Polymer-in-Salt Electrolytes Based on Acrylonitrile/Butyl Acrylate Copolymers and Lithium Salts (original) (raw)

2004, Journal of Physical Chemistry B

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 (CtN and CdO) 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.