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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Computationally Assisted Design of Ion-conducting Polymers for Anion Exchange Membrane Fuel Cells (2nd Year Report) [Slides]

Phosphonated polymers have been proposed as proton conductors for fuel cells; however, the anhydride formation of phosphonic acid functional groups lowers proton conductivity and hinders their use in fuel cell applications. We used calculations to support this hypothesis by correlating calculated Gibbs free energies for the formation of the anhydride with pK values of the corresponding acid. The results showed that stronger acids are less likely to form an anhydride even at elevated temperatures and supported the design of a new polymer and the high-temperature proton exchange membrane fuel cell (HT-PEMFC) that outperformed other state-of-the-art HT-PEMFCs.

30 DIRECT ENERGY CONVERSION↗
DOE OSTI2020

Improved Single-Ion Conductivity of Polymer Electrolyte via Accelerated Segmental Dynamics

Single-ion conducting polymer electrolytes (SICPEs) have many advantages for solid-state battery applications, while low conductivities remain the bottleneck for their practical applications. In this paper, a strategy that can significantly improve the ionic conductivity of SICPEs based on the concept of accelerated segmental dynamics was demonstrated by the evaluation of the thermal property, rheological behavior, morphology analysis, molecular dynamics simulation, and conductivity performance. With both “soft” poly(dimethylsiloxane) (PDMS) backbone and poly(ethylene glycol) (PEG) side chains, the obtained SICPE possesses faster segmental relaxation and higher lithium-ion conductivity. With lithium “transference” number close to unity, the obtained SICPE also shows excellent electrochemical stability against lithium metal electrodes. The clear relationship established between the segmental dynamics of polymer electrolyte and its ionic conductivity should contribute to achieve a solid electrolyte with improved ionic conductivity toward the next-generation solid-state battery.

Segmental Dynamics↗
DOE OSTI2021

Dependence of Linker Length and Composition on Ionic Conductivity and Lithium Deposition in Single-Ion Conducting Network Polymers

In this report, single-ion conducting electrolytes stand as promising alternatives to state-of-the-Art electrolytes in lithium batteries, although a single-ion conducting material with high Li + conductivity, stability in contact with lithium, and suitable mechanical properties has been slow to emerge. Here, we describe the synthesis of a series of single-ion conducting network polymers from the reaction of tetrakis(4-(chloromethyl)-2,3,5,6-Tetrafluorophenyl)borate with oligoethylene glycoxide linkers Li 2 O[(CH 2 CH 2 )O] n (n = 1, 2, 3, 9, and 22). Polymers with the longest linkers (n = 9 and 22; ANP-9 and ANP-10, respectively) form materials with conductivities of ~ 10 -6 S cm -1 at 100 °C. With the addition of 65 wt % propylene carbonate (PC), all the network polymers in the series exhibit high conductivities at ambient temperatures, with the n = 1 material (ANP-6) achieving a bulk ionic conductivity of 2.5 x 10 -4 S cm -1 at 25 °C. More conductive single-ion conducting gels could be prepared by using the less coordinating pentanediol dilithium salt as a linker (ANP-11; σ = 3.5 x 10 -4 S cm -1 at 25 °C), although this material exhibited a surprisingly high interfacial resistance in contact with a lithium electrode. In contrast, the gel formed with ANP-6 is notably stable in contact with metallic lithium electrodes, displays a lithium-ion transference number of unity, and boasts a wide electrochemical stability window of greater than 4.5 V. Temperature-dependent ac impedance analysis reveals that the ionic conductivity of this material-and likely the other gels in the series-matches closely to a Vogel-Tamman-Fulcher temperature model.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Impact of Side Chain Chemistry on Lithium Transport in Mixed Ion–Electron-Conducting Polymers

We discuss how typical design strategies for mixed ion-electron conduction in polymers have focused on overall ionic conductivity, without specificity for anion vs. cation conduction. Here, we demonstrate that side chain chemistry can be used to control Li+ conductivity in semiconducting polymers. This design principle is significant for applications which require Li+ specific transport, such as Li-ion batteries. We show that a polythiophene functionalized with an ionic liquid side chain demonstrates higher conductivity and lithium transference than a more commonly studied ether-functionalized P3AT derivative. Poly(3-(6’-(N-methylimidazolium) hexyl)thiophene TFSI–) (P3HT-Im+TFSI–) can solvate and conduct ions up to salt concentrations of r=1.0 (where r = [moles of salt]/[moles of monomer]) while achieving ionic conductivity of ≈10–3 S/cm at 80°C, and a lithium transference number of 0.36. On the other hand, poly(3¬-(methoxyethoxyethoxymethyl) thiophene) (P3MEEMT) shows a peak conductivity of ≈10–5 S/cm at r=0.05 and 80°C, with near zero lithium transport. This work shows that multiple high dielectric moieties can be used to drive ion conduction in semiconducting polymers, but diffuse, cationic side chains such as imidazolium are preferred for Li-ion conduction.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Helical Covalent Polymers with Unidirectional Ion Channels as Single Lithium-Ion Conducting Electrolytes

Single-ion conducting polymer electrolytes have attracted great attention as safe alternatives to liquid electrolytes in high energy density lithium-ion batteries. Herein, we report the first example of a crystalline anionic helical polymer as a single lithium-ion conducting solid polymer electrolyte (SPE). Single-crystal X-ray analysis shows that the polymer folds into densely packed double helices, with bundles of unidirectional negatively charged channels formed that can facilitate lithium-ion transportation. Such a helical covalent polymer ( HCP) exhibits excellent room temperature lithium-ion conductivity (1.2 x 10 -3 S cm -1 ) in the absence of external lithium salts, a high transference number (0.84), low activation energy (0.14 eV), and a wide electrochemical stability window (0.2-5 V). We found that nonflammable, nonvolatile ionic liquid can serve as a solvating medium and excellent conductivity enhancer (>1000 times increase). These ion-conducting properties are comparable to the best polyethylene oxide-based polymer electrolytes mixed with lithium salts. Finally, we show that the solvated HCP SPE enables the reversible cycling of an all-solid-state cell prepared with a high-voltage NMC 811 cathode. Our study opens up new possibilities for developing next-generation high-performance solid-state electrolytes.

25 ENERGY STORAGE↗
DOE OSTI2023

Tuning Transport via Interaction Strength in Cationic Conjugated Polyelectrolytes

Tuning polymer-ion interaction strength is critical for balancing ion solvation and transport in solid polymer electrolytes for battery applications. In mixed Li + /electron conducting systems for improved battery binders, the design space is further complicated by seemingly opposing design rules for electron and ion conducting polymers. Conjugated polymers functionalized with cationic side chains have demonstrated high ionic conductivity, lithium transport, and electronic conductivity by combining long-range polymer ordering with diffuse ion interactions. Herein, we demonstrate a family of mixed conducting polythiophenes functionalized with a range of cationic side chains, namely imidazolium, trimethylammonium, and ammonium groups. The strength of ionic interactions and structure of the side chains govern lithium-selective transport, resulting in high Li + conductivity (~10 –4 S/cm at 80 °C) and electronic conductivity. The more diffuse imidazolium ion affords labile ionic interactions, resulting in higher lithium transference than the other cations studied. Electronic conductivity is also higher in the imidazolium system, stemming from the ability of the planar side chains to stack while also accommodating the bulky TFSI – counterions. Finally, these results demonstrate the importance of interaction strength in ion transport while also indicating that the physical structure of the side chain has an impact on electronic conduction. The imidazolium group strikes a balance, achieving superior properties across all metrics.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Perspectives for Polymer Electrolytes: A View from Fundamentals of Ionic Conductivity

We present a brief overview of current developments in the field of polymer electrolytes, with the focus on single-ion conducting polymers. The latter have significant advantages relative to electrolytes with dual-ion conductivity for use in energy storage devices. First we discuss various mechanisms of ionic conductivity in polymers and fundamental limitations imposed by these mechanisms. We also emphasize the role of ion–ion correlations in conductivity that are not negligible in concentrated and semidilute ionic systems. Next we discuss several classes of polymer electrolytes (gels, block copolymers, and composites) that are already employed or have good potential to be employed in current battery technologies. At the end we discuss perspectives for the design of dry single-ion conducting polymer electrolytes with required room temperature conductivity.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

A review of composite polymer-ceramic electrolytes for lithium batteries

All solid-state lithium batteries are garnering attention in both academia and industry. Lithium-ion conductive polymers and lithium-ion conductive ceramics are the two major classes of solid electrolytes that have prevalently been pursued for many years. However, each of them has its own advantages and disadvantages. One approach to overcome the disadvantages and get the best out of each of those materials is a solid composite electrolyte that combines the advantages of inorganic ceramic electrolytes and solid polymer electrolytes. Such composite electrolytes can offer acceptable ionic conductivity, high mechanical strength, and favorable interfacial contact with electrodes, which can greatly improve the electrochemical performance of all-solid-state batteries compared to cells based on a polymer electrolyte alone or a ceramic electrolyte alone. We present in this review the state-of-the-art composite polymer-ceramic electrolytes in view of their electrochemical and physical properties for the applications in lithium batteries. The review mainly encompasses the polymer matrices, various ceramic filler materials, and the polymer/ceramics composite systems. Specifically, the structures, ionic conductivities, electrochemical/chemical stabilities, and fabrications of solid composite electrolytes are discussed in-depth. On the basis of previous work, a perspective on future research directions is highlighted for developing high-performance composite polymer-ceramic electrolytes.

25 ENERGY STORAGE↗
DOE OSTI2024

Selective ion transport through hydrated micropores in polymer membranes

Abstract Ion-conducting polymer membranes are essential in many separation processes and electrochemical devices, including electrodialysis 1 , redox flow batteries 2 , fuel cells 3 and electrolysers 4,5 . Controlling ion transport and selectivity in these membranes largely hinges on the manipulation of pore size. Although membrane pore structures can be designed in the dry state 6 , they are redefined upon hydration owing to swelling in electrolyte solutions. Strategies to control pore hydration and a deeper understanding of pore structure evolution are vital for accurate pore size tuning. Here we report polymer membranes containing pendant groups of varying hydrophobicity, strategically positioned near charged groups to regulate their hydration capacity and pore swelling. Modulation of the hydrated micropore size (less than two nanometres) enables direct control over water and ion transport across broad length scales, as quantified by spectroscopic and computational methods. Ion selectivity improves in hydration-restrained pores created by more hydrophobic pendant groups. These highly interconnected ion transport channels, with tuned pore gate sizes, show higher ionic conductivity and orders-of-magnitude lower permeation rates of redox-active species compared with conventional membranes, enabling stable cycling of energy-dense aqueous organic redox flow batteries. This pore size tailoring approach provides a promising avenue to membranes with precisely controlled ionic and molecular transport functions.

Science & Technology - Other Topics↗
DOE OSTI2020

Quantifying Single-Ion Transport in Percolated Ionic Aggregates of Polymer Melts

Single-ion conducting polymers such as ionomers are promising battery electrolyte materials, but it is critical to understand how rates and mechanisms of free cation transport depend on the nanoscale aggregation of cations and polymer-bound anions. We perform coarse-grained molecular dynamics simulations of ionomer melts to understand cation mobility as a function of polymer architecture, background relative permittivity, and corresponding ionic aggregate morphology. In systems exhibiting percolated ionic aggregates, cations diffuse via stepping motions along the ionic aggregates. These diffusivities can be quantitatively predicted by calculating the lifetimes of continuous association between oppositely charged ions, which equal the time scales of the stepping (diffusive) motions. In contrast, predicting cation diffusivity for systems with isolated ionic aggregates requires another time scale. Finally, our results suggest that to improve conductivity the Coulombic interaction strength should be strong enough to favor percolated aggregates but weak enough to facilitate ion dissociation.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2026

Tuning Anion Composition and Mobility to Balance Ionic Conductivity and Cation Selectivity in Solid Polymer Electrolytes

Solid polymer electrolytes (SPEs) offer a promising route toward safe and high-performance electrochemical energy storage, yet a fundamental challenge in SPEs involves improving ionic conductivity while maintaining selective cation transport. The hurdle exists because ion transport is typically coupled closely to polymer segmental dynamics. Herein, a glassy single-ion-conducting polymer, poly[lithium sulfonyl(trifluoromethane sulfonyl)imide methacrylate] (PLiMTFSI), in which the anions were tethered to the polymer, was blended with a flexible polymer, poly(oligo-oxyethylene methyl ether methacrylate) (POEM), and a series of small-molecule lithium salts, in which the anions were untethered [lithium bis(trifluoromethane­sulfonyl)imide (LiTFSI), lithium bis(fluorosulfonyl)imide (LiFSI), lithium trifluoromethanesulfonate (LiTf), or lithium perchlorate (LiClO 4 )]. The impact of salt anion volume and tethered-to-untethered anion ratio on the ion conduction behavior and thermal properties of blend electrolytes was investigated. In some cases, conductivity could be enhanced through this ternary blend approach. For example, a POEM-based polymer blend containing a bulky salt anion (TFSI⁻) and an equimolar mixture of PLiMTFSI and LiTFSI exhibited a Li + conductivity (4.8×10 -4 S/cm) an order of magnitude higher than that of a comparable POEM / LiTFSI system (6.3×10 -5 S/cm) at 100 °C. This enhancement was attributed to a more than ninefold increase in lithium transference number (0.66 in the ternary blend vs. 0.07 in POEM / LiTFSI). Overall, this study highlights the potential for tuning anion composition and mobility to achieve relatively high ionic conductivities and maintain selective cation transport in SPEs, offering a pathway to enable batteries that tolerate elevated temperatures.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗