Oxygen Defect Engineering toward Zero-Strain V 2 O 2.8 @Porous Reticular Carbon for Ultrastable Potassium Storage.

Potassium-ion batteries (KIBs) are promising candidates for large-scale energy storage devices due to their high energy density and low cost. However, the large potassium-ion radius leads to its sluggish diffusion kinetics during intercalation into the lattice of the electrode material, resulting in electrode pulverization and poor cycle stability. Herein, vanadium trioxide anodes with different oxygen vacancy concentrations (V 2 O 2.9 , V 2 O 2.8 , and V 2 O 2.7 determined by the neutron diffraction) are developed for KIBs. The V 2 O 2.8 anode is optimal and exhibits excellent potassium storage performance due to the realization of expanded interlayer spacing and efficient ion/electron transport. In situ X-ray diffraction indicates that V 2 O 2.8 is a zero-strain anode with a volumetric strain of 0.28% during the charge/discharge process. Density functional theory calculations show that the impacts of oxygen defects are embodied in reducing the band gap, increasing electron transfer ability, and lowering the diffusion energy barriers for potassium ions. As a result, the electrode of nanosized V 2 O 2.8 embedded in porous reticular carbon (V 2 O 2.8 @PRC) delivers high reversible capacity (362 mAh g -1 at 0.05 A g -1 ), ultralong cycling stability (98.8% capacity retention after 3000 cycles at 2 A g -1 ), and superior pouch-type full-cell performance (221 mAh g -1 at 0.05 A g -1 ). This work presents an oxygen defect engineering strategy for ultrastable KIBs.