Results of Screening over 200 Pristine Lithium-Ion Cells

This paper presents and analyses results from simplified screening tests conducted on more than 200 large format Kokam NMC lithium-ion pouch cells at their beginning of life. Such data are not common in the literature. The cells were sandwiched between two large heat sinks for testing, which was conducted using an automated dis/charge test system and thermal chambers. Analysis of the screening data gives valuable quantitative information, but also qualitative insights into the nature of cell-to-cell variations and the complex interactions between battery temperature, capacity, voltage or internal resistance. In this paper, statistical results show that the cells under test present small cell-to-cell differences in capacities and internal resistances at their beginning-of-life. For example, the relative standard deviation is below 0.4 % for the capacities and 2.5 % for the pure ohmic plus polarization resistances. However, these differences may be enhanced by system level issues, and exacerbated over time by complex degradation mechanisms.