Alkali ion doping in ammonium vanadate nanoflowers for superior aqueous zinc-ion batteries

Abstract

Layered vanadium-based cathodes are promising for high-capacity aqueous zinc-ion batteries (AZIBs), but suffer from structural instability, rapid capacity decay, and sluggish kinetics. Herein, we develop an alkali metal ion (Na⁺, K⁺) doping strategy enhancing the performance of (NH₄)₂V₆O₁₆ nanoflowers through the synergistic integration of interlayer engineering, defect engineering, and morphological optimization. In particular, the optimized NaNVO exhibits superior capacity (585 mAh g⁻¹ at 0.2 A g⁻¹) and remarkable cycling stability (87% retention over 4000 cycles at 10 A g⁻¹). Alkali ions dually stabilize V–O interlayers and generate oxygen vacancies via charge compensation, synergistically expanding Zn²⁺ diffusion channels and creating additional storage sites. DFT calculations reveal that vacancy-induced band structure modulation weakens Zn²⁺–host interactions, reduces migration barriers, and improves charge transfer efficiency. The hierarchical nanoflower architecture further establishes continuous charge transport networks via shortened ion pathways and maximized interfacial reactivity, enhancing the kinetics. These distinct structural and electronic modifications work in concert, with pillars suppressing lattice distortion, defects enabling charge redistribution, and morphology ensuring cycling integrity. The combined modifications favor Zn²⁺-dominated co-intercalation, suppressing H⁺-induced distortion and enabling reversible byproduct evolution. This work offers new perspectives for rationally designing high-performance AZIB cathodes.