Δ-MnO₂ / Carbon Material Nanocomposites for Aqueous Metal-Ion Electrochemical Energy Storage Devices

In this study, we successfully synthesized δ-MnO 2 /reduced graphene oxide (rGO) and K-doped MnO₂/graphite nanofibers (GNF) nanocomposite cathode materials for Mg/Zn-ion electrochemical energy storage applications. The device based on the δ-MnO 2 /rGO nanocomposite cathode showed a high operating voltage of 2V. At a power density of 823 W kg −1 , it delivered a maximum energy density of 29.8 Wh kg −1 . The device displayed impressive discharge capacity and excellent cycling stability even at a low temperature of −20 °C. Additionally, the K-doped MnO₂/GNF electrode exhibited a high specific capacitance of 410.31 F g⁻¹ at a current density of 0.5 A g⁻¹, while also demonstrating superior cycle stability under high current density, retaining 57.0% of the charge/discharge efficiency at 4 A g⁻¹. Furthermore, the device based on the K-doped MnO₂/GNF electrode delivered a high specific capacitance of 32.51 F g⁻¹ at 0.5 A g⁻¹ and maintained 88.2% of the initial capacitance after 20000 cycles.