The stability of Li3.8Ge0.9S0.1O4 lithium-conducting solid electrolyte versus lithium metal and Li–V bronze Li1.3V3O8 is studied in the present research. Isothermal heat treatment and thermal analysis of the mixtures of Li1.3V3O8 and Li3.8Ge0.9S0.1O4 powders indicate that there is no interaction between them below 300–350 °C. Moreover, Li3.8Ge0.9S0.1O4 solid electrolyte is stable versus lithium at 100 °C for 240 h. A model of a lithium-ion power source with a Li1.3V3O8-based cathode and a lithium metal anode is assembled and tested. The data obtained show that Li3.8Ge0.9S0.1O4 can be used in all-solid-state medium-temperature lithium and lithium-ion batteries.

Samples of Na4–xZr2-xNbxSi3O12 (x = 0–0.4) system are synthesized, phase analysis is performed, and the conductivity is measured. Samples with x = 0–0.25 are single-phase with a NASICON-type trigonal symmetry, space group R-3c. Na3.85Zr1.85Nb0.15Si3O12 solid electrolyte exhibits the highest sodium-cation conductivity (1.7 × 10−2 S × cm−1 at 300°, 10−5 S × cm−1 at 25 °C). High-temperature X-ray studies in the range of 25 to 727 °C were performed for this composition. Full-profile analysis was carried out for all temperatures to refine the structural parameters. Based on the experimental data, two elementary channels open for sodium cation migration were found using the method of tilings; the channels form a continuous three-dimensional network of migration paths. It is shown that the break of the lgσ–1/T plot at 480 °C is due to a sharp decrease in the strength of the Na–O bond in NaO6 octahedra and the consequent increase in the mobility of sodium cations in 6b (000) sites.

With the view of developing new materials for sodium and sodium-ion power sources, NaFeO2-SnO2 (0–50 mol.% SnO2) powders were synthesized using a solid state method, and their phase composition and crystal structure were studied. A phase of the Na0.8Fe0.8Sn0.2O2 composition with a layered rhombohedral structure of the α-NaFeO2 type was found when the tin dioxide content was 20 mol.%. The phase produced was of an O3 structural type. O3-type phases have sufficiently good performance when used as cathode materials in sodium-ion batteries and, moreover, often have a rather high sodium-cation conductivity. A two-dimensional migration map was built using Voronoi–Dirichlet partition and TOPOS software package. The sodium-ion conductivity of Na0.8Fe0.8Sn0.2O2 at room temperature was rated low (10−8 S × cm−1 at 20 °C), which may be the result of channels too narrow for Na+ migration. The results obtained show that the application of the compound studied in this work as a solid electrolyte in sodium power sources is unlikely. It is the potential use of Na0.8Fe0.8Sn0.2O2 as the active material of cathodes in Na and Na-ion power sources that presents practical interest.

Sodium–vanadium oxide NaV3O8 is synthesized via solid-state method and optimum synthesis conditions are chosen based on the data of DSC and TG analysis. The material synthesized is characterized by X-ray phase analysis, Raman spectroscopy and scanning electron microscopy. The ratio V4+/V5+ in the sample obtained is determined by X-ray photoelectron spectroscopy. Conductivity of the material synthesized was measured by impedance spectroscopy, pulse potentiometry and DC method over the range RT–570 °C. It is shown that NaV3O8 has rather high conductivity essentially electron in type (6.3 × 10−2 at room temperature). AC and DC conductivity measurements are performed and cycling of symmetricNaV3O8|Na3.85Zr1.85Nb0.15Si3O12|NaV3O8 cell in galvanostatic conditions. Thermal stability is studied across 25–570 °C temperature range. The results obtained are compared with the properties of NaV3O8 produced via aqueous solution.

Li6-xZr2-xAxO7 (A = Nb; Ta) system with 0 < x < 0.30 is synthesized by glycine-nitrate method. Boundaries of solid solutions based on monoclinic Li6Zr2O7 are determined; temperature (200–600 °C) and concentration dependences of conductivity are investigated. It is shown that monoclinic Li6Zr2O7 exhibits better transport properties compared to its triclinic modification. Li5.8Zr1.8Nb(Ta)0.2O7 solid solutions have a higher lithium-cation conductivity at 300 °C compared to solid electrolytes based on other lithium zirconates due the “open” structure of monoclinic Li6Zr2O7 and a high solubility of the doping cations.

Samples from the Li2 – 2xMxZrO3 (M = Ca, Zn), Li2 –xZr1 –xNbxO3, and Li2 +xZr1– xYxO3 systems were synthesized by conventional solid-state reaction. Estimated domains of Li2ZrO3-based solid solutions were established for all above-mentioned systems. The transport properties of the samples (temperature and composition dependences of their conductivity, and the conductivity activation energy) were studied by electrochemical impedance spectroscopy in the temperature range from 300 to 600°С. The most probable lithium-ion migration mechanisms depending on the Li2ZrO3 crystal structure were discussed. According to the obtained results, the synthesized materials are typical solid electrolytes with extrinsic disorder and quite low ionic conductivity (σ ∼ 10–2 –10–5 S cm–1).

Crystal structure features of NaFeO2 and NaAlO2 were studied using neutron diffraction and X-ray powder diffraction. The conductivity of these compounds was also investigated. The migration paths in the structure of sodium ferrite and aluminate were modeled by topological (tiling) and DFT methods. The sizes of through sodium-cations migration channels in low-temperature β-modifications of the compounds in question were determined using the ToposPro software package. It is shown that an increase in the size of these migration channels correlates with an increase in ionic conductivity. The conductivity in high-temperature γ-phases of NaFeO2 and NaAlO2 is determined by two competing processes: an increase in activation energy caused by a decrease in the cross-sections of the channels and a transition from one-dimensional conductivity to three-dimensional one.

Lithium metazirconate Li2ZrO3 was synthesized by various methods, and its electric conductivity was studied in the range 300–600°C. For the sample obtained by solid-phase synthesis, the temperature dependence of conductivity is linear in the Arrhenius coordinates and coincides with the literature data for Li2ZrO3 obtained by the similar procedure. The sample synthesized and sintered in vacuum has higher electric conductivity, but contains a Li2CO3 impurity. Possible reasons for the abrupt change in the conductivity of Li2ZrO3 at 430–470°C reported in some works were considered.

Lithium-vanadium oxide with the formal composition Li6V5O15, uniform microsctructure, and the particle size of 100 nm is synthesized by a solution method. The synthesized compound is characterized by the methods of X-ray diffraction analysis, Raman spectroscopy, and synchronous thermal analysis. The total electric conductivity is measured by the method of impedance spectroscopy and its electronic component is estimated by dc method. In the temperature range of 200–400°C, Li6V5O15 represents a mixed electronic- ionic conductor with predomination of the ionic component and is thermally stable up to 550°С. Preliminary tests of a laboratory model of electrochemical cell Li|LiPF6|Li6V5O15 are carried out.

Crude vanadium-containing dump slimes can be used as a raw material for preparing lithium vanadium oxides suitable as cathode materials for lithium-ion chemical current sources. A simple procedure for preparing LiV3O8 from the slime was suggested. The synthesized compound was characterized by X-ray diffraction, Raman spectroscopy, scanning electron microscopy, and synchronous thermal analysis. The material prepared from vanadium-containing dump slimes has uniform microstructure and high electronic conductivity of the order of 1.4 × 10–2 S cm–1; it is thermally stable in the interval 30–550°С and capable of intercalation/deintercalation of lithium ions in its structure in the course of cycling in lithium-ion current sources.

The authors are grateful to A. L. Buzlukov and I. Y. Arapov for performing the 7 Li NMR experiments.

Синтезированы и исследованы новые керамические материалы на основе Rb3PO4 с высокой проводимостью по катионам рубидия в системе Rb3-2xPbxPO4. Введение катионов Pb2+ приводит к резкому возрастанию электропроводности ортофосфата рубидия за счет образования катионных вакансий, а при температурах 350-550oC и за счет стабилизации высокотемпературной кубической модификации Rb3PO4. В области высоких температур полученные электролиты обладают очень высокой ионной проводимостью, превышающей 10-1 S·cm-1 при 700oC, что выше значений, полученных ранее в аналогичных системах с добавками ионов цинка и кадмия. Обсуждаются факторы, влияющие на транспортные свойства исследованных материалов. DOI: 10.21883/FTT.2017.07.44599.402

Analysis of correlation between structural features and rubidium ion conductivity is performed for RbFeO2 polymorphs in a wide temperature range of 296–843 K. To explore the migration maps of Rb+ cations, we used neutron diffraction data for low- and high-temperature RbFeO2 polymorphs and natural tiling concept implemented in the TOPOS software. Five independent elementary channels for the Rb+ cation migration have been revealed whose cross- sections were found to be essentially different in the low-temperature form, indicating a high anisotropy of the cation conductivity. During the transition to the cubic high-temperature phase all five channels become equivalent with sharply increased cross-sections, which accounts for the increase of cations mobility and gives rise to the three-dimensional character of conductivity.

The structure peculiarities of K0.9Fe0.9Ti0.1O2 that favor the emergence of a superionic state have been studied using neutron powder diffraction data as a function of temperature. The migration paths in the structure of both, undoped and doped potassium ferrite were modeled by topological (tiling) and DFT methods. It is shown that heating of the low-temperature phase leads to increase of the ionic conductivity thanks to widening the migration channels and the appearance of thermally induced cation vacancies. The calculated migration barrier is found to not exceed 0.3 eV/ion in all phases, which is consistent with the experimental data. Doping also increases the ionic conductivity, but up to about 10% of Ti only; then the experimental activation energy even increases. The DFT modeling shows that it can be caused by growth of the regions unavailable for the mobile cations; the regions are formed around the dopant atoms.

New Rb 3 PO 4 -based ceramic materials with high rubidium-cation conductivity in the Rb 3–2 x Pb x PO 4 system have been synthesized and studied. Introduction of Pb 2+ cations leads to a sharp increase in the conductivity of rubidium orthophosphate due to formation of cation vacancies and, at temperatures 350–550°C, also due to the stabilization of high-temperature cubic modification Rb 3 PO 4 . At high temperatures, the electrolytes prepared have very high ion conductivity higher than 10 –1 S cm –1 at 700°C, which is higher than the values previously obtained in similar systems with additions of tin and cadmium ions. The factors influencing the transport properties of the materials under study are discussed.

Lithium-vanadium bronze Li1+xV3O8 was produced by the solid-phase method and its electrical conductivity was measured with silver and platinum electrodes. X-ray diffraction and thermal analyses demonstrated that Li1+xV3O8 interacts at a temperature of 480°C with metallic silver to give AgV2O5 and AgV3O8, which is responsible for the poor reproducibility of results in electrical conductivity measurements with silver electrodes.