<i>(Invited)</i> Achieving 1,000 Kwh/Kg Energy Density Using Li-O ₂ Batteries

The lithium-oxygen (Li-O 2 ) battery is known for its exceptionally high theoretical energy density, driven by the high specific capacity of lithium metal (3,864 Ah/kg) and the abundant oxygen sourced from ambient air. However, to achieve optimal performance, it is critical to design flow channels that ensure uniform oxygen delivery throughout the system. Maximizing energy density at the cell and pack levels necessitates the use of thick lithium metal (~0.5 mm) and robust positive electrodes with high surface area and pore volume to accommodate the formation of solid products (primarily Li 2 O 2 ) during discharge and charge cycles. A simple mass balance analysis shows that the positive electrode in Li-O 2 batteries should have a high mass loading (approximately 50 mg/cm 2 ) of active materials. Electrodes with high mass loading and significant thickness present considerable challenges for mass transfer during the oxygen reduction and evolution reactions, which significantly impacts the utilization of both positive and negative materials. In this talk, we will present our recent advancements in Li-O 2 flow batteries, which have achieved capacities greater than 100 mAh/cm 2 and energy densities exceeding 1,000 Wh/kg. The calculation of energy density includes the weights of lithium, oxygen, the separator, the positive electrode, and the electrolyte within the separator and positive electrode. We emphasize the high utilization of both the positive and negative electrodes and focus on areal capacity and cell-level energy density. Our flow battery design investigates the pivotal roles of convection, the properties of porous positive electrodes, and electrolytes in achieving high areal capacity, specific energy, and specific power of Li-O 2 batteries. By setting new benchmarks in cell-level energy density for next-generation energy storage technology, our research aims to inspire renewed interest in Li-O 2 batteries and guide new research directions in developing rechargeable batteries with both high energy and power densities.