Urchin-like (NH₄)₂V₁₀O₂₅·8H₂O hierarchical arrays with significantly expanded interlayer spacing for superior aqueous zinc-ion batteries

The practical application of zinc ion batteries (ZIBs) can be facilitated by designing cathode materials with unique structures that can overcome the critical problems of slow reaction kinetics and large volume expansion associated with the intercalation reaction of divalent zinc ions. In this study, a novel urchin-like (NH₄)₂V₁₀O₂₅·8H₂O assembled from nanorods was synthesized by a simple hydrothermal method, noted as U-NVO. The interlayer organic pillar of cetyltrimethylammonium cation (CTAB) has been intercalated between layers to regulate the interlayer microstructure and expand the interlayer spacing to 1.32 nm, which effectively increased the contact between the electrode and electrolyte interface and shortened the diffusion path of electrolyte ions. The interlayer pillars of structural H₂O and NH₄⁺ provide a flexible framework structure and enhance the cohesion of the layered structure, which helps to maintain structural stability during the charging and discharging process, resulting in long-term durability. These unique properties result in the U-NVO cathodes demonstrating high specific capacity (401.7 mA h g⁻¹ at 0.1 A g⁻¹), excellent rate capability (99.6 % retention from 0.1 to 5 A g⁻¹ and back to 0.1 A g⁻¹), and long-term cycling performance (∼87.5 % capacity retention after 2600 cycles). These results offer valuable insights into the design of high-performance vanadium oxide cathode materials.