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. O 2 released from the metal oxide cathode starting at ∼250 °C reacts with molten Li metal to form Li 2 O 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 O 2 or Li through the solid-state separator (e.g., through cracks), and the passivation of Li metal by solid products such as Li 2 O, are key determinants of the peak temperature. Our work demonstrates the critical importance of the management of molten Li and O 2 gas within the cell, and the importance of future modeling and experimental work to quantify the rate of the 2Li+1/2O 2 →Li 2 O reaction, and others, within a large format solid-state battery.