How to Tackle the Killer of Supercapacitors: Self-Discharge

Supercapacitors have emerged as a vital component in electrochemical energy storage, owing to their compelling advantages including high power density, long cycle life, fast charge/discharge capability, wide operating temperature range, high safety, and environmental friendliness. However, the severe self-discharge phenomenon causes spontaneous voltage decay and continuous energy loss under open-circuit conditions, significantly restricting their practical deployment in independent energy storage and long-term reliability scenarios. To address this critical bottleneck, this review first decouples the three dominant self-discharge mechanisms from a fundamental perspective, namely ohmic leakage, parasitic Faradaic reactions, and charge redistribution. Anchored in device architecture, it then systematically summarizes the influence of each component, including the current collector, electrode material, electrolyte, and separator, on self-discharge behavior and the corresponding suppression strategies. This work aims to provide directional guidance for constructing high-energy supercapacitors with ultralow self-discharge.