Double-buffer silicon-carbon anode material by a dynamic self-assembly process for lithium-ion batteries

High-Temperature Magnesiothermic Reduction Enables HF-Free Synthesis of Porous Silicon with Enhanced Performance as Lithium-Ion Battery Anode

Porous silicon-based anode materials have gained much interest because the porous structure can effectively accommodate volume changes and release mechanical stress, leading to improved cycling performance. Magnesiothermic reduction has emerged as an effective way to convert silica into porous silicon with a good electrochemical performance. However, corrosive HF etching is normally a mandatory step to improve the electrochemical performance of the as-synthesized silicon, which significantly increases the safety risk. This has become one of the major issues that impedes practical application of the magnesiothermic reduction synthesis of the porous silicon anode. Here, a facile HF-free method is reported to synthesize macro-/mesoporous silicon with good cyclic and rate performance by simply increasing the reduction temperature from 700 °C to 800 °C and 900 °C. The mechanism for the structure change resulting from the increased temperature is elaborated. A finite element simulation indicated that the 3D continuous structure formed by the magnesiothermic reduction at 800 °C and 900 °C could undertake the mechanical stress effectively and was responsible for an improved cyclic stability compared to the silicon synthesized at 700 °C.

Assembly: A Key Enabler for the Construction of Superior Silicon-Based Anodes

Silicon (Si) is regarded as the most promising anode material for high-energy lithium-ion batteries (LIBs) due to its high theoretical capacity, and low working potential. However, the large volume variation during the continuous lithiation/delithiation processes easily leads to structural damage and serious side reactions. To overcome the resultant rapid specific capacity decay, the nanocrystallization and compound strategies are proposed to construct hierarchically assembled structures with different morphologies and functions, which develop novel energy storage devices at nano/micro scale. The introduction of assembly strategies in the preparation process of silicon-based materials can integrate the advantages of both nanoscale and microstructures, which significantly enhance the comprehensive performance of the prepared silicon-based assemblies. Unfortunately, the summary and understanding of assembly are still lacking. In this review, the understanding of assembly is deepened in terms of driving forces, methods, influencing factors and advantages. The recent research progress of silicon-based assembled anodes and the mechanism of the functional advantages for assembled structures are reviewed from the aspects of spatial confinement, layered construction, fasciculate structure assembly, superparticles, and interconnected assembly strategies. Various feasible strategies for structural assembly and performance improvement are pointed out. Finally, the challenges and integrated improvement strategies for assembled silicon-based anodes are summarized.

Industrial Silicon-Wafer-Wastage-Derived Carbon-Enfolded Si/Si-C/C Nanocomposite Anode Material through Plasma-Assisted Discharge Process for Rechargeable Li-Ion Storage

Silicon is a promising anode material for high-performance Li-ion batteries as a result of its high theoretical specific capacity and elemental abundance. Currently, the commercial application of the Si-based anode is still restricted by its large volume changes during the lithiation cycles and low electrical conductivity. To address these issues, we demonstrate a facile plasma-assisted discharge process to anchor nano-sized Si particles into methanol with quick quenching. After the subsequent sintering process, we obtained a Si/SiC/C composite (M-Si). The unique structure not only allowed for the electrolyte infiltration to enhance lithium ion diffusion during charge and discharge process, but also buffered the volume expansion of silicon particles to enhance the rate capability and cycle stability. The M-Si cell electrochemical results exposed good Li-ion storage performance compared to that of the bare Si used cell (B-Si). The electrode cell consisting of M-Si exhibited remarkable enhanced cyclic stability and sustained the reversible specific capacity of 563 mAhg-1 after 100 cycles, with a coulombic efficiency of 99% at a current density of 0.1C, which is higher than that of the B-Si electrode cell that was used. Hence, the as-prepared Si/SiC/C composite is an efficient anode material for Li-ion battery applications. Moreover, these results indicate that the novel plasma-assisted discharge technique will bring a potential durable methodology to produce novel high-performance electrode materials for future advanced large-scale energy-storage applications.