Sonochemical and soft-chemical intercalation of lithium ions into MnO 2 polymorphs

We explored routes for the synthesis of LiMn ₂O ₄ spinel from five different polymorphs of MnO ₂ as the manganese source. These included α and β-MnO ₂ and three types of γ MnO ₂ (electrochemically produced EMD, and two types of chemically produced CMD). The synthesis included a lithiation step by mild reduction of the MnO ₂ with glucose in a LiOH solution, followed by calcination of the lithiated product. This route was shown in a previous study to produce highly pure, nanocrystalline LiMn ₂O ₄. The effect of the application of ultrasound radiation in the lithiation step on the quality of the products was also explored. It was found that the degree of lithiation, the purity of the Li _xMn ₂O ₄ spinel phase obtained and its electrochemical behavior as a Li insertion electrode material depend strongly on the nature of the MnO ₂ material in terms of crystal structure and morphology. The effect of ultrasound radiation was found to be detrimental. A very good electrochemical performance (capacity, stability) in repeated Li intercalation–deintercalation cycling was obtained with LiMn ₂O ₄ originating from nanometric CMD. The tools for this study included XRD, TEM, surface area measurements (BET method), atomic absorption and standard electrochemical techniques (voltammetry, chronopotentiometry).