Physicochemical and electrochemical properties of imidazolium ionic liquids: Cycling performance of low cost lithium ion
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Physicochemical and electrochemical properties of imidazolium ionic liquids: Cycling performance of low cost lithium ion batteries with LiFePO4 cathode Hassan. Srour1,2, Hélene. Rouault2 and Catherine C. Santini1. 1 UMR 5265 CNRS- C2P2, 43 Boulevard du 11 Novembre 1918, 69616 Villeurbanne, France. 2 CEA-Liten, 17 rue des Martyrs 38054 Grenoble Cedex 9, France. [email protected] ABSTRACT This manuscript reports investigation conducted on room temperature ionic liquids (RTILs) C1CnImNTf2/n=4, 6 in order to use it as electrolyte solvent in lithium ion battery. The ionic conductivity, viscosity, ion self-diffusion coefficients, and electrochemical stability in C1CnImNTf2 are presented. A solution of C1CnImNTf2/n=4, 6 containing 1.6 mol.L-1 of LiNTf2 has been used as the electrolyte in a Li-ion battery with graphite and LiFePO4 as respectively negative and positive active materials. [Li][C1C6Im][NTf2] shows the best cycling performance: a capacity up to 120 mAh.g-1 at C/10 rate at 25°C. INTRODUCTION Room temperature ionic liquids attract the attention of many scientists dealing with lithium-ion batteries. This interest is caused by their unique properties: wide liquid range, a wide electrochemical stability, good ionic conductivity, negligible volatility, non-flammability, etc. [1]. The interest in lithium rechargeable batteries in electric vehicles (EVs) has been significantly increased in recent years [2]. The substitution of a common, organic carbonate-based electrolyte with an IL-based electrolyte leads to a significant improvement in system safety and the reduction of environmental risks and negative impacts on human health. Transition metal oxides, such as LiNiO2 and spinel LiMnO4 have been studied as positive electrode materials in lithium batteries. These materials have shown good cyclibility and high capacity at potential (around 4 V versus Li/Li+). So far, LiCoO2 has been the main positive electrode material used in Li-ion batteries due to its high energy density. However, the long term supply of cobalt based material remains questionable to ensure HEV’s application. Since the demonstration of LiFePO4 by Padhi et al [3] as potential positive electrode material, considerable interest has been generated due to its safety, low cost and environmentally friendly nature [4]. The suitability of any particular ionic liquid for use in a lithium battery is heavily dependent on the type of negative and positive electrode materials used. One negative electrode material that is of particular interest to researchers is lithium metal. Lithium offers an high specific capacity (3860 mAh.g-1) compared to graphite (380 mAh.g-1) which is commonly used in commercial lithium-devices [5]. However lithium metal exhibits high reactivity in the presence of electrolytes based on organic solvents, leading to excessive electrode-electrolyte side reactions and degradation eventually. Moreover dendrite formation during successive recharge steps stifles the proper functioning of the battery, making the commercialization of recha
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