Bulletin of the American Physical Society
APS March Meeting 2016
Volume 61, Number 2
Monday–Friday, March 14–18, 2016; Baltimore, Maryland
Session B33: Polymers in BatteriesFocus
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Sponsoring Units: DPOLY Chair: Brad Frieberg, NIST Room: 336 |
Monday, March 14, 2016 11:15AM - 11:27AM |
B33.00001: Correlating morphology to dc conductivity in polymerized ionic liquids Ciprian Iacob, Atsushi Matusmoto, Tadashi Inoue, James Runt Polymerized ionic liquids (PILs) combine the attractive mechanical characteristics of polymers and unique physico-chemical properties of low molecular weight ionic liquids in the same material. PILs have shown remarkable advantages when employed in electrochemical devices such as dye-sensitized solar cells and lithium batteries, among others. Understanding their ionic transport mechanism is the key for designing highly conductive PILs. In the current study, the correlation between morphology and charge transport in two homologous series of PILs with systematic variation of the alkyl chain length and anions is investigated using broadband dielectric spectroscopy, rheology, differential scanning calorimetry and X-ray scattering. As the alkyl chain length increases, the backbone-to-backbone separation increases, and dc-conductivity consequently decreases. The cations dominate structural dynamics since they are attached to the polymer chains, while the anions are smaller and more mobile ionic species thereby controlling the ionic conductivity. Further interpretation of decoupling of dc conductivity from the segmental relaxation enabled the correlation between polymer morphology and dc conductivity. [Preview Abstract] |
Monday, March 14, 2016 11:27AM - 11:39AM |
B33.00002: Formation and growth of lithium metal dendrites through solid block copolymer membranes Katherine Harry, Kenneth Higa, Nitash Balsara Dendrite growth from lithium metal in electrochemical systems is the primary problem that precludes the wide use of lithium metal as an anode material. While polystyrene-block-poly(ethylene oxide) copolymer electrolytes extend cell life by suppressing dendrite growth, dendrites eventually do grow and the batteries fail by a short-circuit. \textit{In situ} hard X-ray microtomography experiments coupled with stress simulations shed light on the formation and growth of dendritic structures through stiff solid polymer electrolyte membranes. [Preview Abstract] |
Monday, March 14, 2016 11:39AM - 11:51AM |
B33.00003: All Solid-State Lithium Metal Batteries Using Cross-linked Polymer Electrolytes Qiwei Pan, Christopher Li Nowadays, to prepare all solid-state lithium metal batteries with high rate capability and stability using solid polymer electrolytes (SPEs) is still a grand challenge because of the interfaces between the SPE and the electrodes. In this presentation, we report a series of hybrid SPEs with controlled network structures by using POSS as cross-linker. These hybrid network SPEs show promising ionic conductivity, mechanical properties, and lithium dendrite growth resistance. All solid-state LiFePO$_{\mathrm{4}}$/Li batteries were also prepared using these SPEs as the electrolytes to study the effect of conductivity and mechanical properties of the SPEs on the performance of the batteries. At 90 \textdegree C, the prepared cells show high rate capability and stability. Capacity up to 160 mAh/g can be obtained at a C/2 rate during the galvanostatic cycling. Capacity retention of the cells is higher than 80{\%} after 250 cycles. Battery performance at 60 \textdegree C and decay mechanism of the batteries will also be discussed. [Preview Abstract] |
Monday, March 14, 2016 11:51AM - 12:27PM |
B33.00004: NMR Investigations of Structure and Dynamics in Polymers for Energy Storage Applications Invited Speaker: Steven Greenbaum Materials innovation is needed to realize major progress in energy storage capacity for lithium batteries and capacitors. Polymers hold considerable promise as ion conducting media in batteries and electrochemical capacitors and as dielectrics in thin film capacitors. Structural studies of materials utilized in lithium battery technology are hampered by the lack of long-range order found in well-defined crystalline phases. Powder x-ray diffraction yields structural parameters that have been averaged over hundreds of lattice sites, and is unable to provide structural information about amorphous phases. Our laboratory uses solid state nuclear magnetic resonance (NMR) methods to investigate structural and chemical aspects of lithium ion cathodes, anodes, electrolytes, interfaces and interphases. NMR is element- (nuclear-) specific and sensitive to small variations in the immediate environment of the ions being probed, for example Li$^{\mathrm{+}}$, and in most cases is a reliably quantitative spectroscopy in that the integrated intensity of a particular spectral component is directly proportional to the number of nuclei in the corresponding material phase. NMR is also a powerful tool for probing ionic and molecular motion in lithium battery electrolytes with a dynamic range spanning some ten orders of magnitude through spin-lattice relaxation and self-diffusion measurements. Broadband relaxometry based on Fast Field Cycling NMR (FFCNMR) methods can span three to four of these orders of magnitude in a single set of measurements. Results of several recent NMR investigations performed on our lab will be presented. We explore the ion transport mechanism in polyether-based and lithium polymer electrolytes and those based on other base polymers, in particular, the extent to which ionic motion is coupled to polymer segmental motion. Polycarbonates are being considered as a possible replacement for polypropylene in high power thin film capacitors due to their favorable dielectric properties. We investigate the effects of incorporation of two types of additives in the polymer film on the ring-flip motions corresponding to the $\gamma $ relaxation: (i) high dielectric constant ceramic particles; (ii) polar organic diluent molecules, The low frequency realm of broadband relaxometry allows meaningful comparison with dielectric relaxation studies of these samples performed by collaborators. [Preview Abstract] |
Monday, March 14, 2016 12:27PM - 12:39PM |
B33.00005: Li conductivity in siloxane-based polymer electrolytes Eric Stacy, Fei Fan, Hongbo Feng, Catalin Gainaru, Jimmy Mays, Alexei Sokolov Polymer electrolytes containing lithium ions are ideal candidates for electrochemical devices and energy storage applications. Understanding their ionic transport mechanism is the key for rational designing of highly conductive polymer matrices. Complementing dielectric spectroscopy investigations by results from rheology and differential scanning calorimetry we focused on the interplay between dynamics of lithium ions and the polymer matrix based on polysiloxane backbone. Our results demonstrate that the conductivity and the degree of decoupling between ion dynamics and structural relaxation depend strongly not only on the ions concentration, but also on the polarity and size of the polymeric side-groups. [Preview Abstract] |
Monday, March 14, 2016 12:39PM - 12:51PM |
B33.00006: Systematic Experimental and Computational Investigation of Ion Transport in Novel Polyether Electrolytes Danielle Pesko, Michael Webb, Yukyung Jung, Qi Zheng, Thomas Miller III, Geoffrey Coates, Nitash Balsara Polyethers, such as poly(ethylene oxide) (PEO), are considered to be the most promising polymer electrolyte materials due to their high ionic conductivity and electrochemical stability, both essential for battery applications. To gain a fundamental understanding of the transport properties of polyether systems, we design a systematic set of linear PEO-like polymers to explore the effect of adding carbon spacers to the backbone of the chain. Ac impedance spectroscopy is employed to measure the ionic conductivity of polyether/lithium salt electrolytes; the results elucidate tradeoffs between lowering the glass transition temperature and diluting the polar groups on the polymer chain. Molecular-level insight is provided by molecular dynamics simulations of the polyether electrolytes. We define the useful and intuitive metric of ``connectivity'', a parameter calculated from simulations which describes the physical arrangements of solvation sites in a polymer melt. Direct comparison of experiment and theory allows us to determine the relationship between connectivity and conductivity. The comparison provides insight regarding the factors that control conductivity, and highlights considerations that must be taken when designing new ion-conducting polymers. [Preview Abstract] |
Monday, March 14, 2016 12:51PM - 1:03PM |
B33.00007: Highly Flexible Self-Assembled V$_{\mathrm{2}}$O$_{\mathrm{5}}$~Cathodes Enabled by Conducting Diblock Copolymers Hyosung An, Jared Mike, Kendall Smith, Lisa Swank, Yen-Hao Lin, Stacy Pesek, Rafael Verduzco, Jodie Lutkenhaus Structural energy storage materials combining load-bearing mechanical properties and high energy storage performance are desired for applications in wearable devices or flexible displays. Vanadium pentoxide (V$_{\mathrm{2}}$O$_{\mathrm{5}})$ is a promising cathode material for possible use in flexible battery electrodes, but it remains limited by low Li$^{\mathrm{+}}$ diffusion coefficient and electronic conductivity, severe volumetric changes upon cycling, and limited mechanical flexibility. Here, we demonstrate a route to address these challenges by blending a diblock copolymer bearing electron- and ion-conducting blocks, poly(3-hexylthiophene)-\textit{block}-poly(ethyleneoxide) (P3HT-$b$-PEO), with V$_{\mathrm{2}}$O$_{\mathrm{5}}$ to form a mechanically flexible, electro-mechanically stable hybrid electrode. V$_{\mathrm{2}}$O$_{\mathrm{5}}$ layers were arranged parallel in brick-and-mortar-like fashion held together by the P3HT-$b$-PEO binder. This unique structure significantly enhances mechanical flexibility, toughness and cyclability without sacrificing capacity. Electrodes comprised of 10 wt{\%} polymer have unusually high toughness (293 kJ/m$^{\mathrm{3}})$ and specific energy (530 Wh/kg), both higher than reduced graphene oxide paper electrodes. [Preview Abstract] |
Monday, March 14, 2016 1:03PM - 1:15PM |
B33.00008: Effects of plasticization on ionic conductivity enhancement of crosslinked polymer electrolyte membrane Ruixuan He, Thein Kyu Glass transition temperatures (Tg) of solid polymer electrolyte membranes (PEM), comprised of polyethylene glycol diacrylate (PEGDA) prepolymer, lithium bis(trifluoromethanesulfonyl) imide (LiTFSI) salt, and succinonitrile (SCN) plasticizer, were systematically examined before and after crosslinking in the isotropic region guided by their ternary phase diagram. With increasing LiTFSI concentration, the Tg of uncured binary PEGDA/LiTFSI mixture increases drastically due to molecular complexation between lithium cation and ether oxygen, but ionic conductivity is very low (\textless 10-6 S cm-1). Upon curing, this Tg increases and further reduces ionic conductivity. Upon adding SCN plasticizer, the Tg of PEM has significantly decreased to -60 oC and ionic conductivity also increased to the superionic conductor level of 10-3 S cm-1. The analysis of ionic conductivity vs. Tg behavior by Vogel-Tamman-Fulcher(VTF) equation revealed that this ionic conductivity enhancement is due to SCN plasticization resulting in lowering the network Tg as well as lowering the activation energy. Supported by NSF-DMR 1161070. [Preview Abstract] |
Monday, March 14, 2016 1:15PM - 1:27PM |
B33.00009: Atomistic Simulations of Ternary Polymer Electrolytes Containing Ionic Liquids: Ion Transport and Viscoelastic Behavior Santosh Mogurampelly, Venkat Ganesan Influence of the BMIMPF$_6$ ionic liquid on ion transport and viscoelastic properties of ternary polymer electrolytes containing polyethylene oxide solvated with LiPF$_6$ salt and the underlying mechanisms are investigated. By employing atomistic molecular dynamics and trajectory extended kinetic Monte Carlo simulation techniques, we observe enhanced ionic mobilities and conductivities of the PEOLiPF$_6$-BMIMPF$_6$ ternary electrolytes upon the addition ionic liquid into the PEOLiPF$_6$ binary electrolyte. The dispersion of the BMIMPF$_6$ ionic liquid into the PEOLiPF$_6$ electrolyte is found to (a) promote dissociation of existing LiPF$_6$ ion-pairs and (b) slightly accelerate the polymer segmental dynamics. Together, these effects are observed to collectively give rise to an increase in ionic mobilities and conductivities of the ternary polymer electrolyte. On the other hand, Rouse analysis reveals that the storage and loss modulus of the ternary polymer electrolytes are coupled to their ion conducting properties. [Preview Abstract] |
Monday, March 14, 2016 1:27PM - 1:39PM |
B33.00010: Effects of cation and anion solvation on ion transport in functionalized perfluoropolyethers electrolytes Ksenia Timachova, Mahati Chintapalli, Kevin Olsen, Joseph DeSimone, Nitash Balsara Advances in polymer electrolytes for use in lithium batteries have been limited by the incorporation of selective lithium binding groups that provide necessary solvation for the lithium but ultimately restrict the mobility of the lithium ions relative to anions. Perfluoropolyether electrolytes (PFPE) are a new class of nonflammable liquid polymer electrolytes that have been functionalized with solvating groups for both lithium ions and fluorinated anions. PFPEs with different endgroups mixed with LiN(SO$_{\mathrm{2}}$CF$_{\mathrm{3}})_{\mathrm{2}}$ salt have shown substantial differences in conductivity and allows us to investigate the effects of varying solvating environments on ion transport. To study the independent motion of cations and anions in these systems, the individual diffusion coefficients of the Li$+$ and (SO$_{\mathrm{2}}$CF$_{\mathrm{3}})_{\mathrm{2}}$- ions were measured using pulsed-field gradient nuclear magnetic resonance (PFG-NMR).~Comparing conductivity calculated using these diffusion coefficients with electrochemical measurements yields an estimation for the number of charge carrier in the system. The amount of salt dissociation, not the mobility of the salt, is the primary driver of differences in electrochemical conductivities between PFPEs with different solvating groups. [Preview Abstract] |
Monday, March 14, 2016 1:39PM - 1:51PM |
B33.00011: Aggregate-mediated charge transport in ionomeric electrolytes Keran Lu, Janna Maranas, Scott Milner Polymers such PEO can conduct ions, and have been studied as possible replacements for organic liquid electrolytes in rechargeable metal-ion batteries. More generally, fast room-temperature ionic conduction has been reported for a variety of materials, from liquids to crystalline solids. Unfortunately, polymer electrolytes generally have limited conductivity; these polymers are too viscous to have fast ion diffusion like liquids, and too unstructured to promote cooperative transport like crystalline solids. Ionomers are polymer electrolytes in which ionic groups are covalently bound to the polymer backbone, neutralized by free counterions. These materials also conduct ions, and can exhibit strong ionic aggregation. Using coarse-grained molecular dynamics, we explore the forces driving ionic aggregation, and describe the role ion aggregates have in mediating charge transport. The aggregates are string-like such that ions typically have two neighbors. We find ion aggregates self-assemble like worm-like micelles. Excess charge, or free ions, occasionally coordinate with aggregates and are transported along the chain in a Grotthuss-like mechanism. We propose that controlling ionomer aggregate structure through materials design can enhance cooperative ion transport. [Preview Abstract] |
Monday, March 14, 2016 1:51PM - 2:03PM |
B33.00012: Versatile cation transport in imidazolium based polymerized ionic liquids Christopher Evans, Rachel Segalman Polymerized ionic liquids (PIL) with tethered imidazolium groups are able to conduct a diverse array of cations relevant for energy applications. The well-known complexation of imidazolium with transition metals is exploited to bind ions such as H$+$, Li$^{\mathrm{+}}$, Cu$^{\mathrm{2+}}$, and Ni$^{\mathrm{2+}}$ by doping the neutral PIL with the appropriate Cation-TFSI$^{\mathrm{-}}$ salt. Conductivities were first determined via AC impedance indicating that H$^{\mathrm{+}}$ salts lead to the highest conductivity (due to low ion mass and potential Grotthus mechanism) followed by Cu$^{\mathrm{2+}}$, Li$^{\mathrm{+}}$, Ag$^{\mathrm{+}}$, and Ni$^{\mathrm{2+}}$. The equilibrium constant for imidazolium complexation is larger for Cu$^{\mathrm{2+}}$ relative to Li-, Ag-, and Ni-imidazolium complexes leading to greater salt dissociation and higher conductivities. For LiTFSI and CuTFSI$_{\mathrm{2\thinspace }}$salts, metallic lithium or copper electrodes were employed in battery cells to pass a steady DC current and confirm that the cations are in fact carrying current. Interestingly, the divalent Cu$^{\mathrm{2+}}$ also ionically crosslinks the polymer leading to a plateau in the viscosity. Thus, divalent ions provide an unique route to high conductivity, high modulus polymeric electrolytes. Future studies involving ZnTFSI$_{\mathrm{2}}$ and MgTFSI$_{\mathrm{2}}$ for battery applications are proposed to examine how versatile the PIL platform is for cation transport. [Preview Abstract] |
Monday, March 14, 2016 2:03PM - 2:15PM |
B33.00013: Ion conduction in high ion content PEO-based ionomers. David Caldwell II, Janna Maranas Solid Polymer Electrolytes (SPEs) can enable the design of batteries that are safer and have higher capacity than batteries with traditional volatile organic electrolytes. The current limitation for SPEs is their low conductivity, resulting from a conduction mechanism strongly coupled to the dynamics of the polymer host matrix. Our previous work indicated the possibility of a conduction mechanism through the use of ion aggregates. In order to investigate this mechanism, we performed a series of molecular dynamics simulations of PEO-based ionomers at high ion content. Our results indicate that conduction through ion aggregates are partially decoupled from polymer dynamics and could enable the development of higher conductive SPEs. [Preview Abstract] |
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