The evaluation of lithium ion battery safety has traditionally focused on the performance of single cells exposed to abusive conditions. As lithium ion batteries are fielded in increasingly large and complex systems, the system level safety performance is becoming of greater concern. Testing laboratories and battery end users have begun to consider the hazards associated with a localized thermal runaway event, a single cell or small group of cells, propagating to the bulk of a large battery system. Evaluating this propagating failure requires initiating thermal runaway of a single cell or group of cells and observing how that failure affects the surrounding system.

A major uncertainty in this testing is the impact of the initial thermal runaway initiation. The common means of initiating this testing is through abusive battery tests, but the intensity of failure may vary with the test performed and the surrounding cells potentially influenced, which in turn leads to uncertainty in the test results. This work looks at the potential impact of various failure initiating methods on the results of a propagating battery failure. Figure 1 shows a comparison of overcharge failure (left) and a nail penetration failure (right) on a 5 cell pouch cell pack. This particular result shows some change in the initial failure intensity, and the time required to initiate a failure is significantly increased in the case of the overcharge test. However, once failure is initiated the propagating behavior is similar in this case. We take a systematic look at similar affects both amongst similar construction and as the same methodology is applied across various formats and cell chemistries.

Sandia National Laboratories is a multimission laboratory managed and operated by National Technology & Engineering Solutions of Sandia, LLC, a wholly owned subsidiary of Honeywell International Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525.

Figure 1 Data showing a propagating battery failure initiated through overcharge (left) and nail penetration (right). While the failure of the initial cell is more energetic, other aspects of the propagating battery failure remain similar between each test.