Unlocking the Zn storage performance of ammonium vanadate nanoflowers as high-capacity cathodes for aqueous zinc-ion batteries via potassium ion and ethylene glycol co-intercalation engineering

Abstract

Ammonium vanadate (NH₄V₄O₁₀) is a highly promising cathode for aqueous zinc ion batteries (AZIBs) due to its tunable layered structure and high specific capacity; however, limited active sites, poor kinetics and irreversible structural collapse during cycling suppress its wide application. Herein, the engineering of the co-intercalation of K⁺ and ethylene glycol molecules is proposed to unlock the Zn storage performance of NH₄V₄O₁₀. It is found that the co-intercalation of K⁺ and ethylene glycol enlarges the interlayer spacing to 11.5 Å, induces a high level of oxygen vacancies and enhances the strength of ionic bonding in NH₄V₄O₁₀, ensuring large Zn²⁺ diffusion channels, efficient redox reactivity and strong layered-structure stability. Meanwhile, K⁺ ions and ethylene glycol also weaken the crystallinity of NH₄V₄O₁₀ and induce the transformation of microscopic morphology from strips to nanoflowers self-assembled from ultrathin nanosheets, promoting the transfer of electrons and ions and complete penetration of the electrolyte during electrochemical reactions. In addition, the band gap is significantly reduced by 0.2 eV after the co-intercalation of K⁺ and ethylene glycol, improving the electronic conductivity and decreasing the diffusion barrier of Zn²⁺. As expected, K⁺ ions and ethylene glycol co-intercalated NH₄V₄O₁₀ exhibits excellent Zn storage properties, delivering an ultrahigh capacity of 614.1 mA h g⁻¹ at 0.5 A g⁻¹ and presenting an outstanding rate performance of 472.9 mA h g⁻¹ and a high retention of 89% after 2000 cycles at 10 A g⁻¹. This work provides a useful reference for unlocking the Zn storage performance of layered V-based cathodes for AZIBs by synergistically modulating the interlayer spacing, oxygen defects and microscopic morphology of the materials.