Optimization of Silicon Alloy Materials for Lithium Ion Batteries

摘要

Silicon is regarded as one of the most promising anode materials because of its high theoretical specific capacity (4200 mAh/g) compared to commercially available graphite anodes (370 mAh/g). However, Si electrodes suffer considerable volume expansion of up to 300% during electrochemical lithiation, leading to electrode cracking and pulverization of the Si, causing rapid capacity degradation. Various approaches have been applied to solve this problem, including graphite nano-silicon structural composites. In this case, the internal spaces in the nanostructure can act as buffer space to accommodate the volume expansion of the silicon particles. Although some of the nanostructured Si materials achieve high capacity and cyclability, they are usually prepared by complicated and high cost synthetic processes which are difficult to extend to large scale. Another approach is using active/inactive alloys as an efficient way to reduce volume expansion and improve cycling performance. The volume expansion of Si can be suppressed by the presence of inactive components, resulting in the maximum energy density at a given volume expansion. Commercially available and low-cost Si alloys can serve as high capacity Li-storage anodic host materials with reasonable cyclability. Such Si alloy compounds can be made with required chemical stoichiometry and structural architecture though a simple mechanochemical process.