Operando Measurements Research Articles

Understanding the Interplay between Electrochemistry and Mechanics at Dendrite Tips in Sulfide and Oxide Electrolytes

Dendrite-induced short circuits threaten the deployment of solid-state batteries with metal anodes. Whether dendrites grow by internal chemical reduction of lithium or because of mechanical stresses has been a topic of debate. For both oxide and electrolyte electrolytes, we address this question by conducting operando microscopy to observe mechanical and electrochemical phenomena underlying dendrite growth. Here, we build upon the method from Athanasiou-Fincher et al. to observe stress-optic couplings around dendrite tips in thin oxide electrolytes[1]. Specifically, operando measurements of dendrite-induced stress fields are measured as a function of applied potential, and then the images are quantitatively analyzed to measure the mechanical driving forces underlying failure (i.e., the energy release rate). These operando measurements demonstrate a complex interplay between electrochemistry and mechanics. We develop a mechanistic framework to describe the observed behavior, discussed in juxtaposition with stress-corrosion cracking and linear elastic fracture mechanics. The resulting implications for electrolyte testing and design are discussed. Lastly, we assess whether mechanical stresses in electrolytes can be used to “steer” the dendrite growth directory. By dynamically applying mechanical loads to growing dendrites in LLZTO, we show that dendrite growth trajectory can be deflected to avoid short-circuit failures in oxide electrolytes[2]. Together, these results demonstrate a complex relationship between electrochemical and mechanical driving forces. Despite the observed complexity, processing-induced residual stresses can deflect dendrites and avert short circuits.[1] CE Athanasiou=, CD Fincher=, C Gilgenbach, WC Carter, H Gao, YM Chiang, BW Sheldon. Manuscript in preparation. “On the Use of Photoelasticity for Operando Dendrite-Induced Stress Quantification in Ceramic Electrolytes,” 2022 Materials Research Society Fall Conference; manuscript in preparation.[2] CD Fincher, CE Athansiou, C Gilgenbach, MJ Wang, BW Sheldon, WC Carter, YM Chiang, “Controlling dendrite propagation in solid-state batteries with engineered stress,” Joule, in press. DOIs: 10.1016/j.joule.2022.10.011

Cu Surface Chemistry in Acid Media: Vibrational Spectroscopy, Mass Spectrometry and ECSTM Measurements

Copper electrodeposition is a central process in the metallization of microelectronics and more recently copper has also found use as an important electrocatalyst in the conversion of CO2 to hydrocarbons. Gaining mechanistic insight into the reactivity of Cu surfaces requires in situ and better still in operando measurements. Herein the utility of the combination of vibrational spectroscopy (SEIRAS, SHINERS), electrochemical mass spectrometry (EC-MS) and scanning tunneling microscopy (ECSTM) to examine the competitive and co-adsorption interactions between potential dependent halide adsorption, molecular adsorption, underpotential metal deposition and hydride formation on low index Cu single crystals surface will be detailed. Further still, the emergent opportunity to study the impact of such interaction on metal deposition reactions will also be explored.1.Raciti and T.P. Moffat, “Quantification of Hydride Coverage on Cu(111) by Electrochemical Mass Spectrometry,” J. Phys. Chem., 126, 18734-18743 (2022).2.Raciti, A.R. Hight Walker, T. P. Moffat, “Mapping Surface Chemistry During Superfilling with Shell- Isolated Nanoparticle Enhanced Raman Spectroscopy and X-ray Photoelectron Spectroscopy,” J. Electrochem. Soc., 169, 082506 (2022).3.B.M. Tackett, D. Raciti, A.R. Hight Walker, T.P. Moffat, “Surface Hydride Formation on Cu (111) and its Decomposition to Form H2 in Acid Electrolytes,” J. Phys. Chem. Lett., 12, 10936-10941 (2021).4. G.Liu, S. Zou, D. Josell, L.J. Richter and T.P. Moffat, “SEIRAS Study of Chloride Mediated Polyether Adsorption on Cu,” J. Phys. Chem. C., 122, 21933-21951, (2018).

Progress Towards the Development and Understanding of Energy Dense Rechargeable Batteries Utilizing Zn and Cu

Batteries are easy to use, remotely monitorable, not fuel dependent, easily permitted and installed, and start automatically and reliably during an electrical outage. This makes them optimal for stationary storage and power assurance applications. Within battery-based grid storage, as of mid-2017, lithium-ion, sodium-ion, and lead-acid systems are the leaders, comprising 59% (~1.1 GW), 8% (0.15 GW), and 3% (0.06 GW) of global operational electrochemical storage, respectively.However, these batteries suffer from low energy density, high cost, poor safety, environmental concerns, and/or cycle life. Existing battery options on the market also do not meet the required market needs for long-duration backup power. For example, lead-acid batteries require too much space, are heavy, and contain toxic materials. Lithium-ion batteries, while compact and capable of excellent cycle life, are too expensive to serve long outages and have notable flammability and environmental risks.Alkaline Zn batteries are a strong candidate for electrical grid storage applications due to Zn’s high capacity (820 mAh/g), established materials supply chain and low cost. To realize the highest energy dense batteries, Zn needs to be coupled with a similarly low cost, abundant and high-capacity cathode. CuO (674 mAh/g) is an intriguing high-capacity cathode when paired with Zn in alkaline electrolyte, a battery that until recently has been relegated to the history books as a primary system. In 2021 Schorr et al. reported a rechargeable Zn/CuO battery that utilized a Bi additive to help facilitate the electrochemical reversibility of the Cu conversion electrode. Bi2O3, a species with comparable redox potentials to Cu2O, promoted reversibility and minimized passivation in the historically non-reversible system. The battery cycled without any observable Cu and Bi mixed oxide phases, cycling between metallic Cu and Bi and Cu2O/Cu(OH)2 and Bi2O3, respectively. Although the Bi additive did not eliminate capacity fade completely, limiting the cells to a 30% depth of discharge (relative to CuO) enabled 250 cycles at > 124 Wh/L. Alternatively, compensating for capacity loss with additional Cu metal provided for very high areal capacities (∼40 mA h/cm2) and energy densities (∼260 W h/L), despite only 65% active material cathode loadings and ∼10% Zn anode utilization; preliminary tests indicated these batteries were prone to shorting.Seeking to improve performance and minimize the spatial segregation of Cu- and Bi-phases observed upon cycling in the prior system, D. Arnot et al. prepared nanoscale carbon coated (Cu/Bi) particles, where the coating partially minimized dissolution and diffusion of soluble cuprate and bismuthate complexes, where ~ 200 cycles at 300 mAh/g was demonstrated (@ ~ 100 Wh/L). CuBi2O4 and CuO phases were formed upon oxidation, indicating carbon coatings can affect the battery cycling mechanism and may have future roles increasing performance. Data collected from a variety of experimental techniques, including cyclic voltammetry, rotating ring-disk electrode voltammetry, electrochemical impedance spectroscopy, electron microscopy, transmission electron microscopy, Raman spectroscopy, operando energy-dispersive X-ray diffraction measurements, battery cycling along with recent DFT modeling will be presented to help elucidate the role of additives, carbon coatings, and ion selective polymers in enabling reversible Zn/Cu based batteries. In addition, the general challenges of achieving a highly reversible energy dense battery based on two conversion electrodes operating in highly alkaline environment will be discussed.The goal is to demonstrate a Zn/CuO battery with long lifetime, at appreciable energy densities (> 200 Wh/L), with excellent safety, lower toxicity and sufficiently low cost to be manufactured and installed on the grid. While the laboratory scale Zn/CuO battery builds have very promising characteristics to date they have not been optimized or adapted for consumer or market-based needs in terms of power performance, energy density, cycle life or stability in terms of shelf life and the ability to tolerate partial state of charge. Progress towards these goals may also be discussed.N. B. Schorr et al. Rechargeable Alkaline Zinc/Copper Oxide Batteries. ACS Applied Energy Mater. 2021, 4, 7, 7073–7082. https://doi.org/10.1021/acsaem.1c01133.D. J. Arnot et al. Rechargeable Alkaline Zn-Cu Batteries Enabled by Carbon Coated Cu/Bi Particles. J. Power Sources 2022, 529, 231168. https://doi.org/10.1016/j.jpowsour.2022.231168.This work was supported by the U.S. Department of Energy, Office of Electricity, and the Laboratory Directed Research and Development program at Sandia National Laboratories. Sandia National Laboratories is a multi-mission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC, a wholly owned subsidiary of Honeywell International, Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA-0003525. The views expressed herein do not necessarily represent the views of the U.S. Department of Energy or the United States Government.

Investigation on Reaction Mechanism in an SOFC Composite Cathode by Using Patterned Thin Film Electrodes

Introduction For the further commercial use of solid oxide fuel cells (SOFCs), operating at intermediate temperatures is demanded. When reducing the operating temperature, the degradation of cathodic activity occupies the largest part of degradation of cell performance. Therefore, to improve the performance of SOFCs at intermediate temperature, the activity of cathodic reaction has to be improved.The cathodic reaction of SOFCs proceeds not only at triple phase boundaries (TPBs) of electrode, electrolyte and gas but also at double phase boundaries (DPBs) of electrode and gas, when a mixed ionic and electronic conductor (MIEC) is used. Thus, increasing the DPB area is considered as the best way to improve the cathodic performance. However, it was reported that composite cathodes of MIEC and electrolyte particles showed better performance than simple MIEC cathodes, despite the DPB area decreased [1]. Possible reasons for such performance enhancement can be considered as (i) promotion of oxide ion diffusion and/or (ii) the increase of TPB concentration. However, the reason for the performance enhancement by making a composite cathode are not-well understood so far.In this study, we aimed to understand the cathodic reaction in a composite cathode of MIEC and electrolyte. For this purpose, we proposed new types of original model electrodes to simulate the reaction in actual porous composite electrodes. From electrochemical and the operando X-ray absorption spectroscopic measurements of the model electrodes, we tried to separately evaluate the contribution of ion diffusion and TPB reactions on the performance improvement of composite cathode. Methods When using a porous electrode, it is difficult to investigate the reaction mechanism because of its complicated microstructures. Our research group proposed so-called “patterned thin film model electrode” like Figure 1(a) as a model electrode to reproduce the reaction in a porous electrode while removing the influence of microstructure [2]. In this model electrode, the contact area of electrode and electrolyte was limited by partially inserting an insulating layer, and thus the reaction distribution was formed in the electrode as a function of the distance from the electrode/electrolyte interface.In this study, we proposed two new types of model electrodes as Figure 1(b) and 1(c) to simulate the porous composite electrode. In the patterned composite electrode (b), an electrolyte layer was inserted between the electrode and insulator. On the other hand, in the patterned composite electrode (c), a part of electrode was removed to introduce TPBs. From the difference between the model electrodes (a) and (b), the contribution of oxide ion diffusion in composite electrode was estimated. From the difference between the model electrodes (b) and (c) the contribution of the TPB reaction was estimated. In this study, we selected La0.6Sr0.4CoO3-δ (LSC64) as an MIEC cathode and Gd0.1Ce0.9O2-δ (GDC10) as an electrolyte material. Operando micro X-ray absorption spectroscopy (μ-XAS) measurement was conducted with the model electrodes to investigate the effective reaction area of the model electrode. In this measurement, a change in the oxygen chemical potential can be detected as a change of X-ray absorbance at the fixed energy near the Co K-edge accompanying a change of the oxidation state of Co in the LSC64 [3]. Thus, the reaction distribution could be evaluated by measuring the change of the X-ray absorbance due to the polarization as a function of the distance from the electrode/electrolyte interface. Results and Discussion Figure 2 shows the results of μ-XAS measurement at 973 K under 1 bar O2 with cathodic polarization. The area where the ratio of absorbance is larger than 1 corresponds to the area where the oxygen chemical potential is changed due to the polarization, i.e. the effective reaction area. The reaction area of the model electrode (b) was longer than that of the model electrode (a). This suggested oxide ion diffusion was improved by inserting the GDC layer. On the other hand, the reaction area of the model electrode (c) was longer than that of the model electrode (b). Generally, the reaction on the mixed conducting LSC64 electrode is supposed to proceed DPB reaction mainly. However, the longer reaction area of model electrode (c) indicated that the contribution of TPB reaction was also significant in the LSC64 composite electrode. As a conclusion, both promotion of oxide diffusion and the increase of TPB effective for the enhancement of the cathodic reaction in MIEC composite electrode.[1] Y. T. Kim, et al., Solid State Ionics, 309, 77-85 (2017).[2] K. Amezawa, et al., ECS transactions, 62(2), 129-135 (2015).[3] Y. Orikasa, et al., Journal of Physical Chemistry C, 115, 16433–16438 (2011). Figure 1

Operando Electrochemical Impedance Spectroscopy and Its Application to Commercial Li-Ion Batteries

Electrochemical impedance spectroscopy (EIS) is a powerful non-invasive tool for characterising electrochemical systems. Applied to Li-ion batteries, EIS is shown to be an informative indicator for their state-of-health (SoH) [1,2,3]. However, EIS is limited by the constraints of linearity and stationarity, while Li-ion batteries inherently behave in a nonlinear and nonstationary way. Regarding linearity, the voltage over the electrodes is a nonlinear function of the current through the electrodes. Linearity is achieved by applying a small amplitude zero-mean current excitation around an operating point, such that the nonlinear function is quasi linear in this range. Regarding time-variation, the impedances of fully charged and fully discharged cells are different, the same for pristine and aged cells, or cells kept at room temperature and in freezing environments. For Li-ion batteries, this means that EIS experiments should be performed in steady-state when at a specific state-of-charge (SoC) and temperature. The impedance therefore depends on the operating point (temperature and SoC) and the constraints of linearity and stationarity are very restrictive.Lately, we have developed operando to reveal impedance data from measurements not satisfying linearity and stationarity [4,5]. This technique allows to measure the impedance of electrochemical systems along a time-varying trajectory, for instance, while charging or discharging Li-ion batteries [5,6]. For this purpose, a nonzero-mean odd random phase multisine current excitation is used, and the time-varying impedance along the trajectory is estimated from the spectrum of the voltage response. Moreover, nonlinear distortions in the measurements are detected and quantified, the noise level is estimated, and uncertainty bounds are enclosed on the time-varying impedance. For Li-ion batteries most time-variation happens at low frequencies. However, obtaining time-varying impedance data at low frequencies is a challenging problem. This on the one hand due to drift signals, for instance the increasing voltage while charging a battery, hiding the low frequency content, and on the other hand due to low-frequency noise. Operando EIS implements a drift signal suppression such that obtaining impedance data at low frequencies becomes attainable [4].In this paper operando EIS measurements while charging and discharging commercial LG M50 Li-ion batteries are presented, demonstrating that the battery’s impedance while charging, discharging and resting are different from each other. Prospectives are given for utilizing operando EIS data for smart-charging and SOH prognosis applications.[1] Pastor-Fernández, C., Uddin, K., Chouchelamane, G.H., Widanage, W.D. and Marco, J., 2017. A comparison between electrochemical impedance spectroscopy and incremental capacity-differential voltage as Li-ion diagnostic techniques to identify and quantify the effects of degradation modes within battery management systems. Journal of Power Sources, 360, pp.301-318.[2] Zhang, Y., Tang, Q., Zhang, Y., Wang, J., Stimming, U. and Lee, A.A., 2020. Identifying degradation patterns of lithium ion batteries from impedance spectroscopy using machine learning. Nature communications, 11(1), pp.1-6.[3] Jones, P.K., Stimming, U. and Lee, A.A., 2022. Impedance-based forecasting of lithium-ion battery performance amid uneven usage. Nature communications, 13(1), pp.1-9.[4] Hallemans, N., Pintelon, R., Zhu, X., Collet, T., Havigh, M.D., Wouters, B., Revilla, R.I., Claessens, R., Ramharter, K., Hubin, A. and Lataire, J., 2022. Trend Removal in Measurements of Best Linear Time-Varying Approximations—With Application to Operando Electrochemical Impedance Spectroscopy. IEEE Transactions on Instrumentation and Measurement, 71, pp.1-11.[5] Hallemans, N., Widanage, W.D., Zhu, X., Moharana, S., Rashid, M., Hubin, A. and Lataire, J., 2022. Operando electrochemical impedance spectroscopy and its application to commercial Li-ion batteries. Journal of Power Sources, 547, p.232005.[6] Zhu, X., Hallemans, N., Wouters, B., Claessens, R., Lataire, J. and Hubin, A., 2022. Operando odd random phase electrochemical impedance spectroscopy as a promising tool for monitoring lithium-ion batteries during fast charging. Journal of Power Sources, 544, p.231852.

Lithium Intercalation Mechanisms in Wadsley-Roth Phases

Wadsley-Roth crystallographic shear phases are complex inorganic compounds that intercalate alkali ions at a rapid rate, allowing for fast charging lithium-ion battery electrodes with high power densities. Wadsley-Roth crystallographic shear phases consist of mxn size blocks of corner-sharing octahedra. These mxn blocks of octahedra share edges with other blocks of corner sharing octahedra, thereby forming what are referred to as crystallographic shear planes. A variety of Wadsley-Roth phases have been synthesized with differing structural features including the size of the blocks of corner-sharing transition metal octahedra, transition metal chemistry, and disorder among the transition metal sites. Using first-principles statistical mechanics methods, we have predicted the electrochemical properties of PNb9O25, TiNb2O7, and Nb2O5 (Figure 1), three important Wadsley-Roth shear phases, to explore the interplay between crystal structure, transition metal chemistry, Li site preferences, and the voltage profile. The computational approach relied on a triptych of ab initio density functional theory calculations, cluster expansion methods and finite temperature Monte Carlo methods. The calculations provide insights about lithium site preferences, strain evolution[1], and electronic structure [2, 3] as a function of state of charge in representative Wadsley-Roth phases.For the PNb9O25 compound, we find that lithium prefers to initially fill pyramidal sites at the crystallographic shear planes. It is not until higher lithium concentrations that Li begins to fill window sites at the center of the 3 by 3 octahedral blocks. This inversion in Li-Va ordering is paired with an increase of crystallographic strain and a decrease in octahedral distortions. In contrast to PNb9O25, the TiNb2O7 compound, a commercialized Wadsley-Roth phase, is characterized by Ti-Nb disorder on the transition metal sublattice. We find that the Nb, due to its higher oxidation state, prefers octahedral sites that share fewer edges with neighboring octahedra, relegating the lower oxidation state Ti cations to octahedra at the block edges. First-principles calculations and Monte Carlo simulations predict that the lithium site stability is paired to the local transition metal chemistry and ordering, with Li preferring to fill sites coordinated by TiO6 octahedra. With the use of symmetry adapted collective displacement order parameters we uncover changes in octahedral distortions that differ between the TiO6 and NbO6 octahedra upon intercalation of lithium. Furthermore, we find a similar evolution in strain upon intercalation as is predicted for PNb9O25. To study the effect of octahedral block size on electrochemical properties of Wadsley-Roth phases, we performed an additional in-depth study on Nb2O5, a Wadsley-Roth structure with 4 by 4 corner-sharing octahedral blocks. Predictions for this phase indicate that the dilute limit Li site preference changes when increasing block sizes. Unlike TiNb2O7 and PNb9O25, which have 3 by 3 octahedral block structures, lithium window sites at the center of the block are stable in Nb2O5 at the dilute limit. We attribute this to differences in octahedral distortions in the 4 by 4 and 3 by 3 blocks. Our results indicate that there are a wide variety of structural and chemical levers with which to modify and further optimize the electrochemical properties of Wadsley-Roth phases. References Saber, M., Preefer, M.B., Kolli, S.K., Zhang, W., Laurita, G., Dunn, B., Seshadri, R. and Van der Ven, A., 2021. Role of Electronic Structure in Li Ordering and Chemical Strain in the Fast Charging Wadsley–Roth Phase PNb9O25. Chemistry of Materials, 33(19), pp.7755-7766.Preefer, M.B., Saber, M., Wei, Q., Bashian, N.H., Bocarsly, J.D., Zhang, W., Lee, G., Milam-Guerrero, J., Howard, E.S., Vincent, R.C. and Melot, B.C., 2020. Multielectron redox and insulator-to-metal transition upon lithium insertion in the fast-charging, Wadsley-Roth phase PNb9O25. Chemistry of Materials, 32(11), pp.4553-4563.Baek, S.W., Preefer, M.B., Saber, M., Zhai, K., Frajnkovič, M., Zhou, Y., Dunn, B.S., Van der Ven, A., Seshadri, R. and Pilon, L., 2022. Potentiometric entropy and operando calorimetric measurements reveal fast charging mechanisms in PNb9O25. Journal of Power Sources, 520, p.230776. Figure 1

In Operando Measurement of the Lithium-Ion Concentration in the Battery Electrolyte to Study Degradation Modes

In operando measurements of the lithium-ion concentration inside a lithium-ion battery (LiB) using a fiber-optic sensor are demonstrated. The concentration changes in the electrolyte are correlated to the incremental capacity response of the battery during charge and discharge. The goal is to study battery degradation based on the dynamic and state-of-charge dependent concentration of lithium ions in the electrolyte.Batteries lose capacity over time, both due to charging/discharging and to shelf ageing (calendar ageing). Extending the lifetime of a battery directly reduces its environmental footprint. This ageing is caused either by i) unwanted chemical reactions, reducing the number of available lithium-ions or increasing the impedance, or ii) by physical changes that reduces the available lithium storage capacity of the electrodes. Both mechanisms affect the spatial distribution of lithium ions.Ageing has traditionally been studied through monitoring the operational performance (e.g., coulombic capacity, internal resistance), or through post-mortem investigations. Other advanced methods, such as thermal neutron imaging or X-ray tomography has also been used to estimate the internal composition of the battery through image analysis [1,2]. This study presents live concentration measurements using an optical fiber placed between the electrodes. The intrinsic properties of optical fibers (e.g., small, chemically inert, electrically insulating) make them ideal for internal sensing in the chemically harsh interior of a battery.The fiber is placed in the electrolyte between the electrodes, see Fig. 1a. Because the reflected intensity depends on the concentration of lithium ions (Fig. 1b), we are able to demonstrate and analyze how the concentration changes during cycling (Fig. 1c). Both single-cycle and long-term effects are investigated. Information about how the lithium concentration changes during cycling is valuable both as an input parameter in battery modelling, and to increase the understanding of battery ageing. For the latter, the lithium-concentration during cycling of batteries is evaluated in correlation with an incremental capacity analysis. Siegel, J.B.; Lin, X.; Stefanopoulou, A.G.; Hussey, D.S.; Jacobson, D.L.; Gorsich, D. Neutron Imaging of Lithium Concentration in LFP Pouch Cell Battery. J. Electrochem. Soc. 2011, 158, A523, doi:10.1149/1.3566341.Senyshyn, A.; Mühlbauer, M.J.; Dolotko, O.; Hofmann, M.; Ehrenberg, H. Homogeneity of lithium distribution in cylinder-type Li-ion batteries. Sci. Rep. 2015, 5, 1–9, doi:10.1038/srep18380. Figure 1

(High-Temperature Energy, Materials, & Processes Division Subhash Singhal Award) From Electrochemical to Mechanical Modeling of SOFCs and Their Experimental Validation

Due to the asymmetric structure with multiple materials, SOFCs are subjected to various modes of mechanical stress, resulting in a risk of failure. Of particular importance are thermal and chemical strains, which depend on the micro- and macroscopic distribution of electrochemical reaction sites. Therefore, SOFC modeling must include electrochemistry, mass and charge transport, thermo-fluid dynamics, and structural analysis. In addition, appropriate experiments must be performed to validate the modeling results. This research group is working to develop a comprehensive environment for modeling and validation in order to evaluate the mechanical reliability of SOFCs.Electrochemical modeling of cathode was made based on the defect chemistry and mass transport of (La,Sr)CoO3 (LSC) and (La,Sr)(Co,Fe)O3 (LSCF). An empirical equation for the surface reaction of the porous electrode was determined by electrochemical analysis of a dense film electrode taking into account the difference between the dense film and porous electrodes [1]. Anode reaction rate on a unit length of triple phase boundary of Ni-YSZ-gas was determined using circular Ni model electrodes of various size [2]. Evaluation of 3D oxygen potential distribution inside the constituent oxides was made using an in-house code called SIMUDEL where mixed ionic/electronic conduction and oxygen nonstoichiometry were taken into consideration [3,4]. It was combined with commercial software to make structural analysis. Mechanical properties used for calculation were obtained from measurements by the resonance method and the small punch method or collected from the literature. Non-linear stress-strain behaviors were observed with Ni-YSZ cermet [5] and inelastic behaviors were found in most nonstoichiometric oxide materials. Large ferro-elasticity emerged in the LSC and LSCF [6] and in Sc stabilized ZrO2 electrolyte at elevated temperatures. Chemical strain in vacancy formation was formulated with a linear function of the defect concentration as an independent factor from the thermal expansion. In the structural analysis, it was treated as the additional temperature change of the local material. Volume change of Ni-YSZ cermet on red-ox operation was a difficult factor to formulate because of its complex dependence on composition, temperature, and atmosphere. As expected, Ni-YSZ showed expansion when oxidized, but under certain conditions at an intermediate temperature range, it rather contracted on oxidation [7].In reality, the calculated stress distribution does not always match the actual behavior of the cell since there often are unconsidered factors. Thus, experimental validation is essential. For this purpose, we have developed methods for in-situ or operando measurements of cell shape and the residual stress. Long-focus laser profilometer was used to measure the warping of a planar cell during heating, operating, and cooling operations. For the change in the diameter of a tubular cell, the laser projection type dimension meter was employed. Residual stress measurements were made with a handy X-ray analyzer (μ-X360s, Pulstec Industrial. Co. Ltd.) combined with a newly developed one- or two-chamber cell holder [8,9]. Anode-supported cells from multiple sources were analyzed, showing different stress histories in red-ox operations depending on the microstructure of the anode support layer.Currently, we are developing a protocol for testing robustness of planar SOFCs. Here, temperature distribution is intentionally applied on a cell with segmented heater allays on the top and the bottom of the cell. Severe condition tests will be performed, and the results will be analyzed with the above-mentioned simulation.AcknowledgementThis study was supported by the New Energy and Industrial Technology Development Organization (NEDO) .[1] T. Kawada, Current Opinion in Electrochemistry, 21, 274-282 (2020) DOI: 10.1016/j.coelec.2020.03.016[2] M. Takeda, Master’s thesis, Graduate School of Environmental Studies, Tohoku University (2016) : M. Takeda, et al. Submitted to J. Electrochem. Soc.[3] K. Terada, et. al., ECS Trans. 35(2 part2), 923-933 DOI: 10.1149/1.3570073[4] M. Sato, et. al., Trans. Jpn. Soc. Comp. Eng. Sci. 2017, 14 (2017) DOI: 10.11421/jsces.2017.20170004[5] S. Watanabe et al., J. Mater. Sci. 55, 8679-8693 (2020) DOI: 10.1007/s10853-020-04624-4[6] Y. Kimura et al., J. Electrochem. Soc. 161(11), F3079- F3083 (2014) DOI: 10.1149/2.0131411jes[7] Y. Morishita et al. , ECS Trans., 91(1) 1979-1984 (2019). DOI: 10.1149/09101.1979ecst[8] K. Yashiro et al., submitted to J. Power Sources[9] K. Oshima et al.,ECS Trans. 103(1), 1251-1260 (2021) DOI: 10.1149/10301.1251ecst

(Digital Presentation) Operando x-Ray Emission/Absorption Spectroscopy to Characterize Electronic Structure Changes of Transition Metals in Lithium-Ion Batteries

Demand for high-performance rechargeable batteries has driven the development of novel electrodes with high reversibility and energy density. Tracking the change in electronic and local structure is crucial to investigate and improve the stability and performance of these batteries. Advanced characterization techniques allow the user to monitor electronic and local atomic structure changes to better understand the role and behavior of different elements during cycling of electrode material for rechargeable batteries.X-ray Absorption and Emission Spectroscopy allow us to explore such changes in 3d transition metal elements through the process of generation and quenching of core holes in the sample. Operando measurements enable real-time monitoring of electronic structure changes in electrode materials which enable us to capture phenomena which are only kinetically accessible.In this study, the change in electronic structure of transition metals present in electrode materials is explored as a function of lithium removal through XES Kβ1,3feature along with K-edge XAFS using a lab-scale instrument. The choice of electrodes explored in this study considers the degree of oxidation, structure, and mechanism for ion storage. Change in peak and edge positions of Kβ1,3and K-edge feature is utilized to monitor oxidation/spin changes in electrode materials during charge/discharge. Further the magnetic behavior for ex-situ samples prepared by electrochemical delithiation of LCO in the range of 2-10% delithiation is investigated using Kα and Kβ fluorescence (spin sensitive) followed by K-edge XAFS for Cobalt and Oxygen. Figure 1

Breaking Local Charge Symmetry of Iron Single Atoms for Efficient Electrocatalytic Nitrate Reduction to Ammonia.

The electrochemical conversion of nitrate pollutants into value-added ammonia is a feasible way to achieve artificial nitrogen cycle. However, the development of electrocatalytic nitrate-to-ammonia reduction reaction (NO3-RR) has been hampered by high overpotential and low Faradaic efficiency. Here we develop an iron single-atom catalyst coordinated with nitrogen and phosphorus on hollow carbon polyhedron (denoted as Fe-N/P-C) as a NO3-RR catalyst electrode. Owing to the tuning effect of phosphorus atoms on breaking local charge symmetry of the single-Fe-atom catalyst, it facilitates the adsorption of nitrate ions and enrichment of some key reaction intermediates during the NO3-RR process. The Fe-N/P-C catalyst exhibits 90.3% ammonia Faradaic efficiency with a yield rate of 17980 μg h-1 mgcat-1, greatly outperforming the reported Fe-based catalysts. Furthermore, operando SR-FTIR spectroscopy measurements reveal the reaction pathway based on key intermediates observed under different applied potentials and reaction durations. Density functional theory calculations demonstrate that the optimized free energy of NO3-RR intermediates is ascribed to the asymmetric atomic interface configuration, which achieves the optimal electron density distribution. This work demonstrates the enhanced function of heteroatom doping on single atoms for NO3-RR, and provides an effective strategy for improving the catalytic performance of single atom catalysts in different electrochemical reactions.

Resonant photoemission spectroscopy of atomic layer Fe2N on Cu(111) with continuous angular rotation of linearly polarized light

Linearly polarized soft x-rays provide information about electronic or magnetic anisotropy through absorption into materials or generation of photoelectrons. In order to change the relative angle between linear polarization and sample crystalline axes, either x-ray polarization or the sample needs to be rotated. Due to difficulties of polarization control in the soft x-ray range, a conventional approach was to rotate the sample. However, this method is not compatible, for example, with operando measurements on non-uniform samples where sample size and rotational motion are severely restricted. At BL07LSU of SPring-8, we developed a new method to rotate the linear polarization angle using a segmented cross undulator. We report an application of this linear polarization rotation to resonant photoemission spectroscopy on an magnetic atomic layer Fe2N on Cu(111) to probe the electronic anisotropy of the 3d states in the vicinity of the Fermi level.

In-situ Raman unveiled Nb-O-bond-dependency selectivity for methanol electro-oxidation at high current density

Selective methanol oxidation reaction (MOR) to value-added formate can maximize the energy utilization by replacing the high onset-potential and sluggish oxygen evolution reaction. However, to date, only first-row 3d transition metal oxides exhibit the capacity of selective MOR, motivating the design of new kinds of electrocatalysts to further enhance the performance. Here we develop amorphous Nb2O5 as an efficient electrocatalyst, for the first time, for selective MOR to formate, with a low operating potential of 1.47 V vs. RHE to achieve the industry-relevant current densities (>100 mA cm−2) with a formate Faradaic efficiency of ∼100 %. We demonstrate, via operando Raman measurements, that this superior electrochemical MOR capacity originates from the in-situ induced short Nb-O bonds from the amorphous structure. Besides, the interface between amorphous Nb2O5 and nickel foam could also faciltate the MOR. This work may provide insights for designing novel transition metal oxides as efficient catalysts for selective MOR.

Present status and recent progress of research, using photoemission-electron microscopy at SPring-8

Photoemission electron microscopy (PEEM), particularly when combined with synchrotron radiation, exerts a powerful functionality in spectroscopy applications. The use of PEEM has steadily expanded the availed analysis objects at the SPring-8 synchrotron facility, such as magnetic materials, thin-film devices, semiconductors, monolayers, extraterrestrial matter, and multiferroics. Some special experimental settings such as time-resolved or operando measurements have also been developed according to user requests. In this paper, we present an overview on the achievements of PEEM studies so far and introduce some recent technical and scientific progress at SPring-8.

Revealing the effects of microstructural changes of graphite anodes during cycling on their lithium intercalation kinetics utilizing operando XRD

Concerning cell ageing and lithium plating, electrode kinetics – in particular the one of the anode - plays an important role. In our study, we applied a holistic physicochemical post-mortem analysis including operando XRD and SEM-studies as well as electrochemical analysis to get deeper insights into the changes of the microstructure and phase composition of graphite anodes from LiNi0.6Co0.2Mn0.2O2//Graphite pouch cells during cyclic ageing and their influence on the lithium intercalation kinetics. The key findings are as follows: Li plating and loss of cyclable lithium is the main source of capacity fade of the investigated cells. Cycling causes pore clogging of the anode leading to an increased transport resistance for Li-ions and slower charge transfer reactions. Visual inspections and operando XRD measurements in turn indicate an inhomogeneous Li intercalation over the thickness of the electrode resulting in a Li gradient. In the cycled electrode LiC6 forms in surface-near regions, whereas in deeper regions LiC12 formation has not finished yet. As a result, Li plating occurs as the surface-near graphite is already fully intercalated and Li-ion transport to deeper regions is hindered due to pore clogging. By combining complementary methods we could consistently prove the hypothesis of pore clogging, deterioration of anode kinetics and subsequent inhomogeneous lithiation which is supposed to trigger the observed Li-plating.

Conversion of LiPSs Accelerated by Pt‐Doped Biomass‐Derived Hyphae Carbon Nanobelts as Self‐Supporting Hosts for Long‐Lifespan Li–S Batteries

Rechargeable Li–S batteries (LSBs) are emerging as an important alternative to lithium‐ion batteries (LIBs), owing to their high energy densities and low cost; yet sluggish redox kinetics of LiPSs results in inferior cycle life. Herein, we prepared multifunctional self‐supporting hyphae carbon nanobelt (HCNB) as hosts by carbonization of hyphae balls of Rhizopus, which could increase the S loading of the cathode without sacrificing reaction kinetics. Trace platinum (Pt) nanoparticles were introduced into HCNBs (PtHCNBs) by ion‐beam sputtering deposition. Based on the X‐ray photoelectron spectroscopy analyses, the introduced trace Pt regulated the local electronic states of heteroatoms in HCNBs. Electrochemical kinetics investigation combined with operando Raman measurements revealed the accelerated reaction mechanics of sulfur species. Benefiting from the synergistic catalytic effect and the unique structures, the as‐prepared PtHCNB/MWNCT/S cathodes delivered a stable capacity retention of 77% for 400 cycles at 0.5 C with a sulfur loading of 4.6 mg cm−2. More importantly, remarkable cycling performance was achieved with an high areal S loading of 7.6 mg cm−2. This finding offers a new strategy to prolong the cycle life of LSBs.

Surface Ferromagnetism of FeO Nanoparticles Revealed by Operando Magnetoelectrochemical Measurements

In view of the long-standing controversy over the surface ferromagnetism of $\mathrm{Fe}\mathrm{O}$, we propose to prepare its nanoparticles based on the lithium-battery reaction mechanism and carry out operando magnetometry measurements. This operando magnetoelectrochemical technology allows accurate magnetic detection of electrochemical synthesis products, effectively avoiding various intractable surface reactions during sample transmission processes. Due to the large surface area of nanosized $\mathrm{Fe}\mathrm{O}$, the magnetometry measurements show strong ferromagnetism and a high Curie temperature of 754 K, which can be attributed to surface frustration and the surface-bulk exchange interaction. These critical results confirm the surface ferromagnetism of $\mathrm{Fe}\mathrm{O}$ and provide valuable insights toward the design of spintronic devices.

Probing lithium mobility at a solid electrolyte surface

Solid-state electrolytes overcome many challenges of present-day lithium ion batteries, such as safety hazards and dendrite formation1,2. However, detailed understanding of the involved lithium dynamics is missing due to a lack of in operando measurements with chemical and interfacial specificity. Here we investigate a prototypical solid-state electrolyte using linear and nonlinear extreme-ultraviolet spectroscopies. Leveraging the surface sensitivity of extreme-ultraviolet-second-harmonic-generation spectroscopy, we obtained a direct spectral signature of surface lithium ions, showing a distinct blueshift relative to bulk absorption spectra. First-principles simulations attributed the shift to transitions from the lithium 1 s state to hybridized Li-s/Ti-d orbitals at the surface. Our calculations further suggest a reduction in lithium interfacial mobility due to suppressed low-frequency rattling modes, which is the fundamental origin of the large interfacial resistance in this material. Our findings pave the way for new optimization strategies to develop these electrochemical devices via interfacial engineering of lithium ions.

Imaging the strain evolution of a platinum nanoparticle under electrochemical control.

Surface strain is widely employed in gas phase catalysis and electrocatalysis to control the binding energies of adsorbates on active sites. However, in situ or operando strain measurements are experimentally challenging, especially on nanomaterials. Here we exploit coherent diffraction at the new fourth-generation Extremely Brilliant Source of the European Synchrotron Radiation Facility to map and quantify strain within individual Pt catalyst nanoparticles under electrochemical control. Three-dimensional nanoresolution strain microscopy, together with density functional theory and atomistic simulations, show evidence of heterogeneous and potential-dependent strain distribution between highly coordinated ({100} and {111} facets) and undercoordinated atoms (edges and corners), as well as evidence of strain propagation from the surface to the bulk of the nanoparticle. These dynamic structural relationships directly inform the design of strain-engineered nanocatalysts for energy storage and conversion applications.

Rapid determination of solid-state diffusion coefficients in Li-based batteries via intermittent current interruption method

The galvanostatic intermittent titration technique (GITT) is considered the go-to method for determining the Li+ diffusion coefficients in insertion electrode materials. However, GITT-based methods are either time-consuming, prone to analysis pitfalls or require sophisticated interpretation models. Here, we propose the intermittent current interruption (ICI) method as a reliable, accurate and faster alternative to GITT-based methods. Using Fick’s laws, we prove that the ICI method renders the same information as the GITT within a certain duration of time since the current interruption. Via experimental measurements, we also demonstrate that the results from ICI and GITT methods match where the assumption of semi-infinite diffusion applies. Moreover, the benefit of the non-disruptive ICI method to operando materials characterization is exhibited by correlating the continuously monitored diffusion coefficient of Li+ in a LiNi0.8Mn0.1Co0.1O2-based electrode to its structural changes captured by operando X-ray diffraction measurements.

Characterization of Nanometric Thin Films with Far‐Field Light

AbstractThe characterization of ultrathin transparent films is paramount for various optoelectronic materials, coatings, and photonics. However, characterizing such thin layers is difficult and it requires specialized clean‐room equipment and trained personnel. Here, a contact‐less, all‐optical method is introduced and validated for characterizing nanometric transparent films using far‐field optics. A series of nanometric, smooth, and homogeneous layered samples are fabricated first, alternating transparent spacer and fluorescent layers in a controlled manner. Fluorescence radiation pattern originating from the thin fluorophore layers is then recorded and analyzed and quantitative image analysis is used to perform in operando measurements of the refractive index, film homogeneity and to estimate axial fluorophore distances at a sub‐wavelength scale with a precision of a few of nanometers. The results compare favorably to measurements obtained through more complicated and involved techniques. Applications in nanometrology and biological axial super‐resolution imaging are presented. It is demonstrated in live cells the precise axial localization of single organelles in cortical astrocytes, an important type of brain cell. The approach is cheap, versatile and it will have applications in various fields of photonics.