High theoretical capacity coupled with low operating potential makes Lithium the most promising choice for next-generation batteries. Replacing graphite by Li metal can enhance the energy density three times as compared to conventional Li-ion battery. Lithium is also an essential part of the next generation high energy batteries such as Lithium-Sulphur and Lithium-air batteries. However, the high reactivity of Li metal with electrolyte leads to dendritic growth, poor cycle life and safety hazards in Li metal batteries. Till date, there has been no study on the thermal characteristics of Li metal batteries.

The thermal characteristics of Li metal batteries using advanced multiple-mode calorimetry (MMC) for the coin cell format under fully charged and discharged conditions is studied. In the conventional differential scanning calorimetry (DSC) ex-situ studies of a component or two from the battery, possibly could lead to some artifacts. Therefore, MMC is utilized to directly study the thermal behavior of whole coin cell comprising anode, cathode, electrolyte, and separator with thermally stable leak proof gasket till 300 ^oC. Thermal runaway of two types of Li metal batteries with different chemistries namely Li-Sulfur and Li-NMC are measured and compared. The MMC of Li-S battery coin cell in fully charged conditions showed a sharp exothermic peak positioned at 180 °C originating from the reaction between the Li metal and sulfur in presence of the electrolyte. Though Li-S batteries are assumed to be safer, an exothermic reaction between Li and S cathode leads to thermal runaway once the Li metal melts. The MMC of Li-NMC cell in the coin cell format also exhibits endothermic and exothermic peaks arising from the melting of Li and reaction of Li with electrolyte/cathode. This exothermic reaction leads to thermal runaway in Li-NMC around 180°C. The detailed endothermic and exothermic heat generation values in J/g, peak temperature, its source based on interfacial reactions and mechanistic elucidation will be discussed.