bluuebunny/crossref_metadata_2025 huggingface dataset:
Research and Development of Ammonia-Fueled SOFC Systems
Authors: Muroyama Hiroki , Srifa Atthapon , Okanishi Takeou , Matsui Toshiaki , Kishimoto Masashi , Saito Motohiro , Iwai Hiroshi , Yoshida Hideo , Eguchi Koichi , Saito Masaki , Koide Takeshi , Iwai Hiroyuki , Suzuki Shinsuke , Takahashi Yosuke , Horiuchi Toshitaka , Yamasaki Hayahide , Matsumoto Shohei , Yumoto Shuji , Kubo Hidehito , Kawahara Jun , Okabe Akihiro , Kikkawa Yuki , Isomura Takenori
Published: February 2020

Hydrogen is the primary fuel source for fuel cells. However, the low volumetric energy density and difficulty in storage and transportation are major obstacles for the practical utilization. Thus, the on-site generation of hydrogen from its carrier is an effective method for the fuel supply. Among various hydrogen carriers, ammonia is one of the promising candidates because of its high hydrogen density, low production cost, and ease in liquefaction and transport.

Ammonia decomposes into nitrogen and hydrogen through a mildly endothermic process. The ammonia decomposition temperature is close to the operating conditions of solid oxide fuel cells (SOFCs). Therefore, the integration of these two devices is beneficial in terms of efficient heat and energy managements and will lead to the development of simplified generation systems. Furthermore, hydrogen and nitrogen produced from ammonia fuel are expected to have little negative effect on fuel cell performance, while hydrocarbon fuels draws some severe problems at electrodes, such as CO poisoning and carbon deposition in low- and high-temperature fuel cells, respectively.

We have investigated three types of ammonia-fueled SOFC systems. In one system, ammonia is directly supplied to the anode chamber. Ammonia decomposes into nitrogen and hydrogen over Ni-based cermet anode, and subsequently the generated hydrogen is electrochemically oxidized to produce steam and electron. The second system consists of ammonia cracker and SOFC. In this case, ammonia is catalytically decomposed through the ammonia cracker, and hydrogen produced is electrochemically oxidized on the anode. Ruthenium catalysts are well-known to promote the decomposition of ammonia, but the limited availability of ruthenium requires the development of new catalyst systems. Then, we have developed nickel-based catalysts and applied them for the ammonia cracker due to their relatively high activity for ammonia decomposition among base metals. The last one is the system combined with auto-thermal ammonia cracker, which will be suitable for the rapid start-up.

In this study, we introduce the development of ammonia-fueled SOFC systems. 200 W-class stacks as well as button-type cells were applied as SOFCs. The performance of the three systems were evaluated and compared with each other.

This work was supported by Council for Science, Technology and Innovation (CSTI), Cross-ministerial Strategic Innovation Promotion Program (SIP), “energy carrier” (Funding agency: JST).
Surface Segregation in Strontium Doped Lanthanum Cobalt Ferrite: Effect of Composition and Strain
Authors: Yu Yang , Ludwig Karl F , Gopalan Srikanth , Pal Uday Bhanu , Woicik Joseph C , Kaspar Tiffany C , Basu Soumendra Nath
Published: February 2020

The oxygen reduction reaction (ORR) at the cathode is often the rate-controlling step in the electrochemical reactions occurring in the solid oxide fuel cells (SOFCs). Strontium doped lanthanum cobalt ferrite (LSCF) is a widely used cathode material due to its high electronic and ionic conductivity, and reasonable oxygen surface exchange coefficient. However, LSCF can have long-term stability issues such as surface segregation of Sr during SOFC operation, which can adversely affect the electrochemical performance. Thus, understanding the nature of the Sr surface segregation phenomenon, and how it is affected by the composition of LSCF and strain are critical.

In this research, heteroepitaxial thin films of La1-x
Sr
x
Co0.2Fe0.8O3-δ
with various Sr contents (x = 0.4, 0.3, 0.2) were deposited by Pulsed Laser Deposition (PLD) on single crystal NdGaO3, SrTiO3 and GdScO3 substrates, leading to different strains in the films. The LSCF thin films were annealed at 800 °C for 10 hours in air. The extent of Sr segregation at the post-annealed film surface was quantified using synchrotron-based total reflection X-ray fluorescence (TXRF) technique. The formation of secondary phases were found and their surface area coverage was quantified by Atomic Force Microscope (AFM). Transmission electron microscope (TEM) and related spectroscopy techniques were used for microstructural and quantitative elemental analyses of the secondary phases on surface which were found to be Sr-rich phases. The bonding environment of the Sr-rich phases formed on the surface were investigated by synchrotron-based hard X-ray photoelectron spectroscopy (HAXPES).

The extent of Sr segregation was found to be a function of the Sr content in bulk. Lowering the Sr content from 40% to 30% reduced the surface segregation, but further lowering the Sr content to 20% increased the segregation. The strains of LSCF thin films on various substrates were measured using high-resolution X-ray diffraction (HRXRD) and the Sr surface segregation was found to be reduced with compressive strain and enhanced with tensile strain present within the thin films. A model was developed correlating the Sr surface segregation with Sr content and strain effects to explain the experimental results.
Chromium Resistive BaCeO3 Infiltrated La0.6Sr0.4Co0.2Fe0.8O3 Cathode of Solid Oxide Fuel Cells
Authors: Chen Kongfa , Li Meng , Ai Na , Jiang San Ping
Published: February 2020

Poisoning of cathodes due to deposition of chromium species from the Fe-Cr alloy interconnect is a major degradation mechanism of solid oxide fuel cell stacks. Our previous studies have shown that the infiltration of gadolinium doped ceria or BaO nanoparticles leads to substantially enhanced chromium resistive ability of La0.6Sr042Co0.2Fe0.8O3 (LSCF) cathodes (Electrochemistry Communications, 37, 84 (2013) and Physical Chemistry Chemical Physics, 17, 4870 (2015)). In this presentation we report BaCeO3 infiltrated LSCF electrodes by co-infiltrating BaO and CeO2 into the LSCF structure and investigate the electrode activity and stability under accelerated chromium poisoning conditions. The results show that 0.8 mg cm-2 BaCeO3 infiltrated LSCF has extraordinary electrocatalytic activity for the oxygen reduction reaction. For example, electrode polarization resistance is 0.12, 0.062, 0.014 and 0.002 Ω cm2 at 650, 700, 750 and 800 oC, respectively. More importantly, the BaCeO3-LSCF electrode is highly tolerant against Cr contamination. For the operation in the presence of bare Fe-Cr alloy without any protective layer, RE
is as low as 0.07 Ω cm2 after the polarization at 200 mA cm-2 and 800 oC for 40 h, much smaller than 0.74 Ω cm2 of pristine LSCF cathode after the test under identical conditions. The results imply that the BaCeO3infiltration is an effective means to enhance the electrode activity and stability of LSCF electrodes for operation in the presence of Fe-Cr interconnect.
Surface Modification of Solid Oxide Fuel Cell Cathodes Using Atomic Layer Deposition
Authors: Choi Hyung Jong , Bae Kiho , Kim Jun Woo , Park Suk Won , Han Gwon Deok , Kim Dong Hwan , Son Ji-Won , Shim Joon Hyung
Published: February 2020

The operating temperature of solid oxide fuel cells (SOFCs) is heading towards lower operating temperature region (< 650 °C) to achieve shorter start-up time, economical use of interconnect materials and avoiding undesirable reaction at the interface. However, at low operating temperature, sluggish oxygen reduction reaction (ORR) at the cathode surface impedes the overall kinetics of electrochemical processes of SOFC, which hinders the practical usage of SOFC in low temperature region. To improve the ORR kinetics, surface modification of the SOFC cathode has been suggested. Surface modification is conducted by distributing catalyst materials on the cathode support. Atomic layer deposition (ALD) is an excellent method for surface modification thanks to its step coverage, precise thickness control and low deposition temperature (< 250 °C) properties. In this study, we modified the surface of La0.6Sr0.4CoO3 (LSC) using ALD CoOx and studied the electrochemical performance of the SOFC cell with the surface modified cathode. As a result, the polarization resistance related to ORR at the cathode was increased after surface modification with CoOx, causing decreased power density. The details of the result will be presented in the conference in addition to the comparison to other surface modification experiment with ALD LSC treatment on La0.6Sr0.4Co0.2Fe0.8O3 cathode.
Application of Electrospun Ba0.5Sr0.5Co0.8Fe0.2O3-
d Nanoweb Cathode for Solid Oxide Fuel Cells
Authors: Kim Chanho , Jang Inyoung , Kim Sungmin , Song Taeseup , Yoon Heesung , Paik Ungyu
Published: February 2020

Research for developing the cathode materials of Solid Oxide Fuel Cells (SOFC) by improving catalytic effect is necessary to enhance the total efficiency. Electrospinning has attracted associated interest in the way that increase of reaction area can be possible. However, complexity and low-yield of process have limited the application of electrospinning to SOFC system. Adopting powder that is composed of nanofiber after sintering also has limitation in terms of inefficient connection among fibers. Path for migration of oxygen ions has to be interconnected for adequate electrochemical mechanism. Herein, nanoweb structure of Ba0.5Sr0.5Co0.8Fe0.2O3-
δ was directly fabricated on a dense electrolyte. Electrospun cathode with uniaxial pressing facilitates the simplification of process and the improvement of contact property. This single cell showed relatively high electrochemical performance with hydrogen fuel due to superior interconnection of fibers. X-ray diffraction measurement (XRD) was conducted to confirm the crystalline property of Ba0.5Sr0.5Co0.8Fe0.2O3-
δnanoweb structure, and scanning electron microscope (SEM) images also verify the morphological advantages. Electrochemical performances were also proven through electrochemical impedance spectroscopy (EIS) and IV analysis.

Figure 1
Semi-Solid Typed Ionic Conductor for Solid-State Electrochromic Approaches
Authors: Kim Joo Yeon , Oh Ji Young , Jeon Sanghoon , Ryu Hojun , Cho Seong M. , Ah Chil-Sung , Kim Yong-Hae , Hwang Chi-Sun
Published: February 2020

Electrochromic (EC) phenomena are that their optical transmittance and/or reflectance change because of chemical reduction/oxidation processes occurred by the ions insertion and extraction when a potential is externally applied. In order to increase the ratio and speed of chemical reduction/oxidation processes, which are essential required property, there are many efforts to prepare the ionic conductors based on such as organic-solvents/liquids, ionic liquids, and polymer/gel.

Although organic-solvent/liquid based ion conductors show better physical properties likely lower viscosity, density, and melting point helps easier ion mobility in medium, they exhibit low stability, high flammability, and low safety which limit the promising wide range application of EC devices (ECDs). Therefore instead of using organic-solvent/liquid based ion conductors, ionic liquids (ILs) are considered because of non-volatility, possibly makes choice and/or certainly increasing ion concentration, etc. In spite of these advantages, polymer and/or gel-typed ion conductors are only suitable in terms of the flexibility and scalability of ECDs.

As their visco-elastic properties, polymer/gel-based ion conductors afford guaranteed good contact with the electrodes, and they also have simple processablity resulted in low production cost and better mechanical properties along with improved stability, reliability, and safety.

Therefore, in the present work, polymer-based ion conductor is prepared and is optimized in order to obtain the efficient contrast ratio and switching speed for ECDs. In order to see the feasibility, the operation of polymer-based ion conductor introduced ECD fabricated on flexible substrate will be also presented.

Acknowledgement

This work was supported by Institute for Information & communications Technology Promotion (IITP) grant funded by the Korea government (MSIP) (B0101-16-0133, The core technology development of light and space adaptable energy-saving I/O platform for future advertising service).
Fabrication and Characterization of LSM/YSZ/GDC Tri-Composite Cathode-Supported Tubular Solid Oxide Direct Carbon Fuel Cell
Authors: Lee Seung-Bok , Rehman Saeed ur , Lee Jong-Won , Lim Tak-Hyoung , Park Seok-Joo , Song Rak-Hyun
Published: February 2020

The purpose of this study was to fabricate a porous and high mechanical strength cathode support for solid oxide direct carbon fuel cells. Therefore, the effect of Gd0.1Ce0.9O2-δ (GDC) addition on the phase stability, sintering behavior, thermal expansion, porosity, electrical conductivity, and mechanical strength of La0.65Sr0.3MnO3-δ/(Y2O3)0.08(ZrO2)0.92 (LSM/YSZ) composite was evaluated. The sintering temperature and the porosity of LSM/YSZ composite were observed to increase with an increase in the amount of GDC, on the contrary, the electrical conductivity and the mechanical strength was decreased. An LSM/YSZ/GDC tri-composite with optimized properties was selected to fabricate the tubular cathode-supported SOFCs (LSM/YSZ/GDC|YSZ|NiO/YSZ) through extrusion and co-firing. A special chamber was designed for the DCFC operation of the tubular cell. Electrochemical characterization was done by measuring the polarization curves and electrochemical impedance spectroscopy using dry hydrogen or the syngas produced by in situ steam gasification of carbon black.
Ion Conduction of BaPrO3-δ Thin Film with Mixed Valence State for SOFC Anode Electrode
Authors: Furuichi Shoto , Tsuchiya Takashi , Minohara Makoto , Kobayashi Masaki , Horiba Koji , Kumigashira Hiroshi , Higuchi Tohru
Published: February 2020

The BaPrO3 (BPO) is expected as a candidate for anode materials in solid oxide fuel cell (SOFC) using oxide protonics material as a solid electrolyte, due to a possible presence of mixed conductivity or holes (electrons)and protons.  BPO ceramics has the possibility of electron-ion mixed conduction because of auto-ionization of Pr+4/Pr+3.  Therefore, the electrode of fuel cell should be used as thin film form.  However, details of high mixed conduction of BPO thin film have not been clarified thus far.

  In this study, we have deposited the BPO thin films on Al2O3 (0001) single crystal and Nb-doped SrTiO3 substrates by radio frequency (RF) magnetron sputtering.  The deposition pressure and substrate temperature were set at 4.0×10-3 Torr and 500 °C, respectively.  In order to obtain the high mixed conduction of the thin film, the influence of film thickness was probed between 60 and 170 nm.  The BPO thin film was characterized by XRD, AC impedance method, X-ray photoemission spectroscopy (XPS), and X-ray absorption spectroscopy (XAS).  The AC impedance was measured by means of a frequency response analyzer in the frequency range of 0.1 Hz – 32 MHz.  Impedance spectra were collected at temperatures between 200 °C and 600 °C with a step of 25 °C.  The measurement atmosphere used dry Air (the mix gas of O2 and Ar) and wet Air (the mix gas of O2 and Ar and H2O).  The electrode made a Pt comb type electrode by RF magnetron sputtering.  In order to probe conducting carriers, the conductivity was measured by changing by gas partial pressure.

  The prepared thin films exhibit highly a-axis orientation.  The lattice constant of a-axis decreases with increasing film thickness.  We conformed the electron structure by XPS and RPES in order to prove the mixed valent states of Pr4+ and Pr3+.  This originates the changes of lattice constant with film thickness.  The electrical conductivity increases and the activation energy decreases with increasing film thickness.  The activation energy does not match with the energy separation between the Fermi level and the top of valence band.  However, the conductivity at 300 °C depends on the oxygen partial pressure, indicating the existence of electron-oxygen ion mixed conduction.  The thin films below 100 nm have proton conductivity in wet atmosphere.  The above results indicates that the thin film has proton conduction in addition to electron-oxygen ion mixed conduction.
Characterization of Reliability of Solid Oxide Fuel Cell Sealants and Anodes
Authors: Wei Jianping , Pećanac Goran , Malzbender Jürgen
Published: February 2020

Typically brittle sealant and anode materials are critical for the reliability of solid oxide fuel cells (SOFCs). Hence, characterization of these failure-relevant materials is crucial for the long term operation. In particular, the mechanical behaviour and elevated temperature stability which is strongly affected by creep has to be thoroughly understood and in terms of property – microstructure correlation, related to the materials’ compositions, crystallization, porosity and phase stability.

Since sealant leakage can lead to malfunction of the whole system, the structural integrity of the sealant is a key issue for the operation of SOFC stacks and systems. Fracture properties and elevated temperature deformation need to be assessed, particularly for partially crystallized glass-ceramic sealants that might suffer from instability issues at operation relevant temperatures due to viscoelastic deformation of the residual glass phase. In this work, a modified sealant, which consists of a composition from the BaO-CaO-SiO2 ternary system with Ag particles reinforcement, was characterized. Bending tests were carried out at room temperature and typical stack operation temperatures on a head-to-head specimen geometry in an as-sintered and annealed state, yielding average fracture stresses and apparent creep data. Since the sealants are exposed to a complex loading state in the stack environment, complementary torsion tests were used to investigate the shear strength. Advanced microstructural characterization was carried out to gain insight into the annealing and reinforcement filler effects. The results are compared and discussed with respect to literature data and their relevance for the application in SOFCs operating at different temperatures in the range of 600°C to 800°C.

Typical anode substrate materials (NiO-3YSZ and NiO-8YSZ) along with their reduced and re-oxidized state were analysed by means of fracture toughness at room temperature and 800 °C. Effects related to porosity and transformation toughening could be verified. Furthermore, creep of porous Ni-YSZ composite has been investigated under H2/Ar atmosphere at typical operating temperatures. Ni-YSZ materials with different porosities and Ni/YSZ ratios were tested in order to investigate material´s composition and porosity effects. Different loading configurations such as compression, four-point bending and ring-on-ring bending have been used to assess the differences in creep response of these materials. Interpretation and analysis of the data were based on analytical and finite element simulation. The systematic comparison and discussion of the results was aided by microstructural investigations.
Research and Development on Oxygen Transport Membranes at the Technical University of Denmark from Materials to Modules
Authors: Kiebach Ragnar , Pirou Steven , Ovtar Simona , Haugen Astri Bjørnetun , Hendriksen Peter Vang
Published: February 2020

Oxygen transport membranes (OTMs) are inorganic, high temperature devices that have the potential to efficiently supply oxygen to combustion processes, for example for oxy-fired (biomass) gasification or in the cement and steel industry.

This work reviews aspects of material selection, design, characterization and testing of single phase and composite based OTMs that are taking place at the Technical University of Denmark (DTU). The focus will be on high performance asymmetric OTMs, in which a dense thin film oxygen separation membrane is deposited on a porous mechanically supporting layer.

An OTM material should ideally have high ionic and electronic conductivity as well as good chemical stability under both oxidizing and reducing conditions. Strategies for increasing the performance by using composite dual phase membranes consisting of an ionic conductor and a electronic conductor will be discussed. Particularly membranes based on i) La0.6Sr0.4FeO3 (LSF) and CGO and ii) 10Sc1YSZ ((Y2O3)0.01(Sc2O3)0.10(ZrO2)0.89) and MnCo2O4 seem to be promising combinations and results on manufacturing and testing, including long-term results for >1500 h, of these membranes will be presented.

The second part of the presentation will focus on module design and application oriented testing. Here first results from integration of OTMs into the slip stream of a biomass gasifier will be shown. Also highlights from the “Highly Efficient Tubular Membranes for Oxy-Combustion (HETMOC)” European FP7 project are included. In this project a proof-of-concept module with 25 one-end closed BCSF (BaxSr1-xCo0.8Fe0.2O3) tubes was designed and tested in a high pressure test stand designed at DTU. To maximize the partial pressure difference across the membrane, high pressure up to 5 bar was applied on the feed side and a vacuum pump was used to lower the pressure on the permeate side. Results on performance and long-term stability as well as problems encountered during the project will be presented.
Synthesis and H- Conductivity of Ba2LiH3-2x
O1+X
Authors: Kobayashi Genki , Watanabe Akihiro , Suzuki Kota , Hirayama Masaaki , Yonemura Masao , Kanno Ryoji
Published: February 2020

Hydride ions are attractive as charge carriers because these have an ionic radius appropriate for fast ionic conduction and also show strong reducing properties with a standard redox potential of H–/H2 (–2.25 V vs. SHE), which is close to that of Mg/Mg2+ (–2.38 V vs. SHE). Therefore, H– conductors may be applied in energy storage and conversion devices with high energy densities. Recently, we have found La2-x-y
Sr
x

+y
LiH1-x+y
O3-y
(LSLHO) oxyhydride system possessing pure H– conductivity, and have confirmed the capability of the oxyhydride to act as an H– solid electrolyte by demonstrating the battery reaction of an all-solid-state Ti/LSLHO/TiH2 cell [1]. The LSLHO system shows H– conductivity of 10-4 S·cm–1 at 300 ºC. However, a higher H– conductivity will be required to make novel electrochemical devices using H– conduction phenomenon. In this study, we attempted to synthesize a new H– conductive oxyhydride, Ba2LiH3-2x
O1+x
(BLHO), in order to achieve a higher H– conductivity than that of LSLHO [2].

BLHO was designed on the basis of LSLHO with the K2NiF4-type structure. La/Sr in LSLHO was substituted by Ba to expand the bottleneck size for H– diffusion in the crystal lattice. Furthermore, H– vacancies were introduced into the structure by controlling H/O ratio in the composition of BLHO. Crystal structure of BLHO was determined by X-ray and neutron diffraction. The X-ray diffraction peak of the sample could be indexed as the K2NiF4-type structure. The crystal structure of Ba2LiH3O (BLHO: x = 0) and Sr2LiH3O (LSLHO: x = 0, y = 2) determined by the Rietveld analysis are compared in Figure 1. The anion arrangement of Ba2LiH3O is basically same with Sr2LiH3O. The two apical anion sites in Li-octahedra are preferentially occupied by oxide ions. Oxide and hydride ions randomly occupy the apical site. In contrast, the four axial anion sites of the Li-anion octahedra prefer to be occupied by only hydride ions. As a result, square-planar LiH4 is formed in the Li-octahedra. When the A-site cation in the composition of A
2LiH3O changed from Sr to Ba, the lattice volume expand depending on the difference of ionic radii between Sr2+ (1.58 Å) and Ba2+ (1.75 Å). In particular, influences of the volume expansion mainly appeared to ab plane in the crystal lattice. The details of H– conduction properties for BLHO will be discussed in our presentation.

References:

[1] Genki Kobayashi et al., Science, 351, 1314-1317 (2016).

[2] Akihiro Watanabe, Genki Kobayashi et al., to be submitted.

Figure 1
Structural and Transport Properties of the Blc-Pbco System; Effects of Cation Ordering
Authors: Druce John , Wang Tianqi , Téllez Helena , Kilner John A. , Ishihara Tatsumi
Published: February 2020

The drive to reduce the operating temperatures of solid oxide fuel cells (SOFCs) and electrolysers (SOECs) requires the discovery of new materials showing enhanced oxygen transport and electrocatalytic properties. As well as modifying the composition of materials with the simple perovskite structure, lately there has also been interest in materials with other, often, layered structures including the Ruddlesden-Popper type materials, such as La2NiO4, and double perovskites such as GdBaCo2O5 (GBCO) and PrBaCo2O5 (PBCO) [1].

 

Whilst Sr-substituted lanthanum cobaltite (La0.6Sr0.4CoO3-d, LSC64) is widely used, the Ba-substituted analogue La1-xBaxCoO3-d (BLC) is attracting recent interest showing competitive electrode performances [2,3]. On the other hand, the double perovskite PrBaCo2O5+d (PBCO) has high diffusivity and surface exchange activity, which is often attributed to the anisotropic diffusion of oxygen due to the ordering of Pr and Ba cations on the A-site. However, experimental measurements suggest that the degree of anisotropy between diffusion in along the c axis and in the ab plane is only around half an order of magnitude [4]. Therefore, the family of compositions between single perovskite BLC and double perovskite PBCO offers an interesting system to study the effects of cation ordering on transport behaviour.

 

In this work, we have studied the structural and oxygen transport properties of materials in the La0.5-x/2Prx/2Ba0.5CoO3-d compositional space. The materials were synthesised by a conventional solid state reaction route, and X-ray diffraction revealed that Pr-rich compositions (0.7 < x < 1) retain the same double perovskite structure as PBCO, with cation ordering on the A-site, and hence more properly written as La1-xPrxBaCo2O5+d. The La-rich compositions (0 < x <0.7) showed a cubic symmetry, similar to the Sr-analogue LSC64.

 

Oxygen isotope exchange studies on the Ba0.5La0.5CoO3 end member show that the oxygen tracer diffusion (D*) and exchange (k*) coefficients are similar to those of PBCO, and of Sm0.5Sr0.5CoO3, which are some of the highest reported [5], explaining the high electrochemical performance of the single perovskite material [2,3]. Preliminary results indicate these values change only slightly across the composition field, with no significant increase as the structure changes from single to double perovskite. These findings seem to suggest that it is not the A-cation ordering in the crystal structure of PBCO that provides per se its high performance, but the defect chemistry, namely the high concentration of oxygen vacancies in the material.

 

References

[1] A. Tarancon et al., J. Mater. Chem. 20, pp 3799 – 3813 (2010)

[2] T. Ishihara et al., Solid State Ionics 152-153, pp 609 - 613 (2002)

[3] G.M. Rupp et al., J. Electrochem. Soc. 163(6), pp F564-F573, (2016)

[4] M. Burriel et al., Chem. Mater. 24, pp 613 – 621 (2012)

[5] I. Fullarton et al., Ionics 1, pp 51 – 58 (1995)
Disorder and Conductivity in Pyrochlore Thin Films
Authors: Kreller Cortney R , Valdez James , Holesinger Terry , Wang Yongqiang , Uberuaga Blas
Published: February 2020

Numerous avenues are currently being explored to enhance ionic conductivity in solid oxide materials including dopants, nano-structuring, and strain engineering. Their effect on material properties, specifically mobile carrier concentration and mobility, needs to be understood and ultimately exploited to develop advanced functional materials. In this work, we seek to explore the relationship between intrinsic disorder and oxygen ion conduction. The pyrochlore compounds, A2B2O7, consist of both ordered cation and anion sublattices. The introduction of anti-site disorder, where the A and B cations switch positions, is accompanied by increasing disorder on the anion sublattice, and complete randomization of the A- and B-site cations results in the defect fluorite phase. Several workers have previously studied the influence of structural disorder on ionic conductivity by introducing disorder through dopants, temperature or pressure. It has previously been suggested that disorder increases carrier concentration by freeing the fixed vacancy from the ordered anion sublattice of the pyrochlore structure, while order, on the other hand, may serve to increase mobility by providing a preferential ion transport pathway. This is in contrast to recent modeling results that indicate that both carrier concentration and mobility increase with disorder. In order to better understand the interplay of disorder and ionic transport, the present work utilizes irradiation as a tool to introduce, and control the extent of, structural disorder in pyrochlore oxide thin films. We have chosen to investigate the end members of the Gd2(ZrxTi1-x)2O7 system as Gd2Zr2O7 is an intrinsic fast-ion conductor that is also very rad tolerant whereas Gd2Ti2O7 is a poor ionic conductor that is much more susceptible to amorphization under irradiation than the zirconates. Electrochemical Impedance spectroscopy is used to measure the conductivity of materials with varying degrees of structural disorder in order to better understand how the underlying transport mechanisms depend on crystalline disorder.

Acknowledgements

This work was supported by the U.S. Department of Energy, Office of Science, Basic Energy Sciences, Materials Sciences and Engineering Division.
Electrolyte Systems for High Energy Cells
Authors: Abraham Daniel P
Published: February 2020

High energy – high voltage lithium-ion cells are being developed at Argonne as part of the U.S. DOE’s Advanced Battery Research program. These cells typically contain transition-metal bearing layered oxide positive electrodes, graphite-bearing negative electrodes and LiPF6-bearing carbonate solvent electrolytes. Although these cells deliver high energy densities initially, they display significant capacity loss and impedance rise during calendar or cycle-life aging. Extensive diagnostic studies indicate that cell impedance rise mainly arises at the positive electrode, and cell capacity fade mainly results from lithium trapping in the solid electrolyte interphase (SEI) at the negative electrode. During electrochemical aging, both electrodes undergo a cycle of surface film formation, decomposition, dissolution, and redeposition; this process results in continuous consumption of lithium ions, thereby reducing cell capacity and often increasing cell impedance.

Electrolyte additives are an economic means of improving cell performance and calendar life. In the past two decades, many organic and inorganic compounds have been identified as effective electrolyte additives: examples include vinylene carbonate, ethylene sulfite, vinyl ethylene carbonate, and fluoroethylene carbonate. However, these additives are mostly used in lithium ion cells that are cycled at relative low voltages (<4.3 V vs Li+/Li). Initial studies indicate that these common electrolyte additives are not effective at enhancing long-term cycling performance of high voltage cells, i.e. stable electrode passivation is not achieved with these traditional additives.

Several promising electrolyte additives for high voltage and high capacity lithium-ion cells are being developed at Argonne; these include LiF2BC2O4 (LiDFOB) and various polyfluoroalkyl (PFA) compounds. The PFA additives have two components: (i) a reactive head-group for attachment onto electrode surfaces via either reductive or oxidative decomposition, so that it becomes an integral part of the surface layer; (ii) a polyfluoroalkyl chain that self-assembles on the electrode surface into a solvophobic passivating layer that reduces both surface degradation and electrolyte decomposition. Various additive combinations are also being studied to minimize the performance degradation observed at high voltages. The rationale for electrolyte additive selection and the performance of the resulting electrolyte systems will be highlighted during this presentation.
Optimization of Dual-Salt Electrolytes for Rechargeable Lithium Metal Batteries
Authors: Jiao Shuhong , Zheng Jianming , Cartmell Samuel , Zhang Ji-Guang , Xu Wu
Published: February 2020

Rechargeable Li metal batteries have been extensively studied over the past 40 years due to an increasing need for high energy batteries. Lithium metal is an ideal anode material for rechargeable batteries, because of its extremely high theoretical specific capacity (3,860 mAh g-1), the lowest negative electrochemical potential (-3.040 V vs. the standard hydrogen electrode) and a low gravimetric density (0.534 g cm-3). However, there are still tremendous challenges hampering its practical applications owing to many issues, such as Li dendrite growth and low Coulombic efficiency during charge/discharge processes are key problems that need be solved. Uncontrollable dendritic Li growth and limited Coulombic efficiency could lead to short cycling life and safety hazards because of potential internal short circuits.

In this work, we will demonstrate a variety of strategies for Li anode protection to improve its Coulombic efficiency and extend the cycling lifespan in traditional Li-ion battery electrolytes. The highly-efficient electrolyte compositions for Li metal batteries will be developed, optimized and evaluated, and especially the dual salt electrolyte system will be thoroughly investigated to dig out a deep understanding of the relationship between electrolyte recipe, solid-electrolyte interphase (SEI) and cell performance. Also, the solvent effect on the stable cycling of Li anode will be explored and discussed. The optimized electrolyte will be evaluated in the Li||LiNi1/3Mn1/3Co1/3O2 (NMC) coin cells with an NMC areal loading of 2.8 mAh cm-2. In addition, the temperature effect on the electrolyte stability in the cells will be studied. Details of the studies will be reported and discussed in the presentation.
Transport Phenomena of Nonaqueous Electrolyte Solutions at High Concentrations: A Comparison Between the Li- and Na-Systems
Authors: Kuratani Kentaro , Kishimoto Iori , Nishida Yasuhiro , Kondo Ryota , Takeshita Hiroyuki T , Senoh Hiroshi , Kiyobayashi Tetsu
Published: February 2020

In order to understand the solution chemistry of electrolyte solutions at concentrations far from infinite dilution, the solution density, viscosity and ionic conductivity of Li- and Na-TFSI dissolved in GBL and PC were measured at 0.1 ≤ C/mol·dm−3 ≤ 2.0 and 278 ≤ T/K ≤ 328 (TFSI = bis(trifluoromethanesulfonyl)imide, GBL = γ-butyrolactone and PC = propylene carbonate). The partial molar volume of the solute, derived from the density, confirmed that the Na-systems occupy more volume in the solution than the Li-systems. On the other hand, the viscosity and ionic conductivity suggested that the Na-systems are more fluid and conductive than the Li-systems. The relative viscosity vs. the molarity follows a modified empirical Jones-Dole equation. The molar conductivity linearly decreased with respect to the cube-root of the molarity, which was analyzed by the pseudolattice model. The Raman spectroscopy revealed that, while the solvation number is comparable at 1-2 for either the Li- or Na-systems, Li+ is more tightly bound to the solvent molecules than Na+. The higher fluidity and conductivity of the Na-systems than those of the Li-systems result from the less occurrence of the solvent-shared ion pairs in the former than in the latter.

Reference: K. Kuratani et al., J. Electrochem. Soc., 163 (6) H417-H425 (2016)
Interfacial Lithium-Ion Transfer Between Graphite Negative Electrode and Sulfide Solid Electrolyte
Authors: Huang Meiqi , Fukutsuka Tomokazu , Miyazaki Kohei , Hayashi Akitoshi , Tatsumisago Masahiro , Abe Takeshi
Published: February 2020

Introduction

All-solid-state lithium secondary batteries using inorganic solid electrolytes instead of liquid electrolytes have been expected as next-generation secondary batteries with high safety and high reliability. Among the inorganic solid electrolytes, sulfide-based solid electrolyte such as Li2S-P2S5 based glass solid electrolyte has received much attention due to the high lithium-ion conductivities and room temperature pressure sintering [1]. Graphite has been used as the negative electrode materials in commercial lithium-ion batteries, and the improvement in interfacial lithium-ion transfer reaction between graphite and liquid electrolyte is recognized as an important issue and this issue should be considered in all-solid-state lithium secondary batteries. In this study, interfacial reaction between graphite and sulfide solid electrolyte was investigated.

Experimental

A layered electrolyte consists of 75Li2S-25P2S5 glass pellet and 1 mol dm-3 LiClO4/propylene carbonate (PC) was used in order to use lithium metal electrode as reference electrode. A three-electrode cell was assembled by using graphite sheet as working electrode, lithium metal as counter and reference electrodes. Cyclic voltammetry and electrochemical impedance spectroscopy were carried out.

Results

Figure 1 shows the cyclic voltammogram of the three-electrode cell using graphite sheet as working electrode. An oxidation-reduction current was observed between 0 – 0.5 V (vs. Li/Li+). Since lithium ion cannot intercalate into graphite sheet in LiClO4/PC, this oxidation-reduction peak indicates that lithium-ion intercalation/de-intercalation proceeded at the interfacial between graphite sheet and 75Li2S-25P2S5 glass pellet. In the Nyquist plot, one semi-circle was observed and assigned to interfacial lithium-ion transfer process. In the meeting, the activation energy for the interfacial lithium-ion transfer process will be discussed.

Reference
 

[1] A. Sakuda et al., Sci.
Rep., 3, 2261 (2013).

Acknowledgement

This work was financially supported by ALCA-SPRING of the JST.

Figure 1
Impact of Proton Contamination on the Solid Electrolyte Li7La3Zr2O12 (LLZO)
Authors: Yu Seungho , Siegel Donald J
Published: February 2020

Inorganic solid-state electrolytes are receiving attention due to the safety issues associated with flammable organic liquid electrolytes used in modern Li-ion batteries. Solid electrolytes can also enable higher energy density batteries by allowing use of metallic anodes. Li7La3Zr2O12 (LLZO) is one of the most promising solid electrolytes due to its high ionic conductivity (∼1 mS/cm), wide electrochemical window, and stability with respect to lithium. However, recent experimental evidence suggests that LLZO is unstable when exposed to humid air, resulting in proton exchange with lithium in the bulk and surface carbonation preceded by hydration (LiOH formation).1 Here, first principles calculations were used to investigate the reaction thermodynamics for surface hydration and carbonation of LLZO. Furthermore, ab-initio molecular dynamics (AIMD) were performed to examine the effect of proton substitution on diffusion within the Li sublattice. AIMD calculations indicate that moderate levels of protonation (up to ~10% H+ substitution) results in only a minor decease in Li-ion conductivity. On the other hand, higher proton concentrations can limit this conductivity significantly.

 [1] G. Larraz, A. Orera and M. L. Sanjuan J. Mater. Chem. A, 1, 11419 (2013)
Stable Cyclability of Novel Triblock Polyelectrolyte Separators for Lithium Metal Battery
Authors: Liu Kun Lin , Chao Chi Yang
Published: February 2020

Lithium metal is a promising anode for next generation lithium batteries due to its high theoretical energy density (3860mAh g-1). However, despite the attractive feature of lithium metal, its dendrite could form short circuit inside the cells and cause serious safety problems during lithium plating and stripping process. Polymer electrolyte with high lithium transference number and high modulus would substantially mitigate dendrite growth in lithium metal battery. According to previous models, structuring the electrolyte to immobilized the anions with high shear modulus is of the various options to suppress dendrite growth. In this work, we designed a single-ion conductor (SIC) based on a block copolymer using sulfonic anion, whose structure covalently bonded with hydoxylated polyisoprene (named as sPI) to reach high transference number. Polystyrene can be used to support the mechanical properties of matrix and the adjacent polyisoprene with double bond main chain plays a decoupling role (PI(1,4)) which separate the stiff PS domain, and the lithium conducting sPI domain (referred to SII block copolymer).

Using small angle X-ray scattering and transmission electron microscopy, nanostructures of membranes were identified as a bi-continuous network structure. Remarkably, the maximum conductivity was 1.4×10-4 S cm-1 at ambient temperature with merely 30 wt% solvent uptake. The lithium transference number (TLi
+) was nearly unity in liquid electrolyte. The Young’s modulus of SII was 53 MPa and storage modulus was nearly 3 GPa at room temperature. This bi-continuous morphology with high TLi
+, high modulus, and moderate conductivity is believed to suppress dendrite grow effectively. From galvanostatic cycling experiments, we found that the presence of PS and the sPI in SII membrane in liquid electrolyte with lithium symmetric cell provides over 245 hr in cell life time. Batteries containing SII membranes in liquid electrolyte are able to cycle at least 20 times with high coulombic efficiency (98%). This results warrant that the sPI can effectively delay lithium dendrite formation due to reduced uneven lithium deposition while maintaining the mechanical property with moderate values by adjusting PS and PI(1,4) length, and this architecture design also made the application of SIC in lithium metal polymer battery possible in the future.
Effects of an Organic Chemical Additive in Electrolyte on the Suppression of Lithium Dendrite in Lithium Metal Based Batteries
Authors: Ho Van-Chuong , Ngo Duc Tung , Le Hang T.T. , Kim Su-Won , Park Chan-Jin
Published: February 2020

Lithium (Li) metal has attracted much attention as an anode material for high energy density batteries due to the high theoretical specific capacity and low negative electrochemical potential of Li. However, the growth of Li dendrite on the metal electrode surface can lead to short circuits during the repeated electrochemical discharge-charge cycles. The control of lithium dendrite is one of the greatest challenges hindering the successful development of Li metal based batteries. In particular, Li metal is generally unstable against most chemical species and reacts with organic solvents as well as salts in liquid electrolyte. Furthermore, repeated stripping and deposition of Li may induce the uncontrolled dendritic growth of Li.

To overcome aforementioned obstacles and difficulties in Li metal anode, we propose the use of an organic chemical as an electrolyte additive for controlling Li dendrite. The base electrolyte of LiTFSI/TEGDME was used for tests. With the addition of the additive, the Li grains formed, while the fiber-like Li dendrite formed in the Li/Li symmetric cell without the additive in electrolyte. Furthermore, the uniform solid electrolyte interphase (SEI) layer formed by the addition of the organic additive, leading to the suppression of Li dendritic growth and electrolyte decomposition. Accordingly, the Li/Li symmetric cell containing the additive operated for longer than 700 cycles, which was four time longer than that of symmetric cell without additive in the electrolyte, under the current density of 0.1 mA cm-2 when the areal capacity was limited to 0.2 mAh cm-2. Under the limited areal capacity of 1 mAh cm-2 at the current density of 0.5 mA cm-2, the cell containing the additive maintained the cycle life longer than 350 h. Further development of this electrolyte additive may enable the practical applications in Li metal based batteries such as Li-air battery.
Li Insertion and Removal Potentials of Li7P3S11 Using VASP Calculation
Authors: Doh Chil-Hoon , Ha Yoon-Cheol , Lee You-Jin , Park Jun-Woo
Published: February 2020

Study on Li7P3S11 material was carried out by ab initio calculation. using the Vienna ab initio Simulation Package (VASP)[1]. Li7P3S11 was known as a super-ionic conductor (5.4 mS/cm at 25℃) to be a solid-electrolyte of all-solid-state lithium batteries. Two different crystal structure of Li7P3S11 were reported by Onodera (2010) and Tatsumisago (2007) with slight difference on atomic positions. Between total energies of VASP calculation on two structures, Tatsumisago’s structure had slightly more stable energy (Etotal –92.573 eV). Among Li7P3S11, Li3PS4, Li4P2S6 and Li4P2S7, the formation potential of Li7P3S11 was the highest value of 2.216 V(Li/Li+) to be the most stable material. Chemical reactivity of Li7P3S11 material toward moisture to be Li7P3O11 had the reaction energy of –0.34 eV. Li+ conduction of Li7P3S11 take place through vacancy and interstitial diffusion pathways. Xiong (2014) reported on the formation potential of Li7-1P3S11. Here, the formation potential of Li14-xP6S22 (x= 1~14) were evaluated briefly through a stepwise removal of Li+ from Li14P6S22 to Li0P6S22 to be a range of 3.2 ~ 2.6 V. Formation potentials of Li14+1P6S22 were also evaluated for four different interstitial sites. Site(III) denoted at Xiong’s report had 0.643 V(Li/Li+) to be the most easy accommodation of Li+ ion. Patterns of the total density of states (TDOS) of Li14+xP6S22 (x=1,0,-1) were not so different and shown ~3.5 eV by the Hyed-Scuseria-Ernzerhof (HSE) hybrid functional and ~2.1 eV by GGA to be electronic insulator.

[1] Kresse,G.; Hafner, J. Phys. Rev. B, 47 (1993) 558; 49 (1994) 14251.

Figure 1
DFT Molecular Dynamics Simulations of Li+
Authors: Leclerc Nima , Adelstein Nicole
Published: February 2020

INTRODUCTION

Using first principle Density Functional Theory (DFT) simulations of both the crystalline and amorphous phases of β-Li3PS4, the cause of high conductivity of Li+ ions in the amorphous phase is explored. β-Li3PS4 
 and other lithium thiosulphates are promising electrolytes for all solid-state batteries, even in their amorphous phases. However, the high conductivity in the amorphous phase is not understood. This research aims to predict conductivity in amorphous electrolytes by comparing diffusion in the crystalline and amorphous phases of a known conductor.

 METHODOLOGY

This project uses first principle DFT simulations to simulate diffusion paths in the β-Li3PS4 solid electrolyte and its amorphous analog. These simulations are done using the planewave DFT in the Quantum ESPRESSO[1] package, with a 128 atom supercell for the crystalline phase and a 640 atom amorphous electrolyte. By varying different factors such as, cell volume and temperature and lattice disorder, we were able to compare and understand the diffusion of Li+.

RESULTS and DISCUSSION

In this research, we aim to improve conductivity in amorphous and crystalline electrolytes by simulating the lithium ion diffusion pathways in lithium thiophosphates. The structure of the unit cell is shown in Fig. 1
[2]
. The data is analyzed to identify the following effects on lithium ion diffusion:

Covalent-type bonding between Li+ and the anion sub-lattice

The disorder within the cell, from local disorder to the full amorphous phase

Lithium ion motion correlations

The results presented will be molecular dynamics of both amorphous and crystalline structures of β-Li3PS4. Comparison of local structure and diffusion pathways in the amorphous and crystalline phase, in particular the effect of covalent bonding and correlated Li+ motion.

[1] P. Giannozzi, et al J.Phys.:Condens.Matter, 21, 395502 (2009) http://dx.doi.org/10.1088/0953-8984/21/39/395502 . (BibTeX format).

[2] VMD- Visual Molecular Dynamics. Computer software. Theoretical and Computational Biophysics Group. Vers. 1.9.2. Board of Trustees of the University of Illinois, n.d. Web. 13 Apr. 2016.

Figure 1