Li-Ion Battery Deactivation through External Short Circuit

Abstract

While electric vehicle battery packs are designed to address safety issues, battery failures can still occur. Most prominently, electric vehicle fires can occur after accidents or from internal shorts due to defects, abuse, or accelerated aging. Battery fires can be difficult to manage due to the active lithium materials and the presence of both the fuel and oxidant produced by thermal decomposition. Typically, after extinguishing the original fire, the main priority is to cool the battery pack by applying a large and continuous volume of water directly to the pack. However, the fire may still reignite hours later, fueled by the remaining stored energy. This highlights the need for further investigation and discussion about how to effectively remove the stored energy from, or deactivate, batteries with the goal to prevent fire re-ignition in battery packs.Batteries at a lower state-of-charge (SOC) are more thermally stable and have a lower energy release during thermal runaway than those at high SOCs. In addition, experimental results from single cells and small, multiple-cell configurations undergoing external short circuits show that thermal runaway (TR) events are rare, and the cell peak temperatures depend on the relative size of the external resistance to the internal cell resistance. To this end, this research aims to evaluate the use of high C-rate discharge and external short circuits to safely deactivate batteries while avoiding TR.External short circuit testing was performed on 4.6Ah pouch cells at 15% and 100% SOC, with measurements of cell current, voltage, temperature, expansion force, and atmospheric CO2 gas concentration. At the end of the test, the cell initially at 15% SOC discharged to -10% SOC and reached a maximum temperature of 64℃. The cell had no visible damage afterwards. For the 100% SOC cell, it reached a maximum temperature of 120℃ and discharged to around 25% SOC at the end. In both cases, neither went into thermal runaway, but the first cell was able to discharge to less than 0% SOC in 5 minutes, while the 100%SOC cell took significantly longer to reach the low current cutoff. This is because during the gas venting process, electrolyte is lost, greatly increasing the internal resistance and increasing the discharge time. In addition, the lower peak temperature of the first cell indicates a reduced likelihood of thermal runaway propagation in a pack, and the lack of toxic and flammable vent gas and electrolyte leakage in the environment improves safety. In order to apply this at a larger level, we will investigate the appropriate external resistance to safely deactivate the cells without leading to hazardous conditions. Figure 1