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Abstract Lithium-selenium (Li-Se) batteries possess high volumetric capacity and have attracted considerable attention as a high energy storage system. However, the shuttling of polyselenides seriously worsens the electrochemical performance and retards their application advancement. Herein, we engineered a bifunctional membrane consisted of polyethylenimine derived carbon quantum dots (Cdots) to efficiently restrict the shuttling of polyselenides under a high Se loading (Se≈70 wt%) and promote Li-Se conversion kinetics, which can be accounted by the greatly accelerated transportation of charge carriers and dipole–dipole interactions between polar moieties and long-chain polyselenides (Li2Se4 and Li2Se6) as corroborated by theoretical calculations. Thus, the bifunctional membrane endows Li-Se batteries with a specific capacity of 658.60 mAh g−1 at 0.1 C and coulombic efficiency of 97.8% in average, and demonstrates the effectiveness of defect-rich Cdots on suppressing polyselenides shuttling and reinforcing Li-Se conversion kinetics in augmenting the battery’s durability and efficiency. Graphical Abstract