Preparation and Application of Si@Void@C Composite Anode Materials for Lithium-Ion Batteries
I. Preparation Methods
Room-Temperature Solution Method for Preparing Si@Void@C Composite Materials
Preparation Process: Initially, silicon nanoparticles are coated with silicon dioxide (SiO₂). Subsequently, polydopamine is applied and carbonized to form a nitrogen-doped carbon coating. Finally, hydrofluoric acid (HF) is used to selectively etch the SiO₂ layer, resulting in a yolk-shell structured Si@void@C.
Structural Advantages: The void space provides a stress-relief area for the volume expansion of silicon particles during lithiation, maintaining the integrity of the carbon shell. This structure achieves an initial specific capacity of 800 mAh/g at a current density of 100 mA/g. After 1000 cycles, the capacity retention rate is 74%, with a Coulombic efficiency as high as 99.84%.
Preparation of Double-Yolk Shell Structure
Preparation Process: The double-yolk shell nanostructure of Si/void/SiO₂/void/C is successfully synthesized by selectively etching SiO₂ in the Si/SiO₂/C structure using HF solution.
Performance: This structure, featuring a SiO₂ coating layer, a conductive carbon coating layer, and two internal voids, exhibits excellent electrochemical performance. After 430 cycles, the reversible specific capacity reaches 956 mAh/g, with a capacity retention rate of 83%.
Preparation of Pyrolytic Asphalt Carbon Matrix
Preparation Process: Pyrolytic asphalt carbon is used as the carbon matrix, embedding nano-silicon into an amorphous carbon substrate to prepare high-tapped density Si@C composite materials.
Performance: When mixed with commercial graphite anode materials, the composite material achieves a specific capacity of 669.5 mAh/g, an initial Coulombic efficiency of 83.76%, an average Coulombic efficiency of 99.88%, and a capacity retention rate of 80.10% after 250 cycles.
Preparation of Double-Conductive Carbon Shell
Preparation Process: Silicon nanoparticles are embedded into a graphite and glucose-derived carbon matrix through a two-step ball milling combined with annealing treatment.
Performance: This double-conductive carbon shell Si/C composite material exhibits ultra-stable capacity (670 mAh/g) and high initial Coulombic efficiency (89.4%). After 850 cycles, the capacity retention rate reaches 85%, and it shows good rate performance at a current density of 5 A/g.
II. Applications and Performance
High Specific Capacity and Cycle Stability
The Si@Void@C composite material effectively alleviates the volume expansion of silicon during lithiation through the design of internal void space, significantly enhancing the cycle stability and Coulombic efficiency of the material. For example, the double-yolk shell structured Si/void/SiO₂/void/C composite material maintains a high specific capacity and capacity retention rate even after multiple cycles.
Rate Performance
By optimizing the carbon coating layer and internal structure, the Si@Void@C composite material exhibits good rate performance at high current densities. For example, the double-conductive carbon shell Si/C composite material maintains a high specific capacity at a current density of 5 A/g.
Commercialization Potential
The high-silicon-content Si@C composite structure is significant for advancing the commercial application of high-specific-capacity silicon-carbon composite materials. For instance, a novel core-shell structured G/Si@C composite material, prepared by mixing nano-silicon particles with graphite and then coating with asphalt pyrolysis, demonstrates excellent structural integrity and electrochemical performance.
III. Future Development Directions
Further Optimization of Structural Design: Enhance the electrochemical performance of Si@Void@C composite materials through nanostructuring, porous structure design, and multi-layer coating.
Cost Reduction and Scalability: Develop more cost-effective and efficient preparation processes to facilitate large-scale production of Si@Void@C composite materials.
Diversified Applications: Beyond lithium-ion batteries, explore the application of Si@Void@C composite materials in other energy storage systems such as sodium-ion and potassium-ion batteries.
In summary, Si@Void@C composite materials show great application potential in the field of lithium-ion battery anode materials. Continuous optimization of preparation processes and structural design is expected to enable their widespread use in high-performance energy storage systems.
