Lithium vacancy migration in Li2O2: From first principles studies

Abstract Li ion diffusion in the discharge products (Li2O2) of the Li-O2 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 ¯ 0) and (1 2 ¯ 00) are considered. Results show that Li-vacancy migration in the Li12O2 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 (1 1 ¯ 00) surface is very difficult with the high migration energy barriers of 1.22 eV and 1.06 eV, respectively, while on the (11 2 ¯ 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 (11 2 ¯ 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 ¯ 0) surface. These results will provide the fundamental understanding of Li ion diffusion in the discharge products of the Li-O2 battery.