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

We report a first-principles study on the initial deposition of Li 2 O 2 on three rutile oxide surfaces, RuO 2 (110)-(1×1)-O, TiO 2 (110), and SnO 2 (110). The intermediate discharge product in a Li–air battery, LiO 2, is found to be less stable on all rutile surfaces and will be further reduced to Li 2 O 2 through disproportionation reaction. For the first and second layers of deposited Li 2 O 2, the adsorption energy is comparable to the cohesive energy of bulk Li 2 O 2, suggesting Li 2 O 2 will likely wet the oxide surfaces and grow into thin films rather than particles. Electronic structure analyses of interfaces demonstrate Li 2 O 2 /TiO 2 (110) is metallic and Li 2 O 2 /SnO 2 (110) is semiconducting with a bandgap of 0.2 eV, substantially smaller than in bulk Li 2 O 2 . The large lattice mismatch at these interfaces could create amorphousness of Li 2 O 2 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 TiO 2 or employing mesoporous TiO 2 nanostructures as cathode could possibly lead to the formation of low-resistance Li 2 O 2 thin films and thereby enhance the rate capacity of Li–air batteries.