Ternary graphite intercalation compounds (GICs), which consist of graphite, alkali metal (Li, Na, K) cations, and organic cointercalates such as ethylenediamine (en) or tetrahydrofuran (thf), are useful precursors to graphene-based materials and tetraalkylammonium GICs. This study investigates the gallery arrangements and intercalate dynamics of the deuterated en(d4), thf(d8), piperazine(d10), or 1,4-diazabicyclo[2.2.2]octane(dabco)(d12) in ternary GICs containing Na+ or K+ cations using XRD and solid state 23Na and 2H NMR line-shape analyses. An en(d4)-graphite oxide (GO) intercalation compound and the trihexylmethyl(d3)-ammonium (thma) GIC were also prepared and evaluated by XRD and NMR. The 2H NMR spectra exhibit a narrow peak ascribed to intercalates undergoing isotropic rotation and a broad powder pattern ascribed to intercalates in a rigid state or undergoing uniaxial rotations. The thma intercalates in thma(d3)-GIC and the en(d4) intercalates in en(d4)-GO are relatively mobile and can diffuse; this may arise because there are no alkali metal cations in the galleries. The molecular dynamics as well as the synthetic challenges presented by some GICs are explained in terms of different affinities of alkali metal cations to the cointercalates.

Lithium ion cells comprising actual components of positive electrodes (LiCoO2, LiNixCoyAlz, and LiMn2O4) and negative electrodes (graphite and hard carbon) were assembled for in situ7Li nuclear magnetic resonance (NMR) experiments. The 7Li NMR measurements of the cells revealed a “relaxation effect” after overcharging: a decrease of the signal assigned to Li metal deposited on the negative electrode surface by overcharging. The reduction of the Li metal signal was inversely proportional to the increase of the signal of lithium stored in carbon. Therefore, the effect was ascribed to absorption of deposited lithium into the carbon of negative electrodes. The effect, which occurred rapidly in a few hours, reached an equilibrium state at 8–15 h. The slight shift of deposited metal suggests that dendritic Li easily re-dissolved, although larger Li particles remained. A hard carbon electrode has a greater effect of Li metal relaxation than graphite electrodes do, which is explainable by the bufferable structure of the carbon. Results are expected to be important for the discussion of the state of lithium, and for safer battery design.

The state of sodium inserted in the hard carbon electrode of a sodium ion battery having practical cyclability was investigated using solid state 23Na NMR. The spectra of carbon samples charged (reduced) above 50 mAh g−1 showed clear three components. Two peaks at 9.9 ppm and 5.2 ppm were ascribed to reversible sodium stored between disordered graphene sheets in hard carbon because the shift of the peaks was invariable with changing strength of external magnetic field. One broad signal at about −9 to −16 ppm was assigned to sodium in heterogeneously distributed closed nanopores in hard carbon. Low temperature 23Na static and magic angle spinning NMR spectra didn't split or shift whereas the spectral pattern of 7Li NMR for lithium-inserted hard carbon changes depending on the temperature. This strongly suggests that the exchange of sodium atoms between different sites in hard carbon is slow. These studies show that sodium doesn't form quasi-metallic clusters in closed nanopores of hard carbon although sodium assembles at nanopores while the cell is electrochemically charged.Highlights► A hard carbon electrode in a sodium ion battery was investigated using 23Na NMR. ► Two peaks at 10 ppm and 5 ppm and a broad signal of Na in carbon were observed at room temperature. ► The signals were assigned to Na stored between disordered graphene sheets and in closed nanopores. ► The sodium doesn't have quasi-metallic property in hard carbon.

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 19F 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.

We produced carbon hybrid materials of graphene sheets decorated with metal or metal oxide nanoparticles of gold, silver, copper, cobalt, or nickel from cation exchanged graphite oxide. Measurements using powder X-ray diffraction, transmission electron microscopy, and X-ray absorption spectra revealed that the Au and Ag in the materials (Au–Gr and Ag–Gr) existed on graphene sheets as metal nanoparticles, whereas Cu and Co in the materials (Cu–Gr and Co–Gr) existed as a metal oxide. Most Ni particles in Ni–Gr were metal, but the surfaces of large particles were partly oxidized, producing a core–shell structure. The Ag–Gr sample showed a catalytic activity for the oxygen reduction reaction in 1.0 M KOH aq. under an oxygen atmosphere. Ag–Gr is superior as a cathode in alkaline fuel cells, which should not be disturbed by the methanol cross-over problem from the anode. We established an effective approach to prepare a series of graphene-nanoparticle composite materials using heat treatment.

Mesoporous carbon having platinum, ruthenium or palladium nanoparticles on exfoliated graphene sheets were produced from graphite oxide (GO) and metal complexes. The Pt included carbon was made by heating of the intercalation compound including tetraammineplatinum (II) chloride monohydrate. Samples having Ru or Pd are producible by heating in nitrogen gas atmosphere using hexaammineruthenium (III) chloride or tetraamminepalladium (II) chloride monohydrate instead of Pt complex. The particle sizes of platinum, ruthenium, and palladium were, respectively, 1–3, 1–2, and 3–7 nm. The platinum- or palladium-containing sample showed catalytic activity for oxygen reduction.

The existence of micropores and the change of surface structure in pitch-based hard-carbon in xenon atmosphere were demonstrated using 129Xe NMR. For high-pressure (4.0 MPa) 129Xe NMR measurements, the hard-carbon samples in Xe gas showed three peaks at 27, 34 and 210 ppm. The last was attributed to the xenon in micropores (<1 nm) in hard-carbon particles. The NMR spectrum of a sample evacuated at 773 K and exposed to 0.1 MPa Xe gas at 773 K for 24 h showed two peaks at 29 and 128 ppm, which were attributed, respectively, to the xenon atoms adsorbed in the large pores (probably mesopores) and micropores of hard-carbon. With increasing annealing time in Xe gas at 773 K, both peaks shifted and merged into one peak at 50 ppm. The diffusion of adsorbed xenon atoms is very slow, probably because the transfer of molecules or atoms among micropores in hard-carbon does not occur readily. Many micropores are isolated from the outer surface. For that reason, xenon atoms are thought to be adsorbed only by micropores near the surface, which are easily accessible from the surrounding space.

Copper(II) compounds {CuCA(phz)(H2O)2}n (H2CA = chloranilic acid, phz = phenazine) having a layer structure of –CuCA(H2O)2– polymer chains and phenazine were studied by 35Cl nuclear quadrupole resonance (NQR). The single NQR line observed at 35.635 MHz at 261.5 K increased to 35.918 MHz at 4.2 K. The degree of reduction of electric field gradient due to lattice vibrations was similar to that of chloranilic acid crystal. Temperature dependence of spin–lattice relaxation time, T1, of the 35Cl NQR signal below 20 K, between 20 and 210 K, and above 210 K, was explained by (1) a decrease of effective electron-spin density caused by antiferromagnetic interaction, (2) a magnetic interaction between Cl nuclear-spin and electron-spins on paramagnetic Cu(II) ions, and (3) an increasing contribution from reorientation of ligand molecules, respectively. The electron spin-exchange parameter ∣J∣ between the neighboring Cu(II) electrons was estimated to be 0.33 cm−1 from the T1 value of the range 20−210 K. Comparing this value with that of J = −1.84 cm−1 estimated from the magnetic susceptibility, it is suggested that the magnetic dipolar coupling with the electron spins on Cu(II) ions must be the principal mechanism for the 35Cl NQR spin–lattice relaxation of {CuCA(phz)(H2O)2}n but a delocalization of electron spin over the chloranilate ligand has to be taken into account.

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.