bluuebunny/crossref_metadata_2025 huggingface dataset:
Origin of the Two-Plateaued or One-Plateaued Open Circuit Voltage in Li/S Batteries from First Principle Calculation
Authors: Lin Yuxiao , Qi Yue
Published: February 2020

Li/S battery is widely considered as one of the next generation energy storage devices because of its high specific energy density. Most of the discharging curves for Li/S batteries can be categorized into two types: with two-plateaus or one-plateau. Two-plateaued discharging curves are typically observed in Li/S batteries with a liquid electrolyte, and they are signatures for the generation of soluble polysulfide (PS). One-plateaued discharging curves have been observed in Li-S batteries with solid electrolytes, indicating direct transformation from S to solid state Li2S2 and Li2S, without the formation of PS. More interestingly, some Li/S batteries with liquid electrolyte also displayed one-plateaued discharging curves, which seems related to the nanopores in cathode materials or the limited solubility of PS in the electrolyte. The fundamental understanding of the mechanism and the conditions for the one-plateaued discharging curve will provide guidelines for Li/S battery design in order to improve its cycle life by preventing the PS dissolution.

In this article, we systematically investigated the influence of temperature and solvation on the predicted free energy and the open circuit voltage (OCV) curves for Li/S batteries. First, we confirmed that S, Li2S and Li should be modeled as crystal structures; while PS, such as Li2S4 should be modeled as monomer under solvation. Secondly, it was shown that the effect of temperature is negligible for predicting OCV curves associated only with solid-phase transformation, but plays a deterministic role in the free energy of dissolved molecules, such as PS. Thirdly, the solvation energy calculations are deemed to be the most accurate with a combined implicit and explicit model, which means the first solvation shell is modeled explicitly with an implicit dielectric continuum media.

With the appropriate treatment of temperature and solvation effect, we demonstrated that the two-plateaued discharging curves occur when the PS is fully solvated (by DOL in our model) and one-plateaued discharging curve occurs when PS is not solvated, in agreement with experimental observation in typical Li/S battery with liquid or solid electrolytes. Furthermore, if PS is only partially solvated, its formation energy increases, leading to a transition from the two-plateaued to the one-plateaued discharging curves, as the PS changes from fully solvation to partial or no-solvation. Partial solvation can be created with a highly concentrated solution or by varying pore size and volume in the carbon matrix to confine S and limit the number of solvents transported into the pores, as practical methods to mitigate the PS shuttle problem from its root cause.
Latex Based Emulsion Functional Conductive Polymer Binder for Si Composite Electrode
Authors: Liu Gao , Zheng Tianyue
Published: February 2020

Functional conducting polymer binders are a class of stable, elastic, electrically conductive adhesive that makes possible the fabrication of silicon composite electrodes for a new generation of low-cost, high-capacity lithium-ion batteries. The vastly higher storage capacity of Si has not been fully realized because silicon swells up to nearly four-times its volume when the Si electrode draws in lithium ions during the charging process. This mechanical expansion and contraction quickly damage the electrode, rendering Si material useless. Functional conductive polymer binder directly addresses the volume-expansion problem by connecting the volume changing Si particles with an elastic polymer to form the anode electrode of a rechargeable lithium battery. This elastic adhesive polymer not only holds the silicon particles in place, but also stretches as those particles expand and contracts when they shrink back to their original volume. We have advanced the functional conductive polymer binder technology into its 4th generation, which is now a water based latex emulsion similar to industry standard styrene-butadiene rubber (SBR) binder, but electronically conductive. The latex based emulsion system of the 4th generation of functional conductive polymer binder ensures that the binder is low cost, and the battery manufacturing process is compatible with the current industry standard.
Quantification and Prediction of NMC Defect Concentrations
Authors: Yin Liang , Mattei Gerard , Li Zhuo , Khalifah Peter
Published: February 2020

Advanced neutron and synchrotron powder diffraction beamlines were utilized to accurately quantify important defects (anti-site, non-stoichiometry) for a large number of NMC cathode compositions, something that cannot readily be done using laboratory diffraction data. A comparison of defect concentrations obtained using neutron and synchrotron data gives good insights into the sensitivity of these methods. Based on these results, it is possible to make predictions about the anti-site defect concentration for arbitrary NMC compositions.
Development of a Novel Cathode Material Na2Fe1.96V0.96(PO4)3 with High Power and Long Cyclability for Na-Ion Batteries
Authors: Kim Jongsoon
Published: February 2020

We report Na2Fe1.96V0.96(PO4)3 (NFVP) as a new cathode material for Na ion batteries with outstanding cycle life and high power density for the first time. Structural characterization of NFVP was performed using Rietveld refinement of X-ray diffraction and neutron diffraction patterns, which revealed large Na diffusion paths in the structure that enabled rapid Na (de)intercalation without a large volume change. Using X-ray diffraction and X-ray photoelectron spectroscopy with charge/discharge measurements, it was confirmed that based on redox reactions of Fe and V ions, ~2 Na ions are reversibly (de)intercalated from the structure with an average voltage of ~3.1 V (vs. Na+/Na). At 30C, which denotes the rapid charge/discharge, ~74% of the theoretical capacity was delivered. Furthermore, NFVP exhibited an outstanding cycle life of over 2500 cycles (70% retention of the initial capacity), which can be attributed to the low volume change (~1%) during charge/discharge.
Elucidating Electrodeposition Mechanisms in Li-Ion Battery Anodes
Authors: Hao Feng , Mukherjee Partha P.
Published: February 2020

Metal plating and dendrite are widely observed in the electrochemical processes, such as electrodeposition and Li-ion battery charging cycles. In this work, a mesoscale modeling approach is developed for investigating the mechanisms of Li plating and dendrite on Li-ion battery anode surface. We explore the possible origins and the kinetics of these phenomena. Specifically, we investigate the effects of the anode surface wetting, Li surface self-diffusion, local overpotential, surface geometry, and temperature on the formation mechanisms of Li plating and dendrite. More importantly, we explicitly clarify the competition between these factors and quantify their contributions to the final Li morphology. From this study, we aim to shed light on the Li deposition behaviors on the anode surface and provide guidance for facilitating Li plating and avoiding Li dendrite.

Figure. Li deposition morphologies: (a) dendrite and (b) layered by layered film.

Figure 1
Atomistic Simulations on the High Rate Sodium Storage Mechanisms in Non-Graphitic Carbons
Authors: Paek Eunsu , Park Sungwon
Published: February 2020

Secondary energy storage technologies based on sodium ions are an important emerging alternative to lithium ion batteries. Sodium is less expensive than lithium, with its supplies being much wider and more democratically distributed throughout the globe. Therefore there is the potential for significantly reduced system cost, as well as for increased energy security due to ease of obtaining sodium precursors. A survey of literature indicates that the most optimum negative electrodes for sodium ion capacitors (NICs) consist of high surface area two-dimensional carbons, such as various high surface area carbon nanosheets. However, to date, fast Na charge storage mechanisms in such carbons are not well understood. In this talk, we will present the adsorption and transport characteristic of Na ion and electrolytes (EC/DMC) at the interface and discuss how Na is reversibly and irreversibly stored within imperfect carbons using combined molecular dynamics and density functional theory calculations. For example, our recent study suggests that N-doping leads to significant enhancement in Na adsorption which could lead to Na trapping. We will discuss the fundamental issues regarding the Na ion storage behavior at the interface with varying carbon ordering and heteroatom chemistry, and the design principles to enhance Na based energy storage and charge rate.
Mixed Organic/Ionic Liquid Electrolytes Compatible with Forcespun Carbon Microfiber Electrodes in Lithium Ion Batteries
Authors: Lopez Jorge , Villarreal Jahaziel , Cantu Jesus , Parsons Jason , Alcoutlabi Mataz
Published: February 2020

We present results on the Forcespinning (FS) of PVP solution precursors for the mass production of porous carbon microfibers as anode materials for Lithium-ion batteries. The porous microfiber carbon anodes are produced using a scalable technique (FS) and subsequent thermal treatment (carbonization). The carbon fiber anodes were porous and flexible. The flexible microfibers were directly used as working electrode in lithium-ion batteries without a current collector, conducting additives, or binder. Mixed organic/ionic liquid electrolytes (MOILEs) were employed in Lithium ion cell cycling studies with the porous carbon anode and commercial cathodes to investigate the electrochemical and cycling performance of the Li-ion cells. A temperature range of 25 to 60 °C and different current rates were used to study the effects of temperature on the ionic conductivity of MOILEs and on the electrochemical performance of LIB cells. 1-Ethyl-3-Methyl-imidazolium Lithium bis(trifluoromethanesulfonyl) imide (EMI-TFSI) ionic liquid was synthesized in our laboratory by reacting the EMI cation and TFSI ion in a 1:1 mole ratio. The EMI-TFSI ionic liquid and LiTFSI salt were mixed with organic liquids (Ethylene carbonate (EC) dimethyl carbonate (DMC) and Succinonitril (SCN) to improve the ionic transport of the electrolyte during the charge/discharge cycles. The carbon microfiber electrodes delivered a good electrochemical performance and Coulombic efficiency when used half and full cells. This study provides a novel and feasible pathway for designing and developing promising anodes with mixed organic/ionic liquid electrolytes for high-performance lithium ion batteries.
Effect of Halide Doping on the Structure and Properties of Na3SbS4 Solid Electrolyte
Authors: Wang Hui , Schultze Trevor M , Kang Luhao , Dewees Rachel , Hood Zachary D.
Published: February 2020

Compared to Li-ion batteries, rechargeable sodium (Na) batteries hold much promise for medium and large-scale energy storage systems due to the decreased price, natural abundance and suitable electrochemical window of Na metal. In addition to Na-S and ZEBRA batteries, solid-state Na batteries that operate at room temperature are highly desirable. To realize this target, solid electrolytes with highly ionic conductivities are necessitated. Na3SbS4 is a newly discovered Na-ion conductor [1] and exhibits an excellent ionic conductivity of 1 mS cm-1. To further improve its performance in solid-state Na batteries, faster Na-ion transportation through Na3SbS4 is expected. In this report, we introduced halide ions into Na3SbS4 solid electrolyte and studied doping effect on the crystal structure and conductive properties of Na3SbS4. It was found that the iodide (I-) doping expanded the lattice structure of Na3SbS4 without generating a new phase. Tuning the dopant concentration led to an overall higher ionic conductivity in doped Na3SbS4. The enhancement of ionic conductivity is explained by the creation of vacancies due to alivolent anion substitution.

Reference

[1] Wang, H., Chen, Y., Hood, Z.D., Sahu, G., Pandian, A.S., Keum, J.K., An, K. and Liang, C., An Air‐Stable Na3SbS4 Superionic Conductor Prepared by a Rapid and Economic Synthetic Procedure. Angewandte Chemie International Edition, 2016, 55(30), pp.8551-8555.
Computational Modeling of Solid State Lithium-Ion Battery Architectures: Opportunities and Challenges
Authors: Cobb Corie Lynn , Allu Srikanth
Published: February 2020

Solid state Lithium-ion (Li-ion) batteries can revolutionize battery design and performance due to their inherent safety, high voltage stability, and potential for high conductivity. As the solid state Li-ion battery field grows, there is a need for simulation tools which allow battery engineers to explore the effects of material and geometry and their subsequent impact on performance, enabling optimization of a given battery design without expansive experimental tests. In this talk, we survey current research literature on modeling of solid state Li-ion batteries and discuss the challenges and opportunities that exist in developing a multi-physics modeling tool. A three-dimensional (3D) computational framework called AMPERES, developed at ORNL, is used as a case study to examine the requirements of modeling the electrode-electrolyte interface of solid state Li-ion batteries. Because AMPERES enables one to model arbitrary battery and electrode configurations, we also discuss potential 3D structures that can enhance mechanical stability and the effective conductivity of a solid state battery medium.
Performance of Magnesium Sulfur Battery Using Sulfur Nanoparticle in 3D Carbon Cloth Cathode
Authors: Muthuraj Divyamahalakshmi , Mitra Sagar
Published: February 2020

Magnesium batteries are promising alternative to Conventional Lithium ion batteries due to their natural abundance, safety and high volumetric capacity. In recent years, the idea of coupling Magnesium with sulfur cathode is introduced where sulfur yields high theoretical capacity of 1671 mAh/g1 which can improve energy density of the system. However, the polysulfide dissolution in electrolyte and the volume expansion of active material during conversion reaction is the key challenge that obstruct practical application. In this work, we chemically encapsulate the polysulfides to 3D carbon cloth current collector. The role of functional groups on current collector in stabilizing the cycle life was performed. In discussion, we will elaborate our results highlight and the performance of Sulfur nanoparticle in conductive carbon cloth.
Structural Stability of LiNiO2 Cycled at Different Cut-Off Voltages(4.1, 4.2, and 4.3V)
Authors: Park Sang-Min , Sun Yang-Kook
Published: February 2020

A spherical stoichiometric LiNiO2 particle, which was composed of compactly packed nanosized primary particles, was prepared and cycled at different cutoff voltages to s demonstrate the effect of phase transitions during Li deintercalation/intercalation on the Li-ion intercalation stability of LiNiO2. The capacity retention was greatly improved by suppressing the H2 → H3 phase transition at 4.1 V, such that 95% of the initial capacity (164 mAh g−
1) was retained after 100 cycles when cycled at 4.1 V. At 4.2 and 4.3 V, continuous capacity loss (81% of 191 mAh g−1 at 4.2 V and 75% of 232 mAh g−1 at 4.3 V after 100 cycles) was observed during cycling, and these electrodes incurred extensive structural damages (micro-, hairline and nanoscale cracks observed by transmission electron microscopy) from the repeated lattice contraction and expansion accompanying the H2 → H3 transition, in agreement with the cycling data.

References

S.-T. Myung, F. Maglia, K.-J. Park, C. S. Yoon, P. Lamp, S.-J. Kim, Y.-K. Sun, ACS Energy Lett. 2017, 2, 196.

J. H. Lee, C. S Yoon, J.-Y. Hwang, S.-J. Kim, F. Maglia, P. Lamp, S.-T. Myung, Y.-K. Sun, Energy & Environ. Sci. 2016, 9, 2152.

B.-B. Lim, S.-J. Yoon, K.-J. Park, C. S. Yoon, S.-J. Kim, J. J. Lee, Y.-K. Sun, Adv. Funct. Mater.
2015, 25, 4673.

B.-B. Lim, S.-T. Myung, C. S. Yoon, Y.-K. Sun, ACS Energy Lett.
2016, 1, 283.
Imaging of Representative Volumes in Battery Electrodes and Direct Visualization of Lithium Atoms: Recent Advances in Electron Microscopy
Authors: Lemmens Herman
Published: February 2020

There are different ways to create a 3D image of the battery electrodes.

MicroCT uses the absorption of X-rays to create a 3D reconstruction. The Field of View is large enough to be representative with regard to the grain sizes (1). However, the submicron porosity in the electrodes is typically not well captured by microCT because of its limited resolution.

The FIBSEM technique which uses a Galium ion beam for sectioning and an electron beam for imaging has high enough resolution to resolve all porosity. However, the Field of View is typically of the order of 10 micrometer; which is not big enough to create a representative model of the pore space.

In this study we have used a plasmabeam for sectioning and an electron beam for imaging. The plasmabeam typically removes a layer of 100 nm followed by imaging by the electron beam. The material removal rate with the plasmabeam is magnitudes higher than with the Ga focused ion beam, allowing to expand the field of view to hundreds of micrometers.

A 3D reconstruction of the anode (Field of View 200micrometer) and the cathode (Field of View 100 micrometer) make it possible to calculate parameters such as the tortuosity on a representative volume.

Segmentation of the pore space is not straightforward due to minimal grey level differences between the different phases. Also, it is not uncommon to see details from layer N+1 through the pores in layer N. This so-called pore-back effect must be taken into account otherwise the permeability will be greatly underestimated.

Direct imaging of light elements such as lithium in the crystal structure of a compound by Transmission Electron Microscopy is typically a difficult task. In most cases the position of the light elements is deduced from image simulations using different defocus and thickness values.

Starting from the theory of scanning transmission electron microscopy imaging we have proven that it is possible to image the phase of a thin sample directly and linearly when use is made of the center of mass (COM) movement of the convergent beam electron diffraction pattern. Integrating the two components of the COM image gives an image which is directly proportional to the phase shift caused by the sample.

Experiments show that both light and heavy elements are visible and that low frequency information is fully transferred. Examples are shown where lithium is directly visualized in the structure of a typical cathode active material.

Cai et al, Electrochimica Acta 56 (2011) 5804–5814
Resolving the Degradation Mechanism of the O3-Type Layered Oxide Cathode Surface through the Nano-Size Aluminum Oxide Coating for High-Energy Density Sodium-Ion Batteries
Authors: Hwang Jang-Yeon , Sun Yang-Kook
Published: February 2020

The increasing concerns regarding the rapid depletion of fossil fuels and their environmental footprint have prompted a strong worldwide interest in the exploration of inexpensive and eco-friendly energy storage technologies.1 Layered sodium oxides, particularly O3-type layered compounds, have been extensively studied due to their adequate capacity and well-established chemistry which was inherited from LIB technologies. So far, various chemical compositions have been introduced through different transition metal substitutions (Ni, Co, Mn, and Fe) such as Na[NixFeyMnz]O2 or Na[NixCoyMnz]O2.2-4 A surface-modified O3-type Na[Ni0.6Co0.2Mn0.2]O2 cathode was covered by Al2O3 nanoparticle using a simple dry ball-milling route. The nanoscale Al2O3 particles (∼15 nm in diameter) densely covering the spherical O3-type Na[Ni0.6Co0.2Mn0.2]O2 cathode particles effectively minimized parasitic reactions with the electrolyte while assisting Na+ migration. The proposed Al2O3 coated Na[Ni0.6Co0.2Mn0.2]O2 cathode showed a high specific capacity of 151 mA h g−1, as well as improved cycling performance and rate capability in a half cell. Furthermore, the Al2O3 coated cathode was scaled up to a pouch-type full cell using a hard carbon anode that exhibited a superior rate capability and capacity retention of 75% after 300 cycles with a high energy density of 130 W h kg−1. In addition, the post-mortem surface characterization of the cathodes from the long-term cycled full cells cooperated with identifying the specific mechanism of the surface reaction with the electrolyte and the reason for its subsequent degradation and showed that the nano-size Al2O3 coating layer was effective at resolving the degradation pathways of the cathode surface from hydrogen fluoride (HF) attack.

References

J.-Y. Hwang, S.-T. Myung and Y.-K. Sun, Soc. Rev., 2017, 46, 3529–3614.

J.-Y. Hwang, S.-T. Myung, D. Aurbach and Y.-K. Sun, Power Sources, 2016, 324, 106–112.

J.-Y. Hwang, S.-M. Oh, S.-T. Myung, K. Y. Chung, I. Belharouak and Y.-K. Sun, Nat. Commun., 2014, 6, 6856.

J.-Y. Hwang, C. S. Yoon, I. Belharouak and Y.-K. Sun, J. Mater. Chem. A, 2016, 4, 17952–17959.
Surface Functionalization of Silicon Nanoparticles with Citric Acid for Enhanced Performance As Lithium Ion Battery Anodes
Authors: Lucht Brett L , Chandrasiri Dilni Kaveendi , Jurng Sunhyung , Subramanian Parimalam Bharathy , Nguyen Cao Cuong , Young Benjamin , Heskett David
Published: February 2020

Among advanced materials studied to enhance the performance and energy storage of Li ion batteries, silicon nanoparticles have shown great potential as an anode material with its high theoretical gravimetric capacity of approximately 4200 mAh/g which is ~10 times higher than that of the commercially used anode material graphite. Nevertheless, the volume expansion of ~400% during the lithiation causes the electrode to suffer from rapid degradation, thus leading to poor cycle life. In this study we discuss the surface modification of silicon nanoparticles with citric acid for better cycling performance and capacity retention of silicon based electrodes. The objective of the study is to form a protective layer on silicon nanoparticles that will reduce the strain caused by volume variation due to lithiation and delithiation in the cycling process.

Cycling performance studies have been conducted on 50% silicon containing electrodes as well as graphite silicon composite electrode (70:15 weight % respectively). Both types of electrodes have shown promising cycling performance data when the surface of was functionalized with citric acid. The results indicate good capacity retention of ~60% after 50 cycles from surface modified silicon electrodes as opposed to 45% with the surface unmodified electrode. Chemical and surface analytical techniques such as Fourier transformation infrared spectroscopy(FTIR), Xray photoelectron spectroscopy (XPS), hard x-ray photoelectron spectroscopy (HAXPES), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), electrochemical impedance spectroscopy was used to analyze the nanoparticle surface as well as the solid electrolyte interphase formed on the electrodes to further understand how this protective layer improve the performance and the results of this study will be discussed.

Figure 1
Synthesis of Cobaltic Oxide/Carbon Nanotube/Graphene Composites for Anode Materials of Lithium-Ion Batteries
Authors: Lin Chuen-Chang
Published: February 2020

Carbon nanotube/graphene composites are directly grown on nickel foil without additional catalysts by chemical vapor deposition (CVD). Next, cobalt is deposited on carbon nanotube/graphene composites by radio-frequency (RF) sputtering with different power levels and time periods. Then the cobalt is transform into cobalt oxide by annealing. The higher specific capacity is obtained at the sputtering conditions (power = 100 W and time = 60 min). The longer the time period, the higher the specific capacity. Furthermore, it also shows higher electrochemical stability for cobaltic oxide/carbon nanotube/graphene composites in comparison with cobaltic oxide.
Mechanochemically Reduced Si/SiO
x
Nanospheres As a High Capacity Anode Material for Lithium-Ion Battery
Authors: Kim Yeong Eun , Park Eunjun , Kim Dae Sik , Kim Ayoung , Kim Hansu
Published: February 2020

Si/SiO
x
composites have attracted much interest as high capacity materials for lithium-ion battery with their good cycle performance. However, the main problem with Si/SiO
x
anode materials is their low initial Coulombic efficiency resulting from the irreversible reaction of SiO
x
with Li. In this work, to improve initial Coulombic efficiency, we propose a mechanochemically reduced Si/SiO
x
nanospheres through high-energy mechanical milling with reactive Mg metal particles. We found that milling time and the relative amount of Mg metal as a reducing agent are key variables to govern the electrochemical performance of mechanochemically reduced Si/SiOx nanocomposite anode materials. The obtained Si/SiO
x
nanospheres exhibited improved initial Coulombic efficiency of 55 % with initial discharge capacity of 1140 mAh g-1. The microstructure and electrochemical properties of the reduced-Si/SiO
x
will be discussed in more detail.
Micro-Size Carbon-Free Iron Sulfides As Advanced High Tap Density Anode Materials for Rechargeable Li- and Na-Ion Batteries
Authors: Yu Taeyeon , Sun Yang-Kook
Published: February 2020

Numerous materials have been considered as promising electrode materials for rechargeable batteries; however, developing efficient materials to achieving good cycling performance and high volumetric energy capacity simultaneously remains a great challenge.1 Considering the appealing properties of iron sulfides, which include low cost, high theoretical capacity, and favorable electrochemical conversion mechanism.2,3 In this work, we demonstrate the feasibility of carbon-free micro-size Fe1–xS as high-efficiency anode materials for rechargeable batteries by designing hierarchical intertexture architecture. The as-prepared intertexture Fe1–xS microspheres constructed from nanoscale units show advantage of both the long cycle life of nanoscale units and the high tap density (1.13 g cm–3) of the micro-intertexture Fe1–xS. As a result, high capacities of 1089.2 mA h g–1 (1230.8 mA h cm–3) and 624.7 mA h g–1 (705.9 mA h cm–3) were obtained after 100 cycles at 1 A g–1 in Li-ion and Na-ion batteries, respectively, demonstrating one of the best performances for iron sulfide-based electrodes. Even after deep cycling at 20 A g–1, satisfactory capacities could be retained. Related results promote the practical application of metal sulfides as high-capacity electrodes with high rate capability for next-generation rechargeable batteries.

References

J.-Y. Hwang, S.-T. Myung and Y.-K. Sun, Soc. Rev., 2017, 46, 3529–3614.

Y. Xiao, J.-Y. Hwang, I. Belharouak and Y.-K. Sun, Nano Energy, 2017, 32, 320–328.

Y. Xiao, S.H. Lee and Y.-K. Sun, Adv. Energy Mater., 2017, 7, 1601329.
Nuclear Magnetic Resonance Investigations of a Next-Generation Battery Lithium Polymer Electrolyte
Authors: Munoz Stephen A , Gobet Mallory , Zimmerman Michael , Leising Randy , Greenbaum Steve
Published: February 2020

The Li-ion battery has served as the workhorse of many industries for a generation. The technology has advanced incrementally over the years, but the underlying chemistry has undergone only minimal changes since its commercialization in the early 90’s. A novel solvent-free polymer electrolyte developed by Ionic Materials, Inc. threatens to shift this paradigm. The polymer electrolyte is based on a crystalline thermoplastic polymer which is treated with an oxidizing agent and then reacted with a lithium salt. This electrolyte displays transport properties suitable for commercial battery use, while retaining the mechanical and safety advantages associated with a solid, and sufficient electrochemical stability to allow its use with Li-metal and high voltage intercalation electrodes. We report here Nuclear Magnetic Resonance (NMR) investigations of this polymer electrolyte. Pulsed-field gradient self-diffusion studies, in tandem with relaxometry and magic angle spinning (MAS), allow characterization of the structure and dynamics of this revolutionary material. Our measurements show room-temperature Li+ self-diffusion coefficients on the order of 10-9 m2/s (an order of magnitude higher than previously reported solid electrolyte candidates), as well as cation transference numbers approaching 0.5. We have also established further evidence that the ionic motion is decoupled from polymer segmental or chain motion, in contrast to the mechanism governing ionic transport in the widely studied polyether-based electrolytes. We discuss some of the challenges of studying this material, as well as the implications of the results for its suitability as an electrolyte for secondary Li metal batteries.
Engineering Novel Fiber Structures As Wearable Supercapacitors
Authors: Gao Wei
Published: February 2020

Recently, fiber/yarn-based energy-storage systems have attracted enormous attention due to their remarkable promises in smart textiles and high-tech sportswear etc., mainly as more pliable energy-storage units being truly “wearable”. Scalable, inexpensive manufacturing processes that produce yarns capable of storing energy are required for new breakthroughs within the wearable electronics sector. For example, US Army is looking for the manufacturing processes capable of producing kilometers of energy-storage yarns that retain desirable mechanical attributes and can be knitted or woven into wearable fabrics. However, so far such processes are still missing. Current technologies include modified textile yarns, composite yarns containing metal wires, polymers, carbon nanotubes (CNTs), metal oxides, and conductive carbon yarns etc. However, several issues exist in current systems, including the biosafety of CNTs, the weight and corrosion of metal wires, and long-term stability of conductive polymers. These issues need to be addressed before they can be employed for practical use.

Here we introduce a unique process of making graphitic yarns (yarns made of graphitic carbon flakes) that has attracted enormous attention internationally. Yarns made of graphite flakes are lighter and more corrosion-resistive than metal wires, and more stable in electrical conductivity than polymers. More importantly, graphite flakes are generally considered to be biofriendly, since they have been used as the major component in pencils for decades. Furthermore, the process of making graphite fibers has several advantages: 1) large-scale availability of the wet-spinning dope, which is graphite oxide dispersions in water; 2) fiber/yarn precursors labile for various chemical/physical modifications; 3) graphite used as the major precursor, which is low cost and abundant in nature; 4) several prototypes have been demonstrated. This talk will introduce our recent research on process engineering and chemical modification of the detailed yarn structures for high energy density and mechanical flexibility.
A Practical Anion Exchange Membrane with Tunable Properties for High Performance and Chemical and Mechanical Stability
Authors: Herring Andrew M , Kuo Mei-Chen , Galito Samuel , Coughlin E. Bryan
Published: February 2020

Many electrochemical processes for energy conversion are more facile in base than in acid. But, there are no good commercial anion exchange membranes (AEM), that are chemically stable, have dimensional stability in water, and still have high ion conductivities resulting in reasonable area specific resistances as thin films. In collaboration with the University of Massachusetts, Amherst we have developed an innovative polymer system that can be tuned for almost any application needing an AEM in electrochemical engineering. The material is a symmetrical ABA triblock polymer with a facile synthesis amenable to large-scale production. The A blocks are the ridged ion conducting hydrophilic blocks and are derived from polymethylchlorostyrene (PCMS) and functionalized with next generation C6 ring cations that give the polymers some of the highest know chemical stability so far observed. Here we functionalize the materials via quaternization of the PCMS with methylpyrrolidinium (MPRD) cations. We can process the A block to control swelling. In addition we can easily achieve ion exchange capacities >2.0meq g-1 which leads to phase separated materials with ionic conductivities > 0.1 S cm-1. The material phase separates into a short range lamella morphology as confirmed by TEM and SAXS. The B block is based on cycloctene or cycloctadiene and is designed to be very soft, so soft in fact that it melts at 50°C. The mechanical properties of the B block are then easily tuned by careful control of a photocrosslinking chemistry involving a dithiol. Through control of the A and B block lengths and the cross-linking steps we can achieve AEMs that can be as little as 10 μm in thickness with some of the highest ionic conductivity, chemical stability, control of swelling, and device ready mechanical properties. Because the material is solvent castable it also makes an excellent starting point to develop ionomers for the electrodes in fuel cells and other devices. We are supplying the material to ProtonOnSite for testing in electrolysis devices, the Army Research Laboratory for testing in fuel cells and JCESR for testing in redox flow batteries, and we will present the results of these studies and discuss the path forward to making our material device ready.
Determining Electro-Osmotic Drag of Water in Anion Exchange Membrane Fuel Cells
Authors: Roy Asa Logan , Peng Jing , Zawodzinski Thomas A.
Published: February 2020

In an effort to reduce the cost of proton exchange membrane fuel cells (PEMFCs), a significant amount of research into non-precious metal (NPM) oxygen reduction catalysts has been conducted in recent decades. Despite this effort, platinum remains the only material with suitable stability and activity for use in the harsh environment of PEMFCs. Anion exchange membrane fuel cells (AEMFCs) have been gaining increased attention in recent years, providing advantages of higher stability and activity of NPM catalysts in alkaline environments.

Unfortunately, the relevant properties, e.g. conductivity and mechanical & chemical stability, of anion exchange membranes (AEMs) are inferior to their proton conducting counterparts. Many studies have been conducted which focus on improving membrane properties such as swelling ratio, conductivity, and stability. In comparison, relatively little attention has been paid to studying ion and water transport in anion exchange membranes.

Previous work conducted in our group has indicated that the majority of AEMFC polarization arises from the anode. The performance is relatively insensitive to catalyst loading and initial results indicate that electrode flooding is the primary cause of poor performance. To improve the performance of AEMFCs and better design AEMs, it is therefore important to study the transport of water and ions within AEMs. One key parameter which has received very little attention in the literature is the electro-osmotic transport of water due to the conduction of anions from the cathode to the anode.

In this work, we study the electro-osmotic drag (EOD) in anion exchange membranes. The cell design and concept for electro-osmotic drag coefficient (ε) measurements in this work follow from the work of Fuller and Newman as adapted by others1–3. Analysis is conducted on the membranes in pure hydroxide form and carbonate form. The conductivity, water uptake and water mobility of the membranes is also studied over a wide range of relative humidities and temperatures.

Better understanding of the transport of water and ions within anion exchange membranes will facilitate the development of models for AEMFC behavior and offer insight for future AEM production.

Figure 1: Effect of water activity on the EOD coefficient (ε) and water content (λ) in Tokuyama A201.

T. F. Fuller and J. Newman, J. Electrochem. Soc., 139, 1332–1337 (1992).

T. A. Zawodzinski, J. Davey, J. A. Valerio, and S. Gottesfeld, Electrochim. Acta, 40, 297–302 (1995).

X. Wang, J. P. Mcclure, and P. S. Fedkiw, Electrochim. Acta, 79, 126–132 (2012) http://dx.doi.org/10.1016/j.electacta.2012.06.098.

Figure 1
Miniature Fuel Cell with Monolithically Fabricated Si Electrodes - Application of a Polymer Electrolyte Membrane with Adapted Shape
Authors: Kushida Yuta , Sawada Asuka , Kono Koichi , Oshiba Yuhei , Yamaguchi Takeo , Hayase Masanori
Published: February 2020

Miniature fuel cells have attracted attention as an ultimate portable power source, and we have developed monolithically fabricated Si electrodes for the miniature fuel cells [1]. In the fuel cells, two Si electrodes with porous Pt catalyst layer are pressed onto either side of a PEM (polymer electrolyte membrane) , and the prototype fuel cells showed promising performances of over 500mW/cm2 output at 313K with H2-O2. However, the high output was obtained with only 1 mm2 reaction area. Along with enhancement of the reaction area, the performance dropped. We assumed that the performance drop is caused by poor adhesion between Si electrodes, because the porous Pt layer becomes depressed several micrometers from the substrate surface during the formation process using anodized porous Si and voids appears at interface between electrodes and PEMs as shown in figure 1(a).

In this study, we attempted to adapt PEM shape to the depression of the porous Pt catalyst layer as shown in figure 1(b). Generally, swelling of PEM caused serious damages to miniature fuel cells because of their fragile nature of porous-Pt and we have employed pore-filling membranes to avoid the swelling in our fuel cells. The pore-filling membrane has two components: a porous polymer substrate to provide mechanical strength and an electrolyte polymer in the pores for proton conductivity. In order to machine the PEM to fit the depression, we decided to apply O2 plasma etching to the porous polymer substrate and fill electrolyte polymer into the substrate after the shaping, because damage to electrolyte with long O2 plasma irradiation was a concern. To protect the central area of the porous polymer substrate from the plasma, circular copper plate was used as a mask and was put on the substrate in the process chamber. Plasma etching was applied on both side of the substrate. Figure 2 shows the porous polymer membrane after the plasma etching. As we expected, the substrate has circular thick area. Gas permeability of the porous polymer substrate did not change even after the several micrometers etching, and it was assumed that porous structure was maintained at plasma irradiated area. After the shaping, 2-acrylamido-2-methylpropan sulfonic acid (AMPS) was filled in to the substrate and the monomer was polymerized by heating [2]. Prototype cells with 4mm2 reaction area with the proposed adapted shape PEM and conventional flat PEM were made and power generation tests were performed. With the adapted shape PEM prototypes, 780 mW/cm2 at average and max. of 1050 mW/cm2 outputs were obtained, which is the best among our results. While with conventional PEMs, average output was 320 mW/cm2 and even maximum was 420 mW/cm2.

References

[1] M. Kobayashi, T. Suzuki, M. Hayase, Journal of Power Sources, 267, 622-628 (2014).

[2] T. Yamaguchi et al., Journal of Membrane Science, 214, 283-292(2013).

Figure 1
Porous Hollow Ptni/C Electrocatalysts: Carbon Support Considerations to Meet Stability Requirements
Authors: Asset Tristan , Job Nathalie , Busby Yan , Crisci Alexandre , Martin Vincent , Stergiopoulos Vaios , Bonnaud Céline , Serov Alexey , Atanassov Plamen , Chattot Raphaël , Dubau Laetitia , Maillard Frederic
Published: February 2020

Porous hollow PtNi/C nanoparticles (NPs), an highly active electrocatalyst for the oxygen reduction reaction (ORR)1, were successfully synthesized on different carbon supports. The latter plays an essential role in the NPs synthesis, providing a way to control their morphology and Ni content. The physico-chemical properties of the different carbon supports were crucial during accelerated stress tests simulating start-stop events at a PEMFC cathode (i.e. step potentials between 1.0 and 1.5 V vs. RHE) and were discussed by the means of identical-location transmission electron microscopy (IL-TEM) and electrochemistry (see. Figure 1). It was observed that electrocatalysts supported on graphene nanosheets and carbon xerogel suffer from NPs detachment and carbon complete corrosion while COsurf forms on carbon blacks supports (i.e. incomplete oxidation of the surface). The degradation of the carbon support resulted in mass activity and specific activity losses, as the result of the increase of the resistance of the catalytic layers (ΔR
k).

Figure 1
Reinforced Nanocomposite Polymer Electrolyte Membrane and Its Characterization Fabricated by an Innovatively Simple Process for PEMFC
Authors: Choi Young-Woo , Jang Seol , Yoon Young-Gi
Published: February 2020

In a different way from the conventional method, reinforced composite membranes were fabricated by using electrospinning and spraying with an accord. The hydrophobic polymer, polysulfone (PSf), was used as a substrate and the hydrophilic polymer, sulfonated poly(arylene ether sulfone) (sPAES), was used as an electrolyte. The ratio of PSf to sPAES was 1.7 : 8.3. The membrane properties and performance of the PSf electrospun / sPAES sprayed reinforced nanocomposite membrane, PSf(ES)+sPAES(SP) was compared with i) pristine sPAES membrane, ii) PSf sprayed / sPAES electrospun reinforced nanocomposite membrane, PSf(SP)+sPAES(ES), and iii) PSf, sPAES blend membrane. Although the PSf(ES)+sPAES(SP) membrane contained the substrate, its cell performance was not significantly different from the pristine sPAES membrane, and its durability was 2 times higher than that of pristine sPAES membrane.
Rational Design of Ir-M Nanoalloy for PEMFC Cathode Application: Combined Computational and Experimental Study
Authors: Cho Jinwon , Jang Injoon , Park Hyun-Seo , Choi Sun Hee , Jang Jong Hyun , Kim Hyoung-Juhn , Yoon Sung Pil , Yoo Sung Jong , Ham Hyung Chul
Published: February 2020

Despite recent efforts on replacing a noble Pt to less expensive catalysts for improving oxygen reduction reaction (ORR) for PEMFC (polymer electrolyte membrane fuel cell) application, the performance and stability of a noble Pt catalyst remains superior. In this presentation, we have systematically designed the novel Ir-based ORR catalyst for the PEMFC application via the combined density functional theory (DFT) and experimental approach.

First, we computationally screened the potential M element and near-surface composition in Ir3M nanoalloy (M = 3d, 4d, 5d metals) for the purpose of enhancing the activity and durability of catalyst in ORR by considering Gibbs free energy change for alloy formation process, oxygen binding energy and segregation energy of inside M element toward surface layer under vacuum and oxygen environment. Our DFT-based screening identified the pure Ir monolayer on the top of Ir3­Cr, Ir3­V, Ir3­Re, and Ir3­Tc alloy cores as the promising candidates for improving ORR activity and durability.

Next, a pure Ir monolayer on the top of Ir3­Cr core (which was expected to show the most enhanced ORR activity among the computationally-screened candidates) was experimentally prepared via physical vapor deposition method (PVD) and electrochemically evaluated for confirming our DFT prediction. We successfully synthesized a 3nm Ir-covered (Ir skinlayer) Ir3­Cr nanoparticle whose surface lattice distance was contracted by 1.03% compared to the pure Ir case. The specific activity (at 0.7 V vs RHE) of a Ir skinlayer/Ir3Cr catalyst with the very high durability (showing only 0.05 % decrease from the initial activity after 3000 potential cycles) was 12.3 times higher than a Ir catalyst. The detail mechanism on the enhanced activity in Ir-M alloy was also examined.

Our theoretical and experimental study highlight the general methodology for designing metal-based alloy catalysts for the application to ORR in PEMFC and such method can be further extended to the development of the next-level electrocatalyst for energy conversion.
Current and Temperature Distribution Measurement in a Polymer Electrolyte Membrane Water Electrolyzer Cell
Authors: Zhou Fan , Al Shakhshir Saher , Kær Søren Knudsen
Published: February 2020

The uniform distribution of the current and temperature under the normal operating conditions of the polymer electrolyte membrane water electrolyzer (PEMWE) cell is important to ensure its high efficiency and durability. In this work, a segmented sensor plate S++ is inserted between the flow field plate and current distributor plate at the cathode side of a single PEMWE cell to measure the local current and temperature distribution under different water flow configurations of the anode and cathode side and various current loads of PEMWE. The active area of the single PEMWE cell is 50 cm2. One hundred segments in the segmented sensor plate provide high resolution in the current and temperature distribution measurement. The current and temperature distribution are measured under co-flow and counter-flow of water recirculation between anode and cathode and under different current loads from 10A to 70A. Besides, the polarization curve and electrometrical impedance spectrum are measured under different water flow configurations.

Initial results reveal that when operated with co-flow of water re-circulation in anode and cathode, the cell shows better performance. With co-flow configuration, the charge transfer for hydrogen evolution and oxygen evolution reaction is larger compared with counter-flow configuration. The current shows similar distribution pattern under different water flow configuration and different current loads. However, uniformity in current distribution becomes better with lower current. The temperature distribution is not significantly influenced by the current load, while the counter-flow of water re-circulation results in more uniform temperature distribution.

Figure 1