Research toolbox and material design to meet the challenge of rechargeable Ca metal batteries.

Ca metal anode batteries have emerged as a potential next-generation battery technology due to the low redox potential of Ca metal, high capacity, and abundance. However, practical development requires further improvements of electrolytes and cathode host materials. Recent advances in the design of weakly coordinating electrolytes have enabled reversible Ca plating/stripping and the testing of practical cathode materials. However, the formation of blocking Ca metal interphases, insufficient electrolyte operating windows, and limited cathode reversibility pose fundamental challenges, requiring new strategies beyond current approaches-in particular, the development of a stable ion-conducting Ca metal interphase through the application of new Ca electrolytes and fine-tuning of ion solvation structures, as well as high-energy-density cathode hosts with improved reversibility. Currently, many literature studies are plagued by direct transfer of methodology from Li battery research, leading to insufficient characterization and erroneous conclusions due to peculiar Ca electrochemistry, which is impeding the progress of the field. Therefore, future Ca battery research should employ an improved research toolbox coupled with computational modeling to accelerate the exploration of chemical space.