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Lithium-ion-conducting oxide glass electrolytes in the multicomponent systems Li2O–B2O3–SiO2–P2O5-LiX (LiX = Li3N, Li2SO4, Li2CO3, and LiI) were synthesized using a mechanochemical technique. The crystallization temperature and ionic conductivity of multicomponent glasses with added lithium salts or Li3N were evaluated. Because the crystallization temperature is a measure of the ability of glasses to resist crystallization at high temperature, glasses with high conductivity and high crystallization temperature are desirable electrolytes. In this study, the lithium-ion conductivity of the glasses was found to be correlated with the crystallization temperature, and it was difficult to increase both the conductivity and crystallization temperature. The addition of lithium salts (Li2SO4, Li2CO3, and LiI) increased the conductivity but decreased the crystallization temperature. Nitrogen doping by the addition of Li3N improved both these properties of the oxide glass electrolyte. Therefore, oxynitride glasses are desirable electrolytes owing to their thermal stability and lithium-ion conductivity.

Hard carbon is a promising negative electrode material for sodium-ion batteries that operate at low potentials. However, reversible and high-capacity charging and discharging in all-solid-state sodium batteries with hard carbon electrodes using sulfide solid electrolytes have not been reported. This study reports that reductive decomposition of the sulfide solid electrolyte occurs at both the negative composite electrode and the interface between the negative electrode layer and the solid electrolyte layer. In the first cycle, the all-solid-state cell with a composite electrode containing a Na3PS4 solid electrolyte exhibited a large irreversible capacity of 561 mAh g−1 because of the reductive decomposition of Na3PS4 to Na2S and Na3P. The use of a Na3BS3 glass electrolyte with reduction stability can lead to the successful charging and discharging of all-solid-state cell that utilizes hard carbon. This glass electrolyte can serve as a solid electrolyte for the negative composite electrode and as a buffer layer between the negative electrode layer and the solid electrolyte layer. Hence, it can also help suppress the irreversible capacity of the cell to 122 mAh g−1.

Development of oxide solid electrolytes for all-solid-state batteries is attracting increasing attention. In this study, amorphous Li2O–LiI materials are prepared via a mechanochemical process to achieve high lithium ionic conductivity and good compatibility to lithium metal. Amorphous 66.7Li2O·33.3LiI (mol%) electrolyte shows a high ionic conductivity of 3.1 × 10−5 S cm−1 at 25 °C with a relative density of 96 %. An all-solid-state Li symmetric cell (Li/66.7Li2O·33.3LiI/Li) operates without an increase in overvoltage. A simple combination of lithium oxide and lithium iodide exhibits high ionic conductivity, ductility, and stability to lithium metal.

All-solid-state Na–S secondary batteries that use sodium and sulfur, both available in abundance, are the most attractive next-generation batteries. In this study, two types of amorphous MoS3 (a-MoS3) were prepared as electrode active materials for use in all-solid-state sodium secondary batteries using the thermal decomposition (TD) of (NH4)2MoS4 and mechanochemical (MC) processes, denoted a-MoS3 (TD) and a-MoS3 (MC), respectively. X-ray diffraction, thermogravimetric-differential thermal analysis, and X-ray photoelectron spectroscopy (XPS) analyses revealed that a-MoS3 (TD) and a-MoS3 (MC) had different local structures. The a-MoS3 (TD) and a-MoS3 (MC) electrodes showed high reversible capacities of 310 mAh g−1 and 260 mAh g−1, respectively, for five cycles in all-solid-state sodium secondary batteries. XPS analysis of the discharge–charge products suggested that the dissociation and formation of disulfide bonds occurred during the discharge–charge reaction. The results show that a-MoS3 is a promising active electrode material for all-solid-state sodium batteries.

The development of solid electrolytes is necessary for practical applications of all-solid-state Na-ion batteries. In this study, we systematically developed sulfide Na-ion conductors with central In cations, prepared by solid-state reaction and mechanochemical methods. Thermodynamically stable crystals of Na5InS4 and NaInS2 were obtained by the solid-state reaction method, whereas amorphous and/or metastable phases were produced by the mechanochemical method. Two new metastable phases, Na5InS4 and NaInS2, are expected to be examined in the future as end-members of sulfide Na-ion conductors with central In cations.

Solid electrolytes with high ionic conductivity, high formability, and high electrochemical properties are required to improve the performance of all-solid-state sodium batteries. In this study, we focus on a combination of Na2.88Sb0.88W0.12S4 and NaI for preparing composite electrolytes Na2.88Sb0.88W0.12S4·xNaI, and investigate their crystal structures, microstructures, and electrochemical properties. NaI is uniformly dispersed in the composites without forming a solid solution with Na2.88Sb0.88W0.12S4. Na2.88Sb0.88W0.12S4·0.50NaI shows a high ionic conductivity of 3.6 × 10−2 S cm−1 after sintering at 275 °C for only 1.5 h. The charge-discharge characteristics of all-solid-state cells using the Na2.88Sb0.88W0.12S4·xNaI composite are also improved.

All-solid-state sodium secondary batteries are expected to be low-cost, next-generation batteries. NiS2 and FeS2 are potential candidates as positive electrode materials owing to their high theoretical capacities. However, it is difficult to achieve sufficient capacity with bulk FeS2. In this study, pyrite Ni1−xFexS2 (x = 0, 0.3, 0.5, 0.7, 0.9, and 1) electrodes are prepared by a mechanochemical process. The all-solid-state sodium cells with Ni1−xFexS2 show higher discharge–charge potentials than those with NiS2, and higher capacities than those with FeS2. In addition, Ni1−xFexS2 exhibits a higher rate performance than those of NiS2 and FeS2. The all-solid-state cells using Ni1−xFexS2 (x = 0.3, 0.5, and 0.7) are discharged and charged with a high capacity of approximately 390 mAh g−1, without significant capacity fading for at least 30 cycles. The solid-solution formation of NiS2 and FeS2 results in lower material cost, higher rate performance, higher discharge–charge potential than those of NiS2, and higher capacity than that of FeS2. Pyrite Ni1−xFexS2 is a promising positive electrode material for all-solid-state sodium secondary batteries.

All-solid-state lithium-ion batteries that use sulfide solid electrolytes have attracted much attention due to their high safety and wide electrochemical window. In this study, highly oriented pyrolytic graphite (HOPG) and 75Li2S-25P2S5 (mol%) glass were used as a model graphite negative electrode and a sulfide solid electrolyte, respectively. Interfacial lithium-ion transfer between 75Li2S-25P2S5 glass and the HOPG electrode was studied by AC impedance spectroscopy measurements. The activation energy of the interfacial lithium-ion transfer was estimated to be around 37 kJ mol−1, which was much smaller than that at the interface between organic liquid electrolytes and HOPG electrode, indicating that the lithium-ion transfer at the interface between 75Li2S-25P2S5 glass and HOPG electrode proceeded quite rapidly. Furthermore, surface deposition of TiO2 and surface oxidation on HOPG electrodes were performed using the atomic layer deposition (ALD) method. Interfacial lithium-ion transfer between 75Li2S-25P2S5 glass and ALD-modified-HOPG electrodes was also investigated. The activation energies of the interfacial lithium-ion transfer were slightly higher than that of HOPG, but the resistance of the charge-transfer process was lower, indicating that the affinity of the HOPG electrode for the glass electrolyte was improved by surface modification.

The need for an effective design of composite electrodes in all-solid-state Na-S batteries is warranted because of their slow charge–discharge reactions. By employing a composite of activated carbon MSP20, sulfur, and Na3SbS4 as the positive electrode material, we developed an effective all-solid-state Na-S battery that demonstrated the advantages of exhibiting a high capacity and good cyclability. Further, we discovered that filling the carbon micropores with sulfur and combining with highly conductive Na3SbS4, results in a reversible two-electron reaction between S and Na2S. This all-solid-state Na-S battery, operating at room temperature, demonstrates a high capacity of 1560 mAh per gram of sulfur (ca. 330 mAh per gram of positive electrode) and a capacity retention of 93% after 50 cycles. Decreasing the size of the S-MSP20 particles coated with Na3SbS4 in a liquid phase process was observed to reduce the volume change of the particles during charge and discharge cycles, which resulted in an excellent electrochemical performance.

Layered double hydroxides (LDHs) are promising solid electrolytes for all solid-state alkaline fuel cells (AFCs) because of inorganic clay-like materials. However, LDHs were usually obtained as powder, and the formation of thin membranes as a separator of a fuel cell is rather difficult. In this study, a glass paper, non-woven fabric of fine glass fibers with more than 90% porosity, was used as a support for Mg-Al LDH powder, and self-standing, thin membranes for all solid-state AFCs were fabricated. Crystals of Mg-Al LDH were deposited in the inside of the glass paper by repeated immersion in Mg-Al LDH-dispersed solution and drying. Thickness of the obtained Mg-Al LDH thin membrane was about 150 μm, and LDH layer showed c-axis orientation because of the plate-like structure. The H2-O2 fuel cell using the Mg-Al LDH thin membrane as an electrolyte showed open circuit voltage of more than 0.9 V, indicating that the Mg-Al LDH thin membrane is dense and has high gas barrier property. The H2-O2 fuel cell using the Mg-Al LDH thin membrane showed higher power density compared with that using pelletized Mg-Al LDH powder as the electrolyte. The glass paper is proved to be very effective support for making thin Mg-Al LDH electrolyte membrane.

Abstract Lithium-ion batteries are widely used as a power source for portable equipment. However, the use of highly flammable organic solvents in the liquid electrolyte component in these batteries presents a serious safety concern. In this study, the thermal stability of battery cathodes comprising LiNi1/3Mn1/3Co1/3O2 (NMC) and LiPF6-based electrolyte solutions have been investigated using transmission electron microscopy (TEM) and differential scanning calorimetry (DSC) methods. Ex situ TEM measurements revealed that significant structural change occurred in the charged NMC composite after heating at a temperature above the exothermal peaks. It was found that LiF nanocrystallites precipitated in LiPF6 and that a number of nanoscale stacking faults developed in the $$R\bar{3}m$$ R3¯m layered structure of NMC. The results suggested that the decomposition reaction of LiPF6 and the structural change of NMC were directly associated with the exothermic reaction in the liquid electrolyte-based NMC electrode composite.

Abstract Sulfide-based all-solid-state lithium batteries are a next-generation power source composed of the inorganic solid electrolytes which are incombustible and have high ionic conductivity. Positive electrode composites comprising LiNi1/3Mn1/3Co1/3O2 (NMC) and 75Li2S·25P2S5 (LPS) glass electrolytes exhibit excellent charge–discharge cycle performance and are promising candidates for realizing all-solid-state batteries. The thermal stabilities of NMC–LPS composites have been investigated by transmission electron microscopy (TEM), which indicated that an exothermal reaction could be attributed to the crystallization of the LPS glass. To further understand the origin of the exothermic reaction, in this study, the precipitated crystalline phase of LPS glass in the NMC–LPS composite was examined. In situ TEM observations revealed that the β-Li3PS4 precipitated at approximately 200 °C, and then Li4P2S6 and Li2S precipitated at approximately 400 °C. Because the Li4P2S6 and Li2S crystalline phases do not precipitate in the single LPS glass, the interfacial contact between LPS and NMC has a significant influence on both the LPS crystallization behavior and the exothermal reaction in the NMC–LPS composites.

Abstract There are two types of solid electrolytes which has been recently expected to be applied to all-solid-state batteries. One is the glasses characterized by an amorphous state. The other is the glass ceramics containing crystalline in an amorphous matrix. However, the non-crystalline state of glasses and glass ceramics is still an open question. It has been anticipated that sea-island and core-shell structures including crystalline nanoparticles have been proposed as candidate models for glass ceramics. Nevertheless, no direct observation has been conducted so far. Here we report the non-crystalline state of Li2S–P2S5 glasses and glass ceramics, and the crystallization behavior of the glasses during heating via direct transmission electron microscopy (TEM) observation. High resolution TEM images clearly revealed the presence of crystalline nanoparticles in an amorphous region. Eventually we suggest that the precipitation and connection of crystalline nanoparticles in an amorphous matrix are key to achieving high ionic conductivity.

The (100 − x)Na3BO3·xNa2SO4 (0 ≤ x (mol%) ≤ 50) glasses were prepared by mechanical milling. Halo patterns were observed in the compositions 0 ≤ x ≤ 50 by XRD measurements. The Raman spectra indicated that all the glasses were composed of BO33− anions, SO42− anions and Na+ cations. The (100 − x)Na3BO3·xNa2SO4 glasses showed good deformation properties and a dense pellet was prepared by cold-press. The conductivities of the glasses increased with increasing Na2SO4 content, and the 50Na3BO3·50Na2SO4 glass showed the highest conductivity of 5.9 × 10−8 S cm−1 at 25 °C.

Spinel Li4Ti5O12 thin films were prepared by a mist CVD process, using an aqueous solution of lithium nitrate and a water-soluble titanium lactate complex as the source of Li and Ti, respectively. In this process, mist particles ultrasonically atomized from a source aqueous solution were transferred by nitrogen gas to a heating substrate to prepare thin films. Scanning electron microscopy observation showed that thin films obtained by this process were dense and smooth, and thin films with a thickness of about 500 nm were obtained. In the X-ray diffraction analysis, formation of Li4Ti5O12 spinel phase was confirmed in the obtained thin film sintered at 700 °C for 4 h. The cell with the thin films as an electrode exhibited a capacity of about 110 mAh g−1, and the cell showed good cycling performance during 10 cycles.

A new process for preparing particles of superconducting oxides was developed by using an aerosol flow reactor in which aqueous solutions of corresponding metal nitrates are atomized and their droplets are evaporated and thermally decomposed. The particles obtained from this process are spherical and their size can be controlled by changing the concentration of the aqueous solutions. For the Y-Ba-Cu-O system, the particles having an orthorhombic YBa2Cu3O7-x phase can be formed directly at the decomposition temperatures from 900 to 1000ºC. The bodies sintered from these particles show the offset temperature of the superconducting transition at 87 K. For the Bi-Ca-Sr-Cu-O system, the superconducting particles of the Bi2Ca2Sr2Cu3Ox and Bi1.8Pb0.2Ca2Sr2Cu3Ox compounds were prepared directly. The crystalline phases of the particles were found to be very sensitive to oxygen pressure in the carrier gas as well as to the decomposition temperature. The sintered bodies from the powders of Bi1.8Pb0.2Ca2Sr2Cu3Ox had onset temperature of 110 K and offset temperature of 80K.† This report was originally printed in J. Soc. Powder Technology, Japan. 26(3), 146-150 (1989) in Japanese, before being translated into English by KONA Editorial Committee with the permission of the editorial committee of the Soc. Powder Technology, Japan.

All-solid-state batteries with inorganic solid electrolytes are recognized as an ultimate goal of rechargeable batteries because of their high safety, versatile geometry and good cycle life. Compared to thin-film batteries, increasing the reversible capacity of bulk-type all-solid-state batteries using electrode active material particles is difficult because contact areas at solid–solid interfaces between the electrode and electrolyte particles are limited. Sulfide solid electrolytes have several advantages of high conductivity, wide electrochemical window, and appropriate mechanical properties such as formability, processability, and elastic modulus. Sulfide electrolyte with Li7P3S11 crystal has the highest Li+ ion conductivity of 1.7 × 10-2 S cm-1 at 25 °C. It is far beyond the Li+ ion conductivity of conventional organic liquid electrolytes. The Na+ ion conductivity of 7.4 × 10-4 S cm-1 is achieved for Na3.06P0.94Si0.06S4 with cubic structure. Moreover, formation of favorable solid–solid interfaces between electrode and electrolyte is important for realizing solid-state batteries. Sulfide electrolytes have better formability than oxide electrolytes. Consequently, a dense electrolyte separator and closely attached interfaces with active material particles are achieved via room-temperature sintering of sulfides merely by cold pressing without heat treatment. Elastic moduli for sulfide electrolytes are smaller than that of oxide electrolytes, and Na2S-P2S5 glass electrolytes have smaller Young’s modulus than Li2S-P2S5 electrolytes. Cross-sectional SEM observations for a positive electrode layer reveal that sulfide electrolyte coating on active material particles increases interface areas even with a minimum volume of electrolyte, indicating that the energy density of bulk-type solid-state batteries is enhanced. Both surface coating of electrode particles and preparation of nanocomposite are effective for increasing the reversible capacity of the batteries. Our approaches to form solid–solid interfaces are demonstrated.