BiOIO₃@Zn₃(PO₄)₂·4H₂O 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 3 is reported as an excellent insertion host and a zinc ion conductor, i.e., Zn 3 (PO 4 ) 2 ·4H 2 O (ZPO), is introduced to construct a BiOIO 3 @ZPO heterojunction with a built-in electric field (BEF). Both ZPO and a BEF obviously enhance Zn 2+ transfer and storage, which is proven by theoretical calculations and experimental studies. The conversion-type mechanism of BiOIO 3 is revealed through ex situ characterizations. The optimized electrode exhibits a high reversible capacity of 130 mAh g –1 at 0.1 A g –1, a low average discharge voltage of 0.58 V, an ultrahigh rate performance with 68 mAh g –1 at 5 A g –1 (52% of capacity at 0.1 A g –1 ), and an ultralong cyclic life of 6000 cycles at 5 A g –1 . Significantly, the BiOIO 3 @ZPO//Mn 3 O 4 full cell shows a good cyclic life of 67 mAh g –1 over 1000 cycles at 0.1 A g –1 . This work provides a new insight into the design of anodes with excellent rate capability.