Electrochemical properties and structural characterization of layered LixNi0.35Co0.3Mn0.35O2+δ cathode materials

To overcome the difficulty of layered LixNi0.35Co0.3Mn0.35O2 compounds synthesis, we employed a sol-gel method that can intermix cations homogeneously in atomic scale and quite effective to synthesize fine single-crystallite oxide electrode material. The hexagonal LixNi0.35Co0.3Mn0.35O2+δ compounds were easily prepared from calcinations of Li-Mn-Ni-Co-O sol-gel dried precursors. That is, firstly, the as-received powders were oxidized at relatively low temperature. Then the oxidized powders were simply calcined at 950 °C for a certain time in air. Finally, the resultants cooled at different rate to room temperature showed well-ordered hexagonal LixNi0.35Co0.3Mn0.35O2+δ single-crystallite particle oxides, as observed by scanning electron micrograph (SEM) and X-ray diffraction (XRD). Since the data of X-ray photoelectron spectroscopy (XPS) suggested that Ni, Co and Mn ions are present as Ni2+, Co3+ and Mn4+, respectively, the formation of a solid solution among LiCoO2, NiO and Li2MnO3 is confirmed. The particles size and crystallites, as well as the structure of the hexagonal LixNi0.35Co0.3Mn0.35O2+δ, were found to play an important role in the capacity retention during electrochemical cycling. The prolonged calcinations time and slow cooling rate result in larger particle size and better electrochemical performance of the Li/LixNi0.35Co0.3Mn0.35O2+δ cell. The effect of various calcinations time and cooling way on the structure, particle size and electrochemical properties of the materials are compared and discussed.