Mechanistic understanding of reproducibility in nail penetration tests

Lithium-ion battery safety evaluation covers a broad spectrum of abuse conditions. One of the popular testing methodologies is nail penetration. However, the reproducibility of nail penetration tests is rather poor, which compromises the credibility of the results. Understanding the underlying mechanisms of this low reproducibility is critical to provide design guidance and develop new testing protocols to accurately and quantitatively characterize battery safety. Here, a detailed computational model is first established to help understand the changes of each component within a cell upon nail penetration. Combined with a series of parametric experiments, the model assists with determining the factors governing reproducibility. Based on the results, it reveals that nail geometry, penetration speed, and cell support are dominant factors in reproducibility. The results lead to a better understanding of the low reproducibility mechanism of nail penetration tests, providing fundamental guidance on testing protocols and standards for battery safety.