Bulletin of the American Physical Society
APS March Meeting 2018
Volume 63, Number 1
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session X56: Polymers for Energy Applications IIFocus
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Sponsoring Units: DPOLY Chair: Chelsea Chen, Oak Ridge National Lab Room: LACC 515B |
Friday, March 9, 2018 8:00AM - 8:12AM |
X56.00001: Correlating Electrode-Electrolyte Interface and Battery Performance in Hybrid Solid Polymer Electrolyte–Based Lithium Metal Batteries Christopher Li, Qiwei Pan, Yongwei Zheng Solid polymer electrolytes (SPEs) are desirable in lithium metal batteries (LMBs) since they are nonflammable and show excellent lithium dendrite growth resistance. However, fabricating high performance polymer LMBs is still a grand challenge because of the complex battery system. In this work, a series of tailor-designed hybrid SPEs were used to prepare LMBs with a LiFePO4–based cathode. High performance LMBs with both excellent rate capability and long cycle life were obtained. The well–controlled network structure in this series of hybrid SPEs offers a model system to study the relationship between the SPE properties and the LMB performance. We show that the cycle life of the polymer LMBs is closely correlated with the SPE-Li interface ionic conductivity, underscoring the importance of the solid electrolyte interface in LMB operation. LMB performance was further correlated with the molecular network structure. We anticipate that results from this study will shed light on designing SPEs for high performance LMB applications. |
Friday, March 9, 2018 8:12AM - 8:24AM |
X56.00002: Study of Ion Conductivity and Chain Dynamics in Polymer-Ceramic Composite Electrolytes Chelsea Chen, Amaresh Samuthira Pandian, Naresh Osti, frank delnick, Nancy Dudney We fabricated polymer-ceramic composite consisting of polyethylene oxide, lithium trifluoromethanesulfonate, and a lithium-conducting glass ceramic from Ohara corporation. We examined the ion conductivity of the composite electrolyte with high volume fractions of Ohara ceramic (30% to 60%) using various processing methods. In this composition range, the composite conductivity was less affected by the volume fraction of the ceramic. Instead, it was strongly affected by processing methods. We found that the composite showed lower ion conductivity than the conductivity of PEO and the Ohara ceramic. A trilayer experiment using polymer electrolyte/Ohara ceramic plate/polymer electrolyte design revealed a very large interfacial resistance between the polymer electrolyte and Ohara ceramic. Quasi-elastic neutron scattering measurements were performed on the system to shed light on underpinnings of the origin of this large interfacial resistance. |
Friday, March 9, 2018 8:24AM - 8:36AM |
X56.00003: Flame retardant lithium ion battery based on a flexible solid-state polymer electrolyte membrane Guopeng Fu, Mark Soucek, Thein Kyu The safety issue of a portable battery has increasingly become paramount importance because of intimate contact of wearable devices with the human body. In this study, a flame retardant, thermally stable polymer electrolyte membrane (PEM) has been fabricated consisting of crosslinkable polyurethane precursor, viz., polyethylene glycol-bis-carbamate dimethacrylate (PEGBCDMA), cyclic ethylene carbonate (EC) as a solid plasticizer, and LiTFSI salt. This PEM is solvent-free, transparent, bendable, and twistable, which makes it an ideal candidate for a flexible all-solid-state lithium ion battery. Moreover, the above PEM exhibits high ionic conductivity at the superionic level of 10-3 S/cm and electrochemical stability in a large operating window of -0.5 V to 4.5 V. The PEM shows over 80% of specific capacity retention up to 250 cycles tested in the LiFePO4/PEM/graphite full cells, which have met most of the requirements of all-solid-state lithium ion battery for portable devices |
Friday, March 9, 2018 8:36AM - 8:48AM |
X56.00004: Lithium Dendrite Growth through Solid Block Copolymer Electrolyte Membranes Jacqueline Maslyn, Whitney Loo, Nitash Balsara Polystyrene-block-poly(ethylene oxide) copolymer electrolytes, which have been shown to prolong the life of lithium metal cells by partially suppressing lithium dendrite growth, were used in X-ray tomography experiments to study lithium plating. Diblock copolymers of high modulus and molecular weight were synthesized, and their nanostructures and electrochemical properties were characterized upon addition of lithium salt. X-ray tomography was used to observe lithium metal plating through these solid polymer electrolyte membranes under a range of electrochemical conditions: regimes of lithium plating behavior as a function of current density through the block copolymer electrolyte were identified. Successful prevention of lithium dendrite growth would enable the wide use of lithium metal as an anode material in next-generation batteries. |
Friday, March 9, 2018 8:48AM - 9:00AM |
X56.00005: Robust Polymer Electrolyte Membranes with High Ambient-Temperature Lithium Ion Conductivity via Polymerization-Induced Microphase Separation Sujay Chopade, Jesus Au, Timothy Lodge, Marc Hillmyer Robust polymer electrolyte membranes (PEMs) exhibiting high conductivity under ambient conditions are vital for designing next-generation electrochemical devices. We present the in-situ preparation of mechanically robust PEMs via polymerization-induced microphase separation, and incorporation of lithium salt into one of the microphase separated domains. The facile design strategy involves controlled growth of polystyrene from a poly(ethylene oxide) macro-chain transfer agent (PEO-CTA) and simultaneous chemical cross-linking by divinylbenzene in the presence of lithium (Li) salt and succinonitrile. Small angle X-ray scattering and transmission electron microscopy confirmed the formation of a disordered structure with bicontinuous morphology and a characteristic domain size of order 13 nm. The long-range continuity of the PEO/Li salt conducting nanochannels and the plasticization of the PEO polymer chains by succinonitrile facilitated outstanding conductivities (~ 0.35 mS/cm) at 30 °C. Concurrently, the mechanical robustness of the hybrid material (modulus E′ ~ 0.3 GPa at 30 °C) was ensured by a densely cross-linked polystyrene framework. |
Friday, March 9, 2018 9:00AM - 9:12AM |
X56.00006: NMR Spin Diffusion Experiments and Simulations for Model Discrimination and Ionic Domain Size Measurements in Proton Exchange Membranes Eric Sorte, Amalie Frischknecht, Todd Alam We detail the development of a flexible simulation program (NMR DIFFSIM) that solves the nuclear magnetic resonance (NMR) spin diffusion equation for arbitrary polymer architectures. The simulated 1H NMR spin diffusion behavior for a range of simple models relevant to proton exchange membranes were compared with the NMR spin diffusion behavior predicted for domain structures obtained from molecular dynamics (MD) simulations. We used DQ 1H NMR spin diffusion experiments to measure the hydrophilic domain sizes in SDAPP polymers as a function of hydration, and compared them with the domain sizes of Nafion polymers at similar hydration levels. The role of interface regions between polymer domains was also explored. Finally, a direct comparison of experimental spin diffusion results in SDAPP membranes to the spin diffusion behavior predicted for MD-proposed morphologies revealed excellent agreement, providing experimental support for the MD structures at low to moderate hydration levels. |
Friday, March 9, 2018 9:12AM - 9:48AM |
X56.00007: Structure and Dynamics in Ion-Conducting Polymers from MD Simulations Invited Speaker: Amalie Frischknecht Simulations of ion transport in ion-conducting polymers such as ionomers are challenging because dynamical processes relevant to the ion transport occur across many orders of magnitude. Additionally, designing improved ionomers requires an understanding of how both polymer architecture and ionomer morphology affect ion dynamics. To build a better understanding of the relationships among ionomer chemistry, morphology, and ion transport, we have performed a series of molecular dynamics simulations and connected aspects of these simulations with experiment. In this talk I will describe our recent results on two different ionic polymers. The first is a series of precise poly(ethylene-co-acrylic acid) ionomers, which have acid groups precisely spaced along the polymer backbone. Recent atomistic MD simulations of these ionomers are in relatively good agreement with quasi-elastic neutron scattering data at short time scales. The comparison with experiment validates the dynamics in the simulations, which we then use to probe ion dynamics at longer time scales. The second system is a sulfonated poly(phenylene), which conducts protons when hydrated. Atomistic simulations of the structure are in good agreement with NMR spin diffusion measurements of domain sizes. I will describe efforts to develop a coarse-grained model of this polymer to extend the length and time scales of the simulations, as well as additional comparisons between simulation and experimental data. |
Friday, March 9, 2018 9:48AM - 10:00AM |
X56.00008: Correlating ionic conductivity and nanoscale morphology of backbone type polymerized ionic liquids Preeya Kuray, Atsushi Matsumoto, Takeru Noda, Ciprian Iacob, Natalie Mamroi, Tadashi Inoue, James Runt Polymerized ionic liquids (PILs) are single ion conducting ionomers in which one ionic species (typically the anion) is free for transport, while the other is either located directly in the polymer chain (backbone PILs) or as a pendant group off the main chain (pendant PILs). In this study, backbone PILs with 3-methyl-pentyl spacers between the imidazolium cation and varying counter anions [trifluoromethane sulfonyl imide (TFSI-), nonafluorobuthane sulfonate (NfO-), and 1,1,2,2,3,3-hexafluoropropane-1,3-disulfonimide (CPFSI-)] were synthesized. Tg-independent ionic conductivities were then characterized using broadband dielectric spectroscopy and correlated to morphology by wide-angle X-ray scattering. It was found that changing the size of the counter anion can yield an up to 1.5 order of magnitude difference in Tg-independent ionic conductivity. Moreover, after comparing these results to pendant PILs of equivalent structure, it was found that backbone PILs result in a lower ionic conductivity, suggesting that pendant PILs yield a more correlated path for charge transport. |
Friday, March 9, 2018 10:00AM - 10:12AM |
X56.00009: Investigation of Morphology and Conductance of Anionic Block Copolymer Membranes for Anion Exchange Membrane Fuel Cells Using Atomic Force Microscopy Austin Barnes, Steven Buratto, Edward Coughlin, Yifeng Du Hydroxide-conducting anion exchange membranes (AEMs) have attracted significant research interest for fuel cell application. Although AEM fuel cells offer improved oxygen reduction reaction kinetics in alkaline media, the mobility of OH- in particular in the presence of CO2 is low. Similar to proton exchange membranes (PEMs), AEMs are copolymers with hydrophobic and hydrophilic components that phase separate to form ~10 nm diameter conducting channels. The conductivity of the membrane is critically tied to channel connectivity. We investigate anionic block copolymer electrolyte membranes previously synthesized by Coughlin et al. The polymers self-assemble into well-ordered morphologies, such as hexagonal and lamellar phases. The structural order of these polymers can better elucidate channel connectivity over random copolymer counterparts. We use conductive probe atomic force microscopy to investigate the nanoscale conductance in a closed fluid cell and find the hexagonal phase has improved channel connectivity over lamellar. Despite perpendicularly aligned hexagonal phase in the bulk, we find cylindrical aggregates prefer to align parallel to the surface. We hypothesize that the reorientation of these domains at the surface improves the mechanical properties of the membrane. |
Friday, March 9, 2018 10:12AM - 10:24AM |
X56.00010: Effect of Side-Chain on Structure/Property Relationship of PFSA Ionomers Ahmet Kusoglu, Peter Dudenas, Adam Weber Perfluorosulfonic-acid (PFSA) ionomers are widely used as solid-electrolytes in electrochemical devices where their transport functionality is controlled by its phase-separated morphology. As an electrolyte, ionomer membranes are in contact with the electrodes thereby forming complex interfaces. In addition, in some devices, such as fuel cells, ionomers form additional interfaces within the porous electrodes to maintain ion-conduction to the catalytic nanoparticles. When confined to nanometer-thick films, a PFSA’s functionality differs at these interfaces and becomes sensitive to the interactions with these particles, resulting in a complex polymer response dependent on thickness, substrate and casting conditions. For the next-generation electrochemical devices, there is need to understand PFSA ionomers with chemistries beyond Nafion and how they form interfaces on substrates. This talk highlights the side-chain chemistry and casting effects on structure/function relationships of PFSA membranes and thin films. The interplay between the chemistry and substrate effects are examined to elucidate the factors controlling ionomer film's hydration as well as nanomorphology during film formation, probed by grazing-incidence X-ray scattering (GIXS). |
Friday, March 9, 2018 10:24AM - 10:36AM |
X56.00011: Effect of Side Chain Length in Polymer Single-Ion Conductors Lauren Abbott, John Lawson Strategies for improving conductivity in polymer single-ion conductors typically focus on increasing polymer segmental motion and encouraging greater ion dissociation. Strong ionic aggregation reduces the polymer segmental motion and can negatively impact ion dynamics. One approach to lowering the glass transition temperature and increasing segmental motion is to increase the length of the side chains. In this work, we present molecular dynamics simulations of polymer single-ion conductors using bead-spring models with ions bound at the end of side chains of varying lengths. We focus on the effect of chain architecture on ionic aggregation in model polymers with short and long side chains at equal ion contents. In systems with longer side chains, we find that ions aggregate more readily due to the increased conformational flexibility of the fixed ions. Additionally, the extent of aggregation and size of aggregates are reduced significantly when the strength of ionic interactions is reduced in systems with either short or long side chains. We discuss the impact of these factors on ion dynamics. |
Friday, March 9, 2018 10:36AM - 10:48AM |
X56.00012: Nanoscale Resolution of Electric-Field Induced Motion in Ionic Copolymer Films Jason Dugger, Wei Li, Jyoti Mahalik, Mingtao Chen, Jim Browning, Rajeev Kumar, Timothy Long, Brad Lokitz The development of ionic block copolymers with a tuneable elctromechanical response to applied electric fields stands to benefit a range of fields including biomimetic devices, flexible electronics, solid electrolytes for energy storage, and nanofluidics. Currently, this area lacks a thorough understanding of how chemical structure, morphology, and counterions dictate electromechanical processes such as expansion, contraction, or ion mobility of these systems on the nanoscale. Our research probes the electromechanical response of ionic block copolymer systems on the nanoscale using neutron reflectometry to elucidate the factors that govern these processes. We have designed and implemented a custom environmental chamber capable of applying electric fields while allowing the in situ collection of reflectivity data. Results indicate that the choice of counterion dictates whether expansion or contraction occurs in these films. Experimental results were compared directly to computational models mimicking the physical samples. These findings establish the drastic impact counterion identity has on electromechanical response and outlines the importance of pushing the resolution of experimental measurements to a length scale that converges with computational efforts. |
Friday, March 9, 2018 10:48AM - 11:00AM |
X56.00013: Characterization of Ion Transport in Asymmetric Block Copolymer Electrolytes Michael Galluzzo, Whitney Loo, Andrew Wang, Nitash Balsara Polystyrene-b-polyethylene oxide (SEO) is an attractive material for enabling lithium metal anodes for secondary batteries. Microphase separation due to competing enthalpic and entropic interactions yield nanostructures which decouple the mechanical and ion conducting properties. SEO electrolytes are synthesized by adding a lithium salt, lithium bis(trifluoromethanesulfonyl)imide for this work. Ion transport has been studied in SEO electrolytes where the volume fraction of polyethylene oxide (PEO) is in the range of 0.4-0.6 and lamellar morphologies are observed via small angle X-ray scattering (SAXS). This work expands on the existing literature by examining SEO electrolytes with volume fractions of PEO in the range of 0.7-0.9 and 0.2-0.3 and which exhibit a variety of morphologies including body centered cubic spheres and hexagonally packed cylinders. Ionic conductivity, cation transference number, and salt diffusion coefficient are reported as functions of salt concentration and related to morphology. |
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