Atomic pair distribution function research on Li₂MnO₃ electrode structure evolution

The mechanism research of structure-related reactions on Li₂MnO₃ is important to enhance the electrochemical performance of lithium-manganese-rich layered oxides. Although there are some reports on the structure evolution of Li₂MnO₃ during cycling process, the employed research techniques are very limited, mainly in/ex-situ X-ray diffraction, X-ray absorption and transmission electron microscopy. Here, atomic pair distribution function, a method to study the local atomic arrangement on the basis of average spectroscopic information, is used for the first time to study the local structure evolution of Li₂MnO₃ during electrochemical charge/discharge cycles. The results clearly demonstrate that Mn³⁺/Mn⁴⁺ redox couple is activated and Mn ions are reduced during discharging process. Some Mn ions in Mn layers can significantly migrate to Li layers and occupy the octahedral sites. As a result, a portion of inserted Li ions can occupy the face-shared tetrahedronsites, accompanied by the formation of local spinel-like structure. This work provides an important and suitable method based on the average spectroscopic information to investigate the local structure of electrode materials of lithium-ion batteries as well as other advanced battery systems.