Mechanistic understanding of ultrafast anomalous lithium-ion transport in supramolecular porous crystals from fused macrocycle cages

Abstract

Fused macrocyclic cages have demonstrated excellent ion transport capabilities, yet the detailed mechanisms underlying their ion transport remain poorly understood, primarily due to the lack of experimental techniques capable of characterizing and visualizing processes at the molecular scale. In this study, we employ reactive molecular dynamics simulations to investigate the lithium-ion transport properties of a supramolecular porous crystal recently synthesized from fused macrocyclic cages arranged around a central prismatic core. Our simulations reveal that this crystal exhibits anomalous, non-Fickian subdiffusive ion transport behavior, which arises from the periodic trapping and release of Li⁺ ions at specific binding sites. Increasing the Li⁺ concentration initially enhances ionic conductivity, but conductivity declines once a critical concentration threshold is surpassed. Likewise, Li⁺ conductivity increases with temperature before declining at higher temperatures due to significant structural disturbances within the nanochannel. When methanol is introduced as a solvent, Li⁺ conductivity decreases because of ion clustering. Therefore, our findings indicate that the fused macrocyclic cage structure operates most effectively as a solid electrolyte in the absence of added solvents. Additionally, we observe that the diffusion coefficient diminishes as the thickness of the 1D nanochannel increases. These results provide important mechanistic insights for the design of all-solid-state lithium-ion batteries with ultrafast lithium transport characteristics.