Bulletin of the American Physical Society
APS March Meeting 2013
Volume 58, Number 1
Monday–Friday, March 18–22, 2013; Baltimore, Maryland
Session N33: Focus Session: Polymers for Energy Storage and Conversion |
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Sponsoring Units: DPOLY Chair: Jodie Lutkenhaus, Texas A&M University Room: 341 |
Wednesday, March 20, 2013 11:15AM - 11:27AM |
N33.00001: Power Factor Improvements in PEDOT:PSS Tellurium Nanowire Composites Shannon Yee, Nelson Coates, Jeffrey Urban, Rachel Segalman The thermoelectric properties of a composite consisting of tellurium nanowires in a conducting polymer, poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS) matrix, is optimized by controlling the shape of the nanowire and doping of the polymeric matrix with polar solvents. The mechanism for an observed improvement in power factor is attributed to the unique conducting nature of PEDOT:PSS, which exhibits a transition from a hopping transport-dominated regime to a diffusive transport-dominated regime upon doping with polar solvents. Near this transition, the electrical conductivity of the composite is improved without significantly reducing the thermopower. Relying on this principle, the power factor optimization for this new thermoelectric material is experimentally carried out and found to exceed 100 $\mu$ W/m-K$^{2}$, which is nearly five orders of magnitude greater than pure PEDOT:PSS. This improvement in power factor suggests a new area of research into polymer based thermoelectric materials where transport interactions between the polymer and an inorganic component can be tuned. [Preview Abstract] |
Wednesday, March 20, 2013 11:27AM - 11:39AM |
N33.00002: Charge Transport Properties of P3HT-PEO block copolymers that are Electrochemically Oxidized in the Solid-State Shrayesh Patel, Anna Javier, Nitash Balsara We report on the relationship between morphology and electronic/ionic charge transport of Poly(3-hexylthiophene)-$b$-Poly(ethylene oxide) (P3HT-$b$-PEO) and lithium bis-(trifluoromethanesulfonyl) imide (LiTFSI) mixtures. Using ac impedance spectroscopy, we show that P3HT-$b$-PEO/LiTFSI mixtures can conduct electronic and ionic charges simultaneously. The electronic resistance of P3HT-$b$-PEO can be controlled through the electrochemical oxidation of P3HT with LiTFSI. We designed an all solid-state electrochemical cell with three terminals to measure the electronic conductivity of P3HT-$b$-PEO under applied potentials. The addition of a third terminal within the P3HT-$b$-PEO layer allows for the \textit{in-situ} measurement of the electronic conductivity as a function of the P3HT electrochemical oxidation level. Our experimental setup is unique in that electrochemical oxidation occurs in the presence of solid-polymer electrolyte. Previous studies on the electrochemical oxidation of polythiophenes have been done in the presence of a liquid electrolyte. The results of the \textit{in-situ} electronic conductivity measurements as a function of electrochemical doping level and block copolymer composition will be presented. [Preview Abstract] |
Wednesday, March 20, 2013 11:39AM - 11:51AM |
N33.00003: Ion Transport in Amorphous Polymer Electrolytes Katherine P. Barteau, Nathaniel A. Lynd, Glenn H. Fredrickson, Craig J. Hawker, Edward J. Kramer Successful development of lithium polymer batteries has been limited by low ionic conductivities in the polymer electrolyte, especially at low temperatures. In order to generate strategies for improvement of ionic conductivity, we have developed highly-controlled syntheses for a number of well-defined poly(glycidyl ether)s, PGEs, to serve as low temperature polymer electrolytes. The properties of PGEs can be tuned through structure control and functionalization, making them model systems for understanding ion transport and elucidating structure-property relationships. In this work we will discuss the synthesis and characterization of a family of PGEs that exhibit systematic differences in glass transition temperature (Tg), viscosity, oxygen-content, dielectric constant, and ionic conductivity. [Preview Abstract] |
Wednesday, March 20, 2013 11:51AM - 12:03PM |
N33.00004: Dynamics of a Novel Class of Polymers: Polymerized Sulfur Kevin Masser, Jenny Kim, Vladimir Oleshko, Jared Griebel, Woo Chung, Adam Simmons, Jeff Pyun, Christopher Soles In this study we investigate the dynamics of a new type of polymer, consisting mainly of sulfur. Room-temperature stable polymerized sulfur samples were prepared by crosslinking the well-known living sulfur polymers formed at elevated temperatures by the addition of a crosslinking agent. This reverse vulcanization process was used to create a series of samples with different amounts of crosslinking agent. These polymers show great promise for use in advanced batteries as cathode materials. Each system exhibits a glassy-state beta relaxation, with the intensity of this relaxation proportional to the crosslinking content. A dynamic glass transition is also observed for each system, and the glass transition temperature/segmental relaxation moves to higher temperatures with increased crosslink content as is typically observed in crosslinked systems. As is typical of polymers, ion motion in these systems is closely coupled to the backbone motion of the host polymer. [Preview Abstract] |
Wednesday, March 20, 2013 12:03PM - 12:15PM |
N33.00005: Investigation of the capacity retention mechanisms in novel composite sulfur copolymer-base cathodes for high-energy density Li-S batteries Vladimir Oleshko, Jenny Kim, Kevin Masser, Steven Hudson, Christopher Soles, Jared Griebel, Woo Jin Chung, Adam Simmonds, Jeffrey Pyun Utilization of the active cathode material in high-energy density Li-S batteries limited by the insulating nature of sulfur and losses in the form of insoluble polysulfides was improved by the use of 1,3-diisopropenylbenzene (DIB) copolymerized with molten sulfur. This approach termed, inverse vulcanization, transforms elemental sulfur into chemically stable processable copolymer forms with tunable thermomechanical properties. According to dielectric spectroscopy and dc conductivity measurements, composite sulfur-DIB copolymer cathodes exhibit a glassy-state beta relaxation related to short sulfur segments or to the DIB cross-linker. High-resolution AEM and FESEM studies down to the atomic scale reveal multiscale 3D-architectures created within the pristine and cycled composite cathodes with various contents of the electroactive copolymers. The morphology, structures, bonding and local compositional distributions of the constituents (sulfur, copolymers, aggregated conductive carbon nanoparticles) as well as extended pore structures and their transformations under cycling have been examined to provide insights into mechanisms of the enhanced capacity retention in the modified Li-S cells. [Preview Abstract] |
Wednesday, March 20, 2013 12:15PM - 12:27PM |
N33.00006: TiO$_{2}$-SEO Block Copolymer Nanocomposites as Solid-State Electrolytes for Lithium Metal Batteries Inna Gurevitch, Raffaella Buonsanti, Alexander Teran, Jordi Cabana, Nitash Balsara Replacing the liquid electrolyte in lithium batteries by a solid has been a long-standing goal of the battery industry due to the promise of better safety and the potential to produce batteries with higher energy densities. Recently, symmetric polystyrene-block-poly(ethylene oxide) (SEO) copolymers/LiX salt mixtures with high ionic conductivity and high shear modulus were developed as solid electrolytes. For an enhancement in mechanical properties and its effect on the dendrite growth from lithium metal electrodes, we study the effect of adding TiO$_{2}$ nanoparticles to the SEO/LiX mixtures. We find that TiO$_{2}$/SEO/LiX nanocomposite electrolytes have stable performance against the lithium metal electrodes. There appears to be a correlation between the stability of the electrolytes, morphology, and mechanical properties. [Preview Abstract] |
Wednesday, March 20, 2013 12:27PM - 12:39PM |
N33.00007: High Aspect Ratio Nanofillers for Solid Polymer Electrolytes Lalitha Ganapatibhotla, Janna Maranas In this study, we explore high aspect ratio nanofillers as additives that enhance solid polymer electrolyte (SPE) conductivity at battery working temperatures.SPEs are the key to light-weight and energy-dense lithium ion batteries but suffer from low room temperature ion conductivities.Spherical ceramic fillers are known to improve SPE conductivity and mechanical properties.Our experiments on spherical Al2O3 particle filled SPEs indicate highest conductivity enhancement at eutectic composition and temperature.A new mechanism, via stabilization of alternating layers of PEO and highly conducting PEO6:LiClO4 tunnels at the filler surface, was suggested by us.More such structures would be stabilized at a filler surface with high aspect ratio.Consistent with this hypothesis, $\gamma$-Al2O3 nanowhiskers intensify the effect of $\gamma$-Al2O3 nanoparticles.Increase in conductivity at eutectic composition, and decrease at non-eutectic compositions is more than the nanoparticles.Diameters of the two fillers are similar, but the change in aspect ratio (1to100) improves conductivity by a factor of 5. The influence of morphology and PEO dynamics on conductivity enhancement will be presented.All measurements are performed at a series of Li compositions, temperatures and nanowhisker loadings. [Preview Abstract] |
Wednesday, March 20, 2013 12:39PM - 12:51PM |
N33.00008: Atomistic Simulations Reveal a Surprising Variety of Morphologies in Precise Ionomers Mark Stevens, Dan Bolintineanu, Amalie Frischknecht Ionomers are being investigated as potential solid electrolytes in battery applications, due to their unique electrical properties. However, the relationships between ionomer chemistry, morphology and ion transport are poorly understood, which has hindered the development of ionomer-based batteries. To this end, we report atomistic molecular dynamics (MD) simulations of a model ionomer (polyethylene-co-acrylic acid) neutralized with different ions at various neutralization levels. The structure factor computed from the simulations is in good agreement with experimental X-ray scattering data. The simulations provide new insight into the shape, size and composition of ionic aggregates. In particular, we observe a wide variety of aggregate morphologies, ranging from small spherical aggregates to string-like shapes and large percolated networks. The unexpected morphologies of these ionic aggregates imply the need for a new interpretation of scattering spectra for these materials. We quantify cation-anion and oxygen-hydrogen association, the two interactions primarily responsible for aggregate formation, and report detailed information pertaining to local structures around cations, which is difficult to obtain experimentally and may have important consequences for ion transport. [Preview Abstract] |
Wednesday, March 20, 2013 12:51PM - 1:03PM |
N33.00009: Mechanism of Ion Diffusion in Coarse-Grained Ionomer Melts Lisa M. Hall, Mark J. Stevens, Amalie L. Frischknecht Ionomers (polymers with a small amount of charged groups) have been identified as possible single ion conducting battery electrolytes. A barrier their use in such applications is that the strong electrostatic interactions lead to ionic aggregation and can make ion diffusion very slow. In order to understand the physics underlying ionomer dynamics and especially how charge transport occurs, we perform molecular dynamics simulations. Our model has polymers with charged groups either in the backbone or pendant to it, explicit counterions, and long-range Coulomb interactions. Depending on placement, amount, and spacing of the ionic groups, various morphologies of ionic aggregates are formed. We find for all systems, ions can rearrange locally within the ionic aggregates on a relatively short timescale. Ions can move a longer distance when they rearrange collectively on a longer timescale, that is especially long for systems with discrete ionic aggregates. Because of this, a typical ion trajectory shows mostly small movements and rare large, sudden movements. However, these features are not due to `hopping' as typically understood. Instead, nearby aggregates of ions join together, rearrange, and later break apart, during which time some ions are exchanged and appear to have `hopped'. [Preview Abstract] |
Wednesday, March 20, 2013 1:03PM - 1:15PM |
N33.00010: Coarse-Grained MD Simulation of String-like Aggregates in Single-Ion Conductors Keran Lu, Janna Maranas, Scott Milner Single-ion conductors, or ionomers, have been investigated as a potential polymer electrolyte for advanced batteries. Ionic aggregates are prevalent in ionomers, and their sizes and shapes are not well characterized by experiment. Atomistic molecular dynamics simulations have been used to explore these aggregates, but may not be fully equilibrated because the aggregrates break and join infrequently. We report on an ion-only coarse-grained molecular dynamics simulation of a well-equilibrated ionomer system that reproduces structural features of the parent united atom simulation. Results for radius of gyration, shape anisotropy, and average ion coordination number from our simulation show that ionic aggregates are string-like, with random-walk configurations. An analogy to worm-like micelle equilibrium predicts an exponential length distribution for aggregates, in agreement with simulations. The implications of the size and structure of aggregates on conduction are discussed. [Preview Abstract] |
Wednesday, March 20, 2013 1:15PM - 1:27PM |
N33.00011: Anion Conduction in PEO-Functionalized Polyphosphazene Ionomers Joshua Bartels, Andrew Hess, Harry Allcock, Ralph Colby, James Runt A series of novel polyphosphazene ionomers with short chain poly(ethylene oxide) (PEO) moieties, bound ammonium cations, and free iodide anions were previously synthesized. Ion dynamics during anion conduction of the ionomers were studied by dielectric relaxation spectroscopy (DRS). These polyphosphazenes provide interesting conductive materials to study because of their low glass transition temperature, high segmental mobility, and high ion content. Analysis of DRS results provides static dielectric constant, conducting ion mobility, and conducting ion content for the materials. An increase in the length of the alkyl group extending from the polymer-bound ammonium cation increases conductivity and conducting ion concentration due to new steric interactions weakening ion-ion associations that restrict segmental mobility. By placing ether oxygens in the short alkyl group a large increase in conductivity and a decrease in the glass transition temperature is observed due to strong associations between the cation and ether oxygen lone pairs. [Preview Abstract] |
Wednesday, March 20, 2013 1:27PM - 1:39PM |
N33.00012: Decoupling ion flux and mechanical strength in polymer battery membranes Derrick Smith, Shan Cheng, Timothy Bunning, Christopher Li While much research has demonstrated repeatable characteristics of electrolyte membranes, the fundamentals behind the interactions during ionic diffusion in solid polymer electrolyte membranes for battery applications are not well understood, specifically the role of nanostructures, which hold the key to improving performance of energy storage devices such as fuel cells and Lithium ion batteries. The challenges in fabricating highly controlled model systems are largely responsible for the interdependent ambiguities between nanostructures and the corresponding ion transport behavior. In this work, Holographic Polymer Electrolyte Membrane (hPEM) volume gratings comprised of alternating layers of cross-linked polymer resin and ionic liquid were fabricated using holographic polymerization with an average d-spacing of 180 nm. These one-dimensional confinement structures were used to quantitatively study the anisotropic ionic conductivity properties, and correlate this behavior to nano-confinement and phase mixing. These membranes provide a platform in decoupling ion flux and bulk mechanical properties for future blend systems for battery applications. These volume gratings also offer an exciting route to fabricate multifunctional gratings for optic and sensing applications. [Preview Abstract] |
Wednesday, March 20, 2013 1:39PM - 1:51PM |
N33.00013: Structure-Property Relationship of Perfluorinated Sulfonic Acid (PFSA) Membranes Ahmet Kusoglu, Adam Weber Perfluorosulfonic-acid (PFSA) membrane is the most commonly used ionomer in electrochemical energy storage and conversion devices thanks to its remarkable proton conductivity, perm-selectivity, wide electrochemical window, and mechanical stability. Most of these properties are the result of the membrane's phase-separated nanostructure where ions and solvents transport through the hydrated domains while the surrounding hydrophobic PTFE backbone acts as a mechanical support. Thus, it is essential to understand the solvent- and humidity-induced morphological changes and their associated impact on the membrane's properties for optimizing the structure-property relationship desired by the electrochemical devices. In this talk, correlations among the mechanical (e.g., modulus), electrochemical (e.g., ionic conductivity) and nanostructural (e.g., domain spacing) properties during hydration is discussed. Moreover, the impact of thermal history, mechanical reinforcement, and side-chain length on the structure-property correlation is examined. Even though the properties vary for the membranes investigated, similar correlations are found between the degree of hydration, domain spacing, and ionic conductivity. [Preview Abstract] |
Wednesday, March 20, 2013 1:51PM - 2:03PM |
N33.00014: Hard X-ray tomography as a non-destructive technique to study the growth of lithium dendrites in lithium polymer batteries Katherine Harry, Daniel Hallinan, Dilworth Parkinson, Alastair MacDowell, Nitash Balsara Lithium metal electrodes have the highest energy density of any battery electrode technology and are, therefore, being considered for electric vehicles. However, lithium metal changes its shape under cycling, resulting in the growth of lithium metal dendrites through the electrolyte that eventually short-circuit the cell. While polystyrene-block-poly(ethylene oxide) copolymer electrolytes extend cell life by suppressing dendrite growth, dendrites eventually do grow. We show that hard X-ray microtomography is a non-destructive tool for studying the formation and growth of lithium dendrites at the interface between lithium metal and a block copolymer electrolyte. [Preview Abstract] |
Wednesday, March 20, 2013 2:03PM - 2:15PM |
N33.00015: A New Mechanical Loading Configuration for Maximizing The Performance of Dielectric Elastomer Generators Samuel Shian, Jiangshui Huang, Zhigang Suo, David Clarke Electrical energy can be generated from mechanical deformations using dielectric elastomers but currently achieved energy densities and conversion efficiencies are still small. In this presentation, we demonstrate that significant improvements, an energy density over 500 mJ/g and up to 10{\%} in efficiency, can be produced using VHB elastomers by altering the mechanical loading geometry. A major limitation is viscous losses in the VHB elastomer indicating that higher efficiencies with other elastomers will be attainable. The basic concept of mechanical energy harvesting with a dielectric elastomer sheet is a straightforward electromechanical cycle leading to a voltage step-up: a sheet is stretched, electrical charge at low voltage is placed on either side using compliant electrodes, the stretch is released causing the sheet's initial thickness and area to be recovered increasing the charge potential which can then be harvested. Integral to maximizing the energy conversion is the amount of mechanical energy that can be stored elastically and the amount of capacitance change in the elastomer sheet during stretching. We show that these factors can be maximized by equi-biaxial loading. Details of our dielectric elastomer generator will be described as well as the procedures we use for quantifying its performance. [Preview Abstract] |
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