[en] Highlights: • A Li-O₂ battery based on amorphous LiO₂ has been built for the first time. • Amorphous LiO₂ has been identified by In-situ Raman spectrum, linear sweep voltammetry and UV–vis measurements. • The LiO₂-based Li-O₂ battery shows an ultralow overpotential, high rate capability and long cycling stability. • A synchronized reduction strategy was proposed to prepare 3D-architectured Pd-rGO catalyst. • The side reactions have been mitigated due to the significant decrease of the oxidation potential. Replacing Li₂O₂ with LiO₂ as the discharge product is a very promising strategy to tackle the problems of high overpotential (~ 1.5 V), inferior rate capability and short cycle life in the current Li-O₂ batteries based on Li₂O₂. But it's very difficult to control LiO₂ due to its thermodynamic instability. Herein, we have successfully built a facile rechargeable Li-O₂ battery based on the formation and decomposition of amorphous LiO₂ with an ultralow overpotential (~ 0.3 V), long cycle life and high rate capability under the catalysis of 3D-architectured Pd-rGO. In-situ Raman spectrum, linear sweep voltammetry, UV–vis measurements and SAED (Selected Area Electron Diffraction) all have identified the amorphous LiO₂-based electrochemical process. Amorphous LiO₂ shows a lower oxidation potential and a faster ionic conductivity contributing to the excellent electrochemical performances and the mitigation of undesirable side reactions. This study opens a new horizon to solve the intrinsic problems of the current Li-O₂ batteries.