Vibrational Spectroscopic Study on Ion Solvation and Association of Lithium Perchlorate in 4-Methoxymethyl-ethylene Carbonate

Solvation interaction and ion association in solutions of lithium perchlorate/4-methoxymethyl-ethylene carbonate （MEC） have been studied by using Infrared and Raman spectra as a function of concentration of lithium perchlorate. The splitting of ring deformation band and ring ether asymmetric stretching band, and the change of carbonyl stretching band suggest that there should be a strong interaction between Li^＋ and the solvent molecules, and the site of solvation should be the oxygen atom of carbonyl group. The apparent solvation number of Li^＋ was calculated by using band fitting technique. The solvation number was decreased from 3.3 to 1.1 with increasing the concentration of LiClO4/MEC solutions. On the other hand, the band fitting for the ClO4^- band revealed the presence of contact ion pair, and free ClO4^- anion in the concentrated solutions.     

Vibrational Spectroscopic Study on Ion Solvation and Ion Association of Lithium Tetrafluoroborate in 4‐Ethoxymethyl‐ethylene Carbonate

应用红外及拉曼光谱研究了不同浓度的四氟硼酸锂在4-乙氧甲基-碳酸乙烯酯溶剂中的离子溶剂化和离子缔合现象。环形变谱带和羰基伸缩振动谱带的分裂,以及骨架环振动谱带的迁移和分裂表明,锂离子与溶剂分子间存在着较强的相互作用,这种相互作用是通过溶剂羰基氧原子实现的。利用光谱拟合技术定量计算了表观溶剂化数。随着电解质锂盐浓度的增加,溶剂化数逐渐由4.32降至1.26。此外,四氟硼酸根v1谱带的分裂表明在高浓度溶液中存在着光谱自由的四氟硼酸根、直接接触离子对和离子对二聚体。     

Structural and transport characteristics of polyethylene oxide/phenolic resin blend solid polymer electrolytes

Details on the structure and transport characteristics of the solid polymer electrolyte polyethylene oxide (PEO)/lithium salt (LiClO₄) modified by novolac phenolic resin are presented here. From IR spectra it could be concluded that complex formation occurred through multiple interactions between the ether oxygen of PEO–lithium, phenolic lithium, and the phenolic ether oxygen of PEO. The free hydroxyl band in phenolic reflected that phenolic closely interacted with both the PEO polymer and ionic salt. With increasing salt content in PEO, the vibration band corresponding to the ClO anion (～623 cm^?1) displayed growth of a shoulder at ～635 cm^?1, suggesting the formation of Li⁺…ClO₄^? ion pairing. However, in the presence of phenolic, ion‐pairing formation was effectively suppressed, which suggested that the phenolic moiety facilitated a greater degree of LiClO₄ salt dissociation. Activation energy analysis revealed two conducting pathways: one through the amorphous PEO and the other through the PEO/phenolic amorphous matrix. The high ion conductivity originated from effective salt dissociation and the establishment of a new conduction network formed by PEO and phenolic. Furthermore, the structural modification also extended the thermal stability and mechanical strength of the solid polymer electrolyte composite. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 3866–3875, 2004     

Raman spectra in the libration region of concentrated aqueous solutions of lithium-6 and lithium-7 halides. Evidence for tetrahedral Li(OH2) 4 +

The Raman spectra of saturated solutions of⁶LiCl and⁷LiCl have been decomposed into Gaussian components, one of which is a polarized band that occurs at 360 cm^–1 when the ion is⁶Li⁺ and shifts to 335 cm^–1 when the ion is⁷Li⁺. Equivalent bands occur in the spectra of saturated solutions of⁶LiBr and⁷LiBr at 343 and 320 cm^–1, respectively. These bands are assigned to solvent-separated ion aggregates. The Raman spectra of 8.0 and 3.5 m solutions of the isotopic lithium chlorides have been decomposed into five Gaussian components, three of which are assigned to water librations. In addition, there is a polarized band at 440 cm^–1 independent of the lithium isotope used, and a depolarized band which occurs at 385 cm^–1 in the⁶LiCl solutions and 360 cm^–1 in the⁷LiCl solutions. We interpret these two additional bands as theA ₁ andF ₂ stretching modes of Li⁺ tetrahedrally solvated by water molecules.     

Changes in the composition of the solvation shell of lithium ions in γ-butyrolactone upon addition of 15-crown-5 as studied by quantum chemistry

Quantum chemical modeling of Li⁺ ion transfer from the solvation shell of γ-butyrolactone (GBL) as the solvent to the cavity of 15-crown-5 (15C5) macrocyclic ligand was carried out. Calculations were performed using the PBE nonempirical density functional and an extended basis for the SBK pseudopotential. The solvation energy was included in the framework of the polarizable continuum model. The calculated geometric parameters of GBL and 15C5 molecules are in good agreement with experimental X-ray data. The energies and structures of the Li(GBL) _n ⁺ (n = 1–5) complexes and Li(GBL) _m (15C5)⁺ (m = 0–3) mixed complexes were calculated. The binding energy of the fifth GBL molecule is low; therefore, the Li⁺ ion is mainly surrounded by four GBL molecules. The formation of mixed complexes by consecutive displacement of GBL molecules from the solvation shell of the lithium ion leads to structures with the coordination number 5. The equilibrium constants of these processes were used to determine the dependence of the composition of the solvation complexes on the concentration of 15C5 in the system. The concentrations of the Li(15C5)⁺ and Li(GBL)(15C5)⁺ complexes appeared to be comparable. The revealed structural features of the Li⁺ solvation complexes in the GBL-15C5 system were used to analyze the operating efficiency of lithium power sources.     

Calculation of solvation free energies of Li+ and O2 ? ions and neutral lithium–oxygen compounds in acetonitrile using mixed cluster/continuum models

Solvation effects play a major role in determining the cycling characteristics of the non-aqueous rechargeable Li-air battery. We use a mixed cluster/continuum solvent model with varying number of explicit solvent molecules (n?=?4–10) to calculate the solvation free energies ( $ \Updelta G_{\text{solv}}^{*} $ ) of Li⁺ and O₂ ^? ions and neutral LiO₂, Li₂O₂, LiO, and Li₂O species in acetonitrile solvent. Calculations for complexes with the full first solvation shell around Li⁺ (n?=?4) and O₂ ^? (n?=?8) show excellent agreement with the solvation free energies obtained using the cluster pair approximation (the error is below 2.0?kcal/mol). The use of the pure continuum model fitted to reproduce the experimental values of $ \Updelta G_{\text{solv}}^{*} $ (Li⁺) and $ \Updelta G_{\text{solv}}^{*} $ (O₂ ^?) gives the solvation free energies of various lithium–oxygen species (Li _x O _y ; x, y?=?1, 2) that are in excellent agreement with the results obtained using mixed cluster/continuum models (n?≥?8). This provides a theoretical framework for including solvent effects in the theoretical models of oxygen reduction and evolution reactions in the aprotic Li-air battery.     

Experimental and Computational Analysis of the Solvent‐Dependent O2/Li+‐O2− Redox Couple: Standard Potentials,Coupling Strength,and Implications for Lithium–Oxygen Batteries

Understanding and controlling the kinetics of O₂ reduction in the presence of Li⁺‐containing aprotic solvents, to either Li⁺‐O₂^? by one‐electron reduction or Li₂O₂ by two‐electron reduction, is instrumental to enhance the discharge voltage and capacity of aprotic Li‐O₂ batteries. Standard potentials of O₂/Li⁺‐O₂^? and O₂/O₂^? were experimentally measured and computed using a mixed cluster‐continuum model of ion solvation. Increasing combined solvation of Li⁺ and O₂^? was found to lower the coupling of Li⁺‐O₂^? and the difference between O₂/Li⁺‐O₂^? and O₂/O₂^? potentials. The solvation energy of Li⁺ trended with donor number (DN), and varied greater than that of O₂^? ions, which correlated with acceptor number (AN), explaining a previously reported correlation between Li⁺‐O₂^? solubility and DN. These results highlight the importance of the interplay between ion–solvent and ion–ion interactions for manipulating the energetics of intermediate species produced in aprotic metal–oxygen batteries.     

Effects of Ions on the OH Stretching Band of Water as Revealed by ATR-IR Spectroscopy

The effects of various cations (Li⁺, Na⁺, K⁺, Rb⁺, Cs⁺, Mg²⁺, Ca²⁺, Sr²⁺, Ba²⁺, Mn²⁺, Co²⁺, and Ni²⁺) and anions (Cl^?, Br^?, I^?, \( {\text{NO}}_{3}^{ - } \) , \( {\text{ClO}}_{4}^{ - } \) , \( {\text{HCO}}_{3}^{ - } \) , and \( {\text{CO}}_{3}^{2 - } \) ) on the molar absorptivity of water in the OH stretching band region (2,600–3,800 cm^?1) were ascertained from attenuated total reflection infrared spectra of aqueous electrolyte solutions (22 in all). The OH stretching band mainly changes linearly with ion concentrations up to 2 mol·L^?1, but several specific combinations of cations and anions (Cs₂SO₄, Li₂SO₄, and MgSO₄) present different trends. That deviation is attributed to ion pair formation and cooperativity in ion hydration, which indicates that the extent of the ion–water interaction reflected by the OH stretching band of water is beyond the first solvation shell of water molecules directly surrounding the ion. The obtained dataset was then correlated with several quantitative parameters representing structural and dynamic properties of water molecules around ions: ΔG _HB, the structural entropy (S _str), the viscosity B-coefficient (B _η ), and the ionic B-coefficient of NMR relaxation (B _NMR). Results show that modification of the OH stretching band of water caused by ions has quasi-linear relations with all of these parameters. Vibrational spectroscopy can be a useful means for evaluating ion–water interaction in aqueous solutions.     

Enhanced lithium-ion intercalation and conduction of transparent tantalum oxide films by lithium addition with an atmospheric pressure plasma jet

An investigation is conducted on enhancing lithium-ion intercalation and conduction performance of transparent organo tantalum oxide (TaO _y C _z ) films, by addition of lithium via a fast co-synthesis onto 40 Ω/□ flexible polyethylene terephthalate/indium tin oxide substrates at the short exposed durations of 33–34 s, using an atmospheric pressure plasma jet (APPJ) at various mixed concentrations of tantalum ethoxide [Ta(OC₂H₅)₅] and lithium tert-butoxide [(CH₃)₃COLi] precursors. Transparent organo-lithiated tantalum oxide (Li _x TaO _y C _z ) films expose noteworthy Li⁺ ion intercalation and conduction performance for 200 cycles of reversible Li⁺ ion intercalation and deintercalation in a 1 M LiClO₄-propylene carbonate electrolyte, by switching measurements with a potential sweep from ?1.25 to 1.25 V at a scan rate of 50 mV/s and a potential step at ?1.25 and 1.25 V, even after being bent 360° around a 2.5-cm diameter rod for 1000 cycles. The Li⁺ ionic diffusion coefficient and conductivity of 6.2?×?10^?10 cm²/s and 6.0?×?10^?11 S/cm for TaO _y C _z films are greatly progressed of up to 9.6?×?10^?10 cm²/s and 7.8?×?10^?9 S/cm for Li _x TaO _y C _z films by co-synthesis with an APPJ.     

Far-infrared and Raman study of lithium and sodium cryptates in nonaqueous solvents

Far-infrared spectra of sodium and lithium cryptates were observed in several nonaqueous solvents. The spectra are characterized by a broad band whose frequency is independent of the solvent or of the anion and which is assigned to the vibration of the cation in the cryptand cavity. The band frequencies were 234±2, 218±1, 243±3, and 348±1 cm^?1 for Na⁺-C222, Na⁺-C221, Li⁺-C221, and Li⁺-C211 cryptates, respectively. These bands were found to be Raman-inactive, indicating that the cation-ligand interaction is very largely electrostatic in nature.     

1,4,7,10-Tetraoxacyclododecane(12-Crown-4) as Neutral Carrier for Lithium Ion in Lithium Ion Selective Electrode

Abstract

1,4,7,10-Tetraoxacyclododecane (12-crown-4) (I) and its lithium complex (II) are used as neutral carriers for lithium ion in polyvinylchloride membrane ion selective electrodes. The lithium response varies with concentration, being near Mernstian at low (10^?5-10^?4 M) concentrations and sub-Nernstian (24-28 aV) at higher concentrations (10^?3 M). The selectivity coefficients K_Li ^Pot _M for II are: Na⁺ (0.12), K⁺ (0.66), Cs⁺ (0.15), Mg²⁺ (1.6 × 10^?4), Ca²⁺ (3.1 × 10^?4), Ba²⁺ (9.5 × 10^?7), NH⁺ ₄ (9.0 × 10^?2), H⁺ (2.2).     

Radiative stabilization of trimethylsilyl adduct ions

Ketones and phenol react with trimethylsilyl ions to form adduct ions by radiatively or collisionally stabilized addition reactions, in contrast to aliphatic alcohols and ethers, which react with trimethylsilyl ions to form adduct ions by a rapid two-step process. Secondorder rate constants for the addition of trimethylsilyl ions to acetone were independent of pressure from 3×10^?7 to 50×10^?7 tort at room temperature; consequently, the adduct ions, [M+73]⁺, are formed primarily by radiatively stabilized addition in these ion cyclotron resonance experiments.     

Electrical conductivity and ionic association of lithium and sodium perchlorates in tetrahydrofuran

The total limiting molar electrical conductivities of ions and triads of ions and the association constants of ions with the formation of ion pairs and triads of ions were calculated from the concentration dependences of the electrical conductivity of solutions of lithium and sodium perchlorates in tetrahydrofuran at 278.15–318.15 K with the use of the method specially developed earlier. The experimental total limiting electrical conductivities were used to calculate the limiting molar electrical conductivities and attraction friction factors of separate ions (Li⁺, Na⁺, ClO ₄ ^? , Li₂ClO ₄ ⁺ , Na₂ClO ₄ ⁺ , Li(ClO₄) ₂ ^? , and Na(ClO₄) ₂ ^? ). The constants of ion association into ion pairs were used to calculate the Gibbs energy of non-Coulomb interionic interaction (ΔG*_+?), and the constants of association into triads of ions, to determine the a ₃ distance parameter between the centers of the ion and the dipole of the ion pair. Positive ΔG*_+?), values and deviations of the experimental a ₃ value from the distance parameter calculated theoretically (a ₃ ⁰ ) for the triad of ions (Δa ₃ = a ₃ ? a ₃ ⁰ ) were related to non-Coulomb repulsion in the region of overlap of the solvation shells of ions and the influence of temperature and ion charge density on this repulsion.     

FTIR study of ion solvation and ion-pair formation in alkaline and alkaline earth metal salt solutions in acetonitrile

The IR spectra of alkaline and alkaline earth metal perchlorate and of lithium bromide solutions in acetonitrile, obtained with the help of FTIR measurements in the region of the C-N stretching mode of the solvent, reveal bands produced by acetonitrile molecules in the solvation shells and bands of ClO ₄ ^– ions in contact and solvent separated ion pairs. The shift and the attenuation of the C-N stretching band of acetonitrile at 2254 cm^–1 is used for the calculation of cation solvation numbers for Li⁺(4), Na⁺(4), Mg²⁺(6), Ca²⁺(6), and Ba²⁺(6). No solvation is assumed for the contact ion pairs of LiClO₄, LiBr, NaClO₄, Mg(ClO₄)₂, Ca(ClO₄)₂, and Ba(ClO₄)₂. The association constants of the symmetrical electrolytes are compared to those obtained from other methods.     

Active centres in the anionic polymerization of methoxypolyethyleneglycol methacrylates

The nature of the propagation sites in the anionic polymerization of methoxypolyethyleneglycol methacrylates in the presence of Li counterion has been studied through i.r. spectra of the model compounds, Li derivatives of isobutyric acid esters, (CH₃)₂CLiCOO(CH₂CH₂O)_nCH₃ with n from 1 to 4, and of 2,2,4-trimethylglutaric acid esters. The wavelength of the absorption band of lithioisobutyrates, due to the vibration of the

grouping, is independent of the nature of the solvent. This fact has been explained by intramolecular solvation of Li⁺ by the polyethereal alcoholic residue. The spectra of the metalated trimethylglutarates give evidence of concurrent solvation of Li⁺ by the alkoxy carbonyl group in the γ-position and the alcoholic residue of the ester group bound to the metalated carbon atom. When the number of ethyleneoxide units in the polyethereal chain is increased, the coordination of Li⁺ to it prevails over the interaction with the γ-malkoxycarbonyl group.     

Solvation environment of lithium ion in a LiBF<Subscript>4</Subscript>–propylene carbonate system in the presence of 1-ethyl-3-methylimidazolium tetrafluoroborate ionic liquid studied by NMR and quantum chemical modeling

Solutions of lithium and 1-ethyl-3-methylimidazolium tetrafluoroborates ([emim][BF₄]) in propylene carbonate (PC) were studied by the high-resolution NMR method on ¹H, ⁷Li, ¹¹B, ¹³C, and ¹⁹F nuclei. The degree of solvation of lithium ions was determined by measuring selfdiffusion coefficients by pulse-field-gradient spin echo NMR method on ¹H, ⁷Li, and ¹⁹F nuclei. The hydrodynamic radii of solvated Li⁺ cations were estimated by the Stokes–Einstein equation. The model structures of the solvation complexes of Li⁺ ion with propylene carbonate molecules and BF ₄ ^– anion and their associates with ionic liquid components were calculated in terms of the density function theory. The calculated values of the chemical shifts were compared with the experimental data. PC molecules were predominantly bound to the Li⁺ cation, while LiBF₄–[emim][BF₄]–PC (1: 4: 4) electrolyte had a maximum conductivity of 9.5 mS cm^–1 at 24 °С compared to the compositions of a lower content of the solvent.     

A Vibrational Spectroscopic Study of Ion Solvation in Lithium Perchlorate/Propylene Carbonate Electrolyte

Abstract

The infrared (IR) and Raman spectra of propylene carbonate (PC) containing various concentrations of LiClO₄ have been measured and analyzed. The difference in spectra of PC with and without LiClO₄ was attributed to the interaction of the PC molecules and lithium ions. This interaction occurs mainly on the carbonyl oxygen atom of the PC molecule. The ring deformation, symmetric ring deformation, carbonyl stretching and stretching of ring oxygens for PC are sensitive to this interaction. The solvation number of Li⁺ is also calculated. On the other hand, the structure of the ClO^? ₄ is also affected by PC molecule, forming the solvent separated ion pairs.     

Supramolecular Polymer Ion Conductor with Weakened Li Ion Solvation Enables Room Temperature All-Solid-State Lithium Metal Batteries

Improved durability, enhanced interfacial stability, and room temperature applicability are desirable properties for all-solid-state lithium metal batteries (ASSLMBs), yet these desired properties are rarely achieved simultaneously. Here, in this work, it is noticed that the huge resistance at Li metal/electrolyte interface dominantly impeded the normal cycling of ASSLMBs especially at around room temperature (<30 °C). Accordingly, a supramolecular polymer ion conductor (SPC) with “weak solvation” of Li⁺ was prepared. Benefiting from the halogen-bonding interaction between the electron-deficient iodine atom (on 1,4-diiodotetrafluorobenzene) and electron-rich oxygen atoms (on ethylene oxide), the O-Li⁺ coordination was significantly weakened. Therefore, the SPC achieves rapid Li⁺ transport with high Li⁺ transference number, and importantly, derives a unique Li₂O-rich SEI with low interfacial resistance on lithium metal surface, therefore enabling stable cycling of ASSLMBs even down to 10 °C. This work is a new exploration of halogen-bonding chemistry in solid polymer electrolyte and highlights the importance of “weak solvation” of Li⁺ in the solid-state electrolyte for room temperature ASSLMBs.     

Kristallstruktur und elektrische Leitfähigkeit von Li2–2xMn1+xCl4-Spinelltyp-Mischkristallen

Crystal Structure and Electric Conductivity of Spinel-Type Li_2–2xMn_1+xCl₄ Solid Solutions The electric conductivity of the fast lithium ion conductors Li_2–2xMn_1+xCl₄ was measured by impedance spectroscopic methods. The conductivities obtained, e.g. ～ 4 × 10^?1 Ω^?2 cm^?1 at 570 K, depend only little on the lithium content. The crystal structure of Li_1.6Mn_1.2Cl₄ was determined by neutron powder and X-ray single crystal diffraction (space group Fd3 m, Z = 8, a = 1 049.39(6) pm, R_w = 1.4% on the basis of 170 reflections). The lithium deficient chloride crystallizes in an inverse spinel structure like the stoichiometric compound Li₂MnCl₄ according to the formula (Li_0,8)[Li_0,4Mn_0,6]₂Cl₄ with vacancies ( ) at the tetrahedral sites. The decrease of the M_oct? Cl distances with the increase of x reveals that the ionic radius of Mn²⁺ in chlorides is equal or even smaller than that of Li⁺ opposite to fluorides and oxides. The ? Cl distances of spinel type chlorides are 237 ( _tet) and 274 pm ( _oct), respectively. The mechanism of the ionic conductivity is discussed.     

Vibrational spectroscopic and density functional theory studies on ion solvation and ion association of lithium tetrafluoroborate in N,N-dimethylcarbamoyl chloride-based solvents

Solvation and association interactions in solutions of LiBF₄/DMCC (DMCC for N,N-dimethylcarbamoyl chloride) and LiBF₄/DMCC–DME (DME for 1,2-dimethoxyethane) have been studied as a function of concentration of lithium tetrafluoroborate by infrared and Raman spectroscopy. Strong interactions between Li⁺ and solvent molecules or BF₄⁻ anions are observed. The apparent solvation numbers of Li⁺ in LiBF₄/DMCC solutions were deduced. Band-fitting to the B–F stretching band of BF₄⁻ anion permits detailed assess of the ion pairing. Based on the calculations of density function theory, optimal structures of Li⁺(DMCC)_n (n = 1–3) were suggested. It is found that the lithium ion was preferentially solvated by DME in DMCC–DME binary solvents. This finding is supported by quantum chemistry calculations.