Grain boundary phase transformations in LiNi0.8Co0.15Al0.05O2 positive electrode material

Abstract

The microstructure of LiNi0.8Co0.15Al0.05O2 positive electrode material before and after the first cycle has been investigated by scanning transmission electron microscopy (STEM) and electron energy loss spectroscopy (EELS). STEM and EELS analysis shows that the thickness of some grain boundary layers increases significantly during the first cycle. Also, from the grain interior to the grain boundary, the structure gradually changes from an ordered layer structure (a-NaFeO2-type) to a partially ordered structure and then to a disordered rock-salt structure. We posit that these microstructural changes are primarily responsible for the irreversible capacity during the first cycle.