A Facile Mechanism for Recharging Li2O2 in Li--O2 Batteries

Li-air is a novel battery technology with the potential to offer very high specific energy, but which currently suffers from a large charging overpotential and low power density. In this work, we use ab initio calculations to demonstrate that a facile mechanism for recharging Li2O2 exists. Rather than the direct decomposition pathway of Li2O2 into Li and O2 suggested by equilibrium thermodynamics, we find an alternative reaction pathway based on topotactic delithiation of Li2O2 to form off-stoichiometric Li2-xO2 compounds akin to the charging mechanism in typical Li-ion intercalation electrodes. The low formation energy of bulk Li2-xO2 phases confirms that this topotactic delithiation mechanism is rendered accessible at relatively small overpotentials of {$\sim$}0.3--0.4 V and is likely to be kinetically favored over Li2O2 decomposition. Our findings indicate that at the Li2O2 particle level there are no obstacles to increase the current density, and point to an exciting opportunity to create fast charging Li-air systems.