Structural and Electrochemical Kinetic Properties of 0.5Li₂MnO₃∙0.5LiCoO₂ Cathode Materials with Different Li₂MnO₃ Domain Sizes

Lithium rich layered oxide xLi₂MnO₃∙(1−x)LiMO₂ (M = Mn, Co, Ni, etc.) materials are promising cathode materials for next generation lithium ion batteries. However, the understanding of their electrochemical kinetic behaviors is limited. In this work, the phase separation behaviors and electrochemical kinetics of 0.5Li₂MnO₃∙0.5LiCoO₂ materials with various Li₂MnO₃ domain sizes were studied. Despite having similar morphological, crystal and local atomic structures, materials with various Li₂MnO₃ domain sizes exhibited different phase separation behavior resulting in disparate lithium ion transport kinetics. For the first few cycles, the 0.5Li₂MnO₃∙0.5LiCoO₂ material with a small Li₂MnO₃ domain size had higher lithium ion diffusion coefficients due to shorter diffusion path lengths. However, after extended cycles, the 0.5Li₂MnO₃∙0.5LiCoO₂ material with larger Li₂MnO₃ domain size showed higher lithium ion diffusion coefficients, since the larger Li₂MnO₃ domain size could retard structural transitions. This leads to fewer structural rearrangements, reduced structural disorders and defects, which allows better lithium ion mobility in the material.