State-of-the-Art, Challenges, Examples, Future Prospects

Title:

In situ/operando characterization of electrochemical interfaces with X-ray spectroscopies

Abstract:

An in depth understanding of the atomistic mechanism underlying different electrochemical processes requires recording large sets of data under operando conditions yielding key information of the electrified interface. Thus, the desired parameters to be known include the chemical composition at the interface, chemical states of the atoms and their variation as a result of the electrochemical reactions as well as the structural evolution. Unfortunately the analytical techniques able to provide interface information are very limited and hardly compatible with liquids allowing usually only ex situ characterizations leading to a loss of important information as in many cases the intermediates and electrocatalytic actives species cannot be “quenched” in post process analysis. X-ray spectroscopy techniques are able to provide relevant information of the electronic structure in an element specific manner but real electrochemical interfaces are buried and most of the time in presence of liquid electrolytes being inaccessible directly to the common surface sensitive techniques like photoelectron spectroscopy requiring new experimental strategies for their operation under these conditions. In this talk I will present some of the new approaches which allow the investigation of the electronic structure variation of the electrocatalysts under reaction conditions using photoelectron spectroscopy, from gas phase up to bulk aqueous electrolyte.

Title:

Atomistic modelling of interfacial reactivity and ionic conductivity in solid electrolytes

Abstract:

Based on quantum chemistry grounds together with the spectacular growing of computational resources, atomistic modelling is able nowadays to bring valuable insight in understanding the structure, properties and function of technological materials. Indeed, computational predictions of the performance of energy materials are now sufficiently mature to be applied successfully in many cases and, in particular, to search for electroactive materials for emerging battery chemistries such as lithium metal electrodes, solid-state electrolytes, and Li-sulfur. In this talk we intend to present some exciting examples of our most recent work in this area. In particular, we will focus on general insights from molecular dynamics simulations that provide valuable understanding into key thermodynamic and kinetic properties related to ion diffusion and interface stability for designing high-performance solid electrolytes.

Title:

Using solid-state NMR to probe bulk and interfacial Li-ion transport in solid-electrolytes

Abstract:

Solid-state NMR is a very versatile technique which allows us to attain element specific information about the local structure and dynamics in materials in a non-destructive manner. Over the course of this lecture I will introduce the basic principles of NMR spectroscopy, and illustrate the application of one- and two-dimensional NMR in the study of interface structure and kinetics in between a Li-metal anode and its SEI and between various components of a composite solid-electrolyte. 

Title:

X-ray spectroscopies of electrochemical interfaces

Abstract:

Lithium-ion batteries (LIBs) are key to the transition from fossil fuels towards increased use of renewable energy sources. However, more widespread deployment requires improvements in energy density, cost and cycle-lifetime. Various cathode and anode materials are under consideration for next-generation LIBs, and the interfacial stability of these materials in contact with the electrolyte is a critical consideration. Interface-sensitive operando characterization techniques are urgently needed to reveal the reactions occurring in working batteries.^1,2

I will present results of detailed ex-situ studies of Ni-rich LiNi_xMnyCo_1-x-yO₂ (NMC) cycled vs. Graphite in full cells, where electrochemical signatures of cell degradation are linked to surface chemistry changes taking place on the electrodes as revealed with Hard X-ray Photoelectron Spectroscopy (HaXPES). This reveals thickening of electrode-electrolyte interphases with cycling, the growth of a reduced surface layer at the cathode, and the incorporation of transition metals at the anode due to cross-over from cathode.

Despite these insights, ex-situ measurements suffer from potential ambiguity due to changes to the electrode surfaces occurring during glovebox disassembly, and can’t capture the intermediate species involved in interface degradation. We therefore introduce several complementary interface-sensitive approaches for performing operando x-ray photoelectron and absorption spectroscopy (XPS/XAS).^2-5 These rely on reaction cells sealed with X-ray/electron-transparent membranes such as thin (<100 nm) silicon nitride or graphene membranes that remain impermeable to liquids. We demonstrate how these approaches can monitor the evolution of solid-liquid interfaces under electrochemical control, ⁵ including solid-electrolyte interphase (SEI) formation on Li-ion battery anodes.⁶

References

1. Wu et al. Phys. Chem. Chem. Phys. 2015, 17, 30229.

2. Weatherup et al. Top. Catal. 2018, 61, 2085.

3. Velasco-Velez  et al. Angew. Chemie 2015, 54, 14554.

4. Weatherup et al. J. Phys. Chem. Lett. 2016, 7, 1622.

5. Weatherup et al. J. Phys. Chem. B 2018, 122, 737.

6. Swallow et al. Nature Commun. 2022, 13, 6070.

Title:

The Use of Small Angle Scattering and Electrochemical Impedance Spectroscopy analysis in Battery Chemistry: From Structure to Operando

Abstract:

Growth in global energy storage and conversion systems demand developing smart materials, such materials in demand should also be sustainable, long-lasting, effective, safe, environmentally friendly, cost-effective and recyclable for use in different electrochemical applications (e.g., Lithium Sulfur Batteries (LSB), Electrochemical Capacitors, Polymer Electrolyte Membrane Fuel Cells).

With the increasing demand for new and more efficient materials, a thorough understanding of the synthesis of nanostructured carbons at the 0.1-10 nm level is needed, which is desirably transferable or usable for the interpretation of the results obtained by other research methods and the future application of this knowledge for the design of efficient electrode materials for future applications. The first part of the talk is related to the model-free analysis by small-angle scattering to obtain reliable data on the inner surface area and the average pore size of the CMs. The small angle scattering method and its potential to study microstructures of CMs of different origins and to identify in more detail the changes in morphology (on the nanometer and angstrom length scales) due to changes in average pore width, average pore wall thickness, internal surface area and degree of disorder will be discussed. A key structural feature of CMs, together with advanced characterization techniques such as real-time testing and state-of-the-art electrochemistry, so-called quasi operando analysis of the LSB will be the subject of a presentation.

References
K.Schutjajew; P.Giusto, E.Härk, M.Oschatz, Preparation of Hard Carbon/Carbon Nitride Nanocomposites by Chemical Vapor Deposition
to Reveal the Impact of Open and Closed Porosity on Sodium Storage Carbon 2021, 185, 697-708, 10.1016/j.carbon.2021.09.051
A.Adamson, R.Väli, M.Paalo, J.Aruväli, M.Koppel, R.Palm, E.Härk, J.Nerut,T.Romann, E.Lust, A. Jänes, Peat-derived hard carbon
electrodes with superior capacity for sodium-ion batteries The Royal Society of Chemistry Advances 10 (2020) 20145-20154.
D. Xie, S. Mei, Y. Xu, T. Quan, E. Härk, Z. Kochovski, Y. Lu, “Efficient Sulfur Host Based on Yolk-Shell Iron Oxide/Sulfide-Carbon
Nanospindles for Lithium-Sulfur Batteries”, ChemSusChem 2021, 14, 1404 – 1413, 10.1002/cssc.202002731
E.Härk, M. Ballauff, Carbonaceous Materials Investigated by Small-Angle X-ray and Neutron Scattering. C Journal of Carbon Research. C
2020, 6(4), 82; https://doi.org/10.3390/c6040082.
S.Risse, E.Härk, B.Kent, M.Ballauff, Operando Analysis of a Lithium/Sulfur Battery by Small-Angle Neutron Scattering, ACS Nano 2019,
13, 9, 10233–10241, 10.1021/acsnano.9b03453

Title:

Catalysis Beyond the Surface: How Bulk Ion Insertion Influences Reactivity in Electrochemical Energy Conversion

Abstract:

Efforts to develop non-precious metal electrocatalysts for low temperature oxygen reduction (ORR) and oxygen evolution (OER) reactions—key reaction bottlenecks in hydrogen generation and use—are increasingly looking towards materials that display bulk ion insertion functionality^[1]. Across emerging electrocatalytic material classes including perovskite oxides^[2,3], transition metal (oxy)(hydr)oxides^[4,5], and organic semiconducting polymers, the activity and stability of the surface is coupled to the reactivity of the bulk through voltage dependent compositional changes driven by electrochemical ion insertion. The catalytic state is thus inherently far from equilibrium, complicating its direct observation and challenging our efforts to design materials based on static ex-situ derived properties.

In this talk, I will provide an overview of the experimental and computational approaches to understand the influence of ion insertion on reactivity in these emerging electrocatalytic systems. The connection between surface and bulk reactivity is characterized through a multi-modal approach integrating electroanalytical techniques and operando X-ray, vibrational, and scanning probe microscopies. The experimental results inform first principles calculations and microkinetic models used to simulate the observed electrochemical behavior. Through this approach, I show how ion insertion can be leveraged to develop new pathways for reactivity and catalyst design for the electrification of chemical production.

[1] A. Sood; A.D. Poletayev; D.A. Cogswell; P.M. Csernica; J.T. Mefford; D. Fraggedakis; M.F. Toney; A.M. Lindenberg; M.Z. Bazant; W.C. Chueh, Electrochemical ion insertion from the atomic to the device scale. Nat. Rev. Mater. 6, 847-867 (2021).

[2] J.T. Mefford; X. Rong; A.M. Abakumov; W.G. Hardin; S. Dai; A.M. Kolpak; K.P. Johnston; K.J. Stevenson, Water electrolysis on La_1-xSr_xCoO_3-d perovskite electrocatalysts. Nat. Commun. 7:11053, (2016).

[3] A.R. Akbashev; V. Roddatis; C. Baeumer; T. Liu; J.T. Mefford; W.C. Chueh, Probing the Stability of SrIrO₃ During Active Water Electrolysis via Operando Atomic Force Microscopy. Energy Environ. Sci. Accepted (2023).

[4] J.T. Mefford; Z. Zhao; M. Bajdich; W.C. Chueh; Interpreting Tafel behavior of consecutive electrochemical reactions through combined thermodynamic and steady state microkinetic approaches, Energy Environ. Sci. 11, 1762-1769 (2020).

[5] J.T. Mefford; A.R. Akbashev; M. Kang; C.L. Bentley; W.E. Gent; H.D. Deng; D.H. Alsem; Y.-S. Yu; N.J. Salmon; D.A. Shapiro; P.R. Unwin; W.C. Chueh; Correlative operando microscopy of oxygen evolution electrocatalysts. Nature 593, 67-73 (2021).

[6] A. De La Fuente Durán; A. Y.-L. Liang; I. Denti; H. Yu; D. Pearce; A. Marks; E. Penn; K. Weaver; L. Turaski; I.P. Maria; S. Griggs; X. Chen; A. Salleo; W.C. Chueh; J. Nelson; A. Giovannitti; J.T. Mefford, “Origins of hydrogen peroxide selectivity during oxygen reduction on organic mixed ionic-electronic conducting polymers,” ChemRxiv (2022) DOI: 10.26434/chemrxiv-2022-r3pkd

Title:

Modelling electrochemical electrolyte/electrode surfaces: concepts and simulations

Abstract:

Structures and processes at electrochemical electrode/electrolyte interfaces play a critical role in our future energy storage and conversion technology based on, e.g., batteries and fuel cells. However, from a modelling perspective the atomistic description of electrochemical interfaces is challenging, in particular for liquid electrolytes, as a proper treatment in principle requires quantum chemical approaches together with an appropriate statistical sampling of the liquid electrolyte [1,2]. In this contribution, I will present techniques to model electrochemical interfaces relevant in electrocatalysis and metal-air batteries using ab initio molecular dynamics simulations [1,2] and grand-canonical approaches [1,3], also taking ions present in the aqueous electrolytes appropriately into account. Furthermore, applications of the techniques to electrocatalysis and batteries will be presented [3,4].

[1]     A. Groß and S. Sakong, Curr. Opin. Electrochem. 14, 1 (2019).

[2]     A. Groß and S. Sakong, Chem. Rev. 122, 10746 (2022).

[3]     F. Gossenberger, F. Juarez, A. Groß, Front. Chem. 8, 634 (2020).

[4]     B. R. Didar, L. Yashina, A. Groß, ACS Appl. Mater. Interfaces 13, 24984 (2021) .

Title:

Operando/in situ imaging in energy research

Abstract:

20 years ago our group at HZB was one of the first to work with in-situ and operando synchrotron X-ray and neutron imaging techniques on energy materials [1-6] and has made numerous pioneering achievements in this field, which have since become established methods. Many of the first in-situ and operando imaging studies were carried out on the synchrotron tomography instrument at the BAMline at BESSY [1-2]. For this reason, this talk will start with a brief historical overview of the early beginnings and developments before continuing with more recent examples. The focus of the talk will be on battery and fuel cell materials. Some examples from battery research include the investigation of the degradation of Li and Si anodes and solid-state batteries [7-10]. While synchrotron phase-contrast imaging is particularly suitable for studying 3D structures and morphologies with a high spatial resolution of about 1 µm, neutron imaging has the advantage of being able to see deep into massive objects while being sensitive to lithium. The second part of the talk will provide insights into research on fuel cells [2, 11] hydrogen electrolyzers [6] and gas diffusion electrodes/catalysts, with some examples being presented. Finally, an outlook on current developments such as 3D data analysis and machine learning tools is given.

[1]          I. Manke et al. APL 2007, 90, 214102.

[2]          I. Manke et al. APL 2007, 90, 174105.

[3]          I. Manke et al. APL 2008, 92, 244101.

[4]          I. Manke et al. APL 2007, 90, 184101.

[5]          I. Manke et al. Adv. Eng. Mater. 2011, 13, 712.

[6]          M. A. Hoeh et al. Electrochem. Comm. 2015, 55, 55.

[7]          F. Sun et al. Materials Today 2019, 27, 21.

[8]          K. Dong et al. ACS Energy Letters 2021, 6, 1719.

[9]          F. Sun et al. Adv. Energy Mat. 2022, 12, 2103714.

[10]        F. Sun et al. Materials Today 2020, 38, 7.

[11]        S. S. Alrwashdeh et al. ACS Nano 2017, 11, 5944.

Title:
Insights into different battery cell designs for in-situ NMR

Abstract:

Nuclear magnetic resonance (NMR) is a non-invasive technique to monitor degradation processes, structural changes and failure mechanisms in batteries. Over the years, a variety of in-situ cell designs were developed and modified to suit their application spanning from initial studies of the cycling behaviour of carbons to more complex methods including (but not limited to) imaging, diffusion and fast-charging studies. This talk will give a snapshot of the benefits of some cell designs including a parallel-plate design used for analyzing fast-charging in lithium-ion batteries and a novel technique which improves the in-situ NMR resolution by applying magic-angle spinning. 

Title:
Multimodal operando analysis of high-capacity electrodes
with photons and neutrons

Abstract:

High-capacity electrodes like sulfur cathodes and silicon anodes are promising candidates for sustainable electrochemical energy storage in a post-lithium-ion era. While Lithium/sulfur (Li/S) batteries have a five-fold higher theoretical gravimetric energy density (ca. 2500 Wh/kg) than state-of-the-art lithium-ion batteries [1], silicon is an interesting anode material for lithium-ion batteries due to its ten times higher specific capacity than commercially used graphite anodes. However, the strong capacity fading with increasing cycle number is still a significant obstacle to broad technical utilization of both electrodes despite decades of research. Operando techniques [2] are very suitable tools for gaining a mechanistic understanding of degradation processes. Especially the simultaneous combination of several independent measurements (multimodal) while the electrodes are in operation allows deep insights into the degradation mechanisms and provides a further mechanistic understanding of both complex chemistries. Here, the results of novel setups are presented where several independent measurements are simultaneously performed. Electrochemical impedance spectroscopy (EIS), temperature measurement, and X-ray imaging [3] or neutron techniques like small-angle neutron scattering and neutron reflectometry were performed over several cycles. At the same time, the cell was galvanostatically or potentiostatically charged and discharged. Structural changes on the macroscopic and microscopic scale can be correlated to characteristic signals in the EIS and charge-discharge curves.

References:
[1] X. Fan, W. Sun, F. Meng, A. Xing, J. Liu, Advanced chemical strategies for lithium-sulfur batteries: A
review, Green Energy Environ. 3 (2017) 2–19. doi:10.1016/j.gee.2017.08.002.
[2] J. Tan, D. Liu, X. Xu, L. Mai, In situ/operando characterization techniques for rechargeable lithium-sulfur
batteries: a review, Nanoscale. (2017) 19001–19016. doi:10.1039/C7NR06819K.
[3] S. Risse, C.J. Jafta, Y. Yang, N. Kardjilov, A. Hilger, I. Manke, M. Ballauff, Multidimensional operando
analysis of macroscopic structure evolution in lithium-sulfur cells by X-ray radiography, Phys. Chem.
Chem. Phys. 18 (2016) 10630–10636. doi:10.1039/C6CP01020B.

Title:
Mechanistic studies of electrochemical devices by photon-in/photon-out x-ray spectroscopy under operating conditions

Abstract:

In context of the growing need for a more sustainable energy sector, the efficient storage of excess energy from intermittent renewable sources is of paramount interest and significant efforts have been devoted to the quest for more efficient electrocatalyst materials for energy conversion and storage devices such as water electrolyzers, fuel cells (FC) and batteries. Thus, in-situ studies of promising energy materials in conditions close to real operation are of crucial importance for understanding of the performance-limiting mechanisms occurring at the electrochemical interfaces

Photon-in/photon-out x-ray absorption spectroscopy (XAS) is an established tool to probe the chemical and electronic structure of solid, liquid, and gaseous samples, providing insights into the local density of states of the studied material, e.g. its oxidation state and local geometry around the probed atom. Due to the shot attenuation length of x-ray photons, application-tailored sample environments bridging the technical requirements of the method and the electrochemical devices are required to monitor real-world materials in liquids under operating conditions.

In this work, we show operando XAS studies of relevant energy materials in the field of electrocatalysis and battery research, showcasing the opportunities and challenges arising from the use of photons energies ranging from the hard to the soft X-ray regime.

Title:
RIXS of transition metal oxides for batteries: why and what

Abstract:

Abstract:

More and more modern sustainable energy systems rely on high-performance electric energy storage solutions through electrochemical devices, i.e., batteries. However, the practical optimization of battery performance, safety, and cost turns out to be formidable, which has triggered fervent debates on the relevant mechanism of battery operations. Incisive tools for directly detecting battery chemistry becomes critical, and synchrotron based soft X-ray spectroscopy has evolved to answer this call.

In this presentation, we will provide an in-depth discussion of the myths and truths of soft X-ray spectroscopy techniques, including soft X-ray absorption spectroscopy (XAS) and resonant inelastic X-ray scattering (RIXS) with many detection channels. Examples will be used to show both the power and the limitations of soft X-ray spectroscopy for battery studies. We try to clarify that conventional XAS, although powerful for detecting conventional chemical states, have experienced severe misuse in battery research on novel chemical states; fortunately, RIXS could successfully circumvent the limitations of conventional XAS through its new dimension of information on the so-called emission energy. Specific examples on RIXS of both transition-metals and oxygen in battery anodes and cathodes will be discussed, which lead to spectroscopy-based guidelines on battery material optimizations and developments.

OPTIONAL Reading Materials:

Wu et al., JACS 2017 https://doi.org/10.1021/jacs.7b10460

Firouzi et al., Nat Comm 2018 https://doi.org/10.1038/s41467-018-03257-1

(Review) Yang & Devereaux, JPS 2019 https://doi.org/10.1016/j.jpowsour.2018.04.018

Wu et al., Sci Adv 2020 https://doi.org/10.1126/sciadv.aaw3871

Zhuo et al., Joule 2021 https://doi.org/10.1016/j.joule.2021.02.004

Title:

Solid-State Batteries – Analytical Challenges solved by FIB-SEM, XPS and ToF-SIMS

Abstract:

Solid-state batteries are considered as next technology step in the continuous development of improved electrochemical energy storage devices.^1-3 While lithium ion batteries with liquid electrolytes have been commercialized 30 years ago – with their development starting probably already 50 years ago – the development of solid-state batteries started only less than 10 years ago. Thus, the speed of development is very fast, and there is a gap between high-flying expectations and reliable and reproducible experimental information.

The focus will be laid on solid-state batteries with inorganic solid electrolytes, and the understanding of their kinetics and their degradation by detailed analytical measurements. As both energy and power density are decisive for the future success of any cell concept, the kinetics of high-performance electrodes will be highlighted. Thus, the kinetics of the lithium (sodium) metal anode, as well as the kinetics of cathode composite electrodes will be discussed in depth.

As analytical techniques, we mostly combine XRD, FIB-SEM, XPS and ToF-SIMS to obtain complementary information. Where possible, we develop operando experiments. Two examples will be discussed in some depth, i.e. operando XPS characterization of solid electrolyte interfaces and operando HRSEM studies of lithium electrode morphology.

References:

¹ A solid future for battery development, J. Janek and W. Zeiger, Nat. Energy 1 (2016) 16141.

² Chemo-mechanical expansion of lithium electrode materials and the route to mechanically optimized all-solid-state batteries, R. Koerver, W. Zhang, L. di Biasi, S. Schweidler, A. O Kondrakov, S. Kolling, T. Brezesinski, P. Hartmann, W. G. Zeier, and J. Janek, Ener. Environ. Sci. 11 (2018) 2142-2158.

³ Benchmarking the performance of all-solid-state lithium batteries, S. Randau, D. Weber, O. Kötz, R Koerver, P. Braun, A. Weber, E. Ivers-Tiffée, T. Adermann, J. Kulisch, W. G. Zeier, F. H. Richter, J Janek, Nat. Ener. 5 (2020) 259-270.

Title:
In situ/operando studies of electrochemical interfaces with neutrons

Abstract:

A review is given on the recent advances in neutron scattering techniques for studying electrochemical interfaces related mostly to the development of lithium power sources of different types. At present, lithium-ion batteries exhibit the highest specific energy storage capacity, the basis of which is the ability of electrode materials to insert (intercalate) and extract (deintercalate) lithium ions during battery charging/discharging, respectively. Further ways to significantly increase the specific capacity of electrochemical sources today are associated with lithium energy storage devices of non-intercalating type, such as lithium-ion sources with metal anodes or lithium-oxygen cells with carbon-based cathodes. In turn, this determines the need for the development of experimental approaches that would make it possible to perform in situ/operando studies of the structure of electrodes and electrolytes in operating cells. Scattering of thermal (energy <0.5 eV) neutrons has proven to be a promising method for this purpose, which allows tracking the structural evolution of the components of electrochemical cells. The report summarizes the experimental studies and diagnostics of electrochemical interfaces using neutron diffraction, reflectometry and small-angle scattering over the past ten years. The data obtained establish relationships between the microstructure of the components and macroscopic characteristics of electrochemical cells in various conditions. A comparison with similar applications of X-ray scattering at the sources of synchrotron radiation is presented.

Title:

On-line Electrochemical Mass Spectrometry (OEMS) – An Operando Technique to Analyze Materials Degradation Processes in Lithium-ion Batteries

Abstract:

Interfacial reactions in lithium-ion batteries often involve gaseous reaction products. Mechanistic investigation of materials degradation processes requires a technique to identify and quantify these gases in battery cells. On-line Electrochemical Mass Spectrometry (OEMS) is an operando gas analysis method that continuously samples the headspace of a custom battery cell. It generates an integral signal of the total evolved/consumed gases with a sensitivity of ~20 ppm (established by calibration gases and a quadrupole mass analyzer at ~10^-7 mbar) and a time resolution of ~100 s (through a one-step pressure reduction from ambient to ~10^-5 mbar in the ionization chamber via a crimped capillary leak of ~1 µl/min). Quantitative OEMS was first applied to Li-O₂ batteries, but then used to study materials degradation processes in lithium-ion cells, which we will review in this lecture.

Title:
In-situ infrared spectroscopy in ultra-high vacuum, in electrochemical, and in photoelectrochemical environments

Abstract:
Infrared spectroscopy is among the most versatile tools to study the interface chemistry of model systems and real materials. This lecture will provide an introduction into the fundamentals of vibrational spectroscopy, into infrared reflection absorption spectroscopy at planar interfaces, and into infrared spectroscopy at solid/liquid interfaces. Finally, the capabilities of the method will be illustrated using application examples from the fields of electrocatalysis and photoelectrochemistry.

Title:
Insights from soft X-ray spectroscopy

Abstract:

Title:

What do we learn by the application of operando soft X-ray spectroscopy to electrochemical reactions?

Abstract:

Title:

In situ XRD characterization of temperature-dependent structural changes in photovoltaic materials

Abstract: