A broad review of recent research work on the preparation and the remarkable properties of intercalation compounds of graphite, covering a wide range of topics from the basic chemistry, physics and materials science to engineering applications.

Intercalation compounds of graphite

Commensurate adsorption of hydrocarbons and alcohols in microporous metal organic frameworks.

The status of room-temperature potassium-ion batteries is reviewed in light of recent concerns regarding the rising cost of lithium and the fact that room-temperature sodium-ion batteries have yet to be commercialised thus far. Initial reports of potassium-ion cells appear promising given the infancy of the research area. This review presents not only an overview of the current potassium-ion battery literature, but also attempts to provide context by describing previous developments in lithium-ion and sodium-ion batteries and the electrochemical reaction mechanisms discovered thus far. Perspectives and directions on the techniques available to characterize newly developed battery materials are also provided based on our experience and knowledge from the literature. It is hoped that through this review, the potential of potassium-ion batteries as a competitive energy-storage technology will be realised, and the accessibility and available knowledge of the techniques required to develop the technology will be made apparent.

An Initial Review of the Status of Electrode Materials for Potassium-Ion Batteries

A quantitative theory of the isotropic electron‐nuclear spin interactions of carbon 13 in pi‐electron radicals is presented and applied to the hyperfine splittings observed in the electron spin resonance spectra of these substances. The splittings arise from sigma‐pi interactions which polarize both the 1s and 2s electrons. The 1s‐orbital spin polarization is shown to contribute a term of negative sign with a magnitude comparable to that from the 2s electrons. For an sp2 hybridized carbon atom that is bonded to three atoms, Xi (i=1, 2, 3), the hyperfine constant aC has the form aC=(SC+ ∑ i=13QCXiC)ρπ+ ∑ i=13QXiCCρiπ, where ρπ and ρiπ(i=1,2,3) are the pi‐electron spin densities on atoms C and Xi, respectively. The contribution of the 1s electrons is determined by SC and that of the 2s electrons by the Q's, where QBCA is the sigma‐pi parameter for the nucleus of atom A resulting from the interaction between the bond BC and the pi‐electron spin density on atom B. Calculations for a planar CHC2 fragment model...

THEORETICAL INTERPRETATION OF CARBON-13 HYPERFINE INTERACTIONS IN ELECTRON SPIN RESONANCE SPECTRA. Technical Note Report No. 9

J-YH and S-TM contributed equally to this work This work was supported by the Human Resources Development program (Grant No 20154010200840) from a Korea Institute of Energy Technology Evaluation and Planning (KETEP) grant, funded by the Ministry of Trade, Industry and Energy of the Korean government, and supported by the Global Frontier RaD program (Grant No 2013M3A6B1078875) of the Center for Hybrid Interface Materials (HIM) of the Ministry of Science and ICT

Recent Progress in Rechargeable Potassium Batteries

Stage transformations in the potassium-graphite intercalation compound have been studied by in situ x-ray diffraction. A precise phase diagram has been determined for the stages up to 7. The stage dependence of $\ensuremath{\Delta}\ensuremath{\mu}(n)$, the stable range of a given stage $n$ in chemical potential, is evaluated from the phase diagram and compared with the theoretical results for the electrostatic model for staging. Time-dependent observation of the stage transformation reveals that only two phases of adjacent stages coexist throughout the process of the stage transformation so that the $c$-axis disorder is insignificant even in the transition region. The kinetics of the stage transformation is also discussed.

In situ observation of staging in potassium-graphite intercalation compounds

Superconductivity in the graphite-potassium intercalation compound C8K

High resolution 13 C NMR has been observed in highly oriented crystals of pristine graphite and K-GIC's. The NMR spectrum consists of several well resolved lines which can be assigned to the interior and bounding carbon layers. The 13 C spin-lattice relaxation time T 1 shows the metallic characteristics, T 1 T = constant between about 1.5 K and R.T. From T 1 of each resolved absorption line, the c-axis charge distribution was quantitatively determined for stage 3 and 6, which is strongly inhomogeneous. The obtained distribution was also supported by an analysis of the frequency shift of 13 C NMR. In stage 1 it was suggested, from a comparison of T 1 with electronic specific heat, that the conduction electrons near the Fermi level spread over not only graphite layers but also interlayer space containing K-atoms.

H. Suematsu

Papers

In situ observation of staging in potassium-graphite intercalation compounds

Superconductivity in the graphite-potassium intercalation compound C8K

High Resolution 13 C NMR in K-Graphite Intercalation Compounds—C-Axis Charge Distribution

Density-of-states investigation of C8K and occurrence of the interlayer band.

Magnetic properties of Europium-graphite intercalation compound C6Eu