Covalent organic framework mediated solvation in gel polymer electrolytes for high-performance lithium metal batteries

Solid polymer electrolytes (SPEs) are critical for enabling high-performance and safe solid-state lithium metal batteries. However, they often suffer from low ionic conductivity and poor interfacial compatibility, particularly at low temperatures. In this study, we address these challenges by incorporating covalent organic frameworks (COFs) into a poly(1,3,5-trioxane) (PTXE)-based composite gel polymer electrolyte (GPE). The GPE is formed via in situ polymerization of TXE monomers at room temperature, using diethylene glycol dimethyl ether (DEGDME) as a lithium-compatible solvent and hydrofluoroether(HFE) as a plasticizer. The resulting COFs-enhanced GPE enables stable cycling of LiNi0.6Co0.2Mn0.2O2 (NCM622) || Li cells for over 275 cycles at 4.5 V with 80.0% capacity retention. Remarkably, it also supports NCM622 || Li full-cell operation with a thin (100 μm) lithium foil at −20 °C for over 70 cycles, retaining 80.5% of its initial capacity. A molecular-level interfacial model is proposed to illustrate how COFs modulate the solvation environment within the GPE, enhancing Li+ transport kinetics and interfacial compatibility. This work demonstrates that simultaneous regulation of bulk-phase properties and interfacial structure via tailored solvation strategies can significantly improve the performance of polymer-based solid-state lithium batteries across a broad temperature range, providing valuable guidance for future electrolyte design.