Three-dimensional morphological measurements of LiCoO_2 and LiCoO_2/Li (Ni_(1/3)Mn_(1/3)Co_(1/3))O_2 lithium-ion battery cathodes

摘要

The three-dimensional (3D) morphologies of two types of lithium-ion battery cathodes, LiCoO_2 (LCO) and LiCoO_2/Li(Ni_(1/3)Mn_(1/3)Co_(1/3)O_2 (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 mkrostructural variations, fguad espe-aally in the ICO/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.