Physicochemical characterization of alternative conducting salts for lithium ion battery electrolytes Monika Vogler 1 , Anna Szczęsna-Chrzan 3, * , Peng Yan 4, * , Grażyna Zofia Żukowska 3 , Christian Wölke 4 ,Agnieszka Ostrowska 3 ,Sara Szymańska 3 , Isidora Cekic-Laskovic 4 , Martin Winter 4 , Marek Marcinek 3 , Władysław Wieczorek 3 , and Helge S. Stein 1,2 1 Helmholtz Institute Ulm, Applied Electrochemistry, Helmholtzstr. 11, 89081 Ulm, Germany, 2 Karlsruhe Institute of Technology, Institute of Physical Chemistry, Fritz-Haber-Weg 2, 76131 Karlsruhe, Germany, 3 Faculty of Chemistry, Warsaw University of Technology, Noakowskiego 3, Warsaw 00664, Poland, 4 Helmholtz Institute Münster (IEK-12), Forschungszentrum Jülich GmbH, Corrensstraße 46, 48149 Münster, Germany * One of the most commonly used conducting salts in non-aqueous electrolytes for lithium ion batteries is lithium hexafluorophosphate (LiPF 6 ) 1 . However, this salt is prone to hydrolysis forming hydrofluoric acid as a decomposition product 2 . Therefore, dry and well controlled conditions during preparation, storage and handling of this material are vital to obtain well-performing electrolyte formulations 1,2 . Efforts are made to find alternative salts, which do not face these challenges and perform well in lithium ion batteries 1 . A variety of properties determines the performance of an electrolyte in a lithium ion battery. Besides the electrochemical stability window and the chemical compatibility with the other battery materials, high ionic conductivity is desired for battery electrolytes 1 . The ionic conductivity of electrolyte formulations is strongly related to physicochemical properties like viscosity and diffusivity 3 . In our study, we compare the electrolytes containing lithium 4,5-dicyano- 2-(trifluoromethyl)imidazole (LiTDI), lithium 4,5-dicyano-2-(pentafluoroethyl)imidazole (LiPDI), lithium 4,5-dicyano- 2-(heptafluoropropyl)imidazole (LiHDI) as conducting salts with respect to their ionic conductivity, viscosity, and self-diffusion coefficients of the respective anions. We systematically vary the concentration of each of the salts in a solvent mixture composed of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in the fixed mass ratio of 3:7. The widely used electrolyte containing 1M LiPF 6 in the same solvent mixture serves as the reference. Among the studied conducting salts, our results suggest LiTDI as the salt with the least ionicity and the strongest influence of viscosity on the ionic conductivity, while the reference electrolyte is found to have the highest ionicity. The ionicity is shown to decrease from 0.05M electrolytes to 0.6M electrolytes. Further increasing concentration does not lead to a significant decrease in ionicity. From our results, we find similarities in the ionicity of the imidazole salts, but LiTDI seems to behave slightly different from LiPDI and LiHDI. References 1. L. Niedzicki, M. Kasprzyk, K. Kuziak, G. Z. Żukowska, M. Marcinek, W. Wieczorek and M. Armand, Liquid electrolytes based on new lithium conductive imidazole salts, J. Power Sources , 2011, 196 , 1386–1391. 2. U. Heider, R. Oesten and M. Jungnitz, Challenge in manufacturing electrolyte solutions for lithium and lithium ion batteries quality control and minimizing contamination level, J. Power Sources , 1999, 81–82 , 119–122. 3. S. Seki, K. Hayamizu, S. Tsuzuki, K. Takahashi, Y. Ishino, M. Kato, E. Nozaki, H. Watanabe and Y. Umebayashi, Density, Viscosity, Ionic Conductivity, and Self-Diffusion Coefficient of Organic Liquid Electrolytes: Part I. Propylene Carbonate + Li, Na, Mg and Ca Cation Salts, J. Electrochem. Soc. , 2018, 165 , A542–A546.
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