Directional Li+ Flux Control via Liquid-Crystalline Polymer Separators for Fast-Charging Lithium Metal Batteries

Abstract

Stabilizing lithium (Li) metal batteries requires precise control of Li+ ion transport, as spatially nonuniform ion flux can induce dendritic Li growth and poor reversibility. Here, we report liquid-crystalline polymers (LCPs) as nanoporous films that regulate Li+ flux through directionally aligned ion pathways. Crosslinked LCP films form aligned nanoporous channels (∼19 nm), while tethered poly(ethylene glycol) (PEG) chains lining the pore walls provide coordination sites that facilitate Li+ transport. Vertically aligned PEG-LCP films establish through-plane ion pathways, reducing effective tortuosity by ∼2.5-fold compared with planar alignment despite comparable pore architectures. This structural anisotropy leads to high ionic conductivity (1.77 mS cm–1) and a reduced activation energy (0.12 eV) for Li+ migration in carbonate-based electrolytes. The resulting uniform Li+ flux suppresses dendritic and porous Li growth, enabling more uniform Li deposition and mitigating excessive interphase formation. Li metal cells employing vertically aligned PEG-LCP films exhibit stable cycling under fast-charging conditions (4 C) with LiNi0.8Co0.1Mn0.1O2, retaining 94% of the capacity after 100 cycles with an average Coulombic efficiency of 99.86%. This work demonstrates that liquid-crystalline alignment can be leveraged to engineer low-tortuosity ion transport pathways, offering a design principle for fast-charging Li metal batteries.