano-silica sol-melamine mixture, the proportion of micropores (30%) decreased, the proportion of macropores (21%) increased slightly, and other parameters were similar to those in Example 1. This indicates that the addition of nano-silica sol can finely adjust the pore distribution, which is beneficial for pre-introducing silicon particles and enhancing the interfacial bonding between silicon and carbon support.

[0114] Combining Examples 1 and 20-22 with Table 1, it can be seen that after laccase-xylanase combined treatment, the specific surface area (2230-2260 m² / g) and mesopore ratio (52%-54%) of Examples 20-22 were significantly higher than those of Example 1, while the micropore ratio decreased. This indicates that enzymatic hydrolysis can remove non-carbon components, optimize the biomass framework, and promote more uniform pore formation during subsequent activation. The optimal ratio of 25 U / g laccase + 55 U / g xylanase is shown to be the best.

[0115] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A method for preparing a biomass porous carbonaceous material for a lithium battery, characterized by, The method comprises the following steps: The biomass raw material is crushed to D90=50-150μm, the crushed biomass raw material is subjected to laccase-xylanase complex treatment, the enzymolysis conditions of the laccase-xylanase complex treatment are pH 4.2-4.8, 45-50℃ for 6-8h, then the biomass raw material is mixed with nano-zinc oxide template agent at a mass ratio of 1:(0.2-0.6), 0.1-0.5mol / L phosphoric acid solution is added for impregnation for 2-6h, and the composite precursor is obtained after drying; the particle size of the nano-zinc oxide template agent is 20-50nm; The pyrolyzable polymer microspheres are further added in the nano-zinc oxide template agent, the particle size of the pyrolyzable polymer microspheres is 200-400nm, and the mass ratio of the biomass raw material:nano-zinc oxide:pyrolyzable polymer microspheres is 1:(0.2-0.4):(0.1-0.3); The composite precursor is pre-carbonized at 400-500℃ for 1-2h under nitrogen protection, then the water vapor and nitrogen mixed gas is switched, the volume fraction of the water vapor is 20-40%, and the activated product is obtained by activation at 800-900℃ for 0.5-1.5h; After cooling, the activated product is washed with 1-3mol / L hydrochloric acid solution to remove the zinc oxide template, and then washed with deionized water until neutral; The washed carbon material is immersed in 0.5-2mol / L melamine solution, stirred at 60-80℃ for 2-4h, and then dried to obtain a nitrogen-doped precursor; The nitrogen-doped precursor is heat-treated at 700-800℃ for 1-2h under argon atmosphere, and then ground to D50=5-10μm by airflow to obtain a biomass porous carbon material; The prepared biomass porous carbon material is further subjected to microwave pore expansion treatment, the microwave pore expansion treatment is carried out under nitrogen atmosphere, and the microwave pore expansion treatment is carried out by microwave irradiation at a power of 800-900W for 8-12min.

2. The method for preparing a biomass-based porous carbonaceous material for a lithium battery according to claim 1, characterized by: The biomass raw material is at least one of walnut shell, apricot shell and coconut shell.

3. The method for preparing biomass porous carbonaceous material for lithium batteries according to claim 1, characterized in that: The melamine solution is selected from nano-silica sol-melamine mixed solution, and the solid content of the nano-silica sol in the nano-silica sol-melamine mixed solution is 18-22%.

4. The method for preparing biomass porous carbonaceous material for lithium batteries according to claim 1, characterized in that: The laccase is added at an amount of 20-30U / g and the xylanase is added at an amount of 50-60U / g based on the mass of the biomass raw material.