Mechanism of Ion Transport in Amorphous Poly(ethylene oxide)/LiTFSI from Molecular Dynamics Simulations

Borodin, Oleg; Smith, Grant D.

doi:10.1021/ma052277v

Cited by 486 publications

(661 citation statements)

References 34 publications

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“…In particular, three different microscopic transport mechanisms typically found for PEO-based polymer electrolytes 29,[33][34][35] are taken into account, of which one mechanism is composed of two subcontributions. To assess their individual impact on the overall lithium dynamics, each mechanism is quantified by a characteristic time scale (see also sketch in Figure 2): First, the lithium ions diffuse along the backbone of the coordinating PEO chains.…”

Section: Theoretical Backgroundmentioning

confidence: 99%

Improving the Lithium Ion Transport in Polymer Electrolytes by Functionalized Ionic-Liquid Additives: Simulations and Modeling

Diddens

Paillard

Heuer

2017

J. Electrochem. Soc.

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We present a theoretical study combining molecular dynamics (MD) simulations with an analytical lithium ion transport model [Maitra and Heuer, Phys. Rev. Lett. 2007, 98, 227802] to highlight a novel strategy to increase the lithium mobility in polymer electrolytes based on poly(ethylene oxide) (PEO). This is achieved by using a pyrrolidinium-based ionic liquid (IL) where the cation has been chemically functionalized by a short oligoether side chain [von Zamory et al., Phys. Chem. Chem. Phys. 2016, 18(31), 21539] as an additive. Since the oligoether moieties at the pyrrolidinium cations form pronounced coordinations to the lithium ions for sufficiently long side chains, the ions can be detached from the PEO backbone. In this way, a fundamentally new lithium ion transport mechanism is established (shuttling mechanism), in which the lithium dynamics is decoupled from the polymer dynamics, the latter typically being slow under experimental conditions. Based on our simulations, we incorporate this novel mechanism into our existing model, which accurately reproduces the observed lithium dynamics. We demonstrate that the use of oligoether-functionalized IL additives significantly increases the lithium diffusivity. Finally, we show that for experimentally relevant electrolytes containing long polymer chains, an even stronger increase of the lithium mobility can be expected.

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Section: Theoretical Backgroundmentioning

confidence: 99%

Improving the Lithium Ion Transport in Polymer Electrolytes by Functionalized Ionic-Liquid Additives: Simulations and Modeling

Diddens

Paillard

Heuer

2017

J. Electrochem. Soc.

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“…[12][13][14][15][16] The electron-donating groups incorporated into the polymer architecture are responsible for solvating the lithium ion while the fast segmental dynamics promote high ionic conductivities through fluctuation-driven diffusion. [17][18][19] However, Type I polymer electrolytes typically suffer from poor mechanical properties, which is an unfortunate compromise for the fast segmental dynamics. Furthermore, Type I polymer electrolytes have relatively poor transference numbers that reflect the relative diffusion of the ions of opposite charge in the high molecular weight polymer.…”

Section: The 21mentioning

confidence: 99%

“…[17][18][19] However, Type I polymer electrolytes typically suffer from poor mechanical properties, which is an unfortunate compromise for the fast segmental dynamics. Furthermore, Type I polymer electrolytes have relatively poor transference numbers that reflect the relative diffusion of the ions of opposite charge in the high molecular weight polymer.…”

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confidence: 99%

Method of Measuring Salt Transference Numbers in Ion-Selective Membranes

Vardner

Ling

Russell

et al. 2017

J. Electrochem. Soc.

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A technique to measure the cation-transference number of salts in fully hydrated ion-selective membranes has been developed and demonstrated on Nafion 117 for LiCl and Li 2 SO 4 . Dilute solution theory is used to identify experimental conditions that reduce the propagation of uncertainties in membrane properties to transference number estimates. This technique has advantages over commonly used methods, including the elimination of the need for the analysis of electrode potentials in approaches that exploit electroanalytical methods or the need for additional information required to reconcile NMR-based methods with the bulk transport property. It additionally allows for numerous measurements per day and offers the possibility to relate trace measurements of either cations or anions to values of transference number. For LiCl both modes of the technique were employed; the anion-tracer method is more precise and gives t + = 0.936 ± 0.010. The experimental procedure was repeated using the cation-tracer method for Li 2 SO 4 , and t + = 0.95 ± 0.06 was estimated. The 21 st century presents a key challenge in energy storage due to the intermittency of wind and solar energy sources. Lithium ion batteries, fuel cells, and redox flow batteries are promising technologies for energy storage since they have high energy densities, are environmentally friendly, and have an array of other desirable properties. [1][2][3][4][5][6] Solid electrolytes are ubiquitous for these energy storage systems since they serve the important function of mechanical separation between electrodes. In addition, solid electrolytes circumvent several problems associated with liquid electrolytes such as the leakage of electrolyte solution and the reaction of volatile organic solvents.7 Of the solid electrolytes, polymer electrolytes have garnered the most interest in recent years. [8][9][10][11] These membranes facilitate ionic transport between electrodes, inhibit electron flow between electrodes, prevent direct contact between electrodes, and minimize mixing of the anolyte and catholyte.In recent decades, researchers have sought to understand the relationship between the molecular structure of polymer electrolytes and their performance. These structure-property relationships have been developed for two major types of polymer electrolytes: (I) mixtures of salts in high molecular weight polymers and (II) polymerized ionic liquids (single ion conductors). Polyethylene oxide (PEO), polypropylene oxide (PPO), and 4 poly[bis(methoxy-ethoxyethoxy) phosphazene] (MEEP) are all promising Type I polymer electrolytes.12-16 The electron-donating groups incorporated into the polymer architecture are responsible for solvating the lithium ion while the fast segmental dynamics promote high ionic conductivities through fluctuation-driven diffusion. [17][18][19] However, Type I polymer electrolytes typically suffer from poor mechanical properties, which is an unfortunate compromise for the fast segmental dynamics. Furthermore, Type I polymer electrolytes have relative...

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“…The correlation between free volume and transport of penetrants through membrane is misused in the preparation of membranes used in a wide variety of processes such as gas separation [7] and electrical energy storage [8]. The term free volume generally refers to disordered voids that occur naturally in polymers or membranes with length scales ranging from 0.1 to 1.5 nm [9].…”

Section: Introductionmentioning

confidence: 99%

Proton Conductivity and Free Volume Properties in Per-Fluorinated Sulfonic acid/PTFE Copolymer for Fuel Cell

2017

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The proton conductivity mechanism in per-fluorinated sulfonic acid/PTFE copolymer Fumapem ® membranes for polymer electrolyte membranes has been investigated. Three samples of Fumapem ® F-950, F-1050 and F-14100 membranes with different ion exchange capacity 1.05, 0.95, and 0.71 meq/g, respectively, were used in this study after drying. The o-Ps hole volume size (VF V,Ps) was quantified using the positron annihilation lifetime technique while the proton conductivities (σ) were measured using LCR Bridge as function of temperature. It was found that as the ion exchange capacity increases, the proton conductivity increases and the free volume expands. Temperature dependences of proton conductivity and the o-Ps hole volume size (VF V,Ps) reflect the glass transition temperature of the membrane. A good linear correlation between the reciprocal of the o-Ps hole volume size (1/VF V,Ps) and log(σ) + ∆Ea/2.303kBT , (where ∆Ea is the activation energy, T is the absolute temperature and kB is the Boltzmann constant) at different temperatures indicate that the ionic motion in dry Fumapem ® is governed by the free volume. A linear relationship between the critical hole size γV * i and the ion exchange capacity was also achieved.

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Mechanism of Ion Transport in Amorphous Poly(ethylene oxide)/LiTFSI from Molecular Dynamics Simulations

Cited by 486 publications

References 34 publications

Improving the Lithium Ion Transport in Polymer Electrolytes by Functionalized Ionic-Liquid Additives: Simulations and Modeling

Improving the Lithium Ion Transport in Polymer Electrolytes by Functionalized Ionic-Liquid Additives: Simulations and Modeling

Method of Measuring Salt Transference Numbers in Ion-Selective Membranes

Proton Conductivity and Free Volume Properties in Per-Fluorinated Sulfonic acid/PTFE Copolymer for Fuel Cell

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