Effect of States of Charge on the Burning Behaviors of Lithium ion Batteries

The burning behaviors of 18650 type lithium ion batteries under various states of charge (SOCs) were investigated using a cone calorimeter under an incident heat flux of 50 kW/m². Several parameters were measured, including heat release rate (HRR), time to ignition and concentration of toxic gases. The experimental results show that the peak HRR, concentration of CO2 and CO increase with the increasing SOCs, whereas the time to ignition, time to explosion and the released energy during the burning decrease. The 100 % SOC is the highest fire risk due to the most serious toxicity (CO concentration: 1500 ppm), the maximum HRR (2.78 kW) and the shortest time to ignition (43 s). Besides, the burning process of the lithium ion batteries with various SOCs could be divided into four phases and the SOCs show important influence on the combustion intensity. The HRR of the fully charged LIBs is fourth power of time, which is much higher than the time-squared fire model mentioned in NFPA for most combustibles. A correlation is developed to predict the peak HRR. This study could serve as a technical guide for safe storage, application, and transportation in lithium ion batteries.