σ‐Hole Interaction‐Driven Enrichment‐Catalysis Cascade Reaction in Covalent Organic Cages Enables Ultrahigh‐Rate Li‐Br ₂ Batteries

ABSTRACT Rechargeable lithium‐bromine (Li‐Br 2 ) battery is a promising battery system due to its high‐energy‐density (1050 Wh kg −1 ). However, the practical implementation of this system is hampered by sluggish reduction kinetics of Br 2 and severe shuttle effect, leading to poor rate performance and inferior low‐temperature performance. Herein, we propose a strategy driven by a σ‐hole interaction, which strengthen the electron donation into the σ* antibonding orbital of Br 2 to enhance its trapping and promote rapid cathode conversion. As a proof of concept, pyridine units—validated by theoretical calculations as effective σ‐hole mediators—were integrated into a structurally engineered covalent organic cage (Bpycage). The Bpycage cathode thereby locally enriches Br 2 and accelerates its electrochemical reduction. Benefiting from this design, the Li‐Br 2 @Bpycage battery achieves exceptional rate capability (up to 20 A g −1 or 25 mA cm −2 ) and long‐term stability over 320 cycles at 10 A g −1 (9 mA cm −2 ), outperforming conventional carbon cathode. Moreover, the σ‐hole interaction effectively decreases the freezing point of Br 2 , enabling stable operation at an ultralow temperature of −45°C, far beyond the limit of −20°C for carbon‐based cathodes. This work highlights the potential of molecularly designed organic cages as high‐performance cathodes for advanced metal‐halogen battery systems.