Concentrational changes in PAN-based polymer gel electrolyte under current flow: 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 polarized membrane a stable gradient of both Li cations and perchlorate anions 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 carriers 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 polarization. The nature of this effect may be ascribed to the polymer mobility due to the strong polymer-electrolyte interaction and/or to the polymer degradation caused by internal heating under applied potential. (C) 2001 Elsevier Science B.V. All rights reserved.