Rice hull-based silicon-carbon composite negative electrode material and preparation method thereof
By constructing rice husk-based silicon-carbon composite anode materials through segmented temperature-controlled heat treatment and freeze-drying technology, the problems of SiC formation and composition control were solved, achieving high-efficiency electrochemical performance and long-cycle stability.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-12-23
- Publication Date
- 2026-04-14
AI Technical Summary
In existing technologies for preparing silicon-carbon composite anode materials using rice husks, excessive SiC formation, difficulty in controlling component content, and insufficient conductive network lead to a decline in material performance.
By employing segmented temperature-controlled heat treatment and freeze-drying technology, combined with chemical vapor deposition, a three-dimensional porous network and hierarchical conductive system are constructed to precisely control the component content and conductive contacts.
It effectively suppresses SiC formation, improves the material's initial coulombic efficiency and cycle stability, and has a charge specific capacity exceeding 1200 mAh/g with excellent cycle stability.
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Abstract
Description
Technical Field
[0001] This invention relates to the field of silicon-carbon anode material technology, and in particular to a rice husk-based silicon-carbon composite anode material and its preparation method. Background Technology
[0002] With the development of modern technology, the theoretical capacity of traditional graphite anodes is relatively low (372 mAh / g), making it difficult to meet the current demands of high-energy-density lithium batteries. Silicon-based anodes, due to their extremely high theoretical specific capacity (4200 mAh / g), are considered ideal alternatives, but they suffer from problems such as large volume changes (>300%) during charge and discharge, easy structural damage, and poor cycle performance. Furthermore, the complex manufacturing process and high cost also limit their commercial application. Therefore, developing low-cost raw materials and simplifying the manufacturing process are crucial for promoting the development of silicon-based anodes. Rice husks, as an abundant agricultural waste, contain approximately 15-20% silica and a large amount of organic matter, making them an ideal precursor for preparing silicon-carbon composite anode materials. However, existing technologies for preparing silicon-carbon materials using rice husks have the following prominent problems: First, a large amount of inactive SiC phase is easily generated during high-temperature processing. SiC has extremely high chemical stability and hardly participates in electrochemical reactions within the battery's operating voltage range, leading to a reduction in the material's effective capacity. Studies have shown that when the SiC content exceeds 10%, the specific capacity of the material will decrease by more than 30%. Second, existing technologies struggle to precisely control the proportions of silicon, silicon dioxide, and carbon in the final product. Excessive silicon content exacerbates the volume effect and deteriorates cycle performance; while insufficient silicon content fails to leverage its high capacity advantage. Although silicon dioxide possesses some lithium storage capacity, its initial coulombic efficiency is low, and excessive presence can severely impact the battery's initial efficiency. Furthermore, rice husk-based silicon-carbon materials prepared by traditional methods typically lack an effective conductive network structure. Silicon materials have low intrinsic conductivity and require good conductive contact with carbon materials to realize their electrochemical performance. Existing technologies mainly achieve silicon-carbon composites through simple mechanical mixing or single heat treatment, making it difficult to construct a continuous three-dimensional conductive network.
[0003] Therefore, developing a method for preparing rice husk-based silicon-carbon materials that can effectively suppress SiC formation, precisely control component content, and construct a multidimensional conductive network has significant theoretical and practical value. Summary of the Invention
[0004] In view of this, the present invention provides a rice husk-based silicon-carbon composite anode material and its preparation method, so as to solve the problems of high SiC content, difficulty in controlling component content and poor conductive contact in existing silicon-carbon composite anode materials.
[0005] To achieve the above objectives, the present invention adopts the following technical solution: A method for preparing a rice husk-based silicon-carbon composite anode material includes the following steps: 1) The rice husks are pretreated by acid washing to obtain pretreated rice husks; 2) The pretreated rice husks were subjected to a first-stage heat treatment. After the first-stage heat treatment was completed, the product was dispersed in a solvent and freeze-dried to obtain a three-dimensional porous precursor. 3) The three-dimensional porous precursor was subjected to a second-stage heat treatment under a reducing atmosphere. After the second-stage heat treatment, carbon coating was performed to obtain rice husk-based silicon-carbon composite anode material.
[0006] Preferably, the pickling solution for the pickling pretreatment includes one or more of hydrochloric acid, nitric acid solution, citric acid solution, sulfuric acid solution, and hydrofluoric acid solution; The molar concentration of the pickling solution is 2~7 mol / L; The pickling pretreatment time is 3-7 hours.
[0007] Preferably, the temperature of the first stage heat treatment is 400~600℃, the time is 1~4h, and the heating rate is 1~5℃ / min.
[0008] Preferably, the solvent in step 2) includes one or more of water, tert-butanol, ethanol and acetone; The mass ratio of product to solvent after the first stage of heat treatment is 3~10:90~97.
[0009] Preferably, the freeze-drying includes a pre-freezing stage and a sublimation drying stage; The temperature during the pre-freezing stage is -30 to -80°C, the time is 2 to 8 hours, and the pressure is 2 to 10 Pa. The sublimation drying stage is carried out at a pressure of 10~100 Pa, at -10~0℃ for 24~48 h, and at 10~25℃ for 2~6 h.
[0010] Preferably, the reducing atmosphere described in step 3) includes a mixed atmosphere of hydrogen and a protective gas; The reducing atmosphere contains 5-30% hydrogen. The protective gas includes one or more of argon, nitrogen, and helium.
[0011] Preferably, the temperature of the second stage heat treatment is 800~1100℃ and the time is 2~6h.
[0012] Preferably, the carbon coating treatment method includes chemical vapor deposition; The thickness of the carbon coating is 20~60nm.
[0013] Another object of the present invention is to provide a rice husk-based silicon-carbon composite anode material prepared by the above preparation method.
[0014] As can be seen from the above technical solutions, compared with the prior art, the present invention has the following beneficial effects: 1. In the conventional process, in order to pursue high crystallinity, a one-step high-temperature direct carbonization reduction is usually adopted. However, in this process, due to local overheating and reaction runaway, a large amount of electrochemically inert SiC phase (usually exceeding 10%) is generated at the high-temperature interface between silicon and carbon, seriously consuming active substances. The present invention adopts a segmented temperature-controlled heat treatment process: first, the carbon source is uniformly pre-coated and stabilized at a lower temperature, and then reduction is carried out under precisely controlled temperature and atmosphere. This method thermodynamically inhibits the explosive nucleation and growth of SiC, and can control its content below 5%, so as to convert more raw materials into effective active silicon and conductive carbon.
[0015] 2. The traditional method physically mixes silicon and carbon, or uses chemical etching to create pores. The obtained materials have loose structures, uneven pore distributions or closed pores, and the buffering effect is limited. The present invention adopts freeze-drying technology. During the rapid freezing process, ice crystals grow directionally, squeezing the silicon / carbon precursor to the grain boundaries. After sublimation, a three-dimensional porous network skeleton with high connectivity and directionality is formed in-situ. This structure is a "bottom-up" fine structure that cannot be achieved by mechanical mixing, providing a pre-designed and isotropic efficient buffering space for the volume expansion of silicon, and fundamentally alleviating the particle breakage caused by the concentration of expansion stress.
[0016] 3. Conventional material design mostly relies on the mixing of raw materials in a fixed ratio, and it is difficult to precisely control the components (especially the reduction degree and residual amount of SiO2) during the heat treatment process, resulting in large performance fluctuations. The present invention realizes the precise regulation of the content and existence form of active silicon (Si), buffer / active interface phase (SiO x , 0 < x < 2) and conductive carbon (C) in the final product through the synergistic effect of temperature-time-atmosphere.
[0017] 4. The prior art mostly focuses on single carbon coating or simply incorporating conductive agents (such as acetylene black). The connection between components is fragile and easily fails under cyclic stress. The present invention constructs a hierarchical conductive system of "core-shell contact (point) + three-dimensional skeleton (body) + nano-bridging (line)". The surface carbon shell ensures point-to-point contact with each active particle; the interconnected porous carbon constitutes a rigid and continuous bulk conductive skeleton. This network can ensure the continuous smoothness of the electron path during long cycling compared with a single structure.
[0018] 5. The silicon-carbon composite material prepared by the present invention has a first Coulomb efficiency of more than 86%, a charge specific capacity exceeding 1200 mAh / g, and excellent cycle stability. Detailed Implementation
[0019] This invention provides a method for preparing a rice husk-based silicon-carbon composite anode material, comprising the following steps: 1) The rice husks are pretreated by acid washing to obtain pretreated rice husks; 2) The pretreated rice husks were subjected to a first-stage heat treatment. After the first-stage heat treatment was completed, the product was dispersed in a solvent and freeze-dried to obtain a three-dimensional porous precursor. 3) The three-dimensional porous precursor was subjected to a second-stage heat treatment under a reducing atmosphere. After the second-stage heat treatment, carbon coating was performed to obtain rice husk-based silicon-carbon composite anode material.
[0020] In this invention, the pickling solution for the pickling pretreatment includes one or more of hydrochloric acid, nitric acid solution, citric acid solution, sulfuric acid solution and hydrofluoric acid solution.
[0021] In this invention, the molar concentration of the pickling solution is 2~7 mol / L, specifically 3 mol / L, 4 mol / L, 5 mol / L, or 6 mol / L.
[0022] In this invention, the pickling pretreatment time is 3 to 7 hours, specifically 4 hours, 5 hours, or 6 hours.
[0023] In this invention, the rice husk acid washing pretreatment preferably includes a grinding step, and the average particle size after grinding is 620~680nm, specifically 640nm, 650nm, or 660nm; the particle size before grinding is preferably 0.5~2mm, specifically 0.8mm, 1mm, 1.2mm, 1.5mm, or 1.8mm.
[0024] In this invention, the temperature of the first stage heat treatment is 400~600℃, specifically 420℃, 450℃, 480℃, 500℃, 520℃, 550℃, or 580℃; the time is 1~4h, specifically 1.5h, 2h, 2.5h, 3h, or 3.5h; and the heating rate is 1~5℃ / min, specifically 1.5℃ / min, 2℃ / min, 2.5℃ / min, 3℃ / min, 3.5℃ / min, 4℃ / min, or 4.5℃ / min.
[0025] In this invention, the solvent in step 2) includes one or more of water, tert-butanol, ethanol and acetone.
[0026] In this invention, the mass ratio of the product to the solvent after the first stage of heat treatment is 3~10:90~97, preferably 4~8:92~96, and more preferably 5~6:94~95.
[0027] In this invention, the freeze-drying includes a pre-freezing stage and a sublimation drying stage.
[0028] In this invention, the temperature of the pre-freezing stage is -30 to -80°C, specifically -35°C, -40°C, -45°C, -50°C, -55°C, -60°C, -65°C, -70°C, and -75°C; the time is 2 to 8 hours, specifically 3 hours, 4 hours, 5 hours, 6 hours, and 7 hours; and the pressure is 2 to 10 Pa, specifically 3 Pa, 4 Pa, 5 Pa, 6 Pa, 7 Pa, 8 Pa, and 9 Pa.
[0029] In this invention, the pressure of the sublimation drying stage is 10~100 Pa, specifically 20 Pa, 30 Pa, 40 Pa, 50 Pa, 60 Pa, 70 Pa, 80 Pa, or 90 Pa; sublimation is carried out at -10~0℃ for 24~48 h, specifically at -8℃, -6℃, -5℃, -4℃, or -2℃; and for 30 h, 36 h, or 42 h. Then, sublimation is carried out at 10~25℃ for 2~6 h, specifically at 12℃, 15℃, 18℃, 20℃, or 22℃; and for 2.5 h, 3 h, 3.5 h, 4 h, 4.5 h, 5 h, or 5.5 h.
[0030] In this invention, the reducing atmosphere described in step 3) includes a mixed atmosphere of hydrogen and protective gas.
[0031] In this invention, the volume percentage of hydrogen in the reducing atmosphere is 5-30%, specifically 10%, 15%, 20%, or 25%.
[0032] In this invention, the protective gas includes one or more of argon, nitrogen, and helium.
[0033] In this invention, the temperature of the second stage heat treatment is 800~1100℃, specifically 850℃, 900℃, 950℃, 1000℃, or 1050℃; the time is 2~6h, specifically 3h, 4h, or 5h.
[0034] In this invention, the carbon coating treatment method includes chemical vapor deposition.
[0035] In this invention, the thickness of the carbon coating layer is 20~60nm, specifically 30nm, 40nm, or 50nm; carbon coating can improve the initial efficiency of silicon-carbon anodes, reduce the cycle expansion rate of silicon-carbon materials, and improve cycle stability.
[0036] The present invention also provides a rice husk-based silicon-carbon composite anode material prepared by the above preparation method.
[0037] In this invention, the preparation of the rice husk-based silicon-carbon composite anode is as follows: First, 4-8g of rice husk-based silicon-carbon composite anode material, 0.9-2g of SP, 10-20g of CNT, and 25-40g of PAA are added, and some zirconium beads are added. The mixture is stirred in a planetary mixer at 800-2000 rpm for 4-10 minutes and then at 1500-2000 rpm for 6-10 minutes. Second, 4-8g of rice husk-based silicon-carbon composite anode material and 3-5g of water are added, and the mixture is stirred at 800-2000 rpm for 4-10 minutes and then at 1500-2000 rpm for 6-10 minutes.
[0038] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.
[0039] Example 1
[0040] Rice husks with a particle size of 1.5 mm were pretreated with a 4 mol / L hydrochloric acid solution for 5 hours to remove metallic impurities, and then ground to an average particle size of 650 nm. The pretreated rice husks were then subjected to a first-stage heat treatment under an argon atmosphere, with a heating rate of 3 °C / min, a temperature controlled at 450 °C, and a holding time of 3 hours. After heat treatment, the resulting product was dispersed in a solvent (ethanol) (product:solvent = 5:95, g / g) and heated at -60 °C and 5P. Pre-freezing for 3 hours under condition a, then adjusting the pressure to 60 Pa, sublimating at -2℃ for 30 hours, and then at 20℃ for 3 hours to form a three-dimensional porous precursor; the precursor is then subjected to a second-stage heat treatment in a reducing atmosphere (10% hydrogen, with the remainder being nitrogen), with the temperature controlled at 900℃ and held for 3 hours; the heat-treated material is then optimized for carbon coating using chemical vapor deposition (CVD) with methane as the carbon source at 700℃, achieving a carbon coating thickness of 55 nm. This yields a rice husk-based silicon-carbon composite anode material.
[0041] Preparation of silicon-carbon electrode: First, add 5g of rice husk-based silicon-carbon composite anode material, 1.3g SP, 13g CNT, 30g PAA, and some zirconium beads. Stir at 1200rpm for 6 minutes and 1800rpm for 8 minutes in a planetary mixer. Second, add 5g of rice husk-based silicon-carbon composite anode material and 3.5g of water. Continue stirring at 1200rpm for 6 minutes and 1800rpm for 8 minutes.
[0042] Example 2
[0043] Rice husks with a particle size of 0.7 mm were pretreated with a 4 mol / L hydrochloric acid solution for 6 hours to remove metallic impurities, and then ground to an average particle size of 650 nm. The pretreated rice husks were then subjected to a first-stage heat treatment under an argon atmosphere, with a heating rate of 2.5 °C / min, a temperature controlled at 480 °C, and a holding time of 3.5 hours. After heat treatment, the resulting product was dispersed in a solvent (propanol) (product:solvent = 5:95, g / g) and heated at -50 °C for 5 hours. Pre-freezing at Pa for 4 hours, then adjusting the pressure to 40 Pa, sublimating at -3℃ for 36 hours and at 20℃ for 4 hours forms a three-dimensional porous precursor. The precursor undergoes a second-stage heat treatment in a reducing atmosphere (15% hydrogen, with the remainder being nitrogen), controlled at 950℃ for 3.5 hours. The heat-treated material is then optimized for carbon coating using chemical vapor deposition (CVD) with methane as the carbon source at 700℃, achieving a carbon coating thickness of 45 nm. This yields a rice husk-based silicon-carbon composite anode material.
[0044] The silicon-carbon electrode was prepared in the same manner as in Example 1.
[0045] Example 3
[0046] Rice husks with a particle size of 2 mm were pretreated by acid washing with a 6 mol / L sulfuric acid solution for 3 hours to remove metallic impurities, and then ground to an average particle size of 650 nm. The pretreated rice husks were then subjected to a first-stage heat treatment under an argon atmosphere, with a heating rate of 5 °C / min, a temperature controlled at 550 °C, and a holding time of 1.5 hours. After heat treatment, the resulting product was dispersed in a solvent (water) (product:solvent = 5:95, g / g) and heated at -40 °C and 8 Pa. Pre-freezing for 7 hours under the specified conditions, followed by sublimation at -5℃ for 36 hours and at 25℃ for 4 hours to form a three-dimensional porous precursor. The precursor underwent a second-stage heat treatment in a reducing atmosphere (30% hydrogen, with the remainder being nitrogen), with the temperature controlled at 800℃ and held for 2 hours. The heat-treated material was then optimized for carbon coating using chemical vapor deposition (CVD) with methane as the carbon source at 700℃, achieving a carbon coating thickness of 50 nm. This yielded a rice husk-based silicon-carbon composite anode material.
[0047] The silicon-carbon electrode was prepared in the same manner as in Example 1.
[0048] Comparative Example 1
[0049] The only difference between this comparative example and Example 1 is that the acid-washed rice husks were directly heated to 1050°C at 5°C / min under argon protection and kept at that temperature for 5 hours.
[0050] The silicon-carbon electrode was prepared in the same manner as in Example 1.
[0051] Experimental Example 1
[0052] The rice husk-based silicon-carbon composite anode materials and silicon-carbon electrodes prepared in Examples 1-2 and Comparative Example 1 were subjected to relevant performance tests, and the test results are shown in Table 1.
[0053] A silicon-carbon electrode was assembled into a coin cell, specifically consisting of a lithium anode, a PP separator, a silicon-carbon electrode cathode, and LB-015 electrolyte from Duoduo Chemical. The silicon-carbon electrode loading was 1.2 mg / cm³. 2 The electrode sheets are not rolled. The assembled button cells are taken to the Blue Electric test cabinet for testing. The specific charging and discharging steps are: let stand for 6 hours, discharge at 0.1C to 0.005V, and charge at 0.1C to 1.5V.
[0054] Table 1 Test results of Examples 1-2 and Comparative Example 1
[0055] As shown in Table 1, the SiC content in Example 1 was 38.3%, in Example 2 it was 35.6%, and in Comparative Example 1 it was 30.1%. This invention, through a staged heat treatment process, effectively suppressed the formation of inactive SiC, controlling the SiC content below 5%, thus improving the initial efficiency of the material. The capacities of Examples 1 and 2 were more than 300 mAh / g higher than that of Comparative Example 1, and the initial efficiency was 20% higher. Because a three-dimensional porous structure was constructed using freeze-drying technology, a buffer space was provided for the volume expansion of the silicon material, and the prepared silicon-carbon batteries maintained a capacity retention of more than 85% over 100 cycles.
[0056] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.
[0057] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.
Claims
1. A method for preparing a rice husk-based silicon-carbon composite anode material, characterized in that, Includes the following steps: 1) The rice husks are pretreated by acid washing to obtain pretreated rice husks; 2) The pretreated rice husks were subjected to a first-stage heat treatment. After the first-stage heat treatment was completed, the product was dispersed in a solvent and freeze-dried to obtain a three-dimensional porous precursor. 3) The three-dimensional porous precursor was subjected to a second-stage heat treatment under a reducing atmosphere. After the second-stage heat treatment, carbon coating was performed to obtain rice husk-based silicon-carbon composite anode material.
2. The method for preparing a rice husk-based silicon-carbon composite anode material according to claim 1, characterized in that, The pickling solution for the pickling pretreatment includes one or more of hydrochloric acid, nitric acid solution, citric acid solution, sulfuric acid solution, and hydrofluoric acid solution; The molar concentration of the pickling solution is 2~7 mol / L; The pickling pretreatment time is 3-7 hours.
3. The method for preparing a rice husk-based silicon-carbon composite anode material according to claim 2, characterized in that, The temperature of the first stage of heat treatment is 400~600℃, the time is 1~4h, and the heating rate is 1~5℃ / min.
4. A method for preparing a rice husk-based silicon-carbon composite anode material according to any one of claims 1 to 3, characterized in that, The solvent mentioned in step 2) includes one or more of water, tert-butanol, ethanol, and acetone; The mass ratio of product to solvent after the first stage of heat treatment is 3~10:90~97.
5. The method for preparing a rice husk-based silicon-carbon composite anode material according to claim 4, characterized in that, The freeze-drying process includes a pre-freezing stage and a sublimation drying stage. The temperature during the pre-freezing stage is -30 to -80°C, the time is 2 to 8 hours, and the pressure is 2 to 10 Pa. The sublimation drying stage is carried out at a pressure of 10~100 Pa, at -10~0℃ for 24~48 h, and at 10~25℃ for 2~6 h.
6. The method for preparing a rice husk-based silicon-carbon composite anode material according to claim 5, characterized in that, The reducing atmosphere mentioned in step 3) includes a mixture of hydrogen and protective gas; The reducing atmosphere contains 5-30% hydrogen. The protective gas includes one or more of argon, nitrogen, and helium.
7. A method for preparing a rice husk-based silicon-carbon composite anode material according to claim 5 or 6, characterized in that, The second stage of heat treatment is carried out at a temperature of 800~1100℃ for 2~6 hours.
8. The method for preparing a rice husk-based silicon-carbon composite anode material according to claim 7, characterized in that, The carbon coating treatment method includes chemical vapor deposition; The thickness of the carbon coating is 20~60nm.
9. Rice husk-based silicon-carbon composite anode material prepared by the preparation method according to any one of claims 1 to 8.