Critical Descriptor for the Rational Design of Oxide-Based Catalysts in Rechargeable Li–O₂Batteries: Surface Oxygen Density

Abstract

Li−O 2 batteries provide high-capacity energy storage, but for aprotic Li−O 2 batteries, it is reported that the charge−discharge efficiency is ultimately limited by the crystal growth of insoluble Li 2 O 2 on the porous cathode. Catalysts have been reported to improve the nucleation and morphology of Li 2 O 2 , which helps achieve high energy densities. We provide a new insight into the catalytic mechanism of the oxygen reduction reaction (ORR) in aprotic Li−O 2 batteriesthe oxygen sites on the surface play a more important role than the exposed metal sitesvia a study based on the density functional theory (DFT) examining α-MnO 2 surfaces. Lithium ions from electrolytes are found to interact with the surface oxygen sites and form surface lithium sites, facilitating further growth of Li 2 O 2 . A larger number of initial growth points with uniform distribution makes Li 2 O 2 well dispersed, forming small particles, which benefit both the ORR and oxygen evolution reactions (OER). This design concept for oxygen sites has been successfully validated by the real Li−O 2 cell experiments with α-MnO 2 nanowire cathodes.

Advances in Manganese‐Based Oxides Cathodic Electrocatalysts for Li–Air Batteries

“…The initial reactions process includes the adsorption, dissociation, and one‐electron reduction of O 2 molecules at cathode/electrolyte interfacewhere the dissolved O 2 molecules in solution are absorbed onto the active sites of the cathode surface in the initial stage of discharging (Equation ). After that, the adsorbed O 2 molecules (expressed as O 2 *, and “*” refers to the adsorbed species) are reduced and bonded with solvated Li + cations to form adsorbed LiO 2 by one‐electron reduction reaction (Equation ) …”

High‐Energy‐Density Metal–Oxygen Batteries: Lithium–Oxygen Batteries vs Sodium–Oxygen Batteries

“…[78] The morphology of the final discharge products can be also tuned by the current density. In metal-oxide catalysts, surface oxygen sites can act as anchoring or growth sites for the discharge product, [82,83] through chemical bonding between surface oxygen sites and Li ions (Figure 9). [78,79] The influence of cell operation temperature has been also studied by Tan et al, who showed that the higher the operation temperature, the larger the particle size of Li 2 O 2 .…”

“…[78,79] The influence of cell operation temperature has been also studied by Tan et al, who showed that the higher the operation temperature, the larger the particle size of Li 2 O 2 . [82] To validate this prediction, [002] and oriented α-MnO 2 nanowires (NWs) were also studied, to investigate the morphological differences of the discharge products after the initial discharge. [80] Because the cathode catalyst can modulate the nucleation and growth of Li 2 O 2 , it can somehow affect the electrochemical performance of Li-O 2 cells.…”

“…Reproduced with permission [82]. The "x"-marked O atoms are in a vertex position, while the others are in a plane position.…”

Anomalous Enhancement of Li‐O2 Battery Performance with Li2O2 Films Assisted by NiFeOx Nanofiber Catalysts: Insights into Morphology Control

“…However, many challenges, including poor rate capability, high charge overpotentials, and limited cyclic stability, should be addressed before any real‐world application of LOBs . The sluggish oxygen evolution, the poor contact with the electrode/electrolyte, and the insulating nature of the discharge product are the intrinsic limit for the aforementioned drawbacks of LOBs . They not only limit the depth of the oxygen reduction reaction (ORR) but also raise the barriers for oxygen evolution reaction (OER).…”