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Zhang Z, Marioni N, Sachar HS, Ganesan V. Polymer Architecture-Induced Trade-off between Conductivities and Transference Numbers in Salt-Doped Polymeric Ionic Liquids. ACS Macro Lett 2023; 12:1351-1357. [PMID: 37728528 DOI: 10.1021/acsmacrolett.3c00376] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 09/21/2023]
Abstract
Recent experiments have demonstrated that polymeric ionic liquids that share the same cation and anion but possess different architectures can exhibit markedly different conductivity and transference number characteristics when doped with lithium salt. In this study, we used atomistic molecular simulations on polymer chemistries inspired by the experiments to probe the mechanistic origins underlying the competition between conductivity and transference numbers. Our results indicate that the architecture of the polycationic ionic liquid plays a subtle but crucial role in modulating the anion-cation interactions, especially their dynamical coordination characteristics. Chemistries leading to longer-lived anion-cation coordinations relative to lithium-anion coordinations lead to lower conductivities and higher transference numbers. Our results suggest that higher conductivities are accompanied by lower transference numbers and vice versa, revealing that alternative approaches may need to be considered to break this trade-off in salt-doped polyILs.
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Affiliation(s)
- Zidan Zhang
- McKetta Department of Chemical Engineering, University of Texas at Austin, Austin, Texas 78712, United States
| | - Nico Marioni
- McKetta Department of Chemical Engineering, University of Texas at Austin, Austin, Texas 78712, United States
| | - Harnoor S Sachar
- McKetta Department of Chemical Engineering, University of Texas at Austin, Austin, Texas 78712, United States
| | - Venkat Ganesan
- McKetta Department of Chemical Engineering, University of Texas at Austin, Austin, Texas 78712, United States
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2
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He F, Xue B, Zhao X, Yin J. Electrorheological effect and dielectric properties of Poly(ionic liquid) microspheres with different length of alkyl chain spacer between ion pair and backbone. POLYMER 2023. [DOI: 10.1016/j.polymer.2023.125714] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
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3
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Qu M, Li S, Chen J, Xiao Y, Xiao J. Ion Transport in the EMITFSI/PVDF System at Different Temperatures: A Molecular Dynamics Simulation. ACS OMEGA 2022; 7:9333-9342. [PMID: 35356691 PMCID: PMC8945056 DOI: 10.1021/acsomega.1c06160] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/03/2021] [Accepted: 02/02/2022] [Indexed: 05/13/2023]
Abstract
We used all-atom molecular dynamics simulations to study the ion transport in the 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide/poly(vinylidene fluoride) (EMITFSI/PVDF) system with 40.05 wt % EMITFSI at different temperatures. The glass-transition temperature (T g = 204 K) of this system shows a good agreement with the experimental value (200 K). With the increase of temperature, the peaks of the pair correlation function show an increasing trend. Interestingly, the coordination numbers of ion pairs and the degree of independent ion motion are mainly affected by the binding energy between ion pairs as the temperature increases. In addition, the ion transport properties with increasing temperature can be studied by the ion-pair relaxation times, ion-pair lifetimes, and diffusion coefficients. The simulation results illustrate that the ion transport is intensified. Especially, the cations can always diffuse faster than the anions. The power law shows that mobilities of anions and cations are seen to exhibit a "superionic" behavior. With the increase of temperature, transference numbers of anions decrease first and then increase and transference numbers of cations show the opposite changes; ionic conductivity increases gradually; and viscosity decreases gradually, indicating that the diffusion resistance of ions decreases. In general, after adding PVDF into the EMITFSI system, the glass-transition temperature and viscosity increase, the ionic conductivity and degree of independent ion motion decrease, and diffusion coefficients of cations decrease faster than those of the anions.
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Affiliation(s)
- Minghe Qu
- Molecules
and Materials Computation Institute, School of Chemistry and Chemical
Engineering, Nanjing University of Science
and Technology, Nanjing 210094, P. R. China
| | - Shenshen Li
- Molecules
and Materials Computation Institute, School of Chemistry and Chemical
Engineering, Nanjing University of Science
and Technology, Nanjing 210094, P. R. China
| | - Jian Chen
- Chuannan
Machinery Manufacturing Plant, Luzhou 646000, P. R. China
| | - Yunqin Xiao
- Molecules
and Materials Computation Institute, School of Chemistry and Chemical
Engineering, Nanjing University of Science
and Technology, Nanjing 210094, P. R. China
- Science
and Technology on Aerospace Chemical Power Laboratory, Hubei Institute of Aerospace Chemical Technology, Xiangyang 441003, P. R. China
| | - Jijun Xiao
- Molecules
and Materials Computation Institute, School of Chemistry and Chemical
Engineering, Nanjing University of Science
and Technology, Nanjing 210094, P. R. China
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4
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Zhang Z, Lin D, Ganesan V. Mechanisms of ion transport in lithium salt‐doped polymeric ionic liquid electrolytes at higher salt concentrations. JOURNAL OF POLYMER SCIENCE 2021. [DOI: 10.1002/pol.20210737] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Affiliation(s)
- Zidan Zhang
- McKetta Department of Chemical Engineering University of Texas at Austin Austin Texas USA
| | - Dachey Lin
- McKetta Department of Chemical Engineering University of Texas at Austin Austin Texas USA
| | - Venkat Ganesan
- McKetta Department of Chemical Engineering University of Texas at Austin Austin Texas USA
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5
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Polarization of ionic liquid and polymer and its implications for polymerized ionic liquids: An overview towards a new theory and simulation. JOURNAL OF POLYMER SCIENCE 2021. [DOI: 10.1002/pol.20210330] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
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6
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Zhang Z, Krajniak J, Ganesan V. A Multiscale Simulation Study of Influence of Morphology on Ion Transport in Block Copolymeric Ionic Liquids. Macromolecules 2021. [DOI: 10.1021/acs.macromol.1c00025] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Affiliation(s)
- Zidan Zhang
- McKetta Department of Chemical Engineering, University of Texas at Austin, Austin, Texas 78712, United States
| | - Jakub Krajniak
- Independent researcher, os. Kosmonautow 13/56, 61-631 Poznan, Poland
| | - Venkat Ganesan
- McKetta Department of Chemical Engineering, University of Texas at Austin, Austin, Texas 78712, United States
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7
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Zhao Q, Evans CM. Effect of Molecular Weight on Viscosity Scaling and Ion Transport in Linear Polymerized Ionic Liquids. Macromolecules 2021. [DOI: 10.1021/acs.macromol.0c02801] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Affiliation(s)
- Qiujie Zhao
- Department of Materials Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, United States
| | - Christopher M. Evans
- Department of Materials Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, United States
- Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, United States
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8
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Liu H, Luo X, Sokolov AP, Paddison SJ. Quantitative Evidence of Mobile Ion Hopping in Polymerized Ionic Liquids. J Phys Chem B 2021; 125:372-381. [PMID: 33393762 DOI: 10.1021/acs.jpcb.0c06916] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Atomistic molecular dynamics simulations were performed, and an extensive set of analyses were undertaken to understand the ion transport mechanism in the polymerized ionic liquid poly(C2VIm)Tf2N. The ion hopping events were investigated at different time scales. Ion hopping was examined by monitoring the instantaneous cation-anion association and dissociation. Ion diffusion was subsequently evaluated with correlation functions and the calculation of relaxation times at different time scales. Dynamical heterogeneity in the mobility of the ions was observed with only a small portion of the anions classified as fast mobile ions. The mobile ions were characterized as the ones traveling farther than a certain distance during a characteristic period, which was much longer than the time scale of the instant ion pair dissociation. Effective hopping of the mobile ions contributed to the diffusivity which was dominated by interchain hopping and generally facilitated with five associating cations from two different polymer chains. Mobile anions had relatively fewer associating cations from more associating chains than immobile anions. The stringlike cooperative motion was observed in the mobile anions. The string length was determined to decrease with increasing temperature. These findings provided an in-depth understanding of the ion transport in polymerized ionic liquids and important information for the rational design of novel materials.
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Affiliation(s)
- Hongjun Liu
- Department of Chemical and Biomolecular Engineering, University of Tennessee, Knoxville, Tennessee 37996, United States
| | - Xubo Luo
- Department of Chemical and Biomolecular Engineering, University of Tennessee, Knoxville, Tennessee 37996, United States
| | - Alexei P Sokolov
- Department of Chemistry, University of Tennessee, Knoxville, Tennessee 37996, United States.,Chemical Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, United States
| | - Stephen J Paddison
- Department of Chemical and Biomolecular Engineering, University of Tennessee, Knoxville, Tennessee 37996, United States
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9
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Chen TL, Sun R, Willis C, Krutzer B, Morgan BF, Beyer FL, Han KS, Murugesan V, Elabd YA. Impact of ionic liquid on lithium ion battery with a solid poly(ionic liquid) pentablock terpolymer as electrolyte and separator. POLYMER 2020. [DOI: 10.1016/j.polymer.2020.122975] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
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10
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Abstract
Solid-state polymer electrolytes and high-concentration liquid electrolytes, such as water-in-salt electrolytes and ionic liquids, are emerging materials to replace the flammable organic electrolytes widely used in industrial lithium-ion batteries. Extensive efforts have been made to understand the ion transport mechanisms and optimize the ion transport properties. This perspective reviews the current understanding of the ion transport and polymer dynamics in liquid and polymer electrolytes, comparing the similarities and differences in the two types of electrolytes. Combining recent experimental and theoretical findings, we attempt to connect and explain ion transport mechanisms in different types of small-molecule and polymer electrolytes from a theoretical perspective, linking the macroscopic transport coefficients to the microscopic, molecular properties such as the solvation environment of the ions, salt concentration, solvent/polymer molecular weight, ion pairing, and correlated ion motion. We emphasize universal features in the ion transport and polymer dynamics by highlighting the relevant time and length scales. Several outstanding questions and anticipated developments for electrolyte design are discussed, including the negative transference number, control of ion transport through precision synthesis, and development of predictive multiscale modeling approaches.
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Affiliation(s)
- Chang Yun Son
- Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California 91125, USA
| | - Zhen-Gang Wang
- Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California 91125, USA
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11
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Zhang Z, Nasrabadi AT, Aryal D, Ganesan V. Mechanisms of Ion Transport in Lithium Salt-Doped Polymeric Ionic Liquid Electrolytes. Macromolecules 2020. [DOI: 10.1021/acs.macromol.0c01444] [Citation(s) in RCA: 16] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Affiliation(s)
- Zidan Zhang
- McKetta Department of Chemical Engineering, University of Texas at Austin, Austin, Texas 78712, United States
| | - Amir T. Nasrabadi
- McKetta Department of Chemical Engineering, University of Texas at Austin, Austin, Texas 78712, United States
| | - Dipak Aryal
- McKetta Department of Chemical Engineering, University of Texas at Austin, Austin, Texas 78712, United States
| | - Venkat Ganesan
- McKetta Department of Chemical Engineering, University of Texas at Austin, Austin, Texas 78712, United States
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12
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Choi UH, Price TL, Schoonover DV, Gibson HW, Colby RH. The Effect of Oligo(oxyethylene) Moieties on Ion Conduction and Dielectric Properties of Norbornene-Based Imidazolium Tf 2N Ionic Liquid Monomers. Macromolecules 2020. [DOI: 10.1021/acs.macromol.9b02420] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- U Hyeok Choi
- Department of Polymer Science and Engineering, Inha University, Incheon 22212, Korea
| | - Terry L. Price
- Department of Chemistry, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061, United States
| | - Daniel V. Schoonover
- Department of Chemistry, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061, United States
| | - Harry W. Gibson
- Department of Chemistry, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061, United States
| | - Ralph H. Colby
- Department of Materials Science and Engineering, Pennsylvania State University, University Park, Pennsylvania 16802, United States
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13
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Keith JR, Ganesan V. Ion transport mechanisms in salt‐doped polymerized zwitterionic electrolytes. JOURNAL OF POLYMER SCIENCE 2020. [DOI: 10.1002/pol.20190099] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
Affiliation(s)
- Jordan R. Keith
- Department of Chemical EngineeringUniversity of Texas at Austin Austin Texas 78712
| | - Venkat Ganesan
- Department of Chemical EngineeringUniversity of Texas at Austin Austin Texas 78712
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14
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Keith JR, Ganesan V. Ion transport in backbone-embedded polymerized ionic liquids. J Chem Phys 2019; 151:124902. [PMID: 31575176 DOI: 10.1063/1.5121436] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Abstract
We use atomistic computer simulations to examine ion-transport phenomena for backbone polymerized cationic liquids with bistrifluoromethylesulfonylimide (TFSI-) counterions. We consider a system in which the polymerized cation moiety is the imidazolium ring and study the structural characteristics and ion mobilities for cases in which the cations are separated by four, six, and eight methylene units on the backbone. A pendant polymerized ionic liquid, 1-butyl-3-vinylimidazolium, is compared to the backbone series across ion coordination and hopping features. The anion diffusivity in backbone polymerized cationic liquids is found to decrease with increasing spacer length, which is shown to result from a decrease in intramolecular and intermolecular hopping frequencies due to an increasing distance separating imidazolium moieties. In comparison with pendant polymerized ionic liquids, we observe that the participation rates of intermolecular hopping events in the backbone polymers far exceed that of the pendant, and the intrapolymeric ionic coordination profile shows the TFSI- of the pendant polymer with a high propensity for coordination by multiple imidazolium, compared with one monomer from a given polymer for the backbone series. Despite these differences, backbone polymerized ionic liquids are seen to possess correlated diffusivity and ion-association relaxation times, in a manner similar to the results observed in past studies for pendant variants.
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Affiliation(s)
- Jordan R Keith
- McKetta Department of Chemical Engineering, University of Texas at Austin, Austin, Texas 78712, USA
| | - Venkat Ganesan
- McKetta Department of Chemical Engineering, University of Texas at Austin, Austin, Texas 78712, USA
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15
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Abbott LJ, Lawson JW. Effects of Side Chain Length on Ionic Aggregation and Dynamics in Polymer Single-Ion Conductors. Macromolecules 2019. [DOI: 10.1021/acs.macromol.9b00415] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
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16
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Zhang Z, Krajniak J, Keith JR, Ganesan V. Mechanisms of Ion Transport in Block Copolymeric Polymerized Ionic Liquids. ACS Macro Lett 2019; 8:1096-1101. [PMID: 35619445 DOI: 10.1021/acsmacrolett.9b00478] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
Abstract
We present the results of a multiscale simulation framework investigating the ion transport mechanisms in multicomponent polymerized ionic liquids. Three different classes of polymeric ionic liquid systems, namely, random copolymers, lamellae forming block copolymers, and homopolymers, are constructed at the coarse-grained scale, and their atomistic counterparts are derived by using a reverse mapping method. Using such a framework, we investigate the influence of morphology on ion transport properties of such polymerized ionic liquids. Our results for ion mobilities are in qualitative agreement with experimental observations. Further analysis of random copolymer and block copolymer systems reveal that the reduced ion mobilities in such systems arise from the influence of architecture and morphology on ion coordination and intramolecular hopping events.
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Affiliation(s)
- Zidan Zhang
- Department of Chemical Engineering, University of Texas at Austin, Austin, Texas 78712, United States
| | - Jakub Krajniak
- Department of Computer Science, Katholieke Universiteit Leuven, Leuven, Belgium
| | - Jordan R Keith
- Department of Chemical Engineering, University of Texas at Austin, Austin, Texas 78712, United States
| | - Venkat Ganesan
- Department of Chemical Engineering, University of Texas at Austin, Austin, Texas 78712, United States
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17
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Zhao Q, Shen C, Halloran KP, Evans CM. Effect of Network Architecture and Linker Polarity on Ion Aggregation and Conductivity in Precise Polymerized Ionic Liquids. ACS Macro Lett 2019; 8:658-663. [PMID: 35619520 DOI: 10.1021/acsmacrolett.9b00293] [Citation(s) in RCA: 21] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
Four polymerized ionic liquids (PILs) were systematically designed to study the effect of polymer architecture and linker polarity on ion aggregation and transport. Specifically, linear and network PILs with the same ammonium cations (Am) and bis(trifluoromethane)sulfonimide (TFSI) anions were prepared by step-growth polymerization, and polarity was tuned by incorporating two precise linkers, either polar tetra(ethylene oxide) (4EO) linker or nonpolar undecyl (C11) linker. The glass transition temperature (Tg) substantially increased with the nonpolar C11 linker or upon cross-linking to form a network. The low wave-vector (q) ion aggregation peak from wide-angle X-ray scattering (WAXS) was not observable in the linear 4EO PIL, while it was most pronounced in the network C11 PIL. The network C11 PIL exhibited the strongest decoupling, where the ionic conductivity at Tg is greater than 1 order of magnitude higher than the other PILs. This systematic comparison suggests that network structure and nonpolar linkers can promote both ion aggregation and ionic conductivity close to Tg.
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18
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Keith JR, Rebello NJ, Cowen BJ, Ganesan V. Influence of Counterion Structure on Conductivity of Polymerized Ionic Liquids. ACS Macro Lett 2019; 8:387-392. [PMID: 35651142 DOI: 10.1021/acsmacrolett.9b00070] [Citation(s) in RCA: 36] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
Abstract
We performed long-time all-atom molecular dynamics simulations of cationic polymerized ionic liquids with eight mobile counterions, systematically varying size and shape to probe their influence on the decoupling of conductivity from polymer segmental dynamics. We demonstrated rigorous identification of the dilatometric glass-transition temperature (Tg) for polymerized ionic liquids using an all-atom force field. Polymer segmental relaxation rates are presumed to be consistent for different materials at the same glass-transition-normalized temperature (Tg/T), allowing us to extract a relative order of decoupling by examining conductivity at the same Tg/T. Size, or ionic volume, cannot fully explain decoupling trends, but within certain geometric and chemical-specific classes, small ions generally show a higher degree of decoupling. This size effect is not universal and appears to be overcome when structural results reveal substantial coordination delocalization. We also reveal a universal inverse correlation between ion-association structural relaxation time and absolute conductivity for these polymerized ionic liquids, supporting the ion-hopping interpretation of ion mobility in polymerized ionic liquids.
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Affiliation(s)
- Jordan R. Keith
- Department of Chemical Engineering, University of Texas at Austin, Austin, Texas 78712, United States
| | - Nathan J. Rebello
- Department of Chemical Engineering, University of Texas at Austin, Austin, Texas 78712, United States
| | - Benjamin J. Cowen
- Sandia National Laboratories, Albuquerque, New Mexico 87185, United States
| | - Venkat Ganesan
- Department of Chemical Engineering, University of Texas at Austin, Austin, Texas 78712, United States
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19
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Paren BA, Raghunathan R, Knudson IJ, Freyer JL, Campos LM, Winey KI. Impact of building block structure on ion transport in cyclopropenium-based polymerized ionic liquids. Polym Chem 2019. [DOI: 10.1039/c9py00396g] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
Cation geometry, size, and polarity all contribute to conductivity in PS-TAC PILs, with highest conductivity from the isopropyl cation geometry.
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Affiliation(s)
- Benjamin A. Paren
- University of Pennsylvania
- Department of Materials Science & Engineering
- Philadelphia
- USA
| | | | | | | | | | - Karen I. Winey
- University of Pennsylvania
- Department of Materials Science & Engineering
- Philadelphia
- USA
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20
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Affiliation(s)
- Santosh Mogurampelly
- Department of Chemical Engineering, University of Texas at Austin, Austin, Texas 78712, United States
- Institute for
Computational Molecular Science (ICMS) and Temple Materials Institute
(TMI), 1925 North 12th St., Philadelphia, Pennsylvania 19122, United States
| | - Venkat Ganesan
- Department of Chemical Engineering, University of Texas at Austin, Austin, Texas 78712, United States
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21
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Wheatle BK, Lynd NA, Ganesan V. Effect of Polymer Polarity on Ion Transport: A Competition between Ion Aggregation and Polymer Segmental Dynamics. ACS Macro Lett 2018; 7:1149-1154. [PMID: 35651266 DOI: 10.1021/acsmacrolett.8b00594] [Citation(s) in RCA: 51] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
In this work, we use computer simulations to demonstrate that there may be limits to which polymer polarity alone can be used to influence the ionic conductivity of salt-doped polymer electrolytes. Specifically, we use coarse-grained molecular dynamics simulations to probe the effect of the polarity of the polymer electrolyte upon ion mobilities and conductivities of dissolved salts. At low polymer polarities, increasing the polymer dielectric constant reduces ionic aggregation and the resultant correlated ionic motion, and increases the ionic conductivity. At higher polymer polarities, polymer-polymer and polymer-ion interactions slows polymer segmental dynamics, leading to a reduction in the conductivity of the electrolyte. As a consequence, ionic conductivity achieves an optimum at an intermediate polymer polarity.
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Affiliation(s)
- Bill K. Wheatle
- McKetta Department of Chemical Engineering, The University of Texas at Austin, Austin, Texas, United States
| | - Nathaniel A. Lynd
- McKetta Department of Chemical Engineering, The University of Texas at Austin, Austin, Texas, United States
| | - Venkat Ganesan
- McKetta Department of Chemical Engineering, The University of Texas at Austin, Austin, Texas, United States
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22
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Keith JR, Mogurampelly S, Aldukhi F, Wheatle BK, Ganesan V. Influence of molecular weight on ion-transport properties of polymeric ionic liquids. Phys Chem Chem Phys 2018; 19:29134-29145. [PMID: 29085931 DOI: 10.1039/c7cp05489k] [Citation(s) in RCA: 35] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
We report the results of atomistic molecular dynamics simulations on polymerized 1-butyl-3-vinylimidazolium-hexafluorophosphate ionic liquids, studying the influence of the polymer molecular weight on the ion mobilities and the mechanisms underlying ion transport, including ion-association dynamics, ion hopping, and ion-polymer coordinations. With an increase in polymer molecular weight, the diffusivity of the hexafluorophosphate (PF6-) counterion decreases and plateaus above seven repeat units. The diffusivity is seen to correlate well with the ion-association structural relaxation time for pure ionic liquids, but becomes more correlated with ion-association lifetimes for larger molecular weight polymers. By analyzing the diffusivity of ions based on coordination structure, we unearth a transport mechanism in which the PF6- moves by "climbing the ladder" while associated with four polymeric cations from two different polymers.
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Affiliation(s)
- Jordan R Keith
- Department of Chemical Engineering, The University of Texas at Austin, Austin, TX, USA.
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