리튬이온 배터리의 화재특성과 정량적 위험성 평가

Abstract

Recently, the use of secondary lithium-ion batteries (LIBs) has significantly increased. These batteries serve to power mobile machines and store energy produced on a small scale. However, given the rapid improvements in energy density, energy per volume, lifespan, and reliability of recharging, such batteries have been increasingly employed in drones, electric vehicles, industrial wireless electric machines, and electronic communication systems. An energy storage system (ESS) is required, along with a smart grid that optimizes energy efficiency. As distributed energy storage technology is essential, LIBs are increasingly utilized due to their applicability and versatility. While LIBs offer many advantages, they exhibit safety problems, with the most serious being fire. Unlike general fires, secondary battery fires pose a high risk of transition due to the rapid explosions associated with battery material and structure. Thermal runaway, caused by both thermal and physical factors, is the most common type of fire. Therefore, evaluating and eliminating instabilities such as fires are crucial when seeking to expand eco-friendly power sources and renewable energy. In this study, we investigated the fire characteristics of LIBs and assessed the risk of fire based on the LIB capacity and state of charge (SOC). The effects of capacity and SOC on fire characteristics were clarified by measuring the concentrations of various gases, pressures, temperatures, and HRRs during LIB fires in cone calorimeters. Smoke yields were derived using a smoke density chamber. Additionally, this study introduced and confirmed an index of overall battery fire risk, including explosion. The characteristics of the spontaneous exothermic reaction and thermal runaway phenomenon at each temperature of an LIB battery were investigated using an accelerating rate calorimeter. The batteries used in the experiments were standard 18650 cylindrical batteries with a capacity of 2600, 3500 mAh, and they were tested at three different state-of-charge (SOC) levels: 0%, 50%, and 100%. The type of heat generated by each experimental condition was classified into four stages, and the existence and temperature rise characteristics of each stage were investigated according to the SOC. Furthermore, this study encompasses information regarding ARC experiments and employs the HWS experimental method to discern the heat generation reactions occurring at each temperature. Moreover, it delves into identifying the onset temperature and magnitude of thermal runaway phenomena. Such research data aids in understanding the thermal runaway characteristics of batteries, thereby providing clarity on their limits and contributing to safer usage. Lastly, this study suggests the effect of charge states and the modeling method of surrogate fuels for battery thermal runaway. Three surrogate fuels were selected based on the components of the battery, and a method of increasing the oxygen concentration was adapted to model the effect that occurs when the charge states of battery fire increase. As a result, temperatures and pressures increased in all cases. This method suggests that the explosion caused by battery thermal runaway can be simulated. These results can be used to understand the characteristics of battery fires and are expected to be useful in calculating the size of fire prevention facilities required for battery use and storage.