Concentrational changes in PAN-based polymer gel electrolyte under currentflow: in situ micro-Raman investigation

The processes occurring in the PAN-based gel polymer electrolyte have been in situ investigated by micro-Raman spectroscopy. It is found that in the p olarized membrane a stable gradient of both Li cations and perchlorate anio ns appears: at the anode side of the assembly, the concentration of cations is essentially higher after polarization, while at the cathode side it is visibly lower; in the middle of the membrane concentration of charge carrie rs remains practically unchanged. While observed gradients are expected in a working electrolyte, an unexpected, and possibly more serious, depletion of the C=N groups of the PAN matrix is observed at the anode side during po larization. The nature of this effect may be ascribed to the polymer mobili ty due to the strong polymer-electrolyte interaction and/or to the polymer degradation caused by internal heating under applied potential. (C) 2001 El sevier Science B.V. All rights reserved.