A comprehensive research on internal short circuits caused by copper particle contaminants on cathode in lithium-ion batteries

Manufacturing defects are one of the main causes of internal short circuits (ISCs) and then lead to thermal runaway accidents of batteries, which seriously threatens the safety of electric vehicles. Cu particle contaminants are one of the most common and dangerous manufacturing defects. Cu particles that may cause ISC by dissolving on the cathode and precipitating on the anode are smaller in size and less likely to be detected during manufacturing, compared with those that cause ISC by directly piercing the separator. However, there is little research on the mechanism and evaluation of ISC caused by cathode Cu particle contaminants. In this paper, Cu particles were intentionally placed on the cathode of lithium-ion batteries (LIBs). The mechanism and type of ISC induced by the Cu dissolution-precipitation process in LIBs were successfully characterized for the first time, and the evolution process was concluded. The ISC introduced by Cu particles was successfully simulated by a pseudo three-dimensional model. And the size boundary of Cu particles causing ISC was also studied. It was found that the implanted Cu particles will necessarily cause ISC in the batteries. The key to the ISC caused by cathode Cu particles is the precipitation of Cu along the pores of the separator from the anode side to the cathode side. The type of ISC caused by this defect is a cathode-anode short circuit, which only induces a soft ISC. The maximum temperature of the battery with this defect can only increase by approximately 2 °C through the calculation of the model under the set conditions of this study, which would not cause thermal runaway of the battery. In addition, even when the size is as small as 20 μm, the cathode Cu particle contaminants will still cause an ISC with short-circuit resistance of tens of kΩ magnitude.