Controlled surface oxidation of mesoporous silicon microparticles to achieve a stable Si/SiOx anode for lithium-ion batteries

Silicon (Si) is the most promising next-generation anode material for lithium-ion batteries. However, it often suffers from a fast capacity fading due to the large volume changes during the lithiation/delithiation resulting in electrical contact loss between different components of the anode and eventually in battery fading. Mesoporous structure of silicon is a potential material to overcome the issue as the pores could accommodate the volume change during the battery cycling. However, its high surface area can cause continuous parasitic electrolyte decomposition reactions, causing low initial coulombic efficiency (ICE), capacity fading, and battery safety issue. In this study, the surface passivation of mesoporous Si microparticles produced with electrochemical etching and milling was realized through thermal oxidation. The silicon oxide (SiOx) layer generated acted as a protective layer to stabilize the Si surface, thus improving Si electrode performance. Electrochemical characterization showed that the electrode performance of Si/SiOx was strongly correlated with the oxygen content. The Si/SiOx anode delivered a discharge capacity of over 2000 mAh g−1 when the oxygen content was less than 34 wt%, but a much lower capacity when there was higher oxygen content. The best sample (oxidation at 700 °C) showed ICE of 78% and a stable cycling performance for over 180 cycles with a limited capacity of 800 mAh g−1. The results indicate that the appropriate oxidation of mesoporous Si surface to get optimized surface/oxygen content enhances the electrochemical performance of Si anodes essentially.