Structure and oxygen-defect regulation of hydrated vanadium oxide for enhanced zinc ion storage via interlayer doping strategy

Hydrated vanadium oxide (VOH) is a promising cathode candidate for the aqueous zinc-ion batteries (AZIBs), due to the large interlayer spacing and high capacity. However, severe pulverization and structure collapse upon cycling limit its practical application. Herein, preintercalation strategy with higher positive charge of Cr³⁺ is proposed to regulate the structure and oxygen defect of the VOH-O_d. The VOH-O_d with moderated amount of Cr³⁺ incorporation (M-CrVOH-O_d), showing a flower-like hierarchical structure assembled with thin nanosheets, can expand the interlayer spacing and increase the oxygen defect, inducing an enhanced high-rate cycling capability. As a result, M-CrVOH-O_d delivers a high capacity of 405 mAh·g⁻¹ at 0.5 A·g⁻¹, high capacity retention of 120% over 3,500 cycles, as well as an extraordinary energy output (297.3 Wh·kg⁻¹ at 355.9 W·kg⁻¹). The density functional theory (DFT) calculations can prove the enhanced reaction kinetics with narrower bandgap and lower Zn²⁺ adsorption energy after the Cr-preintercalation. Meanwhile, based on the ex-situ X-ray diffraction (XRD) analysis, synergistic intercalation of the Zn²⁺/H⁺ into the interlayers of M-CrVOH-O_d can bring the high specific capacity. This work could help us understand the enhanced performance of VOH from the point of the chemical reactions.