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

Abstract

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 T g than the parent copolymer (decrease of over 60 K for high salt content). By extrapolation of the dependence of the T g on the salt content, the value of T g for pure LiTFSI was estimated as 232 K. The decrease of T g was correlated with the increase of the decoupling index, R τ , which is proportional to the value of conductivity measured at T g. 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.