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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 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Self-Assembled Solute Networks in Crowded Electrolyte Solutions and Nanoconfinement of Charged Redoxmer Molecules

Redoxmers are electrochemically active organic molecules storing charge and energy in electrolyte fluids circulating through redox flow batteries (RFBs). Such molecules typically have solvent-repelling cores and solvent-attracting pendant groups introduced to increase solubility in liquid electrolytes. These two features can facilitate nanoscale aggregation of the redoxmer molecules in crowded solutions. In some cases, this aggregation leads to the emergence of continuous networks of solute molecules in contact, and the solution becomes microscopically heterogeneous. In this study, we used small-angle X-ray scattering (SAXS) and molecular dynamics modeling to demonstrate formation of such networks and examine structural factors controlling this self-assembly. We also show that salt ions become excluded from these solute aggregates into small pockets of electrolytes, where these ions strongly associate. This confinement by exclusion is also likely to occur to charged redoxmer molecules in a “sea” of neutral precursors coexisting in the same solution. Here, we demonstrate that the decay lifetime of the confined charged molecules in such solutions can increase several fold compared to dilute solutions. We attribute this behavior to a “microreactor effect” on reverse reactions of the confined species during their decomposition.

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

In Operando Calorimetric Measurements for Activated Carbon Electrodes in Ionic Liquid Electrolytes under Large Potential Windows

This study aims to investigate the effect of the potential window on heat generation in carbon-based electrical double layer capacitors (EDLCs) with ionic-liquid (IL)-based electrolytes using in operando calorimetry. The EDLCs consisted of two identical activated-carbon electrodes with either neat 1-butyl-1-methylpyrrolidinium bis(trifluoromethane-sulfonyl)imide ([Pyr 14 ][TFSI]) electrolyte or 1.0 m [Pyr 14 ][TFSI] in propylene carbonate (PC) as electrolyte. The instantaneous heat generation rate at each electrode was measured under galvanostatic cycling for different potential windows ranging from 1 to 4 V. First, the heat generation rates at the positive and negative electrodes differed significantly in neat IL owing to the differences in the ion sizes and diffusion coefficients. However, these differences were minimized when the IL was diluted in PC. Second, for EDLC in neat [Pyr 14 ][TFSI] at high potential window (4 V), a pronounced endothermic peak was observed at the beginning of the charging step at the positive electrode owing to TFSI - intercalation in the activated carbon. On the other hand, for EDLC in 1.0 m [Pyr 14 ][TFSI] in PC at potential window above 3 V, an endothermic peak was observed only at the negative electrode owing to the decomposition of PC. Third, for both neat and diluted [Pyr 14 ][TFSI] electrolytes, the irreversible heat generation rate increased with increasing potential window and exceeded Joule heating. This was attributed to the effect of potential-dependent charge redistribution resistance. Additionally, a further increase in the irreversible heat generation rate was observed for the largest potential windows owing to the degradation of the PC solvent. Finally, for both types of electrolyte, the reversible heat generation rate increased with increasing potential window because of the increase in the amount of ion adsorbed/desorbed at the electrode/electrolyte interface.

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

The organic redox transistor for neuromorphic computing

Inspired by the in-memory computing architectures of biological systems, neuromorphic computing using crossbar arrays of artificial synapses based on non-volatile memory (NVM) devices with variable conductances has emerged as a new paradigm to enable massively parallel and ultra-low power computing hardware for data centric applications. Although inference has been demonstrated successfully using crossbars based on a variety of NMV technologies, efficient learning and scaling to large arrays (>10 6 elements) remains a challenge due to the synaptic elements' non-ideal electrical characteristics which degrades ANN accuracy. A further challenge is that in the conductive state memristors draw large currents >μA resulting in significant voltage drops in the interconnect wires and increased probability of failure in scaled arrays. We suggest the organic polymer redox transistor (RT) is an alternate approach that could solve many of these challenges, enabling both inference and parallel outer product updates, as recently demonstrated by Fuller et al. An RT consists of redox-active channel and gate electrodes in contact with a liquid or solid electrolyte. lon insertion through the electrolyte controls the channel electronic conductivity, while electron transfer through an external circuit maintains overall charge neutrality. Unlike a rechargeable battery, in the RT the voltage built-up across the electrolyte is kept to a minimum (typically <100 mV) by using the same material for the gate and channel. Elimination of the voltage offset simplifies integration of the RT into programmable arrays by enabling the use of various selectors. RTs based on inorganic and organic materials have been recently demonstrated with conductance tuning occurring at potentials of just a few mV and hundreds to thousands of linearly and symmetrically programmable conductance states, enabling near ideal accuracy in neural network simulations. Introduced in the 1980's, redox transistors with metallic gate electrodes and organic channel materials, also known as organic electrochemical transistors (OECTs), have been explored for a variety of applications such as chem- and bio-sensing, neural interfaces, and low cost printed circuits. A typical channel material for OECTs is the conducting polymer poly(3,4-ethylenedioxythiophene) doped with poly(styrene sulfonate) (PEDOT:PSS). PEDOT is a p-type semiconducting polymer with mobile positively charged polarons that hop chain-to-chain.

Talin, Albert Alec↗
DOE OSTI2020

Competitive Pi-Stacking and H-Bond Piling Increase Solubility of Heterocyclic Redoxmers

Redoxmers are organic molecules that carry electric charge in flow batteries. In many instances, they consist of heteroaromatic moieties modified with appended groups to prevent stacking of the planar cores and increase solubility in liquid electrolytes. This higher solubility is desired as it potentially allows achieving greater energy density in the battery. However, the present synthetic strategies often yield bulky molecules with low molarity even when they are neat and still lower molarity in liquid solutions. Fortunately, there are exceptions to this rule. Here, we examine one well-studied redoxmer, 2,1,3-benzothiadiazole, which has solubility similar to 5.7 M in acetonitrile at 25 degrees C. We demonstrate computationally and prove experimentally that the competition between two packing motifs, face-to-face it-stacking and random N-H bond piling, introduces frustration that confounds nucleation in crowded solutions. Our findings and examples from related systems suggest a complementary strategy for the molecular design of redoxmers for high energy density redox flow cells.

25 ENERGY STORAGE↗
DOE OSTI2022

Infrared Spectroscopy of Li + Solvation in EmimBF 4 and in Propylene Carbonate: Ab Initio Molecular Dynamics and Experiment

Infrared (IR) spectra of solutions of the lithium salt LiBF 4 in the ionic liquid 1-ethyl-3-methylimidazolium tetrafluoroborate (EmimBF 4 ) and in the organic solvent propylene carbonate (PC) are studied via infrared spectroscopy and ab initio molecular dynamics (AIMD) simulations. The measurements show that the major effects of LiBF 4 in both solutions, compared to their neat counterparts, are the appearance of a new broad band in the 300-450 cm -1 frequency region and a broadening of the IR structure in the 900-1200 cm -1 region with the development of a new peak at 980 cm -1 . Computational analysis indicates that hindered translational motions of Li + in its solvation cage are mainly responsible for the former, while the latter is due to Li + -induced structural changes and accompanying vibrational frequency shifts of constituent ions and molecules of the solutions. In addition, molecular motions in these and lower frequency regions are generally correlated, disclosing the collective nature of the vibrational dynamics, which involve multiple ions/molecules. Herein, detailed analysis of these features via AIMD simulations of the spectrum and its components arising from auto- and cross-correlations of motions of constituent molecular species, combined with generalized normal modes of the solutions and normal modes of small Li + -containing clusters, is presented. Furthermore, other minor spectral changes caused by the lithium salt as well as the interaction-induced effect on IR spectra are also discussed.

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

A high-performance organic cathode customized for sulfide-based all-solid-state batteries

All-solid-state batteries (ASSBs) have become increasingly attractive recently due to their better safety and prospective long-term stability compared with conventional liquid batteries. However, obtaining a sustainable cathode candidate to match the solid electrolyte with regards to operating potential, chemical compatibility, and mechanical property is still an open challenge. In this work, the chemical incompatibility of quinone-based active materials and sulfide-based electrolyte were unveiled for the first time through a heteroconjugate addition reaction mechanism. To develop a quinone cathode customized for sulfide-based ASSBs, poly-(anthraquinonyl sulfide)-graphene (PAQS-G) nanocomposite was reported. The stable polymer framework of PAQS can protect the quinone redox center by preventing nucleophilic attack from sulfide-based solid electrolytes. The graphene additives can ameliorate redox kinetics and improve active material utilization. The PAQS-G cathode exhibited a specific capacity of ~178 mAh g -1 and a high material utilization of ~79%. Excellent cycling stability was achieved with 94 % capacity after 200 cycles in lithium batteries and 95.5 % capacity after 300 cycles in sodium batteries at 0.1C rate, respectively. A promising potential for energy storage applications was demonstrated.

25 ENERGY STORAGE↗
DOE OSTI2020

Molecular simulation of liquid–vapor coexistence for NaCl: Full-charge vs scaled-charge interaction models

Scaled-charge models have been recently introduced for molecular simulations of electrolyte solutions and molten salts to attempt to implicitly represent polarizability. Although these models have been found to accurately predict electrolyte solution dynamic properties, they have not been tested for coexistence properties, such as the vapor pressure of the melt. In this work, we evaluate the vapor pressure of a scaled-charge sodium chloride (NaCl) force field and compare the results against experiments and a non-polarizable full-charge force field. The scaled-charge force field predicts a higher vapor pressure than found in experiments, due to its overprediction of the liquid-phase chemical potential. Reanalyzing the trajectories generated from the scaled-charge model with full charges improves the estimation of the liquid-phase chemical potential but not the vapor pressure.

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

Refined Classical Force Field for Choline Chloride and Ethylene Glycol Mixtures over Wide Composition Range

In this work, a classical force field based on the General Amber Force Field (GAFF) was refined for the simulation of choline chloride (ChCl) and ethylene glycol (EG) mixtures over a wide composition range by scaling the partial charges and van der Waals parameters. The scaling factors were derived by fitting the simulation results to only eight experimental density and viscosity data points of pure EG, and ChCl/EG mixtures at 1:2, 1:4, and 1:6 molar ratios. Using the refined force field, properties essential for electrochemical applications such as density, viscosity, self-diffusion coefficient, and ionic conductivity were calculated, and excellent agreement to experimental results was found even for compositions and temperatures not used in the fitting procedure. In addition, new experimental data for density, viscosity, and ionic conductivity are reported as a function of temperature and composition for this mixture. To the best of our knowledge, this is the first classical force field developed for the study of ChCl/EG mixtures over a composition range that includes the eutectic point. Using the new model, the liquid dynamics was studied in terms of ionic conductivity. It was found that the dynamics in ChCl/EG mixtures with ChCl mole fraction higher than 20% is similar to that of ionic liquids, high temperature molten salts, and highly concentrated water-in-salt electrolytes.

25 ENERGY STORAGE↗
DOE OSTI2020

Polysulfide entrapment and retardation in gel electrolyte Li–S batteries: experiments and modeling

Gelling the electrolyte in lithium–sulfur (Li–S) batteries provides advantages in terms of safety and mitigating polysulfide shuttling leading to reduced side reactions and dendrite growth on the anode side. In the current study, organic and ceramic crosslinkers have been used to improve the entrapment of polysulfides and prevent them from shuttling to the anode side. However, the performance of gel electrolytes is still far from being on par with liquid electrolytes in terms of raw capacity. The discharge curves exhibit an extended first plateau for gel electrolyte batteries compared to liquid electrolytes, showing that polysulfides are better trapped in the gel system. Yet, in the conversion of soluble polysulfides into insoluble polysulfides, the second plateau was delayed. Qualitative and quantitative analysis of the polysulfide diffusion in the liquid electrolyte and gel electrolyte systems were also conducted to predict the relative diffusivity ratio between the liquid electrolyte and gel electrolyte for simulation. To probe what happens at the end of the discharge, where the mass transport in the gel electrolyte appears to be slow, a modified discharge procedure was used where the cell is first paused after discharge and then discharged a second time before recharging normally. Coin cell tests for two gel electrolytes in addition to liquid electrolyte show up to 7% capacity recovery after the pause, which indicates that the diffusion of species during the pause is responsible for the failure recovery. Additionally, the recovery is higher for gel electrolytes compared to liquid, for higher C-rates, and for longer pause times. To better understand this behavior, a Li–S numerical model with mass transport limited reactions was used to examine the polysulfide diffusion coefficients expected in different electrolyte systems. The model is able to reproduce the trends seen in experiments and yields a higher recovery for smaller Li 2 S 4 diffusion coefficients, suggesting that insufficient Li 2 S 4 mass transport is responsible for failure at the end of discharge. By identifying the effect that gel electrolytes have on the state of the battery during discharge using both experimental and simulation methods, this work is a step towards leveraging the advantages of gel electrolytes and mitigating their weaknesses.

25 ENERGY STORAGE↗
DOE OSTI2025

Identifying High Ionic Conductivity Compositions of Ionic Liquid Electrolytes Using Features of the Solvation Environment

Binary mixtures of ionic liquids with molecular solvents are gaining interest in electrochemical applications due to the improvement in their performance over neat ionic liquids. Dilution with suitable molecular solvents can reduce the viscosity and facilitate faster diffusion of ions, thereby yielding substantially higher ionic conductivity than that for a pure ionic liquid. Although viscosity and diffusion coefficients typically behave as monotonic functions of concentration, ionic conductivity often passes through a peak value at an optimum molar ratio of the molecular solvent to the ionic liquid. The ionic conductivity maximum is generally explained in terms of a balance between the ease of charge transport and the concentration of the charge carriers. In this work, fluctuation in the local environment surrounding an ion is invoked as a plausible explanation for the ionic conductivity mechanism with a binary mixture of 1-ethyl-3-methylimidazolium tetrafluoroborate and ethylene glycol as an example. The magnitude of the dynamism in the local environment is captured by measuring the spatial and temporal features of the solvation environment. Standard deviation in the number of ions in the solvation environment serves as a spatial feature, while the cage correlation lifetimes for oppositely charged ions within the first solvation shell serve as a temporal feature. Large standard deviations in the cluster ion population and short cage correlation lifetimes are indicators of highly dynamic ionic environment at the molecular level and consequently yield high ionic conductivity. Such compositions were found to be in good agreement with the optimum ionic liquid mole fractions obtained through experimental measurement. Short cage correlation lifetimes enable the identification of optimum mixture compositions using simulation trajectories significantly shorter than those required to implement the Nernst–Einstein or Einstein formalisms for calculating ionic conductivity. We validated the applicability of this approach across force fields and in six ionic liquid-molecular solvent electrolytes formed with combination of cations, anions, and solvents. We offer a computationally efficient approach of screening ionic liquid-molecular solvent binary mixture electrolytes to identify molar ratios that yield high ionic conductivity.

25 ENERGY STORAGE↗
DOE OSTI2021

Chemical Understanding of Actinide Separations

This work provides a broad overview of the separation processes used to isolate actinides and the experimentally and computationally determined chemical characteristics that define those separations. The redox chemistry of the actinides plays a pivotal role in both aqueous and pyrochemical processing separations. The near-overlapping energies of the 6d and 5f orbitals in the light actinides allow for facile adjustment of actinide oxidation states, which is used in many established separation methods. In contrast, the stable, generally 3+ oxidation states of the mid- and heavy actinides can make it difficult to separate them from the similarly lanthanides(III). In aqueous separations, the tendency of the actinides to form anionic and neutral aqueous complexes with a variety of complexants (especially soft donors) is used to achieve high separation factors between chemically similar elements in both solid–liquid separations and liquid–liquid extraction. This selectivity can be further tuned through the use of specialized organic or solid-phase ligands. Pyroprocessing separations utilize the unique redox behavior of the actinides to adjust their distribution between a molten salt electrolyte and either a solid electrode or molten metal phase. Atomic-level insights into the mechanisms underlying actinide separation processes, with the ultimate goal of predicting separation behavior, can be provided by electronic structure and statistical mechanical-based calculation methods.

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

Lithium oxidation and electrolyte decomposition at Li-metal/liquid electrolyte interfaces

In this work, we examine the evolution of events occurring when a Li metal surface is in contact with a 2 M solution of a Li salt in a solvent or mixture of solvents, via classical molecular dynamics simulations with a reactive force field allowing bond breaking and bond forming. The main events include Li oxidation and electrolyte reduction along with expansion of the Li surface layers forming a porous phase that is the basis for the formation of the solid-electrolyte interphase (SEI) components. Nucleation of the main SEI components (LiF, Li oxides, and some organics) is characterized. The analysis clearly reveals the details of these physical–chemical events as a function of time, during 20 nanoseconds. The effects of the chemistry of the electrolyte on Li oxidation and dissolution in the liquid electrolyte, and SEI nucleation and structure are identified by testing two salts: LiPF 6 and LiCF 3 SO 3 , and various solvents including ethers and carbonates and mixtures of them. The kinetics and thermodynamics of Li 6 F, the core nuclei in the LiF crystal, are studied by analysis of the MD trajectories, and via density functional theory calculations respectively. The SEI formed in this computational experiment is the “native” film that would form upon contact of the Li foil with the liquid electrolyte. As such, this work is the first in a series of computational experiments that will help elucidate the intricate interphase layer formed during battery cycling using metal anodes.

25 ENERGY STORAGE↗
DOE OSTI2023

Utilizing Conjugated Imine Polymers to Stabilize Nanoparticle Silicon Anodes

Silicon anodes provide a compelling route towards delivering high-capacity lithium-ion batteries, however they are notoriously difficult to stabilize in conventional liquid electrolytes that are compatible with high performance cathodes. Furthermore, the drastic changes in volume that occur as silicon is lithiated and delithiated can lead to rapid cell failure and novel polymeric binders are known to help mitigate mechanical issues. We have recently developed a novel method to synthesize the conjugated polymer phenylmethylimine (polyPMI) using an imine metathesis reaction. We have demonstrated that this polymer can be used to stabilize silicon nanoparticles to produce a composite lithium-ion battery anode that is electrochemically stable for hundreds of lithiation and delithiation cycles with a Coulombic efficiency that is greater than 99.95% in a traditional carbonate liquid electrolyte. This work covers the structure and properties of polyPMI within the context of the unique mechanical and electrochemical requirements of nanoparticle silicon anodes. The electrochemical behavior of this polymer also offers new opportunities as an organic lithium-coordinating material that can be used to stabilize a variety of other battery electrodes. More broadly, we posit that this solution-processed, ionically conductive, and electronically conductive polymer is applicable for a variety of energy storage and conversion technologies. Finally, this work demonstrates how this novel polymer chemistry provides additional opportunities for tuning electrode architecture to target high energy full cells.

conjugated polymers↗
DOE OSTI2022

Effects of dilution in ionic liquid supercapacitors

Room-temperature ionic liquids (RTILs) are synthetic electrolytes that have a large electrochemical stability window, making them attractive candidates for electric double-layer capacitor (EDLC) applications. Due to their high viscosities and low ionic conductivities, RTILs are often diluted with organic solvent for practical use. Here, we study the effects of dilution on the performance of RTIL EDLCs using a simple mean-field model. We find that dilution diminishes the unfavorable hysteresis that results from a spontaneous surface charge separation (SSCS). As a result, the RTIL concentration can be used to modulate the proximity to the SSCS transition, and maximize capacitance. The interplay between the concentration and the correlation strength gives rise to complex zero-potential phase behavior, including a tricritical point and a λ-line, very similar to the Blume–Capel dilute Ising model. Additionally, electrodes that are solvophilic aid in the prevention of SSCS by drawing solvent molecules to the electrode and displacing ions. Solvophilic electrodes give rise to a phase transition at finite potential where the surface charge rapidly increases with a small increase in potential, leading to a substantial increase in capacitance and energy storage.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Revealing the Anion–Solvent Interaction for Ultralow Temperature Lithium Metal Batteries

Anion solvation in electrolytes can largely change the electrochemical performance of the electrolytes, yet has been rarely investigated. Herein, three anions of bis(trifluoromethanesulfonyl)imide (TFSI), bis(fluorosulfonyl)imide (FSI), and derived asymmetric (fluorosulfonyl)(trifluoro-methanesulfonyl)imide (FTFSI) are systematically examined in a weakly Li + cation solvating solvent of bis(3-fluoropropyl)ether (BFPE). In-situ liquid secondary ion mass spectrometry demonstrates that FTFSI - and FSI - anions are associated with BFPE solvent, while weak TFSI - /BFPE cluster signals are detected. Molecular modeling further reveals that the anion–solvent interaction is accompanied by the formation of H-bonding-like interactions. Further, anion solvation enhances the Li + cation transfer number and reduces the organic component in solid electrolyte interphase, which enhances the Li plating/stripping Coulombic efficiency at a low temperature of -30 °C from 42.4% in TFSI-based electrolytes to 98.7% in 1.5 m LiFTFSI and 97.9% in LiFSI-BFPE electrolytes. The anion–solvent interactions, especially asymmetric anion solvation also accelerate the Li + desolvation kinetics. The 1.5 m LiFTFSI-BFPE electrolyte with strong anion–solvent interaction enables LiNi 0.8 Mn 0.1 Co 0.1 O 2 (NMC811)||Li (20 µm) full cell with stable cyclability even under -40 °C, retaining over 92% of initial capacity (115 mAh g -1 , after 100 cycles). The anion–solvent interactions insights allow to rational design the electrolyte for lithium metal batteries and beyond to achieve high performance.

25 ENERGY STORAGE↗
DOE OSTI2021

Do Deep Eutectic Solvents Behave Like Ionic Liquid Electrolytes? A Perspective from the Electrode-Electrolyte Interface

The differential capacitance as a function of potential and composition for choline chloride (ChCl) and ethylene glycol (EG) at 1:2,1:4, 1:6, and 1:20 molar ratios were studied using electrochemical impedance spectroscopy (EIS) on glassy carbon. In addition, ChCl:EG at the known ethaline DES composition (1:2) and 1:20 molar ratio were studied on Au and Pt electrodes, and compared to glyceline (ChCl:glycerol, 1:2). The capacitance-potential curves on glassy carbon were best interpreted by the modified Gouy-Chapman model. A dampened U-shape was observed similar to dilute electrolytes, however, the non-negligible ionic and H-bonding interactions in these electrolytes resulted in ambiguity about the point of zero charge where capacitance was weakly dependent on potential. Additionally, the differential capacitance was independent of composition on glassy carbon due to limited availability of mobile free ions and constraints by solvated ion sizes within the interface. Increases in capacitance are observed with Au as a result of desolvation and specific adsorption of Cl, and with Pt upon decreased Cl concentrations. These results indicate DESs and H-bonded electrolytes with high salt concentrations are distinct from ionic liquids and present no pronounced over screening or crowding with applied potential.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗