An elucidative investigation of unique charge storage mechanism and exceptional stability over long cycles in polycrystalline polythiophene-graphene composite using b-value determination and EIS data analysis

Abstract

The stability of an electroactive material is crucial for the development of practical capacitor devices, specifically for industrial applications. Herein, we report on the synthesis, characterization, electrochemical behavior, and device performance of temperature-induced, in-situ engineered polycrystalline unsubstituted polythiophene (PTh) and its composite with graphene. The electroactive materials have been investigated as electrodes in a 3-electrode electrochemical cell and a 2-electrode symmetrical device setups. Both electroactive materials exhibit interesting electrochemical behavior and exceptionally robust material integrity. In symmetrical device configurations, the PTh and PTh-graphene delivered capacities of 87.4 F g−1 at 0.2 A g−1 and 73.2 F g−1 at 0.2 A g−1, respectively. The energy and power densities delivered by pristine PTh-electrode-based devices were 7.43 Wh kg−1 and 4.5 kW kg−1, respectively, at 0.2 A g−1

and those by PTh-graphene-electrode-based devices were 6.5 Wh kg−1 and 3.75 kW kg−1 at 0.2 A g−1, respectively. ‘ b -value’ analyses reveal a dominant diffusion-controlled charge storage mechanism at anodic potentials and a combination of surface-controlled and diffusion-controlled charge storage mechanisms at cathodic potentials. The Rs (solution resistance) and n -values (heterogeneity factor) determined from the EIS data do not exhibit any significant changes over long cycling (10,000 continuous GCD cycles). This implies no significant material loss from the electrode surface and exceptional material integrity. The n -values show a shift towards unity at the end of the long cycling test, indicating an increase in the capacitive share in the charge storage mechanism. We further propose that the b -value analysis and EIS-based investigative method can be adopted as reliable testing tools to determine the materials’ integrity in addition to conventional CV and GCD techniques. Copyright © 2026. Published by Elsevier B.V.