Search

The stability of a zirconium (Zr)-substituted face-centered cubic (FCC) yttrium (Y) hydride (Y1-xZrx hydride) phase was investigated experimentally and theoretically. Two possible sites for hydrogen atoms exist in the FCC structure, namely, T- and O-sites, where hydrogen is present at the center of the tetrahedron and the octahedron composed of Y and/or Zr metals. The P-C isotherms revealed that the hydrogen content per metal (H/M) with 33% Zr-substituted YH3-δ was 2.2-2.3, which was lower than the expected value calculated from the starting composition of YH3-33% ZrH2 (Y0.67Zr0.33H2.67, H/M = 2.67). Hydrogen at the O-site in Y1-xZrx hydride mainly reacted during hydrogen desorption/absorption. On the basis of theoretical analyses, the hydrogen atoms do not occupy the center of the octahedron, when at least two of the six vertices of the octahedron were composed of Zr. The O-sites, where more than two Zr atoms coordinate, nonlinearly increased with the Zr content, and when the Zr content was >50%, almost no hydrogen atoms occupy the O-sites. The theoretical discussion supported the experimental results, and the Zr substitution was confirmed to reduce the occupancy of H at the O-site in the FCC YH3 significantly.

Designing a high-capacity positive electrode material is critical for the advancement of lithium-ion batteries. Sulfurized polyethylene glycol (SPEG), containing ca. 61 wt% of sulfur, is a promising positive electrode material that exhibits a large initial discharge capacity of more than 800 mAh g−1. In this study, we present the local structure and electrochemical performances of SPEG. A high-energy X-ray total scattering experiment revealed that sulfur in SPEG is predominantly fragmented and bound to carbon atoms. The changes in the physicochemical properties of SPEG due to heat treatment with nitrogen gas at various temperatures were investigated using thermogravimetric analysis, Raman spectroscopy, X-ray absorption near edge structure, and extended X-ray absorption fine structure. Comparing the electrochemical performances of SPEG after heat treatment at various temperatures, it was found that S–S and C=S bonds contribute to the overall electrochemical performance of SPEG.

Organic compounds as electrode materials can contribute to sustainability because they are nontoxic and environmentally abundant. The working mechanism during charge–discharge for reported organic compounds as electrode materials is yet to be completely understood. In this study, the structural behavior of 2,5‐dimethoxy‐1,4‐benzoquinone (DMBQ) during charge—discharge is investigated by using NMR spectroscopy, energy‐dispersive X‐ray spectroscopy, magnetic measurements, operando Raman spectroscopy, and operando X‐ray diffraction. For both lithium and sodium systems, DMBQ works as a cathode accompanied with the insertion and deinsertion of Li and Na ions during charge—discharge processes. The DMBQ sample is found to be in two‐phase coexistence state at the higher voltage plateau, and the radical monoanion and dianion phases have no long‐distance ordering. These structures reversibly change into the original neutral phase with long‐distance ordering. These techniques can show the charge–discharge mechanism and the factors that determine the deterioration of organic batteries, thus guiding the design of future high‐performance organic batteries., Made to measure: The crystallographic structure change of 2,5‐dimethoxy‐1,4‐benzoquinone (DMBQ) during charge–discharge is investigated by using operando X‐ray diffraction, which reveals that the DMBQ sample is found to be in two‐phase coexistence state at the higher voltage plateau. Radical monoanion and dianion phases have no long‐distance ordering for either Li or Na systems.

A face-centered-cubic (FCC) YH3 phase is known to be stable only under high pressure (HP) of more than gigapascal order, and it reverts to the hexagonal YH3 ambient-pressure phase when the pressure is released. We previously found that the FCC YH3 can be stabilized even at ambient pressure by substituting Y for 10 mol % Li (LiH-stabilized YH3, LSY). The LSY was synthesized by heat treatment under gigapascal HP, but this process is unfavorable for mass production; that is, only a few tens of milligrams of a sample can be obtained in a single batch. In this study, we overcame this problem by applying a ball milling (BM) process for synthesizing the LSY phase, and the yield by the BM process reached on the order of grams. We confirmed that the structure of the BM sample was the same as that of the HP sample by X-ray diffractometry, Raman spectroscopy, and neutron total scattering pair distribution function analyses. The crystallinity of the BM sample, however, was lower than that of the HP sample. The difference in the crystallinity affects the thermal stability of the LSY. The BM sample with a lower crystallinity released hydrogen at a lower temperature. The BM sample was found to reversibly desorb/absorb hydrogen maintaining its initial FCC structure when the rehydrogenation temperature was at 423 K. However, when the rehydrogenation temperature of BM sample was more than 573 K, the FCC structure changed to the hexagonal ambient pressure phase due to thermal instability of FCC phase for the BM sample.

The practical realization of rechargeable organic batteries is stalled by their low electron conductivity, which limits the organic-active material content in the electrode composite and results in a low net electrode energy density. Additionally, the dissolution of active materials into the electrolyte causes a short cycle life. In this study, a conductive polymer mixture, poly(3,4-ethylenedioxythiophene)/polystyrenesulfonate, containing a small amount of sugar alcohol was used as the binder and separator in a rechargeable organic battery. Consequently, the active material content was increased up to 80 wt%, and the cycle life was extended.

Spinel-type Li4Ti5O12 (LTO) is expected as a safe and stable negative electrode material of sodium-ion batteries (SIBs). However, its small lattice volume is not sufficient as the Na+ intercalation...

An anthraquinone (AQ)-based dimer and trimer linked by a triple bond (-C≡C-) were newly synthesized as active materials for the positive electrode of rechargeable lithium batteries. These synthesized oligomers exhibited an initial discharge capacity of about 200 mAh g-1 with an average voltage of 2.2-2.3 V versus Li(C.E.) . These capacity values are similar to that of the AQ-monomer, reflecting the two-electron transfer redox per AQ unit. Regarding their cycling stability, the capacity of the monomer electrode quickly decreased; however, the electrodes of the prepared oligomers showed an improved cycling performance. In particular, the discharge capacities of the trimer remained almost constant for 100 cycles. A theoretical calculation revealed that the intermolecular binding energy can be increased to the level of a weak covalent bonding by oligomerization, which would be beneficial to suppress the dissolution of the organic active materials into the electrolyte solutions. These results show that the cycle-life of organic active materials can be extended without lowering the discharge capacity by the oligomerization of the redox active molecule unit.

The electrochemical property of a silicon electrode in a half-cell was investigated using the mixture of monoglyme-based solvents and lithium bis(trifluoromethanesulfonyl)amide (LiTFSA) with 2:1 stoichiometry. The solvents used in this study are monoglyme (G1), 1,2-diethoxyethane (DEE), 1,2-dibutoxyethane (DBE), and 1,2-dimethoxypropane (P-G1). When Li (DEE)2 or Li(P-G1)2 was used, the cell retained ca. 20% capacity at a rate of 3 C, while the other samples showed almost no capacity under the same conditions. Raman spectroscopy measurement revealed that Li+ exists as two forms in the mixture, that is, a solvent shared ion pair (SSIP) [ Li+ ··· solvent ··· TFSA– ] and a contact ion pair (CIP) [ Li+ ··· TFSA– ]. According to the spectroscopic analysis, SSIP is the dominant species for Li (DEE)2 and Li(P-G1)2, and CIP for Li (G1)2 and Li (DBE)2. The order of the rate property was Li(P-G1)2 ∼ Li (DEE)2 > Li (DBE)2 ∼ Li (G1)2, which is almost consistent with the stability of free energy levels of Li+ in the respective monoglymes against CIP Li+ ··· TFSA– evaluated from the Raman spectra.

This study highlights the design concept of a positive electrode material which can accommodate both cations and anions during the charge/discharge process for realizing high energy density rechargeable batteries. Fusing an electron-acceptor (N type) and donor (P type) would endow such properties. In addition, unlike rigid inorganic frameworks, flexible organic compounds have the potential to adopt a variety of ion species. We examined the electrochemical properties of a fused triad molecule incorporating N-type benzoquinones and a P-type tetrathiafulvalene (Q-TTF-Q). Preliminary electrochemical measurements revealed Q-TTF-Q to be electrochemically active, exhibiting a high capacity at a decent voltage, comparable to reported organic cathode materials not only for the current lithium ion technology but also for the emerging sodium and potassium-ion batteries. For instance, Q-TTF-Q has a capacity of 236 mA h g−1 with the decent average potential of 2.8 V vs. Li+/Li, translating to the high energy density of 661 mW h g−1. A carrier ion analysis based on energy dispersive X-ray spectrometry (EDX) proved that Q-TTF-Q indeed stores both anions and cations during the charge/discharge processes. The approach of fusing P- and N-type organic moieties, as described in this study, provides a rational design strategy to further develop high-energy-density organic electrode materials.

Li2MnO3, a layered lithium-rich manganese oxide, is one of the potential high-capacity positive electrode materials among the Li containing transition metal oxide materials but its low electrical conductivity restricts its electrochemical activity. In our previous study, Li–Mn cation disorder in Li2MnO3 resulting in the formation of a NaCl-type structure was found to improve its electrochemical activity, i.e., a high initial discharge capacity of 320 mA h g−1. However, it still suffered from a poor cycling performance probably due to another problem, e.g., its structural instability, i.e., oxygen emission during charging. In this study, we found that the structural stability of NaCl-type Li2MnO3 was significantly improved by forming a composite with spinel-type LiMn2O4 by mechanical milling. The initial discharge capacity of the composite was close to 400 mA h g−1 and its 15th discharge capacity still showed more than 80% of the initial one, while less than 50% for NaCl-type Li2MnO3. The oxide ions in the composite were found to be more stable than those of NaCl-type Li2MnO3 during the electrochemical redox reaction, which was confirmed by O K-edge XAS measurements, resulting in the higher reversible capacity and better cycling performance.

The recent research studies of the Li2S cathodes are reviewed. The cathode showed a high capacity of about 1000 mAh/g, and maintaining about 600 mAh/g after one hundred cycles thanks to nanocompositing, carbon coating, and new electrolyte components or additives. Expensive Li2S production can be reduced by the heat-treatment of cheap carbon and Li2SO4. Precise investigations of the synthesis methods of the Li2S-graphene composite are described.

Replacing the scarce metal-based positive electrode materials currently used in rechargeable lithium ion batteries with organic compounds helps address environmental issues and might enhance gravimetric electrochemical capacity. The challenge has been to find organic materials with both high capacity and long-cycle life. Here, we study the naphthazarin (5,8-dihydroxy-1,4-naphthoquinone) skeleton as a high capacity candidate electrode for lithium-ion batteries, showing a multielectron-transfer type redox reaction. We also use electron energy-loss spectroscopy to reveal the reaction stoichiometry during charge/discharge processes. While the lithium salt of naphthazarin itself helped deliver a high initial capacity, its cycle-life was not satisfactory. Instead, a newly synthesized naphthazarin-dimer shows a lengthened cycle-life without sacrificing the initial high capacity of 416 mAh g−1 and energy density of 1.1 Wh g−1. Replacing metal electrodes in lithium-ion batteries with organic materials reduces environmental impact and might lead to high gravimetric capacity. Here, organic electrodes containing a naphthazarin-dimer skeleton achieve an initial capacity of 416 mAh g−1 and energy density of 1.1 Wh g−1 in a lithium-ion battery.

Rare-metal-free and high-performance secondary batteries are necessary for improving the efficiency of renewable energy systems. Organic compounds are attractive candidates for the active material of such batteries. Many studies have reported organic active materials that show high energy density per active material weight. However, organic active materials, most of which exhibit low conductivity and low specific density, typically require a large amount of a conductive additive (>50 wt %) to obtain a high utilization rate. Therefore, organic active materials rarely display high energy density per electrode weight. High energy densities per electrode weight can be obtained using high weight fractions of active materials and low weight fractions of conductive additives. Herein, we report that a low-conductivity organic active material, indigo, showed improved net discharge capacity density when even a small amount of a conductive polymer composite, poly(3,4-ethylenedioxythiophene)/polystyrene sulfonic acid (PEDOT/PSS) with d-sorbitol, was used as both a binder and conductive additive. The cycle life was also improved by coating one side of the separator with the composite, which probably hindered the dissolution of the active material. A discharge capacity of 96% of the theoretical capacity of indigo and an improved cycle life were achieved with an electrode containing 80 wt % indigo and with a PEDOT/PSS-coated separator. The optimal fraction of the conductive binder was examined, and the mechanism of conductivity enhancement was discussed. The present scheme allows us to replace the dispersion solvent of the slurry, N-methylpyrrolidone, with water, which can reduce the environmental load during battery manufacturing processes.

Heavy rare-earth trihydrides such as GdH3, DyH3, and yttrium trihydide (YH3) usually show a hexagonal crystal structure under ambient pressure. This structure is known to transform to a face-centered cubic (FCC) one at higher pressures (at the order of GPa), and the FCC one returns to the hexagonal structure when the applied pressure is released. In this study, we investigated the structure of alkaline or alkaline-earth (A)-substituted REH3 (RE = Y, Gd, Dy; A = Li, K, or Mg) using X-ray diffraction, and measured the phase transition pressure. We found that this FCC high-pressure phase can be stabilized by 10-33 mol % A substitution for RE in the REH3. The mechanism of phase stabilization is simply explained by the ionic radius ratio between the cation and anion ( rcat/ rani), as well as the stabilities of other ionic crystals such as perovskite materials. For all considered REH3 samples, the FCC phase becomes stable when rcat/ rani > 0.856, such as in the case of 10 mol % Li-substituted YH3.

The use of redox active organic compounds as an alternative positive electrode material of rechargeable lithium batteries can be a solution for the resource issues of the current battery system. To satisfy both the high capacity and long cycle life of the batteries using organic active materials, naphthazarin (5,8-dihydroxy-1,4-naphthoquinone) derivatives, which potentially exhibit a four-electron transfer redox reaction, were investigated. While the unsubstituted naphthazarin lithium salt (1), having a high theoretical capacity of up to about 550 mAh g−1, showed only half the expected capacity and a short cycle life as a positive electrode active material, the chloro-substituted ones (1-Cl 2 , 1-Cl 4 ) exhibited improved properties in both their initial capacity utilization and cycle life. In addition, the high stability of a chloro-substituted naphthazarin salt (1-Cl 4 ) was supported by a reversible electrochromic behavior during the redox reaction. The substituent effect of the naphthazarin derivatives on the cycle stability was discussed with respect to the battery performance and electrochromic behavior. Also, a guide for designing a new organic active material which shows a high capacity and long cycle life is suggested.

A surface-roughened clad (S-clad) current collector significantly extends the cycle-life of the lithium ion negative electrode composed of a silicon micropowder and an aqueous binder. The high tensile strength of the S-clad is also proved to be important for improving the battery performance of the electrode by comparison to a surface-roughened pure Cu current collector. Moreover, adding 10 vol.% fluoroethylene carbonate to the electrolyte further extends the cycle-life of the Si electrode. The synergic effect of the high adhesive and tensile strength of the S-clad current collector as well as the electrolyte additive results in maintaining the reversible capacity of 1000 mA h g−1 for more than 1000 cycles, in which 1.0–1.2 mg cm−2 of the active material is loaded on the electrode.

A face-centered-cubic (FCC) YH

The crystal structure of yttrium trihydride (YH 3 ) is usually characterized by hexagonal close-packed (HCP) metal ordering at ambient conditions and transforms into an FCC structure (FCC-YH 3 − δ ) at pressures greater than 8 GPa. FCC-YH 3 − δ was previously considered to only be stable under high pressures, but we found that it can be stabilized even at ambient pressures by the mechanical milling of hexagonal YH 3 (HCP-YH 3 ) in this study. The lattice constant of the FCC-“YH 3 − δ ” sample was evaluated to be a = 0.52801(2) nm, which corresponds to the expected value calculated in other studies. This structural change from HCP to FCC enlarged band gap of the YH 3 from 2.2 eV to 2.45 eV measured by UV–vis spectrometry. FCC-YH 3 was dehydrogenated to an FCC “YH 2 ” dihydride phase at 520 K, which is known to be conventionally present at ambient pressures. However, the YH 2 generated from FCC-YH 3 − δ maintained its FCC structure upon re-hydrogenation to trihydride, unlike how YH 2 usually changes its structure from FCC to HCP. The volume change after the dehydrogenation of FCC-YH 3 − δ was approximately 5%, which is smaller than that of HCP-YH 3 (approximately 10%).

Yttrium in YH3 was shown to be substituted by zirconium in a ball milling process, yielding FCC-YH3, a zirconium-hydride-stabilized YH3 (ZSY) structure. FCC-YH3, which is stable only under the pressure greater than 7.8 GPa, has previously been reported to be stabilized at ambient pressure by alkaline or alkaline earth metal substitution, but only in a limited compositional range. In contrast, we demonstrated solid solubility of Y and Zr in ZSY in a wide compositional range, with a Y/Zr molar ratio between 4 and 0.333, as confirmed by changes in the lattice constants of ZSY with various amounts of Zr. A color of ZSY changed from yellowish (transparent) to black by Zr substitution. The UV–vis spectroscopy revealed that Zr substitution narrowed the bandgap of YH3. At a molar fraction of 33 mol%, Zr-substituted ZSY was shown to maintain its FCC structure during dehydrogenation and rehydrogenation cyclirng, and its volume change ( Δ V ) was estimated to be 1%, with an accompanying H2 emission of 0.5 wt%. This volume change was significantly lower than that of conventional hydrogen storage alloys such as LaNi5 and Mg–La–Ni alloys, i.e., Δ V is about 10 ∼ 20% when they desorb same amount of hydrogen.

Perovskite-type oxide-based La0.6Sr0.4Mn(1-x)Co x O3/carbon (x = 0, 0.1, 0.2, 0.3, 1) catalysts were prepared by calcination of a mixture of metal nitrates and PVP at 600 °C, followed by milling of the calcined powder with a carbon support. The catalytic activities for the oxygen reduction reaction (ORR) were tested in alkaline electrolyte by using a rotating ring-disk electrode (RRDE) at 25 °C. With an increase in the doping amount of Co, the onset potential of the La0.6Sr0.4Mn(1-x)Co x O3/carbon catalyst was found to be shifted in a positive direction and the ring current during ORR decreased. Especially, the La0.6Sr0.4Mn0.7Co0.3O3/carbon (x = 0.3) catalyst showed the highest ORR activity among the prepared catalysts. The La0.6Sr0.4Mn0.7Co0.3O3/carbon was tested as the cathode of an alkaline membrane-type direct hydrazine fuel cell (DHFC), and a maximum power density of 133 mW cm−2, which exceeded that for the MEA using Pt/C (73.4 mW cm−2), was obtained at 50 °C. In addition, the open circuit voltage (OCV) for the DHFC (0.846 V) was greater than that of a commercial Pt/C cathode (0.788 V). Thus, the perovskite-type La0.6Sr0.4Mn0.7Co0.3O3 catalyst is expected to be a good candidate for use as a catalytic material for a DHFC cathode as an alternative to Pt.

A potential positive electrode material, α-NaFeO2, can be viewed one of the base material for rechargeable Na batteries. In this study, we found that its structural evolution during charge process differentiates depending on its synthesis route. The α-NaFeO2 is prepared by three methods: one is by the hydrothermal technique (HT), and the other two by solid-state reactions, SSn and SSμ, in which nano-sized Fe3O4 and micro-sized Fe3O4 are used as the Fe source, respectively. The synchrotron radiation X-ray diffraction profiles of the initial state suggest that all three samples are apparently identified as the target product, α-NaFeO2, with rhombohedral structures. Though all three samples remain stable for more than 50 cycles under the cycling conditions of a constant amount of charging (Na extraction) to 70 mA h g−1, their structural evolution differs during the sodium extraction. The SSμ transitions from the rhombohedral structure to a spinel-like cubic structure, while the HT transforms into a monoclinic structure. On the other hand, both the monoclinic and cubic phases co-exist in SSn. What produces these differences among the seemingly identical materials is discussed.

Heavy rare-earth trihydrides such as GdH

We investigate the structural changes of spinel lithium titanate (LTO; Li 4 Ti 5 O 12 ) via the electrochemical Na insertion-extraction cycles, using X-ray diffraction (XRD) and analytical transmission electron microscopy (A-TEM). The XRD reveals that an extra phase with an about 4‑5% larger unit cell volume is generated in pristine LTO during the first cycle. The A-TEM reveals that the extra phase co-exists with Li 4 Ti 5 O 12 in a single particle and is identified as a Na-substituted LTO phase (Na-LTO; Li 4- x Na x Ti 5 O 12 , 0 x −1 ) is more than 90% of the theoretical one, suggesting that both LTO and Na-LTO are involved in the charge-discharge reactions.

The hydrides of zirconium based pseudobinary alloys Zr(Co1-xTx)2, (T = Fe, V or Cr) and Zr1-xRxCo2 (R = Y, La, Pr) were synthesized under 1.2 GPa of hydrogen pressure. It was revealed that partial substitution of cobalt by V, Cr or Fe increases hydrogen absorption capacity and stability of derived hydrides. Especially, it was found that ZrCo1:8V0:2 alloy exposed to high hydrogen pressure can absorb 50% more hydrogen than pure ZrCo2 and the hydride ZrCo1:8V0:2Hy has surprisingly high stability. Substitution of zirconium by Y, La or Pr in ZrCo2 alloys improved hydrogen absorption but hydrides derived from La and Pr substituted alloys were less stable than ZrCo2H2. Only for Zr0:7Y0:3Co0:2Hy the hydrogen absorption was higher and desorption rate markedly smaller comparing ZrCo2H2.

We assembled a sodium-ion capacitor (Na-IC) by combining sodium pre-doped hard carbon (HC) as the negative- and activated carbon (AC) as the positive-electrode. The electrochemical properties were compared with two lithium-ion capacitors (Li-ICs) in which the negative electrodes were prepared with Li pre-doped HC and mesocarbon microbeads (MCMB). The positive and negative electrodes were prepared using the established doctor blade method. The negative electrodes were galvanostatically pre-doped with Na or Li to 80% of the full capacity of carbons. The potential of the negative electrodes after pre-doping was around 0.0 V vs. Na/Na + or Li/Li + , which resulted in the higher output potential difference of the Na-IC and Li-ICs than that of the conventional electrochemical double-layer capacitors (EDLCs) because AC positive electrode works in the same principle both in the ion capacitors and in the EDLC. The state-of-charge of the negative electrode varied 80 ± 10% during the electrochemical charging and discharging. The capacity of the cell was evaluated using galvanostatic charge–discharge measurement. At the discharge current density of 10 mA cm −2 , the Na-IC maintained 70% of the capacity that obtained at the current density of 0.5 mA cm −2 , which was comparable to the Li-ICs. At 50 mA cm −2 , the capacities of the Li-IC(MCMB) and the Na-IC dropped to 20% whereas the Li-IC(HC) retained 30% of the capacity observed at 0.5 mA cm −2 . The capacities of the Na-IC and Li-ICs decreased by 9% and 3%, respectively, after 1000 cycles of charging and discharging.

A powder mixture of MgH2:VH2:NaH = 6:1:n is treated under 8 GPa at 873 K using an eight-anvil apparatus in order to investigate the influence of NaH addition to Mg6VHy, a Ca7Ge-type FCC hydride. Synchrotron radiation X-ray diffraction (SR-XRD) of the obtained sample reveals that Na occupies the vacant 4b site in Mg6VHy to form Mg6VNaxHy (0 ≤ x ≤ 1) as the main product while retaining its Ca7Ge-type structure. The Rietveld analysis of the SR-XRD data suggests that the bond lengths between hydrogen and magnesium remain constant through the Na addition. All the samples reversibly desorb and absorb hydrogen at 620–630 and 590–600 K, respectively, under 0.5 MPa (H2). These temperatures are, respectively, about 70 and 120 K lower than those of MgH2. The hydrogen capacity of the main product phase, Mg6VNaxHy, is estimated to be 5–6 mass% from the pressure-composition isotherms (PCIs) by taking its content rate in the specimen into account. The reaction enthalpies calculated from the van’t Hoff relation of the PCIs do not significantly differ from that of MgH2. The bond lengths and energies between hydrogen and magnesium are not affected by the perturbation by the NaH addition in the lattice in Mg6VNaxHy.

It is important to develop the hydrogen storage technology by creating novel metal hydrides. In the present study, the powder mixtures of 6MgH 2 + ZrH 2 + n AH (A = Li, Na; n = 0, 0.3, 0.7, 1.0) were reacted to synthesize quaternary hydrides by use of a high pressure technique. The crystal structures of the new hydrides were refined by the Rietveld method based on the synchrotron XRD data. By reacting 6MgH 2 + ZrH 2 + n LiH, the quaternary hydrides with simple FCC-type structure were formed. In the case of 6MgH 2 + ZrH 2 + n NaH, novel quaternary hydrides with Ca 7 Ge type structure were formed as well as the hydrides with simple FCC structure. The hydrogen storage capacities were around 6 wt.% according to the pressure-composition isotherm measurements. The formation enthalpies of the quaternary hydrides with simple FCC structure were proved to be lower while the enthalpies of the Mg–Zr–Na–H hydrides with Ca 7 Ge type structure were higher, than that of the ternary Mg–Zr–H hydride obtained by reacting the basic system 6MgH 2 + ZrH 2 . The hydrogen releasing temperatures of the quaternary Mg–Zr–A–H hydrides were slightly lower than that of the ternary Mg–Zr–H hydride.

Lithium vanadium metasilicate (LiVSi 2 O 6 ) with pyroxene structure has been exploited as an electrode material for Li-ion batteries. Galvanostatic charge and discharge tests show that LiVSi 2 O 6 is able to deliver a capacity of 85 mAh g −1 at 30 °C, and a high capacity of 181 mAh g −1 at 60 °C. The high capacity is believed to be due to the reactions of V 3+ /V 4+ and V 2+ /V 3+ redox couples, accompanied by the excess 0.42 Li + insertion into the lattice forming a Li-rich phase Li 1.42 VSi 2 O 6 . High-energy synchrotron XRD combined with the Rietveld refinement analysis confirms that the electrochemical delithiation–lithiation reaction proceeds by a single phase redox mechanism with an overall volume variation of 1.9% between LiVSi 2 O 6 and its delithiated state, indicating a very stable framework of LiVSi 2 O 6 for Li + ions extraction–insertion.

Well-crystallized LiFePO 4 nanoparticles have been directly synthesized in a short time via hydrothermal process in the presence of organic acid, e.g. citric acid or ascorbic acid. These acid-mediated LiFePO 4 products exhibit a phase-pure and nanocrystal nature with size about 50–100 nm. Two critical roles that the organic acid mediator plays in hydrothermal process are recognized and a rational mechanism is explored. After a post carbon-coating treatment at 600 °C for 1 h, these mediated LiFePO 4 materials show a high electrochemical activity in terms of reversible capacity, cycling stability and rate capability. Particularly, LiFePO 4 mediated by ascorbic acid can deliver a capacity of 162 mAh g −1 at 0.1 C, 154 mAh g −1 at 1 C, and 122 mAh g −1 at 5 C. The crystalline structure, particle morphology, and surface microstructure were characterized by high-energy synchrotron X-ray diffraction (XRD), transmission electron microscopy (TEM) and scanning electron microscopy (SEM), and Raman spectroscopy, respectively. And the electrochemical properties were thoroughly investigated by galvanostatic test and electrochemical impedance spectroscopy (EIS).

High hydrogen pressure technique up to 1.2 GPa has been used for synthesis of novel hydrides in RFe 2 Laves phases (R = Gd, Tb, Dy, and Ho) compounds as well as in pseudobinary ZrCo 2 − x Fe x and Y x Dy 1 − x Mn 2 Laves phases. Existence of new orthorhombic hydrides HoFe 2 H 5 , and DyFe 2 H 5 , isostructural with YFe 2 H 5 , was found, whereas GdFe 2 H 5 and TbFe 2 H 5 kept the cubic C15 lattice. Pseudobinary Zr(Fe x Co 1 − x ) 2 D y (2 ≤ y ≤ 4) hydrides were synthesized and their stability was discussed as a function of Fe/Co content. It was revealed that the formation of non-interstitial YMn 2 H 6 -type Fm-3m hydrides is possible in the whole range of pseudobinary (Y x Dy 1 − x )Mn 2 compositions.

Super-laminates have been attracting attention since co-authors Ueda et al. reported that Mg/Cu super-laminates showed reversible hydrogenation and dehydrogenation at 473K. The Mg/Cu super-laminates were prepared by a repetitive fold and roll method. Initial activation at 573 K led the super-laminates to absorb hydrogen at 473K. TEM observations of micro/nano-structures in the Mg/Cu super-laminates and Mg2Cu powder were performed in order to clarify the process of hydrogenation and dehydrogenation at 473K. The as-rolled Mg/Cu super-laminates have laminated structures sub-micrometer thick composed of Mg and Cu layers with dense lattice defects. The super-laminates after initial activation keep laminated structure and have uniformly distributed pores sub-micrometer in diameter. It is considered that these micro/nano-structures of Mg/Cu super-laminates lead to lower dehydrogenation temperature and better kinetics.

The spark plasma sintering (SPS) technique was successfully used to mold a hydrous amorphous RuO 2 electrode without any additives and binders. At the cyclic voltammetry (CV) scan rate of 1 mV s −1 , the electrochemical capacitances of the RuO 2 electrodes are 600–700 F g −1 for the entire electrode. An increase in the SPS current during the compaction led to the crystallization and dehydration of RuO 2 , which in turn, resulted in a significant decrease in its capacitance. There is room to improve the rate properties as we observed a steep drop in the capacitance when the CV scan rate was raised.

A simple model to understand the phase behavior of RNi5–H ( R = La , Pr, Nd and Sm) systems is proposed based on the statistical mechanics. The essential parameters in the present model, hydrogen site energies and lattice relaxation term, were optimized so as to reproduce the experimentally determined pressure–composition isotherms (PCIs) of these four alloys. The qualitative difference in the PCI of LaNi5 from other alloys – at room temperature the former tends to show a single plateau while the latter have two plateaux – is explicable in terms of hydrogen site energies as follows. In case of LaNi5, four hydrogen sites, which are considered to belong to 3f, 12n, 6m and 12o sites, are stable in α phase, leading to a wide single plateau upto N ∼ 6 where N is in RNi5HN below room temperature. At higher temperature, small differences in site energies for these sites brings the appearance of the second plateau. In case of other three alloys, on the other hand, the 6m site (or 12o) is less stable than LaNi5 in the α phase. After obtaining enough lattice relaxation energy by around N = 4 through hydrogenation, the 6m site becomes favorable for hydrogen, bringing the sencond plateau spanning from N ∼ 4 to N ∼ 6 . Predicted T–C phase diagrams are also shown.

Micro/nano-structures and hydrogen storage properties of Mg/Cu super-laminates were investigated. Mg/Cu super-laminates showed reversible hydrogenation and dehydrogenation at 473 K. In order to clarify the process of hydrogenation and dehydrogenation at 473 K, we performed TEM observations of micro/nano-structures of the Mg/Cu super-laminates and Mg2Cu powder prepared by conventional casting method. TEM observations revealed that the as-rolled Mg/Cu super-laminates had laminated structures in size of sub-micrometer thickness composed of Mg and Cu layers with dense lattice defects. The super-laminates after initial activation kept laminated structures and had uniformly distributed pores with a sub-micrometer diameter. On the other hand, the cast Mg2Cu powder after initial activation had pores only beneath the surface oxide layers. It is considered that these micro/nano-structures of Mg/Cu super-laminates lead to lower dehydrogenation temperature and better kinetics, which would contribute to achieve high-performance hydrogen storage materials.

We investigated by differential scanning calorimetry the effect of ball milling on the hydrogenation properties of Mg 2 Cu, a hydrogen storage alloy, prepared by two methods: One is mechanically alloyed Mg 2 Cu using Mg and Cu powders as starting materials. Eight hours (= 28.8 ks) of ball milling transformed the Mg : Cu = 2 : 1 mixture into Mg 2 Cu single phase which reacts reversibly with hydrogen. The other is prepared by ball milling a cast Mg 2 Cu alloy. While the as-cast Mg 2 Cu undergoes neither hydrogenation nor dehydrogenation under 3 MPa of hydrogen in the temperature range of 300-773 K, just an hour of ball milling activates the inert Mg 2 Cu to react with hydrogen reversibly. Examining the milling period dependency of the particle size, crystallite size, activation energy and the apparent heat of dehydrogenation which reflects the fraction of activated part in a specimen, we found that the ball milling firstly influenced the particle size and the activated fraction of the sample, and then followed the effect on the crystallite size and kinetic properties. We also found that a trace amount of oxygen could significantly spoil the benefits brought by the ball milling for longer period of milling.