Porosity-driven electrochemical divergence in structurally polymorphic 2D metal-organic frameworks for lithium-ion storage

Abstract

Two-dimensional metal-organic frameworks (2D MOFs) have emerged as promising materials for electrochemical energy storage owing to their controllable architectures, high surface area, and redox-active frameworks. Here, we report a systematic study on two structurally distinct Cu-based 2D MOFs―porous p-Cu-THQ and nonporous d-Cu-THQ―constructed from the same metal nodes and organic linkers, to elucidate the influence of framework porosity on lithium-ion storage behaviour. p-Cu-THQ exhibits mesoporosity with a BET surface area of ~80 m2g-1, while d-Cu-THQ displays a denser, low-porosity structure (~30 m2g-1). Electrochemical measurements reveal that d-Cu-THQ delivers a higher initial capacity (~1050 mAh g-1) and superior rate performance, attributed to its compact conductive framework and pseudocapacitive charge storage. In contrast, p-Cu-THQ demonstrates enhanced long-term cycling stability, retaining ~785 mAh g-1 after 300 cycles due to improved Li-ion diffusion and structural robustness. Capacitive analysis confirms that Li ion storage in d-Cu-THQ is surface-controlled, whereas p-Cu-THQ operates via diffusion-dominated intercalation. Finally, galvanostatic intermittent titration technique (GITT) was employed to quantitatively estimate the Li+ diffusion coefficients for both the p-Cu-THQ and d-Cu-THQ systems. This comparative investigation highlights a key structure-property relationship in 2D MOFs, establishing porosity engineering as a crucial design strategy for optimizing the trade-off between energy density, conductivity, and cycling stability in next-generation Li-ion battery (LIB) anodes.