Halogen Electrochemistry Enabled Complementary Lithium/Halogen Dual-Ion Batteries with Enhanced Capacity and Cyclability

Rechargeable dual-ion batteries are promising supplements to lithium-ion batteries for fast charging and stationary energy storage but suffer from sluggish kinetics, low capacity, and poor durability caused by the insertion of bulky anions. Here, we introduce a halogen electrochemistry strategy employing small halogen ions as charge carriers to achieve efficient anion redox reactions. Among them, bromide ions exhibit superior electrochemical performances due to a suitable size and redox potential. The charge storage mechanisms involving Br^- intercalation (or adsorption) and conversion are demonstrated using graphite, a Co-terephthalic metal-organic framework (Co-BDC), and zeolitic imidazolate framework-67 (ZIF-67) as cathodes, delivering specific capacities of 197, 226, and 291 mAh g^-1 at 100 mA g^-1, respectively. Electrochemical and spectroscopic analyses confirm that replacing large anions with small halogen ions brings enhanced ion storage capacities and redox kinetics. This work establishes halogen electrochemistry as a new paradigm for high-performance and scalable dual-ion secondary batteries.