Ion-solvation structure and battery electrode characteristics of nonflammable organic electrolytes based on tris(trifluoroethyl)phosphate dissolving lithium saltsElectronic supplementary information (ESI) available. See DOI: 10.1039/c7cp06438a

• Main Authors: Todorov, Yanko Marinov, Fujii, Kenta, Yoshimoto, Nobuko, Hirayama, Daisuke, Aoki, Masahiro, Mimura, Hideyuki, Morita, Masayuki
• Format: Journal Article
• Language: English
• Published: 29.11.2017
• ISSN: 1463-9076; 1463-9084
• DOI: 10.1039/c7cp06438a

The structure and properties of lithium salt solutions based on tris(2,2,2-trifluoroethyl)phosphate (TFEP) solvent have been studied to design a safer electrolyte system for large-sized lithium-ion battery applications. Influences of the ionic structure on the polarization behavior of the LiCoO 2 (LCO) positive electrode were investigated. The ionic conductivity and viscosity of the solution consisting of lithium salts dissolved in TFEP, LiX/TFEP (X = PF 6 , BF 4 and TFSA) (TFSA = (CF 3 SO 2 ) 2 N), were measured. The results suggest that the ion-solvation structure greatly depends on the anionic species in the salt. Spectroscopic measurements also support the conclusion that the Li + -solvation structure varies with the lithium salts. The differences in the ionic structure of LiX/TFEP influence the electrochemical oxidation potential of the solution and the polarization behavior of the LCO electrode. The overvoltage for Li-desertion/insertion from/into LCO in LiX/TFEP, being much higher than that observed in conventional LIB electrolyte solutions, shows the order of BF 4 < PF 6 < TFSA. The addition of ethylene carbonate (EC) to LiX/TFEP increases the ionic conductivity, which is probably caused by changes in the Li + -solvation structure in TFEP. The overvoltage for the Li-desertion/insertion of LCO is much lowered by the addition of EC to LiX/TFEP. Different ion-solvation structures greatly influence the battery electrode characteristics in a nonflammable electrolyte system.