Extensive Experimental Thermal Runaway and Thermal Propagation Characterization of Large-Format Tabless Cylindrical Lithium-Ion Cells with Aluminum Housing and Laser Welded Endcaps

Large-format tabless cylindrical lithium-ion cells are expected to enhance performance and reduce cost of next generation vehicles. The influence of innovative new tab designs, increased dimensions and new housing materials are however still unexplored and must be revealed to unlock safe future battery systems. In this study, the thermal runaway and thermal propagation characteristics of sophisticated state-of-the-art large-format tabless cylindrical cells with aluminum housing and laser welded endcaps are extensively characterized. Multiple abuse test setups on cell and battery level are custom designed close to the true boundary conditions in real world applications. Results show cells with aluminum housing require careful choice of trigger methods as the low melting point and less mechanical strength compared to conventional nickel-plated steel housings introduce additional challenges. The tabless design was found to act as a strong mechanical connection that prevents shifting of the electrode assembly. Instead, axial ruptures of the jelly roll may occur. The leftover high density material conglomeration that is in tight contact with the inner housing wall transfers heat into the surroundings and is critical for thermal propagation safety. Strong interstitial potting compound with low thermal conductivity successfully prevented any major convective heat transfer into the neighboring cells by venting gas.