High-capacity battery cathode materials containing Li2MnO3 appear to be activated during the first electrochemical cycle through the generation of oxygen vacancies. These oxygen vacancies have been predicted to alter the atomistic scale structure of Li2MnO3 and thus impact the delithiation process. In order to understand the effects of these oxygen vacancies we computationally determine the location of lithium removal in Li2MnO3-delta (delta = 0, 0.0625 and 0.125) and study lithium diffusion in Li2-xMnO3-delta. This study shows that it is energetically favorable for the lithium vacancies to form in the neighboring positions of the oxygen vacancies, suggesting that there is a strong interaction between the two vacancy types. This interaction also inhibits the diffusion of the lithium ions, as seen in ab-initio molecular dynamics simulations where less hopping of lithium atoms is observed when oxygen vacancies are present. Additionally, the oxygen vacancy containing structures lead to an increase in the energy barrier for lithium and the calculated diffusion coefficient decreases by similar to 5 orders of magnitude from the perfect crystal structure. (C) 2016 Elsevier B.V. All rights reserved.