Enhancing the Cycle Life of Aqueous Zinc-Ion Batteries via Acid-Assisted Ammonium Vanadate Nanoflower Cathodes

Abstract

Aqueous zinc-ion batteries offer inherent safety and cost-effectiveness for grid-scale energy storage, but their practical use is hindered by the lack of high-performance cathode materials. Vanadium-based oxides with their layered structures and high theoretical capacities are promising candidates. However, issues such as vanadium dissolution and irreversible structural degradation during cycling lead to rapid capacity fading and poor cycle stability. Herein, precise structural modulation of ammonium vanadate ((NH₄)₂V₁₀O₂₅·8H₂O) is achieved via an acid-assisted hydrothermal synthesis, elucidating intrinsic structure–property relationships. Systematic studies reveal that the oxalic acid concentration in the precursor solution is the key factor governing the morphological evolution from aggregated nanoparticles to hierarchical nanoflowers. Benefiting from expanded interlayer spacing and optimized charge-transfer kinetics, the modified cathode achieves a remarkable capacity retention of 76% after 300 cycles at 1 A g^–1, outperforming most reported vanadium-based cathodes. Moreover, the assembled Zn//(NH₄)₂V₁₀O₂₅·8H₂O battery achieves a high specific capacity of 518 mAh g^–1 at 0.1 A g^–1 and exhibits excellent cycling stability, with a per-cycle capacity decay rate of only 0.0045% after 10,000 cycles at 5 A g^–1, highlighting its potential for practical applications. This work presents a universal acid-assisted synthesis strategy for designing durable cathodes in multivalent-ion battery systems.