Symposium Organizers
Kejie Zhao, Purdue University
Palani Balaya, National University of Singapore
Jianlin Li, Oak Ridge National Laboratory
Partha Mukherjee, Texas Aamp;M University
ES6.1: Ionic Conductors
Session Chairs
Tuesday PM, April 18, 2017
PCC North, 200 Level, Room 228 A
12:00 PM - ES6.1.02
Anion-Frenkel Defect Pair as Dominant Source for O Ion Conductions in Pyrochlore Type SOFC
Mingzi Sun 1 , Bolong Huang 1
1 , Hong Kong Polytechnic University, Hong Kong Hong Kong
Show AbstractLanthnoid oxides Ln2Hf2O7(Ln=La-Lu) with special pyrochlore-type structure have been systematically studied for many applications based on their great structure tolerance and mobility of anion ions. The excellent ion conductivity of Ln2Hf2O7 makes them become potential materials for electrolyte in solid oxide fuel cells(SOFCs). The ion conductivity of Ln2Hf2O7 arises because of oxygen atoms transportation in the crystal structure. However, the microcosmic detailed studies of how oxygen atoms escape from original positions and form anion-Frenkle defects are insufficient. Therefore, we will use the first-principle method to simulate various transporting behaviors of O atoms in the structure and demonstrate relationships between oxygen transportation and electronic properties of host lattice.
In this work, the first-principles total energy calculations within the density functional theory (DFT) framework are carried out with generalized gradient approximation(GGA) method. All the calculations are performed with the Cambridge Serial Total Energy Package(CASTEP) codes. As a representative pyrochlore-type compound, La2Hf2O7 will be our structural model built with lattice constants from former experiments. To figure out the oxygen atom transporting behavior and self-defect formation, we firstly set up a series of oxygen atom migrated position models with different moving distances. Then the corresponding defect formation energies are calculated and the distortion of crystal structure has been monitored. Combining with these models and data, we can suggest reasonable routes for oxygen atoms transporting in the La2Hf2O7 and understand the detailed process of Frenkel-type defects formation, in both short-range and long-range orders(SRO and LRO), which can better explain the high ionic conductivity of pyrochlore-type materials.
Results show that three characteristic migration paths in different environment for the oxygen atom have been found. First is the vacant 8b site(0.5,0.5,0.5)which is in the center of Hf-tetrahedral. Regardless of the moving distance, the defect formation energy maintains similar. Second stable site found for oxygen atom is near the 48f(0.302,0,0)site between two nearest Hf-tetrahedra where oxygen atom can form a plane quadrangle and cause distortion of oxygen atom at 48f site. This site has 1.0 eV lower defect formation energy than the vacant 8b site. However, when the moving distance exceeds 5Å, the formation energy will increase about 5.5 eV. The last migration site is near La-tetrahedral, where the oxygen atom will form three-fold coordinated with three adjacent La atoms stably. At this site, the defect formation is about 1.8 eV higher than the vacant 8b site. These three sites can link together to supply a relatively stable pathway for oxygen atom moving continually. The pattern on the migration distance versus energy shows certain degree of periodicity which is consistent with experimentally reported continuous migration pathway.
12:15 PM - ES6.1.03
Ab Initio Modeling of Strain Effects on Lithiation of Vanadium Pentoxide
Casey Brock 1 , Nitin Muralidharan 1 , Cary Pint 1 , Greg Walker 1
1 , Vanderbilt University, Nashville, Tennessee, United States
Show AbstractVanadium pentoxide (V2O5) has been extensively studied as a promising cathode material for Li-ion batteries because of its availability and high energy storage capability . However, it suffers from a low diffusion coefficient. We hypothesized that applying strain to V2O5 could further enhance the capacity and improve the diffusion coefficient by lowering the energy barrier for intercalation of lithium ions. In our work, we use density functional theory (DFT) to model the effects of strain on the performance of V2O5 as a battery cathode. Preliminary experimental results show that applied strain alters lithiation behavior, however many strain configurations are not easily accessible via experiment. Thus we have used DFT to supplement the experimental data. We perform ab-initio calculations of lithium intercalation energies in V2O5 using plane wave DFT implemented in the Abinit code. Low energy sites of lithium ions are determined by probing various sites and relaxing the structure. With both lithiated and non-lithiated V2O5, we can control the amount and direction of strain on the unit cell and calculate the effects on total energy. By comparing lithiated and non-lithiated V2O5 while applying compressive, tensile or zero strain, we can gain an understanding of strain effects on energy of intercalation. The calculated changes correspond to observed changes in measured samples.
12:30 PM - ES6.1.04
Influence of Defect Induced Lattice Distortion on Vibrational Dynamics and Ionic Transport in Doped Perovskites
Janakiraman Balachandran 1 , Jilai Ding 1 , Nazanin Bassiri-Gharb 2 , Gabriel Veith 1 , Craig Bridges 1 , Raymond Unocic 1 , Panchapakesan Ganesh 1
1 , Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 2 Materials Science and Engineering, Georgia Institute of Technology, Atlanta, Georgia, United States
Show AbstractSolid oxide materials that can selectively transport protons with high ionic conductivity can ac- celerate the deveopment of proton based solid oxide fuel cells (P-SOFC). Y doped BaZrO3 is one of the important perovskite materials with high proton conductivity. However numerous questions on this material remains unanswered such as the nature of dopant distribution and its influence on defect interaction and proton mobility. Our recent efforts on understanding epitaxial films of Y doped BaZrO3 at different dopant concentrations employing an integrated computational and experimental approach provides some important insights towards answering these questions.
This work convincingly demonstrates that the activation energy and the lattice distortion increases with dopant concentration even though the dopants are distributed homogeneously upto 20% doping. We attribute this result to the defect induced lattice distortion (small polarons) which increases with dopant concentration and in turn trap protons. Further, our ab initio models seem to indicate that the magnitude of the local distortion correlates well with the dopant ionic radius and the dopant-proton interaction energy that quantifies the strength of the proton trapping.
We perform ab initio based phonon and molecular dynamics simulations benchmarked with Raman spectroscopy to gain further insights on the lattice vibrational modes affected by these lattice distortion and how these vibrations in turn influence proton transport. We extend these insights by interfacing these simulations with a high throughput framework that enables us to gain systematic understanding on the influence of different dopant atoms and macroscopic strain on defect induced polaron and in turn on the proton dynamics and transport properties.
Acknowledgement
This work was sponsored by Laboratory Directed Research and Development Program of Oak Ridge National Laboratory (ORNL). Computations were performed at NERSC and OLCF supercomputing facilities. Neutron experiments were performed at Spallation Neutron Source (SNS) at ORNL. Transport, raman and microscopy measurements were performed at Center for Nanophase Materials Sciences (CNMS) at ORNL.
12:45 PM - ES6.1.05
Mechanical Properties of Oxide Based Li-Ion Conducting Solid Electrolytes
Jeff Wolfenstine 1 , Jan Allen 1 , Travis Thomspson 2 , Jeff Sakamoto 2 , Donald Siegel 2 , Heeman Choe 5
1 , Army Research Laboratory, Adelphi, Maryland, United States, 2 , University of Michigan, Ann Arbor, Michigan, United States, 5 , Kookmin University, Seoul Korea (the Republic of)
Show AbstractMany new types of high energy Li batteries may require a solid Li-ion conducting electrolyte. The major requirements for the solid Li-ion electrolyte are: high Li-ion conductivity, low electronic conductivity and chemical stability with the anodes/cathodes. In many applications adequate mechanical properties are also required. At present information on the mechanical properties of solid Li-ion conductors is lacking. It is therefore the purpose of this talk to present some of the first information on the room temperature mechanical properties of three oxide-based Li-ion solid electrolytes: Li6.19Al0.27La3Zr2O12, Li0.35La0.55TiO3, and Li1.2Zr1.9Sr0.1(PO4)3. The mechanical properties discussed include: elastic modulus, fracture strength, fracture toughness, hardness and coefficient of thermal expansion. The results will compared to theoretical predictions and existing data for sulfide Li-ion conductors.
ES6.2: Solid-State Batteries I
Session Chairs
Jianlin Li
Partha Mukherjee
Tuesday PM, April 18, 2017
PCC North, 200 Level, Room 228 A
2:30 PM - *ES6.2.01
Atomic Scale Simulations of Solid Electrolytes—Mechanical Properties and Beyond
Donald Siegel 1
1 , University of Michigan, Ann Arbor, Michigan, United States
Show AbstractThe development of a viable solid electrolyte would transform mobile energy storage by enabling batteries with higher energy densities and safer operation. Developing such an electrolyte remains a challenge, however, as the candiate material must satisfy several requirements simultaneously: it must exhibit sufficient mechanical properties to suppress dendrite initiation on the negative electrode; it must display high ionic conductivity, with limited electronic transport; it should have a large electrochemical window, enabling its use with high voltage positive electrodes; it must be stable in contact with both electrodes; finally, it should be easy to manufacture. This talk will describe atomic scale simulations aimed at understanding several of these phenomena in the garnet solid electrolyte, LLZO. After discussing the elastic properties of LLZO, emphasis will be given to predicting the electrochemical window and impact of surface contamination on transport properties. Finally, the role of solid electrolytes in minimizing crossover of species from the cathode will be described.
3:00 PM - ES6.2.02
Electrochemical Force Microscopy—Probing Local Diffuse Charge Dynamics and Electrochemical Processes at the Solid Liquid Interface
Liam Collins 1 , Nina Balke 1 , Stephen Jesse 1 , Sergei Kalinin 1
1 , Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States
Show AbstractUnderstanding the relationship between structure and electrochemical functionality is crucial for the future development of energy materials and devices such as supercapacitors, batteries, and biocatalysts amongst a myriad of other applications. In virtually all cases, local electrochemical inhomogeneities act as nucleation centres of failure sites, and must be correlated with microstructure on the level of individual structural elements (i.e. defects, step edges, grain boundaries) to achieve knowledge-driven design and optimization. Only by understanding local electrochemical functionality can we hope to bridge the gap between local nanoscopic electrochemical processes and the macroscopic device behaviour, and in doing so understand how to improve the next generation of high power and long lifetime energy storage or conversion materials and devices.
In this work we describe the development and implementation of electrochemical force microscopy (EcFM),[1] a technique developed to probe local bias- and time-resolved ion dynamics and electrochemical processes at the solid liquid interface using the lateral resolution afforded by atomic force microscopy (AFM). We establish EcFM as a force-based imaging mode, allowing visualization of the spatial variability of sample-dependent local electrochemical processes with nanoscale resolution. Using EcFM, we demonstrate electrochemical potential difference measurements as well as capturing charge screening processes and electrochemical reactions in the probe–sample junction. We believe the work presented herein represents a paradigm shift in local force based electrochemical measurements. We fully expect EcFM to allow local overpotentials to be characterized on the sub-100 nm scale, ultimately leading to an improved lifetime and performance of energy materials and devices achieved through knowledge driven optimization.
[1] Collins, Liam, et al. "Probing charge screening dynamics and electrochemical processes at the solid–liquid interface with electrochemical force microscopy." Nature communications 5 (2014).
3:15 PM - ES6.2.03
Dynamic Nano-Indentation Studies to Probe Solid Electrolyte/Lithium Interfaces
Erik Herbert 2 , Nancy Dudney 1 , Jeff Sakamoto 3
2 , Michigan Technological University, Houghton, Michigan, United States, 1 , Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 3 , University of Michigan, Ann Arbor, Michigan, United States
Show AbstractUnderstanding the mechanical properties of both metallic lithium and a ceramic or glass solid electrolyte may elucidate why it is difficult to form and maintain good, low resistance interfaces that are stable for extended cycling of lithium in rechargeable batteries. The plasticity of lithium metal requires adaptation of typical dynamic analysis, but determinations of the elastic properties and hardness have been accomplished. The surfaces of several solid electrolytes have been mapped with attention to the grain structure and surface purity, both of which impact the quality of the interface and current distribution. This is leading to the ultimate goal of detecting changes as they occur when lithium is deposited or adsorbed across and along the solid electrolyte interface.
Acknowledgement: This research was sponsored by the U.S. Department of Energy (DOE), Office of Energy Efficiency and Renewable Energy for the Vehicle Technologies, Advanced Battery Materials Research program.
3:30 PM - *ES6.2.04
Mechano-Electrochemical Aspects in Solid-State Batteries
Jeff Sakamoto 1 2 3 , Asma Sharafi 1 , Jeff Wolfenstine 4 , Yunsung Kim 1
1 Mechanical Engineering, University of Michigan, Ann Arbor, Michigan, United States, 2 Materials Science and Engineering, University of Michigan, Ann Arbor, Michigan, United States, 3 Macromolecular Science and Engineering, University of Michigan, Ann Arbor, Michigan, United States, 4 , Army Research Lab, Adelphi, Maryland, United States
Show AbstractSolid-state electrolytes and solid-state batteries are garnering significant interest for their potential to enable batteries exhibiting unprecedented energy density and safety. While in theory, the performance of solid-state batteries is appealing, in practice numerous manufacturing and cell design challenges are expected owing to the brittle nature of ceramic-based solid electrolytes. To address these challenges, the mechanical properties of solid electrolytes must be characterized. The purpose of this work is to characterize the salient mechanical properties of promising oxide, sulfide, and polymer solid electrolytes and cathode materials to facilitate their transition into solid-state batteries. Mechanical properties such as the elastic and shear moduli, Poisson’s ratio, fracture toughness, and hardness will be discussed. Comparisons and the implications of these properties are also analyzed. Additionally, a novel approach to conduct in situ, non-invasive, non-destructive mechanical characterization during and after cycling solid-state prototype cells will be presented.
ES6.3: Cathode
Session Chairs
Craig Arnold
Partha Mukherjee
Tuesday PM, April 18, 2017
PCC North, 200 Level, Room 228 A
4:30 PM - ES6.3.01
In Situ Mapping and Dynamic Investigation of State-of-Charge Mechanics in Lithium Ion Batteries
Joon Sang Kang 1 , Ming Ke 1 , Yongjie Hu 1
1 Mechanical and Aerospace Engineering, University of California, Los Angeles (UCLA), Los Angeles, California, United States
Show AbstractDeveloping high energy density batteries has attracted intensive efforts during past decades. However, today’s batteries are prone to unexpected failure and performance degradations. Fundamental understanding of their in-situ dynamic properties during normal operation condition has become a critical demand and will lead to new solutions to improve battery performance and safety. So far, most traditional techniques are limited to external evaluation of the whole cell pack and are based on homogenous material modeling. As a result, a dynamic measurement on these key properties of each component material during the battery operation cycle remains challenging [1]. Here we develop an in-situ and non-invasive experimental apparatus by combining electrochemical control and high spatial and temporal resolution readouts, based on our recent progress on ultrafast optic and nanoscale electronic sensors [2, 3]. We demonstrated in-situ experimental measurement on battery electrodes to map multi-physical dynamic properties, including diffusion, heat dissipation, and mechanical evolution of lithium cobalt oxide electrodes in a battery charging/discharging cycle. These results show that in contrary to classical assumptions, a highly non-uniform dynamics are present for different battery charge states. Our results represent a key step toward establishing an in-situ property-structure relationship to predict and improve battery performance. Multi-scale modeling considering materials non-uniformity to improve battery safety will be discussed. This developed generic approach can be applied to various forms of batteries including lithium-ion, lithium-air, sodium-ion, lithium-sulfur systems.
Reference:
[1] Nature 488, 294-303 (2012).
[2] Nature Nanotechnology 10, 701-706 (2015).
[3] Nature Nanotechnology 7, 47–50 (2012).
4:45 PM - *ES6.3.02
A Multiscale Approach to Cathode Design Based on Mapping Intercalation Gradients within Individual Particles and across Particle Aggregates
Sarbajit Banerjee 1
1 Department of Chemistry, Texas A&M University, College Station, Texas, United States
Show Abstract
Limitations to the power and energy densities of Li-ion batteries constitute a major impediment to our energy future, particularly with regards to electric vehicles and grid-level storage. The development of novel battery architectures and altogether new battery chemistries is imperative to address this challenge. Scaling materials to nanoscale dimensions holds profound significance for their potential as electrode materials owing to the superior power densities that can be realized at the nanoscale as a result of the shorter diffusion paths that need to be traversed by ions, the relatively facile accommodation of strain inevitable from ion intercalation, and the faster kinetics of intercalation-induced phase transitions. In recent work, we have used V2O5 as a model system to seek atomistic understanding of lithiation/delithiation pathways upon scaling to nanometer-sized dimensions. Scanning transmission X-ray microscopy (STXM) studies in conjunction with density functional theory suggest that polaron localization plays a key role in limiting cation mobility at low levels of intercalation, giving rise to heterogeneous lithiation across individual cathode particles. V K-edge X-ray absorption near-edge structure spectroscopy measurements suggest that polaron localization inhibits equilibration of charge density, resulting in slower phase nucleation and growth phenomena. STXM imaging further indicates that adjacent particles are lithiated at vastly distinct rates in a quasi-sequential manner. As a means of circumventing polaron localization and reducing barriers for cation diffusion, metastable polymorphs accessible from topochemical synthesis represent a particularly useful set of compounds. I will discuss some recently discovered metastable phases that allow for unprecedented Li-ion and even multivalent cation mobility. These compounds represent particularly excellent examples of the concept of “frustrated coordination” and mitigate polaron confinement by dint of greater degeneracy and energetic overlap of orbitals at the conduction band edge.
5:15 PM - ES6.3.03
Mechanism of Secondary Particle Disintegration in LiNi0.5Mn0.3Co0.2O2 Electrode Caused by Electrochemical Cycle
Rong Xu 1 , Luize Vasconcelos 1 , Kejie Zhao 1 , Jianlin Li 2
1 , Purdue University, West Lafayette, Indiana, United States, 2 , Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States
Show AbstractMechanical degradation caused by the repetitive swelling and shrinking of electrodes upon lithiation cycles limits the electrochemical performance and service life of the Li-ion batteries. For LiNi0.5Mn0.3Co0.2O2 electrode, while the disintegration of secondary particles upon lithiation cycles has been observed, less understood is the mechanism of the formation and evolution of secondary particle fracture. In particular, the microstructure of the LiNi0.5Mn0.3Co0.2O2 electrodes is highly heterogeneous, making the track and characterization of the morphology evolution of secondary particle a challenging task. In this paper, we employ scanning electron microscope (SEM) to track the morphology evolution of the exactly same locations within LiNi0.5Mn0.3Co0.2O2 electrode before and after electrochemical cycle. The secondary particle fracture induced by electrochemical cycle is significantly determined by the cyclic rate where the relatively fast cyclic rate generates micro-crack in the particle while the extremely fast cyclic rate does not. Electrochemical impedance spectroscopy (EIS) analysis also confirm that cyclic rate were responsible for the accumulated disintegration of LiNi0.5Mn0.3Co0.2O2 secondary particles. We also perform the numerical analysis of Li diffusion and deformation to investigate the stress evolution within the LiNi0.5Mn0.3Co0.2O2 secondary particles. The cohesive zone model is employed to simulate the crack formation and propagation in the particles.
5:30 PM - *ES6.3.04
Effects of Mechanical Stress on Electrochemical Performance in Lithium-Ion Batteries
Craig Arnold 1
1 , Princeton University, Princeton, New Jersey, United States
Show AbstractBecause of their high energy densities and high working voltages, lithium-ion batteries are the most suitable energy storage choice for a variety of applications from large scale battery electric vehicles to small scale implantable medical devices. These systems are well-known to experience mechano-electrochemical phenomena and in this presentation, we discuss the how the evolution of internal and external mechanical stress affects the electrochemical performance over the life of a battery. Starting with the internal stress state of the battery, we identify the dynamic nature of this quantity, fluctuating with charge/discharge and gradually increasing irreversibly over long times with electrochemical cycling correlating to the state of charge and state of health of the system. The implication of such stress evolution on the electrochemical processes and materials are explored and further probing of the system behavior reveals that not only the stress state, but regions of stress localization within the cell can lead to electrochemical phenomena which further accentuate performance degradation.
ES6.4: Poster Session I
Session Chairs
Wednesday AM, April 19, 2017
Sheraton, Third Level, Phoenix Ballroom
9:00 PM - ES6.4.01
Thermoelectric Properties of High-Performance and Flexible Cu2Se Thin Films Fabricated by Wet-Deposition Methods
Courtney Hollar 1 , Zhaoyang Lin 2 , Xiangfeng Duan 2 , Yanliang Zhang 1
1 , Boise State University, Boise, Idaho, United States, 2 Chemistry and Biochemistry, University of California, Los Angeles, Los Angeles, California, United States
Show AbstractThermoelectric generators provide a solid-state conversion between heat and electricity which is an environmentally-friendly alternative. In particular, flexible thermoelectric devices allow for waste heat recovery along irregularly shaped surfaces and provides energy harvesting applications to wearable electronics and sensors. In order to keep up with the growing market of sensors and flexible electronics flexible thermoelectric devices with low fabrication costs and high materials efficiency are necessary.
The thermoelectric material efficiency is determined by the figure of merit, ZT = S2σT/k, where S, σ, k, and T are the Seebeck coefficient, electrical conductivity, thermal conductivity, and absolute temperature, respectively. A high efficiency thermoelectric material will exhibit a high Seebeck coefficient and electrical conductivity and a low thermal conductivity. It has been shown that nanostructured thermoelectric materials exhibit superior material efficiency compared to their bulk counterpart by tailoring electron and phonon transport.
Many flexible thermoelectric devices are high cost due to the rare materials used. In addition, the fabrication process remains unrealistic for practical applications. This research reports a flexible thermoelectric Cu2Se thin film prepared by a low cost and scalable solution process. The ink solution was synthesized using a wet deposition method consisting of dissolving solid Cu2Se into a cosolvent at room temperature. The thin films were then prepared by spin coating the ink onto a flexible polyimide substrate. Cu2Se thin films annealed at 703K exhibited the highest power factor of 0.62 mW/mK2 at 684K, which is among the highest values of all reported flexible thermoelectric films (~0.5 mW/ mK2). In addition, the electrical resistance increase was only 8% after 1000 bending cycles. This study demonstrates the ability to fabricate high-performance flexible thin films from relatively earth-abundant elements in a low cost and scalable manner which are important factors for commercial production.
9:00 PM - ES6.4.02
New MOF-Modified Nitrogen-Doped Graphene ORR Catalyst Synthesized By Nanoscale High Energy Wet Ball Milling
Shiqiang Zhuang 1 , Bharath Babu Nunna 1 , Eon Soo Lee 1
1 , New Jersey Institute of Technology, Newark, New Jersey, United States
Show AbstractNitrogen-doped graphene (N-G), which is one of non-platinum group metal (non-PGM) catalysts, has a huge potential in many electrochemical systems such as fuel cells due to the high raw material cost of PGM catalyst. However, there is a significant gap between the current level of electrochemical performance of N-G catalysts and that of PGM catalysts. A new set of N-G catalysts that is synthesized with a new synthesis approach in the lab shows a promising results as an alternative electrochemical catalyst materials, and is investigated for the characterization of the new materials. Another set of N-G catalysts, which is modifying the N-G catalyst by metal-organic framework materials (MOFs) with nanoscale high energy wet ball milling method, is investigated to enhance the electrochemical performance of N-G catalysts. The physical and chemical properties and electrochemical performance of the new synthesized N-G and N-G/MOF catalysts are characterized several characterization methods such as Zetasizer, X-ray photoelectron spectroscopy (XPS), X-ray absorption spectroscopy (XAS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), BET and rotating ring disk electrode (RRDE). The control of the synthesis process is studied by characterizing a series of N-G and N-G/MOF catalysts which are synthesized with different grinding speed and grinding time. The successful accomplishment of the new N-G and N-G/MOF catalysts will provide the substantial way to the cost-effective and fuel-efficient energy conversion system.
9:00 PM - ES6.4.03
Tuning Thermocell Power Performance Using Forced Convection
Ali Hussain Kazim 1 , A. Sina Booeshaghi 2 , Baratunde Cola 1
1 , Georgia Institute of Technology, Atlanta, Georgia, United States, 2 , Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Show AbstractAs the detrimental effects of climate change are better understood and more widely accepted by the public, there comes an increased need to develop renewable energy systems that reduce our reliance on fossil fuels. In addition to new clean sources of prime generation, strategies to harvest waste heat from existing infrastructure could play a key role in improving our overall carbon footprint. Thermo-electrochemical cells (thermocells) are inexpensive electrochemical devices that directly convert temperature differences to an electromotive force with no moving parts. They are comprised of an electrolyte which is sandwiched between two electrodes. When a temperature difference is applied at the electrodes, reduction and oxidation reactions drive ions through the electrolyte and electrons through an external circuit. The mode of mass transport for ions are migration, diffusion and convection, which together determine the ohmic resistance of the electrolyte.1 Ohmic resistance is one of the primary performance-determining characteristics of thermocells.2 In this work, we have fabricated a thermocell with flowing electrolyte as opposed to the traditional stationary electrolyte for thermocell. Thus adding a forced convection component to mass transport of ions. The effect of forced convection on thermocell performance is recorded. Here we report a five-fold increase in thermocell power by decreasing the Reynolds number by a factor of three. The lower Reynolds number increases the temperature of electrolyte and hence the thermocell power. This work gives us the ability to tune thermocell power based on Reynolds number. More importantly this has been achieved by adding a functionality to existing commercial cold plate designed to provide cooling with that of harvesting waste heat.
1) Bard, A.J., Faulkner, L.R., Leddy, J. and Zoski, C.G., 1980. Electrochemical methods: fundamentals and applications (Vol. 2). New York: Wiley.
2) Quickenden, T.I. and Vernon, C.F., 1986. Thermogalvanic conversion of heat to electricity. Solar Energy, 36(1), pp.63-72.
9:00 PM - ES6.4.04
Novel N & P-Type Half Heusler Compounds for Intermediate Temperature Thermoelectric Energy Conversion
Nagendra Chauhan 1 , Bathula Sivaiah 1 , Bhasker Gahtori 1 , Ajay Dhar 1
1 Advance Materials and Devices Division, CSIR-National Physical Laboratory, New Delhi India
Show AbstractCurrently thermoelectric research worldwide is concentrated in developing thermoelectric device for energy generation for operation in the mid-temperature range, where most of these application exists. Half-Heusler (HH) compounds, as a class of stable thermoelectric materials, have received considerable attention in recent past for such applications. In the present study, we report the development of novel and compatible n-type Zr0.7Hf0.3Ni1+xSn & p-type ZrCo1+xSb0.9Sn0.1 HH alloys for thermoelectric conversion in the mid-temperature range. These alloys were synthesized employing arc-melting of the constituent elements in stoichiometric proportions followed by Spark Plasma Sintering (SPS) of their pulverized powders. A thermoelectric figure of merit (ZT) of 1.1 for n-type and 0.56 for p-type synthesized HH alloys was realized with a similar value of Seebeck coefficient, which is one of the prerequisite for efficient thermoelectric devices. Nanostructuring employing high energy ball milling of arc-melted ingot followed by SPS yielded substantially enhanced ZT for both the synthesized n-type and p-type HH material. Nanostructuring induces high density of interfaces between the surfaces, grain and phase boundaries resulting in significant reduction of thermal conductivity. Such enhancement in phonon scattering via. synergistic combination of mass fluctuation, alloy and boundary scattering helps in overcoming the major challenge of high thermal conductivity in HH compounds.
9:00 PM - ES6.4.05
Implications of Different Modes of Intrinsic Proton Diffusion in BaZrO3 and Y-Doped BaZrO3 for High Temperature Proton Conducting Membranes
Foram Thakkar 1 , Sudip Roy 1 , Hans Geerlings 2 , Suchismita Sanyal 1
1 , Shell India Markets Pvt. Ltd., Bangalore India, 2 , Shell Global Solutions International, B.V., Amsterdam Netherlands
Show AbstractPerovskites are ceramics with general formula ABO3. Proton conductivity in perovskites is of interest for various applications viz., sensors, separators, hydrogen pumps and fuel cells. High temperature proton conducting properties of perovskites have also recently been used for constructing membranes for cell reactors for catalytic dehydrogenation/hydrogenation processes. It is known that perovskites with more cubic structure have higher proton mobility. Pure Barium Zirconate (BaZrO3) crystal has high proton conductivity due to its cubic structure. Perovskites are often doped with trivalent ions by replacing tetravalent ions, which provides the necessary charge balance for proton conduction. Y doped BaZrO3 can reach proton conductivities of 50 mS/cm but factors like grain boundary resistance, Ba loss during sintering reduces the conductivity significantly.
In order to estimate the proton conductivity, it is important to understand the intrinsic proton diffusion of the material as a function of doping and the factors mentioned above. This study focuses on benchmarking pure and Y-doped BaZrO3 by calculating the dynamical and thermodynamic energy barriers of proton diffusion process.
In this work, we have used ab-initio molecular dynamics simulations (MD) to compute the diffusion coefficients and the activation energies from trajectories obtained from pure and Yttrium doped BaZrO3 at different concentrations and temperatures. Thermodynamics of proton conductivity in these systems were addressed by performing activation energy barrier calculations for proton hopping transition states using Nudged Elastic Bands (NEB) theory and ab-initio quantum chemical calculations. Finally, we have compared the activation barriers from MD (dynamical energy barriers) with thermodynamic barriers. Apart from this, we have analyzed the MD trajectories for proton conduction to separate out slower and faster paths of diffusion by using the van-Hove correlation and correlated it with the rate-determining step.
9:00 PM - ES6.4.07
Desulfurization Materials Based Nano-Adsorbents for Army Logistics Jet Fuel
Dat Tran 1
1 , U.S. Army Research Laboratory, Adelphi, Maryland, United States
Show AbstractThe U.S. Army has a one fuel policy, which requires the use of logistics fuel for most power and mobility applications. JP-8, the Army’s one and only logistical fuel has a high sulfur-content so hydrogen produced from JP-8 poisons a fuel cell unless remediated. This fuel is a complex hydrocarbon mixture containing many contaminants such as organic sulfur compounds. However, fuel cells require clean hydrogen. Thus, reducing the logistic burden through the integration of more efficient power sources such as autonomous fuel cells is a primary goal of the Army. This presentation will discuss the design and characterization of sorbent materials within the U.S. Army Research Laboratory that can remove organic sulfur contaminants at room temperature directly from the liquid JP-8 and H2S gas phase ≥ 400 oC. This technology may extend the life of the reformer and fuel cell catalysts and enable the removal of additional fuel processing components/steps for compact power sources.
9:00 PM - ES6.4.08
Development of High Temperature Measurement Sensor Using Pyroelectric Ceramic Material
Jorge Silva 1 , Md.Rashedul H. Sarker 1 , Mariana Castaneda 1 , Yirong Lin 1 , Norman Love 1 , Luis Chavez 1
1 , The University of Texas at El Paso, El Paso, Texas, United States
Show AbstractTemperature is one of the most important thermodynamic properties measured and controlled in energy generation systems. Continuous monitoring of real time temperature can lead to enhance efficiency in these systems. Maintaining an optimum temperature on specific components of a system is desired since an increase or decrease in temperature could compromise the mechanical properties of a material. Furthermore, harsh temperature sensing materials are desired since temperature measuring becomes critical to some energy systems that operate under high temperature and high corrosive environments. In this study, a high temperature measurement method is developed using lithium niobate (LiNbO3) ceramic as a sensor material. Lithium niobate (LiNbO3) is a pyroelectric material that generates current while experiencing rate of temperature change with time and this property enables the measurement of temperature. Lithium niobate (LiNbO3) was selected for its high Curie temperature (1210 °C) thus making it suitable for high temperature applications. Before using LiNbO3 as a sensor material, temperature dependent pyroelectric coefficient of LiNbO3 was measured by dynamic measurement technique for several temperature ranges up to 500 °C. Temperature dependent pyroelectric coefficient of LiNbO3 was found in between -8.5x10-5 C/m2 °C to -23.7x10-5 C/m2 °C from room temperature to 500 °C. This temperature dependent pyroelectric coefficient values were used to measure the temperature using LiNbO3 as a sensor. A 1 cm x 1 cm with 0.01 cm thickness sample of LiNbO3 was prepared with high temperature resistive electrode on top and bottom surfaces of the sample. The sample sensor was placed inside of a tube furnace along with a thermocouple. The sensor successfully measured the temperatures up to 220 °C, 280 °C, 410 °C, and 500 °C with 4.31 %, 2.1 %, 0.4 %, and 0.6 % deviation respectively from thermocouple measurement. This study demonstrates the ability of a self-power pyroelectric ceramic to successfully measure high temperatures up to 500 °C and thought to be of interest to those designing and developing similar type of temperature sensors for various industrial and commercial applications.
9:00 PM - ES6.4.09
High-Performance and Flexible Thermoelectric Devices by Screen Printing Colloidal Nanocrystals
Yanliang Zhang 1 , Tony Varghese 1 , Courtney Hollar 1 , Joseph Richardson 1 , Nicholas Kempf 1
1 , Boise State Universit, Boise, Idaho, United States
Show AbstractThermoelectric generators (TEGs) produce electrical power using thermal energy from various sources, including the waste heat. Thermoelectric materials have undergone tremendous improvement of the figure of merit ZT in recent two decades largely attributed to nanostructuring. Despite these progresses in materials performances, the high cost of manufacturing the nanostructures into functional materials and devices is still a significant barrier to bring these materials into commercial domain.
Screen printing allows for direct conversion of thermoelectric nanocrystals into flexible energy harvesters and coolers. However, obtaining flexible thermoelectric materials with high figure of merit ZT through printing is an exacting challenge due to the difficulties to synthesize high-performance thermoelectric inks and the poor density and electrical conductivity of the printed films. Here, we demonstrate high-performance flexible films and devices by screen printing bismuth telluride based nanocrystal inks synthesized using a microwave-stimulated wet-chemical method. Thermoelectric films of several tens of microns thickness were screen printed onto a flexible polyimide substrate followed by cold compaction and sintering. The n-type and p-type films demonstrate peak ZTs of 0.43 and 0.8 along with superior flexibility, which is among the highest reported ZT values in flexible thermoelectric materials. A flexible thermoelectric device fabricated using the printed films produces a high power density of 4.1 mW/cm^2 with 60 K temperature difference between the hot side and cold side. The highly scalable and low cost process to fabricate flexible thermoelectric materials and devices demonstrated here opens up many opportunities to transform thermoelectric energy harvesting and cooling applications.
9:00 PM - ES6.4.10
Modelling of the Solid Electrolyte Interface (SEI) Layer to Study Capacity Fade, Aging and Cycle Life of Lithium Ion Batteries Using Kinetic Monte Carlo Approach
Bigyan Khanal 1 , Behzad Bahrami 1 , Huitian Lu 1 , Qiquan Qiao 1
1 , South Dakota State University, Brookings, South Dakota, United States
Show AbstractThe accurate model which could predict the growth of Solid-Electrolyte Interface (SEI) layer of Lithium ion batteries is very useful to study the capacity fade, ageing and the cycling life and the model can also provide significant contributions to ensure safety. The model for the SEI layer formation is based on Kinetic Monte Carlo Approach, in which four process adsorption, absorption, diffusion and passivation are described by their individual rates determined from chemical and physical properties of materials used in the battery. The formation of a passive SEI layer along with its thickness was predicted and the thickness was calculated using the mathematical model. For every cycle, the coverage and the thickness were updated and the interfacial resistance was calculated. The simulations are found to be consistent with literature that the thickness increase as proportional to the square root of the time (cycle).The interfacial resistance obtained from the simulation is used in the one dimensional electrochemical model, and the charge-discharge behavior of the battery in each cycle was obtained. After the coupling of SEI layer model to 1D electrochemical model, the results obtained from the simulation will be validated against the experimental results.
9:00 PM - ES6.4.11
Development of LCFCN System Perovskites as Interconnect and Cathode Materials for SOFCs
Sai Ram Gajjala 1 , Abhigna Kolisetty 1 , Zhezhen Fu 1 , Rasit Koc 1
1 , Southern Illinois University, Carbondale, Carbondale, Illinois, United States
Show AbstractOver the past few decades solid oxide fuel cells (SOFCs) have attracted much attention due to their huge potential for clean power generation in stationary, portable, transport applications and also our increasing need for sustainable energy resources. The purpose of this research is to develop an interconnect and cathode material for use in SOFCs which demonstrates desired properties of high electrical conductivity, excellent chemical stability at high temperatures, desirable thermal expansion characteristics and which can be easily manufactured by sintering in conditions acceptable with other cell components. This research is important because there are a few shortcomings in the materials that are currently being used as cathodes and interconnects in the SOFCs. In this study, five different perovskite oxides comprising of lanthanum in combination with chromium, iron, cobalt and nickel oxides powders (LaCr0.7Co0.1Fe0.1Ni0.1O3, LaCo0.7Cr0.1Fe0.1Ni0.1O3, LaFe0.7Cr0.1Co0.1Ni0.1O3, LaNi0.7Cr0.1Co0.1Fe0.1O3, LaCr0.25Co0.25Fe0.25Ni0.25O3), were synthesized through Pechini method. Obtained powders were characterized by X-ray diffraction (XRD) to observe crystal structure. XRD results show that all materials are single phase few with rhombohedral and few with orthorhombic crystal structure. The resulting powders were then sintered at a temperature of 1400°C in air. Properties of sintered samples, including relative density, mechanical properties, and electrical conductivity from room temperature to 800°C were studied and evaluated. The microstructure of sintered samples were characterized by Scanning Electron Microscope (SEM). The material with the desired properties such as highest electrical conductivity of 88 S/cm along with a relative density of 94% was then doped on the A-site with Ca at different concentrations (La0.9Ca0.1Ni0.25Cr0.25Co0.25Fe0.25O3, La0.8Ca0.2Ni0.25Cr0.25Co0.25Fe0.25O3, and La0.7Ca0.3Ni0.25Cr0.25Co0.25Fe0.25O3) and the properties were studied. A significant drop in the electrical conductivity was observed when the A-site was doped along with the B-site. After sintering, all the three samples were found to be fully dense with a relative density of 100%. The material which has the desired properties is considered and elemental modifications can be done to it for application in practical purposes.
9:00 PM - ES6.4.12
Cost and Performance Optimization of Wearable Thermoelectric Devices Based on Human Thermoregulatory Model
Dimuthu Wijethunge 1 , Dong-Gyu Kim 1 , Woochul Kim 1
1 , Yonsei University, Seoul Korea (the Republic of)
Show AbstractPerformance of thermoelectric materials are improving day by day at a rapid pace, enabling thermoelectric devices to be used for many applications such as in human wearable devices. But cost of the thermoelectric materials are not yet satisfactory. Therefore thermoelectric devices are not been utilized to its full potential in wearable device applications. This paper mainly discuss about the strategies to optimize the performance and reduce the cost of wearable thermoelectric devices. It also can be used as a guideline to construct accurate computational model for wearable thermoelectric device. One of the key features of this paper is computational model which includes accurate and simple human thermoregulatory model to simulate the skin. This human skin model is capable of predicting skin temperature of certain location under different external conditions like ambient temperature, humidity and most importantly, insulation thickness on the skin. By using the developed thermal model, accuracy of the simulations can be highly improved. Optimization is mainly carried out by considering geometrical aspects of gap fillers and thermoelectric elements. Even though gap fillers will increase the parasitic heat loss, due to their low thermal conductivity (<0.2 W/ m-K), using them in correct proportions can sustain the performance and add extra flexibility and strength to the device. Optimum geometry for thermoelectric elements and fillers are strictly depended on material and external conditions, according to simulations maximum power is obtainable when thermoelectric elements occupying below 30% of the total area which is true for majority of conditions. Furthermore, highly electrically conductive material can be used to increase the thermoelectric element height without significant increase of the electrical resistance. By this method $ per Watt value can be increased but overall power output is reduced in most cases. This novel method of reducing the cost is also thoroughly discussed in the paper. Additionally, possibility of using thermoelectric wearable cooling devices are also discussed in this paper with similar optimization techniques.
9:00 PM - ES6.4.13
Origin of Fast Proton Transport in Stoichiometric Acceptor Doped Perovskites
Jilai Ding 1 2 , Janakiraman Balachandran 2 , Xiahan Sang 2 , Wei Guo 2 , Jonathan Anchell 2 , Christopher Rouleau 2 , Gabriel Veith 2 , Craig Bridges 2 , Yongqiang Cheng 2 , Jonathan Poplawsky 2 , Nazanin Bassiri-Gharb 1 , Raymond Unocic 2 , Panchapakesan Ganesh 2
1 , Georgia Institute of Technology, Oak Ridge, Tennessee, United States, 2 , Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States
Show AbstractIonic transport in solids underpins the functionality of most energy storage and conversion technologies. Acceptor doped perovskites, a promising electrolyte for proton-conducting solid oxide fuel cells, has been widely studied, among which yttrium doped barium zirconate (Y-BZO) exhibits one of the highest proton conducting rates and excellent chemical stability at intermediate operating temperatures (400-700 °C) at an optimal doping level of 20%.1 The presence of extended defects in Y-BZO such as grain boundaries has led to a wide variability in the measured conductivity values, and thus hindered the basic understanding of the conduction mechanisms. In order to identify the fundamental role of dopants on the proton transport mechanisms, it is vital to understand the defect distribution and dopant-induced lattice distortion at the atomic scale, thereby elucidating the correlation between dopants and lattice distortions and their role on proton conduction.
To achieve this goal, in this study, a series of epitaxial Y-BZO thin films (Y = 0 to 20 %) with limited extended defects were prepared on (100) oriented MgO substrates by pulsed laser deposition.2 Time resolved Kelvin probe force microscopy was used to obtain the surface potential mapping in both the space and time domains, from which the activation energy for proton transport was calculated. It was found that the activation energy increases from 0.45 V to 0.64 V with increasing dopant concentration from 5% to 20%, which is confirmed by impedance spectroscopy measurements. We found that this monotonic increase of activation energy with increasing dopant concentration correlates with strong local lattice distortions, as confirmed by bond-angle and displacement analysis of atomic resolution STEM images. The defect-cluster induced distortion results in the formation of defect-polarons that influence the mobility of the ionic transport as observed by the increase in activation energy. Raman spectroscopy was performed at controlled temperature and humidity under external applied bias, to identify the nature of the polaron and how it evolves with dopant concentration and in turn influence the proton transport. Understanding these defect induced polarons on ionic mobility will enable us to develop novel design strategies to develop new proton conducting oxides with improved transport properties.
The research was sponsored by the Laboratory Directed Research and Development Program fund at the Oak Ridge National Laboratory. Computations were performed at National Energy Research Scientific Computing Center, which is supported by the Office of Science of the U.S. Department of Energy.
9:00 PM - ES6.4.14
Electrospun N-Doped Carbon Nanofibers Encapsulating Co Nanoparticles as Efficient ORR Catalyst
Chaoqun Shang 1 , Minchan Li 1 , Zhenyu Wang 1 , Shaofei Wu 1 , Zhouguang Lu 1
1 , South University of Science and Technology of China, Shenzhen China
Show AbstractThe development of low-cost, high-performance non-precious electrocatalysts for ORR is highly desirable to reduce the cost of fuel systems. Self-supported nitrogen-doped carbons with a mount of cobalt have been developed by electrospinning ensuing pyrolysis treatment. Polyacrylonitrile (PAN) with abundant carbon and nitrogen sources serves as the polymer to fabricate one dimensional nanofibers by electrospinning. After calcined at various temperature, the obtained nitrogen-doped carbon nanofiber encapsulating Co nanoparticles at 800 °C (Co-PAN-800) exhibits the highest ORR activity with onset and half-wave potentials of -0.02 V and -0.092 V (vs. Hg/HgO) in 0.1 M KOH, respectively. Besides, the optimal Co-PAN-800 shows remarkable stability and strong tolerance against methanol crossover. The promising ORR performance of Co-PAN-800 is attributed to the high surface area (407.43 m2 g-1), which ensures sufficient exposure of electrocatalytically active sites. The XPS analysis further demonstrates that pyrrolic N and highly graphitized carbon structure may be responsible for the enhanced ORR activity of Co-PAN-800 and the cobalt gets involved in the creation of pyrrolic N during pyrolysis treatment.
Acknowledgements
This work was supported by the National Natural Science Foundation of China (No. 21671096 and 21603094), the Shenzhen Key Laboratory Project (ZDSYS201603311013489), the Shenzhen Peacock Plan (No. KQCX20140522150815065), the Natural Science Foundation of Shenzhen (No. JCYJ20150630145302231, JCYJ20150331101823677), the Natural Science Foundation of Guangdong Province (2016A030310376),and the Postdoctoral Research Fellowship of SUSTC.
References
[1] C. Shang, M. Li, Z. Wang, S. Wu, Z. Lu, ChemElectroChem 2016, 3, 1437-1445.
[2] S. Dou, L. Tao, J. Huo, S. Wang, L. Dai, Energy Environ. Sci. 2016, 9, 1320-1326.
[3] G. Wu, K. L. More, C. M. Johnston, P. Zelenay, Science 2011, 332, 443-447.
[4] S. Wang, Z. Cui, M. Cao, Chem. Eur. J. 2015, 21, 2165-2172.
[5] G. Wu, P. Zelenay, Acc. Chem. Res. 2013, 46, 1878-1889.
9:00 PM - ES6.4.15
Effect of Interfacial Resistance on the Thermal Conductivity of Superlattice Structures of Organic-Inorganic Perovskites
Rahul Singh 1 , Ganesh Balasubramanian 1 , Vikram Dalal 1
1 , Iowa State University, Ames, Iowa, United States
Show AbstractSuperlattice structures increase the thermal resistance of the system by increasing the scattering at interfaces. We have used this idea to create superlattice structures of organic-inorganic halide perovskites that have shown significant potential in thermoelectric applications. We consider the thermal resistances of superlattices consisting of varying numbers of distinct nanolayers of different perovskites. An interatomic potential has been developed using First principle calculations for these hybrid structures. Using this potential molecular dynamics simulations have been done to calculate the thermal conductivity of these structures. The interfacial resistances produced between different solid layers can significantly lower heat transfer for a specified temperature difference. Using Equilibrium and Non-equilibrium molecular dynamics (NEMD), we calculate the lattice thermal conductivities in order to study the effects of interface scattering, boundary scattering, and elastic strain on lattice thermal conductivity.
9:00 PM - ES6.4.16
Factors Controlling Surface Oxygen Exchange in Oxides
Yipeng Cao 1 , Milind Gadrea 1 , Anh Ngoa 1 , Stuart Adlerb 2 , Dane Morgan 1
1 , University of Wisconsin-Madison, Madison, Wisconsin, United States, 2 , University of Washington, Seattle, Washington, United States
Show AbstractReducing the working temperature of solid oxide fuel cells (SOFCs) is primarily inhibited by the slow oxygen exchange kinetics at the cathode, thereby limiting the overall rate of the oxygen reduction reaction (ORR). A quantitative molecular understanding of oxygen exchange at the cathode surface remains elusive, as well as understanding of the catalytic properties of the (001) BO2 terminated surface, which is generally not stable under operating conditions.
In this work, the ab-initio methods were used to develop a quantitative elementary reaction model of oxygen exchange in a representative SOFC cathode material, La0.5Sr0.5CoO3-δ (LSC-50), and demonstrate that under SOFC operating conditions, the rate limiting step for oxygen incorporation from O2 gas at the stable, (001)-SrO surface is oxygen finding a vacancy to incorporate. Here we predict that a high vacancy concentration on the metastable CoO2 termination enables a vacancy-assisted O2 dissociation that is 102-103 times faster than O2 dissociation on the Sr-rich (La,Sr)O termination. This result implies that dramatically enhanced oxygen exchange performance could be obtained by suppressing the (La,Sr)O layer that is known to form on many commercial cathodes under fabrication and in-situ conditions.
We further use the kinetic theory of O2 adsorption to set an upper limit for the oxygen exchange rate and rate coefficient and show that stabilizing highly active, metastable surfaces such as the CoO2 termination of LSC-50 may achieve this upper limit, providing an assessment of the remaining opportunities available for enhanced oxygen exchange.
9:00 PM - ES6.4.17
Long-Term Cyclic Sealing Performance of a Glass Composite Seal for Solid Oxide Fuel Cells
Sueng-Ho Baek 1 , Min-Kyun Kim 1 , Sung Park 1 , Jae Chun Lee 1
1 , Myongji University, Yongin Korea (the Republic of)
Show AbstractSolid oxide fuel cell (SOFC) technology requires a reliable seal that works for 40,000 hours at high temperatures above 700°C, and also overcomes the thermal stress problem induced by cyclic heating and cooling. Recent studies on SOFC glass-based seals have focused on low viscosity self-healing glass, such as those made of compliant alkali-containing silicate glass. However, thermochemical and
thermomechanical properties of self-healing alkali-silicate glasses are usually weaker than those of alkaline-earth silicate glasses. One way to overcome such weaknesses is to use fillers to modify glass properties. For example, Al2O3 filler can strengthen alkali-silicate glass network structure since the trivalent aluminum ions act as network formers in alkali aluminosilicate glasses. However, the Al2O3 filler enhanced the devitrification of the glass phase, which is not desirable for long-term sealing performance. The objective of this study is to find oxide fillers and seal compositions showing long-term cyclic sealing performance for solid oxide fuel cells applications. This was accomplished by using mixed fillers such as Al2O3 and ZrO2 for the alkali-containing borosilicate sealing glass prepared in this work. A glass composite seal containing mixed fillers has survived more than 10,000 hours of leak test at 750°C for 25 thermal cycles. In this work, the effect of these fillers on the high temperature cyclic sealability, viscosity, electrical conductivity, strength and phase transformation of the seals were investigated to design strengthened glass seal structure.
Symposium Organizers
Kejie Zhao, Purdue University
Palani Balaya, National University of Singapore
Jianlin Li, Oak Ridge National Laboratory
Partha Mukherjee, Texas Aamp;M University
ES6.5: Anode Materials for Batteries
Session Chairs
Craig Arnold
Hui-Ming Cheng
Wednesday AM, April 19, 2017
PCC North, 200 Level, Room 228 A
9:15 AM - *ES6.5.01
Mechanical Effects on the Electrode Materials in Li-Ion Batteries during Electrochemical Process
Joseph Gnanaraj 1 , Richard Lee 1 , Alan Levine 1 , Jonathan Wistrom 2 , Skyler Wistrom 2 , Yunchao Li 3 , Jianlin Li 4 , Amit Naskar 5 , Mariappan Paranthaman 3
1 Energy Division, RJ Lee Group, Monroeville, Pennsylvania, United States, 2 , Practical Sustainability, Maryville, Missouri, United States, 3 Chemical Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 4 Energy & Transportation Science Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 5 Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States
Show AbstractLithium-ion batteries are being used in portable electronics, and electric vehicles applications. The lithium ions batteries undergo significant stresses and strains in the electrodes due to various factors such as high power operation, pressure, temperature, that lead to degradation in the cell performance. The stiffness occurs in electrodes due to the formation of lithium intercalation compounds during cycling. These effects are pronounced at high charge discharge cycling rates and elevated temperatures of operations. Such prolonged stiffness during cycling damages the nanostructured crystallites in the graphitic carbon negative electrode and affects the thickness and composition of the interface layer between electrode and electrolyte resulting in severe capacity loss. The mechanical measurements during electrochemical process provide new insights into the origin and the driving force for mechanical deformation of the electrode in lithium ion battery. The relationship between electrochemical process, discharge capacity, cycle life and mechanical deformation is examined.
9:45 AM - *ES6.5.02
Fatigue in High C-Rate Lithium-Ion Anodes with Porous Silicon
Sibani Biswal 1
1 , Rice University, Houston, Texas, United States
Show AbstractSilicon anodes draw considerable attention in recent years owing to their high specific capacity (3572mAh/g versus 372mAh/g for graphite). However, the large volume expansion of silicon during lithium insertion/extraction, poor charge /discharge rates and low cycle life pose a major hurdle for commercializing this material. We have reported a macroporous silicon-polyacrylonitrile (MPSP-PAN) composite with optimized cycling strategy that addresses the issues above. This electrode shows a significant improvement of cycle life (1000 mAh/g @C/5 for 570 cycles) while also achieving high C-rates (1000 mAh/g @8C rate, 340 cycles), illustrating excellent rate capability and structural stability. The porous structure of silicon combined with a conductive polyacrylonitrile polymer and optimized cycling strategy helps alleviate the mechanical stress from volume expansion. A fluoroethylene carbonate electrolyte additive aids in the formation of a stable SEI that can prolong the cycling stability of the anode. Here we will examine how the mechanical stresses in the porous silicon alter its structure and eventually its performance.
10:15 AM - ES6.5.03
Atomistic Structural Evolution and Li Trapping Due to Delithiation Rates in Si Electrodes
Kwang Jin Kim 1 , Wortman James 1 , Sung-Yup Kim 1 , Yue Qi 1
1 , Michigan State University, East Lansing, Michigan, United States
Show AbstractTo minimize the irreversible capacity loss and enhance the long-term capacity retention of Si anode, it is important to gain fundamental understanding of the intrinsic response of Si upon delithiation with different rates. In this study, we developed a new continuous delithiation algorithm based on ReaxFF-MD simulations by utilizing a lithiated Al2O3 coating layer on fully lithiated Si to generate a driving force for Li to naturally diffuse out of the LixSi. Specifically, we investigate the mechanism of irreversible structural changes and its consequences on subsequent lithiation process.
The delithiation rate is considered to be “slow”, with respect to the size of Si and the diffusion rate, when Li can completely diffuse out of Si (the residual Li in Si is less than Li0.2Si) and the Si exhibits negligible amount of isolated inner-pore. However, upon fast delithiation (10 times faster), a Li concentration gradient with higher Li concentration in the center of Si and lower Li concentration near the surface is formed which ensembles a cage-like structure with locally dense Si network near the surface. As we have demonstrated before that Li diffusion in Si increases with Li concentration, this concentration gradient leads to significant amount of Li trapped inside Si. As a result, at the end of fast delithiation process, a- Li1.2Si with non-uniform Li concentration distribution shows 141 % volume inflation. Meanwhile, during fast delithiaon, isolated inner-pores continuously collapse and reform, and eventually, agglomerates into a large pore with severe coating delamination. However, irreversible structure change was discovered even during the slow delithiaton process, where the delithiated a-Li0.2Si remains 44 % inflated with uniform Li concentration at the end of slow delithiation. This is due to the loss of directly bonded Si-Si pairs, which makes the delithiated a-Li0.2Si exhibit faster lithiation rate in the next cycle.
10:30 AM - ES6.5.04
Electrochemical Acoustic Structural Determination of Lithium Ion Batteries
Daniel Steingart 1 , Greg Davies 1
1 , Princeton University, Princeton, New Jersey, United States
Show AbstractIn recent work we have shown that there is a simple but effective methods to determine the ID of battery and its SOC and SOH using acoustics. Regardless of chemistry, is a reactor in which density must redistribute as a function of state of charge. In most batteries, as the elastic modulus of electrodes change as a function of state of charge as well, it then follows that the sound speed is a function of charge and state of health.
Beyond this the acoustic signal, in both reflection and transmission, is a fingerprint of the coupled chemistry/geometry of the battery. We have demonstrated the fidelity of the relation between acoustic response and battery type, state of charge, and state of health for over 30 different chemistries/geometry combinations of cells. Each battery indicated shows a strong fingerprint of structure, SOC and SOH.
In this effort we use forward and reverse models in combination with our acoustic data to determine _what_ is changing in the battery in a real time, in operando experiment. Models indicate that with proper experimental resolution we can determine up to 0.1% slip in capacity between electrodes, and well within 3% of SoC based on the expected moduli changes through the cell.
10:45 AM - ES6.5.05
In Situ Measurement of Elastic and Viscoplastic Properties of Lithiated Silicon and Lithium Metal for Li-Ion Batteries
Luize Vasconcelos 1 , Rong Xu 1 , Kejie Zhao 1
1 , Purdue University, West Lafayette, Indiana, United States
Show AbstractIn-situ mechanical characterization of electrode materials require experiments to be conducted in inert atmosphere with controlled electrochemical conditions. The variation of experimental setups reported in existing studies has introduced substantial spread in the measurement of mechanical properties – the stress exponent of lithiated silicon, for example, is estimated anywhere between 2.58 and 50. Moreover, while it is expected that the strain-rate sensitivity will vary with the state-of-charge, there are no known quantitative studies on the relationship between the rate sensitivity and lithium concentration. In the present study, we implement an in-situ characterization platform where a nanoindenter, a liquid cell, and an electrochemical station are integrated into an inert gas filled glovebox. The experimental setup allows mechanical measurements to be performed continuously during controlled charging. We measure the elastic modulus, hardness, and strain-rate sensitivity as a function of lithium concentration in silicon thin films as well as in pure lithium metal. Results provide a comprehensive and definite answer for the elastic and viscoplastic properties of silicon electrodes. Such measurements are crucial for realistic predictions of the coupling between mechanical behaviors and electrochemical processes of lithium insertion at varied C-rates and wide range of lithiation states.
ES6.6: Fuel Cells
Session Chairs
Wednesday PM, April 19, 2017
PCC North, 200 Level, Room 228 A
11:30 AM - ES6.6.01
A Novel Scanning Probe Microscopy Technique for Ultrafast Imaging of Polarization Switching in Ferroelectric and Multiferroic Materials
Suhas Somnath 1 , Sergei Kalinin 1 , Stephen Jesse 1
1 , Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States
Show AbstractPolarization switching in ferroelectric and multiferroic materials underpins the next generation of electric and electronic devices such as tunneling devices, field effect transistors, and race-track memories. The switching mechanisms in these materials are exquisitely sensitive to local defects and structural imperfections at the micro- and nanometer scale which have undesirable effects on ferroelectric domains. Measurement of hysteretic loops on very dense spatial grids is therefore necessary for understanding nanoscale polarization dynamics and phenomena such as polarization fatigue or local wall displacements that remain difficult to study at the desired spatial and temporal scales. These considerations led to the development of Piezoresponse Force Microscopy (PFM) for imaging and manipulating local polarization states. In PFM, a micro-cantilever with a sharp and conductive tip is brought into contact with the surface of the specimen. Bias applied to the cantilever deforms the material, which in-turn causes the cantilever to deflect, and these vibrations are recorded using an optical setup in the microscope. However, the current state-of-art PFM spectroscopy techniques suffer from serious compromises in the measurement rate, measurement area, voltage and spatial resolutions since they require the combination of a slow (~ 1 sec) switching signal and a fast (~ 1 – 10 msec) measurement signal.
We report on a PFM spectroscopy technique that is significantly faster than currently available spectroscopy techniques. This technique uses intelligent signal processing techniques to filter the complete cantilever response enable the direct measurement of material strain in response to the probing bias. Our technique enables precise spectroscopic imaging of the polarization switching phenomena 3,500 times faster than currently reported methods. The probing bias waveform can be modulated such that the material response can be measured for all combinations of electric field which allows rapid construction of Preisach density maps as well. The improved measurement speed enables dense 2D maps of material response with minimal drift in the tip position, which are crucial for integration of ferroelectric nanostructures in future electric and electronic devices.
This research was conducted at the Center for Nanophase Materials Sciences, which is sponsored at Oak Ridge National Laboratory by the Scientific User Facilities Division, Office of Basic Energy Sciences, U.S. Department of Energy.
11:45 AM - ES6.6.02
Strain Effects in Surfaces of Doped Ceria for Solid Oxide Fuel Cell Applications
Aoife Lucid 1 , Graeme Watson 1
1 , Trinity College Dublin, Dublin Ireland
Show AbstractCurrent solid oxide fuel cells (SOFCs) require temperatures in the region of 1000°C to operate. This is primarily due to the fact that current generation SOFC electrolytes, such as yttria stabilized zirconia (YSZ), require high temperatures in order for sufficient ionic diffusion of the O2- ions to occur.1 It has been suggested that replacing YSZ with samarium doped ceria (SDC) or gadolinium doped ceria (GDC)2 would reduce the operating temperature of SOFCs into the intermediate temperature (IT) range of 600-800°C, thus greatly reducing operating costs and increasing efficiency. The oxide ion conductors which are used in SOFCs are often multi-crystalline which results in an induced strain in these materials.
The effect of strain at surfaces and interfaces on the oxide ion conductivity in these materials is essential to their performance as SOFC electrolytes. It has been suggested that the strain which is induced in epitaxial films of these materials can result in enhancements in conductivity.3,4 There has been little theoretical investigation into oxide ion conductivity of SDC and GDC at surfaces and interfaces. Classical molecular dynamics (MD) can be used to study the strain effects in these systems. We utilize a polarizable force field, known as the dipole polarizable ion model (DIPPIM)5, which has been derived by our group (from ab-initio data) for ceria with a range of trivalent dopants.6 It is important to take polarizability into account when modelling these materials due to the highly polarisable nature of the oxide ions (O2-). We will discuss the effect of low-index surfaces and strained surfaces on the performance of SDC and GDC as oxide ion conductors.
[1] Boudghene et al, Renew. Sust. Energ. Rev., 6, 433-455 (2002)
[2] Zha et al, J. Power Sources, 115, 44-48 (2003)
[3] De Souza et al, Energy Enviorn. Sci., 5, 5445-5453 (2012)
[4] Burbano et al, J. Electroceram., 32, 28-36 (2014)
[5] Castiglione et al, J. Phys: Condens. Matter, 11, 9009-9024 (1999)
[6] Burbano et al, Phys. Chem. Chem. Phys., 16, 8320-8331 (2014)
12:00 PM - ES6.6.03
Multiscale Modeling of Solid-State Phase Transformations in Metal Hydrides for Hydrogen Storage
Tae Wook Heo 1 , Xiaowang Zhou 2 , Shinyoung Kang 1 , Mark Allendorf 2 , Brandon Wood 1
1 , Lawrence Livermore National Laboratory, Livermore, California, United States, 2 , Sandia National Laboratories, Livermore, California, United States
Show AbstractThe thermodynamics and kinetics of (de/re)hydrogenation of metal hydrides for hydrogen storage are strongly coupled with complicated phase transformation mechanisms. These mechanisms usually involve several chemical and materials processes at multiple length and time scales including gas-surface reaction, surface/bulk/interface diffusion, structural modification, and phase nucleation-and-growth. In this talk, we present our integrated effort as part of the new DOE Hydrogen Storage Materials—Advanced Research Consortium (HyMARC) towards the multiscale modeling of solid-state phase transformations in metal hydrides. Using phase-separating PdHx as the simplest model system, we introduce a comprehensive phase-field model integrating both bulk and surface thermodynamic/kinetic processes. The phase-field model is informed by the full atomistically-derived descriptions of temperature- and composition-dependent materials parameters such as chemical free energy, interfacial energy, surface energy, lattice parameter, elastic modulus, and diffusivity from molecular dynamics and density functional theory calculations. In particular, the relevant inhomogeneous elastic effects arising from interfacial coherency as well as surface relaxation are naturally incorporated into the model by Khachaturyan-Shatalov microelasticity theory within the context of the diffuse-interface description. We discuss the mechanical effects of interfacial coherency, surface stress relaxation, surface segregation of hydrogen, and surface geometry on the kinetics of bulk and surface phase transformations during (de/re)hydrogenation employing systematically designed phase-field simulations.
*This work of was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344 (T.W. Heo, S. Kang, and B.C. Wood) and by Sandia National Laboratories under contract DE-AC04-94AL85000 (X.W. Zhou and M.D. Allendorf).
12:15 PM - *ES6.6.04
Photo-Induced Ferroelectric Switching in Perovskite CH3NH3PbI3 Films
Peiqi Wang 1 , Ehsan Nasr Esfahani 1 4 , Jinjin Zhao 1 2 , Liyu Wei 2 , Qingfeng Zhu 3 , Shuhong Xie 3 4 , Jinxi Liu 2 , Xiangjian Meng 5 , Jiangyu Li 1 4
1 , University of Washington, Seattle, Washington, United States, 4 Shenzhen Key Laboratory of Nanobiomechanics, Shenzhen Institutes of Advanced Technology, Chinese Academy of Sciences, Shenzhen China, 2 School of Materials Science and Engineering, and Department of Engineering Mechanics, Shijiazhuang Tiedao University, Shijiazhuang China, 3 Key Laboratory of Low Dimensional Materials and Application Technology of Ministry of Education, School of Materials Science and Engineering, Xiangtan University, Xiangtan China, 5 5. National Laboratory for Infrared Physics, Shanghai Institute of Technical Physics, Chinese Academy of Sciences, Shanghai China
Show AbstractThe photovoltaic conversion efficiency of perovskite solar cells based on organic-inorganic CH3NH3PbI3 has risen spectacularly from 3.8% to over 20% in just seven years, yet quite a few important fundamental issues have not been settled, and the role of spontaneous polarization remains poorly understood. Here, using a combination of carefully designed piezoresponse force microscopy (PFM), Kelvin probe force microscopy (KPFM), and macroscopic polarization measurement under light illumination and in dark, we unambiguously establish the linear piezoelectricity of CH3NH3PbI3 that arises from its spontaneous polarization, and we show that different surface charges and potentials can be induced as a result. The surface potential can be shifted in opposite direction by light illumination, depending on the nature of substrates, and the spontaneous polarization can be reversed by external electric field, revealed by both microscopic and macroscopic measurements. Most interestingly, the light illumination can also switch the spontaneous polarization, and the photo-induced current contributes to apparent macroscopic polarization as well. This set of studies offer strong evidence on the interplay among photo-induced charges, polarization, and possibly ions in perovskite CH3NH3PbI3, and their implications on photovoltaic performance are also discussed.
12:45 PM - ES6.6.05
Grain Boundaries as Hierarchical Phonon Scatters—A Computational Mechanistic Approach
Stefano Leoni 1 , Duncan Hardie 1
1 , Cardiff University, Cardiff United Kingdom
Show AbstractRecent years have seen a massive resurgence of interest in thermoelectric materials, due to their ability to generate electrical energy from waste heat. Improving the efficiency of thermoelectric materials is achieved by means of affecting the thermoelectric figure of merit, by manipulation of the electrical and thermal conductivity; many innovative techniques have been developed to this end. Here we demonstrate the use of grains and grain boundaries in crystalline lead selenide to achieve the theorised ‘electron crystal, phonon glass’ material with ideal thermoelectric properties. By exploiting the grain boundaries formed in the reconstruction process of the phase transition between the rock salt structure and its high pressure analogue, we can affect the scattering of phonons over large wavelengths, leading to reduced lattice conductivity. Scattering is a function of grain size, and the natural generation of grains of various size and orientation means a wider range of wavelengths are affected, than by nanoscale design alone. By affecting grain morphology only i.e. at constant composition, two distinct features emerge: Lattice thermal conductivity is considerably lowered with respect to the perfect crystal, and the temperature dependence is strikingly suppressed. We propose a viable, general process for the production of hierarchical, anisotropic thermoelectric materials by means of the application of mechanical pressure, shock, or designed synthesis.
ES6.7: Mechanics in Nano-Structure and Interface
Session Chairs
Wednesday PM, April 19, 2017
PCC North, 200 Level, Room 228 A
2:30 PM - ES6.7.01
Electrochemical Kinetics and Dimensional Considerations at the Nanoscale
Prabhakar Bandaru 1 2 , Hidenori Yamada 3
1 , University of California, San Diego, La Jolla, California, United States, 2 Program in Materials Science, University of California, San Diego, La Jolla, California, United States, 3 Electrical Engineering, University of California, San Diego, La Jolla, California, United States
Show AbstractWe indicate a comprehensive theoretical and experimental investigation of electrochemical kinetics, with applications to meso- and nano-scale structures, and the discovery and design of new materials configurations. It is shown that the consideration of the density of states variation in nanoscale electrochemical systems yields modulations in the rate constant and concomitant electrical currents. The proposed models extend the utility of Marcus-Hush-Chidsey (MHC) kinetics to a larger class of materials and could be used as a test of dimensional character. We have obtained confirmation of our initial formulations through the fit of existing data on molecular systems, which clearly indicate deviations from standard electrochemical kinetics. Moreover, we predict novel phenomena and characteristics that have never previously been observed, as a function of dimensionality, e.g., the occurrence of electrical current oscillations in one-dimensional nanostructures as a function of chirality index for a (i) metallic: (9,0), and a (ii) semiconducting: (10,0) nanotubes. The implications of the study are of much significance to an understanding and modulation of charge transfer in nanostructured electrodes and potential usage in electrochemical charge storage.
2:45 PM - ES6.7.02
Contact Mechanics in Vertical-Contact-Mode Triboelectric Nanogenerators
Congrui Jin 1
1 , Binghamton University, Binghamton, New York, United States
Show AbstractThe triboelectric nanogenerators have attracted enormous amount of attention in the research community in recent years because of its simple design, high energy conversion efficiency, broad application areas, a wide materials spectrum, and low-temperature easy fabrication. A key factor that dictates the performance of the triboelectric nanogenerators is the surface charge density, which can be taken as a standard to characterize the performance of a triboelectric nanogenerator. The triboelectric charge density can be improved by increasing the effective contact area, and thus, to increase the contact area in a limited device size, micro-/nano-structures are often designed at the contact surfaces. Expert knowledge in contact mechanics, especially in adhesion and detachment mechanisms of the micro-/nano-structured interface, is thus becoming essential for a better understanding of the impact of interfacial design on the power generation of triboelectric nanogenerators. Such an emerging field provides a platform for materials sciences, mechanics, chemistry and engineering communities to share knowledge and build collaborations, which will enable the TENG researchers to pursue new design philosophies for enhanced performance. For this purpose, our group has conducted systematical numerical studies on the adhesive contact at the micro-/nano-structured interface are presented. We used a numerical simulation package in which the adhesive interactions are represented by an interaction potential and the surface deformations are coupled by using half-space Green’s functions discretized on the surface. The results confirmed that the deformation of interfacial structures directly determines the pressure-voltage relationship of triboelectric nanogenerators, and it can be seen that our numerical results provided a better fit with the experimental data than the previous studies.
3:00 PM - *ES6.7.03
Multiscale Computational Modeling for the Engineering of Rechargeable Batteries
Alejandro Franco 1 2 3
1 , Université de Picardie Jules Verne - LRCS UMR 7314 CNRS, Amiens France, 2 , Institut Universitaire de France, Paris France, 3 , RS2E, Amiens France
Show Abstract
In this talk i will review some of our latest progresses on the development of computational models for the engineering of rechargeable batteries at multiple scales, from the material to the cell level. These multiscale models combine an in house kinetic Monte Carlo package simulating in three-dimensions electrochemical reactions with a continuum simulation package simulating the transport processes of ions, reactants and products in electrolytes within discharging and charging porous electrodes. These models allow simulating electrochemical observables, such as charge/discharge curves, by simultaneously tracking the morphology evolution of the reaction products at the electrode mesoscopic level. I will discuss efficient strategies for the numerical parameterization of these models and for their use for predicting optimized electrode and cell designs. Application examples of these models will be provided for Li-O2, Li-S and Redox Flow Batteries with particle suspensions. Finally, i will discuss the potential of combining this type of computational approaches with cutting-edge data post-processing tools such as (immersive) virtual reality.
References
[1] Yin, Y., Gaya, C., Torayev, A., Thangavel, V., & Franco, A. A. (2016). Impact of Li2O2 Particle Size on Li-O2 Battery Charge Process: Insights from a Multi-Scale Modeling Perspective. The Journal of Physical Chemistry Letters, 7(19) (2016) 3897–3902.
[2] Thangavel, V., Xue, K.H., Quiroga, M.A., Mammeri, Y., Mastouri, A., Guery, C., Johansson, P., Morcrette, M., Franco, A.A., A microstructurally resolved model for Li-S batteries assessing the impact of the cathode design on the discharge performance, Journal of The Electrochemical Society, accepted, in press (2016).
[3] Blanquer, G., Yin, Y., Quiroga, M. A., & Franco, A. A. (2016). Modeling Investigation of the Local Electrochemistry in Lithium-O2 Batteries: A Kinetic Monte Carlo Approach. Journal of The Electrochemical Society, 163(3), A329-A337.
[4] Franco, A. A., Doublet, M. L., & Bessler, W. G. (Eds.). (2015). Physical Multiscale Modeling and Numerical Simulation of Electrochemical Devices for Energy Conversion and Storage: From Theory to Engineering to Practice. Springer.
[5] Quiroga, M. A., Malek, K., & Franco, A. A. (2016). A Multiparadigm Modeling Investigation of Membrane Chemical Degradation in PEM Fuel Cells. Journal of The Electrochemical Society, 163(2), F59-F70.
ES6.8: Lithium-Sulfur Batteries
Session Chairs
Wednesday PM, April 19, 2017
PCC North, 200 Level, Room 228 A
4:30 PM - *ES6.8.01
Issues and Potential Solutions in Li/S Batteries
Perla Balbuena 1
1 , Texas A&M University, College Station, Texas, United States
Show AbstractThe extremely complex and interconnected chemistry of the Li/S batteries poses many interesting and challenging problems. First-principles simulations are used here to investigate the Li metal anode reactivity and the discharge reactions at the S cathode. We will discuss the formation of a Li2S film at the Li anode surface in presence of a typical electrolyte and LiNO3 as an additive. We also explore the consequences of increased molar salt concentrations on the Li metal anode reactivity. On the cathode side, we characterize the sulfur/carbon composite and we study in detail the energetics and dynamics of the discharge reactions, dissolution of the long-chain polysulfides in the electrolyte, and deposition of the insoluble polysulfides.
5:00 PM - *ES6.8.02
Observation of Dendrite/Separator Interaction in Experimental Li-Ion Battery Cells
Corey Love 1 , Rebecca Mays 2 , Danny Liu 1 3
1 Chemistry Division, US Naval Research Laboratory, Washington, District of Columbia, United States, 2 , Thomas Jefferson High School, Alexandria, Virginia, United States, 3 , NRL/NRC Post-doctoral Associate, Washington, District of Columbia, United States
Show AbstractPolymer separators are passive components in lithium battery systems yet play a critical role in cell safety. Separators must maintain dimensional stability to provide electronic isolation of the active electrodes and resist puncture and penetration from lithium dendrites. The polyolefin class of polymers have been used extensively for this application with mixed success. Recently, we have show lithium dendrite formation and growth to display distinct temperature-dependent morphologies: rounded blunt mushroom-shaped, sharp jagged needle-like and granular particulates. Each of these dendrite morphologies will induce a difference physical interaction with the polymer separator. Anticipating this interaction is difficult since the mechanical properties of the polymer separator itself are largely temperature dependent. This talk describes the anticipated physical interaction of three different dendrite morphologies and the local physical properties of the commercial polymer separator. Time-lapsed microscopy images show dendrite formation, growth and interaction with polymer separators at various temperatures. The result of this work is important towards the design of safe recharging lithium batteries as well as guidance for best practices to match polymer separators with properties sufficient to withstand attack from anticiapted lithium dendrite morpholgies.
5:30 PM - *ES6.8.03
Role of Electrocatalyst in High Energy Density Li-Ion Sulfur Battery
Leela Mohana Reddy Arava 1
1 Department of Mechanical Engineering, Wayne State University, Detroit, Michigan, United States
Show AbstractRechargeable lithium-sulfur (Li-S) batteries have emerged as the most promising electrochemical energy storage systems due to their high energy density, wide range of temperature operation, cost effectiveness, and eco-friendly in nature. Nevertheless, the drawbacks associated with the Li-S batteries such as insulating nature of sulfur species, corrosive nature of pre-deposited polysulfides at electrodes during discharge-charge processes, and formation of thick solid electrolyte interface (SEI) layer still need to be circumvented. Herein, we present electrocatalysis approach with preferential adsorption of soluble-polysulfide species, formed during discharge process, towards the catalyst anchored sites of graphene and their efficient transformation to long-chain polysulfides in the subsequent redox process. Uniform dispersion of catalyst nanoparticles on graphene layers has shown 40% enhancement in the specific capacity over pristine graphene and stability over 100 cycles with a coloumbic efficiency of 99.3% at a current rate of 0.2 C. Further, metallic lithium-free sulfur configuration has been demonstrated using such a cathode vs. pre-optimized lithiated porous silicon electrodes with 400 Wh/kg (double the energy density as that of currently available Li-ion battery).
ES6.9: Poster Session II
Session Chairs
Thursday AM, April 20, 2017
Sheraton, Third Level, Phoenix Ballroom
9:00 PM - ES6.9.01
G-Mode KPFM—Bringing Kelvin Probe Force Microscopy into the Information Age
Liam Collins 1 , Alex Belianinov 1 , Suhas Somnath 1 , Nina Balke 1 , Sergei Kalinin 1 , Stephen Jesse 1
1 , Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States
Show AbstractAtomic force microscopy (AFM) has advanced well beyond simple topographical imaging to allow simultaneous imaging of material functionality including; magnetic, electrostatic, electrochemical properties, amongst a myriad of other material properties. In particular, Kelvin probe force microscopy (KPFM) has provided deep insights into the local electronic, ionic and electrochemical functionalities in a broad range of energy storage and conversion materials and devices. Despite the popularity of KPFM, the level of information available is not sufficient for some electroactive materials or devices which typically involve time and bias dependent electrostatic and/or electrochemical phenomena. Practically, the detection methodologies adopted in classical KPFM limit its output in terms of channels of information available and the time resolution of the measurement (e.g. ~1-10 MHz AFM photodetector stream is down sampled to a single readout of electrochemical potential per pixel). In this presentation, the foundations are laid for a new era in functional imaging utilizing big data collection and analytics. General Acquisition mode (G-Mode) KPFM will be introduced,[1-3] in which high speed data acquisition combined with physics based analysis and multivariate statistical analysis are shown to allow the extraction of dynamic information on the local electrochemical processes taking place with nanometer resolution and on microsecond timescales. G-Mode KPFM is immediately implementable on all AFM platforms, and allows simultaneous capture of numerous channels of information simultaneously, as well as increased flexibility in terms of data exploration across frequency, time, space, and noise domains. G-Mode KPFM can provides significant insight into the electrochemical dynamics taking place on the nanometere level and ultimately on the length scales of a step edge or single point defect.
[1] Collins, Liam, et al. "G-mode magnetic force microscopy: Separating magnetic and electrostatic interactions using big data analytics." Applied Physics Letters 108.19 (2016): 193103.
[2] Collins, Liam, et al. "Full data acquisition in Kelvin Probe Force Microscopy: Mapping dynamic electric phenomena in real space." Scientific Reports 6 (2016).
[3] Collins, Liam, et al. "Multifrequency spectrum analysis using fully digital G Mode-Kelvin probe force microscopy." Nanotechnology 27.10 (2016): 105706.
9:00 PM - ES6.9.02
Probing Separator Defect Geometries and Localized Deposition in Lithium-Ion Batteries
Xinyi Liu 1 , Craig Arnold 1
1 , Princeton University, Princeton, New Jersey, United States
Show AbstractLithium plating is an important degradation mechanism in Li-ion batteries that can lead to premature and catastrophic failure in cells. In previous work, we demonstrated a correlation between lithium plating and non-uniform ionic transport through separators, resulting in locally high current density and localized lithium deposition. In this work, we probe further into the effect of separator defect size and shape on the induced lithium plating. By mechanically compressing separators to close the pores, we produce local defects with various geometries and sizes. The deformed separators are then placed into coin cells and each coin cell is cycled for 300 cycles at a rate between C/2 and 1 C before being dissembled to observe plating. Upon disassembly, we find lithium plating in accordance with the location of stress concentrators. Through finite element analysis, we verify the creation of high electrochemical activity associated with transport limitations corresponding to places of lithium deposition. Moreover, we show that a threshold exists for defect size and spacing below which plating is not enhanced. The results can also be generalized to other forms of defects that create spatially non-uniform current distributions across the cell. This work aims to help to understand the coupling between mechanical stress, local defects, and locally induced plating, and provide insights on consequences and prevention of defects that arise from manufacturing and operation.
9:00 PM - ES6.9.03
High-Energy X-Ray Scattering Analysis of Structure and Microstrain in Electrochemically Charged δ-MnO2
Peng Gao 1 , Peter Metz 1 , Scott Misture 1
1 , Alfred University, Alfred, New York, United States
Show AbstractCyclic stability of electrochemical energy storage materials is a key challenge in the development of new electrochemical energy storage materials. We address the cyclic stability of δ-MnO2 nanosheet electrodes in Na-electrolytes using a combination of electrochemical and high energy X-ray probes. The quantity of sodium intercalated is shown to correlate with the surface Frenkel defect density in δ-MnO2 nanosheet assemblies equilibrated at low pH, as determined respectively by gravimetric and X-ray pair distribution function (PDF) analysis. X-ray absorption spectroscopy (XAS) demonstrates δ-MnO2 nanosheets equilibrated at pH 2 have mixed 3+/4+ valence and an average oxidation state of 3.24, indicating extensive reduction of in-plane manganese in the uncharged state. Upcoming XAS measurements of electrochemically charged and discharged δ-MnO2 electrodes will further examine the distribution of valence states following alkali insertion. Meanwhile, Mn-O bond length obtained from PDF measurements is shown to be nearly invariant with respect to charge state. These results indicate that faradaic charge storage of up to 300 F/g by pseudocapacitive δ-MnO2 electrodes results in almost no in-plane electrochemical strain. However, observed cyclic stability of 83% over 1000 charge cycles indicates electrode connectivity does degenerate over time. The question of what, atomistically, leads to electrode detachment remains to be answered.
9:00 PM - ES6.9.04
Electronic Structure and Comparative Properties of LiNixMnyCozO2 Cathode Materials
Hong Sun 1 , Kejie Zhao 1
1 , Purdue University, West Lafayette, Indiana, United States
Show AbstractWe study the electronic structure and valence states in LiNixMnyCozO2 (NMC) materials and compare the resulting electronic, structural, mechanical, and thermal properties of a class of NMC compositions. The Jahn-Teller distortion in the transition metal (TM) octahedral complex allows us to determine the ionic states of the TM elements. The variation of Ni2+/Ni3+ and Co2+/Co3+ as the NMC composition changes alter the structural stability, electrical conductivity, lattice parameters, elastic modulus, and thermal stability. The theoretical predictions are in excellent agreement with the experimental results. Through intensive computational screening, we further show that long-range atomic ordering is absent in NMC lattice due to the mixture of the ionic states and similar ionic radii of the TM elements. The first-principles modeling provides a theoretical foundation on complete understanding of the physicochemical properties of NMC at the level of electronic structures.
9:00 PM - ES6.9.05
Structural Characterization of Nanoencapsulated Phase Change Materials Undergoing Thermal Processes
Sasanka Garapati 1 , John Shelton 1
1 , Northern Illinois University, DeKalb, Illinois, United States
Show AbstractCurrent limits in thermal energy storage capabilities utilized in concentrated solar power plants applications are a critical challenge towards meeting future sustainable energy demands. A key component in overcoming this challenge is through the enhancement of latent heats of fusion characteristics in the thermal energy storage medium, which can increase storage energy density while reducing operating costs. In this investigation, latent heats of fusion enhancement is proposed through the use of nanoencapsulated phase change materials (PCM). Synthesized silicon dioxide nanocapsule shells containing palmitic acid (PA) as the phase change material core are investigated for their shell structural stability during phase transformation of the PCM core. Differential scanning calorimetry is used to determine the effect of the fixed volume nanocapsule shell on the latent heat of fusion for the PA core. Surface, subsurface, and microstructural characteristics of the nanocapsule are investigated using SEM, TEM, and XRD.
9:00 PM - ES6.9.06
Thermoelectric Properties of Molybdenum Disulfide (MoS2) with Noble Metal Doping
Gilbert Kogo 1 , Aswini Pradhan 1
1 , Norfolk State University, Norfolk, Virginia, United States
Show AbstractTwo-dimension transition metal dichalcogenides like Molybdenum disulfide (MoS2) has recently been a subject of intensive research because of its excellent electrical, optical properties, and its applications in rechargeable batteries, sensors, transistors and integrated circuits. Due to its low thermal conductivity, high electrical conductivity, and high Seebeck coefficient, MoS2 is a promising candidate for thermoelectric applications. Its room temperature figure of merit (zT=S2σT/Ktot) exceeds the performance of most laboratories reported thus far. We report on the thermoelectric performance of MoS2 thin films grown by Pulse Laser Deposition (PLD) on Silicon and Sapphire substrates. Its resistivity displays semiconductor behavior, electrical conductivity increases with temperature. The Power factor (PF=S2σ) increases with temperature until it reaches a value of 3.86x10-4Wm-1K-2 at 300 K and 4.5x10-4Wm-1K-2 at 320 K. The thermal conductivity of 5.16E-02 W/mK was achieved at 300 K. The figure of merit (zT) increases to about 2.24 at 300 K. Our results show that Molybdenum disulfide (MoS2) efficiency is slightly higher than other promising thermoelectric conventional materials with lower thermal conductivity and higher Seebeck coefficient at room temperature. Detailed studies with doping of noble metals will also be reported.
This work is supported by NSF-CREST-CREAM.
9:00 PM - ES6.9.07
An Mg-Ion Battery Cell Constructed Entirely from Solid-Phase, Flexible Materials
Todd Houghton 1 , Gamal Eltohamy 1 , Hongbin Yu 1
1 , Arizona State University, Tempe, Arizona, United States
Show AbstractWhile lithium ion batteries continue to enjoy widespread adoption, the technology has some drawbacks that limit its use in next generation energy storage devices. Materials used in Li-ion batteries are relatively costly, while capacity is ultimately limited by the monovalent nature of the lithium ion. From the theoretical perspective, magnesium ion batteries overcome many of the limitations present in current Li-ion battery technology. Magnesium is divalent, allowing for twice the theoretical capacity of a lithium ion cell. Additionally, magnesium is a much more abundant material than lithium, lowering potential production costs.
Here, we present a magnesium half-cell battery built entirely from solid-phase, flexible materials. A polymer electrolyte made of ethylene carbonate, propylene carbonate, magnesium perchlorate, and Poly(vinylidene fluoride-co-hexafluoropropylene) was attached to a Molybdenum Oxide/graphite sheet cathode, and a tin insertion anode. Cell construction and electrical performance/characterization will be discussed in detail.
9:00 PM - ES6.9.09
A Study of Diffusion in Lithium-Ion Electrodes under Fast Charging Using Electrochemical Impedance Spectroscopy
Kazi Ahmed 1 , Jeffrey Bell 1 , Rachel Ye 1 , Bo Dong 1 , Cengiz Ozkan 1 , Mihri Ozkan 1
1 , University of California, Riverside, Riverside, California, United States
Show AbstractAn in-depth look at diffusion mechanics within lithium-ion electrodes under fast charging conditions is presented. Electrochemical impedance spectroscopy is used as the primary technique to investigate lithium diffusion within electrode material and in electrolyte near the electrode-electrolyte interface. Half-cells of sulfur and silicon are charged under varying galvanostatic rates while obtaining impedance data. Collected data is analyzed with the help of an electrical equivalent circuit model that provides mechanical and electrochemical parameters for each instance. The novelty of this equivalent circuit partly lies in its ability to resolve between solid-phase diffusion and liquid-phase diffusion, both of which occur during cycling of a lithium-ion electrode. Observed patterns in the parameters of this circuit provide insight into impact of fast charging on mechanics of lithium diffusion, both inside the electrode matrix and within electrolyte.
9:00 PM - ES6.9.10
Life Expectancy of Lithium Ion Batteries with Silicon Particles in Electrode
Abhishek Sarkar 1 , Abhijit Chandra 1 , Pranav Shrotriya 1
1 , Iowa State University, Ames, Iowa, United States
Show AbstractNewer battery technologies utilize high lithium storage capacity of silicon particles for better battery performance. However, silicon expands by three hundred percent during charging which leads to severe straining and consequently degrades the battery life. The previous work on theoretical modelling of particle failure in lithium ion systems generally assume the particle to be either linear elastic or perfectly plastic.
The present work reports a self-consistent elasto-plastic model combining the stress equilibrium equations with electrochemical diffusion of lithium ion into the silicon particle. Spherical symmetry utilizing a plastic shell encapsulating an elastic sphere is utilized for modelling the deformation field in the silicon particle. The lithium ion flux on the particle surface acts as the driving force for stress generation. With this framework, we investigate the diffusion characteristics of lithium ion in the silicon particle and stress generated due to the concentration gradient during a charge/discharge cycle. At first we model the critical crack length for a circumferential flaw as function of particle size and fast charging rate. Model predictions are compared to experimental observations in order to validate the modelling assumptions. A parametric study is conducted next over a wide range of particle sizes and charging rates. It is observed that very rapid charging rates are detrimental to battery life. A life expectancy model under such conditions are presented.
9:00 PM - ES6.9.11
Multiscale Model to Predict Thermal Performance of Lithium Ion Batteries
Abhishek Sarkar 1 , Pranav Shrotriya 1 , Abhijit Chandra 1
1 , Iowa State University, Ames, Iowa, United States
Show AbstractFailure due to overheating and melting of lithium ion batteries is a primary concern in the battery industry. Experimental studies in the battery thermal management have found that increased charging rates during battery cycling is the main reason behind the overheating of lithium ion batteries. The previous work in the field of thermal management of lithium electrode material primarily deal either with experiments on batteries as macroscale collection of electrode sheets or theoretical study of individual particles generating heat.
The present work reports a multiscale thermal model that allows incorporation of the heat generation at individual electrode particles into the thermal transport inside the lithium ion battery. A coupled thermomechanical model that incorporates elasto-plastic deformation of charged particles is used to determine concentration profile and heat generated as a funciton of the lithium ion flux on the particle surface. The heat generation associated with lithium transport and mechanical deformation is computed from joule heating, entropic heating and resistive heating due to surface over potential. The particle scale model is utilized to determine the thermal transport inside batteries consisting of multiple layers of electrodes. In order to model realistic electrode layers, thermal analysis is conducted with a range of distribution and sizes of particles. The thermal analysis is performed using Euler Implicit finite difference with convective boundary condition. The results predicted by the thermal diffusion model are compared with experimental data to validate the model predictions. A parametric study is conducted over a range of charging/discharging rates and different convection coefficients leading to overheating and meltdown of the battery. Finally, the paper predicts the rate of surface cooling needed to prevent the cell from tipping over the meltdown temperature.
9:00 PM - ES6.9.12
Electronic Properties of Organic-Inorganic Halide Perovskite Superlattice Structures
Rahul Singh 1 , Ganesh Balasubramanian 1 , Vikram Dalal 1
1 , Iowa State University, Ames, Iowa, United States
Show AbstractRecently a lot of focus has shifted to organic/inorganic lead and tin halide perovskites (CH3NH3PbI3 and CH3NH3SnI3) because of their promising potential in photovoltaic (PV) applications. This is due to their large absorption coefficient, high charge carrier mobility, and diffusion length. In addition, it has been found that both CH3NH3PbI3 and CH3NH3SnI3 may present a large Seebeck coefficient (depending on the doping level), indicating that these materials might be potential candidates for thermoelectric applications. The structure of perovskite, CH3NH3MX3, can be altered by using different carbon group elements, M = Pb or Sn or by using different halides (X = Cl, Br, I). Using the Boltzmann theory and first-principles electronic structure calculations, we have predicted the thermoelectric properties of two organic-inorganic halide perovskites and three superlattice structures obtained from the same two basic structures so as to identify the potential thermoelectrics in this newly discovered family of perovskite materials. Among the Structures considered, we found one of the superlattice structures (Structure 4) shows the highest thermoelectric figure of merit, ZT. The other perovskite Structures also show ZT greater than 1 at certain range of carrier concentrations and have the potential to show even greater values. All the Structures show high values of electrical conductivity, Seeback coefficient and thus have a great potential in thermoelectric applications. Exploring other Structures and tuning the structures to create potential barriers for phonons, thereby reducing thermal conductivity, can further optimize this.
9:00 PM - ES6.9.13
Three-Dimensional Hierarchical Porous Electrodes for Li-Ion Batteries
Mohammad S. Saleh 1 , Jie Li 2 , Jonghyun Park 2 , Rahul Panat 1
1 , Washington State University, Pullman, Washington, United States, 2 , Missouri University of Science and Technology, Rolla, Missouri, United States
Show AbstractMechanical stresses induced by electrochemical reactions in the Li-ion batteries limits the use of high specific energy density materials for their electrodes. Large number of Li atoms adsorbed per unit volume of an electrode leads to high specific capacity for the battery, but induces larger stresses that results in cracks and a rapid capacity fade. One of the solutions applied to resolve these issues is to use 1D or 2D nanoscale architecting of the materials to provide a high surface area to volume ratio to relax the stresses. This approach, however, has limits since the total volume of the electrode that can be built in 1D and 2D at nanoscale is severely limited.
To address these problems, we propose a breakthrough pointwise additive printing technique to extend the micro and nano-architecting of materials to the third dimension that can result in hierarchical void structures in the electrode for over about 5 orders of magnitude in length scale. The resulting structures have a controlled porosity from 10s of nm to several mm, i.e., they have a ‘breathing’ structure that not only can relax the mechanical stress but also provide an access to the electrolyte and reduce the length scale for diffusion/lithiation; thereby increasing the performance. We demonstrated this technique by making electrodes in scaffold form having controlled void structures at 10s to 100s of nm, and at 50-300 um (spread across all the three dimensions), with the total structure at several mm in size. An electrochemical half-cell system is used to evaluate the performance of these electrodes showing significant improvement in charge-discharge rate and life cycling.
9:00 PM - ES6.9.15
Addressing Lithium-Ion Battery Safety and Failure Containment for Modern Grid Energy Storage
Heather Barkholtz 1 , Sergei Ivanov 2 , Armando Fresquez 1 , Joshua Lamb 1 , Babu Chalamala 1 , Summer Ferreira 1
1 , Sandia National Labs, Albuquerque, New Mexico, United States, 2 , Los Alamos National Lab, Albuquerque, New Mexico, United States
Show AbstractThe issue of lithium-ion battery (LIB) safety is becoming more widely researched as several high-profile failures have garnered the public’s attention and criticism.[1, 2] Much effort has been devoted to increasing the safety and reliability of LIBs for large-scale applications, e.g. electric vehicles and grid load-leveling. One strategy to improve LIB safety is to design and test inherently safe cell components.[3] Additionally, many researchers study how commercially available cells fail and how that failure cascades through the cell module.[4, 5] All things considered, the safety of LIBs depend on a fundamental understanding of cell components, their interactions, and potential contributions to failure. Absent from the field of LIB safety are clearly defined electrode decomposition pathways and their connection to whole cell failure behavior. To fill this knowledge gap, a holistic approach to failure, connecting material instability quantification and whole cell failure, is explored. Parallel studies investigating tolerance to elevated temperatures will be discussed. The physical and chemical state of components from LIBs with various chemistries, states of charge, and age under abuse and non-abuse conditions were assessed. Concurrently, whole cell electrochemical performance and failure behavior as a function of cathode chemistry, environment temperature, and applied current was surveyed. Specifically, TGA/DSC is used to decouple anode/cathode reactivity with and without LiPF6 in thermal runaway situations. Temperature-resolved XRD then provided details of thermal instability, offering average structure changes during decomposition. Material properties were associated with whole cell electrochemical performance and failure at high temperatures. Ultimately, shining light on these complex thermal decomposition and component interaction reaction mechanisms will increase the predictability of high temperature behavior and with it LIB safety.
References:
[1] AAIB, Air Accident Report 2/2015, 2015.
[2] Bullis, K. MIT Tech. Rev., 2013, https://www.technologyreview.com/s/521976/are-electric-vehicles-a-fire-hazard/.
[3] Kalhoff, J.; Eshetu, G. G.; Bresser, D.; Passerini, S. Chem. Sus. Chem., 2015, 8, 2154-2175.
[4] Lamb, J.; Orendorff, C. J.; Steele, L. A. M.; Spangler, S. W. P. Power Sources, 2015, 283, 517-523.
[5] Muenzel, V.; Hollenkamp, A. F.; Bhatt, A. L.; Hoog, J. D., Brazil, M.; Thomas, D. A.; Mareels, I. J. Electrochem. Soc., 2015, 162, A1592-A1600.
Sandia National Laboratories is a multi-mission laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-AC04-94AL85000. SAND NO. SAND2016-10637 A
9:00 PM - ES6.9.16
The Study for the Effect of New Cathode on Cell Performance in Molten Carbonate Fuel Cells
Shin Ae Song 1 , Ki Young Kim 1 , Sung Nam Lim 1 , Yong-Cheol Jeong 1 , Jonghee Han 2 , Sung Pil Yoon 2
1 , KITECH, Gyeoggi-do Korea (the Republic of), 2 , KIST, Seoul Korea (the Republic of)
Show AbstractFuel cell is one of the best solutions for distributed powder for the city. In fuel cells, molten carbonate fuel cell(MCFC) (operated at 650 oC) is very close to commercialization. However, MCFC have the problem about long-term operation over 80,000h. If MCFC shows the high power density, MCFC operation time can be extended via lowering the operation temperature. To enhance the cell performance of MCFC, new cathode has to be developed because the cathode has much higher polarization compared with anode. In the oxygen reduction reaction (ORR) in MCFC cathode, it is known that the step of dissociation between the O-O bond after electrolyte dissolution of O2 gas is the rate-determining step. If the catalyst which can easily dissociate the O-O bond can be developed, it is surely expected that the ORR is improved and the cell performance can be also enhanced. In this study, Cu coated cathode were prepared and its cell performance was investigated. Single cell using Cu coated cathode shows the much higher cell voltage of 0.87 V at initial stage of the cell operation than that of uncoated cathode, 0.79V at current density of 150 mAcm-2. The charge transfer resistance is also reduced dramatically at that same time. It can be confirmed that the high cell performance is presented when the Cu state is Cu2O. It can be inferred that the catalytic activity of Cu2O on NiO cathode on ORR makes the cathode performance enhanced because Cu2O have a strong ability on O2 adsorption and dissociation.
9:00 PM - ES6.9.18
Toughening of Mg2Si Thermoelectric Material by Addition of Nano-SiC Particle
Yasuo Kogo 1 , Takashi Nakamura 1 , Ryo Inoue 1 , Shota Tanabe 1 , Tsutomu Iida 1
1 , Tokyo University of Science, Katsushika Japan
Show AbstractMg2Si has been expected for the component of next generation thermoelectric modules because of its low density, excellent thermoelectric properties. In order to apply this material for above-mentioned application, improvement of mechanical properties is necessary. The authors reported the addition of SiC particle is effective to enhance fracture toughness of polycrystalline Mg2Si. Our previous study showed that SiC particle was dispersed grain boundaries between Mg2Si grains and caused some toughening mechanisms, i.e., crack deflection and crack pinning. Their contribution to toughness is small and further improvement is necessary. In the present study, we fabricated SiC-particle dispersed Mg2Si composite both within the Mg2Si grains and along grain boundaries.
Sb-doped Mg2Si powders (25-75 um) and SiC nano particle (35nm) was used as raw material. Mg2Si particles with intra-SiC particle inclusions were fabricated by melting at 1085 C. After mixing, the mixture was sintered by spark plasma sintering technique. The Specimen (15mm in diameter, 6mm in thickness) was successfully fabricated. Apparent density was measured by Archimedes method.
After polishing, microstructure of as-sintered specimen was observed by scanning electron microscopy(SEM). Elemental analysis was also carried out by energy dispersive X-ray spectroscopy(EDX). Fracture toughness was measured by the indentation fracture (IF) method with the indentation load of 300 and 500 gf.
The density of the as-sintered specimen is more than 95%. The microstructural observation showed that SiC particles were dispersed within Mg2Si particles and along grain boundaries, respectively. Some particles at grain boundaries are aggregated, however, they are relatively dispersed homogeneously. The fracture toughness of the composite is higher than that of Mg2Si (1MPam1/2). Crack propagation from Vickers impression showed Zig-Zag fashion and toughening mechanisms, crack deflection and pinning was observed. It seems that addition of SiC within Mg2Si grains is effective to enhance fracture toughness of Mg2Si thermoelectric material. From these experimental results. toughening effect of SiC particles within Mg2Si particles was discussed.
9:00 PM - ES6.9.19
Optimization for the Thermoelectric Characteristics of Rough Nano-Ridge GaAs/AlAs Superlattice Structures
Chaowei Wu 1 , Yuhrenn Wu 1 , Cheng-Ying Chen 1
1 , National Taiwan University, Taipei Taiwan
Show AbstractThe optimizations for the thermoelectric(TE) characteristics with the rough surface at both sidewalls of the nano-ridge GaAs/AlAs superlattice(SL) structures are studied. Different from the traditional SL structures, we proposed the nano-ridge featured with rough surface at both sides of the SL structure, where the modification of the phonon spatial confinement and phonon surface roughness scattering are considered. The elastic continuum model is adapted to calculate the phonon dispersion relation and the related phonon group velocity. Reported experimental results with SL structures were used to verify our model. The electrical conductivity, Seebeck coefficient, electronic thermal conductivity, and the lattice thermal conductivity are calculated by Boltzmann transport equations and relaxation time approximation. We consider two and four layers nano-ridge GaAs/AlAs SL structures to find the optimal configurations of lattice thermal conductivity kph , where the lateral confined nano-ridge width is W=25nm. Our calculations show that kph is 2.17W/mK for two layers nano-ridge GaAs(4nm)/AlAs(1nm) SL structures. Moreover, we find that the lowest lattice thermal conductivity kph is 1.60W/mK, which occurs at the optimal configuration nano-ridge four layers GaAs(4nm)/AlAs(1nm)/GaAs(4nm)/AlAs(2nm) SL structure. However, we fell that it is not enough to design a high performance TE devices. Therefore, if we make the surface rough between the GaAs/AlAs SL structure and air boundary intentionally, we obtain the lower lattice thermal conductivity. The lowest lattice thermal conductivity kph obtained in this study is around 0.10W/mK for the surface roughness characteristics with the auto-covariance length L=6.0nm and the roughness degree RMS Δ=1.5nm. At the nano-ridge GaAs/AlAs SL and air surface, the electrons would be pushed away from the surface to the center of the nano-ridge SL structures due to the Fermi level pinning. Hence, this surface roughness degree RMS was properly chosen to prevent the electrons suffering from this surface roughness scattering to reduce its mobility. The proposed rough surface of the nano-ridge GaAs/AlAs SL structure shows the significant reduction of lattice thermal conductivity than that of the bulk GaAs and AlAs. However, different from the bulk cases, the influence of the electronic thermal conductivity, ke, cannot be neglected and the figure of merit ZT will be restricted by the effect of the electronic thermal conductivity, which is mainly decided by the electron doping concentration. Our simulation results show that the optimal configuration of electron doping density at T=300K is ND=3.46×1019 cm−3 , and at T=1000K is approximately ND=2.81×1019 cm−3. The highest ZT is 1.285 at 300K and the ZT value is 3.04 at 1000K.
9:00 PM - ES6.9.20
Thin Flexible Lithium Ion Battery Featuring Graphite Paper Based Current Collectors with Enhanced Conductivity
Hang Qu 1 , Jingshan Hou 1 , Yufeng Tang 2 , Oleg Semenikhin 3 , Maksim Skorobogatiy 1 , Xin Lu 1
1 , Ecole Polytechnique de Montreal, Montreal, Quebec, Canada, 2 , CAS Key Laboratory of Materials for Energy Conversion, Shanghai Institute of Ceramics, Shanghai China, 3 , University of Western Ontario, London, Ontario, Canada
Show AbstractA flexible, light weight and high conductivity current collector is the key element that enables fabrication of high performance flexible lithium ion batteries (LIBs). Traditionally, to fabricate flexible LIBs, battery active materials are directly deposited onto current collectors based on thin metallic foils. The as-fabricated LIBs have limited flexibility, and the adhesion between battery active layers and metallic current collector is weak, especially when the battery is subject to repeated bending actions. Recently, several flexible current collectors based on carbon nanotubes (CNT) have been demonstrated, and they showed appealing mechanical and electrochemical properties. However, note that the synthesis of CNT films normally requires a sophisticated process, and cost of such materials is high, thus creating significant barriers that prevent the utilization of LIBs in the wearable devices.
In this abstract, we report fabrication of an inexpensive, highly conductive and highly flexible lithium-ion battery using conductivity-enhanced graphite paper (GP) current collectors. The enhancement of conductivity of GP was achieved by depositing a metallic layer onto a commercial graphite paper by physical vapor deposition. In particular, we deposited a sub-micron thick Al layer on a GP as the cathode current collector and a sub-micron copper layer on a GP as the anode current collector. To prepare the anode and cathode, LiFePO4 (LFP) and Li4Ti5O12 (LTO) were first mixed with multi-walled carbon nanotubes, respectively. Then mixture was then dispersed in polyvinylidene fluoride (PVDF)/1-methyl-2-pyrrolidone (NMP) solution using a magnetic stirrer. The obtained slurry was casted onto the cathode or anode current collector, and then dried to form electrode films. Finally, the lithium-ion battery was assembled by stacking the as-prepared electrode films together with a PE separator layer soaked with LiPF6 electrolyte (Fig. 1(a)). We then characterized the performance of this battery using standard charge-discharge measurements. The battery could achieve a rate capacity of ~100 mAhg-1 under standard 0.2 C charge/discharge rate. Besides, the battery could retain its capacity even after intensive cyclic charge/discharge operation. During all the battery operation, the coulombic efficiency of the battery remained above 94%. We believe that this battery could find its niche markets in numerous fields relevant to portable or wearable electronic devices.
9:00 PM - ES6.9.21
Mechanical Properties and Fracture Behavior of Mg2Si after Heat Exposure
Takashi Nakamura 1 , Ryo Inoue 1 , Shuhei Hasegawa 1 , Yasuo Kogo 1 , Tsutomu Iida 1
1 , Tokyo University of Science, Tokyo Japan
Show AbstractIn order to generate electric power from waste heat, thermoelectric (TE) conversion technologies have been focused. The performance of TE modules strongly depends on properties of constituent materials. Magnesium silicide (Mg2Si) is one of the candidate materials for the component of TE modules using at 873K. It is well known that oxidation of Mg2Si occurs during the heating at ~873K in air and MgO can be found. The effect of MgO formation on the thermoelectric performance has been focused, however, conclusive studies have been not reported. In addition, there are quite limited works to investigate the effect of oxidation on mechanical properties. The objective of this research is to understand oxidation mechanism and the effect of oxidation on macroscopic mechanical properties.
The specimen with the dimension of 3 × 4 × 38 mm was cut from disk shaped specimen fabricated by spark plasma sintering technique. The specimens were polished and heated in air and low oxygen partial pressure at 873 K for 100 h and 250 h, respectively. In addition, surface morphology was monitored by specially designed optical system. After heat exposure, microstructural change was examined using a optical microscope (OM), and a field-emission scanning electron microscope (FE-SEM). Elemental analysis was also carried out by energy dispersive X-ray spectroscopy (EDS) to identify oxidation product. Four-point bending test was carried out using as-sintered and heat exposed specimen. Surface crack was introduced by Vickers indentation at the various load levels.
Surface observation shows that oxidation products nucleate just after oxidation test. Thickness of surface oxidation product is almost same even after heat exposure test for 100h and 250h. XRD profile and EDS mapping confirms that oxidation product is mainly composed of MgO. Si is also identified. Cross-sectional observation suggests that oxidation mainly occurs at the specimen surface. Stress-strain curves during the loading shows linear elastic behavior and unstable crack propagation along through-the-thickness direction occurs at the maximum stress. Maximum bending stress decreases with the increasing of indentation load. Fracture surface observation clearly shows that fracture initiates form the surface median crack. After heat exposure, surface cracks are covered with oxidation product and degradation of strength is small. These results suggest that crack healing probably contributes to macroscopic mechanical properties.
9:00 PM - ES6.9.22
A Strategic Approach to Design Binder Free Standing 3D Carbon Nanotubes with High Sulfur Loading for Li-S Batteries
Mumukshu Patel 1 , Chiwon Kang 1 , Eunho Cha 1 , Wonbong Choi 1
1 , University of North Texas, Denton, Texas, United States
Show AbstractRechargeable Li-S batteries represents advanced battery system offering high energy density with low cost and environmentally benign electrochemical energy storage. The basic principle of Li-S systems (Theoretical specific capacity of S = 1672mAh/g) has been investigated for decades, but the inherent cell chemistry hampers the commercial realization of this alluring technology. The critical limitations are mainly associated with the insulating nature of sulfur (5 x 10-30 S/m), and formation and dissolution of intermediate polysulfides (Li2Sx; 2 less than x less than 8) into the electrolyte during charge/discharge processes resulting in capacity fading and low cycling stability. Most of the previous strategies reported in trapping polysulfides considered the areal density of the sulfur in the cathode is less than 2mg/cm2. However, in order to obtain superior electrochemical performance (high volumetric and gravimetric energy density) compared to currently available state-of-the art Li-ion batteries, the sulfur loading amount has to be atleast 6mg/cm2 and optimize with the electrolyte (µL)/sulfur (mg) ratio for maximum electrochemical performance. The 3D CNTs provides micro channeled conducting framework promoting effective utilization of sulfur particles, high electrolyte absorbability facilitating well-localized polysulfides within the 3D CNTs, and maintaining good structural integrity during volume expansion. Here in, we develop a simple and facile method by mechanical pressing of sulfur at 155°C to impregnate different loading amount into 3D CNTs without the use of any complex chemical routes (use of carbon black, PVDF, and NMP). The proposed strategy delivered a specific capacity of ~1285, 790, and 528 mAh/g after 50 cycles at different loading amount of 1.86, 3.72, and 5.57 mg/cm2 at 0.5C rate (1.55, 3.11, and 4.66 mA/cm2), implying excellent electrochemical performance. Furthermore, in this presentation the detailed synthesis for higher loading amount of sulfur and their structural characterization will be described in detail.
9:00 PM - ES6.9.23
Bifunctional 2D TMD Nanocomposites for Oxygen Reduction Reaction and Hydrogen Evolution Reaction
Liangjun Zhou 1 2 , Xingzhong Zhao 2 , Zhouguang Lu 1
1 Department of Materials Science and Engineering, South University of Science and Technology of China, Shenzhen, Guangdong, China, 2 School of Physics and Technology, Wuhan University, Wuhan, Hubei, China
Show AbstractUp to now, fuel cells have gained lots of attentions of researchers, due to their high energy density and high energy conversion efficiency. These cells have provided another way for solving the worldwide energy challenge. Electrocatalysts for oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER) are the heart of the key components for commercial applications of fuel cells and water splitting, respectively. However, the most efficient ORR and HER catalysts are still Pt and its alloys, hampering further development of energy technologies based on these materials due to their high cost and scarcity.[1] Hence, it is attractive to design and synthesize non-Pt-group metal electrocatalysts as alternatives for ORR and HER. In the past years, a great number of work have been done. As an exciting family of electrocatalysts, transition-metal materials based compounds have been intensively studied, including transition-metal dichalcogenide (TMD)，CoSe2，MoC2. In particular, they show either limited ORR/HER activity or poor stability in alkaline/acidic solutions, and can only be used for ORR or HER. Thus, the development of bifunctional and alternative electrocatalysts for efficiently catalyzed ORR and HER with high activity and strong long-term stability is urgently needed.[2]
In this work, we have successfully designed and synthesized the nanocomposites, which contain 2D layered nanomaterials MoS2 and CoS2 nanoparticles, realizing the bifunctional applications for ORR and HER. The MoS2@CoS2 nanocomposites were prepared through a simply but effectively hydrothermal method, and these powders were characterized by SEM, TEM, XRD, XPS. The size of MoS2 was about 150 nm coating CoS2 nanoparticles of ca. 80 nm，which still kept the same after high-temperature calcination. The MoS2@CoS2 nanocomposites exhibited good enhanced electrocatalystic activity for ORR, including positive onset potential (∼-0.15 V), limited current density (-0.4 mA/cm2) and long-term stability. Moreover, the MoS2@CoS2 catalyst also showed remarkable HER activity with a high overpotential of -0.45 V at the current density of 10 mA/cm2, as well as an excellent stability in acidic media. These results demonstrated the excellent bifunctional properties for ORR and HER, providing a new approach.
References:
[1] X. J. Fan, Z. W. Peng, R. Q. Ye, H. Q. Zhou, X. Guo, Acs Nano 2015, 9, 7407.
[2] Z. H. Zhao, Z. H. Xia, ACS Catal. 2016, 6, 1553.
Acknowledgements
This work was supported by the National Natural Science Foundation of China (No. 21671096 and 21603094), the Shenzhen Key Laboratory Project (ZDSYS201603311013489), the Shenzhen Peacock Plan (No. KQCX20140522150815065), the Natural Science Foundation of Shenzhen (No. JCYJ20150630145302231, JCYJ20150331101823677), and the Postdoctoral Research Fellowship of SUSTC.
*Corresponding auther：Zhouguang Lu, Advanced Energy Materials, Email: luzg@sustc.edu.cn
Symposium Organizers
Kejie Zhao, Purdue University
Palani Balaya, National University of Singapore
Jianlin Li, Oak Ridge National Laboratory
Partha Mukherjee, Texas Aamp;M University
ES6.10: Solid-State Batteries II
Session Chairs
Perla Balbuena
Matt Pharr
Thursday AM, April 20, 2017
PCC North, 200 Level, Room 228 A
9:30 AM - *ES6.10.01
Reliability and Durability of Materials and Components for Solid-State Energy Conversion Systems
Edgar Lara-Curzio 1
1 , Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States
Show AbstractThe failure rate of many engineering systems can be described by the bathtub curve, which is characterized by three well-defined regimes. In the first regime, the failure rate is controlled by infancy failures; in the second regime the failure rate is expected to be zero for properly designed systems, but failures may occur when the system is subjected to unplanned loads; in the third regime, the failure rate and the durability of the system are controlled by degradation mechanisms.
In this presentation the reliability and durability of relevant solid-state energy conversion technologies, such as solid-oxide fuel cells and thermoelectric generators will be reviewed in the context of the bathtub curve. The types of loads involved in the operation of these systems will be discussed, as well as the implications of stochastic strength of materials and the nature of degradation mechanisms limiting their durability.
Strategies for improving the reliability of solid-state energy conversion technologies will also be reviewed.
10:00 AM - ES6.10.02
Controlling the Microstructure of Polycrystalline Li7La3Zr2O12 Solid State Electrolyte to Mitigate Li Dendrite Propagation
Asma Sharafi 1 , Jeff Sakamoto 1 2
1 Mechanical Engineering, University of Michigan, Ann Arbor, Michigan, United States, 2 Material Science and Engineering, University of Michigan, Ann Arbor, Michigan, United States
Show AbstractHigh energy density and safe energy storage are critical aspects to enable viable electric vehicles (EV) technology. Li-ion is the leading technology to meet current and midterm needs, however, the widespread implementation of EVs will require a step increase in energy storage technology. One approach is to use metallic Li as the anode. Batteries employing metallic Li anodes (3860 mAh.g-1) can lead to a tenfold increase in anode specific capacity by replacing the use of a conventional low capacity LiC6 anode (360 mAh.g-1 capacity). These advances would lead to batteries with a 100 % increase in energy density compared to state-of-the-art Li-ion batteries. Historically, the non-uniform deposition and dendrite formation on the negative electrode during repeated cycles has limited the use of metallic Li anodes when paired with liquid electrolytes. One of the most promising approaches to resolve this issue is the use of all solid-state-batteries (SSB) based on solid-state ceramic electrolytes (SSE). Ceramic electrolytes are believed to exhibit adequate stiffness (shear modulus) to prevent Li filament initiation and propagation. Even though it was believed this approach should work, high deposition rates result in Li metal propagation through polycrystalline ceramic electrolytes. Thus, understanding the fundamental underpinning mechanism that govern Li filament propagation in polycrystalline solid electrolytes is necessary. This study presents precise microstructural optimization and analysis to observe the propagation of Li metal through one of the most promising polycrystalline SSE with the garnet-type structure Li6.25Al0.25La3Zr2O12 (LLZO). Moreover, the engineering approaches will be shown to control the microstructure to mitigate the metal propagation in polycrystalline LLZO. The results of this work can provide insight into phenomena that control the stability of metallic Li electrode/polycrystalline SSE interface, which is essential to mature, commercialize and deploy SSB in large-scale applications.
10:15 AM - ES6.10.03
"Dendrites" in Lithium Solid Electrolytes?
Lukas Porz 1 3 , Tushar Swamy 1 , Daniel Rettenwander 1 , Till Froemling 3 , Brian Sheldon 2 , Yet-Ming Chiang 1
1 , Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 3 , Technische Universität Darmstadt, Darmstadt Germany, 2 , Brown University, Providence, Rhode Island, United States
Show AbstractInorganic solid electrolytes are proposed as a route to safe, high energy density rechargeable batteries, firstly, by replacing flammable liquid electrolytes, and secondly by suppressing metal dendrites and thereby enabling use of high energy density lithium metal electrodes.
Using translucent solid electrolytes and in situ SEM, here, we show that metallic lithium is able to penetrate polycrystalline solid electrolytes and propagate as a branching network of lithium filaments. Mechanical modelling shows stresses due to electrodeposition of lithium at a pre-existing flaw of high aspect ratio to be more easily accommodated by forward propagation of the filament (or crack) than by metal flow in the reverse direction. Experiments conducted in the two solid electrolyte families of greatest current interest, lithium phosphorus sulfides (LPS) and garnet oxides (here, a Li-La-Zr-Ta oxide, LLTZO), show that the initial flaw population is critical to determining whether metal propagation occurs, and that a previously-proposed shear modulus criterion for “dendrite” suppression is necessary but not sufficient.
Once filaments extend into the solid electrolyte, the resistance to propagation is surprisingly low and potentially even lower than in liquid electrolytes. Hence, the start of growth has to be suppressed. The capability of solid electrolytes to endure a current density of beyond 10 mA/cm2 for extended periods of time was experimentally demonstrated on a glassy LPS sample by plating a lithium layer of 890 µm. However, polycrystalline samples show a high tendency to penetration by lithium filaments.
10:30 AM - ES6.10.04
Determining Viscoplastic Properties of Lithium Metal by Nanoindentation
Yikai Wang 1 , Yang-Tse Cheng 1
1 Department of Chemical and Materials Engineering, University of Kentucky, Lexington, Kentucky, United States
Show AbstractLithium (Li) metal has long been considered as a promising negative electrode for rechargeable batteries because of its high specific capacity of 3862mAh/g. However, the formation of mossy lithium and lithium dendrites has impeded the practical application of Li metal negative electrodes. Applying mechanical stress to suppress dendrite and mossy lithium has been one of the possible approaches to solving this longstanding problem. Motivated by this idea, we have performed instrumented nanoindentation measurements of lithium metal inside an argon filled glovebox to study its viscoplastic behaviors. Combined with an iterative finite element (FE) modeling procedure, we measured the parameters of an overstress viscoelastic constitutive law for Li. In addition, FE modeling results showed that elastic modulus, on the order of several gigapascals, has negligible influence on the nanoindentation response of Li at ambient temperature.
10:45 AM - ES6.10.05
Silica-Based Organic-Inorganic Hybrid Materials for All-Solid-State Battery Electrolyte Application
Weimin Wang 1 , John Kieffer 1
1 , University of Michigan, Ann Arbor, Michigan, United States
Show AbstractDesired properties of solid electrolytes are high lithium conductivity and transference number, high shear modulus to prevent dendrite growth, chemical compatibility with electrodes, and ease of fabrication into thin films. We use sol-gel method to synthesize silica-based hybrid organic-inorganic materials for this application. The silica phase provides electrochemical stability and mechanical rigidity. We use polyethene glycol (PEG), covalently grafted onto the silica backbone, as the organic filler that provides the environment for ion conduction. We have developed synthesis methods in which grafting and sol-gel process are done in one step or the grafting occurs after the silica gel forms. In the latter one, silica network pore walls are functionalized so as to react with organic polymer when permeating the 3D silica network with poly(ethylene oxide) solution, which also contains dissociated lithium ions. The polymer chains so anchored inside the silica network provide highly conductive pathways. IR spectroscopy, Raman and Brillouin light scattering, impedance spectroscopy, small angel x-ray scattering (SAXS), charge-discharge cell testing are performed to identify the structural and chemical origins that underlie the performance of these hybrid electrolytes. SAXS measurements indicate two different structures are achieved with the two-step synthesis procedure, which allows us to embed a larger weight fraction of ion conducting polymer into network pores than the one-pot method. This greatly enhances the ionic conductivity without sacrificing mechanical stability because a continuous silica backbone is ensured. In both cases, a room temperature ionic conductivity in excess of 10-5 S/cm is reached. Here we provide a cumulative account of a systematic materials design effort, in which we sequentially implemented several important design aspects so as to identify their respective importance and influence on the materials performance characteristics.
ES6.11: Batteries
Session Chairs
Perla Balbuena
Jianlin Li
Thursday PM, April 20, 2017
PCC North, 200 Level, Room 228 A
11:30 AM - ES6.11.01
Mechanics of Battery and Catalysis Materials
Yi Cui 1
1 , Stanford University, Stanford, California, United States
Show AbstractMechanics has played critical role in designing next generation of energy conversion and storage materials. Here I will show exciting examples on battery and catalysis materials, including: 1) The mechanical stress induced by volume expansion and contraction of Si anode materials and the materials design principle to overcome these issues. 2) Straining tuning of catalysis materials to control the activity.
11:45 AM - *ES6.11.02
Needs and Challenges Associated with High Energy Batteries with an Emphasis on Thermodynamic Underpinnings
Mark Verbrugge 1 , Daniel Baker 1
1 , General Motors, Warren, Michigan, United States
Show AbstractFor personal transportation, vehicle electrification continues to grow in importance. This is particularly true for EREVs (Extended Range Electric Vehicles such as the 2016 Chevrolet Volt). We review recent electrified vehicle architectures and battery technologies. For strongly electrified vehicles, including EREVs and BEVs (Battery Electric Vehicles such as the 2017 Chevrolet Bolt), significant improvements in battery technology are needed, particularly in terms of decreased cost and increased energy density (energy per unit volume). The second portion of this talk is focused on these needs, associated cell requirements, and new research on electrode thermodynamics, including lattice model formulations and hysteresis.
12:15 PM - ES6.11.03
Coupling In Situ TEM and Ex Situ Analysis to Understand Heterogeneous Sodiation of Antimony
David Mitlin 1
1 , Clarkson University, Edmonton, Alberta, Canada
Show AbstractWe employed an in-situ electrochemical cell in the transmission electron microscope (TEM) together with ex-situ time-of-flight, secondary-ion mass spectrometry (TOF-SIMS) depth profiling, and FIB - helium ion scanning microscope (HIM) imaging to detail the structural and compositional changes associated with Na/Na+ charging/discharging of 50 and 100 nm thin films of Sb. TOF-SIMS on a partially sodiated 100 nm Sb film gives a Na signal that progressively decreases towards the current collector, indicating that sodiation does not proceed uniformly. This heterogeneity will lead to local volumetric expansion gradients that would in turn serve as a major source of intrinsic stress in the microstructure. In-situ TEM shows time-dependent buckling and localized separation of the sodiated films from their TiN-Ge nanowire support, which is a mechanism of stress-relaxation. Localized horizontal fracture does not occur directly at the interface, but rather at a short distance away within the bulk of the Sb. HIM images of FIB cross-sections taken from sodiated half-cells, electrically disconnected and aged at room temperature, demonstrate non-uniform film swelling and the onset of analogous through-bulk separation. TOF-SIMS highlights time-dependent segregation of Na within the structure, both to the film-current collector interface and to the film surface where a solid electrolyte interphase (SEI) exists, agreeing with the electrochemical impedance results that show time-dependent increase of the films’ charge transfer resistance. We propose that Na segregation serves as a secondary source of stress relief, which occurs over somewhat longer time scales.
12:30 PM - ES6.11.04
Measurements of Stress and Fracture in Germanium Electrodes of Li-Ion Batteries
Matt Pharr 1 , Yong Seok Choi 2 , Joost Vlassak 3
1 , Texas A&M, College Station, Texas, United States, 2 , Seoul National University, Seoul Korea (the Republic of), 3 , Harvard University, Cambridge, Massachusetts, United States
Show AbstractWe have measured stresses that develop in sputter-deposited amorphous Ge thin films (a-LixGe) during electrochemical lithiation and delithiation. The stress measurements allowed for quantification of the elastic modulus of a-LixGe as a function of lithium concentration, indicating a much-reduced stiffness compared to pure Ge. Moreover, a-LixGe electrodes were found to flow plastically at stresses that are significantly smaller than those of their a-LixSi counterparts. Additionally, by monitoring the critical conditions for crack formation, the fracture energy of a-LixGe was measured using an analysis from fracture mechanics. The fracture energies were determined to be Γ = 8.0 J/m2 for a-Li0.3Ge and Γ = 5.6 J/m2 for a-Li1.6Ge. These values are similar to the fracture energy of pure Ge and are typical for brittle fracture. Despite being brittle, the ability of a-LixGe to flow at relatively small stresses during lithiation results in an enhanced ability of a-Ge electrodes to endure electrochemical cycling without fracture.
12:45 PM - ES6.11.05
Stress Induced Ionic Interplay in Lithium Sulfur Battery Electrodes
Aashutosh Mistry 1 , Partha Mukherjee 1
1 Mechanical Engineering, Texas A&M University, College Station, Texas, United States
Show AbstractLithium-sulfur batteries are a promising energy storage technology. The high capacity and energy density stem from the reduction of elemental sulfur (S8) to sulfide (S2-) ions, involving 16 electrons per mole of sulfur. Both the initial active material (S8) and the final product (Li2S) are solid and the reaction pathway progresses through a multi-step formation of ionic species in the electrolyte phase. However, the conversion from S8 to Li2S leads to 80% volume expansion. Accommodating this precipitation induced expansion in the porous cathode generates stress, which may affect the ionic interaction in the electrolyte, cause local reactant starvation and adversely affect subsequent electrochemical and chemical reactions. The importance of the mechanics-ionics interplay will be elucidated in this work. The analysis accounts for precipitation induced stress, electrolyte pressure variation, local electrolyte flow and the combined effect on the electrode electrochemical property and performance. An emphasis of the work is to discern the relative importance of reactant starvation, and transport in the electrolyte.
ES6.12: Modeling and Diagnostics in Batteries
Session Chairs
Thursday PM, April 20, 2017
PCC North, 200 Level, Room 228 A
2:30 PM - *ES6.12.01
Nanoscale Structural Dynamics in Lithium Ion Batteries Measured by Coherent X-Rays
Andrej Singer 1 , Chengcheng Fang 1 , Oleg Shpyrko 1 , Y. Shirley Meng 1
1 , University of California, San Diego, La Jolla, California, United States
Show AbstractAmong major scientific challenges related to energy storage materials is the detailed understanding of nanoscale processes involved in ionic diffusion during charge and discharge. The intercalation and extraction of lithium ions from the host materials typically results in an inhomogeneous distribution of strain, nucleation of topological defects and structural phase transformations in the electrode, leading to degradation of battery performance. These effects are especially important near surfaces and interfaces, since structural degradation of near-surface regions can prevent ions from diffusing deeper into the bulk of the electrode material. We have developed operando Bragg coherent diffractive imaging (BCDI) to study strain dynamics of single cathode nanoparticles. The high penetration depth of x-rays allows studying materials in real environments ‘in situ’, while the coherence of x-rays at novel x-ray sources allows imaging of the nanoscale disorder. The technique is based on focusing the x-ray beam on a single nanoparticle, measure the Bragg peak while slightly rocking the crystal, and inverting the data via a phase retrieval algorithm. The method not only yields the external shape of the nanoparticle, but also allows looking inside the particle and determining the crystal displacement field in 3D. Due to extreme angular sensitivity of Bragg diffraction minute displacement fields can be measured on the order of 10-4 relative to the lattice constant and elastic energy on the order of femto Joule can reliably be obtained.
Here a summary of our recent results will be presented. We applied BCDI to investigate a variety of high voltage cathode materials, including the spinel, layered oxide, and lithium excess layered oxide materials. We will present our findings on strain dynamics during charge and discharge, nucleation of topological defects, and their dynamics. Particularly, we will show how charge transport initiates mobility of otherwise static edge dislocations and how topological defects emerge in single nanoparticles during battery operation. We have also used the characteristic displacement field around the dislocations as a local nanoprobe of the internal materials properties. Our results shed light on intricate internal strain dynamics and may lead to better understanding of in lithium diffusion, structural failure, oxygen mobility, and oxygen redox activity.
3:00 PM - ES6.12.02
Design and In Situ Lithiation of Mechanically Robust, Nano-Architected Battery Electrodes
Xiaoxing Xia 1 , Claudio Di Leo 2 , Wendy Gu 3 , Julia Greer 1
1 , California Institute of Technology, Pasadena, California, United States, 2 School of Aerospace Engineering, Georgia Institute of Technology, Atlanta, Georgia, United States, 3 Department of Chemistry, University of California at Berkeley, Berkeley, California, United States
Show AbstractSilicon anodes for Li-ion batteries have a 10-fold enhancement in theoretical capacity compared with intercalation-type graphite anodes. The alloying nature of Li insertion in Si allows each Si atom to accommodate up to four Li atoms, but it also causes up to ∼300% Si volume expansion/contraction during lithiation/delithiation, which leads to mechanical degradation and a reduced cycling life. Nano-structuring Si can alleviate this problem for each nanoscale element such as nanowires and nanoparticles, but the traditional slurry fabrication method, suitable for intercalation materials with minimal volume expansion, does not provide efficient and reliable assembly of the nanoscale Si building blocks. Here, we demonstrate how 3-dimensional nano-architecture design could potentially resolve some of the key limitations of high-energy-density electrode materials that undergo alloying or conversion reactions upon lithiation: mechanical failure, sluggish kinetics, and low active material loading.
Nano-architected lattice electrodes are designed in computer and fabricated using two-photon lithography of polymer photoresist as scaffolds or inverse-shape templates with post-processing metal and Si deposition steps such as electroplating, sputtering and chemical vapor deposition. Via such additive manufacturing approach, mechanical failure can be reduced by the small-scale beam dimensions due to size-induced ductility in lithiated Si; electron and ion conductivity are enhanced by the metallic scaffold and the low-tortuosity pore network for electrolyte infusion; active material loading can be fine-tuned by lattice geometry and 3D tessellation of lattice unit cells. As a prototypical system, Cu−Si core−shell nanolattices were fabricated and tested as mechanically robust electrodes which accommodate ∼250% Si volume expansion during lithiation [1]. The superior mechanical performance of the nanolattice electrodes is directly observed using an in situ scanning electron microscope, which allows volume expansion and morphological changes to be imaged at multiple length scales, from single lattice beam to the architecture level, during electrochemical testing. Finite element modeling of lithiation-induced volume expansion in a core−shell structure reveals that geometry and plasticity mechanisms play a critical role in preventing damage in the nanolattice electrodes. Current efforts focus on designing nanolattice architectures with built-in mechanism for localized beam buckling during lithiation. Such anisotropic structural transformation would reduce electrode-wide volume expansion, relieve lithiation-induced stresses, and potentially enable novel functional materials such as electrochemical actuators and tunable photonic crystals.
Reference:
[1] Xia, X.; Di Leo, C. V.; Gu, X. W.; Greer, J. R. (2016) In Situ Lithiation-Delithiation of Mechanically Robust Cu-Si Core-Shell Nanolattices in a Scanning Electron Microscope. ACS Energy Lett., 1, 492–499.
3:15 PM - *ES6.12.03
A First Principles Comparative Study of Lithium, Sodium and Magnesium Storage in Pure and Gallium-Doped Germanium—Competition between Interstitial and Substitutional Sites
Fleur Legrain 1 , Sergei Manzhos 1
1 , National University of Singapore, Singapore Singapore
Show AbstractWe study by means of density functional theory the thermodynamics and kinetics of Li, Na, and Mg storage in Ge. We find that, depending on the concentration, the most stable configurations for Li, Na, and Mg insertion can consist of tetrahedral sites, substitutional sites, or a combination of the two types of sites. This is an important finding, as most of the previous ab initio studies of alloying type electrode materials ignored substitutional sites. The defect formation energies Ef computed at dilute concentration (x = 1/64) show that Na and Mg insertion are not thermodynamically favored in Ge vs formation of bulk Na and Mg, as opposed to Li insertion which is favored.
We show that a larger mechanical stress generated by Na and Mg insertion, compared to Li insertion, contributes to the high energy cost of insertion.
We investigate the effect of pdoping of Ge (with Ga) on the thermodynamics and find that it considerably lowers the defect formation energies associated with the insertion of Li/Na/Mg at tetrahedral sites. On the other hand, the energetics associated with Li/Na/Mg insertion at substitutional sites are not significantly affected.
In addition, we compute the migration energy barriers for Li/Na/Mg diffusion between two tetrahedral sites (0.38/0.79/0.66 eV), between two substitutional sites (1.11/1.20/2.14 eV), and between two sites of different type (2.15/1.78/0.85 eV).
3:45 PM - ES6.12.04
First-Principle Density Functional Theory (DFT) Calculations for Screening Functional Additives in High-Voltage Lithium Ion Batteries
Chia-Jung Lee 1 , Wen-Dung Hsu 1
1 , National Cheng Kung University, Tainan City Taiwan
Show AbstractNowadays, a great deal of research regarding energy density and voltage of lithium ion batteries (LIBs) are being developed for applications in electric vehicles, mobile devices and large power equipment. However, high voltage application in LIBs makes it unstable and lowers performance crucially. One way to address the issue is to stabilize the electrolytes using various solvent formulas and functional additives. The selection of the best additive among phosphides, sulfonate esters and lactam, etc., which perfectly fits the electrodes, can accelerate and improve the developments in LIBs. Several parameters, such as energy of lowest unoccupied molecular orbital (LUMO), highest occupied molecular orbital (HOMO), oxidation potentials (OPs), reduction potentials (RPs) and lithium ion binding affinities can be used to do first screening for the additive selection. In this study, first-principle density functional theory calculations were utilized and the solvent effect has been considered. It is inferred that the HOMO energy of both gas state and solvent state are highly correlated, as well as for the LUMO energy of both states. It is also shown that the HOMO energy with oxidation potential and LUMO energy with reduction potential, both at solvent phase, are also highly correlated. In terms of substituents, large atoms don’t have significant effects on the HOMO energy. However, halogens and short carbon chains greatly affect the HOMO energy of the additives. This computational screening technique is promising for selecting the best additive for high-voltage LIBs.
4:30 PM - *ES6.12.05
Predicting Mechanical Stresses in Lithium-Ion Battery Electrodes Using Mesoscale Simulations
Scott Roberts 1 , Bradley Trembacki 1 , Mark Ferraro 1 , Hector Mendoza 1 , Anne Grillet 1
1 , Sandia National Laboratories, Albuquerque, New Mexico, United States
Show AbstractLithium-ion battery electrodes (cathodes and anodes) mechanically degrade throughout battery cycling, degrading the performance of the entire battery. This mechanical degradation is driven by stresses that arise from electrochemical lithiation-induced swelling of the constituent active material particles coupled with the presence of polymeric binder materials and macroscale mechanical confinement. These phenomena inherently occur at the mesoscale (capturing hundreds of particles), where highly aspherical particles are packed into a bi-continuous percolated network that yields the macroscale behaviors that battery designers care about. Processes for manufacturing these electrodes can have a significant impact on battery performance.
In this talk we use mesoscale simulations to study the coupled electrochemical-mechanical response of lithium-ion cathodes. Mesoscale geometries are generated directly from image-based tomographic reconstruction data to capture the complexities of the electrode mesostructure. A variety of simulations that capture coupled electrochemical and mechanical effects are performed, including prediction of effective properties (electrical conductivity, tortuosity, mechanical moduli) and fully-coupled electrochemical-mechanical simulations of electrode charge and discharge at various rates. Two materials are studied; Lithium Cobalt Oxide (LCO) and Lithium Nickel Cobalt Manganese Oxide (NMC/NCM). The role of the conductive polymeric binder (polyvinylidene fluoride [PVDF] and carbon black [CB]) on electrical transport and the production of mechanical stresses is also explored.
Sandia National Laboratories is a multi-mission laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-AC04-94AL85000. SAND2016-10067 A.
5:00 PM - ES6.12.06
The Densification of Sulfur and Silicon Electrodes for Lithium-Ion Battery Large Scale Production
Jeffrey Bell 1 , Rachel Ye 1 , Kazi Ahmed 1 , Leon Peng 1 , Andrew Scott 1 , Daisy Patino 1 , Cengiz Ozkan 1 , Mihri Ozkan 1
1 , University of California Riverside, Riverside, California, United States
Show AbstractElectrochemical storage has gained momentum amid increasing concerns for a cleaner, more environmentally friendly future. Currently, lithium ion battery systems do not meet the requirements to quell the increasing concerns and it is therefore imperative to move in a new direction. The current top contenders for ‘beyond lithium’ is lithium-sulfur (Li-S) and silicon (Si). In order to scale up these new battery systems to industry it is crucial to study the effects of calendering on their performance. Calendaring (densification), may alter the robustness of the electrode’s conductive network and ability of the electrolyte to penetrate the electrode. Through altering the electrodes with calendaring to the correct density is it possible to improve network conductivity while also maintaining electrolyte penetration. Silicon and Sulfur electrodes were calendared at different densities and then characterized using gravimetric cycling and electrochemical impedance spectroscopy. Herein we report the fabrication of simple sulfur and silicon electrodes that have undergone calendaring to different densities and their long term positive effects on cycling, rate performance, and capacity.