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

• We explore Si-based anodes for calcium ion batteries combining DFT and experiments.
• Predicted voltage of Ca alloying with Si (CaxSi x ≤ 2 300% volume change) is 0.4 V.
• Calculated voltage for Ca deinsertion from CaSi2 is 1.2 V (28% volume variation).
• A capacity of 400 mAh/g is delivered by charging CaSi2//Ca cells at 100 °C.
• The decalciation process of CaSi2 is confirmed by SXRDP, SEM and EDS.

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 CaxSi 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.