Unraveling Charging and Discharging Processes in Organic Radical-Based Electrodes: A Hierarchical Molecular and Quantum Mechanical Approach.

Organic batteries represent a promising class of energy storage materials, due to their mechanical flexibility and sustainability. Typically, stable radicals, lacking intrinsic conductivity, are utilized as redox-active materials. A recently introduced strategy to overcome this shortcoming is to incorporate stable radicals, i.e., (2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO), into a polythiophene backbone. Thereby, an electrode material was obtained which does not require conductive additives. The current computational study aims to elucidate the functionality of this material by drawing in-depth structure-property relationships utilizing a hierarchical molecular and quantum mechanical approach. Initially, structural properties of the electrode material's macroenvironment-containing the functionalized polythiophene, electrolyte, and solvent-were assessed in various charging states by molecular dynamics simulations. Subsequently, electronic properties were investigated by time-dependent density functional theory for 564 microenvironments. Via this computational setup, the electronic communication within the material was assessed along intrastrand and interstrand CT processes involving the respective TEMPO and polythiophene units. Thereby, our hierarchical computational approach reveals that the intrinsic conductivity and charge storage capacity of the electrode material stems from efficient intrastrand TEMPO-polythiophene CT processes along short and rigid amid linkers. These insights help to tailor improved conductive organic electrode materials with higher charging and discharging rate capabilities.