Sulfide‐based solid electrolytes (SEs) are amongst the most promising solid electrolytes for the development of solid‐state batteries (SSBs) due to their high ionic conductivity and processing advantage over oxide‐based SEs. However, one of the main drawbacks of sulfide SEs is their rapid degradation in presence of humidity. In this study, we investigated the effect of exposing three different sulfide SEs (Li₇P₃S₁₁, the argyrodite Li₆PS₅Cl and the chloride‐doped argyrodite Li_6‐xPS_5‐xCl_1+x) to the atmosphere of a dry room at a dew point (DP)=−40 °C. For the first time to the best of our knowledge, enhanced infra‐red (IR) laser technology was employed to follow and quantify online and in‐situ H₂S evolution by the SEs in a dry room environment over 16 h. It was found that argyrodite compounds evolved approximately 8 times less H₂S compared to Li₇P₃S₁₁ over 16 h of exposure with peak concentrations between 5 and 16 ppm vol. The exposed materials were studied using X‐ray diffraction, Raman spectroscopy, electrochemical impedance spectroscopy, X‐ray photoelectron spectrometry (XPS) and galvanostatic cycling. XPS results revealed a formation of Li₂CO₃ on the surface of argyrodite SEs, which served as a robust passivation layer limiting considerably reactions with the dry room atmosphere.

Development of efficient accelerated stress test protocols for polymer electrolyte membrane fuel cells (PEMFCs) is an extremely important topic closely related to FC lifetime prediction and a decrease of the FC test costs. This work is dedicated to precise investigation of the impact of various accelerating factors on a FC performance over 1000 h scale. Five identical membrane electrode assemblies with Pt-based catalysts on the cathode and PtRu-based catalyst on the anode were studied using load cycling protocols. The impact of accelerating aging stressors and their combinations, such as carbon monoxide in fuel, frequency and amplitude of current cycling and regular electrochemical diagnostics via polarization curves and cyclic voltammograms measurements was thoroughly investigated. In addition, electrochemical cell behavior under fixed and varied fuel compositions is addressed. Total and irreversible cell performance losses are quantified for different aging tests. It is shown that the importance of aging factors can change depending on a test duration. This study combines large amount of experimental electrochemical data giving quantitative ranking for the importance of factors accelerating cell aging in operation conditions close to real ones for stationary fuel cells.

Wide commercialization of Li-ion batteries (LIBs) for electric transport stimulates a demand for safer batteries with higher energy density. Thiophosphate solid electrolytes (TSEs) for LIBs are one of the most promising candidates to replace a classical liquid electrolyte with volatile components owing to their high ionic conductivity values and appropriate mechanical properties for processing [1]. However, one of the main drawbacks of TSEs is their high sensitivity towards humidity even in trace amounts. The reactivity with water and moisture impacts the electrochemical properties of the electrolytes and leads to toxic H₂S emissions. This aspect plays a crucial role for the choice of LIB manufacturing environment (dry room characteristics) and requires fine understanding of underlying mechanisms to optimize a performance / cost ratio for solid-state batteries (SSBs). In the present study, a unique combination of characterisation methods was applied to investigate the reaction between densified Li₃PS₄ pellet and different levels of humidity (dew point (DP) -40 °C and DP=12 °C for 15 min and 2 h) from chemical and morphological/microstructural points of view. H₂S gas evolution was accurately quantified upon a TSE exposure to humid atmosphere using a home-made flow-through setup with differentiation between surface and bulk pellet reactivity [2]. Further, top-view propagation of Li₃PS₄ pellet degradation was investigated using SEM and EDX techniques showing fractures generated through gas released leading to some increase in the pellet porosity at DP= -40 °C; apparition of cracks and oxygen content raise in case of DP = 12 °C exposure. The bulk of the exposed pellets was probed using non-destructive X-ray nanotomography (ESRF, ID16b). Different scenarios were observed at low and high levels of humidity during 15 min and 2 h of the pellet exposure (see Fig.). Degradation front containing large pores and cracks propagated up to 50 µm to the depth of the pellet (~400 µm total thickness) after 2 h of exposure to DP= 12 °C. X-ray diffraction-computed tomography (XRD-CT, ESRF, ID15a) was employed to observe structural changes in 3D for Li₃PS₄ SE upon its reaction with humidity at different depths. Minor changes were find in crystalline structure of Li₃PS₄ after DP= -40 °C exposure while a reaction at DP=12 °C provoked formation of new phases propagating up to 90 µm depth of the pellet. Some of newly formed compounds were identified, i.e. P₂S₂O₃, Li₂HPO₃, P₂O₅ and Li₂S₂O₆.2H₂O. Structural strains for Li₃PS₄ crystalline phase after its exposure to DP=12 °C were revealed thanks to advanced XRD-CT analysis. Finally, the impact of the pellet exposure to humidity at different conditions on its ionic conductivity was investigated. As a result of this study, a solid link was found between the morphological, microstructural, chemical degradation of the TSE and its ionic conductivity upon reaction with water. It was evidenced that the crack formation and propagation to the bulk of TSE pellet is a result of a complex cyclic mechanism, which includes chemical attack of H₂O molecules on Li₃PS₄ pellet surface, creation of mechanical strain for the TSE lattice, formation of solid degradation products and gaseous H₂S, crack propagation due to the strain release and the gas evolution, further penetration of water to the bulk of the pellet, etc. To the best of our knowledge, this is a first comprehensive study of reaction between SSE and humidity taking into account all the aspects above. This work contributes to understanding of key triggers for TSE deterioration in contact with different concentrations of water and to definition of proper environment for solid-state batteries production and handling. Beamtime at the ESRF was granted within the Battery Pilot Hub MA4929 “Multi-scale Multi-techniques investigations of Li-ion batteries: towards a European Battery Hub. References: [1] Y. Zheng et al., A review of composite solid-state electrolytes for lithium batteries: fundamentals, key materials and advanced structures, Chem. Soc. Rev., 2020, 49, 8790. [2] X. Randrema, I. Leteyi Mfiban, M. Soler, I. Profatilova et al, Towards a Practical Use of Sulfide Solid Electrolytes in Solid-State Batteries: Impact of Dry Room Exposure on H₂S Release and Material Properties, Batteries& Supercaps 2024, 7, e20230038. Figure 1