Atsushi Unemoto

Ultrathin Nanosheets of Li2MSiO4 (M = Fe, Mn) as High-Capacity Li-Ion Battery Electrode

Novel ultrathin Li(2)MnSiO(4) nanosheets have been prepared in a rapid one pot supercritical fluid synthesis method. Nanosheets structured cathode material exhibits a discharge capacity of ~340 mAh/g at 45 ± 5 °C. This result shows two lithium extraction/insertion performances with good cycle ability without any structural instability up to 20 cycles. The two-dimensional nanosheets structure enables us to overcome structural instability problem in the lithium metal silicate based cathode materials and allows successful insertion/extraction of two complete lithium ions.

Exceptional Superionic Conductivity in Disordered Sodium Decahydro-closo-decaborate

Na2 B10 H10 exhibits exceptional superionic conductivity above ca. 360 K (e.g., ca. 0.01 S cm(-1) at 383 K) concomitant with its transition from an ordered monoclinic structure to a face-centered-cubic arrangement of orientationally disordered B10 H10 (2-) anions harboring a vacancy-rich Na(+) cation sublattice. This discovery represents a major advancement for solid-state Na(+) fast-ion conduction at technologically relevant device temperatures.

Unparalleled lithium and sodium superionic conduction in solid electrolytes with large monovalent cage-like anions

Solid electrolytes with sufficiently high conductivities and stabilities are the elusive answer to the inherent shortcomings of organic liquid electrolytes prevalent in todays rechargeable batteries. We recently revealed a novel fast-ion-conducting sodium salt, Na2B12H12, which contains large, icosahedral, divalent B12H122- anions that enable impressive superionic conductivity, albeit only above its 529 K phase transition. Its lithium congener, Li2B12H12, possesses an even more technologically prohibitive transition temperature above 600 K. Here we show that the chemically related LiCB11H12 and NaCB11H12 salts, which contain icosahedral, monovalent CB11H12- anions, both exhibit much lower transition temperatures near 400 K and 380 K, respectively, and truly stellar ionic conductivities (> 0.1 S cm-1) unmatched by any other known polycrystalline materials at these temperatures. With proper modifications, we are confident that room-temperature-stabilized superionic salts incorporating such large polyhedral anion building blocks are attainable, thus enhancing their future prospects as practical electrolyte materials in next-generation, all-solid-state batteries.

Development of bulk-type all-solid-state lithium-sulfur battery using LiBH4 electrolyte

Stable battery operation of a bulk-type all-solid-state lithium-sulfur battery was demonstrated by using a LiBH4 electrolyte. The electrochemical activity of insulating elemental sulfur as the positive electrode was enhanced by the mutual dispersion of elemental sulfur and carbon in the composite powders. Subsequently, a tight interface between the sulfur-carbon composite and the LiBH4 powders was manifested only by cold-pressing owing to the highly deformable nature of the LiBH4 electrolyte. The high reducing ability of LiBH4 allows using the use of a Li negative electrode that enhances the energy density. The results demonstrate the interface modification of insulating sulfur and the architecture of an all-solid-state Li-S battery configuration with high energy density.

Novel processing of lithium manganese silicate nanomaterials for Li-ion battery applications

Lithium manganese silicate positive electrode materials have received great attention because of the two lithium ion capacities and can be realized in ultrafine nanoparticles due to their low volumetric changes upon lithium insertion and extraction. A supercritical fluid process has been adopted to synthesize monodisperse Li2MnSiO4 ultrafine particles and hierarchical nanostructures with a mean particle diameter of 4–5 nm and successfully shown to attain a high electrochemical performance. A reversible capacity (190–220 mA h g−1) of more than one lithium ion was obtained for the ultrafine monodisperse nanoparticles and hierarchical nanostructures with good cyclability. The enhanced cyclability was found to be due to the monodisperse nanoparticles, which provide a short length for Li-ion diffusion, and possess low volumetric changes. In addition, the varyingly sized Li2MnSiO4 particles were also synthesized via a supercritical fluid process. This process is simple, rapid, energy saving and broadly applicable to other functional materials.

Pseudo-binary electrolyte, LiBH4–LiCl, for bulk-type all-solid-state lithium-sulfur battery

The ionic conduction and electrochemical and thermal stabilities of the LiBH4-LiCl solid-state electrolyte were investigated for use in bulk-type all-solid-state lithium-sulfur batteries. The LiBH4-LiCl solid-state electrolyte exhibiting a lithium ionic conductivity of [Formula: see text] at 373 K, forms a reversible interface with a lithium metal electrode and has a wide electrochemical potential window up to 5 V. By means of the high-energy mechanical ball-milling technique, we prepared a composite powder consisting of elemental sulfur and mixed conductive additive, i.e., Ketjen black and Maxsorb. In that composite powder, homogeneous dispersion of the materials is achieved on a nanometer scale, and thereby a high concentration of the interface among them is induced. Such nanometer-scale dispersals of both elemental sulfur and carbon materials play an important role in enhancing the electrochemical reaction of elemental sulfur. The highly deformable LiBH4-LiCl electrolyte assists in the formation of a high concentration of tight interfaces with the sulfur-carbon composite powder. The LiBH4-LiCl electrolyte also allows the formation of the interface between the positive electrode and the electrolyte layers, and thus the Li-ion transport paths are established at that interface. As a result, our battery exhibits high discharge capacities of 1377, 856, and 636 mAh g(-1) for the 1st, 2nd, and 5th discharges, respectively, at 373 K. These results imply that complex hydride-based solid-state electrolytes that contain Cl-ions in the crystal would be integrated into rechargeable batteries.

Fast sodium ionic conduction in Na2B10H10-Na2B12H12 pseudo-binary complex hydride and application to a bulk-type all-solid-state battery

In the present work, we developed highly sodium-ion conductive Na2B10H10-Na2B12H12 pseudo-binary complex hydride via mechanically ball-milling admixtures of the pure Na2B10H10 and Na2B12H12 components. Both of these components show a monoclinic phase at room temperature, but ball-milled mixtures partially stabilized highly ion-conductive, disordered cubic phases, whose fraction and favored structural symmetry (body-centered cubic or face-centered cubic) depended on the conditions of mechanical ball-milling and molar ratio of the component compounds. First-principles molecular-dynamics simulations demonstrated that the total energy of the closo-borane mixtures and pure materials is quite close, helping to explain the observed stabilization of the mixed compounds. The ionic conductivity of the closo-borane mixtures appeared to be correlated with the fraction of the body-centered-cubic phase, exhibiting a maximum at a molar ratio of Na2B10H10:Na2B12H12 = 1:3. A conductivity as high as log(σ/S cm−1) = –3.5 wa...

Carbon‐Rich Active Materials with Macrocyclic Nanochannels for High‐Capacity Negative Electrodes in All‐Solid‐State Lithium Rechargeable Batteries

A high-capacity electrode active material with macrocyclic nanochannels is developed for a negative electrode of lithium batteries. With appropriate design of the molecular and crystal structures, a ubiquitous chemical commonly available in reagent stocks of any chemistry laboratories, naphthalene, was transformed into a high-performance electrode material for all-solid-state lithium batteries.

Hydrogen Permeation Properties in ( Ce , Sr ) PO4

Ceramic membranes of a proton-electron hole mixed conductor, Ce 0.97 Sr 0.03 PO 4-δ , were prepared for hydrogen permeation measurements. Hydrogen was found to be considerably permeated with the ambipolar diffusion kinetics through the ceramic membranes. In addition, use of surface catalysts, such as pure platinum, palladium-Ce 0.97 Sr 0.03 PO 4-δ , and platinum-Ce 0.97 Sr 0.03 PO 4-δ composites, enhanced the hydrogen permeation flux, suggesting that the contribution of the surface reaction to the hydrogen permeation process is remarkable. The hydrogen permeation flux of (Ce,Sr)PO 4 was found to be comparable to or slightly lower than that of perovskite-type mixed conductors of proton and electron holes reported in the preceding works. This paper reports on the hydrogen permeability of ceramic membranes, in which any alkaline earth metals are not included as main components. High chemical stability in atmospheres containing carbon dioxide and water vapor is expected for the class of this material contrary to some perovskite-type mixed proton and electron hole conductors.

Proton-Electron Mixed Conduction Properties in (Ce,Sr)PO4

Mixed conductivity of proton and electron hole in (Ce,Sr)PO4 have been investigated by electrical conductivity and hydrogen permeation measurements. The partial conductivity contributions of proton and electron hole were separately evaluated from the total conductivity by assuming the defect model proposed in the preceding work. Hydrogen permeation measurements were demonstrated in order to check if and how much hydrogen permeates across the (Ce,Sr)PO4 membranes. As expected, hydrogen successfully permeated across the membranes. Use of surface catalysts was found to enhance the hydrogen permeation fluxes. This suggested that the contribution of the surface reaction to the hydrogen permeation process is remarkable. Hydrogen permeation flux through the (Ce,Sr)PO4 membranes is concluded to be essentially determined by the surface reaction process.