Nanofibrous Covalent Organic Frameworks Based Hierarchical Porous Separators for Fast‐Charging and Thermally Stable Lithium Metal Batteries

Abstract Engineering multifunctional smart separators are important for the ongoing pursuit of fast‐charging and safe batteries. Herein, a novel nanofibrous covalent organic framework (COF) based separator with well‐designed hierarchical porous channels is fabricated to effectively regulate mass transport for fast‐charging and thermally stable lithium metal batteries (LMBs). Such a hierarchical porous separator consists of electrospun polyacrylonitrile nanofibers with macroporous channels (average diameter of 323 nm) and mesoporous channels (≈7 nm) created between amide‐group‐bonded COF nanoparticles with intrinsic 1.6 nm lithiophilic microporous channels (PAN/AM‐COF). Computational fluid dynamics and density functional theory calculations demonstrate that PAN/AM‐COF can simultaneously facilitate high‐speed and selective transport of Li⁺, as well as homogeneous deposition of Li, achieving high conductivity (3.33 mS cm⁻¹) and high Li⁺ transference number (0.79). As a result, Li || LFP full cell with PAN/AM‐COF displays superior cycling stability at 10 C with an acceptable capacity attenuation (0.037% per cycle) over 1000 cycles. Moreover, when operating under an extreme temperature of 100 °C, the Li || LFP full cell with PAN/AM‐COF can still operate stably for 300 cycles at 30 C, highlighting its potential processing scalability for ultrafast‐charging energy storage systems. This study gives insights into designing functional separators for fast‐charging LMBs.