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.