Effect of Volume Expansion on SEI Covering Carbon-Coated Nano-Si/SiO Composite

Abstract

We prepared nano-sized Si clusters dispersed uniformly in carbon-coated SiO (C-Si/SiO) and thoroughly investigated the morphology of the solid electrolyte interface (SEI) formed on the C-Si/SiO electrodes before and after a charge-discharge cycling test. The 30 cycles at 1000 mAh/g (deep) showed an excellent durability compared to those at 500 mAh/g (shallow). The different SEIs with the crack-contained and smooth electrode surfaces were formed after the deep and shallow cycles, respectively. Their SEI components which originated from hydrocarbons, Li alkyl carbonate, Li₂CO₃, LiF, and phosphorus oxide, were almost identical, even though the surface morphology was much different. When charge-discharge from 0.02 V to 0.7 V with large-volume change was applied, large cracks were formed on the SEI surface of the C-Si/SiO electrode after shallow cycles, which was similar to that after deep cycles. As a result, the cell properties for shallow cycles corresponded roughly to those for deep cycles. This suggests that the charge-discharge of a C-Si/SiO electrode is strongly related to the surface morphology, meaning that stable cycle properties can be achieved by controlling the morphology of the SEI.