Calculation of chemical bonds and diffusion path of Li ion in (LaLi)Ti2O6 by DV-Xα cluster method

The chemical bonds and lithium diffusion of La_4/3−y Li_3y Ti₂O₆ (y = 0.21) were investigated by using the DV-Xα cluster method. The cluster model used is the formula La₈Li₂Ti₂O₁₁. A Li ion was moved on the ab plane at z = 1/2. The Na ion was moved along the x axis in the cluster model La₈Na₂Ti₂O₁₁ for comparison. The total bond overlap population (BOP) between the moving Li ion and the other ions was calculated on the ab plane at z = 1/2. The total BOP of the Li ion along the x axis increased near the oxygen ion site, whereas the BOP of the Na ion decreased. The decrease in total BOP indicates the decrease in covalent interaction between the Na and the other ions. The change of the net charge of the Li ion was almost the same as that of the Na ion. This suggests that the smaller change of covalent interaction in the mobile Li ion determines the diffusion path of Li ion.     

An ab initio molecular dynamics study of ionic conductivity in hexagonal lithium lanthanum titanate oxide La0.5Li0.5TiO3

To date, the fastest lithium ion-conducting solid electrolytes known are the perovskite-type ABO₃ oxide, with A = Li, La and B = Ti, lithium lanthanum titanate (LLTO) Li_3x La_{( 2 \mathord}

Electronic energy calculation in three models of (La,Li)Ti2O6 ionic conductor with vacancies

The electronic energy calculation using the linear-muffin-tin-orbital method is performed to study the property of Li ion diffusion in La_{4/3 − y}Li_3yTi₂O₆ (y = 0.21) with vacancies. The total electronic energy of three models, LiTi₂O₆, LaLiTi₂O₆, and La₂LiTi₄O₁₂ shows the stable position of Li ions strongly dependent on each model, suggesting that the stable position and the activation energy change with the existence of vacancy.     

Calculation of 7Li MAS NMR chemical shift in La4/3−yLi3yTi2O6

The chemical shifts of ⁷Li MAS nuclear magnetic resonance spectra in La_4/3−yLi_3yTi₂O₆ (LLTO) showed negative values and decreased with increasing lithium concentration. The chemical shifts were interpreted by Pople’s theory in which the ⁷Li chemical shifts were due to the local paramagnetic currents of the closest oxygen ions. Lattice parameters and coordination of oxygen were obtained by Rietveld analysis of X-ray diffraction data. The gross population and electron excitation energy were calculated by DV-Xα method.     

Gas-sensing studies on SnO<Subscript>2</Subscript> or NASICON-type composite materials

NASICON powders were prepared by solid-state synthesis, a fraction was ion exchanged by Li or K, verified by X-ray diffraction and energy dispersive X-ray analysis, blended with tin oxide powder, transferred to thick film pastes, and dispensed on a commercial sensor substrate (Heraeus, Germany). Simultaneous gas sensitivity measurements on nine SnO₂/NASICON-type (, x = 0, 2.2, 3, M = Li, Na, K) composites in thermocyclic sensor operation mode by exposure to different concentrations of Ethanol, Toluene, Propylene, CO, and H₂ in humidified synthetic air show a strong correlation of the gas-sensing properties with the mobile ion concentration and type of the solid electrolyte additive.     

Lithium ion conductivity of Li5+xBaxLa3?xTa2O12 (x?=?0–2) with garnet-related structure in dependence of the barium content

The stoichiometry range and lithium ion conductivity of Li_5+x Ba _x La_3−x Ta₂O₁₂ (x = 0, 0.25, 0.50, 1.00, 1.25, 1.50, 1.75, 2.00) with garnet-like structure were studied. The powder X-ray diffraction data of Li_5+x Ba _x La_3−x Ta₂O₁₂ indicated that single phase oxides with garnet-like structure exist over the compositional range 0 ≤ x ≤ 1.25; while for x = 1.5, 1.75 and 2.00, the presence of second phase in addition to the major garnet like phase was observed. The cubic lattice parameter increases with increasing x and reaches a maximum at x = 1.25 then decreases slightly with further increase in x in Li_5+x Ba _x La_3−x Ta₂O₁₂. The impedance plots of Li_5+x Ba _x La_3−x Ta₂O₁₂ samples obtained at 33 °C indicated a minimum grain-boundary resistance (R _gb) contribution to the total resistance (R _b + R _gb) at x = 1.0. The total (bulk + grain boundary) ionic conductivity increases with increasing lithium and barium content and reaches a maximum at x = 1.25 and then decreases with further increase in x in Li_5+x Ba _x La_3−x Ta₂O₁₂. Scanning electron microscope investigations revealed that Li_6.25Ba_1.25La_1.75Ta₂O₁₂ is much more dense, and the grains are more regular in shape. Among the investigated compounds, Li_6.25Ba_1.25La_1.75Ta₂O₁₂ exhibits the highest total (bulk + grain boundary) and bulk ionic conductivity of 5.0 × 10⁻⁵ and 7.4 × 10⁻⁵ S/cm at 33 °C, respectively.     

Structure and lithium ionic conduction of B-site Al-ion substitution in La4/3-yLi3yTi2O6

The Al-substitution effect was studied in solid solutions La_4/3-yLi_3y□_2/3-2yTi₂O₆ (LLTO). The ionic conductivity strongly depended on the Al concentration. The crystal structure, lattice parameters, ions occupation and bottleneck size were obtained by Rietveld analysis. Finally, the ionic conduction mechanism was discussed from the viewpoint of crystallographic factors.     

Recent progress in solid oxide and lithium ion conducting electrolytes research

Recent material developments of fast solid oxide and lithium ion conductors are reviewed. Special emphasis is placed on the correlation between the composition, structure, and electrical transport properties of perovskite-type, perovskite-related, and other inorganic crystalline materials in terms of the required functional properties for practical applications, such as fuel or hydrolysis cells and batteries. The discussed materials include Sr- and Mg-doped LaGaO₃, Ba₂In₂O₅, Bi₄V₂O₁₁, RE-doped CeO₂, (Li,La,)TiO₃, Li₃La₃La₃Nb₂O₁₂ (M=Nb, Ta), and Na super-ionic conductor-type phosphate. Critical problems with regard to the development of practically useful devices are discussed.     

Growth by laser ablation of Ti-based oxide films with different valency states

x La_2/3+yTiO_3-δ perovskite (with δ≤0.5) were deposited by the laser ablation technique from Li_0.33La_0.56TiO₃ targets. Their growth onto MgO substrateswas studied as a function of the oxygen pressure. For films grown in vacuum (10^-6 mbar), a La_0.63TiO_2.5 composition was obtained, meaning that Ti³⁺ alone is present in the films, while Li ions are not incorporated under these conditions. This material shows good electric conductivity (ρ=500 mΩ cm). By contrast, insulating films with a Li_0.1La_0.70TiO₃ composition corresponding to the Ti⁴⁺ species were obtained at high oxygen pressures (>0.05 mbar). For all conditions, textured films were grown with different orientations depending on the temperature and the oxygen pressure. Received: 10 September 1997/Accepted: 24 November 1997     

An EIS study of La2 − x Sr x NiO4 + δ SOFC cathodes

La_2 − x Sr _x NiO_{4 +  δ} materials were investigated as cathodes for the electrochemical reduction of oxygen on a Ce_1.9Gd_0.1O_1.95 (CGO10) electrolyte using cone-shaped electrodes together with electrochemical impedance spectroscopy. The area-specific resistance (ASR) of the La_2 − x Sr _x NiO_{4 +  δ} nickelates towards the reduction of oxygen is equal to the ASR of perovskites; however, it is not as low as for the best Fe–Co-based perovskites. The lowest ASR is found for the compound La_1.75Sr_0.25NiO_{4 +  δ} with an ASR of 23.8 Ωcm² measured on a cone-shaped electrode in air at 600 °C. It is suggested that difference in oxide ionic conductivity of the nickelates is the main cause for the different activity of the nickelates towards the electrochemical reduction of oxygen.     

New observation of the , 1Δg, and 2Πg states and molecular constants with all Li2, Li2, and LiLi data

This paper reports our new observation of the , 1³Δ_g (v = 2–4), and 2³Π_g (v = 2–8) states of ⁶Li⁷Li by continuous wave perturbation facilitated optical–optical double resonance spectroscopy. Combining our new experimental term values of ⁶Li⁷Li with the available experimental data of ⁶Li₂ and ⁷Li₂, molecular constants and potential energy curves by Rydberg–Klein–Rees and direct-potential-fit techniques have been determined. Born-Oppenheimer breakdown parameters of the Li₂ 1³Δ_g and 2³Π_g states are calculated.     

The NASICON solid solution Li1−x La x /3Zr2(PO4)3: optimization of the sintering process and ionic conductivity measurements

The Li_1−x La _{x /3}Zr₂(PO₄)₃ NASICON-type compounds (0 ≤ x ≤ 1) have been synthesized in powder form by a sol-gel method and sintered for ionic conductivity measurements. In order to improve the compactness of the ceramic without decomposition of the compound, several sintering processes have been tested for one member of the solid solution (x = 0.6): the use of sintering aids (ZnO, B₂O₃, TiO₂ and LiNO₃), a ball-milling of the synthesized powder, a flash heating, high isostatic pressure, and spark plasma sintering. Finally, a satisfactory compactness of 85% is obtained compared to the referenced value (63%) obtained by uniaxial and isostatic pressing. The ionic conductivity study was performed by impedance spectroscopy. It shows that, despite the formation of vacancies, the substitution Li⁺→ 1/3 La³⁺ + 2/3 □ has unfortunately no influence on the conduction for 0 ≤ x ≤ 0.7 since the ionic conductivity remains identical to the LiZr₂(PO₄)₃ one. For higher x values, the ionic conductivity strongly decreases.     

Enhanced cycling properties of transition metal molybdates, Li x M2(MoO4)3 {0?≤ x

K. M. Begam  M. S. Michael  S. R. S. Prabaharan 《Ionics》2007,13(6):467-471

Identification of the Li sites in the Li ion conductor, Li6SrLa2Nb2O12, through neutron powder diffraction studies

In this paper a neutron powder diffraction structural study of the Li ion conducting garnet-related system, Li₆SrLa₂Nb₂O₁₂, is reported. The results show that this phase is cubic, space group Ia-3d, and contains Li in two partially occupied crystallographic sites. The first site, Li1, corresponds to the ideal tetrahedral site in the garnet framework and possesses an occupancy of 0.59(1). The second site, Li2, is significantly more distorted and possesses an occupancy of 0.352(3). Compared to the related Li₅La₃Nb₂O₁₂ system, the Li2 site occupancy is greatly increased, while the Li1 site occupancy is reduced. Despite these large differences in site occupancies, the reported conductivities for Li₅La₃Nb₂O₁₂ and Li₆SrLa₂Nb₂O₁₂ are similar, showing the complexities of these new garnet Li ion conductors.     

New prospects in studying Li diffusion—two-time stimulated echo NMR of spin-3/2 nuclei

The measurement of diffusion parameters like activation energies and translational jump rates of small cations plays a key role in materials science. Especially the in-depth investigation of Li diffusion in ionic conductors is of great interest, because suitable ionic conductors are needed for, e.g., the development of new secondary ion battery systems. As the standard tracer method is not applicable to study Li diffusion due to the lack of a suitable radioactive isotope, Li diffusion is alternatively probed by solid state NMR techniques. With the different NMR methods being available, diffusion processes can be studied on different length- and timescales. In the present paper we use two-time spin-alignment echo (SAE) NMR for the direct, i.e., model independent, measurement of extremely small translational Li jump rates. To this end, different crystalline and glassy ion conductors like Li_xTiS₂, Li₄SiO₄ as well as LiNbO₃ served as model substances to reveal the special features of this technique. SAE-NMR, which was originally developed for deuterons, has also been applied in a few cases to spin-3/2 nuclei, like ⁷Li, before. The corresponding correlation functions yield not only information about diffusion parameters but also about geometric properties of the diffusion pathways, making SAE-NMR a powerful method which complements well-established NMR techniques.     

Effect of V5+ in the complex Li3xLa2/3−xTiO3-LaPO4 system

Lithium fast ion conductors of the composition Li_0.3La_2/3Ti_0.7P_0.3−xV_xO_3.3 (LTV) based on mixtures of Li_3xLa_2/3−xTiO₃ and LaPO₄ were prepared by solid state reaction at high temperature (≈ 1300 °C). AC impedance measurements indicate total conductivities of about 1 × 10⁻⁴ Scm⁻¹ for compositions of x=0∼0.3 at room temperature with an activation energy of ≈18 kJ·mol⁻¹ in the temperature range from 30 to 400 °C. X-ray powder diffraction patterns showed that the LTV system is composed of Li_3xLa_2/3−xTiO₃ perovskite solid solution and LaP_1−xV_xO₄ solid solution.     

The effect of LaPO4 in the LixLa2/3Ti1−xPxO3+x system

Lithium ion conductors of the overall composition Li_xLa_2/3Ti_1−xP_xO_3+x (hereafter referred to as LTP) based on La_2/3TiO₃ were prepared by solid state reaction at high temperature (1300 °C). AC impedance measurements indicate that the total conductivities are of the order of 10⁻⁴ S·cm⁻¹ when x=0.28 − 0.35 at room temperature and have an activation energy of 18 kJ·mol⁻¹ in the temperature range from room temperature to 400 °C. X-ray powder diffraction patterns showed that the LTP system has a complex composition, which contains the solid solution perovskite Li_3xLa_2/3−xTiO₃ and LaPO₄.     

Ionic conduction and chemical bonds of Li ion in La4/3−yLi3yTi2O6

The electronic state of La_4/3−yLi_3yTi₂O₆ (y=0.21) was studied by the DV-Xα cluster method. Four model clusters were used to calculate the density of state (DOS), the bond overlap population (BOP) and the net charge (NC). A Li ion in the model cluster was moved from 1b site to another 1b site along the x axis, and the BOP and the NC calculated were discussed. Furthermore, we calculated the potential energy with the movement of the Li ion along the x axis. Paper presented at the Patras Conference on Solid State Ionics - Transport Properties, Patras, Greece, Sept. 14 – 18, 2004.     

Enhanced cyclability of triple-metal-doped LiMn2O4 spinel as the cathode material for rechargeable lithium batteries

To improve the cycle performance of spinel LiMn₂O₄ as the cathode of 4-V-class lithium secondary batteries, spinel phases LiM _x Mn_2 − x O₄ (M=Li, Fe, Co; x = 0, 0.05, 0.1, 0.15) and LiFe_0.05M _y Mn_{1.95 − y} O₄ (M=Li, Al, Ni, Co; y = 0.05, 0.1) were successfully prepared using the sol–gel method. The spinel materials were characterized by powder X-ray diffraction (XRD), elemental analysis, and scanning electron microscopy. All the samples exhibited a pure cubic spinel structure without any impurities in the XRD patterns. Electrochemical studies were carried out using the Li|LiM _x Mn_2 − x O₄ (M=Li, Fe, Co; x = 0, 0.05, 0.1, 0.15) and LiFe_0.05M _y Mn_{1.95 − y} O₄ (M=Li, Al, Ni, Co; y = 0.05, 0.1) cells. These cathodes were more tolerant to repeated lithium extraction and insertion than a standard LiMn₂O₄ spinel electrode in spite of a small reduction in the initial capacity. The improvement in cycling performance is attributed to the stabilization in the spinel structure by the doped metal cations.     

AC conductivity scaling behavior in grain and grain boundary response regime of fast lithium ionic conductors

AC conductivity spectra of Li-analogues NASICON-type Li_1.5Al_0.5Ge_1.5P₃O₁₂ (LAGP), Li–Al–Ti–P–O (LATP) glass–ceramics and garnet-type Li₇La₂Ta₂O₁₃ (LLTO) ceramic are analyzed by universal power law and Summerfield scaling approaches. The activation energies and pre-exponential factors of total and grain conductivities are following the Meyer–Neldel (M-N) rule for NASICON-type materials. However, the garnet-type LLTO material deviates from the M-N rule line of NASICON-type materials. The frequency- and temperature-dependent conductivity spectra of LAGP and LLTO are superimposed by Summerfield scaling. The scaled conductivity curves of LATP are not superimposed at the grain boundary response region. The superimposed conductivity curves are observed at cross-over frequencies of grain boundary response region for LATP by incorporating the \( \exp \left( {{{ - (E_{A}^{t} - E_{A}^{g} )} \mathord{\left/ {\vphantom {{ - (E_{A}^{t} - E_{A}^{g} )} {kT}}} \right. \kern-0pt} {kT}}} \right) \) factor along with Summerfield scaling factors on the frequency axis, where \( E_{A}^{t} \) and \( E_{A}^{g} \) are the activation energies of total and grain conductivities, respectively.