Ultra-long life and high rate performance zinc-iodine batteries simultaneously enabled by a low-spin electrode

Abstract

Enhanced iodine redox chemistry and iodine species anchoring play a determining role in the advancement of zinc-iodine (Zn-I₂) batteries, and it remains a major challenge to meet the application requirements with current strategies. In this work, the Ni-spin state is altered from high spin to low spin through the incorporation of monodispersed Zn atoms surrounding individual Ni atoms. The experimental and theoretical analyses reveal that the low-spin state optimizes the d-p orbital hybridization between Ni and I atoms, reducing the antibonding electron occupation of the Ni-I coupling orbitals. The low-spin state enhances the iodine species redox conversion kinetics and prevents rampant iodine species shuttling. Consequently, long-life (70% capacity retention after 30,000 cycles) and high rate performance are simultaneously achieved, with the pouch cell maintaining a capacity of 164 mAh g^-1 after 500 cycles at 2 A g^-1. This Ni-spin state control strategy inspires a deeper understanding of catalytic activity-electronic structure relationships in the fields of catalysis and redox conversion energy storage.