Anionic effect on ion transport properties in network polyether electrolytes

Abstract

The anionic effect on ion transport properties in network polyether electrolytes has been studied. A novel lithium salt of polymeric imide anion, poly(5-oxo-3-oxy-4-trifluoromethyl-1,2,4-pentafluoropentylene sulfonylimide lithium) (LiPPI), has a structure resembling highly dissociable imide salts such as lithium bis(trifluoromethylsulfonyl)imide (LiTFSI), and is considered as their polymer analogue. LiPPI has a long spacer between anionic sites in the polymer backbone, compared with a polymeric lithium salt, poly(2-oxo-1-difluoroethylene sulfonylimide lithium) (LiPEI), as reported before. Network polymer electrolytes were prepared by dissolving LiPPI in polyether networks to afford a compatible polymer alloy. The ionic conductivity of the new polymer alloy electrolytes reached ca. 10 −5 S/cm at 30°C, which was higher than those containing LiPEI by two orders of magnitude. Such difference of ionic conductivity between LiPPI and LiPEI was caused by the variation of dissociation ability of these polymeric lithium salts. The apparent Li + transference number of the network polymer alloy electrolyte containing LiPPI was higher than 0.7, considerably higher than that of the network polymer electrolytes containing a monomeric lithium salt, LiTFSI. In this study, the possibility to control the Li + transference number by using polymeric lithium salts in polymer electrolytes is demonstrated.