Thermal safety analysis of sulfide solid-state batteries
Research Associate: Alexander Sedykh
Solid-state batteries (SSB) are the technological progression of lithium-ion batteries based on the expected energy density due to the usage of lithium metal anodes and higher safety due to the absence of the organic liquid electrolyte. Thiophosphate-based (sulfide) solid electrolytes (SE) are one of the best-suited ionic conductors for SSB. This brings the safety concerns forward, as there is a potential for the formation of H2S or SO2. The reaction of sulfide electrolyte with moisture or oxygen can be caused by the degeneration products of the cathode active material during charge and discharge or can be a result of external battery damage.[1]
The thermal stability of batteries is a main concern in their operation safety. As the efficiency of the charge and discharge is not quantitative, the energy is partially converted to heat. Local overheating could damage the components or directly induce an unwanted reaction that might be potentially hazardous. In the worst-case scenario, an exothermic reaction starts, leading to thermal runaway – an uncontrollable self-feeding process that overheats the whole battery. This is a recipe for a self-ignition or even an explosion.[2,3]
Therefore, the investigation of the thermal safety of SSB is a must before their mass production. For that, an holistic risk assessment and a fundamental understanding of thermally induced processes of sulfidic SSB and degradation pathways is required. Within the FB2-SAFE platform of the Cluster Competence for Solid-state Batteries (FestBatt), the thermal stability of the sulfide-based SSB is investigated. The focus of our research group’s investigations is the thermal analysis of battery materials, their combinations, and the different states of the battery lifecycle.
As part of the thermal studies, a classical simultaneous thermal analysis (STA) is used where the mass change and the heat flow of the compound or a mixture are recorded (NETZSCH STA F3 Jupiter®). An additional method is calorimetry, which allows the screening of processes with high energies. The measurement is done in a closed system that withstands the pressure of 15 MPa allowing safe investigations of explosive reactions with gaseous products (NETZSCH MMC 274 Nexus®, Scanning Module). The highlight of thermal investigations within this project is the possibility of measuring the thermal properties of the assembled cells while charge-discharge cycling (NETZSCH MMC 274 Nexus®, Coin Cell Module). This set of analytical equipment allows the all-around investigation of the thermal (runaway) reactions within the SSB to increase their operational safety.
The project is done in cooperation with numerous research groups with a high degree of intertwining. The major supply of battery materials and post mortem analysis of samples after thermal investigations is done by groups of Prof. Dr. Janek (Justus Liebig University Giessen) and Prof. Dr. Zeier (University of Münster). Investigation of the local heat formation and heat dissipation is done within the groups of Prof. Dr. Gasteiger (Technical University of Munich) with a focus on the development and validation of cell formats and of Prof. Dr.-Ing. Jossen (Technical University of Munich) by modelling of current & temperature distribution in SSB.
References:
[1] J. Janek, W. G. Zeier, Nature Energy 2016, 1, 16141.
[2] T. Kim, K. Kim, S. Lee, G. Song, M. S. Jung, K. T. Lee, Chem. Mater. 2022, 34, 9159–9171.
[3] X. Rui, D. Ren, X. Liu, X. Wang, K. Wang, Y. Lu, L. Li, P. Wang, G. Zhu, Y. Mao, X. Feng, L. Lu, H. Wang, M. Ouyang, Energy Environ. Sci. 2023, 16, 3552–3563.
This project is funded as a part of the FB2-SAFE platform of the Cluster Competence for Solid-state Batteries (FestBatt) by Bundesministerium für Bildung und Forschung.
