Rationalizing the Effect of Oxygen Vacancy on Oxygen Electrocatalysis in Li–O₂ Battery

Abstract

Albeit the effectiveness of surface oxygen vacancy in improving oxygen redox reactions in Li–O2 battery, the underpinning reason behind this improvement remains ambiguous. Herein, the concentration of oxygen vacancy in spinel NiCo2O4 is first regulated via magnetron sputtering and its relationship with catalytic activity is comprehensively studied in Li–O2 battery based on experiment and density functional theory (DFT) calculation. The positive effect posed by oxygen vacancy originates from the up shifted antibond orbital relative to Fermi level (Ef), which provides extra electronic state around Ef, eventually enhancing oxygen adsorption and charge transfer during oxygen redox reactions. However, with excessive oxygen vacancy, the negative effect emerges because the metal ions are mostly reduced to low valence based on the electrical neutral principle, which not only destabilizes the crystal structure but also weakens the ability to capture electrons from the antibond orbit of Li2O2, leading to poor catalytic activity for oxygen evolution reaction (OER).

Optimizing Redox Reactions in Aprotic Lithium–Sulfur Batteries

“…The vacancy defects in materials can induce more exposed active sites for guest ions and intermediate species and thus effectively facilitate ion diffusion and charge transfer through regulating the electronic structure. [ 164–166 ] As a kind of typical defects, oxygen vacancies (V O ) in S hosts were proven to efficiently anchor LiPSs and highly facilitate the S redox reaction. [ 167 ] An example is that Ba 0.5 Sr 0.5 Co 0.8 Fe 0.2 O 3– x perovskite nanoparticles (PrNPs) as catalysts can immobilize LiPSs and induce the Li 2 S deposition in Li–S battery.…”

Optimization Design and Application of Niobium‐Based Materials in Electrochemical Energy Storage

“…[147] 2) Doped ions of different sizes or generation of certain vacancy defects can change crystal cells structure, expand lattice channels, thus enhance ions diffusion coefficient. [148] 3) Doped ions can hinder grain growth, resulting in smaller average particle size than pure. [149] In previous reports, doping and vacancy has been studied in Nb-based materials.…”

“…[149] Vacancies can significantly change the oxide electronic structure or the adsorption intermediate stability, thereby greatly enhance the electrochemical activity of oxide surface. [148] Meanwhile, the vacancy structure will greatly affect material properties, such as electronic structure, conductivity, and ion/electron diffusion rate. In fact, the electronic properties adjusted by vacancies can effectively promote charge transfer and redox reaction kinetics.…”

Challenges and Strategy on Parasitic Reaction for High‐Performance Nonaqueous Lithium–Oxygen Batteries

“…Meanwhile, the Lewis basic surface formed by high oxygen vacancy concentration leads to the unfavorable electron transfer from the discharged products to the low‐valence metal ions and hindering the decomposition of Li 2 O 2 , thereby aggravating the OER performance (Figure 7c). [ 193 ] Although cationic vacancies can also greatly affect the properties of metal compounds, large formation energy limits their application in the field of Li–O 2 battery. Metal atom doping can also be used to enhance the activity of catalysts.…”

“…Reproduced with permission. [ 193 ] Copyright 2020, Wiley. d) DEMS analysis of the evolved gases during the charge of a Li–O 2 cell with Co single‐atom catalysts/N–C and N–C cathode.…”