Li-NMR study of the stoichiometry, stability and exchange kinetics of Li ion with 12-Crown-4, 15-Crown-5 and cryptands C222, C221 and C211 in 50% ionic liquid-acetonitrile mixtures

⁷Li-NMR spectroscopy was used to study the complexation of Li⁺ ion with 12C4, 15C5, C222, C221, C211 in acetonitrile (AN) and its 50% (wt/wt) mixtures with two new room temperature ionic liquids, 1-ethyl-3-methylimidazolium hexafluorophosphate (EMim PF₆) and 1-ethyl-3-methylimidazolium tetrafluoroborate (EMim BF₄) at 298 K. Excluding the cases of Li⁺-C211 in all solvents and Li⁺-C221 in AN and 50% (wt/wt) AN-EMim PF₆, in other cases, the exchange between free and 1:1 complexed Li⁺ was fast on the NMR time scale and only a single population average ⁷Li signal was observed. Formation constants of the resulting 1:1 complexes were evaluated by computer fitting of the chemical shift-mole ratio data and integration of two ⁷Li signals. All complexes in EMim PF₆ were found to be more stable than those in EMim BF₄. ⁷Li-NMR line-shape analysis was used to determine the kinetic parameters and the mechanism for the chemical exchange of Li⁺ between the free and 1:1 complex with C221 in 50% (wt/wt) AN-EMim PF₆ mixtures solution. By comparing our study with the previous one, it is derived that, increasing the percentage of ion liquid in acetonitrile, changes the mechanism and decrease the exchange rate constant of Li⁺ ion between free and complex sites.     

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.     

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。     

Ionic processes in solid-electrolyte passivating films on lithium

The electrochemical behaviour of a Li electrode in solutions of LiAlCl₄ in thionyl chloride, LiBF₄ in γ-butyrolactone and LiClO₄ in the mixed solvent propylene carbonate (PC) + dimethoxyethane (DME) in the process of cell storage has been investigated by the methods of electrode impedance spectroscopy and pulse voltammetry. Analogous studies have been carried out in PC + DME solution with the Li electrode coated with a specially formed protecting film of Li₂CO₃. The results have been compared with those obtained earlier for other lithium electrochemical systems. The general regularities of the Li electrode electrochemical kinetics attributed to the process of Li⁺ ion transport through a passivating film coating a lithium surface have been discussed. Received: 22 February 1999 / Accepted: 20 June 1999     

Lithium,rubidium and cesium ion removal using potassium iron(III) hexacyanoferrate(II) supported on polymethylmethacrylate

Potassium iron(III) hexacyanoferrate(II) supported on poly methyl methacrylate, has been developed and investigated for the removal of lithium, rubidium and cesium ions. The material is capable of sorbing maximum quantities of these ions from 5.0, 2.5 and 4.5 M HNO₃ solutions respectively. Sorption studies, conducted individually for each metal ion, under optimized conditions, demonstrated that it was predominantly physisorption in the case of lithium ion while shifting to chemisorption with increasing ionic size. Distribution coefficient (K _d) values followed the order Cs⁺ > Rb⁺ > Li⁺ at low concentrations of metal ions. Following these findings Cs⁺ can preferably be removed from 1.5 to 5 M HNO₃ nuclear waste solutions.     

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.     

Ionic Covalent Organic Frameworks with Spiroborate Linkage

A novel type of ionic covalent organic framework (ICOF), which contains sp³ hybridized boron anionic centers and tunable countercations, was constructed by formation of spiroborate linkages. These ICOFs exhibit high BET surface areas up to 1259 m² g^?1 and adsorb a significant amount of H₂ (up to 3.11 wt %, 77 K, 1 bar) and CH₄ (up to 4.62 wt %, 273 K, 1 bar). Importantly, the materials show good thermal stabilities and excellent resistance to hydrolysis, remaining nearly intact when immersed in water or basic solution for two days. The presence of permanently immobilized ion centers in ICOFs enables the transportation of lithium ions with room‐temperature lithium‐ion conductivity of 3.05×10^?5 S cm^?1 and an average Li⁺ transference number value of 0.80±0.02. Our approach thus provides a convenient route to highly stable COFs with ionic linkages, which can potentially serve as absorbents for alternative energy sources such as H₂, CH₄, and also as solid lithium electrolytes/separators for the next‐generation lithium batteries.     

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.     

Intercalation processes influence the structure and electrophysical properties of lithium-conducting compounds having defect perovskite structure

The structural features and electrophysical properties of lithium-conducting compounds having defect perovskite structure based on Li_0.5La_0.5Nb₂O₆ and Li_0.5La_0.5TiO₃ were studied using X-ray diffraction and synchrotron analyses, potentiometry, and complex impedance spectroscopy. Intercalated lithium was found to differently influence ion conductance in titanium- and niobium-containing materials. This difference was found to arise from the structural features of the materials. The systems studied have high chemical diffusion coefficients of lithium (D _Li⁺ = 1 × 10⁻⁶ cm²/s for Li_0.5La_0.5Nb₂O₆ and D _Li⁺ = 3.3 × 10⁻⁷ cm²/s for Li_0.5La_0.5TiO₃).     

Profiling lithium distribution in Sn anode for lithium-ion batteries with neutrons

Measuring the distribution of lithium in high capacity lithium-ion battery (LIB) electrodes is essential to understanding the coulombic losses during the lithiation/delithiation processes that occur while charging and discharging the cell. In this research, two half-cell prototypes were fabricated by electrochemically lithiating Sn foil anodes in 1M LiBF₄ in a 1:1 (wt:wt) ethylene carbonate and dimethyl carbonate solutions at a constant potential of 0.50 and 0.67 V (vs. Li/Li⁺). The neutron depth profiling (NDP) technique was employed to study the Li distributions in the anodes. Li concentration profiles were resolved for the samples lithiated under different conditions for LIB studies. In addition, this paper demonstrated an in situ NDP measurement of an electrochemical cell with a thin window design, which reveals the dynamics of lithium distribution within the Sn anode.     

Polymer electrolytes based on poly(ester diacrylate), ethylene carbonate, and LiClO4: a relationship of the conductivity and structure of the polymer according to IR spectroscopy and quantum chemical modeling data

New polymer electrolytes based on poly(ester diacrylate) (PEDA), LiClO₄, and additives of ethylene carbonate (EC) have a Li⁺ ion conductivity comparable with that of liquid electrolytes. The conductivity first decreases by an order of magnitude at an EC content of ??5 wt.% and then increases by three orders of magnitude at 55 wt.% EC. To understand the nature of this extreme dependence, a comprehensive study using IR spectroscopy and quantum chemical modeling was performed. It was found that the changes in the IR spectra with an increase in the EC content were stepwise to form at final stage the same absorption peaks that were observed for the IR spectra of LiClO₄ solutions in EC. The density functional theory studies of the energy and structures of mixed Li⁺ complexes and LiClO₄ with EC and PEDA, which was modeled by oligomers H-((CH₂)₂COO(CH₂)₂O) _n -CH₃ (n ?? 10) showed a stronger binding of the lithium ion with the polymer matrix in the mixed complexes with one EC molecule at a low content of EC resulting, most likely, in a decrease in the conductivity. Less stable mixed complexes with three EC molecules can be formed with an increase in the EC fraction and they become unstable in EC excess because of the transition of the Li⁺ ions to solvate complexes containing only EC molecules.     

Spectroscopic studies of ionic solvation. XVIII. Solvation of the lithium ion in acetone and acetone-nitromethane mixtures

Solvation of the lithium ion by acetone was studied in acetone-nitromethane solutions by Raman, infrared, and⁷Li and³⁵Cl NMR spectroscopic techniques. It was confirmed that the 390-cm^?1 IR acetone band is split by the lithium ion and that a 369-cm^?1 IR band, attributed by other authors to Li⁺-nitromethane vibration, is due to the vibration of acetone in the lithium inner solvation shell. The frequency of the Li⁺-nitromethane vibrational band is strongly anion dependent due to contact-ion-pair formation. Several different techniques indicate that Li⁺ is solvated by four acetone molecules, and approximate equilibrium-constant values for the stepwise solvation reaction were calculated. The influence of weak complexing agents on Li⁺ ClO ₄ ^? ion-pair formation was investigated.     

New NASICON type oxyanion high capacity anode, Li2Co2(MoO4)3, for lithium-ion batteries: preliminary studies

We describe in this paper the lithium insertion/extraction behavior of a new NASICON type Li₂Co₂(MoO₄)₃ at a low potential and explored the possibility of considering this new oxyanion material as anode for lithium-ion batteries for the first time. Li₂Co₂(MoO₄)₃ was synthesized by a soft-combustion glycine-nitrate low temperature protocol. Test cells were assembled using composite Li₂Co₂(MoO₄)₃ as the negative electrode material and a thin lithium foil as the positive electrode material separated by a microporous polypropylene (Celgard® membrane) soaked in aprotic organic electrolyte (1 M LiPF₆ in EC/DMC). Electrochemical discharge down to 0.001 V from OCV (～3.5 V) revealed that about 35 Li⁺ could ^possibly be inserted into Li₂Co₂(MoO₄)₃ during the first discharge (reduction) corresponding to a specific capacity amounting to 1,500 mAh g^?1. This is roughly fourfold higher compared to that of frequently used graphite electrodes. However, about 24 Li⁺ could be extracted during the first charge. It is interesting to note that the same amount of Li⁺ could be inserted during the second Li⁺ insertion process (second cycle discharge) giving rise to a second discharge capacity of 1,070 mAh g^?1. It was also observed that a major portion of lithium intake occurs below 1.0 V vs Li/Li⁺, which is typical of anodes being used in lithium-ion batteries.     

Alkali fluoride containing fluorozirconate glasses: Electrical properties and NMR investigation

Electrical properties of glasses inside the ZrF₄BaF₂ThF₄LiF system have been studied as a function of composition by conductivity and NMR measurements. Two series of materials can be distinguished. The transport properties of highly concentrated Li⁺ glasses seem only to result from the Li⁺ concentration and to increase with that concentration. On the contrary, a mixed contribution of F^? and Li⁺ ions must be considered for the low Li⁺ concentration glasses. On the other hand, the modifier cations (Ba²⁺ at low concentrations of lithium, Li⁺ at high ones) can greatly influence the transport properties. Glasses with a high Li content exhibit good electrical performance (e.g., $\text{σ}{}_{\mathrm{<mtext>175°</mtext><mtext>C</mtext>}}\text{? 2 × 10}{}^{\mathrm{?4}}\text{Ω}{}^{\mathrm{?1}}\text{cm}{}^{\mathrm{?1}}$ for the glass of composition Zr_0.20Ba_0.10Li_0.60Th_0.10F₂).     

Polyethylene-supported poly(acrylonitrile-co-methyl methacrylate)/nano-Al2O3 microporous composite polymer electrolyte for lithium ion battery

Nano-Al₂O₃ was doped in poly(acrylonitrile-co-methyl methacrylate) (P(AN-co-MMA)), and polyethylene(PE)-supported P(AN-co-MMA)/nano-Al₂O₃ microporous composite polymer electrolyte (MCPE) was prepared. The performances of the prepared MCPE for lithium ion battery use, including ionic conductivity, electrochemical stability, interfacial compatibility, and cyclic stability, were studied by scanning electron spectroscopy, linear sweep voltammetry, and electrochemical impedance spectroscopy. It is found that the nano-Al₂O₃ significantly affects the MCPE performances. Compared to the MCPE without any nano-Al₂O₃, the MCPE with 10 wt.% nano-Al₂O₃ reaches its best performances. Its ionic conductivity is improved from 2.0 × 10⁻³ to 3.2 × 10⁻³ S cm⁻¹, its decomposition potential is enhanced from 5.5 to 5.7 V (vs Li/Li⁺), and its interfacial resistance on lithium is reduced from 520 to 160 Ω cm². Thus, the battery performance is improved.     

Facile Preparation and Lithium Storage Properties of TiO2@Graphene Composite Electrodes with Low Carbon Content

Over the past decade, TiO₂/graphene composites as electrodes for lithium ion batteries have attracted a great deal of attention for reasons of safety and environmental friendliness. However, most of the TiO₂/graphene electrodes have large graphene content (9–40 %), which is bound to increase the cost of the battery. Logically, reducing the amount of graphene is a necessary part to achieve a green battery. The synthesis of TiO₂ nanosheets under solvothermal conditions without additives is now demonstrated. Through mechanical mixing TiO₂ nanosheets with different amount of reduced graphene (rGO), a series of TiO₂@graphene composites was prepared with low graphene content (rGO content 1, 2, 3, and 5 wt %). When these composites were evaluated as anodes for lithium ion batteries, it was found that TiO₂+3 wt % rGO manifested excellent cycling stability and a high specific capacity (243.7 mAh g^?1 at 1 C; 1 C=167.5 mA g^?1), and demonstrated superior high‐rate discharge/charge capability at 20 C.     

Two-Plateau Li-Se Chemistry for High Volumetric Capacity Se Cathodes

For Li-Se batteries, ether- and carbonate-based electrolytes are commonly used. However, because of the “shuttle effect” of the highly dissoluble long-chain lithium polyselenides (LPSes, Li₂Se_n, 4≤n≤8) in the ether electrolytes and the sluggish one-step solid-solid conversion between Se and Li₂Se in the carbonate electrolytes, a large amount of porous carbon (>40 wt % in the electrode) is always needed for the Se cathodes, which seriously counteracts the advantage of Se electrodes in terms of volumetric capacity. Herein an acetonitrile-based electrolyte is introduced for the Li-Se system, and a two-plateau conversion mechanism is proposed. This new Li-Se chemistry not only avoids the shuttle effect but also facilitates the conversion between Se and Li₂Se, enabling an efficient Se cathode with high Se utilization (97 %) and enhanced Coulombic efficiency. Moreover, with such a designed electrolyte, a highly compact Se electrode (2.35 g_Se cm⁻³) with a record-breaking Se content (80 wt %) and high Se loading (8 mg cm⁻²) is demonstrated to have a superhigh volumetric energy density of up to 2502 Wh L⁻¹, surpassing that of LiCoO₂.     

Thermochemistry of Complex Formation of Endofullerene Li<Superscript>+</Superscript>@C<Subscript>60</Subscript> with the Triflate Ion

The density functional theory method at the M06-2X/6-31G(d,p) level was used to calculate the optimal geometry and thermodynamic parameters of formation of the Li⁺CF₃SO₃^? and Li⁺@C₆₀(CF₃SO₃^?) ion pairs, as well as topological characteristics of the electron density distribution in the critical point (3,?1) of bonds between lithium cation endofullerene Li⁺@C₆₀, and the triflate anion in a vacuum and in chlorobenzene.