Lithium is the least dense metallic element. It can store a lot of energy in a lightweight and compact form. It is a highly reactive substance which belongs to alkali metal group. Small fault /damage occur on the extremely thin separators, which leads to an internal short-circuit & excessive heat build-up. A “Thermal Runaway” is triggered overheating the battery which burst into flames. Also, hot environments & excessive discharging/charging can trigger overheating.