Regulating Solvation Structure and Ion Transport via Lewis-Base Dual-Functional Covalent Organic Polymer Separators for Dendrite-Free Li-Metal Anodes.

Abstract

The high Li⁺ desolvation energy barrier causes sluggish kinetics and uncontrolled dendrite growth, leading to severe solid electrolyte interface (SEI) instability and hindered ion transport across lithium-metal anodes (LMAs), which remains a major barrier to commercialization. Herein, a Lewis-based N/O dual-functional covalent organic polymer (COP-DQCC) with abundant carbonyl components was designed and integrated into a commercial polypropylene (PP) separator. Experimental and theoretical calculations show that the high lithiophilicity of Lewis base N/O atoms enhances lithium salt dissociation, promotes Li⁺ desolvation from the solvation shell, reduces solvent molecule transport, simplifies the solvated structure of Li⁺, lowers ion diffusion activation energy, and accelerates Li⁺ migration. Additionally, the suitable pore size of the triazine composite carbonyl organic unit regulates the electroplating/stripping behavior of LMA. In situ optical microscopy reveals that the COP-DQCC layer effectively inhibited dendrite growth. Time-of-flight secondary ion mass spectrometry further confirms that the COP-DQCC layer promotes the formation of a stable LiF-rich SEI layer, regulates Li⁺ transport and uniform deposition. Ultimately, the Li/COP-DQCC@PP/Li symmetric cell demonstrated stable cycling for over 2400 h at 1.0 mA cm^-2/1.0 mAh cm^-2, maintaining a low overpotential, and continued stable cycling for over 900 h at 4.0 mA cm^-2/4.0 mAh cm^-2. Additionally, the LiFePO₄/COP-DQCC@PP/Li cell shows remarkable cycling stability, retaining 84.6% of its capacity after 1200 cycles at 1.0 C, and excellent cycling performance at higher loading of LiFePO₄. This work highlights the development of a durable, dendrite-free anode, offering significant potential for advancing high-energy-density LMAs.