Multifunctional Covalent Organic Framework Solid Electrolyte Facilitating Fast Li-Ion Diffusion in Solid-State Batteries

Ensuring the safety, high energy density, and long-term cycling performance of all-solid-state Li metal batteries (LMBs) requires the development of compatible organic solid electrolytes. However, it remains a challenge to develop an approach that enables organic solid electrolytes to easily dissociate strong Li-ion pairs and facilitate rapid Li-ion transport. In this study, a diethylene glycol-modified pyridinium covalent organic framework (DEG-PMCOF) with a well-defined periodic structure is prepared as a multifunctional solid electrolyte with a cationic moiety of high polarity, an additional flexible ion-transporter, and an ordered ionic channel for all-solid-state LMBs. The DEG-containing pyridinium groups within DEG-PMCOF lower the dissociation energy of Li salts as well as the energy barrier for Li-ion transport, resulting in an enhanced ion conductivity and a high Li-ion transfer number at room temperature in the solid electrolyte. Furthermore, the DEG-PMCOF solid electrolyte offers a wide electrochemical stability and effectively prevents the formation of Li dendrites and dead Li in all-solid-state LMBs. Molecular dynamics and density functional theory simulations provide insights into the mechanisms underlying the improved Li-ion transport in DEG-PMCOF, involving integrated diffusion processes such as hopping motion, vehicle motion, and free diffusion. The all-solid-state LMB constructed with a DEG-PMCOF solid electrolyte exhibits a high specific capacity, excellent retention, and outstanding Coulombic efficiency at various C-rates during long-term cycling. This DEG-PMCOF approach represents an effective strategy for designing a variety of solid-state Li batteries.