Structural Study of Novel Graphite−Lithium−Calcium Intercalation Compounds

Egyptian blue: from pigment to battery electrodes

Herein we report on using Egyptian blue as an anode material for Li-ion batteries. A 1^st cycle lithiation capacity of 594 mA h g^-1 and reversible capacity of 210 mA h g^-1 at 20 mA g^-1, and at 500 mA g^-1 a reversible capacity of 120 mA h g^-1 (stable over 1000 cycles) were achieved with coulombic efficiency more than 99.5%. Using X-ray diffraction, and FTIR and X-ray absorption spectroscopies we found that the material goes through a conversion reaction during the 1^st cycle that results in the formation of amorphous mixed oxides with copper nanoclusters.

Electronic Structure and Charge Transfer in the Ternary Intercalated Graphite β-KS0.25C3

The electronic structure of the ternary intercalated graphite beta-KS(0.25)C3 is studied by means of a first-principles density functional theory approach. The nature of the partially filled bands is analyzed, and the K sublayers of the intercalate are shown to have an important contribution to the Fermi surface. This K-based contribution confers a sizable three-dimensional character to the conductivity even if considerably less than that for the related binary KC8. The electronic structure of beta-KS(0.25)C3 differs noticeably from that of the related ternary compound, KH(x)C4. The charge transfer is analyzed, and a way to evaluate it, which can be used in general for intercalated graphites, is proposed. The charge transfer per C atom in this ternary material is shown to be smaller than that in the KC8 binary compound despite a more favorable stoichiometry ratio between K and C.

Specific heat of the Ca-intercalated graphite superconductor CaC6

The superconducting state of Ca-intercalated graphite CaC6 has been investigated by specific heat measurements. The characteristic anomaly at the superconducting transition (Tc = 11.4 K) indicates clearly the bulk nature of the superconductivity. The temperature and magnetic field dependence of the electronic specific heat are consistent with a fully gapped superconducting order parameter. The estimated electron-phonon coupling constant is lambda = 0.70 +/- 0.04, suggesting that the relatively high Tc of CaC6 can be explained within the intermediate coupling BCS approach.