Polymer-in-Salt Electrolytes Based on Acrylonitrile/Butyl Acrylate Copolymers and Lithium Salts

Abstract

Solid polymeric electrolytes for battery purposes in the form of composites of lithium salts [LiI, LiN(CF 3 SO 2 ) 2, LiClO 4, LiAlCl 4, LiCF 3 SO 3, and LiBF 4 ] and acrylic polymeric matrixes [poly(acrylonitrile- co- butyl acrylate), poly(methyl methacrylate), and poly(butyl acrylate)] have been obtained by film casting from acetonitrile. The ionic conductivity ( σ ) as a function of temperature was studied by the impedance spectroscopy method. These systems show the highest σ values, on the order of 10 -4 −10 -7 S·cm -1, at high salt concentrations (above 50 wt %), characteristic of polymer-in-salt electrolytes. The ionic conductivity and mechanical properties of composites depend on the chemical structure of the polymer matrix, the anion, and the salt concentration. The glass transition temperature ( T g ) was determined from DSC studies. The introduction of a salt causes, in a majority of the composites studied, a considerable decrease in the T g values, indicating a strong plasticizing effect. DSC studies show a multiphase character of the composites, in which, with the exception of the amorphous system with LiN(CF 3 SO 2 ) 2, phases of the plasticized matrix, complexes of the salt with the matrix of varying stoichiometry, and often the separating salt are observed. The logarithm of the decoupling index (log R τ ) on the order of 3−5 as well as the shift in the IR spectrum of the groups present in the polymer (C⋮N and C O) by about 20−30 cm -1 indicate a weak interaction of the salt with the matrix. The ion transference numbers (0.5−0.8) determined by the electrochemical method indicate an increased participation of cations in the electrical charge conduction and a different conduction mechanism compared to that of classical electrolytes based on complexes with polyethers.