Surface-Oxidation-Induced Constrained Volume Expansion of Commercial Silicon Flakes as High-Performance Anode Material for Lithium-Ion Batteries

The performance of silicon (Si) material as the anode of lithium-ion batteries (LIBs) depends on its size, structure, morphology, composition, etc. Commercial Si flakes produced by sawing waste Si wafers, which are promising for application as the anode material in LIBs, have been investigated. The Si flakes were thermally treated at 800°C under N₂ gas at a flow rate of 150 mL min⁻¹. The limited oxidation reaction between the Si flakes and residual oxygen with the assistance of N₂ generated a thin layer of SiO_x on their surface, effectively suppressing the volume expansion during Li⁺ insertion/deinsertion, as evidenced by the well-maintained surface morphology of thermally treated Si electrodes in charge–discharge testing. Indeed, the electrochemical performance of the Si material was greatly enhanced. Capacity as high as 2131.8 mAh g⁻¹ was obtained for thermally treated Si after 30 cycles, whereas pristine Si almost lost its activity. Moreover, the initial coulombic efficiency was greatly increased from 63.1% to 87.9%. Overall, the findings of this work indicate that this approach is appropriate to synthesize high-performance Si anode material that can also be considered as a Si source for further synthesis of Si-based composites.