Enabling Fast and Stable Zinc-Ion Storage in Vanadyl Phosphate Cathodes

Abstract

VOPO₄·2H₂O (VOP) has attracted significant attention as a cathode material for aqueous zinc-ion batteries owing to its layered structure and high-voltage plateau. However, its application is hindered by sluggish Zn²⁺ transport kinetics and instability in aqueous electrolytes, leading to rapid capacity fading over cycling. In the present work, a diethylene glycol (DEG) pre-intercalated VOP (DEG-VOP) with flower-like morphology is prepared by a facile hydrothermal method. The DEG molecules enlarge the interplanar lattice of the (001) plane and introduce oxygen vacancies, accelerating the mass and charge transfer kinetics. In addition, the pre-intercalation induces the self-assembly of nanosheets into a flower-like structure, which exposes more (201) planes, providing additional ion channels. The pre-intercalation of DEG also enhances the hydrophobicity of VOP, effectively suppressing its decomposition and dissolution. These result in a significantly improved discharge capacity, with a capacity retention of 86% after 2000 cycles at 1 A g^–1.