Understanding the Origin of Li2MnO3Activation in Li-Rich Cathode Materials for Lithium-Ion Batteries

摘要

Li-rich layered cathode materials have been considered as a family of promising high-energy density cathode materials for next generation lithium-ion batteries (LIBs). However, although activation of the LiMnO phase is known to play an essential role in providing superior capacity, the mechanism of activation of the LiMnO phase in Li-rich cathode materials is still not fully understood. In this work, an interesting Li-rich cathode material LiMnNiO is reported where the LiMnO phase activation process can be effectively controlled due to the relatively low level of Ni doping. Such a unique feature offers the possibility of investigating the detailed activation mechanism by examining the intermediate states and phases of the LiMnO during the controlled activation process. Combining powerful synchrotron in situ X-ray diffraction analysis and observations using advanced scanning transmission electron microscopy equipped with a high angle annular dark field detector, it has been revealed that the subreaction of O generation may feature a much faster kinetics than the transition metal diffusion during the LiMnO activation process, indicating that the latter plays a crucial role in determining the LiMnO activation rate and leading to the unusual stepwise capacity increase over charging cycles.