Due to their high theoretical specific capacity and energy density, Li-O-2 batteries are considered as candidates for next-generation battery systems in place of conventional Li-ion batteries for advanced applications such as electric vehicles. However, low energy efficiency, poor cycle life, and Li-metal safety issues make the use of Li-O-2 batteries yet impractical. In addition, actual cell capacities are very low, and since only small-scale electrodes are currently tested, it is hard to predict the properties of large-size electrodes and cells, thus evaluating and judging real practical challenges related to this battery technology. In this work, the behavior of pouch-type Li-O-2 cells using 3 Chi 5 cm(2) sized electrodes is investigated and it is confirmed that Li-metal is a key issue for the upscale of Li-O-2 cells. This study can help to determine which parameters are the most important for developing practical Li-O-2 batteries.