Solvent-Free, Single Lithium-Ion Conducting Covalent Organic Frameworks

Porous crystalline materials such as covalent organic frameworks and metal–organic frameworks have garnered considerable attention as promising ion conducting media. However, most of them additionally incorporate lithium salts and/or solvents inside the pores of frameworks, thus failing to realize solid-state single lithium-ion conduction behavior. Herein, we demonstrate a lithium sulfonated covalent organic framework (denoted as TpPa-SO3Li) as a new class of solvent-free, single lithium-ion conductors. Benefiting from well-designed directional ion channels, a high number density of lithium-ions, and covalently tethered anion groups, TpPa-SO3Li exhibits an ionic conductivity of 2.7 × 10–5 S cm–1 with a lithium-ion transference number of 0.9 at room temperature and an activation energy of 0.18 eV without additionally incorporating lithium salts and organic solvents. Such unusual ion transport phenomena of TpPa-SO3Li allow reversible and stable lithium plating/stripping on lithium metal electrodes, demonstrating its potential use for lithium metal electrodes.