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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 199 records · Page 11
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Molecular Engineering to Enable High-Voltage Lithium-Ion Battery: From Propylene Carbonate to Trifluoropropylene Carbonate

Molecular engineering of electrolyte structures has led to the successful application of trifluoropropylene carbonate (TFPC), a fluorinated derivative of propylene carbonate (PC), in next-generation high-voltage high-energy lithium-ion cell. Additionally, in contrast to a PC-based electrolyte which cointercalates in the form of Li + -solvated species into the graphene layer and exfoliates a graphite anode, a TFPC-based electrolyte is highly compatible with a graphite anode at low potential. Additionally, it shows exceptional oxidation stability on the charged cathode surface owing to the presence of the -CF 3 group. An all-fluorinated electrolyte, that is, 1.0 M LiPF 6 TFPC/2,2,2-trifluoroethyl carbonate (FEMC) (1/1 volume ratio) + FEC additive, was formulated and demonstrated excellent cycling stability in a high-voltage LiNi 0.5 Mn 0.3 Co 0.2 O 2 /graphite cell cycled between 3.0 and 4.6 V.

25 ENERGY STORAGE↗
DOE OSTI2025

Influence of Ether-Functionalized Pyrrolidinium Ionic Liquids on Properties and Li + Cation Solvation in Solvate Ionic Liquids

Ionic liquids are tunable solvents composed entirely of ions that have properties desirable as electrolytes for lithium batteries such as non-flammability and a large electrochemical stability window. Solvate ionic liquids are a subclass of ionic liquids that consist of a glyme-based solvent and lithium salt in an equimolar ratio, where Li + cation-glyme solvation interactions result in ionic liquid-like properties. LiG4TFSi is a well-studied solvate ionic liquid consisting of equimolar amounts of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and tetraglyme (G4). In this work, pyrrolidinium ionic liquids with ether-functionalized side chains were synthesized containing either one ether (EO1) moiety or three ether (EO3) moieties and mixed with LiG4TFSI to form a new class of electrolyte mixtures. Their physical and transport properties, as well as ion solvation structures, were characterized by electrochemical, thermal, rheological, and spectroscopic measurements. The conductivity of the electrolyte mixture composed of EO1:LiTFSI:G4 in a 1:1:1 molar ratio is 2.54 mS/cm at 30 °C, compared to 1.53 mS/cm for LiG4TFSI, an increase of 67%. A significant decrease in the conductivity to 0.279 mS/cm is observed for the EO3:LiTFSI:G4 mixture in a 1:1:0.4 molar ratio. Pulsed-field gradient nuclear magnetic resonance (PFG-NMR) measurements revealed that the EO1 cation diffuses significantly faster than the EO3 cation in their respective mixtures. Liquid-state 13 C NMR experiments indicate that Li + cations preferentially coordinate with tetraglyme. Li + cations do not coordinate with the EO1 cation and only coordinate with EO3 ether side chains at lower concentrations of tetraglyme. We hypothesize that the oligoether EO3 cation competes with G4 and TFSI - for lithium cation solvation in G4 deficient compositions, leading to a largely adverse effect on the mass transport properties of the electrolyte.

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

Generalizable, tunable control of divalent cation solvation structure via mixed anion contact ion pair formation

Multivalent batteries are a promising new technology for energy storage, but they face challenges to developing suitable electrolytes that can support reversible deposition/dissolution at the metal anode and enable compatibility with high voltage oxide cathode materials. Here, in this work, we investigate the solvation behavior of Zn 2+ , Mg 2+ , Ca 2+ and Cu 2+ in mixed anion electrolytes containing TFSI - and Cl - . Raman and nuclear magnetic resonance spectroscopies are utilized to probe the bulk solvation structure of these electrolytes and demonstrate that mixed anion contact ion pairs (CIPs) are formed in all four systems, indicating this behavior is likely general to divalent cations. Furthermore, the relative population of mixed anion CIPs can be tuned by controlling the relative ratio of TFSI : Cl, with significant CIP populations observed even at low relative fractions of Cl - . These findings imply that modifying the anion chemistry can easily adjust the solvation structure of bulk cations, which has important implications for the development of next-generation electrolytes. By understanding the factors that influence the formation of mixed anion CIPs, we can design systems that promote the formation of electrochemically-active solvation structures that can enable multivalent batteries with improved performance and lifetimes.

25 ENERGY STORAGE↗
DOE OSTI2024

Molecular Engineering Enabled Stable Deep Eutectic Amide-Based Electrolyte for High-Temperature Lithium–Metal Batteries

The development of advanced lithium-metal batteries (LMBs), such as high-temperature LMBs and high-energy-density LMBs, has critical requirements for electrolytes. However, conventional electrolytes suffer from thermal instability and insufficient electrolyte/Li interfacial compatibility, severely limiting their utilization in high-temperature LMBs. Herein, we design a high-temperature N-methylacetamide (NMAc)-based deep eutectic electrolyte (DEE) by molecular engineering on a solvation structure via a sacrificial additive of vinyl ethylene carbonate (VEC). Specifically, VEC interacts with the Li prior to NMAc, facilitating the formation of a solid electrolyte interphase to inhibit the reaction between Li and NMAc. The stable VEC-DEE effectively suppresses the growth of lithium dendrites and ensures the battery a cycling stability of 550 cycles at 80 °C. Additionally, we also demonstrate the application of VEC-DEE in high-energy-density LMBs with a high mass loading of 2.5 mAh/cm 2 . In conclusion, this research opens a new avenue for the rational design of advanced high-temperature electrolytes.

25 ENERGY STORAGE↗
DOE OSTI2025

Atomistic Insights into Lithium–Glyme Solvate Ionic Liquids: Effects of Chain Length and Anion Coordination

For this study, mixtures of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) in diglyme (G2), triglyme (G3) and tetraglyme (G4) at solvate ionic liquid (SIL) concentrations were investigated using classical molecular dynamics (cMD) simulations with a physically motivated force-field specifically developed for modeling these systems. The structural and dynamical properties of the mixtures were computed and analyzed. Lithium solvation shells, radial distribution functions, and X-ray structure factors were studied across the different SIL systems. Translational diffusion and rotational relaxation times were also evaluated, exhibiting similar trends with increasing glyme chain length. The results are consistent with experimental data and in good agreement with previous computational studies on G3 and G4. These findings validate the accuracy of the force field in modeling glyme systems and its use for describing the [Li(G2) 4/3 ][TFSI] mixture. Additionally, the thermal and electrochemical stability of these electrolytes were systematically examined. The thermal stability appears to be governed by cooperative interactions among glyme molecules, while the electrochemical stability is primarily influenced by Li + -anion interactions, which vary significantly with glyme chain length. Overall, the study sheds light on the crucial role of the anion in these glyme-based SILs and offers valuable insights into Li + -glyme systems at SIL concentrations, highlighting their promise as potential Li-ion battery electrolytes.

anions↗
DOE OSTI2022

Sulfone-based electrolytes for high energy density lithium-ion batteries

Here, in this work, localized high concentration electrolytes (LHCEs) based on tetramethylene sulfone (TMS) were designed. Similar to LHCEs based on other solvents, TMS-based LHCEs can achieve excellent compatibility with high energy density lithium ion batteries (LIBs) when combined with a proper additive. By comparing LHCEs based on different solvents and additives, it was revealed that the unique solvation structure of LHCEs facilitates the synergetic decomposition of anion, solvent and additive in the solid electrolyte interphase (SEI) formation. Proper combinations of the three constituents of the solvation sheaths in LHCEs can promote the formation of highly effective SEI on graphite negative electrode. The absence of LiPF 6 in LHCEs also suppresses the degradation of positive electrode materials in LIBs. The superior interphasial properties of LHCEs is the key to realizing the long lifespan of high energy density LIBs.

25 ENERGY STORAGE↗
DOE OSTI2023

Enabling selective zinc-ion intercalation by a eutectic electrolyte for practical anodeless zinc batteries

Abstract Two major challenges hinder the advance of aqueous zinc metal batteries for sustainable stationary storage: (1) achieving predominant Zn-ion (de)intercalation at the oxide cathode by suppressing adventitious proton co-intercalation and dissolution, and (2) simultaneously overcoming Zn dendrite growth at the anode that triggers parasitic electrolyte reactions. Here, we reveal the competition between Zn 2+ vs proton intercalation chemistry of a typical oxide cathode using ex-situ/ operando techniques, and alleviate side reactions by developing a cost-effective and non-flammable hybrid eutectic electrolyte. A fully hydrated Zn 2+ solvation structure facilitates fast charge transfer at the solid/electrolyte interface, enabling dendrite-free Zn plating/stripping with a remarkably high average coulombic efficiency of 99.8% at commercially relevant areal capacities of 4 mAh cm −2 and function up to 1600 h at 8 mAh cm −2 . By concurrently stabilizing Zn redox at both electrodes, we achieve a new benchmark in Zn-ion battery performance of 4 mAh cm −2 anode-free cells that retain 85% capacity over 100 cycles at 25 °C. Using this eutectic-design electrolyte, Zn | |Iodine full cells are further realized with 86% capacity retention over 2500 cycles. The approach represents a new avenue for long-duration energy storage.

25 ENERGY STORAGE↗
DOE OSTI2025

Rational Electrolyte Design for Elevated-Temperature and Thermally Stable Lithium-Ion Batteries with Nickel-Rich Cathodes

As the energy density of lithium-ion batteries (LIBs) increases, the shortened cycle life and the increased safety hazard of LIBs are drawing increasing concerns. To address such challenges, a series of localized high-concentration electrolytes (LHCEs) based on a solvating-solvent mixture of tetramethylene sulfone and trimethyl phosphate and a high flash-point diluent 1H,1H,5H-octafluoropentyl 1,1,2,2-tetrafluoroethyl ether were designed. The LHCEs exhibited non-flammability and greatly suppressed heat release at high temperatures, which would potentially improve the safety performance of the LIBs. Moreover, the optimal LHCE achieved capacity retentions of 87.1% and 81.7% in graphite||LiNi 0.8 Mn 0.1 Co 0.1 O 2 cells after 500 cycles at 25 °C and 45 °C, respectively, which were significantly better than the conventional electrolyte, whose capacity retentions were only 75.2% and 38.5% under the same condition. Mechanistic studies revealed that the LHCE not only formed a more robust solid electrolyte interphase, but also exhibited improved anodic stability, compared with the conventional electrolyte. Further, this work sheds light in rational electrolyte design for high energy density LIBs with high battery performance and low safety concerns.

25 ENERGY STORAGE↗
DOE OSTI2022

Revitalizing Iron Redox by Anion-Insertion-Assisted Ferro- and Ferri-Hydroxides Conversion at Low Alkalinity

Iron hydroxides are desirable alkaline battery electrodes for low cost and environmental beneficence. However, hydrogen evolution on charging and Fe 3 O 4 formation on discharging cause low storage capacity and poor cycling life. Here, we report that green rust (GR) (Fe 2+ 4 Fe 3+ 2 (HO – ) 12 SO 4 ), formed via sulfate insertion, promotes Fe(OH) 2 /FeOOH conversion and shows a discharge capacity of ~211 mAh g –1 in half-cells and Coulombic efficiency of 93% after 300 cycles in full-cells. Theoretical calculations show that Fe(OH) 2 /FeOOH conversion is facilitated by intercalated sulfate anions. Classical molecular dynamics simulations reveal that electrolyte alkalinity strongly impacts the energetics of sulfate solvation, and low alkalinity ensures fast transport of sulfate ions. Anion-insertion-assisted Fe(OH) 2 /FeOOH conversion, also achieved with Cl – ion, paves a pathway toward efficient utilization of Fe-based electrodes for sustainable applications.

25 ENERGY STORAGE↗
DOE OSTI2022

A Sobering Examination of the Feasibility of Aqueous Aluminum Batteries

Recent reports on aqueous aluminum (Al) batteries boast encouraging metrics including high energy density, nonflammability, and low raw material cost. However, the poorly understood solvation environment around the trivalent aluminum ions (Al3+) raises uncertainty regarding their feasibility. Furthermore, the corrosiveness of the acidic solutions and degree of hydration of aluminum trifluoromethanesulfonate (Al(OTf)3) salt is routinely mischaracterized. This study provides a rigorous examination of aqueous Al electrolytes, with the first compelling evidence for a dynamic octahedral solvation structure around Al3+ dominated by labile water and OH-, without Al-OTf contact ion pairs, at high concentrations. This solvation behavior and the concomitant electrostatic hydrolysis differs greatly from previously reported water-in-salt electrolytes, and occurs due to the high charge density of the Lewis acidic Al3+. Nuclear magnetic resonance spectroscopy and other physicochemical measurements quantitatively reveal how species activity evolves with concentration. The high proton activity observed in transport and electrochemical measurements constitutes a prohibitive barrier to the feasibility of rechargeable aluminum batteries with aqueous electrolyte.

Pastel, Glenn R.↗
DOE OSTI2023

Coordination-Dependent Chemical Reactivity of TFSI Anions at a Mg Metal Interface

Charge transfer across the electrode–electrolyte interface is a highly complex and convoluted process involving diverse solvated species with varying structures and compositions. Despite recent advances in in situ and operando interfacial analysis, molecular specific reactivity of solvated species is inaccessible due to a lack of precise control over the interfacial constituents and/or an unclear understanding of their spectroscopic fingerprints. However, such molecular-specific understanding is critical to the rational design of energy-efficient solid–electrolyte interphase layers. We have employed ion soft landing, a versatile and highly controlled method, to prepare well-defined interfaces assembled with selected ions, either as solvated species or as bare ions, with distinguishing molecular precision. Equipped with precise control over interfacial composition, we employed in situ multimodal spectroscopic characterization to unravel the molecular specific reactivity of Mg solvated species comprising (i.e., bis(trifluoromethanesulfonyl)imide, TFSI – ) anions and solvent molecules (i.e., dimethoxyethane, DME/G1) on a Mg metal surface relevant to multivalent Mg batteries. In situ multimodal spectroscopic characterization revealed higher reactivity of the undercoordinated solvated species [Mg-TFSI-G1] + compared to the fully coordinated [Mg-TFSI-(G1) 2 ] + species or even the bare TFSI – . These results were corroborated by the computed reaction pathways and energy barriers for decomposition of the TFSI – within Mg solvated species relative to bare TFSI – . Finally, we evaluated the TFSI reactivity under electrochemical conditions using Mg(TFSI) 2 –DME-based phase-separated electrolytes representing different solvated constituents. Based on our multimodal study, we report a detailed understanding of TFSI – decomposition processes as part of coordinated solvated species at a Mg-metal anode that will aid the rational design of improved sustainable electrochemical energy technologies.

25 ENERGY STORAGE↗
DOE OSTI2023

Tuning Transport via Interaction Strength in Cationic Conjugated Polyelectrolytes

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

36 MATERIALS SCIENCE↗
DOE OSTI2024

Hyperconjugation-controlled molecular conformation weakens lithium-ion solvation and stabilizes lithium metal anodes

Tuning the solvation structure of lithium ions via electrolyte engineering has proven effective for lithium metal (Li) anodes. Further advancement that bypasses the trial-and-error practice relies on the establishment of molecular design principles. Expanding the scope of our previous work on solvent fluorination, we report here an alternative design principle for non-fluorinated solvents, which potentially have reduced cost, environmental impact, and toxicity. By studying non-fluorinated ethers systematically, we found that the short-chain acetals favor the [gauche, gauche] molecular conformation due to hyperconjugation, which leads to weakened monodentate coordination with Li + . The dimethoxymethane electrolyte showed fast activation to >99% coulombic efficiency (CE) and high ionic conductivity of 8.03 mS cm -1 . The electrolyte performance was demonstrated in anode-free Cu$∥$LFP pouch cells at current densities up to 4 mA cm -2 (70 to 100 cycles) and thin-Li$∥$high-loading-LFP coin cells (200–300 cycles). Overall, we demonstrated and rationalized the improvement in Li metal cyclability by the acetal structure compared to ethylene glycol ethers. We expect further improvement in performance by tuning the acetal structure.

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

Solvation Structure and Electrochemical Properties of a New Weakly Coordinating Aluminate Salt as a Nonaqueous Electrolyte for Zinc Batteries

In continuation of our interest in developing multivalent electrolytes for energy storage, we report a new zinc salt with a weakly coordinating anion, tetrakis(perfluoro-tert-butoxy) aluminate (TPFA), as a stable electrolyte for nonaqueous systems. We examined the electrochemical and structural properties of this nonaqueous electrolyte in various solvents. ZnTPFA 2 supports highly reversible Zn deposition and stripping behavior in acetonitrile and ethereal solvents, with up to 91% Coulombic efficiency. A variety of analytical techniques were used to identify the local coordination structure around Zn 2+ in both the crystal phase and the solution phase, providing clear evidence of solvent coordination around the cation.

25 ENERGY STORAGE↗
DOE OSTI2024

Enhancing Cycling Stability of Lithium Metal Batteries by a Bifunctional Fluorinated Ether

Abstract The lifespan of lithium (Li) metal batteries (LMBs) can be greatly improved by the formation of inorganic‐rich electrode‐electrolyte interphases (EEIs) (including solid‐electrolyte interphase on anode and cathode‐electrolyte interphase on cathode). In this work, a localized high‐concentration electrolyte containing lithium bis(fluorosulfonyl)imide (LiFSI) salt, 1,2‐dimethoxyethane (DME) solvent and 1,2‐bis(1,1,2,2‐tetrafluoroethoxy)ethane (BTFEE) diluent is optimized. BTFEE is a fluorinated ether with weakly‐solvating ability for LiFSI so it also acts as a co‐solvent in this electrolyte. It can facilitate anion decomposition at electrode surfaces and promote the formation of more inorganic‐rich EEI layers. With an optimized molar ratio of LiFSI:DME:BTFEE = 1:1.15:3, LMBs with a high loading (4 mAh cm −2 ) lithium nickel manganese cobalt oxide (LiNi 0.8 Mn 0.1 Co 0.1 ) cathode can retain 80% capacity in 470 cycles when cycled in a voltage range of 2.8–4.4 V. The fundamental understanding on the functionality of BTFEE revealed in this work provides new perspectives on the design of practical high‐energy density battery systems.

25 ENERGY STORAGE↗
DOE OSTI2023

Localized high-concentration electrolytes get more localized through micelle-like structures

Liquid electrolytes in batteries are typically treated as macroscopically homogeneous ionic transport media despite having a complex chemical composition and atomistic solvation structures, leaving a knowledge gap of the microstructural characteristics. Here, we reveal a unique micelle-like structure in a localized high-concentration electrolyte, in which the solvent acts as a surfactant between an insoluble salt in a diluent. The miscibility of the solvent with the diluent and simultaneous solubility of the salt results in a micelle-like structure with a smeared interface and an increased salt concentration at the centre of the salt–solvent clusters that extends the salt solubility. These intermingling miscibility effects have temperature dependencies, wherein a typical localized high-concentration electrolyte peaks in localized cluster salt concentration near room temperature and is used to form a stable solid–electrolyte interphase on a Li metal anode. Importantly, these findings serve as a guide to predicting a stable ternary phase diagram and connecting the electrolyte microstructure with electrolyte formulation and formation protocols of solid–electrolyte interphases for enhanced battery cyclability.

25 ENERGY STORAGE↗
DOE OSTI2022

Polyacrylonitrile-based electrolytes: How processing and residual solvent affect ion transport and stability

Polyacrylonitrile (PAN) is one of the alternative candidate polymer hosts to form solid polymer electrolytes (SPEs) besides the widely used poly(ethylene oxide). In this study, we systematically investigate the processing of PAN based SPEs containing lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) salt, using dimethylformamide (DMF) as the solvent. The effects of PAN processing procedure including solution mixing, casting, and drying on the morphology, ion transport, solvation structure, Li and oxidative stability of PAN electrolytes are thoroughly examined. In particular, four drying conditions are investigated and the amount of residual DMF is accurately determined using infrared (IR) spectroscopy. Varying the drying conditions can lead to five orders of magnitude decrease in the ionic conductivity. As DMF content decreases, the SPE's stability again Li metal dramatically improves. The practical oxidative stability is also strongly affected by the residual DMF content, ranging from 2.5 V to 3.5 V, much lower than reported values. Finally, the role of the residual DMF solvent is elucidated. DMF content vitally influences ion solvation structure at different concentration regimes, which ultimately dictates the ion conduction mechanism and oxidative stability of PAN based SPEs. In conclusion, this thorough study lays the groundwork for future development of PAN based electrolytes.

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

Superior long-term cycling of high-voltage lithium-ion batteries enabled by single-solvent electrolyte

A new single-solvent electrolyte system comprising lithium bis(fluorosuflonyl) imide (LiFSI) and beta-fluorinated sulfone (TFPMS) was designed to enable very stable long-term cycling of high-voltage lithium-ion batteries. Compared to other fluorinated solvents such as alpha-fluorinated sulfone (FMES) and fluorinated carbonate (FEMC), which are prone to reduction on the graphite anode, the LiFSI-TFPMS system displayed outstanding compatibility with graphite. While regular carbonate and sulfone from the LiFSI electrolyte system are compatible with the graphite anode, their high solvating power not only induces severe corrosion on the aluminum cathode current collector at high voltage, but also renders a low aggregation level at a normal salt concentration (about 1.0 M), resulting in the formation of an unstable solid-electrolyte interphase (SEI) on the graphite anode. Owing to the low solvating power of TFPMS, the aggregation level of the LiFSI-TFPMS system is relatively high even at normal salt concentration, which not only facilitates the formation of a robust SEI by the sacrificial decomposition of LiFSI, but also suppresses the aluminum corrosion of the LiFSI electrolyte system at high voltage. Together with the high intrinsic anodic stability of TFPMS, the superior cycling performance of graphite parallel to LiNi 0.6 Co 0.2 Mn 0.2 O 2 cells was achieved by employing the non-flammable LiFSI-TFPMS single-solvent electrolyte system.

25 ENERGY STORAGE↗