Investigating Polaron Dynamics in Conjugated Polymers Using Molecular Dynamics Simulations

<b>Abstract:</b> Development of safe, sustainable, and cost-effective electrochemical energy storage devices is a priority for the energy transition. Batteries and pseudo capacitors enable the storage and stabilization of intermittent power from renewable energy sources, but new materials are still needed to minimize concerns about materials availability and sustainability. Recently conjugated polymers have received attention for electrode applications. The redox properties and nature of charge transport in such materials determine their suitability as n-type or p-type electrodes. In such structures, redox potentials are primarily controlled by tuning the conjugated backbone, whilst side chains influence the compatibility with different electrolytes and the electrode stability under electrochemical cycling [1, 2]. In practice, the ease of formation and the stability of the charged species, polarons and bipolarons, are influenced by choice of both backbone and side chain [3]. In order to design higher performance polymer electrodes, we need tools to model the nature and dynamics of polarons in conjugated polymer electrodes. Polarons carry non-zero net charges and result in complex interactions between charged species, neutral species and or ions, posing several challenges for molecular dynamics simulation. In the present work we use molecular dynamics to study the structural and ion dynamics of conjugated polymers based on diketopyrrolopyrrole and thiophene backbone. We study how the choice of backbone, side chain, solvent and electrolyte affect polaron formation, polaron stability and redox behavior. These methods can help to design suitable polymer materials for electrode applications in batteries.<br/><b>Keywords:</b> Polymer batteries, Molecular Dynamics, Polarons, Redox Behavior, organic mixed ionic-electronic conductors, electrochemistry,<br/><b>References:</b><br/>[1] S. Moro, N. Siemons, O. Drury, D. Warr, T. Moriarty, L. Perdigão, D. Pearce, M. Moser, R. Hallani, J. Parker, I. McCulloch, J. Frost, J. Nelson, G. Costantini, ACS Nano, 16, 21303-21314 (2022).<br/>[2] E. Tan, J. Kim, K. Stewart, C. Pitsalidis, S. Kwon, N. Siemons, J. Kim, Y. Jiang, J. Frost, D. Pearce, J. Tyrrell, J. Nelson, R. Owens, Y. Kim, J. Kim, Advanced Materials, 34, (2022).<br/>[3] D. Giri, S. Saha, N. Siemons, I. Anderson, H. Yu, J. Nelson, R. Canjeevaram Balasubramanyam, S. Patil, ACS Appl. Mater. Interfaces, 15, 17767-17778 (2023).