Reversible Oxygen Redox Chemistry in Aqueous Zinc-Ion Batteries: Hype or Reality?

Conventional rechargeable aqueous Zn-ion batteries (ZiBs)storecharges through the ion insertion/extraction process involving thecationic redox conversion mechanism. However, the ZiB based on thecationic redox conversion mechanism provides limited specific capacityand energy density, which can be enhanced by triggering the oxygenredox chemistry (ORC). Therefore, the ORC has received significantattention from the perspective of innovative material design and electrolyteformulation. Only a few reports are available on the ORC process inZiBs, but the in-depth understanding of the process is still unclear.A layered-type V2P2O9 cathode materialis proposed for enhancing the ZiB performance, which exhibited theORC process at a high working potential window along with cationicredox conversion in the 1 M Zn(OTf)(2) + 21 M LiTFSI "water-in-salt"(WiS) electrolyte. The ORC process not only enhanced the capacityperformance but also improved the electrochemical stability windowup to & SIM;3.0 V. The ORC and cationic redox conversion processeswere investigated through several ex situ and in situ techniques by O-18 isotope labeling. The in situ Raman spectra by O-18 isotope labelingand ex situ XPS spectra confirmed the ORC pathwaydemonstrating the 2O(2-) & LRARR; O-2 ( n-) redox conversion. This finding opensup an opportunity to design a suitable cathode material and electrolyteformulation for high-performance ZiBs.