Single-ion-conducted covalent organic framework serving as Li-ion pump in polyethylene oxide-based electrolyte for...

Poly(ethylene oxide) (PEO)-based electrolytes are widely used for building solid-state lithium-sulfur (Li-S) batteries but suffer from poor lithium-ion (Li⁺) transportation kinetics. Here, a lithium-sulfonated covalent organic framework (TpPa-SO₃Li) was synthesized and functionalized as a Li⁺ pump in a PEO-based solid-state electrolyte to fabricate robust Li-S batteries. The designed TpPa-SO_3, Li with its porous skeleton and abundant lithium sulfonate groups not only provided iontransport channels but also enhanced the fast migration of Li⁺. The PEO composite electrolyte containing 5 %-TpPa-SO₃Li exhibited a notable ionic conductivity of 6.28 × 10^-4 S cm^-1 and an impressive Li⁺ transference number of 0.78 at 60 °C. As a result, Li-Li symmetric batteries with the optimized PEO/TpPa-SO₃Li composite electrolyte stably cycled for 300 h, with a minimal overpotential of only 100 mV at 0.5 mA cm^-2. Moreover, the customized solid-state Li-S batteries based on PEO/TpPa-SO₃Li were stable for 600 cycles at 60 ^oC with a high Coulombic efficiency of approximately 98 %. This study provides a promising strategy for introducing covalent-organic-framework (COF)-based Li⁺ pumps to build robust solid-state Li-S batteries.