Fluorinated Carbamates as Suitable Solvents for LiTFSI-Based Lithium-Ion Electrolytes: Physicochemical Properties and Electrochemical Characterization

Herein, we present an extensive physicochemical characterization of a series of fluorinated and nonfluorinated carbamates and their application as electrolyte solvents comprising lithium trifluoromethanesulfonyl imide (LiTFSI) as conducting salt. In a second step, these electrolyte compositions were characterized with respect to their ionic conductivity, salt dissociation, and electrochemical stability toward oxidation. In a third step, selected fluorinated electrolytes were studied concerning their ability to enable the utilization of LiTFSI as a conducting salt in the presence of an aluminum current collector by forming a protective aluminum fluoride surface layer, thus preventing the continuous anodic aluminum dissolution, i.e., aluminum corrosion. Finally, their electrochemical performance in combination with a state-of-the-art lithium-ion cathode material, Li(Ni1/3Mn1/3Co1/3)O2 (NMC), was investigated. It is shown that higher fluorinated carbamates reveal a very stable cycling performance of such cathodes due to their ability to form a sufficiently thick, i.e., protective, aluminum fluoride layer on the surface of the aluminum current collector. These findings confirm their suitability as electrolyte solvents in combination with LiTFSI as a conducting salt, enabling the successful replacement of toxic and unstable LiPF6 for the development of intrinsically safer lithium-ion batteries.