Utilizing hybrid faradaic mechanism via catalytic and surface interactions for high-performance flexible energy storage system

Abstract

Improving the capacitance and energy density is a significant challenge while developing practical and flexible energy storage system (ESS). Redox mediators (RMs), as redox-active electrolyte additives, can provide additional energy storing capability via electrochemical faradaic contribution on electrodes for high-performance flexible ESSs. Particularly, determining effective material combinations between electrodes and RMs is essential for maximizing surface faradaic redox reactions for energy-storage performance. In this study, an electrode-RM system comprising heterostructured hybrid (carbon fiber (CF)/MnO2) faradaic electrodes and iodine RMs (I-RMs) in a redox-active electrolyte is investigated. The CF/MnO2 with the I-RMs (CF/MnO2-I) induces dominant catalytic faradaic interaction with the I-RMs, significantly enhancing the surface faradaic kinetics and increasing the overall energy-storage performance. The CF/MnO2-I ESSs show a 12.6-fold (or higher) increased volumetric energy density of 793.81 mWh L−1 at a current of 10 µA relative to ESSs using CF/MnO2 without I-RMs (CF/MnO2). Moreover, the CF/MnO2-I retains 93.1% of its initial capacitance after 10,000 cycles, validating the excellent cyclability. Finally, the flexibility of the ESSs is tested at different bending angles (180° to 0°), demonstrating its feasibility for flexible and high-wear environments. Therefore, CF/MnO2 electrodes present a practical material combination for high-performance flexible energy-storage devices owing to the catalytic faradaic interaction with I-RMs.