Lithium vacancy migration in Li2O2: From first principles studies

Li ion diffusion in the discharge products (Li2O2) of the Li-O-2 batteries is relevant to the performance of the battery. In this paper, Li-vacancy migration in the bulk and at the surfaces of Li2O2 are studied from first principles calculations. Three low index surfaces (0001), (11 (2) over bar0) and (1 (2) over bar 00) are considered. Results show that Li vacancy migration in the Li1(2)O(2) bulk is slow with the energy barrier of 0.41 eV. On the other hand, it is found that Li-vacancy migration on the (0001) and (11 over bar 00) surface is very difficult with the high migration energy barriers of 1.22 eV and 1.06 eV, respectively, while on the (112 over bar 0) surface, Li-vacancy migration is fast with the low energy barrier of 0.34 eV. Moreover, the formation energy of Li-vacancy on the (112 over bar 0) surface is 2.65 eV, suggesting that the formation of Li-vacancy is the bottleneck for creating fast enough Li diffusion at the Li2O2 (11 (2) over bar0) surface. These results will provide the fundamental understanding of Li ion diffusion in the discharge products of the Li-O-2 battery.