Discovery of Calcium-Metal Alloy Anodes for Reversible Ca-Ion Batteries

Ca-ion batteries (CIBs) show promise to achieve the high energy density required by emerging applications like electric vehicles because of their potentially improved capacities and high operating voltages. The development of CIBs is hindered by the failure of traditional graphite and calcium metal anodes due to the intercalation difficulty and the lack of efficient electrolytes. Recently, a high voltage (4.45 V) CIB cell using Sn as the anode has been reported to achieve a remarkable cyclability (>300 cycles). The calciation of Sn is observed to end at Ca7Sn6, which is surprising, since higher Ca-content compounds are known (e.g., Ca2Sn). Here, the Sn electrochemical calciation reaction process is investigated computationally and the reaction driving force as a function of Ca content is explored using density functional theory (DFT) calculations. This exploration allows the identification of threshold voltages which govern the limits of the calciation process. This information is then used to design a four-step screening strategy and high-throughput DFT is utilized to search for anode materials with higher properties. Many metalloids (Si, Sb, Ge), (post-)transition metals (Al, Pb, Cu, Cd, CdCu2) are predicted to be promising inexpensive anode candidates and warrant further experimental investigations.