Experimental Study on External Short Circuit and Overcharge of Lithium-ion Battery Packs for Electric Vehicles

External short circuit (ESC) and overcharge are two types of electrical failures in lithium-ion batteries for electric vehicles. Experimental study has been conducted to quickly and accurately diagnose these faults, which is critical to ensure battery safety. In this study, three contributions are made: (1) Battery cells with ten different SOCs (10%, 20%\cdots 100%) are short-circuited at three ambient temperatures of 20{\circ}\mathrm{C}, 30{\circ}\mathrm{C}, and 45{\circ}\mathrm{C} to investigate the effect of SOCs and temperatures on the ESC fault characteristics. (2) The ESC experiments are performed in 4-series and 2-parallel connected battery packs. In these experiments, one cell is short-circuited while the whole battery pack is being charged or discharged. It can be found that the ESC fault triggers different degrees of overcharge faults in a battery pack, and these overcharge faults are also influenced by charging/discharging strategies on the whole pack (3) Based on experimental data, an equivalent circuit model is employed to simulate electrical behaviors of battery cells under ESC and overcharge conditions. It is found that both ESC model and overcharge model are capable to capture electrical performances under abusing tests.