A Wholly Degradable, Rechargeable Zn-Ti3C2 MXene Capacitor with Superior Anti-Self-Discharge Function

Abstract

Degradable energy storage systems (ESSs) have been proposed to tackle increasing e-wastes such as heavy metals and toxic organic electrolytes. However, currently reported degradable ESSs are scarce because it is very difficult to make all of the electrochemical components degradable as they must be stable for energy storage. Here, we designed an all-component degradable and rechargeable Zn-MXene capacitor with outstanding anti-self-discharge function using zinc nanosheets and Ti<inf>3</inf>C<inf>2</inf> MXene as electrodes. The whole capacitor can retain ca. 82.5% of the capacitance after 1000 cycles and be totally degraded within 7.25 days, comprehensively surpassing the current degradable supercapacitors (120 days, 400 cycles) and batteries (19 days, 0-20 cycles). In addition, while supercapacitors are notorious for intensive self-discharge, the Zn-MXene capacitor demonstrated the lowest self-discharge rate of 6.4 mV h^-1, better than all the previous supercapacitors with specifically designed anti-self-discharge components including electrodes (>300 mV h^-1), electrolytes (12-50 mV h^-1), and separators (20-400 mV h^-1). This is illustrated by the as-proposed "static electricity-immune mechanism" which refers to breaking the electrostatic adsorption. This Zn-MXene capacitor represents a great advance in degradable rechargeable ESSs and provides a strategy to fundamentally overcome the self-discharge problem encountered by supercapacitors.