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Perovskite-type lithium ionic conductors were explored in the (LixLa1&minus, x/3)ScO3 system following their syntheses via a high-pressure solid-state reaction. Phase identification indicated that a solid solution with a perovskite-type structure was formed in the range 0 &le, x &lt, 0.6. When x = 0.45, (Li0.45La0.85)ScO3 exhibited the highest ionic conductivity and a low activation energy. Increasing the loading of lithium as an ionic diffusion carrier expanded the unit cell volume and contributed to the higher ionic conductivity and lower activation energy. Cations with higher oxidation numbers were introduced into the A/B sites to improve the ionic conductivity. Ce4+ and Zr4+ or Nb5+ dopants partially substituted the A-site (La/Li) and B-site Sc, respectively. Although B-site doping produced a lower ionic conductivity, A-site Ce4+ doping improved the conductive properties. A perovskite-type single phase was obtained for (Li0.45La0.78Ce0.05)ScO3 upon Ce4+ doping, providing a higher ionic conductivity than (Li0.45La0.85)ScO3. Compositional analysis and crystal-structure refinement of (Li0.45La0.85)ScO3 and (Li0.45La0.78Ce0.05)ScO3 revealed increased lithium contents and expansion of the unit cell upon Ce4+ co-doping. The highest ionic conductivity of 1.1 &times, 10&minus, 3 S cm&minus, 1 at 623 K was confirmed for (Li0.4Ce0.15La0.67)ScO3, which is more than one order of magnitude higher than that of the (LixLa1&minus, x/3)ScO3 system.

The novel lithium-ion conductor Li7Ge3PS12 was synthesized by slow cooling from the ternary Li2S–GeS2–P2S5 system, and was shown to exhibit a cubic argyrodite-type structure. The phase composition was determined by varying the ratio of starting materials; the observed monophasic properties were close to those for the Li7Ge3PS12 composition. The lattice parameter (a =9.80192(3) A) of Li7Ge3PS12 was slightly smaller than that of Li7PS6 (a =9.993 A), indicating that substitution of a Li cation by the smaller Ge cation contracted the cubic lattice. In addition, the novel structure consisted of a framework composed of four isolated (Ge/P)S4 tetrahedra. Li+ ions occupied tetrahedral sites within the framework, forming a three-dimensional conduction pathway. Finally, Li7Ge3PS12 exhibited a high ionic conductivity of 1.1×10−4 S cm−1 at 25 °C and an activation energy of 25 kJ mol−1.

A solid solution of the lithium superionic conductor Li10+δGe1+δP2−δS12 (0 ≤ δ ≤ 0.35) was synthesized and its structure and ionic conductivity were examined. The highest ionic conductivity value of 1.42 × 10−2 S cm−1 was obtained at 300 K with a sintered pellet of the sample having the highest solid solution lithium content of δ = 0.35. The Arrhenius conductivity curves obtained for this material exhibited a gradual change in slope over the temperature range of 193–373 K and the activation energy for ionic conduction decreased from 26 kJ mol−1 below 373 K to 7 kJ mol−1 above 573 K, which is typical of highly ionic conducting solids. The crystal structures of the solid solutions were determined using neutron diffraction, and conduction pathways were visualized through analysis by applying the maximum entropy method. The lithium distribution was found to disperse significantly throughout a one-dimensional conduction pathway as the temperature was increased from 4.8 K to 750 K. In addition, two-dimensional distribution of lithium along the ab plane became apparent at high temperatures, suggesting that the conduction mechanism changes from one-dimensional to three-dimensional with increasing temperature.

In general, the ionic conductivity of sulfide glasses decreases with their crystallization, although it increases for a few sulphide glasses owing to the crystallization of a highly conductive new phase (e.g., Li7P3S11: 70Li2S-30P2S5). We found that the ionic conductivity of 75Li2S-25P2S5 sulfide glass, which consists of glassy and crystalline phases, is improved by optimizing the conditions of the heat treatment, i.e., annealing. A different mechanism of high ionic conductivity from the conventional mechanism is expected in the glassy phase. Here, we report the glassy structure of 75Li2S-25P2S5 immediately before the crystallization by using the differential pair distribution function (d-PDF) analysis of high-energy X-ray diffraction. Even though the ionic conductivity increases during the optimum annealing, the d-PDF analysis indicated that the glassy structure undergoes no structural change in the sulfide glass-ceramic electrolyte at a crystallinity of 33.1%. We observed the formation of a nanocrystalline phase in the X-ray and electron diffraction patterns before the crystallization, which means that Bragg peaks were deformed. Thus, the ionic conductivity in the mixture of glassy and crystalline phases is improved by the coexistence of the nanocrystalline phase.

Lithium superionic conductors with the Li10GeP2S12 (LGPS)-type structure are promising materials for use as solid electrolytes in next-generation lithium batteries. A novel member of the LGPS family, Li9.42Si1.02P2.1S9.96O2.04, and its solid solutions were synthesised by quenching from 1273 K in the Li2S–P2S5–SiO2 pseudoternary system. The material exhibited an ionic conductivity as high as 3.2×10−4 S cm−1 at 298 K, as well as the high electrochemical stability to lithium metal, which was improved by the introduction of oxygen into the LGPS-type structure. An all-solid-state cell with a lithium metal anode and Li9.42Si1.02P2.1S9.96O2.04 as the separator showed excellent performance with a high coulomb efficiency of 100%. Thus, oxygen doping is an effective way of improving the electrochemical stability of LGPS-type structure.

An oxide ion conductor, La2Li2x(CO3)1−xO2+x (x=0.15), was synthesized using a solid-state reaction, and its structure was subsequently determined by Rietveld refinement analyses of synchrotron X-ray and high-resolution powder neutron diffraction data. These analyses determined that carbonate groups are situated between (La2O22+)n layers in an ordered arrangement and that both oxygen vacancies and interstitial oxygen ions exist within the carbonate layers, resulting in a composition of La2Li0.3(CO3)0.85O2.3. This material is structurally stable up to 500 °C and exhibits a conductivity of 5.5×10−5 S cm−1 at 450 °C. Oxide vacancies associated with carbonate anions appear to be responsible for the ionic conduction observed in this material.

For the lithium super-ionic conductor Li 10 GeP 2 S 12 , the partial substitution of sulfur by oxygen is achieved via a solid-state reaction. The solid-solution range of oxygen is found to be 0 ≤ x 10 GeP 2 S 12− x O x . Structure refinements using synchrotron X-ray diffraction data confirm the preference for oxygen substitution in the PS 4 tetrahedra. The local structural change in the P(S/O) 4 tetrahedra upon substitution is also indicated by Raman spectroscopy. Ionic conduction properties are maintained even after the oxygen substitution in Li 10 GeP 2 S 12 ; the ionic conductivity of Li 10 GeP 2 S 12− x O x (0.3 ≤ x ≤ 0.6) ranges from 1.03 × 10 −2 to 8.43 × 10 −3 S cm −1 at 298 K. No redox current is observed by cyclic voltammetry from nearly 0 to 10 V versus Li/Li + except for that due to the lithium deposition/dissolution reactions. All-solid-state batteries using Li 10 GeP 2 S 12− x O x ( x = 0.3 and 0.6) as solid electrolytes with Li metal anodes show discharge capacities exceeding 100 mAh g −1 and better cycling performance compared to batteries using the original Li 10 GeP 2 S 12 . The partial substitution of oxygen for sulfur in Li 10 GeP 2 S 12 affords a novel solid electrolyte, Li 10 GeP 2 S 12− x O x , with high conductive properties and electrochemical stability.