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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 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Ion Exchange Gels Allow Organic Electrochemical Transistor Operation with Hydrophobic Polymers in Aqueous Solution

Conjugated-polymer-based organic electrochemical transistors (OECTs) are being studied for applications ranging from biochemical sensing to neural interfaces. While new polymers that interface digital electronics with the aqueous chemistry of life are being developed, the majority of high-performance organic transistor materials are poor at transporting biologically relevant ions. Here, the operating mode of an organic transistor is changed from that of an electrolyte-gated organic field-effect transistor (EGOFET) to that of an OECT by incorporating an ion exchange gel between the active layer and the aqueous electrolyte. This device works by taking up biologically relevant ions from solution and injecting more hydrophobic ions into the active layer. Using poly[2,5-bis(3-tetradecylthiophen-2-yl) thieno[3,2-b]thiophene] as the active layer and a blend of an ionic liquid, 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, and poly(vinylidene fluoride-co-hexafluoropropylene) as the ion exchange gel, four orders of magnitude improvement in device transconductance and a 100-fold increase in kinetics are demonstrated. The ability of the ion-exchange-gel OECT to record biological signals by measuring the action potentials of a Venus flytrap is demonstrated. These results show the possibility of using interface engineering to open up a wider palette of organic semiconductors as OECTs that can be gated by aqueous solutions.

Bischak, Connor G.↗
DOE OSTI2023

Poly(diallylmethylammonium) proton conducting membranes with high ionic conductivity at intermediate temperatures

High temperature proton exchange membrane fuel cells are being lately investigated because of their high energy efficiency, their superior heat/water management, CO tolerance, and electrode reaction kinetics. To further advance this technology, the polymer membrane portfolio and performance should be improved for intermediate or high temperature operation (>100 °C). In this work we present new poly(diallylmethylammonium) proton conducting membranes with high ionic conductivity at 120 °C. First, new protic ionic liquids, hereafter called DAMAH + X - , were synthesized leading to diallylmethylammonium monomers with different counter-anions. By radical cyclopolymerization through thermal and photoinitiation mechanisms, self-standing protic polymeric membranes of poly(diallylmethylammonium X - ) were obtained. Membranes showed good thermal stability (>250 °C) and mechanical properties without the need of additives such as (protic) ionic liquids, solvents or inorganic charges. Great attention was paid to understand the effect of the different counter-anions on the membrane properties. As a general trend, fluorinated anions coming from strong acids confer high ionic conductivity and allow to reduce the hygroscopic properties on the protic polymeric membranes. Proton structural and dynamical stability at different temperatures and humidification conditions were investigated by Neutron Scattering (QENS and NR). The optimized poly(diallylmethylammonium X - ) shows similar ionic conductivity values than Nafion 212 under varying relative humidity conditions at 80 °C. Furthermore, it shows a high ionic conductivity value of 1.9 × 10 -3 Scm -1 at 120 °C under dry conditions.

08 HYDROGEN↗
NASA NTRS2007

Composite Electrolytes for Lithium Batteries: Ionic Liquids in APTES Crosslinked Polymers

Solvent free polymer electrolytes were made consisting of Li(+) and pyrrolidinium salts of trifluoromethanesulfonimide added to a series of hyperbranched poly(ethylene oxide)s (PEO). The polymers were connected by triazine linkages and crosslinked by a sol-gel process to provide mechanical strength. The connecting PEO groups were varied to help understand the effects of polymer structure on electrolyte conductivity in the presence of ionic liquids. Polymers were also made that contain poly(dimethylsiloxane) groups, which provide increased flexibility without interacting with lithium ions. When large amounts of ionic liquid are added, there is little dependence of conductivity on the polymer structure. However, when smaller amounts of ionic liquid are added, the inherent conductivity of the polymer becomes a factor. These electrolytes are more conductive than those made with high molecular weight PEO imbibed with ionic liquids at ambient temperatures, due to the amorphous nature of the polymer.

Tigelaar, Dean M.↗
DOE OSTI2021

Room Temperature to 150 °C Lithium Metal Batteries Enabled by a Rigid Molecular Ionic Composite Electrolyte

Molecular ionic composites (MICs), made from ionic liquids and a rigid-rod polymer poly(2,2'-disulfonyl-4,4'-benzidine terephthalamide) (PBDT), are a new type of rigid gel electrolyte that combine fast ion transport with high thermal stability and mechanical strength. In this work, a MIC electrolyte membrane is prepared that is composed of PBDT, lithium bis(trifluoromethylsulfonyl)imide (LiTFSI), and 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide (Pyr 14 TFSI) in a mass ratio of 10:10:80. The ionic conductivity at 25 °C is 0.56 mS cm –1 with no added flammable/volatile components. Although the polymer content is only 10 wt%, this MIC membrane is rigid with a tensile modulus of 410 MPa at room temperature. The MIC membrane remains stable and rigid at 200 °C with the shear storage modulus (G') only slightly decreasing by 35%. Li/MIC/LiFePO 4 cells demonstrate stable cycling performance over a wide temperature range from 23 to 150 °C. The specific discharge capacity at 100 and 150 °C at 1 C rate exceeds 160 mAh g –1 . The discharge capacity retention is 99% after 50 cycles at 150 °C. Furthermore, this stable battery performance shows that this low polymer content MIC membrane qualifies for use as a solid electrolyte in lithium metal batteries operating over a wide temperature range.

25 ENERGY STORAGE↗
DOE OSTI2021

Solvent-Cast Solid Electrolyte Membranes Based on a Charged Rigid-Rod Polymer and Ionic Liquids

Solid-state electrolytes are attractive for use in electrochemical devices because they remove the need for a flammable liquid electrolyte while contributing to the structural integrity of the device. We have recently developed a class of solid electrolytes, termed molecular ionic composites (MICs), composed of ionic liquids (ILs) and a rigid-rod polyelectrolyte, poly(2,2'-disulfonyl-4,4'-benzidine terephthalamide) (PBDT). MIC materials, originally obtained through an ion-exchange process between IL and PBDT aqueous solution, possess an unprecedented combination of high ionic conductivity, high thermal stability, low flammability and widely tunable tensile storage moduli. Here we present a facile solvent casting method for preparing MIC membranes. These membranes are uniform, flexible, and tough, with tunable composition and thickness (≥ 40 μm). Unlike the previous ion-exchange method, which only allowed incorporation of hydrophilic ILs, we can now incorporate hydrophobic ILs to prepare MIC membranes for, e.g. battery electrolytes. A sodium (Na) metal symmetric cell constructed with a PBDT-Pyr 14 TFSI membrane as the solid electrolyte shows long-term stable cycling (> 500 h.) at 60 °C. Furthermore, the ability to prepare MICs using both hydrophilic and hydrophobic ILs initiates a wider range of MIC materials and broadens the array of applications accessible by MIC membranes.

25 ENERGY STORAGE↗
DOE OSTI2024

Imaging a solvent-swollen polymer gel network by open liquid transmission electron microscopy

Visualizing the network of a solvent-swollen polymer gel remains problematic. To address this challenge, open transmission electron microscopy (TEM) was applied to thin gel films permeated by a nonvolatile ionic liquid. The targeted physical gels were prepared by cooling concentrated solutions of poly(ethylene glycol) in 1-ethyl-3-methyl imidazolium ethyl sulfate [EMIM][EtSO 4 ]. During the cooling, gelation occurred by a frustrated crystallization of the dissolved polymer, leading to a percolated, solvent-permeated semicrystalline network in which nanoscale polymer crystals acted as crosslinks. Crystalline features ranging from ~5 to ~200 nm were observed, with the visible network strands dominantly consisting of long curvilinear crystallites of ~15–20 nm diameter. Nascent spherulites irregularly decorated the network, creating a complex structural hierarchy that complicated analyses. Lacking diffraction contrast, TEM did not visualize the many disordered, fully solvated PEG chains present in the voids between crystals. Finally, recognizing that a network's three dimensionality is ambiguous when assessed through two-dimensional microscopy projections, a small gel region was studied by TEM tomography, revealing a nearly isotropic three-dimensional arrangement of the curvilinear crystallites, which displayed remarkably uniform cylindrical cross sections.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Structural effects of composition tuning in A-site disordered perovskite La0.5Li0.5−xMxTiO3 (M = Na, K) nanorods for fast interfacial transport for solid composite electrolyte design

Polymer-ceramic composite electrolytes (CPE) have emerged as promising replacements for currently used liquid organic electrolytes, which pose as safety hazards, in Li-ion batteries. Limits in conductivity enhancement in CPEs is often attributed to a high resistance for Li-ion transport along the interface due to the incompatibility of the polymer and ceramic phases. A clear understanding of the interfacial structure and how this impacts interfacial Li-ion transport is needed in order to efficiently design a CPE with optimal ionic conductivity. In this study, density functional theory (DFT) calculations, in conjunction with scanning transmission electron microscopy (STEM) and electron energy loss spectroscopy (EELS), are used to unveil the bulk and surface structure of La0.5Li0.5−xMxTiO3 (M = Na, K) (LMTO) nanorods, a newly-reported ceramic system with promising applications in CPEs, and the LMTO interactions with the poly(lithium sulfonyl (trifluoromethane sulfonyl)imide methacrylate) (p(MTFSILi)) polymerized ionic liquid. Substitution of lithium for sodium and potassium onto the A-site perovskite lattice is shown to increase the stability of the preferred pseudocubic perovskite phase because of their increased cation size which allows them to reduce the TiO6 octahedral rotations in the bulk and at the surface. STEM and EELS results show that LMTO nanorods with differing compositions have Ti-enriched (110)-oriented surfaces. Increased sodium and potassium compositions in LMTO is also shown using the DFT calculations to weaken the binding of the lithium atom to the MTFSI unit when LiMTFSI is adsorbed to the LMTO surface. This weakening of lithium binding to the polymer at the LMTO interface indicates that the lithium mobility is increased, correlating to an increase in interfacial Li-ion transport. Overall, this work provides insights into how to tune the interfacial interactions between the polymer (p(MTFSI)) and ceramic (LMTO) for optimal CPE design.

Shepard, Lauren B [Pennsylvania State University, ↗
DOE OSTI2024

Ionic Thermoelectric Generators in Vertical and Planar Topologies Based on Fluorinated Polymer Hybrid Materials with Ionic Liquids

Abstract Ionic thermoelectrics (TEs), in which voltage generation is based on ion migration, are suitable for applications based on their low cost, high flexibility, high ionic conductivity, and wide range of Seebeck coefficients. This work reports on the development of ionic TE materials based on the poly(vinylidene fluoride‐trifluoroethylene), Poly(VDF‐co‐TrFE), as host polymer blended with different contents of the ionic liquid, IL, 1‐ethyl‐3‐methylimidazolium bis(trifluoromethylsulfonyl)imide, [EMIM][TFSI]. The morphology, physico‐chemical, thermal, mechanical, and electrical properties of the samples are evaluated together with the TE response. It is demonstrated that the IL acts as a nucleating agent for polymer crystallization. The mechanical properties and ionic conductivity values are dependent on the IL content. A high room temperature ionic conductivity of 0.008 S cm −1 is obtained for the sample with 60 wt% of [EMIM][TFSI] IL. The TE properties depend on both IL content and device topology‐vertical or planar‐the largest generated voltage range being obtained for the planar topology and the sample with 10 wt% of IL content, characterized by a Seebeck coefficient of 1.2 mV K −1 . Based on the obtained maximum power density of 4.9 µW m −2 , these materials are suitable for a new generation of TE devices.

Pereira, Nelson↗
DOE OSTI2020

Ion Transport and Mechanical Properties of Non-Crystallizable Molecular Ionic Composite Electrolytes

Polymer electrolytes show promise as alternatives to conventional electrolytes in energy storage and conversion devices but have been limited due to their inverse correlation between ionic conductivity and modulus. In this study, we examine surface morphology, linear viscoelastic, dielectric and diffusive properties of molecular ionic composites (MICs), materials produced through the combination of a rigid and charged double helical polymer, known as poly(2,2’)-disulfonyl-4,4’benzidine terepthalamide (PBDT), with ionic liquids (ILs). To probe temperature extremes, we incorporate a non-crystallizable IL to allow measurements from to -90 to 200°C. As we increase PBDT weight percentage (wt%), shear moduli increase and do not decay up to 200°C while maintaining room temperature ionic conductivity within a factor of two of the neat IL. We connect diffusion coefficients of IL ions with ionic conductivity through the Haven ratio across a wide temperature range and analyze trends in ion transport based on a relatively high and composition-dependent static dielectric constant. This behavior may result from collective rearrangement of IL ions in these networks. We propose that these properties are driven by a two-phase system in MICs corresponding to IL-rich “puddles” and PBDT-IL associated “bundles” where IL ions form alternating sheaths of cations and anions around each PBDT rod. Furthermore, these polymer-based MIC electrolytes show great promise for use in electrochemical devices that require fast ion transport, high modulus, and a broad thermal window.

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

Aqueous ionic liquid–mediated depolymerization of textile waste

Textile waste, dominated by polyester-cotton blends, largely evades recycling and ends up in landfills or incinerators. Here, we demonstrate an aqueous ionic liquid–mediated route for selective depolymerization of textile waste, including polyester and polycotton (polyester/cotton blend). Using aqueous cholinium lysinate ([Ch][Lys]), we depolymerized poly(ethylene terephthalate) (PET) textiles with over 95 % terephthalic acid (TPA) yields, comparable to virgin PET resin. Notably, colored fabrics showed no inhibitory effect from dyes. While protic ionic liquids such as ethanolammonium acetate showed limited efficiency, their precursor amine enabled near-complete PET conversion—ethanolamine promoted aminolysis with byproduct formation whereas butylamine achieved higher TPA recovery through combined hydrolysis and aminolysis. Importantly, polycotton blends achieved complete PET depolymerization with TPA yield above 85 % and preserved cotton. These results establish aqueous ionic liquids as efficient, selective agents for deconstructing polyester in blended textiles, offering flexible product and ionic liquid management pathways toward scalable and facile textile recycling.

Amines↗
DOE OSTI2021

Molecular Weight Dependence of Block Copolymer Micelle Fragmentation Kinetics

The effect of molecular weight (M) on the fragmentation kinetics of micelles formed by 1,2-polybutadiene-block-poly(ethylene oxide) (PB-PEO) copolymers was studied in the ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide. A series of six samples, with total M ranging from 10 4 to 10 5 g mol –1 and nearly constant composition (f PEO ≈ 0.4), were examined; all six formed spherical micelles with PEO coronas. Nonequilibrium PB-PEO micelles were prepared by direct dissolution, a process that systematically produces nanoparticles with mean aggregation numbers more than twice the equilibrium values. When subjected to high temperature annealing (170 °C), the average micelle radius was found to decrease substantially, as determined by temperature-jump dynamic light scattering (T-jump DLS) and time-resolved small-angle X-ray scattering (TR-SAXS). Furthermore, the characteristic fragmentation times (τ) were found to increase strongly with increasing degree of polymerization N, as τ ~ N 1.8 . This result compares favorably with the prediction of a previously untested model.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2023

Transition from Vogel-Fulcher-Tammann to Arrhenius Ion-Conducting Behavior in Poly(Ethyl Acrylate)-Based Solid Polymer Electrolytes via Succinonitrile Plasticizer Addition

Solid polymer electrolytes (SPEs) offer potential advantages over liquid electrolytes, including flexibility, safety, and processability. However, they suffer from low room-temperature ionic conductivity. Recently, it has been reported a poly(ethyl acrylate) based (polyEA) SPE, by incorporating 50 wt% of succinonitrile (SN) solid plasticizer, 30 wt% of lithium salt and 5 wt% of fluoroethylene carbonate additive, which achieves a high room-temperature ionic conductivity of 1.01 × 10 −3 S cm −1 (Nat. Nanotechnol, 2022, 17, 768-776). This novel SPE exhibits stability against Li 0 and anodic stability up to 4.9 V vs Li + /Li. However, the specific mechanism responsible for its high ionic conductivity remains elusive. In this work, by adjusting the weight ratio of SN in the SPE, a transition from Vogel-Fulcher-Tammann to Arrhenius ion-conducting behavior is observed. It is demonstrated that the addition of SN leads to the gradual decoupling of Li-ion from the polymer backbone and its coordination with SN, as revealed by 6 Li solid-state nuclear magnetic resonance spectroscopy. As a result, Li-ion migration primarily occurs through SN rather than the segmental motion of the polymer backbone. Performances of the SPE in Cu||Li, Li||Li and a LiFePO 4 ||Li pouch cells are shown to demonstrate the commercial viability of this SPE in Li 0 -anode solid-state batteries.

Electrochemistry↗
DOE OSTI2022

Tuning conformational structures of imidazolium ionenes with 1-ethyl-3-methylimidazolium ionic liquid solvents

In this report the structures and conformations of imidazolium ionenes solvated in 1-ethyl-3-methylimidazolium ionic liquids (ILs) ([C 2 mim + ][X - ]) are investigated using molecular dynamics simulations. Four different ionenes poly(decylimidazolium) (PD 10 ), poly(tetraethyleneglycolimidazolium) (PE 10 ), alternating copolymer (P(ED) 5 ), and a block copolymer PE 5 D 5 are immersed in [C 2 mim + ][X - ], where [X - ] = thiocyanate [SCN - ], tetrafluoroborate [BF 4 - ], and trifluoromethanesulfonate [TfO - ]. The radius of gyration indicates that the ionene chains are more extended when immersed in [TfO - ] compared to [BF 4 - ] and [SCN - ], while the solvent accessible surface area shows that PE 10 is the most contracted ionene among all systems. The electrostatic interactions between the ionenes and the ILs are very consistent with the inherent electrostatic characteristics of the different anions, which can be quantified using the Ionic Polarity Index (IPI). The ionene configurations and dynamics strongly depend on the backbone functionality and architecture of the chain, due to the balance between the inter- and intra-molecular interactions in these systems.

42 ENGINEERING↗
DOE OSTI2021

Molecular-level insights into structure and dynamics in ionic liquids and polymer gel electrolytes

We report designing new electrolytes requires a better understanding of the correlation between their transport properties and their molecular structure. In this work, we present a detailed study of ionic liquids and polymer gel electrolytes probing their structure and dynamics by nuclear magnetic resonance (NMR) spectroscopy. In particular, ammonium- and phosphonium-based ionic liquids (ILs) are combined with different LiTFSI concentrations, and then with different ratios of poly(methylmethacrylate) polymer. The temperature dependence of self-diffusion coefficients of mobile species, D Li+ , D TFSI- and D P4441+ or D N4441+ , measured by pulsed field gradient (PFG) NMR spectroscopy obeys the Arrhenius equation. Diffusivity of [P4441][TFSI] ILs is found to be greater than those of the [N4441][TFSI] ILs in both liquid and gel electrolytes. Solid state NMR experiments including 13 C and 19 F MAS, 13 C{ 19 F}, 13 C{ 1 H} CPMAS probe the local structure and molecular-level interactions between ions and polymer in gel electrolytes, particularly for samples with higher PMMA content (≥25 wt%). Finally, the fast field cycling relaxometry has been used to unveil the rotational and translational dynamics of P4441 + or N4441 + and TFSI - by measuring 1 H and 19 F R 1 relaxation rate profiles at different temperatures. A comprehensive NMR analysis including relaxation studies at low magnetic field provides decisive new insights regarding the formation of ionic clusters and the interaction of ions with the polymer chain in the case of the gel electrolytes.

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

Polymers in molten inorganic salt hydrate phase change materials: solubility and gelation

Inorganic salt hydrates are of interest as phase change materials (PCMs) for thermal energy storage because of their unique properties, such as high latent heats of fusion, moderate melting temperatures, high volumetric energy storage densities, and enhanced thermal conductivities compared to their organic counterparts. Because of the low viscosities of molten salt hydrates, the leakage and settling of solids can easily occur during their application. Polymers are promising candidates for preventing these issues. In addition, the non-flammability, non-volatility, and nontoxicity of many molten salt hydrates make them attractive options as “green” solvents for polymers. However, solutions of polymers in molten salt hydrates have rarely been studied and are poorly understood. The highly ionic environments in these materials created due to a scarcity of hydration water for ions leads to strong ionic interactions, with ramifications for polymer solubility and chain expansion. This Perspective article aims to focus on polymer solutions and gels in inorganic salt hydrates by comparing these systems with existing knowledge of polymers in traditional ionic liquids and aqueous salt solutions. To provide insight into the states of ions and water in molten salt hydrates and the degree of hydration of polymers in these solvents, infrared spectroscopy experiments have been performed, and the data are correlated with the temperature-responsive gelation of poly(vinyl alcohol), one candidate material currently used for the shape stabilization of inorganic PCMs. Finally, the thermal properties of inorganic salt hydrates and ionic liquids are compared and strategies for the shape stabilization of inorganic salt hydrates using polymers, through the formation of physical gels, are discussed.

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↗