Formation of small polarons in Li$_{2}$O$_{2}$ and implications for Li-air batteries*

Lithium-air batteries (LABs) have recently been revitalized as a promising electrical energy storage system due to their exceptionally high theoretical energy density. However, its usage is limited by poor rate capability and large polarization in the cell voltage due primarily to the formation of Li$_{2}$O$_{2}$ in the air cathode. Here, using hybrid density functional theory, we found that the formation of small polarons in Li$_{2}$O$_{2}$ is the origin that limits the electron transport in Li$_{2}$O$_{2}$. Consequently, the low electron mobility contributes to the hysteresis in cell voltage and limits the power density of the LABs. We suggest that similar behavior should exist in other peroxides, and p-type doping in Li$_{2}$O$_{2}$ could significantly improve the performance of LABs at high current densities.