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Hydrogen trapping state associated with the low temperature thermal desorption spectroscopy peak in hydrogenated nanostructured graphite J. Appl. Phys.

Two desorption peaks of hydrogen molecule ͑mass numberϭ2͒, starting at about 600 and 950 K, respectively, are observed in thermal desorption mass spectroscopy of nanostructured graphite mechanically milled for 80 h under hydrogen atmosphere. It follows from a combined analysis of thermal desorption mass spectroscopy and thermogravimetry, that ϳ6 mass % of hydrogen ͑corresponding to 80% of the total amount of hydrogen͒ is desorbed at the first desorption peak as a mixture of pure hydrogen and hydrocarbons. Below the temperature of the second desorption peak, at which recrystallization related desorption occurs, nanostructured graphite is expected to retain its specific defective structures mainly with carbon dangling bonds as suitable trapping sites for hydrogen storage. The formation process of the nanostructures during milling under hydrogen atmosphere is also discussed on the basis of the profile of Raman spectroscopy.

The atomic and electronic structures of binary Li2S-P2S5 glasses used as solid electrolytes are modeled by a combination of density functional theory (DFT) and reverse Monte Carlo (RMC) simulation using synchrotron X-ray diffraction, neutron diffraction, and Raman spectroscopy data. The ratio of PSx polyhedral anions based on the Raman spectroscopic results is reflected in the glassy structures of the 67Li2S-33P2S5, 70Li2S-30P2S5, and 75Li2S-25P2S5 glasses, and the plausible structures represent the lithium ion distributions around them. It is found that the edge sharing between PSx and LiSy polyhedra increases at a high Li2S content, and the free volume around PSx polyhedra decreases. It is conjectured that Li+ ions around the face of PSx polyhedra are clearly affected by the polarization of anions. The electronic structure of the DFT/RMC model suggests that the electron transfer between the P ion and the bridging sulfur (BS) ion weakens the positive charge of the P ion in the P2S7 anions. The P2S7 anions of the weak electrostatic repulsion would causes it to more strongly attract Li+ ions than the PS4 and P2S6 anions, and suppress the lithium ionic conduction. Thus, the control of the edge sharing between PSx and LiSy polyhedra without the electron transfer between the P ion and the BS ion is expected to facilitate lithium ionic conduction in the above solid electrolytes.

Neutron elastic scattering was used to determine the structure of as-received and lithiated amorphous SiO which has been proposed as an anode material for lithium ion secondary batteries. Based on a comparison between the total radial distribution functions ͓RDF(r)͔ of SiO and SiO 2 , it was suggested that amorphous SiO is composed of a three-dimensional SiO 4 tetrahedral network similar to silica (SiO 2 ) glass and metallic silicon clusters, and that the latter were finely dispersed in the SiO 4 matrix. On the other hand, electrochemically lithiated SiO showed a typical lithium negative correlation together with the disappearance of the Si-Si correlation in the RDF(r) which indicated that lithium predominantly reacted with the metallic silicon to form Li-Si alloys.