Stacking Faults Inducing Oxygen Anion Activities in Li 2 MnO 3 .

Controllable anionic redox for a transformational increase in the energy density is the pursuit of next generation Li-ion battery cathode materials. Its activation mechanism is coupled with the local coordination environment around O, which posts experimental challenges for control. Here w e show the tuning capability of anionic redox by varying O local environment via experimentally controlling the density of stacking faults in Li 2 MnO 3 , the parent compound of Li-rich oxides. By combining computational analysis and spectroscopic study, w e quantitatively reveal that more stacking faults can trigger smaller Li-O-Li bond angles and larger Li-O bond distance in local Li-rich environments and subsequently activate oxygen redox reactivity, which, in turn enhances the reactivity of Mn upon the following reduction process. This study highlights the critical role of local structure environment in tunning the anionic reactivity, which provides guidance in designing high-capacity layered cathodes by appropriately adjusting stacking faults. This article is protected by copyright. All rights reserved.