Basic Medium Heterogeneous Solution Synthesis of α-MnO₂ Nanoflakes as an Anode or Cathode in Half Cell Configuration (vs. Lithium) of Li-Ion Batteries.

Abstract

Nano α-MnO2 is usually synthesized under hydrothermal conditions in acidic medium, which results in materials easily undergoing thermal reduction and offers single crystals often over 100 nm in size. In this study, α-MnO2 built up of inter-grown ultra-small nanoflakes with 10 nm thickness was produced in a rapid two-step procedure starting via partial reduction in solution in basic medium subsequently followed by co-proportionation in thermal treatment. This approach offers phase-pure α-MnO2 doped with potassium (cryptomelane type K0.25Mn8O16 structure) demonstrating considerable chemical and thermal stability. The reaction pathways leading to this new morphology and structure have been discussed. The MnO2 electrodes produced from obtained nanostructures were tested as electrodes of lithium ion batteries delivering initial discharge capacities of 968 mAh g−1 for anode (0 to 2.0 V) and 317 mAh g−1 for cathode (1.5 to 3.5 V) at 20 mA g−1 current density. At constant current of 100 mA g−1, stable cycling of anode achieving 660 mAh g−1 and 145 mAh g−1 for cathode after 200 cycles is recorded. Post diagnostic analysis of cycled electrodes confirmed the electrode materials stability and structural properties.