High Performance Nonaqueous Ca-Ion Cathodes Based on NASICON-NaV₂(PO₄)₃ and the Way to Activate Their Structure

Calcium-ion batteries (CIBs) are gaining attention as a promising energy storage technology due to their high theoretical capacity, attributed to the divalency of calcium, low redox potential, and natural abundance. However, the limited availability of calcium insertion electrode materials and their tendency to exhibit low capacity or poor cyclability remain critical challenges. In this study, the activation mechanism underlying calcium ion storage in NASICON-type NaV₂(PO₄)₃ structures are investigated using advanced structural analyses and elemental analyses. NaV₂(PO₄)₃ is identified as an efficient cathode material for CIBs, demonstrating a reversible discharge capacity of 106.9 mAh g⁻¹ at 10 mA g⁻¹—an 82% improvement compared to the pristine material—while maintaining an average operating voltage of ≈3.5 V (vs Ca/Ca²⁺) and good cyclability in a nonaqueous electrolyte. These findings offer valuable insights into the design and development of advanced oxide-based cathodes, enhancing their performance through activation processes for nonaqueous CIBs.