Elucidating Activation in Metal–Organic Coordination Polymer Electrodes for Li-Ion Batteries and the Critical Roles of Supramolecular Interactions

Coordination polymers (CPs) are appealing as battery electrode materials because they offer great features from organic redox centers (i.e., structural design flexibility, redox tunability, fast kinetics, and resource abundance/sustainability) together with enhanced structural stability due to metal–ligand coordination. Organic-based polymeric electrodes are often found to undergo a long activation period before the highest capacity can be reached. Even though this phenomenon is commonly encountered, the underlying mechanisms and controlling factors remain poorly understood. Herein, two redox-active 1D CPs, [MgL(DMF)2]n and [ZnL(DMA)2]n (LH4 = 1,4-dicyano-2,3,5,6-tetrahydroxybenzene, DMF = N,N-dimethylformamide, DMA = N,N-dimethylacetamide), with different degrees of supramolecular interactions, have been revealed to distinctively undergo in situ activation, accompanied by transformation of rod-like CP particles into 2D flake-like morphologies during cycling in Li cells, which leads to significantly more highly accessible active sites and facilitates charge transport. [ZnL(DMA)2]n, with more flexible packing due to weaker interactions of metal–ligand chains, allows more reversible morphological change, which leads to faster, nondestructive activation, as observed in superior capacity retention and rate capability compared to [MgL(DMF)2]n. These findings highlight the crucial role of supramolecular interactions in determining activation behavior and electrochemical performance and provide insights into the rational design of metal–organic and organic-based materials for sustainable energy storage systems.