Pseudocapacitive Charge Storage in MXene–V₂O₅ for Asymmetric Flexible Energy Storage Devices

Abstract

Pseudocapacitive asymmetric supercapacitors are promising candidates for achieving high energy density in flexible energy storage devices. However, seeking suitable positive electrode materials that are compatible with negative electrode materials remains a considerable challenge. In the current study, a pseudocapacitive Ti₃C₂T_<i>x</i> MXene used as negative electrodes is rationally compatible with redox-type V₂O₅ as positive electrodes, resulting in the assembly of an all-pseudocapacitive Ti₃C₂T_<i>x</i> MXene//V₂O₅ asymmetric flexible energy storage device. The solid-state asymmetric device can deliver an energy density of 8.33 mW h cm^-3 at a current density of 0.5 A g^-1. Moreover, it can operate in an expanded voltage window of 1.5 V, with dominant surface-capacitive charge-storage mechanisms. Additionally, the device can power a yellow light-emitting diode for up to 7 s, indicating the potential of the device for use in practical applications. This study demonstrates the possibility of using other two-dimensional transition-metal carbide nanosheets for high-energy density flexible energy storage devices.