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

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:
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: