Abstract
Lithium rich layered oxide xLi(2)MnO(3)∙(1-x)LiMO(2) (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 0.5Li(2)MnO(3)∙0.5LiCoO(2) materials with various Li(2)MnO(3) domain sizes were studied. Despite having similar morphological, crystal and local atomic structures, materials with various Li(2)MnO(3) domain sizes exhibited different phase separation behavior resulting in disparate lithium ion transport kinetics. For the first few cycles, the 0.5Li(2)MnO(3)∙0.5LiCoO(2) material with a small Li(2)MnO(3) domain size had higher lithium ion diffusion coefficients due to shorter diffusion path lengths. However, after extended cycles, the 0.5Li(2)MnO(3)∙0.5LiCoO(2) material with larger Li(2)MnO(3) domain size showed higher lithium ion diffusion coefficients, since the larger Li(2)MnO(3) 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.