Thermal runaway behavior of nickel–manganese–cobalt 18650 lithium-ion cells induced by internal and external heating failures

Lithium-ion cells can fail in thermal runaway in a number of ways. Thermally-induced failures can be initiated by either external heating or an internal failure which leads to internal heating. Internal failures such as dendrite growth can lead to an internal short circuit (ISC) which subsequently causes internal heating. Internal failures are a common cause for lithium-ion battery thermal runaway that leads to fire incidents. Preventing and mitigating thermal runaway failure is of great interest in battery fire safety research and development. To evaluate safety measures in a repeatable manner, there is a need for a simple and repeatable technique to reliably fail a given cell, while minimally affecting the pack prior to cell failure. This paper introduces an internal failure mechanism targeted on a single (or multiple) 18650 cell(s) to trigger thermal runaway by (1) modifying commercially acquired 18650s to accommodate a mini-heater cartridge, (2) performing cycling tests on the modified cells and comparing their performance to that of the as-received (pristine) cells in a custom-built failure tube environment, and (3) experimentally examining the characteristics (temperature, flux-time product, voltage drop, and mass loss) of internally heated and failed cells in comparison to externally heated and failed cells. The results show that the modification procedures do not alter a cell’s performance and its charge capacity. Failure tube tests show that the thermal runaway behavior and damage to the modified cells are representative of ”real-world” cell failures. The internally heated cells had different venting behavior relative to externally heated cells, which affects mass loss profiles. When inserting a single, modified cell into a battery package (laptop power bank) and triggering it to cause thermal runaway, failure propagation to the surrounding cells can be characterized. Overall, this study introduces a realistic cell internal failure approach that can benefit the development of battery safety techniques in a variety of applications. The internal-heater failure approach is proven to be easily prepared with standard laboratory apparatus without affecting the battery performance and produces repeatable failure results for single and multiple cell systems.