On the road toward calcium-based batteries

Summary This article reviews the progress in the development of a possible battery technology based on calcium, which is an abundant element and has an interesting standard reduction potential. The main bottleneck has been to find electrolytes enabling reversible plating and stripping of calcium, which has been overcome recently. Ongoing efforts focus in optimizing them to enable effective operation of calcium anodes at room temperature and within a large redox potential operation window, despite the formation of a passivation layer at the electrolyte/anode interface. In parallel, researchers are looking for suitable cathode materials enabling reasonably fast insertion and de-insertion of Ca 2+ ions, which need to be probed using diverse complementary characterization techniques to avoid biased interpretation of results derived from possible side reactions.