Revolutionizing Micro‐Supercapacitors: Tuning MnO₂ Electrode Polarity and Redox Activity for Superior Energy Storage

Abstract Micro‐supercapacitors (MSCs) have emerged as indispensable power solutions for modern microelectronics, offering rapid charge/discharge capabilities, high power delivery, and exceptional cycling stability. However, their energy density remains limited due to the lower electrode capacitance and narrower voltage window of conventional symmetrical micro‐supercapacitors (SMSCs). In this study, a novel strategy is presented to maximize the energy density of MnO₂‐based SMSCs by modulating their electrode polarity and redox activity. Specifically, the non‐lattice oxygen concentration in MnO₂ is focused on tuning to introduce additional redox‐active sites, thus improving charge storage capacity and energy density. Using operando electrochemical quartz crystal microbalance (EQCM) analysis reveals a multi‐step redox mechanism involving lattice water‐assisted transformations and non‐lattice oxygen pathways, providing unprecedented insights into MnO₂’s electrochemical behavior in alkaline electrolytes. The engineered symmetric MnO₂ MSCs achieve an outstanding energy density of 33.63 µW h cm⁻² at a power density of 1.12 mW cm⁻², retaining full performance under mechanical deformation. The alkaline electrolyte further inhibits disproportionation reaction, preserving active material integrity and cycling durability. This work not only unveils the pivotal role of non‐lattice oxygen in MnO₂ electrochemical polarity but also provides a promising pathway for designing high‐energy‐density, flexible MSCs to power next‐generation microdevices.