Timo Weintraut

As an alternative to hexavalent chromium plating, chloride-based hydrate melts enable crystalline chromium electrodeposition from trivalent chromium without the use of organic complexing agents. Cr films deposited from these hydrate melt-based baths uniquely contain a metastable δ -Cr phase absent in conventional baths. Achieving hard coatings with adequate mechanical properties requires a systematic understanding of the crystallographic features including phase formation. In this study, the deposition of δ -Cr and its subsequent phase transformation to α -Cr were systematically investigated from the perspectives of crystal growth mode and hydrogen incorporation. The results indicate that δ -Cr preferentially forms during the initial nucleation and coalescence stage, where isotropic fine grains are generated. As electrodeposition proceeds, the crystal growth mode transitions to columnar growth, in which α -Cr becomes the dominant phase. The obtained δ -Cr was confirmed to transform into α -Cr at relatively low temperatures ranging from room temperature to 250 °C. The thermal desorption spectrum of hydrogen and time-of-flight secondary-ion mass spectrometry (ToF-SIMS) experiments using deuterium as a stable isotope label suggest that the formation and stability of the electrodeposited δ -Cr phase may well be attributed to incorporated hydrogen. These findings provide a fundamental basis for microstructural control of electrodeposited Cr from chloride-based hydrate melts.

Although lithium–oxygen batteries (LOBs) offer an exceptionally high theoretical gravimetric energy density, the long‐standing trade‐off between high capacity and cyclability remains unsolved. In particular, discharge via the solution pathway, which enables three‐dimensional deposition of Li ₂ O ₂ within the porous cathode and thus high capacity, has generally been regarded as detrimental to rechargeability because discharge products can also be deposited onto electrochemically isolated off‐cathode sites. Here, we provide direct and unambiguous experimental evidence that such off‐cathode discharge products—formed on electrically insulating polyphenylene sulfide (PPS) fibers interwoven with conductive carbon fibers—are completely decomposed during charging in an amide‐based electrolyte. This finding overturns the prevailing assumption that solution‐mediated discharge inherently compromises rechargeability. Our findings indicate that, with appropriate control of cathode architecture and electrolyte chemistry, the solution pathway may be compatible with reversible charging. This insight reshapes the fundamental understanding of Li ₂ O ₂ redox chemistry in LOBs.

Sulfide‐based solid electrolytes (SEs) are among the most promising candidates for solid‐state batteries due to their high ionic conductivity and low grain boundary resistance. However, their chemical and electrochemical instability when paired with lithium metal renders them susceptible to severe degradation reactions. To prevent contact between lithium metal and SEs, polymer electrolyte (PE) interlayers are proposed as a solution, enabling the potential use of SEs in lithium metal solid‐state batteries. These interlayers, however, lead to the formation of rarely studied PE|SE interfaces, which significantly influence battery performance. This study examines the interphase formed and charge transfer process at the PE|SE interface between polyethylene oxide (PEO)‐based PE and Li ₁₀ GeP ₂ S ₁₂ (LGPS) SE using a four‐electrode cell configuration. X‐ray photoelectron spectroscopy (XPS) and time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS) reveal that thermal degradation at the PEO‐LiTFSI|LGPS interface leads to the formation of a low resistance interphase containing polysulfides (S _n ²⁻ ), sulfites (SO ₃ ²⁻ ), LiF, and P‐[S] _n ‐P type bridged PS ₄ ³⁻ units. Overall, the interface resistance is only 4.4 Ω cm ² at 80°C. Given the diverse chemical and electrochemical interactions of sulfide‐based SEs with PEO‐based PEs, our findings contribute to a deeper understanding of the low‐resistive interphase, aiding in optimizing PE‐SE combinations for lithium metal solid‐state batteries.

Electrolyte interfaces with freshly plated lithium metal are crucial for the development of reservoir‐free all‐solid‐state batteries (ASSBs). This study provides an in‐depth characterization of the polyethylene oxide (PEO) lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) interphase with lithium metal resembling reservoir‐free cell conditions. Using an in situ setup in both secondary ion mass spectrometry (SIMS) and X‐ray photoelectron spectroscopy (XPS), the dynamic evolution of the solid electrolyte interphase (SEI) layer is investigated at 60 °C. Lithium metal plating is conducted with an electron flood gun, ensuring controlled lithium deposition and enabling direct identification of intermediate reaction products. Time‐of‐flight‐ (ToF‐) and Orbitrap‐SIMS are employed to provide high‐resolution insights into the formation of inorganic and organic SEI components coming from PEO and LiTFSI degradation after plating. XPS further reveals chemical transformations occurring at the interface. Additionally, coulometric titration time analysis (CTTA) captures the kinetic aspect of PEO: LiTFSI reaction with lithium metal, highlighting the influence of molecular weight and salt concentration on initial reaction speed and long‐term stability. By integrating high‐resolution SIMS analysis with surface‐sensitive XPS and electrochemical methods, a comprehensive approach is offered to better understand the dynamic behavior of the polymer electrolyte | lithium metal interphase under conditions relevant to reservoir‐free battery concepts.

In mass spectrometry imaging (MSI), ion suppression can lead to a misinterpretation of results. Particularly phospholipids, most of which exhibit high gas-phase basicity (GB), are known to suppress the detection of metabolites and drugs. This study was initiated by the observation that the signal of an herbicide, i.e., atrazine, was suppressed in MSI investigations of earthworm tissue sections. Herbicide accumulation in earthworms was investigated by time-of-flight secondary ion mass spectrometry and matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI-MSI). Additionally, earthworm tissue sections without accumulation of atrazine but with a homogeneous spray deposition of the herbicide were analyzed to highlight region-specific ion suppression. Furthermore, the relationship of signal intensity and GB in binary mixtures of lipids, amino acids, and atrazine was investigated in both MSI techniques. The GB of atrazine was determined experimentally through a linear plot of the obtained intensity ratios of the binary amino acid mixtures, as well as theoretically. The GBs values for atrazine of 896 and 906 kJ/mol in ToF-SIMS and 933 and 987 kJ/mol in MALDI-MSI were determined experimentally and that of 913 kJ/mol by quantum mechanical calculations. Compared with the GB of a major lipid component, phosphatidylcholine (GBPC = 1044.7 kJ/mol), atrazine’s experimentally and computationally determined GBs in this work are significantly lower, making it prone to ion suppression in biological samples containing polar lipids.