Polypyrrole pre-intercalation engineering-induced NH removal in tunnel ammonium vanadate toward high-performance zinc ion batteries.

Ammonium vanadate with stable bi-layered structure and superior mass-specific capacity have emerged as competitive cathode materials for aqueous rechargeable zinc-ion batteries (AZIBs). Nevertheless, fragile NH…O bonds and too strong electrostatic interaction by virtue of excessive NH will lead to sluggish Zn ion mobility, further largely affects the electro-chemical performance of ammonium vanadate in AZIBs. The present work incorporates polypyrrole (PPy) to partially replace NH in NHVO (NVO), resulting in the significantly enlarged interlayers (from 10.1 to 11.9 Å), remarkable electronic conductivity, increased oxygen vacancies and reinforced layered structure. The partial removal of NH will alleviate the irreversible deammoniation to protect the laminate structures from collapse during ion insertion/extraction. The expanded interlayer spacing and the increased oxygen vacancies by the virtue of the introduction of polypyrrole improve the ionic diffusion, enabling exceptional rate performance of NHVO. As expected, the resulting polypyrrole intercalated ammonium vanadate (NVOY) presents a superior discharge capacity of 431.9 mAh g at 0.5 A g and remarkable cycling stability of 219.1 mAh g at 20 A g with 78 % capacity retention after 1500 cycles. The in-situ electrochemical impedance spectroscopy (EIS), in-situ X-ray diffraction (XRD), ex-situ X-ray photoelectron spectroscopy (XPS) and ex-situ high resolution transmission electron microscopy (HR-TEM) analysis investigate a highly reversible intercalation Zn-storage mechanism, and the enhanced the redox kinetics are related to the combined effect of interlayer regulation, high electronic conductivity and oxygen defect engineering by partial substitution NH of PPy incorporation.