Correlation between Electrolyte Chemistry and Solid Electrolyte Interphase for Reversible Ca Metal Anodes

Abstract The development of rechargeable Ca metal batteries (RCMBs) is hindered by the Ca 2+ passivating solid electrolyte interphases (SEIs). The cation solvation structure dictated by electrolyte chemistry plays a critical role in the SEIs properties. While a relatively weak cation‐solvent binding is preferred in Li metal anodes to promote anion‐derived SEIs, we demonstrate an enhanced Ca deposition/stripping reversibility under a strong cation‐solvent interaction, which is materialized in strongly‐solvating solvent and highly‐dissociated salt combinations. Such electrolyte formulations benefit the formation of solvent‐occupied solvation structure and minimize the anion reduction, resulting in organic‐rich/CaF 2 ‐poor SEIs for reversible Ca metal anodes. Furthermore, RCMBs paired with an organic cathode using the optimized electrolytes are demonstrated as a proof‐of‐concept. Our work reveals the paradigm shift in SEIs design for Ca metal anodes, opening up new opportunities for emerging RCMBs.