Aprotic Li-O 2 batteries are regarded as the most promising technology to resolve the energy crisis in the near future because of its high theoretical specific energy. The key electrochemistry of a nonaqueous Li-O 2 battery highly relies on the formation of Li 2 O 2 during discharge and its reversible decomposition during charge. The properties of Li 2 O 2 and its formation mechanisms are of high significance in influencing the battery performance. This review article demonstrates the latest progress in understanding the Li 2 O 2 electrochemistry and the recent advances in regulating the Li 2 O 2 growth pathway. The first part of this review elaborates the Li 2 O 2 formation mechanism and its relationship with the oxygen reduction reaction/oxygen evolution reaction electrochemistry. The following part discusses how the cycling parameters, e.g., current density and discharge depth, influence the Li 2 O 2 morphology. A comprehensive summary of recent strategies in tailoring Li 2 O 2 formation including rational design of cathode structure, certain catalyst, and surface engineering is demonstrated. The influence resulted from the electrolyte, e.g., salt, solvent, and some additives on Li 2 O 2 growth pathway, is finally discussed. Further prospects of the ways in making advanced Li-O 2 batteries by control of favorable Li 2 O 2 formation are highlighted, which are valuable for practical construction of aprotic lithium-oxygen batteries.