Modeling Thermal Behavior and Safety of Large Format All-Solid-State Lithium Metal Batteries under Thermal Ramp and Short Circuit Conditions

Abstract

Solid-state batteries are often considered to have superior safety compared to their liquid electrolyte counterparts, but further analysis is needed, especially because the higher specific energy of a solid-state lithium metal battery results in a higher potential temperature rise from the electrical energy in the cell. We construct a model of the temperature rise during a thermal ramp test and short circuit in a large-format solid-state LCO∣LLZO∣Li battery based on measurements of thermal runaway reaction thermochemistry upon heating. O2 released from the metal oxide cathode starting at ∼250 °C reacts with molten Li metal to form Li2O in an exothermic reaction that may drive the cell temperature to ∼1000 °C in our model, comparable to temperature rise from high-energy Li-ion cells. Transport of O2 or Li through the solid-state separator (e.g., through cracks), and the passivation of Li metal by solid products such as Li2O, are key determinants of the peak temperature. Our work demonstrates the critical importance of the management of molten Li and O2 gas within the cell, and the importance of future modeling and experimental work to quantify the rate of the 2Li+1/2O2→Li2O reaction, and others, within a large format solid-state battery.