Morphology Dependent Electrochemical Performance of Hydrothermally Synthesized Birnessite-Type Manganese Dioxide in Aqueous Aluminum Ion Batteries

Abstract

Three distinct morphologies of δ-MnO2, including a mixed morphology with nanofibers and nanosheets, smaller nanosheets, and larger, more organized nanosheets, were synthesized by controlling the hydrothermal synthesis parameters. The aim is to use these materials in aqueous aluminum ion batteries (AIBs). The materials were characterized using X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), and energy-dispersive X-ray spectroscopy (EDS). The electrochemical performance of the δ-MnO2 electrodes was evaluated using cyclic voltammetry (CV), galvanostatic charge-discharge (GCD), and electrochemical impedance spectroscopy (EIS) techniques.It was found that the morphology of the δ-MnO2 had a significant impact on the electrochemical properties of AIBs. Specifically, among the δ-MnO2|0.5 M Al2(SO4)3 0.4MMnSO4|Al batteries, the δ-MnO2 with larger, more organized nanosheets exhibited the highest specific capacity of 320 mAh/g, followed by the mixed morphology (213 mAh/g), and the smaller nanosheets (140 mAh/g). Furthermore, the δ-MnO2 with smaller nanosheets demonstrated the best capacity retention over 70 cycles, retaining 98% of its initial capacity, while the δ-MnO2 with larger, more organized nanosheets exhibited the lowest capacity retention, retaining only 9.3% of its initial capacity after 70 cycles.In conclusion, this study highlights the impact of the δ-MnO2 morphology on the electrochemical properties of AIBs, with smaller nanosheets exhibiting superior performance in terms of capacity retention. These findings could be valuable for the rational design and optimization of high-performance AIB electrodes.Keywords: aqueous aluminum ion batteries, manganese dioxide