Single-ion-conducted covalent organic framework serving as Li-ion pump in polyethylene oxide-based electrolyte for robust solid-state Li–S batteries

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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-SO3, 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.