Polycrystalline Solid Electrolytes Research Articles

Roles of lithium ions and La/Li-site vacancies in sinterability and total ionic conduction properties of polycrystalline Li 3 xLa 2/3− xTiO 3 solid electrolytes (0.21 ≤ 3 x ≤ 0.50)

The Li 0.33La 0.55TiO 3 solid electrolyte has a maximum grain ionic conductivity of 1.13 × 10 −3 S cm −1 among the Li 3 x La 2/3− x TiO 3 oxides (0.21 ≤ 3 x ≤ 0.50), but the total ionic conductivity of its polycrystalline phase is not the highest. Owing to the grain-boundary resistances controlling the total resistances of bulk samples, an excellent solid electrolyte is mainly characterized by the grain-boundary resistances. With regard to the role of lithium ions, the substitution of La 3+ ions by the Li + ions weakens the strength of inter-ionic forces, leading to the decrease in the sintering temperature. The presence of La 3+/Li +-site vacancies promotes the densification and grain growth and further results in rapid decreases in porosity and grain-boundary resistances. Li 0.21La 0.60TiO 3 with a larger amount of La 3+/Li +-site vacancies can therefore exhibit the highest total ionic conductivity through rapidly decreasing its grain-boundary resistances by changing its microstructure, and it becomes a better polycrystalline solid electrolyte than Li 0.33La 0.55TiO 3 in the Li 3 x La 2/3− x TiO 3 system studied, in spite of its lower grain ionic conductivity.

New type of potassium ion conducting solid based on lanthanum oxysulfate

A new type of potassium ion conducting polycrystalline solid electrolyte, (1 − x)La 2O 2SO 4 − x(0.8K 2SO 4 − 0.2CaSO 4), with the high ion conductivity at the elevated temperature region was developed by doping potassium and calcium sulfates into the thermally stable lanthanum oxysulfate. Among the samples of the single phase La 2O 2SO 4, the 0.8La 2O 2SO 4 − 0.2(0.8K 2SO 4 − 0.2CaSO 4) ( x = 0.2) shows the highest ion conductivity reaching values potentially suitable for applications, i.e. σ is greater than 10 −2 S cm −1 above 800 °C.

Extraordinary high potassium ion conducting polycrystalline solids based on gadolinium oxide–potassium nitrite solid solution

A new type of potassium ion conducting polycrystalline solid electrolyte was prepared by forming the Gd 2O 3–KNO 2 solid solution. Since KNO 2 is dissolved in the Gd 2O 3 crystal lattice scale, a considerable enhancement in K + ion conductivity was successfully realized. The K + ion conductivity is more than three orders of magnitude higher than that of the well-known K + ion conducting K 2SO 4 polycrystal solid and the value also exceeds that of K +–β ″-alumina single crystal, demonstrating the highest ion conductivity among the K + ion conducting solid series.

Ion-transport phenomena in concentrated PEO-based composite polymer electrolytes

The enhancement of the ionic conductivity of Li–P(EO) n -based polymer electrolytes by the addition of finely divided inorganic oxides is the subject of considerable discussion. The increase in ionic conductivity in concentrated composite solid polymer electrolytes (CSPE) is related both to the suppression of the formation of crystalline PEO and PEO-salt phases and to interfacial conduction. In the case of polycrystalline or polyparticle solid electrolytes, however, grain-boundary (GB) resistance, which is associated with the crossover of ions from particle to particle across grain boundaries orthogonal to the direction of current flow (or parallel to the field lines), must be considered. The conduction across grain boundaries in polymer appears to be ignored so far. In this work, we provide SEM and ECS experimental data on LiI–P(EO)–Al 2O 3 CSPEs. The effects of plasticizers, doping by CaI 2, change in Li/EO ratio, and nanosize alumina concentration on the interior grain ionic conductivity and on the resistance of the orthogonal grain boundaries are addressed.

Optimization of divalent magnesium ion conduction in phosphate based polycrystalline solid electrolytes

A highest Mg2+ ion conducting polycrystalline solid electrolyte was successfully realized by improving the characteristics of both grain bulks and grain boundaries simultaneously. The former improvement was achieved by making a solid solution to substitute cation site for higher valent one to create Mg2+ ion vacancies in grain bulks. The latter was realized by obtaining a composite in such a manner to microscopically deposit the insulating secondary phase in grain boundaries. By combining above mentioned two effects, the optimization of Mg2+ ion conductivity at around 800 °C was effectively achieved to reach the total Mg2+ ion conductivity of approximately 10−2 S·cm−1 which is applicable in a practical range.

Effective medium theory for ionic conductivity in polycrystalline solid electrolytes

It is usually found that for the relatively poor ion conducting solids, the ionic conductivity for the pure polycrystalline sample is higher than that of the single crystal. The difference has been suggested to be due to the presence of dislocations grain boundaries etc. in the polycrystal. In this paper we propose a theoretical model for the polycrystal including these defects. A quantitative estimate of the grain boundary contribution to conductivity is made using an effective medium theory and it is found to exhibit an Arrhenius behaviour. The results for calcium fluoride, thallium chloride and cuprous chloride show that the grain boundary conductivity is ≈ 10 5 times that of the single crystal. The ratio of activation energy for grain boundary conduction to that of the single crystal is found to be 0.5–0.6 which is consistent with results obtained from other sources.

Electrical and acoustical relaxation in fast ionic conductors

The ultrasonic velocity, attenuation coefficient, electric conductivity and dielectric permittivity have been measured in wide temperature and frequency ranges in various crystalline, polycrystalline and glassy solid electrolytes. The high relaxational ultrasonic attenuation maxima and corresponding velocity dispersion have been observed. Such behaviour is supposed to be determined by acoustoionic interactions of two types: (i) the piezoelectric in the piezoelectric superionic; (ii) interaction caused by acoustic wave modulation of chemical potential felt by mobile ions in the centrosymmetric materials. In polycrystalline and glassy superionics the non-Debye behaviour for ultrasonic relaxation has been established. In such materials the characteristic frequency dependencies of ionic conductivity and dielectric permittivity were obtained. A simple theoretical model describing both frequency and temperature dependencies of electrical and acoustical properties of solid electrolytes is proposed. This model is based on continuous distribution of activation energies in a limited interval and describes the experimental data fairly well.

On the dispersion of ionically conducting glass into the Li 2SO 4-Li 2CO 3 eutectic composite system

Mixed phase electrolytes consisting of mixture of Li 2SO 4-Li 2CO 3 eutectic and different ionically conducting glasses have been prepared in an attempt to combine some of the advantages of polycrystalline and glassy ion conductors. At 20 wt% of glass, the low temperature conductivity is an order of magnitude larger than that of the pure sulphate-carbonate eutectic. These results can provide a new approach for the development of polycrystalline solid electrolytes.

On the Insertion of 7Li2 O : 3 B 2 O 3 Glass into the Polycrystalline 6Li2 SO 4 : 4Li2 CO 3 Composite System

The ionic conductivity of glass inserted in eutectic has been studied as a function of temperature and frequency. With such insertion, a prominent increase in the conductivity (by two orders of magnitude at low temperature) has been observed. The results have been explained in the light of dispersed phase theory, and supported by microstructural evidence. These results could provide a new approach for the development of polycrystalline solid electrolytes.

Comparative conductivity measurements on ß″-alumina isomorphs by two-probe and four-probe techniques

The usefulness of two a.c. techniques for conductivity measurements of polycrystalline solid electrolytes was assessed. For the comparison, two (Na, Sr)-ß″-alumina isomorphs were chosen. The two-probe data for the 10% exchanged material in the cell Pt/(Na, Sr)-ß″-alumina/Pt did not allow a simple extrapolation procedure to determine the bulk resistance (sum of crystal and grain boundary contributions). Simulation of the frequency dependence by analogue circuits, the parameters of which were obtained by optimization programmes, was not successful either. In contrast, the four-probe technique yielded useful values. Both techniques yielded similar conductivity values for the 70% exchanged material.

ChemInform Abstract: (Na,Sr) Beta′′ Aluminas ‐ Preparation and Characterization of New Polycrystalline Solid Electrolytes with Mixed Conductivities.

AbstractIsomorphs of the β''‐alumina family have a wide range of technical applications.

(Na, Sr) Beta″ Aluminas – Herstellung und Charakterisierung neuer polykristalliner Festelektrolyte mit gemischter Leitfähigkeit

AbstractTechnical applications of isomorphs of the beta″ alumina family are described in the beginning of the paper. The production and characterization of new polycrystalline solid electrolytes, obtained by partial replacement of the monovalent sodium cation by the bivalent strontium cation in the starting material, sodium beta″ alumina from Ceramatec Inc., is reported next. The equilibrium distribution curve and the conductivities are discussed.

Properties of surface layers formed on lithium in Li-SOCl2 cells: synergetic effect of SO2 and LiAl(SO3Cl)4

Kinetic and morphological properties of surface layers formed on the Li anode during storage in SOCl2/LiAlCl4 solution have been investigated. The synergetic effect of SO2 and LiAl(SO3Cl)4, used for voltage delay alleviation, changes the shape and size of the microcrystals of LiCl constituting the surface layer. It also leads to separate and modify the conduction and charge transfer processes involved in the kinetic properties of the surface layer at the equilibrium potential. These properties appear to be similar to those of a polycrystalline solid electrolyte where the grain boundaries induce an intergranular conduction process.

Ageing of ZrO 2-based solid electrolytes

An investigation has been carried out on the regularities of ageing of ZrO 2-based solid electrolytes stabilized with Y 2O 3, Ho 2O 3, So 2O 3 of various concentrations in the single-and two-phase regions of the solid solution phase diagram. For electrolytes pertaining to the two-phase region of the phase diagram, time dependences of electrical conductivity adequately describing its variation in a wide-time interval are proposed. Causes of ageing in single-phase electrolytes are discussed. A noticeable contribution, which can be both positive and negative, to the ageing intensity by the change in elecelectrical conductivity of grain boundaries of polycrystalline solid electrolytes has been established. The effect of high ageing rate on the results of measurement of electrical conductivity of solid electrolytes is noted.

Secondary Calcium Solid Electrolyte High Temperature Battery

not Available.

Ionic conductivity of ThO 2- and ZrO 2-based electrolytes between 300 and 2000 K

A conductivity vs temperature relationship is derived which results from simplified geometrical considerations of a polycrystalline solid electrolyte, assuming that oxygen ion diffusion only takes place through the grains or along the grain boundaries. The relationship proves to be capable of describing conductivity data of YDT, CDT, YSZ and CSZ between 300 and 2000 K. The data analysis reveals that the activation enthalpy as well as the activation entropy of grain conductivity are significantly higher in comparison with grain-boundary conductivity. It may be concluded that BAUERLE's electrical equivalent circuit which underlies the interpretation of dispersive type measurements aiming at separate determination of grain and grain-boundary conductivity ought to be revised.

7Li NMR and related studies in LISICON system

7Li NMR studies in the polycrystalline solid electrolytes Li 14Zn(GeO 4) 4 and Li 12Zn 2(GeO 4) 4 (LISICON System) have been carried out in the temperature range 209 K to 398 K. Onset of NMR line narrowing was observed at 230 K for Li 14Zn(GeO 4) 4 and at 240 K for Li 12Zn 2(GeO 4) 4 and became appreciable with increasing temperature in both the cases. Activation energies calculated were 0.19 eV and 0.17 eV respectively. The conductivity variation with temperature was qualitatively similar to that of the NMR linewidth but the activation energies of 0.60 eV and 0.47 eV respectively obtained were much higher. Possible reasons for the difference are discussed. Conductivity, DTA, TGA and 1H and 7Li NMR studies on unsealed samples show the important role played by moisture in blocking the motion of Li + ions in these compounds.

A new method for analysing the a.c. behaviour of polycrystalline solid electrolytes

A new method for analysing the a.c. behaviour of polycrystalline solid electrolytes

A new method for analysing the a.c. behaviour of polycrystalline solid electrolytes

A new method for analysing the a.c. behaviour of polycrystalline solid electrolytes