Conversion mechanisms of cobalt oxide anode for Li-ion battery: In situ X-ray absorption fine structure studies

Co sub(3)O sub(4) powders as anode active materials for Li-ion battery are synthesized by a simple precipitation method. Physical properties of the prepared Co sub(3)O sub(4) are characterized by N sub(2) physisorption, transmission electron microscopy, and X-ray diffraction. Conversion mechanisms upon the structural changes of Co sub(3)O sub(4) anode are thoroughly studied by an in situ X-ray absorption fine structure (XAFS) technique. In the first cycle of discharge/charge, the X-ray absorption near-edge structure of Co reveals that the 1.1 V plateau of the discharging is ascribed to the direct conversion of Co sub(3)O sub(4) to Co metal, and the 2.0 V plateau of the charging to the conversion of Co metal to CoO and Co sub(3)O sub(4). In the second cycle of discharge/charge, the XAFS analysis reveals that a part of Co metal phase remains unconverted due to the phase isolation. It is demonstrated that the addition of a conductive material can significantly improve the redox reaction of the Co sub(3)O sub(4) anode material by minimizing the phase isolation.