Abstract
The thesis work, presented in this manuscript, is devoted to the study of new materials used as negative electrode in Li-ion batteries and more particulary the transition metals phosphides (TMP). Generally, these materials exhibit high gravimetric and volumetric capacities, about 600-1200mAh/g, much higher than those of the carbonaceous compounds used nowadays in the devices on the market. The phases of the two binary systems Fe-P and Ni-P were studied in this work as negative electrodes in Li-ion batteries. Nickel and iron phosphides present interesting electrochemical performances and mechanisms toward lithium uptake. Various methods of synthesis were employed to obtain materials with varied morphology, structure and stoichiometry. Several techniques of characterization were employed to help the analysis of the electrochemical mechanisms : X-ray diffraction, XANES spectroscopy, 57Fe Mössbauer spectroscopy, 31P NMR an,d magnetic measurements. The thorough study of the reactivity of these phases toward lithium enabled us to explain their high specific capacities by a redox mechanism involving phosphorus network. Attempt to improve the electrochemical performances, various designs of electrode were undertaken and studied.