Xianglin Li

The lithium-oxygen (Li-O₂) battery has great potential as the next-generation energy storage technology due to the high specific capacity of lithium metal (3,864 Ah/kg) and abundant oxygen supply from the surrounding air. However, Li-O₂ batteries necessitate flow channels to deliver air or oxygen throughout the system uniformly. This requirement for flow channels, along with the balance of plant, increases the weight and volume of the entire battery system. It’s critical to maximize the mass fraction of cell materials, including lithium metal, separator, electrolyte, and positive electrode to develop practical Li-O₂ battery packs with high specific energy. Therefore, utilizing lithium metal with a decent thickness is essential to compete with other energy storage systems such as Li-ion batteries. Meanwhile, the positive electrode must be porous, with high surface area and pore volume, to accommodate the solid product (primarily Li₂O₂) during discharge and charge cycles. A simple mass balance analysis suggests that the positive electrode in Li-O₂ batteries should have a thickness on the order of 0.5 mm, and the mass loading of the active positive materials (e.g., carbon) should be on the order of 50 mg/cm² or higher.

However, positive electrodes with high mass loading and thickness pose challenges for mass transfer during oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). This presentation will focus on the importance of transport phenomena in positive electrodes, where ORR and OER occur. We will discuss the critical role of convection, pore size, porosity, and electrode wettability in Li-O₂ batteries. Understanding these factors will establish design criteria for advanced positive electrodes, significantly enhancing the area capacity, specific energy, and specific power of Li-O₂ batteries.