Fluorinated alkyl-phosphate-based electrolytes with controlled lithium-ion coordination structure

Sawayama, Saki; Todorov, Yanko; Mimura, Hideyuki; Morita, Masayuki; Fujii, Kenta

doi:10.1039/c9cp01974j

Cited by 13 publications

(15 citation statements)

References 58 publications

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“…Solvents with higher D N values lead to full ion dissociation to yield successfully solvated metal ions and counteranions, whereas solvents with lower D N values cause ions to form contact ion-pairs due to low solvation power, resulting in poor ionic conductivity and battery performance. Furthermore, it has been reported that solvent bulkiness (molecular size of the solvent) is an important factor in controlling ion solvation; specifically, a bulky solvent tends to reduce the solvation number of the metal ion to induce ion-pair formation in the electrolyte solution. − …”

Section: Introductionmentioning

confidence: 99%

2,2,2-Trifluoroethyl Acetate as an Electrolyte Solvent for Lithium-Ion Batteries: Effect of Weak Solvation on Electrochemical and Structural Characteristics

et al. 2021

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We report the characteristics of 2,2,2-trifluoroethyl acetate (TFEAc) as a new type of electrolyte solvent for lithium (Li)-ion batteries. TFEAc-based electrolyte solutions containing 1.0 mol dm–3 LiTFSA salt [TFSA: bis(trifluoromethanesulfonyl)amide] exhibited a Li-ion insertion reaction into the negative graphite electrode in the first cycle; however, the performance was noticeably degraded during subsequent cycles due to the lack of solid electrolyte interphase (SEI) formation on the electrode. The electrode reaction was markedly improved when a small amount of ethylene carbonate (EC) was added into the LiTFSA/TFEAc solution, which demonstrated a high-rate charge/discharge performance superior to that of the conventional carbonate-based Li-ion battery electrolyte, that is, 1.0 mol dm–3 LiPF6 in the EC + dimethyl carbonate mixture. Quantitative Raman spectral analysis and density functional theory calculations revealed that TFEAc could be categorized as an organic solvent with low solvation power (i.e., with a predicted Gutmann donor number of 9.1); thus, Li ions mainly formed contact ion-pair complexes, [Li(TFEAc)2(TFSA)], in binary LiTFSA/TFEAc solutions. Adding EC into the TFEAc electrolyte modified the Li-ion complex structure; namely, Li ions were coordinated with each TFEAc, EC, and TFSA component to yield [Li(TFEAc)(EC)(TFSA)] as the major species, which coexisted with the ion pair [Li(TFEAc)2(TFSA)]. We discuss the effect of the weak coordination solvent and EC additive on the graphite electrode reaction from the aspects of Li-ion desolvation and SEI formation.

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Section: Introductionmentioning

confidence: 99%

2,2,2-Trifluoroethyl Acetate as an Electrolyte Solvent for Lithium-Ion Batteries: Effect of Weak Solvation on Electrochemical and Structural Characteristics

et al. 2021

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“…The composition (i.e., the number of each cation and anion) in the simulation box and the resulting box size and density at equilibrium are presented in Table S1. Details of the procedure are also similar to those carried out in our previous study. , The data acquired at 0.1 ps intervals for the last 500 ps were evaluated to determine the X-ray weighted structure factors [ S MD ( q )] and radial distribution functions [ G MD ( r )]. The CLaP force field (originally OPLS-AA/Amber force fields), including the intermolecular Lennard-Jones, Coulombic interactions, and intramolecular interactions (i.e., bond stretching, angle bending, and torsion of dihedral angles), was used for C 2 mIm and TFSA ions. , The OPLS-AA force field was used for PGA and GA ions. , The partial charges ( q + and q – ) used in MD simulations in this study are presented in Table S2; the PGA + and GA + values were obtained from quantum chemical calculations (using the ChelpG method; the details are described in the Supporting Information).…”

Section: Methodsmentioning

confidence: 99%

Physicochemical and Structural Properties of a Hydrophobicity/Hydrophilicity Switchable Ionic Liquid

et al. 2020

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Herein, we report the physicochemical and structural properties of a new solubility-switchable ionic liquid (IL) comprising the glycerammonium (GA) cation with a hydrophilic group, the GA cation attached to an acetal-based protective group [protected GA (PGA)], and bis-(trifluoromethanesulfonyl)amide (TFSA). The interionic volumes (V inter ) of the hydrophobic [PGA][TFSA] and hydrophilic [GA][TFSA] ILs were evaluated based on solution density, revealing weaker ion−ion interactions in these relative to conventional ILs. The [PGA][TFSA] and [GA][TFSA] also exhibit poor ion-conducting properties, with up to an order of magnitude lower ionic conductivity (σ) and self-diffusion coefficient (D), as compared with conventional ILs. Radial distribution functions derived from high-energy X-ray total scattering experiments [G exp (r)] and molecular dynamics (MD) simulations [G MD (r)] indicate that nearest-neighbor ion−ion interactions in the [PGA][TFSA] and [GA][TFSA] are comparable to those in imidazolium-based IL. Conversely, these are appreciably weakened at the second-and third-neighbors and thus less structured in the long range (r > 12 Å) and very different from the highly ordered imidazolium IL. The atom−atom pair correlation function derived from the MD simulations disclose that at a local scale, specific interactions are absent, with only an electrostatic interaction in the [PGA][TFSA], whereas the GA cations interact with TFSA anions via hydrogen bonding of diol groups in the GA and O atoms in the TFSA. No hydrogen bonding group within the PGA cation leads to weak ion-hydration resulting in a phase separation of [PGA][TFSA] and water; in contrast, the GA cations are easily hydrogen-bonded with water molecules to be miscible in aqueous solutions.

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“…These techniques can provide useful structural information on the number and the type of the functional groups coordinating to the metallic ions based on the chemical shifts and the vibrational spectra. Also, secondary ion mass spectroscopy serves to understand the details of ion–solvent interactions. − In comparison to these techniques, X-ray − and neutron − total scattering techniques can characterize the structures of electrolytes in a more direct manner through the so-called pair distribution function (PDF). Moreover, in combination with the Reverse Monte Carlo (RMC) or Empirical Potential Structure Refinement (EPSR) methods, the three-dimensional coordinate of the constituent atoms of the electrolyte can be derived.…”

Section: Introductionmentioning

confidence: 99%

Application of Anomalous X-ray Scattering Method to Liquid Electrolytes Used in a Battery: Local Structural Analysis around a Dilute Metallic Ion

et al. 2020

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In liquid electrolytes used for a battery, various metal complexes are formed as a result of ion–solvent and ion–ion interactions, which strongly influence the properties of the electrolyte and thus the performance of the battery. Therefore, the structural characterization of such complexes is of great importance. In this study, the anomalous X-ray scattering (AXS) technique was applied to the potassium hydroxide solution including ∼0.3 mol % zinc, which is widely used in various batteries such as the alkaline battery. In spite of the small amount of the metallic ions, we have successfully extracted a local structure around zinc after careful data analysis. The obtained pair distribution function exhibited not only the short-range correlation corresponding to the Zn–O bond within the zincate anion but also a medium-range correlation above 3.5 Å. The present study demonstrates the capability of the AXS technique to detect local structures around dilute metallic ions in liquid electrolytes, which will largely extend the applicable range of this technique, especially to the field related to batteries.

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Fluorinated alkyl-phosphate-based electrolytes with controlled lithium-ion coordination structure

Abstract: Graphite electrode reaction in coordination-controlled LiFSA/TFEP electrolytes.

Cited by 13 publications

References 58 publications

2,2,2-Trifluoroethyl Acetate as an Electrolyte Solvent for Lithium-Ion Batteries: Effect of Weak Solvation on Electrochemical and Structural Characteristics

2,2,2-Trifluoroethyl Acetate as an Electrolyte Solvent for Lithium-Ion Batteries: Effect of Weak Solvation on Electrochemical and Structural Characteristics

Physicochemical and Structural Properties of a Hydrophobicity/Hydrophilicity Switchable Ionic Liquid

Application of Anomalous X-ray Scattering Method to Liquid Electrolytes Used in a Battery: Local Structural Analysis around a Dilute Metallic Ion

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