Establishing the criteria and strategies to achieve high power during discharge of a Li–air battery†
The capacity of lithium–air (Li–air) batteries fades quickly with an increase in the operating current density resulting in a trade-off between energy and power. Improvements in energy and power densities are possible through appropriate material selection which is, however, impeded by the complexity in relating the rate dependent discharge capacity to the physicochemical properties of the electrode and electrolyte of the cell. Here, we investigate the capacity decay of Li–air batteries with an increase in the discharge current and our results show that oxygen-transport limitation is the most critical factor at high rates. We also demonstrate that for a certain cell configuration there is a critical current density above which the discharge capacity decays at a faster rate setting a criterion of an upper limit of the operating current before the energy–power-trade-off becomes more significant. We further show that this critical current is directly related to the area, porosity and thickness of the electrode as well as the concentration and diffusion coefficient of oxygen in the electrolyte. This relationship makes it possible to establish a strategy for high-power discharge in Li–air batteries by manipulating the material properties of the cell.