| dc.description.abstract | Lithium-ion batteries (LIBs) have become increasingly popular for commercial use in recent years, however, the frequency of accidents involving LIBs raises concerns over their safety. A commonly experienced condition for batteries is an external short, which causes the cell to discharge at a high rate and, hence, at large currents, resulting in rapid heat generation in the wire as well as within the cell. Another condition, known as overdischarge, is also becoming a common safety issue as greater numbers of cells are being connected in series, as is the case in systems requiring high voltages, such as Electric Vehicles (EVs). This work seeks to explain the mechanisms that cause internal damage to cells during external shorting and overdischarge and to determine the most dangerous conditions that can exist during these types of abuse. An external short test using a commercial 18650 cell (Panasonic) was conducted by subjecting the cell to a constant resistance discharge with resistors of decreasing value (from 100-0.01 Ω). To perform the overdischarge test, a constant current discharge phase with no lower cutoff voltage was used to overdischarge the same type of cells to -100% SOC. The phenomenon of copper dissolution from the anodic current collector was observed in each overdischarged cell. Voltage, current, and temperature behavior was monitored throughout the cycling of all cells in order to determine the cell response to the abnormal cycling. The internal damage of the cells was studied by conducting a Destructive Physical Analysis (DPA) and by analyzing cell components via Scanning Electron Microscopy (SEM). The external shorting results showed that a single 18650 cell experiencing external short can produce potentially dangerous amounts of heat when the resistance of the short is between 0.47 Ω and 1 Ω. Cracking was observed on both the anode and cathode surface of the externally shorted cell, indicating a loss of capacity. The overdischarge test results confirmed that copper dissolution occurs when the cell voltage reaches -1.1 V in the Panasonic cells. The deposition of copper on the cathode surface can lead to the trapping of lithium ions within the cathode. Loss of copper material from the anodic current collector can cause loss of adhesion of the anode material to the collector and loss of mechanical stability of the anode roll. This work will provide a better understanding of LIB behavior under abusive conditions. | en |
