Assessing Si-based anodes for Ca-ion batteries: Electrochemical decalciation of CaSi2

Density functional theory (DFT) calculations are used to investigate the basic electrochemical characteristics of Si-based anodes in calcium ion batteries (CIBs). The calculated average voltage of Ca alloying with fcc-Si to form the intermetallic Ca_xSi phases (0.5 < x ≤ 2) is of 0.4 V, with a volume variation of 306%. Decalciation of the lower Ca content phase, CaSi₂, is predicted at an average voltage between 0.57 V (formation of Si-fcc, 65% volume variation) and 1.2 V (formation of metastable deinserted-Si phase, 29% volume variation). Experiments carried out in conventional alkyl carbonate electrolytes show evidence that electrochemical “decalciation” of CaSi₂ is possible at moderate temperatures. The decalciation of CaSi₂ is confirmed by different characterization techniques.