Fire-Extinguishing Microcapsule Composite Separator for Chemical Safety Management in Lithium-Ion Battery System
Authors: Kim Ki Jae , Yang Jin Hyeok , Ha Ye Ji 
Published: July 2022

With recent rapid technological developments, the use of fossil fuels has drastically increased, posing environmental concerns such as global warming and air quality deterioration due to the presence of particulate matter such as fine dust. Renewable energies, such as solar energy and wind energy, have been considered as promising alternatives to reduce the use of fossil fuels. However, the energy generated by renewable energy sources varies significantly and is dispersed because of its strong dependence on environmental conditions. Therefore, energy storage systems (ESSs) should be installed for the stable use of renewable energy systems and stable delivery in response to consumer demand.
Among the many batteries used in ESSs, lithium-ion batteries (LIBs) have been used widely as a power source because of their relatively high voltage (~4.7 V vs Li) and high energy density (650 W h kg−1). Long-term reliability is necessary to utilize LIBs in ESSs; however, many drawbacks associated with the long-term use of LIBs have been reported recently in ESSs employing LIBs. Although the performance of LIBs is gradually improving, safety issues such as fire and explosion remain a major issue and disturbed the development of LIBs. In this study, we manufactured Fire-extinguishing Microcapsule (FEMC) containing extinguishing substances for the safety of the battery. Encapsulation of the extinguishing material inside a stable polymer shell prevented the extinguishing material from reacting directly with the electrolyte in the battery. The direct reaction of the extinguishing material with the electrolyte negatively affects the battery performance and causes a short circuit in the battery. When thermal runaway occurs in the battery, the outer shell material melts and the internal fire extinguishing material is released, effectively preventing fire and explosion of the battery.
The FEMC was encapsulated by using solvent evaporation technique. To confirm FEMC’s extinguishing effects self-extinguishing time (SET) was measured, and we observed FEMC’s physical properties such as encapsulation, size by using characterization techniques (FE-SEM, TEM, TGA, etc). As a result, the size of the FEMC was evenly distributed about 2 μm to 5 μm, and the surface was generally smooth. In addition, extinguishing material was largely located in the middle of the interior, and the core-shell structure in which stable polymer shell was wrapped around a very thin wall was confirmed. The fire extinguishing effect by FEMC was confirmed in the electrolyte, and as a result, the bare electrolyte without a fire extinguishing additive was extinguished in about 115 sec. On the other hand, when FEMC containing extinguishing material was conducted SET test, it was confirmed that the combustion time decreased by about 12 sec. Compared with bare electrolyte, the combustion time was reduced by about 84.4%. Through this, it was confirmed that the FEMC had an excellent effect in extinguishing the fire in the electrolyte.