No abstract

Some basic but important guidelines for the development of sheet-type all-solid-state batteries using a practical slurry coating process are described in this paper. Li 3 PS 4 glass powder that had been passed through a 25 μm sieve was prepared. Positive and negative electrode sheets with capacities of more than 1.5 mAh cm −2 were developed. An all-solid-state full cell was constructed using the electrode sheets and the self-standing solid electrolyte sheets. The energy density of the cell was ca. 155 Wh kg −1 , where the weight of the current collectors and the exterior package was excluded from the weight for calculation.

One way of increasing the energy density of lithium-ion batteries is to use electrode materials that exhibit high capacities owing to multielectron processes. Here, we report two novel materials, Li2TiS3 and Li3NbS4, which were mechanochemically synthesised at room temperature. When used as positive-electrode materials, Li2TiS3 and Li3NbS4 charged and discharged with high capacities of 425 mA h g−1 and 386 mA h g−1, respectively. These capacities correspond to those resulting from 2.5- and 3.5-electron processes. The average discharge voltage was approximately 2.2 V. It should be possible to prepare a number of high-capacity materials on the basis of the concept used to prepare Li2TiS3 and Li3NbS4.

Dense BaTiO 3 ceramics consisting of submicrometer grains were prepared using the spark plasma sintering (SPS) method. Hydrothermally prepared BaTiO 3 (0.1 and 0.5 µm) was used as starting powders. The powders were densified to more than ≈95% of the theoretical X-ray density by the SPS process. The average grain size of the SPS pellets was less than ≈1 µm, even by sintering at 1000-1200°C, because of the short sintering period (5 min). Cubic-phase BaTiO 3 coexisted with tetragonal BaTiO 3 at room temperature in the SPS pellets, even when well-defined tetragonalphase BaTiO 3 powder was sintered at 1100°and 1200°C and annealed at 1000°C, signifying that the SPS process is effective for stabilizing metastable cubic phase. The measured permittivity was ≈7000 at 1 kHz at room temperature for samples sintered at 1100°C and showed almost no dependence on frequency within ≈10 0 -10 6 Hz; the permittivity at 1 MHz was 95% of that at 1 kHz.

The effect of the particle sizes of LiNi 1/3 Co 1/3 Mn 1/3 O 2 and Li 2 S-P 2 S 5 solid electrolytes (SEs) on the electrode morphology was investigated. Smaller-sized SE particles were advantageous in fabricating dense and homogeneous electrode layers with an effective lithium-ion conduction pathway and a large electrode-electrolyte interfacial contact area because of the unique mechanical properties of sulfide-based SEs. The homogeneous distribution of the SE is also effective in the suppression of cracking and fracturing of LiNi 1/3 Co 1/3 Mn 1/3 O 2 because of the favorable mechanical properties of the sulfide-based SEs. The capacity of the all-solid-state cells under high-rate operation was thus remarkably improved.

A unique charge/discharge mechanism of amorphous TiS is reported. Amorphous transition metal polysulfide electrodes exhibit anomalous charge/discharge performance and should have a unique charge/discharge mechanism: neither the typical intercalation/deintercalation mechanism nor the conversion-type one, but a mixture of the two. Analyzing the mechanism of such electrodes has been a challenge because fewer tools are available to examine the "amorphous" structure. It is revealed that the electrode undergoes two distinct structural changes: (i) the deformation and formation of S-S disulfide bonds and (ii) changes in the coordination number of titanium. These structural changes proceed continuously and concertedly for Li insertion/extraction. The results of this study provide a novel and unique model of amorphous electrode materials with significantly larger capacities.

It is demonstrated that a ZnRh2O4 normal spinel with a band gap of ∼2.1 eV is a unique material as a p type wide-gap semiconductor. The electrical conductivity of the sputtered film was 0.7 S cm−1 at 300 K with no intentional doping. The electronic structure was investigated by photoemission and inverse photoemission measurements and indicated that the band gap is composed mainly of ligand field splitting of an octahedrally coordinated Rh3+ octahedron between fully occupied t2g6 and empty eg0 sets.

An oxide thermoelectric device was fabricated using Gd-doped Ca3Co4O9 p-type legs and La-doped CaMnO3 n-type legs on a fin. The power factors of p legs and n legs were 4.8×10−4 Wm−1 K−2 and 2.2×10−4 Wm−1 K−2 at 700 °C in air, respectively. With eight p–n couples the device generated an output power of 63.5 mW under the thermal condition of hot side temperature Th=773 °C and a temperature difference ΔT=390 °C. This device proved to be operable for more than two weeks in air showing high durability.