Ionic covalent organic frameworks-based electrolyte enables fast Na-ion diffusion towards quasi-solid-state sodium batteries

Solid-state sodium batteries present a high potential for future energy technology due to their high safety and energy density. However, sluggish Na+ transportation of solid-state electrolytes and serious Na dendrites hinder their further development. Herein, we propose a negatively charged-modified covalent organic framework (COF) with -SO3Na as a Na-ion quasi-solid-state electrolyte (QSSE-COF-SO3Na) for the first time to enhance the Na+ transportation. Density functional theory calculations and molecular dynamics simulations prove that the nanoscale ion channels of the COF-SO3Na and the interaction between the -SO3- and the anion PF6- effectively enhance the Na+ diffusion kinetics. The QSSE-COF-SO3Na exhibits a high ionic conductivity of 4.1 x 10-4 S cm-1 at room temperature and a high transference number of 0.89. Particularly, Na|QSSE-COF-SO3Na|Na symmetric cells show a stable Na plating/stripping process without Na dendrites over 1000 h and 800 h at 0.05 and 0.2 mA cm-2, respectively. Additionally, the QSSE-COF-SO3Na supports full cells, which respectively use NaTi2(PO4)3, Na3V2(PO4)3, and NaFePO4 as cathodes, to display good cycling stability and rate performance. This work highlights the novel strategy to develop the Na-ion quasi-solid-state devices.