Simulations of vibrational and solvation properties of nano-confined electrolyte solutions.
Abstract not provided.
Senanayake, Hasini↗
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Results for “Solvate Electrolytes”
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Design Criteria of Dilute Ether Electrolytes toward Reversible and Fast Intercalation Chemistry of Graphite Anode in Li-Ion Batteries
To date, dilute ether electrolytes have been believed to be incompatible with graphite in Li-ion batteries due to the detrimental solvent cointercalation and graphite exfoliation. Here, in this paper, we provide design criteria of dilute ether electrolytes for a reversible graphite anode based on tailoring the solvation structures and thermodynamic properties. We clarify that ether solvents can support graphite reversibly by modulating the anion. Our redesigned electrolyte consisting of a single-solvent 1,3-dioxolane (DOL) and 1 M single-salt lithium bis(fluorosulfonyl)imide (LiFSI) shows weakened Li-solvent interaction and results in an inorganic-rich solid-electrolyte interphase. Consequently, we achieved ~99.9% Coulombic efficiency with >96% capacity retention (~350 mAh/g) after 300 cycles at C/5 using natural graphite. The weakly solvated electrolyte maintains desirable transport properties, enabling better rate capability than carbonate electrolytes with an areal capacity of 2–4 mAh/cm 2 . We have demonstrated the potential of dilute ether electrolytes for facile desolvation-based intercalation chemistry in graphite, creating a viable path toward fast-charge Li batteries.
25 ENERGY STORAGE↗
Correction: The solvation structure, transport properties and reduction behavior of carbonate-based electrolytes of lithium-ion batteries
Correction for ‘The solvation structure, transport properties and reduction behavior of carbonate-based electrolytes of lithium-ion batteries' by Tingzheng Hou et al. , Chem. Sci. , 2021, 12 , 14740–14751, https://doi.org/10.1039/D1SC04265C.
Hou, Tingzheng↗
Solvation vs. surface charge transfer: an interfacial chemistry game drives cation motion
Electrolyte structure and ion solvation dynamics determine ionic conductivities, and ion (de)solvation processes dominate interfacial chemistry and electrodeposition barriers. In this work, we elucidate electrolyte effects facilitating or impeding Li + diffusion and deposition, and evaluate structural and energetic changes during the solvation complex pathway from the bulk to the anode surface.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Probing the Solvation Shells of Lithium Ions in Glyme-Based Electrolytes
Glymes have been extensively studied as solvents for Li-battery electrolytes, most recently in equimolar mixtures with lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), due to their ability to form stable solvates. However, directly quantifying free and coordinated glyme molecules in the liquid state has been challenging due to several experimental limitations. Here, in this work, new vibrational probes are demonstrated for studying the solvation structures of diglyme and triglyme in LiTFSI electrolytes. These IR probes make use of an amine group to report the solvation state of glymes at salt-to-solvent molar ratios ranging from 1:5 to 1:10. Characterization of the thermodynamic properties of the solvent exchange occurring in the first solvation shell of lithium ions (Li + ) showed an equilibrium constant for these probes close to unity at room temperature. This result demonstrates that the probes exhibit a similar solvation behavior to their glyme analogue. Concentration dependence studies also revealed a lack of significant amounts of contact ion pairs at the studied concentrations. Moreover, the first solvation shell of Li + appears to be formed by two partially chelating glyme molecules, establishing that even triglyme with multiple chelation sites does not fully coordinate the cation. Complementary molecular dynamics (MD) simulations agree with the experimental results and suggest that at these concentrations, TFSI – predominantly forms solvent-separated ion pairs. However, the simulations do not properly capture the partial solvation structure of the glyme molecules in the solvation shell of Li + as derived from the experiments.
electrolytes↗
Establishing a unified framework for ion solvation and transport in liquid and solid electrolytes
Electrolytes used in rechargeable batteries must enable rapid translation of the working ion between macroscopically separated electrodes. These electrolytes are, however, usually designed and synthesized using atomic-level insights. Whether the ideal electrolyte for a particular battery is a solid or a liquid remains an important unresolved question, especially as solids with conductivities comparable with liquids are discovered. Here, to help resolve such questions, we present the first steps toward a unified framework for relating atomic and continuum scale phenomena. Solvation shells in liquids are entities that translate with the working ion for a short while before they break up due to Brownian motion. By contrast, solvation cages in classical solids and polymers cannot not translate with the working ion. Mobility of the entities that make up the cages and shells, which is quantified by an order parameter, is shown to influence translation of the working ion on continuum length scales.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
A Systematic Study on the Effects of Solvating Solvents and Additives in Localized High‐Concentration Electrolytes over Electrochemical Performance of Lithium‐Ion Batteries
Abstract Localized high‐concentration electrolytes (LHCEs) based on five different types of solvents were systematically studied and compared in lithium (Li)‐ion batteries (LIBs). The unique solvation structure of LHCEs promotes the participation of Li salt in forming solid electrolyte interphase (SEI) on graphite (Gr) anode, which enables solvents previously considered incompatible with Gr to achieve reversible lithiation/delithiation. However, the long cyclability of LIBs is still subject to the intrinsic properties of the solvent species in LHCEs. Such issue can be readily resolved by introducing a small amount of additive into LHCEs. The synergetic decompositions of Li salt, solvating solvent and additive yield effective SEIs and cathode electrolyte interphases (CEIs) in most of the studied LHCEs. This study reveals that both the structure and the composition of solvation sheaths in LHCEs have significant effect on SEI and CEI, and consequently, the cycle life of energetically dense LIBs.
Jia, Hao↗
Solid-state interphases design for high-safety, high-voltage and long-cyclability practical batteries via ethylene carbonate-free electrolytes
In this study, ethylene carbonate (EC) plays a crucial role in current electrolytes for batteries. However, EC reacts exothermically with the electrode to trigger thermal runaway and undergoes continuous oxidative decomposition at high voltages, hindering it application for next-generation batteries. Here we report a simple and effective strategy to design sulfolane(SL)-based electrolyte with reshaped anions-dominated solvation structure, forming highly stable inorganic-dominated electrode-electrolyte interphases that efficiently stabilize nickel-rich cathode and graphite anode. Compared with the conventional electrolyte, practical pouch-type LiNi 0.8 Co 0.1 Mn 0.1 O 2 |Graphite cell with SL-based electrolyte significantly improve self-generated heat T 1 and thermal runaway triggering T 2 by 9.6 and 42.0 °C, respectively. More surprisingly, the pouch cell with SL-based electrolyte exhibits outstanding capacity retention of 88 % after 1000 cycles charged up to 4.5 V. The study brings new insights for unlocking advanced electrolyte candidates to build next-generation practical safer high-energy batteries.
25 ENERGY STORAGE↗
Tailored Solvation and Interface Structures by Tetrahydrofuran-Derived Electrolyte Facilitates Ultralow Temperature Lithium Metal Battery Operations
Ineffectiveness of Li-ion batteries (LIBs) in cold climates hinders electronics to work in various conditions including frigid environments, despite high demands. Given that intrinsic properties of LIB materials cause this problem, optimized cell chemistries ultimately are required for low-temperature usage. In this study, Li-metal batteries (LMBs) composed of a Li-metal anode (LMA) stabilized by a localized high-concentration electrolyte (LHCE) are found to significantly enhance low-temperature performance. The LHCE allows the LMA to have compact and regular deposition and excellent plating/stripping efficiency at sub-zero temperatures. The LHCE produces an inorganic-rich solid-electrolyte interphase with larger amounts of Li 2 O/LiF interfaces, dominance of ion aggregates in Li + solvation, and enhanced Li + transport, which can greatly improve the LMA stability. LMB full cells based on LiNi 0.8 Co 0.1 Mn 0.1 O 2 cathodes with the tailored electrolyte show high retentions of 75 and 64 % at -20 and -40 °C, respectively. Furthermore, the LMB configuration retains its charge-discharge capability even at -60 °C.
25 ENERGY STORAGE↗
Quantifying the Correlation between Coordination Chemistry, Interfacial Formation, and Electrochemical Performances for Mg Battery Electrolytes
Here, the rise of magnesium batteries as promising post-Li-ion energy storage technologies has sparked considerable attention toward understanding the fundamental aspects of coordination chemistry concerning Mg cations in multivalent electrolytes. This exploration includes investigating how coordination influences crucial electrolyte properties like solubility, electroreduction stability, and the formation of the interphase, all of which are pivotal for practical battery applications. Despite recent progress in developing a few functional electrolytes, a comprehensive understanding of the solvation structure that can facilitate efficient Mg deposition performance and the formulation of general design rules based on the solvation structure is still lacking. In our study, we endeavor to establish a connection between solvent and anion interactions with Mg 2+ , interface formation, and cycling performance through a series of organic ether solvents (tetrahydrofuran, glyme, diglyme, and triglyme) and amine solvents (dimethylamine, 3-methoxypropylamine, and dimethoxyethylamine). Our findings reveal a distinct coordination trend for solvent/Mg 2+ and (Mg-TFSI):solvent across various solvents, which dictates the extent of ion pairing for TFSI salts with increasing solvent molecule size and denticity. The solvated species in the bulk electrolyte across different solvents lead to diverse interfacial chemistries with varying decomposition components. We also explore the cycling efficiency as well as Mg deposition overpotentials for different solvents. A correlation analysis was conducted to assess the interplay between the structure and performance. Lastly, we apply the insights gained from these results to tailor the relative anion/Mg 2+ coordination structures using cosolvent systems, aiming for improved cell performance.
25 ENERGY STORAGE↗
Tailoring Electrolytes by Decoupling the Roles of Li + and Lithium Polysulfides in Li–S Batteries
Understanding the distinct roles of lithium ions (Li + ) and lithium polysulfide intermediates, Li 2 S x (LiPS) is critical for designing electrolytes that can extend the practical cycle life of lithium–sulfur (Li–S) batteries. Here, in this work, we decouple the solvation and solubility effects of Li + and LiPS and correlate them with electrochemical performance through a cosolvent strategy. Li + solubility and solvation primarily dictate the electrolyte’s ionic conductivity and the reversibility of lithium anode stripping/plating. In contrast, LiPS solvation governs the thermodynamics of sulfur (S 8 ), LiPS, and lithium sulfide (Li 2 S) interconversion, while the LiPS solubility determines their redox kinetics. By employing a fluorinated–glyme (F-glyme) cosolvent, specifically 1,2-bis(2,2-difluoroethoxy)ethane (F4DEE), that exhibits low LiPS solubility yet moderate Li + solvation, we designed an electrolyte that enhances lithium anode stability while maintaining sufficient sulfur cathode kinetics, thereby prolonging Li–S cell cycle life. This study provides mechanistic insights into the interplay between Li+ and LiPS in Li–S electrochemistry and offers design principles for next-generation electrolytes for Li–S batteries.
Yang, Jingtian [Argonne National Laboratory (ANL),↗
Solvation Structure and Dynamics of Mg(TFSI) 2 Aqueous Electrolyte
Using ab initio molecular dynamics (AIMD) simulations, classical molecular dynamics (CMD) simulations, small-angle X-ray scattering (SAXS), and pulsed-field gradient nuclear magnetic resonance (PFG-NMR), the solvation structure and ion dynamics of magnesium bis(trifluoromethanesulfonyl)imide (Mg(TFSI) 2 ) aqueous electrolyte at 1, 2, and 3 m concentrations are investigated. From AIMD and CMD simulations, the first solvation shell of an Mg 2+ ion is found to be composed of six water molecules in an octahedral configuration and the solvation shell is rather rigid. The TFSI - ions prefer to stay in the second solvation shell and beyond. Meanwhile, the comparable diffusion coefficients of positive and negative ions in Mg(TFSI) 2 aqueous electrolytes have been observed, which is mainly due to the formation of the stable [Mg(H 2 O) 6 ] 2+ complex, and, as a result, the increased effective Mg ion size. Finally, the calculated correlated transference numbers are lower than the uncorrelated ones even at the low concentration of 2 and 3 m, suggesting the enhanced correlations between ions in the multivalent electrolytes. This work provides a molecular-level understanding of how the solvation structure and multivalency of the ion affect the dynamics and transport properties of the multivalent electrolyte, providing insight for rational designs of electrolytes for improved ion transport properties.
36 MATERIALS SCIENCE↗
Li/CFx Cells Optimized for Low-Temperature Operation
Some developments reported in prior NASA Tech Briefs articles on primary electrochemical power cells containing lithium anodes and fluorinated carbonaceous (CFx) cathodes have been combined to yield a product line of cells optimized for relatively-high-current operation at low temperatures at which commercial lithium-based cells become useless. These developments have involved modifications of the chemistry of commercial Li/CFx cells and batteries, which are not suitable for high-current and low-temperature applications because they are current-limited and their maximum discharge rates decrease with decreasing temperature. One of two developments that constitute the present combination is, itself, a combination of developments: (1) the use of sub-fluorinated carbonaceous (CFx wherein x<1) cathode material, (2) making the cathodes thinner than in most commercial units, and (3) using non-aqueous electrolytes formulated especially to enhance low-temperature performance. This combination of developments was described in more detail in High-Energy-Density, Low- Temperature Li/CFx Primary Cells (NPO-43219), NASA Tech Briefs, Vol. 31, No. 7 (July 2007), page 43. The other development included in the present combination is the use of an anion receptor as an electrolyte additive, as described in the immediately preceding article, "Additive for Low-Temperature Operation of Li-(CF)n Cells" (NPO- 43579). A typical cell according to the present combination of developments contains an anion-receptor additive solvated in an electrolyte that comprises LiBF4 dissolved at a concentration of 0.5 M in a mixture of four volume parts of 1,2 dimethoxyethane with one volume part of propylene carbonate. The proportion, x, of fluorine in the cathode in such a cell lies between 0.5 and 0.9. The best of such cells fabricated to date have exhibited discharge capacities as large as 0.6 A h per gram at a temperature of 50 C when discharged at a rate of C/5 (where C is the magnitude of the current, integrated for one hour, that would amount to the nominal charge capacity of a cell).
Smart, Marshall C.↗
Development of Electrolytes under Lean Condition in Lithium–Sulfur Batteries
Lithium–sulfur (Li–S) batteries stand out as one of the promising candidates for next-generation electrochemical energy storage technologies. A key requirement to realize high-specific-energy Li–S batteries is to implement low amount of electrolyte, often characterized by the electrolyte/sulfur (E/S) ratio. Low E/S ratio aggravates the known challenges for Li–S batteries and introduces new ones originated from the high concentration of polysulfides in limited electrolyte reservoir. Here, in this review, the connections between the fundamental properties of electrolytes and the electrochemical/chemical reactions in Li–S batteries under lean electrolyte condition are elucidated. The emphasis is on how the solvating properties of the electrolyte affect the fate of polysulfides. Built upon the mechanistic analysis, different strategies to design lean electrolytes to improve the overall process of Li–S reactions and Li anode protection are discussed.
25 ENERGY STORAGE↗
Solvate Structures and Computational/Spectroscopic Characterization of LiCF3SO3 Electrolytes
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Yun, Sung-Hyun↗
Exploring the Ion Solvation Environments in Solid-State Polymer Electrolytes through Free-Energy Sampling
The success of poly(ethylene oxide) (PEO) in solid-state polymer electrolytes for lithium-ion batteries is well established. Recently, in order to understand this success and to explore possible alternatives, we studied polyacetal electrolytes to deepen the understanding of the effect of the local chemical structure on ion transport. Advanced molecular dynamics techniques using newly developed, tailored interaction potentials have helped elucidate the various coordination environments of ions in these systems. In particular, the competition between cation-Anion pairing and coordination by the polymer has been explored using free-energy sampling (metadynamics). At equivalent reduced temperatures, with respect to the polymer-specific glass-Transition temperature, two-dimensional free-energy plots reveal the existence of multiple coordination environments for the lithium (Li) ions in these systems and their relative stabilities. Furthermore, we observe that the Li-ion movement in PEO follows a serial, stepwise pathway when moving from one coordination state to another, whereas this happens in a more continuous and concerted fashion in a polyacetal such as poly(1,3-dioxalane) [P(EO-MO)]. The implication is that interconversion between coordination states of the Li ions may be easier in P(EO-MO). However, the overarching observation from our free-energy analysis is that Li-ion coordination is dominated by the polymer (in either case) and contact-ion pairs are rare. We rationalize the observed higher increase in glass-Transition temperature (Tg) with salt loading in polyacetals as due to intermolecular Li-ion coordination involving multiple polymer chains, rather than just one chain for PEO-based electrolytes. This interchain coupling in the polyacetals, resulting in the higher Tg, works against any gains due to variations in Li-ion coordination that might enhance transport processes over PEO. Further research is required to overcome the interdependence between local coordination and macroscopic properties to compete with PEO electrolytes at the same absolute working temperature.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Conformational Isomerization of Imide Anions Governs Solvation and Transport in Water-in-Salt Electrolytes
The behavior of highly concentrated electrolytes departs radically from the dilute-solution theory, yet the molecular origin of this transformation remains unresolved. Here, we identify the conformational isomerization of molecular ions as a decisive, previously unrecognized control parameter governing structure and transport in crowded aqueous electrolytes. Across a series of fluorosulfonimide anions, we show that increasing concentration drives a collective shift from extended transoid to compact cisoid conformers, revealed by small-angle X-ray scattering, vibrational spectroscopy, pulsed-field gradient NMR, and molecular dynamics simulations. This conformational transition triggers a collapse of the hydrogen-bonded water network and the emergence of densely packed ionic domains with confined water, producing a qualitative change in Li+ transport from solvent-mediated diffusion to network-confined hopping. Anion size and asymmetry systematically tune the onset of this transition, demonstrating that molecular geometry dictates mesoscale organization and dynamics in the ion-rich regime. Our results establish ion conformation, not merely composition or coordination, as a fundamental thermodynamic variable in concentrated solutions, providing a chemical framework that unifies solvation structure and transport in water-in-salt electrolytes and suggesting new principles for designing dense ionic media.
Nguyen, Huong TD↗
Non‐Flammable Ester Electrolyte with Boosted Stability Against Li for High‐Performance Li Metal Batteries
Abstract In traditional non‐flammable electrolytes a trade‐off always exists between non‐flammability and battery performance. Previous research focused on reducing free solvents and forming anion‐derived solid‐electrolyte interphase. However, the contribution of solvated anions in boosting the stability of electrolyte has been overlooked. Here, we resolve this via introducing anions into Li + solvation sheaths using anions with similar Gutmann donor number (DN) to that of solvents. Taking trimethyl phosphate fire‐retardant (DN=23.0 kcal mol −1 ) and NO 3 − (DN=22.2 kcal mol −1 ) as an example, NO 3 − is readily involved in the Li + solvation sheath and reduces the polarity of solvent. This results in boosted stability of electrolyte against Li. The developed non‐flammable electrolyte has low viscosity, high ionic conductivity and is low cost. The reversibility of Li‐Cu cell was improved to 99.49 % and the lifespan of practical LMBs was extended by >100 %.
Wang, Zhijie↗