Magnetic studies of phospho-olivine electrodes in relation with their electrochemical performance in Li-ion batteries

Currently, LiFePO4 is considered a good candidate as a positive electrode in rechargeable lithium-ion batteries for hybrid-electric vehicle (HEV) applications. A major difficulty with the preparation of the olivine structure (LiFePO4) comes from the existence of two oxidation states of iron, namely Fe(II) and Fe (III). Careful control of the synthesis procedure is needed to avoid any impurity which can poison the electrochemistry of LiFePO4 electrodes in Li-ion batteries. Analysis of the structure and morphology of the phospho-olivine LiFePO4 is presented as a function of the synthetic conditions. The combination of analytical methods, i.e. magnetization, M(H), susceptibility, χm(T), and Raman scattering spectroscopy, appears to be a powerful tool for the detection of small amount of impurities. The electrochemical performance of optimized LiFePO4 is evaluated in Li4Ti5O12/LiPF6-EC-DEC/C-LiFePO4 cells operating at high temperature (60 °C).