Failure and stabilization mechanisms in multiply cycled conducting polymers for energy storage devices

We report herein new results on the application of the electrochemical quartz crystal microbalance (EQCM) method to study multiple cycling electrodes comprising improved poly-3-octylthiophene (P3OTh) films under various conditions. Emphasis is given to the n-doped P3OTh films with their retarded initial kinetics of doping due to the negative charge carriers and solvent trapping. Further tests included studying the release of trapped charges and solvent during p-redoping and assessing the interactions between the oppositely charged carriers via a coupled (intermittent) n-p-doping in the widest potential window of 3.3 V. A complete deconvolution of the EQCM response in terms of the contributing counterion, co-ion, and solvent fluxes has been done. A remarkable feature discovered was a gradual decrease of exchangeable solvent molecules in the films as a result of their long-term cycling and cycling conditions. This was correlated to a gradual progressing of the n-type carriers trapping at high and long-term cathodic polarization of the films (confirmed by impedance and UV-vis spectropies and by in situ conductance measurements). The unique information obtained about long-term cycling of P3OTh films under various conditions is used to create a broader context of evaluation of cycling ability of conducting polymer electrodes, compared to typical Li-insertion electrodes. The present studies render applications of EQCM for more complicated systems such as nanocomposites comprising conducting polymer and carbon nanotubes that can be used as superb electrode's materials for advanced supercapacitors.