Since the sluggish oxygen reduction/evolution reaction (ORR/OER) hinders the practical application of Li-O-2 batteries, low cost and efficient bifunctional cathode catalysts are highly desired. LaFeO3 has attracted great interest as a promising electrocatalyst due to the abundance, low cost and non-toxity of Fe. But LaFeO3 bulk is almost inactive. Herein, we have developed a facile novel soft-template route to successfully prepare oxygen vacancies-enriched LaFeO3-x nanosheets which show a largely enhanced electrocatalytic activity on both ORR and OER. The electronic structure, bonding and coordination environment of O, Fe and La atoms have been comprehensively analyzed by X-ray photoelectron spectroscopy, Raman and soft X-ray absorption spectroscopy. Li-O-2 battery with LaFeO3-x nanosheets as catalysts show a high specific capacity, low overpotential and long cycle stability owing to the synergy of oxygen defect, Fe valence modulation and 2D nanosheets engineering. DFT calculation further reveals that oxygen adsorption will more likely occur on vacancy sites. In addition, the overpotential can be further lowered to about 0.6 V by LiI making the Li-O-2 battery with the catalysis of LaFeO3-x more practical. This study presents some insights into designing the efficient electrocatalysts for Li-O-2 battery through an integration of defect engineering, 2D nanosheets architecture and metal valence modulation. (C) 2020 Elsevier Inc. All rights reserved.