Replacing Li2O2 with LiO2 as the discharge product is a very promising strategy to tackle the problems of high overpotential (~ 1.5V), 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 (~ 0.3V), 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.