Investigation of Exothermic Reaction Pathways in Solid-State Batteries: Implications for Safety

It has been assumed that replacing the liquid electrolyte (LE) in a Li-ion battery (LIB) with a nonflammable solid electrolyte (SE) provides inherent safety. However, results from prior thermodynamic modeling¹show that batteries containing a SE still have the potential to reach high temperatures during certain failure scenarios. Even if these temperatures do not lead to ignition of the battery contents, they could ignite surrounding flammable packaging material. The reaction pathways leading to thermal runaway are not well understood.<br/><br/>This work investigates those pathways for battery materials undergoing external heating and compares the results with thermodynamic modeling. The following battery configurations were explored: all solid-state batteries (ASSBs), solid-state batteries (SSBs) containing some amount of LE, and LIBs. A Ta-doped LLZO SE was used in the ASSB and SSB configurations. Differential scanning calorimetry (DSC) was used for thermal characterization of individual and combinations of battery components as well as complete microcells to differentiate between contributing factors in heat release scenarios. Calorimetry was halted and materials characterization completed at each distinct exotherm to isolate specific reaction pathways. Microstructure changes were characterized in a scanning electron microscope (SEM) and crystal structure transitions and chemical compositions were obtained through x-ray diffraction (XRD). Avoidance or mitigation of critical component-level interactions leading to thermal runaway will help pave the way towards improving SSE battery safety.<br/><br/>1. Are solid-state batteries safer than lithium-ion batteries? Bates AM, Preger Y, Torres-Castro L, Harrison KL, Harris SJ, Hewson J. Joule. 2022;6(4):742-55<br/> <br/>Sandia National Laboratories is a multimission laboratory managed and operated by National Technology and Engineering Solutions of Sandia LLC, a wholly owned subsidiary of Honeywell International Inc. for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525. SAND No. 2022-15109 A.