Abstract
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.
Highlights
IntroductionThackeray et al.[4] reported that this material class is a composite material
This indicates that the electrochemical performance of lithium rich layered oxide cathode materials is largely determined by the Li2MnO3 component
The electrochemical kinetics of lithium rich layered oxide cathode materials have been studied by a few research groups using an electrochemical impedance spectroscopy (EIS) and a galvanostatic intermittent titration technique (GITT)[23,24,25,26,27]
Summary
Thackeray et al.[4] reported that this material class is a composite material These cathode materials often present domains of Li2MnO3 and LiMO2 components with a high degree of structural integration in the nanoscale regime. This can be observed using high-resolution transmission electron microscopy (HRTEM). The low electrical conductivity of the Li2MnO3 component leads to poor rate capability[18] This indicates that the electrochemical performance of lithium rich layered oxide cathode materials is largely determined by the Li2MnO3 component. This work provides a better understanding of the important parameters that influence electrochemical kinetic behaviors of lithium rich layered oxide materials for generation cathodes for lithium ion batteries
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