Li Metal Solid State Battery Safety Assessed with Calorimetry and Modeling of Large-Format Cells

It is commonly assumed that the introduction of solid-state electrolytes implies the improved safety of high-energy batteries due to the removal of the combustible organic solvents in present Li-ion cells. However, safety is a multifaceted issue that involves thermal runaway onset temperature, self-heating rates, total heat production, maximum temperature, gas or other material release from a cell, thermal runaway prevention mechanisms, and other factors.[1-3] In addition, the use of lithium metal anodes (which melt at 180°C) for high energy density cells may introduce previously unconsidered safety issues due to the presence of molten and reactive lithium metal during a thermal runaway.<br/><br/>This talk will present results on the modeling of thermal runaway in a Li metal solid state battery, under both thermal ramp (e.g., in an oven) and short circuit conditions, with quantitative assessments of the mole fractions of key species in the cell and the temperature.[3] Key assumptions and parameter sensitivities will be shared, to clarify the most important areas for attention and analysis regarding Li metal solid state battery safety. In addition, results from differential scanning calorimetry (DSC) measurements of mg-scale quantities of solid state battery material sets will be presented, which provide quantitative information on onset temperatures and heat flows of key reactions. These experimental results will focus on cells with Li metal, an LLZO-based solid electrode, and metal oxide cathodes.<br/><br/>Finally, perspectives will be given on the early-stage (e.g., for materials and single-layer coin and pouch cells) evaluation of safety for prospective high-energy cells, for which commercial-scale cells (e.g., multi-layer cells of at least several Ah) are not yet available.<br/>References<br/>1. Bates, A.M., et al., Are solid-state batteries safer than lithium-ion batteries? Joule, 2022. 6(4): p. 742-755.<br/>2. Inoue, T. and K. Mukai, Are All-Solid-State Lithium-Ion Batteries Really Safe?–Verification by Differential Scanning Calorimetry with an All-Inclusive Microcell. ACS Applied Materials & Interfaces, 2017. 9(2): p. 1507-1515.<br/>3. Johnson, N. and P. Albertus, Modeling Thermal Behavior and Safety of Large Format All-Solid-State Lithium Metal Batteries under Thermal Ramp and Short Circuit Conditions. Journal of The Electrochemical Society, 2022. 169(6).