Open Access

Solid electrolytes (SEs) enable the use of alkali-metal negative electrodes (NEs) in solid- and semi-solid-state sodium batteries, increasing both energy density and safety for stationary and portable applications. NASICON (NA Super Ionic CONductor) ceramics provide 3-dimensional Na+ migration pathways and exhibit room-temperature (RT) ionic conductivities of ~1 mS/cm, a wide electrochemical stability window, and high thermal, mechanical and thermodynamic stability. As a result, they are among the most promising candidates for high-energy, RT sodium-sulfur (Na-S) batteries. A major challenge in the development of these systems is the poor interfacial contact between the SE and metallic NE, which leads to locally high current densities and frequent cell failure. Current research at BAM is focused on the development of novel NASICON electrolytes for room-temperature Na-S cells employing a liquid sodium-potassium (Na-K) alloy at the SE/NE interface. The Na-K alloy can significantly improve interfacial contact, but it also introduces new challenges related to interfacial stability and materials compatibility. To study and improve the stability of this interface, NASICON electrolytes are synthesized and tested at BAM. Different stoichiometries and synthesis routes are explored. The high-temperature reaction behavior is studied by thermogravimetric analysis (TGA), while key material properties - including densification, phase purity, grain size, and grain-boundary composition - are characterized by XRD, SEM/EDX, TGA, and ICP-OES. The conductivity of electrolytes is measured at different temperatures in a blocking electrode setup. Half cells employing Na metal and Na-K alloy interfaces are tested to assess interfacial stability and cyclability of the different electrolytes. The analysis establishes a link between synthesis routes, material properties, and electrochemical performance. This systematic study of the SE/NE interface provides fundamental insight into interfacial stability in the presence of Na–K alloys. It forms the basis for future work aimed at the rational design of tailored NASICON electrolytes with improved stability and performance for room-temperature Na–S batteries.

Ensuring the safety of electrochemical energy storage systems is a key challenge for the large-scale deployment of batteries in the energy transition. Incidents involving lithium battery fires have increased public and regulatory attention to battery safety, particularly for high-energy systems. A major safety concern is thermal runaway (TR), a critical failure process that can lead to rapid self-heating, the release of toxic and flammable gases, and ultimately fire and toxic gases. Solid-state batteries (SSBs) are widely considered a promising pathway to improve battery safety by replacing flammable liquid electrolytes with solid materials. While some SSB concepts still use polymer or hybrid electrolytes, all-solid-state batteries (ASSBs) rely entirely on solid components such as ceramic electrolytes and are therefore often expected to suppress classical TR mechanisms. However, experimental data enabling a comprehensive safety assessment of ASSBs remain limited. This work systematically investigates failure scenarios in liquid, semi-solid, and all-solid battery systems using electrical, mechanical, and thermal abuse methods. The resulting failure characteristics and safety-relevant mechanisms are compared providing new insights into the safety behavior of solid-state battery technologies.

Der Vortrag gibt einen kompakten, fachlich fundierten Überblick über aktuelle Entwicklungen in der Batterie-Sicherheit mit Schwerpunkt auf Lithium- und Natrium-Ionen-Batterien. Im Zentrum stehen deren sicherheitstechnische Bewertung als Gefahrgut, die Risiken des thermischen Durchgehens sowie die Bedeutung von Zellchemie, Ladezustand und Propagationsverhalten für Brand- und Transportgefahren. Darauf aufbauend werden bestehende und künftige Prüf- und Klassifizierungssysteme, insbesondere im Kontext der UN 38.3-Prüfungen und neuer gefahrbasierter Einstufungen, vorgestellt. Ergänzend beleuchtet der Vortrag aktuelle Arbeiten zu Verpackungsanforderungen, beschädigten oder defekten Batterien sowie zu neuen Batterietechnologien wie Natrium-Ionen-, Lithium-Luft- und Festkörperbatterien.

The reuse of lithium-ion batteries (LIBs) from electric vehicles (EVs) in second-life applications such as battery energy storage systems (BESSs) offers significant environmental and economic benefits. Beyond economic considerations, safety management is a key challenge for large-scale deployment, yet the influence of ageing on LIB safety remains insufficiently understood. Preger et al., emphasized in their review the existing gap on data about electrical abuse and high-capacity cells. This laboratory-scale study investigates the evolution of key safety parameters over battery lifetime. The present study contribute to closing this gap studying three types of LIB cells (Nickel Manganese Cobalt (NMC) chemistry) from EV and hybrid EV batteries that were artificially aged and tested at three representative states of health (SOH): 100% (beginning-of-life, BOL), 80% (end of first life), and 60% (midpoint of second life). Cells were subjected to thermal abuse, overcharge, and accelerating rate calorimetry, with selected tests coupled to online gas analysis. Results show a pronounced ageing effect on thermal stability. The onset temperature of thermal runaway was reduced by 17–69 ◦C for aged cells (60% SOH) compared with BOL cells, while overcharge acceptance decreased by 13–78%. Although aged cells exhibited lower thermal stability, their thermal runaway reactions under inert conditions were less severe, as indicated by lower maximum temperatures. These findings highlight the need to account for ageing-induced shifts in exothermic reaction onset and thermal runaway behavior when designing safe second-life BESS. Future work should extend the analysis to LFP chemistries especially as the market is expected to shift towards this chemistry and consider battery and system levels, including influence of ageing on thermal runaway propagation.

The present work demonstrates the application of a multimodal non-contact ultrasonic test technique as diagnostic tool for lithium-ion pouch cells. Different propagation modes of elastic waves (shear and longitudinal), different propagation directions (from normal to the cell plane to in the cell plane), and different wave analysis techniques (including time and frequency domain analysis, and propagation and resonant techniques) are applied. Air-coupled ultrasonic waves with frequencies ranging from 0.15 to 1.4 MHz were used in a through transmission configuration with varying incident angles from 0 to 60◦. As practical example, degradation in lithium-ion pouch was investigated. For this purpose, pristine and two types of altered cells were used. Alterations were induced by two deliberate degradation processes (deep discharge and calendar ageing). The information provided by the proposed multimodal ultrasonic technique is analyzed in combination with structural and electroanalytical data, and the a priori knowledge about the induced alterations to provide a first insight into the capabilities of the proposed technique. While the deep-discharge process introduces minor modifications in the ultrasonic response, the calendar ageing process produces a severe change, most likely, the result of a local and randomly distributed degradation of the mechanical continuity between the different layers (linked to electrodes modification, solid electrolyte interface modification, loss of compactness, appearance of cracks, gas generation, delaminations, etc.). These technologies can find applications in the research of new batteries, for inline quality test in fabrication and for second-life battery sorting.