New Insights into Nail Penetration of Li‐Ion Batteries: Effects of Heterogeneous Contact Resistance

Abstract Nail penetration is one important mode of catastrophic failure in Li‐ion batteries, and the contact resistance between a nail and electrodes is a dominant factor for heat generation. Surprisingly, previous studies always assume uniform resistance and there is no experimental measurement of contact resistance, to the best of our knowledge. In this report, the contact resistance is determined experimentally. The contact resistance between a nail (diameter=1.25 mm) and a Cu/graphite electrode is 2.5±1.5 Ω, and a nail and Al/LiCoO 2 is 20.3±12.4 Ω. These values are in the same order of the geometric mean of the resistance between nail/metal substrate and nail/active materials, suggesting a random connection network among the nail, the metal substrate, and active materials. It is found that the resistance can vary as large as 1–2 orders of magnitude, and such fluctuation is critical to the magnitude of temperature rise during nail penetration, which can increase temperature rise by ∼93 % compared to homogeneous contact resistance. The results show that the heterogeneity in contact resistance should be considered. Based on such new understanding, a simple approach to reduce the temperature increase during nail penetration was proposed by having the anode as the outermost layer.