The propagation of thermal runaway in a battery system is safety-critical in almost every application, such as electric vehicles or home storage. Abuse models can help to undestand propagation mechanisms and assist in designing safe battery systems, but need to be well-parametrized. Most of the heat during thermal runaway is released by venting that is why the characteristic of the vent flow plays an important part in the safety assessment. During venting, the cell generates a recoil force like a rocket, which depends on the flow speed and flow rate of the gas. This principle is used in this work to measure the velocity and mass flow rate of the vent gas. High-power and high-energy 18650 format lithium-ion batteries were overheated and the recoil and weight forces were measured to determine the venting parameter during thermal runaway. Our results show, that the linearized gas flow rate for the high-power and high-energy cell is $22.15{\mathrm{gs}}^{-1}$ and $27.92{\mathrm{gs}}^{-1}$, respectively. The progress of the gas velocity differs between the two cell types and in case of the high-energy cell, it follows a single peak asymmetrical pattern with a peak of $398.5{\mathrm{ms}}^{-1}$, while the high-power cell shows a bumpy pattern with a maximum gas velocity of $260.9{\mathrm{ms}}^{-1}$. The developed test bench and gained results can contribute insights in the venting behavior, characterize venting, support safety assessments, simulations and pack design studies.

Temperature monitoring of Lithium-Ion Batteries (LIBs) and Sodium-Ion Batteries (SIBs) is essential for safe operation, as excessive temperature can trigger a Thermal Runaway (TR) event. Although surface temperature sensors have traditionally been used, their limitations have led to the exploration of alternative methods. Notably, estimating temperature based on pulse resistance (RDC) has emerged as a promising approach. Nonetheless, this method has not yet been investigated at temperatures exceeding the cell’s safety specifications, highlighting a research gap for its application in TR early detection. In this study, the RDC-temperature relationship was characterized at temperatures exceeding the cell’s safety limits for two different LIB technologies and a SIB. The results revealed a turning point in the RDC-temperature relationship between 60 °C and 70 °C for both LIB technologies and at approximately 110 °C for the SIB. From this turning point, RDC increases with increasing temperature. This contradicts the loss of sensitivity of RDC to temperature variations predicted by the Arrhenius model at temperatures typically encountered during a TR event. Finally, a novel TR early detection approach based on the characterized RDC behavior during a TR event is proposed. The strength of the method lies in the combination of two monitored RDC properties changing during TR.