Calcium nitrate (Ca(NO3)2)-based inorganic salt electrode for supercapacitor with long-cycle life performance

A novel water-soluble inorganic Ca(NO3)2 salt electrode is investigated for its pseudocapacitance in an aqueous KOH electrolyte. Commercially available Ca(NO3)2 salt is directly used as the key electrode material. The supercapacitor electrode contains Ca(NO3)2 salt, carbon black, and polyvinylidene fluoride (PVDF) in a ratio of 80:10:10. The Ca(NO3)2-based electrode demonstrates an exceptionally long life cycling stability, and a reasonably sound specific capacitance of 234 F/g is obtained at a current density of 3 A/g. Via chemical and electrochemical reactions, the in-situ activation of the Ca(NO3)2 forms an intermediate CaO which contributes to the pseudocapacitance of the electrode. The electrode undergoes a reversible redox reaction between Cu2+ ↔ Cu+ during the charge-discharge process. Superior rate capability and excellent specific capacitance retention of ∼120% over 2000 cycles are achieved compared with other inorganic salt electrodes.