Activating lithium storage in 2D CaSi₂ anode via enhancing pseudocapacitive properties with oxygen modification engineering

Silicon (Si) has emerged as a promising anode material for lithium-ion batteries (LIBs) due to its extremely high theoretical capacity of 4200 mAh·g⁻¹. However, its practical application is limited by several critical challenges, including severe volume expansion and poor electrical conductivity. Herein, we employ a two-dimensional (2D) oxygen modification engineering approach to fabricate 2D oxygen-functionalized CaSi₂ (CaSi₂O_x) layers. During the preparation of 2D CaSi₂ layers, O atoms are gradually incorporated onto their surface. The resulting 2D CaSi₂O_x layers have a thickness of 3–5 nm, closely matching the theoretical thickness of 6–10 layers. When used as lithium anodes, the 2D CaSi₂O_x layers exhibit exceptional electrochemical performance, maintaining stability over 3000 cycles at an ultrahigh current density of 30 A·g⁻¹. By tailoring the surface properties, their pseudocapacitive charge storage mechanism is significantly enhanced, effectively overcoming the intrinsic limitations of traditional Si anodes. This study highlights the promise of 2D surface engineering in the development of advanced materials for next-generation LIBs.