Mn 2 O 3 is and has received widespread attention in fields such as catalysis and energy storage. However, its poor conductivity limits its application as an electrode material for supercapacitors. Here, flower-like spheroidal δ-MnO 2 /Mn 2 O 3 composites composed of two-dimensional (2D) hierarchical nanosheets were prepared by the template method and a simple hydrothermal process. The growth process and electrochemical properties of δ-MnO 2 /Mn 2 O 3 composites were investigated by adjusting the concentration of KMnO 4 in the hydrothermal process. Since the introduction of δ-MnO 2 brings more pseudocapacitance to the composite, the synergistic effect between MnO 2 and Mn 2 O 3 reduces the interfacial resistance, and the unique nanosheet structure increases its specific surface area, which alleviates the volume expansion during the cycling, the δ-MnO 2 /Mn 2 O 3 composite electrode exhibits high specific capacitance (182 F g −1 at 0.5 A g −1 ), fast rate performance (74.2% capacitance retention at 5 A g −1 ), and excellent cyclic stability (90.1% capacitance retention after 5000 cycles at 5 A g −1 ). Symmetric supercapacitors assembled with δ-MnO 2 /Mn 2 O 3 electrodes also exhibit a high energy density of 9.1 Wh kg −1 . δ-MnO 2 /Mn 2 O 3 composites have greater application prospects in energy storage, and are expected to achieve further applications in lithium/sodium ion batteries, zinc ion batteries and other fields.
Herein, a novel rechargeable button zinc‑manganese ultra-high temperature battery is first reported for the efficient utilization and conversion of thermal and electrical energy. The battery system uses zinc anode , Zn-K-Cl molten salt electrolyte and MnO 2 /Mn 2 O 3 composite cathode to work at 300 °C. In this study, MnO 2 /Mn 2 O 3 composites were synthesized by molten salt method, and the crystal structure of the materials was adjusted by adding reduced graphene oxide (rGO). The results showed that the spherical nanoparticles and nanobelts of MnO 2 /Mn 2 O 3 composite cathode materials increased the active sites and ion transport channels of the electrochemical reaction , thus providing high coulombic efficiency. By modifying with rGO, the MnO 2 /Mn 2 O 3 (Mn-O-2) composite cathode material exhibits excellent electrochemical performance in the button zinc‑manganese ultra-high temperature battery. The as-prepared button ultra-high temperature battery exhibits a relatively high specific capacity (300 and 175 mAh g −1 at 1 mA cm −2 and 30 mA cm −2 ) and competent cyclability (> 95 % coulombic efficiency after 50 cycles). This work firstly and systematically reveals the role of the Mn cathode materials and shows that the application in button molten salt batteries.
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