Abstract
This thesis is devoted to finding new negative electrode materials for Li-ion batteries and more particularly to tin-based intermetallic compounds. These materials have gravimetric and volumetric capacities greater than those of carbon compounds used in current devices, but when they are in the form of micron-sized particles, they show a significant irreversible capacity and low cycleability.<br /> A detailed analysis of electrochemical reactions was made by combining different techniques: X-ray diffraction, X-ray photoelectron spectroscopy, 119Sn Mössbauer spectrometry and magnetic measurements. Only tin-rich phases present interesting capacities. In this case, the first discharge is a restructuring step that transforms the electrode material into a composite made of pure metal nanoparticles and Li7Sn2. The primary mechanism is a partially reversible displacement reaction, metallic nanoparticles reducing volume variations of the electrode.<br /> The observed irreversibility during the first cycle has been studied by X-ray photoelectron spectroscopy and electrochemical impedance spectroscopy. This irreversibility is related to the formation, at the beginning of the first discharge, of a stable passivating layer on the surface of intermetallic particles which is mainly composed of Li2CO3 and LiF. This formation is associated to a sharp decrease of the electrode potential which allows the initiation of its restructuration. The importance of this layer is obviously linked to the specific surface particles, which explains the poor performances of nanomaterials for which no displacement reaction has been highlighted.