December 1-6, 2013 | BostonMeeting Chairs: Charles Black, Elisabetta Comini, Gitti Frey, Kristi Kiick, Loucas Tsakalakos
The development of improved electrochemical energy storage devices depends critically on a detailed understanding of the physical and electrochemical processes at the electrode-electrolyte solid-liquid interface. Recent advances in in situ liquid cell electron microscopy, with its unique ability to provide simultaneous temporally and spatially resolved information as well as electrochemical parameters, enable exploration of the underlying physics of electrochemical reactions at the solid-liquid interface. Here we apply liquid cell electron microscopy to investigate the effect of additives on the morphology of electrochemical deposits. We have examined the deposition of zinc, an attractive anode material for low cost, recyclable batteries. Morphological control of zinc during deposition is required to avoid the formation of dendrites which may short the battery during charging. The inclusion of additives such as Bi in the electrolyte is known to modify the morphology and growth kinetics of Zn. Here, we use a liquid cell with three electrodes and the capability of liquid flow so that we can introduce acidic electrolytes of varying composition. We observe the deposition of Zn under galvanostatic conditions in electrolytes with different concentrations of the Bi additive, as well as changes in the Zn morphology when the additive is first supplied. We will compare these flow cell results to static liquid cell experiments (in a custom built liquid cell, the nanoaquarium) in which we have recorded Zn morphology during galvanostatic deposition, and we will discuss the benefits and pitfalls of flow capabilities in in situ electron microscopy for the study of processes during battery operation.
Cryo-Transmission electron microscopy is regarded as a powerful tool for the investigation of samples in a solution-like state. Due to the rapid freezing of the samples the sample is trapped in a thin ice layer and can be imaged under mild imaging conditions. However, dynamical processes are also trapped in this frozen state and cannot be analyzed easily. There is a growing demand for the in-situ investigation of such events and recently the utilization of specially constructed liquid cells for the investigation of solutions and dynamic processes are frequently use. Because of the expenses as well as because of the rather thick boundaries of such liquid cells, which require the utilization of scanning transmission electron microscopy techniques, we introduce here a simple and straightforward technique for the in-situ observation of nano-objects in liquid environments. Ionic liquids are molten salt-like compounds which virtually have no vapor pressure and remain liquid over a wide range of temperatures. These ionic liquids are known as excellent solvents for many materials and are used in synthesis as well as alternative solvents for nanoparticles, cellulose derivatives, nanoparticles, etc.. They have been also used to study self-organization processes of block copolymers.Due to the negligible vapor pressure ionic liquids are also compatible with the ultrahigh vacuum requirements of TEM and can be prepared as a free-standing liquid support film in which the visualization of particles or suspended nanostructures can be achieved. This approach permits the study of particle movement, crystal formation in ionic liquids, or the growth of nanoparticles. Additionally, it will be demonstrated that ionic liquids provide useful intrinsic staining properties, which enable the visualization of e.g. core-shell polymer nanostructures, etc. This approach is able to close an important gap in the characterization of nanoparticles and small structures in the solution as it provides the possibility to study individual nano-objects in the solution-like state with high lateral resolution. U. Mansfeld, S. Hoeppener, U.S. Schubert, Adv. Mater. 2013, 25, 761-765.
Since the inception of the concept of nanobattery with a single nanowire, tremendous progress has been made over the last few years on the direct in-situ TEM observation of structural and chemical evolution of materials related to energy storage. This is especially true for the case of anode materials for lithium ion battery. These in-situ TEM work have helped us to gain some insights on dynamic structural and chemical evolution of electrode materials that cannot be captured before. However, the design of the in-situ cell in the previous work, especially, the operating parameter of the cell during the in-situ testing is still far deviated from a real battery operating condition. Much effort is needed on designing of new cells that enable in-situ TEM study of battery under more realistic conditions. In this presentation, we will review, in retrospective and perspective, the overall progress of in-situ TEM study of battery materials, especially focusing on the challenges that related to anode, cathode, and solid electrolyte interface (SEI) for lithium ions battery and beyond, such as sodium ions and magnesium ions as well.
Battery cycle-life and safety depend critically on the morphological evolution of the electrode-electrolyte interface during charging and discharging. The potentially catastrophic formation of dendrites is one morphological evolution to be avoided. Recent advances in in situ liquid cell electron microscopy allow us to image the evolution of electrochemical deposition and stripping in real time with nanoscale resolution while controlling the current or potential during the process. The information acquired this way permits us to study process physics as a function of process conditions and electrolyte composition to obtain insights into the mechanisms leading to dendrite formation with the aim of devising means to avoid the same. Here we show in situ electron microscopy videos and electrochemical measurements obtained in a test system, the deposition and stripping of copper in an acidified copper sulphate solution. The experiments were carried out using our custom made liquid cell, the nanoaquarium, which is equipped with micropatterned platinum electrodes. These integrated electrodes were connected to a potentiostat to control and record the current and potential as functions of time during galvanostatic deposition. Simultaneously, the interface morphology evolution was imaged at video rate (30 images per second) as a function of current density using a Hitachi H9000 transmission electron microscope operated at 300kV. Correlating the imaging and electrical measurements facilitates synchronization between the morphology and the electrical data. We will describe the interface morphology and growth kinetics as functions of current density and time. We will show how this data can be used to measure the critical current at the transition from uniform growth to dendritic growth, and we characterize the onset of instability in the growth front. We will finally discuss the results within the context of battery cycling.
An understanding of the materials transformation and interfaces in electrochemical processes is critically important for identifying the failure mechanism or improving the lifetime of batteries and other relevant devices. In-situ transmission electron microscopy, which allows for real-time imaging of electrochemical processes in realistic liquid electrolyte environments with high spatial and temporal resolution, has attracted significant attention. Here, we report using an environmental biasing liquid cell operated in a transmission electron microscope to study electrochemical deposition and dissolution of metal dendrites and structural phase transformation during charge cycles in situ. A commercial electrolyte for lithium ion batteries (ethylene carbonate, dimethyl carbonate and LiPF6) was used. Phase transition of gold nanowires due to lithium ion insertion, solid electrolyte interface (SEI) layer formation, deposition and dissolution of lithium dendrites have been observed in real time. The current-voltage curve was recorded simultaneously during the charge cycles. Based on the combined in situ and ex situ studies we discuss novel mechanisms of transformation during charge cycles.Electron Microscopy (NCEM) of the Lawrence Berkeley National Laboratory, which is supported by the U.S. Department of Energy (DOE) under Contract No. DE-AC02-05CH11231. HZ thanks the funding support from U.S. DOE Office of Science Early Career Research Program.
Although lithiation has been investigated extensively by theoretical simulation over a wide range of different electrode materials, there is a lack of experimental evidence and fundamental understanding on the initiation and evolution of lithiation atomically, which hinders our understanding of the fundamental operation mechanisms in a lithium ion battery. In this talk, using in-situ high resolution TEM, we report that the atomic scale lithiation process of a single SnO2 nanowire anode immersed in an ionic liquid electrolyte. We discovered unexpectedly a multiple-stripe and multiple-reaction-front lithiation mechanism that differs completely from the expected core shell lithiation mechanism. More specifically, the lithiation initiated multiple stripes with width of a few nanometers parallel to the (020) plane traversing the entire wires, serving as multiple reaction fronts for later stages of lithiation. Inside the stripes, we identified a high density of dislocations and enlarged inter-planar spacing caused by lithiation.
When crystalline particles are dispersed in their matrix, such as a solution or vapor, it is readily observed that particles larger than those of average size grow, accompanying the dissolution of smaller particles into the matrix at the same time. This particle coarsening process has generally been referred to as Ostwald ripening. As the physical properties of crystals significantly vary with their ultimate size and shape, observation and appropriate control of their growth and dissolution behavior during the ripening process have been recognized as important issues in crystallization studies over the past several decades. Recent advances in transmission electron microscopy (TEM) enable atomic-scale imaging in Li intercalation compounds for direct visualization of lattice defects, phase transition, and structural evolution (S.-Y. Chung et al., Angew. Chem. Int. Ed.48, 543 (2009); S.-Y. Chung et al., Adv. Mater.23, 1398 (2011)). In particular, a variety of techniques have been utilized for real-time observations in TEM, providing unexpected and new experimental findings (S.-Y. Chung et al., Nature Phys.5, 68 (2009); S.-Y. Chung et al., Nano Lett.12, 3068 (2012)). Using in situ high-resolution electron microscopy (HREM) with a heating specimen holder, in this study we demonstrate, for the first time, the atomic-level evaporation behavior of LiFePO4 crystals in real time at high temperature (S.-Y. Chung et al., J. Am. Chem. Soc. (in press)). Prior to detailed observation of crystal evaporation, we also investigated the growth behavior of atomically flat low-index surfaces. A systematic comparison with image simulations along with density-functional theory calculations demonstrated that the cations evaporate preferentially over the [PO4]3- oxyanions, accompanying fast charge transfer from the nearest-neighboring Fe and O. The present study thus shows that our combined technique based on high-temperature HREM and systematic image simulations is a powerful tool to understand the dynamic characteristics of crystal growth and evaporation.
Observation of electrochemical phenomena at nano-scale in an all-solid-state lithium ion battery is important for understanding of the role of interfaces. High resolution transmission electron microscopy (TEM) coupled with electron energy loss spectroscopy (EELS) is ideal to track lithium ion movement with high spatial resolution. Functional thin film battery prepared by sputtering has been sliced by focused ion beams and mounted on commercial grids to produce nano-batteries. First to establish consistent electrical biasing of nano-batteries, an in-situ FIB biasing method was accomplished followed by ex-situ TEM/EELS investigation. After successful in-situ FIB biasing, samples with suitable thickness are biased in-situ in TEM. We will present lithium ion tracking by EELS in the nano-scale batteries ex situ and in situ and correlate with their electrochemical profiles.
Li ion based energy storage devices with high energy density and long-term stability are considered as one of the most suitable candidates applied for consumer electronics and electric vehicles (EV). Nanostructured materials, especially nanowires, have attracted great interests due to a range of advantages in many energy related fields, such as short Li-ion insertion/extraction distance, facile strain relaxation upon electrochemical cycling, enhanced electron transport, and very large surface to volume ratio. Although the electrochemical properties could be improved, the fast capacity fading is still one of the key issues and the intrinsic reasons need be further understood.To find out the reasons of fast capacity fading, the process was usually studied ex-situ after disassembling the devices. In-situ probing has been increasingly employed in nanotechnology, such as in-situ XRD, NMR or TEM. Here, we reported the single nanowire electrode devices designed as a unique platform for in situ probing the intrinsic reason for electrode capacity fading in Li ion based energy storage devices. In this device, a single vanadium oxide nanowire or single Si/a-Si core/shell nanowire was used as working electrode, and electrical transport of the single nanowire was recorded in situ to detect the evolution of the nanowire during charging and discharging. Along with lithium ion intercalation by shallow discharge, the vanadium oxide nanowire conductance was decreased over 2 orders. The conductance change can be restored to previous scale upon lithium ion deintercalation with shallow charge. However, when the nanowire was deeply discharged, the conductance dropped over 5 orders, indicating that permanent structure change happens when too many lithium ions were intercalated into the vanadium oxide layered structures. Different from vanadium oxide, the conductance of a single Si/a-Si core/shell nanowire monotonously decreased along with the electrochemical test, which agrees with Raman mapping of single Si/a-Si nanowire at different charge/discharge states, indicating permanent structure change after lithium ion insertion and extraction. We demonstrate that during the electrochemical reaction conductivity of the nanowire electrode decreased, which limits the cycle life of the devices. The intrinsic reason for electrode capacity fading in Li-ion based energy storage devices was concluded, which may push the fundamental limits of the nanowire materials for energy storage applications.
The need for new materials with improved ion transfer properties continues to be one of the main pressing concerns in energy storage materials research. In accompanying this search for optimal materials, appropriate characterization tools to assess key parameters of newly developed materials are required. This paper will focus on coupling electrochemical impedance spectroscopy (EIS) with fast gravimetric methods (fast quartz crystal microbalance (QCM)) under dynamic regime. This coupling, so called ac-electrogravimetry measures the usual electrochemical impedance, ΔE/ΔI (omega;), and the mass/potential transfer function, Δm/ΔE (omega;), simultaneously.[1-3] The main interests of this coupling are its ability to indicate the contribution of the charged and uncharged species and to separate the anionic, cationic, and free solvent contributions during the electrochemical/chemical processes. These features make the ac-electrogravimetry as an attractive and appropriate tool to investigate transfer/transport phenomena of charged and uncharged species in ion insertion materials.As a pertinent example, the adaptation of ac-electrogravimetry to evaluate the ion (Li+, Na+hellip;) transfer phenomena in MnO2 based thin films will be discussed. As a functional metal oxide, MnO2 is one of the most attractive inorganic materials because of its physical and (electro)chemical properties, particularly in energy storage. Thin films of MnO2 with Li+ ion intercalated are synthesized by a one-step electrodeposition method and the electrodeposition process is monitored by QCM.[5,6] The resulting LixMnO2 thin films are studied by classical (micro)structural characterization methods. The ion transfer properties (Li+ and Na+ in aqueous and acetonitrile solutions) are investigated by electrochemical quartz crystal microbalance (EQCM) and ac-electrogravimetry. Our primary findings based on the mass/potential transfer function, (Δm/ΔE (omega;)) report that the cations are inserted under their hydrated form and the free solvent molecules participate indirectly in the charge compensation process with different kinetic constants.References:. S. Bourkane, C. Gabrielli, M. Keddam, J. Electroanal. Chem. 256 (1988) 471.. S. Cordoba-Torresi, C. Gabrielli, M. Keddam, H. Takenouti, R. Torresi, J. Electroanal. Chem. 290 (1990) 261.. C. Gabrielli, J.J. Garcia-Jareno, M. Keddam, H. Perrot, F. Vicente, J. Phys. Chem. B 106 (2002) 3182.. L. Athoueuml;l, F. Moser, R. Dugas, O. Crosnier, D. Bélanger, T. Brousse, J. Phys. Chem. C 112 (2008) 7270.. M. Nakayama, T. Kanaya, J.W. Lee, B.N. Popov, Journal of Power Sources 179 (2008) 361.. N. Cherchour, C.Deslouis, B. Messaoudi, A. Pailleret, Electrochimica Acta 56 (2011) 9746.
Activated carbons with well developed surface area and porosity are very interesting materials especially for electrochemical capacitor (EC) applications. Because of the fact that EC charging/discharging process has strictly electrostatic character, electrochemical double layer capacitors are able to be charged and discharged even in a few seconds. Additionally, to achieve good performance and satisfy high power demands it is necessary to exploit materials characterized with great conductivity and very often with tailored porosity which is responsible for preserving excellent charge propagation. However, the capacitance values reported for these electrodes do not exceed 150-180 F/g. Higher capacitance values can be provided from additional faradaic reactions. Unfortunately, their high price completely eliminates them from commercial using. Very interesting way to increase capacitance is to use electrode materials (activated carbons) which are electrochemically grafted by using different electrolytes. It means that electrolyte can generate particular functional groups on the surface of carbon electrode which are able to reversible redox reactions. It is a great advantage over pseudocapacitance received directly from the pseudocapacitive electrode material (e.g. transition metal oxides, conducting polymers) where the most limiting factors are slow diffusion and penetration of electrolyte. Electrochemical grafting is also much easier and quicker methods than chemical generation of electroactive groups on the electrode material&’s surface (e.g. during synthesis of electrode material), because this process proceeds in the same assembled system as further electrochemical investigation of its performance. Three electrode cell investigation revealed changes in behaviour of positive and negative electrode when compared with performance of pure sulphuric acid. The origin of positive electrode capacitance changes from typical electrical double layer to faradaic one after grafting process which is in a great accordance with data obtained from cyclic voltammetry and galvanostatic charging/discharging technique. Apart from electrochemical investigation other techniques were used to confirm if the additional pseudocapacitance really comes from already grafted functional groups on the carbom electrode or directly from redox active electrolyte. For that purpose thermogravimmetric analysis conjugated with mass spectrometer was used and gave very promising results. Investigated electrode after grafting process revealed much higher weight loss than ungrafted one because of significant CO gas evacuation which might be related to decomposition of carbonyl groups. Additionally, Raman spectroscopy was used in order to follow the change in the material functional structure and the results will be discussed.
It is widely believed that hydrogen is an ideal clean and efficient carrier for storage and transport of energy. In this context storage of hydrogen is one of the key challenges in developing hydrogen economy. One of the most attractive ways for hydrogen storage is using magnesium hydride. Magnesium can absorb hydrogen in atomic form and thereby act as hydrogen "sponges". It gives not only an important safety advantage over the gas and liquid but also high hydrogen uptake (7.6 wt %). Hence, magnesium hydride is a safe, volume-efficient method for hydrogen storage. However, the slow reaction kinetics and high thermodynamic stability hinder practical applications of this material. To enhance the kinetics and modify the thermodynamics of hydrogenation, it is essential to study the hydrogenation process on the atomic scale by using transmission electron microscopy (TEM). In this study, we investigated the hydrogenation of magnesium films decorated with palladium particles at room temperature by using environmental TEM. In addition, the vacuum transfer specimen holder was also used in order to minimize the formation of oxide during sample loading. Samples were exposed to hydrogen at the pressure up to 10 mbar in the ETEM. During the hydrogen exposure, we observed of the formation of magnesium hydride successfully. In electron diffraction mode, the formation of two different hydride phases (β-MgH2 and γ-MgH2) was observed. We believe that this experimental observation leads to the fundamental understanding of the reaction mechanism of a hydrogen gas with magnesium.
Oxide materials are known to be active in a variety of redox reactions, making them important for many energy technologies. Unfortunately, the complex interactions between such reactions and the structural/chemical evolution of the oxide surface are not well understood. This has hindered progress in many areas, including solid oxide fuel cells, corrosion, and the development of new heterogeneous catalysts. However, with the advent of high precision growth techniques, epitaxial oxide heterostructures can now be synthesized with controlled strain, orientation, and surface termination, thereby allowing model studies of surface behavior. We examine the reactivity of epitaxial SrCoO3-δ thin films using in situ X-ray studies at the synchrotron, focusing on the kinetics of oxidation and reduction in these materials. Both the dynamics of surface reactions and phase transitions are studied, using both incoherent scattering techniques and x-ray photon correlation spectroscopy. We find that oxidation can be characterized by two distinct time constants, and different mechanisms for the spread of oxygen in this material will be discussed.
Few methods exist for examining SOFC surfaces under conditions that approach the operating conditions of a SOFC. A JEOL environmental scanning microscope with a hot stage permits imaging of samples under vacuum at temperatures up to 1000C. Because of thermal emission, images free of charging artifacts are obtainable on insulating and conducting surfaces without application of conducting coatings. Ni/YSZ anodes exposed to fuel mixtures with low levels of phosphine (PH3) often exhibit new phases on the surface. Previous work suggests that the new phases are nickel phosphides. To confirm this hypothesis, a Ni/YSZ surface with visible micron-size particles was examined at temperatures of 500C to 1000C. The particles melted between 900C and 1000C, while the Ni/YSZ structure exhibited no visible change. This result is consistent with the known lower melting temperatures of nickel phosphides relative to nickel.
Many important material systems in catalysis work at atmospheric or higher gas pressure environments but yet these catalysts are characterized in vacuum in a conventional transmission electron microscope (TEM) or at sub-atmospheric pressures in an environmental TEM. The use of hermetically sealed environmental cells (constructed within the specimen holder) can overcome this pressure gap by containing the gas between electron transparent silicon nitride windows etched in silicon microchips while the gas environment is changed via a gas inlet connected to the outside of the microscope. This in-situ characterization technique is crucially needed to provide mechanistic insights to the structural and chemical changes that occur in real world catalytic reactions. However, the relationship between the differential pressure of the system and the operating pressure at the sample is not necessarily straightforward. Experimental parameters, such as the spacing between the SiN windows, can affect the resulting flow of gas near the sample. Furthermore, the thin SiN windows are subject to mechanical bowing, such that the spacing between windows varies both spatially across a window and with pressure. Chemical reactions in gaseous environment are influenced by the flow rate of the gas, which depends on both the channel size and the pressure. Here we present in-situ TEM observations in atmospheric pressure gas at elevated temperatures and high resolution images of different catalytic materials at a range of pressures, where we have used Electron Energy Loss Spectroscopy (EELS) to more accurately determine the pressure in a gas flow stage at the sample. This is done by assessing the electron inelastic mean free path through the gas flow stage for a range of input gas flow rates. The results of this work will enable a greater understanding in morphological changes in catalytic materials as reactions are occurring, which in turn can lead to development of more efficient catalytic materials.
In spite of tremendous progress in recent years in nanowire gas sensorics, very little research has been done on the fundamental understanding of the interplay between surface reactivity and electronic transport in working nanowires devices under realistic operation conditions. Another rarely addressed issue is the electron transport and chemical sensing performance of the nanowire, which is affected by local electroactive inhomogeneities and potential barriers in nanowire such as near surface depletion regions and Schottky contacts. This work is aimed to address the above deficiency via in situ imaging electroactive inhomogeneities and electron transport inside the nanowire as a function of gas environment and temperatures. In a course of this work, a single nanowire gas sensor was fabricated inside the membrane based-environmental cell equipped with a heater. The nanowire&’s strong temperature dependent conductivity was used as a thermometer of the entire device assembly. It was demonstrated that often the asymmetric Schottky barrier is formed at the nanowire&’s contacts what dominated the transport characteristics of the conducting channel. The nanowire responses to gas (2-propanol) with and without electron beam were analyzed quantitatively via conductometric measurements. The effect of electron beam irradiation as chemical activation mechanism of nanowire sensor has been discussed. EBIC technique was used for the first time to characterize the nanowire sensor during its operation in ambient pressure environment. The modulations of the EBIC resistive contrast were observed as a result of exposure to the analyte. The contrast forming mechanisms were qualitatively addressed in this work.
Micropatterned CdTe-CdS islands have been prepared through SiO2 windows to enhance photovoltaic performance by relieving lattice mismatch stress. To efficiently measure their local response down to the nanoscale, a new measurement scheme is presented for mapping PV performance. The specimens are illuminated from below through an inverted optical microscope, during simultaneous scanning from above with a conductive atomic force microscopy (cAFM). Sequences of images are then acquired for a single area, each with incremented DC applied biases. The local I-V response for any given pixel position is then easily determined based on the cAFM contrast (current) at the corresponding location in each distinct image (voltage). Crucially, this provides drift-free photoconduction maps based on the resulting array of I/V spectra, here ranging from 0 to 240 picoSiemens (pS), with spatial resolution of ~5 nm based on 65,536 pixels that would take orders of magnitude longer to acquire using conventional cAFM based methods. The PV performance of continuous and microstructured films will be compared, and related to orientations within the polycrystalline cell based on EBSD results. For the CdTe-CdS films, enhanced photoconductivity is clearly observed for certain grains, and grain boundaries are clearly resolved, confirming the importance of microstructural control and grain boundary conductivity on polycrystalline PV performance.
Here we show that lithiation and delithiation of the electrode materials in lithium-ion batteries can induce significant variations in their properties, including their thermal conductivity and elastic modulus. The varying thermal conductivity electrode mateirals during lithiation and de-lithiation may be important to better understand thermal events in electrochemical energy storage systems, and in addition, may provide new opportunities for active control of thermal conductivity. We present in-situ thermal and elastic measurements of LiCoO2 as a function of lithiation via a time-domain thermoreflectance (TDTR) technique using an electrochemical cell consisting of a Li foil anode, a liquid electrolyte, and a thin film LiCoO2 cathode constructed in such a way to enable direct real time measurement of thermal and elastic properties during electrochemical cycling. The LiCoO2 thin film is deposited by RF sputtering and annealed at 500°C in air. The thermal conductivity of the LiCoO2 is determined by the best fit between calculation and the measured TDTR data. Along with thermal conductivity, the elastic modulus is evaluated by monitoring acoustic signals. We conclude the thermal conductivity decreases from ~6.4 to 4.6 W m-1 K-1 and elastic modulus decreases from 325 to 225 GPa as the cathode is delithiated from Li1.0CoO2 to Li0.6CoO2. Moreover, the thermal conductivity and elastic modulus change is reversible. The dependence of the thermal conductivity on lithiation appears to be related to crystalline phase transformations.
High voltage Ta capacitors have broad applications for energy storage in electric systems, where there are very strict requirements for stability and reliability. In situ stress measurements were employed to provide new insight into failure mechanisms in these materials. In particular, field induced crystallization of the capacitor dielectric at high voltages was investigated in detail. This work demonstrates that different mechanisms produce both tensile and compressive stresses during the operation of these materials. The magnitude of these stresses is large enough to substantially impact observed failure processes. Stresses are generated in the amorphous tantalum oxide (ATO)/Ta system during operation by hydration process, electrophoresis, further oxidization and crystallization. These stresses have been evaluated by in situ stress measurement on a thin film model system. Futhermore, the details and direct evidences of failure process of ATO under high electric field have also been investigated in this report. Stress results are paired with data from techniques including focused ion beam (FIB) lift-out, electron scanning microscopy (SEM), transmission electron microscopy (TEM), selected area diffraction (SAD), Energy-dispersive X-ray spectroscopy (EDS) and high resolution transmission electron microscopy (HRTEM) to explore the details and to provide direct evidence for the failure mechanism. Based on this series of results, the failure mechanism has been reassessed. This will guide the new approaches for improving the stability and reliability of Ta capacitor in future and open a door to study the failure mechanism of other capacitors.1 School of Engineering, Brown University, Providence, RI 02912, USA. 2 Medtronic Energy and Components Center, 6800 Shingle Creek Parkway, Brooklyn Center, MN 55430, USA. a firstname.lastname@example.org, b email@example.com, c firstname.lastname@example.org, e email@example.com. * Corresponding author, B.W. Sheldon.
Interfacial reactions on electrical energy storage (EES) materials mediate their stability, durability, and cycleablity. Understanding these reactions in situ is difficult since they occur at the liquid-solid or solid-solid interface of optically absorbing materials that hinder the use of traditional spectroscopic techniques. Furthermore, since some interfaces involve liquids classic vacuum-based analytical methods can only probe reaction products that are stable under vacuum. NR is a neutron scattering technique highly sensitive to morphological and compositional changes occurring across surfaces and interfaces, including buried interfaces. It can be used to study such changes over lengths scales extending 1 nm to hundreds-of-nanometers. Neutrons, by virtue of their nature, are deeply penetrating and therefore ideally suited as a probe to study materials in complicated environments, such as electrochemical cells. Unlike x-rays, neutrons interact with the nuclear potential of constituent elements and are sensitive to light elements like Li and H. Neutrons are also sensitive to isotopic differences allowing for selective contrast variation in the design of experiments. For instance, 6Li and 7Li look very different to neutrons and this difference can be exploited in studying the exchange of Li during cycling to study the diffusion of Li through the solid electrolyte interphase (SEI) layer. We will present results of in situ NR studies of the high voltage thin film cathode material LiMn1.5Ni0.5O4 and a thin film anode material Li4Ti5O12 against a 1.2 molar LiPF6 in 1:1 ethylene carbonate - dimethyl carbonate electrolyte solution.
Safety is a critical issue for rechargeable battery technology. Due to the structure variation and complexity of battery systems, thermal properties of battery components are largely unknown. Here we perform in-situ thermal transport measurement on a micro-fabricated lithium ion battery. We observe highly reversible thermal behaviors of electrode materials during the charging/discharging cycles. The thermal conductivity of electrodes can be regulated by controlling lithium concentration and shows a significant contrast at different phases. This real time observation represents structure evolution during lithiation and delithiation process. The experimental results will help design safer batteries.This material is partially based upon work supported as part of the “Solid State Solar-Thermal Energy Conversion Center (S3TEC)," an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Award Number: DE-SC0001299/DE-FG02-09ER46577.
Capacitors store energy in the form of an electric field. At small scales, the use of 3D structures increasing the effective surface of the capacitor is a potential route for the development of high capacitance components . In addition, there is an interest for low temperature processes to avoid thermal stress damages in more complex structures and to reduce the energy consumption of the fabrication process , which is profitable from the economical and environmental point of view.In this context, electrochemical processes are a potential route for the fabrication of 3D capacitors because anodic porous silicon formation can be used to shape the 3D structure and a dielectric layer can be grown by anodic oxidation of silicon. However, the electrical properties of silicon oxide obtained by anodic oxidation are inferior to those of thermal oxide . To produce anodic silica layers of higher quality, it is first necessary to better understand and control the growth of anodic silica. In this work, we report on the electrochemical formation of anodic silicon oxide, the in-situ characterization of the growing film by different techniques, and the comprehension of the growth mechanism. The growth of anodic silica films is intimately linked to electrochemical oscillations related to the periodic variation of the electrical or morphological properties of the film . To understand the link between the growth, the silica properties and the oscillations, we monitored the silica film during its electrochemical growth by combined in-situ Optical Stress Sensing (MOSS) and Spectroscopic Ellipsometry (SE), as well as by in-situ Inductive Coupled Plasma Spectrometry (ICP-OES). The high temporal resolutions (0.3 sec for the MOSS and 2 sec for the SE) allow the very precise monitoring of the change of internal stress and morphology of the silica film during the anodic polarization of silicon. ICP provides in-situ information about the film dissolution rate in hydrofluoric acid solutions. It appears that, depending on the growth regime and the associated oscillatory behavior, some of the thin film properties are either constant or variable with time. From the mechanical point of view, the internal stress is about -325 MPa in the constant regime and varies between -100 MPa and -300 MPa during the growth in the variable regime. We determined the relation between the two growth regimes in order to advance the understanding and control of 3D porous anodic silica formation. M Nongaillard, F Lallemand, B Allard, Design for manufacturing of 3D capacitors (2010) Microelectronics Journal 41:845-85 K Ohnishi, I Akira, Y Takahashi, S Miyazaki, Growth and characterization of anodic oxidized films in pure water (2002) Jpn J Appl Phys 41:1235-1240 K Schönleber, K Krischer, High-Amplitude versus Low-amplitude current oscillations during the anodic oxidation of p-type silicon in fluoride electrolyte (2012) Chem.Phys.Chem. 13:2989-2996
Understanding lithiation process of Si at nanoscale becomes of prime importance to develop next generation Li-ion batteries since the nanostructured Si such as Si nanowires and porous nanostrcutrues were reported to enhance charging rate and avoid mechanical degradation due to the dramatic volume expansion of Si during lithiation. However, affirmative description of Li kinetics in nanostructured Si anode is still very limited. In the present work, we demonstrated in-situ lithiation of diverse Si nanostructures. First, our in-situ lithiation test showed unprecedentedly fast lithiation of a pristine Si nanowire. The measured diffusivity is even faster than any other in-situ lithiation test of Si and matching with the theoretically calculated diffusivity values. The mechanical properties of lithiated Si nanowires were also investigated using in-situ tensile testing, which provides a guidance of new nanostructure design of Si anode. Subsequently, we introduced a new design of nanostructured Si anode on a Polyimide (PI) substrate for future applications of flexible energy storage devices. Unlike other technique to fabricate nanostructure Si anodes, amorphous-Si was deposited directly on the polymer substrate having nano-hair like surface structure. In-situ lithiation tests found that this unique nanostructured Si anode hinders the delamination of an anode component resulting in higher capacity and longer life cycle than that of a-Si on the non- PI substrate or on a typical Cu foil substrate. We also characterized the lihitation behavior of carbon-fiber encapsulated Si nanoparticles which enhance mechanical reliability of Si based anodes during cyclic lithiation.
Lithium-ion batteries are critically important for a wide range of applications, from portable electronics to electric vehicles. However, the high-capacity electrodes in Li-ion batteries, such as Si and Ge, suffer from electrochemically-induced mechanical degradation that causes capacity fading. Drastic improvement of Li-ion batteries is hinged on the fundamental understanding of the physical mechanisms underlying lithiation/delithiation processes. We have developed methods for in-situ electrochemistry within a transmission electron microscope (TEM) to investigate phase transformation and morphological evolution in real-time during battery cycling. This presentation will focus on our recent progress using in-situ high-resolution TEM (HRTEM) to study the lithiation of Si electrodes (Liu et al, Nature Nanotechnology, 7, 749-756, 2012), which cannot be achieved using conventional battery testing techniques. Novel mechanistic information can be revealed by HRTEM, such as how lithium ions react with the crystalline electrodes to cause solid-state amorphization, and how dislocations form and evolve. A comparison was made for Si and Ge, having the same crystal structure, we found that the lithiation of crystalline Si is highly anisotropic but the lithiation of crystalline Ge is almost isotropic. HRTEM imaging of the atomic-scale lithiation processes reveals the root cause of this difference. In addition, this presentation will demonstrate that the synergistic integration of in-situ HRTEM and multiphysics modeling provides a powerful means to advance the fundamental understanding of the lithiation/delithiation mechanisms, shedding new light onto the development of durable electrodes for high performance Li-ion batteries.Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.
Two-dimensional early transition metal carbides or carbonitrides, MXenes, are promising as a new class of energy storage materials for applications such as anodes in lithium-ion batteries or electrodes in electrochemical capacitors. Their two-dimensional structures, which contain more than one element, can offer comparable or even superior properties, in comparison with graphene, due to tunable compositional variables. To better understand their performance and develop their applications, their stability in air and oxidation behavior need to be investigated. In this research, we characterized oxidation of multilayered Ti3C2 under pure oxygen environment at different pressures, inside transmission electron microscope (TEM) using an environmental TEM holder.Two-dimensional Ti3C2 particles were transferred onto the bottom chip of the environmental cell and then the temperature was increased to initiate the oxidation process under different oxygen pressures. Real-time observation of structural evolution was captured by high-resolution imaging and diffraction patterns. Formation and growth of anatase nanoparticles, as a result of oxidation, was identified. This study can further reveal the underlying mechanism of MXene oxidation and titanium oxide formation in order to produce hybrid carbide-oxide materials.
The use of patterned electrodes with well-defined geometric features has emerged as a valuable approach for elucidating electrochemical reaction pathways. The methods are hampered, however, by the need to create individual electrode configurations using lengthy microfabrication approaches and subsequently conduct measurements of many different samples to access a range of geometric features. Furthermore, subtle variations in fabrication steps for samples produced in series can lead to sample-to-sample variations that mask trends with the parameters of interest. Here we address these challenges using a parallel fabrication methodology that allows access to hundreds of dimensionally varied electrodes on a single electrolyte substrate in combination with an automated microprobe measurement system that enables rapid acquisition of electrochemical data from each of these electrodes. Example results are presented for solid oxide fuel cell (SOFC) cathode materials. Scaling behavior of both resistance and capacitance with electrode geometry is presented.
Solid oxide fuel cells (SOFCs) are energy conversion devices that rely on nonstoichiometric oxides to convert chemical energy into electrical energy with higher efficiency and lower environmental impact compared to typical combustion processes. Under the operating conditions of fuel cells, which include high temperatures and large oxygen partial pressure gradients across the cell, these materials may undergo changes in lattice parameter due to differences in the level of nonstoichiometry within the material, a phenomenon known as chemical expansion. This chemical expansion can also affect the mechanical properties, such as the Young's elastic modulus E, of these oxides. PrxCe1-xO2-δ (PCO, where δ represents oxygen vacancy content) is a model SOFC cathode material that displays significant nonstoichiometry in air at high temperatures. The magnitude of E for thin films of PCO is measured at room temperature for several compositions, establishing that Pr-content alone in this mixed ionic-electronic conducting system does not impact E. Through the use of environmentally controlled instrumented indentation at high temperatures relevant to SOFC operation (>500 °C), the effect of nonstoichiometry on the magnitude of E of PCO thin films is measured in situ, and the relative impact of thermal and chemical expansion on E are discussed. The consequences of such stiffness variation with temperature for more durable, portable SOFCs are considered.
In order to meet emerging electrical energy storage challenges, novel devices such as electrochemical double layer capacitors (EDLCs), or supercapacitors, are rapidly attracting interest. They rely on electrosorption of ions by porous carbon electrodes and offer a higher power and a longer cyclic lifetime compared to batteries. Room temperature ionic liquids (RTIL) are gaining increasing interest to further enhance the systems&’ operating voltage windows and charge storage densities. These electrolytes can broaden the operating voltage window and increase the energy density of EDLCs. While they may offer multiple performance advantages, the dynamic processes that govern their mobility in and out of pores, long-range transport, and differential behavior in a neat or solvated state are not thoroughly understood. Our work presents direct measurements of ion dynamics of 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMIm-TFSI) in an operating EDLC with electrodes composed of endohedral nanosized carbide-derived carbons (CDCs) and exohedral onion-like carbons (OLCs) with the use of in situ infrared spectroelectrochemistry. For CDC electrodes, absorbance measurements correlated charging and discharging of EDLCs with RTIL ions (both cations and anions) entering and exiting CDC nanopores. Conversely, for OLC electrodes, ions were observed in close proximity to the OLC surface without any change in the bulk electrolyte concentration during charging and discharging of the EDLC. This provides experimental evidence that charge is stored on the carbon surfaces of OLC EDLCs without long-range ion transport through the bulk electrode, contradicting the traditional wisdom of diffusion-driven ion mobility. Systems of RTIL ions solvated using organic propylene carbonate (PC) solvents showcased ion-dominated mobility in and out of confined porous architectures, excluding PC from the nanopores and corroborating the expected desolvation of electrolyte components in systems with matching ion/pore diameters. The experimental measurements presented here provide deep insights about the molecular level transport of RTIL ions in EDLC electrodes that will impact the design of electrode materials. This in situ technique, which can be applied to a wide range of electrochemical systems, is essential towards understanding ion mobility and selecting the optimal electrode/electrolyte configurations for novel electrical energy storage systems.
This study demonstrates the use of the in-situ spectroscopy for the characterization of spontaneous dehydrogenation reactions and being a tool to investigate possible routes of stabilization and control of thermodynamically unstable species. The corresponding results give crucial parameters helping to properly tune the properties of materials for energy storage applications. Metathesis and reactive milling are established methods to synthesize new compounds for energy storage materials. In many cases, intermediates and/or products formed are thermodynamically unstable. Their characterization and measurement as a function of time and temperature is a key problem for technologic transfer . We demonstrate the formation of intermediate species, studying one of the most promising materials for hydrogen storage, LiBH4, and specifically the reaction:TiCl3 + 3 LiBH4 → Ti(BH4)3 + 3 LiCl → 3/2 B2H6 + 1/2 H2 + TiH2 + 3 LiClThe identification and characterization of Ti(BH4)3 is a technical issue because it is extremely reactive in air, spontaneously decomposes within few hours at room temperature and it is volatile. Therefore the combination of different in situ techniques is required. The bulk analysis by Thermal Desorption Spectroscopy and Thermogravimetric Balance gives insight on the thermodynamic properties of the reaction products; the surface analysis by Raman Spectroscopy, Mass Spectroscpy and X-ray Photoelectron Spectroscopy gives insight on the chemical composition; the gas phase analysis by Infra-Red Spectroscopy gives insight on the volatile reaction products . Moreover the formation of unstable intermediate species might catalytically act on the kinetics of the overall reactions and yield to the emission of unwanted side products. To control and exploit new materials for energy storage the complementary results of the presented in situ analyses are necessary. In addition, the thermodynamycal unstability of the intermediate species is a challenge for in situ spectroscopy because of their short life time: for some reactions these intermediate species have been theoretically predicted but never experimentally shown. To address this challenge, spontaneous release of hydrogen from mixtures of LiBH4 with AlCl3 , ZnCl2, CuCl2 and VCl2, will be analyzed. A comprehensive bulk, surface and gas phase analysis of the reactions products and eventually formed intermedaite species will be presented, pointing out the route towards the control of spontaneous dehydrogenation reactions and the stabilization of the intermediate species. References E. Callini, et al., Dalton Transactions 42, 719 (2013).  A. Borgschulte, et al., J. Phys. Chem. C 115 (34), 17220 (2011). I. Lindemann, et al., Int. J. of Hydrogen Energy 38, 2790 (2013).
Characterization of catalytic reactions is often hindered by the fact that the behavior the system is mesoscopic, while the materials involved are nanoscale, with features that can span a broad range of temporal and spatial scales and which involve a broad range of competitive interactions. As a result, the description of a catalytic system requires interrogation with a variety of techniques - involving imaging, diffraction and spectroscopy - to describe the dynamic changes in structure that can occur during reactions. Commonly, this is done by simple use of standard techniques, and inference of how the results relate to the working condition of the system. It is, however, preferable that multiple probes are used to characterize physical and electronic structure of the catalyst during reaction, over multiple time and length scales. To date it has not been possible to directly link the observations across these techniques in such a way as to confirm that the data (imaging, diffraction, spectroscopy) is obtained from the system in the exact same “working” state. Here we report an experimental approach that allows:#9679; characterization - via x-ray absorption spectroscopy, extended x-ray absorption fine structure, x-ray fluorescence, Raman spectroscopy, transmission electron microscopy, scanning transmission electron microscopy, electron energy loss spectroscopy and energy dispersive electron microscopy - from the same sample,#9679; characterization at atmospheric pressures in reactive environments, and#9679; simultaneous, real-time and on-line analysis of the reaction products - i.e. “operando” experimentationWe take advantage of recent developments in sample holders for transmission electron microscopy that allow catalysts to be confined between two, thin nitride membrane supports that are separated by a narrow gap, and that allow continuous flow of liquid or gas through the system. We exploit the simplicity of this system in such a way as to allow utilization in both synchrotron x-ray beamlines and transmission electron microscopes. We have chosen a simple, model catalyst reaction for the demonstration phase of this work, the catalyzed conversion of ethylene to ethane, though the use of Pd/SiO2 and Pt/SiOnot;2 heterogenous catalysts. This reaction occurs at room temperature, thereby greatly simplifying the initial experimentation. We demonstrate the ability to measure reactive products in this system, and demonstrate that the measurements made in each technique are from the same “working” catalytic system. The combination of measurement approaches allows us to directly correlate “ensemble-average” properties (such as can be obtained with x-ray absorption and Raman approaches) with measurements of individual particles, at the atomic scale. Extension to high-temperature experimentation will be reported, thereby demonstrating the extension of this approach to the full class of catalytic systems. We will describe how this technique will be improved with the presence of ‘first light&’ at the new National Synchrotron Light Source - II at Brookhaven National Laboratory, a third generation light source with dedicated beamlines for micro- and nano-fcoused imaging and spectroscopy.References:#8232; Research carried out at the Center for Functional Nanomaterials, Brookhaven National Laboratory, which is supported by the U.S. Department of Energy, Office of Basic Energy Sciences, under Contract No. DE-AC02-98CH10886. Y.L and A.F.F acknowledge additional support through the Synchrotron Catalysis Consortium, U.S. Department of Energy, Office of Basic Energy Sciences, under Contract No. DE-FG02-03ER15476.
The ability to tune the size, composition, shape, and surface properties of nanoparticles is important for achieving high performance of nanocatalysts in energy storage and conversion. The development of this ability requires understanding of the detailed structural evolution in the actual catalyst treatments and catalytic reaction processes. This report describes recent findings of an in-situ high-energy x-ray diffraction (HE-XRD) study of Pt-based binary and ternary alloy nanoparticles in catalytic oxidation reaction of carbon monoxide. Synchrotron x-ray sources were used. An intriguing trend of catalytic activity of the catalysts for CO oxidation was revealed, exhibiting Ternary > Binary > Pt. The HE-XRD coupled to atomic pair distribution function analysis (PDFs) and reverse Monte Carlo simulation were used for the detailed structural characterization. The in-situ HE-XRD/PDFs monitoring of the structural evolution of the nanoalloys in the oxidative - reductive thermochemical treatment revealed an intriguing lattice expansion and shrinking characteristics, which depends on the chemical nature composition of a second or third metal added in the Pt-nanoalloy. The 3D modeling of the data provided useful information for assessing the chemically disordering or ordering or metal-enrichment behavior under different thermochemical conditions.
In-situ X-ray Absorption Fine Structure (XAFS) combined with Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS) experiments will be carried out to determine the structural changes of gold on ceria (Au/CeO2) catalyst under “transient” conditions for the water-gas shift (WGS) reaction. The oxidation of gold (Au(0),Au(I) or Au(III)) will be traced by XANES (Au L-III edge, 11.9 KeV) under fluorescence mode. The chemical bonding between Au and CO (e.g. Au0-CO or Au+-CO) on the oxide surface will be monitored by DRIFTS. The time-scale for each technique will be less than 3-4 min for XAFS and less than 1 min for DRIFTS, respectively. The simultaneous XAFS/DRIFTS measurements will provide the fingerprints on gold chemistry. The related “transient” conditions, realized by the use of multi-position switching valve, will build the relationship between the eletronic structure of low-concentration (1 at.%) active metal and the surface interaction with reacting molecules. Meanwhile, the gold catalysts under "transient" conditions will be governed by the chemical reaction only, instead of the diffusion process (mass transfer limination) under "steady-state" conditions. The tested gold catalyst is highly homogenous and well dispersed on the related oxide matrix, which guarantees the specific measuring areas by XAFS (below the surface of sample powders) and DRIFTS (the surface of sample powders) stand for the whole tested catalysts. Therefore, we are expecting that the current combined surface (DRIFTS) and bulk (XAFS) characterizations can be used to give a full scheme on the water-gas shift reaction mechanism in gold-ceria system.
The characterization methods available at today&’s synchrotron light sources are ideally suited to unravel the complexity of a practical working catalyst. This will be illustrated using examples from our work using a combination of synchrotron techniques including: X-ray micro- and nano-tomography, and in situ XAFS combined with density functional theory (DFT) and DFT/MD calculations. The use of in situ XAFS is a powerful catalyst characterization technique as it provides detailed element-specific atomic-level structural and chemical information of the active catalyst. Often this information cannot be obtained by any other method. We have developed and implemented the appropriate equipment to allow these in situ studies to be performed. This equipment ranges from a plug flow reactor that operates at high pressure, to equipment that allows rapid collection of XAFS data from multiple samples simultaneously. Examples of our recent work will be presented. Each example will highlight a different aspect of the use of in situ XAFS in an industrial research environment. These examples will include mirco- and nano-characterization of an FCC catalyst, in situ sulfidation of experimental hydroprocessing catalysts, the use of ligand XAFS as a quick screening method, and operando XAFS of rhenium-based catalysts.
There exists a current necessity in real time in situ (photo-) electron spectroscopy and microscopy under ambient pressure to study the processes taking place at solid-liquid-gas interfaces relevant to energy harvesting/storage, sensing, biomedical applications and etc. To address these needs, advanced differentially pumped electron optics for the electron energy analyzer has been implemented more than a decade ago. In our work, we propose to use quasi-2D materials such as graphene and its derivatives to design electron transparent but molecularly impenetrable windows, which separate UHV environment of the analyser(s) from the sample immersed in gas or liquid environment under ambient pressure. Based on unique combination of graphene&’s electron transparency, mechanical strength and its gas impermeability coupled with well developed graphene transfer protocols, we demonstrate the capability to perform XPS and electron microscopy studies of the processes taking place at liquid-solid interface through graphene-based membranes. In addition, we report on the development and tests of the sample platform that is compatible with standard XPS setups and does not require microsroscopy to probe liquid samples.
Soft-landed, size and composition selected subnanometer Ag clusters are active for the selective partial oxidation of propylene at relatively low temperatures. Activity and selectivity for the creation of propylene oxide vs. acrolein is found to be size and support dependent, determined through the investigation of three cluster sizes between 3 and 20 atoms and three supports (Al2O3, TiO2, and ZnO). Temperature programmed reactivity (TPRx) was performed with in situ synchrotron X-ray characterization, Grazing Incidence Small Angle X-ray Scattering (GISAXS) and X-ray Absorption Spectroscopy (XAS), to determine structural morphology and oxidation state during catalytic activity. The oxidation state of the Agn clusters (XAS) varies significantly due to size and support, the largest clusters exhibit entirely different oxidation state due to the support on which they have been soft-landed. At higher temperatures, changes in size and assembly are observed through GISAXS with marked dependence on support. The aggregates show distinct properties and activity due to being formed from different cluster building blocks and on different supports. Utilizing the presented method of catalyst synthesis and in situ characterization, it is feasible to investigate single active sites without the convolution that occurs in many studies from a range of particles sizes and active sites being present as well as study the aggregates that form at higher temperature and present unique reactivity.References:1) Y. Lei, F. Mehmood, S. Lee, J. P. Greeley, B. Lee, S. Seifert, R. E. Winans, J. W. Elam, R. J. Meyer, P. C. Redfern, et al., Science 328, 224-228 (2010)2) S. Lee, B. Lee, S. Seifert, S. Vajda and R. E. Winans, Nucl. Instr. and Meth. A, 649. 200-203 (2011)3) L. M. Molina, S. Lee, K. Sell, G. Barcaro, A. Fortunelli, B. Lee, S. Seifert, R. E. Winans, J. W. Elam, M. J. Pellin, et al., Catal. Today 160, 116-130 (2011)4) S. Vajda, S. Lee, K. Sell, I. Barke, A. Kleibert, V. von Oeynhausen, K.-H. Meiwes-Broer, A. F. Rodriguez, J. W. Elam, M. J. Pellin, et al., J. Chem. Phys. 131, 121104 (2009)
Chemical, solar, and electrochemical energy conversion processes rely on a variety of materials functionalities which include catalysis, light harvesting and charge/mass transfer. Exposing materials to combinations of gas or liquid environments, photon fluxes and electrical biasing may result in surface restructuring, localized or interfacial phase changes or even complete phase transformation. Advances in in situ environmental transmission electron microscopy (ETEM) allow materials to be observed under a wide range of energy relevant stimuli including temperature, gas and liquid environments, light and electrochemical bias. Coupling these in situ approaches with aberration correction and monochromation promises to revolutionize our ability to characterize the local structure and electronic bonding of materials in their working state. Moreover simultaneous measurement of structure and function leads to the so-called operando techniques which attempt to strongly correlate functionality with the active structures.We are developing a variety of in situ and operando techniques on FEI Tecnai and Titan ETEM platforms targeted at elucidating structure-property relations for materials relevant to catalysis, photocatalysis and solid oxide fuel cell applications. We have recently employed electron energy-loss spectroscopy and mass spectrometry to detect gas phase catalytic products directly inside the ETEM while performing atomic resolution image . This provides an operando approach to catalyst characterization in which catalyst structure can be directly correlated with in situ measurements of catalytic activity. By installing a light source in the ETEM we have been able to investigate changes taking place in photocatalysts during vapor phase water splitting [2, 3]. We are currently extending this approach using liquid cells. A recently delivered NION UltraSTEM has delivered energy resolution below 20 meV in electron energy-loss spectroscopy. This provides additional capability to probe electronic structure including bandgap mapping, surface plasmon resonances and adsorbate structures.  Chenna S., and P.A. Crozier, (2012) ACS Catalysis 2: 2395-2402. Miller, B. K., Crozier, P. A. (2013), Microscopy and Microanalysis, 19 461-469. Zhang, L. X., Miller, B. K., Crozier, P. A. (2013), Nano Letter, 13 679-684. The support from the National Science Foundation (NSF-CBET 1134464), US Department of Energy (DE-SC0004954) and the use of TEMs at the John M. Cowley Center for High Resolution Microscopy at Arizona State University are gratefully acknowledged.
Recent progress made in transmission electron microscopy is beneficial for the study of heterogeneous catalysts used in energy and environmental technologies. Advancements in electron optics have made transmission electron microscopy of catalysts available with atomic resolution and sensitivity, and parallel developments in gas cells enable in situ observations of catalysts during the exposure to reactive gas environments of up to atmospheric pressure levels and several hundred degrees Celsius. It is desirable to take advantage of such emerging instrumentation and imaging methodologies to uncover the dynamic behavior of heterogeneous catalysts and to improve the understanding of structure-sensitive catalytic functionality. In this presentation, I will outline work that exploits transmission electron microscopy to monitor catalysts in situ and discuss how such dynamical observations can be used to elucidate the role of gas-surface interactions on the working catalyst, e.g. (1-8).1. C.F. Kisielowski et al, Angew. Chemie Int. Ed. 49, 2708 (2010).2. L.P. Hansen, Q.M. Ramasse et al. Angew. Chemie. Int. Ed. 50, 10153 (2011).3. J.R. Jinschek, S. Helveg, Micron 43, 1156 (2012).4. J.F. Creemer et al, Ultramicroscopy 108, 993 (2008).5. S.B. Vendelbo et al, Ultramicroscopy, in press (2013).6. S.B Simonsen et al, J.Am.Chem.Soc. 132, 7968 (2010); J. Catal. 281, 147 (2011).7. S. Saadi et al, J.Phys Chem. C 114, 11221 (2010).8. Z. Peng et al. J. Catal. 286, 22 (2012).
Silver thin films are used as a functional layer in many applications such as low-emissivity and solar control coatings on glass for insulating windows, as well as transparent conducting electrodes for OLEDs and PV. For these applications, the conductivity of the film is critical; it is linked to the crystallinity and the grain size of silver layers which thickness ranges from 5 to 15nm. Such coatings often undergo thermal treatments up to 700°C aimed at toughening the glass substrate or improving the coating itself by promoting grain growth and curing point defects. This treatment can however dramatically damage the silver layer by inducing the formation of defects in the layer, such as holes or silver domes, decreasing both conductivity and light transmission of the coatings. Because of the extreme thinness of the films (less than 15 nm), the investigation of these phenomena requires in situ imaging at the nanoscale. In this study, grain growth and defects formation were observed in 15 nm-thick Ag films encapsulated with zinc oxide and silicon nitride using Transmission Electron Microscopy with in-situ heating from ambient temperature to 600°C. Significant grain growth was found to occur only from 400°C, and from 500°C holes in the silver layer started to form and grow, as well as thick silver domes formed by dewetting. Irradiation by the electron beam was also found to cause grain growth.
Atomic level understanding of metal surfaces under environmental conditions is critical for developing a structure-property relationship in a range of scientific disciplines, including materials science, catalysis or solid-state physics to name few examples. In this work, we will present atomic-level in-situ TEM observations of oxidation of Pd nanoparticles supported by model and high-surface-area substrates. The in-situ Transmission Electron Microscopy observations were performed with environmental FEI Titan 80-300 equipped with a CEOS Cs -image corrector operated at 80kV and 300kV. The imaging was performed in the presence of reactive gases of up to ~10 mbar, and the samples were heated with MEMS based AduroTM Protochips heating holder. The presentation will focus on the atomic-scale analysis of PdOx formation on Pd-nanoparticles (5-15nm in size) at temperatures 400-500 °C. We will discuss the mechanism of oxide formation and the structural nature of well-defined surface oxide. The detected surface oxide phase PdOx will be placed into perspective with the known Pd oxides. Lastly, we will discuss the electron beam effect and present examples where high dose electron beam is observed to cause structural transformation. This research is part of the Chemical Imaging Initiative at Pacific Northwest National Laboratory. The work was conducted in the William R. Wiley Environmental Molecular Sciences Laboratory (EMSL), a national scientific user facility sponsored by DOE&’s Office of Biological and Environmental Research and located at PNNL.
Lithium-ion batteries (LIBs) have been used as power sources for mobile devices such as cell phones and mobile PCs because of their large energy densities. In order to enhance LIB performance, it is very important to understand the electrode/electrolyte interface reactions because these reactions greatly affect the cyclability and power density of LIB. However, the mechanisms of such interface reactions have not yet been fully understood due to the difficulty of their direct observation for the reactions at nanoscale. Our group has directly observed the interface reactions of a thin-film model electrode of LiCoO2 by in-situ total-reflection fluorescence X-ray absorption spectroscopy (in-situ TRF-XAS) [1-3]. LiFePO4 shows higher cyclability in terms of capacity during the charge/discharge process than LiCoO2. A higher degree of reversibility of the electronic states at the surface of LiFePO4 is expected during the charge/discharge process. In this work, we have investigated the reversibility of the surface of a LiFePO4 thin-film electrode by using in-situ TRF-XAS.Cyclic voltammogram of the LiFePO4 thin-film shows a couple of anodic and cathodic peaks, which are characteristic of LiFePO4, were observed at 3.47 and 3.37 V, respectively. During the charge/discharge process, in-situ TRF-XAS were measured by setting the sample angle (0.13°) to detect fluorescence X-ray from the surface region (about 3 nm). After electrolyte, the Fe-K edge XANES spectrum of LiFePO4 did not shift. This result indicates that the surface does not react with the electrolyte. In the case of LiCoO2, Co3+ on the surface is reduced by electrolyte soaking. The difference between the surface XANES spectra of LiFePO4 and LiCoO2 indicates that LiFePO4 surface is more stable than LiCoO2 surface in a reduction atmosphere. In the charge process, the Fe-K edge XANES spectra of LiFePO4 surface exhibited a shift towards higher energy region thereby indicating that the Fe in the LiFePO4 surface was oxidized. When the discharge was proceeded, the XANES spectra shifted towards the lower energy region thereby indicating that the Fe in the LiFePO4 surface was reduced. The XANES spectra before and after the charge/discharge process were well reversed ; this reversal was not observed for LiCoO2. This result indicates that the surface of LiFePO4 is more stable than LiCoO2. References1) D. Takamatsu, Y. Koyama, Y. Orikasa, S. Mori, T. Nakatsutsumi, T. Hirano, H. Tanida, H. Arai, Y. Uchimoto, Z. Ogumi, Angew. Chem. Int. Ed., 2012, 51, 11597 - 116012) D. Takamatsu, S. Mori, Y. Orikasa, T. Nakatsutsumi, Y. Koyama, H. Tanida, H. Arai, Y. Uchimoto, Z. Ogumi, J. Electrochem. Soc., 2013, 160, A3054 - A30603) D. Takamatsu, T. Nakatsutsumi, S. Mori, Y. Orikasa, M. Mogi, H. Yamashige, K. Sato, T. Fujimoto, Y. Takamashi, H. Murayama, M. Oishi, H. Tanida, T. Uruga, H. Arai, Y. Uchimoto, Z. Ogumi, J. Phys. Chem. Lett, 2011, 2, 2511 - 2514
The rate dependency of electrochemical reactions in Li2MnO3 cathode material was investigated by X-ray absorption spectroscopy. It is well known that during activation (i.e. first charge), Li extraction occurs with the concurrent removal of oxygen, giving rise to the formation of a layered MnO2-type structure. However, the irreversible oxygen release from the material is a sluggish process and observed to occur at a slower activation rate (C/50). At a faster activation rate (~C/10), oxygen anions appears to undergo partial oxidation without their significant removal from the material. Electrolyte oxidation, on the other hand, also contributes to the observed charge capacity above 4.5 V. Protons thus generated as a result of electrolyte oxidation displace Li in the interslab region. The presence of protons in the interslab region shears the oxygen layers due to strong O-H-O bonding, altering their stacking sequence from O3-type to P3-type. During discharge, Li re-insertion occurs by exchanging already present protons and reverts the stacking sequence of oxygen layers from P3-type back to the original O3-type.The re-lithiated structure closely resembles that of the parent Li2MnO3, except that it contains less Li and O. Mn4+ remains electrochemically inactive at all times. It is observed that a certain amount of oxygen is released from the material during activation in order to facilitate the structural flip-over between O3-type and P3-type during subsequent cycles. A small amount of oxygen removed at a faster activation rate does not accommodate these structural changes and leads to the poor electrochemical performance of the material during subsequent cycles.
A full understanding of the operation of a battery and supercapacitor requires that we utilize methods that allow devices or materials to be probed while they are operating (i.e., in-situ). This allows, for example, the transformations of the various cell components to be followed under realistic conditions without having to take apart the cell. To this end, the application of new in and ex-situ Nuclear Magnetic Resonance (NMR) and magnetic resonance imaging (MRI) approaches to correlate structure and dynamics with function in lithium-ion and lithium air batteries and supercapacitors will be described. The in-situ approach allows processes to be captured, which are very difficult to detect directly by ex-situ methods. For example, we can detect side reactions involving the electrolyte and the electrode materials, sorption processes at the electrolyte-electrode interface, and processes that occur during extremely fast charging and discharging. Ex-situ NMR investigations allow more detailed structural studies to be performed to correlate local and long-range structure with performance in both batteries and fuel cell materials. This talk will describe the use of in situ NMR methods to probe local structural changes in lithium ion batteries and supercapacitors discussing our work on the anode material Si, manganese spinel cathodes, and Li dendrite formation in lithium metal batteries. Finally, the application of NMR and MRI to examine double layer formation in electrolytic double layer capacitors (supercapacitors) will be described.
Electrical transport in Si based rechargeable Li-ion batteries (LIBs) plays an important role for the lithiation processes. However, local structural changes of the Li-silicide (LixSi) formation  depending on initial Si conductivity are poorly investigated at realistic cycling conditions, which is of high importance not only for realising fast charge/discharge, but also for understanding the phase formation dependence on the conductivity. Here we investigated the lithiation of P-doped Si nanowires (SiNWs) as a model system by 7Li in situ NMR spectroscopy , comparing their structural changes on (de)lithiation with those of intrinsic SiNWs. The work is accompanied with systematic electrochemical, ex situ XRD, and MAS NMR studies.1 Huggins, R. A. Materials Science Principles Related to Alloys of Potential Use in Rechargeable Lithium Cells. J Power Sources. 26, 109-120, (1989).2 Key, B. et al. Real-Time NMR Investigations of Structural Changes in Silicon Electrodes for Lithium-Ion Batteries. J. Am. Chem. Soc. 131, 9239-9249, (2009).
We have recently proposed an approach using both Mossbauer spectroscopy and magnetic measurements to follow the conversion of anode materials upon lithiation/ delithiation processes. These methods are very general and have been applied to the study of numerous systems involving a ferromagnetic transition metal (Fe, Co or Ni) and a Mössbauer active element (Fe, Sn, Sb), namely the alloys FeP,  FeP2, FeP4, CoSn2, Ni3Sn4, FeSn2, FeSb2, NiSb2 .Combining Mössbauer spectroscopy and magnetic measurements is an interesting approach to the analysis of electrode materials if different magnetic phases are involved (antiferromagnetic, ferromagnetic, paramagnetic). Their detection is possible even in cases where Mössbauer spectroscopy fails to reveal them unambiguously due to overlap with absorption lines of other phases.In this communication, we shall report on the development of the first in-situ magnetic measurements during battery cycling and explore the insights brought through this unique methodology. S. Boyanov, M. Womes, L. Monconduit, D. Zitoun Chem. Mater. 2009, 21 (15), 3684 S. Boyanov, D. Zitoun, M. Menetrier, J.C. Jumas, M. Womes, L. Monconduit J. Phys. Chem. C 2009, 113 (51), 21441 S. Naille, R. Dedryvère, D. Zitoun, P.E. Lippens J. Power Sources, 2009, 189, 806. C. Villevieille, C.M. Ionica-Bousquet, B. Fraisse, D. Zitoun, M. Womes, J.C. Jumas, L. Monconduit Solid State Ion. 2010, http://dx.doi.org/10.1016/j.ssi.2010.04.029
Lithium ion batteries must have higher volumetric and gravimetric energy densities to be successfully deployed into many emerging applications, such as transportation. Silicon-based anodes for lithium-ion batteries are promising candidates for increasing capacity and energy density because they possess a maximum capacity over ten times that of graphite, the current standard anode material. However, dramatic volume changes (up to 400%) during (de)lithiation limit the durability and cycle life of these anode materials. Nanostructured anodes represent one possible route for reversibly accommodating large volume changes, but their design is hindered by a lack of experimentally measured quantitative data describing these strains. Additionally, the air sensitivity and amorphous nature of lithium insertion and extraction process in silicon anodes has greatly hindered the measurement of strain in operando. As such, the evolution of strain and volume change in these anodes is poorly understood and design of new nanostructures to accommodate these strains reversibly is still a qualitative process.Here, we examined a bicontinuous anode consisting of a nickel inverse opal scaffold 10 um in height coated with a 50 nm thick silicon film, which was found to reversibly accommodate the mismatch strains due to (de)lithiation over a high number of cycles. Using synchrotron based X-ray diffraction techniques at the Advanced Photon Source, lattice strains in the nickel scaffold were measured in operando in order to deduce the stresses and strains present in the silicon coating. Since the silicon film forms a strong bond with the nickel scaffold, the elastic strains measured in the nickel are similar to those present in the silicon, and thus the stress and strain state in the silicon can be indirectly measured. These nickel/silicon inverse opal anodes were cycled with different voltage windows and (dis)charge rates in order to explore the sensitivity of strain evolution to changes in the electrochemical conditions associated with cycling. Strains measured in the nickel scaffold were directly correlated with the electrochemical cycling of the anode. The results indicate that at maximum lithiation, the strains measured in the nickel scaffold approach the yield point of the nickel and suggest incremental plastic deformation occurring during each cycle coupled with a high stress state in the elastic silicon.
The manganese olivine LiMnPO4 has substantially higher energy density as battery cathode than its iron counterpart, due to a higher voltage plateau at ~4.1 V vs. Li/Li+ compared to 3.45 V for LiFePO4. However, LiMnPO4 exhibits slow charge-discharge kinetics even at nanoscale particle size, which has prevented its commercial use. Interestingly, with even a modest Fe addition, nanoscale LiMnyFe1-yPO4 exhibits amongst the highest rate capabilities of all the olivines. It has been suggested that this is due to the existence of an intermediate solid solution (here denoted LxMFP) that reduces the misfit strain by breaking the single phase transition (observed for LFP) into two stages, first a transition of MFP to an intermediate phase LxMFP, then between LxMFP and LMFP. However, at this stage there is still no clear conclusion as to whether the transformations are two-phase first-order reactions or involve formation of solid solutions, which may be metastable. Significant discrepancies are found in the literature between the (x,y)-compositional phase diagrams for LiMnyFe1-yPO4 determined computationally versus experimentally (by chemical delithiation of large particle powders). Furthermore, previous studies have not been carried out in-situ under dynamic electrochemical conditions. The phase evolution dependency on particle size has also not been investigated. This is of importance as the particle size is known to alter the Li-miscibility gap for LFP significantly.Here we present a systematic screening of the electrochemical driven phase transitions in a series of LiMnyFe1-yPO4 (y = 0.1, 0.2, 0.4, 0.6 and 0.8) powders with particle size of ~50 and 250 nm (based on BET surface area) during charge and discharge at different C-rates as well as selected over- and undervoltages. The screening is carried out using in situ Synchrotron Radiation Powder X-ray diffraction (SR-PXD) and Pair Distribution Function (PDF) analysis. The high quality data allows for Rietveld refinement (>1000 PXD patterns have been refined for this study) and thereby detailed analysis of cell parameters providing new information about the volume misfits during the formation of non-equilibrium solid solution as well as the structural evolution as a function of both Li- and Mn-content in LMFP olivine phases. These findings will be addressed in the presentation.Furthermore, from the in situ SR-PXD data a series of (x,y)-compositional phase diagrams have been constructed. These illustrate the phase evolution as a function of Mn- and Li-content, as well as elucidate the effects of different electrochemical driving forces and particle sizes. Interestingly, they reveal a strong hysteresis between charge and discharge giving rise to a reduced Li-miscibility gap at the Fe2+/Fe3+ plateau for materials of lower Mn-content. The origin of the hysteresis as well as the study of local structure using PDF analysis will be discussed in this talk.
Lithium iron phosphate is a lithium ion battery positive electrode material with widespread use, as well as unusually complex redox chemistry. E.g. it has been unclear for a long time, why lithium iron phosphate can be delithiated electrochemically and chemically with some oxidants, while ambient atmosphere oxidizes it by formation of iron oxides and mixed hydroxides. Here we report on the discovery of a direct gas-solid delithation reaction: lithium iron phosphate reacts with nitrogen dioxide gas to form lithium nitrate and iron phosphate. The absence of a solvent is noteworthy, as lithium accumulates at the particle surface without interfering with the delithiation reaction. Moreover, the reaction shows remarkably fast kinetics. In situ X-ray diffraction, corroborated by elemental analysis, shows for the first time that lithium iron phosphate bulk diffusion supports nearly complete delithiation / charging of carbon coated lithium iron phosphate micro powder at ambient temperature at very high rate.
Zinc is an attractive material for energy storage applications because it is both gravimetrically and volumetrically energy dense. For rechargeable battery systems, however, the zinc electrode is typically the limiting electrode due to its propensity to form detrimental morphologies (e.g. dendrites). This research aims to understand the deposition behavior of zinc within an ionic liquid electrolyte and to link the initial growth behavior during electrodeposition to the formation of macroscopic morphologies. In-situ analyses of the zinc deposition behavior were conducted using atomic force microscopy (AFM) and ultra-small-angle X-ray scattering (USAXS). In-situ AFM analysis showed that zinc deposition within the ionic liquid electrolyte exhibited a compact and dense morphology composed of hexagonal platelets. Under certain electrochemical conditions the interface evolved to a steady state condition where the root mean square roughness remained constant as new zinc was deposited. In contrast, the roughness grows steadily with thickness in traditional alkaline electrolytes. This finding has implications for battery applications because a stable interface with low RMS roughness has a lower probability of initiating dendritic growth. The growth behavior observed by AFM was confirmed by in-situ USAXS. In addition, the in-situ USAXS analysis showed that the zinc deposition had a hierarchical morphology composed of highly textured aggregates of ~8 nm thick hexagonal platelets. The results show that the in-situ USAXS and AFM analysis techniques are complementary allowing one to gain further insight into the electrochemical growth behavior of the zinc and to help understand how to avoid the formation of detrimental morphologies for energy storage applications.Portions of this work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. This project was supported by Lab Directed Research and Development Grant 12-LW-030.
In the last 20 years in situ techniques proved to be exceptionally useful tools to understand electrode materials for Li-ion batteries. Indeed, they allow observing the mechanisms of lithium insertion and extraction in real time, i.e. operando during the cycling of the battery. This is a great advantage because the phenomena involved are dynamical in nature and therefore their comprehension is limited if they are only looked at through a series of snapshots, such as those obtained from ex-situ studies. X-ray diffraction, as well as other techniques like Raman spectroscopy, XANES, NMR, Mössbauer etc. have widened their application range thanks to in-situ measurements, always providing useful contributions.In-situ neutron diffraction (ND) knew a slower development, due to the intrinsic difficulties it held (rare neutron sources with sufficient flux, strong background from conventional hydrogenated electrolytes, big amounts of electrode material required for ND that make electrochemistry challenging). Despite these issues, the field evolved pushed by the promise of neutrons&’ high sensitivity to lithium. Many electrochemical cells&’ designs have been proposed, often good in some aspect but deceiving in others. Some reports even showed the possibility to exploit ND to study whole commercial batteries, although the result is a mixture of many phases coming from all the components of the battery, thus not permitting reliable refinements.We have designed an electrochemical cell able to combine, for the first time, good electrochemical properties (cycling of more than 200 mg of active material with small polarization) with the ability to collect neutron diffraction patterns operando, with good statistics and no other Bragg peaks than those of the electrode material of interest. To allow this, the cell was manufactured a TiZr alloy, almost completely neutron-transparent. These made the obtained ND patterns of sufficient quality for detailed structural determinations. First case studies, investigated at the D20 diffractometer of ILL (Grenoble), have been:- the olivine LiFePO4, where a 2 phases reaction is clearly observed upon lithium extraction. Cell parameters, atomic positions and weight fractions of the two phases have been successfully refined.- the overstoichiometric spinel Li1.1Mn1.9O4, showing complex processes upon lithium extraction. Cell parameter, oxygen coordinates and lithium content have been refined.Newer and more challenging materials are currently investigated, such as Na3V2(PO4)2F3 and LiVPO4O above all, and the results are under study, while the use of our cell with many other materials is planned in the future.
This presentation will discuss the difficulties in interrogating the nanoscale behavior of electrochemical energy storage systems while preserving complex material interactions that may be a function of millimeter to meter scale geometry as well as caustic/acidic environment. The dichotomy of in situ and in operando is not arbitrary: in situ systems are willing to sacrifice the representation of the device for resolution, in operando systems are not. We will use the hoary example of the Zn MnO2 primary battery (e.g. a “AA” flashlight battery) to provide examples of how in situ TEM, TXM and microdiffraction complement in operando EDXRD studies. By running both sets of experiments, structural and interfacial insights approaching the atomic scale are obtained and can be rectified to true battery scale phenomena.
Advances in energy storage materials have taken on expanded significance due to the needed ability to store electricity for many applications. The relatively recent exploration of phosphate based materials has shown the potential for increased cathode stability, with a notable example being lithium iron phosphate, LiFePO4. Full implementation of the material demanded that the the inherently low electrical conductivity of the phosphate based materials be addressed. Even though the voltage and energy density of phosphate based materials may be lower than oxide materials when used for lithium based systems, the chemical and electrochemical stability of the phosphate based materials may be a significant asset for some applications. Bimetallic cathode materials are of interest and have been employed in batteries partly because they can provide multiple electron reduction per formula unit. A notable example is the silver vanadium oxide (Ag2V4O11) system used in biomedical batteries that power implantable cardiac defibrillators (ICDs). Lithium batteries using Ag2V4O11 cathodes provide the opportunity for multiple electron reduction per Ag2V4O11 formula unit and in the case of vanadium, per metal center. An additional beneficial aspect of silver vanadium oxide (Ag2V4O11) as a cathode material is its ability to form in-situ silver metal nanoparticles upon reduction of Ag+ to Ag0, contributing to the high electrical conductivity of partially discharged silver vanadium oxide. We have embarked on the rational study of a new family of cathode materials for lithium batteries, namely silver vanadium phosphorous oxides (AgwVxPyOz), with the broad goal of combining the thermal stability of lithium iron phosphate with the enhanced electrical conductivity of partially reduced silver vanadium oxide. This would enabling the use of phosphate based materials directly without the need for nanosizing or carbon coating. Three members of the AgwVxPyOz family of compounds have been explored, Ag2VO2PO4, Ag0.48VOPO4 and Ag2VP2O8. Discharge behavior as well as mechanistic insights on the reduction of these materials gained from in-situ as well as ex-situ techniques will be presented.
Incisive characterization tools can facilitate the material breakthrough for building better batteries. Various in situ techniques have been developed and highly appreciated in battery research, However, soft X-ray spectroscopy, as one of the most sensitive probes of electronic states, has so far been limited to ex situ experiments for lithium-ion batteries (LIBs). Here, we realize in situ and operando soft X-ray absorption spectroscopy of LIB cathodes. By virtue of the elemental and surface sensitivity of soft X-ray, we found distinct lithium-ion and electron dynamics in Li(Co1/3Ni1/3Mn1/3)O2 and LiFePO4 cathodes with standard polymer electrolyte. The contrast and relaxation effect in LiFePO4 cathodes are attributed to phase transformation mechanism, and the mesoscale morphology of the electrodes. Our intriguing findings demonstrate the feasibility and power of in situ soft X-ray spectroscopy for studying batteries materials under realistic reaction conditions.
Many Sn-based materials demonstrate superior electrochemical performance to that of traditional graphite anodes in lithium-ion batteries. In addition to the high capacity inherited from the pure metallic Sn, Sn-based inter-metallic structures and composites greatly mitigate the volumetric expansion upon lithiation, a practical problem present in pure Sn that prevents its application as the anode materials. Recently, Sony successfully commercialized the Nexelion battery, the anode of which is based on nanostructured SnCo embedded in carbon. However, it is very challenging to understand the reaction mechanism of lithiation/delithiation, for which the study by conventional laboratory techniques is inadequate due to nanoscale size (about 5 nm) and amorphous origins of these anode materials. Here we report a study of Sn-based anode materials by applying in-situ synchrotron x-ray absorption spectroscopic methods (XAS). XAS is a powerful technique that provides element specific information on the electronic and structural properties of materials through its two respective modifications: x-ray absorption near edge structure (XANES) and extended x-ray absorption fine structure (EXAFS). As a local probe, XAS can be used to study disordered structures, which is a significant advantage over crystallographic methods and is well-suited for this work. In this study, in addition to visual inspection of XANES and EXAFS data, the XAS analysis was further carried out by fitting the theoretical signals to the EXAFS experimental data, to better illustrate the structural evolution of the anode material during electrochemical process. High reversibility in local and electronic structure was demonstrated by both Co and Sn K-edge XAS for the commercial SnCo alloy anode material during lithiation/delithiation process, which provides an insightful evidence for the good rechargability of this anode material. We have also observed the formation of segregated phase of metallic Co toward the end of lithium insertion, consistent with the reaction mechanism of gradual conversion upon lithiation of this SnCo alloy-based anode. The XAS studies were also performed on more crystalline SnCo alloy and novel SnyFe-based composites. Brief comparative analysis of these systems will be presented. This research is supported by the Northeastern Center for Chemical Energy Storage, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Award Number DESC001294, and by NYSERDA. XAS experiments were performed at National Synchrotron Light Source of Brookhaven National Laboratory and the use of NSLS of BNL is supported by the U.S. Department of Energy, Office of Science, Basic Energy Sciences, under Contract No. DE-AC02-98CH10886.
Degradation mechanisms within lithium ion battery porous electrodes remain poorly understood yet critically linked to battery performance and lifetime. We present in operando, high-resolution, and large-volume synchrotron x-ray tomographic microscopy for 3D visualization of porous electrodes during electrochemical operation. As a model system, we study tin (II) oxide (SnO), which undergoes a conversion reaction and subsequent alloying with lithium. Visualization and quantification of phase transformations within a single particle are possible due to changes in attenuation coefficient, which is intimately linked to the composition and mass density of a material. Tomography also allows quantification of the related volume expansion at both the single particle and electrode scales. Volume expansion is observed to induce crack formation and growth in the active particles and permanently distort the polymer binder and carbon black matrix. This simultaneous quantification of chemical and mechanical effects over multiple length scales highlights the potential of in operando tomography for the rational development of next generation battery materials.
In-situ X-ray diffraction studies on lithium-ion battery materials typically involve transmission geometry either in “coffee bag” pouch cells or in specially constructed cells that do not reflect the geometries typically used in battery research. A new cell type has been developed and constructed mainly from standard compression fittings, similar to the designs commonly used to make research cells for electrochemical testing in our and other laboratories. The major modification is an aluminium foil window to allow access to one of the electrodes by a synchrotron X-ray beam. Apart from the simplicity of the cell design, a key advantage is that the curved top surface allows the beam incident angle to be adjusted to vary the depth of electrode that is probed so that any heterogeneous processes such as a phase front moving through the electrode could be observed experimentally.We have used these cells on beam line I07 at the Diamond synchrotron to examine in-situ phase behaviour in lithium iron phosphate and hence directly observed the effects of electrolyte depletion. We have also carried out a phase mapping exercise on a series of Li(Fe,Mn)PO4 solid solutions to examine changes in their phase composition and lattice parameters during charge and discharge processes where one- or two-phase behaviour is observed in the electrochemical data.
This presentation will deal with the development of operando methods for the study and characterization of fuel cell and battery materials. The presentation will begin with a brief overview of the methods employed. Particular emphasis will be placed on the use of X-ray based methods including X-ray diffraction (XRD) and X-ray absorption spectroscopy (XAS), transmission electron microscopy (TEM) under active potential control, Fourier Transform Infra Red (FTIR) spectroscopy, confocal Raman and differential electrochemical mass spectrometry (DEMS). The utility of these methods will be illustrated by selected examples including conversion reactions of Mn3O4 as anode material for lithium ion batteries (LIBs), lithiation/de-lithiation of LiFePO4 via TEM, spectroscopic studies of Li/S batteries and the use of DEMS to characterize electrolyte systems for LIBs. The presentation will conclude with an assessment of future directions.
The processes that take place inside commercially relevant battery cells are deeply buried, yet quantifying their extent and location during cell use is of great interest for improving cell performance and cycle life. Energy dispersive x-ray diffraction (ED-XRD) using high energy polychromatic synchrotron radiation is one of the few techniques that can probe inside such cells under operating conditions. GE&’s sodium metal halide DurathonTM batteries are particularly challenging to study due to their large dimensions, dense materials of construction and 300°C operating temperature. Yet ED-XRD is capable of characterizing the structural changes and electrochemistry with sub-millimeter spatial resolution and 1-2 minute temporal resolution. Herein we describe the optimization of the ED-XRD technique for studying deeply buried systems under extreme conditions, such as in-operando Durathon cells, and describe how the resulting data can be used to inform and validate cell-level finite-element electrochemical models. We will report on our progress towards integrating characterization and modeling tools to yield greater fidelity predictions that can compress the design cycle and speed time to market.
An ever-increasing development for advanced batteries has spurred an intense activity in search of proven, in-situ and non-destructive techniques for monitoring the electrochemical process and structural changes that occur inside working batteries. Here we demonstrate a technique based on high-energy X-ray Compton scattering. This presentation focuses on a commercial coin cell, and the intensity of Compton-scattered X-rays from the discharging cell has been monitored as a function of one-dimensional position inside the cell and discharging time. The position-time intensity map has captured the migration of lithium ions in the positive electrode and has revealed the change in position of the separator due to the volume expansion of the electrode. This is a critical step for further development.The experiment was performed at the BL08W beamline of SPring-8, Japan. The incident 115 keV X-ray beams with a size of 20mu;m (v)x500mu;m(h) were guided to the coin cell (CR2023) and the scattered X-rays from a local area inside the cell were collected with a Ge solid state detector at a scattering angle of 90 degrees. Placing a slit with a width of 500mu;m in front of the detector, the detection area at each position was 20mu;mx500mu;mx500mu;m. The intensity of Compton-scattered X-rays is proportional to the average electron density in the detection area . Therefore, the position profile line of the X-ray intensity reveals more detailed structures inside the cell than the X-ray transmission images, and the time profile line at a position in the active electrode shows intensity variation due to lithium migration. In this paper we will also present a future direction of this technique.This work was supported by the Development of Systems and Technology for Advanced Measurement and Analysis program under Japan Science and Technology Agency. J. M. Sharaf, Applied Radiation and Isotopes, 54 (2001) 801-809.
Earth-abundant iron fluoride (FeF3) is a representative conversion cathode material that can potentially deliver a much higher Li-storage capacity (712 mAh/g) compared to the current lithium cobalt oxide cathode (~140 mAh/g), because it can theoretically react with up to three lithium ions through electrochemical conversion reaction. Due to the significant structural and phase changes involved, despite the high capacities attainable in the first few cycles, fast capacity fading and large voltage hysteresis are commonly observed. Solving these fundamental challenges facing FeF3 (and other conversion cathode materials) requires a better understanding and control of the nucleation and growth of nanophases (Fe, LiF, and other Li-Fe-F ternary phases) to enable fast reaction kinetics and favorable interfacial contact. We have recently synthesized FeF3 nanowires (NWs) with rational control over their diameter for the first time. These NWs exhibit respectable electrochemical properties and provide a unique and convenient platform for fundamental studies. We will report our in situ transmission X-ray microscopy (TXM) and X-ray absorption near-edge structure absorption spectroscopy (XANES) measurements on FeF3 NW electrodes in operating battery coin cells to reveal the morphological and chemical changes upon battery cycling. New important insights into the conversion mechanism gleaned from these in situ TXM-XANES experiments and possible strategies to further improve the cycling performance of FeF3 conversion cathodes will be presented.
Olivine structure lithium iron phosphate (LiFePO4) shows a high power density. Understanding the mechanism of the phase transition can be of help in providing the origin of this fast charge-discharge ability. The material undergoes phase reactions between Li-rich phase(LFP) and Li-poor phase(FP). However, the LFP-FP phase transition model underlying battery operation has been the subject of debate for a decade. In this work, we conducted in situ time-resolved XRD and XAS measurements and studied the dynamic behavior of the LiFePO4/FePO4 phase transition. in situ time-resolved XRD measurements were performed on a diffractometer on BL46XU and BL28XU at SPring-8 (Hyogo, Japan), using lambda; = 0.9995 Å monochromated by a Si (111) double crystal in the transmittance mode at room temperature. The X-ray beam size was 0.5 × 0.5 mm2. The snapshot of diffraction patterns was recorded using a two-dimensional hybrid pixel array detector, PILATUS 100K, in the range of 2theta; = 18° to 21°. The XRD pattern was obtained with 0.5 s exposure time per shot. XAS measurements were performed on BL01B1 and BL28XU at SPring-8 (Hyogo, Japan). Fe K-edge XAS spectra were measured at room temperature in the transmission mode using two ion-chambers. The XAS spectra were acquired every 15 s during the charge reaction. We examined XRD peak change during the charge-discharge reaction with a rate of 10C and relaxation process after the cycles. Before the charge, a peak at 19.15° can be observed, which corresponds to diffraction from the (211) and (020) planes of LFP. The charge reaction causes the appearance of peaks at 19.50 and 19.87°, which reflect the (211) and (020) planes of the FP phase, respectively. In addition, an unexpected peak can be seen at 19.35° during the first discharge and the following charge-discharge reactions. The new peak reversibly forms and disappears in synchronization with the electrochemical cycling, and the new peak is located between the peaks of LFP and FP. These results suggest that the new peak is related to an olivine-type LixFePO4 phase with an intermediate composition. This study experimentally observes the phase transition through the metastable phase under nonequilibrium battery operation for the first time.
The (AO)(ABO3)n Ruddlesden-Popper (RP) phases where ABO3 perovskite layers are sandwiched between AO rock-salt layers, have been considered a potential candidate for solid-oxide fuel cell cathodes, oxygen separation membranes, and thermoelectrics. However, the synthesis of these phases has been challenging, especially for epitaxial thin films, owing to the multivalent nature of the transition metals, intergrowth defects, and variable oxygen stoichiometry. In order to understand the growth of layered oxide films and to synthesize higher order RP compounds, we employ in-situ surface x-ray diffraction (SXRD) during the initial layer-by-layer growth of SrTiO3 and LaNiO3 RP phases by oxide molecular beam epitaxy at the Advanced Photon Source. In both cases, the deposition sequence of SrO-SrO-TiO2 and LaO+-LaO+-NiO2- results in the formation of SrO-TiO2-SrO and LaO+-NiO2--LaO+ without SrO-SrO or LaO+-LaO+ rock-salt layers, which is essential for RP structure. By comparing the energies of different stacking sequences using density functional theory, we find the observed perovskite structure is more favorable than the rock-salt structure. Utilizing the oxide layer rearrangement behavior and following unconventional deposition sequence, we synthesize single crystalline, higher order Lan+1NinO3n+1 thin films on various substrates. The nickel valance state and lattice constant of La2NiO4 and La3Ni2O7 epitaxial films on (001)-oriented SrTiO3 is close to bulk values. The detailed growth dynamics of these new RP films will be presented, demonstrating the power of quantitative x-ray probes for understanding the process of thin film synthesis.
Rare earth based magnets provide the backbone for clean technology applications such as electric cars and wind powered generators. However, because of the limited availability and high cost of rare earth elements, which are expensive to mine and process, there is a growing interest in developing new magnetic materials without these rare earth elements. The rare earth free permanent magnet alternative should offer similar or enhanced magnet properties. Recently, our research team reported on the synthesis of mixed phase cobalt carbide nanoparticles which show room temperature coercivities greater than 3.1 kOe. However, in order to take great advantage of their magnetic performance, a fundamental understanding is required along with the need for the particles to be synthesized with an appropriate composition (Co2C/C3C) and structure at the nanoscale level. We believe that the carbide system, in its current design, has significant potential to be a breakthrough technology for permanent magnet applications. However, in order to fully understand this material, we need to investigate the formation mechanism and kinetics of nucleation and growth of both Co2C and Co3C nanoparticles for the fundamental studies.Here we show a quantitative study, through in-situ quick-X-ray Absorption Fine Structure Spectroscopy (QXAFS), the “real time” nucleation and growth mechanism of cobalt metal and carbide nanoparticle formation. We demonstrate how (i) the concentration of metal precursor and (ii) the concentration and power of the reductant affect on the nucleation and growth rates during the polyol synthesis. These observations are also corroborated by the general nucleation and growth theory.
Intense interest is focused on the growth science and behavior of epitaxial oxide thin films because of continuing discoveries of new interesting and important energy-related properties. The key to achieving desired functionality of oxide heterostructures is the ability to synthesize high-quality films with full control of factors such as composition, crystallographic orientation, surface termination, and strain state. Many of the most promising thin film synthesis techniques involve non-vacuum, high-temperature environmental conditions that are difficult or impossible to probe using standard spectroscopic or structural probes. However, the use of high-energy x-rays available at synchrotron sources such as the Advanced Photon Source (APS) provides an opportunity to obtain real-time atomic-level structural and chemical information during synthesis, and to characterize post-growth behavior in high temperature controlled gas environments. This presentation will describe results from recent in-situ x-ray studies of the growth behavior and properties of oxide heterostructures with polar surfaces. Heterostructures are being grown by either metal-organic chemical vapor deposition (MOCVD) or rf-magnetron sputtering, using facilities that we have built for in-situ x-ray studies at the APS. We are studying the effects of ferroelectric polarization on oxygen vacancy distributions in epitaxial (001)-oriented PbTiO3 (PTO) / LaGaO3 (LGO) heterostructures. LGO layers in those heterostructures have been grown using a new sputter deposition system mounted on a diffractometer. We have observed that LGO films grown on PTO in the 180° ferroelectric stripe phase exhibit diffuse x-ray intensity around LGO Bragg reflections, consistent with there being an ordered distribution of oxygen vacancies in the LGO that is influenced by the stripe phase of the underlying PTO film. Evidence for vacancy ordering is not observed in films grown on PTO films in the paraelectric phase. The possibility of controlling oxygen ion conductivity in such heterostructures will be discussed. Studies of the growth behavior and structure of LGO / MgO and LGO / SrO superlattices will also be described, focusing on the effects of MgO or SrO layer spacing on octahedral tilt behavior in LGO. Possible implications of the results on energy applications will be discussed.
Perovskite oxides play a crucial role in applications such as gas separation  and catalysis [2, 3]. However, the interaction of perovskite surfaces with the environment and how this influences and/or reflects their functionality remains largely unexplored. For low temperature hydrogen-oxygen fuel cells, in which H2O is a byproduct of the cathodic oxygen reduction reaction (ORR), the wetting of the catalyst layer can significantly affect the diffusion of the reactant O2 to the surface . Missing, however, are measures of the intrinsic wettability of catalyst surfaces, as well as a complimentary microscopic chemical understanding of how the interaction with H2O influences the reactivity. Ambient pressure X-ray photoelectron spectroscopy (APXPS) enables investigation of the chemical state of specific elements via the binding energy of ejected photoelectrons in equilibrium with an H2O-rich environment . By studying the surface chemistry of LaMO3 perovskites in a range of relative humidities, where M is a transition metal Cr-Ni, we provide a molecular picture of how wetting and oxygen catalysis occurs in an aqueous environment. References Y. Teraoka, H.-M. Zhang, S. Furukawa, N. Yamazoe, Chemistry Letters 14, 1743 (1985). D. B. Meadowcroft, Nature 226, 847 (1970). J. Suntivich et al., Nat Chem 3, 546 (2011). H. M. Yu, C. Ziegler, M. Oszcipok, M. Zobel, C. Hebling, Electrochimica Acta 51, 1199 (2006). M. Salmeron, R. Schlögl, Surface Science Reports 63, 169 (2008).
The concentration and mobility of oxygen vacancies is crucial for Oxygen Reduction Reaction (ORR) properties of Solid Oxide Fuel Cell cathodes. Recent report by Kim et al. demonstrates that static distribution of vacancies in oxygen-deficient lanthanum strontium cobaltite can be quantitatively characterized on a unit cell level by mapping local lattice perameters , similar to dilatometric experiments conducted in the bulk . The composition studied in  is remarkably beam resistant, however, in other compounds such as LaCoO3 (LCO) the appearance of ordered structures can be observed under the electron beam. This study is aimed to characterize this process and develop approaches for quantitative characterization of vacancy dynamics in situ. For this study we use 3x3 LaCoO3/SrTiO3 superlattices, which are examined by high angle annular dark field (HAADF) and annular bright field (ABF) STEM. At initial examination, the superlattices show little contrast associated with ordering, but continued beam exposure results in development of pronounced ordered structure. This process happens over several minutes, providing an excellent opportunity for a dynamic study. First lattice expansion takes place at some point in the central LCO layer, then it propagates in lateral direction. Simultaneously, lattice spacing in adjacent layers decreases, such that the average of the spacings in the entire 5 unit-cell LCO block stays the same, suggesting redistribution of vacancies under the beam rather than creation of new ones. Furthermore, image correlation studies imply that vacancy transport is highly localized, confined almost entirely to the unit cells exactly adjacent to the newly depleted layer. Simultaneous HAADF and ABF imaging shows gradual transformation of the central CoOx layer into brownmillerite-like structure with half of the oxygen sites missing. New data analysis methods to obtain quantitative kinetic parameters and characterize different ordering scenarios will be discussed. * Research supported by the U.S. Department of Energy (DOE), Basic Energy Sciences (BES), Division of Materials Sciences and Engineering, and through a user project supported by ORNL&’s Shared Research Equipment (ShaRE) User Program, which is also sponsored by DOE-BES.References Y.M. Kim et al., Nat. Mater. 11 888 (2012).  X. Chen et al., Chem. Mater. 17 4537 (2005).
Perovskite oxides have long been studied for use in electronic devices due to their novel electronic and magnetic effects. Ferroelectric perovskites such as BaTiO3 (BTO), Pb(Zr0.2Ti0.8)O3 (PZT) and BiFeO3 (BFO) show promise for use in memory storage devices due to their excellent power efficiency and speed. In order for perovskite oxides to be incorporated into modern device structures, the mechanisms behind ferroelectric switching in the presence of defects must be characterized. Defects have been shown to have a profound effect on the switching dynamics of ferroelectric perovskite films with various defects functioning as nucleation or pinning sites. While recent advances have been made in the study of domain wall-defect interactions, these studies are still in their infancy and must be further expanded in order to be understood.We use a biasing holder to apply DC voltage to the BTO, PZT and BFO thin films in the TEM. We perform a full ex-situ and in-situ characterization of defect densities and interactions with domains under an applied electric field in order to quantify the effects of defects on domain motion. As a result of these combinations of techniques, we are able to determine the effects of both line and point defects on the switching dynamics of ferroelectric domains.
Third generation nanocrystal-based photovoltaics exhibit low experimental vs. theoretical efficiencies (5 %, 65 % respectively); however, the reasoning as to why this is so remains predominantly unanswered. The methodology presented here takes a crucial step toward solving this problem with a characterization technique that provides a simplistic, yet informative visualization of the ability of the photoactive layer to separate and collect charge carriers. An improved understanding of the nanoscale function of these devices will not only lead to the optimization of current photovoltaic technology, but it will also assist in developing the next generation of solar cells. With this technique, certain experimental steps can be omitted expediting the advancement process.The method utilized to investigate the photoactive layer in this study is electron beam-induced current (EBIC), which uses an electron beam to generate electron-hole pairs in a highly localized region (~300 nm), mimicking the behavior of photons in a more localized manner. This allows for the current generated by the photoactive layer to be collected externally, producing a map of the electronic activity within the device at a nano- and micrometer scale. Simultaneously, a scanning electron micrograph is taken of the specimen topography and nanometer features, to which the electronic map can be correlated. EBIC measurements were performed on a photovoltaic device consisting of a photoactive layer containing a matrix of CdSe nanorods and poly(3-hexylthiophene) polymer sandwiched between aluminum and indium tin oxide. This is the first time that the photoactive layer of an inorganic, organic hybrid device has been imaged using SEM EBIC.Initial experiments suggest that the device appears to be exhibiting asymmetric charge mobility (high hole mobility relative to the electron mobility); this finding corroborates the argument that the addition of hole extracting polymers is influencing the device performance. This is evident simply from observing the EBIC image collected: the active layer close to the Al interface produces a stronger, more localized signal in comparison to the active-layer at the ITO interface. The remainder of the sample displays as a dark region (lack of current generation) meaning that it is exhibiting recombination as a result of the low electron mobility. Further investigations to explore this finding include varying the active layer thickness to either optimize charge transport throughout the entire CdSe:P3HT region or elucidate additional information regarding the dependencies of the device architecture.This exceptional method allows a more precise determination of the photoactivity of a post-fabricated device. The ability to visualize the photovoltaic function at nanometer length scale with EBIC will inevitably guide efforts toward the successful development of efficient nanostructured solar cells.
Thin film polycrystalline CdTe is a promising material for solar applications due to its low production costs and high theoretical efficiency of 32%. However, the highest thin film CdTe laboratory cell efficiency is 18.7% and the best CdTe module efficiency is 16.1%. The major limitation of the efficiency of CdTe solar cells is the low open circuit voltage (Voc), which was only ~0.86 V or ~59% of the band gap for the best laboratory CdTe solar cell. The relatively poor Voc of CdTe cells is largely attributed to the low average minority carrier lifetime caused by nonradiative recombination in grain boundaries (GBs), the CdTe/CdS interface, and other defects. Typically, post-deposition heat treatment (HT) in a CdCl2 environment and Cu diffusion in the active layers is necessary for making high efficiency CdTe thin film solar cells. Although these methods increase the efficiency and Voc of CdTe thin films, the mechanisms for the increase in efficiency are not well known. A combination of cross-sectional in-situ electron beam induced current (EBIC) and electron backscatter diffraction (EBSD) measurements have been used to study the structural and electronic nature of grain boundaries (GBs) in three CdTe samples grown in the same manner except for the CdCl2 HT and Cu diffusion steps. The samples studied were Cl heat treated with Cu diffusion, non-Cl heat treated with Cu diffusion, and non-Cl heat treated without Cu diffusion CdTe/CdS solar cell devices. The results of these measurements directly show that the CdCl2 HT and Cu diffusion growth steps passivate recombination centers at the CdTe/CdS interface and GBs. To further corroborate these findings, a U200 Nion UltraSTEM in-situ electronic probing STEM EBIC system is being developed capable of revealing solar cell performances at the atomic scale. With this setup, charge carrier separation efficiencies can be correlated to the structure and chemical composition of the CdTe in highly localized regions. The innovative cross-section STEM EBIC sample preparation techniques, the EBIC setup, and preliminary measurements will be presented.
Controlled atmosphere thermal annealing of bulk and nanostructured group III-nitride and ZnO semiconductors as well as devices based on these materials can be studied in-situ using scanning cathodoluminescence (CL) microanalysis in a variable pressure SEM equipped with a hot stage. These materials emit characteristic CL well above room temperature due to their wide band gaps (around 3.37 eV), large exciton binding energies (ZnO 60 meV and GaN 25 meV respectively) and the presence of deep levels arising from dopants and defects with large thermal ionisation energies. As a result, the CL signal can be used to control and monitor in-situ thermal processing of these materials as well as measuring their performance at temperatures where practical devices based on these materials typically operate. The utility of high temperature CL microscopy and spectroscopy will be demonstrated for thermal processing of InGaN/GaN multi-quantum-well (MQW) LED devices, activation of p-type GaN and ZnO nano-structures and single crystals. CL signal from all these specimens can be measured up to ~ 800K before the tail of the incandescence starts to noticeably spread into the visible spectral region. In all three samples, heating to elevated temperatures causes the near band edge emission (NBE) to red shift initially due to lattice expansion and then band gap renormalization from the electron-phonon interaction. The NBE also broadens with rising temperature because of increased electron-phonon coupling and greater scattering into LO-phonon replicas due to the larger exciton momentum. By collecting temperature-resolved CL at elevated temperatures, the effect of increasing temperature on the performance of an InGaN/GaN MQW device can be measured directly. It was found that heating from room temperature to 725K caused MQW emission at 473 nm to steadily red shift to 492 nm, broaden and reduce intensity by a factor of 40. In-situ temperature-resolved CL imaging has been used to monitor and analyse H trapping and diffusion in Mg doped p-type GaN during electron beam dissociation of (Mg-H) complexes as a function of temperature. During high temperature hydrogen can de-trap and re-passivate Mg acceptors, lowering the hole conductivity. The effectiveness of Mg activation using rapid thermal annealing using various gas atmospheres, such as O2, Ar and N2, can be established using the in-situ CL signal. In ZnO nano-structures, the role of absorbed gas species, such as water vapour, on near surface CL mediated by band bending was measured in-situ by measuring the CL signal during heating and cooling in vacuum to remove absorbed water and then again after flooding the sample with water vapour. These studies have confirmed that absorbed water increases the surface CL intensity in ZnO nanostructures. Finally the CL signal can used to image the concentration and distribution of defect centers around indents in ZnO as a function of temperature to study their diffusion kinetics.
Organic electronics have been considered a leading candidate to make transparent and flexible electronics at a low cost. The main building block of an organic circuit is the organic thin film transistor (OTFT), which is created by using organic semiconductors (OSCs) as the charge transporting layer. It is preferred that OTFTs are formed using solution processing methods, so that the time frame for processing is more compatible with industrial fabrication time scales. We have previously shown that the solution shearing method (SSM) is a process that improves OTFT performance for a range of OSCs, and the method is compatible with roll to roll industrial processing. This method can also tune the polymorph formation in OSCs, enabling high performance OTFTs and organic photovoltaics by tuning the electronic properties without changing the OSC chemical structure. In SSM, it is difficult to study the morphological and polymorph growth that enable high OTFT performance. Not only does the thin film crystallize at a fast time scale, the evaporation front, where the crystal grows from the solution, is very small. The entire evaporation front can be less than 200 microns. Thus, the solution evolves into a crystallized thin film within seconds, and within an area less than 0.2 mm wide. We use an X-ray ‘microbeam&’ at the Cornell High Energy Synchrotron Source, with a beam width of < 20 microns, in conjunction with a high speed CCD detector to resolve and follow crystallization from solution of the OSC during solution shearing. We have collected up to 100 frames per second X-ray images, and are able to create grazing incidence x-ray diffraction movies to easily see how crystallization occurs in the solution shearing system in real time. We also use an optical microscope trained at the evaporation front, which we can use to collect optical videos of the evaporation front at up to 10,000 frames per second. Being able to simultaneously study kinetic crystallization using both optical and X-ray movies helps us understand how different processing conditions result in various crystal morphologies and polymorphs. We study the model OSC 6,13-bis(triisopropyl)-silylethynyl pentacene (TIPS-pentacene) and the polymer poly 3(hexyl-thiophene) (p3HT) in various organic solvents in order to see how SSM based crystallization occurs. We are able to study drying times of the thin films, the evolution of the solvent evaporation front as well as polymorph formation of different OSCs in real time. We have been able to get metastable crystal polymorphs in other solution processing methods using the knowledge from our studies.
Thin film solar cells, such as CdTe/CdS devices, are based on polycrystalline materials that are structurally and electronically non-uniform. To effectively engineer and mitigate the recombination sources and to further boost the efficiency of such inhomogeneous devices, it is imperative to understand how the grain cores (GCs) and grain boundaries (GBs) within these materials affect the overall photoelectronic properties. We use an extension of laser-beam-induced current (LBIC) microscopy based on a sub-wavelength apertured Near Field Scanning Optical Microscope (NSOM) to locally probe the photoconductivity of GCs and GBs in commercially available solar cells. The photocurrent generated by the local light injection within the GCs and at the GBs is measured under different excitation wavelengths. This technique potentially allows us to evaluate local electric field and bandgap and, therefore, composition variations at the GBs providing valuable information about the recombination sources at the grains&’ interfaces. In the current study, we examine the effects of the surface topography on the signal contrast. The photocurrent maps acquired over native rough CdTe surface and over smooth CdTe surface obtained by milling grazing angle wedges are compared. In both cases, higher photocurrent was generated in the vicinity of GBs that can be related to the band bending efficiently separating electrons and holes. As a function of illumination wavelength, the spatial resolution and the contrast generally scales with the absorption length of CdTe. However, at the wavelengths corresponding to the absorption of CdTe at the band edge, the contrast and resolution of the maps sharpens noticeably. We will discuss 3D finite-difference time-domain simulations of the near-field light-semiconductor interaction to quantify the effects of surface roughness and bandgap variations.
Silver-coated ultra-clear glasses are largely used for solar concentrator applications. However, durability issues can occur during longterm use by changes in morphology of the ultra-thin Ag coatings induced by thermal cycling, leading in turn to reflectivity losses and therefore a decrease in energetic performance. To partly overcome such longterm stability issues, the additional use of a Pd-based adhesion layer and a protective Sn film has been suggested .To unravel the mechanistic origins of the potentially beneficial effect of such multi-layers, we have monitored in real time their morphological changes occurring during repeated and accelerated thermal cycling using a combination of two independent in-situ probes : on the one hand in-situ monitoring of internal stresses by means of high resolution (10 km-1 every 0.1 sec) curvature measurements using a Multi-beam Optical Stress Sensor, and on the other hand in-situ resistivity monitoring using an adapted four point probe technique. Three sets of wet-chemically coated mirrors have been considered: glass/Ag, glass/Pd/Ag and glass/Ag/Sn, all with a constant Ag thickness of 140 nm. To simulate the thermally-induced degradation occurring in operando under solar illumination, these samples were then heated up in various controlled atmospheres upto different temperatures at varying ramp rates, maintained at this temperature between 20 and 120 minutes, and naturally let cool-down. The in-situ resistivity measurements, combined with ex-situ X-ray analysis, indicated that structural recovery occurs in all Ag-coatings when exceeding 250°C. This microstructural evolution as such did not lead to any optically detrimental morphological changes. At the same time however, once above 200°C, morphological changes do take place in the form of local surface protrusions (hillocks) and, still at higher temperatures, by void formation. In-situ curvature measurements have shown that the initial internal stress state of the as-deposited films is compressive at room temperature, and further increases in the compressive direction upon heating, reaching several 100's of MPa in some cases. Our unique combination of in-situ curvature and resistivity monitoring has thereby indicated that it is this compressive internal stress that is the driving force for both the structural recovery as well as for the stress-relaxing morphological changes in the form of hillocks and voids. Finally, when comparing the three different coatings, it was found that hillock and void growth could be limited in the case of glass/Pd/Ag and glass/Ag/Sn samples. It was therefore concluded that both the Pd and the Sn layers allow for an improved morphological stability of the reflective Ag coating by hindering its stress relaxation in the form of hillocks or voids.  B. Schweig, Mirrors: A guide to the manufacture of mirrors and reflecting surfaces, (Pelham, London, 1973) pp 149 - 155
Electrochemical reactions in solids underpin multiple applications in energy storage and conversion systems including metal-air batteries and fuel cells. Understanding the functionality in these systems requires probing reversible (oxygen reduction/evolution reaction) and irreversible (cathode degradation and activation, formation of conductive filaments) electrochemical processes. Traditionally, these effects are studied only on the macroscopically averaged level. In this talk, I summarize recent advances in probing and controlling these transformations locally and in-situ on nanometer level using scanning probe microscopy. The localized tip concentrates the electric field in the nanometer scale volume of material, inducing local transition. Measured simultaneously electromechanical response or current (conductive AFM) provides the information on the bias-induced changes in material. Here, I illustrate how these methods can be extended to study local electrochemical transformations, including bias-induced metal nanoparticle formations and vacancy dynamics in oxides such as titanates, LaxSr1-xCoO3, BiFeO3, and YxZr1-xO2. The formation of electromechanical hysteresis loops indistinguishable from those in ferroelectric materials illustrate the role ionic dynamics can play in piezoresponse force microscopy and similar measurements. In materials such as lanthanum-strontium cobaltite, mapping both reversible vacancy motion and vacancy ordering and static deformation is possible, and can be corroborated by post mortem STEM/EELS studies. We further extend this approach for irreversible electrochemical processes, and discuss the degree to which these studies can be quantitative. Using active device structures, SPM can be further extended to study phenomena in lateral electrochemical devices, decoupling the electrochemical processes and visualizing active reaction regions. Future potential for high-resolution STEM-SPM based studies are discussed.This research was conducted at the Center for Nanophase Materials Sciences, which is sponsored at Oak Ridge National Laboratory by the Scientific User Facilities Division, Office of Basic Energy Sciences, U.S. Department of Energy.
Silicon has potential to greatly increase the capacity of negative electrodes in Li ion batteries, and like many of the new materials it has stability issues. Mechanical degradation is particularly challenging in silicon, which has a high Li capacity and a correspondingly large volume expansion. Our work employs in situ AFM to investigate amorphous Si electrodes and Solid Electrolyte Interphase (SEI) formation on the surface, using lithographically patterned islands. The patterned films enabled direct in situ comparison between the Si and the copper current collector. These experiments were conducted in a closed electrochemical cell. In addition to monitoring volume and surface morphology evolution, the mechanical properties of the surface were probed relative to fixed voltages. These experiments allowed us to investigate SEI behavior in different electrolytes and with different cycling conditions. Both the electrolyte composition and the formation potential had significant effects on the SEI formation. An irreversible Si volume expansion was measured during the first cycle and is likely the product of lithiation induced changes to the silicon structure. Complimentary in situ stress measurements were performed to provide additional information. The cycled films were also examined with detailed TEM to characterize the SEI thickness and changes in Si. The results from this full range of experiments were used to characterize changes in Si electrodes and to develop a detailed model of SEI formation, which was then employed to develop strategies for designing more stable electrodes.
A number of key science questions must be answered to establish the limits of achieving reversible and efficient oxygen electrochemistry in aprotic organic electrolytes. Such information is essential for the development of rechargeable alkali metal - oxygen batteries. One critical question is determining how the solid product peroxide maintains electrochemical contact with electrode sites responsible driving the oxygen reduction and evolution reactions. Establishing the spatial relationships between these electron transfer sites and peroxide nucleation and growth sites is a critical step in determining how contact is maintained and therefore how to design a functional, efficient cathode. Operando imaging of peroxide particle nucleation, growth, as well as charging cycle decomposition is required to establish these relationships. Probe microscopy is ideally suited for such purposes. In this paper, we report on electrochemical AFM and STM studies of the basal plane of graphite and Au(111) in 1 M LiTFSI in TEGDME or DME at variable oxygen concentrations including saturated levels. Voltammetry and chronopotentiometric cell discharging and charging are conducted to explore the formation of lithium peroxide structures on these surfaces as a function of applied potential and current density. Results show that the steps edges are active first in the case of graphite and exhibit particle nucleation and growth after a period of oxygen reduction activity, consistent with an electrolyte mediated superoxide disproportionation to peroxide. Longer duration holds at low current densities show that the peroxide film continues to nucleate and grow outward onto the terrace. The structure of this film is nodular in appearance and at higher current densities, and consequently more cathodic potentials, a film of finer particles of peroxide forms across the entire graphite surface without preference to step edges. Given sufficient time comparable film morphologies form independent of the rate at which they were produced. The lack of a stronger morphological variation with formation rate is hypothesized to result from an electrode capable of supporting a more uniform current density. Anodic dissolution of these films occurs nominally at 4.2 V with preferential dissolution around and apparently underneath the individual nodules. Small fractions of the film appear to separate from the graphite terrace during the final stage electrochemically driven dissolution. We contrast these results for graphite with the more strongly passivated response of the Au(111) surface upon which significantly thinner peroxide films form. Supported as part of the Joint Center for Energy Storage Research, an Energy Innovation Hub funded by the U.S. Department of Energy, Office of Science. Sandia is a multiprogram laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Company, for the U.S. DOE&’s NNSA under contract DE-AC04-94AL85000.
Understanding the fundamental activity of metal-oxide particles attached to a carbon support is critical to a number of electrochemical energy storage applications including batteries and supercapacitors. The origin and subsequent evolution of the particle-carbon interface during device operation dictates the ease of charge transfer across this interface and, ultimately, ensemble electrode performance. In order to better understand the fundamental properties of composite electrodes we have developed an in situ SPM platform based on a metal-oxide nanoparticle deposition scheme that takes advantage of our ability to tune the functionality of a graphitic (HOPG) surface in UHV. By engineering this functionality and, consequently, the surface mobility of metal-oxide (in this case manganese) adatom clusters we are able to control the nucleation and resulting location and size of β-MnO2 nanoparticles. Manipulating the particle deposition conditions (e.g. by changing the reactive gas from molecular O2 to atomic O or by pre-irradiating the substrate with low energy O2+) leads to distinct particle populations due to nucleation at graphite step-edges, induced terrace defects, or intrinsic terrace defects. Characterization of the HOPG surface after exposure to these variable conditions demonstrates that the extent of disorder and oxidation of the graphitic basal planes are controllable, and subsequent MnO2 particle deposition illustrates the dramatic influence that these surface properties have upon metal-oxide cluster transport and nucleation tendencies. This differentiation enables us to correlate the chemical origin of a particle-carbon interface with the particle&’s physical and electrochemical properties as observed in operando. We employ several SPM techniques including dynamic AFM, STM, and KFM in order to study the structural, mechanical, and electronic property changes of these nanoparticles during potential-controlled electrochemical processes such as lithium-ion insertion/extraction in order to assess individual particle activity, which depends upon its degree of electronic connectivity to the graphite support. These techniques are used in conjunction with ex situ characterization tools to form a more complete picture of the β-MnO2 particle-carbon system. These particle deposition and in situ characterization schemes can be applied to a variety of metal-oxide energy storage materials of interest.This work was supported the NEES EFRC project. Sandia is a multiprogram laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Company, for the U.S. DOE&’s NNSA under contract DE-AC04-94AL85000.
A membrane electrode assembly (MEA) has been probed by confocal RAMAN microscopy. In addition to depth profiling of the MEA, the potential dependence spectra of a non-PGM catalyst at the cathode is studied. Adsorption of oxygen is detected as the potential of the MEA electrode is lowered from the open circuit voltage. Details of the experimental cell will be described.
Efforts to reduce CO2 emissions, spurred by concerns about climate change, are driving a shift from our hydrocarbon based economy to a hydrogen economy. To ensure a carbon-free energy cycle, electricity must be used to generate hydrogen through water electrolysis. In electrolyzers, the oxygen evolution reaction (OER) is the rate limiting reaction, both in terms of high overpotentials but also its low stability. These limitations must be overcome in order to improve efficiency and improve system lifetime.RuO2 is the most active OER catalyst in both acid and alkaline electrolytes, however its stability is inadquate for commercial electrolysis. IrO2 is more stable than RuO2, but its activity and cost are not suitable for real systems. Alloying Ru and Ir provides a compromise between activity and stability.In order to better understand the mechanism of the OER on these oxides, we conducted a systematic in situ electrochemical X-ray Absorption Spectroscopy (XAS) study of RuxIr1-x alloy metals and oxides. Typical fluorescence XAS has no surface sensitivity, which is important for electrochemical characterization. To overcome this limitation, we used Ru and Ir thin films of optimized thickness on carbon to monitor the change of Ru, Ir oxidation state and the formation of Ru-O and Ir-O bonds under applied potential. Our experimental results will help advance understanding of the activity and stability processes at OER in RuxIr1-x alloys and oxides.
Fast acquisition in-situ XRD was performed to investigate the chemical and structural modifications in a MgH2 - based composites upon successive processes of hydrogenation and dehydrogenation. The in-operando study was carried out using a dedicated high pressure, high temperature gas loading system on the ID15 beam line at ESRF, Grenoble, France. Magnesium hydride has been studied for decades as it is considered as a competitive material for solid hydrogen storage due to its high H2 gravimetric capacity (7.6 wt%) and relative low-cost. In particular, transition metal elements and intermetalic alloys have been identified as efficient additives that allow to overcome the slow reaction kinetics of the Mg - H system. Moreover, dehydrogenation and hydrogenation kinetics are even improved in composite materials, where the combination of reduced MgH2 grain size, high dispersion of additives, and mechanical microstrains greatly enhances the hydrogen atomic diffusivity. However, the mechanism of the catalytic effect is not clearly explained. We performed in situ synchrotron XRD experiments in the course of hydrogenation and dehydrogenation of MgH2 - TiVCr composites in order to investigate in operando the chemical and structural evolution of the constituent phases of the composite. Sequential Rietveld refinement was performed on the diffraction patterns collected during the experiment. The data analysis revealed that significant non-monotonic changes in the lattice volume of the TiVCrHx solid solution were observed concomitantly to the MgH2 formation and decomposition. These volume changes have been assigned to the variation of the hydrogen content in TiVCrHx. The present in-operando study allows to get insights on the cooperative effect between the TiVCr additive and hydrogen storage material while the reversible reaction MgH2 harr; Mg + H2.
Understanding the oxygen nonstoichiometry and the oxygen surface exchange reaction of oxide materials is essential for achieving improved performance of solid oxide fuel cells (SOFCs), permeation membranes, and oxygen storage materials, the latter used in emission catalysts. The ability to diagnose a material&’s behavior is therefore of importance, especially under operating conditions such as elevated temperatures and reducing/oxidizing atmosphere. Even though oxide thin films are widely studied as model systems, given their well-defined properties and reproducibility, conventional methods are often limited in their ability to properly characterize their key properties. For example, thermogravimetric analysis (TGA) is unsuitable for monitoring oxygen nonstoichiometry changes in thin films, given that corresponding mass changes fall below microbalance sensitivities. Electrochemical impedance spectroscopy (EIS) and electrical relaxation measurements, for investigation of surface exchange kinetics, on the other hand, require metal contacts that can potentially impact the reaction kinetics by their catalytic activity or serve to block reaction sites on the film surfaces. In this work, we describe a non-contact optical means for in situ recording of transient redox kinetics as well as the equilibrium oxygen nonstoichiometry of the model thin film fluorite structured oxide Pr0.1Ce0.9O2-δ (10PCO), by monitoring the change in its absorption spectra upon change in pO2 or temperature. We further combine this with chemical capacitance measurements, thereby enabling the simultaneous investigation of 1) nonstoichiometry via chemical capacitance and absorption change and 2) surface exchange reaction kinetics via reaction resistance and absorption relaxation. These results will be compared with data obtained independently from thermogravimetric measurements on bulk PCO specimens. The impact of different metal contacts on the reaction kinetics and surface chemistry changes, following extended time measurements, and the potential distinction between bulk and thin film properties will also be discussed.
La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) is a promising mixed-conducting cathode for solid oxide fuel cells (SOFCs) due to its catalytic activity. Studies have shown that the oxygen reduction reaction at the cathode surface is a rate-limiting step in the performance of SOFCs; however, the factors that affect this process are not well understood. For example, Sr segregation at the cathode surface has been linked to performance degradation. There is evidence that this surface segregation is affected by the gas environment during cell operation, but the specific impact of operating environments containing water or CO2 on cathode performance is not well understood.In the current work, the oxygen exchange reaction of LSCF pseudo half-cells was investigated using in situ synchrotron x-ray diffraction during cell operation. The cells consisted of a thin film of LSCF (60 nm) grown by pulsed laser deposition on a yttria-stabilized zirconia (YSZ) substrate, with a gadolinium-doped ceria (GDC) buffer layer. Synchrotron x-ray diffraction was used to measure changes in the c-lattice parameter, which increases with increasing oxygen vacancy concentration. The time constants of these changes in the oxygen vacancy concentration in response to electrochemical bias were used to determine activation energies and surface exchange rates for oxygen transport into and out of the cathode. These measurements were repeated at different oxygen partial pressures (1.5, 15, and 150 Torr) at temperatures between 350 and 700°C. To investigate the effect of water and CO2 on surface exchange and cathode performance, this process was repeated in atmospheres of up to 8% H2O and 90% CO2. Implications of the results on SOFC cathode performance will be discussed.
Complex metal hydrides&’ high storage capacities make them candidate hydrogen storage materials for automotive applications provided the high uptake/release temperatures and slow kinetics are resolved. Confinement within nanoporous scaffolds has the potential to overcome these challenges by constraining the particle size to the nanoscale - decreasing diffusion distances and increasing surface area and interfacial contact between phases. Infiltration of lithium borohydride (LiBH4, 18.5 wt% hydrogen content) into highly ordered nanoporous carbon scaffolds has significantly improved its sorption properties by decreasing the desorption temperature from 460 to 220°C, improving reversibility, and eliminating toxic diborane production . Though promising, a reduced practical loading limit of LiBH4 compared to expectations based on pore volume and decreasing hydrogen storage capacity with cycling were observed. To explain this behavior, and thus facilitate the optimization and performance, we explored these systems with a variety of in situ electron microscopy techniques.Investigation of the scaffolds revealed a complex morphology: rather than being composed of thin columns packed in a monolithic hexagonal arrangement, the scaffolds are subdivided into domains possessing different column orientations. Domain orientation and location with respect to scaffold surfaces can limit the accessibility of pores during infiltration. In situ STEM heating experiments allowed the direct observation of microstructural changes during desorption. We discovered that during dehydrogenation, LiH is ejected from the scaffold, forming a crust of nanocrystals on the outer surface. Furthermore, if the scaffold is in contact with another object, e.g. a carbon support film, the nanocrystals can migrate away from the scaffold entirely. This preferential ejection/segregation of Li offers a plausible explanation for the observed reduction in hydrogen capacity during cycling and has implications for long-term system use.  Liu, et al., Chem. Mater, 2011. 23, p.1331-1336
In order to meet emerging electrical energy storage challenges, novel devices such as electrochemical double layer capacitors (EDLCs), or supercapacitors, are rapidly attracting interest. They rely on electrosorption of ions by porous carbon electrodes and offer a higher power and a longer cyclic lifetime compared to batteries. Room temperature ionic liquids (RTIL) are gaining increasing interest to further enhance the systems&’ operating voltage windows and charge storage densities. These electrolytes can broaden the operating voltage window and increase the energy density of EDLCs. While they may offer multiple performance advantages, the dynamic processes that govern their mobility in and out of pores, long-range transport, and differential behavior in a neat or solvated state are not thoroughly understood. We present a novel method qualitatively describing the ion dynamics of 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMIm-TFSI) in an operating EDLC with electrodes composed of endohedral nanosized carbide-derived carbons (CDCs) and exohedral onion-like carbons (OLCs) with the use of in situ infrared spectroelectrochemistry. For CDC electrodes, absorbance measurements correlated charging and discharging of EDLCs with RTIL ions (both cations and anions) entering and exiting CDC nanopores. Conversely, for OLC electrodes, ions were observed in close proximity to the OLC surface without any change in the bulk electrolyte concentration during charging and discharging of the EDLC. This provides experimental evidence that charge is stored on the carbon surfaces of OLC EDLCs without long-range ion transport through the bulk electrode, contradicting the traditional wisdom of diffusion-driven ion mobility. Our approach allows us to demonstrate ion-dominated mobility in and out of confined porous architectures and corroborate the expected desolvation of electrolyte components in systems with matching ion/pore diameters. The experimental measurements presented here provide deep insights about the molecular level transport of RTIL ions in EDLC electrodes that will impact the design of electrode materials. This in situ technique, which can be applied to a wide range of electrochemical systems, is essential towards understanding ion mobility and selecting the optimal electrode/electrolyte configurations for novel electrical energy storage systems.