Defect Chemistry in Discharge Products of Li–O2 Batteries

Abstract Li–O 2 batteries, possessing the highest theoretical specific energy density among all known Li‐ion‐based batteries, demonstrate great potential as energy storage devices for powering electric vehicles. However, their battery performance is significantly limited by the insulating nature of the discharge product Li 2 O 2 , which has a wide bandgap (4–5 eV), resulting in high charge overpotential. Defect engineering of the discharge product emerges as a very promising strategy to improve the electrical conductivity and hence reduce the charge overpotential. The aim of this review is to highlight recent advances and progress in understanding and controlling the defect chemistry of discharge products in Li–O 2 batteries. First, the theoretical perspectives of defects in Li 2 O 2 are reviewed, with particular emphasis on defect design and engineering strategies to significantly improve the charge transport properties of Li 2 O 2 . Then intermediate defects in Li 2 O 2 formed during the discharge and charge processes and materials with induced defects, including Li 2− x O 2 , doped Li 2 O 2 , Li 2 O 2 with surface/grain boundaries, and amorphous Li 2 O 2 , which are tailored by engineered catalysts and electrolyte additives are discussed. Finally, other alternative energy carriers for new energy storage chemistry of Li–O 2 batteries, such as lithium superoxide, lithium hydroxide, and lithium carbonate, will also be discussed.