A Hierarchical Interconnected Nanosheet Structure of Porous δ-MnO<sub>2</sub> on Graphite Paper as Cathode with a Broad Potential Window for NaNO<sub>3</sub> Aqueous Electrolyte Supercapacitors
Jun Wang, Ling Tian, Wenlu Xie, Xiao Wang, Xiao Long, Kai Sun, Adil Emin, Dequan Liu, Yujun Fu, Qiang Chen, Junshuai Li, Yali Li, Deyan He
Abstract
The potential window for aqueous supercapacitor cathodes greatly depends on the electrochemical stability of water, and thus is generally limited to ∼1.2 V. Herein, a 1.4 V potential window (vs Ag/AgCl) in the 5 M NaNO3 aqueous electrolyte for porous δ-MnO2 with a hierarchical interconnected nanosheet structure grown on electrochemically roughened graphite paper by electrodeposition is reported. A specific capacitance of ∼407.6 F g–1 is delivered at 1 A g–1, and capacitance retention up to ∼90.7% is achieved after 5000 cycles at 8 A g–1. The aqueous asymmetric supercapacitors of 2.4 V are assembled with the configuration of δ-MnO2//activated carbon, and an energy density (E) of ∼38.4 Wh kg–1 is obtained at 599.7 W kg–1 (even at 12 kW kg–1, E of ∼21.7 Wh kg–1 is still delivered). Moreover, the asymmetric supercapacitors exhibit good rate and cycling performance. Thanks to the simple preparation for the electrode materials/structures and high device performance, it is believed that this work provides valuable contributions to developing aqueous supercapacitors delivering a broad working voltage window and thus an elevated energy density.