Suppressing self-discharge of vanadium based Na-supercapacitor based on conjugated device configuration

Among various efficient and rapid energy storage devices, vanadium-based Na-supercapacitors have emerged as highly competitive candidates. However, severe self-discharge behavior has critically restricted their practical implementation. Currently, despite various strategies based on optimizing the component (such as electrode and electrolyte optimization), it still remain difficult to fundamentally resolve this challenge. Herein, we propose a conjugatedly configured device fabricated by coupling pairs of pre-sodiated vanadium pentoxide as both the positive and negative, forming a pre‑sodium vanadium pentoxide (Na x V 2 O 5 ) vs. pre‑sodium vanadium pentoxide (Na (1- x ) V 2 O 5 ) configuration. Unlike conventional electric double-layer capacitors (EDLCs), the working process of such device involves the insertion/extraction of single type of charge carrier on both electrodes, thus simplifying the reaction condition and stabilize the concentration of charge carrier in the electrolyte. As a result, conjugated supercapacitor displays a lower self-discharge rate (2.7–5.0 mV/h at 1.4, 1.8, and 2.2 V) and a smaller leakage current (1.8–2.2 μA after stabilization at 2.2 V). Such strategy for alleviating self-discharge is not limited to specific materials system, thus providing a general solution strategy for various supercapacitors that are currently limited by self-discharge issues.