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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 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Stable Cycling of Mg Metal Anodes by Regulating the Reactivity of Mg 2+ Solvation Species

Rationally designing stable nonaqueous electrolytes for Mg metal anodes demands a thorough understanding of their interfacial behaviors. Here, the critical role of cation–anion pairing in improving the cathodic stabilities of amine-based electrolytes against solvent reduction and H 2 evolution is identified. It is demonstrated that strong coordination between solvating amine groups and the Mg 2+ cation facilitates the dehydrogenation of the -NH 2 group, which is mainly responsible for low reversibility during Mg metal plating and stripping. Introducing ion-pairing into the primary solvation shell can effectively weaken the amine coordination such that its reduction is suppressed. A novel interfacial behavior regarding parasitic reaction product dissolution is also identified, which is responsible for the failure of interfacial passivation. An ion-pairing electrolyte is developed based on a weakly-solvated amine molecule and strongly coordinating Mg 2+ salt. This electrolyte composition delivers long-term Mg metal anode cycling with 99.6% Coulombic efficiency for 800 cycles.

25 ENERGY STORAGE↗
DOE OSTI2023

Ambipolar Electrochemistry of Pre‐Intercalated Ti 3 C 2 T x MXene in Ionic Liquid Electrolyte

Abstract Cation intercalation with or without redox remains the dominant charge storage mechanism for two‐dimensional (2D) Ti 3 C 2 T x MXene. Anion‐based charge storage remains unexplored due to intrinsic negative surface charge of MXenes preventing spontaneous intercalation of anions and irreversible oxidation of Ti at anodic potentials in aqueous electrolytes. In this work, we report on the ambipolar electrochemical behavior of the Ti 3 C 2 T x in ionic liquid electrolyte over a 2.5 V electrochemically stable window. The experiments are conducted on a thin Ti 3 C 2 T x film current collector coated with an electroactive layer of small flakes (∼150 nm) of Ti 3 C 2 T x pre‐intercalated with 1‐ethyl‐3‐methylimidazolium bis‐(trifluoromethylsulfonyl)‐imide (EMIM‐TFSI) ionic liquid. Couples of redox peaks with a very small potential separation during the voltage sweep are observed at high negative (−0.75 V vs. Ag wire) and high positive (+0.75 V vs. Ag wire) potentials. Our experimental electrochemical data combined with density functional theory (DFT) calculations suggest feasibility of pseudo‐intercalation of TFSI anions between Ti 3 C 2 T x flakes. This study provides a pathway for elucidating anion intercalation for different MXene chemistries in solvent‐free electrolytes, which can lead to development of MXene based energy storage devices with improved performance.

Electrochemistry↗
DOE OSTI2025

Understanding Redox Organic Behavior in Deep Eutectic Solvents: Considerations for Molecular Design

Electrolytes based on deep eutectic solvents (DESs) coupled with redox active organic molecules have shown potential as a versatile and energy dense electrochemical energy storage system. However, progress in these systems has been held back by a lack of understanding of the irregular behavior displayed when redox active organic molecules are transitioned from other solvent systems. In this work, the hydrogen bonding characteristics of a series of redox organic molecules were investigated through infrared spectroscopy and molecular modeling. New understanding of these interactions was then used to explain their electrochemical behavior in a DES electrolyte. A model was used to predict the behavior of new derivatives towards the design of an optimized redox organic-DES system. Hydrogen bonding between the redox molecules and the solvent was found to significantly shift the potential of a redox reaction more positive when a hydrogen bond forms at the redox active site. It was predicted that functionalizing a molecule with electron withdrawing groups to lower the electron density of the redox active functional group lowers the strength of the hydrogen bond and thus alleviates the undesirable potential shift. This hypothesis was demonstrated by the addition of nitro groups to fluorenones.

25 ENERGY STORAGE↗
DOE OSTI2025

Tracking Spatiotemporal Electric Potential in Batteries Using High-Resolution Operando X‑ray Transmission Imaging

The formation of significant concentration gradients across electrolytes in batteries affects the rate at which electrochemical reactions occur. In this work, we use high-resolution operando X-ray transmission imaging to capture spatiotemporal salt concentration profiles c(x,t) in a symmetric cell comprising a polymer electrolyte sandwiched between two lithium–indium alloy electrodes during a constant-current experiment followed by open-circuit relaxation. The decay of open-circuit potential is related to the concentration dependence of the potential across concentration cells, U. We show how operando c(x,t) data can be used to calculate the spatiotemporal electric potential “inside” the polarized electrolyte. We track the spatial- and time-dependent cell potential during the constant-current step and distinguish its two contributions: a concentration overpotential governed by U. and an ohmic contribution governed by ionic conductivity. Over most of the time window, the concentration overpotential dominates. At steady state, it is a factor of 7 larger than the ohmic contribution. Such findings indicate that efforts to design new polymer electrolytes should focus on minimizing concentration gradients.

Electrical conductivity↗
DOE OSTI2025

Interfacial Cation Arrangement Controls Electrocatalytic Kinetics in CO 2 Reduction

The identity of electrolyte cations is known to strongly influence electrocatalytic activity, but the relationship between their interfacial arrangement and observed performance remains poorly understood. Organic cations, with their molecular tunability, provide a powerful platform for systematically probing these effects. Here, we leverage phosphonium-based geminal dications to control interfacial cation arrangement and identify the variables that most strongly influence catalytic rates. As a case study, we examine CO 2 reduction to CO over polycrystalline silver electrodes in dry aprotic acetonitrile. Through a combination of rotating disk electrode measurements, electrochemical impedance spectroscopy, and molecular dynamics simulations, we decouple the effects of cation–electrode distance and interfacial cation density on catalytic rates. We find that smaller, more densely packed cations induce stronger interfacial electric fields, which lower the activation barrier for CO 2 adsorption and increase reaction rates. Using geminal phosphonium dications [C n (P mmm ) 2 ][ClO 4 ] 2 , we demonstrate that both the vertical and lateral positioning of organic cations within the electrical double layer independently affect reactivity. These results demonstrate that electrolyte cation identity primarily influences catalytic kinetics by determining how efficiently charge can be arranged at electrochemical interfaces. Altogether, our findings support an electrostatic view of cation effects in catalysis and provide design principles for next-generation electrolytes.

Cations↗
DOE OSTI2020

Solvent oligomerization pathways facilitated by electrolyte additives during solid-electrolyte interphase formation

The solid–electrolyte interphase (SEI) layer formation is known to play an important role in determining the lifetime of lithium-ion batteries. A thin, stable SEI layer is linked to overall improved battery performance and longevity, however, the factors and mechanisms that lead to optimal SEI morphology and composition are not well understood. Inclusion of electrolyte additives (fluoroethylene carbonate, FEC; and vinylene carbonate, VC) is often necessary for improving SEI characteristics. To understand how these electrolyte additives impact SEI formation, we employed molecular dynamics (MD) and density functional theory (DFT) simulations to study the reaction networks and oligomerization pathways, respectively, for three systems containing ethylene carbonate (EC), a lithium ion, and FEC or VC. MD simulations suggest radical oligomerization pathways analogous to traditional oligomerization with nucleophilic alkoxide species via SN1 reaction mechanisms. Both S N 1 and S N 2 mechanisms were studied for all three systems using DFT. Oligomerization reactions were studied with both a standard alkoxide species and a ring-opened EC radical as the nucleophiles and EC, FEC, and VC as the electrophiles. For all cases, FEC and VC exhibited lower free energy barriers and more stable adducts when compared with EC. We conclude that one of the role of additives is to modify the oligomerization process of EC by introducing branching points (FEC) or termination points (VC).

25 ENERGY STORAGE↗
DOE OSTI2020

Tracking ion intercalation into layered Ti 3 C 2 MXene films across length scales

Enhancing the energy stored and power delivered by layered materials relies strongly on improved understanding of the intricate interplay of electrolyte ions, solvents, and electrode interactions as well as the role of confinement. Here we report a highly integrated study with multiscale theory/modelling and experiments to track the intercalation of aqueous Li + , Na + , K + , Cs + , and Mg 2+ ions into Ti 3 C 2 MXene. The integrated analysis of experiments assisted by theory/modelling allows for a deep understanding of energy storage processes highlighting the importance of the dynamics of cations, their positionings between MXene sheets, their effects on mechanical properties and capacitive energy storage. Computational simulations and operando calorimetry measurements prove the processes involving cation dehydration and H+ rehydration, showing a good correlation for heat variations between experiments and theory. Operando liquid AFM mapped energy dissipation of ions appears non-uniformly across the MXene surface, indicating heterogeneities of ions inside the MXene and confirming partially the ion behaviour obtained in theory. We directly demonstrate that the average distance between the cation and MXene surface follows a modified two-sided Helmholtz model when plotted versus the open circuit potential capacitance, revealing a different electrical double layer mechanism in confinement. This new fundamental understanding lays the foundation for improved functional devices utilizing electrodes and membranes made of two-dimensional materials.

36 MATERIALS SCIENCE↗
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↗
DOE OSTI2023

High Quantum Yield Sensitization of Single Crystal TiO 2 Electrodes with CsPbBr 3 Nanocrystals

Lead halide perovskites are promising materials for solar cells and photodetectors. Nanocrystals of this family of perovskites also have distinct properties. In this study we report the attainment of high quantum yield sensitized photocurrents from stabilized CsPbBr 3 perovskite nanocrystals thermally evaporated onto doped single crystal rutile (110) TiO 2 electrodes. Sensitized photocurrent stabilization was achieved by capping the nanocrystals with a thin NiO x layer and a Au carrier transport and protection layers respectively as well as the judicious choice of solvent and electrolyte.

Materials Science↗
DOE OSTI2022

A System Engineering Approach in the Analysis of Ionic Liquids Properties [Thesis]

Room temperature ionic liquids (RTIL) are ionic compounds, comprised of a cation and anion, in the liquid state at temperatures below 100 ⁰C. There are estimated 10 18 anion and cation combinations, which can create RTILs with unique properties. While the ionic character of RTILs made them attractive in a wide variety of electrochemical applications, their behaviors under electrochemical conditions are not well understood. In this research, we developed a RTIL testbed to investigate how RTILs differ from molecular solvents and electrolytes in electrochemical systems through the study of the effects of their morphology and chemical properties on the electron transfer processes. The test bed is composed of three modules: Electrochemistry, Material characterization, Computational. All modules have been completely developed, verified, and integrated and two of them, i.e., Electrochemistry and Material characterization have been validated in this dissertation. To evaluate the proposed system, experiments were performed on solutions of a redox active species in RTILs. It was found that it is possible to investigate the RTIL's morphology and chemical properties' impact on the electron transfer processes of the solute based on the outcomes and evaluations of tests performed by the RTIL testbed.

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

Factors Influencing Preferential Anion Interactions during Solvation of Multivalent Cations in Ethereal Solvents

Most multivalent secondary batteries have employed electrolytes composed of cyclic ether solvents such as tetrahydrofuran or linear glycol ether solvents (glymes) such as 1,2-dimethoxyethane (G1). A robust understanding of multivalent cation solvation tendencies in these classes of solvents provides insight into corresponding structure–property relationships which, in turn, promotes the design and discovery of improved electrolytes. In this work, our goal is to systematically address how electrolyte constituent properties, namely, ether solvent structure and dication size, direct the solvation interactions of divalent electrolytes and their resultant properties. This study utilizes pulsed-field gradient (PFG) nuclear magnetic resonance (NMR) spectroscopy in conjunction with Raman spectroscopy and ionic conductivity measurements to elucidate the preferential interactions between multivalent cations, anions, and solvent molecules along with their correlated ion dynamics. These investigations incorporate two representative divalent cations (Ca 2+ and Zn 2+ ) as well as two ethereal solvent representatives from both the cyclic ether and glyme structural classes. The results reveal that anions coordinate more readily with divalent cations in cyclic ethers than in glymes. Furthermore, the coordination of the anions with Ca 2+ , i.e., contact-ion pair (CIP) formation is more pronounced than with Zn 2+ in a glyme solvent of limited chain length (G1), providing insight into cation size effects that are important for translating solvation behavior across various multivalent electrolytes. Importantly, we find that specific anion coordination is more strongly controlled by solvent structure than by salt concentration in the practical range of 0.1–0.5 M. However, simply reducing these inner-sphere inter-ionic interactions by changing solvent structure does not necessarily de-correlate ionic motion. Instead, concentration-dependent changes in molar ionic conductivity suggest that second-shell interactions, i.e., solvent separated ion pairs (SSIPs), are prevalent in these electrolytes and that the solution dielectric constant, which is increased by the presence of dipolar ion pairs, is critical for controlling these interactions. These findings thus provide a basis for understanding the physical chemistry of multivalent battery electrolytes.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Tailoring Solvation Solvent in Localized High-Concentration Electrolytes for Lithium||Sulfurized Polyacrylonitrile

Sulfurized polyacrylonitrile (SPAN) is a promising cathode material for lithium-sulfur (Li-S) batteries due to its significantly reduced polysulfide (PS) dissolution compared to the elemental S cathode. Although conventional carbonate-based electrolytes is stable with SPAN electrodes, it is less stable with Li metal anode (LMA). Recently, localized high-concentration electrolytes (LHCEs) have been developed to improve the stability of LMA. Here, we report a new strategy to further improve the performance of LI||SPAN batteries by replacing the conventional solvating solvent 1,2-dimethoxyethane (DME) in the LHCE with a new solvating solvent, 1,2-diethoxyethane (DEE), the new LHCEs exhibits less reactivity against Li 2 S 2 , alleviates PS dissolution, forms a better cathode-electrolyte interphase layer on the SPAN, and enhances structure reversibility even at elevated temperature (ET, 45°C). With the same salt and diluent as in other LHCEs, the LHCE with DEE leads to better performance in Li||SPAN batteries (with 82.9% capacity retention after 300 cycles at ET), preservation of SPAN cathode structure, and suppression of the volume change of LMA. The similar strategy on tailoring the solvating solvents in LHCEs can also be used in other rechargeable batteries to improve their performances.

1,2-diethoxyethane↗
DOE OSTI2021

Improved Low Temperature Performance of Graphite/Li Cells Using Isoxazole as a Novel Cosolvent in Electrolytes

An investigation of novel electrolyte formulations to improve low temperature performance of Li/graphite half cells has been conducted. A novel electrolyte co-solvent, isoxazole (IZ), has been investigated in electrolyte systems composed of lithium difluoro(oxalato)borate (LiDFOB) in fluoroethylene carbonate (FEC) and LiDFOB in ethylene carbonate (EC). Cells containing 1 M LiDFOB FEC: IZ electrolyte have a significant improvement in capacity retention and reversible capacity at −10 °C. Ex-situ surface analysis of the cycled electrodes suggests that reduction of LiDFOB results in an oxalate rich solid electrolyte interphase (SEI). Addition of FEC, results in improved stability of the anode SEI preventing further decomposition of isoxazole solvent and improving cycling performance.

25 ENERGY STORAGE↗
DOE OSTI2024

Condensation-based redox flow battery rebalancing

In a redox flow battery (RFB), the base solvent of the electrolytes tends to migrate across the barrier layer from one electrode toward the other. This can result in a volume and concentration imbalance between the electrolytes that is detrimental to battery efficiency and capacity. Compatible electrolytes can be mixed to rebalance the system, but for incompatible electrolytes mixing is not a viable option. To this end, the RFB herein includes a separator that recovers base solvent from the vapor phase of one of the electrolytes and returns the recovered base solvent to the other electrolyte to thereby reverse the imbalance.

Saraidaridis, James D.↗
DOE OSTI2023

Navigating the complexities of solvent and binder selection for solution processing of sulfide solid-state electrolytes

We introduce a paradigm of solvent and binder selection for solution-processing Li 6 PS 5 Cl solid-state electrolyte particles based on Hansen solubility parameters. Treatment of the Li 6 PS 5 Cl in selected solvents results in particle morphological change, but crystallographic structure remains intact. Although solution processing reduced the Li 6 PS 5 Cl ionic conductivity, it promotes interfacial stability by alleviating reduction of the solid electrolyte in contact with Li metal. In conclusion, these findings have the potential to enhance the stability, structural integrity, and performance of sulfide solid-state electrolytes in practical applications.

25 ENERGY STORAGE↗
DOE OSTI2026

Solvent–Diluent Engineering of Normal-Concentration Organosulfur Electrolytes for High-Voltage Lithium-Ion Batteries

Enabling high‑voltage batteries depends critically on rational electrolyte design. Conventional carbonate electrolytes with LiPF 6 suffer from insufficient oxidative stability, motivating the use of lithium bis(fluorosulfonyl)imide (LiFSI) for its superior high‑temperature and high‑voltage performance. However, LiFSI is relatively costly, and its electrolytes often require high concentrations to suppress aluminum current collector corrosion in cathode architectures and to adequately passivate electrode interfaces. Here, a low‑concentration LiFSI electrolyte is realized by combining a high‑voltage organosulfur solvent, ethyl methyl sulfone (EMS), with a non‑solvating fluorinated diluent, fluorobenzene (FB). Extended cycling of LiNi 0.8 Mn 0.1 Co 0.1 O 2 (NMC811) full cells to 4.5 V reveals substantial long‑term performance advantages over conventional carbonate electrolytes. Comparison with a popular cyclic sulfone, tetramethylene sulfone (TMS), shows that ring‑containing structures such as TMS strongly influence passivation behavior, ultimately limiting performance and narrowing the viable operating window. Overall, EMS is identified as a uniquely stable solvent for LiFSI‑based electrolytes operating at moderately high voltages.

Dato, Michael A. [Argonne National Laboratory (ANL↗
DOE OSTI2025

Critical Insights into Solvent Choice for High-Voltage Organosulfur Electrolytes

Organosulfur electrolytes are promising candidates for enabling high-voltage cathodes due to their superior oxidative stability compared to conventional carbonate-based systems. However, their viscous nature and inability to passivate the anode necessitate the use of passivating agents and diluents to achieve meaningful charge/discharge rates. In this study, we investigate the use of cyclic fluorinated carbonates (CFCs) to form passivating interphases on electrode surfaces, aiming to optimize electrolyte performance in high-voltage systems. Electrolyte formulations containing 1.2 M LiPF 6 in a CFC:sulfone:1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropylether (TTE) mixture (2/5/3 V/V/V) were assessed in full-cell configurations with a LiNi 0.8 Mn 0.1 Co 0.1 O 2 (FCG-NMC) cathode and a 4.5 V upper cutoff potential. The results reveal that 3-3-3-trifluoropropylene carbonate (TFPC) combined with ethyl methyl sulfone (EMS) optimizes electrolyte performance, resulting in lower resistance buildup and reduced capacity loss compared to commercial electrolytes. We also explore the failure mechanisms of several carbonate/sulfone mixtures and identify key considerations for electrolyte compatibility in high-voltage systems. TFPC enhances cycling stability and lowers overall cell resistance, while fluoroethylene carbonate (FEC) formulations, despite higher ionic conductivity, fail to form adequate passivation layers, leading to rapid capacity loss. Additionally, EMS provides superior physical properties that avoid common failure modes seen with other sulfone solvents like methyl isopropyl sulfone and tetramethylene sulfone. Furthermore, this study underscores the importance of carefully selecting passivating carbonates and sulfone solvents to improve electrolyte performance and expand the viability of high-voltage electrolyte systems.

LiNi0.8Mn0.1Co0.1O2 cathode↗
DOE OSTI2020

Controlling Ion Coordination Structure and Diffusion Kinetics for Optimized Electrode-Electrolyte Interphases and High Performance Si Anodes

The cycling performance of batteries is largely determined by electrode-electrolyte interphase associated with the chemical and electrochemical properties of electrolyte salts and solvents. In this work, we used a localized high concentration electrolyte (LHCE) that enables high performance of Si anodes as a model system and investigated the scientific mechanism behind the optimization of electrolyte. The correlation between electrode (cathode/anode)-electrolyte interphase and ion coordination structure and diffusion kinetics were elucidated systematically. Among all the LHCEs tested, the one with 1.8M LiFSI concentration and 1:2 molar ratio of carbonate solvents and fluorinated diluents has the highest proportion of solvent-separated ion pairs and contact ion pairs and fastest ion diffusion. It enables the most stable electrode-electrolyte interphase and hence the best Si anode performance. These results reveal the fundamental mechanism behind the stability of LHCEs and provide guidance on the new electrolyte design for Si anodes and other battery systems.

Jia, Haiping↗