Electrochimica Acta, Vol.53, No.16, 5322-5333, 2008
Influence of metal coordination on conductivity behavior in poly(butadiene-acrylonitrile)-CoCl2 system
The metal complex formation and the electrical properties of amorphous solid polymer electrolytes, based on poly(butadiene-acrylonitrile) copolymer (PBAN) and CoCl2, have been studied over the homogeneity region of the system limited by the CoCl2 concentration of 1.89 mol kg(-1). It has been found that ionic conductivity is carried out by the unipolar anion transfer at lower CoCl2 concentrations (up to 0.10 mol kg(-1)). As the CoCl2 concentration increases, electronic conductivity appears in addition to ionic conductivity, and the former becomes dominant, starting from 0.38 mol kg(-1). It has been shown that the nature of charge carriers is determined by the composition of metal complexes formed by CoCl2 and the macromolecular solvent: PBAN. At lower concentrations, the [Co2L2Cl4](0) dimers are the predominant species (L being macromolecule side groups C N), and their dissociation is followed by the formation of mobile Cl- anions and immobile binuclear [Co2Cl3](+) complexes. As CoCl2 concentration increases, polynuclear [ConL2Cl2n](0) (n > 2) complexes appear (L being C N and C=C groups of PBAN). Specific features of chemical bonds in pi-complexes of transition metals result in the appearance of electronic charge carriers. The abrupt increase in conductivity observed at the highest CoCl2 concentration is connected with the formation of a percolation network of polynuclear [ConL2Cl2n](0) complexes. (c) 2008 Elsevier Ltd. All rights reserved.
Keywords:solid polymer electrolytes;poly(butadiene-acrylonitrile);Cobalt(H) complexes;ionic conductivity;electronic conductivity