Lithium-rich transition metal oxide cathodes are of intense current interest as higher capacity alternatives to the stoichiometric layered cathodes currently used in today’s automotive applications. These Li-rich cathodes store extra energy through extensive high-voltage oxygen oxidation. The mechanism by which the changes in oxygen redox chemistry is accommodated by the cathode remains actively debated, particularly in terms of the structure changes. How does the change in O chemistry impact the structure and dynamics of the transition metal and lithium cations? Without understanding how oxygen oxidation is accommodated by the cathode structure, and how this is linked to performance limitations, we cannot design strategies to mitigate limitations and displace current automotive electrodes or develop new robust electrode chemistries that access additional O-based redox capacity.

Using operando and complementary ex situ X-ray scattering studies (XRD and SAXS) we explore the dynamic restructuring of transition metal cathodes that occurs during cycling. We identify — for the first time — the formation of nanopores within the cathode during O oxidation. Upon extended cycling, coarsening of residual pores can be linked to performance degradation

Li-ion batteries are ubiquitous in our society. However, producing high performance, safe, and sustainable batteries remains a great challenge to foster the industrial development towards e-mobility, portable and stationnary applications. Materials engineering and new chemistries are key in this objective, as well as advanced characterization tools to probe the bulk & interfacial properties of active materials. In particular, investigations in operando mode, e.g. during battery cycling under realistic conditions, are currently attracting an enormous interest. Synchrotron techniques have been widely employed to probe in real-time a large variety of battery technologies, e.g. Li-ion and beyond, to observe and map the evolving structures, in relation to materials composition & design and battery operating conditions. In this talk, we will focus on the lithiation and ageing mechanisms in advanced electrodes, and show how operando X-rays (XRD/WAXS/SAXS) experiments can provide unique insights into the structural changes in graphite [1], silicon [2] and silicon-graphite [3-4] anodes with high time/spatial resolution. In particular, spatially-resolved mXRD gives access to 2D information in the depth of the electrode, as lithiation heterogeneities and phase distributions [1], while combined SAXS/WAXS allow to determine the sequential lithiation mechanism of active phases in a composite nanostructured material [3-4]. We will also adress the challenge to build beam-compatible battery cells, which is the pre-requisite to correlate real-time microscopic information to the electrochemical performance. Last, we will introduce the novel possibilities of performing 3D quantification of structural features evolutions in complex materials.

[1] S. Tardif et al, J. Mat. Chem. A, 2021.

[2] S. Tardif et al, ACS Nano, 2017, 11, 11306–11316.

[3] C. Berhaut et al, ACS Nano, 2019, 13, 10, 11538-11551.

[4] C. Berhaut et al, Energy Storage Materials, 2020

Magnetite (Fe3O4) has emerged as a promising electrode material in rechargeable batteries because of its natural abundance, low cost, low toxicity and high specific capacities. Fe3O4 exhibits both intercalation and conversion mechanism and it involves 8 Li ions during its reduction. The multi electron transfer enables higher energy density of these electrodes compared to purely intercalation electrodes. However, it suffers from high hysteresis and high capacity loss with cycling. The reasons for the capacity fading in conversion electrodes are still not very clear and lot of research is going on with an aim to design a high capacity electrode with performance stability over a large number of cycles. In-situ/operando research in the area of batteries has gain popularity in recent past as it can give valuable information regarding changes taking place in the electrode materials during the charging-discharging of the batteries and thus can address various problems associated with battery performance [1,2].
In the present work we have used operando XAS to understand the structural changes around Fe cations during the charging-discharging of the Fe3O4 electrodes in Li ion battery. The Fe3O4 electrode has been charges and discharged at the rate of 53mAg-1 in the voltage range of 0.03-3V. The XANES data recorded during the first discharge was analysed using chemometric techniques like Principal Component Analysis (PCA) and Multivariate Curve Resolution- Alternate Least Square (MCR-ALS).
The components of the MCR-ALS analysis during the first discharge of Fe3O4 electrode have been identified respectively as Fe3O4, LixFe3O4, FeO and metallic Fe. The EXAFS analysis shows that the fraction of tetrahedral Fe cations decreases and after 0.4 electron equivalent Fe cations exists in octahedral coordination environment only. Therefore, from the operando XANES and EXAFS analysis, it becomes evident that the lithiation of magnetite during the first discharge is a multi-step process, where Li insertion in the Fe3O4 structure results in migration of Fe cations in the tetrahedral 8a site to octahedral sites (16c or 16d) and finally formation of LixFe3O4 where all Fe cations exist in octahedral coordination. The next step is conversion of LixFe3O4 phase into the rocksalt FeO phase, which finally converts to metallic Fe phase. It can also be inferred that the intercalation of Fe3O4 which results in formation of LixFe3O4, overlaps with the conversion reaction of LixFe3O4 to FeO. Further XANES and EXAFS analysis of the first charge and second discharge of Fe3O4 electrodes show that the completely lithiated electrode material never returns to Fe3O4 phase on charging, instead the subsequent cycles after the first discharge are due to the conversion reaction between FeO and metallic Fe. In conclusion, this study gives a detailed structural analysis of the Fe3O4 electrodes in Li ion battery during charging-discharging cycles.
[1] Huie, M. M., Bock, D. C., Wang, L., Marschilok, A. C., Takeuchi, K. J. & Takeuchi, E. S. (2018) J. Phys. Chem. C 122, 10316.
[2] Zhang, W., Bock, D. C., Pelliccione, C. J., Li, Y., Wu, L., Zhu, Y., Marschilok, A. C., Takeuchi, E. S., Takeuchi, K. J. & Wang, F. (2016) Adv. Energy Mater. 6, 1502471.

Recent transformations and expected growth in global energy storage and conversion systems demand developing materials [1]. Such materials in demand should be a long lasting, effective, safe, environmentally friendly, cost-effective and recyclable for use in different electrochemical applications (e.g., Lithium Sulfur Batteries, Electrochemical Capacitors, Polymer Electrolyte Membrane Fuel Cells). These requests by consumers require an innovative non-linear approach combining the materials synthesis, advanced multi-dimensional characterization techniques, real-time testing and state of art electrochemistry [2,3]. Despite efforts there are still critical challenges that have to be addressed in order to overcome intrinsic limitations and achieve both - a high energy density and a high power density [4,5]. The common denominator that the above mentioned energy storage and conversion devices share is the carbonaceous material (CM). The amount of carbonaceous material used in the electrode is approx. 30%. The CMs have different physico-chemical properties such as surface area, porosity, electronic and ionic conductivity, hydrophilicity and electrocatalytic activity. Thus, the well-tailored CM’s structural features enhance ion transport and minimize initial capacity losses even with an increase in energy density [6]. A key structural feature of carbonaceous materials together with advanced multi-dimensional characterization techniques, real-time testing and state of art electrochemistry so called operando analysis of the Lithium Sulfur Battery (LiSB) will be the subject of a presentation (Fig.1) [6,7]. The first part is related to the model-free analysis by small-angle X-ray scattering. The structural characterization of the well-tailored CMs is a crucial step towards a better understanding of the elucidation of structure-morphology-property-relationships [6]. This in turn will shed light on the processes occurring in complex energy storage and conversion systems and helps to design cost-effective, safe devices with preferably high capacities and longer lifetime over many cycles. In the second part, the simultaneous performance of several independent techniques: small-angle neutron scattering, electrochemical impedance spectroscopy, galvanostatic/potentsiostatic cycling of the LiSB test cell will be presented [7]. A nanoporous and binder-free carbon electrode was applied as a model electrode for further in situ/operando analysis, which is deemed of great importance for mechanism study of batteries. Results obtained by in situ/operando SAS techniques are scientifically interesting and technologically very relevant for next generation energy storage and conversion systems. The outline of challenges will be presented and discussed.

Compton scattering imaging is a unique technique to visualize lithiation state on electrodes of large-scale lithium-ion batteries in-situ and in-operando conditions. This technique characterized by high-energy synchrotron X-rays allows the non-destructive observation of the reaction in closed electrochemical cells and enables us to analyze quantitatively the concentration of light elements, like lithium since incoherent scattering effects are enhanced. In this study, Compton scattering imaging is applied to a 18650-type cylindrical lithium-ion cell to visualize a spatiotemporal lithiation state, called Turing pattern [1].

The Compton scattering imaging was performed at the high-energy inelastic scattering beamline BL08W of the SPring-8. The energy of the incident X-rays and the scattering angle is fixed at 115.56 keV and 90 degrees, respectively. The Compton scattered X-ray energy spectrum is measured by 9-segments Ge solid-state detector. An observation region of the cell is limited by incident and collimator slits. The size of these slits is 5 mm in height, 750 mm in width, and 500 mm in diameter, respectively. The state of charge of the sample cell was controlled using a potentiostat/galvanostat.

Figure 1 (a) shows the result of line shapes of the Compton scattering spectra, called S-parameter analysis [2], which obtained by changing the sample position along z-direction during the charging. By charging the cell, the position of each component of the cell is shifted, which is induced by intercalation/deintercalation of the lithium. Moreover, we observed S-parameter oscillations by a depth-resolved analysis of the anode and cathode. Fig. 1 (b) shows the space-time S-parameter modulation DS obtained by subtracting from S-parameter its average value in the upper cathode region. A Fourier analysis of DS shows that the dominating period of the S-parameter oscillation corresponds to the timescale of the charging curve and the dominating wavelength of the S-parameter oscillation is related to the size of the grains of the active material. The reason for the appearance of this S-parameter pattern is due to different mobilities of lithium ions and electrons and non-linear effects in the chemical reaction. Therefore, the existence of the S-parameter modulation implies that the cell can have an optimal cycle speed with a more homogeneous flow of ions.

[1] Suzuki, K., Suzuki, S., Otsuka, Y., Tsuji, N., Jalkannen, K., Koskinen, J., Hoshi, K., Honkanen, A.-P., Hafiz, H., Sakurai, Y., Kanninen, M., Huotari, S., Bansil. A., Sakurai, H. & Barbiellini, B. (2021). Appl. Phys. Lett. 118, 161902.

[2] Suzuki, K., Barbiellini, B., Orikasa, Y., Kaprzyk, S., Itou, M., Yamamoto, K., Wang, Y.J., Hafiz, H., Uchimoto, Y., Bansil, A., Sakurai, Y., & Sakurai, H. (2016). J. Appl. Phys. 119, 025103.

Over the last decades, the increased environmental pollution and vast fossil consumption generated a need for renewable energy sources. As these renewable energy sources are not always available, this also needs next-generation energy storage devices, such as lithium-ion batteries and solid oxide fuel cells. Despite the great interest in these systems, there are still gaps in the knowledge about the crystal structure evolution and phase transitions of these energy materials during the electrochemical reactions due to the submicron size of the active particles, which impede single crystal diffraction with X-rays or neutrons. Filling these gaps is crucial for understanding why a particular material functions better or worse than other closely related materials.

3D electron diffraction can be applied to submicron sized single crystals and is a powerful tool for determining the crystal structure and studying the structural changes during the electrochemical reaction [1]. However, ex situ experiments are not sufficient to solve all the questions and leave room for misinterpretation of artefacts due to, for instance, air and vacuum exposure and relaxation between cycling and structure determination and inherent differences between different crystals. Therefore, we aim to apply in situ 3D electron diffraction in a liquid filled electrochemical cell to study the crystal structure evolution upon electrochemical cycling in the transmission electron microscope.

Whereas our group was able to obtain in situ 3DED data of charged particles after a single cycle [2], in situ observation of ongoing reactions with electron diffraction has not been realized yet. One challenge is the strong scattering of the electrons by the thick liquid layer, which significantly decreases the signal-to-noise ratio [3, 4]. For obtaining data after a single cycle, this thick layer of liquid can be partially evaporated using an intense electron beam [3]. However, this procedure leaves contamination behind and prevents further cycling.

Our study aims to perform in situ 3D electron diffraction at different stages of the electrochemical process within the same experiment and therefore, without the need for evaporating part of the liquid. Our preliminary experiments on gold nanoparticles established this possibility. However, gold is an ideal system because of its high atomic number and the possibility to introduce the particles into the electrochemical cell by flushing. Studying complex and lower atomic number compounds of which the particles cannot be flushed through the cell will require optimization of the experimental conditions. Controlling all the parameters during the experiments, such as particle deposition, liquid thickness, bulging of the windows, beam irradiation and flow rate, is challenging. In this presentation, I will discuss the hurdles, the solutions and the results I have obtained so far.

[1] Hadermann J. & Abakumov A. M. (2019). Acta Cryst. B75, 485-494.

[2] Karakulina O., Demortière A., Dachraoui W., Abakumov A. M. & Hadermann J. (2018). Nano Lett. 18, 6286-6291.

[3] De Jonge N. & Ross F. M. (2011). Nature Nanotech. 6, 695-704.

[4] Tanase M., Winterstein J., Sharma R., Aksyuk V., Holland G. & Liddle J. A. (2015). Microsc Microanal. 21 (6), 1629-1638