bluuebunny/crossref_metadata_2025 huggingface dataset:
In-Situ Visualization of Solid-Electrolyte Interphase in Lithium-Ion Batteries
Authors: Chen Liwei
Published: February 2020

Solid electrolyte interphase (SEI) is a layer of in-situ formed thin film at the electrolyte-electrode interface in lithium ion batteries. Stable SEI films help to pretect the electrolyte and the electrode, and thus are critically important for the cycle life, stability, and safety of batteries. Ideal SEI shall be electronically insolating, ionic permeable, and mechanically elastic and robust. However, the investigation of SEI strcuture-property relationship has been difficult because of the in-situ formation characteristic of SEI films.

This presentation talks about the investigation of SEI morephology, structure and mechanical properties, as well as the control of SEI using SEI-forming additives, by using scanning probe microscopy and spectroscopy. On a MnO thin-film electrode as the model system, in-situ atomic force microscopy (AFM) was applied to visualize the formation of SEI, and force spectroscopy was used to probe the structure and the mechanical modulus of the SEI. Highly inhomogeneous SEI film was found to form on the first cycle, and the SEI was shown to be unstable upon charging. SEI forming additives such as vinyl carbonate and LiBOB lead to SEI films with different properties and a mixture of the two additives was found to give the best SEI with cycle stability as well as good mechanical stability.

Cathodic SEI was also investigated on high-voltage LiCoO2. The formation of filamentous SEI was found the be highly dependent of the crystalline plane as well as the exposure of Co ions to the electrolyte.

These study establish a new method in the investigation of SEI structure-property relationship. Future developments on SPM based approach on the electronic and ionic conductivity will further enable mapping of SEI characteristics at a nanometer scaled spatial resolution.

References:

1. Jie Zhang, Xiaocheng Yang, Rui Wang, Weiling Dong, Wei Lu*, Xiaodong Wu, Xiaoping Wang, Hong Li and Liwei Chen*,”Inﬂuences of Additives on the Formation of a Solid Electrolyte Interphase on MnO Electrode Studied by Atomic Force Microscopy and Force Spectroscopy”,
Journal of Physical Chemistry C
, 118, 20756-20762 (2014)

2. Jie Zhang, Rui Wang, Xiaocheng Yang, Wei Lu, Xiaodong Wu, Xiaoping Wang, Hong Li and Liwei Chen*, “Direct observation of inhomogeneous solid electrolyte interphase on MnO anode with atomic force microscopy and spectroscopy”
Nano Lett.
,12, 2153-2157, (2012)
Simultaneous Acquisition of Differential Electrochemical Mass Spectrometric and Infrared Spectroscopic Data for in Situ Characterization of Gassing Processes in Lithium-Ion Batteries
Authors: Berkes Balázs B. , Jozwiuk Anna , Sommer Heino , Brezesinski Torsten , Janek Jürgen
Published: February 2020

A considerably contributing process to the capacity fading of lithium-ion batteries is gas evolution. The understanding of its mechanism is inevitable to develop better battery components. These are especially tailor-made electrolyte mixtures and additives, as well as cathode and anode structures/composites.

In the past, differential electrochemical mass spectrometry (DEMS) already served us with important facts on the gassing behavior of electrochemical systems, particularly in lithium-ion batteries. However, it cannot always unambiguously unveil certain important features of the ongoing gas evolution reactions. In the case of overlapping m/z values, like 28, the species can be either assigned to C2H4, CO as an individual reaction product or as a fragment of CO2 too. Furthermore, the quantification of the gaseous products might be extremely difficult due to matrix effects caused by the volatile electrolyte components. A hands-on supplementary technique is infrared spectroscopy (IR), since the majority of the products in question have characteristic absorption bands. Simultaneously acquired with the DEMS measurements, they give a more complete and unequivocal picture on the nature of gases. Additionally, with the help of IR, the quantification of the products is straightforward and more precise.

In this talk, we present the results on the development of a novel, combined in-situ DEMS-IR (DEIRS) analysis method. We show that our approach is unique with regard to long-term battery cycling tests as well. We compare different cathode materials or modified versions of the given material and demonstrate the effect of chemical composition/structure on the gassing behavior. The effect of solvent mixtures and some additives, like vinylene carbonate, on the stability of the electrolyte is elucidated. With the help of our setup, a method to optimize the amount of additives is suggested. Supported by precise pressure measurements, we give a comprehensive picture on the gassing processes in closed systems and compare those with the continuous flow DEMS-IR results. The quantification of the gaseous reaction products together with versatile, potential resolved electrochemical tests enables the establishment of kinetic models of the gas evolution, which will be illuminated. Unanticipated gas formation in certain cycling steps will be manifested too.
Enhanced Lithium Ion Conductivity in Lithium Lanthanum Titanate Solid Electrolyte Nanowires Prepared By Electrospinning
Authors: Yang Ting , Li Ying , Chan Candace K.
Published: February 2020

Solid electrolytes have great potential to address the safety issues of Li-ion batteries, but better synthesis methods are still required for ceramics such as lithium lanthanum titanate (LLTO) since current techniques require high-temperature calcination for long times. Here we report a new approach that utilizes electrospinning to prepare phase-pure polycrystalline LLTO nanowires with well-crystallized tetragonal phase.

To synthesize LLTO nanowires, the electrospinning precursor was prepared by mixing a LLTO sol into a polymer solution [1]. In a typical electrospinning experiment, the voltage was set to 7 kV, the distance between the needle tip and the collector was kept at 10 cm, and the feed rate was 0.3 mL/h. The as-spun fibers were calcined at 1000 °C for 3 h to get the LLTO nanowires.

Pellets of electrospun LLTO and LLTO prepared with conventional sol-gel method [2] were made and sintered. Electrochemical impedance spectroscopy (EIS) was used for ionic conductivity measurement. Pellets prepared from the electrospun LLTO nanowires had higher density, less void space, and higher Li+ conductivity compared to those made from conventional sol-gel method. This work demonstrates the potential that electrospinning can provide towards improving the properties of sol-gel derived ceramics.

Acknowledgements

This work was supported by new faculty startup funds from the Fulton Schools of Engineering at ASU. We gratefully acknowledge the use of facilities within the LeRoy Center for Solid State Science and Goldwater Environmental Laboratory at ASU.

References

[1] T. Yang, Y. Li and C. K. Chan, Journal of Power Sources 287 (2015) 164-169.

[2] T. Wöhrle, P. Gómez-Romero, T. Fries, K. West, M.R. Palacín, N. Casañ-Pastor, Ionics 2 (1996) 442.
The Joint Center for Energy Storage Research (JCESR): A New Paradigm for Energy Storage Research
Authors: Crabtree George
Published: February 2020

The Joint Center for Energy Storage Research (JCESR) pursues high performance, low cost beyond lithium ion electricity storage that will transform transportation and the electricity grid. JCESR will leave three legacies:

a library of fundamental knowledge of the materials and phenomena of energy storage at the atomic and molecular level

two prototypes, one for the grid and one for transportation, that, when scaled to manufacturing will be able to deliver five times the energy density at one-fifth the cost

a new paradigm for battery R&D that combines discovery science, battery design, research prototyping and manufacturing collaboration in a single highly interactive organization, accelerates the pace of discovery and innovation and significantly shortens the time from discovery to commercialization.

An introduction to JCESR’s vision, mission and legacies will be followed by research highlights illustrating its advances in fundamental science and the promising pathways to transformational battery designs and prototypes.

This work was supported as part of the Joint Center for Energy Storage Research, an Energy Innovation Hub funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences

Contact information

George Crabtree

Director, Joint Center for Energy Storage Research (JCESR)

Argonne National Laboratory

9700 S. Cass Ave

Argonne, IL 60439

630 252 5509

crabtree@anl.gov

Departments of Physics, Electrical and Mechanical Engineering

University of Illinois at Chicago

845 W. Taylor St. M/C 273

Chicago, IL 60607

Tel 630 252 5509

crabtree@uic.edu

Executive Assistant

Bernadette (Nada) Petrovic

Joint Center for Energy Storage Research (JCESR)

Argonne National Laboratory

9700 S. Cass Ave

Argonne, IL 60439

(630) 252-1420

bpetrovic@anl.gov
Surface Reaction, Solvent Inhomogeneity, and Ion Transport in Electric Double Layers: Predictions from a Classical Density Functional Theory
Authors: Lian Cheng , Wu Jianzhong
Published: February 2020

Electric double layers (EDLs) are formed at the interface of a charged fluid in contact with an electrified surface or an electrode leading to drastic changes in the fluid structure and local thermodynamic properties. Whereas conventional theories of EDLs are often concerned with the local inhomogeneity in terms of ionic distributions near a planar surface, the simplistic model is insufficient to capture many important properties relevant to emerging electrochemical processes for energy storage and conversion. In this talk, we present a few recent applications of the classical density functional theory (CDFT) that account for not only ionic excluded volume effects and electrostatic correlations ignored in conventional theories of EDLs but also electrode geometry and pore size distributions, the local solvent and dielectric inhomogeneity, surface reactions, and hydrodynamic effects. The CDFT calculations will be illustrated with practical examples for unusual ion transport in nanopores, optimization of capacitive energy extraction processes, design of nanostructured electrodes for flow supercapacitors and pseudo-capacitors. The theoretical predictions are validated with experiment results and provide insights for novel electrochemical behavior that are not captured in conventional EDL theories. 

Acknowledgements: This research is sponsored by the Fluid Interface Reactions, Structures, and Transport (FIRST) Center and the U.S. Department of Energy (DE-FG02-06ER46296). The numerical calculations were performed at the National Energy Research Scientific Computing Center (NERSC).
Ionic Liquid Structure and Dynamics at Charged Graphene Interface
Authors: Uysal Ahmet
Published: February 2020

Supercapacitors with room temperature ionic liquid (RTIL) electrolytes and graphene-based electrodes are promising candidates for small electronic devices, especially flexible and wearable ones. The theoretical upper limit for the electric double layer (EDL) capacitance of graphene is the highest in all carbon materials. Also, graphene-based electrodes open up novel designs that are free of binders and inert conductive additives [1]. Furthermore, RTILs stand out as safe, non-volatile electrolytes with a wide potential window. However, our knowledge of these highly dense ionic plasmas at electrified interfaces is still at its infancy due to the lack of in situ experimental data about their potential-dependent EDL structures and dynamics [2].

Here, we use in situ real-time X-ray reflectivity integrated with fully atomistic molecular dynamics (MD) simulations to elucidate the interfacial ionic liquid structure and dynamics at epitaxial graphene electrode during cyclic voltammetry and potential steps [3]. Our results suggest that the graphene-RTIL interfacial structure is bistable in which the EDL structure at any intermediate potential can be described by the combination of two extreme-potential structures whose proportions vary depending on the polarity and magnitude of the applied potential. This picture is supported by the EDL structures obtained by MD simulations at various static potentials [4]. The potential-driven transition between the two structures is characterized by an energy barrier (~0.15 eV) that is independent of temperature. The model nicely explains the coexistence of distinct anion and cation adsorbed structures and provides further insights to ultra-slow response of the interfacial structure to potential steps.

References

1- Y. Shao et al. Chemical Society Reviews DOI:10.1039/C4CS00316K (2015)

2- M. Fedorov and A. Kornyshev. Chemical Reviews 114, 2978-3036 (2014)

3- A. Uysal et al. Journal of Physical Chemistry C, 118, 569-574 (2014)

4- A. Uysal et al. Journal of Physics: Condensed Matter, 27, 032101 (2015)

* This effort was supported as part of the Fluid Interface Reactions, Structures and Transport (FIRST) Center, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences.  The research described here was done in collaboration with S. S. Lee, H. Zhou, P. Fenter (Argonne National Laboratory), G. Feng, S. Li, P. Cummings (Vanderbilt University), P. Fulvio, P. Zhang, S. Dai (Oak Ridge National Laboratory), J. McDonough, Y. Gogotsi (Drexel University)
Electronic Structure Calculations and Synergistic Experimental Work in the Nanostructures for Electrical Energy Storage (NEES) Energy Frontier Research Center
Authors: Leung Kevin
Published: February 2020

In this presentation, we will review computational effort and synergistic experimental activities in the Nanostructures for Electrical Energy Storage (NEES) Energy Frontier Research Center, and discuss future research directions.  Interfaces and interphases constitute a main theme of our research. Nanoscale structures exhibit enhanced surface areas, and fundamental understanding and smart design of interfaces can help exploit their kinetic advantages while mitigating undesirable parasitic reactions. Thus electrochemical reactions responsible for liquid electrolyte degradation are examined using both large scale ab initio molecular dynamics (AIMD) simulations and complementary ultrahigh vacuum (UHV) measurements. Electrolyte decomposition on lithium peroxide surfaces, a key obstacle in Li-air battery implementation, is examined using analytical/spectroscopic techniques and DFT calculations. Artificial "solid electrolyte interphase" are deposited on amorphous carbon electrodes via atomic layer deposition (ALD) processes, and its electrode-passivating property is characterized by microgravimetric measurements and modelled using DFT calculations coupled with Marcus Theory constructions. This ALD study highlights a second key theme in our research: that necessary fundamental science, computational- and nano-electrochemistry advances emerge naturally in the ostensibly "applied" field of energy storage. We will discuss other examples of method development, such as rigorous voltage calibration in AIMD/DFT calculations, and measurement/control of minute currents associated with single nanowires. Going forward, our new computational approaches will be applied to model solid-solid interfaces pertinent to solid electrolytes, artificially-coated, nanostructured interfaces, and electrode degradation studies.

This work was supported by Nanostructures for Electrical Energy Storage (NEES), an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under award no. DESC0001160.  Sandia National Laboratories is a multiprogram laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corpo ration, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.
The Challenge of 3D All Solid State Li-Ion Battery
Authors: Talin A. Alec , Ruzmetov Dmitry , Haney Paul , Kolmakov Andrei , Kozen Alexander C , Pearse Alex , Gregorczyk Keith , Schmitt Tom , Rubloff Gary W
Published: February 2020

Demonstration of all-solid state 3-dimensional (3D) Li-ion batteries has been a long standing goal for numerous researchers in the battery community interested in developing high power and high areal energy density storage solutions for variety of applications. The basic idea is to use the 3D geometry to maximize the volume of active material per unit area, while keeping its thickness sufficiently small to allow for fast Li diffusion. The 3D approach also leads to high electrode/electrolyte interface area, which should prove beneficial by lowering the local current density and therefore the charge transfer resistance, assuming that the interface is stable against parasitic reactions and breakdown. While simple conceptually, realizing working all solid state Li ion batteries has proven to be a significant challenge.  Specifically, the physical vapor deposition processes which have been successfully implemented for planar, thin film solid state Li ion batteries, fail miserably when applied to 3D substrates, particularly with high aspect ratio features. In our presentation, we will describe the structure and performance of all solid state 3D Li ion batteries fabricated by physical vapor deposition.  Although these can be charged and discharged at low C-rates, their capacity decreases rapidly at higher C-rates. In our presentation we will discuss the underlying reasons for the poor performance and demonstrate how these problems can be addressed using atomic layer deposition, a thin film deposition method compatible with high aspect ratio geometries.

Figure 1
Investigating Synthetic Effects on Ni-Based Oxide As a Cathode Material for Li-Ion Batteries
Authors: Xu Jing , Tong Wei
Published: February 2020

Lithium-ion battery (LIBs) technology has already disrupted the consumer electronic industry that has a continuous requirement on lighter weight and smaller size. Nowadays, it has been considered as the most promising power source for electric vehicles (EVs) and hybrid electric vehicles (HEVs). However, the mass adoption is still hindered by the battery performance and cost. Therefore, there is a definitive focus on increasing the energy density and lowering the cost in addition to ensure the other performance metrics such as in lifetime and safety. In the commercial Li-ion batteries, the layered transition metal oxides, such as LiCoO2, are widely used. Despite of its high theoretical capacity (> 270 mAh/g), LiCoO2 can only deliver about 140 - 170 mAh/g. This limited capacity as well as the high cost originated from the usage of Co has driven the research focus from LiCoO2 to other potential alternatives.

The extensive research on the search of an alternative to LiCoO2 has identified LiNixMnyCozO2 (NMCs) (0 < x, y, z < 1) as a category of promising compositions for the use of cathode materials in Li-ion batteries in terms of energy density, cost and safety. Ni content has been recognized to play a key role in an effort to push towards the high-capacity end. There have been renewed interests in this research direction. However, high Ni content causes the tendency of lithium and transition metal cation mixing and propensity to catalyze the electrolyte oxidation. Additionally, there is an evidence of preferential segregation of Ni on the surface for both NMC and Li-rich NMCs. Here we are investigating the synthetic effects on the cation distribution, and electrochemical performance of Ni-based layered oxide in a battery. The influence of synthetic routes on the bulk and surface will be systematically investigated by synchrotron XRD and soft X-ray absorption spectroscopy. These findings will hopefully shed light on the further development of Ni-based electrode materials for Li-ion batteries.
Evolution of the Surface and Subsurface Chemical Environment of LixNi0.8Co0.15Al0.5O2 electrodes
Authors: Sallis Shawn , Pereira Nathalie , Huang Yiqing , Quackenbush Nicholas F. , Whittingham M. Stanley , Amatucci Glenn G , Piper Louis F.J.
Published: February 2020

The nickel-based layered positive electrode, LiNi0.8Co0.15Al0.05O2 (NCA) has a high discharge capacity of ~ 200 mAhg-1 making it promising for potential electric vehicle applications. However, NCA displays drastic capacity fade with cycling. Accelerated cycling tests at elevated temperatures have shown that NCA electrodes undergo significant power fading. The significant power fading has been largely attributed to the formation of insulating and electrochemically inactive phases at the NCA surface. These include Li2CO3 surface species and a NiO-like rocksalt phase at particle surface due to oxygen loss. The literature of NCA surface and subsurface studies have highlighted the complexity of studying electrodes, with many reactions occurring that may not be inherent to NCA.

Here we report on our studies of the surface and subsurface of NCA electrodes with and without a binder additive (i.e. PVDF) as a function of initial charging and cycling. The chemical composition and transition metal oxidation states were determined from a combination of x-ray photoelectron and absorption spectroscopy techniques. Our results reveal dramatic differences in the surface environments between our NCA electrodes with and without binder. Our results suggest that the PVDF may play a more significant role in degrading the surface of the NCA i.e. oxygen loss, than previously thought. We also report our surface analysis of our extended cycled NCA binder free electrodes. This work was supported as part of NECCES, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Award Number DE-SC0001294.
Molybdenum Substituted Vanadyl Phosphate Îµ-VOPO4 with Enhanced Two-Electron Transfer Reversibility and Kinetics for Lithium-Ion Batteries
Authors: Wen Bohua , Wang Qi , Lin Yuh-Chieh , Chernova Natasha , Karki Khim , Chung Youngmin , Omenya Fredrick , Sallis Shawn , Piper Louis F.J. , Ong Shyue Ping , Whittingham M. Stanley
Published: February 2020

Structural reversibility of multiple electron transfer cathodes is the key challenge for the consequent intercalation process, which can double the energy density of current commercialized lithium-ion batteries. VOPO4 is a promising cathode that can possibly involve two redox transitions of V3+/V4+ and V4+/V5+, while in fact the structure easily loses the reversibility with only ~1.2 lithium inserted1. Here, we report ε-VOPO4 from hydrothermal precursor with 5 % Mo substituted at V site with improved reversible initial capacity to as much as ~250 mAh/g (total ~1.6 Li) and ~80 % retention for up to 20 cycles at C/25. Faster kinetics and lower hysteresis of Mo substituted VOPO4 can be attributed to the smaller and less ordered particles as shown by HRTEM images. X-ray absorption and X-ray photoelectron spectroscopy show the Mo6+ oxidation state with the charge compensated by the corresponding amount of V4+ confirmed by the magnetic analysis. The Mo6+ coordination and charge compensation mechanisms are also confirmed by hybrid density functional theory calculations. This work was supported as part of the NorthEast Center for Chemical Energy Storage (NECCES), and Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences under Award # DE-SC0012583.

1. Z. Chen, Q. Chen, L. Chen, R. Zhang, H. Zhou, N. A. Chernova and M. S. Whittingham, J. Electrochem. Soc., 2013, 160, A1777

Figure 1
Liquid Phase Exfoliation of Two Dimensional Transition Metal Oxides for Electrochemical Applications
Authors: O'Brien Sean , Nicolosi Valeria
Published: February 2020

Transition metal oxides (TMOs) represent an attractive family of materials for their electrochemical charge storage properties. The theory is mainly based on the two dimensional layered structure of these materials providing increased surface area for charge storage alongside decreased diffusion paths for lithium and other intercalation ions. Much work is done into the exfoliation of two dimensional materials such as V2O5 and anatase TiO2, however many methods require multistep chemical processes which can be lengthy and introduce the possibility of unwanted by-products. Liquid phase exfoliation by sonolysis provide a simple cost effective method to exfoliate these two dimensional TMOs to produce relatively thin nanoflakes with impressive charge storage capacities, cycle lifetime and efficiency. This work aims to show the charge storage capabilities of V2O5 and anatase TiO2 which both exceed their theoretical capacities without the use of polymer binders or conductive additives. Sonication of bulk material in common solvents for a relatively short time scale produces desirable nanoflakes while ultrasonic spraying produces uniform electrodes which are tested electrochemically vs. Li/Li+. In conclusion, this project, using simple methodology, produces electrochemically impressive two dimensional materials.

Figure 1
Designing Polyoxometalate Thin Films on Carbon Nanomaterials for Pseudocapacitive Electrodes
Authors: Genovese Matthew , Foong Yee Wei , Lian Keryn
Published: February 2020

Multi-Walled Carbon Nanotubes (MWCNTs) modified with mixtures of polyoxometalate (POM) ions were investigated as pseudocapacitive electrodes for electrochemical capacitors.  POMs undergo fast reversible multi-electron transfer reactions, and different POM molecules such as PMo12O40
3-
(PMo12) and PW12O40
3- (PW12) demonstrate characteristic electrochemical activity related to their chemical composition.  However, we have discovered that when these molecules are combined in aqueous solutions, the resulting mixture shows unique electrochemical properties leading to cyclic voltammograms (CVs) very different from those of the constituent molecules.  Further analyses revealed that these POM ions do not just mix physically in aqueous solutions, but instead react spontaneously to form PMo12-xWx mixed addenda chemistries.  By simply mixing PMo12 and PW12 in different ratios, a variety of mixed addenda ions, each with unique electrochemical properties, can be easily synthesized.        

This control over POM redox behavior afforded by the novel mixed addenda synthesis is used along with layer-by-layer (LbL) deposition to design molecular coatings that demonstrate desired pseudocapacitive characteristics. The best performance was achieved with a coating that superimposed a 3:1 PMo12O40
3−-PW12O40
3− mixed layer on a 1:1 GeMo12O40
4−-SiMo12O40
4− mixed layer, which resulted in an 11X capacitance enhancement over unmodified CNT. This dual layer electrode also demonstrated a close to rectangular CV profile due to the overlapping redox features of the POM combination (Figure 1).  In this talk we will discuss the unique electrochemistry of various POM mixtures, the mechanisms of the novel mixed addenda synthesis, and our approach for using these molecules to design high performance composite EC electrodes.

Figure 1
(Invited) Three-Dimensional Freestanding Nanofiber Electrodes for Electric Double Layer and Pseudo-Capacitors
Authors: Kalra Vibha
Published: February 2020

Fabrication of novel three-dimensional material architectures is essential for development of energy storage devices that allow high rate operation with sufficient energy capacity. In this talk, I will present our work on development of freestanding nanofiber-based electrodes using a simple electrospinning methodology for application in supercapacitors (EDLC/Pseudocapacitors)

We have developed porous carbon nanofibers (PCNF) that exhibit specific surface area of >1500 m2/g and multi-levels of pore sizes in the range of micro (< 2 nm), meso (< 50 nm) and macropores (> 50 nm). We studied these materials as freestanding electrodes in 1) electric double layer capacitors (EDLC) using liquid (aqueous and ionic liquid), as well as solid-state electrolytes and 2) as platforms for polyanilene (PANi) electrodeposition to develop hybrid supercapacitors that integrate electric double layer and pseudocapacitive energy storage.  The unique combination of pores at different length scales allows us to achieve a battery-like energy density of up to 80 Wh/kg, while retaining high power and cycle life in EDLCs. In-operando infrared spectroelectrochemistry was conducted to understand the transport of ions through the carbon electrode pores and its effect on performance in ionic liquid-based EDLCs. In the hybrid supercapacitor devices, we demonstrated that the PCNF mats retain their EDLC behavior post PANi coating providing a 366 F g–1 gravimetric capacitance, 140 F cm–3 volumetric capacitance, and up to 2.3 F cm–2 areal capacitance at 100 mV s-1 scan rate based on the weight, volume and area of the complete hybrid electrode – polyaniline coating and carbon substrate.
Ionic Liquid Mixtures As Electrolytes for Electrochemical Capacitors
Authors: Van Aken Katherine L , Beidaghi Majid , Gogotsi Yury
Published: February 2020

While known for a higher power density than batteries, electrochemical capacitors are limited by their energy density for some energy storage applications. Since the energy density of the device is proportional to the square of operating potential window, an effective way to increase energy density of the device is by increasing this voltage window.  Ionic liquid electrolytes are beneficial for this reason since they can theoretically operate at up to 6 V, though experimentally, the value is between 3-4 V, depending on the properties of electrode materials. Electrode materials can be made from high surface area carbons that contain a network of pores (activated carbon, carbide-derived carbon) or lower surface area carbons that consist of an outer surface where charging and discharging takes place. Though they boast a large operating potential window, ionic liquids are known to contain large and bulky ions. This can make it difficult to use an ionic liquid on a porous carbon with a range of pore sizes, some being very small, even though the specific surface area of the electrode material is higher. It has also been shown that the capacitance of porous electrodes is maximized when the ion size and pore size are equal.1  In this case, the ion is small enough to fit inside the pores while still large enough to take advantage of the surface area within the pore walls. While the outer surface materials allow a more accessible surface for adsorbing large ions, their capacitance is limited by their specific surface area. By designing an electrolyte based on mixed ionic liquids, 2 we can match the ions in the mixture to the multiple pore sizes of the electrode material. Imidazolium-based ionic liquids are chosen based on their variable alkyl chain length which alters the cation size and the TFSI is chosen as the anion for all ionic liquids.  Different porous carbons with varying pore size distributions are used to illustrate the effect of ionic liquid mixture electrolytes.

1.        Lin, R. et al. Solvent effect on the ion adsorption from ionic liquid electrolyte into sub-nanometer carbon pores. Electrochim. Acta
54, 7025–7032 (2009).

2.        Van Aken, K. L., Beidaghi, M. & Gogotsi, Y. Formulation of Ionic-Liquid Electrolyte to Expand the Voltage Window of Supercapacitors. Angew. Chemie
127, 4888–4891 (2015).
Electrochemical Performance of Solid Oxide Cell Oxygen Electrodes Under Pressurization
Authors: Hughes Gareth , Railsback Justin , Butts Danielle , Barnett Scott A
Published: February 2020

Pressurized operation is of interest for solid oxide fuel cells used in combined cycle applications, and for solid oxide electrolysis cells to influence the chemical constitution of the fuel produced.  Here we present results on the effect of oxygen pressure on the electrochemical performance of a number of solid oxide cell (SOC) oxygen electrodes, studied in symmetrical cells by impedance spectroscopy. Electrodes investigated include single-phase (La0.8Sr0.2)0.98MnO3-δ (LSM), LSM - Zr0.84Y0.16O2-γ (YSZ) composite, LSM-infiltrated YSZ, single-phase La0.6Sr0.4Fe0.8Co0.2O3-d (LSCF), and LSCF-Ce0.8Gd0.2O1.95 (GDC) composite. All electrodes exhibited reduced electrode resistance with increasing oxygen pressure, with all but the single-phase LSM showing a resistance decrease of around pO2
-0.18. The single-phase LSM electrode displayed a pO2
-0.28 dependence. Two primary features were found in the impedance spectra equivalent model fits. A higher frequency peak around 103 Hz had around a pO2
-0.25 dependence and was attributed to charge transfer reaction limitations. Of all the electrodes, only the single-phase LSM sample did not exhibit the higher frequency peak. A lower frequency peak around 102 Hz had around a pO­2
-0.15 dependence, which was attributed to either ionization of an adsorbed oxygen atom or oxygen ion transport from the electrode material to the electrolyte material. Only the LSM-infiltrated electrode did not display the lower frequency peak. Overall, these results indicated that performance losses due to oxygen electrode resistance can be reduced by operating a SOC at elevated pressure.
Design and Fabrication of a 600W Anode Supported Flat Tubular SOFC Stack
Authors: Ji Weijie , Zhang Lei , Ming Li , Jiang Yousong , Xie Bin
Published: February 2020

Keywords: SOFC stack, flat tube, metallic support, Ag-Cu air braze,

  Introduction

Recently, great interests are focused on Solid Oxide Fuel Cells for future energy economy. In order to reduce the cost and increase the lifetime of SOFCs, lowering the working temperature is necessary. To meet the demands, new stack structures and materials are developed. Among them, flat tubular stacks are shown to be promising for their performance and fabrication techniques, and also metallic materials are applied as interconnect and support for their characteristics [1].    

In this work, we design and fabricate a 600W anode supported flat tubular SOFC stack. The stack is composed of 36 flat tubular cassettes made by FeCrAl alloy. Cells composed of NiO-YSZ (anode)/ YSZ (electrolyte)/LSM-YSZ (cathode) are sealed on cassettes by Ag-Cu air braze. Experimental

The schematic diagram of stack structure is shown in Fig 1. A short stack is composed of several metallic cassettes made by FeCrAl (a commercial product: 1Cr21Al4). Five frames are located on the surface of the cassette, on which cells are sealed on the anode side by Ag-Cu air brazing. Ag-Cu brazes also serve as the electrical connect to the anode. FeCrAl interconnects with Ag mesh serve as the electrical connect to the cathode. Ag wires connect th e Ag-Cu braze with interconnects. Fuel inlet pipe is located at one end of the cassette and outlet is on the other end. Pipes are sealed by Ag rings with ceramic tubes. Fuel flows along the pipes and the ceramic tubes.      

Cells of 5x5cm2 are produced as described in previous results [2]. Anode substrates of NiO-YSZ are produced by conventional tape casting and sintering methods. YSZ electrolytes of 15 um are produced by spray and cathodes of 4x4cm2 LSM/YSZ are produced by screen printing.

Results and Discussion

   Stack of 36 cassettes are produced and tested. Humidified H2(2-3% H2O) is applied as the fuel and air as the oxidant. A mean open circuit voltage of 1.03V per cassette is obtained under working temperature 750 centigrade. The stack has been tested for 1000 hours. Ag-Cu braze and FeCrAl show good stability and reliability.

  Fig.2 shows the performance of the 36-cassette stack under different fuel flow. When 15slm H2 is supplied to the stack, a maximum output of 614W and an average power density of 213mw/cm2are obtained. The fuel utilization efficiency is 51%.

Conclusions

  An anode supported flat tubular stack is designed and produced. Stack of 36 cassettes are produced and tested with humidified H2 as fuel. An average power density of 213mw/cm2is obtained, higher than those reported results of the stacks [1].

References

[1] Ludger Blum etc, Int. J. Appl. Ceram. Technol., 2 [6] 482–492 (2005).

[2] Lei Zhang etc, Journal of Alloys and Compounds 586 (2014) 10–15

Figure 1
Development of Modelling and Testing for Analysis of Degradation in Solid Oxide Fuel Cells
Authors: Maillard John Geoffrey , Steinberger-Wilckens Robert
Published: February 2020

The ability to predict the lifetime performance of an SOFC can give guidelines for where improvements and alterations can be made in terms of production, operating parameters and cell design.  Multiple attempts have been made to implement models which can respond to all the varying parameters to give their characteristic performances over longer operational lifetimes than is feasible to physically test.

This study focuses on continuous degradation mechanisms and the impact they have on the components of a single repeating unit level, i.e. the anode, cathode, electrolyte, metal interconnect and sealants. Currently the model being developed deals specifically with anode and electrolyte degradation. Depending on operating conditions, SOFC cells suffer from Ni particle agglomeration, coarsening, and volatilisation which lead to increased overpotential in the anode. A loss in the ionic conductivity in the electrolyte is also observed.

Using models derived for these degradation mechanisms combined with percolation models, Matlab ® coding has been developed to outline the loss of performance in a single repeating unit for a given set of operating parameters. These equations will be tested against real life data to establish their validity and, where necessary, adjusted for accuracy.  Further progress will allow for accelerated testing of components and cells to determine the long term performance of a given material alteration or design change.
Fabrication of Large-area Multi-scale-architectured Thin-Film SOFC via Commercially Viable Thin-film Technology
Authors: Noh Ho-Sung , Hong Jongsup , Kim Hyoungchul , Yoon Kyung Joong , Kim Byung-Kook , Lee Jong-Ho , Son Ji-Won
Published: February 2020

We have reported the ultimate performance level that the anode-supported solid oxide fuel cell (SOFC) can reach by employing thin-film electrolytes and nano-structure electrodes, without drastically changing the component materials. Based on the platform named as multi-scale-architectured thin-film SOFC (TF-SOFC), thin-film electrolytes of thickness less than 1 micron and electrodes with particle size in nm scale are successfully realized on NiO-YSZ anode supports, and a peak power density exceeding 500 mWcm-2 at 500 oC is obtained.

Although this approach proves the potential of the thin-film technology to significantly improve the low-temperature performance of the SOFC, it is highly questionable that this platform can be transferred to the commercial sector because pulsed laser deposition (PLD) is employed to fabricate the cells. PLD is the best thin-film deposition research tool for the oxide with complex composition and has a high deposition rate, which is tremedous advantages for the thin film components in the TF-SOFC. Nevertheless, PLD has a small deposition area which cannot be larger than several cm by several cm in general, which is the most critical disadvantage of PLD to be employed as a commerciallization processing technique.

Therefore, to be employed in the commercial sector, it is the prerequisite that the multi-scale-architectured TF-SOFC should be realized by commercially viable techniques other than PLD. In this regard, the present study deals with the realization of the same platform by using other technique, specifically sputtering. Several key issues, such as nano-composite deposition, stoichiometry transfer, crystallinity of the thin films, etc., will be identified and the possible solutions to resolve these issues in sputtering will be suggested. A larger area (~ 5 cm by 5 cm) TF-SOFC using a 2-inch sputtering system will be fabricated to check the fesibility and its chracteristics will be compared with that of the cell fabricated using PLD.
Thermo-Mechanical Reliability of SOFC Stacks during Combined Long-Term Operation and Thermal Cycling
Authors: Greco Fabio , Nakajo Arata , Wuillemin Zacharie , Van herle Jan
Published: February 2020

Thermo-mechanical issues in planar solid oxide fuel cells (SOFC) must be understood and overcome to meet the reliability standards for market implementation. This study presents a modelling framework constituted by a thermo-mechanical and electrochemical model of a SOFC stack. Rate-independent plasticity and creep of the component materials have been considered. Modified periodic boundary conditions have been implemented to simulate the behaviour of a single repeating unit (SRU) in a stack.

The analysis starts with the simulation of stack conditioning procedures, which aims at capturing the stress build-up/relaxation throughout the several steps in the stack components production and assembly.

The simulated stresses after the initialisation sequence provide the initial stress state for the simulation of stack operation, which consists in importing into Abaqus software the temperature profiles from thermo-electrochemical simulations. The study includes long-term steady-state operation in both co-flow and counter-flow configuration, interrupted by thermal cycling. The temperature profiles implemented in the long-term operation cases correspond to operation under internal steam-methane reforming.

The simulation results show that the contact pressure is significantly lower at room temperature, after a first thermal cycle after stack qualification. The contact pressure is lost in large regions, which is expected to alter in the long-term the electrical conductivity of the interface. It also progressively decreases during long-time operation. Thermal cycling after long-term operation worsens the extent of loss of contact pressure at room temperature. Most of the active area is close to no-contact pressure.

No critical stresses were found in the sealant joining the cell to the SRU. In contrast, the stresses in the manifold sealants were found to be relevantly high. Similarly to the evolution of contact pressure, long-term operation increases the risks of sealant failure during thermal cycling.

Figure 1: On the top side, temperature field in co-flow configuration plotted on the deformed shape of a short stack (deformation along the z-axis magnified by 300:1), state: “Start Operation”. On the bottom side, contact pressure at the interface anode/GDL fuel along the symmetry line of the SRU. Lines 3b, 4 and 5 are referred to the case of long-term operation in co-flow configuration.

Figure 1
Development of Electrolyte Supported Cells Based on a Thin 3YSZ Substrate: Through Optimized Contact Layer to High Power Density
Authors: Trofimenko Nikolai , Kusnezoff Mihails , Klemm Denis , Schimanke Danilo
Published: February 2020

The 3YSZ substrates with thickness between 90-200 μm are excellent from mechanical and economical points of view, but its main disadvantage is rather low ionic conductivity when compared with scandia-doped zirconia or fully stabilized 8YSZ. With decreasing electrolyte thickness between 40-60 μm, it is possible to significantly improve the electrochemical performance of the 3YSZ based electrolyte-supported cell (ESC) thereby fully utilizing the available mechanical stability. Development and progress in manufacturing of high power density electrolyte supported cell based on a thin (50 µm) 3YSZ substrate is presented. The cells with improved cathode based on LSMM’/ScSZ and the multilayer anode based on Ni/GDC cermet show very good electrochemical performance. The maximum power density increases up to 750 mW/cm2 for developed cell without additional contact layer at 0.7V@860 °C and is greater than one of the commercial cells based on partially scandia stabilized zirconia electrolytes as well as 95 µm 3YSZ. The changes in polarization resistance of tested cells under different operating conditions as well as during redox-cycling and durability tests are discussed on basis of analysis of impedance spectra. The developed cells show a good long-term stability (proved for >1300 h) under high current density (500 mA/cm²@850 °C, N2:H2:H2O=55:40:5, air). The estimated power degradation rate is lower than 0.5%/1300 h. By using Ni/GDC anode the redox cycle ability of cell under real operating conditions is considerably improved. To reduce the contacting losses in stack different contacting layers have been tested and optimized in test bench. The influence of different parameters on electrochemical performance of the cell as well as first results for cells integration in stack are presented and discussed.
Status of Light Weight Cassette Design of SOFC
Authors: Margaritis Nikolaos , Blum Ludger , Batfalsky Peter , Bohmann Dirk , Ceschini Sergio , Fang Qingping , Federmann Dirk , Kroemer Joachim , Peters Roland , Steinberger-Wilckens Robert
Published: February 2020

Lightweight SOFC stacks are currently being developed for stationary applications such as residential CHP units, for automotive applications such as APU and for portable devices. Within the EU funded project the so-called Jülich CS-design has been improved for lightweight SOFC stacks using glass-ceramic sealings that decouple the thermal stresses within the stack and at the same time allows optimal sealing and contacting. The design is highly suitable for industrial low-cost manufacturing and automated assembly. To determine the effect on the thermomechanical behaviour of the fuel cell stack, modelling and coupled thermomechanical analysis have been performed. Based on the analysis results in combination with the manufacturing experience, test results, and post-test analysis from previous stack design, substantial changes have been made to the CS-design in order to improve mechanical robustness of the stack.

The manufacturing of single parts, particularly due to the improved design of sheet metal interconnects, as well as the assembling processes are suitable for low-cost mass manufacturing. The novel decal concept of glass-ceramic sealant screen printed on foil in order to produce green tapes is used for joining the stack layers offering an enormous potential for cost savings in industrial assembly process. The new design CSV(D2.0 in the MMLCR=SOFC project) furthermore has extended the process window of the laser welding joining process.

First CSV–design stack tests showed a comparable electrochemical performance to the previous CSIV design. The good adhesion of the glass sealant applied on steel sheet by screen printed tape and good contacting behaviour between cells and interconnects were furthermore confirmed by post-test analysis.