Study on Thermal Safety of the Overcharged Lithium-Ion Battery

Since safety hazards may occur during the life of a Li-ion battery, it is important to learn the behavior under abuse conditions. In this paper, the variation of each characteristic parameter of the thermal runaway process for 32,650, NCM, and LiFePO₄ square batteries are analyzed based on an overcharge experiment in Adiabatic Rate Calorimeter. NCM batteries at different charging rates and three kinds of single batteries at 1.00 C charging rate are tested for exploring the variation of thermal safety of lithium-ion batteries under overcharge conditions and getting the characterization of overcharge battery safety. Furthermore, a new index overcharge degree is introduced to evaluate the safety state of lithium batteries under different overcharge conditions given the comprehensive analysis of the variation trend of overcharged battery characteristic parameters, which provides ideas for the early safety warning of batteries at overcharging conditions. It is found that the initial runaway temperature of NCM battery decreases gradually with the increase of charging rate, but the initial runaway temperature of overcharge at 2.00 C is slightly lower than 1.50 C, the maximum runaway temperature of battery increases first and then decreases, the rate of voltage rise in the early stage increases with the increase of charging rate, the change rate of voltage and temperature of the battery increases as a whole, the voltage before thermal runaway decreases first and then increases, the total charging capacity shows a linear decline. In the 1.00 C overcharge experiments of the three batteries, the initial runaway temperature of 32,650 battery is the lowest, the maximum runaway temperature of square lithium iron phosphate battery is the highest, the temperature change rate of square lithium iron phosphate battery is the largest, the voltage of square lithium iron phosphate battery drops to 0 V first, and the overcharge time of NCM battery is the longest.