Lithiophilic Covalent Organic Framework-Bridged Interface Enables Fast Ion Transport in Ultrathin Gel Polymer Electrolyte Membranes

Abstract Gel polymer electrolytes (GPEs) require a homogeneous polymeric structure, processability, and excellent chemical stability for high-performance lithium metal battery configurations. However, heterogeneous electrolyte polymerization, which constrains ion transport, limits the practical deployment of GPEs. Herein, a universal interface engineering strategy is proposed to construct an oligomer-functionalized covalent organic framework bridging layer on PVDF nanofibers, which bridges the GPE and forms an integrated architecture. Its distinctive nanoconfinement effect efficiently immobilizes guest molecules and homogenizes the Li+ flux, thereby connecting the two phases to form a homogeneous, continuous ion-conductive network. The modified electrolyte with a minimal thickness of 17 μm exhibits significantly enhanced ionic conductivity, reaching 2.96 × 10–4 S cm–1 at 30 °C. Additionally, Li|Li symmetric cells with the modified electrolyte can achieve highly stable cycling over 1000 h at 0.2 mA cm–2, and the LFP|Li cells demonstrate exceptional electrochemical performance, achieving 98.35% capacity retention after 200 cycles at 1 C rate. As a broadly applicable approach, this strategy not only provides enhanced structural integrity but also forms continuous Li+ transport channels, offering considerable potential for practical application in high-performance energy storage systems.