Evaluation of commercial lithium-ion cells based on composite positive electrode for plug-in hybrid electric vehicle applications. Part II. Degradation mechanism under 2 C cycle aging

Degradation phenomena and inference of their underlying mechanisms during 2 C cycle aging in a cell design comprising {LiMn1/3Ni1/3Co1/3O2 + LiMn2O4} composite positive electrode are studied and reported in this work. We describe how aging phenomena in the cells were studied and incremental capacity analysis applied to infer cell degradation mechanisms in the cycle aging process. Two stages of degradation were observed in the life cycle under this aging regime. In the first stage, we conclude that loss of lithium inventory was the cause of capacity fade. As a result of such parasitic loss, the cell further suffered from loss of active materials in the second stage, in which the positive electrode kinetics was hampered and the capacity loss accelerated.

► Cell variations in performance and quantitative assessment of cell quality. ► The incremental capacity signature of the cell chemistry, which was indexed and explained. ► Cell degradation characterization using a 2 C cycle aging regime. ► A unique analysis and logic development to identify the cell performance changes and the underlying mechanisms. ► A map of the cell degradation that exhibits the quantitative correlations of degree of capacity fades with fading mechanism and cycle number.