Halide Exchange in Perovskites Enables Bromine/Iodine Hybrid Cathodes for Highly Durable Zinc Ion Batteries.

With the increasing need for reliable storage systems, the conversion-type chemistry typified by bromine cathodes attracts considerable attention due to sizeable theoretical capacity, cost efficiency, and high redox potential. However, the severe loss of active species during operation remains a problem, leading researchers to resort to concentrated halide-containing electrolytes. Here, profiting from the intrinsic halide exchange in perovskite lattices, a novel low-dimensional halide hybrid perovskite cathode, TmdpPb 2 [IBr] 6 , which serves not only as a halogen reservoir for reversible three-electron conversions but also as an effective halogen absorbent by surface Pb dangling bonds, C─H…Br hydrogen bonds, and Pb─I…Br halogen bonds, is proposed. As such, the Zn||TmdpPb 2 [IBr] 6 battery delivers three remarkable discharge voltage plateaus at 1.21 V (I 0 /I - ), 1.47 V (I + /I 0 ), and 1.74 V (Br 0 /Br - ) in a typical halide-free electrolyte; meanwhile, realizing a high capacity of over 336 mAh g -1 at 0.4 A g -1 and high capacity retentions of 88% and 92% after 1000 cycles at 1.2 A g -1 and 4000 cycles at 3.2 A g -1 , respectively, accompanied by a high coulombic efficiency of ≈99%. The work highlights the promising conversion-type cathodes based on metal-halide perovskite materials.