Electron Storage Performance of Metal-Organic Frameworks Based on Tetrathiafulvalene-Tetrabenzoate as Cathode Active Materials in Lithium- and Sodium-Ion Batteries

Tetrathiafulvalene (TTF) derivatives are wellknown molecular-based conductors. They are used to prepare porous crystalline structures with efficient charge transport properties and suitable chemical design, such as metal-organic frameworks (MOFs), covalent organic frameworks (COFs), and hydrogen-bonded organic frameworks (HOFs). MOFs based on TTF derivatives have attracted attention as electrode-active materials for rechargeable metal-ion batteries owing to multi electron redox reactions, resulting in improved battery capacity. This study focuses on TTF-tetrabenzoate (H4TTFTB), which exhibits good redox and mechanical properties as the ligand of MOFs. We evaluated the battery performance using MOFs based on H4TTFTB with three types of core metals ([M2(TTFTB)], where M = Zn, Co, and Mn) as cathode active materials for rechargeable lithium-ion and sodium-ion batteries (LIBs and SIBs). The cycle stability and battery capacity at high current densities were improved by MOF formation in both LIBs and SIBs, indicating that MOF formation has the potential to achieve improved charging/discharging rates. In addition, the battery capacities and cycle stability of SIBs were larger than those of LIBs for all materials. These results demonstrate the interesting battery performance of MOFs based on H4TTFTB as cathode active materials for LIBs and SIBs. This implies that the application of redox-active and rigid H4TTFTB as the ligand of MOFs is an effective method for realizing high-performance energy storage devices. These findings can contribute to an improved design of cathode active materials for high-performance rechargeable metal-ion batteries for sustainable energy storage.