Twisted Perylene Diimides with Tunable Redox Properties for Organic Sodium-Ion Batteries

Organic rechargeable batteries gain huge scientific interest owing to the design flexibility and resource renewability of the active materials. However, the low reduction potentials still remain a challenge to compete with the inorganic cathodes. This study demonstrates a simple and efficient approach to tune the redox properties of perylene diimides (PDIs) as high voltage cathodes for organic-based sodium-ion batteries (SIBs). With appropriate electron-withdrawing groups as substituents on perylene diimides, this study shows a remarkable tunability in the discharge potential from 2.1 to 2.6 V versus Na+/Na with a sodium intake of approximate to 1.6 ions per molecule. Further, this study explores tuning the shape of the voltage profiles by systematically tuning the dihedral angle in the perylene ring and demonstrates a single plateau discharge profile for tetrabromo-substituted perylene diimide (dihedral angles theta(1) & theta(2) = 38 degrees). Detailed structural analysis and electrochemical studies on substituted PDIs unveil the correlation between molecular structure and voltage profile. The results are promising and offer new avenues to tailor the redox properties of organic electrodes, a step closer toward the realization of greener and sustainable electrochemical storage devices.