Influence of arylene diimide linker aromaticity on the electrochemical performance of redox-active metal-organic framework cathodes for lithium-ion storage.

Organic electrode materials represent an attractive alternative to inorganic cathodes because they are based on abundant elements and offer tunable electrochemical performance through molecular design. Among them, metal-organic frameworks (MOFs) incorporating redox-active organic linkers have attracted considerable attention as electrode materials for metal-ion batteries. Herein, a series of isoreticular redox-active MOFs based on pyromellitic diimide (PMDI), naphthalene diimide (NDI), and perylene diimide (PDI) linkers were investigated as cathode materials for lithium-ion storage to elucidate the influence of arylene diimide aromaticity on electrochemical performance. Among the Zn-XDI (XDI = PMDI, NDI, PDI) MOFs, Zn-PDI and Zn-NDI exhibited excellent cycling stability, retaining 98% and 87% of their initial capacities after 500 cycles at 2C, respectively, whereas Zn-PMDI showed poor capacity retention, highlighting the importance of the aromatic core in stabilizing reduced states. Post-mortem X-ray photoelectron spectroscopy (XPS), powder X-ray diffraction and Raman studies confirmed the preservation of the framework structure of Zn-PDI and Zn-NDI after extended cycling. Density functional theory (DFT) calculations revealed that increasing the aromatic core size in the Zn-XDI series stabilizes the reduced states, lowers the LUMO energy, enhances electron affinity, and facilitates Li+ uptake through the carbonyl oxygen atoms. These findings establish a direct relationship between linker aromaticity and electrochemical performance and provide molecular-level design principles for the development of high-performance redox-active MOF cathodes for sustainable energy storage.