Increase In Ion Size Research Articles

(Invited) How Does Intercalation Ion Species Determine the Electrochemical Properties of Cathode Materials for Rechargeable Batteries?

Alkali-ion intercalation compounds are widely used as cathode materials for rechargeable batteries, including Li-, Na-, and K-ion batteries. For many years, researchers have developed layered oxide cathode materials for Na- and K-ion batteries given that the layered oxides show high reversible capacity and high working voltage in Li-ion technology. However, our works have demonstrated that the layered oxide compounds may not be good cathode candidates for Na and K systems. There are two main issues:[1-4] (i) Na and K transition metal oxide compounds form non-stoichiometric composition (x<1.0 in A x MO2, A= Na and K). It leads practical difficulty of realizing Na- and K-ion batteries because all the Na and K ions should come from the cathode in rocking-chair batteries. (ii) As the insertion ion size increases, the voltage curve becomes much sloped. The sloped voltage curves result in low specific capacity and average voltage. Both the problems are attributable to much stronger Na+-Na+ and K+-K+ interaction than Li+-Li+ in the layered oxide structure. In this respect, polyanion compounds that have 3 dimensional arrangements of Na and K ions, resulting in longer Na+-Na+ and K+-K+ distance, will be better candidates. We proposed KVPO4F[5] as an example of polyanion compounds and it has stoichiometric composition and provides high average voltage of ~4.3 V (vs. K/K+) with a reversible capacity of ~105 mAh/g.We further investigated the effect of intercalation ion species in K x VPO4F (x~0).[6] Our work demonstrates the voltage for Na intercalation is even higher than that for Li insertion unlike the common belief that Li insertion voltage is always higher than Na insertion. The lower Li intercalation voltage is likely attributed to unstable Li site in large cavity, making less stable discharged product upon Li insertion vs. Na insertion. In addition, we found that Li intercalation is more sluggish than Na and K intercalation in K x VPO4F (x~0). Since Li ion is too small compared to cavity in the cathode, Li ions are undercoordinated in the transition state, in which a Li ion is coordinated by two anions only. Therefore, Li ion migration barrier is much higher than Na and K migration. This finding teaches us that large cavity size (or channel size) is not always good for fast alkali ion migration and we need to finely tune the cavity size suitable for each intercalating ion species.

Reaction Mechanism and Surface Film Formation of Conversion Materials for Lithium- and Sodium-Ion Batteries: An XPS Case Study on Sputtered Copper Oxide (CuO) Thin Film Model Electrodes

Charge storage based on conversion reactions is a promising concept to store electrical energy. Many studies have been devoted to conversion reactions with lithium; however, still many scientific questions remain due to the complexity of the reaction mechanism combined with surface film formation. Replacing lithium by sodium is an attractive approach to widen the scope of conversion reactions and to study whether the increase in ion size changes the reaction mechanisms and whether the cell performance benefits or worsens. In this study, we use thin film electrodes as a additive-free model system to study the conversion reaction of CuO with sodium (CuO/Na) by means of electrochemical methods, microscopy, and X-ray photoelectron spectroscopy. The reaction mechanism and film formation are being discussed. Some important differences to the analogue lithium-based system (CuO/Li) are found. Whereas CuO has been reported as charge product in CuO/Li cells, charging is incomplete in the case of CuO/Na and only Cu2...

SIZE DEPENDENCE OF SOLVATION STRUCTURE AND DYNAMICS OF IONS IN LIQUID N-METHYLACETAMIDE: A MOLECULAR DYNAMICS SIMULATION STUDY

The solvation structure and dynamics of alkali metal (Li+, Na+, K+, Rb+, Cs+) and halide (F-, Cl-, Br-, I-) ions in liquid N -methylacetamide (NMA) are calculated at two different temperatures T = 313 K and 453 K, by using classical molecular dynamics simulations. We have also considered [Formula: see text] and some larger cations such as I +, Me 4 N +, and Et4N+ in this study to investigate the size dependence solvation structure and dynamics of ions in liquid NMA. With the increase of ion size, the self-diffusion coefficients of cations are found to increase and the maximum is observed at Me4N+ , whereas for halide ions the increase of diffusion coefficient with ion size continues up to I- and no maximum is observed. However, the relative increase of the diffusion coefficients of larger ion compared to those of Li+ and F+ are found to be significantly higher at low temperature. Results are very good in agreement with experimental observation.

Voids and necks in liquid ammonia and their roles in diffusion of ions of varying size

Voids in a medium are defined as the regions that are located outside an appropriately defined occupied space associated with molecules. Dynamical properties like diffusion can be related to the structure and distribution of voids present in the medium. This work deals with an analysis of voids and diffusion in liquid ammonia. The analysis of voids is done by the construction of Voronoi polyhedra and Delaunay tessellation. We have performed a series of molecular dynamics simulations of monovalent cations and anions of varying size in liquid ammonia at two different temperatures of 210 and 240 K to investigate the effects of ion size on the diffusion of ions and roles of voids in determining the observed diffusion behavior. It is found that with the increase of ion size, the diffusion coefficients first increase and then pass through a maximum similar to the behavior observed earlier for diffusion in water. The observed results are explained in terms of passage through voids and necks that are present in liquid ammonia.

Diffusion of ions in supercritical water: Dependence on ion size and solvent density and roles of voids and necks

We have performed molecular dynamics simulations of alkali metal (Li +, Na +, K +, Rb +, Cs +) and halide (F −, Cl −, Br −, I −) ions in supercritical water at 673 K. The calculations were done for water at three different densities of 1.0, 0.7 and 0.35 g cm −3 to investigate the effects of solute size on the diffusion of ions in supercritical water. On increase of ion size, we observe a maximum for diffusion of ions in supercritical water of higher densities (1.0 and 0.7 g cm −3). However, no such maximum is found for ion diffusion in the supercritical water of low density (0.35 g cm −3) or for diffusion of neutral solutes at all densities. These results are analyzed in terms of passage through voids and necks present in supercritical water. Correlations of the observed diffusion behavior with the sizes of ions and voids present in the systems are discussed.

Structural diversification of the coordination mode of divalent metals with 1,3-propanediaminetetraacetate (1,3-pdta): The missing crystal structure of the s-block metal complex [Sr 2(1,3-pdta)(H 2O) 6]·H 2O

This paper reports the synthesis and X-ray characteristics of the missing homonuclear s-block metal complex {[Sr 2(1,3-pdta)(H 2O) 6]·H 2O} n . In the title compound, the hexadentate 1,3-propanediaminetetraacetate (1,3-pdta) ligand joins to two Sr(II) centers via the diamine chain. Moreover, each Sr(II) is bridged through two carboxylate O atoms and a water molecule to two neighboring Sr(II) ions. The coordination sphere around each Sr(II) ion consists of one diamine nitrogen, four carboxylate oxygens and four water molecules. Comparison with the previously reported M(II)–1,3-pdta complexes reveals that increasing of the ion size results in the incorporation of water molecules into its first coordination sphere and consequent increase of the coordination number (C.N.) from six to seven or eight, while keeping the hexadentate coordination mode of the ligand. Further increase of the metal ion size leads to the loss of the chelating properties of the diamine and formation of a bis-tridentate complex. Associated with it is the change in the binding mode of the carboxylate groups. This forms the basis for classification of divalent metal 1,3-pdta complexes into five distinct structural classes. Additionally, in the present study X-ray powder diffraction and IR spectroscopy were used to distinguish the different structural types of M(II)–1,3-pdta complexes, including Ba[Ba(1,3-pdta)]·2H 2O which has been used for their preparation.

Effect ofA-site size difference on polar behavior inMBiScNbO6(M=Na, K, and Rb): Density functional calculations

We investigate the effect of $A$-site size differences in the double perovskites ${\text{BiScO}}_{3}\text{\ensuremath{-}}M{\text{NbO}}_{3}$ ($M=\text{Na}$, K, and Rb) using first-principles calculations. We find that the polarization of these materials is $70--90\text{ }\ensuremath{\mu}\text{C}/{\text{cm}}^{2}$ along the rhombohedral direction. The main contribution to the high polarization comes from large off-centerings of Bi ions, which are strongly enhanced by the suppression of octahedral tilts as the $M$-ion size increases. A high Born effective charge of Nb also contributes to the polarization and this contribution is also enhanced by increasing the $M$-ion size.

Molecular dynamics study of hydrated alkali and halide ions in liquid nitrobenzene

The structure, dynamics and energetics of hydrated alkali and halides ions in bulk nitrobenzene are studied using molecular dynamics computer simulations. The number of water molecules in the ions’ hydration shell (hydration number) and their orientational distribution, hydration water residence time and several important energy terms are calculated and compared with the same quantities in bulk water. The water molecules in the first hydration shell of the ion are more tightly bound to the ion in bulk nitrobenzene than in bulk water as reflected by the longer lifetime in the former case. As the ion size increases, the average hydration number in nitrobenzene decreases, which is the reverse trend to that found in bulk water. The calculated hydration numbers are in reasonable agreement with experimental data.

Structure and Dynamics of Hydrated Ions in a Water-Immiscible Organic Solvent

The structure and dynamics of hydrated alkali and halide ions in bulk 1,2-dichloroethane (DCE) are studied using molecular dynamics computer simulations. The number of water molecules in the ions' hydration shell and their orientational distribution, hydration water residence time, and ion diffusion constant are calculated and compared with the same quantities in bulk water. As the ion size increases, the average hydration number in DCE decreases, which is the opposite trend found in bulk water. The water molecules in the first hydration shell of the ion in bulk DCE are more tightly held to the ion, with a longer residence time than in bulk water. The hydrated ions in DCE are more mobile than in bulk water, and their mobility is much less sensitive to the ion size compared with the size dependence in bulk water.

Electrolyte-Concentration and Ion-Size Dependence of Excited-State Intramolecular Charge-Transfer Reaction in (Alkylamino)benzonitriles: Steady-State Spectroscopic Studies

Steady-state spectroscopic studies have been performed with three intramolecular charge-transfer molecules, 4-(1-azetidinyl)benzonitrile (P4C), 4-(1-pyrrolidinyl)benzonitrile (P5C), and 4-(1-piperidinyl)benzonitrile (P6C), in ethyl acetate and acetonitrile in presence of lithium perchlorate (LiClO(4)) at room temperature to investigate the effects of electrolytes on excited-state intramolecular charge-transfer reaction. Electrolyte-concentration and ion-size dependences of several spectroscopic properties such as quantum yield, absorption and emission transition moments, radiative and nonradiative rates, and changes in reaction free energies associated with LE --> CT conversion have been determined for these molecules and reported. For P4C, quantum yield decreases by a factor of approximately 7 at the highest electrolyte concentration relative to that in pure ethyl acetate whereas it is a factor of approximately 4 for both P5C and P6C. However, in acetonitrile with 1.0 M LiClO(4), quantum yield reduces to almost half of that in the pure solvent. Formation of a charge-transfer (CT) state is found to be strongly favored over the locally excited (LE) state as the electrolyte (LiClO(4)) concentration is increased, electrolyte effects being more pronounced in ethyl acetate than in acetonitrile. Relative to pure ethyl acetate, reaction free energy change (-DeltaG(r)) increases by a factor of approximately 5, approximately 4, and approximately 2 for P4C, P5C, and P6C, respectively, at 2.5 M LiClO(4) in this solvent. -DeltaG(r) for P4C exhibits a change in sign (from negative to positive) upon addition of electrolyte in ethyl acetate. In acetonitrile, however, these changes are within a few percent, except for P4C where it is about 4 times greater at 1.0 M LiClO(4) than that in pure acetonitrile. The electrolyte-induced total red shift of the CT band of these TICT molecules is 3 times higher in ethyl acetate than in acetonitrile. Although both the quantum yield and CT emission peak frequency decrease linearly with the increase in ion size, -DeltaG(r) remains largely insensitive. Further studies using a nonreactive probe (coumarin 153) in concentrated electrolyte solutions also show qualitatively similar results.

Fragmentation of rare-gas clusters ionized by electron impact: new theoretical developments and comparison with experiments

The fragmentation of rare-gas clusters Rg n (2≤n≤14 and Rg = Ne, Ar and Kr) following electron-impact ionization is reviewed, with a focus on the comparison of experiment and theory. The most pertinent results are selected in this view, i.e. experiments with size selection of the neutral clusters and simulations taking into account all the relevant electronic states of the ions and their couplings. Simulation results obtained for argon and krypton clusters are compared to abundances determined by experiments. Very good qualitative agreement is found for both types of clusters, concerning the extensive character of the dissociation and the tendency to form larger fragments when the parent ion size increases. For instance, no trimer fragments are found for clusters smaller than the pentamer. In addition, very good quantitative agreement is obtained for argon clusters, especially if the possibility for secondary ionization of the neutral monomer fragments is taken into account. On the other hand, some discrepancies are found between experiment and theory for krypton clusters. Even though the experimental results for the sum of the monomer and dimer ionic fragment proportions are well reproduced in the simulation, there is a disagreement concerning the relative proportion of monomers and dimers. The experiment shows a large predominance of monomers which is not found in the simulation. Several possible reasons for this difference are discussed. The simulation results for neon, argon, and krypton cluster ionization are analysed in detail and provide crucial information on the kinetics of the fragmentation and its mechanism. It is shown that parent ion dissociation occurs within the first picoseconds, and that most of the dynamics is completed within 10 picoseconds. However, the existence of long-lived (more than 100 picoseconds) intermediate species is revealed for clusters larger than hexamers, which are shown to preferentially lead to larger fragments. New results rationalizing the parent ion lifetime dependence with size in terms of the number of coupled electronic states and the symmetry of the neutral precursor are presented. Internal energy distributions and the number of fragmentation events are shown to characterize the fragmentation mechanism as explosive rather than evaporative. The effect of the spin–orbit coupling on the different aspects of the fragmentation process is also examined.

Solute size effects on the solvation structure and diffusion of ions in liquid methanol under normal and cold conditions

We have performed a series of molecular dynamics simulations of alkali metal (Li+, Na+, K+, Rb+, and Cs+) and halide (F-, Cl-, Br-, and I-) ions in liquid methanol at two different temperatures to investigate the effects of ion size on the hydration structure and diffusion of ions in methanol under normal and cold conditions. Simulations are also carried out for some of the larger cations such as I+, (CH3)4N+, and (C2H5)4N+ and also neutral alkali metal atoms in methanol at both temperatures. With the increase of ion size, the diffusion coefficients of both positive and negative ions are found to show anomalous behavior. For cations, it is found that the maximum of the diffusion coefficient versus ion size curve occurs at the rather large cation of (CH3)4N+ unlike in water where the maximum occurs at the relatively smaller ion of Rb+. For halide ions, the anomalous behavior, i.e., the increase of diffusion with ion size, continues up to iodide ion and no maximum is observed. These results are in good agreement with experimental observations. The diffusion coefficients of neutral atoms are found to be greater in methanol than that in water and they decrease monotonically with solute size, whereas the diffusion coefficients of the corresponding ions are found to be smaller in methanol. Accordingly, an ion experiences a smaller Stokes friction and a higher dielectric friction in methanol than in water. These contrasting effects are believed to be responsible for the shift of the maximum of ion diffusion toward a larger ion size when compared with similar anomalous size dependence in liquid water.

Hydration structure and diffusion of ions in supercooled water: Ion size effects

We have performed a series of molecular dynamics simulations of alkali metal (Li+, Na+, K+, Rb+, and Cs+) and halide (F−, Cl−, Br−, and I−) ions in water at infinite dilution at T=258 K to investigate the effects of ion size on the hydration structure and diffusion of ions in supercooled water. Simulations are also performed at T=298 K in order to compare the results of the hydration structure and diffusion in supercooled water with those in ambient water. With increase of ion size, like in ambient water, in supercooled water also the diffusion coefficients of alkali metal and halide ions are found to fall in different curves with distinct maxima. However, the relative increases of the diffusion coefficients of larger ions compared to those of Li+ and F− are found to be significantly higher in the supercooled water.

Dynamics of ions in liquid water: An interaction-site-model description

We present a molecular theory for investigating the dynamics of ions in polar liquids. The theory is based on the interaction-site model for molecular liquids and on the generalized Langevin equation combined with the mode-coupling theory. The velocity autocorrelation function, diffusion and friction coefficients of ions in water at 25 °C and at infinite dilution are studied. The theoretical results for the velocity autocorrelation functions exhibit a gradual change from oscillatory to monotonic decay as the ion size increases. The diffusion (friction) coefficients of ions in aqueous solutions pass through a maximum (minimum) as a function of the ion size, with distinct curves and maxima (minima) for positive and negative ions. These trends are in complete accord with those of the molecular dynamics simulation results performed on the same system by Rasaiah and co-workers [J. Phys. Chem. B 102, 4193 (1998)]. It is worthwhile to mention that this is the first molecular theory that is capable of describing the difference in the dynamics of positive and negative ions in aqueous solutions. A further analysis of the friction coefficients of ions in water is presented in which the friction is decomposed into the “Stokes,” dielectric and their cross terms. The Stokes and dielectric terms arise from the coupling of the ion dynamics to essentially the acoustic dynamics of the solvent via the short-range interaction, and from the coupling to the optical mode of the solvent via the long-range interaction. The most striking feature of our results is that the Stokes friction so defined does not increase monotonically with increasing ion size, but decreases when ions are very small, implying a formation of a molecular “complex” comprising the ion and its nearest neighbor solvent molecules. Interesting observations concerning the cross term are: (1) its magnitude is rather large for small ions and cannot be neglected at all, and (2) the cross term for small ions seems to cancel out the Stokes part, and consequently the total friction for small ions seems to be to a large extent determined by its dielectric component.

Ion-molecule reactions relevant to Titan's ionosphere

Twenty four new ion-molecule reactions are presented for inclusion in the modeling of the ionosphere of Saturn's satellite Titan. Sixteen reactions were re-examined to reduce uncertainties in the previous literature results. In this study we have examined the reactions of N + and N 2 + with CH 4, C 2H 2, C 2H 4, C 2H 6, HCN, CH 2CHCN and HC 3N; the reaction of N + with CH 3CN; the reactions of C 3H 5 + with CH 4, C 2H 2, C 2H 4, C 2H 6, H 2, HCN, HC 3N and CH 2CHCN; the reactions of C 2N 2 + with C 2H 2; C 2H 2 + and C 2N 2; C 2H 4 with C 2H 3 +, C 2H 4 , CHCCNH +, and HC 5N +; HCNH + with C 2H 6; C 3H 6 + with C 3H 6; HCN with C 2 H 6 +, C 3H 6 + , cC 3H 6 + ,C 2N 2 + and NO +; N 2 with C 2H 2 + and C 2H 5 +; C 2H 4 + and HC 3N. The ions selected for this study were derived either from nitrogen, appropriate hydrocarbons or nitrites. The reactant neutrals were selected on the basis of their known presence in Titan's atmosphere. The reaction products are consistent with the expected increase in ion size through ion molecule reaction processing. Data are also presented for the reactions of 23 ions with molecular nitrogen. Almost all of these ions are unreactive with N 2.

Ion Solvation in Polarizable Chloroform: A Molecular Dynamics Study

The structural, thermodynamic, and dynamical properties of the alkali-metal cations and the halide anions in liquid chloroform are investigated using molecular dynamics simulation techniques. From the atomic radial distribution analysis, the chloroform molecules are found to form well-defined solvation shells around the alkali-metal cations and the halide anions. The size of the solvation cage and the coordination number both increase with increasing ion size. In liquid chloroform, all these ions are shown to induce a strong orientational order in the surrounding chloroform molecules as evidenced by the angular distribution functions. We found that the mean electric potentials induced by the chloroform molecules shifted to smaller magnitudes with increasing ion size. Because of the greater electric polarizabilities of the larger ions, the average induced dipole moments were enhanced with increasing ion size. The diffusion coefficients of the alkali-metal cations and the halide anions in liquid chloroform are estimated from the mean-square displacements and the velocity autocorrelation functions. Generally, the diffusion constants of the cations are larger than those of the anions. For the cations, the diffusion constants are of similar magnitudes and do not depend on the ion size. However, the diffusion coefficients of the halide anions show a strong dependence on the ion size. The motion of the first coordination shell chloroform molecules is examined via their velocity autocorrelation functions. These correlation functions behave very similarly, suggesting that the motion of the first solvation shell is not governed by the sizes or the charges of these ions. In addition, the residence time autocorrelation functions of the first solvation shell are evaluated. As expected, the residence time decreases as the ion size increases.

Ion-molecule chemistry in Titan's ionosphere

A summary is presented of the information available from laboratory studies of ion-molecule reactions that is relevant to the chemistry occurring in Titan's ionosphere. Reaction information from the literature has been collated and many new reactions have been measured, including some ion-atom reactions. The sequences of ion-neutral reactions can lead to a rapid increase in ion size. How this increase may lead to aerosol production at the base of the ionosphere is briefly discussed. Laboratory observations of extremely rapid termolecular ion-neutral association reactions indicate that these association reactions are viable contribution to the ion chemistry at the base of Titan's ionosphere.

高圧下におけるハロゲン化物イオンの水中での電気伝導度に対する溶媒同位体効果

For the purpose of disclosing the mechanism of conductivity for halide ions, the limiting molar conductivities of Br- and I- ions in heavy and light water have been determined at 25°C as a function of pressure up to 196.1MPa (2000kgf cm-2). The residual friction coefficients (Δζobs) of the halide ions were compared with the dielectric friction coefficients (ΔζHO) obtained from the Hubbard-Onsager dielectric friction theory. The continuum theory showed a serious limitation: (1) Contrary to the theoretical prediction, Δζobs was negative at each pressure in both D2O and H2O, and was smaller in D2O than in H2O. These discrepancies between the theory and the experiment became larger with an increase in ion size. (2) With increasing pressure, Δζobs (Cl-) and Δζobs (Br-) decreased, while Δζobs (I-) showed a reverse tendency. These results were discussed in terms of the passing through cavities mechanism and the specific interaction between halide ions and water molecules.

The Ca channel in skeletal muscle is a large pore.

The permeability of Ca channels to various foreign cations has been investigated in the absence of external Ca2+. All physiological metal cations are clearly permeant, including Mg2+. The large organic cation n-butylamine+ is sparingly permeant or impermeant, but its larger derivative 1,4-diaminobutane2+ is highly permeant. Among the cations of the methylated ammonium series, permeability diminishes in a graded fashion as ion size increases. Tetramethylammonium, the largest cation found to be permeant, has a diameter of about 6 A; hence, the aqueous pore of the Ca channel at its narrowest point can be no smaller. That the pore is so large strengthens our view that, under physiologic conditions, the high selectivity of Ca channels is due to selective binding of Ca2+ rather than to rejection of other cations by, for example, a sieving mechanism.

Ions-gas phase and solution-dipolar aprotic solvents

Abstract