A novel hydrated eutectic electrolyte advances calcium-ion batteries toward comprehensive

Ca-ion batteries (CIBs) have garnered significant attention in the past few years by virtue of their economic and physicochemical advantages, positioning them as a promising electrochemical energy storage technology in the post-lithium-ion battery era. However, the current research progress is insufficient, leaving this emerging field far from practical application, most of which focuses on developing high-performance electrode materials. Herein, we design a novel hydrated eutectic electrolyte (HEE) prepared by mixing Ca(ClO4)2·4H2O and acetamide at room temperature. The solvation structure of Ca2+ can be precisely regulated by controlling the molar ratio of two chemical components. The HEE with optimal formulation features a wide electrochemical stability window, good ionic conductivity, appropriate viscosity, and a low melting point. In this novel HEE, a full CIB assembled with a high-performance PEDOT/V2O5 cathode and a commercial PTCDI anode demonstrated outstanding electrochemical performance at room temperature (30 mAh·g−1 at 0.5 A·g−1 after 30,000 cycles) and environmental adaptability within a wide operating temperature range (−20~60 ℃). This work may not only provide a sustainable, safe, and cost-effective electrolyte for CIBs but also pave the way for the comprehensive development of CIBs.