Melt-spun calcium disilicide and its exfoliation performance

Silicon nanosheets (SiNS) have garnered significant interest due to their high surface area and tunable electronic properties. Calcium disilicide (CaSi 2 ), a layered Zintl phase, serves as a promising precursor for SiNS, but commercial CaSi 2 is often plagued by impurities that hinder exfoliation. This study reports a melt-spinning synthesis method to produce CaSi 2 with controlled stoichiometry (Ca 1+x Si 2 , x = 0, 0.05, 0.10), aiming to improve phase purity and exfoliation performance. Ex-situ analyses suggest that Ca-rich phases contribute to disrupting the layered structure and facilitating decalcification. Post-annealing, the materials were exfoliated using CuCl 2 and characterized by SEM, XRD, BET, and particle size analysis. The SiNS derived from Ca 1.10 Si 2 demonstrated the highest exfoliation efficiency, exhibiting a well-defined lamellar structure in SEM, excellent suspension stability, and the largest pore-volume fraction—substantially exceeding those of Ca 1.05 Si 2 and Ca 1.00 Si 2 -thereby confirming enhanced exfoliation in the Ca-rich composition, ultimately forming amorphous SiO x with no detectable bulk silicon in the excess-calcium composition through XRD. These findings highlight the potential of melt-spun CaSi 2 as a scalable precursor for high-quality 2D silicon materials. Given their large surface area and structural tunability, the obtained silicon nanosheets are promising for applications in electronics, optoelectronics, and sustainable energy conversion technologies. • Melt-spinning enables phase-controlled synthesis of CaSi 2 thin sheets. • Ca-rich stoichiometry improves exfoliation efficiency of silicon nanosheets. • Annealing promotes crystallinity and 2D layer formation with both 3R and 6R phases. • Ca 1.10 Si 2 yields the largest pore volume and most pronounced lamellar aggregates, indicating superior exfoliation behavior.