Intercalant-induced V <i>t</i>_<i>2</i><i>_g</i> orbital occupation in vanadium oxide cathode toward fast-charging aqueous zinc-ion batteries.

Abstract

Intercalation-type layered oxides have been widely explored as cathode materials for aqueous zinc-ion batteries (ZIBs). Although high-rate capability has been achieved based on the pillar effect of various intercalants for widening interlayer space, an in-depth understanding of atomic orbital variations induced by intercalants is still unknown. Herein, we design an NH₄⁺-intercalated vanadium oxide (NH₄⁺-V₂O₅) for high-rate ZIBs, together with deeply investigating the role of the intercalant in terms of atomic orbital. Besides extended layer spacing, our X-ray spectroscopies reveal that the insertion of NH₄⁺ could promote electron transition to 3<i>d_xy</i> state of V <i>t</i>_<i>2</i><i>_g</i> orbital in V₂O₅, which significantly accelerates the electron transfer and Zn-ion migration, further verified by DFT calculations. As results, the NH₄⁺-V₂O₅ electrode delivers a high capacity of 430.0 mA h g^-1 at 0.1 A g^-1, especially excellent rate capability (101.0 mA h g^-1 at 200 C), enabling fast charging within 18 s. Moreover, the reversible V <i>t</i>_<i>2</i><i>_g</i> orbital and lattice space variation during cycling are found via ex-situ soft X-ray absorption spectrum and in-situ synchrotron radiation X-ray diffraction, respectively. This work provides an insight at orbital level in advanced cathode materials.