( )Insights to the variation of oxygen content and reasons for improved electrochemical performance of annealing SiOx anodes for Li-ion battery

SiOx-based anodes have attracted great attention due to its relatively stable cycle performance and high specific capacity. However, SiOx also suffers from low initial coulombic efficiency (ICE) and electronic conductivity which are alleviated by disproportionation or compositing with other materials, and it's inevitably to go through annealing during these processes. Whereas the changes in oxygen content and structural composition inside particles during heat treatment are still ambiguous. In this work, we make a thorough inquiry in these issues through an annealing-etching combined processing of SiOx for the first time. The results reveal that oxygen diffuses to the surface during the heating treatment, while small Si domains are surrounded by amorphous oxygen-rich areas inside the particles, leading to the decay of electrochemical activity which can be recovered by HF etching. As a result, the modified SiOx exhibits an excellent performance with a reversible capacity of 1364.8 mAh g(-1) and an ICE of 67.8% at 0.1 A g(-1). After 500 cycles, it shows a reversible capacity of 1285.2 mAh g(-1) at 0.5 A g(-1). This work provides a novel modification strategy with controlment of the oxygen content and distribution inside the particles, thereby effectively adjusting the electrochemical performance.