Morphology and crystallinity-controlled synthesis of MnO2 hierarchical nanostructures and their application in lithium ion batteries

Abstract

We demonstrate a novel strategy for the well-controlled preparation of MnO₂ hierarchical nanostructures, i.e. MnO₂ submicron fibers composed of nanosheets or nanorods with different crystalline phases (δ- and α-MnO₂), by integrating electrospinning, hydrothermal synthesis and subsequent heat-treatment. Specifically, δ-MnO₂ submicron fibers with different surface morphologies are synthesized via a template-assisted hydrothermal process and by using electrospun nanofibers (Polyacrylonitrile (PAN), oxidized PAN and carbonized PAN nanofibers); after that, α-MnO₂ nanostructures composed of different nanorod-like nanostructures are prepared by the heat-treatment of the corresponding δ-MnO₂ nanostructures at 700 °C in air. The effects of the reaction parameters (i.e. different templates and growth conditions) on the morphology and crystal phase are investigated in detail. The results demonstrate that the microstructures and structural conversion of the MnO₂ nanostructures are closely correlated with the initial templates. Furthermore, the potential application of the α-MnO₂ hierarchical nanostructures as the anode for a lithium ion battery is studied, and the results show that the pine-like α-MnO₂ exhibits a stable capacity up to 380 mA h g⁻¹ after 150 cycles.