Probing the Thermal Safety of Li Metal Batteries

Li metal batteries (LMBs) with high energy density electrodes have emerged as the primary candidate for next-generation batteries owing to its superiority over conventional Li-ion technology. However, the safe operation of these systems under thermal abuse conditions remains primary concern regardless of the tremendous efforts to prevent short circuits through dendrite formation. In this context, we employ differential scanning calorimetry technique to investigate the thermal stability of Li-S and Li-NMC532 metal batteries. The calorimetric measurements identify separator melting together with anode-centric thermal degradation reactions as the primary mechanism of thermal runaway. Separator with poor thermal stability (low melting point), could instigate an internal short circuit that leads to exponential temperature rise due to the rapid release of electrical energy. An in-house physics-based modeling technique utilizes the knowledge of thermal stability at the materials level to predict the thermal safety of LMBs for pouch cell configuration. Simulations reveal that the thermal stability of the separator and parasitic reactions at the anode (Li metal) dictate the critical onset temperature of thermal runaway in Li metal batteries. The severity of thermal runaway can be modulated by carefully designing (capacity loading ratio (N/P)) the thickness of metal anode and advanced separator with better thermal stability.