Correlation of electrochemical and ab initio investigations of iron poly-bipyridine coordination complexes for battery applications: impact of the anionic environment and the local geometries of the redox complexes on the electrochemical response

Although they exhibit huge versatility, coordination complexes have been rarely investigated in the field of cathode materials for batteries. Despite their relatively high molecular mass, according to the nature of the metallic center and that of the ligand, the E degrees value and the electron transfer kinetics can be adjusted to develop a performant material compatible with the electrolyte. Here, we propose to investigate Fe-II poly-bipyridine complexes with a view to check the impact of the nature of the electrolyte as well as the influence of the distance between two redox centers when polymerized on the electrochemical response in battery conditions. To understand these changes, three lithium salts have been studied: LiClO4, LiPF6 and LiTFSI (TFSI = bis(trifluoromethane)sulfonimide). In order to mimic these impacts, monomer complexes (mono- and binuclear) have been electrochemically studied, whereas, thanks to ab initio calculations, their redox behavior has been correlated to the ligand environment of the metallic center. Finally, despite their expected low mass capacity, these polymeric coordination complexes have been involved in battery conditions.