Mn Valence Regulated Manganese Dioxide Porous Nanoflowers As High-Performance Cathodes at Large Current Densities in Aqueous Magnesium Ions Battery Capacitor

Abstract

The aqueous magnesium ion battery capacitor (AMIBC) is more attractive now as a novel second-generation energy storage system, due to its similar electrochemical characteristics to lithium, low cost and safety properties. In this work, due to the promotion of Faradic reaction contribution by Mn³⁺ introducing and high capacitive absorption contribution from its high specific surface area, manganese dioxide porous nanoflowers are demonstrated to be a promising cathode material for AMIBC. Sample with 16% Mn³⁺/Mn can exhibit a high capacity of 260 mAh g^-1 at 0.2 A g^-1 in 1M MgSO₄ electrolytes with greatly improved rate and cycle performance at large current densities. As assembled with active carbon (AC), MnO₂//AC device shows a high energy density of 60.8 W h kg^-1 at 180 W kg^-1 with a cycling stability of 74.1% after 3500 cycles at 2 A g^-1.