Branched\nPoly(ethylene glycol)-Functionalized Covalent\nOrganic Frameworks as Solid Electrolytes

Abstract

Poly­(ethylene\nglycol) (PEG)-derived electrolytes can promote not\nonly conduction of lithium ions but also that of anions. To avoid\nanion conduction and increase the Li-ion transference number, we propose\na new concept that utilizes crowded space to restrict anion movement.\nBranched PEG chains with different lengths were covalently grafted\ninto the pore surface of covalent organic frameworks (COFs) and construct\ncrowded nanochannels. After incorporating LiTFSI, the COF with longer\nPEG chains achieves an ionic conductivity of 1.5 × 10^–3 S cm^–1 at 200 °C and an activation energy\nof 0.60 eV. It also inhibits anion movement in a certain direction\nand obtains a higher transference number than other COFs with shorter\nPEG chains. The full cell is further assembled, finally obtaining\na specific discharge capacity of 153 mAh g^–1 after\n60 cycles at 100 °C.