Li2O2 Wetting on the (110) Surface of RuO2, TiO2, and SnO2: An Initiating Force for Polycrystalline Growth

Abstract

We report a first-principles study on the initial deposition of Li2O2 on three rutile oxide surfaces, RuO2(110)-(1×1)-O, TiO2(110), and SnO2(110). The intermediate discharge product in a Li–air battery, LiO2, is found to be less stable on all rutile surfaces and will be further reduced to Li2O2 through disproportionation reaction. For the first and second layers of deposited Li2O2, the adsorption energy is comparable to the cohesive energy of bulk Li2O2, suggesting Li2O2 will likely wet the oxide surfaces and grow into thin films rather than particles. Electronic structure analyses of interfaces demonstrate Li2O2/TiO2(110) is metallic and Li2O2/SnO2(110) is semiconducting with a bandgap of 0.2 eV, substantially smaller than in bulk Li2O2. The large lattice mismatch at these interfaces could create amorphousness of Li2O2 and grain boundaries might form abundantly thereafter, both of which can provide charge and ion transport channels needed for oxygen reduction and evolution reactions in Li–air batteries. Therefore, coating nanostructured carbon cathode with thin films of TiO2 or employing mesoporous TiO2 nanostructures as cathode could possibly lead to the formation of low-resistance Li2O2 thin films and thereby enhance the rate capacity of Li–air batteries.