Properties of a novel hard-carbon optimized to large size Lion secondary battery studied by 7Li NMR

The state of lithium in a novel hard-carbon optimized to the anode of large size Li ion secondary battery, which has been recently commercialized, was investigated and compared with other existing hard-carbon samples by 7Li NMR method. The new carbon material showed a peak at 85 ppm with a shoulder signal at 7 ppm at room temperature in static NMR spectrum, and the former shifted to 210 ppm at 180 K. The latter at room temperature was attributed to Li doped in small particles contained in the sample. The new carbon sample showed weaker intensity of cluster-lithium signal than the other hard-carbon samples in NMR, which corresponded to a tendency of less "Constant Voltage" (CV) capacity in charge-discharge curves of electrochemical evaluation. Smaller CV capacity and initial irreversible capacity, which are the features of the novel hard-carbon, are considered to correspond to a blockade of the diffusion of Li into pore of carbon.</p

Analysis of bis(trifluoromethylsulfonyl)imide-doped paramagnetic graphite intercalation compound using F-19 very fast magic angle spinning nuclear magnetic resonance

F atoms bonding to paramagnetic/conductive graphene layers in accepter-type graphite intercalation compounds (GICs) are analyzed using very fast magic angle spinning nuclear magnetic resonance, which is applied for the first time on F-19 nuclei to investigate paramagnetic materials. In the bis(trifluoromethylsulfonyl)imide(TFSI)-doped GIC, C-F bonds between fluorine atoms and graphene layers conform to a weak bonding of F to the graphene sheets. TFSI anions intercalated in the GIC do not show overall molecular motion; even at room temperature only the CF3 groups rotate

11B nuclear magnetic resonance in boron-doped diamond

This review summarizes recent results obtained by 11B solid-state nuclear magnetic resonance (NMR) on boron-doped diamond, grown by the high-pressure high-temperature (HPHT) or chemical vapor deposition techniques. Simple single-pulse experiments as well as advanced two-dimensional NMR experiments were applied to the boron sites in diamond. It is shown that magic-angle spinning at magnetic fields above 10 T is suitable for observation of high-resolution 11B spectra of boron-doped diamond. For boron-doped HPHT diamonds, the existence of the excess boron that does not contribute to electrical conductivity was confirmed and its 11B NMR signal was characterized. The point-defect structures (B+H complexes and -B-B-/-B-C-B- clusters), postulated previously for the excess boron, were discarded and graphite-like structures were assigned instead

Quaternary Wurtzitic Nitrides in the System ZnGeN₂–GaN: Powder Synthesis, Characterization, and Potentiality as a Photocatalyst

We developed a new quaternary wurtzitic nitride system by formation of the solid solution between ZnGeN₂ and GaN. Near stoichiometric and monophasic powder samples in the composition Zn_1–<i>x</i>Ge_1–<i>x</i>Ga_2<i>x</i>N₂ (<i>x</i> ≤ 0.50) were obtained by the reduction–nitridation synthesis conducted at 900 °C. The results of crystal structure refinement clearly revealed that the cation ordering in the structure of ZnGeN₂ (<i>Pna</i>2₁) tends to disappear by introducing Ga into the lattice, and the structure transforms to a simple wurtzite phase (<i>P</i>6₃<i>mc</i>) with the composition of <i>x</i> ≥ 0.33. The observed structural evolution was further confirmed by the results of ⁷¹Ga solid-state nuclear magnetic resonance (NMR) spectroscopy, showing an unsplit single peak observed for <i>x</i> ≥ 0.33. The dissolution of GaN into ZnGeN₂ also resulted in a marked narrowing of the band gap, from the ultraviolet region of 3.42 eV to the visible-light range of 3.02–3.05 eV, depending scarcely on the value of <i>x</i>. The results of photocatalytic test reactions for water splitting showed that the synthesized Zn_1–<i>x</i>Ge_1–<i>x</i>Ga_2<i>x</i>N₂ solid solution possessed the H₂ evolution rate of 2.8–3.6 μmol/h and the relatively high O₂ evolution rate of 100.4–126.6 μmol/h, as well as the capability for overall water splitting under the visible-light irradiation of λ > 400 nm

Oxygen-17 nuclear magnetic resonance measurements on apatite-type lanthanum silicate (La9.33(SiO4)6O2)

We used magic angle spinning (MAS), multiquantum (MQ)-MAS, and high-temperature (HT) nuclear magnetic resonance (NMR) measurements to investigate the oxide-ion conduction path of oxygen-17 (O-17) in apatite-type lanthanum silicate La9.33(SiO4)6O2. A highly crystalline apatite-type lanthanum silicate was specifically synthesized for the measurements. MAS and MQ-MAS NMR confirmed that four kinds of oxide-ion sites are present in the structure and showed a small extra peak (< 1%) possibly due to an interstitial site. The high-temperature measurements showed that the line shape changed and sharpened with increasing temperature from 200 °C, and the peak position shifted at 700 °C. The comparison of the results between MAS NMR (room-temperature) and HT static NMR showed the exchange of oxide ions bonded to Si (O1, O2, and O3) but the apparent exchange between the oxide ions (O1, O2, and O3) and the oxide ion at the isolated site (O4) is not observed. The exchange of the oxide ions that are bonded to Si (O1, O2, and O3) suggests that they are the main diffusion species in oxide-ion conductivity