Showing papers by "Kota Suzuki published in 2020"

Ionic conduction mechanism of a lithium superionic argyrodite in the Li–Al–Si–S–O system

Abstract: We report the conduction mechanism in oxygen-substituted lithium conductors composed of the Li6.15Al0.15Si1.35S6−xOx (LASSO) system, which is a novel member of the argyrodite-type family and has superionic conductivities, making it suitable for all-solid-state batteries. The crystal structures, ionic conductivities, and electrochemical properties of these systems were examined using powder X-ray and neutron diffractometry combined with impedance spectroscopy and cyclic voltammetry measurements. The optimal Li6.15Al0.15Si1.35S5.4O0.6 (x = 0.6) material exhibited a high ionic conductivity of 1.24 mS cm−1 at 25 °C with a low activation energy of 36.6 kJ mol−1. Rietveld refinement and maximum-entropy-method analysis using neutron diffraction data revealed unique interstitial Li+ and O2−/S2− site disorder, which led to a flatter energy landscape for migrating Li+ ions and, thus, a low percolation threshold for three dimensional (3D) Li-ion diffusion. Oxygen substitution also stabilized the structure, and a wide electrochemical window from −0.1 V to 5 V vs. Li/Li+ was achieved. The significant improvements in the ionic conductivity and stability owing to structural changes after cation and anion substitutions reveal an important strategy toward the development of argyrodite-type superionic conductors.

Fast material search of lithium ion conducting oxides using a recommender system

Abstract: A practical material search using a recommender system is demonstrated to obtain novel lithium ion conducting oxides. The synthesis of unknown chemically relevant compositions (CRCs) proposed by the recommender system and their related materials effectively reveals two kinds of novel lithium ion conductors using different approaches. In the Li2O–GeO2–P2O5 system, Li6Ge2P4O17 is found, which has the same composition as the recommended unknown CRC. Less-than-10-time synthesis following the ranking order in the diagram provides evidence of the discovered new phase. In the other quasi-ternary diagram of the Li2O–ZnO–GeO2 system, Li3Zn0.65Ge4.35O10.85 is discovered by a combination of a recommender system and synthetic chemistry, because the composition of the novel phase is different from that of the recommended unknown CRC. Here too, the required time for material discovery is reduced to one-third of that required for random search without the recommender system. Phase identification and elemental analysis suggest that these discovered materials could have unique compositions and crystal structures. The room-temperature (∼300 K) ionic conductivity (10−9–10−6 S cm−1) of the novel phases can be improved by compositional and structural optimisations. The recommender system could emerge as a practical material search tool for enhancing the discovery rate of solid lithium ion conductors.

Oxygen Substitution for Li–Si–P–S–Cl Solid Electrolytes toward Purified Li10GeP2S12-Type Phase with Enhanced Electrochemical Stabilities for All-Solid-State Batteries

Abstract: Li9.54Si1.74P1.44S11.7Cl0.3 (LSiPSCl), which exhibits a Li10GeP2S12 (LGPS)-type structure, presents the highest reported Li-ion conductivity for solid electrolytes, but the formation of a secondary...

The effect of cation size on hydride-ion conduction in LnSrLiH2O2 (Ln = La, Pr, Nd, Sm, Gd) oxyhydrides

Abstract: Hydride-ion conductors have attracted great interest as solid electrolytes due to the highly negative redox potential of the hydride ion. This study provides direction for effective design of materials that enhance H− conductivity by exploring the relationship between cation size and hydride-ion conductivity using LnSrLiH2O2 (Ln = La, Pr, Nd, Sm, Gd), which are K2NiF4-type oxyhydride materials, synthesised under ambient and high pressures. The size of the A-site cation and the activation energy for H− conduction were found to be strongly correlated. GdSrLiH2O2 exhibits the lowest activation energy of 67 kJ mol−1. Crystal structure analysis and first principles calculations revealed that H− is more displaced along the conduction pathway for smaller A-site cations in LnSrLiH2O2 due to lower repulsion between A-site cations and H−. These findings contribute to the further development of K2NiF4-type oxyhydrides with high H− conductivities.

Application of precise neutron focusing mirrors for neutron reflectometry: latest results and future prospects

Abstract: Neutron reflectometry (NR) is a powerful tool for providing insight into the evolution of interfacial structures, for example via operando measurements for electrode–electrolyte interfaces, with a spatial resolution of nanometres. The time resolution of NR, which ranges from seconds to minutes depending on the reflection intensity, unfortunately remains low, particularly for small samples made of state-of-the-art materials even with the latest neutron reflectometers. To overcome this problem, a large-area focusing supermirror manufactured with ultra-precision machining has been employed to enhance the neutron flux at the sample, and a gain of approximately 100% in the neutron flux was achieved. Using this mirror, a reflectivity measurement was performed on a thin cathode film on an SrTiO3 substrate in contact with an electrolyte with a small area of 15 × 15 mm. The reflectivity data obtained with the focusing mirror were consistent with those without the mirror, but the acquisition time was shortened to half that of the original, which is an important milestone for rapid measurements with a limited reciprocal space. Furthermore, a method for further upgrades that will reveal the structural evolution with a wide reciprocal space is proposed, by applying this mirror for multi-incident-angle neutron reflectometry.

Precipitation of the Lithium Superionic Conductor Li10GeP2S12 by a Liquid-phase Process

Abstract: The Li10GeP2S12-type solid electrolyte was obtained by a liquid-phase process. A small amount of solids (1–3 wt %) in MeOH solvent formed a homogeneous solution. Stirring for 2 h and subsequent dry...

X-Ray CT 3D Structure Measurement and Performance Evaluation of All Solid-State Lithium-Ion Battery Anode

Abstract: X-ray CT and battery performance measurements of LiIn-SE-Anode (SE + Graphite) half cell are conducted to elucidate the relationship between electrode performance and 3D internal structure. LGPS that is one of the highest lithium-ion conductive solid electrolyte are used in this study. Fig.1 illustrates an experimental setup in this study. The anode half sell is installed in high pressure X-ray CT measurement jig. The X-ray CT are conducted with In-situ high pressure condition (100MPa) to measure the volume ratio of SE and graphite and tortuosity of SE network those can be changed with decompression. The battery performance are measured by a potentiogalvanostat with CC charging and discharging and an electrochemical impedance spectroscopy (EIS) are conducted to measure the overpotential in the cell. The performance measurement and EIS are conducted for the same X-ray CT measured anode half sell, therefore, the battery performance can be directory discussed with 3D structure.Figure 2 illustrates the ratio of actual capacity to theoretical capacity as a function of electrode thickness and volume ratio of active material (graphite). The highest capacity ratio is obtained for thin electrode (30um) and low active material volume ratio (50%) and is decreased by increase in the electrode thickness and the active material ratio.Table.1 shows the electrode structure parameters measured by the X-ray CT and high-frequency and low-frequency resistance measured by the EIS. The high frequency resistance of the anode half-cell is originated from overpotential of lithium ion transportation in SE network and activation overpotential on graphite and that of low-frequency resistance is diffusion of Li-ion in graphite particle. From table.1, in the case with graphite ratio of 50%, both high frequency and low frequency resistance are increased with increase in the electrode thickness. It is considered that the low frequency resistance is increased with the increase of SE network resistance by increase in the length of the lithium-ion transportation length. The increase of the electrode thickness decreases the lithium ion flux for each graphite particle and the diffusion in the graphite is suppressed and the low frequency resistance is increased. The increase of graphite volume ratio dramatically decreases the ratio of actual capacity to theoretical capacity as shown in fig.2. The tortuosity of SE network that has a positive correlation to the resistance of the SE network is increased with the increase in the graphite volume ratio. It can be a reason of the increase of the high frequency resistance. Moreover, the specific surface area between SE and graphite is decreased with the increase in graphite volume ratio. It means the graphite is condensed in the electrode and the contact surface of the graphite to SE is decreased and the diffusion length of lithium ion in the graphite is increased. This suppression of the lithium ion diffusion in graphite particle is corresponds to the increase of the low frequency resistance as shown in table 3.From the mentioned above, it can be said that the battery performance improvement with high volume ratio of graphite for would be achieved with the improvement of the dispersiveness of graphite and ion conductivity of the solid electrolyte.Figure 1

Nanostructure, electrode, cell, and method for manufacturing nanostructure

Abstract: A nanostructure containing a plurality of substances obtained by accumulation of nano-sized particles, wherein the average particle diameter of the nano-sized particles is 5-30 nm. The nano-sized particles are of a metal or a metal oxide. The nano-sized particles are at least one of Zr, Li, Si, Cu, and Nb.