BiOIO@Zn(PO)·4HO Heterojunction with Fast Ionic Diffusion Kinetics for Long-Life "Rocking-Chair" Zinc Ion Batteries.

Increasing insertion host materials are developed as high-performance anodes of "rocking-chair" zinc ion batteries. However, most of them show unsatisfactory rate capabilities. Herein, layered BiOIO is reported as an excellent insertion host and a zinc ion conductor, i.e., Zn(PO)·4HO (ZPO), is introduced to construct a BiOIO@ZPO heterojunction with a built-in electric field (BEF). Both ZPO and a BEF obviously enhance Zn transfer and storage, which is proven by theoretical calculations and experimental studies. The conversion-type mechanism of BiOIO is revealed through ex situ characterizations. The optimized electrode exhibits a high reversible capacity of 130 mAh g at 0.1 A g, a low average discharge voltage of 0.58 V, an ultrahigh rate performance with 68 mAh g at 5 A g (52% of capacity at 0.1 A g), and an ultralong cyclic life of 6000 cycles at 5 A g. Significantly, the BiOIO@ZPO//MnO full cell shows a good cyclic life of 67 mAh g over 1000 cycles at 0.1 A g. This work provides a new insight into the design of anodes with excellent rate capability.