Ultrafast Zinc-Ion Diffusion Ability Observed in 6.0-Nanometer Spinel Nanodots

Rechargeable aqueous Zn-ion batteries (ZIBs) have recently attracted much attention due to their low cost and superior safety. Unfortunately, their low capacity and poor cycle life still hinder their practical application. Here, we have developed a general synthesis strategy for ultrasmall spinel oxide nanodots (Mn3O4, CoMn2O4, MnCo2O4.5, Co3O4, and ZnMn2O4) with abundant oxygen vacancies and highly active surface. Among them, 6.0-nanometer-sized Mn3O4 nanodots deliver the best Zn-ion storage ability with a high reversible capacity of 386.7 mA h g-1 at 0.1 A g-1, excellent rate performance, and a long-term stability of 500 cycles at 0.5 A g-1. Taking advantage of the highly activated surficial atoms, shortened transfer pathway, and introduction of numerous oxygen vacancies, an ultrahigh Zn2+ diffusion coefficient of 2.4 × 10-10 cm2 s-1 has been detected during the discharge process. This value is more than 2 orders of magnitude higher than that of other spinel oxide nanostructures in previous reports and also the highest one in all of the as-reported ZIB cathode materials to date. Our finding offers promising opportunities for the development of ZIB cathode materials with high energy density, long-term cycling stability, excellent flexibility, and wearability.