Electrolyte Solvation Manipulation Enables Unprecedented Room‐Temperature Calcium‐Metal Batteries

Calcium‐metal batteries (CMBs) provide a promising option for high‐energy and cost‐effective energy‐storage technology beyond the current state‐of‐the‐art lithium‐ion batteries. Nevertheless, the development of room‐temperature CMBs is significantly impeded by the poor reversibility and short lifespan of the calcium‐metal anode. A solvation manipulation strategy is reported to improve the plating/stripping reversibility of calcium‐metal anodes by enhancing the desolvation kinetics of calcium ions in the electrolyte. The introduction of lithium salt changes the electrolyte structure considerably by reducing coordination number of calcium ions in the first solvation shell. As a result, an unprecedented Coulombic efficiency of up to 99.1 % is achieved for galvanostatic plating/stripping of the calcium‐metal anode, accompanied by a very stable long‐term cycling performance over 200 cycles at room temperature. This work may open up new opportunities for development of practical CMBs. Lithium salt added to the electrolyte of a calcium‐metal battery reduces the oxygen coordination number for the 43Ca nucleus in the first solvation shell, thereby promoting the desolvation kinetics of Ca2+ ions and the cycling performance of the calcium‐metal anode. Excellent reversibility of calcium plating and stripping is realized.