Insights into Micromorphological Effects of Cation Disordering on Co-Free Layered Oxide Cathodes

Controlling Li/Ni disordering has always been a priority in designing Co-free layered oxide cathodes. The Li/Ni disordering is an atomic-scale structural defect that has been extensively studied by macroscopic statistical characterizations. Significantly less is known about its microstructure in the layered structure and correlations with electrochemical performance. In this work, combining multiscale structural characterizations, it is found that Li/Ni disordering surprisingly takes various microstructural forms in Co-free layered cathodes. Li/Ni disordering at insufficient calcination temperature tends to manifest as localized rock salt nanodomain in the layered structure. However, an excessively high calcination temperature causes Li/Ni disordering as a massive rock salt phase inside the particles. Only at an appropriate calcination temperature, the Li/Ni disordering is present in the layered structure as the form of well-known anti-site defects. These microstructural differences lead to widely varying electrochemical performance, and an in-depth structure-performance connection is built. Besides, the above results also reflect that more careful and precise control of experimental conditions is required to synthesize Co-free layered cathodes. These findings may inspire the design of novel Co-free cathodes and light the way forward.