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.