Site occupancy studies of cobalt doping in a lithium iron phosphate material using combined electrochemical and X-ray based techniques

The influence of dopants in improving the intrinsically poor electrical properties of insulating and semiconducting materials is well-known. For multi-cation systems, such as LiFePO4 material, dopant elements can be theoretically substituted into the M1 (Li) or/and M2 (Fe) sites. However, it is difficult to identify the occupancy site(s) of the dopant, making relevant defect types and charge compensation mechanisms unclear. In this study, Co2+ are used as a substitutional defect, preferentially into Li or Fe sites. Combined techniques including electrochemical studies, X-ray diffraction (XRD) and X-ray absorption spectroscopy (XAS) can be used to identify site occupancies of Co2+ in LiFePO4. The results show that Co2+ can occupy both the Li and Fe sites depending on the ion being controlled as well as the dopant content. The dopant occupancy sites affect the LiFePO4 electrochemical characteristics and structural properties. This makes the role of doping and creating defect types and well as that of charge compensation mechanisms become deeper understood.