Lithium-oxygen (Li-O₂) batteries have been considered as an ideal solution to solving the global energy crisis. Silver (Ag) and Ag-based catalyst have been extensively studied due to their high catalytic activities in Li-O₂ batteries. However, it remains a challenge to track the catalytic mechanism during the charge/discharge process. Here, a nanoscale processing method was used to assemble a Li-O₂ nanobattery in an aberration-corrected environmental transmission electron microscope (ETEM), where a single Ag nanowire (NW) was used as catalyst for O₂ electrode. A visualization of the lithium ion insertion process during the electrochemical reactions was achieved in this nanobattery. Numerous Ag nanoparticles (NPs) were observed on the surface of the Ag NW, which were covered by the discharge product Li₂O₂. By simultaneously studying the evolution of the interface and the phase transformation, it can be concluded that these Ag NPs wrapped around Ag NW acted as catalyst during the subsequent charge/discharge reaction. Based on these studies, Ag NPs decorated on porous carbon were synthesized, and it can simultaneously improve the cycling stability (100 cycles) and the maximum specific capacity (17,371 mAh·g⁻¹ at a current density of 100 mA·g⁻¹) in a coin cell Li-O₂ battery. This study suggests that nanoscale Ag may be a promising catalyst for Li-O₂ battery.