Discharge Behavior and Rate Performances of Lithium-Ion Batteries in Nonflammable Hydrofluoroethers(II)

Hydrofluoroethers (HFEs) of 2-trifluoromethyl-3-methoxyperfluoropentane (TMMP) and 2-(trifluoro-2-fluoro-3-difluoropropoxy)-3-difluoro-4-fluoro-5-trifluoropentane (TPTP) were investigated as cosolvents of ethylene carbonate (EC) carbonate (DEC). Both lithium bis(pentafluoroethylsulfonyl)imide and lithium hexafluorophosphate () are soluble in (5:45:50 in volume), while is not soluble in (5:45:50). The enhanced discharge properties of Li-ion batteries (typically graphite/) in those electrolyte systems were evaluated and compared with the conventional carbonate mixed ones. The TPTP-mixed electrolyte [ (5:45:50)] gave a high capacity retention of 80% at an extremely high rate of 12C. An -based electrolyte normally exhibited poor retention of less than 40%. Such a rate-enhancing effect of HFEs (TPTP and TMMP) was manifested by observation over a wide temperature range from . The striking enhancement was observed at and at the first 10% dosage and level off at 50%. The activation energy, as substantiated by microvoltammetry, for the desolvation process decreases from (over the concentration range of , respectively) to by adding TMMP or TPTP. This implies that in the presence of HFEs, the kinetics for the rate-determining intercalation process is enhanced by an accelerated transport with a reduced solvation number.