COFs-based electrolyte accelerates the Na+ diffusion and restrains dendrite growth in quasi-solid-state organic batteries

Solid-state sodium-ion batteries exhibit a great promising opportunity for the future energy storage, and thus exploring a high-efficiency sodium-ion conductor is the urgent challenge. Covalent organic frameworks (COFs) have accurately directional and well-defined ion channels and are a promising and optimal platform for solid-state Na-ion conductor. In this work, we study the first example of carboxylic acid sodium functionalized polyarylether linked COF (denoted as NaOOC-COF) as an advanced Na-ion quasi-solid-state conductor film. Benefiting from the well-defined ion channels, the functionalized NaOOC-COF exhibits an outstanding Na+ conductivity of 2.68 × 10−4 S cm−1 at room temperature, low activation energy (Ea) with 0.24 eV and high transference number of 0.9. Particularly, the NaOOC-COF shows long-time cycling performance in the assembled quasi-solid-state battery, and can restrain dendrite growth through interface regulation. Furthermore, the Na+ diffusion mechanism in whole-cell system is investigated thoroughly. Such extraordinary Na-ion transport result based on COFs is achieved for the first time. This novel strategy may exploit the new area of Na-ion quasi-solid-state electrolytic devices, and simultaneously accelerate the progress of functionalized COFs.