Silicon-Based Anodes with Long Cycle Life for Lithium-Ion Batteries Achieved by Significant Suppression of Their Volume Expansion in Ionic-Liquid Electrolyte.

Elemental Si has a high theoretical capacity and has attracted attention as an anode material for high energy density lithium-ion batteries. Rapid capacity fading is the main problem with Si-based electrodes; this is mainly because of a massive volume change in Si during lithiation-delithiation. Here, we report that combining an ionic-liquid electrolyte with a charge capacity limit of 1000 mA h g-1 significantly suppresses Si volume expansion, improving the cycle life. Phosphorus-doping of Si also enhances the suppression and increases the Li+ diffusion coefficient. In contrast, the Si layer expands significantly in an organic electrolyte even with the charge capacity limit and even in an ionic-liquid electrolyte without the limit. We demonstrated that the homogeneously distributed Si lithiation-delithiation, phase-transition control from the Si to Li-rich Li-Si alloy phases, formation of a surface film with structural and/or mechanical stability, and faster Li+ diffusion contribute to suppressing Si volume expansion.