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Compréhension des phénomènes de « cross-talking » au sein des accumulateurs Li-ion

Abstract : Many different degradation mechanisms can occur during the ageing of Li-ion batteries. Among them, a particular phenomenon takes place within the LiFePO4 (LFP)/graphite system during battery cycling operation, namely the “cross-talking”. The LFP material dissolves and the Fe2+ species migrate toward the graphite electrode and then reduce to form iron deposits in its protective layer (SEI). This poisoning entails a linear storage capacity fading during cycling and therefore reduces the life of the battery.The methodology used in this work bears on accelerated ageing tests carried on LFP/graphite coin cells and also relies on the characterization of the electrodes materials and the electrochemical processes thanks to a non-destructive technique, namely the electrochemical impedance spectroscopy (EIS). This approach is a preliminary step in the study of aging because it is necessary to understand the mechanisms at stake at each electrode.As a first step, several studies have been carried out in order to attribute the obtained EIS signals for each electrode material to their physico-chemical properties. In a second part, the performance and properties of accumulators during cycling were investigated. Thanks to the studies previously carried out by EIS, we were able to characterize the deterioration of the properties of the graphite electrode and its SEI due to the cross-talking from the early stage of the battery cycling. We have also shown that this phenomenon is thermally activated with greater degradation following high-temperature cycling.
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Submitted on : Tuesday, September 29, 2020 - 6:37:10 PM
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Guillaume Portalis. Compréhension des phénomènes de « cross-talking » au sein des accumulateurs Li-ion. Chimie théorique et/ou physique. Sorbonne Université, 2020. Français. ⟨NNT : 2020SORUS001⟩. ⟨tel-02953064⟩

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