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Controlling trace humidity is vital for both the fabrication and long-term stability of metal halide perovskite (MHP) solar cells. Relevant humidity levels are typically below 10 ppmV, especially in glovebox-based processing and in well-encapsulated devices. Even minute amounts during fabrication can influence crystallization, introducing defects and lowering efficiency. Over time, humidity accelerates degradation of the perovskite layer and internal interfaces, ultimately reducing operational lifetime. Probing these effects at low concentrations under operando conditions is therefore essential for advancing device performance and durability. In this work, we employed a high-precision transfer standard dew point hygrometer to investigate humidity levels between 5 and 35 ppmV in non-encapsulated MHP solar cells. To permit unobstructed water migration during operation, we fabricated interdigital back contact devices. Operando measurements revealed water transport through the perovskite layer and enabled quantification of outgassing. Under trace-humidified conditions, devices exhibited initial charge-carrier quenching, followed by gradual recovery. Notably, the photocurrent response to humidified nitrogen demonstrated that the MHP layer behaves fully reversibly within the explored timescale and across the investigated humidity levels and conditions. These findings establish a systematic operando framework for examining extrinsic stressors in perovskites and highlight opportunities for assessing passivation strategies.
Controlling trace humidity is vital for both the fabrication and long-term stability of metal halide perovskite (MHP) solar cells. Relevant humidity levels are typically below 10 ppmV, especially in glovebox-based processing and in well-encapsulated devices. Even minute amounts during fabrication can influence crystallization, introducing defects and lowering efficiency. Over time, humidity accelerates degradation of the perovskite layer and internal interfaces, ultimately reducing operational lifetime. Probing these effects at low concentrations under operando conditions is therefore essential for advancing device performance and durability. In this work, we employed a high-precision transfer standard dew point hygrometer to investigate humidity levels between 5 and 35 ppmV in non-encapsulated MHP solar cells. To permit unobstructed water migration during operation, we fabricated interdigital back contact devices. Operando measurements revealed water transport through the perovskite layer and enabled quantification of outgassing. Under trace-humidified conditions, devices exhibited initial charge-carrier quenching, followed by gradual recovery. Notably, the photocurrent response to humidified nitrogen demonstrated that the MHP layer behaves fully reversibly within the explored timescale and across the investigated humidity levels and conditions. These findings establish a systematic operando framework for examining extrinsic stressors in perovskites and highlight opportunities for assessing passivation strategies.
Lithium isotopic fractionation is well-established in dynamic geochemical systems; however, its role in lithium-ion batteries (LIBs) remains uninvestigated. Herein, we report the first depth-resolved demonstration that isotopic separation occurs during Li-ion cell operation whose magnitude depends on the cycling history. Using depth-resolved glow discharge mass spectrometry, we monitored the 7Li/6Li ratio in LiNi0.333Mn0.333Co0.333O2 (NMC111)||graphite coin cell electrodes at defined life-cycle stages. Different charging rates were examined to get mechanistic insight into kinetic and thermodynamic control in the fractionation process. Although pristine electrodes exhibit a uniform isotopic ratio, cycled electrodes show a distinct 7Li enrichment in the positive electrode and a corresponding accumulation of 6Li at the surface of the negative electrode. The degree of isotopic separation varies with the charging rate. Isotopic signatures correlate with capacity fading, indicating lithium isotope mapping as a sensitive diagnostic tool for tracking electrode degradation and the evolution of the electrode–electrolyte interphases in LIBs.
The research conducted at the Federal Institute for Material Research and Testing (BAM) focuses on key challenges of the energy transition, spanning hydrogen technologies, electrical energy storage, and renewable energy systems. In the field of energy storage, our primary areas of interest include the safety of electrical energy storage systems, sustainable energy materials, and advanced battery diagnostics.
One of our central objectives is to deepen our understanding of the processes contributing to lithium-ion cell degradation, an essential step toward improving next-generation systems and meeting the rapidly growing demand for lithium-ion battery technology. The complexity of these systems, which comprise organic and inorganic compounds in multiple aggregation states, presents significant analytical challenges.
To address these challenges, we are developing novel analytical methods to further expand our insight into battery degradation mechanisms. Using GD-MS for depth-resolved lithium isotope analysis, we have recently established a correlation between lithium isotope fractionation and the growth of electrode–electrolyte interphases at electrode surfaces. In addition, we are developing GD-OES and LIBS methods for depth-resolved and lateral fluorine analysis, respectively, of lithium-ion battery electrodes to monitor electrolyte and additive degradation. These approaches might also provide valuable analytical tools for assessing the homogeneity of fluorinated active materials.
The research conducted at the Federal Institute for Material Research and Testing (BAM) focuses on key challenges of the energy transition, spanning hydrogen technologies, electrical energy storage, and renewable energy systems. In the field of energy storage, our primary areas of interest include the safety of electrical energy storage systems, sustainable energy materials, and advanced battery diagnostics.
One of our central objectives is to deepen our understanding of the processes contributing to lithium-ion cell degradation, an essential step toward improving next-generation systems and meeting the rapidly growing demand for lithium-ion battery technology. The complexity of these systems, which comprise organic and inorganic compounds in multiple aggregation states, presents significant analytical challenges.
To address these challenges, we are developing novel analytical methods to further expand our insight into battery degradation mechanisms. Using GD-MS for depth-resolved lithium isotope analysis, we have recently established a correlation between lithium isotope fractionation and the growth of electrode–electrolyte interphases at electrode surfaces. In addition, we are developing GD-OES and LIBS methods for depth-resolved and lateral fluorine analysis, respectively, of lithium-ion battery electrodes to monitor electrolyte and additive degradation. These approaches might also provide valuable analytical tools for assessing the homogeneity of fluorinated active materials.
The research conducted at the Federal Institute for Material Research and Testing (BAM) focuses on key challenges of the energy transition, spanning hydrogen technologies, electrical energy storage, and renewable energy systems. In the field of energy storage, our primary areas of interest include the safety of electrical energy storage systems, sustainable energy materials, and advanced battery diagnostics.
One of our central objectives is to deepen our understanding of the processes contributing to lithium-ion cell degradation, an essential step toward improving next-generation systems and meeting the rapidly growing demand for lithium-ion battery technology. The complexity of these systems, which comprise organic and inorganic compounds in multiple aggregation states, presents significant analytical challenges.
To address these challenges, we are developing novel analytical methods to further expand our insight into battery degradation mechanisms. Using GD-MS for depth-resolved lithium isotope analysis, we have recently established a correlation between lithium isotope fractionation and the growth of electrode–electrolyte interphases at electrode surfaces. In addition, we are developing GD-OES and LIBS methods for depth-resolved and lateral fluorine analysis, respectively, of lithium-ion battery electrodes to monitor electrolyte and additive degradation. These approaches might also provide valuable analytical tools for assessing the homogeneity of fluorinated active materials.
Since their introduction, Lithium-ion batteries (LIBs) have revolutionized the world of portable electronics and sustainable mobility[1]. LIBs currently play a pivotal role across several sectors, thanks to their long cycle life, fast-charging capabilities, unmatched energy densities, and a broad operating temperature range. Given the increasing demand of this technology[2,3], challenges including safety concerns, limited resource availability, and environmental impact need to be addressed. To improve the next-generation systems, understanding the cell degradation pathways is crucial. However, the complexity of these systems, comprising organic and inorganic compounds in various aggregation states, poses challenges to studying the involved degradation processes.
Inspired by geochemical studies, which displayed lithium isotope fractionation in dynamic natural systems, attributed to the high mass difference (ca. 16%) between the heavier (ca. 7Li, 92.5%) and the lighter isotope (ca. 6Li, 7.5%)[4], this work investigates weather a difference in Li isotope distribution within battery components can serve as a diagnostic and/or predictive tool for determining the remaining useful lifetime (RUL) of batteries[5].
Initial observations of Li isotope variation during battery aging were made in commercial cells. This was followed by systematic studies based on lab-scale coin-cells fabricated with different cathode materials[6]. While multicollector ICP-MS (MC-ICP-MS) investigation of each cell component enabled quantification of Li isotope fractionation in new and aged batteries with a 0.2 ‰ precision, glow discharge mass spectrometric (GD-MS) analysis provided spatially resolved information on Li isotopic distribution variation upon cells aging. The results display a meaningful correlation between post-mortem chemical analysis and electrochemical cells’ performance, highlighting the potential of Li isotope distribution in the electrodes as both a benchmark for battery degradation and a valuable indicator for assessing battery RUL.
Primary gas standards for the determination of sulfur-based impurities at trace level in hydrogen
(2026)
Hydrogen fuel quality needs to comply with ISO 14687:2025 to avoid harmful impact on applications using proton-exchange membrane (PEM) fuel cells. For total sulfur as one of the most impactful contaminants, an amount fraction of 4 nmol/mol has been set as threshold (so-called Grade D quality). In this study, novel gaseous primary gas standards (PGS) of seven sulfur compounds were prepared either gravimetrically at 1000 nmol/mol, 100 nmol/mol, and 10 nmol/mol, or dynamically diluted down to 4 nmol/mol in hydrogen and argon matrices with relative expanded uncertainties well below 10 % (k = 2) and proven stability of at least 9–12 months. Two different cylinder passivation treatments were compared, with one treatment identified as unsuitable since reactions took place within the mixture. By performing a cross-check study, equivalence between both sets of PGS could be demonstrated (≤ 5 % relative deviation for most of the sulfur species).
Trace ammonia impurities in hydrogen fuel poison proton-exchange-membrane fuel cells (PEMFC), causing irreversible performance degradation. Accurate quantification of ammonia in so-called Grade D hydrogen fuel is crucial for ensuring PEMFCs long-term operational stability and performance. According to ISO 14687 grade D hydrogen fuel sets a stringent threshold value of just 100 nmol/mol for ammonia impurities. Given the potential of an ammonia-based hydrogen supply chain, reliable quantification of ammonia contamination appears even more relevant.
Hydrogen quality assessments for ammonia impurities typically employ techniques such as gas chromatography, cavity-enhanced absorption spectroscopy, or mass spectrometry. These techniques, however, require stable reference gases for calibration and long-term method validation. Typically, gravimetrically produced reference gases are used. However, ammonia poses unique challenges due to its chemical reactivity and stickiness. By applying (ultra )long-path Optical Feedback Cavity Enhanced Absorption Spectroscopy we observed that above a certain amount of ammonia, the gravimetric amount deviates from the analytically determined amount. This discrepancy most likely arises due to strong adsorption of ammonia onto the inner surface of the gas cylinder. Therefore, we investigated the lowest gravimetrically preparable amount of ammonia in hydrogen for which the analytically measured amount of the cylinder remains congruent with the gravimetric amount of substance. We further investigated the applicability of passivated cylinders for trace ammonia gas standards and compared their performance to aluminum alloy cylinders. To confirm reproducibility of our results, we conducted three independent gravimetric preparation campaigns, each employing optimizations, or changes in methodology, at different times. Finally, we investigated whether those gravimetrically prepared trace amounts of ammonia in hydrogen gas standards were long-term-stable.
Beyond gravimetrically prepared gas standards, we evaluated how a cutting-edge dynamic dilution system could reliably extend trace-ammonia calibration down to the ISO limit of 100 nmol/mol. For this purpose, we developed an advanced dynamic dilution system capable of a one-in-a-billion dilution ratio, validated for its SI traceability, reproducibility, and operational limits by applying an internal standard.
In summary, our results demonstrate that precise dynamic dilution, coupled with concentrated gravimetrically prepared ammonia gas mixture, provides a route to full SI-traceable trace-ammonia reference sample gases.