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

Single-ion quasi-solid-state electrolytes (SIQSSEs) attract increasingly attention recently, due to their ability in suppressing the growth of lithium dendrite and offering higher safety. However, the low ionic conductivity is still the major bottleneck for preventing the practical application. Covalent organic frameworks (COFs) are considered as 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 high lithium transference number (LTN, ~0.90) and a low activation energy (0.24 eV). We also find both strong electron-withdrawing substituent and delocalized substituent could promote lithium-ion transportation. Furthermore, the Li||LiFePO4 (LFP) cells based on the sulfonimide-functionalized covalent organic framework (SF-COF) electrolytes deliver outstanding rate performance with 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.