In partnership with the National Renewable Energy Laboratory (NREL), we have invented (U.S. Patent #9,142,829) an on-demand internal short circuit (ISC) device that is activated by raising the cell temperature > 57 degC, rather than > 130 degC required without the device. We have achieved > 90% success rate in driving a 2.4Ah (180 Wh/kg) cell design into thermal runaway with a device designed for an anode active material to cathode current collector short and usign a non-shutdown separator (M. Keyser, ECS Phoenix mtg, Oct 2015). Building on this success, we are now implanting the device in cell designs exceeding 250 Wh/kg to learn their design vulnerabilities and effectiveness of safety features like shutdown separators, cathode coatings, current interrupt devices, positive thermal coefficient switches, center mandrels, cell vents, and crimped headers. We are providing our cells to researchers conducting in-operando tomography on cells during thermal runaway (Finegan et. al, Nature Communications, 7924, 2015) for first time video insight into the response of an 18650 cell to a thermal runaway that is internally induced by an internal short circuit instead of external driven by thermal, mechanical, or electrical abuse. This enables the study of conditions that replicate latent defect induced field failures with the most fidelity.

As the specific energy of commercially available 18650 cell designs exceed 250 Wh/kg, we are presented with additional challenges for integrating them into safe, high performing (> 200 Wh/kg) battery designs for manned spacecraft applications. Specifically, these cell designs are susceptible to side wall rupturing and/or eletrode jellyroll ejection during thermal runaway. Such packs require cell interstitial materials that provide high thermal conductivity and structural structural strength. This leaves very little cell surface area for heating unmodified cells into thermal runaway for battery safety testing. In fact, the only way to acheive single cell thermal runaway in these battery designs is by triggerring cells implanted with the ISC device. These tests give us insight into the impact of battery design parameters life cell-cell spacing, cell electrical isolating wraps, and features that protect the adjacent cells from propagating into thermal runaway. Finally, battery flame arresting materials and vents are crucial to prevent flames and sparks for exiting battery enclosures. Our IMLB submission will be our first public forum disclosure of these results.