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Aiming at a molecular-level understanding of the processes at the electrode|electrolyte interface (EEI), we investigated the interaction between the battery-relevant ionic liquid (IL) 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide ([BMP]+[TFSI]−), Li, and CoO(111) thin films on Ru(0001) as a model study of the solid|electrolyte interphase (SEI) in Li-ion batteries. Employing mainly angle-dependent X-ray photoelectron spectroscopy and scanning tunneling microscopy, in combination with dispersion-corrected density functional calculations for characterization of the CoO(111) surface, we found that vapor deposition of metallic Li on CoO(111) at 300 K results in the conversion of Co2+to Co0, together with the formation of Li2O and adsorbed surface Li2O2. The conversion starts in the near-surface region (1–2 nm) and proceeds in the extended-surface region (6–8 nm). If the surface is precovered by molecularly adsorbed [BMP][TFSI] species (solvent/electrolyte), stepwise postdeposition of small amounts of Li results in gradual decomposition of [TFSI] and [BMP] (=SEI formation), forming products such as Li3N, Li2S, LiF, LiwCxHyNz, and other Li-bound fragments of the anion (e.g., LiNSO2CF3). For higher amounts of Li deposition, relative to the IL precoverage, IL decomposition is followed by conversion of CoO(111). Hence, the SEI resulting from IL decomposition is permeable for Li, which is essential for the storage of Li in the CoO(111) anode. This study demonstrates the potential of model studies for a molecular-scale understanding of the initial stages of SEI formation at the EEI and its role in Li storage in a CoO(111) model anode.

We report results of a combined experimental and computational model study on the interaction of the battery-relevant ionic liquid (IL) 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide ([BMP]+[TFSI]−) with Li on pristine highly oriented pyrolytic graphite (HOPG), which aims at a molecular-/atomic-level understanding of the processes at the electrode|electrolyte interface of Li-ion batteries. Employing mainly X-ray and ultraviolet photoelectron spectroscopy as well as dispersion-corrected density functional calculations (DFT-D), we find intact anion–cation pairs for adsorbed [BMP]+[TFSI]−(sub)monolayers on HOPG at 300 K and also on lithiated HOPG at 80 K, that is, under conditions where the mobility of Li+in the bulk is low. Vapor deposition of [BMP]+[TFSI]−on lithiated HOPG at 300 K results in rapid accumulation of Liδ+at the surface or in the surface region, indicating that deintercalation is activated under these conditions. This is explained by a dynamic equilibrium between bulk Li+and surface Liδ+, which is established independent of whether Li is deposited as metallic Li0from the vacuum side or segregates as Li+from the bulk of lithiated HOPG to the surface and which is shifted to the side of surface Liδ+by stabilization of these species. Stabilization occurs either by formation of stable Li-containing surface compounds by reactive decomposition mainly of the [TFSI]−anions (Li3N, Li2S, LiF, etc.) or by interaction of partially charged Liδ+species with [TFSI]−anions in the adlayer. DFT-D calculations reveal that a possible initial step in the reactive decomposition is the transfer of electrons from the HOPG surface covered with Liδ+into the lowest unoccupied molecular orbital of [TFSI]−, resulting in elongation and cleavage of the S–N bond and finally insertion of Li into it. Alternatively, stabilization of Liδ+is possible by formation of a polar bond with the oxygen atoms of [TFSI]−within the IL adlayer. The resulting calculated work function decrease ΔΦ with respect to that of the bare graphite (0001) surface is in excellent agreement with experimental observations. The interaction of [BMP]+[TFSI]−and Li at the HOPG interface is considered as the initial stage of the solid|electrolyte interphase formation at the electrode|electrolyte interface in Li-ion batteries.

In this work, we aim at a molecular scale understanding of the interactions and structure formation at the electrode|electrolyte interface (EEI) in Li-ion batteries. Therefore, the interaction of the key electrolyte component ethylene carbonate (EC) with Cu(111) was investigated under ultrahigh vacuum conditions. Scanning tunneling microscopy (STM), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIRS), and dispersion-corrected density functional theory (DFT-D) calculations were employed. After vapor deposition of EC (sub-) monolayers on Cu(111) at 80 K, STM measurements (100 K) reveal a well-ordered commensurate superstructure, in which EC molecules assume different configurations and whose total adsorption energy is mainly governed by van der Waals interactions, as demonstrated by DFT-D. In the temperature range between 150–220 K, competing desorption and decomposition into −CO, −C–O–C–, −C–H, and −C–C– compounds, as derived by XPS and confirmed by FTIRS, result in distinct changes of the adlayer composition. Similar heating of an EC multilayer film from 80 K to room temperature results in a surface that is almost completely covered with adsorbed, carbon-containing decomposition products. This can be interpreted as the initial stage of chemical EEI formation, and the relevance of these results for battery applications is discussed.

The electrochemical activation of Li2MnO3domains in Li- and Mn-rich layered oxides (LRLO) is highly important, and can be tuned by surface modification of the active materials to improve their cycling performance. In this study, citric acid was employed as a combined organic acid, reducing agent, and carbon precursor in order to remove surface residues from the calcination process, implement an oxygen deficient layer on the surface of the primary LRLO particles, and cover their surface with a carbon-containing coating after a final annealing step. A broad selection of bulk and surface sensitive characterization methods was used to characterize the post-treated spherical particles, providing the evidence for successful creation of an oxygen deficient near-surface region, covered by carbon-containing deposits. Post-treated materials show enhanced electrochemical discharge capacities after progressive Li2MnO3activation, reaching maximum capacities of 247 mAh g−1. Gassing measurements reveal the suppression of oxygen release during the first cycle, concomitant with an increased CO2formation for the carbon-coated materials. The voltage profile analysis in combination with post-mortem characterization after 300 cycles provide insights into the aging of the treated materials, which underlines the importance of the relationship between structural changes during scalable post-treatment and the electrochemical performance of the powders.

The ionic liquid (IL) 1-butyl-1-methylpyrrolidinium bis(trifluoro-methylsulfonyl)imide [BMP][TFSA] is a promising candidate for improved next-generation rechargeable lithium–ion batteries. We here report results of a model study of the reactive interaction of (sub-)monolayers and multilayers of [BMP][TFSA] with lithium (Li) on Cu(111), employing scanning tunnelling microscopy (STM), X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared spectroscopy (FTIRS) under ultrahigh vacuum (UHV) conditions. Upon post-deposition of Li on [BMP][TFSA] multilayers at 80 K, we identified changes in the chemical state of the [TFSA] anion and the [BMP] cation as well as in the IR absorption bands related to the anion. These changes are most likely due to the decomposition of the IL adlayer into a variety of products like LiF, Li2S, and Li2O upon anion decomposition and LiN3, LiCxHyN, and LixCHyupon cation decomposition, where the latter includes cracking of the pyrrolidinium ring. Deposition of Li on [BMP][TFSA] (sub-)monolayer-covered surfaces led to similar decomposition patterns, and the same was also observed for the reverse deposition order. The addition of the corresponding amounts of Li to a [BMP][TFSA] adlayer resulted in distinct changes in the STM images, which must be due to the surface reaction. After annealing to 300 K, the core-level peaks of the cation lose most of their peak area. Upon further heating to 450 K, the anion is nearly completely decomposed, resulting in LiF and Li2S decomposition products that dominate the interface.

Supported gold nanoparticles are widely studied catalysts and are among the most active known for the low-temperature water–gas shift reaction, which is essential in fuel and energy applications, but their practical application has been limited by their poor thermal stability. The catalysts deactivate on-stream via the growth of small Au nanoparticles. Using operando X-ray absorption and in situ scanning transmission electron microscopy, we report direct evidence that this process can be reversed by carrying out a facile oxidative treatment, which redisperses the gold nanoparticles and restores catalytic activity. The use of in situmethods reveals the complex dynamics of supported gold nanoparticles under reaction conditions and demonstrates that gold catalysts can be easily regenerated, expanding their scope for practical application.

The morphology and stability of well-ordered, nanostructured Au/TiO2(110) surfaces, prepared by deposition of Au loaded micelles on TiO2(110) substrates and subsequent oxidative removal of the polymer shell in an oxygen plasma, was investigated by noncontact AFM, SEM and XPS. The resulting arrays of Au nanoparticles (particle sizes 1−5 nm) form a nearly hexagonal pattern with well-defined interparticle distances and a narrow particle size distribution. Particle size and particle separation can be controlled independently by varying the Au loading and the block-copolymers in the micelle shell. The oxygen plasma treatment does not affect the size and distance of the Au nanoparticles; the latter are fully metallic after subsequent UHV annealing (400 °C). The particles are stable under typical CO oxidation reaction conditions, up to at least 200°C, making these surfaces ideally suited as defined model systems for catalytic studies. Significant changes in the height distributions of the Au nanoparticles are found upon 400 °C annealing in O2. For adlayers with small interparticle distances, this leads to a bimodal particle size distribution, which together with the preservation of the lateral order points to Ostwald ripening.

Investigations of the electronic and magnetic properties of oxygen adsorbed on magnetized iron films have been carried out by means of angle and spin resolving photoelectron spectroscopy. Iron, epitaxially grown on W(100) and W(110) crystals, served as the ferromagnetic substrate. Exchange splittings of the O 2px derived level have been detected, demonstrating a magnetic coupling between the chemisorbate and the iron layer. Variations of the exchange splitting have occurred as a function of the oxygen coverage, photon energy, and emission angle. High oxygen exposures have lead to a FeO overlayer at the surface.

The electronic and magnetic properties of different kinds of adsorbates on thin magnetized Fe(100) films have been investigated by means of spin resolving photoelectron spectroscopy. The study has been carried out with atomically physisorbed xenon, the molecule carbon monoxide, and metallic gold. The spin splitting of the Xe 5p signal can be explained by magnetic interactions with the final ionic hole state. By spin analysis, it could be shown that at room temperature for low exposures the adsorption of CO is dissociative and with increasing exposure additionally molecular. The Au related features for the monolayer show different line shapes in both spin channels but no splittings due to an sp-like behavior of this interface state being dominated by minority character.