Single-ion quasi-solid-state electrolytes based on sulfonimide-functionalized covalent organic framework

Abstract

Single-ion quasi-solid-state electrolytes (SIQSSEs) have attracted increasing attention recently due to their ability to suppress the growth of lithium dendrite and higher safety. However, their low ionic conductivity is still the major bottleneck preventing their practical application. Covalent organic frameworks (COFs) are considered to be potential candidates for quasi-solid-state electrolytes (QSSEs) due to their high porosity and ordered structures. Herein, we demonstrate a series of crystalline covalent organic frameworks with sulfonimide groups as a new class of single-ion electrolytes. Owing to the directional lithium transport pathway and adequate binding site for lithium ions, these COF-based electrolytes deliver good ionic conductivity (4.3 × 10⁻⁴ S cm⁻¹) at 298 K, with a high lithium transference number (LTN, ∼0.90) and a low activation energy (0.24 eV). We also found that strong electron-withdrawing substituents and delocalized substituents could promote lithium-ion transportation. Furthermore, Li||LiFePO₄ (LFP) cells based on sulfonimide-functionalized covalent organic framework (SF-COF) electrolytes deliver outstanding rate performance with a long cycle life (99% capacity retention after 100 cycles at 0.2 C). Our work demonstrates that crystalline covalent organic frameworks show great potential for application as building blocks of solid electrolytes in lithium metal batteries.