Polymer electrolytes based on acrylonitrile–butyl acrylate copolymers and lithium bis(trifluoromethanesulfone)imide

Novel “polymer-in-salt“ electrolytes were prepared by mixing random copolymers of acrylonitrile and butyl acrylate [poly(AN-co-BuA)] with lithium bis(trifluoromethanesulfone)imide (LiTFSI). The interaction of Li+ ions and polymeric groups was investigated by DSC and IR methods; electrical properties were studied by impedance spectroscopy. The properties of the new system were compared to those of the well-known poly(ethylene oxide) (PEO)–LiTFSI polymer electrolytes. The mixtures of poly(AN-co-BuA) and LiTFSI exhibit much lower glass transition temperature Tg than the parent copolymer (decrease of over 60 K for high salt content). By extrapolation of the dependence of the Tg on the salt content, the value of Tg for pure LiTFSI was estimated as 232 K. The decrease of Tg was correlated with the increase of the decoupling index, Rτ, which is proportional to the value of conductivity measured at Tg. The interactions of LiTFSI with poly(AN-co-BuA) lead to high flexibility of this system; a property that is opposite to the behavior of the PEO–LiTFSI system, where interactions between the salt and polyether lead to stiffening of the polymer with increasing salt content.