Commercial-level mass-loading MnO2 with ion diffusion channels for high-performance aqueous energy storage devices

Abstract

Transition metal oxides have shown renewed interest as promising electrode materials for high-performance electrochemical energy storage devices. However, their cycle stability deteriorates significantly with increasing mass loading due to the sluggish electrolyte ion diffusion kinetics and limited accessible surface area. Herein, commercial-level mass-loading MnO₂ up to 9.14 mg cm⁻² with rational ion diffusion channels was fabricated by a gassing-assisted electrodeposition route, in which MnO₂ was deposited at an over-potential with an obvious oxygen evolution reaction. The robust channels in MnO₂ not only facilitate the electrolyte ion diffusion process but also increase the accessible area for the insertion/extraction of electrolyte ions during electrochemical reactions. The resultant MnO₂-based electrode exhibits the highest areal capacitance of 1.57 F cm⁻² (in a Na⁺-based aqueous electrolyte), with a rate retention percentage of 76% when the current density increases by 20-fold. More impressively, the configured hybrid ion supercapacitor device with the fabricated MnO₂ as a cathode delivers excellent cycle stability (in ion electrolytes Na⁺, Zn²⁺, and Mg²⁺), superior to most reported state-of-the-art energy storage devices. The proposed strategy here will provide a new opportunity for promoting the further development and practical application of aqueous energy storage devices by enhancing the true performance under a commercial-level mass-loading.