Single-Layer Nail Penetration for Lithium-Ion Battery Safety Characterization

Abstract

Nail penetration is widely used to characterize lithium-ion (Li-ion) battery safety during internal short circuit (ISC) that has caused many high-impact field failures (e.g. Samsung Note 7 battery fires in 2016 [1]). Compared with other ISC triggering methods that require embedding some devices into Li-ion battery cells [2], nail penetration is much easier to implement without cumbersome modification of testing cells. A challenge for nail penetration, however, is poor control of ISC electrode layers while those methods with embedded devices can accurately achieve single layer ISC [2]. This challenge makes nail penetration triggered ISC less representative of field failures than using those device-embedded methods. It also leads to poor reproducibility of testing results. Here we report a single-layer nail penetration method based on in situ temperature sensing. The method not only keeps nail penetration’s advantage of easy implementation, but also makes nail penetration more representative of field failure ISC with testing results more reproducible. The method works with three key elements. First, a micro temperature sensor is embedded into the tip of a nail, similar to those "smart nails" in earlier reports [3-6], for in situ sensing of ISC temperature. Second, a temperature controller is used to stop the nail penetration when the ISC temperature reaches set value. Third, the nail penetration speed (0.1 mm/s or lower) is much lower than conventional nail penetration speed (up to 80 mm/s [7]). The figure below shows ISC temperature and surface temperature of a 2.4 Ah pouch Li-ion cell during single-layer nail penetration. It can be seen that the ISC temperature is much more sensitive than surface temperature. There is only one ISC temperature peak, suggesting single layer penetration, as compared with our earlier work of full nail penetration which has multiple ISC temperature peaks [8]. With this method, the effects of key parameters, such as ISC resistance, cell dimension and jelly roll structure, on Li-ion battery safety behaviors can be characterized.