Understanding reactions at the electrode/electrolyte interface (EEI) is essential to developing strategies to enhance cycle life and safety of lithium batteries. There is limited understanding by what means different components are formed at the EEI and how they influence EEI layer properties for positive electrodes. High-capacity layered oxides, which can generate highly reactive species toward the electrolyte via oxygen anion redox, highlight the critical need to understand reactions with the electrolyte and EEI layers for advanced positive electrodes.