Correlating Structure Change With Magnetic Ordering and Spin Fluctuation During Delithiation of Transition Metal Layered Oxide

ABSTRACT Current Li‐ion battery technology relies on Li + insertion/extraction coupled with electron gaining/loss at both cathodes and anodes. Although extensive efforts have been devoted to studying the structure change of cathode materials with Li + extraction/insertion, changes in the magnetic properties arising from the accompanying redox processes have been largely overlooked. Here, we systematically investigate both the structure evolution and magnetic‐property changes during the delithiation of the representative layered oxide LiCoO 2 , by combining the operando synchrotron‐based x‐ray diffraction with dedicated magnetic measurements. We construct a magnetic phase diagram as a function of Li content x in Li x CoO 2 , which closely mirrors the corresponding structure evolution diagram. The results reveal a series of complicated magnetic transitions upon Li extraction: paramagnetic → antiferromagnetic → paramagnetic → diamagnetic → paramagnetic. Moreover, the variation in the effective magnetic moment of Co 4+ is strongly correlated with local structural changes within the CoO 6 octahedra, indicating that the Co 4+ spin‐state fluctuation may play an important role in the structure evolution and electrochemical performance. These findings help close a critical gap in understanding structure‐magnetism coupling during the electrochemical cycling and may inspire the design of new layered oxide cathodes from a spin‐electronics perspective.