Branched Poly(ethylene glycol)-Functionalized Covalent Organic Frameworks as Solid Electrolytes

Poly(ethylene glycol) (PEG)-derived electrolytes can promote not only conduction of lithium ions but also that of anions. To avoid anion conduction and increase the Li-ion transference number, we propose a new concept that utilizes crowded space to restrict anion movement. Branched PEG chains with different lengths were covalently grafted into the pore surface of covalent organic frameworks (COFs) and construct crowded nanochannels. After incorporating LiTFSI, the COF with longer PEG chains achieves an ionic conductivity of 1.5 × 10–3 S cm–1 at 200 °C and an activation energy of 0.60 eV. It also inhibits anion movement in a certain direction and obtains a higher transference number than other COFs with shorter PEG chains. The full cell is further assembled, finally obtaining a specific discharge capacity of 153 mAh g–1 after 60 cycles at 100 °C.