Hierarchically assembled 2D nanoplates and 0d nanoparticles of lithium-rich layered lithium manganates applicable to lithium ion batteries

The porous hierarchical assembly of lithium-rich Li_1+xMnO _3-δ 2D nanoplates as well as isolated 0D nanocrystalline homologues has been synthesized via lithiation reactions of nanostructured manganese oxides under hydrothermal conditions. According to powder X-ray diffraction and electron microscopy, a hydrothermal LiOH treatment for nanostructured δ-MnO₂ precursor produces a lithium-rich Li _1+xMnO_3-δ phase with the nanoworm-like hierarchically assembled 2D nanoplate morphology. After the lithiation reaction under identical conditions, the 1D nanowires of the α-MnO₂ precursor are transformed into the 0D nanoparticles of the Li _1+xMnO_3-δ phase. The Mn K-edge X-ray absorption spectroscopic analysis for the lithiated materials clearly demonstrated that tetravalent manganese ions are stabilized in octahedral sites of a Li ₂MnO_3-type layered structure composed of edge-shared MnO₆/LiO₆ octahedra. From electrochemical measurements, it was found that the lithiated Li_1+xMnO_3-δ nanostructured materials show much superior electrode performance over the precursor manganese oxides and bulk lithium-rich manganate. The powder X-ray diffraction analyses for the electrochemically cycled derivatives clearly demonstrated that the improvement of electrode performance after lithiation can be attributed to the phase transformation to the Li-rich Li _1+xMnO_3-δ phase with high structural stability. On the basis of the present experimental findings, we are able to conclude that the present phase transformation route provides a new method not only to synthesize nanostructured lithium-rich manganese oxides with controllable dimensionality and morphology but also to improve the electrode performance of nanostructured manganese oxides.