Garnet-type Li7La3Zr2O12 (LLZO) is a potential electrolyte material for all-solid-state Li-ion batteries mainly because of its reported excellent chemical stability in contact with Li metal. But good wettability of LLZO and 100% surface coverage of lithium are still a challenge. This study elucidated the suitability of magnetron-sputtered indium in Li(In)/LLZO/Li(In) symmetrical model cells as one of the promising interfacial modifications reported in the literature. Importance was given to the impact of preparation parameters on the surface coverage of Li(In)/LLZO interfaces and the consequences of impedance, cycling stability, and critical current density. SEM and EDXS analyses of In layers of thickness 100 nm to 1 μm revealed complete dissolution of indium in the lithium anode after annealing; 300 nm In layers annealed at 220 °C/10 h provided a surface coverage of >80%, best reproducibility, and a supreme interface resistance Rint of 12.4 Ω·cm2. Presuming a surface coverage of 100%, an ultimate interface resistance close to 1 Ω·cm2 can be expected. The critical current density was determined as 200-500 μA/cm2 at a charge of 100-250 μAh, whereas 500 μA/cm2 and above affected cell stability. The increasing voltage plateau was assigned to the increase of the interface resistance Rint and the electrolyte resistance RG+GB. SEM, EDXS, and X-ray microtomography analyses after voltage breakdown confirmed Li-dendrite growth along grain boundaries into LLZO, often curved parallel to the interface, indicating short-circuiting of the solid electrolyte. Grain boundary characteristics are supposed to be decisive for lithium deposition in and failure of garnet-type solid electrolytes after cycling.

The performance of lithium‐ion batteries can be analyzed and improved by appropriate electrochemical models. A challenging yet crucial part is the parameterization of these models. Until now, the literature has incompletely investigated and cited the charge transfer process parameters describing the lithium transfer between the active material particles in the electrode and the liquid electrolyte. Herein, a novel approach is presented for obtaining these charge transfer parameters. The well‐established experimental methods of electrochemical impedance spectroscopy and focused ion beam tomography are applied. By introducing both experimental results into a transmission line model, a reliable determination of the charge transfer parameters j0, k, and rCT can be achieved. The new approach is validated by comparing the results of four cathodes, all containing the state‐of‐the‐art active material NixMnyCo1−x−y (NMC), but with different microstructures and/or stoichiometries.

Porous electrode models are essential for inexpensively predicting the performance and lifetime of lithium‐ion batteries. Physics‐based models range from microscopic 3D models, which spatially resolve the microstructural characteristics of all phases in porous electrodes, to reduced and computationally effective models, which do not resolve the microstructure. The homogenized Newman model, also known as the pseudo‐2D (P2D) model, is well established and widely used. However, the necessary simplification shows its weaknesses, especially for high charge and discharge rates, and these lead to significant differences in comparison with the microscopic 3D model. Herein, the validity of the homogenized Newman model is investigated with respect to variations of the microstructural characteristics of a porous cathode. The effects of 1) a homogenized conductive additive; 2) non‐spherical particle geometries; and 3) overlapping particles on charge/discharge curves are analyzed. The result is a better understanding of the validity limits of P2D models. These new insights about the individual influences of the simplifications will be used to improve the homogenized model. The simulation of complex cathode structures, where several homogenization assumptions are violated, shows that the improved homogenized model reaches a very high accuracy, and, thus, overcomes the existing limitations of the P2D model approach.

Microstructural characteristics of lithium‐ion battery cathodes determine their performance. Thus, modern simulation tools are increasingly important for the custom design of multiphase cathodes. This work presents a new method for generating virtual, yet realistic cathode microstructures. A precondition is a 3D template of a commercial cathode, reconstructed via focused ion beam/scanning electron microscopy (FIB/SEM) tomography and appropriate algorithms. The characteristically shaped micrometer‐sized active material (AM) particles and agglomerates of nano‐sized carbon‐binder (CB) particles are individually extracted from the voxel‐based templates. Thereby, a library of roughly 1100 AM particles and 20 CB agglomerates is created. Next, a virtual cathode microstructure is predefined, and representative sets of AM particles and CB agglomerates are built. The following re‐assembly of AM particles within a predefined volume box works using dropping and rolling algorithms. Thereby, one can generate cathodes with specified characteristics, such as the volume fraction of AM, CB and pore space, particle‐size distributions, and gradients thereof. Naturally, such a virtual twin is a promising starting point for physics‐based electrochemical performance models. The workflow from the commercial cathode microstructure through to a full virtual twin will be explained and assessed for a blend cathode made of the two AMs, LiNiCoAlO 2 (NCA) and LiCoO 2 (LCO).

The microstructure of lithium-ion battery cathodes rules their performance. However, the production of a variety of cathodes with different microstructures through laboratory experiments is very expensive with respect to costs and time. Thus, model-based simulation approaches, i.e., virtual microstructures generated and analyzed on a computer, have become an important tool for microstructural optimization. In this work, tools for the generation of realistic yet virtual microstructures are presented. Basically, three dimensional reconstructions of cathode microstructures are established by FIB tomography, and the individually shaped particles of the active material phase as well as the carbon black are extracted. A representative set of extracted particles is used to create structures with specified characteristics, such as e.g. the desired mass content of active material and conductive additive or specific particle size distributions. In combination with performance models, a preselection of promising design concepts can be conducted. The complete workflow from the generation of realistic virtual microstructures based on 3D reconstruction via FIB tomography towards the simulation of discharge curves will be shown using the example of a commercial blend cathode consisting of the two active materials LiNiCoAlO 2 (NCA) and LiCoO 2 (LCO). Figure 1

A deep knowledge of the 3D microstructure is essential for optimizing performance in Lithium ion battery electrodes. Tomography methods like focused ion beam-secondary electron microscopy (FIB-SEM) and X-ray tomography are the most frequently used 3D characterization techniques for battery electrodes. While each method has advantages and disadvantages, understanding the complex morphology of electrodes requires a complementary, multi-scale 3D approach. In this work, the possibilities and limitations for both 3D techniques, X-ray and FIB-SEM tomography, are studied using the example of a LiNiCoAlO2-LiCoO2 blend cathode from a commercial cell. The same cathode sample was analyzed with both techniques and moreover with different devices to enable a comparison of the obtained data quality. The material fractions, porosity, surface area and tortuosity are calculated from the different data sets and the results are compared with special emphasis on the differentiation of the different active materials and the carbon-binder phase. The reliable determination of these parameters is essential because they are needed, for example, to compare different electrode structures or to study the influence of the microstructure on the electrode performance to optimize the electrode structure. Figure 1

Four positive electrodes are extracted from two high-power and two high-energy Li-ion battery consumer cells, and then analyzed by focused ion beam-scanning electron microscopy (FIB-SEM) tomography. The active material phase, carbon black-binder phase and pore phase are quantitatively evaluated using adequate 3D analysis techniques by their volume fractions, surface areas, particle size distributions and tortuosities. The active material phase is composed of LiCoO2 (Sanyo 1500 mA h), or LiNiCoAlO2 (Sony 2600 mA h) or one of two LiNiCoAl2-LiCoO2 blends (Kokam high-power 350 mA h and high-energy 560 mA h). Special emphasis was put on the three-dimensional distribution of the submicron-sized (yet highly agglomerated) carbon black-binder phase. Vacuum infiltration with a two-component silicone resin gave greyscale contrast between the carbon black-binder and pore phases for contour description at voxel sizes from 30 to 50 nm. This study elucidates the cathode microstructural features for high-energy and high-power application and provides a complete parameter set of commercial electrodes with differing chemical composition. This information can be used by the scientific community as input parameters in simulations and models, filling the gap between the experimental and the simulation fields.

Optimizing the performance of the Lithium ion batteries requires further understanding of the relationship between the electrode microstructure and the electrochemical performance. Advanced microscopy methods like focused ion beam-secondary electron microscopy (FIB-SEM) and X-ray tomography have been lately used to characterize the battery electrodes [1,2]. However, the study of the complex morphology of the electrodes is not a trivial task, since relevant details take place at different length scales. One single technique is thus meaningful up to a certain extend but not enough to achieve information of the battery as a whole [3]. By a correlative approach the central issues arising during post-processing the image data can be investigated: (1) segmentation of the carbon (carbon black-binder) domain limited by the lower X-ray tomography resolution, (2) reliability of the small volume fractions of the active material and/or other large features taken by FIB-SEM tomography and (3) impact of inner porosity, fissured texture or agglomerated particles, which demand a high resolution technique, in the transport properties. In this work, LiNixMnyCo1-x-y (NMC) cathodes are characterized by correlation of both FIB-SEM and X-ray tomography. Relevant microstructural information of each individual phase (i.e. active material, carbon, and pore phases) is determined with their respective volume fraction, surface area, particle size distribution and tortuosity at the different relevant length scales. In addition, the electrochemical performance of the cathodes is studied by impedance spectroscopy (EIS) combined with distribution of relaxation times (DRT) depicting information about the ohmic resistance (R0), charge transfer (e-) at the interface cathode/current collector (RCC), charge transfer (Li+) at the interface cathode/electrolyte (RCT) and the ionic and electronic transport [4]. As a whole, the possibilities, limits and prospects of both microstructural characterization methods will be critically discussed along with the impact on the results. References M. Ender, J. Joos, T. Carraro, E. Ivers-Tiffée, J. Electrochem. Soc. 159 (2012) A972-A980. P.R. Shearing, L.E. Howard, P.S. Jorgensen, N.P. Brandon, S.J. Harris, Electrochem. Comm., 12 (2010) 374-377. R. Moroni, M. Börner, L. Zielke, M. Schroeder, S. Nowak, M. Winter, I. Manke, R. Zengerle, S. Thiele, Sci. Rep., 6 (2016) 30109. J. Illig, J.P. Schmidt, M. Weiss, A. Weber, E. Ivers-Tiffée, Journal of Power Sources, 239 (2012) 670-672. Figure 1

The efficiency and long-term stability of Solid Oxide Fuel Cells (SOFC) are both highly reliant on the performance of the porous fuel electrode. The electro-oxidation reactions and transport processes that take place in the nickel/yttria stabilized zirconia cermet anode can be described by a transmission line model (TLM). Herein, the ionic conduction pathway in the electrolyte matrix is coupled to the electronic conduction pathway in the nickel matrix at every individual triple phase boundary point, where the gaseous species H-2 and H2O react. With a well-parametrized TLM, the spatial expansion of the electro-oxidation reaction into the anode volume becomes predictable as a function of temperature and gas composition. In this work, a physicochemically meaningful TLM was set up using parameters acquired by (i) EIS measurements on patterned model anodes, (ii) 4-point DC conductivity measurements on porous YSZ-matrix samples and (iii) microstructure characteristics gained from FIB/SEM-tomography. The application of these parameters in the TLM provided a good agreement with measured impedance spectra over a wide temperature and fuel composition range. Further, the representation of the impedance spectra became even more precise when they were used as starting values in a CNLS-fit, with all parameters kept within physicochemically meaningful ranges. As such, the TLM can predict the impact of microstructural and material properties on the anode performance. Simulation studies were performed and we evaluated the impact of tortuosity, volume specific triple phase boundary length, double layer capacity and ionic conductivity on the impedance spectrum. (c) 2017 Elsevier Ltd. All rights reserved.

Materials with spatially organized and multimodal porosities are very attractive in catalysis, as they can reconcile nano-confinement effects in microand mesopores with fast molecular transport in wide macropores. However, the associated large pore volumes often result in low overall thermal conductivities, and thus suboptimal heat management in reactions with a high thermal signature, usually with a deleterious impact on the catalytic performance. Here we report the directional freeze-casting assembly of bimodally meso-macroporous micromonolithic bodies with a hybrid backbone composed of intimately bound carbon nanotubes (CNTs) and ZrOx–Al2O3 nanocrystals. A honeycomb-shaped and axially oriented macroporous architecture is achieved through the use of zirconium acetate as an ice growth modulator. (S)TEM and EDX nanospectroscopy show that the nanoscale intimacy between the CNT and oxide backbone components depends on the synthesis route of the mother slurry. As revealed by X-ray tomography, coupled to quantitative image analysis, not only the macrochannel size and wall thickness, but also the extent of axial heterogeneities in macropore diameter and spatial orientation depend on the axial temperature gradient rate during casting. The structured bodies are explored as carriers for cobalt-based catalysts for the Fischer–Tropsch production of synthetic hydrocarbons from syngas, of central significance in intensified X-to-liquid processes. Hybrid CNT-Al2O3 backbone micromonolith catalysts show a high selectivity to C3–8 olefins, owing to the fast evacuation of these primary reaction products from the metal active sites through the directional macropore system. Remarkably, the high olefin selectivity is maintained up to higher operating temperatures compared to reference catalysts based on all-oxide supports, due to a higher effective thermal conductivity which inhibits the development of hotspots under industrially relevant operating conditions.

The mixed ionic-electronic conducting cathode (La, Sr)(Co, Fe)O 3-δ (LSCF) is utilized worldwide for solid oxide fuel cells (SOFCs) operated at intermediate temperatures [1] because of its excellent oxygen reduction reaction rate. The challenge of using LSCF as cathode material is the complex nature of the interface to Zirconia-based electrolytes, which may counteract this advantage [2, 3]. The composite cathode (La, Sr)MnO 3 (LSM) – Y 2 O 3 doped ZrO 2 (YSZ) is an adequate alternative for higher temperatures only. LSM-YSZ offers fewer regions of oxygen reduction (triple phase boundaries) due to spatially separated ionically (YSZ) and electronically (LSM) conductive phases. If electrochemical and microstructural parameters of both types of electrodes are quantified by appropriate techniques, the performance can be modeled and compared for different operating conditions. Advanced imaging techniques such as focused ion beam/scanning electron microscopy (FIB/SEM) or X-ray tomography are promising techniques for microstructure quantification enabling 3D reconstructions of µm- and sub-µm-scaled multiphase electrodes [4, 5, 6]. Reconstructing the composite cathode, in particular, comprises the challenge of overcoming the weak material contrast between LSM and YSZ using scanning electron microscopy. This contribution will show how FIB/SEM tomography can help to identify different microstructural parameters such as porosity, particle size, surface area and tortuosity. We will compare LSCF and LSM-YSZ cathodes and enlighten new challenges in image reconstruction, parameter acquisition and parameter interpretation for the different material sets. [1] H. Yokokawa, et al., J. Power Sources , 182 , p. 400 (2008) [2] J. Szasz, et al., ECS Trans. , 66 (2), p. 79 (2015) [3] Yokokawa, et al., Solid State Ionics , 262 , p. 454 (2014) [4] J.R. Wilson, et al., Nature Materials 5 (17), p. 541 (2006) [5] J. Joos, et al., Electrochim. Acta 82 , p. 268 (2012) [6] Y. C. K. Chen-Wiegart, et al., J. Power Sources , 218 , p. 348 (2012) Figure 1

A finite element method (FEM) based model was developed for performance simulation in SOFC, using a homogenized electrode microstructure at the cell level. The model was parametrized with electrode kinetics determined by electrochemical impedance spectroscopy (EIS) on planar anode supported cells and validated by current/voltage characteristics (C/V) over the technical relevant operating condition range of SOFC [1]. Model calculations on planar stack layer level have demonstrated that (i) cathode layer thickness and (ii) cathode layer porosity is key to avoid gas transport limitations and performance loss [2]. The model has been advanced by adopting mixed-ionic/electronic cathode (MIEC) kinetics, thus enabling the simulation of stack layer performance depending on the cathode’s chemical composition. Furthermore, it will be demonstrated how a functional gradient in pore and particle size distribution enhances stack performance compared to state-of-the-art cathodes. These simulations are not based on artificial, but on “real” microstructures, which were determined using a combined focused ion beam/scanning electron microscopy (FIB/SEM) and X-ray tomography reconstruction of a two-layer cathode. [1] H. Geisler, A. Kromp, A. Weber and E. Ivers-Tiffée, JES 161 (6) F778-F788 (2014) [2] H. Geisler, J. Joos, A. Weber and E. Ivers-Tiffée, ECS Transactions , 68 (1) 3043-3050 (2015)

This paper introduces a correlative tomography technique. It visualizes the spatial organization of primary and secondary phases at the interface of La0.58Sr0.4Co0.2Fe0.8O3-delta cathode/10 mol% Gadolinia doped Ceria/8 mol% Yttria stabilized Zirconia electrolyte. It uses focused ion beam/scanning electron microscope tomography (FIB/SEM), and combines data sets from Everhart-Thornley and Inlens detector differentiating four primary and two secondary material phases. In addition, grayscale information is correlated to elemental distribution gained by energy dispersive X-ray spectroscopy in a scanning transmission electron microscope. Interdiffusion of GDC into YSZ and SrZrO3 as secondary phases depend (in both amount and spatial organization) on the varied co-sintering temperature of the GDC/YSZ electrolyte. The ion-blocking SrZrO3 forms a continuous layer on top of the temperature-dependent GDC/YSZ interdiffusion zone (ID) at and below a co-sintering temperature of 1200 degrees C; above it becomes intermittent. 2D FIB/SEM images of primary and secondary phases at 1100, 1200, 1300 and 1400 C were combined with a 3D FIB/SEM reconstruction (1300 degrees C). This reveals that "preferred" oxygen ion transport pathways from the LSCF cathode through GDC and the ID into the YSZ electrolyte only exist in samples sintered above 1200 degrees C. The applied correlative technique expands our understanding of this multiphase cathode/electrolyte interface region. (C) 2017 Elsevier B.V. All rights reserved.

The mixed ionic-electronic conducting cathode (La, Sr)(Co, Fe)O3-δ (LSCF) is utilized worldwide for solid oxide fuel cells (SOFCs) operated at intermediate temperatures [1] because of its excellent oxygen reduction reaction rate. The challenge of using LSCF as cathode material is the complex nature of the interface to Zirconia-based electrolytes, which may counteract this advantage [2, 3]. The composite cathode (La, Sr)MnO3 (LSM) – Y2O3 doped ZrO2(YSZ) is an adequate alternative for higher temperatures only. LSM-YSZ offers fewer regions of oxygen reduction (triple phase boundaries) due to spatially separated ionically (YSZ) and electronically (LSM) conductive phases. If electrochemical and microstructural parameters of both types of electrodes are quantified by appropriate techniques, the performance can be modeled and compared for different operating conditions. Advanced imaging techniques such as focused ion beam/scanning electron microscopy (FIB/SEM) or X-ray tomography are promising techniques for microstructure quantification enabling 3D reconstructions of µm- and sub-µm-scaled multiphase electrodes [4, 5, 6]. Reconstructing the composite cathode, in particular, comprises the challenge of overcoming the weak material contrast between LSM and YSZ using scanning electron microscopy. This contribution will show how FIB/SEM tomography can help to identify different microstructural parameters such as porosity, particle size, surface area and tortuosity. We will compare LSCF and LSM-YSZ cathodes and enlighten new challenges in image reconstruction, parameter acquisition and parameter interpretation for the different material sets. [1] H. Yokokawa, et al., J. Power Sources, 182, p. 400 (2008) [2] J. Szasz, et al., ECS Trans., 66(2), p. 79 (2015) [3] Yokokawa, et al., Solid State Ionics, 262, p. 454 (2014) [4] J.R. Wilson, et al., Nature Materials 5(17), p. 541 (2006) [5] J. Joos, et al., Electrochim. Acta 82, p. 268 (2012) [6] Y. C. K. Chen-Wiegart, et al., J. Power Sources, 218, p. 348 (2012) Figure 1

(La, Sr)(Co, Fe)O3-delta (LSCF) and the composite (La, Sr)MnO3 (LSM) - Y2O3 doped ZrO2 (YSZ) are the most commonly used cathode materials for solid oxide fuel cells (SOFCs). If electrochemical and microstructural parameters of these electrodes are known from appropriate techniques, the performance can be modeled and compared for different operating conditions. Advanced imaging techniques such as focused ion beam/scanning electron microscopy (FIB/SEM) tomography have shown their potential for microstructure quantification. This contribution will show how FIB/SEM tomography can be used to identify microstructural parameters such as porosity, particle size, surface area and tortuosity. A comparison between LSCF and LSM-YSZ cathodes is given, including a demonstration of how a change in tomography parameters allows distinguishing the different phases especially in composite cathodes to overcome challenges in reconstruction and parameter acquisition.

Electrode performance of lithium ion battery cathodes is strongly affected by its microstructure parameters. FIB (focused ion beam) / SEM (scanning electron microscopy) tomography is a powerful tool for determining microstructure parameters. The application of this method and processing of images has been optimized for battery electrodes [1], enabling an accurate detection of the three components (1) carbon black, (2) pore phase and (3) active material. A special challenge is to distinguish between different active materials which are combined in blend electrodes for optimizing their performance and energy density. In this study, a dual beam modus is applied for analyzing the composition and microstructure of a blended battery cathode consisting of three active materials (NMC, NCA and LMO). By combining the information of InLens and Everhart-Thornley detector it was possible to reconstruct a volume of 35µm x 37µm x 20µm consisting of 1010 x 1070 x 570 voxel (isotropic voxelsize of 35 nm). The pore phase and the carbon black were segmented by evaluating images acquired using the Everhart-Thornley detector, due to lower falsification by local charging, whereas the active material was separated into its three components interpreting information of InLens detector which provides a better contrast of specific material. It was possible to clearly assign the three materials, confirmed by EDX analysis, and to calculate microstructure parameters for every specific component, as particle size distribution, active surface area, porosity and tortuosity. Limiting factor for an application of this method is the representative volume element size which is dependent of the number of active materials as well as their maximum particle size, as reported in [2] for solid oxide fuel cells. For prospective studies, an increased reconstruction volume is necessary while maintaining high resolution of images, which is challenging with regard to FIB-procedure as well as processing of big data amount. Alternative tomography methods as X-ray tomography enable the reconstruction of larger volumes, but suffer from low contrast of carbon black and limited resolution. Advantages and disadvantages of the different tomography methods are discussed and assed. [1] M. Ender, J. Joos, T. Carraro and E. Ivers-Tiffee, Journal of the Electrochemical Society, 159, A972-A980 (2012) [2] J. Joos, M. Ender, T. Carraro, A. Weber and E. Ivers-Tiffée, Electrochemica Acta, 82, 268-276 (2012)