An air-electrode with hierarchically continuous pore architecture: a step toward “true” lithium–air batteries working with atmospheric oxygen

Lithium – air batteries (LABs) are a technology beyond lithium-ion batteries that have high energy density, but they can only operate in high-O2 atmosphere because of their low power output capability. The localized oxygen reduction reaction (ORR) clogs the porous air-electrode, prematurely stopping power generation in an air atmosphere that is ~21% O2. Here, we have developed a carbon nanotube (CNT)-based air-electrode combined with a carbon paper (CP) gas diffusion layer (GDL), denoted as CNT-with-CP. X-ray computed tomography (XCT) and mercury porosimetry reveal a hierarchical pore architecture between the CNT/CP layers. This architecture has a continuous pore distribution between the nanopores of the CNT layer and micrometer-sized CP voids, which is artificially supported inside the high porosity CP. This pore structure allows continuous O2 inhalation without the air-electrode pores being clogged, facilitating uniform ORR across the air-electrode under low-O2 gas atmosphere. This enables a fast discharge under an atmospheric O2 environment and extends the cycle life of LAB cells. Multiple stacks of CNT-with-CP air-electrodes and lithium foil anodes produced a lightweight Ah-class LAB with high energy density that operates under atmospheric O2. This battery had a discharge capacity of 1.6 Ah at a current of 0.10 A per a 5.2 g device, corresponding to an energy density of 740 Wh kg−1 at a power density of 48 W kg−1. This is the first study demonstrating a step toward ‘true’ LAB working with atmospheric O2 to provide a feasible power output in ambient air.