Manganese valence state regulated beta‑manganese dioxide porous nanoflowers as high-performance cathodes at large current densities for aqueous magnesium ions battery capacitor

Abstract

Aqueous magnesium ion battery capacitor (AMIBC) is a promising sustainable clean and safe energy storage system to replace lithium-ion batteries, due to its similar electrochemical characteristics to lithium, low cost and safety. In this work, beta‑manganese dioxide (β-MnO2) porous nanoflowers with Mn valence modulation are demonstrated to be a promising cathode material for AMIBC. Due to the promotion of Faradic reaction by Mn3+ introduction and the high capacitive absorption from its high specific surface area, sample with 16 % Mn3+/Mn can exhibit a high specific capacity of 260 mAh g−1 at 0.2 A g−1 in 1 M MgSO4 electrolytes with greatly improved rate and cycle performance at large current densities. As assembled with active carbon (AC), β-MnO2//AC AMIBC 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.