Experimental and numerical study of internal pressure of lithium-ion batteries under overheating

The safety of lithium-ion batteries remains one of the major public concerns as electric vehicle fires are frequently reported. Currently, understanding the thermal runaway characteristics and mechanisms via the combination of thermal runaway modelling and tests using in-situ internal pressure measurements in 21,700-format lithium-ion cells has rarely been reported. This work presents a lumped thermal runaway model and thermal runaway experimental results with instrumented 21,700-format cells (equipped with pressure/temperature sensors) to understand thermal runaway characteristics and mechanisms based on the evolution of the internal pressure. The internal temperature recorded by an embedded thermocouple reached up to 1008.9 °C. The average internal pressures for the first peak (vent disc pressure) and the second peak (during thermal runaway) were 20.43 bar and 18.27 bar, respectively. The thermal runaway mechanisms were further explained based on experimental results and the developed model. Finally, the influence of both vent area and gas generation on the evolution of internal pressure was investigated based on the developed model. A larger opening in the bottom vent would decrease the internal pressure, which would reduce the risk of sidewall rupture. The study addressed the key role of bottom vent played during thermal runaway especially the evolution of internal pressure. • Developed a lumped model to explore the evolution of battery internal pressure. • Investigated internal pressure dynamics using cells equipped with pressure sensors. • Characterized and explained gases, sparks, and flames during thermal runaway linked to internal pressure.