Three-dimensional morphological measurements of LiCoO2 and LiCoO2/Li(Ni1/3Mn1/3Co1/3)O2 lithium-ion battery cathodes

The three-dimensional (3D) morphologies of two types of lithium-ion battery cathodes, LiCoO2 (LCO) and LiCoO2/Li(Ni1/3Mn1/3Co1/3)O2 (LCO/NMC) composites, have been measured using focused ion beam – scanning electron microscopy (FIB-SEM) and transmission X-ray microscopy (TXM). TXM measurements were taken at X-ray energies that can provide clear contrast between LCO and NMC particles in the composite cathodes. Multiple three-dimensional image volumes were collected and statistical analyses were done to assess the accuracy and spatial variation of structural parameters including oxide volume fractions, surface areas, and particle size distributions. Comparisons of un-cycled and cycled batteries showed small changes in structure, but spatial and cell-to-cell microstructural variations, found especially in the LCO/NMC cathodes, were large enough to limit the ability to distinguish actual cycling-induced structure changes. The observation of cathode metal cations on the battery anode after cycling may explain, at least in part, the observed ∼30% capacity loss.

► 3D morphologies of LiCoO2 and LiCoO2/Li(Ni1/3Mn1/3Co1/3)O2 cathodes were evaluated.
► FIB-SEM and transmission X-ray microscopy (TXM) tomographic methods were compared.
► Statistical analyses were done on multiple image volumes to assess data accuracy.
► Spatial and cell-to-cell microstructure variations were found in cathodes.
► Transition metal elements found on anode may explain the capacity fade.