Studies of Lithium-Oxygen Battery Electrodes by Energy- Dependent Full-Field Transmission Soft X-Ray Microscopy

Energy‐dependent full‐field transmission soft X‐ray microscopy is a powerful technique that provides chemical information with spatial resolution at the nanoscale. Oxygen K‐level transitions can be optimally detected, and we used this technique to study the discharge products of lithium‐oxygen batteries, where this element undergoes a complex chemistry, involving at least three different oxidation states and formation of nanostructured deposits. We unambiguously demonstrated the presence of significant amounts of superoxide forming a composite with peroxide, and secondary products such as carbonates or hydroxide. In this chapter, we describe the technique from the fundamental to the observation of discharged electrodes to illustrate how this tool can help obtaining a more comprehensive view of the phenomena taking place in metal air batteries and any system involving nanomaterials with a complex chemistry

Chapter Studies of Lithium-Oxygen Battery Electrodes by Energy- Dependent Full-Field Transmission Soft X-Ray Microscopy

The employment of printing techniques as cost-effective methods to fabricate low cost, flexible, disposable and sustainable solar cells is intimately dependent on the substrate properties and the adequate electronic devices to be powered by them. Among such devices, there is currently a growing interest in the development of user-oriented and multipurpose systems for intelligent packaging or on-site medical diagnostics, which would greatly benefit from printable solar cells as their energy source for autonomous operation

Facile preparation of glycine-based mesoporous graphitic carbons with embedded cobalt nanoparticles

This research was supported by the Spanish Ministry of Science and Innovation, through the "Severo Ochoa" Programme for Centers of Excellence in R&D (CEX2019-000917-S), the projects MAT2017-91404-EXP, RTI2018-096273-B-I00, RTI2018-3097753-B-I00, with FEDER co-funding, the CSIC program for the Spanish Recovery, Transformation and Resilience Plan "Plataforma Temática Interdisciplinar Transición Energética Sostenible+ (PTI-TRANSENER +)" funded by the Recovery and Resilience Facility of the European Union, established by the Regulation (EU) 2020/2094. The authors also acknowledge the Generalitat de Catalunya (2017SGR1687). W.W. gratefully acknowledges the support from the China Scholarship Council (CSC No.:201808340076). This work has been performed within the framework of the doctoral program in materials science of UAB (W. W.).A simple route has been developed for the preparation of mesoporous graphitic carbons with embedded cobalt nanoparticles just using glycine as a nitrogen source, cobalt nitrate and distilled water. After heating the mixture to 300 °C under magnetic stirring, a dry solid product was obtained, which was then carbonized at 900 ºC under argon atmosphere. Changing the glycine/Co molar ratio allowed controlling the size of the cobalt particles and their dispersion in the carbon matrix, the porosity of the carbon and its graphitic character. The carbon-metal composites obtained were tested as oxygen cathodes in Li-O batteries. Cells assembled exhibited a full discharge capacity up to 2.19 mAh cm at a current of 0.05 mA cm and over 39 cycles at a cutoff capacity of 0.5 mAh cm. This work provides a green, feasible and simple way to prepare mesoporous graphitic carbons with embedded cobalt nanoparticles without involving templates

Mapping Heterogeneity of Pristine and Aged Li‐ and N‐Mnhcf Cathode by Synchrotron‐Based Energy‐Dependent Full Field Transmission X‐ray Microscopy

Manganese hexacyanoferrate is a promising cathode material for lithium and sodium ion batteries, however, it suffers of capacity fading during the cycling process. To access the structural and functional characteristics at the nanometer scale, fresh and cycled electrodes are extracted and investigated by transmission soft X-ray microscopy, which allows chemical characterization with spatial resolution from position-dependent x-ray spectra at the Mn L-, Fe L- and N K-edges. Furthermore, soft X-rays prove to show superior sensitivity toward Fe, compare to hard X-rays. Inhomogeneities within the samples are identified, increasing in the aged electrodes, more dramatically in the Li-ion system, which explains the poorer cycle life as Li-ion cathode material. Local spectra, revealing different oxidation states over the sample with strong correlation between the Fe L-edge, Mn L-edge, and N K-edge, imply a coupling between redox centers and an electron delocalization over the host framework

Soft x-ray transmission microscopy on lithium-rich layered-oxide cathode materials

Energy-dependent full field transmission soft X-ray microscopy (TXM) is able to give a full picture at the nanometer scale of the chemical state and spatial distribution of oxygen and other elements relevant for battery materials, providing pixel-by-pixel absorption spectrum. We show different methods to localize chemical inhomogeneities in Li$_{1.2}$Mn$_{0.56}$Ni$_{0.16}$Co$_{0.08}$O$_{2}$ particles with and without VOx coating extracted from electrodes at different states of charge. Considering the 3d(Mn,Ni)-2p(O) hybridization, it has been possible to discriminate the chemical state of Mn and Ni in addition to the one of O. Different oxidation states correspond to specific features in the O-K spectra. To localize sample regions with specific compositions we apply two different methods. In the first, the pixel-by-pixel ratios of images collected at different key energies clearly highlight local inhomogeneities. In the second, introduced here for the first time, we directly correlate corresponding pixels of the two images on a xy scatter plot that we call phase map, where we can visualize the distributions as function of thickness as well as absorption artifacts. We can select groups of pixels, and then map regions with similar spectral features. Core-shell distributions of composition are clearly shown in these samples. The coating appears in part to frustrate some of the usual chemical evolution. In addition, we could directly observe several further aspects, such as: distribution of conducting carbon; inhomogeneous state of charge within the electrode; molecular oxygen profiles within a particle. The latter suggests a surface loss with respect to the bulk but an accumulation layer at intermediate depth that could be assigned to retained O$_{2}$

Photoelektronspektroskopie zur Interkalationsreaktion von Alkalimetallen in Übergangsmetalldichalkogeniden

### Cover and Abstracts ### Table of contents ### 1 Introduction ### 2 Fundamentals 2.1 Transition metal dichalcogenides 2.2 The intercalation reaction 2.3 Motivation and outline of the present work ### 3 Experimental 3.1 Photoelectron spectroscopy 3.2 UHV equipment and spectrometer systems 3.3 Preparative methods 3.4 Ex-situ characterization techniques ### 4 Thin film synthesis 4.1 Low-pressure growth techniques 4.2 The electronic structure of TiX2 4.3 Optimization 4.4 The reaction mechanism 4.5 Ex-situ characterizations ### 5 Intercalation 5.1 Deposition on single crystals 5.2 Co-deposition experiments 5.3 Deposition on thin films 5.4 In-situ electrochemical intercalation ### 6 Discussion and conclusions 6.1 Binding energy shifts and charge transfer 6.2 The ionic and electronic contributions to the electrochemical potential 6.3 Summary of results and perspectives ### References ### List of abbreviations ### PublicationsThe insertion of alkali atoms into appropriate solid materials, also known as intercalation, is thermodynamically strongly favored for certain host-guest combinations, and advanced batteries are based on this process. Goal of the present work was a systematic investigation by photoelectron spectroscopy of the intercalated phase as a function of the host, the guest and its concentration. Na has been deposited onto layered dichalcogenides of formula MX2, using transition metals of the groups IVb (Ti) and Vb (Ta) and chalcogens of different size (S and Se). In spite of the different electronic properties of the host, only similar general features could be observed between TiX2 and TaX2: shift of the chalcogen levels to higher binding energies, broadening of the transition metal levels, and a small decrease of the work function. Instead, whereas the opening of a large gap was induced between the valence states Ti 3d and S 3p states of TiS2 no comparable effect was observed in the corresponding states of TiSe2. Alkali metals of different size have been compared by co-deposition onto the same host sample. It has been found that in general smaller atoms have a higher intercalation driving force, even being able to induce the deintercalation of larger species if previously deposited. Due to fast alkali diffusion into the bulk of the crystals it was not possible to study highly intercalated samples. For this purpose an UHV preparation of TiS2 thin films has been developed. With TiS2 thin films as substrate no limiting alkali concentration was observed, demonstrating the possibility to in-situ prepare fully intercalated materials. With the same preparation TiS2 thin films could be deposited onto Na-b ''-Al2O3, a well-known solid Na+ ion conductor. Therefore it was possible to in-situ prepare a solid-state electrochemical cell, which could be operated in UHV in a coupled electrochemical and PES measurement. Thus, not only the guest concentration can be controlled at unparalleled level by keeping the electronic structure under control. Since the electrode potential depends on the chemical potential of the guest in the host matrix, a correlation between thermodynamic data and electronic structure is possible. The chemical potential of the guest atom is considered to split in an electronic and an ionic contribution corresponding to the separated interactions of inserted electrons and ions with the host. Both contributions vary along intercalation following the potential drop. The ionic component contributes for about one third to the battery voltage. A detailed analysis of the shifts of binding energies suggests a partial charge transfer from the intercalated alkali metal to the transition metal, but also to the chalcogen.Die Einlagerung von Alkaliatomen in geeignete Festkörper, auch bekannt als Interkalation, ist für geeignete Wirt-Gast-kombinationen thermodynamisch stark bevorzugt, und hochentwickelte Batterien basieren auf diesem Prozeß. Ziel dieser Arbeit war die systematische Untersuchung durch Photoelektronspektroskopie der Interkalationsphasen in Abhängigkeit von dem Wirt, dem Gast und seiner Konzentration. Na wurde auf Schichtgitter der Formel MX2 mit Übergangsmetallen der Gruppen IVb (Ti) und Vb (Ta) und Chalkogene von unterschiedlicher Größe (S und Se) aufgedampft. Trotz der unterschiedlichen elektronischen Eigenschaften des Wirtes, wurden im Allgemein ähnliche Eigenschaften zwischen TiX2 und TaX2 beobachtet: die Verschiebung der elektronischen Niveaus des Chalkogen zu höheren Bindungsenergien, Verbreiterung der Übergangmetallniveaus und eine geringe Abnahme der Austrittsarbeit. Andererseits konnte die Ausbildung einer großen Bandlücke zwischen den Ti 3d und S 3p Zuständen im TiS2 in den entsprechenden Zuständen von TiSe2 nicht beobachtet werden. Alkalimetalle unterschiedlicherer Größe sind durch sequentielles Aufdampfen auf die gleiche Probe verglichen worden. Es konnte festgestellt werden, daß kleinere Atome eine höhere Interkalationstriebskraft aufweisen. Sie können sogar die Deinterkalation der größeren Alkaliatome verursachen. Wegen der schnellen Alkalidiffusion in das Kristallvolumen war es nicht möglich, interkalierte Proben mit hohen Konzentrationen herzustellen. Zur Untersuchung höherer Konzentrationen ist eine UHV-Herstellung von dünnen TiS2 Filmen entwickelt worden. Mit diesen dünnen Schichten wurde keine alkali Begrenzungskonzentration beobachtet. Das beweist die Möglichkeit in-situ völlig interkalierte Materialien zu präparieren. Bei der gleichen Herstellung konnten TiS2 Schichten auf Na-b ''-Al2O3, ein bekannter Na+ Festkörper-Ionenleiter, abgeschieden werden. Folglich war die Untersuchung einer in-situ hergestellten elektrochemischen Festkörperzelle möglich, die im UHV in einer gekoppelten elektrochemischen und PES-Messung verwendet werden könnte. Die Gastkonzentration wurde damit auf bisher unerreichter Stufe kontrolliert, und die elektronische Struktur wurde gleichzeitig beobachtet. Da die Elektrodenspannung vom chemischen Potential des Gastes in der Wirtsmatrix abhängt, ist damit ein Zusammenhang zwischen thermodynamischen Daten und elektronischer Struktur herzustellen. Das chemische Potential des Gastatoms wurde in einen elektronischen und ionischen Beitrag aufgeteilt, was den getrennten Wechselwirkungen zwischen eingelagerte Elektronen und Ionen mit dem Wirt entspricht. Beide Beiträge ändern sich mit der Interkalation und ergeben den entsprechenden Spannungsabfall. Der Ionenanteil beträgt ungefähr ein Drittel des gesamten Spannungsabfalls. Detallierte Analysen der Verschiebungen von Bindungsenergien zeigen einen Ladungtransfer von Alkaliatom auf das Übergangmetall, aber auch auf das Chalcogen

Combined Influence of Meso- and Macroporosity of Soft-Hard Templated Carbon Electrodes on the Performance of Li-O2 Cells with Different Configurations

Li-O2 batteries can offer large discharge capacities, but this depends on the morphology of the discharged Li2O2, which in turn is strongly affected by the nanostructured carbon used as support in the air cathode. However, the relation with the textural parameters is complex. To investigate the combined effect of channels of different sizes, meso-macroporous carbons with similar mesopore volume but different pore size distribution were prepared from the polymerization of resorcinol-formaldehyde (RF) in the presence of surfactants and micro-CaCO3 particles. The carbon materials were used as active materials of air cathodes flooded by ionic liquid-based electrolytes in Li-O2 cells with two different configurations, one with a static electrolyte and the other with a stirred electrolyte, which favor a film-like and large particle deposition, respectively. The presence of large pores enhances the discharge capacity with both mechanisms. Conversely, with respect to the reversible capacity, the trend depends on the cell configuration, with macroporosity favoring better performance with static, but poorer with stirred electrolytes. However, all mesoporous carbons demonstrated larger reversible capacity than a purely macroporous electrode made of carbon black. These results indicate that in addition to pore volume, a proper arrangement of large and small pores is important for discharge capacity, while an extended interface can enhance reversibility in Li–O2 battery cathodes.This research was supported by the Spanish Government, through the “Severo Ochoa” Programme for Centers of Excellence in R&D (SEV- 2015-0496), and through the projects MAT2015-64442-R and MAT2015-68394-R with FEDER co-funding; the European Commission (contract no. 265971 “Lithium-Air Batteries with split Oxygen Harvesting and Redox processes, LABOHR)”. M.O. acknowledges CSIC for a JAE-DOC research contract cofinanced by European Social Fund.Peer reviewe

Electrochemical growth of two-dimensional tin nano-platelet as high-performance anode material in lithium-ion batteries

A template free, single-step process is developed for fabrication two-dimensional tin nano-platelets by electrochemical deposition in the presence of Triton X100 (TX100). Electrochemical studies combined with structural characterization revealed that during electrodeposition, TX100 molecules adsorb preferentially on {022} planes of Sn and highly anisotropic growth promotes in [200] direction which results in the formation of platelet morphology. The deposited platelets exhibit a high aspect ratio of 30 (width to thickness) and thickness of 25 ± 5 nm that uniformly covered the substrate with a high platelet density of 9 × 108 cm−2. The electrochemical performance of nano-platelets for lithium storage was studied in detail and compared with other morphologies of tin. Tin nano-platelets exhibited high reversible capacity and excellent cycling performance, the capacity was maintained at 820 mA h g−1 for 100 cycles and more, far superior to the other structures. Excellent rate capability was also observed for nano-platelets up to 5 C, with the ability to be operated at 20 C without damage. The superior electrochemical performance of tin platelets is mainly attributed to its two-dimensional structure that efficiently distributes strain, allowing high mechanical stability even after 100 cycles, as confirmed by Scanning Electron Microscopy (SEM).This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.Peer reviewe

Combined Influence of Meso- and Macroporosity of Soft-Hard Templated Carbon Electrodes on the Performance of Li-O₂ Cells with Different Configurations

Li-O2 batteries can offer large discharge capacities, but this depends on the morphology of the discharged Li2O2, which in turn is strongly affected by the nanostructured carbon used as support in the air cathode. However, the relation with the textural parameters is complex. To investigate the combined effect of channels of different sizes, meso-macroporous carbons with similar mesopore volume but different pore size distribution were prepared from the polymerization of resorcinol-formaldehyde (RF) in the presence of surfactants and micro-CaCO3 particles. The carbon materials were used as active materials of air cathodes flooded by ionic liquid-based electrolytes in Li-O2 cells with two different configurations, one with a static electrolyte and the other with a stirred electrolyte, which favor a film-like and large particle deposition, respectively. The presence of large pores enhances the discharge capacity with both mechanisms. Conversely, with respect to the reversible capacity, the trend depends on the cell configuration, with macroporosity favoring better performance with static, but poorer with stirred electrolytes. However, all mesoporous carbons demonstrated larger reversible capacity than a purely macroporous electrode made of carbon black. These results indicate that in addition to pore volume, a proper arrangement of large and small pores is important for discharge capacity, while an extended interface can enhance reversibility in Li−O2 battery cathodes