(Invited) Carbon Nanostructure for Flexible Zinc Ion Storage

Abstract

We will discuss various carobn nanostructures and their derivates for zinc ion storage, for example, a zinc ion capacitor based on carbon nanotubes. In addition, prussian blue analogue (PBA)-type metal hexacyanoferrates have been considered as significant cathode materials for aqueous rechargeable zinc batteries (ZBs) due to the open face centered cubic framework, multiple active sites, and environmental benign. However, these PBA-type cathodes, such as cyanogroup iron hexacyanoferrate (FeHCF), suffer from ephemeral lifespan (≤1000 cycles), inferior rate capability (1A g-1), and low operating voltage (ca. 1.2 V). This is because the redox active sites of multivalent iron (Fe(III/II)), which dominates its electrochemical activities, can only be very limited activated and thus utilized. The limited activity is attributed to the spatial resistance caused by the compact cooperation interaction between Fe and the surrounded six cyanogroup per unit, and the inferior conductivity. In this paper, surprisingly, we found high-voltage-scanning can effectively activate the C-coordinated Fe (redox active sites) in FeHCF cathode in ZBs. The activation spurred the increase of capacity at a high operating voltage plateau of ca. 1.5 V. Thanks to this activation, the Zn-FeHCF hybrid-ion battery achieved a record-breaking cycling performance of 5000 (82% capacity retention) and 10000 cycles (73% capacity retention), respectively, together with a superior rate capability of maintaining 53.2% capacity at super-high current density of 8 A g-1 (ca. 97 C). Figure 1