Ca 2+ Solvation and Electrochemical Solid/Electrolyte Interphase Formation Toward the Multivalent-Ion Batteries

Calcium is a promising candidate for future efficient and economical energy storage, as it is one of the most abundant elements and offers a more than twofold increase in the volumetric capacity compared to monovalent lithium-ion batteries. Compared to other widely explored multivalent ions such as magnesium, calcium did not receive as much attention until the discovery of Ca(BH 4 ) 2 in THF as an electrolyte, in which calcium can be plated and stripped at room temperature with low polarization. Since then, a wide array of computational methods and experimental approaches have aided in improving the performance of calcium-ion batteries. Because the solvation and desolvation on the cathode anode are simultaneous, complementary reactions, i.e., oxidation and reduction, an understanding of the dynamic Ca 2+ solvation process at the electrode/electrolyte interface is critical in designing an electrolyte that is compatible with both electrodes. In this article, we will deliver a comprehensive review of the Ca 2+ solvation study through computation and experimental approaches, multi-ion strategy for better battery performance, and also the involvement of in situ advanced characterization in the probing of the mechanisms.