Electrolytes for rechargeable calcium batteries: Addressing the constraints imposed by battery configuration and electrode materials

Increasing energy consumption is driving the development of renewable energy technologies. Currently, there is a growing interest in developing battery systems that can support large-scale energy storage. Rechargeable calcium batteries are potential candidates for such applications because of the reliable safety, affordable pricing and abundant reserves of Ca. Nevertheless, the exploitation of rechargeable Ca batteries faces challenges in seeking suitable electrolytes and cathode materials. Considering the importance of electrolyte in achieving rechargeable Ca batteries, this work presents a comprehensive overview of all types of electrolytes (aqueous, organic, hybrid, ionic liquid, and polymer) applied in rechargeable Ca batteries, analyzing their compatibility with specific electrode materials in diverse battery configurations (Ca-metal batteries, Ca-O₂ batteries, Ca-S batteries, rocking chair Ca-ion batteries and Ca-based dual ion batteries), concentrating on how key electrolyte parameters such as solvent, salt, and concentration influence battery performance. It is hoped that this review could provide inspiration for advanced electrolytes research and further the progress of high-capacity and long-cycle life rechargeable Ca batteries.