Structural and electrochemical properties of Li[CoxLi(1/3−x/3)Mn(2/3−2x/3)]O2 cathode materials

Solid solutions between Li2MnO3 (Li[Li1/3Mn2/3]O2) and LiCoO2, Li[CoxLi(1/3−x/3)Mn(2/3−2x/3)]O2, were prepared using a simple combustion method. The X-ray diffraction (XRD) pattern and Rietveld analysis confirmed that these compounds have the same structure as those of O3-LiCoO2 and Li2MnO3. The oxidation state of Mn and Co ion in Li[CoxLi(1/3−x/3)Mn(2/3−2x/3)]O2 compounds was confirmed to be tetravalent and trivalent by X-ray absorption near-edge structure (XANES) analysis, respectively. From the cyclic voltammograms for the compounds, two peaks at around 4.0–4.4 and 4.4–4.7 V were observed in the initial oxidation curves. As the Co content decreased, the peak positions shifted to higher voltage. After the first cycle, subsequent oxidation and reduction profiles were significantly changed. Li[Co0.50Li0.17Mn0.33]O2 compound delivered an initial discharge capacity of about 265 mA h/g. The discharge capacity gradually decreased as the Co content decreased. Considering high discharge capacity and simple processing method, it is possible to use this material as a cathode material for lithium secondary battery.