Order chiral nematic liquid crystal of hydroxypropyl methylcellulose coating on PE separator for highly stable lithium metal batteries

Surface coating designing of the separator is an effective way to enhance the cycling stability of lithium metal batteries (LMBs). Commercial polyolefin separators serve as the coating substrate, and their pore structure, mechanical strength, and electrochemical properties constitute the foundation determining the overall performance of the composite separator. Herein, the self-assembly behavior of hydroxypropyl methylcellulose (HPMC) on the surface of polyethylene (PE) separators under different drying conditions has been investigated. Chiral nematic liquid crystal (CLC) phases of HPMC are formed through self-assembly on PE under both ambient and 60 °C drying preparation conditions. The experimental and theoretical results show that the introduction of HPMC can reduce the involvement of carbonate-based solvent (for example, ethylene carbonate) in the Li⁺ solvation sheath, which improves Li⁺ desolvation kinetics and facilitates the formation of a LiF-enriched solid electrolyte interphase (SEI). The ordered CLC structure of HPMC guides a uniform Li⁺ flux and dense lithium deposition, contributing to high cycling stability and Coulombic efficiency. Consequently, Li//LFP cells assembled with separators featuring the ordered CLC structure demonstrate improved cycling performance, sustaining over 2000 cycles at 1C.