Regulating oxygen vacancies and coordination environment of manganese dioxide for enhanced high-mass-loading energy storage†

Although manganese oxide (MnO₂) has been extensively studied for energy storage, further applications are limited due to its sluggish electron/ion-transfer kinetics and insufficient active sites, especially under high-mass-loading conditions. Regulating the electronic structure of MnO₂ at the atomic level and revealing its energy-storage mechanism will be beneficial for solving these scientific problems. Herein, an oxygen-vacancy-modulated MnO₂ (O_v–MnO₂) electrode with fully exposed active sites is fabricated at large-scale via an electrodeposition and chemical reduction procedure. Experimental characterizations and theoretical calculations were performed and the results verified that the optimized Mn coordination environment with oxygen vacancies could induce a local built-in electric field and additional active sites, allowing achieving exceptional ionic-adsorption/transport rates and pseudocapacitive capacity. As a result, the obtained O_v–MnO₂ electrode showed a superior areal capacitance of 4831.6 mF cm⁻² and prominent rate performance (46.3% at 60 mA cm⁻²) comparable to those of low-mass-loading electrodes. Remarkably, a planar asymmetric supercapacitor (ASC) was assembled with a distinguished areal energy density of 103.9 μW h cm⁻² and excellent mechanical flexibility. This work provides not only an effective strategy for regulating the coordination environment of metal atoms in metal oxides but also a deeper understanding of the electrochemical properties related to the electronic structure of such materials.