Lithium-ion batteries have become essential in recent years. Due to both the difficult access and the cost of the alkaline element, a new field of research concerning sodium-ion batteries has recently emerged. Among the major challenges inherent to this new battery type, the aim of the work developed during this PhD thesis is to explore new negative electrode materials. Two material types have been studied: metallic tin, and the chalcogenides AV4S8 (A=Ga, Ge). Tin was obtained with dense or dendritic form by electrolchemical deposition. In sodium-ion battery, this material presents interesting properties since during the first discharge, a specific capacity of 1 Ah/g at a working potential below 0.6 V relative to Na+/Na0 can be obtained. However, a volume expansion of 350% during the sodiation causes a significant capacity loss, which is under 100 mAh/g after around ten cycles. The AV4S8 chalcogenides (A = Ga, Ge) have been the main subject of this PhD thesis. The reaction mechanism with sodium, close to a conversion mechanism, has been studied by in situ X -ray diffraction, X-ray absorption spectroscopy and electron energy loss spectroscopy in order to observe the oxidation number evolution of the elements involved in the reaction with sodium. These materials exhibit remarkable electrochemical properties, with an initial specific capacity of more than 800 mAh/g at low potential with excellent capacity retention upon cycling.
from HAL : Dernières publications http://ift.tt/1tp6BG7
from HAL : Dernières publications http://ift.tt/1tp6BG7
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