Facet dependent cation segregation in layered lithium transition-metal oxide cathode materials

The development of energy storage devices with enough power and energy density, long term stability, and extended cycle life that are capable of meeting environmental constraints is an important challenge for modern electrochemistry. Lithium-ion batteries are the primary energy storage devices for electric vehicles. However, there are still challenges for making this technology more competitive. Improving the understanding of the fundamental processes taking place in such materials is a prerequisite to accomplish any significant improvement. For example, the segregation of transition metals (TM) from the bulk to the surface of typical cathode-oxide particles plays a critical role in the formation and composition of surface reconstruction layers (SRL) that appear on pristine and cycled materials. Such layers have been indicated as the origin of cathode impedance rise with cycling, and hence, may significantly decrease the performance of batteries. The origin and thermodynamic driving force for such segregation processes are not clear yet. In the present work, we propose a facet dependent TM segregation/phase-change mechanism to explain observed experimental results.