Owing to the multi-gas venting process during a battery thermal runaway (TR), we can use the first gas venting signal for an early warning of battery failure. In this study, an experimental investigation obtained the char-acteristic parameters for the 21700 battery cell TR and venting process. A three-dimensional (3D) single-cell TR model and closed box venting gas diffusion model were built. The TR model can describe the 3D temperature distribution and predict the first venting moment based on the internal pressure. The gas diffusion model can describe the first venting gas diffusion in the closed box system. The first venting diffusion model can be used to optimize the number and layout of early warning gas sensors. In flat air domains, at least 1, 3, and 11 early warning sensors are required for an over-20 s warning time for regular, long-shape, and cell-to-chassis battery systems, respectively. The results can provide a beneficial tool for engineers to design a battery thermal runaway early warning system based on the gas venting signal.
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