Effective Methods to Screen out Li-Ion Cells with Subtle Defects

Several methods are currently being used to predict and reject lithium-ion cells for soft or subtle shorts.  Some of the methods include self-discharge tests at full SOC, self-discharge tests at 0% SOC, self-discharge tests at very low SOC, etc.  An elaborate test program was carried out to compare these tests and determine if these are a true reflection of contaminants or other defects inside a lithium-ion cell.  Cycle life testing of cells that failed the criteria established as well as destructive physical analysis with SEM and EDS analysis were also carried out on the samples tested under these different self-discharge tests protocols.  In addition, traditional tests carried out at NASA-JSC to stringently screen cells for defects and internal shorts will also be discussed. This paper will address the topic of whether there are good methods to detect internal cell defects in li-ion cells.