Molten Salt Electrochemical Synthesis of Layered CaSi ₂ Followed by Decalcification for the Anode of Lithium Ion Battery

Abstract Layered calcium disilicide (CaSi ₂ ) has emerged as a promising precursor for 2D silicon‐based nanomaterials. However, achieving a rapid and environmentally friendly synthesis of CaSi ₂ remains challenging. In this study, molten salt electrochemical co‐reduction in CaCl ₂ ‐CaO‐SiO ₂ molten salts at 1123 K for 4 h is reported for the rapid preparation of layered and well‐defined hexagonal CaSi ₂ (h‐CaSi ₂ ) crystals with an average particle size of 5–10 µm. Electrochemical investigations, including cyclic voltammetry and square‐wave voltammetry, provide insights into the reduction mechanisms of Ca ² ⁺ and Si⁴⁺ ions. Additionally, the dynamic formation pathways of monolithic Si and h‐CaSi ₂ are elucidated through time‐ and potential‐ dependent electron microscopy studies. Si nanowire/nanosheet composites (h‐Si and c‐Si) are obtained from h‐CaSi ₂ and commercial CaSi ₂ (c‐CaSi ₂ ), respectively, via molten chloride‐assisted exfoliation, and assessed for lithium storage performance. The results show that h‐Si and c‐Si anodes present capacities of 235 mAh g ⁻¹ and 20 mAh g ⁻¹ after 300 cycles at 1A g ⁻¹ , which indicates that Si‐based anode derived from molten salt electrochemically synthesized CaSi ₂ has shown superior structural and electrochemical properties. This research provides a sustainable and cost‐effective strategy for the controllable preparation of high‐purity layered CaSi ₂ under low‐temperature conditions.