Unlocking the Capacity of Bismuth Oxide by a Redox Mediator Strategy for High-Performance Aqueous Zn-Ion Batteries.

Many cathode materials store zinc ions based on the intercalation reaction mechanism in neutral aqueous Zn-ion batteries, and the structural design of the cathodes has been stuck in the curing mode by extending the ion diffusion channel. Here, we first develop halide ions to unlock the electrochemical activity of conversion-type BiO in aqueous Zn-ion batteries. Notably, the iodide ion shows the best performance compatibility with the BiO cathode. The electrochemical reaction mechanism studies show that iodide ions can be regarded as a redox medium to reduce the charge-transfer activation energy and motivate the conversion of BiO from Bi to Bi during the cycle. Unsurprising, the discharge-specific capacity can reach 436.8 mAh g at 0.5 A g and achieve a cyclic lifespan of 6000 cycles at a current density of 3 A g. The activation of the BiO conversion reaction by iodide ions is of great significance for broadening the research range of ZIB cathode materials.