bluuebunny/crossref_metadata_2025 huggingface dataset:
Limitations of Grain Boundary Engineering - Ionic Versus Electronic Conductivity
Authors: Huber Tobias M. , Navickas Edvinas , Sasaki Kazunari , Yildiz Bilge , Tuller Harry L. , Fleig Juergen , Chen Yan
Published: February 2020

Much attention has recently been focused on the oxygen reduction via Sr-doped lanthanum manganite grain boundaries (GBs) since oxygen transport, as well as surface exchange is approximately 1000x faster at the GBs than for the LSM bulk. With this in mind, there is a strong incentive to tailor properties of thin films by GB engineering. To date, the effect on the el. conductivity has not been studied for such engineered films. In this study, changing microstructure, as well as strain, were found to heavily influence el. charge transport. More specifically, for example, the el. conductivity decreased while ionic conductivity increased with decreasing grain size. For given current collector distance, one could optimize grain size to achieve optimum mixed conductivity. In addition 18O tracer exchange experiments were performed on the same thin films in a novel operando experimental design to study the influence of cathodic bias upon surface exchange and transport properties of both LSM grains and GBs.

LSM thin films were deposited by PLD and analyzed by ToF-SIMS, Van der Pauw and impedance spectroscopy. SIMS profiles showed a large increase in 18O concentration in the LSM films with an apparent uphill diffusion. Such experiments were prior performed on microelectrode which require specially designed exchange equipment and a high degree of user expertise. Therefore a novel experimental design was developed which can be performed in conventional set-ups to study the influence of polarization in-operando. This new experimental design facilitates the ability to investigate several voltage changes in every required voltage region under SOFC operation conditions within one and the same thin film sample. The apparent uphill diffusion could be simulated by a 3D finite element model with two parallel and interacting diffusion pathways.
Elucidating the Origin of Oxide Ion Blocking Effect at GDC/Srzr(Y)O3/YSZ Heterointerfaces
Authors: Bagarinao Katherine Develos- , Yokokawa Harumi , Kishimoto Haruo , Ishiyama Tomohiro , Horita Teruhisa , Yamaji Katsuhiko
Published: February 2020

Solid oxide fuel cells (SOFCs) have attracted significant attention over recent years due to their promising use as source of clean and efficient power generation. Towards the goal of enhancing the efficiency of these devices, it is important to eludicate the mechanisms governing fundamental electrochemical processes, specifically incorporation and transport of oxygen species across heterostructures. Degradation of cell performance has been attributed to the formation of SrZrO3 (SZ), especially along the GDC/YSZ interface, resulting from cation interdiffusion across LSCF/GDC/YSZ heterostructures. In this study, using a combination of isotope oxygen tracer and secondary ion mass spectroscopy (SIMS) depth profiling, we examined oxide ion transport in dense SZ and Y-doped SrZrO3 (SZY) thin films in conjunction with other oxide materials in a multilayered heterostructure, viz., GDC/SZ(Y)/YSZ. The GDC/SZ(Y) multilayers were prepared on (100) YSZ single crystal substrates using pulsed laser deposition; X-ray diffraction results confirmed that the SZ and SZY films were highly oriented along (h00). SIMS depth profile measurements after isotope exchange revealed that ionic transport is drastically inhibited at the SZ(Y)/YSZ interface, indicating the existence of an oxide ion barrier which blocks ionic flow. A similar behavior was also observed at the GDC/SZ interface; however, this was not observed for GDC/SZY. To elucidate the mechanism for the oxide ion blocking effect, we performed detailed microstructural analyses of the interfaces using transmission electron microscopy (TEM) and spatially resolved electron energy loss spectroscopy (EELS) technique. TEM results showed that the GDC/SZ(Y) and SZ(Y)/YSZ interfaces are atomically sharp and devoid of any secondary phases. The SZ film also appears to contain a high density of microstructural defects such as stacking faults which extend across its thickness. Furthermore, evident changes in the O K-edge EELS spectra measured across the heterostructures suggest the possible existence of oxygen disorder in the YSZ region adjacent to the SZ(Y)/YSZ interface. This may indicate a possible link between oxygen disorder, which can effectively break the oxygen diffusion pathways, and blocking of oxide ion transport across the SZ(Y)/YSZ interface.
First-Principles Analysis of Oxygen Incorporation into Sr(Ti1-xFex)O3-D : Using External Dopants to Tune the Incorporation Mechanism
Authors: Kim Namhoon , Ertekin Elif
Published: February 2020

Although solid oxide fuel cells have been under intensive investigation for several decades, their practical development is hindered still by several fundamental challenges. One in particular is related to the kinetics of the electrode reactions, especially with respect to oxygen exchange at the cathode. Oxygen exchange requires chemisorption, dissociation, and incorporation, and can involve a complicated set of competing processes: for example, it may occur through directly via gas phase oxygen interaction with a surface vacancy through an active site-mediated mechanism, or it may occur directly onto a pristine surface with vacancies in the interior serving only as the final sink for the incorporated oxygen species. Often, resolving the rates of the relevant processes is challenging.

The material Sr(Ti1-xFex)O3-
d(STF) is a model system for the study of oxygen exchange mechanisms on electrodes of solid oxide electrodes. The perovskite material is stable in a wide range of oxygen partial pressures, and exhibits a flexible defect chemistry and electronic structure. The B-site substitution of Ti for Fe results in fast oxygen exchange kinetics. Even so, there remain several questions about the rate limiting steps to oxygen exchange in these materials, with contradictory suggestions that oxygen incorporation is limited by either electron transfer to the adsorbed molecules at the electrode surface or by the vacancy concentration at the surface.

In this work, we will present the results of our first-principles calculations to provide some clues to the nature of oxygen incorporation in STF. We use density functional theory to consider several incorporation mechanisms under different environmental conditions. In particular, we consider how the presence of external dopants (eg A-site doping with La) might allow access to different ranges of oxygen vacancy concentrations and carrier concentrations in the material. We will show (i) the results of a defect chemistry equilibrium model to calculate the equilibrium defect concentrations and carrier concentrations in different chemical environments and under different degrees of extrinsic doping, and (ii) the reaction mechanism for oxygen molecule adsorption at the surface for different degrees of doping. The defect chemistry model shows that the concentration of oxygen vacancies and the Fermi level of the material can be tuned by the incorporation of external dopants. Further, according to our simulations, we predict that the most favorable pathway for oxygen incorporation can be controllably changed from an active-site mediated mechanism to a direct adsorption mechanism by appropriately tuning the dopant concentration.
GDC Diffusion Layer for Improving Electrochemical and Mechanical Property of the Intermediate Temperature Solid Oxide Fuel Cell
Authors: Kim Sungmin , Jang Inyoung , Kim Chanho , Song Taeseup , Yoon Heesung , Paik Ungyu
Published: February 2020

The yttrium stabilized zirconia (YSZ) electrolyte with La0.6Sr0.4Co0.2Fe0.8O3 (LSCF) cathode system was studied for the intermediate temperature solid oxide fuel cell which operate 650℃. However, the reaction that occurs at the interface of YSZ electrolyte and LSCF creates the insulating layer. In this study, to prevent the reaction, 500nm thickness of Ce0.9Gd0.1O2−δ (GDC) diffusion layer was loaded at the surface of the YSZ electrolyte by dip coating method and it effectively limited the creation of the secondary phase. Also, more connecting points with LSCF cathode were created and it improved the conductivity and the mechanical wettability with LSCF cathode. Before and after operating, the microstructure of the surface and cross-section were observed with Scanning Electron Microscopy (SEM) analysis. The creation of the secondary phase and composition of each layer were examined by Energy Dispersive X-ray Spectroscopy (EDS) mapping. The Electrochemical Impedance Spectroscopy (EIS) plot showed that when the GDC diffusion layer was loaded the ohmic and polarization resistances were significantly decreased. Current-Voltage curve (IV-curve), Power density and Electrochemical Impedance Spectroscopy (EIS) were measured and it demonstrated the enhanced performance.
Synthesis and Evaluation of Ni/BaCe0.5Zr0.3Y0.2O3-d Hydrogen electrode for Proton Conducting Soecs
Authors: Nishikawa Ryosuke , Nishino Hanako , Kakinuma Katsuyoshi , Brito Manuel E. , Uchida Hiroyuki
Published: February 2020

Solid oxide electrolysis cells (SOECs) are promising candidates for highly efficient hydrogen generation. In particular, proton-conducting SOECs have the advantage of producing high-purity dry hydrogen. For the practical application of proton-conducting SOECs, the development of highly efficient hydrogen electrodes with gas diffusion pathways and proton-electron mixed conducting pathways is required. In this research, we propose a new design concept of a current collecting / catalyst double layer (CCL/CL) hydrogen electrode using a proton-electron mixed conductor, BaCe0.8-xZrxY0.2O3-δ (BCZY), with a unique fused-aggregate network structure (Fig. 1) for proton-conducting SOECs. We also evaluated the performance of the hydrogen electrode as a function of the Ni loading amount.

The proton-electron mixed conductor (BCZY (x = 0.3)) powder was synthesized by the flame oxide-synthesis method. The BCZY (x = 0.7) electrolyte was prepared by solid state reaction. The BCZY (x = 0.3) scaffold was synthesized on the BCZY (x = 0.7) electrolyte by sintering at 1000°C for 4 h in air. The CCL of Ni-BCZY (x = 0.3) composite was formed on the BCZY (x = 0.3) scaffold at 1050°C after 4 h. The Ni nanoparticle catalysts were loaded on the BCZY (x = 0.3) scaffold by an infiltration method to obtain the CL. The counter electrode was a Pt-BCZY (x = 0.3) composite. The crystal phases were characterized by XRD, ICP-MS and STEM-EDX. The performance of the double-layer electrode was evaluated under hydrogen flow at 700°C.

The XRD patterns for BCZY (x = 0.3) and BCZY (x = 0.7) were consistent with a single perovskite phase. BCZY (x = 0.3) had a unique microstructure, with a fused-aggregated network structure, which was able to provide a gas diffusion pathways and proton-electron mixed conducting pathways while maintaining the high surface area (Fig. 2(a)). The STEM-EDX image of a cross-section of the CL showed that the Ni nanoparticles (diameter 70 ± 12 nm) were highly dispersed on the fused-aggregated BCZY (x = 0.3) scaffold (Fig. 2(b)). The polarization curves of the double-layer electrode showed that the electrode performance improved with increasing Ni loading amount up to 20 vol.%. The Ni particles maintained a highly dispersed state on the BCZY (x = 0.3) scaffold, indicating that the increased effective reaction zone (ERZ) was able to enhance the performance of the double-layer electrode. At Ni content ≥ 20 vol.%, the electrode performance decreased significantly. This was ascribed with certainty to a decrease in the extent of the ERZ, because the aggregation of Ni particles was observed by STEM.

Reference

K. Katahira, Y. Kohchi, T. Shimura and H. Iwahara Solid State Ionics,
138, 91 (2000).

Figure 1
Feasibility of (Ni-GDC/GDC half-cell) Manufactured By Tape Casting and Reactive Magnetron Sputtering Processes
Authors: Hernandez Londono Carlos , Combemale Lionel , Gao Fei , Billard Alain , Briois Pascal
Published: February 2020

Nickel Oxide and Gadolinium Doped Ceria (10% Gd) powders, with -40 mesh and -100 mesh particle size respectively, were mechanically milled in a Turbular-(System Schatz Willy a Bachofeng) up to 24 to 48 hours. Half-cells, 28 mm of diameter, Ni-GDC composite anodes have been fabricated by slurry based tape casting (Elcometer4340 Automatic Film Applicator) method for anode supported solid oxide fuel cell [1]. The chosen ceramic powders in suspension was prepared with the mass ratio of 65:35 for NiO to GDC10 maintained constant. The microstructural evolution of powders (crystallite size) was followed by means of X-ray diffraction (XRD) and Scanning electron microscopy (SEM). The anode porosity was examined by Archimedes method [2]. The pre-sintered anode green tape were coated with a GDC electrolyte film by reactive magnetron sputtering using PEM techniques [3]. An Alcatel SCM650 sputtering chamber was used for synthesizing the dense GDC layers. A Ce-Gd metallic target (90-10% at) was powered by a pinnacle + pulsed current generator from Advanced Energy. The structural, microstructural and morphological features of the half-cells were determined by XRD, SEM and 3D profilometry as deposited and after different annealing treatments. Finally, the EIS measurements were performed on Ni-GDC/GDC half-cells under 60 sccm nitrogen by the means of a Solartron SI 1260 impedance / gain analyzer from 20 MHz to 0.1 Hz with 11 points per decade.

References

[1] Fabrication and characterization of Ni-SSZ gradient anodes/SSZ electrolyte for anode-supported SOFCs by tape casting and co-sintering technique. Chao Jin, Yachun Mao, Naiqing Zhang, Kening Sun. Harbin, China. Institutional Journal of Hydrogen Energy.

[2] Manufacturing and Characterization of Single cell Intermediate-Temperature Solid Oxide Fuel Cells for APU in transportation application. Visweshwar Sivasankaran. Dijon France. 2ICB- Département I.RM. Université de Bourgogne-CNRS

[3] F. Perry, A. Billard, C. Frantz, Surface Coatings Technology 94-95 681 (1997).
Nanocomposite YSZ-NiO Particles with Tailored Structure Synthesized in a Two-Stage Continuous Hydrothermal Flow Reactor
Authors: Zielke Philipp , Xu Yu , Kiebach Wolff-Ragnar , Simonsen Søren Bredmose , Norby Poul , Hendriksen Peter Vang
Published: February 2020

The increasing amount of fluctuating electricity generation from renewable sources requires a flexible energy system and storage technologies to ensure that energy services can be covered in a stable and affordable manner. In order to become truly independent from fossil fuels, increasing the performance of energy storage and conversion devices such as fuel cells, electrolyzers and batteries is important. One promising approach to further improve these devices is the use of carefully structured nanosized materials. Nano-composite particles combining different materials in advanced geometries like core-shell structures or surface decorated particles could exhibit better performance compared with single phase materials. To obtain such advanced structures is the aim of the ProEco project (www.proeco.dk). In this project, a two-stage continuous reactor is built and used to synthesize such nano-composites.

Here we report on the design of the two-stage continuous hydrothermal flow synthesis reactor and first results on obtaining structured nano-composite consisting of yttria-stabilized zirconia (YSZ) and NiO materials. These materials are commonly applied in the fuel electrodes of today’s state-of-the-art solid oxide fuel and electrolysis cells. The prepared particles were characterized by X-ray powder diffraction, (high resolution) transmission electron microscopy, scanning tunnel transmission microscopy and Raman spectroscopy in order to determine crystal structure, particle size, surface morphology and element distribution.
Understanding the Conductivity Degradation Mechanism of Er2O3-Stabilized Bi2O3
Authors: Yun Byung-Hyun , Lee Kang Taek
Published: February 2020

Rare earth stabilized bismuth oxides have attracted much attention due to their high oxygen ionic conductivity. Among singly-doped stabilized bismuth oxides, the Er2O3-stabilized Bi2O3, which is generally abbreviated to ESB, is particularly known for its superior ionic conductivity to even other stabilized Bi2O3s, not to mention conventional oxygen ion conductors such as doped ceria and stabilized zirconia[1]. In spite of its remarkable ionic conductivity (≈ 0.3S/cm at 700℃), ESB has not been practically employed as a SOFC electrolyte. This is not only because ESB has thermodynamic instability under reduction conditions, but also because it experiences time-dependent conductivity degradation on extended annealing below 600℃.

 In this study, the crystallographic structure and conductivity of ESB were analyzed using X-ray diffraction and electrochemical impedance spectroscopy, respectively, during its prolonged annealing at 600℃ over 400h in order to investigate the mechanism of the time-dependent conductivity degradation of ESB. It was found that the initial cubic phase of ESB was mostly transformed to the rhombohedral phase within first 100h. At the same time, the discrepancy in time constant of the phase transformation(65h) and the conductivity degradation(52h) was observed. In order to elucidate this time constant discrepancy, the activation energies of low temperature domain before and after annealing were evaluated. The activation energy of as-sintered ESB was approximately 1.2eV, whereas that of the annealed ESB was approximately 1.01eV. Such a decrease in the activation energy can be attributed to order-disorder transition of the oxygen sub-lattice in ESB[2]. Therefore, the conductivity degradation of ESB is probably the combined effect of the phase transformation from cubic to rhombohedral as well as the order-disorder transition.

Acknolwdge

This research was supported by (1) Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (2014R1A1A2057681), (2) the DGIST R&D Program of the Ministry of Science, ICT and Future Planning of Korea (1501- HRLA-01) and (3) the Global Frontier R&D on Center for Multiscale Energy System funded by the National Research Foundation under the Ministry of Science, ICT & Future Planning, Korea (2014M3A6A7074784).

References

[1] M.J. Verkerk et al., J. Appl. Electrochem., 1980, 10, 81.

[2] E.D. Wachsman, J. Eur. Ceram. SOC., 2004, 24, 1281

Figure 1
Electron-Ion Mixed Conduction of Nd0.6Sr0.4FeO3 Cathode Electrode Thin Film for Solid Oxide Fuel Cell
Authors: Namiki Wataru , Tsuchiya Takashi , Minohara Makoto , Kobayashi Masaki , Horiba Koji , Kumigashira Hiroshi , Higuchi Tohru
Published: February 2020

Ln1-x
Sr
x
FeO3 (Ln=La, Nd) bulk crystal exhibits various electrical and magnetic properties by Ln substitution.  In particular, Ln1-xSrxFeO3 has been extensively studied in the bulk and thin film forms due to electrochemical application of cathode electrode for Solid Oxide Fuel Cell (SOFC).  However, La1-x
Sr
x
FeO3 thin film as electrode is not practical material since the mixed conduction is low.  Therefore, new cathode material with high mixed conduction and durability is necessary for realization a practical SOFC device.  In this study, we have prepared the Nd0.6Sr0.4FeO3 thin film on Al2O3 substrate by RF magnetron sputtering and characterized its electrical conductivity.

The Nd0.6Sr0.4FeO3 (NSFO) thin film was deposited on Al2O3 (0001) substrates by RF magnetron sputtering using a ceramics target.  The NSFO ceramics target for sputtering was prepared by the solid-state reaction method.  The flow rate of Ar gas, the deposition pressure , and substrate temperature were set at 0.67 sccm , 8.0×10-3 Torr and 700 ˚C, respectively.  The film thickness was changed between ~42 and ~160 nm. The structural properties of the NSFO thin films were characterized by powder X-ray diffraction (XRD) analysis.  

The electrical conductivity was measured by the AC impedance method in dry atmosphere in a temperature region from 300 to 700 ˚C.  The measurement frequency region was from 0.1 Hz to 32 MHz. In order to probe conducting carriers, the conductivity was measured by changing oxygen gas partial pressure (PO2).

The electronic structure was characterized by photoemission spectroscopy (PES) and X-ray absorption spectroscopy (XAS).  The energy resolutions of PES and XAS were 100 and 60 meV, respectively, at hν=1010 eV. 

The lattice constant of the (112)-oriented thin film increases with increasing film thickness due to relaxation of lattice distortion.  The chemical composition of the thin film was confirmed by PES.  The electrical conductivity depends on film thickness.  The conductivity increases with film thickness in 40~112 nm and decreases in 156 nm.  This result is closely related to the lattice constant.  The 112 nm thick film exhibits high conductivity and low activation energy (EA) of 0.45 eV.  The EA is in a good agreement with the band gap obtained by PES and XAS, indicating the electron conduction.  Furthermore, the conductivity above 500 ˚C does not depend on oxygen gas partial pressure, which corresponds to ionic conduction.  The above results indicate that the Nd0.6Sr0.4FeO3 thin film has the oxygen ion-electron mixed conduction.
System Design Optimization with Process and Heat Balance Analysis to Enhance SOFC Performance
Authors: Tachikawa Yuya , Matsuzaki Yoshio , Somekawa Takaaki , Taniguchi Shunsuke , Sasaki Kazunari
Published: February 2020

Higher fuel utilization (Uf) improves SOFC electrical efficiency. However, a high Uf operation causes nickel-oxidation-induced SOFC anode degradation. One solution to operate an SOFC system under high Uf conditions without severe damage could be a multi-stage fuel oxidation concept. Electrical efficiency improvement by system design with a two-stage SOFC stack model has been presented in our previous study. The SOFC system using the multi-stage concept kept enough low Uf on each stack to prevent from the damage and could achieve totally high gross fuel utilization. In this study, to achieve much higher electrical efficiency using the multi-stage concept, a synergistic effect to combine the multi-stage stack concept and an anode offgas recirculation was evaluated using process and heat balance analysis. In the case of a methane-fueled two-stage SOFC system, much higher gross fuel utilization was obtained when the anode offgas recirculation was applied. An electrical efficiency of 77% LHV could be obtained to keep operating under a lower Uf condition on each stack than 75%. When a different kind of fuel such as biogas, composed of 60% CH4 and 40% CO2, was fueled to the same SOFC system, the electrical efficiency slightly dropped but achieved over 72% LHV. Although it should be necessary to optimize the operating condition such as the amount of water vapor supply fed to a fuel pre-reformer, a multi-stage fuel-recycled SOFC system can achieve highly-efficient power generation using various fuels.
Oxygen Activity in a-Site Ordered Perovskites through in-Situ Neutron and Synchrotron X-Ray Diffraction
Authors: Taylor Daniel D. , Levitas Benjamin D. , Rodriguez Efrain E.
Published: February 2020

A-site ordered perovskites have been investigated for a number of solid-state oxide conducting applications including oxygen storage, solid oxide fuel cells, and solid oxide electrolysis cells. By combining a large divalent cation (e.g. Ba2+) with a smaller trivalent cation (e.g. Y3+), it is possible to form 2 dimensional layers of highly mobile oxide anions. This stems from the smaller coordination number typically stable around the trivalent cation than is present in the prototypical perovskite structure – the A-site ordered structure is provided in Figure 1. Within these layers, oxygen is able to quickly and topochemically be inserted or extracted in the case of oxygen storage materials, or transported in the case of solid oxide fuel and electrolysis cells.

Despite this link between these materials’ layered structures and their high oxygen activity, fundamental questions remain as to which structural features are key in determining their performance. Furthering this understanding will help in the future design of oxygen conducting and storing materials.

To this end, we used in-situ neutron and synchrotron X-ray diffraction to study the structure of BaYM2O5+δ for M = Mn, Fe, and Co, under operating conditions - both oxidizing and reducing conditions at elevated temperatures. With an aim to link the local coordination around the redox active transition metals to the materials performance, we were able to track how the structure of the materials change with oxygen content and temperature. A number of different phase transitions were observed for each material potentially affecting the oxygen mobility within these materials. These insights into how the chemical environment of oxygen changes under operation conditions will aid in the future design of materials with high oxygen mobility.

Figure 1
Controlled SOFC Anode Porosity Using Aligned Sacrificial Fibers
Authors: Hays Thomas H , Wachsman Eric D
Published: February 2020

Solid oxide fuel cell anode supports serve a multipurpose role. This layer must be both the mechanical backbone of the cell and an active electrode. While high porosity is desired to maximize reaction sites, it negatively impacts strength. Therefore, efforts should be made to design anode microstructure for high strength while maintaining electrochemical performance.

Currently, solid oxide fuel cell anodes are fabricated such that there is little control over the final microstructure. A new technique for creating porous anode support layers in solid oxide fuel cells was developed. Using sacrificial, high aspect ratio pore formers, anode support layers with non-random porosity networks were created utilizing dielectrophoresis. Variation in applied voltage and frequency during dielectrophoretic treatment allowed control over the resulting structure. Microstructure analysis and electrochemical testing of novel anode support layers was performed and compared to results of standard SOFC designs.
Novel Thin Film Solid State Ionic Device with Electrochemically Tunable Resistance Based on Lithium Plating/Stripping
Authors: Oukassi Sami , Berr Bruce , Poncet Séverine , Secouard Christophe , Amiran Johnny , Poulet Sylvain , Salot Raphaël
Published: February 2020

Electrochemically induced property tuning has recently emerged as a promising pathway to achieve accordable devices and reconfigurable circuits, in most cases making use of the change of one or several material properties with ion exchange or the local electroformation of conducting structures in an insulating material [1–3]. In the present work we report on the electrochemical tuning of a solid state ionic device impedance using lithium ion plating and stripping at a current collector/solid electrolyte interface [4,5].

The device presented a design with two actuation vertical metal electrodes separating a Cu/LiPON/Li multilayer, and two measurement interdigitated electrodes embedded in the LiPON layer. The measurement electrodes were isolated from the bottom actuation electrode by an Al2O3 dielectric layer (Fig1). The devices were microfabricated on silicon substrates with varied architectures including lithium plating surfaces ranging between 1µm² and 3000µm² (Fig.2).

Upon chrono-potentiometric stimuli, lithium was plated between the measurement electrodes, thus changing significantly the impedance, and more particulary the electrical resistance. Fully reversible variation of the real part of the impedance (Re Z) over a range of more than 3 decades was observed by electrochemical impedance spectroscopy upon the formation and dissolution of nanometric lithium layer (Fig.3). Particular attention was put on the investigation of the influence of the current density during plating/stripping (plated lithium morphology), and the architecture (interdigitated electrodes design, plating surface) on the device performance.

References

[1] X. Meng, F. Quenneville, F. Venne, E. Di Mauro, D. Işlk, M. Barbosa, et al., Electrolyte-Gated WO3 Transistors: Electrochemistry, Structure, and Device Performance, J. Phys. Chem. C. 119 (2015) 21732–21738. doi:10.1021/acs.jpcc.5b06777.

[2] I. Valov, R. Waser, J.R. Jameson, M.N. Kozicki, Electrochemical metallization memories--fundamentals, applications, prospects., Nanotechnology. 22 (2011) 254003. doi:10.1088/0957-4484/22/28/289502.

[3] F. Xiong, H. Wang, X. Liu, J. Sun, M. Brongersma, E. Pop, et al., Li Intercalation in MoS2: In Situ Observation of Its Dynamics and Tuning Optical and Electrical Properties, Nano Lett. 15 (2015) 6777–6784. doi:10.1021/acs.nanolett.5b02619.

[4] M. Motoyama, M. Ejiri, Y. Iriyama, Modeling the Nucleation and Growth of Li at Metal Current Collector/LiPON Interfaces, J. Electrochem. Soc. 162 (2015) A7067–A7071. doi:10.1149/2.0051513jes.

[5] M. Motoyama, M. Ejiri, Y. Iriyama, In-Situ Electron Microscope Observations of Electrochemical Li Deposition/Dissolution with a LiPON Electrolyte, Electrochemistry. (2014) 3–7. doi:10.5796/electrochemistry.82.364.

Figure 1
(Invited) Electrochemical Properties of Graphite Electrode in Propylene Carbonate-Based Electrolyte Solution Containing Mg Salt
Authors: Abe Takeshi , Takeuchi Saya , Song Heeyoub , Kokumai Ryohei , Miyazaki Kohei , Fukutsuka Tomokazu
Published: February 2020

It is well-known that charge-discharge reactions of graphite electrode cannot take place in propylene carbonate (PC) based electrolyte solutions. Since the melting point of PC is much lower than that of ethylene carbonate (EC), PC-based electrolyte solutions are preferable when lithium-ion batteries are operated in the lower temperature regions.

Vast work has been done on graphite electrodes in PC-based electrolyte solutions. One of our colleagues, Jeong found that concentrated salt PC solutions enabled charge-discharge reactions at graphite electrodes [1]. This was the first approach for use of concentrated salt electrolyte solutions. The concept of the concentrated electrolyte solutions was the change of the solvation states of lithium-ion.

We also found that the addition of divalent cations such as calcium ion and magnesium ion in the PC-based electrolyte solutions also made graphite electrode active for the intercalation/de-intercalation of lithium-ion [2,3]. Since the Lewis acidities of Mg2+ and Ca2+ are higher than that of Li+, PC should preferentially solvate with the divalent cations. This will result in the change of solvation states of lithium-ion. Then, charge-discharge reactions could take place at graphite electrode.

Further, we used “in situ” atomic force microscopy (AFM) for the understanding of the formation of solid electrolyte interface (SEI) on graphite electrode in PC-based electrolyte solutions containing Mg2+. As a result, we found the co-intercalation of lithium-ion and solvent was suppressed by the addition of Mg2+. The detail will be reported in the conference.

References

[1] S. K. Jeong, Electrochem. Solid State Lett. 6, A13 (2003)

[2] S. Takeuchi et al., Electrochim. Acta, 56 (2011) 10450.

[3] S. Takeuchi et al., submitted.

Acknowledgement

This work was partially supported by CREST, JST and JSPS KAKENHI Grant Number 16H04216.
High Voltage Compatible Bi-Functional Electrolyte for Li Metal Batteries
Authors: Chang Won-seok , Sugimoto Toshinori , Mizumo Tomonobu , Lee Yong-Gun , Choi Hong Soo , Kang Hyorang , Yu Taehwan , Doo Seokgwang
Published: February 2020

In a few decades, the huge advancement was achieved via successful commercialization of Li ion batteries. As the demand for more stable energy supply source grows, the necessity to replace the conventional carbon anode also is being increased. Lithium metal has been suggested as one of the candidates. However, it has few critical barriers regarding the safety which must be overcome to be successful alternative for the next generation batteries. Among diverse approaches, introducing a safe electrolyte to the system could be one step forward for Lithium metal to be used as the next generation batteries.

In this study, the glyme based electrolyte was formulated by simply making a solution with Lithium bis(fluorosulfonyl)imde (LiFSI), 1-2, dimethoxy ethane and the fluorinated ether. This mono-glyme has been known to be effective to restrain Lithium dendritic growth1. Also, it can dissolve LiFSI salt up to 9.6 mol. Since, highly concentrated electrolyte is able to put up with relatively high electrochemical stability2, thus, it could be a favorable solvent for the electrolyte. On the other hand, the fluorinated part of the electrolyte (1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether) could not dissolve the salt at all, but, it functions as an anti-oxidation agent and a viscosity lowering agent at the same time.  In Figure 1(a), it was proven that the electrolyte comprising those two components is quite effective to maintain the stability within the practical voltage window ranged from 3.0 ~ 4.5 V (vs. Li/Li+) via cyclic voltammetry (CV).

Based on the stability, it also shows the full cell test results indicating outstanding cycle performance over 200 cycle even with highly packed cathode (c.a. 4g/cc) as illustrated in Fig. 1(b). The extended performance is attributed to the synergistic contribution from each component of the electrolyte.
Highly-Ordered Structural Deposition of Li2O2 in Li-O2 Battery
Authors: Hase Yoko , Seki Juntaro , Shiga Tohru , Nishikoori Hidetaka , Iba Hideki , Takechi Kensuke
Published: February 2020

Non-aqueous Li-O2 battery is one of the possible alternatives to current lithium ion batteries due to its theoretical high energy density, however, it still presents unsolved fundamental issues related to poor cycle life and low current density. Li2O2, which has been accepted as a discharge product, shows inherently low electron conductivity and its deposition on cathodes leads the obstruction of continuing discharge reaction. Therefore, in many cases, nano-structural carbon materials with large surface area have widely been applied as cathode to obtain specific high discharge capacity.

Herein we present an alternative strategy to enhance the discharge capacity in the Li-O2 batteries with controlling the morphology of the deposition. We anticipated that the continuous steady discharging could be obtained if the reaction active sites on the cathode were not clogged with discharge products which were deposited in highly-order structure. In this study, we focused on the effect of the combination of cathode materials and electrolytes on the discharge capacity and the morphology of Li2O2. Figure 1. shows that relatively high current density (0.2 mA/cm2) and high discharge capacity (> 600 mAh/g) were obtained with the carbon paper cathode and the acetonitrile (AN) electrolyte (0.5 M LiTFSI in AN). In contrast, tetraethylene glycol dimethyl ether (TEGDME) or dimethyl sulfoxide (DMSO), which have higher viscosity and lower O2 solubility than acetonitrile, 1 resulted in the lower discharge capacity (< 30 mAh/g) when they were used as a solvent of the electrolyte under the same condition. We figured out the interesting correlation between the characteristic structure of Li2O2formed in the AN electrolyte and the discharge behavior that showed the oscillatory phenomena in the galvanostatic discharge process.

1) Laoire, C. O.; Mukerjee, S.; Abraham, K. M.; Plichta, E. J.; Hendrickson, M. A. J. Phys.Chem. C
2010, 114, 9178-9186.

Figure 1
Monte-Carlo Simulation of the Ionic Transport of Electrolyte Solutions at High Concentrations Based on the Pseudo-Lattice Model
Authors: Kiyobayashi Tetsu , Kuratani Kentaro , Ozaki Hiroyuki
Published: February 2020

The theoretical understanding of the ionic transport in electrolyte solutions is not yet well-established at high concentrations, such as at C/M > 1. In our present study, two transport phenomena---self-diffusion and ionic conduction---of the electrolyte solution at high concentrations (roughly 0.05 ≤ C/M ≤ 3) are computationally simulated by a kinetic Monte-Carlo scheme. A swap mechanism in the three-dimensional pseudo-lattice is proposed to model the movement of ions and solvent, in which only the nearest-neighbor interaction is considered. The energy difference between the before- and after-swap states, based on which the stochastic Monte-Carlo process occurs, is found to be expressed in only two energetic terms; the coulombic repulsion between ions with the identical sign, +εii, and the heat of dissolution of the ionic crystal, Δdiss
H. The self-diffusion coefficients of both ions and solvent decrease with the increase in the ionic concentration, which qualitatively agree with the experimental observation. The asymmetric bell-shape of the specific conductivity, σ, principally originates from the coulombic repulsion. The ionic concentration at which the maximum σ occurs well coincides with that of the experimentally observed results. The Δdiss
H-dependency reveals that, ceteris paribus, σ marks the highest at around -2kT < Δdiss
H< 0, out of the range of which σ is attenuated by either the ion-ion or ion-solvent interaction. Finally, the limitations in the model are addressed.

The detail of the study is in press at the date of 15 April 2016 in J. Electrochem. Soc.

Figure 1
Applications of Solution Process for Li4SnS4-Based Solid Electrolytes to All-Solid-State Lithium-Ion Batteries
Authors: Kim Dong Hyeon , Park Kern Ho , Choi Young Eun , Oh Dae Yang , Jung Sung Hoo , Jung Yoon Seok
Published: February 2020

As the application of lithium-ion batteries (LIBs) has been expanded to large-scale systems such as electric vehicles and energy storage systems, their safety becomes the most important characteristic. However, conventional LIBs contain flammable liquid electrolyte which can cause serious safety concerns. In this regard, all-solid-state lithium-ion batteries (ASLBs) using inorganic solid electrolytes (SEs) are the most promising candidate to compete with the conventional LIBs. Especially, bulk-type ASLBs are considered to be highly competitive in terms of their potential for large-scale manufacturing, which is contrasted by high cost in vacuum-deposition-based fabrication for thin-film-type ASLBs. For the bulk-type ASLBs, inorganic sulfide SEs such as Li10GeP2S12 and glass-ceramic Li2S-P2S5 are appropriate because they show high ionic conductivity and deformability. The bulk-type ASLBs employing these sulfide SEs have demonstrated promising electrochemical performances.1

 However, the severe discrepancy between the obtained performances and the expected ones from the extremely high conductivity values of sulfide SEs has been overlooked. The governing origin for this discrepancy is the poor ionic contacts in the composite electrode structures. As all components in bulk-type ASLB are solid, the surfaces of active materials are not fully covered by the SEs as far as the electrodes are fabricated by the mixing process.2 As efforts to circumvent this problem, direct coating of SEs by laser vapor deposition3 was reported. The laser vapor deposition technique should be, however, ruled out for scale-up because of the high cost. In this regard, development of the wet SE-coating process can be thus more attractive. However, the wet process for sulfide SEs has been hindered by instability of sulfide materials with solvents, which leads to too low ionic conductivity of the resulting precipitated materials. Also, the most sulfide SE with various solutions did not form coatable homogeneous solutions and the used solvents were not environmentally friendly. Recently, our group reported new solution processable SE, LiI-Li4SnS4, which was prepared from methanol-based solution. The resulting glass phase LiI-Li4SnS4 showed the high ionic conductivity of 0.41 mS cm-1 and the excellent dry-air stability.2

In this presentation, we will report facile electrode fabrication procedure employing the solution process of Li4SnS4, and its electrochemical performances will be presented.

References

Y. S. Jung, D. Y. Oh, Y. J. Nam, K. H. Park, Israel J. Chem.
55, 472 (2015).

K. H. Park, D. Y. Oh, Y. E. Choi, Y. J. Nam, L. Han, J.-Y. Kim, H. Xin, F. Lin, S. M. Oh, Y. S. Jung, Adv. Mater.
28, 1874 (2016).

A. Sakuda, A. Hayashi, M. Tatsumisago, Sci. Rep.
3
, 2261 (2013).
Ion-Conductive Properties of Novel Polymer Electrolytes Based on Ethylene Oxide/Ethylene Carbonate Copolymers
Authors: Morioka Takashi , Nakano Koji , Tominaga Yoichi
Published: February 2020

Solid polymer electrolytes (SPE) are expected to be useful as an electrolyte for batteries because of its safety, flexibility and lightweight. Many attempts for polyether type SPE have since been made to improve their electrochemical and physicochemical properties. Poly(ethylene oxide) (PEO) and its derivatives have usually low glass transition temperatures (T
g) and those electrolytes exhibit relatively high ionic conductivity. However, PEO-based electrolytes suffer from low Li transference numbers (t
+), less than 0.3. In PEO-based electrolytes, a cross-linking structure based on strong ion-dipole interactions between cations and polar ether oxygen is usually formed. Ionic conduction in PEO-based electrolytes therefore strongly depends on the migration of anions, which is known to occur in materials unsuitable for practical batteries. To overcome these problems we recently suggested polycarbonates, such as poly(ethylene carbonate) (PEC), as a new polymer matrix for SPE. However, PEC-based electrolytes have a issue with low ionic conductivity relative to PEO-based electrolytes at low salt concentrations, because of the high T
g of the original polymer. In this study, we focus on the copolymerization of ether and carbonate units as novel candidates for the electrolytes. The ether/carbonate copolymers can be obtained with suitable ratio by the optimization of the polymerization condition. We investigated the influence of the ether units on the ion-conductive properties of poy(ethylene oxide/ethylene carbonate) (P(EO/EC))-based electrolytes. The electrolytes were prepared with lithium bis(fluorosulfonyl)imide (LiFSI). The LiFSI content in the electrolyte varied from 5 to 160 mol% to an average monomer unit of each EO and EC unit. We found that the T
g of neat copolymers and the electrolytes decreased with increasing the contents of EO unit, while the conductivity for the electrolytes increased with increasing both EO unit and salt concentration. The t
+ of P(EO/EC) electrolyte having EO unit of 53% and 80mol% of LiFSI had high t
+ 0.65 at 60 oC. This value was very high and comparable with that of the PEC-based electrolytes. The dissociation states of Li ions is essential to reveal ion-conductive properties of P(EO/EC) electrolytes, so the measurement of FT-IR was carried out. The results of characterization of FT-IR spectra suggest that Li ions interact preferentially with carbonate groups but hardly with ether groups in P(EO/EC). Thus, the P(EO/EC) electrolytes showed novel ion-conductive behavior which has advantages of both EO and EC-based electrolytes. The optimization of the copolymerization ratio for EO and EC units in the copolymers are expected to further improvement in the conductivity.

This work was supported financially by a Grant-in-Aid for Scientific Research (B) (No. 25288095, 16H04199) of JSPS KAKENHI ,Japan.
Thin Film Processing of Amorphous Lithium Lanthanum Titanate Based Solid-State Microbatteries
Authors: Lee Jungwoo Zema , Wang Ziying , Rustomji Cyrus Sam , Wynn Thomas Andrew , Meng Ying Shirley
Published: February 2020

Next generation batteries will require a broad range of energies to meet the challenges of portable electronic storage from electric vehicles to microelectromechanical systems (MEMS). Solid state electrolytes are researched heavily because they have the potential to improve capacity loss, cycle lifetime, operation temperature, and safety [1]. Lithium lanthanum titanate (LLTO), with the perovskite structure (ABO3), has gained interest due to its high bulk conductivity (10-3 S cm-1) at room temperature [2]. LLTO has many advantages including negligible electronic conductivity, high voltage stability (> 8 V), atmospheric stability, and temperature stability [3]. Furthermore, LLTO is transferable to thin film structures for fabricating microbatteries for powering portable electronics on-chip [4].

However, crystalline LLTO has a relatively low grain boundary conductivity (<10-5 S cm-1), lowering the overall material conductivity [3]. Therefore, in this work, we investigate amorphous LLTO thin films grown by pulsed laser deposition (PLD). By controlling the laser fluence, background pressure, and temperature we are able to grow dense films with an ionic conductivity of 8x10-4 S/cm and electronic conductivity of 5x10-11 S/cm. Secondly, we explore LiNi0.5Mn1.5O4 (LNMO) spinel thin films deposited via PLD as a potential high voltage cathode for our battery. We report on LNMO/LLTO half cells and novel full LLTO based thin film microbatteries.

[1] A. Hayashi et. al.“ Superionic glass-ceramic electrolytes for room-temperature rechargeable sodium batteries,” Nature Communications. 3 (2012) 856–860.

[2] O. Bohnke.  “The fast lithium-ion conducting oxides Li3xLa2/3 − xTiO3from fundamentals to application,” Solid State Ionics. 179 (2008) 9-15.

[3] C. Cao et. al.“Recent advances in inorganic solid electrolytes for lithium batteries,” Frontiers in Energy Research. 2 (2014) 1-10.

[4] A. Furusawa et. al. “Ionic conductivity of amorphous lithium lanthanum titanate thin film,” Solid State Ionics. 176 (2005) 553-558.
(Invited) Electrochemical Reduction of CO2 to Value-Added Chemicals: Status and Remaining Challenges
Authors: Kenis Paul J.A.
Published: February 2020

Significant reduction in atmospheric CO2 emissions as well as in the development of alternative energy sources will be critical to curb the unwanted effects of climate change (e.g., global warming, erratic weather patterns) and to reduce our dependence on fossil fuels. A variety of strategies needs to be pursued to curb the increase in atmospheric CO2 level. One potential strategy that can be employed to overcome this challenge is the electrochemical reduction of CO2 into useful chemicals such as formic acid, carbon monoxide, hydrocarbons, or alcohols. To drive thus process in a cost effective manner otherwise-wasted renewable energy that is produced in excess of grid demand can be used. A key challenge is the development of catalyst materials that are active and selective for the electrochemical reduction of CO2, i.e., catalysts that can reduce CO2 at low overpotentials (and thus high energetic efficiency), produce desired products at high current densities over long periods of time, and do so selectively while suppressing unwanted reactions.

Most present efforts to re-energize spent CO2 via electrochemical methods struggle to achieve simultaneously high energetic efficiency, high product selectivity, and high throughput. This presentation will provide an overview of progress by us and others in (i) developing suitable cathode catalysts for CO2 reduction (primarily to CO) as well as suitable anode catalysts (typically for the oxygen evolution reaction) needed for a CO2 electrolysis cell; (ii) optimizing operation conditions for these catalysts (pH, electrolyte composition, …); and (iii) developing gas diffusion electrodes suitable for a CO2 electrolysis cells. A projection for the potential for further improvement of catalysts, electrodes, operation conditions, and electrolysis cell designs will be made. Also, a gross margin model to estimate economic feasibility, as well as the results of a techno-economic analysis of a process that converts the CO2 of a 0.5 MW power plant to fuel via electroreduction of CO2 to CO, followed by Fischer-Tropsch will be presented.