While the presence of defects has been known for many years in the important family of NMC cathodes with the general formula of Li(NixMnyCoz)O2, the thermodynamics of defect formation and the influence of defects on the electrochemical performance of these compounds has been poorly understood due to the challenges of accurately resolving and quantifying these defects. We have recently developed innovative new powder diffraction methods that provide unprecedented sensitivity to defects in these materials, allowing them to be accurately quantified with an accuracy of nearly 0.1% (absolute). A systematic study of the composition dependence of the defect type and quantity has been carried out for a variety of NMC compounds using high resolution synchrotron and neutron powder diffraction data. Based on these results, it is found that the defect concentration is generally governed by thermodynamic considerations, allowing us to predict the defect concentration for any NMC composition. Furthermore, it is found that the thermodynamics of defect formation is strongly composition dependent, contradicting the most common model for defect formation and favoring an alternative driving force for defect formation.

Thermodynamic relationships between composition and defect concentration in NMC cathodes resolved using novel high-precision powder diffraction methods

2019 Fall National Meeting

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