Symposium CH01—In Situ and Operando Techniques Applied to Electrochemical Systems—A Key Toolkit for Deep Understanding

EIS is one of the most practical in situ analysis technique, which can discriminate electrochemical processes by their time constant. EIS gives information from the electrode/electrolyte interface (MHz) to the bulk electrode (µHz). The frequency region scanned mainly concerns ionic mobility and is thus well adapted to evidence matter transport limitations (both in electrolyte and in active materials).
In that way, EIS is particularly interesting to check the interface since it is a non-destructive investigation method, giving access to several electrochemical parameters of major interest (charge transfer, passivation film, adsorption, corrosion, ionic diffusion...).
However, interpreting EIS data still requires specific attention.

For that purpose, in this tutorial, some fundamentals of Electrochemical Impedance Spectroscopy will be reminded.
Different examples (from liquid-based and solid-state batteries) will be shown in order to illustrate the tutorial’s theoretical aspects.

The goal of this tutorial is actually to give some keys for:
convenient experimental set-up in order to record unambiguous EIS data
use of adequate EIS signal (a special attention will be given to GEIS and PEIS)
data analysis through the use of both Nyquist and Bode diagrams
understanding the interest and limits of equivalent electrical circuit models

Electrochemical impedance spectroscopy is a very powerful tool, however its actual implementation in standard electrochemical instrumentation does not allow looking into the dynamic behavior of the electrochemical systems. For this reason, classic impedance spectroscopy fails for the investigation of aging of materials, corrosion, self-oscillation, poisoning and others. In order to achieve an understanding of the effect of such degradation mechanisms on the materials and their electrochemical properties, it is necessary to use a methodology, which is able to look at systems while they are changing. The tutorial will start by introducing the concept of dynamic impedance and its connection to the Volterra series of the electrochemical system will be given. An overview of the experimental methodologies for the measurement and extraction of dynamic impedance spectra will follow, accompanied by an analysis of the experimental artefacts related to the electrochemical instrumentation. Different examples of dynamic impedance spectra acquired for different electrochemical reactions will be shown: redox couple in solution; intercalation of ions in host structures; hydrogen evolution on platinum electrodes. The data will be analyzed using at first a statistical approach based on the concept of Pade’ approximants, using as weighting factor the theoretical variance of the admittance. The connection between equivalent circuits and Pade’ approximants will be explored, as well as their connection to the Kramers-Kronig transformations. Finally, a physico-chemical model will be established in order to describe the phenomena occurring during the electrochemical reaction and the dynamic impedance spectra will be fitted using such model, in order to quantify the kinetic constants of the reaction. The tutorial will close with an summary of the main important points and an overview of the possible applications in the field of energy storage and energy conversion.

Lithium-rich nickel manganese cobalt oxide (LRNMC) is being explored as an alternative to stoichiometric nickel manganese cobalt oxide (NMC) cathode materials due to its higher, initially accessible, energy-storage capacity. This higher capacity has been associated with reversible O oxidation, however, the mechanism through which the change in O chemistry is accommodated by the surrounding cathode structure remains incomplete, making it challenging to design strategies to mitigate poor electrode performance resulting from extended cycling. Focusing on LRNMC cathodes, we identify nanoscale domains of lower electron density within the cathode as a structural consequence of O oxidation using small-angle X-ray scattering (SAXS) and operando X-ray diffraction (XRD). A feature observed in the small angle scattering region suggest the formation of nanopores, which first appear during O oxidation, and is partially reversible. This feature is not present in traditional cathode materials, including stoichiometric NMC and lithium nickel cobalt aluminum oxide (NCA), but appears to be common to other Li-rich systems tested here, Li₂RuO₃ and Li_1.3Nb_0.3Mn_0.4O₂.

Lithium-rich layered oxides (LRLO) have drawn great attention recently as a high energy density cathode material. However, the practical deployment of these materials is hindered by voltage and capacity decay during electrochemical cycling. Applying mild thermal energy to cycled LRLO materials allows to recover the voltage profile and to alleviate the voltage decay problem in the following cycling. In this work, a detailed mechanism study of the voltage and structure recovery is conducted through various analytical tools. The recovery of the lattice structure is investigated through in-situ neutron powder diffraction and synchrotron X-ray diffraction. The reordering of the transition metal environment is explored by in-situ extended X-ray absorption fine structure and pair distribution function. A transition metal reordering pathway is proposed and evaluated through computation methodology. Heat treatment provides the necessary energy for the transition metal to overcome the kinetic barrier to move from the honeycomb center to the honeycomb vertex and recover the honeycomb ordering in the transition metal layer. An ambient-air relithiation using Li⁺ molten salt was also conducted along with the heat treatment to the cycled LRLO cathode and lead to a material regeneration in both the voltage and capacity. This work identifies the transition metal reordering as the key factor under the structure recovery of degraded LRLO materials. It opens a door for promising strategies to mitigate the voltage and capacity degradation problem in LRLO and provides the potential routes to recycle degraded LRLO materials.

The inevitable and necessary green transition towards sustainable energy sources depends completely on the ability to store energy. One possibility is to store the excess energy from renewable energy sources electrochemically in rechargeable batteries. A possibility that has also been realized for the substitution of combustion engines in vehicles.

To develop the rechargeable batteries of tomorrow, fundamental understanding of relations between material structure and properties is essential. Here, operando experiments are essential, as they provide insight into material behavior under the true dynamic conditions relevant for real applications. For the material structure at the atomic and nano length scales, x-rays, neutrons, and electrons are excellent probes.

If materials are crystalline and well-ordered on the atomic and nano length scales, traditional diffraction methods are ideal to probe the long-range order of the material structure, as the relevant information lies in the Bragg peaks. In recent years, it has been realized that crystallinity is not a given for all battery materials at all states-of-charge or at all stages of a battery’s lifetime. However, for non-crystalline materials, whether they are nanocrystalline, disordered, or even amorphous, the more traditional diffraction methods fall short. Now, the relevant information does not lie in the Bragg peaks but underneath them in the diffuse scattering.

To probe the material structure of crystallographically challenged materials, total scattering experiments, which involve both the Bragg and diffuse scattering, hold the key. From total scattering data, the reduced atomic pair distribution function (PDF) can be obtained, which takes the scattering data from reciprocal space and into real space. The PDF can be thought of as a probability distribution of the interatomic distances in the material and the very local structure down to nearest-neighbor distances in materials can now be probed. Everything is seen in the PDF, which is a blessing as well as a curse for battery scientists, as batteries are multicomponent systems with complicated PDFs, which calls for battery-specific PDF methodologies.

This contribution will address how to obtain operando PDFs for battery materials during cycling and especially how to analyze data.

In our studies, we utilize model-dependent PDF analysis, sometimes referred to as ‘real-space Rietveld refinement’, via a least-square optimization method, like Rietveld refinement, where an input model is refined against experimental data, such that the residual between the two is minimized. The user-friendly PDFgui and the more versatile and advanced DiffPy Complex Modelling Interface (DiffPy-CMI) software are two examples on tools to conduct model-dependent, quantitative PDF analysis. In addition, we employ novel tools for model-free PDF analysis.

During summer 2021, ‘PDF in the cloud’ (PDFitc) was launched at ‘pdfitc.org’, where multiple apps for PDF analysis are available to users. This includes the model-free ‘similarityMapping’ app, which is a statistical analysis based on Pearson correlation. During fall 2021, another model-free statistical method will become available as an app: non-negative matrix factorization (NMF), which is somewhat like principal component analysis (PCA). Automated methods are also starting to enter the ballpark of PDF analysis. The ‘structureMining’, ‘spacegroupMining’, and ‘clusterMining’ apps at PDFitc mine structural databases and guide users in their PDF analyses to enable the users to explore the atomic level structure of their materials.

The prevalence of both structural and sodium-ion ordering phase transitions in sodium-ion intercalation materials limits their useful cycle life. The multitude of transitions creates complex phase behavior that is difficult to investigate, especially on the single nanoparticle scale and under operating conditions. Here, we develop operando single particle x-ray diffraction to observe single particle rotation, interlayer spacing, and layer misorientation. We apply the technique, during charge, to a model P2-type sodium ion cathode material, Na_x[Ni_1/3Mn_2/3]O₂ (NNMO), where 0<x<2/3, which exhibits the detrimental P2-O2 transition. From operando observations of single particle misorientation and layer spacing changes, we propose a model for the phase evolution of NNMO that includes a localized to correlated Jahn-Teller distortion phase transformation. Through this work, the proposed model can serve to guide further characterization of NNMO and other materials with P2-O2 type transitions, and operando single particle x-ray diffraction has the demonstrated potential to be used in other systems to reveal phase behavior at the nanoscale.

Development of cathode structures suitable for Na-ion and K-ion batteries is still one of the major challenges on the way to the design of next-generation alkali metal-ion batteries. Although Li, Na and K belong to the same alkali metal group with a single charge in their cation form, intercalation of Na⁺ and K⁺ ions in electrodes is difficult since ionic radii of Na⁺ (0.98 Å) and K⁺ (1.38 Å) are larger than that of Li⁺ (0.69Å). Therefore, physical, and electrochemical behavior of the cathode materials in response to Na⁺ and K⁺ ion intercalation is expected to be fundamentally different than the response to Li⁺ ion. However, there is not much known about how electrochemical reactions and transport of ions take place in cathode materials with different alkali metal ions. There have been several studies focusing on electrochemical characterization and investigation of the structural changes in the electrode materials. Lack of insight into these reaction-transport mechanisms limits the design of novel cathode materials for Na-ion and K-ion batteries. Comparative studies between Li-ion, Na-ion and K-ion battery cathodes are critical to identify fundamental similarities and differences during intercalation. Even modest expansions in brittle cathodes can cause particle fracturing in a larger crystalline-size scale. Intercalation of larger ions can cause structural collapse and amorphization induced by continuous strains and distortions. Although the amorphization in the structure can be easily identified by conventional diffraction or electron microscopy techniques, quantitative analysis of the physical changes in the structure during and after amorphization while cycling the battery electrode is critical.

In the first part of the talk, we will first report the utilization of in situ digital image correlation and in-operando X-ray diffraction (XRD) techniques to probe dynamic changes in the amorphous phase of iron phosphate during potassium intercalation¹. A new experimental approach allows to monitor dynamic physical and structural changes in the amorphous phase of the electrodes. In-operando XRD demonstrates amorphization in the electrode’s nanostructure during the first charge / discharge cycle. In situ strain analysis detects the reversible deformations associated with redox reactions in the amorphous phases. This method offers new insights to study mechanics of ion intercalation in the amorphous nanostructures.

In the second part of the talk, we will compare the electrochemical and mechanical response of the iron phosphate cathodes upon Li, Na and K ion intercalation by using electrochemical techniques and in situ digital image correlation. Iron phosphate model electrodes were prepared by electrochemical displacement technique in order to ensure identical morphology, structure and chemistry in the pristine iron phosphate electrodes. Strain evolution during Li and Na intercalation results in more linear dependence on the state of charge / discharge. However, strains generated in the eletrode shows nonlinear behavior during insertion / extraction of K ions. Interestingly, when the same amount of K and Na ions are intercalated, similar chemomechanical expansions were observed. However, strain rate calculations showed that K ion intercalation results in a progressive increase in the strain rate, whereas Li and Na intercalation induce nearly constant strain rates. Potential-dependent behaviors also demonstrate more sluggish redox reactions during K intercalation, compared to the Li and Na intercalation. These observations provide a fundamental insight into the impact of alkali ions on the redox chemistry and associated chemomechanical deformations.

Reference
1. B. Ozdogru, Y. Cha, V. Murugesan, M-K Song, Ö. Çapraz. In Situ Probing Potassium-ion Intercalation-induced Amorphization in Crystalline Iron Phosphate Cathode Materials. ChemRxiv. Cambridge: Cambridge Open Engage; 2021.

Cycling lithiated metal oxides to high potential (>4.5 V vs Li) is of significant interest for the next generation of lithium ion batteries. Cathodes cycled to high potential suffer from rapid capacity fade due to a combination of thickening of the anode solid electrolyte interphase (SEI) and impedance growth on the cathode. While transition metal catalyzed degradation of the anode SEI has been widely proposed as a primary source of capacity loss, we propose a related acid induced degradation of the anode SEI. A systematic investigation of LMO, LNMO, NMC622, and MNC811 cathodes will be presented. The role of potential on the generation of soluble acidic fluorophosphates crossover species and the impact of these species on the structure and stability of the SEI will be presented.

In-operando Visualization of ion transport in electrolyte provides fundamental understandings of electrolyte dynamics and electrolyte-electrode interaction, shedding light on material designs to enhance device performance, such as batteries and fuel cells. However, this task is extremely challenging for existing techniques, since it is difficult to capture the low ionic concentration (<1 M) and the fast dynamics (1-10 s) of the electrolyte. Here we show that an emerging Stimulated Raman Scattering (SRS) microscopy offers the required spatial (sub-micrometer optical resolution), temporal (faster than 1 s per frame) and chemical (around mM) sensitivities to address this challenge.

The SRS microscopy has been used to study ion depletion and lithium dendrite growth in both liquid and polymer electrolyte, and distinct behaviors are observed. In liquid electrolyte, we observe a three-stage lithium deposition process, each corresponding to no-depletion, partial-depletion and full-depletion regime of Li+, respectively. A positive feedback mechanism between the inhomogeneous growth of lithium and the local ionic concentration or flux. In polymer electrolyte, we clearly see phase separation due to ion depletion and observe the accompanying transport of plasticizer inside, which was not observed in the past. These new understanding also leads to new strategies to suppress lithium dendrites. Moreover, the high-speed image acquisition also enables data-driven modeling to understand the relation between local material properties (e.g. salt concentration) and dendrite growth. A neural network modeling is built to understand how different factors affect dendrite growth.

Understanding the formation and operation of the solid electrolyte interphase (SEI) is critical to the development of lithium metal batteries because of the continuous evolution of new surface area which necessitates a rapidly passivating SEI to minimize capacity loss. However, because of the highly sensitive, heterogeneous, and continuously evolving nature of the SEI, it remains challenging to develop a fundamental understanding of how SEI morphology relates to key metrics such as ionic conductivity and formation rate. To probe the role of these parameters in the SEI evolution, we combine operando atomic force microscopy (AFM) with electrochemical characterization to extract the relationships between the SEI’s roughness and it’s efficacy at forming a self-passivating layer.
Using a combination of electrochemical impedance spectroscopy (EIS) and capacity measurement during constant voltage holds, we observe formation process in which the initially deposited SEI substantially increases the ionic impedance while subsequently grown SEI produces limited impedance increases despite consuming significant amounts of lithium. These observations are supported by operando AFM measurements taken during the SEI formation process. The AFM topography measurements reveal a two part SEI microstructure composed of a compact film interspersed with large nuclei that make up a substantial fraction of the SEI volume but cover relatively little of the surface area. This observation matches our electrochemical observation of SEI composed of both passivating and non-passivating components.
To further investigate the morphology and composition of the SEI layer, we leverage the AFM system to scrape away the soft outer layer of the solid electrolyte interphase and quantify roughness and thickness properties of both the inner and outer layers of the SEI to further understand the role the SEI components play in the previously measured EIS and SEI growth rate measurements. Ultimately, by relating electrochemical properties of the SEI - both in steady state and EIS measurement modes - to its morphology and thickness we provide correlations between easily measured average electrochemical properties and critical but hard-to-measure nanoscale properties that we hope will inform the development of advanced electrolytes and formation protocols for anode free and lithium metal batteries.

The solid-liquid interface plays a crucial role in many natural process and practical applications, such as corrosion, electrochemical catalysis and energy storage. Fundamental insights of solid-liquid interface are necessary to understand these processes, but currently these studies are hampered by the shortage of appropriate characterization tools. Extensive efforts have been made to develop or improve in-situ or operando characterization techniques to study the information of solid phase near interface, while the knowledge on the liquid layers at interface, including ion concentration, double layer structure and speciation, is still limited.
Here we present a new nondestructive methodology that enables molecular study of liquid layer near interface with nanoscale spatial resolution. It is based on Fourier transform infrared nanospectroscopy (nano-FTIR), where the infrared (IR) field is plasmonically enhanced near the tip apex of an atomic force microscope (AFM). Ultra-thin freestanding membrane (single layer graphene or 2-5nm thick metal oxide film grown by atomic layer deposition (ALD)) separates AFM tip and electrolyte while acting as working electrode. We illustrate this method by comparing interface-sensitive nano-FTIR spectra with bulk-sensitive spectra obtained by ATR-FTIR and demonstrate its capability to determine changes in chemical composition and molecular structure near solid-liquid interface under electrochemical condition. These membranes can be further functionalized with synthesized nanoparticles to study the catalytic microenvironment under electrochemical condition. This platform developed and presented here will open up new avenues for the study of catalytic, electrochemical, geochemical, and other reactions at interfaces in practical conditions.

Energy dispersive X-ray diffraction (EDXRD) from a high energy source enables operando study of battery materials within their real-world form factor and containment. This is thanks to the (a) use of a highly penetrating incident X-ray white beam (20-200 keV) and (b) placement of the detector and sample to define a well-controlled diffraction gauge volume in space. The shape of this gauge volume allows spatial resolution of ten of microns when positioned inside a battery, and movement of the battery along a scanning direction allows construction of diffraction profiles across electrodes, all with time resolution of tens of seconds. This technique can identify formation of new phases as well as map fine changes in active material lattice parameters, the latter of which is equivalent to obtaining spatially resolved state-of-charge information in the case of intercalation electrodes. Because development of both high energy density and low cost batteries is enabled by designs with thick electrodes, the types of material profiles provided by EDXRD are highly relevant for the present day thrust of battery engineering. Thick electrodes, while desirable, bring extra challenges because they can cause inhomogeneities within the battery that lead to uneven active material utilization and/or battery failure. While the fundamental electrochemistry of battery active materials can be known from laboratory experiments, system-level phenomena not necessarily inherent to the active materials can have an equally profound impact on battery performance. EDXRD is a powerful tool for probing this information, with no need to adjust the cell construction, which could alter the resultant electrochemistry. Due to its highly penetrating nature, EDXRD is also ideally suited for collecting operando data from within batteries at high temperature or under high pressure. Some current solid-state battery designs require high cell compression to ensure good interfacial contact, and this makes operando data collection challenging using techniques other than EDXRD.

This talk will address the fundamentals of EDXRD, as well as provide examples of its use to establish mechanistic knowledge in several types of batteries, including (1) rechargeable alkaline batteries with electrodes of thicknesses of >1mm, (2) sulfide all solid-state batteries tested under high compression, and (3) multivalant ion batteries tested at elevated temperature within unmodified coin cells. In alkaline rechargeable batteries, EDXRD was used to establish a catalytic effect by Bi-containing additives to favor formation of rechargeable Mn(OH)₂ over terminal Mn₃O₄. In all solid-state batteries, EDXRD demonstrated a crystalline instability of a sulfide solid-state electrolyte, Li_6.6Ge_0.6Sb_0.4S₅I (LGSSI), which was observed only in the cathode and not elsewhere in the cell. This was due to reduction of the LGSSI when in contact with active material and conductive carbon in the cathode during discharge. It was also shown that this crystalline change was reversible if the cell lower voltage limit was correctly chosen. Finally, operando observation of the intercalation reaction of both Al³⁺ and Zn²⁺ was collected for Chevrel Mo₆S₈ and Mo₆Se₈ cathode hosts. This was accomplished from within unaltered, sealed coin cells, which was important as previous literature has suggested that the fully intercalated species can be inadvertently oxidized during destructive sample preparation.

Acknowledgments
This work was supported by the U.S. Department of Energy (DOE) Office of Electricity Delivery and Energy Reliability, Dr. Imre Gyuk, Energy Storage Program Manager. We also acknowledge financial support from the National Science Foundation under Award Number CBET-ES-1924534.

Parasitic side reactions can limit the capacity and efficiency of the energy storage system, via formation of resistive interfaces and consumption of redox active material/s. Transport limitations can also impact functional capacity of systems, and can mainfest at different states of (dis)charge and as a function of time over extended cycling. In this presentation, insights in elucidating and quantifying productive and parasitic processes from complementary in situ, and operando spectroscopy, diffraction and electrochemistry studies will be highlighted.

New configurations and chemistries for next generation batteries are currently in focus as a response to needs from sustainable energy technologies and transport applications. The electrochemical mechanism for next generation batteries is often based on conversion reactions and transport of active material, which is different from the “Rocking Chair” concept in current state-of-the-art, the Li-ion battery. To probe these processes operando computed X-ray tomography is a powerful technique which allows nondestructive and quantitative imaging in 3D of materials and components during operation. A particular advantage is the possibility to quantitatively correlate the 3D morphology to electrochemical data recorded simultaneously if the whole cell can be within the field of view. With the high flux of 3^rd and 4^th generation synchrotron sources rapid acquisition (sub minute for a full tomogram with sub µm resolution) opens the possibility for operando studies, even at high discharge rates.

In this contribution we show how X-ray tomography can be used to provide insights on processes in Li-sulfur (LiS) cells and the Li-plating process in Li-metal batteries, two promising next generation battery concepts. In LiS-cells the electrochemical conversion of elemental sulfur delivers a very high theoretical specific capacity (1672 mAh/g). The conversion takes place through a series of soluble intermediate polysulfide species (Li₂S_n) whereas the end product, Li₂S, is insoluble in the common electrolytes used [1]. This mechanism leads to continuous dissolution/precipitation processes during cycling which are closely related to the difficulty in reaching a high specific capacity in practice due to poor active material utilization. This can be related to elemental sulfur in the cathode not being converted, dissolved polysulfides diffusing out of the cathode and not being further converted, or Li₂S forming a continuous insulating layer that blocks access to the conducting part of the cathode matrix and stops the conversion reaction. With an operando X-ray tomography experiment we are able to directly follow the dissolution/precipitation processes at discharge with the whole cathode within field of view using a capillary operando cell. This enables us to quantitatively correlate the sulfur conversion/dissolution process to the charge delivered by the cell. In a multi-modal approach we also follow the diffusion of polysulfides species in the electrolyte with an operando optical imaging experiment in the same cell.

Common for several of the high-capacity concepts is the use of Li-metal as the anode. However, preferred electrodeposition of Li-metal can lead to a mossy or dendritic morphology, as a result of depletion of Li-ions at the electrode surface [2,3]. In combination with the high reactivity of Li this results in a continuous breakdown of the electrolyte during cycling and the formation of “dead Li”, manifesting in a low coulombic efficiency. These phenomena are accelerated at low operating temperatures, in dilute electrolytes or high applied current densities. To build an understanding of the plating process we use operando X-ray tomography to reveal the 3D-geometry and kinetics of dendrite growth during cycling to build a connection between the properties of the new electrolytes, and the microstructure formed on the Li-metal anode. These results are correlated to phase-field modelling to provide a mechanistic understanding of the plating process.

References
[1] M. Agostini, J. Y. Hwang, H. M. Kim, P. Bruni, S. Brutti, F. Croce, A. Matic, Y. K. Sun, Adv. Energy Mater. 8, 1801560 (2018)
[2] Y. Liu, X. Xu, M. Sadd, O. O. Kapitanova, V. A. Krivchenko, J. Ban, J. Wang, X. Jiao, Z. Song, J. Song, S. Xiong, A. Matic, Adv. Sci. 8, 2003301 (2021)
[3] X. Xu, Y. Liu, J. Y. Hwang, O. O. Kapitanova, Z. Song, Y. K. Sun, A. Matic, S. Xiong, Adv. Energy Mater. 10, 2002390 (2020)

Future energy solution require development of advanced composite materials. Such materials are for example catalyst layers of polymer electrolyte membrane fuel cells (PEMFCs) where electricity is generated by electrochemical reactions that take place in a complex environment. These layers are porous materials built up from three different components; chemically active sites, electron conducting support and proton conducting binder. This study focusses on investigating Pt nanoparticles on carbon black support (PTC, HiSPEC 3000), spray-coated on a polymer membrane with varying amounts of binder (PTFE – ionomer) but an equal loading of catalyst (m_Pt = 0.2 mg/m²).

The meso and nanoscale structure of the catalyst is investigated by a correlative approach based on two techniques; scanning small-angle X-ray scattering (SAXS) and ptychographic X-ray computed nanotomography (PXCT). From scanning SAXS we obtain statistical information about the nanostructure, in the range of 1 to 300 nm, probed in local areas of 10x10 µm² which correspond to the scanning step size over macroscopic areas of 1x1 mm². X-ray fluorescence spectra were simultaneously collected, with which we can then map the Pt content in the layers based on the Pt-M_α emission line at 2.05 keV. 2D maps of X-ray scattering and XRF, integrated over a specific q-range and energy-range, respectively, were processed and allow quantification of sample homogeneity in terms of nanostructure and Pt distribution across the macroscopic length scale. This data was further used to choose specific representative areas to mill out cylindrical 20 µm sized pillars using FIB/SEM. These pillars were investigated under cryogenic temperatures to avoid radiation damage with the OMNY setup at the cSAXS beamline to reveal the 3D nanostructure with PXCT down to a 3D half-period resolution of 26 nm.

PXCT measures the 3D electron density from 20 µm down to 26 nm, which perfectly bridges the gap between the macroscopic domains probed by scanning SAXS (1 mm to 10 µm), and the statistically averaged information of the nanoscale probed by SAXS (1 nm to 300 nm) for local areas of 10x10 µm². PXCT measurements alone are already able to provide valuable information to distinguish structural features of the three different catalysts. Threshold segmentation reveals differences in the pore size distribution as well as connectivity of pores. This information is crucial for a better understanding of gas and liquid transport mechanisms within the catalyst. However PXCT cannot reveal the chemically active sites due to limitations in spatial resolution, namely the Pt nanoparticles of 2-3 nm diameter where the electrochemical reaction takes place. In this work, we explore different approaches to correlate the imaging data from PXCT with the statistical data from SAXS and XRF. Our vision is to generate 3D representative models for catalyst layers based on its imaged structure by PXCT, but further complemented with statistical data from SAXS and XRF measured from the exact same sample. Such models are strongly desired in flow simulations on PEMFCs to further understand limiting factors for their performance. In addition, our study also explores novel routes in correlative data analysis combining imaging with scattering experiments. These insights may further lead to new approaches and studies in investigating porous materials.

This project has received funding from the European Union’s Horizon 2020 research and innovation program under the Marie Sklodowska-Curie grant agreement No 701647 (PSI-FELLOW-III-3i) and funding from the Chalmers initiative for advancement of neutron and x-ray techniques. The authors acknowledge the funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation program (grant agreement No. 681719). We also acknowledge the Paul Scherrer Institut, Villigen, Switzerland for provision of synchrotron radiation beamtime at beamline cSAXS of the SLS.

Multivalent ion batteries represent a unique approach to increasing energy capacity for electrochemical storage. While Li-ion batteries (LIB) are the dominant technology that continues to advance with novel architectures and engineering, there still exists serious issues of thermal sensitivity and runaway. Aqueous systems would significantly reduce these thermal concerns and also drop the economic costs associated with the organic solvents that compose the electrolytes in LIBs. The Zn ion (+2) gives twice the capacity and the ionic radii (0.78 angstroms) matches closely to the Li ion. The increased electronic/structural disruption imposed by intercalating a +2 ion finds some relief by co-intercalation of H₂O along with sandwich layered structures often associated with the multitude of vanadium oxide polymorphs.
Synchrotron work at NSLS-II BM-6 looked at the XANES and EXAFS dependence on voltage. Using crystal structure data for the material, theoretical XAFS scattering was compared to the experimental data to establish possible local site occupancy for the intercalated Zn ion. Further in-situ experiments on both Zn_0.25V₂O₅ and Ca_0.25V₂O₅ were performed using a novel electrochemical cell. Both materials exhibit a clear change in the local geometry and oxidation state of the vanadium in the active material with early cycle reversibility. Integrated XANES difference spectra are correlated with the approximate shift of vanadium from a nominal oxidation state of +4.75 down to +4.00 if assuming an approximate fully discharged state stoichiometry of Zn₁V₂O₅ or Ca_0.25V₂O₅.

Probing processes at electrode-electrolyte interfaces promises new insights into electrochemical reactions, which are inherent to many sustainable energy storage and conversion technologies.
Kelvin Probe Force Microscopy (KPFM) is widely used to map work function (surface potential) variations at the nanoscale in ambient or vacuum conditions. KPFM could be of great importance for electrochemical systems, but is impractical in polar liquids due to screening and interference from surrounding fluid. Capping a liquid-cell by free-standing single-layer graphene (SLG) serving as the working electrode, enables a stable KPFM measurement on the SLG working electrode to monitor its Fermi-level shift and is sensitive to processes occurring at the liquid-solid interface. The graphene-membrane physically separates the scanning tip from the conducting solution. With KPFM, localized information can be obtained for single SLG regions, unlike techniques like cyclic voltammetry (CV), where the signal is averaged over the entire reactor-cell.
We have applied this approach to study small electrochemical cells of 500 nm diameter capped by SLG under electrochemical reaction conditions. We used a polymer-free transfer method in order to avoid the presence of polymer residues that would alter the measured WF and the interfacial activity of the graphene. Measurement at different alkaline pH values enabled investigation of the influence of the electrical double layer (edl). This method enabled us to perform statistical measurements by monitoring several cells, following them through a few cycles while correlating the different signals recorded simultaneously (Topography, phase, KPFM).
Our experimental results correlate well with a simple electrochemical gating model, shedding light on the interplay between electronic and electrochemical doping (through redox of water) processes in the suspended graphene. The observed topographical changes in the suspended graphene in the form of bulging are attributed to electro-wetting of graphene induced by charge-carrier doping.
The experimental approach and results presented here serve as a benchmark for future studies of the electrochemical behavior of two-dimensional materials both in aqueous and organic electrolytes, and the underlying mechanisms of doping.

Li-metal has a theoretical specific capacity of 3860 mAh/g, ten times larger than that of graphite (372 mAh/g). In combination with the low reduction potential of Li, this entails Li-metal batteries (LMB) with significantly higher energy densities compared to Li-ion batteries. [1] However, the long-term cycling of LMBs is hindered by several parasitic effects linked to Li deposition. In the worst case scenario, uncontrolled Li-plating results in dendrites that can pierce the separator and short circuit the cell. Lithium plated in a dendritic morphology is also more prone to lose contact with the electrode, forming so called dead Li, leading to loss of active material and poor columbic efficiency. Furthermore, uneven Li-morphologies expose more fresh Li to the electrolyte, leading to continuous electrolyte consumption in side reactions.

To stabilize the Li-metal anode, one of several routes is to tune the electrolyte composition. Recently, we have shown that electrolytes with higher salt concentrations can enable stable cycling and uniform Li-plating [2]. This improvement in electrochemical performance can be rationalized by (1) a mitigated risk of Li-ion depletion at the electrode surface (Li-ion depletion would cause rapid dendrite growth) (2) the tendency for these electrolytes to form a stable surface layer at the anode. However, more work is needed to fully understand the mechanism for the improved efficiency of Li-plating in highly concentrated electrolytes.

Due to the very low potential of the anode during Li plating, the electrolyte will tend to decompose on the electrode surface to form a surface layer, the solid electrolyte interphase (SEI). This layer is an important factor for efficient Li plating and stripping. [3] However, the sensitivity of the SEI makes several characterization methods elusive. Any ex situ characterization, like x-ray photoelectron spectroscopy, is associated with large uncertainties regarding the stability of the SEI under a change of environment.

Instead, in situ and operando characterization of the SEI layer becomes important for building a better understanding of its role in Li deposition. In this contribution we report on a neutron reflectometry study of SEI formation and early stages of Li-metal plating, performed with the reflectometer SuperADAM at ILL. Due to the weak interaction of neutrons with matter it is possible to build an in-situ sample environment where the neutron beam can enter the cell through the back side of the working electrode. Using a custom made Li-Cu cell, we probe the formation of surface layers on the Cu working electrode. By measuring the reflectivity as a function of momentum transfer, we detect the changes in the neutron scattering length density arising as a result of a changing surface layer, thickness and composition, on the working electrode. In this study we compare Li deposition in a highly concentrated electrolyte (4M salt concentration) with an electrolyte with conventional salt concentration (1M) and discuss how the electrode/electrolyte interface evolves and influences the Li deposition.

[1] Li, L.; Basu, S.; Wang, Y.; Chen, Z.; Hundekar, P.; Wang, B.; Shi, J.; Shi, Y.; Narayanan, S.; Koratkar, N. Science 2018, 359 (6383), 1513-1516.
[2] Xu, X., Liu, Y., Hwang, J.-Y., Kapitanova, O. O., Song, Z., Sun, Y.-K., Matic, A., Xiong, S. Adv. Energy Mater. 2020, 2002390. https://doi.org/10.1002/aenm.20200239
[3] Lin, D.; Liu, Y.; Cui, Y. Nat. Nanotechnol. 2017, 12 (3), 194-206.

Operando electron paramagnetic resonance (EPR) enables to monitor the evolution of the local crystal and electronic structure of lithium-ion electrodes in real time, by following changes in EPR spectral linewidth and intensity.¹ These spectral changes are induced by the evolving magnetic-exchange interactions between transition metal species in the electrode material during battery operation. However, ambiguities can still arise as to the exact interpretation of operando EPR datasets since different charge-compensation reactions can lead to similar trends in linewidth and intensity. Additionally, traditional EPR detection is limited to transition metal species with spin-allowed transitions (spin ½ species) and favorable spin relaxation times. We address these shortcomings by conducting operando EPR in tandem with operando magnetometry, where the bulk magnetic susceptibility is used as an additional filter to parse out different local redox processes. This combined operando electron spin probe approach is applied to the LiNi_0.5Mn_0.5O₂ cathode, and complemented with DFT calculations of magnetic J-couplings. EPR results show an evolving signal that disappears at high potentials and Mn dissolution after the initial cycle. Operando magnetometry is used to decipher electrode changes during the regions of undetectable EPR.
Other applications of our operando magnetometry cell include probing reaction mechanisms and estimating irreversibility in the conversion-type Na₃FeF₆ cathode. Magnetic susceptibility changes during cycling suggest Na-ion initially intercalates into carbon additives before the active material is converted into NaF and Fe. The reaction products are unable to convert back to Na₃FeF₆ as indicated by an irreversible change in magnetic susceptibility. Furthermore, the instability of this system is highlighted by a growing magnetic susceptibility during a relaxation period after cycling.
(1) Nguyen, H.; Clément, R. J. Rechargeable Batteries from the Perspective of the Electron Spin. ACS Energy Lett. 2020. https://doi.org/10.1021/acsenergylett.0c02074.

Li ion batteries, one of the most popular energy conversion and storage devices, are widely applied as power sources for electronics, electric vehicles, and medical devices. However, when current flows through Li ion batteries upon charge or discharge, heat is triggered and can lead to many undesirable consequences: (1) heat is considered wasted energy that is typically not converted to useful electrical work; (2) heat could provoke a local temperature increase within the battery that accelerates the ageing of electrodes and electrolyte for those with poor thermal stability; (3) the accumulation of heat, especially in large-scale battery packs, may cause safety hazards. Therefore, monitoring thermal behavior of Li ion batteries under load currents is an insightful way to understand electrochemical mechanisms, diagnose batteries’ failure mechanisms, and navigate safety management.
Operando isothermal microcalorimetry (IMC) is a precise characterization method that can measure the real-time heat flow dissipated from batteries while cells are undergoing synchronous electrochemical cycling. We applied the IMC method to investigate multiple lithium storage systems covering both conversion and insertion type electrode materials. Heat flow features visualized by the IMC provide information on the kinetics and thermodynamics of electrode materials’ chemistry and electrode-electrolyte interactions. Among sources of cell’s heat generation, the heat flow associated with parasitic reactions can be quantified as an indicator of interfacial reactions, mainly the formation and evolution of the SEI. Further, the structural change of electrode materials was also found to be a factor governing the heat generation. These results inspire us to pave new ways of understanding phase evolution of Li storage materials via thermodynamics.

Advances in rechargeable batteries rely on the discovery of high power, high energy density electrode materials, but also on mitigating degradation mechanisms. Understanding how a battery works and why it fails requires the development of cutting-edge characterization tools capable of monitoring structural changes and redox reactions at the surface and in the bulk of the electrodes as the battery is (dis)charged. The fundamental insights thereby gained are key to designing new compounds for high performance batteries.
Electron paramagnetic resonance (EPR) and magnetometry offer a rare perspective on structural and redox processes from the standpoint of electron spins and magnetic interactions between redox-active species, holding promise for breakthroughs in our understanding of charge-discharge phenomena in battery materials. Our group has recently developed operando EPR and magnetometry cells to investigate such processes in real time. In this talk, I will briefly discuss when EPR and magnetometry are best used and how operando datasets are analyzed. Specifically, our recent work has shown that the interpretation of the broad EPR spectra obtained on paramagnetically-concentrated electrodes is challenging and requires the tandem use of magnetometry.¹ I will also present our recent (and preliminary) work on both intercalation and conversion electrodes using these powerful tools.

References
1. H. Nguyen and R. J. Clément, ACS Energy Letters, 5, 3848–3859 (2020).

Reaction mechanisms underlying energy storage and intercalation in lithium/sodium/potassium-ion batteries (LIB, NIB, KIB) were investigated in few layers 2D FeS₂, SnS₂, TiS₂ and MoS₂ by means of operando surface enhanced Raman spectroelectrochemistry (SERSEC).

The few-layers 2D materials were prepared by anodic exfoliation from bulk in mild K₂SO₄ media and characterized by HRTEM, XPS, Raman and EDX. Each sample exhibited similar Raman signature of two most prominent modes- A_1g and E_g, which were basis for the operando experiments. During the operando SERSEC A_1g mode in SnS₂ exhibited considerable red shift by 20 cm^-1 in the anodic oxidation scan, due to the generation of Sn-S-Li bond, as evaluated by the post-mortem XPS after the reaction. On the contrary the intercalation of Li⁺-ion in FeS₂, TiS₂ and MoS₂ was purely physical, as based on ion insertion between the the layers of 2D materials.

All operando electrochemical and SERSEC measurements were performed in a specially-designed spectroelectrochemical cell equipped with borosilicate windows modified with mercaptosilicate gold clusters of varying sizes attached covalently to the window, which were able to create hot-spots with localized plasmon resonances (LPR). The clusters were designed to be electrochemically inert (silicate shell) and LPR Raman active (gold core), as proven by the electrochemical DPV scan. The MALDI-TOF/TOF MS analysis has revealed that the gold clusters were created in mostly icosahedral shapes, as based on m/z analysis. The electrochemically inert borosilicate windows have allowed for performing of highly precise operando experiments (analytical enhancement factor: 4282).

In addition we discuss the potential of expanding SERSEC with the spectroscopic LPR windows by introduction of e.g. time-resolved operando 4D and 5D electrochemical impedance spectroscopy (EIS) for exact Raman mapping of bulk RedOx reactions with spatial resolution at the Abbé limit.

References
C. Hess, Chem. Soc. Rev., 2021,50, 3519-3564

M. Radtke, C. Hess Operando Raman shift replaces current in Butler-Volmer analysis of Li-ion batteries: a comparative study (submitted) 2021

M. Radtke, C. Hess, K. Kopp Coupling long-range Raman with X-ray Photoelectron Spectroscopy for complementary bulk and surface characterization of battery materials (submitted) 2021

Graphene liquid cell transmission electron microscopy (TEM) has enabled the observation of a variety of nanoscale transformations. Yet understanding the chemistry of the liquid cell solution and its impact on the observed transformations remains an important step towards translating insights from liquid cell TEM to bench-top chemistry. Gold nanocrystal etching can be used as a model system to probe the reactivity of the solution. FeCl₃ has been widely used to promote gold oxidation in bulk and liquid cell TEM studies, but the roles of the halide and iron species have not been fully elucidated. In this work, we observed the etching trajectories of gold nanocrystals in different iron halide solutions. We observed an increase in gold nanocrystal etch rate going from Cl^–- to Br^–- to I^–-containing solutions. This is consistent with a mechanism in which the dominant role of halides is as complexation agents for oxidized gold species. Additionally, the mechanism through which FeCl₃ induces etching in liquid cell TEM remains unclear. Ground state bleaching of the Fe(III) absorption band observed through pulse radiolysis indicates that iron may react with Cl₂^– radicals to form an oxidized transient species under irradiation. Complete active space self-consistent field (CASSCF) calculations indicate that the FeCl₃ complex is oxidized to an Fe species with an OH radical ligand. Together our data indicates that an oxidized Fe species may be the active oxidant, while halides modulate the etch rate by tuning the reduction potential of gold nanocrystals.

Liquid-cell scanning/transmission electron microscopy (S/TEM)has emerged as an effective in-situ / operando approach to characterize electrochemical systems. This approach confines both the sample of interest, electrolyte and microfabricated electrodes between two silicon nitride membranes to allow materials characterization in aqueous environments. While powerful, the thickness of the liquid layer and the nitride membranes inhibits high-resolution characterization. We will show that it is possible to overcome these limits to a great extent by utilizing electrochemical water splitting to generate a gas bubble that reduces the liquid to a film that is approximately 30 nm thick and which remains on the sample. This reduction in liquid thickness permits the acquisition of atomically resolved S/TEM images, electron diffraction patterns, and electron energy loss spectra with sufficiently high signal to noise to allow characterization of valence. After high-resolution characterization, the gas bubble can be eliminated by water oxidation. This allows us to alternate between a full cell and thin-film condition so that we can obtain optimal electrochemical cycling (full cell) and intermittent, controllable analytical characterization. We will show how we use this method to advance our understanding of several different electrochemically driven processes, including dealloying of nanoporous AuAg alloys and CO2-driven shape changes in copper nanoparticle systems.

Complex early transition metal oxides have emerged as leading candidates for fast charging lithium-ion battery anode materials. Framework crystal structures with frustrated topologies are good electrode candidates because they may intercalate large quantities of guest ions with minimal structural response. Starting from the empty perovskite (ReO₃) framework, shear planes and filled pentagonal columns are examples of motifs that decrease the structural degrees of freedom. As a consequence, many early transition metal oxide shear and bronze structures do not readily undergo the tilts and distortions that lead to phase transitions and/or the clamping of lithium diffusion pathways that occur in a purely corner-shared polyhedral network.

In this work, we explore the relationship between composition, crystal structure, and reduction pathway in a variety of mixed transition metal and main group oxides. The electrochemical properties of a series of sodium and lithium niobates are studied as new fast-charging lithium-ion battery electrode materials. High-resolution neutron diffraction is used to resolve structural questions in the host materials related to sodium disorder, space group subtleties, lithium positions, and second-order Jahn–Teller distortions of the d⁰ Nb⁵⁺ redox centers. Structural evolution is followed in real-time at rapid discharge/charge rates with operando synchrotron X-ray diffraction, collecting high-resolution diffraction patterns in a few seconds. The structure models from diffraction are informed by the local structure perspective from solid-state NMR spectroscopy and operando X-ray absorption spectroscopy (XANES and EXAFS), while the structural (meta)stability and ionic properties are probed through density functional theory (DFT) calculations. A comprehensive picture of the charge storage mechanisms in these complex oxides are described. Prospects for tunability and implications for charge rate and structural stability will be discussed.

Nanoscale characterization of solid-state electrochemical devices is crucial for understanding functional mechanisms and limiting factors in device operation. Many characterization techniques use electron microscopy and associated electron and X-ray spectroscopies, but these techniques are limited by electron- or X-ray-radiation-induced modification of the device. While the standard solution to this problem is to limit the irradiation dose to a minimum, we demonstrate the utility of some electron-beam-induced changes to probe nanoscale electrochemistry. Careful selection of electron beam parameters allows the employment of the electron beam not just as a probe, but as an active electron source to create a nanoscopic virtual anode and cathode to study in situ and in vacuo solid-state electrochemistry. We quantify electron-beam-induced variation in surface potential in electrochemical systems using in situ Kelvin probe force microscopy. Correlation of the surface potential and material’s work function changes with the electron beam dose and energy as well as with the amount of the reaction products, revealing details of the electrochemical transformation mechanisms. We compare local oxidation and reduction in several systems, including lithiated silicon, a Li-ion conductor, metallic lithium, magnesium and platinum, to establish the transformation mechanism.

Porous electrodes are a crucial hardware for many sustainable electrochemical energy devices. They are broadly used in redox flow batteries and fuel cells as well as in electrochemical synthesis and separation. Although porous electrodes with many different internal fibre architectures have been studied, there is no clear consensus as to what structural features affect electrode performance. Recent results revealing heterogeneities on length scales an order of magnitude greater than the pore size challenge the common assumption that transport in porous electrodes can be approximated by a homogeneous Darcy-like permeability, particularly at the length scales relevant to many electrochemical systems. [1]
In this study, we investigate various porous electrodes with different fibre architectures by visualization of the electrolyte charging process via in-situ confocal microscopy at length scales down to the single digit micron scale. We present fluorescent electrochemical microscopy, a strategy to couple confocal fluorescence microscopy with electrochemical monitoring as a new analytical method to investigate electrochemical flow systems in operando. The fluorescent signature of quinone electrolytes differs for the charged and discharged redox states, which enables us to map the local state of charge in three spatial and one temporal dimension (4D imaging). In addition, we use 4D fluorescent particle tracking to evaluate local velocity fields, fluid streamlines, and spatial heterogeneities. The correlation between flow fields and electrochemical concentration maps shows that not only the surface area limits the electrode efficiency but also the fibre arrangement affecting the overall electrolyte flow.
Literature cited:
[1] A.A. Wong, S.M. Rubinstein and M.J. Aziz, “Direct visualization of electrochemical reactions and heterogeneous transport within porous electrodes in operando by fluorescence microscopy” Cell Reports Phys. Sci. 2021, 100388; https://doi.org/10.1016/j.xcrp.2021.100388

Li-ion batteries structure and purity have been characterized ex-situ classically by neutron powder diffraction for a long time. More recently, there has been a huge effort to provide scientists with a tool to study Li-ion batteries operando, in order to obtain better insights of the processes involved during charge and discharge. Several electrochemical cells have been developed in various facilities [1]
At the ILL, we have designed our own custom-made electrochemical cell to respond to some specific requirements (cell fully transparent to neutrons, sample amount between 100mg to 300mg, easy to use, extremely good quality neutron powder diffraction patterns) #ILLBAT1 [2].

We showed that this cell could function properly electrochemically, whilst enabling, at the same time, the acquisition of NPD patterns of high quality for Rietveld structural refinements using D20 at the ILL. We have used this cell to study different classes of materials and it has proven very effective. We therefore decided to give users access to this new, powerful tool.

The next step was the development of similar electrochemical cells for operando studies on all-solid-state lithium batteries. This cell #ILLBAT2 has a similar design as the original one, the main difference being that it can be used at non-ambiant temperature (either high or low temperature) [3].

We are now still working on improving our cells in order to fullfill our users requests. ILLBAT#3 is a cell designed to work on ASSB as ILLBAT#2, but its specificity is that it will be possible to maintain a high pressure on the sample while measuring. And finally a cylindrical cell will also be soon available. All made in TiZy alloys. These two lasts cells are still prototypes but they will be soon available for our users community.

In parallel, in order to give more beamtime available for such studies we are developping the possibility to perform operando experiments using such cells on D19 which is a single-crystal diffractometer with a large bi-dimensionnal detector. The results of the preliminary tests are extremely possitive and there is no doubt that D19 will be a good alternative to D20.

Finaly, to give the best possible experimental conditions to our users, we are now building a Small Electrochemistry Laboratory (SEL) near D20, for the purpose of preparing these cells in a clean environment.

Of course, Operando experiments are not the only measurements using NPD. In-situ experiments using furnaces, cryostats are also common to study phase transformations or follow the phase diagram depending during the synthesis.

This conference is an opportunity to present the possibilities offered by the ILL to characterize the crystallographic structure and monitor the Li atoms position and content either operando or in-situ in Li-ion batteries using Neutron Powder Diffraction

[1] L. Vitoux, M. Reichardt, S. Sallard, P. Novák, D. Sheptyakov, C. Villevieille Frontiers in Energy Research, 6 (2018).

[2] M. Bianchini, J.B. Leriche, J.L. Laborier, L. Gendrin, E. Suard, L. Croguennec, C. Masquelier, Journal of the Electrochemical Society, 160 (2013) A2176-A2183.


[3] Tatiana Renzi PhD manuscript (in preparation)

CELLS-ALBA is the Spanish synchrotron located in the Barcelona area. The facility started in 2011 and is now prospecting machine upgrade. Along last years, several synchrotron techniques were applied using In Situ data collection on Operando electrochemical systems. Synchrotron X-ray Powder Diffraction (SXRPD) performed on BL04-MSPD has been the most productive tool in the study of new electrode materials and in particular the realized crystallographic phases settling in during (des-)insertion of alakline ions. Typical example is the Na₃V₂(PO₄)₂F₃ system for which the high angular resolution allowed whol structure determination of all occuring phases in the charge/discharge process [1]. The same system was studied using hard X-ray Absorption (XAS) techniques on the BL22-CLEASS beamline highlighting the electronic configuration of the V pairs when desinserting two Na⁺ [2]. The presentation will cover selected examples for which both SXRPD and XAS has been applied to electrochemical systems as well an insight to the presently commissioned BL16-NOTOS beamline principally offering the possibility to collect both SXRPD and XAS data "quasi" simultaneously. Soft X-ray spectroscopy and Imaging techniques have been applied using the BL09-MISTRAL beamline in the study of Ca intercalation in TiS₂. Differential absorbtion tomography allowed reconstruction in direct space of Ca distribution at several steps of intercalation.[3] In the same trend of multivalent based batteries, the identification, quantification and morphology of materials built at solid electrolyte interphase (SEI) has been tackled by InfraRed (IR) spectroscopy techniques on BL01-MIRAS beamline [4]. So far soft X-ray techniques are only availbale on Ex Situ prepared samples but development of In SItu cells is ongoing at ALBA. Deteils on devlopment will be presented.
The move towards All Solid State batteries focus now the search on solid electrolytes exhibiting high ionic conductivity and stable crystal structures. Temperature dependent SXRPD sounds a valuable technique in the understanding of such materials as demonstrated in studies of Na₃PS₄ [5] and Li₆Zn(P₂O₇)₂ [6] performed on BL04-MSPD.
Another approach in optimization and better understanding of cathode material production involves In Situ synthesis studies as recently exemplified in temperature dependent SXRPD under controlled gas atmosphere performed during synthesis of LiNiO₂ [7] and Ni-rich layered Li(NiCoMn)O₂ oxides [8].

[1] Bianchini et al, Comprehensive Investigation of the Na3V2(PO4)2F3-NaV2(PO4)2F3 System by Operando High Resolution Synchrotron X-ray Diffraction, 10.1021/acs.chemmater.5b00361
[2] Broux et al, VIV Disproportionation Upon Sodium Extraction From Na3V2(PO4)2F3 Observed by Operando X-ray Absorption Spectroscopy and Solid-State NMR 10.1021/acs.jpcc.6b11413
[3] Tchitchekova et al, Electrochemical Intercalation of Calcium and Magnesium in TiS2: Fundamental Studies Related to Multivalent Battery Applications, 10.1021/acs.chemmater.7b04406
[4] Forero-Saboya et al, Understanding the nature of the passivation layer enabling reversible calcium plating, 10.1039/d0ee02347g
[5] Famprikis et al, A New Superionic Plastic Polymorph of the N^a+ Conductor Na₃PS₄, 10.1021/acsmaterialslett.9b00322
[6] Saha et al, Influence of Temperature-Driven Polymorphism and Disorder on Ionic Conductivity in Li₆Zn(P₂O₇)₂ 10.1021/acs.inorgchem.8b01800
[7] Bianchini et al, From LiNiO2 to Li2NiO3: Synthesis, Structures and Electrochemical Mechanisms in Li-Rich Nickel Oxides 10.1021/acs.chemmater.0c02880
[8] Wang et al, Kinetic Control of Long-Range Cationic Ordering in the Synthesis of Layered Ni-Rich Oxides, 10.1002/adfm.202009949

Aiming for high capacity and high energy density batteries, combined with the strive to reduce the use of Co has resulted in significant demand for Ni-rich cathode layered materials (Li[Ni_1-xCo_xAl_y]O₂, so-called NCA, and Li[Ni_1-xMn_xCo_y]O₂, so-called NMC) on the EV market. Structure driven deterioration together with mechanical degradation hinder the full potential of the NCA and NMC materials. During cycling to higher voltages (above 4.2 V) the layered oxide materials exhibit significant reactivity of the active material with electrolyte with further gas evolution¹. Along with studies demonstrating structural fatigue facilitating rapid degradation while reaching high potentials, the high relevance of studies focused on the dependence of oxygen release and structural degradation is justifyed². We will present insights into the relation of structural changes coupled with gas evolution and advanced electrochemical characterisation that expand understanding of the limits of Ni-rich cathode material and clarify strategies for surmounting these limits. Specifically, the current study is focused on investigating the origins of NCA cathode material degradation at higher operating potentials in commercial electrodes. We use a combination of intermittent current interruption technique³ with operando XRD and operando gas analysis on electrodes extracted from commercial cells (Tesla Model 3 18650 cylindrical cells). This work allows to expound the degradation processes in Ni-rich layered oxides at high operating potentials.

1. Tao, Q. et al. Understanding the Ni-rich layered structure materials for high-energy density lithium-ion batteries. Materials Chemistry Frontiers 5, 2607–2622 (2021).
2. Xu, C. et al. Bulk fatigue induced by surface reconstruction in layered Ni-rich cathodes for Li-ion batteries. Nat. Mater. 20, 84–92 (2021).
3. Chien Y-C, Liu H, Menon AS, Brant WR, Brandell D, Lacey MJ. A fast alternative to the galvanostatic intermittent titration technique. ChemRxiv. Cambridge: Cambridge Open Engage; 2021; This content is a preprint and has not been peer-reviewed.

For many years already, we have shown that the electrochemical intercalation and deintercalation of alkali ions in a battery is a very powerful technique for determining phase diagrams in MO₂-AMO₂ systems (where A is an alkali ion and M is a 3d or 4d transition metal ion) by combining in situ powder X-ray diffraction and electrochemistry. In the molybdenum systems MoO₂-LiMoO₂ and MoO₂-NaMoO₂, it has been found that many phase transitions occur during the deintercalation of alkali ions without being able to determine the origin. We proposed that these phase transitions arose in part from the rearrangement of molybdenum atoms in MoO₂ sheets formed of MoO6 octahedra.

In order to validate this hypothesis, we performed operando pair distribution function analysis (PDF) experiments during battery cycling using Li_2/3MoO₂ and Na_2/3MoO₂ phases as positive electrode materials in lithium batteries and sodium, respectively. These experiments were performed at the XPDF beamline of the Diamond synchrotron using the electrochemical cells specifically dedicated to PDF analysis designed by Diamond. These experiments confirmed that molybdenum atoms shifted slightly from the center of MoO₆ octahedra during electrochemical (de)intercalation of alkali ions and thus formed short (approximately 2.5 Å) and long (approximately 3.2 Å) Mo-Mo bonds. The length and the distribution of the different Mo-Mo bonds have been analyzed. We concluded that different geometries of molybdenum clusters can be observed in the Li_xMoO₂ and Na_xMoO₂ phases during the alkali electrochemical deintercalation (for example, zig-zag chains or diamond-like chains).

Understanding lithiation and ageing mechanisms in Li-ion batteries requires ad hoc tools to probe the real-time evolution of active materials during charge and discharge of a battery. Neutron & synchrotron techniques have been widely employed to probe the structural, morphological and chemical changes occurring in electrodes, as both high energy X-rays and neutrons can deeply penetrate into matter, therefore enabling to monitor key processes in realistic devices with ultimate space and time resolutions. Recently, composite anodes made of (nano)silicon and graphite have attracted attention due to the high specific capacity of silicon. However, these are extremely complex materials where the volume changes due to silicon alloying with lithium generate ageing on the long-term, therefore hindering their potential use towards viable high energy density anodes. We will present in this talk a toolkit of techniques employed to quantify strain in crystalline silicon by operando synchrotron XRD [1], nanoscale morphological changes in composite anodes by synchrotron SAXS and SANS [2,3], 3D lithiation heterogeneities and microstructural ageing by SAXS/WAXS synchrotron tomography and synchrotron mXCT [4]. These investigations established the details of core-shell lithiation mechanism as well as the correlations between electrochemistry, materials design and ageing process, allowing to highlight the key features for a better engineering of novel silicon-based anodes.

[1] S. Tardif et al, ACS Nano, 2017, 11, 11306–11316.
[2] C. Berhaut et al, ACS Nano, 2019, 13, 10, 11538-11551.
[3] C. Berhaut et al, Energy Storage Materials, 2020, 29, 190–197.
[4] Vorauer et al, Comm. Chemistry, 2020, 3, 141.

Complete physico-chemical operando characterization of electrochemical devices in whole, or it’s constituent materials separately, is necessary to guide the development and to improve the performance. High brilliance synchrotron X-ray sources play a crucial role in this respect as they act as a probe with relatively high penetration power and low damage potential. Synchrotron sources will undergo major upgrades in next decade and will provide even higher brilliance and, more importantly, coherence. These upgrades will be particularly advantageous for beamlines providing high energy X-rays as they will allow use of advanced scattering techniques with highly penetrating probe. Therefore, the techniques typically used for ex-situ measurements or at lower X-ray energies could be used on materials in liquid half-cells and operating electrochemical devices. In this contribution the new possibilities of using high energy, high intensity, coherent X-rays to probe model systems and whole electrochemical devices will be presented. The focus will be on defects tracking, local structure determination and correlative multimodal characterization using advanced WAXS, SAXS and surface scattering techniques.
To study fuel cells or batteries as a whole, elastic scattering techniques such as wide angle and small angle scattering are typically employed, as they can provide important complementary information to more standard X-ray imaging and tomography. The advantage is that the chemical contrast and sensitivity at atomic and nm scales is superior. Coupling these technique with the tomographic reconstruction (XRD-CT and SAXS-CT) is much less common as it requires bright synchrotron sources, fast 2D detectors and advanced instrumentation [1]. However, such combination allows spatial reconstruction of materials important atomic parameters in operando conditions. This will be demonstrated on imaging of standard 5 cm2 PEM fuel cell during operation.
Furthermore, local atomic and mesoscale structure, together with defect content, can also be determined by using Rietveld fitting, Pair Distribution Function (PDF) analysis and advanced SAXS theory. This in principle allows holistic investigations of interfaces at the device level, specification of defects’ role in catalysis and determination of interplay between different phases during operation. These are critical questions needed to be answered in order to incorporate novel materials into the electrochemical devices. Examples will be given on studies of the defectous ORR catalysts [2,3] and amorphous Li-ion anodes.
HESXRD (High Energy Surface X-ray Diffraction) [4] and TDS (Transmission Surface Diffraction) [5] provide ideal tools to study structural changes during reaction conditions on single crystal model electrodes. The main advantage of both techniques is the possibility to follow the surface structural changes precisely with atomic resolution. While HESXRD is ideally used to determine exact atomic position, the TSD is easier from experimental perspective and allows studies with high spatial resolution. Advantages and disadvantages of both approaches will be discussed and examples of measurements on ORR and OER catalysts will be given. The future possibility to use high energy coherent beams will open new opportunities for both techniques to study single defects and surface dynamics in operando conditions.

References :
1) A. Vamvakeros et al., Nat. Commun., 9, 4751 (2018)
2) R. Chattot et al., Nat. Matter., 17(2018)
3) C.J. Gommes et al., J. Appl. Cryst., 52(2019)
4) J. Gustafson et al., Science 343, 758 (2014)
5) F. Reikowski et al., J. Phys. Chem. Lett., 5, 1067-1071 (2017)

In situ liquid phase transmission electron microscopy (LPTEM) is a promising technique to visualize and study real-time dynamic processes happening during electrochemical cycling of Li-, Zn-, Na- and other types of ion batteries. The in situ LPTEM allows to reveal morphological and structural changes occuring in the sample in a liquid environemnt and to correlate it with the electrochemistry. On the other hand, this method has a number of drawbacks which reduces its success rate and limits wide practical application. First of all, high resolution (∼ nm scale) and analytical capabilities (Electron Diffraction-ED, Energy Dispersive X-ray Spectroscopy-EDXS and Electron Energy Loss Spectroscopy-EELS) are substiantilly hindered by the uncotrlled thick liquid layer ( ≥ 500 nm). Furthremore, the current designs of the liquid flow cells used for in situ liquid phase TEM have no direct control over the liquid flow as they possess multiple fluidic pathways with considrably higher fluidic resistance in the sample area. This prevents measuring the flow rate around the sample and studying the effect of the flow on the dendrite growth. Furthermore, bubbles, often created in the imaging area while performing electrochemical cycling abort the whole experiment as these are impossible to remove from the current liquid cells.

To solve the above-mentioned limitations and to increase the success rate, we revolutionazed the design of the liquid cell. Unlike existing solutions, where the liquid inlet and the outlet are located in the TEM holder, the new design has the liquid inlet/outlet directly in the liquid cell. The spacers inside the cell guide the liquid from the inlet to the outlet, forming a fluidic channel that goes through the imaging area. This innovation made it possible to have a direct flow control over the sample. In combination with a new type of liquid delivery system based on pressure-driven flow, the new liquid cell has a well-defined flow direction, allows to control the pressure of the liquid inside the cell and thus the liquid thickness, enables quantification of liquid flow rates, enables bubbles removal and much more.
In this work we are going to present the design of the new liquid cell together with the new liquid delivery setup and show how this new system can be used to remove bubbles from the region of interst by means of the liquid flow or the liquid pressure, how it is possible to minimize the effect of the electron beam with the flow, how to make high resolution imaging and enable elemental mapping in liquid and how to define the mass transport in the electrochemical cell and to study kinetics of redox reactions.

Materials science in the field of batteries as dominating electrochemical energy storage systems is forced to follow a systems approach as the interactions between active materials, the electrolyte, the separator and various inactive materials (binder, current collector, conductive fillers, cell housing, etc.), are of similar or even higher importance as the properties and performance parameters of the individual materials. Successful operation of batteries relies significantly on a series of interrelated mechanisms, some involving instability of the constituting components induced by charge/discharge cycles and some also encompassing formation/reaction of metastable phases. With this in line, the ability to achieve long-term stability requires careful elucidation of the physical and chemical processes governing charge/discharge cycling and storage. The key performance requirements of a battery for different applications might look very similar at first sight, however, each application calls for different requirement prioritization. Frequently, they conflict with one another and call for inevitable trade-offs. The objective of advanced battery research and development relates to obtaining the best compromise among the determined goals, followed by a decision whether the balanced system should be implemented instead of a competing technology. In all types of batteries, electrolyte as the only component in direct contact with all other active and inactive parts, plays a key role in terms of overall performance, life and safety. Chemistry of liquid electrolytes and their interaction with anode and cathode materials is complex and yet not fully understood, thus representing a delicate balance of various properties. Despite our limited knowledge, modern needs for battery electrolytes require the development of sophisticated electrolyte solutions with multifunctional components, able to simultaneously fulfill several duties. Typical requirements include combined roles as salt dissolution enhancers, viscosity decreasers, flame-retardants or effective electrolyte interphase formers at the electrodes. The introduction of these modern components can be regarded as a paradigm shift in order to increase the efficiency and safety of lithium-based and post-lithium-based batteries, when compared with nowadays technologies.
This talk is an invitation to a journey of the scientific development, technology as well as engineering of selected classes of advanced liquid electrolytes for lithium-based batteries under systematic approach that allows to understand the structure-property-performance relationships of the selected compounds/formulations, their impact on the overall battery chemistry, performance and safety, thus helping to further tailor relevant properties of electrolyte components/formulations for targeted applications.

Lithium Ion Batteries (LIB) find not only wide use in portable devices and consumer electronics, but also attract increasing attention in stationary energy storage and the automotive sector. In this regard, LIBs play a significant role as intermediate energy storage due to their high volumetric and gravimetric energy, high power density, and long cycle life. With respect to larger battery packs safety became a major concern and attracted increasing research interest in this field.

To achieve the required performance, the interaction of novel anode and high-voltage cathode materials with the electrolyte is of paramount interest. Safety and performance issues arise from degradation reactions of the conducting salt and electrolyte solvent, due to the formation of flammable, corrosive and toxic gas species. Particularly, the safety must be assessed with respect to the formation of volatile and reactive species during cell operation which can negatively alter cell components. Gas chromatography / mass spectroscopy (GC/MS) has proven to be a reliable tool for species detection. Unfortunately, conventional GC systems lack time resolution for operando gas analysis regarding fast processes, for example battery failure. Therefore, developing operando testing methods with improved time resolution is key to giving insight into electrolyte alterations during battery operation.

Here one of them, an operando GC/MS for LIBs is presented as a gas monitoring technique for volatile organic species arising from the decomposition of conventional LIB electrolytes. The combination of a continuous sampling technique with GC/MS allows an increased time resolution for the analysis of products from fast decomposition processes. Commercially produced NMC-based pouch cells and coin cell-sized batteries were monitored with respect to evolving gas species during battery operation. Especially, the degradation products of organic carbonate- based electrolytes, such as derivatives that appear in the presence of decomposed LiPF₆, have been evaluated in respect to the cell potential.

The author gratefully acknowledges the FFG (Austrian Research Promotion Agency) for funding this research within project No. 879613.

Li-metal is the ultimate anode for Li-batteries from the perspective of energy density. However, reversible cycling is challenged by dendrite formation and the irreversible reactions with the electrolyte, a topic that is intensively investigated for many decades. Here we show the use of operando Neutron Depth Profiling (NDP) and Solid State NMR to monitor the some of the espects of Li-metal deposition. Neutron Depth Profiling provides the Li density profile perpendicular to the electrode place in modified pouch cells. Solid state NMR is able to monitor the evolution of dead Li metal in a full cell geometry, as well as the nature of the deposited Li metal. Both techniques are applied to different solution strategies, such as electrolyte/solvent additives and a host scaffold for Li metal plating. Operando NDP is employed on a regular LiPF6 EC/DMC electrolyte [1], to illustrate the NDP principle and the type of data that can be extracted, as well as on an amide electrolyte [2], highlighting how this changes the Li metal plating and stripping. Operando 7Li solid state NMR on full anodeless cells is performed [3], with and without a high dielectric scaffold that is intended to induce more compact Li metal growth. These examples provide insight in the underlying mechanism of these strategies, illustrating the value of these operando techniques in Li metal studies.

[1] Operando monitoring the lithium spatial distribution of lithium metal anodes, S. Lv et al., https://doi.org/10.1038/s41467-018-04394-3
[2] Interface chemistry of an amide electrolyte for highly reversible lithium metal batteries, Q. Wang et al., https://doi.org/10.1038/s41467-020-17976-x
[3] Under review

The evolution of local chemistry determines the performance of electrodes and electrolytes used in batteries because limitations can be tracked to slow kinetics and transport, and irreversibilities in the storage reaction. Tools that provide insight into local chemistry are critical for identifying the underpinnings of electrochemical function. This information must be resolved within architectures, from individual particles to microscale domains, to pinpoint the relationship between local phenomena and their role in macroscopic metrics and degradation. Technical developments in X-ray microscopy and mapping have built a flexible suite of tools that combine the desired spatial resolution and 3D capabilities with a suite of possible contrasts mechanisms, such as diffraction and spectroscopy. In this talk, we will discuss our recent research that demonstrates the diversity of length scales at which important chemical heterogeneity can be induced in battery electrodes. For this purpose, the systems of study will be the leading cathodes for Li-ion batteries, but the insight is expected to be generalizable to “beyond” technologies, such as Na-ion or Mg. We will highlight the new fundamental insight generated by the tools. The mechanisms of transformation will be related to their impact on material and architecture properties. Along the way, we will also provide a glimpse into the future by showing how emerging synchrotron techniques can enhance the impact of X-ray microscopy in fundamental battery science. Particularly, in the spirit of this Symposium, we will discuss the prospects of probing time-resolved phenomena using operando measurements to avoid uncertainty due to relaxation under open circuit conditions.

Li_xCoO₂ (LCO) is a common battery cathode material that exhibits phase transformations that are significantly complicated by the coupling of correlated electronic effects, strain and diffusional anisotropy. At compositions 0.96<x<1 LCO remains insulating, while at compositions x<0.75 it is metallic. Between these two compositions, the insulating and metallic phases coexist. While the bulk phase diagram has been studied extensively [1, 2], it remains unclear how the electronic and structural phases scale to nanometer particle dimensions, and the effects of strain and diffusional anisotropy on the phase morphology [3]. We have investigated nanoscale, epitaxial LiCoO₂ islands grown by pulsed laser deposition onto SrTiO₃ substrates. After charge cycling of the islands, conductive atomic force microscopy (c-AFM) is used to image the spatial distribution of conductive and insulating phases at various states of charge and under strain conditions. Above island thicknesses of 25 nm, we resolve a diffusion-limited intercalation wavefront propagating along the Li-planes. Thinner islands (~11nm) are found to exhibit a striping pattern which suggests the surface energy plays a critical role in the phase morphology when particles are scaled below a critical dimension. The effects of strain are investigated through the application of force with the c-AFM tip. Above a critical force threshold, the insulating regions of the islands are found to undergo an insulator-metal transition. The results suggest that the morphology of phase segregation and strain play a critical role in charge-cycling of nanoscale particles.

[1] K. Mizushima, P.C. Jones, P.J. Wiseman and J.B. Good-enough, Mater. Res. Bull. 55, 783 (1980)
[2] A. Van der Ven, M.K. Aydinol and G. Ceder, Phys. Rev. B 58, 2975 (1998)
[3] Nadkarni et al., Adv. Funct. Mater., 29, 1902821 (2019)

Driven by the increasing need for energy storage, especially for electric vehicles and electronic devices, the technological advancements of lithium-ion batteries (LIBs) are urgently in demand to increase energy density while reducing the cost. Battery performance is largely determined by the phase constitution and properties of electrodes and electrolytes and, therefore, can be advanced by synthesis/processing, in making certain phases with controlled structure and material properties. This is particularly true for high-Ni layered oxides, LiNi_xMn_yCo_1-x-yO₂ (NMC; x>0.7), the most promising low-cost, high energy density cathodes for next-generation LIBs. In such cathode materials, the increasingly high Ni loading worsens the surface instability and, consequently, lowers the cells’ lifespan and brings issues to materials production and storage, posing a practical challenge to their commercial deployment.
In this work, a multimodal in situ synchrotron X-ray characterization approach is employed to investigate the thermodynamic and kinetic pathways in the synthesis/processing of high-Ni NMC materials. A combination of in situ X-ray diffraction, total scattering (coupled with pair distribution function analysis), X-ray absorption spectroscopy, and imaging is applied to tracking structural/chemical evolution at short, intermediate, and long-range ordering of intermediates in preparing NMC811, LiNiO_2, and other layered oxides from their hydroxide counterparts. Results of our recent studies reveal the strong composition dependence of the structure and morphology evolution as a result of the preferential oxidation of Mn/Co over Ni. We show Mn and Co play an important role in facilitating Li/O incorporation, consequently leading to more continuous structural ordering and crystal growth in Mn/Co containing high-Ni NMC compared to the pure LiNiO₂. Those findings shed light on the rational design of synthesis/processing in preparing high-Ni layered cathodes of optimized performance for next-generation LIBs.

Paving new pathways for in situ and/or operando characterizations of buried and intact electrochemical interfaces is critically important for, in the least, (i) advancing basic energy storage science and for (ii) optimizing the efficacy of engineered interfaces/interphases in batteries. In this talk, we first present a brief overview of near-field based infrared nanospectroscopy (true nanoscale Fourier transform infrared spectroscopy) and nanoimaging. We follow this by sharing how we have demonstrated such techniques can be utilized to study graphene/liquid-electrolyte interfaces, with sensitivity to even species within the electric double layer. Finally, we discuss our most recent data in which we extend such near-field methods to characterize buried and intact electrode/electrolyte interface evolution in solid-state polymer battery (SPB) devices, in situ. The SPB devices are capped with graphene, which operates as both infrared transparent window and current collector for Li plating and stripping (similar in function to anode-less batteries). In situ infrared imaging and spectroscopic measurements are performed at pristine, heated, plated, and stripped interfaces, where we find that the interfacial solid-state polymer-electrolyte (SPE) intrinsically possesses nanoscale heterogeneities that contribute to plating inhomogeneities on a similar length scale. Additionally, we find that a mosaic-like solid-electrolyte interphase forms at the Li/SPE interface consisting of decomposition products amongst SPE. Our approach paves a way for SPB optimization (or other chemistries), by providing a method for unprecedented nanoscale measurements of crystallinity, structure, conductivity, and chemistry of intact and buried electrochemical interfaces in their native environments.

There is considerable interest in the study of electrochemical processes in calcium batteries since the demonstration of room temperature plating and stripping of calcium with high capacities and low polarization using Ca(BH₄)₂ as the electrolyte. The greater polarizability of Ca²⁺ over Mg²⁺ represents greater configurational flexibility, facilitating ionic cluster formation and rapid delivery of Ca²⁺ ions to the electrode interface. To promote the development of calcium batteries, it is critical to probe the solvation and charge transfer mechanism at the electrode/electrolyte interface. It has been reported that when Ca(BH₄)₂ is substituted by the weakly coordinated calcium hexafluoroisopropoxyborate (Ca(Bhfip)₂), ionic conductivity increases by an order of magnitude, which demonstrates the strong coordination of BH₄^- compared to Ca²⁺ in THF. In this work, the coordination of Ca²⁺ at this electrolyte/electrode interface as a function of the type of anions is probed by the in-situ/operando soft X-ray absorption (XAS) spectroscopy under operando electrochemical conditions. The total electron yield (TEY) mode XAS is sensitive to the interfacial speciation under in-situ and operando conditions. It was observed that the Ca(Bhfip)₂ in THF shows a small shoulder on the right side of the L₂-edge and a pre-edge peak on the left side of the L₂-edge peak. A less prominent pre-edge peak is also observed on the left side of the L₃-edge peak. These signatures become more prominent when the potential is swept negatively and are not reversible when the potential is swept positively in a cyclic voltammetry cycle. On the other hand, the Ca(BH₄)₂ in THF is more reversible, and no shoulder peak on the right side of the L₂-edge peak was observed. The effect of cations was also compared by investigation of the calcium L-edge and fluorine K-edge TEY mode XAS from the 0.5M calcium bis(trifluoromethanesulfonyl)imide (Ca(TFSI)₂) in THF vs. 0.45M Ca(TFSI)₂ + 0.05M LiTFSI in THF. The TEY-XAS spectra from these operando studies indicate their differences in the Ca²⁺ coordination chemistry at the electrode/electrolyte interface as a result of the anions and cations, and will path the way for the future development of electrolytes for calcium batteries.

Laboratory-based x-ray photoelectron spectroscopy (XPS) is a ubiquitous, powerful technique for analyzing surfaces and interfaces to reveal compositions and chemical states. Beyond these typical applications, in recent years there has been growing interest around in situ and operando XPS approaches that can elucidate dynamic interfacial phenomena, including charge- and mass-transfer processes relevant to renewable technologies including lithium-ion batteries (LIBs). This presentation will discuss recent efforts to develop and apply in situ and operando approaches to probe interfacial charge transfer and phase transformations relevant to the formation and evolution of the solid-electrolyte interphase (SEI) in silicon-anode LIBs. These experiments are enabled by the so-called virtual electrode (VE) approach [1,2], in which electrochemical currents are driven during VE-XPS measurements on exposed interfaces via a combination of low-energy Li⁺ion and electron guns and ultraviolet-based photoemission. Key recent findings that will be discussed include: (i) conversion of native SiO_x to Li_ySiO_x phases; (ii) lithium-induced band-alignment shifts at the SiO_x|silicon interface; (iii) observed correlations between lithium chemical potential (m_Li) and ionic vs. electronic conductivities of SEI constituent phases such as LiF and Li₂CO₃; and (iv) in situ reduction of ethylene carbonate (EC) on various model-system electrodes.

[1] K.N. Wood, K.X. Steirer, S.E. Hafner, C. Ban, S. Santhanagopalan, S.-H. Lee, G. Teeter, “Operando X-ray photoelectron spectroscopy of solid electrolyte interphase formation and evolution in Li₂S-P₂S₅ solid-state electrolytes,” Nature Communications 9, 2490 (2018).
[2] A.L. Davis, R. Garcia-Mendez, K.N. Wood, E. Kazyak, K.-H. Chen, G. Teeter, J. Sakamoto, N.P. Dasgupta, “Electro-chemo-mechanical evolution of sulfide solid electrolyte/Li metal interfaces: operando analysis and ALD interlayer effects,” Journal of Materials Chemistry A 8, 6291 (2020).

Vast efforts have been devoted over the last decade to develop new techniques and approaches to obtain critical information about interfacial phenomena during device operation to establish direct correlations towards their electrochemical performance. However, the sophistication of some of the most powerful techniques, such as isotopic ion exchange methods, in situ TEM and synchrotron radiation based techniques, limits the routine access to essential information for developing next-generation batteries. In addition, commonly available techniques have also been explored including X-ray diffraction, atomic force microscopy, Raman spectroscopy and Fourier transform infrared (FTIR) spectroscopy showing different compromises between spatial and time resolutions. Surprisingly, and despite the well-known capabilities of Spectroscopic Ellipsometry (SE) to infer the properties of thin film systems (including multilayers), the use of this affordable, non-destructive technique in the field of Li-ion batteries is very limited. In short, SE measures the change in the polarization state of a light beam reflected in the sample. By comparing with a suitable model, the relevant optical properties of the material, such as the dielectric function and extinction coefficients, are extracted as a function of the wavelength. This technique is typically sensitive to parameters such as crystallinity, materials ratio in mixtures, roughness, structure of the interfaces, etc

In this talk, we will discuss the basic theory and our implementation of Spectroscopic Ellipsometry to perform operando experiments thanks to its fast response and the strong effect of the oxidation state on the optical properties of the films. We will exemplify the power of the technique with two examples. First, we have used SE to monitor Li⁺ transport properties through real-time tracking of the valence changes associated with lithium insertion and extraction along LiMn₂O₄ thin films and interfaces¹. Second, we have employed SE to interrogate the formation of a Solid Electrolyte Interphase (SEI) during the first cycle on spinel-based anode and cathodes over the extended voltage range. Here, we link the changes in the optical properties of the films with the capacity losses associated with the first cycle, and provide guidelines for SEI-resistant coatings at the cathode and anode interfaces².


References
1 A. Morata, V. Siller, F. Chiabrera, M. Nuñez, R. Trocoli, M. Stchakovsky and A. Tarancón, J. Mater. Chem. A, 2020, 8, 11538–11544.
2 J.C. Gonzalez-Rosillo, V. Siller, M. Nuñez, , M. Stchakovsky, A. Morata and A. Tarancón, In preparation

Fast charging of lithium-ion batteries (LIBs), being developed for electric vehicles, is needed to meet customer demands of time-parity with today’s gasoline-powered cars. The U.S. Department of Energy (DOE) has set a target charging time of 15 minutes (4C rate) as a near-term goal, further indicating that a 10-minute charge (6C rate) could be a long-term goal. This talk will present an overview of fast charge studies being conducted at Argonne National Laboratory as part of projects funded by the U.S. DOE. In-situ and operando methods to examine electrode and cell behavior will be discussed: results from cells containing layered oxide cathodes and graphite anodes will be highlighted. The use of a microprobe reference electrode to monitor the onset of Li plating conditions and to determine develop cycling protocols that minimize cell performance degradation will be presented. X-ray methodologies to characterize spatial distribution of the active materials and investigate lithium concentration gradients that develop in electrodes will be examined. The heterogeneities that develop and persist in the electrodes cause non-uniform degradation across the electrodes thus making it a challenge to predict cell life.

X-ray reflectivity and crystal truncation rod measurements, performed at the Advanced Photon Source at Argonne National Laboratory, monitored structural changes of Ti₃C₂ MXene films as a function of applied potential between 0.3 and −0.7 V in an aqueous 0.1 M Li₂SO₄/H₂O electrolyte. Static measurements show negative potential sweeps lead to a contraction in the interlayer spacing of 1.2 Å upon Li insertion and a net loss of electron density between the layers (Sobyra et al. ACS AMI, 2021, Under Review). The layer spacing changes continuously, except for an additional discrete contraction that occurs near −0.35 V having the characteristics of a first-order transition. The continuous change in the MXene layer spacing is associated with the capacitive charge, while the discrete change in structure correlated with the weak feature in the cyclic voltammogram at −0.35 V can be interpreted as either a pseudocapacitive charging process or a potential-dependent change in capacity.

New dynamic in-situ measurements observe the change in lattice spacing and MXene layer widths in real-time as a function of sweep rate to provide insight into the mechanisms of intercalation as the system is forced to respond to the rapidly changing environment. Potential sweep rates were varied from 1 mV/s to 500 mV/s. The Ti₃C₂ MXene response at slow sweep rates, less than 10 mV/s is similar to the static charging, but at faster rates, the system shows less contraction in the Ti₃C₂ layer spacing as the Li insertion becomes transport limited.

Analysis of the MXene electrochemical response reveals a charging mechanism that is sweep rate-dependent and not diffusion-limited as the Li⁺ ions diffuse slower than the bulk diffusion rate through the interlayer spacing. These measurements with varying sweep rates, in conjunction with the dynamic X-ray measurements, confirm the rapid change in layer spacing that occurs below −0.3 V is directly associated with the broad redox peak seen in the cyclic voltammogram.

Magnetic resonance tools for in situ and in operando investigations of electrochemical processes have provided many new insights into electrochemical processes in lithium ion batteries. We have recently reported the application of a parallel-plate NMR probe to monitor Li metal deposition on a graphite anode during the charging of a single layer prismatic cell.^[1] The probe provides an enhanced sensitivity and an ideal orientation of the cell relative to the applied electromagnetic fields, and allows the quantification of the lithiation of the graphite anode throughout the duration of cell charging.
A new version of this parallel-plate resonator for ⁷Li ion cell studies is introduced along with a removable cartridge-like electrochemical cell for studies of LIBs.^[2] This geometry separates the RF probe from the electrochemical cell permitting charge/discharge of the cell outside the magnet and introduces the possibility of multiplexing samples. The cell and RF probe dramatically increase the sample volume compared to traditional MR compatible battery designs. The cell and RF probe may be employed for spectroscopy, imaging, and relaxation studies.
Here we report the application of this probe, together with a custom electrochemical cell assembly, to monitor Li plating on a graphite anode of a full-cell LIB using in operando NMR spectroscopy and imaging. We are able to quantify the amount of Li metal deposited on the anode surface and correlate it to the relative amounts of Li species within the graphite anode with high time resolution relative to the high charging rate of 1C. Our data demonstrate that most of the Li metal deposited on the anode surface can be intercalated into graphite during rest periods when no current is applied, and that the formation of Li metal correlates to the loss of capacity of the cell over multiple high-rate charge cycles. Moreover, we demonstrate that this methodology can be extended to a variety of battery chemistries, with an emphasis on full-cell behaviour.
Finally, we demonstrate a magic-angle spinning (MAS) based in situ electrochemical NMR method that offers significantly improved resolution over conventional static NMR experiments. We demonstrate that it is possible to monitor both the anode and cathode simultaneously making it possible to track the Li distribution in a full cell.^[3] The state of charge, metallic Li plating and SEI formation was captured for the first charge/discharge cycle of a full electrochemical cell using conventional liquid electrolytes. The use of a polymer electrolyte membrane offers improvements over the original design.

References:
[1] Krachkovskiy, S. A., Reza, M., Ramírez Aguilera, A. R., Halalay, I. C., Balcom, B. J., Goward, G. R. J. Electrochem Soc. 167(13), 130514 (2020)
[2] Ramírez Aguilera, A. MacMillan B., Krachkovskiy, S. Sanders, K.J. Alkhayri, F., Dyker, A., Goward, G.R., Balcom, B.J., J. Magn. Reson. 325, 106943 (2021).
[3] Freytag, A, Pauric, A, Krachkovskiy, S, and Goward, GR. J. Am. Chem. Soc. 141 (35), 13758-13761 (2019).

Many catalysts for energy related applications, in particular metallic nanoalloys, undergo atomic-level changes during electrochemical reactions. The nature and dynamics of the changes and their impact on the catalyst performance, however, are not well understood. This is largely because they are studied on model nanocatalysts under controlled laboratory conditions. We will present results from recent studies [1, 2, 3] on the dynamic behavior of metallic nanoalloy catalysts inside an operating proton exchange membrane fuel cell. Results show that the nanocatalyst change profoundly, from their initial state to the active form and further along the cell operation. Their electrocatalytic activity also changes, as reflected by the cell’s performance. We will also show that the rate and magnitude of the changes may be rationalized when the limits of traditional relationships used to connect the composition and structure of nanoalloys with their electrocatalytic activity and stability, such as Vegard’s law, are taken into account. The new insight into the atomic-level evolution of nanoalloy electrocatalysts is likely to inspire new efforts to stabilize transient structure states beneficial to their activity and stability under operating conditions, if not synthesize them directly.

V. Petkov et al. Nanoscale 11, 5512 (2019).
Zh. Kong et al. J. Am. Chem. Soc. 142, 1287 (2020).
Z. –P. Wu et al. Nature Commun. 12, 8597 (2021)

MnO₂ nanosheets demonstrate an interesting response to reduction of Mn⁴⁺ to Mn³⁺, where Jahn-Teller distorted Mn³⁺ is displaced out of the plane of the nanosheet forming a “surface Frenkel” defect. Atomic scale point defects enhance capacitance beyond 300F/g while lowering charge transfer resistance of δ-MnO₂ nanosheets by a factor of 10. X-ray total scattering was teamed with X-ray absorption spectroscopy and Raman spectroscopy probe the local atomic structure, defect chemistry, and strain during electrochemical cycling. All methods employed in-situ or real-time in-operando study using custom sample environment cells and porous agglomerated nanosheet active materials. Specimens prepared by exfoliation of pristine powder grains to form nanosheet clusters with 2-5 individual layers were processed into nanosheet floccules, which are of high surface area (over 200 square meters per gram) and can be deposited as thick films using electrophoretic deposition. The result of the studies is a description of the charging mechanism in high surface area MnO2 nanosheet electrodes and related nanosheet oxides: in-plane strains of up to 0.7% occur during charging, accompanied by Mn reduction. The initial number of Mn3+ defects determines the magnitude of the charge stored and consequently the electrochemical strain. In-situ XANES showed 16% of the Mn in MnO₂ reduced from Mn⁴⁺ to Mn³⁺ during electrochemical cycling. In agreement, in-situ Raman spectra demonstrate an increase in the number of Jahn-Teller distorted MnO₆ octahedra in the charged state as well as changes in the polarizability of vibrational modes that are affected by interlayer cations and interlayer water, though there is only very limited restacking of a few nanosheets. The excellent cycling stability of the nanosheet electrodes vs. bulk solids is attributed to the free space in the floccules that allows electrochemically-driven expansion and contraction without degrading the charge transfer pathways and without microcracking the active electrode. Another new discovery is Mn3+ defects also induce enhanced mass transport, resulting in formation of tunnel-like fragments which disrupt the sheet-like motif. Heat treatments expedite this layer-to-tunnel conversion which has a profound impact on the electrochemical properties and cycling stability. At low scan rates the capacitance of δ-MnO₂ heat treated at 60°C is ~6 times larger than the 400°C samples indicating a change in the charge storage mechanism that cannot be detected by diffraction studies alone, and requires PDF analyses. Kinetic analysis paired with PDF refinements demonstrate tunnel formation hinders the intercalative ion diffusion, reaching a percolation threshold around 25-30% tunnel structured MnO₂.

The performance of rechargeable batteries is determined largely by materials structure- and dynamic-function relations. During battery function, materials undergo change, such as the experienced by electrode materials during the compositional change that occurs during battery cycling. Robust characterization methods that quantitatively and accurately capture structure- and dynamic-function relations across the relevant length and timescales for batteries are essential to the strategic design of materials with superior function.

Neutrons have attributes that make them exceptionally useful for this purpose. The predominantly nuclear interaction of neutrons with matter results in both high penetration, allowing the analysis of materials within whole commercial batteries, as well as an elemental sensitivity that is particularly well suited to battery materials composition.

This talk will give examples of neutron characterization of rechargeable battery materials, with a focus on instrumentation at the Australian Centre for Neutron Scattering, and much of which examines materials within whole batteries during operation. Examples using neutron powder diffraction,^1-5 neutron imaging,^6,7 small and ultra small angle neutron scattering,⁸ and quasielastic neutron scattering,⁹ will be presented.

¹ N. Sharma, V. K. Peterson, M. M. Elcombe, M. Avdeev, A. J. Studer, N. Blagojevic, R. Yusoff, N. Kamarulzaman, J. Power Sources, 2010.
² C. Didier, W. K. Pang, Z. Guo, S. Schmid, V. K. Peterson, Chem. Mater., 2020.
³ G. Liang, C. Didier, Z. Guo, W. K. Pang, V. K. Peterson, Adv. Mater., 2020.
⁴ W. K. Pang, V. K. Peterson, N. Sharma, J. -J. Shiu, S. -h. Wu, Chem. Mater., 2014.
⁵ W. K. Pang, V. K. Peterson, J. Appl. Cryst., 2015.
⁶ D. Petz, M. J. Mühlbauer, A. Schökel, K. Achterhold, F. Pfeiffer, T. Pirling, M. Hofmann, A. Senyshyn, Batteries & Supercaps, 2021.
⁷ D. Petz, M. J. Mühlbauer, V. Baran, M. Frost, A. Schökel, C. Paulmann, Y. Chen, D. Garcés, A. Senyshyn, J. Power Sources, 2020.
⁸ S. Seidlmayer, J. Hattendorff, I. Buchberger, L. Karge, H. A. Gasteiger, R. Gilles, J. Electrochem. Soc. 2015
⁹ M. J. Klenk, S. E. Boeberitz, J. Dai, N. H. Jalarvo, V. K. Peterson, W. Lai, Solid State Ionics, 2017

Platinum (Pt)-based electrocatalysts are widely used in many fields such as energy, environment, medicine, and so on. The activity can be improved by composition, structure, morphology control while the performance degradation still occurs during the operation. Therefore, it is of great importance to investigate the degradation mechanism of the Pt-based electrocatalysts. Herein, we chose Pd@Pt core-shell structure, a promising electrocatalyst toward oxygen reduction reaction (ORR) as the study system. In-situ liquid cell transmission electron microscopy (LC-TEM) technique was utilized to explore the nanoscale corrosion kinetics of the electrocatalysts. The corrosion of Pd@Pt core-shell nanoparticles with different morphology like cube and octahedra were studied. The results indicate that the defects are the inducing factors of corrosion and the sequential corrosion process is controlled by both the local strain and evolving curvature. Strain plays a major role in the early process, and the local curvature dominates gradually in the later process. In addition, the sites with high surface energy like corners are the preferential etching areas. We sequentially designed and synthesized corner-protected Pd@Pt nanocubes and small size octahedral nanoparticles with fewer defects and smaller strains based on these insights in nanoscale corrosion behaviors. Both in-situ LC-TEM study and ex-situ stability tests confirmed that the newly designed electrocatalysts were much more corrosion-resistant.


References
1 Shi, F. et al. Nat. Commun. 9, 1011, 2018.
2 Shi, F. et al. Chem 6, 2257-2271, 2020.
3 Shi, F. et al. ChemNanoMat 5, 1439-1455, 2019.
4 Shi, F. et al. Adv. Mater. accepted, 2021.

A fundamental understanding of mass transport properties in electrolytes during electrochemical reaction is important for optimal operation and design of energy conversion/storage devices, including batteries, fuel cells and water electrolysis. It is known that internal resistance of the lithium-ion batteries (LIBs) temporarily rises by repeating high-rate charge/discharge cycles and that it decreases by stopping the battery operation and rest. Because such a reversible resistance rise occurs only during the battery operation, this phenomenon is speculated to be related to the ion concentration distributions in the electrolyte. Such ion concentration distributions in the electrolyte give also serious effect on the performance of lead-acid batteries (LABs). The development of a vertical ion concentration gradient of sulfuric acid is called electrolyte stratification, which causes inhomogeneous current distribution in the vertical distribution of the electrodes by frequent charging-discharging, reducing the life of LABs. However, there are few techniques that can be used to quantitatively characterize ion concentration distribution that arise in electrolytes during the battery operation.
Phase-contrast X-ray imaging is a technique that can be used to visualize density differences by detecting the X-ray phase shift caused by an X-ray passing through a sample. The sensitivity of the phase-contrast X-ray imaging is about 1000 times higher than that of conventional X-ray absorption imaging in a hard X-ray region for light elements. Since the electrolytes of batteries are composed of light elements, the phase-contrast X-ray imaging is expected to be effective in visualizing small density differences in an electrolyte during battery operation. We have demonstrated that phase-contrast X-ray imaging technique can quantitatively visualize ion concentration distributions that arise in electrolytes during battery operation (cf. LIBs [1], LABs [2]).
Recently, hydrogen energy systems that use hydrogen as an energy carrier, such as fuel cells (hydrogen-to-power) and water electrolysis cells (power-to-hydrogen), is a growing interest to realize carbon emission-free energy technologies. Among the various types of hydrogen energy devices, the proton exchange membrane fuel cell (PEFC) and water electrolysis (PEM-WE), which use solid polymer membrane as electrolyte, have been used in practical applications. For further improvement of PEFC and PEM-WE performance, there are several obstacles to be solved include sluggish reaction kinetics, complex water management, limited lifetime due to membrane degradation. However, characterization of mass transport phenomena (e.g., ion transport, thermal transport, etc.) in polymer electrolyte membrane under device operating conditions remains insufficient because of the lack of suitable observation techniques. We have demonstrated that phase-contrast X-ray imaging can visualize the behavior of the water distribution of polymer electrolyte membranes during water electrolysis operations [3].
In this presentation, we will introduce operando phase-contrast X-ray imaging technique can quantitatively evaluate mass transport phenomena in the electrolyte simultaneously during electrochemical device operation with high temporal (a few seconds) and spatial (a few microns) resolutions.

References: [1] Takamatsu, et al. J. Am. Chem. Soc., 140, 1608 (2018). [2] Takamatsu, et al. Chem. Commun., 56, 9553 (2020). [3] Takamatsu, et al., submitted.

A significant challenge in sodium-ion batteries relative to lithium-ion batteries is the larger size of the sodium cation especially for host structures. An ideal electrode should be able to reversibly insert/extract large quantities of sodium ions with minimal structural distortions or with distortions that can be managed. The positive electrode active material is a significant source of the sodium ions during battery function and can be one of the most expensive and toxic components. Layered transition metal (TM) oxides of the general formula, Na_xTMO₂ have shown excellent electrochemical properties but are plagued in part by the structural changes during battery function. Our work has utilized in situ and operando synchrotron X-ray diffraction to probe the relationship between structure and electrochemistry during battery function in this class of materials with a variety of compositions.

Here, the focus will be on Mn-rich compositions which represent one of the cheapest and least toxic candidates for positive electrodes. The parameter space covered in this talk will include the structural and phase evolution of - Mn-rich P2 Na_2/3Fe_1-yMn_yO₂ highlighting the differences based on composition, P2- Na_2/3Mn_0.8M_0.1M’_0.1O₂ (M = Zn, Fe and M’ = Cu, Al, Ti) showing how the choice of transition metals influences structural evolution, and P2/O3-Na_2/3Li_0.18Mn_0.8Fe_0.2O₂ illustrating the role of a multi-component electrode.

Operando analysis under both in-situ and non-equilibrium conditions offers information on how battery materials actually function during battery operation. The behavior of interest includes not only continuous status changes during discharging and charging but relaxation phenomena and even degradation.
The time resolutions of analytical methods limit their application to operando analysis; 6 min is required to observe each 10% change of battery materials during 1C rate operation. Electrochemical analysis generally shows high time resolutions but offers only limited physico-chemical information of the material. To support the phenomena observed by electrochemical analysis, a variety of operando methods have been proposed and applied such as X-ray diffraction, X-ray absorption and neutron magnetic resonances.
Operando analysis of practical cells has been difficult due to the limited penetration depths of the analytical probes. Neutron analysis can be applied to look through the practical cells while it generally lacks sufficient time resolutions. SPICA, a diffractometer installed at Material and Life Science Experimental Facility of Japan Proton Accelerator Research Complex [1], uses strong neutron beam to enable operando analysis of 18650 cells during battery operation up to 1C [2,3] to allow simultaneous observation of positive and negative electrodes.
In this study, we apply the operando neutron analysis to clarify the degradation behavior of commercially available 18650 lithium-ion cells under float-charging, cycling and the mixture of them. We first anticipated that occasional cycling releases the cell from continuous float-charging to decrease side reactions and thus prolong the life. Against our expectations, it turned out that there is a negative synergy effect on the cell life when the float-charging and cycling were mixed. The dV/dQ curve [4] of the degraded cell was totally different from the original one, showing the limitation of the dV/dQ analysis to clarify the origin of the degradation. Neutron diffraction analysis indicated that the serious degradation chiefly originated from the positive electrode side, with its resistance increase. This is in contrast to the soft degradation caused by either float-charging or cycling, which can be attributed to loss of lithium inventory due to side reactions at the negative electrode [5] (clarified by the dV/dQ curve analysis and the neutron diffraction).
It is noted that the degraded positive electrode showed reaction inhomogeneity during discharging, which has rarely been reported by neutron diffraction. Such reaction inhomogeneity can be ascribed to the ion transportation limitation, as shown by X-ray diffraction [6] and optical measurement [7]. We assume that the surface film formation caused by the float-charging was accelerated by the particle cracking due to cycling, and considerable ion transportation limitation finally resulted in the high resistance of the positive electrode. These results prove that operando neutron analysis is a powerful tool for clarifying the degradation mode of practical cells.

Acknowledgment
The authors acknowledge the collaborative work by NTT facilities, Inc. and by High Energy Accelerator Research Organization.

References
[1] M. Yonemura et al., J. Phys.: Conf. Ser., 502, 012053 (2014).
[2] S. Taminato et al., Sci. Rep., 6, 28843 (2016).
[3] S. Shiotani et al., J. Power Sources, 325, 404 (2016).
[4] I. Bloom et al., J. Power Sources, 139, 295-303 (2005).
[5] J. Vetter et al., J. Power Sources, 147, 269–281 (2005).
[6] H. Murayama et al., J. Phys. Chem. C, 118, 20750 (2014).
[7] H. Arai et al., J. Phys. Chem. C, 125, 3776 (2021).

The past decade has seen the rapid development and proliferation of three-dimensional X-ray imaging tools applied to Li-ion batteries, providing a framework to improve the understanding of electrode morphology and its influence on transport processes, electrochemistry and mechanical behaviour. The non-destructive, and multi-scale characteristics of X-ray imaging tools provide benefits to quantify hierarchical complexity from the particle to the electrode and device level. Through the application of image-based modelling tools, it has become possible to simulate a range of phenomena using a computational framework derived directly from tomographic images. Here, we will review this progress and reflect on recent developments using multi-modal methods to understand the performance of Li-batteries: this includes XRD-CT to reconcile chemical, crystallographic and morphological behaviour, Bragg Coherent Diffraction Imaging to access sub-particle behaviour and complementary neutron and X-ray imaging techniques, leveraging the benefits of the alternative contrast modes possible.
In concert, the portfolio of imaging and modelling tools provides a platform to explore the performance, degradation and failure of Li-ion batteries and post Li-ion chemistries, including LiS and solid state batteries, which will also be presented here.

Electrochemical CO₂ reduction reaction (CO₂RR) aims at reusing waste CO₂ and turning it into fuels and chemical feedstock. Ongoing development of catalysts focuses at reducing overpotentials and improving selectivity and stability. Cu is the most promising catalyst for multi-carbon products. Here, we describe a mechanism responsible for evolution of a Cu-based catalyst during CO₂RR by relying on in-situ techniques. Liquid cell electrochemical transmission electron microscopy is complemented by x-ray absorption near edge structure.

Metallic Cu nanospheres were shown to evolve into larger particles selective for C2 products during CO₂RR.¹ We describe a series of subsequent stages responsible for the catalyst reconstruction. Initially, the catalyst oxidizes to Cu₂O upon exposure to the cell environment at open circuit voltage, while releasing Cu ions into the electrolyte. During the cell startup, the dissolved Cu ions redeposit, while the bulk of the catalyst is reduced back to metallic Cu. Surprisingly, the catalyst dissolution and redeposition continues under cell operation at reductive potential, despite the absence of oxidized phases. We exclude a previously proposed process of particle migration and coalescence by resolving individual particles in an operating CO₂RR cell. The observed process is instead similar to Ostwald ripening and proceeds through a soluble intermediate.²

The observed dissolution/reprecipitation process does rationalize the reported evidence of catalyst activation¹ as well as the loss of initial selectivity in precision synthesized nanocrystals.³ By understanding the processes responsible for CO₂RR catalyst reconstruction, we direct the efforts in synthesis of long-term stable catalysts and motivate future research aimed at controlling the redeposition to continuously refresh the catalysts active sites.

1. Kim, D. et al., Proc. Natl. Acad. Sci. 114, 10560–10565 (2017).
2. Vavra, J. et al., Angew. Chem. Int. Ed. 60, 1347–1354 (2021).
3. Huang, J. et al., Nat. Commun. 9, 3117 (2018).

The use of operando methods for the study of electrochemical processes occurring in energy storage systems has become increasingly popular in recent years. Operando experiments represent a powerful tool for the monitoring of internal processes upon battery cycling that provide valuable insights regarding the fundamental electrochemical redox mechanisms and ageing phenomena in battery materials. Nevertheless, obtaining high-quality, representative and exploitable data from operando measurements requires careful control of many experimental parameters (i.e. cell configuration, electrode preparation, optical/goniometer geometry, data acquisition protocols and data interpretation methodology).
In this talk we aim to share our experience and draw the attention into several aspects that we consider important for effective data acquisition and exploitation using both lab-scale and synchrotron powder X-ray diffraction (PXRD) and Small Angle X-ray Scattering (SAXS) instruments. The impact of several key factors, related to the cell design, the experimental setup as well as the sample and experiment preparation, will be discussed.¹ Next, several case studies will be shown to illustrate the effectiveness of operando experiments to understand the electrochemical signature of several Na-ion battery materials,^2-3 including asymetric reaction mechanisms and order-disorder transitions.

1. Damien Saurel, Afshin Pendashteh, María Jáuregui, Marine Reynaud, Marcus Fehse, Montserrat Galceran, Montse Casas-Cabanas, Experimental Considerations for Operando Metal-Ion Battery Monitoring using X-ray Techniques, Chemistry methods, 1(6), 249-260, 2021.
2. Damien Saurel, Montserrat Galceran, Marine Reynaud, Henri Anne, Montse Casas-Cabanas, Rate dependence of the reaction mechanism in olivine NaFePO₄ Na-ion cathode material, Int. J. Energy Res., 42(10), 3258-3265, 2018.
3. Benoit Mortemard de Boisse, Marine Reynaud, Jiangtao Ma, Jun Kikkawa, Shin-ichi Nishimura, Montse Casas-Cabanas, Claude Delmas, Masashi Okubo, Atsuo Yamada, Coulombic self-ordering upon charging a large-capacity layered cathode material for rechargeable batteries, Nat Commun 10, 2185, 2019.

Over the past decade, we have witnessed a rapid growth in liquid and gas phase, heating and electrochemistry holders for transmission electron microscopy. These holders have enabled direct imaging of material transformations in liquid and gaseous environments with submicron-scale to atomic-scale spatial resolution under operando conditions. In particular, research regarding electrode materials in lithium ion batteries and nanocatalysts in heterogeneous catalysis has greatly benefited from the emergence of these capabilities. In this talk, I will showcase the capability of direct nanoscale visualization of electrochemical nucleation, growth and degradation of electrode materials and electrocatalysts utilizing operando and in-situ TEM techniques and discuss the insights extracted from these experiments for improving the electrochemical devices.

Organic molecules used for aqueous redox flow batteries hold great promise in significantly lowering levelized costs of electricity storage and potentially outperforming their inorganic counterparts, representing one class of promising candidates for grid-scale electricity storage.^[1] Short lifetime of aqueous organic redox flow batteries, caused by the instability of organic molecules, has been considered the biggest obstacle for successful commercialization. In situ NMR metrology offers a unique, non-invasive opportunity to observe dissolved redox-active organic molecules undergoing electrochemical reactions in an operating flow battery.^[2]
2,6-Dihydroxyanthraquinone (DHAQ^2-) shows a fast instantaneous temporal fade rate (~5%/day) due to the instability of the reduced form (DHAQ^4-), which disproportionates to 2,6-dihydroxyanthrone (DHA) along with its tautomer, 2,6-dihydroxyanthranol (DHAL), and DHAQ^2-.^[3] In the present work, we employ in situ NMR to observe reversible and irreversible reactions among these DHAQ-related species as we vary the cell voltage.
DHAQ (100 mM) was first charged at 30 mA/cm² and held at 1.7 V vs. Fe(CN)₆^3-/4- (100 mM) in a full cell, then it was discharged at 30 mA/cm² while the voltage decreased from 0.9 V to a cut-off voltage of 0.5 V, followed by a voltage hold at 0.5 V for 7.4 hours. During the voltage hold at 1.7 V, ¹H NMR signals of DHAQ^4- are visible; signals from DHA(L) were also observed. During discharge, the fast electron transfer between DHAQ³⁻ radical and DHAQ⁴⁻ anions causes the corresponding aromatic peak broadening, allowing the DHA²⁻ and DHAL²⁻ signals to be revealed as they remain unaffected. During the voltage hold at 0.5 V, aromatic peaks of DHAQ²⁻ and the new signals at 6.36, 6.41, 7.40 and 7.41 ppm grow in, accompanied by the decrease of signal intensities of DHA(L). The chemical shifts of these new signals were assigned to (DHA)₂. These results indicate that, at 0.5 V, DHA(L) can be electrochemically oxidized to (DHA)₂.
To determine whether (DHA)₂ can be further oxidized, the cell voltage was decreased from 0.1 V to −0.3 V, stepping in decrements of 0.1 V, holding for 2 hours at each voltage step. The intensity of the (DHA)₂ signals remains unchanged at 0.1 V and starts to decrease at 0 V, and the signals disappear completely at −0.2 V, accompanied by the increase of signal intensities of DHAQ²⁻. This observation indicates that (DHA)₂ has been electrochemically oxidized to DHAQ²⁻.
The concentration of DHAQ²⁻ as a function of battery voltage has been quantified. It remains at 72 mM at 0.1 V, starts to increase to 80 mM, 95 mM and 100 mM at 0 V, −0.1 V and −0.2 V, respectively. A comparison of the initial concentration of DHAQ²⁻ (i.e., 100.4 mM 0.25 mM) with the concentration after electrochemical regeneration (i.e., 99.9 mM 0.44 mM) indicates complete regeneration within the experimental resolution. This result demonstrates the circularity of the electrochemical reactions from DHAQ to DHA(L), to (DHA)₂ and back to DHAQ at different potentials.
The electrochemical regeneration technique rejuvenates not only DHAQ, but also the positive electrolyte – rebalancing the states of charge of both electrolytes without introducing extra ions. The strategy should extend to other water-soluble anthraquinones susceptible to anthrone formation; it may also be applicable for other redox-active organic molecules. The strategy could permit redox-active organic molecules to reach the combination of performance, cost, and lifetime necessary for AORFBs to become an attractive solution to the intermittent renewable electricity storage problem.
Reference:
[1] D. G. Kwabi, et al., Chem. Rev., 2020, 120, 6467–6489.
[2] E. W. Zhao, et al., Nature, 2020, 579, 224–228.
[3] M.-A. Goulet, et al., J. Am. Chem. Soc., 2019, 141, 8014–8019.

One of the weak point of batteries is their low cycling rate. It takes tens of minutes to charge a mobile phone (in the best cases) and even hours to charge an Electrical Vehicle and they fail delivering instant high power. High rate materials, i.e. materials able to be charge and discharge in the scale of the minutes or seconds, are of most interest. Some cathode materials such as Na₃V₂(PO₄)₂F₃ (NVPF) can be cycled at high rate (10C) with a limited loss of capacity [1]. A key point to develop such materials is the understanding of the cycling mechanisms involved. Fast operando measurements are thus crucial. Such measurements on electrode materials can easily be performed thanks to the high photons brilliance provided by third generation synchrotron light sources and the fast detection modes. In this field, the LRCS already demonstrated its ability to innovate by developing cells allowing concomitant measurement of the electrochemical and structural properties of electrode materials. Since the first operando-cell developed 15 years ago (for Lab X-ray diffraction), continuous improvements have been made. More recently, the cell was updated for transmission measurements in transmission mode [2] successfully used at both SOLEIL (France) and ALBA (SPAIN) synchrotrons. Additionally, this cell can be utilized for both absorption (EXAF/XANES) and diffraction measurements. In parallel, a cell suitable for neutron diffraction has also been developed (collaboration between LRCS, the ICMCB in Bordeaux, France and the Laue Langevin Institute (ILL) in Grenoble) [3]. These various innovations shed lights on the reaction mechanism as well as Li/Na diffusion paths into the electrode material as demonstrated by some of our experiences in ALBA [4].
However, it is not easy to access large-scale facilities and beam time is rare. Being able to perform x-ray diffraction measurements in the time scale of a minute “at home” would indeed be a strong asset.
Thanks to a new diffractometer equipped with a Molybdenum rotating anode source, a highly efficient detector and a specific operando cell, those measurements are now doable in laboratories.
As it will be shown in this talk, fast measurements (less than a minute per diagram) can be performed allowing following the different phase changes during the charge or discharge of high rate electrode materials and identifying the formation of new metastable phases. Moreover, thanks to the high energy of the molybdenum radiation, we can do X-Ray diffraction in transmission mode through full All Solid State Batteries and study at the same time the anode and cathode.



1. Wang, M. et al. Synthesis and electrochemical performances of Na3V2(PO4)2F3/C composites as cathode materials for sodium ion batteries. RSC Adv. 9, 30628–30636 (2019).
2. Leriche, J. B. et al. An electrochemical cell for operando study of lithium batteries using synchrotron radiation. J. Electrochem. Soc. 157, A606–A610 (2010).
3. Bianchini, M. Spinel materials for Li-ion batteries: new insights obtained by operando neutron and synchrotron X-ray diffraction.
4. Bianchini, M. et al. Comprehensive Investigation of the Na3V2(PO4)2F3–NaV2(PO4)2F3 System by Operando High Resolution Synchrotron X-ray Diffraction. Chem. Mater. 27, 3009–3020 (2015).

Over the last decades, with increasing energy demand along with the shift towards greener energy solutions, Li-ion batteries have gained attraction for energy storage applications.^[1] Due to the high complexity in the hierarchical architecture of composite electrodes, it is extremely challenging to ensure a homogenous electrode structure. The non-uniform distribution of phases, leading to microstructural heterogeneities, has been shown to induce a non-uniform electrochemical behavior, which can deteriorate the performance, and cause macroscopic failures.^[2,3] Therefore, the identification of these microstructural heterogeneities and understanding their effects on the dynamics of (de)lithiation is crucial to improve electrode design.

Lithium compositional distributions in composite electrodes can also be investigated using various techniques such as Raman microscopy,^[4] X-ray diffraction,^[5] or 2D X-ray absorption near-edge structure spectroscopy (XANES).^[6] However, these methods have been restricted to low spatial resolution or spatially integrated signal along the depth direction and cannot accurately capture the spatial distributions and can lead to a limited interpretation of the mechanism.

Several works have combined XANES and X-ray tomography ^[7] to generate a rich data set that allows a direct correlation of the chemical information and the microstructure. Meirer et al.^[8] used 3D XANES to probe the conversion of NiO to Ni metal in a partly reduced electrode. They found significant inhomogeneities in terms of chemical states across particles as well as evidence of fracturing caused by volume expansion during the reaction. More recently, Wang et al. ^[9] collected a 46-point spectrum across the iron K-edge of a LiFePO₄ cathode particle and developed a run-out correction system to enable automated tomography.

Here, we perform XANES coupled with transmission X-ray computed tomography at nanoscale in operando mode to investigate LiNi_0.5Mn_0.3Co_0.2O₂ (NMC) positive electrodes. In this work, we demonstrate that operando XANES-TXM nanoCT allows access to the Li distribution at nanoscale within the LiB electrodes during the operation. We also proposed a method that relies on just three energy levels located at pre-edge, edge, post-edge for minimization of radiation damage to the sample. Also, a specific electrochemical cell and a sample preparation process were introduced, which make the use of electrodes typical to those used in real-life applications possible.

Our experimental results unveil the non-uniformity of the Li repartition throughout the LiB porous electrodes during operation. As a result, there are regions being more active than the others as well as preference spots on the particle surface where the reactions are more likely to occur. The Li repartition across the electrode depth is adequately uniform, which indicates a negligible effect from porous electrode. In addition, some of the reconstructed slices also revealed that the lithiation process could also happen from internal pores of the AM particles. This observation also implies that the electrolyte along with the carbon conductive can penetrate some internal pores through the AM grain boundaries and allow the (de)lithiation process to occur from the inside of the NMC secondary particles. This multiscale insight can shed light to the optimization of the electrode design to improve the electrode performance.

[1] J. B. Goodenough, Energy Environ. Sci. 2014, 7, 14.
[2] Y. Yang, et al. Adv. Energy Mater. 2019, 9, 1900674.
[3] X. Lu, et al. Nat. Commun. 2020, 11, 1.
[4] J. Nanda, et al. Adv. Funct. Mater. 2011, 21, 3282.
[5] J. Liu, et al.J. Phys. Chem. Lett. 2010, 1, 2120.
[6] K. Chen, et al. J. Phys. Chem. C 2019, 123, 3292.
[7] D. P. Finegan, et al. Nat. Commun. 2020, DOI 10.1038/s41467-020-14467-x.
[8] Meirer, F et al. Journal of Synchrotron Radiation 2011, 18 (5), 773–781.
[9] Wang, J et al. J. Nature Communications 2016, 7, 1–7.

In situ transmission electron microscopy (TEM) experiments on electrochemical systems require highly sensitive detectors in order to minimize the electron beam dose incident on the specimen, and thereby minimize the potential effects of electron beam damage. Highly sensitive detectors are also advantageous for in situ and operando experiments that aim to observe phenomena on millisecond timescales, where electron beam dose per frame is necessarily limited¹.

Monolithic active pixel sensor (MAPS) based direct detectors such as the DE-12 and DE-16 offer higher detective quantum efficiency (DQE) and sensitivity compared to conventional, scintillator-coupled detectors, and have been employed in a variety of in situ TEM experiments^2-4, including studies of lithiation and delithiation⁵, sodium electrodeposition⁶, and CO₂ reduction⁷. More recently, Direct Electron has developed two new MAPS detectors, Apollo and Celeritas, that offer significant advances in the capability of direct detectors with potential applications to in situ experiments.

The event-based Apollo detector provides a fast-imaging speed whilst operating in an electron counting mode. Although MAPS based detectors achieve greater DQE than conventional TEM detectors when operating in charge integrating mode, DQE is further enhanced when performing electron counting. For frame-based MAPS based detectors, electron counting requires a very sparse signal per frame (~1 electron per 50 pixels), meaning that many frames must be summed to obtain interpretable images, effectively reducing imaging speed by one or two orders of magnitude. At the same time, enormous computational power is required to identify and count sparse events in individual frames. Instead of generating frames of data, event-based detectors only generate data from pixels in which an event occurs, causing intensity to exceed a threshold level. The generation of data from select pixels, rather than entire frames means fewer computational resources are needed to generate interpretable data, yielding a potential increase in speed. In the Apollo detector, events occur when pixels are excited by an electron hitting the sensor. These events are compiled into interpretable counting mode images, which are output at a rate of 60 images per second in 8192 x 8192 super-resolution mode.

The Celeritas detector offers very fast frame rates compared to previous TEM detectors. The physical sensor is 1024 x 1024 pixels with a 15 µm pixel size. At full frame size the frame rate exceeds 1950 fps, allowing phenomena to be observed with a time step of just 512 µs between images. With a reduced sub-area of 256 x 64 pixels, a frame rate of up to 87,000 fps can be achieved. This allows the Celeritas detector to be used to collect in situ 4D STEM datasets, where a time step of less than 0.2 seconds between entire 128 x 128 probe position datasets is possible. This is a comparable speed to conventional 2D STEM imaging and is one to two orders of magnitude faster than is currently possible with typical 4D STEM detectors.

The speed and sensitivity of the Celeritas and Apollo detectors may be advantageous for in situ electrochemical TEM experiments, such as studies of dendrite growth and formation, or of atomic structural fluctuations in electrocatalysts, where high-speed imaging will be valuable for understanding fundamental mechanisms.

References:
B.D.A. Levin J. Phys. Mater. 4 042005 (2021).
Chee et. al. Nano Letters, 19, 5, 2871-2878 (2019)
Liu et al. PNAS, 118 (10) e2008880118 (2021)
Gavhane et al. npj 2D Materials and Applications, 5, 24 (2021)
Zeng et al. Nano Letters, 15, 5214-5220 (2015)
Zeng et al. Nano Energy, 72, 104721 (2020)
Vavra et al. Angewandte Chemie, 60, 1347-1354 (2021)

Acknowledgements: This material is based upon work supported by the US Department of Energy, Office of Science under award numbers DE-SC0020577 & DE-SC0018493

A promising pathway to surpass the energy storage capabilities of Li-ion is to incorporate a Lithium (Li) metal anode into a rechargeable battery. However, challenges, such as poor cycle life and safety concerns, severely hinder the performance of Li metal anodes. Dendritic growth has been shown to contribute to poor cycle life, but the impact pit formation has performance is not fully understood. In our previous work, we implemented operando video microscopy to study the nucleation of Li metal and demonstrated the impact pits have on Li metal cycling¹. The edges of pits were observed to be “hot” spots for dendrite nucleation¹. Furthermore, the size of the pits was observed to influence the reversibility of dendrites when nucleation occurred in a pit¹. However, a mechanistic understanding of how pit formation influences dendrite nucleation and reversibility is lacking. To better understand how pits evolve and how this evolution impacts dendrites, we have enabled focus variation microscopy in our operando visualization platform². This technique captures the areal surface topography of sample with sufficient temporal resolution for operando measurements.

Using this capability, we: (1) explore the morphological evolution of individual pits; (2) demonstrate the anisotropic expansion of pits; (3) correlate electrode surface microstructure and crystallographic orientation with stripping anisotropy; and (4) demonstrate pit faceting. The results of this study highlight the anisotropic nature of Li metal stripping and identify the critical role of electrode crystallographic orientation and microstructure on stripping. Furthermore, this study illuminates how the observed anisotropic stripping can promote dead Li formation and suggests potential pathways to improve reversibility.

A. J. Sanchez et al., ACS Energy Lett., 5, 994–1004 (2020).
A. J. Sanchez, E. Kazyak, Y. Chen, J. Lasso, and N. P. Dasgupta, J. Mater. Chem. A (2021).

Understanding high temperature corrosion of molten salt containment materials is of great importance to improve energy-efficiency and reduce cost of thermal energy storage systems used with concentrating solar power plants. We have developed and implemented an in situ high-temperature transmission electron microscopy (TEM) diffraction and imaging approach to monitor corrosion of Inconel-625 alloy by molten eutectic MgCl₂–NaCl–KCl with 3 ± 1 nm spatial resolution and sub-second temporal resolution in real time. The experimental setup uses a micro-environmental cell (MEC) assembly inside a TEM with a gas flow channel and substrate heating (25-1000 °C), manufactured by Hummingbird Scientific. We also developed procedures involving a mobile vacuum transfer vessel and encapsulation in inert gas in a glove box to avoid incorporation of significant H₂O and O₂ in a Mg-chloride based salt-stack to be used for controlled corrosion studies. Quantitative in situ diffraction pattern analysis is implemented using a numerical clustering algorithm and 2D Gaussian fit functions to determine diffraction spot intensities as a function of space and time. This facilitates determination of overall corrosion rates as well as quantitative observation of the evolution of individual grains, providing microscopic insight into the nucleation and growth of the corrosion process. Multi-layered salt films (25 nm MgCl₂, 13 nm NaCl, and 12 nm KCl) on50 nm-thick Inconel-625 layers on TEM heater-chips are assembled into a MEC for corrosion experiments at various temperatures and ambients inside a TEM. The isothermal corrosion rate for an anhydrous, unoxidized salt-stack is 25 ± 3 nm hr^-1 (220 ± 30 μm year^-1) at 700 °C. It increases to 40 ± 2 nm hr^-1 (350 ± 20 μm year^-1) at 800 °C. The corrosion rate at 700 °C increases five-fold to 114 ± 19 nm hr^-1 (1000 ± 170 μm year^-1) when the salt stack is air-exposed. These isothermal corrosion rates indicate that the molten chloride corrosion is significantly accelerated by salt hydration from air exposure. Real-time imaging of the microstructure suggests that corrosion is initiated at grain-boundaries.

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The modeling of lithium ion batteries (LIB) requires to fulfill two main aspects to: i) finding a system of relevant equations and ii) defining adequate unambiguous parameters. Actually, the parameterization of an electrochemical LIB model could be time consuming and the choice of the inputs is thus crucial. However, among all the parameters needed for an accurate model, the kinetic rate constants is often forgotten in the literature, when it comes to identify its value and dependency, whereas it takes a major part in electrochemical processes. Moreover, this parameter is believed to have a huge sensitivity over the entire model. Thus, our study is exploring, suggesting and comparing different approaches to estimate this reaction rate constant value and its dependency over other state variables, in order to identify an efficient method to determine this important parameter while accelerating parameterization phase and getting a more trustful result of the overall model.

The improvement of the electrocatalyst performance for the oxygen evolution reaction (OER, 4OH⁻ → O₂ + 2H₂O + 4e⁻) requires fundamental understanding of the active sites during operation [1]. Here, we use electrochemical liquid-phase transmission electron microscopy (TEM) in combination with electron energy-loss spectroscopy (EELS) to probe solid-liquid interfacial interactions of the OER catalysts in real-time. The wetting behavior of Co-oxide particles is revealed and the catalytic products during the oxygen evolution reaction are detected at a single particle level. Three different crystal structures were evaluated: the rocksalt CoO, the spinel Co₃O₄, and the highly OER-active perovskite Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3-δ (BSCF) [2]. By analyzing the contrast of sequences of TEM images, the oxide surfaces are found to switch from hydrophobic to hydrophilic character under anodic potential due to electrowetting induced by OH^- accumulation at the interface [3]. The process is fully reversible and the extent of its stability is linked to the underlying Co^2+/3+ redox reaction as well as the oxyhydroxide phase transformation on the spinel surfaces [4]. At high anodic applied potential, the evolution of molecular oxygen, probed site-specifically from areas surrounding the single particles, enhances the apparent hydrophilicity of the surfaces. These observations, performed in real-time and at a single particle level, provide unique nanoscale insights into the solid-liquid interactions of catalysts in their native environment.

[1] 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, and W. C. Chueh, Nature 593, 67 (2021).
[2] J. Suntivich, K. J. May, H. A. Gasteiger, J. B. Goodenough, Y. Shao-horn, F. Calle-vallejo, A. D. Oscar, M. J. Kolb, M. T. M. Koper, J. Suntivich, K. J. May, H. A. Gasteiger, J. B. Goodenough, and Y. Shao-horn, Science (80-. ). 334, 2010 (2011).
[3] T. H. Shen, L. Spillane, J. Peng, Y. Shao-Horn, and V. Tileli, submitted (2021).
[4] T. H. Shen, L. Spillane, J. Vavra, T. H. M. Pham, J. Peng, Y. Shao-Horn, and V. Tileli, J. Am. Chem. Soc. 142, 15876 (2020).

The three-dimensional structure and morphology of the electrode has a strong influence on the performance characteristics of a battery. Optimizing 3D structure and morphology is one of the key issues in the development of battery materials. Good electrical conductivity and sufficient Li-ion transport must be ensured at every point of the entire electrode at all times. Furthermore, changes of the 3D structure during cycling are often a main reason for capacity fading. The 3D structure has to be stable over hundreds of cycles. Therefore, a well designed 3D structure is essential for improving storage capacities and longevity. Radiographic and tomographic measurement techniques based on (synchrotron) X-rays and neutrons are ideally suited to obtain detailed information on the electrode structures. If properly used these techniques are non-destructive and allow for operando studies of structural changes during cycling in the cell.
This presentation will give an overview of recent developments in the field of operando imaging on batteries at Helmholtz-Zentrum Berlin (HZB) with a special focus on lithium mapping. To study the distribution of lithium and/or the lithiation process in a battery electrode different imaging techniques are of particular importance: 1. Synchrotron X-ray phase contrast imaging is well suited for analysis of lithium degradation when no strong X-ray absorbers are nearby. The high spatial resolutions allow studying small effects at interfaces of Li anodes or inside of a separator material. Some examples for Li anode degradation and Li dendrite formation will be shown. 2. X-ray absorption edge spectroscopic imaging at a synchrotron provides spatially resolved chemical information on the lithiation process even inside strong X-ray absorbers like NMC particles. The high spatial resolution also allows the analysis of individual battery particles. 3. Neutron imaging has a high sensitivity to lithium and allows studying in particular solid state electrolyte batteries during cycling. Some results will be presented and the use of Li isotopes for contrast enhancement will be discussed.
Finally, the talk will give some insights into the use of machine learning tools and the training of neural networks for optimized data segmentation and data analysis.

Electrochemical carbon dioxide reduction (CO₂R) to renewable chemical feedstocks and fuels at high current density creates a high local concentration of hydroxide near the cathode. Due to diffusion limitations of hydroxide and homogeneous carbonate/bicarbonate reactions being out of equilibrium, this creates a pH gradient in the electrolyte between the cathode and the electrolyte bulk. Knowing this gradient is important for accurate analysis of CO₂R mechanisms, but it has yet to be measured in industrially relevant conditions. Using atomic force microscope-scanning electrochemical microscopy, we have measured this pH gradient above a gas diffusion electrode (GDE) and compared it with different transport models to determine the models’ accuracy.

Ageing mechanisms have a great impact into batteries calendar life and performance. A better understanding of these complex processes is critical to improve the lifetime of the battery. Electrolyte ageing plays a key role in the decrease of capacity since insoluble species and gas by-products are formed during the electrochemical cycling of the battery. Fluorescent species are formed during cycling of lithium ion batteries as a result of electrolyte decomposition due to the instability of the non-aqueous electrolytes and side reactions that occur at the electrode surface. The increase in the background fluorescence due to the presence of these components makes it harder to analyse data due to the spectroscopic overlap of Raman scattering and fluorescence. Herein we will demonstrate both ex situ and operando Kerr gated Raman spectroscopy as an effective technique for the isolation of the scattering effect from the fluorescence. This enabled the collection of the Raman spectra of LiPF₆ salt and LiPF₆-based organic carbonate electrolyte, without the interference of the fluorescence component and the measurement of Raman bands of graphite carbon at high states of lithiation.

Operando Raman spectroscopy is a powerful analytical technique for observing real-time chemical changes in energy storage materials under electrochemical cycling conditions. However, the requirement for optical access to the sample surface of interest places constraints on cell geometry, leading to an unavoidable trade-off between electrochemical performance and spectral data quality. This issue is particularly prominent in the case of commercially-sourced electrode samples that have been densely processed onto metal foil current collectors, for which spectro-electrochemical cycling at industrially relevant current densities is highly challenging.

In this work we present an improved configuration for performing operando Raman spectroscopy on commercially-sourced alkali-ion battery electrodes, in which a spacer is used to alleviate electrolyte ion accessibility limitations and improve electrochemical cell performance compared to a previously established spectro-electrochemical cell configuration. Electrochemical simulation predicts an improvement in lithiation homogeneity and electrochemical cycling performance at higher specific currents, and this is corroborated experimentally for a foil-backed graphite Li-ion negative electrode. The wider applicability of this configuration is also demonstrated by way of a case study of hard carbon Na-ion negative electrodes measured over 50 cycles. We show that this approach enables reliable operando Raman spectroscopy on commercial battery electrodes under conditions of more practical relevance to industry than previous cell configurations.

The “EC-PC mystery” has puzzled electrochemists for decades. The historically persistent use of propylene carbonate (PC) rather than ethylene carbonate (EC) as electrolyte solvent in lithium based batteries significantly delayed their realization. The additional methyl group in PC is surprisingly the root cause of the failure of PC to form a stable solid electrolyte interphase (SEI) on the negative Li-ion electrode, but the underlying reason remains debated.¹ Several explanations have been hypothesized, mostly based on ex situ measurements of electrolytes and electrodes.^1,2 However, in order to obtain a detailed mechanistic understanding of the highly elusive interphase formation, in situ and operando techniques are needed.

In the presented study, electrode interphases formed as a result of EC and PC reduction are analyzed by two state-of-the-art operando techniques, Online Electrochemical Mass Spectroscopy (OEMS) and Electrochemical Quartz Crystal Microbalance with Dissipation monitoring (EQCM-D). OEMS and EQCM-D are techniques highly dedicated for analyzing volatile species³ as well as viscoelastic properties of electrode interphases during their formation in operating Li-ion cells.⁴ Both EC and PC based electrolytes show similar evolution profiles of H₂ and CO₂ while the extent of propylene (in the PC-based electrolyte) was significantly larger than the corresponding amount of ethylene (in the EC-based electrolyte). The findings correlate well with the EQCM measurements where a clear dissolution behavior of SEI in the PC-electrolyte was observed, while electrode mass deposition was irreversible when EC was present. Clearly, solubility of the various SEI components (primarily the dicarbonate) leads to dramatic differences in performance of PC as opposed to EC.¹ The presented study serves as a model for how operando techniques may provide deeper insights into well studied subjects, such as the EC-PC mystery.

1. Xu, K. Whether EC and PC Differ in Interphasial Chemistry on Graphitic Anode and How. J. Electrochem. Soc. 156, A751 (2009).
2. Spahr, M. E. et al. Exfoliation of Graphite during Electrochemical Lithium Insertion in Ethylene Carbonate-Containing Electrolytes. J. Electrochem. Soc. 151, A1383 (2004).
3. Lundström, R. & Berg, E. J. Design and validation of an online partial and total pressure measurement system for Li-ion cells. J. Power Sources 485, (2021).
4. Kitz, P. G., Lacey, M. J., Novák, P. & Berg, E. J. Operando EQCM-D with Simultaneous in Situ EIS: New Insights into Interphase Formation in Li Ion Batteries. Anal. Chem. 91, 2296–2303 (2019).

Advances in methodologies for real-time analysis of batteries have come an extraordinarily long way [1], especially with the development of Operando Electrochemical Mass Spectrometry (OEMS) . These approaches allow for the determination of side reactions during battery cycling with unprecedented selectivity and sensitivity, thus providing vital information necessary for determination of lifetime-limiting processes. However, the work thus far has primarily been carried out on model battery systems, where cell configurations and atmospheres are largely tampered with (through continuous flow [2] [3] in the open approach and purging [4] in the semi-closed approach [5]) and the operation conditions are therefore not comparable with real-life situations. Herein, the development and validation of an entirely closed OEMS system adapted for readily available commercial batteries is showcased. We provide a detailed description of two unique analysis designs with subsequent comparisons between them and other existing OEMS setups. Additionally, time-resolution modelling is applied to the data to determine precise gas onset points, ultimately eliminating diffusion related time delays. The prospects of utilizing OEMS for the study of commercially available rechargeable batteries after production or usage is evaluated.

[1] A. M. Tripathi, W. N. Su, and B. J. Hwang, “In situ analytical techniques for battery interface analysis,” Chem. Soc. Rev., vol. 47, no. 3, pp. 736–751, 2018, doi: 10.1039/c7cs00180k.
[2] P. Novák et al., “Advanced in situ characterization methods applied to carbonaceous materials,” J. Power Sources, vol. 146, no. 1–2, pp. 15–20, 2005, doi: 10.1016/j.jpowsour.2005.03.129.
[3] N. Tsiouvaras, S. Meini, I. Buchberger, and H. A. Gasteiger, “ A Novel On-Line Mass Spectrometer Design for the Study of Multiple Charging Cycles of a Li-O 2 Battery ,” J. Electrochem. Soc., vol. 160, no. 3, pp. A471–A477, 2013, doi: 10.1149/2.042303jes.
[4] R. Lundström and E. J. Berg, “Design and validation of an online partial and total pressure measurement system for Li-ion cells,” J. Power Sources, vol. 485, no. December 2020, 2021, doi: 10.1016/j.jpowsour.2020.229347.
[5] L. A. Kaufman and B. D. McCloskey, “Surface Lithium Carbonate Influences Electrolyte Degradation via Reactive Oxygen Attack in Lithium-Excess Cathode Materials,” Chem. Mater., pp. 1–7, 2021, doi: 10.1021/acs.chemmater.1c00935.

The advent of solid-state batteries has spawned a recent increase in interest in lithium conducting solid electrolytes, especially in the lithium thiophosphates. However, many open questions remain when trying to optimize electrolytes and understand solid state battery chemistries. Among the interesting solid-state battery systems, the conversion reaction of sulfur has been recently of interest.

In this presentation, we will show how an understanding of the chemomechanical changes as well as the interfacial decomposition reactions in Li-S solid state batteries help to better understand and design these systems.

Further, we will show that fast ionic conduction is paramount within solid state battery composites. Measuring the effective ionic transport in cathode composites provides an avenue to explore transport and stability limitations that in turn provide better criteria for solid state battery performance

Solid electrolyte interphase (SEI) formed due to the reductive decomposition of electrolytes on the graphite negative electrode is one of the most widely studied phenomenon in Li-ion batteries[1]. Yet, no real consensus of the governing processes has been established due to their inherent complexity and lack of dedicated characterisation techniques[2]. Herein we have employed Operando surface enhanced Raman spectroscopy (SERS) to investigate the SEI formation in a model electrolyte based on Lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) in ethylene carbonate (EC). We observe a stepwise potential-dependent reaction process involving decomposition of both electrolyte impurities and the EC solvent. The SERS enhancement has enabled us to also identify several metastable intermediates. For instance, Li₂CO₃ is observed as an interphasial component formed primarily due to the electrochemical reduction of residual contaminants in the electrolyte. SERS provides a deeper understanding of the underlying processes during SEI formation and the dynamics of the interfacial composition during the battery cycling. Challenges when analysing the SEI and prospects for development of this approach will further be highlighted.

Reference:
[1] M. Winter, “The solid electrolyte interphase - The most important and the least understood solid electrolyte in rechargeable Li batteries,” Zeitschrift fur Phys. Chemie, vol. 223, no. 10–11, pp. 1395–1406, 2009, doi: 10.1524/zpch.2009.6086.
[2] A. J. Cowan and L. J. Hardwick, “Advanced Spectroelectrochemical Techniques to Study Electrode Interfaces Within Lithium-Ion and Lithium-Oxygen Batteries,” Annu. Rev. Anal. Chem., vol. 12, pp. 323–346, 2019, doi: 10.1146/annurev-anchem-061318-115303.

The solid electrolyte interphase (SEI) is key to battery performance. The composition of the SEI is an assortment of decomposition products, mainly from reduced electrolyte species but also from residual contaminants, such as H₂O. The SEI both forms and changes during operation of a Li-ion battery. A full understanding of the SEI is challenging to attain with only post-mortem analysis. Therefore, analytical techniques monitoring the battery during operation, or operando, are needed to deconvolute the SEI formation in Li-ion batteries.
Many side-reactions, including SEI formation, in Li-ion batteries have volatile species forming as some of the decomposition products. Online Electrochemical Mass Spectrometry (OEMS) can sample the gas composition of a battery.¹ By sampling the volatile species from a battery cell during operation, a voltage-dependent gas evolution profile is gained. The result is a holistic overview of side-reactions in Li-ion batteries.
In this presentation, we deepen the study of the SEI formation on carbon electrodes and demonstrate how it is impacted by residual H₂O. Glassy carbon electrodes in carbonate-based electrolyte are studied using OEMS. More H₂O present in the battery cell has been linked to an increase² in CO₂ and decrease in C₂H₄ evolution³. We show that CO₂ and C₂H₄ evolution are connected with a linear relationship in relative amounts depending on H₂O content.
The thermal reaction between H₂O and electrolyte components can result in HF forming over time. A high HF concentration in the electrolyte breaks the linear relationship of CO₂ and C₂H₄ gas evolution, as a new major decomposition reaction affects the SEI formation. Different stages of CO₂ evolution and consumption during the formation cycle will be shown, where multiple processes are present. Unintended reactions taking place in the glassy carbon model system will be shown to have a significant impact on the SEI composition.⁴ The influence of H₂O on the SEI formation in Li-ion battery systems and especially in model systems are highlighted.


(1) Lundström, R.; Berg, E. J. Design and Validation of an Online Partial and Total Pressure Measurement System for Li-Ion Cells. J. Power Sources 2021, 485, 229347.
(2) Bernhard, R.; Metzger, M.; Gasteiger, H. A. Gas Evolution at Graphite Anodes Depending on Electrolyte Water Content and SEI Quality Studied by On-Line Electrochemical Mass Spectrometry. 2015, 162 (10), 1984–1989.
(3) Joho, F. et al. Key Factors for the Cycling Stability of Graphite Intercalation Electrodes for Lithium-Ion Batteries. J. Power Sources 1999, 81–82, 243–247.
(4) Lundström, R.; Berg, E. J. In manuscript.

Metal-sulfur batteries have been proposed in the last years as a promising energy storage technology for the future, due to the high theoretical capacity, remarkable energy density, and low cost. However, the major drawbacks of sulfur positive electrodes, such as the well known polysulfide shuttle effect and the low electrical conductivity of elemental sulfur, add to those specific of each negative electrode, such as the side reactions between metal anodes and electrolytes, are currently preventing their possible commercialization. All these effects are often interconnected, and strongly dependend upon the type and the amount of electrolyte used in the cells. Therefore a thorough understanding of the mechanisms of all these processes, both in the bulk and at the interfaces, during the lifetime of metal-sulfur batteries is necessary for mastering them and producing a viable metal-sulfur system.
Among the different technniques that have been developed for understanding these processes, in situ X-ray spectroscopies are among the most interesting ones. For instance, sulfur K-edge X-ray absorption and X-ray emission spectroscopies have been used to follow the evolution and the dynamics of the sulfur species in a working battery, while ex situ X-ray photoelectron spectroscopy was employed to study the evolution of the interfaces and the aging mechanisms of the metal-sulfur cells.
In this presentation, an overview of the application of X-ray spectroscopy methods to the study of metal-sulfur batteries is presented. It will be shown how these techniques together provide a unified view of metal-sulfur systems, suggesting possible strategies to circumvent their main drawbacks and thus enabling their practical applications.

Properties and function of beyond intercalation-type batteries are not only rooted in the chemistry but at least as much in the structure all the way from atomic to sub-micrometer length scales. This concerns specifically complex transformations such as the electrodeposition of insulating materials in conversion-type lithium-sulfur (Li-S) or lithium-air (Li-O₂) battery electrodes. Substantial performance improvements, therefore, rely on a quantitative physico-chemical understanding at all relevant length scales, which puts high demands on (operando) analytical techniques.
Here we present operando small and wide angle X-ray scattering (SAXS / WAXS) as a suitable method to study the nanoscale phase evolution of solid Li₂O₂ during charging and discharging a custom-built operando Li-O₂ cell. For data analysis, our recently developed method used for supercapacitors was adapted [1] and synergistically combined with modelling of Li₂O₂ nucleation and growth in a realistic 3D carbon pore model generated via stochastic modelling. This allows visualizing the nanoscale product formation in real-time and distinguishing between Li₂O₂ formed via disproportionation (solution mechanism) or direct electroreduction (surface mechanism). Contrary to what current knowledge predicts, we find that Li₂O₂ is formed to the widest extend via solution mediated disproportionation of LiO₂, even under conditions previously considered prototypical for Li₂O₂ surface growth [2]. Results were backed up by hydrodynamic voltammetry, electron microscopy and numerical modelling, and question significant parts of the currently accepted reaction model in Li-O₂ batteries [3].
Next to Li-O₂ batteries, the potential of the method is demonstrated by quantifying the reversible electrodeposition of solid reaction products during charging and discharging a custom-built operando Li-S cell. In situ SAXS / WAXS data analysis was combined with stochastic modelling of the three-phase nanostructure Li₂S / Li₂S₄ / electrolyte using the concept of PluriGaussian random fields [4]. The hierarchical Li₂S₄ – Li₂S composite nanostructures formed during Li-S discharge indicate that Li₂S forms via solid-state disproportionation of higher-order polysulfides rather than direct electroreduction at the carbon-electrolyte interface. Structural information derived from X-ray scattering was complemented by cryo (scanning and transmission) electron microscopy and small angle Neutron scattering. The found mechanism provides novel design criteria for improved capacities and improved cycle life in Li-S batteries.

References:
1 Prehal, C., Koczwara, C. et al. Quantification of ion confinement and desolvation in nanoporous carbon supercapacitors with modelling and in situ X-ray scattering. Nature Energy 2, 16215, (2017).
2 Aurbach, D., McCloskey, B. D., Nazar, L. F. & Bruce, P. G. Advances in understanding mechanisms underpinning lithium–air batteries. Nature Energy 1, 16128, (2016).
3 Prehal, C., Samojlov, A. et al. In situ small angle X-ray scattering reveals solution phase discharge of Li-O2 batteries with weakly solvating electrolytes. PNAS 118, e2021893118, (2021).
4 Prehal, C., Fitzek H. et al. Persistent and reversible solid iodine electrodeposition in nanoporous carbons. Nature Communications 11, 4838, (2020).

Solid-state batteries hold the promise of safer, cheaper, and longer-lasting batteries. Its largest bottleneck lies in their interfaces, including both interfaces with electrodes and internal grain boundaries. For example, many current solid electrolytes either involve concerning interfacial stability with electrodes and/or an unexpected dendrite growth along their grain boundaries. The associated underlying origins however remain unknown. To understand the interfacial mechanisms at play, the electrochemical stability, mechanical stability, and local potential variations, must be studied correlatively and ideally, under simulated operation. In this talk, I will show several examples of elucidating the interface stability, overpotential, and dendrite growth mechanism in model solid electrolytes, including lithium phosphorus oxynitride (LiPON), Li_xLa_2/3-x/3TiO₃ (LLTO) and Al- Li₇La₃Zr₂O₁₂ (LLZO). This presentation will also demonstrate the power of utilizing a suite of scanning transmission electron microscopy techniques, including cryogenic high-resolution imaging, in situ biasing microscopy, differential phase-contrast imaging, and low loss electron energy loss spectroscopy (EELS) to probe features defining the function of interfaces in solid-state batteries.

This research was supported by an Early Career project supported by the DOE Office of Science FWP #ERKCZ55. All microscopy technique development was performed and supported by Oak Ridge National Laboratory’s (ORNL) Center for Nanophase Materials Sciences (CNMS), which is a DOE Office of Science User Facility.

The increasing demand of large-scale energy storage with improved performance, safety and sustainability for renewable variable energy sources drives the search for post-Li-ion batteries based on multivalent cation chemistries (e.g., Mg, Zn and Ca). However, poor electrolyte stability against metal anodes and high voltage cathodes has been so far one of many barriers to the development of multivalent cation rechargeable batteries. (Electro)chemistry at the electrolyte-electrode interface is critical to battery performance. Multivalent cations are prone to complex formation with solvent molecules and anions, leading to different interfacial species with characteristic (electro)chemical properties. Although multivalent cation solvation/complexation structures have been investigated in the bulk, fundamental understanding of speciation at the interface is lacking.

Fluorinated anions are often used in multivalent and other post-Li-ion electrolytes. Fluorine K-edge X-ray Absorption Spectroscopy provides access to a surprising level of detailed electronic structure information about the anion coordination and decomposition process, despite the relatively predictable oxidation state and ionicity of the fluoride ion. In this work, we examine the sensitivity of the F K-edge to the fluorine bonding environment in solid, liquid and interfacial species relevant to energy applications. Utilizing a combination of Molecular Dynamics simulations and a recently developed many-body approach based on the $\Delta$SCF method, we calculate the X-ray absorption spectra of multiple fluoride salts using density functional theory. Thin films and surfaces are also explored to establish whether they provide distinct spectral signatures that might be observable in the solid electrolyte interphase of working electrodes. At last, the solid-liquid interface of non-aqueous, Mg based electrolytes with fluorinated anions are examined.

The nucleation and growth of crystalline nanoparticles is an important fundamental process of synthesis in many applications to better control and engineer the properties of nanoparticles. In-situ studies of electron beam-induced formation of metal nanoparticles from the precursor solution in the liquid-cell transmission electron microscopy (LCTEM) is one of the helpful methods to reveal the nucleation and growth mechanism.^1,2 Especially, employing graphene liquid-cell (GLC) which encapsulates the liquid solution between thin graphene layers allows high-resolution imaging and better visualization of the important steps of nanocrystals nucleation and growth.^3,4 In this work, using the GLC microscopy technique, nucleation and growth of transition metal alloys in an equimolar aqueous mixture of Mn, Fe, Ni, and Zn chloride salt precursor solution under electron beam is studied.
The radio-chemistry formation of metallic particles commonly involves three major steps of (1) production of metal atoms in solution by electron beam-induced reduction of metal ions; (2) nucleation of solid-phase by atom clustering; and (3) growth of nucleated particles by monomer addition and particle coalescing. Solvated electron () produced by the radiolysis of water is a very strong reducing agent to reduce the transition metal ions with negative reduction potential to their zerovalent state. However, other ionic and radical species products of water radiolysis present in the solution can also react with metal atoms and oxidize them back to positive valence ionic states. Polyvinylpyrrolidone (PVP) is added to precursor solution can act as a strict stabilizer and a scavenger of OH radicals and minimize their oxidizing effect.
The transition metal salts dissolved in water were initially found as nanorod shape crystallin precipitates inside the GLC (Figure 1a). The analysis of the fast Fourier transforms (FFT) diffraction pattern matches the monoclinic crystalline structure of used transition metal hydroxide (TM(OH)₂). (Figure 1b). The direct transformation of metal hydroxide nanorods to metal nanoparticles was observed by focusing the electron beam on a smaller screening area. As a result of increasing the magnification, the electron dose increases, and metal ions are reduced to metal atoms. The nucleation of nanoparticles is detected in few seconds at two sides of the long rods and they grow to 2 nm size particles in 10 s. Then 3-4 adjacent small particles start to coalescence and make the bigger particles. The growth of particles is slowed down after reaching 5 nm in less than 60 s. (Figure 2). The in-situ formed nanoparticles have a FFC crystalline structure close to the FCC structure of transition metals used which shows a single-phase multi-metallic alloy is formed in the solution and at room temperature. (Figure 2c-d)

References

(1) Ngo, T.; Yang, H. Toward Ending the Guessing Game: Study of the Formation of Nanostructures Using in Situ Liquid Transmission Electron Microscopy. J. Phys. Chem. Lett. 2015, 6 (24), 5051–5061. https://doi.org/10.1021/acs.jpclett.5b02210.
(2) Woehl, T. J. Metal Nanocrystal Formation during Liquid Phase Transmission Electron Microscopy: Thermodynamics and Kinetics of Precursor Conversion, Nucleation, and Growth †. Chem. Mater. 2020, 32 (18), 7569–7581. https://doi.org/10.1021/acs.chemmater.0c01360.
(3) Fendler, J. H.; Kholkin, A.; Kingon, A.; Tokumoto, H.; Sinnamon, L. J.; Gregg, J. M.; Sharma, P.; Ke, X.; Rzchowski, M.; Eom, C. B.; Anglada, M.; Sharma, P.; Cross, L. E. References and Notes 1. 2012, No. April, 61–65.
(4) Ghodsi, S. M.; Megaridis, C. M.; Shahbazian-Yassar, R.; Shokuhfar, T. Advances in Graphene-Based Liquid Cell Electron Microscopy: Working Principles, Opportunities, and Challenges. Small Methods 2019, 3 (5), 1–16. https://doi.org/10.1002/smtd.201900026.
(5) The authors gratefully acknowledge the financial support from National Science Foundation (NSF Award number DMR-1809439)

Multi-element alloy nanoparticles are important materials for different catalysis and energy conversion applications due to the compositional complexity and lattice distortion.[1-2] Yet, fabrication of homogenous multi-metallic particles composed of miscible and immiscible elements is challenging and needs special kinetically controlled synthesis methods. [3-4]
In this work, we studied the in-situ colloidal synthesis of multi-element alloys through different equilibrium and non-equilibrium growth mechanisms. An equimolar aqueous mixture of Au, Pt, Ir, Cu and Ni chloride is used as the precursor solution and polyvinylpyrrolidone (PVP) is added as a stabilizer. A liquid flow holder integrated with microfluidic tubing is used to gradually inject the precursor solution into the liquid cell. The time-lapse series of TEM images show the fast formation of particles in solution entered into the liquid cell by electron beam reduction of metal ions, followed by nucleation of and growth id particle seeds. The crystalline phase structure, elemental composition and distribution of formed nanoparticles are identified by ex-situ aberration-corrected scanning transmission electron microscopy (STEM), energy-dispersive X-ray spectroscopy (EDS) and high angle annular dark field imaging (HAADF) characterization techniques.
Due to the difference in miscibility and reduction rate kinetics of metallic elements, particles formed in liquid cells have different sizes, morphologies, and compositions. Three different types of particles are detected as AuCu alloy, PtCuIrNi alloy and Ni@Cu core-shell nanoparticles. Larger particles with a size of 20-30 nm are gold-rich AuCu alloy with near hexagonal morphologies. The second type of detected particles are Ni@Cu core-shell 8-10 nm in size. Nickel has the lowest reduction potential and is more likely to be oxidized by oxidizing radicals and ions product of water radiolysis. The formation of Ni@Cu core-shell nanoparticles can be explained by the slower reduction rate of transition metal elements compare to noble metals used in the mixture. The third type of particle has the smallest size and most complex composition. The PtCuIrNi particle are 2-3 nm in size and have a single FCC crystal structure. The crystal of these multicomponent nanoparticles is composed of atoms with different size and binding energies which results in lattice distortion and complex surface energies of lattice planes. This complex structure and surface energies of crystal facets hinder the fast coalesce of nanoparticles and further growth of particles. This is n promising mechanism for the synthesis of small nanoparticles with increased surface area and highly active surface sites for many catalysis applications.
(1) Buck, M. R.; Schaak, R. E. Emerging Strategies for the Total Synthesis of Inorganic Nanostructures. Angew. Chemie - Int. Ed. 2013, 52 (24), 6154–6178. https://doi.org/10.1002/anie.201207240.
(2) Amiri, A.; Shahbazian-Yassar, R. Recent Progress of High-Entropy Materials for Energy Storage and Conversion. J. Mater. Chem. A 2021, 9 (2), 782–823. https://doi.org/10.1039/d0ta09578h.
(3) Chen, P.-C.; Liu, X.; Hedrick, J. L.; Xie, Z.; Wang, S.; Lin, Q.-Y.; Hersam, M. C.; Dravid, V. P.; Mirkin, C. A. Targets. In This Way, We Can Characterize Cross-Talk and Extract Errors per Gate from Errors per Gate Pair. For Target Atoms, E. Nanoscale 2015, 352 (6293), 0–5.
(4) Kwon, S. G.; Krylova, G.; Phillips, P. J.; Klie, R. F.; Chattopadhyay, S.; Shibata, T.; Bunel, E. E.; Liu, Y.; Prakapenka, V. B.; Lee, B.; Shevchenko, E. V. Heterogeneous Nucleation and Shape Transformation of Multicomponent Metallic Nanostructures. Nat. Mater. 2015, 14 (2), 215–223. https://doi.org/10.1038/nmat4115.
- The authors acknowledge the financial support from National Science Foundation (NSF Award number DMR-1809439)

Operando X-ray diffraction (XRD) is an established technique to observe cathode active materials (CAMs) and their crystallographic transformations upon Li (de)intercalation in Li-ion batteries.¹ With synchrotron radiation, high intensity and excellent temporal and angular resolution can be obtained, yielding accurate Rietveld refinement results.² This allows tracking unit cell symmetry and volume, atomic positions and even site occupancy factors; in other words it allows real-time investigations of compositional phase diagrams as a function of lithium content. In this respect, a complex and still debated CAM is LiNiO₂, which benefits nowadays of a wave of renewed interest fueled by the industry moving towards high-Ni layered CAMs.³ In this respect, it also becomes important to study LNO with operando XRD in electrochemical setups resembling commercial applications, such as unmodified pouch cells.
In this presentation we will show that synchrotron XRD can indeed be used to measure pouch half cells in transmission mode to investigate CAMs, with a focus on LiNiO₂. Despite the fact that its phase diagram has been the object of numerous experimental and computational studies over the last two decades, even between recent experimental studies inconsistencies emerge on the position and width of single- and two-phase fields^4,5. Modelling of the phase diagram has always been a daunting task and resulted in the prediction of several stable Li phases that were not observed experimentally. Aiming at resolving the sources of discrepancy among experiments and between experiments and theory, we combine operando synchrotron XRD and Rietveld refinement with Monte-Carlo Simulation using a modified cluster expansion formalism at the Density Functional Theory (DFT) level⁶. A surrogate lattice model pinpoints the influence of off-stoichiometry (Li_1-zNi_1+zO₂) and elemental substitution on the phase diagram and yields an unprecedented match to experimental ones. The dominant effect of both off-stoichiometry and elemental substitution is to disrupt Li ordering, suppressing phase transitions and promoting solid-solution behavior and the corresponding smoothing of voltage curves. Our model is particularly effective at reproducing the monoclinic domain and allows to draw a correspondence between electrochemical features (dx/dV curve) and Li-vacancy orderings (including the first identification of a Li_5/8NiO₂ superstructure). Deviations from experiments at both ends of the phase diagram are resolved and attributed to faulting and sluggish kinetics at high and low state of charge, respectively. The formation of stacking faults, in particular, known from ex situ observations⁷, is investigated for the first time under operando conditions.

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Conventional lithium-ion batteries (LiB)¹ are the most efficient energy storage devices that triggered the transformation of our lifestyle into a digital nomad with the revolution of portable electronics. Compare to conventional liquid electrolyte, inorganic solid-state electrolytes (SSE) represent a promising alternative due to their nonflammable nature, broader temperature operating range and larger electrochemical window. Therefore, all-solid-state-batteries (ASSB) made an important step toward new-generation in electrochemical energy storage systems². However, several limitations still impact the performances of ASSBs such as SSE ionic conductivity, chemical evolution of SSE/active-materials interface, lithium dendrite growth, grain boundary conductivity and solid/solid interfacial resistance³.
To get a better insight into the limiting parameters of the performances of the ASSBs, a better quantification of the relationship between the structural and electrochemical properties is strongly required. In this study, we propose an approach to carry out Operando Transmission Electron Microscopy (TEM) measurements⁴ and X-ray micro computed tomography (XCT)⁵ to study the chemical and morphological modifications while operating the ASSB focusing on the multiple solid/solid interfaces at a local scale using the TEM, but also having a general view using the XCT.
For this study ASSB using a oxide solid electrolyte, Li_1.5Al_0.5Ge_1.5(PO₄)₃ (LAGP)⁶ was used due to their high stability in the air. Different batteries configuration was used for the operando TEM experiment and XCT. In the case of Operando TEM an LiFePO₄ (LFP)/LAGP/Li₃V₂(PO₄)₃ (LVP) battery was studied where LFP was choose as cathode material due to its safety and price attractions. One of the most difficult part in the realization process of the operando TEM experiment was represented by the production nanobattery process where the electrolyte layer must be thin enough (maximum 20 nm) to allow a full battery to be connected to the chip which allows applying bias. In the case of operando XCT NMC/LAGP/Li metal battery was studied where NMC and Li metal were chosen due to their high energy density.
A home-made electrochemical cell designed for tomography requirements has been used for monitoring Li dendrite, cracks formation, LAGP degradation in real-time during (de)lithiation process. The contact between lithium metal and solid electrolyte generated the formation of an instable interface where dendrites penetration in the solid electrolyte throw a delamination effect was spotted. Lithium exchange process produced extra stress and volume increase in the material which generated the production of the cracks in the battery. Once the irreversible process of the cracks started, lithium metal penetrated inside the cracks and slowly filled them, in the end producing the short-circuit the battery.
Operando TEM analysis allowed us a more local analysis where the solid/solid interface between cathode and solid electrolyte was studied at nanoscale. The appearance of cracks while cycling that was noticed using XCT was confirmed also with the TEM analysis. The migration of the cathode elements inside the solid electrolyte at the local scale upon cycling was noticed after the bias was applied offering us insights of the solid/solid interface in the ASSB at a local scale. The quantification of the dynamics of Li dendrite formation and the morphological changes within ASSB open new opportunities to attenuate failure processes occurring during the (de)lithiation mechanism.

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