Investigation on thermal runaway characteristics and flame dynamics of overcharged NCM523 lithium-ion batteries with different charge rate

Lithium-ion batteries (LIBs) are the primary energy source for new energy vehicles and electronic products, and enhancing their charging rates is a key direction for their development. To investigate the thermal runaway (TR) characteristics and flame ejection dynamics of LIBs under different charging rates and overcharge levels, this study developed a coupled TR experimental platform. A systematic experimental study was conducted on the TR behavior and flame ejection dynamics of overcharged 18650 NCM523 batteries under thermal abuse, from both macroscopic and microscopic perspectives. The results indicate that the charging rate affects the thermal stability of LIBs, while the state of charge (SOC) influences the heat accumulation during the TR process. The temperature triggering TR decreases as both SOC and charging rate increase, and the abnormal voltage drop occurs earlier than the rapid temperature rise associated with battery TR. The flame area increased from 13,212.21 cm 2 at 1C to 21,061.43 cm 2 at 3C, a 59.41% increase, and from 3,046.43 cm 2 at 100% SOC to 10,895.65 cm 2 at 150% SOC, a 257.65% increase. The impact of SOC on the TR mass loss rate is greater than that of the charging rate. Higher charging rates and greater overcharge levels result in more significant structural damage to the battery’s positive electrode, and as the charging rate increases, cavity-like structural damage inside the battery is also observed. This study provides important experimental data for a deeper understanding of the TR flame ejection dynamics of LIBs under overcharge and different charging rate conditions. It has significant theoretical and practical implications for enhancing battery safety and accident traceability.