by Hongyi Zhang, Garrett L. Grocke, George Rose, Stuart J. Rowan, Shrayesh N. Patel
This study focuses on the synthesis and electrochemical characterization of nanoscale particles of semiconducting poly-3,4-ethylenedioxythiophene (PEDOT) functionalized with a disulfide/thiolate redox couple, specifically 2,5-dimercapto-1,3,4-thiadiazole (DMcT), allowing for dual redox particles designed for use as an organic cathode electrode. The nanoscale PEDOT-DMcT-Li dual redox particles have specific discharge capacities in a lithium half-cell of 91.9 mAh/g (85% of the maximum theoretical specific capacity, assuming both disulfide and polaron access on PEDOT) at low C-rates. This accessible capacity is attributed to the nanoscale particle size and the integration of a semiconducting conjugated backbone, which reduces internal resistance during oxidation. Comprehensive analyses, including cyclic voltammetry and galvanostatic cycling, reveal the contribution of the two individual redox components, namely, disulfide/thiolate and PEDOT, in this redox active material. Long-term cycling stability tests further suggest minimal degradation over 400 cycles with the observed capacity decay primarily attributed to charge trapping. Using an asymmetric charge/discharge rate cycling method to mitigate charge trapping results in an increase in Coulombic efficiency as well as capacity. Moreover, asymmetric cycling improved discharge capacity retention to 69% compared with 52% under symmetric rate cycling conditions after 400 cycles, without additional chemical modifications. These findings outline the redox behavior of the PEDOT-DMcT-Li system with dual-redox properties and point to their potential use as a cathode in organic batteries.