A method for preparing microcrystalline graphite porous carbon material based on microbial purification and structural reconstruction
By using microbial inoculant leaching and low-temperature catalytic treatment, the impurity and structural problems of microcrystalline graphite as a negative electrode material for sodium-ion batteries were solved, and a high-efficiency porous carbon material was prepared, which is suitable for sodium-ion battery negative electrodes, achieving the effects of environmental protection and energy consumption reduction.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- HUNAN QINGYI NEW MATERIAL TECHNOLOGY CO LTD
- Filing Date
- 2026-02-27
- Publication Date
- 2026-06-12
AI Technical Summary
Existing microcrystalline graphite as a negative electrode material for sodium-ion batteries suffers from problems such as high impurity content, small interlayer spacing, and dense structure. Existing preparation technologies also suffer from problems such as environmental pollution, high energy consumption, and complex processes.
Microcrystalline graphite was leached and purified using microbial agents, and then combined with low-temperature catalysts and heat treatment to prepare porous carbon materials. Impurities were selectively dissolved by microbial metabolites, thereby controlling the interlayer spacing and the formation of nanopores.
A porous carbon material with high initial coulombic efficiency and excellent rate performance was prepared. It is environmentally friendly, energy-efficient, and suitable for sodium-ion battery anodes.
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Figure CN122187031A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of sodium-ion battery anode material technology, specifically, it relates to a method for preparing microcrystalline graphite porous carbon material based on microbial purification and structural reconstruction. Background Technology
[0002] With sodium-ion batteries gaining widespread attention as a potential alternative to lithium-ion batteries in the energy storage and low-power markets, the development of high-performance, low-cost sodium-ion battery anode materials has become a research focus. Porous carbon materials are considered one of the most promising sodium-ion battery anode materials due to their abundant sodium storage sites and good structural stability.
[0003] Microcrystalline graphite, as a natural carbon source, has a low cost, but its direct application as a negative electrode material for sodium-ion batteries presents the following problems: 1. High impurity content: Natural microcrystalline graphite often contains impurities such as quartz, silicates, mica, and pyrite, which affect its electrochemical performance.
[0004] 2. High purity: Microcrystalline graphite itself has a highly ordered graphite structure with a small interlayer spacing (about 0.335nm), which is not conducive to the reversible insertion / extraction of sodium ions.
[0005] 3. Dense structure: The lack of sufficient nanopores and defect sites limits the transport and storage of sodium ions.
[0006] Existing technologies for purifying microcrystalline graphite and preparing porous carbon materials mostly employ strong acid-base chemical methods or high-temperature physical methods, which suffer from problems such as severe environmental pollution, high energy consumption, and stringent equipment requirements. For example, some technologies use hazardous chemicals such as hydrofluoric acid for impurity removal or require purification temperatures as high as 3000℃, resulting in high costs. Some studies have attempted to prepare porous carbon using biomass precursors (such as cotton and bamboo processing waste), but the source of raw materials and the consistency of performance may face challenges.
[0007] In addition, although doping or template methods can effectively control the structure, the process is complex or may introduce inactive components. Summary of the Invention
[0008] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide a sodium-ion battery anode material that can overcome or at least partially solve the above problems.
[0009] To solve the above-mentioned technical problems, the basic concept of the technical solution adopted by the present invention is: a method for preparing microcrystalline graphite porous carbon materials based on microbial purification and structural reconstruction, comprising the following steps: Microbial agents were used to leach and purify the treated microcrystalline graphite. The purified microcrystalline graphite was impregnated with a catalyst. The impregnated material is heat-treated under high temperature and inert gas. After heat treatment, the material is cooled to room temperature before undergoing post-treatment.
[0010] Furthermore, the microorganisms are a mixed bacterial solution of *Thiobacillus ferrooxidans* and silicate bacteria, and a culture medium is prepared. The mixed bacterial solution is placed in the culture medium for activation culture to obtain the activated microbial agent.
[0011] Furthermore, the culture medium contains ammonium sulfate, dipotassium hydrogen phosphate, magnesium sulfate, calcium chloride, and sodium thiosulfate.
[0012] Furthermore, the mixed bacterial solution is placed in a culture medium at 28-32℃ and pH 1.5-2.5 to activate it, and cultured with aeration for 3-7 days until the bacterial concentration reaches 108-109 CFU / mL.
[0013] Furthermore, the microcrystalline graphite is processed by grinding to obtain particles with a particle size D50 of 10-50 μm.
[0014] Furthermore, the treated microcrystalline graphite is mixed with the activated microbial inoculum at a solid-liquid ratio of 1:5 to 1:10 (w / v) and placed in a bioleaching reactor; The temperature was controlled at 30-35℃, the stirring speed at 100-200rpm, the pH value at 1.8-2.5, and the leaching time at 5-15 days.
[0015] Furthermore, the catalyst is a soluble transition metal salt solution, the mass ratio of the transition metal salt to microcrystalline graphite is 0.5:100 to 5:100, and the impregnation time is 2-12 hours.
[0016] Furthermore, the impregnated microcrystalline graphite is placed in a high-temperature furnace and heat-treated under inert gas protection.
[0017] Furthermore, the high-temperature furnace first raises the temperature to 800-1000℃ at a rate of 2-5℃ / min for pre-carbonization to stabilize the structure, and then raises it to 1800-2200℃ at a rate of 3-8℃ / min, holds it at that temperature for 0.5-2 hours, and uses argon gas for protection.
[0018] Furthermore, the microcrystalline graphite, after being cooled to room temperature, is pulverized and sieved to obtain the final product.
[0019] After adopting the above technical solution, the present invention has the following beneficial effects compared with the prior art: The present invention uses a specific microbial agent to bio-leach and remove impurities from natural microcrystalline graphite, combined with low-temperature catalytic purification technology, to prepare porous carbon materials with suitable interlayer spacing and abundant nanopores; Meanwhile, this invention utilizes microbial metabolites to selectively dissolve impurities such as silicates and iron compounds in microcrystalline graphite, avoiding the use of strong acids and alkalis, thus being environmentally friendly. Furthermore, through catalyst selection and process parameter control, precise regulation of graphite-like microcrystal size and interlayer spacing is achieved at relatively low temperatures. The resulting porous carbon material exhibits high initial coulombic efficiency, excellent rate performance, and cycle stability, making it suitable for sodium-ion battery anodes. Attached Figure Description
[0020] In the attached diagram: Figure 1 This is a schematic diagram of the steps in the preparation method of microcrystalline graphite porous carbon material based on microbial purification and structural reconstruction proposed in this invention. Figure 2 This is a flowchart illustrating a method for preparing microcrystalline graphite porous carbon materials based on microbial purification and structural reconstruction, as proposed in this invention. Figure 1 ; Figure 3 This is a flowchart illustrating a method for preparing microcrystalline graphite porous carbon materials based on microbial purification and structural reconstruction, as proposed in this invention. Figure 2 ; Figure 4 This is a flowchart illustrating a method for preparing microcrystalline graphite porous carbon materials based on microbial purification and structural reconstruction, as proposed in this invention. Figure 3 . Detailed Implementation
[0021] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments will be clearly and completely described below with reference to the accompanying drawings. The following embodiments are used to illustrate the present invention, but are not intended to limit the scope of the present invention.
[0022] Example: Refer to Figure 1-4 A method for preparing microcrystalline graphite porous carbon materials based on microbial purification and structural reconstruction includes the following steps: Step 1: Cultivation and Activation of Microbial Agents Culture medium preparation: mainly contains ammonium sulfate, dipotassium hydrogen phosphate, magnesium sulfate, calcium chloride, and sodium thiosulfate or elemental sulfur as energy substances.
[0023] Inoculate with a mixed bacterial culture of *Thiobacillus ferrooxidans* and silicate bacteria, and culture under aeration at 28-32℃ and pH 1.5-2.5 for 3-7 days until the bacterial concentration reaches 10⁸-10⁹ CFU / mL.
[0024] By optimizing the ratio of mixed bacteria and culture conditions, the bacterial agents can work synergistically to efficiently leach out metal sulfides and silicate impurities.
[0025] Step 2: Bioleaching and impurity removal of microcrystalline graphite powder Natural microcrystalline graphite is crushed and ground to a particle size D50 of 10-50 μm.
[0026] Graphite powder and the above-mentioned activated bacterial solution are mixed at a solid-liquid ratio of 1:5 to 1:10 (w / v) and placed in a bioleaching reactor.
[0027] Control conditions: temperature 30-35℃, stirring speed 100-200rpm, pH value maintained at 1.8-2.5, leaching time 5-15 days.
[0028] This process involves microbial metabolism that produces sulfuric acid, organic acids, and chelating agents, which can effectively dissolve and remove metallic impurities such as Fe, Al, and Ca, as well as some silicon, from graphite. The impurity removal rate can reach over 85%, and the use of strong acids and alkalis is avoided.
[0029] Step 3: Catalyst Impregnation The purified microcrystalline graphite, after being bioleached, washed, and dried, is dispersed in a solution of soluble transition metal salts (such as ferric nitrate, nickel nitrate, and cobalt acetate), with the mass ratio of transition metal salts to microcrystalline graphite being 0.5:100 to 5:100.
[0030] After impregnation for a certain period of time (e.g., 2-12 hours), dry to remove moisture, so that the catalyst precursor is evenly attached to the surface and pores of the graphite particles.
[0031] The selection and loading of catalysts are key to achieving subsequent low-temperature purification and structural control.
[0032] Step 4: Low-temperature catalytic purification The impregnated material is placed in a high-temperature furnace and heat-treated under an inert atmosphere (such as argon or nitrogen).
[0033] Key process: The temperature is programmed. First, the temperature is raised to 800-1000℃ at a rate of 2-5℃ / min for pre-carbonization to stabilize the structure. Then, the temperature is raised to the target temperature of 1800-2200℃ at a rate of 3-8℃ / min and held for 0.5-2 hours.
[0034] In this process, transition metal catalysts can lower the activation energy of carbon atom rearrangement, promote the formation of graphite-like microcrystalline structures with suitable size (e.g., Lc < 2 nm) and expanded interlayer spacing (d002 > 0.36 nm) at relatively low temperatures, and simultaneously form abundant nanopores.
[0035] This differs from existing high-temperature (e.g., 3000℃) purification technologies.
[0036] Step 5: Cooling and Post-processing After purification, the furnace is cooled or the temperature is controlled to room temperature.
[0037] The obtained porous carbon material is crushed and sieved to obtain the final product, which can be further surface modified or doped as needed to facilitate its application as a lithium battery anode.
[0038] Performance testing was conducted using X-ray diffraction, which determined the interlayer spacing (d002) of the porous carbon material to be 0.37 nm and the graphite-like crystallite size (Lc) to be 1.8 nm. This material was used as the anode in a sodium-ion battery, and a CR2032 coin cell was assembled. Electrochemical performance was tested at a current density of 0.1 A / g. The initial coulombic efficiency was 86.2%, the specific capacity was 305 mAh / g, and the capacity retention was 92% after 1000 cycles.
[0039] Specifically, the following methods can be used when culturing and activating microbial agents: Accurately weigh 2.0g of ammonium sulfate, 0.5g of dipotassium hydrogen phosphate, 0.5g of magnesium sulfate, 0.1g of calcium chloride, and 10g of sodium thiosulfate. Add them sequentially to 1000mL of deionized water and stir with a magnetic stirrer (300rpm) for 30 minutes until completely dissolved.
[0040] The pH of the system was then adjusted to 2.0 with a 1 mol / L dilute sulfuric acid solution, with continuous stirring during the adjustment process to ensure a uniform and stable pH. The prepared culture medium was then transferred to a 2L Erlenmeyer flask, sealed with double-layered gauze, and sterilized in an autoclave (121℃, 0.1MPa) for 20 minutes. After cooling to room temperature, it was ready for use.
[0041] Single colonies of *Thiobacillus ferrooxidans* and silicate bacteria were picked from refrigerated slant culture medium and inoculated separately into two 50 mL aliquots of sterilized basal medium. The cultures were then placed in a bioincubator and incubated for 48 hours at 30°C and an aeration rate of 0.3 L / min to allow for resuscitation, until the bacterial suspension turned pale yellow-green and showed a significant increase in turbidity. The two resuscitated bacterial suspensions were then mixed at a 1:1 volume ratio to obtain a mixed bacterial suspension. 10 mL of this mixed bacterial suspension was inoculated into 1000 mL of the aforementioned sterilized and cooled culture medium for scale-up culture.
[0042] The inoculated culture medium was placed in a biological incubator, with the culture temperature controlled at 30℃ and the aeration rate at 0.5 L / min, and cultured continuously for 5 days. During the culture period, samples were taken daily at regular intervals, and the bacterial concentration was counted using a hemocytometer. Simultaneously, the pH of the culture medium was monitored (maintained between 1.9 and 2.1). On day 5, the bacterial concentration reached 5 × 10⁻⁶. 8 The bacterial solution is CFU / mL, dark yellow-green in color, and odorless, indicating that activation is complete and ready for use.
[0043] This process optimizes the inoculation ratio of the two strains and the culture conditions such as ventilation and temperature, enabling ferrooxidizobacillus to efficiently metabolize and produce sulfuric acid, while silicate bacteria produce organic acids and chelating agents, thus achieving a synergistic leaching effect on different types of impurities.
[0044] Specifically, the following methods can be used for leaching and impurity removal: At a solid-liquid ratio of 1:8 (w / v), 100g of ground graphite powder was mixed with 800mL of activated bacterial solution and slowly added to the bioleaching reactor to avoid generating too many bubbles. The reactor's stirring device was turned on, and the stirring speed was adjusted to 150rpm to ensure full contact between the mineral powder and the bacterial solution. The temperature was set to 32℃ using an automatic temperature control system with a temperature control accuracy of ±0.5℃. The pH value of the system was monitored in real time using an online pH monitor. When the pH value was higher than 2.3, 0.5mol / L dilute sulfuric acid solution was automatically added. When the pH value was lower than 2.1, 0.1mol / L sodium bicarbonate solution was added to maintain the system pH value at around 2.2.
[0045] Specifically, the following methods can be used when impregnating the catalyst: Accurately weigh 1.0 g of ferric nitrate (mass ratio of 1:100 to microcrystalline graphite), add it to 500 mL of deionized water, and stir with a magnetic stirrer (400 rpm) for 60 minutes until the ferric nitrate is completely dissolved, resulting in a ferric nitrate solution with a concentration of 0.02 g / mL. The solution is clear and transparent, without any precipitate or suspended particles.
[0046] Weigh 100g of the dried purified microcrystalline graphite and slowly add it to the prepared ferric nitrate solution. Place the solution on a magnetic stirrer and stir continuously at room temperature (25℃) for 6 hours for impregnation. During the impregnation process, manually stir with a glass rod once every 1 hour to ensure that the graphite particles are fully dispersed and avoid agglomeration that would lead to uneven catalyst loading.
[0047] After impregnation, the suspension is transferred to a drying oven for drying.
[0048] Specifically, the following methods can be used for low-temperature catalytic purification: The quartz reaction tube of the tubular high-temperature furnace was cleaned to remove residual impurities from the inner wall. Then, the microcrystalline graphite precursor loaded with the catalyst was loaded into a graphite crucible, which was placed in the constant temperature zone in the middle of the reaction tube.
[0049] Close the flanges at both ends of the reaction tube, and introduce argon gas as a protective atmosphere. Adjust the argon gas flow rate to 50 mL / min and continue purging for 30 minutes to replace the air in the reaction tube and ensure that the oxygen content in the furnace is below 0.1%. Then, start the high-temperature furnace's programmed temperature rise system and set the temperature rise program: The first stage (pre-carbonization) raises the temperature from room temperature to 900°C at a rate of 3°C / min, and holds it at the set temperature for 1 hour. The purpose is to remove residual moisture, organic impurities, and catalyst decomposition products from the material and stabilize the material structure. The second stage (catalytic graphitization) raises the temperature from 900°C to 2000°C at a rate of 5°C / min, and holds it at the target temperature for 1 hour. During this process, Fe2O3 produced by the decomposition of ferric nitrate is reduced to metallic Fe, which acts as a catalytic active center, lowers the activation energy of carbon atom rearrangement, and promotes the formation of graphite-like microcrystalline structures and the regulation of interlayer spacing.
[0050] Specifically, the following methods can be used for cooling and post-processing: After the catalytic purification reaction is completed, turn off the heating device of the high-temperature furnace and keep argon gas continuously introduced (flow rate 50 mL / min) to allow the material to cool naturally to room temperature (about 24 hours) to avoid material structure cracking or performance changes due to rapid cooling.
[0051] The cooled product was taken out as a black blocky solid and placed in a high-speed pulverizer (FW100, Tianjin Tester Instrument Co., Ltd.) for pulverization for 3 minutes. Then it was sieved through a 200-mesh standard sieve (pore size 75μm), and the sieved material was collected. Large particles that were not completely pulverized were removed to obtain microcrystalline graphite porous carbon material with a particle size of less than 20μm.
[0052] This invention achieves the green and efficient preparation of microcrystalline graphite porous carbon materials through a technical route combining microbial leaching and low-temperature catalytic purification.
[0053] Compared with existing technologies, its core advantages are: 1. Green and environmentally friendly: The microbial leaching and purification process is under mild conditions and has virtually no emissions of waste, meeting the requirements of green manufacturing.
[0054] 2. Significantly reduced energy consumption: Catalytic purification technology significantly reduces the processing temperature, thereby reducing production energy consumption and costs.
[0055] 3. Excellent electrochemical performance of the product: Through precise control of the size and interlayer spacing of graphite-like microcrystals, the obtained porous carbon material has a high initial coulombic efficiency (up to 85% or more), moderate specific capacity (about 300 mAh / g), and long cycle life when used as the negative electrode of sodium-ion batteries.
[0056] 4. Good process adaptability: The method of this invention has good adaptability to microcrystalline graphite raw materials of different grades and is easy to achieve large-scale production.
[0057] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-described technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.
Claims
1. A method for preparing microcrystalline graphite porous carbon materials based on microbial purification and structural reconstruction, characterized in that, Includes the following steps: Preparation and activation of microbial agents; The treated microcrystalline graphite was leached, purified, and impurities removed using activated microbial agents. The purified microcrystalline graphite was impregnated with a catalyst. The impregnated material is heat-treated under high temperature and inert gas. After heat treatment, the material is cooled to room temperature before undergoing post-treatment.
2. The method for preparing microcrystalline graphite porous carbon materials based on microbial purification and structural reconstruction according to claim 1, characterized in that, The microorganisms used are a mixed bacterial solution of ferrooxidase and silicate bacteria, and a culture medium is prepared. The mixed bacterial solution is placed in the culture medium for activation culture to obtain the activated microbial agent.
3. The method for preparing microcrystalline graphite porous carbon materials based on microbial purification and structural reconstruction according to claim 2, characterized in that, The culture medium contains ammonium sulfate, dipotassium hydrogen phosphate, magnesium sulfate, calcium chloride, and sodium thiosulfate.
4. The method for preparing microcrystalline graphite porous carbon materials based on microbial purification and structural reconstruction according to claim 2, characterized in that, The mixed bacterial solution was placed in a culture medium at 28-32℃ and pH 1.5-2.5 to activate it. It was cultured with aeration for 3-7 days until the bacterial concentration reached 108-109 CFU / mL.
5. The method for preparing microcrystalline graphite porous carbon materials based on microbial purification and structural reconstruction according to claim 1, characterized in that, The microcrystalline graphite is processed by grinding to obtain particles with a particle size D50 of 10-50 μm.
6. The method for preparing microcrystalline graphite porous carbon materials based on microbial purification and structural reconstruction according to claim 1, characterized in that, The treated microcrystalline graphite and the activated microbial inoculum were mixed at a solid-liquid ratio of 1:5 to 1:10 (w / v) and placed in a bioleaching reactor. The temperature was controlled at 30-35℃, the stirring speed at 100-200rpm, the pH value at 1.8-2.5, and the leaching time at 5-15 days.
7. The method for preparing microcrystalline graphite porous carbon materials based on microbial purification and structural reconstruction according to claim 1, characterized in that, The catalyst is a soluble transition metal salt solution, with a mass ratio of transition metal salt to microcrystalline graphite of 0.5:100 to 5:100, and an impregnation time of 2-12 hours.
8. The method for preparing microcrystalline graphite porous carbon materials based on microbial purification and structural reconstruction according to claim 1, characterized in that, The impregnated microcrystalline graphite is placed in a high-temperature furnace and heat-treated under inert gas protection.
9. The method for preparing microcrystalline graphite porous carbon materials based on microbial purification and structural reconstruction according to claim 1, characterized in that, The high-temperature furnace is first heated to 800-1000℃ at a rate of 2-5℃ / min for pre-carbonization to stabilize the structure, and then heated to 1800-2200℃ at a rate of 3-8℃ / min, held for 0.5-2 hours, and protected with argon gas.
10. The method for preparing microcrystalline graphite porous carbon materials based on microbial purification and structural reconstruction according to claim 1, characterized in that, The microcrystalline graphite, after being cooled to room temperature, is then pulverized and sieved.