Interlayer-modified pseudocapacitive ammonium vanadium with high reversibility and stability enabling high-performance aqueous zinc-ion battery

Vanadium oxides are vital electrode material for zinc-ion batteries (ZIBs). However, the structural instability of vanadium oxides and sluggish reaction kinetics of large radius Zn2+ hinder the development of ZIBs. In this work, interlayer engineering and intercalation pseudocapacitance are adopted by phosphating to obtain modified NH4V4O10 with a stable structure, stronger intercalation pseudocapacitive behavior, and high reversibility for ion transportation. The phosphating introduces phosphate groups and oxygen vacancies in the lattice of NH4V4O10. The phosphate groups strengthen the connection between [VO] layers and immobilize the intrinsic interlayer NH4+ through electrostatic interaction to inhibit the irreversible transport of NH4+. The phosphating treatment disorders the crystal structure of the material and enlarges the crystal plane spacing to accelerate the diffusion of the ions, leading to high reversibility and structural stability, which prevents the irreversible phase transition of active material to inactive by-product during the cycle. Combined with the kinetics analysis and density functional theory (DFT), the phosphating enhances the intercalation pseudocapacitive response (pseudocapacitive contribution of 84.9%), reduces the migration barrier of Zn2+, as well as improves the electronic conductivity of cathode and affords extra electrons for energy storage, thus resulting in superior performance. Therefore, the PNVO-2 electrode delivers a brilliant rate performance of 300.9 mAh g-1 at 10 A g-1, and high capacity retention of 92.3% after 7000 cycles at 10 A g-1. P-NVO-2 exhibits brilliant electrochemical performance when applied to the flexible soft-packaged battery, confirming the application potential. Therefore, the exploration of phosphating to vanadium oxides supplies a promising route for designing high-rate and long-cyclicality zinc-ion batteries.