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Graphite is widely used as an anode material in almost all Lithium (Li)-ion batteries. Li is easily absorbed into the layer structure of graphite, forming lithium-carbon intercalation compounds LixC between LiC6 and C. However, although they are simple binary compounds, their structures have been left unelucidated for a long time, especially for the compounds between LiC12 and C. This is probably because the Li concentrations are too low to make a big difference in diffraction pattern between these Li-intercalated graphites and pure graphite. It has been known, however, that they have stacked layer structures, which strongly suggests that they are very likely to form modulated structures. Structural analyses of these compounds based on the modulated structure model were successfully performed, comprehensively elucidating all the LixC structures lying between LiC6 and C.

Lithium sulfide (Li2S) is one of the promising positive electrode materials for next-generation rechargeable lithium batteries. To improve the electrochemical performance of electronically resistive Li2S, a Fe-doped Li2S-based positive electrode material (Li8FeS5) has been recently designed and found to exhibit excellent discharge capacity close to 800 mAh g−1. In the present study, we investigate the structural and dynamic behavior of Li8FeS5 during charge–discharge cycling. In Li8FeS5, Fe ions are incorporated into the Li2S framework structure. The Li2S-based structure is found to transform to an amorphous phase during the charge process. The delithiation-induced amorphization is associated with the formation of S-S polysulfide bonds, indicating charge compensation by S ions. The crystalline to non-crystalline structural transformation is reversible, but Li ions are extracted from the material via a two-phase reaction, although they are inserted via a single-phase process. These results indicate that the delithiation/lithiation mechanism is neither a topotactic extraction/insertion nor a conversion-type reaction. Moreover, the activation energies for Li ion diffusion in the pristine, delithiated, and lithiated materials are estimated to be in the 0.30–0.37 eV range, which corresponds to the energy barriers for local hopping of Li ions along the Li sublattice in the Li2S framework.

Fluoride shuttle batteries (FSBs), which utilize F– ion migration in electrochemical reactions, have recently advanced in academic research as next-generation rechargeable batteries. Bismuth trifluoride (BiF3) and its relatives are expected to be promising positive electrode materials for FSBs because of their high theoretical capacity. Herein, the defluorination/fluorination reaction of a BaF2-doped BiF3, Bi0.8Ba0.2F2.8, positive electrode was investigated using synchrotron-radiation X-ray diffraction, X-ray absorption spectroscopy, and transmission electron microscopy. The Bi0.8Ba0.2F2.8 electrode showed a higher reversible capacity in the first cycle and improved capacity retention compared to the BiF3 electrode. The pristine Bi0.8Ba0.2F2.8 showed a tysonite-type structure, and metallic Bi and BaF2 nanoparticles were observed in the fully defluorinated state. Moreover, we found that the (re-)fluorinated material consisted of BiF3 and BaF2 nanoparticles, indicating that bismuth is the only redox-active element, and that the tysonite structure is not recovered after the initial discharging. This suggests that the cycle performance of the Bi0.8Ba0.2F2.8 electrode may be improved due to the suppression of the coarsening of BiF3 nanoparticles by the adhesion of BaF2 nanoparticles formed after initial defluorination.

We investigated the oxygen contributions on delithiation process of different types of layered 3d transition metal oxides, Li2TiO3, Li2MnO3, and LiCoO2, using X-ray spectroscopies with the aid of density functional theory calculations. In delithiatied LiCoO2, electrons are extracted from highly hybridized Co 3d and O 2p orbitals without O2 loss. In Li2TiO3, the hybridized Ti 3d and O 2p orbitals at the valence band is mainly contributed by O 2p orbitals, and delithiated Li2TiO3 loses oxygen as the electrons are extracted. Li2MnO3 exhibits some hybridization. In delithiated Li2MnO3, a certain amount of oxygen is lost, but the large amount of oxidized O anions remains as peroxide and superoxide-like states, which would work as the redox active species. Therefore, the degree of hybridization between metal 3d and O 2p orbitals is a key factor to influence the stability of O anion redox during the oxidation process, which determines the electrode performance.

FeF3 has attracted considerable attention as a positive electrode material for next-generation rechargeable lithium ion batteries, because of its low cost, low risk, and high energy density, which facilitate a conversion-type lithiation/delithiation reaction. However, the conversion reaction of the FeF3 electrode is known to suffer from capacity fading during repeated discharge–charge cycles. Herein, we find an interesting correlation between capacity fading behavior and spectral evolutions in electrochemical operando nuclear magnetic resonance (NMR) measurements. The operando 7Li NMR spectra demonstrate the reversible formation of metallic Fe by the conversion process during the early discharge–charge cycles. However, it is gradually suppressed after repeated cycles. Moreover, LiF is augmented at the fully charged states, indicating that FeF3 is no longer recovered after repeated cycles. The active material can converge into FeF2 and LiF in the degraded electrode. Another factor associated with capacity degradation is the electrolyte decomposition occurring at high voltages, which results in a resistive film coating the electrode surface. We therefore conclude that the film accumulation on repeated discharging inhibits the conversion reaction to metallic Fe and LiF, leading to a characteristic capacity fading behavior of FeF3.

Li2TiO3 is a Li-rich cathode/anode material similar to Li2MnO3. These materials crystallize into monoclinic structures with ABC-stacked atomic layers, approximated by pseudo-trigonal cells. In these crystals, transition-metal layers are occupied not only by transition-metal atoms but also by Li atoms, forming ordered/disordered atomic arrangements. Faults Rietveld analysis was conducted, showing that Li2TiO3 crystalizes into a monoclinic structure with the space group C2/c, in which Li and Ti atoms are configured in an imperfectly ordered arrangement at the transition-metal layer and a large number of stacking faults are generated in the crystal. To precisely evaluate the site occupancies in such imperfect crystals, our structural analysis found that the structures should be analyzed by powder diffraction while taking stacking faults and atomic mixing into account. The atomic mixing at the transition-metal layer tends to gradually increase as the synthesis temperature is raised.

The mixtures of scandium hydride ScH2 and metal boride MBn, which is MgB2 or CaB6, were hydrogenated by mechanical milling under hydrogen pressure at room temperature. ScH2–MgB2 and ScH2–CaB6 desorbed 3.4 and 2.3 mass% of H2, respectively, with peaks below 300 °C. The results of synchrotron radiation X-ray powder diffraction and X-ray absorption spectroscopy at the Sc K-edge indicated that ScB2 was produced by milling. Fourier-transform infrared spectroscopy suggested that hydrogen was stored as B–H bonds in the as-milled samples. Nuclear magnetic resonance spectroscopy clarified the presence of metal borohydrides M(BH4)2 (M = Mg and Ca) in the as-milled ScH2–MBn mixtures. These results indicate that M(BH4)2 is synthesized by milling the ScH2–MBn mixtures under hydrogen pressure at room temperature, and hydrogen was desorbed from M(BH4)2. The by-products of M(BH4)2 are MgH2 in the M = Mg case, which was observed by transmission electron microscopy, and ScB2 in both cases.

Magnesium (Mg) and carbon (C) compounds were synthesized by ball-milling a mixture of Mg and different graphites with different crystallinities. The materials were characterized by X-ray diffraction, X-ray absorption spectroscopy, and X-ray total scattering techniques. Hydrogen storage properties were also investigated. In the case of the material using low-crystalline graphite, a Mg and C compound was formed as main phase, and its chemical bonding state was similar to that of magnesium carbide (Mg 2 C 3 ). The hydrogen absorption reaction of the Mg–C compound occurred at around 400 °C under 3 MPa of hydrogen pressure to form magnesium hydride (MgH 2 ) and the C–H bonds in the carbon material. The hydrogenated Mg–C material desorbed about 3.7 mass% of hydrogen below 420 °C with two processes, which were the decomposition of MgH 2 and the subsequent reaction of the generated Mg and the C–H bonds. From the results, it is concluded that the Mg–C compound absorb and desorb about 3.7 mass% of hydrogen below 420 °C.

The Metal–N–H system for hydrogen storage has been developed in recent years and is considered to be a promising solution. Here we report a potential compound for hydrogen storage, LiNHNH2, which is a white solid with 8.0 mass% theoretical hydrogen content and can be synthesized from anhydrous hydrazine and n-butyllithium in diethyl ether. The thermodynamic behaviours and hydrogen storage properties of this compound were firstly investigated and are discussed in this paper. We demonstrate the decomposition pathway of LiNHNH2 and reveal that an alkali metal hydride such as LiH can significantly increase the hydrogen desorption from LiNHNH2. Moreover, LiNHNH2 can also be used for destabilizing other hydrogen storage systems owing to its instability.

Metal aluminum amides M[Al(NH2)4]x (M = K, Mg, and Ca; x = 1 and 2) were synthesized along with previously reported LiAl(NH2)4 and NaAl(NH2)4 by ball milling technique under liquid NH3. The profiles of synchrotron radiation X-ray diffraction suggest that KAl(NH2)4, Mg[Al(NH2)4]2 and Ca[Al(NH2)4]2 have been indexed with single phases, which have never been reported so far. Combination of both FT-IR and 27Al MAS/3QMAS nuclear magnetic resonance suggest that they all have an anion complex unit [Al(NH2)4]− as a basic component, indicating successful synthesis of the metal aluminum amides. Thermogravimetry-differential thermal analysis coupled with mass spectroscopy showed the release of NH3 below the temperatures of 140 °C during the thermal decomposition and a NH3 desorption peak temperature (Tdes) decreased with the increasing atomic number. Additionally, a relationship between 27Al isotropic chemical shift and Tdes was discussed. The present study gives an useful information that the thermal stability of the anion complex [Al(NH2)4]− can be controlled by a cation M.

Local environments of all constituent elements (Si, Al, O, Mg, and Ca) in an amorphous slag were examined using multi-nuclear solid-state NMR under high magnetic field (16.4 T). The amorphous slag framework structure can be generally described as a depolymerized, chain-like network of SiO4 tetrahedra branched with AlO4 tetrahedra. 17O multiple-quantum magic angle spinning (MQMAS) spectrum demonstrated that oxygens occupy structurally inequivalent sites, depending on their bonding nature. 25Mg and 43Ca MQMAS spectra also showed multi-site occupancy of the ions, and the average coordination numbers were estimated to about 6 and 7, respectively. Our results should underscore the impact of the high magnetic field NMR techniques, especially MQMAS, when applied to non-crystalline solids.

We determined the structural changes in CaSiO 3 and CaMgSi 2 O 6 glasses recovered from high pressure and temperature conditions (up to 7.5 GPa and 500 °C) using X-ray diffraction, Raman, infrared and X-ray emission spectroscopy. Densities of the metasilicate glasses increase with applied pressure at high temperature; CaMgSi 2 O 6 glass is more compressed than CaSiO 3 glass when recovered from 7.5 GPa and 500 °C. We propose a mechanism for densification of these glasses, that is mainly due to the compaction in medium-range scale (i.e. decrease in cluster size of SiO 4 anionic units with Ca, Mg polyhedra). Reduction of Si–O–Si bond angle is very small in the recovered CaSiO 3 and CaMgSi 2 O 6 glasses, as previously suggested.