Practical Aqueous Calcium-Ion Battery Full-Cells for Future Stationary Storage

Abstract

There is a pressing need for high rate cycling, and cost-effective stationary energy storage systems in concomitance with the fast development of solar, wind and other types of renewable sources of energy. Aqueous rechargeable Ca-ion batteries have the potential to meet the growing demands of stationary energy storage devices because of their natural abundance, safety, low-cost proposition and higher volumetric capacity. In this study, a low cost, safe aqueous Ca-ion battery based on low potential, lower specific weight in-situ polymerized polyaniline as an anode and a high redox potential open framework structured potassium copper hexacyanoferrate as a cathode is demonstrated. The charge-discharge mechanism of this battery include dopind/dedoping of NO3- at the anode and intercalation and deintercalation of Ca-ion at the cathode. This Ca-ion battery works successfully in 2.5 M Ca(NO3)2 aqueous electrolyte, exhibiting 70 Wh kg-1 specific energy at 250 W kg-1 and even maintains 53 Wh kg-1 at 950 W kg-1 attributing to a good rate capability. At 0.8 A g-1 the battery provides an average specific capacity of 130 mAh g-1, exhibiting high Coulombic efficiency (~ 96%), with 95% capacity retention over 200 cycles life span, acquiring a new achievement in the electrochemical performance of aqueous Ca-ion batteries. Furthermore, the calcium-ion storage mechanism is investigated using high-end XANES and EXAFS measurements. Thus, this significant electrochemical performance of anode and cathode makes the battery as a promising candidate for grid-scale storage applications.