Recent research advances of self-discharge in supercapacitors: Mechanisms and suppressing strategies

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This review summarized and discussed the mechanisms of self-discharge supercapacitors, with a focus on suppressing strategies in terms of electrode, electrolyte, and separator. The remained challenges and the promising directions in suppressing the self-discharge of supercapacitors were also presented and summed up. Supercapacitors are one of the most promising energy storage devices in the fields of vehicle transportation, flexible electronic devices, aerospace, etc. However, the existed self-discharge that is the spontaneous voltage decay after supercapacitors are fully charged, brings about the wide gap between experimental studies and practical utilization of supercapacitors. Although eliminating the self-discharge completely is not reachable, suppressing the self-discharge rate to the lowest point is possible and feasible. So far, the significant endeavors have been devoted to achieve this goal. Herein, we summary and discuss the possible mechanisms for the self-discharge and the underlying influence factors. Moreover, the strategies to suppress the self-discharge are systemically summed up by three independent but unified aspects: modifying the electrode, modulating the electrolyte and tuning the separator. Finally, the major challenges to suppress the self-discharge of supercapacitors are concluded and the promising strategies are also pointed out and discussed. This review is presented with the view of serving as a guideline to suppress the self-discharge of supercapacitors and to across-the-board facilitate their widespread application.