Molecular Engineering as a Strategy to Unlock Hidden Redox Activity in Perylene-Based Organic Electrode Materials

Organic electrode materials provide an alternative to transition-metal-based cathodes, yet many molecular systems utilize only a fraction of their redox-active sites. Here, we demonstrate that molecular functionalization enables the utilization of multiple carbonyl redox sites in perylene-based organic cathodes. While perylene tetracarboxylic dianhydride (PTCDA) is limited to a two-lithium redox process, a phenyl-substituted perylene diimide derivative (P-PTCDI) reversibly accommodates nearly four lithium ions. Combined electrochemical measurements and spectroscopic analyses, including soft X-ray absorption spectroscopy, Fourier-transform infrared spectroscopy, and X-ray photoelectron spectroscopy, reveal increased involvement of carbonyl participation and confirm reversible lithiation and delithiation in P-PTCDI. Density functional theory calculations indicate that phenyl substitution induces molecular distortion and promotes π-electron-mediated electrostatic stabilization, reducing lithium–lithium repulsion and enabling thermodynamically favorable multilithium storage. This work establishes a molecular design principle for activating additional redox capacity in perylene-based organic electrode materials.