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Nouvelles membrane polymères et électrolytes liquides pour batteries Li-ion.

Abstract : Li-ion batteries have become the dominant power storage devices for portable electronics, and researchers are still at work to broaden their field of use to high energy density devices, like cars. Within the framework of the collaborative project AMELIE - Green car, this study articulates along 2 main axes. The first one deals with the synthesis and characterization of new fluorinated solvents and salts to replace, for the use with high potential materials such as LiNi1/3Mn1/3Co1/3O2 or LiNi0,4Mn1,6O4, the commonly used LiPF6 and carbonate-based electrolytes, which suffer from a high self-discharge ratio, and an insufficient thermal and chemical stability. The use of fluorinated carbonates, carbamates, and sulfonamides as solvents provides performances as good as the commercial references, even if we register a visible loss in conductivity. Moreover, the fluorination provides these molecules with higher thermal and electrochemical stabilities. About the salts, several new structures of sulfonamide salts were synthesized and tested in combination with commercial solvents, with interesting results from the point of view of conductivity and the electrochemical stability.The second part of this study deals with the development of thin perfluorinated separators, which could compete with commercial references such as Celgard® separators and whose production could be easily up-scale. To do this, dense and porous separators were prepared from several PVdF grades. Since the porous membranes, the most promising for the battery applications, suffer from a relatively low mechanical strength, 2 reinforcement techniques were also evaluated: the first one consists in cross-linking the polymer after grafting of polymerizable groups; the second one consists in adding Nano Cristalline Cellulose (NCC) particles to form a reinforcing percolating network. Both methods give promising results with dense membranes: a 2- to 5-fold increase of storage modulus is observed at 25°C, in addition to interesting electrochemical properties. The transfer of these promising results to the porous membranes is still to be optimized, but a partial reinforcement was obtained for nano-composites porous membranes, while the good conductivity (still largely superior to 1 mS/cm) and porosity make them attractive options for high charge rate batteries.
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Marco Bolloli. Nouvelles membrane polymères et électrolytes liquides pour batteries Li-ion.. Matériaux. Université de Grenoble, 2014. Français. ⟨NNT : 2014GRENI110⟩. ⟨tel-01687595⟩

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