Evaluation of Commercial Li-ion Cells Based on Composite Electrode for Plug-In EVs

Evaluating commercial Li-ion batteries presents some unique benefits. One of them was to use cells made from established fabrication process and form factor, such as those offered by the 18650 cylindrical configuration, to provide a common platform to investigate and understand performance deficiency and aging mechanism of target chemistry. Such an approach afforded to derive relevant information without influence from processing or form factor variability that may skew our understanding on cell-level issues.

A series of 1.9 Ah 18650 lithium ion cells developed by a commercial source using a composite positive electrode comprising {LiMn_1/3Ni_1/3Co_1/3O₂ + LiMn₂O₄} were being used as a platform for the investigation of certain key issues, particularly path-dependent aging and degradation in future plug-in hybrid electric vehicle (PHEV) applications, under the US Department of Energy’s Applied Battery Research (ABR) program.

Due to the composite nature of the positive electrode, the features (or signature) derived from the incremental capacity (IC) of the cell appear rather complex. In this work, the method to index the observed IC peaks was discussed. Being able to index the IC signature in detail was critical for analyzing and identifying degradation mechanism later in the cycle aging study. Research conducted for this project was completed in the PakaLi Battery Laboratory.