Porous Silicon Anodes Derived from Molten Salt Dealloying of CaSi₂ for Lithium-Ion Batteries

A micro-sized porous crystalline silicon was successfully synthesized through a molten salt decalcification approach by treating CaSi₂ in both CaCl₂ and CaCl₂-KCl melts. Upon treatment in CaCl₂ at 900°C for 6, 12, and 24 h, the residual calcium content in the silicon products decreased to 6.03%, 4.05%, and 1.30%, respectively. Similarly, in CaCl₂-KCl melts held at 700°C, 800°C, and 900°C for 24 h, the calcium content dropped to 9.38%, 6.64%, and 1.48%, respectively. Higher temperatures and extended durations facilitated more efficient calcium removal, yielding silicon with increasingly porous and dendritic features. One representative sample, MC-3 (derived from CaCl₂ melts at 900°C for 24 h), was coated with a polydopamine-derived carbon layer via polymerization and subsequent carbonization, forming a uniform shell of 10-30 nm thickness. The resulting MC-3@C composite, when employed as an anode material for lithium-ion batteries, delivered a reversible specific capacity of 647.5 mAh g^{- 1} after 700 cycles at 1 A g^{- 1} and demonstrated outstanding rate capability. This work presents an efficient molten salt strategy for fabricating microporous crystalline silicon with enhanced electrochemical performance, offering a scalable and cost-effective alternative to conventional silicon-based anode materials.