Lithium Metal Batteries Enabled by Ion Flux-Regulating Coating on Separator

Abstract

Separator modification is a facile approach for ensuring stable cycling of lithium metal batteries. Here, a hybrid polymer coated separator with high Young's modulus and ion conductivity is designed by integrating proton-doped polyaniline (PANi) nanosheets with poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP). Density functional theory (DFT) calculation confirms that the proton-doped PANi nanosheets interact with TFSI⁻ anions and its 2D confinement effect induces conformational transition of PVDF to the polar β phase. These synergistic effects optimize Li⁺ transport. Besides, finite element simulations and in situ optical microscopy indicate that the conjugated structure of PANi promotes electron delocalization and homogenizes the potential across lithium anode surface, guiding a uniform Li⁺ flux and dense lithium deposition. Moreover, the hybrid polymer coating leads to the formation of LiF-enriched SEI on lithium metal surfaces. As a result, Li||Li symmetric batteries with the hybrid polymer coated separator exhibit stable cycling for over 2000 h at a current density of 10 mA cm⁻². In additoin, Li||LFP batteries using the modified separator has a stable cycling for over 200 cycles at 3 C, maintaining a capacity of 99.25 mAh g⁻¹ with a high areal loading of 13.5 mg cm⁻².