Design of Isomeric Covalent Organic Frameworks for Realizing Low-Temperature Sodium Storage

High-performance low-temperature sodium-ion batteries (SIBs) are essential for energy storage in extreme environments, which, however, is severely hindered by the sluggish reaction kinetics due to the slow ionic diffusion and lattice shrink. Herein, we report an isomeric design strategy for anthraquinone-based covalent organic frameworks (TPAQ-COF) to optimize sodium storage by regulating the spatial arrangement of carbonyl groups. By engineering TPAQ-COF with adjacent carbonyl coordination sites (isomeric TPAQ-COF, i-TPAQ-COF), we successfully leverage a synergistic chelation effect to facilitate sodium ion storage at low temperature. As a result, i-TPAQ-COF exhibits a superior reversible capacity of 153 mAh g^{- 1} at 0.1 A g^{- 1} and an outstanding long-term cycling stability (95% retention after 5000 cycles at 2 A g^{- 1}) under ambient conditions. More importantly, the i-TPAQ-COF demonstrates remarkable low-temperature resilience, delivering 124 mAh g^{- 1} at -30°C (representing 82% of capacity at room-temperature) with negligible decay over 200 cycles, and retaining 75% of room-temperature capacity (114 mAh g^{- 1}) even at -40°C. Molecular dynamics (MD) simulations and density functional theory (DFT) calculations reveal that the adjacent carbonyl groups in i-TPAQ-COF exhibit a synergistic chelation effect, which not only elevates the discharge voltage, facilitates the capture of sodium ions but also effectively promotes ion transport.