Lithium Diffusion Mechanisms in β-LiMO2 (M = Al, Ga): A Combined Experimental and Theoretical Study

Abstract

Lithium diffusion mechanisms in β-LiMO2 (M = Al, Ga) were studied in a combined experimental and theoretical approach based on Li tracer diffusion experiments and climbing-image nudged-elastic-band (cNEB) calculations at density functional theory (DFT) level, respectively. Secondary ion mass spectrometry (SIMS) investigations were carried out for β-LiAlO2 and β-LiGaO2 polycrystalline films in the temperature range between 473 and 773 K. A thin layer of ion-beam sputtered isotope-enriched 6LiAlO2 or 6LiGaO2 was used as a tracer source. The diffusivities of β-LiGaO2 polycrystalline films are in good agreement with those measured on single crystals of the same type. The diffusivities of β-LiAlO2 are higher than in β-LiGaO2 by almost 2 orders of magnitude. This can be traced back to a lower activation energy for diffusion in β-LiAlO2. Our computational study shows that the formation energy of a Li vacancy (VLi) is much higher than that of the Li Frenkel pair (VLi + Lii) showing that Li vacancies are not abund...