Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session V50: Ion Transport Mechanisms in Ionic Liquid/Polymer HybridsFocus
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Sponsoring Units: DPOLY Chair: Lisa Hall, Ohio State University Room: BCEC 252B |
Thursday, March 7, 2019 2:30PM - 2:42PM |
V50.00001: Influence of Side-chain Chemistry on Structure and Ionic Conduction Characteristics of Polythiophene Derivatives: A Computational and Experimental Study Ban Dong, Christian Nowak, Jonathan Onorato, Fernando A Escobedo, Christine Luscombe, Paul F Nealey, Shrayesh Patel While extensive efforts have been devoted to understand electronic transport in conjugated polymers, little is known about their ionic conduction characteristics in relation to polymer chemistry and morphology. This work presents a combined computational and experimental study on morphology and ion transport in thin film blends of polythiophene derivatives and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI). Using molecular dynamics (MD) simulation, we show that in the amorphous phase, a polythiophene derivative P3EGT bearing oligoethylene glycol side-chains with an oxygen directly attached to the thiophene rings possesses lower Li+ ion conductivity compared to its analog P3MEGT that has a methyl spacer between the oxygen and the thiophene rings. Structural characterization of P3EGT- and P3MEGT-LiTFSI thin films indicates that LiTFSI preferably resides in the amorphous domain especially at high LiTFSI concentrations. Ionic transport measured by impedance spectroscopy is found to occur in amorphous domain, and ionic conductivity in P3MEGT is always higher than in P3EGT, consistent with prediction from simulation. Our work provides a platform to predict and study the influence of polymer chemistry on ionic conductivity of conjugated polymers. |
Thursday, March 7, 2019 2:42PM - 2:54PM |
V50.00002: Ion-Transport Properties of Nanothin Film Dry Polymer Electrolytes Ban Dong, Paul F Nealey, Shrayesh Patel Polymer electrolytes have demonstrated promise as dry electrolyte materials to enable lithium-metal batteries. However, majority of studies have focused only on thick samples (100’s of microns). However, interfaces play a critical role on the performance of batteries, thus investigating polymer electrolyte in the context of nanothin films (5-100 nm) will lead to better understanding of the role of interfaces on charge transport properties. Here, we report on ion transport characteristics of nanothin films of PEO and LiTFSI blends as a function of salt concentration, temperature and film thickness. Ion transport measurements were successfully performed using impedance spectroscopy on films fabricated on custom-designed nanofabricated interdigitated electrode (IDE) devices. Importantly, thickness dependence study of ion transport shows a monotonic decrease in ionic conductivity upon decreasing film thickness from 250 nm to ca. 10 nm, and the effect is stronger at low salt concentrations. The decrease of ionic conductivity at thinner films originate from the increasing fraction of the immobilized layer near the polymer/substrate interface. Our results suggest that using nanothin film configuration is a promising strategy to probe interfacial effects on ion conducting properties. |
Thursday, March 7, 2019 2:54PM - 3:06PM |
V50.00003: Proton transport through acid aggregates in a hydrated precise sulfophenylated polyethylene Benjamin Paren, Lionel Picard, Patrice Rannou, Manuel Marechal, William Neary, Aaron Kendrick, Justin G Kennemur, Amalie Frischknecht, Karen Winey Hydrated acid aggregates in a precise sulfophenylated polyethylene exhibit high proton conductivity. This study focuses on a new precise polymer, synthesized by ring-opening polymerization, that has a polyethylene backbone with a sulfonated phenyl group pendant on every 5th carbon, p5PhSA. The structure of p5PhSA is characterized with X-ray scattering and the proton conductivity is characterized with electrical impedance spectroscopy. Both experiments are performed as a function of relative humidity and temperature. Sorption measurements determined the water uptake in p5PhSA as a function of humidity as well. Atomistic molecular dynamics simulations are used to elucidate the structure of the acid aggregates in the amorphous polymer matrix and are directly compared to absolute X-ray scattering data. At 40°C and 90% relative humidity, the proton conductivity of p5PhSA is 0.17 S/cm, exceeding that of Nafion. At room temperature, interaggregate distance nearly doubles from 1.8 nm at 0% relative humidity, to 3.4 nm at 100% relative humidity. The swelling of these ordered acid aggregates with water is reversible, and facilitates the proton transport through p5PhSA. |
Thursday, March 7, 2019 3:06PM - 3:42PM |
V50.00004: Mesoscale Organization and Dynamics in Ionic Liquids Invited Speaker: Joshua Sangoro The impact of mesoscale organization on transport and dynamics in ionic liquids is investigated by broadband dielectric spectroscopy and dynamic mechanical spectroscopy as well as x-ray and neutron scattering techniques, complemented by computational approaches. Signatures of slow, sub-α dynamics are identified in the dynamic-mechanical and dielectric spectra and employed to probe lifetimes and dynamics of mesoscale aggregates in ionic liquids. It is found that the dynamics of mesoscale aggregates dominate many physicochemical properties such as the static dielectric permittivity and viscosity. By using mixtures of ionic liquids to tune composition-dependent evolution of the morphology, it becomes possible to realize ionic liquids with enhanced physicochemical properties that are otherwise inaccessible in neat systems. This talk will discuss the role of mesoscale organization and dynamics on macroscopic physical properties of ionic liquids. |
Thursday, March 7, 2019 3:42PM - 3:54PM |
V50.00005: Diffusion of Ions in Diblock Copolymers: Understanding the Molecular Weight Effect Through Coarse-Grained Modeling Youngmi Seo, Lisa Hall Diblock copolymers in which one microphase is mechanically robust while the other solvates and allows conduction of ions are of interest as solid battery electrolytes. The transport of ions through the conducting microphase is generally slower than through the analogous homopolymer, and is thought to depend on the distribution of ions within the conducting phase, among other factors. To understand these effects, we use coarse-grained molecular dynamics simulations and consider a wide range of systems with various ion-polymer and ion-ion interaction strengths. Our model reproduces the experimental trend of increasing ion transport with copolymer molecular weight, and this trend is more dramatic as ions are solvated in one polymer block more strongly or as the ion-ion interactions get stronger. The degree to which ions are locally concentrated, quantified by their average number of nearest ion neighbors out to a distance of approximately three diameters, is a good predictor of the ion diffusion constant. Specifically, systems whose ions are more locally aggregated (have more ion neighbors) have a reduced diffusion constant. |
Thursday, March 7, 2019 3:54PM - 4:06PM |
V50.00006: Study of Segmental Dynamics in Polymer-Ceramic Composite Electrolytes using Quasi-elastic Neutron Scattering Chelsea Chen, Naresh Osti, Robert L Sacci, Nancy J Dudney Composite solid electrolytes consisting of a polymer electrolyte and an ion-conducting ceramic electrolyte have potential in achieving high ionic conductivity, high mechanical modulus and good processability to enable higher energy density technologies. In this work we fabricated composite electrolyte consisting of poly(ethylene oxide) (PEO), lithium trifluoromethanesulfonate (LiTf), and a lithium-conducting glass ceramic (LICGC) from Ohara corporation. We discovered that thermal history has a profound impact on the PEO segmental dynamics, resulting in drastically different conductivities below the melting point of PEO in the first heating and cooling cycles. The average relaxation time of PEO chains decreased with the presence of LICGC. However, the enhanced segmental motion contradicts the decrease in the ionic conductivity of the composite electrolyte. The relationship between ionic conductivity, segmental motion, crystallinity and tortuosity in the composite electrolyte will be discussed. |
Thursday, March 7, 2019 4:06PM - 4:18PM |
V50.00007: Transport of Associated Particles in Polymeric Melts: A Dynamic Bonding Approach Zhen Cao, Jonathan P Mailoa, Alfredo Alexander-Katz We developed a coarse-grained molecular dynamics simulation model incorporating a dynamic bonding scheme to study the transport properties of associated particles in polymeric melts. In order to mimic the hopping of lithium ions in polymer electrolytes, a probability of breaking a dynamic bond between an associated particle and an active bead along polymer chains, Pbreak, was introduced to tune the activation energy between bound and unbound states. Both static (Kuhn length of solvated polymer chains, radial distribution functions, and connectivity of associated particles) and dynamic (mean squared displacement, and diffusion coefficient) properties of two classes of macromolecules were studied: a linear chain system with various bending rigidity and a brush system with various architectures. Simulation results show that the diffusion coefficient of associated particles is linearly proportional to Pbreak, and scales with the diffusion coefficient of polymer chains as Dassoc ~ Dpoly3/2. These results provide insight in understanding the design rules of polymeric materials for solid-state lithium-ion batteries. |
Thursday, March 7, 2019 4:18PM - 4:30PM |
V50.00008: Study of Diffusion of Lithium Salt in Block Copolymer Kyoungmin Kim, Daniel Hallinan In this study, the diffusion coefficient of lithium salt through a polystyrene-poly(ethylene oxide) block copolymer (SEO) was investigated using time-resolved Fourier Transform infrared - attenuated total reflectance (FTIR-ATR) spectroscopy. FTIR-ATR directly measures change of concentration in response to a concentration gradient, which is relevant for battery operation. FTIR-ATR is simpler and faster than electrochemical measurements, such as restricted diffusion, that require calibration and assumption about how cell potential relates to concentration gradient. Since the measurements are made in the absence of other driving forces, such as applied potential, the diffusion coefficient is independent of ionic conductivity and transference number. We studied the effect of salt concentration on the diffusion coefficient above the melting temperature of the electrolyte. Our results indicate that the diffusion coefficient is concentration-dependent, but not monotonic. |
Thursday, March 7, 2019 4:30PM - 4:42PM |
V50.00009: Influence of Doping on performance of Solid Polymer Electrolyte for Lithium-ion Batteries Shankar Ram Chithur Viswanathan, Janna Maranas We investigate the influence of doping on the conductivity of high molecular weight, crystalline PEO6 based solid polymer electrolytes (SPEs). Polyethylene oxide (PEO) based SPEs are an attractive alternative to the flammable liquid/gel electrolytes currently used in rechargeable lithium ion batteries. But, SPEs suffer from low ionic conductivity. The conductivity is linked to PEO segmental motion; In order to increase the segmental motion, we must reduce the glass transition temperature Tg. Unfortunately increase in polymer dynamics reduces mechanical strength of SPE. PEO6-LiClO4 complex is a tunnel like PEO/salt co-crystal which conducts Li+ based on a mechanism that decouples conductivity and segmental motion of the polymer. Inspired from ceramics, we dope small amounts of anions or cations to disrupt the PEO6-LiClO4 lattice. We vary the size of the anion, and cation to create defects in the crystal lattice. We observe up to 900% increase in the conductivity of doped samples even with small amount dopant (1 %). Interestingly, the increase in conductivity is not correlated with the decrease in Tg of the SPEs. With wide angle X-ray scattering, we observe transition from single crystalline phase to mixed phase morphology with increase of the dopant concentration. |
Thursday, March 7, 2019 4:42PM - 4:54PM |
V50.00010: Investigation of Ion Transport Properties of Stockmayer-Type Polymers Bill Wheatle, Erick Fuentes, Venkatraghavan Ganesan In recent work [ACS Macro Lett. 2018, 7, 1149-1154], we explored the role of polymer host polarity on ionic conductivity using the Stockmayer model of polar fluids applied to a coarse-grained Kremer-Grest polymer. In this model, a freely rotating electric dipole moment is embedded in each monomer bead. We found that the ionic conductivity maximized at some intermediate host polarity, as measured by the monomeric point dipole moment strength. We demonstrated that this maximization arises from a tradeoff between reduced ionic aggregation and slowed segmental dynamics as the host polarity increased. In this work, we investigate the influence of salt concentration, temperature, and host molecular weight on ionic conductivity and the nonmonotonic variations with the polarity of the host polymer medium. |
Thursday, March 7, 2019 4:54PM - 5:06PM |
V50.00011: Analyzing Ion Conductivity in Block Copolymer Electrolytes from Molecular Dynamics Simulations with an Applied Electric Field Kuan-Hsuan Shen, Lisa Hall Salt-doped block copolymers can be created with one microphase that is mechanically robust and another that solvates and conducts ions. A variety of polymer and ion types can be chosen, and molecular simulations can show how these choices impact ion motion to guide design of new materials. One strategy to increase conduction is to tune dielectric constant to reduce the degree of correlation of cation and anion motion, which can be significant in salt-doped copolymers. However, it is difficult to assess such a strategy in simulations, which often calculate self-diffusion constants of ions and estimate conductivity using the Nernst-Einstein equation (neglecting ion correlations). Conductivity can be directly calculated, including effects of correlated ion motion, from equilibrium simulations. However, this approach introduces a large statistical uncertainty. We aim to calculate conductivity from ion mobilities under an applied electric field. We ensure the field is low enough that the systems are in the linear response regime while still allowing for mobility high enough to measure accurately in the timescale of the simulation. We then compare conductivity of various systems as a function of Coulombic and polymer-ion interactions. |
Thursday, March 7, 2019 5:06PM - 5:18PM |
V50.00012: Dissolution of Lithium Metal in Poly(ethylene oxide) Michael Galluzzo, Whitney Loo, Nitash Balsara Salt doped poly(ethylene oxide) (PEO) has been studied extensively as a model polymer electrolyte system for lithium metal battery applications. In this study, we examine the widely accepted assumption that a stable interface forms between lithium and PEO above the PEO melting temperature by studying lithium symmetric cells. Using Li7 NMR, we show that a lithium species dissolves from the lithium electrode and diffuses into the bulk of initially neat PEO. Impedance spectroscopy is used to demonstrate that the lithium species contributes to ionic conductivity, and small angle X-ray scattering demonstrates that the dissolution also occurs in a PEO containing block copolymer, resulting in a significant increase (>20°C) of the order-to-disorder transition temperature. The results indicate that the lithium/PEO interface is not stable at elevated temperatures and there are clear implications for lithium metal batteries using PEO-based electrolytes. |
Thursday, March 7, 2019 5:18PM - 5:30PM |
V50.00013: Designing efficient polymer electrolytes via end-group controls Ha Young Jung, GYEONG-CHAN KANG, Moon Jeong Park There has been an increasing demand for the development of high-conductivity solid-state polymer electrolytes (SPEs) to be used in lithium batteries by replacing liquid electrolytes. The most widely studied SPEs are based on poly(ethylene oxide) (PEO) and its derivatives owing to PEO’s high solvating capability for lithium salt and low glass transition temperature. Given that lithium ion conduction occurs through the segmental motion of PEO chains, high mobility of lithium ion was feasible in amorphous phases. This prompted extensive research efforts to suppress PEO crystallinity by various physical and chemical approaches. In the present study, we investigate PEO-based polymers incorporated with various terminal functional groups as an effective means of controlling crystallinity of PEO phases. Further, by attaching various di-functional groups to the end of PEO chains, it has been revealed that morphology, ionic conductivity, and lithium transference number of PEO electrolytes are fine-tunable, attributed to the alteration of inter- and intramolecular interactions within. |
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