Ca-ion storage enhancement of Ca-pillared vanadium oxide using a malonic-assisted solution combustion process and a novel aqueous AC//Ca(NO3)2//CaVO/C hybrid cell

Abstract

Herein, we report the pioneering electrochemical investigation of calcium vanadium oxide (CaV<inf>2</inf>O<inf>6</inf>) cathode as a pillared-structure host for Ca²⁺ ion storage in aqueous rechargeable batteries. CaV<inf>2</inf>O<inf>6</inf> (CaVO) is synthesized using a malonic-assisted solution-combustion process, followed by calcination at 400 °C (CaVO400) and 700 °C (CaVO700). Once integrated with carbon, the oxide becomes highly active due to the initial irreversible Ca²⁺/H⁺ exchange, as evidenced by Cyclic Voltammetry, Chronopotentiometry and Impedance combined with ex-situ XRD as well as Raman and FTIR measurements. The removal of an accompanying CaV<inf>2</inf>O<inf>7</inf> phase favors Ca²⁺ and H⁺/H<inf>3</inf>O⁺ insertion by leading to an increased proton concentration in the electrolyte and liberating active sites on the CaVO surface. As a result, a very high capacity of about 87 mAh g⁻¹ is obtained in half-cells at 1 A g⁻¹, which originates from an extrinsic pseudocapacitive behavior. When CaVO400/C is combined with a carbon anode in full-cells, it reaches about 90 mAh g⁻¹, at 100 mA g⁻¹ and exhibits very stable cycling for 100 cycles.