Stabilizing Lithium Metal Anodes via Tuned Li+–π Interactions in Nanoporous Porous Aromatic Framework-Coated Separators

Abstract

Lithium metal batteries (LMBs) offer exceptionally high theoretical capacity but face challenges such as dendrite growth and unstable Li metal surfaces. To overcome these issues, functional separators coated with porous aromatic frameworks (PAFs) are designed as nanoporous interfacial layers to regulate Li+ transport and stabilize the Li metal anode. The PAF, characterized by tetrahedrally arranged phenyl rings with an ultrahigh surface area (~5,000 m2/g), provides abundant cation–π interaction sites and nanoporous channels that promote uniform Li+ distribution and mitigate local Li+ depletion near the anode surface. As a result, the PAF-coated polypropylene separator (PAF/PP) shows enhanced ionic conductivity and Li+ transference number relative to bare PP, enabling a stable Li+ flux and prolonged cycle life. Furthermore, the cation–π interactions combined with nanoconfinement modulate the Li+ solvation structure, favoring aggregated species such as contact ion pairs and inducing the formation of an inorganic-rich solid electrolyte interphase that improves interfacial stability. To fine-tune these interactions, PAFs were functionalized with electron-withdrawing NO2 (PAF-NO2) and electron-donating NH2 (PAF-NH2) groups. While NO2 substitution weakens cation–π interactions and reduces ionic conductivity, NH2 substitution strengthens Li+ binding but hinders Li+ migration due to excessive interaction strength. Consequently, the pristine PAF achieves the optimal balance between Li+ solvation and transport behavior, leading to uniform Li deposition, low nucleation overpotential, and superior cycling stability. This study demonstrates that precise control of nanoporous architecture and cation–π interactions is an effective strategy for stabilizing Li metal anodes.