전기자동차용 원통형 리튬이온 배터리의 열폭주에 대한 수치해석적 연구

Abstract

Recently, climate change has been mentioned as a serious problem, which is mainly attributed to human use of fossil fuels. Therefore, movements for carbon neutrality are becoming more active around the world, and Korea is also announcing its goal of realizing a carbon-neutral society by 2050 and preparing specific realization measures. In order to cope with climate change, major countries around the world regulate carbon dioxide emissions, and in particular, the EU imposes fines on all new vehicles sold in Europe if they fail to meet their carbon dioxide emission targets. As the existing internal combustion engine vehicles cannot satisfy the regulations, eco-friendly vehicles, including electric vehicles, have become a must, not an option. However, as it is confirmed that the cause of the fire that has recently occurred in electric vehicles is due to the NCM battery, the safety of the LFP battery is drawing attention again. This research aims to numerically analyze and compare the thermal runaway of lithium-ion batteries widely used in electric vehicles depending on the cathode electrode active material and size, and to find out the stability of NCM batteries and LFP batteries. As a result of comparing the thermal runaway phenomenon of the cylindrical NCM battery and the LFP battery through the simulation, it was confirmed that the NCM622 battery with a high nickel ratio in the NCM battery very first thermal runaway occurred at 110°C, and at this time, the time to reach the thermal runaway was extended. In addition, even if it leads to thermal runaway, the maximum temperature of the LFP battery is relatively low due to the low increase in internal temperature. Thus, if the positive electrode active material is highly reactive, to a low temperature for a long time, thermal runaway could occur, so it could be verified that the stability of the NCM622 battery is the lowest than the LFP battery. Currently, battery safety is the biggest issue in electric vehicles, and accordingly, automobile manufacturers are expected to use LFP batteries in the entry model and NCM batteries in the advanced model. NCM batteries with high energy density but relatively low safety and LFP batteries with small energy density but excellent safety are dividing the electric vehicle battery market. Thus, improving the energy density of LFP battery and improving the safety of NCM battery remains a major challenge, and also, research and development are being actively conducted.