New nanocrystalline manganese oxides as cathode materials for lithium batteries: Electron microscopy, electrochemical and X-ray absorption studies

Abstract

New nanostructured manganese oxy-iodides were prepared by redox reaction of sodium permanganate with lithium iodide in aqueous medium at room temperature. Transmission electron microscopy (TEM) showed that they are nanocrystalline with grain size in the 5–10 nm range. TEM and X-ray absorption confirmed the short-range ordered structure of these compounds, which contain octahedrally coordinated manganese atoms. The electrochemical properties were studied as a function of preparation conditions (Li/Mn ratio, carbon incorporation at the synthesis stage and grinding). Best electrochemical results were obtained either on samples with carbon black incorporated directly in the aqueous reaction medium at the synthesis stage, or on samples with carbon mixed after synthesis, submitted to extensive grinding. Typical capacities in the potential window 1.8–3.8 V are 160 and 130 mAh/g at the 40th and 100th cycle, respectively. Step-potential electrochemical spectroscopy and the evolution of X-ray absorption spectra on discharge are consistent with a single-phase lithium intercalation reaction with simultaneous manganese oxidation–reduction.