In recent years, the rapid development of new energy vehicles has raised higher demands for battery performance. Traditional graphite-based anode materials have low specific capacity and are difficult to meet the demand. Silicon has an extremely high theoretical specific capacity, which can effectively improve battery performance. It has great potential for development as an anode material. The silicon source material, particle morphology, and processing methods significantly impact the performance of silicon-based negative electrodes.
Let’s take a look at the silicon sources of silicon-based negative electrodes.
Diatomite, Zeolite, sand and Other Mineral Silicon Sources
Mineral silicon is the most abundant and widely distributed silicon source today. It mainly exists in the form of silicon oxides and silicates, such as sand, zeolite, feldspar, and clay. Silicon minerals have high silicon content and properties like high hardness, thermal stability, and bahan kimia stability. Some silicon minerals contain numerous small pores in their microstructure, giving them a large specific surface area. This makes them suitable for preparing porous silicon-based anode materials.
Diatomite
Diatomite is a sediment formed by the accumulation of tiny diatom remains from ancient seas. It is widely distributed as a siliceous rock with a high storage capacity on Earth. The main chemical component of diatomaceous earth is SiO2, with a maximum content of up to 94%. In addition, it contains trace amounts of metal impurities and organic matter. The SiO2 obtained from diatomaceous earth has a good porous structure. Compared to biomass silicon sources, it contains less carbon, but its silicon content is higher. The silica structure exhibits a unique, highly ordered 3D network structure. Through simple extraction and compounding, porous nano-silicon materials can be used to prepare silicon-based anodes.
Clinoptilolite
Clinoptilolite is mainly composed of silicates, with a high silicon content (57%–70%) and a complex cage-like channel structure. This structure is beneficial for preparing uniformly porous silicon-based anode materials. Researchers use mechanical grinding to open the internal transmission channels of clinoptilolite. They then apply heat to promote a magnesium thermal reduction reaction, extracting elemental silicon. Further, the vapor deposition method is used to crack toluene on the surface of nano-silicon, forming a carbon film. This results in a sponge-like structure of nanoporous silicon-based negative electrodes materials. These pores effectively buffer the volume changes of the silicon-based anode during charge and discharge cycles. This ensures the material’s mechanical integrity, with advantages such as simple preparation and good cycling stability.
Sand
The main component of sand is quartz, which has advantages such as abundant reserves, low cost, and easy extraction compared to other silicon ores. However, the silicon dioxide in sand is formed by a large number of SiO4 tetrahedra linked through shared oxygen atoms, forming a strong silicon-oxygen network. This structure is highly stable and difficult to utilize. Researchers use NaCl to absorb the heat generated during the magnesium reduction process, preventing particle melting. Nano-silicon is extracted from sea sand, and the high temperature pyrolysis of acetylene is used to achieve carbon lapisan on the silicon particles. This results in well-coated silicon-carbon anode materials.
Biomass Silicon Sources Such as Rice Husks and Reeds
Silicon-rich plants include rice husks, reeds, horsetails, tea leaves, and bamboo. The silicon content varies among different plants. In biomass, silicon mainly exists as free silica in stems, bark, and leaves. Chemical reactions are used to convert it into elemental porous silicon. This is followed by a carbon coating process to prepare silicon-based negative electrodes materials.
Silica in biomass, after reduction, can largely retain its porous structure. During the preparation of silicon-based anodes, a simple process can preserve its porous framework. This effectively increases the internal space of the material, alleviating silicon’s volume expansion during charge and discharge cycles. Using biomass as a silicon source for preparing silicon-based negative electrodes materials has advantages such as wide availability and sustainability. It aligns with current low-carbon and environmentally friendly development concepts, making it an ideal silicon source.
Rice husk is a byproduct of rice, with over 100 million tons produced globally each year. Although the composition of rice husk varies by variety and origin, it mainly consists of lignin, cellulose, hemicellulose, and silica. Typically, the ash remaining after burning rice husks accounts for about 20% of the husk’s mass, with silica content reaching 87–97%. Through methods such as calcination, washing, impurity removal, and reduction reactions, elemental silicon can be extracted from rice husks. The silica in rice husks has a porous structure, and simple reactions can yield 3D porous nanosiilicon. When combined with organic carbon, this enhances the material’s electrochemical performance.
In addition to rice husks, reeds are also a good silicon-based anode material. They have orderly arranged nanoscale silica and a flake-like 3D layered structure. Using a simple magnesium thermal reduction reaction, highly porous 3D silicon can be obtained.
Silane and Other Chemical Gas Silicon Sources
Gaseous silicon sources are commonly used for preparing silicon-based anodes, including silane (SiH4), trichlorosilane (SiHCl3), and silicon tetrachloride (SiCl4). These gaseous silicon sources can be used in vapor deposition techniques like CVD to prepare nano-silicon under appropriate conditions. Among them, silane is the main gaseous silicon source used for silicon-based anode preparation. Silane, a silicon-hydrogen compound, is primarily used in the form of methylsilane (SiH4) for this purpose. Typically, the vapor deposition method is employed, where silane undergoes decomposition to generate nano-silicon that adheres to a substrate.
Carbon coating is then achieved by decomposing carbon-containing gases, resulting in silicon-carbon anode materials.
Gaseous silicon sources are suitable for preparing next-generation silicon-carbon anode materials. By producing smaller nano-silicon particles and surface modifications, they effectively address the volume expansion issue during actual use. However, gaseous silicon sources (such as silane) are highly unstable, flammable, and toxic. Therefore, strict control of temperature, pressure, and gas flow is required during preparation and use to ensure safety and stability. This leads to higher requirements for production equipment, process control, and increased production costs.
Photovoltaic Silicon Waste and Other Waste Materials
Photovoltaic silicon often requires cutting and shaping during the manufacturing process, resulting in silicon waste from edge and corner scraps. With the widespread use of photovoltaic silicon, the generation of silicon waste has been increasing year by year. Silicon waste is inexpensive and readily available, with relatively high purity and low impurity content. It is suitable for preparing silicon-based anode materials.
To address the issues of complex preparation processes and high material costs, researchers have used industrial photovoltaic cutting silicon waste as a silicon source. Through high-energy ball milling, the silicon is reduced to nanoscale size. Then, sucrose is used as a carbon source to coat the nano-silicon, resulting in Si@C microsphere anode materials. This approach reduces material costs and simplifies the preparation process. The coating structure design encapsulates the nano-silicon inside, preventing direct contact with the electrolyte and reducing electrolyte consumption. The nano-silicon undergoes volume fluctuations within the carbon spheres, maintaining good contact with the carbon material and enabling rapid lithium-ion transport.
Recycled quartz glass, after treatment, can also yield silicon anode materials with stable cycling performance. Researchers used discarded broken glass and, through magnesium thermal reduction, directly obtained a Si interconnection network. After surface coating with carbon material, the material was assembled into a battery. At a C/2 current density, after 400 cycles, the capacity remained at 1420 mAh/g. The carbon coating on the surface has limitations in restricting the expansion of silicon material, which is a key reason for significant capacity loss in the initial cycles. However, the structure retained after glass treatment provides excellent anti-expansion ability, achieving a capacity retention rate of up to 74%.
Kesimpulan
In conclusion, the “silicon” in silicon-based anodes comes from various sources. It can be obtained from minerals, plants, waste materials, and gaseous silicon sources. With technological advancements, the utilization of these silicon sources is becoming more efficient and sustainable. These diverse silicon sources offer various options for developing silicon-based anode materials. This has the potential to drive the development of higher-performance battery technologies
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