Potassium Ammonium Vanadate with Rich Oxygen Vacancies for Fast and Highly Stable Zn-Ion Storage

Vanadium-based materials have been extensively studied as promising cathode materials for zinc-ion batteries because of their multiple valences and adjustable ion-diffusion channels. However, the sluggish kinetics of Zn-ion intercalation and less stable layered structure remain bottlenecks that limit their further development. The present work introduces potassium ions to partially substitute ammonium ions in ammonium vanadate, leading to a subtle shrinkage of lattice distance and the increased oxygen vacancies. The resulting potassium ammonium vanadate exhibits a high discharge capacity (464 mAh g(-1) at 0.1 A g(-1)) and excellent cycling stability (90% retention over 3000 cycles at 5 A g(-1)). The excellent electrochemical properties and battery performances are attributed to the rich oxygen vacancies. The introduction of K+ to partially replace NH4+ appears to alleviate the irreversible deammoniation to prevent structural collapse during ion insertion/extraction. Density functional theory calculations show that potassium ammonium vanadate has a modulated electron structure and a better zinc-ion diffusion path with a lower migration barrier.

Automated summary

This study improves the structure and electrochemical properties of ammonium vanadate by introducing potassium ions, resulting in excellent cycling stability and high discharge capacity. The introduction of potassium ions alleviates deammoniation and prevents structural collapse, providing a better ion diffusion pathway.