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DOE OSTI2025

Enhancing Cycle Life in Superoxide‐Based Na–O 2 Batteries by Reducing Interface Reactivity

Abstract Sodium–oxygen (Na–O 2 ) batteries are considered a promising energy storage alternative to current state‐of‐the‐art technologies owing to their high theoretical energy density, along with the natural abundance and low price of Na metal. The chemistry of these batteries depends on sodium superoxide (NaO 2 ) or peroxide (Na 2 O 2 ) being formed/decomposed. Most Na–O 2 batteries form NaO 2 , but reversibility is usually quite limited due to side reactions at interfaces. By using new materials, including a highly active catalyst based on vanadium phosphide (VP) nanoparticles, an ether/ionic liquid‐based electrolyte, and an effective sodium bromide (NaBr) anode protection layer, the sources of interface reactivity can be reduced to achieve a Na–O 2 battery cell that is rechargeable for 1070 cycles with a high energy efficiency of more than 83%. Density functional theory calculations, along with experimental characterization confirm the three factors leading to the long cycle life, including the effectiveness of the NaBr protective layer on the anode, a tetraglyme/EMIM‐BF 4 based electrolyte that prevents oxidation of the VP cathode catalyst surface, and the EMIM‐BF 4 ionic liquid aiding in avoiding electrolyte decomposition on NaO 2 .

Azaribeni, Adel [Department of Chemical and Biolog↗

DOE OSTI2024

Mechanically Reinforced Pseudosolid Polyelectrolyte Membranes via Layer-by-Layer Assembly for High-Performing Lithium-Metal Batteries

Ionogels are emerging as high-potential pseudosolid electrolytes for lithium-metal batteries (LMBs), leveraging their intrinsic high ionic conductivity from entrapped ionic liquid (IL) electrolytes. However, their practical application is hindered by poor mechanical strength stemming from the confinement of ILs within a polymer matrix. To address this challenge, the formation of conformal polyion coatings with functional groups is reported to be relevant to LMBs’ application on ionogels, utilizing a layer-by-layer (LbL) assembly strategy. Here, this approach significantly enhances the mechanical strength (Young's modulus and tensile strength) and electrochemical performance of ionogels, owing to the tailored interface modifications introduced by functional groups’ specific conformal polyion coatings. The core of this methodology leverages the inherent ionic structure of ionogels to enable facile interface modification through Coulombic interactions between polyanions and polycations. These conformally coated interface functionalized membranes show improved electrochemical performance when integrated with cathode materials such as LiFePO 4 (LFP) and LiNi 0.8 Mn 0.1 Co 0.1 O 2 (NMC811) in an LMB configuration, underscoring their potential for robust, high-conductivity, pseudosolid membranes for LMB applications. These innovative pseudosolid membranes offer improved mechanical and electrochemical properties, leading to higher battery efficiency and safety, making them promising candidates for next-generation LMB technology.

25 ENERGY STORAGE↗

DOE OSTI2021

Enhancing the performance of lithium oxygen batteries through combining redox mediating salts with a lithium protecting salt

Li–O 2 batteries have recently emerged to meet nowadays elevated electric energy demands. Redox mediators (RMs) for solution-inducing decomposition of discharge products are one approach to increase energy efficiency and reduce high overpotentials in these batteries. However, multiple obstacles hinder their usage such as redox shuttling, capacity fading, electrolyte degradation, etc. Herein, we present a new chemistry based on a combination of LiNO 3 , TEGDME and an ionic liquid that enables LiI (1 M) to lower the charge potential (3.5V) with a long cycle life of 270 cycles. 0.1 M LiI increases the cyclability up to 500 with a slightly increased charge potential (~4V) for a fixed capacity of 1000 mAh/g. Up to 100 cycles, this battery system retained ~95% Li 2 O 2 capacity with a ~0.8 V charge-discharge polarization gap. The addition of LiNO 3 to the electrolyte provides a protective solid electrolyte interface (SEI) on anode that works in synergy with the LiI RM. Moreover, we found that this electrolyte blend results in domain formation of ionic and neutral species enhancing the discharge and charge processes. Finally, DFT calculations provide a better understanding of the role of the anode SEI layer and the Li 2 O 2 decomposition promoted by the LiI during charge on the cathode.

25 ENERGY STORAGE↗

DOE OSTI2023

Recent advances in biomass pretreatment using biphasic solvent systems

The complexity and recalcitrance of lignocellulosic biomass seriously hinder its subsequent conversion to liquid fuels. To achieve high-value utilization of lignocellulosic biomass, the physical–chemical barrier should be overcome through appropriate pretreatment techniques to improve the accessibility of cellulose for efficient enzymatic hydrolysis. With the rapid emergence of novel pretreatment solvents, biphasic solvent pretreatments represent a nascent and green pretreatment method that has shown outstanding advantages and broad application prospects in the biorefinery of lignocellulosic substrates due to its ability to provide economically viable biomass upgrading, the separation process for products in the solvent phase, and the reutilization of solvents. Herein, different types of biphasic solvents (e.g., 2-methyltetrahydrofuran, methyl isobutyl ketone, 1-butanol, phenoxyethanol, ionic liquids, and deep eutectic solvents) were reviewed systematically, including the fundamental designs of biphasic solvents for biomass pretreatment, their effect on the fractionation of individual biomass components (e.g., carbohydrate and lignin) and the enzymatic hydrolysis performance, and the coproduction of furan and hydroxymethylfurfural. Finally, the main pros and cons of these different biphasic solvent systems are summarized, and the future development direction is also proposed. Finally, this review can provide a reference for designing and selecting effective biphasic pretreatment methods for various types of lignocellulosic biomass.

09 BIOMASS FUELS↗

DOE OSTI2017

Phosphoranimines containing cationic N-imidazolinium moieties

For this study, three new monomeric phosphoranimines (PAs; R'—N=PR 3 ) were synthesized by the Staudinger route using 2-azido-1,3-dimethylimidazolinium hexafluorophosphate [ADMImPF] and various phosphines to form their respective PA salts of triphenylphosphine (1), tri(n-octyl)phosphine (2), and tris(2,2,2-trifluoroethoxy)phosphite (3). These PA salts have a cationic imidazolinium moiety attached to nitrogen. Interestingly, 2 is a room temperature ionic liquid (RTIL) with a melting point around -5°C and a viscosity of 740cP at 25.5°C. 1 and 2 show stability to moisture exposure and atmosphere for weeks whereas 3 is not stable toward atmospheric moisture undergoing decomposition to form 2-amino-1,3-dimethylimidazolinium phosphate (4). Thermal analyses reveal that 1 and 2 are stable to 90°C under nitrogen, but 3 undergoes degradation by exposure to moisture and/or elevated temperature. All compounds exhibit similar multinuclear NMR chemical shifts as compared to their corresponding phosphine oxide counterparts. However, their respective X-ray structure determinations indicate that 2 has an open structure with the octyl groups that avoid the ionic charges, whereas 1 and 3 have tighter structural packing of the hexafluorophosphate to their pendant groups.$\longequal$

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 OSTI2021

Liquid desiccant based dehumidification and cooling system

A liquid desiccant system including a high desorber, a low desorber, and an absorber that are in fluid communication with a working solution, where the high desorber provides rejected water vapor from the working fluid for condensation in a condenser of the low desorber that provides heat for rejection of additional water from the working solution in the low desorber effectively multiplying the heat provided for desorption. The low desorber provided the concentrated working solution to the absorber where water from ambient air is condensed into the concentrated working solution to provide a dilute working solution within a working solution conduit of the absorber that is thermally coupled to an internal cooler of the absorber. In some embodiments, the working solution can be an aqueous solution of at least one ionic liquid.

Moghaddam, Saeed↗

DOE OSTI2021

Liquid desiccant based dehumidification and cooling system

Moghaddam, Saeed↗

DOE OSTI2026

Higher_wood_density_lowers_feedstock_cost_and_has_minimal_impact_on_biomass_conversion_to_biofuels

Poplar and other woody feedstocks have the potential to provide up to 200 million tons of biomass per year that could be converted to liquid fuels. Most forestry strategies that aim at increasing biomass productivity per hectare rely on short rotation plantations of fast-growing varieties. The improvement of wood density as a key trait itself has largely been overlooked. We evaluated natural variation in wood density across a population of genetically diversePopulus trichocarpatrees grown in a common garden. Wood density varies greatly within this population but is heritable higher wood density was not systematically associated with reduced growth, challenging assumptions of a trade-off between wood density and biomass accumulation. Furthermore, denser wood led to significant improvements throughout the supply chain, including, lowering biomass production and transportation costs. Higher density not correlate to changes in biomass composition. Density did not impact bioconversion in the two feedstock-to-fuel pipelines tested (pretreatment by ionic liquids or soaking in aqueous ammonia, and fermentation to ethanol) on a representative subset of poplars. These findings highlight wood density as a promising breeding target for accelerating the development of high-yielding, conversion-efficient bioenergy crops and as an avenue for increasing land-use efficiency and reducing biomass transportation cost. This data set contain three datasets.

CBI↗

DOE OSTI2016

The Influence of Water on the Alkyl Region Structure in Variable Chain Length Imidazolium-Based Ionic Liquid/Water Mixtures

In this work, solutions of room temperature ionic liquids (RTILs) and water were studied by observing the reorientational dynamics of the fluorescent probe perylene. Perylene is solvated in the alkyl regions of the RTILs. Its D 2h symmetry made it possible to extract dynamical information on both in-plane and out-of-plane reorientation from time resolved fluorescence anisotropy measurements. Perylene reorientation reports on its interactions with the alkyl chains. The RTILs were a series of 1-alkyl-3-methylimidazolium tetrafluoroborates (C n mimBF 4 , where n is the number of carbons in the alkyl chain), and the effects on perylene’s dynamics were observed when varying the alkyl chain length of the cation (n = 4, 6, 8, and 10; butyl, hexyl, octyl, decyl) and varying the water content from pure RTIL to roughly three water molecules per RTIL ion pair. Time correlated single photon counting was used to measure the fluorescence anisotropy decays to determine the orientational dynamics. The friction coefficients for both the in-plane and out-of-plane reorientation were determined to eliminate the influence of changes in viscosity caused by both the addition of water and the different alkyl chain lengths. The friction coefficients provided information on the interactions of the perylene with it alkyl environment and how these interactions changed with chain length and water content. As chain length increased, the addition of water had less of an effect on the local alkyl environment surrounding the perylene. The friction coefficients generally increased with higher water contents; the inplane orientational motion was hindered significantly more than the out-of-plane motion. The restructuring of the alkyl regions is likely a consequence of a rearrangement of the ionic imidazolium head groups to accommodate partial solvation by water, which results in a change in the arrangement of the alkyl chains. At very high water content, BmimBF4 broke this general trend, with both in-plane and out-of-plane rotational friction decreasing above a water content of one water per ion pair. This decrease indicates a major reorganization of the overall liquid structure in high water content mixtures. In contrast to BmimBF 4 , the longer chain length RTILs are not infinitely miscible with water, and do not show evidence of a major reorganization before reaching saturation and phase-separating. The results suggest that phase separation in longer chain length BF 4 RTILs is a consequence of their inability to undergo the reorganization of the alkyl regions necessary to accommodate high water concentrations.

14 SOLAR ENERGY↗

NASA NTRS2017

Ionic Polyimides: New High Performance Polymers for Additive Manufacturing

There is currently a very limited set of engineering polymers that have been demonstrated as viable for use in 3-D printing. Additive manufacturing of custom components will require a much larger array of polymers, especially those with physical, thermal, chemical, and mechanical properties that can be tailor-made. The development of ‘Ionic Polyimides’ offers a solution to this shortage by combining the well understood and widely accepted properties of conventional polyimides, with a new approach to polymer synthesis. Polyimides and polymeric ionic liquids (poly(ILs)) are at the forefront of advanced polymer materials, each with their own set of advantages and disadvantages. While it is clear that more types of polymer materials are needed for fused deposition modeling (FDM) additive manufacturing, there is a need to explore these classes of materials. The synthesis process developed by the Bara Research Group at the University of Alabama allows full control over polymer structure, nanostructure, thermal, electrical, and physical properties making them a prime candidate for use in the additive manufacturing process. Furthermore, the new process allows us to tailor-make a high strength polymer that can be used to fabricate filament feedstock instead of pellets for 3D printing. The primary objective of this proposal is to determine the relationship between molecular structure, physical properties, and performance of ionic polyimides. Further, we seek to determine their utility as materials suitable for additive manufacturing of components used in aerospace vehicles, with an emphasis on characterizing and simulating their thermal behaviors and properties. This proposal addresses the need for fundamental research on a customizable polymer filament feedstock for 3-D printing with tailor-made properties potentially making it superior to the commercial blends offered in industry today. The deliverables for this project are the creation of a database that will detail the relationships between the molecular structure and physical properties for the ionic polyimide of interest (e.g. Tg/Tm (Glass Transition Temperature divided by Melting Point)) relative to different ionic polyimide structures). This new database will provide a “road map” to the development of the first generation of materials and ultimately proof-of-concept.

Jackson, Enrique↗

DOE OSTI2019

Electric Field–Controlled Multistep Proton Evolution in H x SrCoO 2.5 with Formation of H–H Dimer

Ionic evolution–induced phase transformation can lead to wide ranges of novel material functionalities with promising applications. Here, using the gating voltage during ionic liquid gating as a tuning knob, the brownmillerite SrCoO2.5 is transformed into a series of protonated HxSrCoO2.5 phases with distinct hydrogen contents. The unexpected electron to charge-neutral doping crossover along with the increase of proton concentration from x = 1 to 2 suggests the formation of exotic charge neutral H–H dimers for higher proton concentration, which is directly visualized at the vacant tetrahedron by scanning transmission electron microscopy and then further supported by first principles calculations. Although the H–H dimers cause no change of the valency of Co2+ ions, they result in clear enhancement of electronic bandgap and suppression of magnetization through lattice expansion. These results not only reveal a hydrogen chemical state beyond anion and cation within the complex oxides, but also suggest an effective pathway to design functional materials through tunable ionic evolution.

36 MATERIALS SCIENCE↗

DOE OSTI2018

Control of Reactivity in Nanoporous Metal/Ionic Liquid Composite Catalysts

In this program, we explored a new concept in nanostructured heterogeneous catalysis design – the nanoporous metal/ionic liquid (IL) composite. Over the course of this entire program from inception, we produced sixteen publications [DOE1-DOE16]. The idea behind this concept was to tailor the chemical environment within and near the pores of a nanoporous high surface area metal electrocatalyst in order to enhance the aggregate composite activity and selectivity. Most electrocatalyst design focuses upon lowering the activation barrier for a particular synthesis reaction. While we also try to minimize this quantity, one should also recognize that significant catalytic enhancements can be made by biasing the reaction to completion via control of the environment in which the reaction occurs. Specific ideas we explored in this program included (a) chemically biasing mass transport of reactants to the catalyst surface and products away from it, and (b) corralling of reactants and products to spatially separate them and reduce side reactions. We made a particular focus on electrocatalysis under kinetically limited conditions, and in which the catalyst is a nanoporous metal and the biasing environment is an ionic liquid impregnating the pores.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2019

Molecular insight into the lower critical solution temperature transition of aqueous alkyl phosphonium benzene sulfonates

Abstract Ionic liquid (IL)-water mixtures can exhibit a lower critical solution temperature (LCST) transition, but changes in long-range order and local molecular environment during this transition are not comprehensively understood. Here we show that in IL-H 2 O LCST mixtures, the IL forms loosely held aggregate structures that grow in size leading up to a critical temperature, whereas the aggregation of a fully miscible aqueous mixture, obtained by minor chemical modification of the anion, decreases with increasing temperature. Radial distribution functions from molecular dynamics simulations support the observation of aggregation phenomena in the IL-H 2 O mixtures. A local molecular structure of the ions is derived from multi-dimensional NMR experiments in conjunction with reported molecular dynamics simulations. In addition to considerable shifts of water’s hydrogen bonding network in the fully miscible phase, by NMR we observe the anion’s protons response to the intermolecular thermal environment and the intramolecular environment and find that the responses are determined by the sulfonate ionic functional group.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2014

Energy Storage

Energy storage technology is critical if the U.S. is to achieve more than 25% penetration of renewable electrical energy, given the intermittency of wind and solar. Energy density is a critical parameter in the economic viability of any energy storage system with liquid fuels being 10 to 100 times better than batteries. However, the economical conversion of electricity to fuel still presents significant technical challenges. This project addressed these challenges by focusing on a specific approach: efficient processes to convert electricity, water and nitrogen to ammonia. Ammonia has many attributes that make it the ideal energy storage compound. The feed stocks are plentiful, ammonia is easily liquefied and routinely stored in large volumes in cheap containers, and it has exceptional energy density for grid scale electrical energy storage. Ammonia can be oxidized efficiently in fuel cells or advanced Carnot cycle engines yielding water and nitrogen as end products. Because of the high energy density and low reactivity of ammonia, the capital cost for grid storage will be lower than any other storage application. This project developed the theoretical foundations of N 2 catalysis on specific catalysts and provided for the first time experimental evidence for activation of Mo 2 N based catalysts. Theory also revealed that the N atom adsorbed in the bridging position between two metal atoms is the critical step for catalysis. Simple electrochemical ammonia production reactors were designed and built in this project using two novel electrolyte systems. The first one demonstrated the use of ionic liquid electrolytes at room temperature and the second the use of pyrophosphate based electrolytes at intermediate temperatures (200 – 300 ºC). The mechanism of high proton conduction in the pyrophosphate materials was found to be associated with a polyphosphate second phase contrary to literature claims and ammonia production rates as high as 5X 10-8 mol/s/cm 2 were achieved.

25 ENERGY STORAGE↗

DOE OSTI2022

Dynamic compression of water to conditions in ice giant interiors

Abstract Recent discoveries of water-rich Neptune-like exoplanets require a more detailed understanding of the phase diagram of H 2 O at pressure–temperature conditions relevant to their planetary interiors. The unusual non-dipolar magnetic fields of ice giant planets, produced by convecting liquid ionic water, are influenced by exotic high-pressure states of H 2 O—yet the structure of ice in this state is challenging to determine experimentally. Here we present X-ray diffraction evidence of a body-centered cubic (BCC) structured H 2 O ice at 200 GPa and ~ 5000 K, deemed ice XIX, using the X-ray Free Electron Laser of the Linac Coherent Light Source to probe the structure of the oxygen sub-lattice during dynamic compression. Although several cubic or orthorhombic structures have been predicted to be the stable structure at these conditions, we show this BCC ice phase is stable to multi-Mbar pressures and temperatures near the melt boundary. This suggests variable and increased electrical conductivity to greater depths in ice giant planets that may promote the generation of multipolar magnetic fields.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2018

X‐Ray Scattering Reveals Ion‐Induced Microstructural Changes During Electrochemical Gating of Poly(3‐Hexylthiophene)

Abstract The heterogeneous microstructure of semicrystalline polymers complicates the relationship between their electrical conductivity and carrier concentration. Charge transport models typically describe conductivity with an assumption of uniform doping throughout the material. Here, the evolution in morphology and optoelectronic properties of poly(3‐hexylthiophene) (P3HT) is reported as a function of carrier concentration in an organic electrochemical transistor using a polymeric ionic liquid (PIL) as the gate insulator. Operando grazing incidence X‐ray scattering reveals that negatively charged ions from the dielectric first infiltrate the amorphous regions of the semiconductor, and then penetrate the crystalline regions at a critical carrier density of 4 × 10 20 cm −3 . Upon infiltration, the crystallites expand by 12% in the alkyl stacking direction and compress by 4% in the π–π stacking direction. The change in crystal structure of P3HT correlates with a sharply increasing effective carrier mobility. UV–visible spectroscopy reveals that holes induced in P3HT first reside in the crystalline regions of the polymer, which verifies that a charge carrier need not be in the same physical domain as its associated counterion. The dopant‐induced morphological changes of P3HT rationalize the dependence of mobility on carrier concentration, suggesting a phase transition of crystalline regions at high carrier concentration.

Thomas, Elayne M.↗

DOE OSTI2021

Manipulation of the Electronic State of Mott Iridate Superlattice through Protonation Induced Electron-Filling

Spin-orbit-coupled Mott iridates show great similarity with parent compounds of superconducting cuprates, attracting extensive research interest especially for their electron-doped states. However, previous experiments have been largely limited within a small doping range due to the absence of effective dopants, and therefore the electron-doped phase diagram remains elusive. Here, an ionic-liquid-gating-induced protonation method is utilized to achieve electron-doping into a 5d Mott-insulator built with a SrIrO 3 /SrTiO 3 superlattice (SL), and a systematic mapping of its electron-doped phase diagram is achieved with the evolution of the iridium valence state from 4+ to 3+, equivalent to doping of one electron per iridium ion. Along increasing doping level, the parent Mott-insulator is first turned into a localized metallic state with gradually suppressed magnetic ordering, and then further evolves into a nonmagnetic band insulating state. This work forms an important step forward for the study of electron-doped Mott iridate systems, and the strategy of manipulating the band filling in an artificially designed SL structure can be readily extended into other systems with more exotic states to explore.

36 MATERIALS SCIENCE↗