Harnessing the neutral Ca(NO₃)₂ electrolyte in CaMnO₃ perovskite systems for calcium-ion supercapacitors

The need for sustainable and high-performance energy storage technologies has intensified the research interest in calcium-ion supercapacitors, driven by the abundance, low cost, and favourable redox properties of calcium. In this study, we present a CaMnO₃ perovskite electrode system operating in a neutral Ca(NO₃)₂ electrolyte, exhibiting outstanding electrochemical characteristics. The optimized CaMnO₃ electrode achieves a specific capacitance of 258.6 F g^-1 at 0.5 A g^-1 within a wide potential window of 1.9 V, achieving unprecedented performance for this material. It retains 72.6% of its initial capacitance even after 1500 charge-discharge cycles, with 100% coulombic efficiency. A CMO‖CMO symmetric device assembled using this electrode delivers a specific capacitance of 76.1 F g^-1, an energy density of 3.8 W h kg^-1, and a power density of 1190 W kg^-1, emphasizing its potential for high-power applications. To demonstrate the practical application of the fabricated device, both red and yellow LEDs were illuminated. Electrochemical analysis indicates that the superior performance results from the synergistic interaction between the CaMnO₃ perovskite structure and the Ca²⁺-based neutral electrolyte, enabling efficient charge storage through combined electrical double-layer capacitance and pseudocapacitance. This work establishes a new benchmark for calcium-ion supercapacitors and provides valuable insights into ion-intercalation and surface-redox behaviour within perovskite-electrolyte interfaces. These findings pave the way for safe, sustainable, and cost-effective energy storage solutions.