Failure Analysis of Short-Circuited Lithium-Ion Battery with Nickel-Manganese-Cobalt/Graphite Electrode

Accidental failures and explosions of lithium-ion batteries have been reported in recent years. To determine the root causes and mechanisms of these failures from the perspective of material degradation, failure analysis was conducted for an intentionally shorted lithium-ion battery. The battery was subjected to electrical overcharging and mechanical pressing to simulate internal short-circuiting. After in situ measurement of the temperature increase during the short-circuiting of the electrodes, the disassembled battery components (i.e., the anode, cathode, and separator) were analyzed by scanning electron microscopy and energy-dispersive X-ray spectroscopy. Regardless of the simulated short-circuit method (mechanical or electrical), damage was observed in the shorted batteries. Numerous small cracks and chemical reaction products were observed on the electrode surface, along with pore shielding on the separator. The event of short-circuiting increased the surface temperature of the battery to approximately 90 °C, which prompted the deterioration and decomposition of the electrolyte, thus affecting the overall battery performance; this was attributed to the decomposition of the lithium salt at 60 °C. The gas generation due to the breakdown of the electrolyte causes pressure accumulation inside the cell; therefore, the electrolyte leaks.