High-energy Mn2V2O7//C asymmetric supercapacitors in aqueous/organic hybrid electrolytes

Abstract

The demand for advanced energy storage devices, such as high-energy density supercapacitors, has spurred efforts to develop new environmentally friendly and efficient electrode materials and electrolyte solutions for sustainable development. A prominent strategy is the fabrication of high-voltage and energy-density asymmetric supercapacitors (AS). In this study, dimanganese divanadate (Mn2V2O7, MVO) particles were synthesized via a hydrothermal process and used as pseudocapacitive electrodes for AS. The pseudocapacitive MVO electrode offered synergistic advantages of reversible surface or near-surface Faradaic reactions for charge storage. Another approach to address the challenges of limited energy density in supercapacitors was modifying the electrolyte solution to widen the operating voltage window and increase energy density. A hybrid electrolyte solution of 5 M sodium perchlorate (NaClO4) in a mixture of (2:1) volume ratio of acetonitrile (AN) and water (H2O) was introduced to expand the voltage window in the AS. The fabricated AS with MVO as a pseudocapacitive electrode and activated carbon as a double-layer capacitive electrode operated in a voltage window > 2.0 V with the hybrid electrolyte. The AS device exhibited a capacitance of 156.9 F g−1 at 0.1 A g−1 and a high energy density of 87.2 Wh kg−1, surpassing the carbon-based symmetric supercapacitor (58.9 Wh kg−1). Furthermore, the pseudocapacitive supercapacitor showed exceptional long-term stability over 50,000 cycles. Structural and surface characterization of the MVO electrode after CV testing validated that the charge storage mechanism in Mn2V2O7//C was a surface-controlled process. The performance of the AS pouch cell revealed the great promise of the pseudocapacitive electrode in practical applications.