Coexistence of both edge plane and basal plane in graphite often hinders the understanding of lithium ion diffusion mechanism. In this report, two types of graphene samples were prepared by chemical vapor deposition (CVD): (i) well-defined basal plane graphene grown on Cu foil and (ii) edge plane-enriched graphene layers grown on Ni film. Electrochemical performance of the graphene electrode can be split into two regimes depending on the number of graphene layers: (i) the corrosion-dominant regime and (ii) the lithiation-dominant regime. Li ion diffusion perpendicular to the basal plane of graphene is facilitated by defects, whereas diffusion parallel to the plane is limited by the steric hindrance that originates from aggregated Li ions adsorbed on the abundant defect sites. The critical layer thickness (lc) to effectively prohibit substrate reaction using CVDgrown graphene layers was predicted to be ∼6 layers, independent of defect population. Our density functional theory calculations demonstrate that divacancies and higher order defects have reasonable diffusion barrier heights allowing lithium diffusion through the basal plane but neither monovacancies nor Stone-Wales defect.

We propose a new material for high power and high density supercapacitors with excellent cycle stability. Graphite oxide (PSS-GO) intercalated with poly(sodium 4-styrensulfonate) showed high performance of electric double layer capacitance (EDLC) compared to that of the pristine graphite oxide. Specific capacitance of the PSS-GO reached 190 F/g, and the energy density was much improved to 38 Wh/kg with a power density of 61 W/kg. Cycle test showed that the specific capacitance decreased by only 12% after 14860 cycles, providing excellent cyclic stability. The high EDLC performance of PSS-GO composite was attributed to the wide interlayer distance and simple pore structures accommodating fast ion kinetics.

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Graphite materials for commercial Li-ion batteries usually undergo special treatment to control specific parameters such as particle size, shape, and surface area to have desirable electrochemical properties. Graphite surfaces can be classified into basal and edge planes in the aspect of the structure of carbons, with the existing defect sites such as functional groups and dislocations. The solid-electrolyte interphase (SEI) mostly forms at the edge plane and defect sites, as Li-ions only intercalate through these non-basal planes, whereas the electrochemical properties of graphite largely depend on its surface heterogeneity due to the difference of reactivity on each plane. In order to quantify the detailed surface structure of graphite materials, local-absorption isotherms were utilized, and the analyzed nanostructural parameters of various commercial graphite samples were correlated with the electrochemical properties of each graphite anode. Thereby, we have confirmed that the fraction of non-basal plane and fast-charging capability has strong linear relations. The pore/non-basal sites are also related to the cycle life by affecting the SEI formation, and the determination of surface heterogeneity and pores of graphite materials can provide powerful parameters that imply the electrochemical performances of commercial graphite.

Silicon-Silicide, Si-TiFeSi 2 , nanocomposite was prepared using a melt-spinning method. Powder neutron diffraction showed a mixing ratio of 38.7(5):61.3(8) and average crystallite sizes of 23.34(3) and 40.60(1) nm for silicon and TiFeSi 2 , respectively. A conchoidal fracture of the Zangboite-structure TiFeSi 2 matrix was observed through microscopy. Electrochemical tests show characteristic features such as rapid stabilization of the first charging profile to about 50 mV and high cyclic performance. The OCP (Open Circuit Potential) measurement and ex-situ XRD represent the Li 15 Si 4 as the final phase. In-situ measurements of the electrode thickness showed improvements of the magnitude and hysteresis of dilation.Silicon, one of the eight most abundant elements on earth, 1 has attracted much attention as a prospective anode material for lithium batteries due to its high capacity, which is about ten times higher than that of graphite. 2,3 Recently, many studies have focused on resolving the rapid degradation caused by the large degree of volume expansioncontraction during the charging-discharging process.Composite forms with various types of electrochemically inactive matrixes were have been investigated to improve these drastic volume changes. 4-8 Recent studies of silicon nanowires have shown a nanometer level morphology control effect that results in high cyclic performance. 9 Silicon nanocomposites will become viable if it is possible to determine a proper matrix to control the morphology and dilation. Silicide is a good candidate as a composite matrix due to its advantage of excessive silicon, which plays role in both the embedding element and the matrix.Zangboite, TiFeSi 2 , is a steel gray mineral silicide with a hardness of about 5.5 Mohs, but it is also brittle and susceptible to conchoidal fractures, 10-12 which describes the way that brittle materials break when they do not follow any planes of separation, as opposed to faceted fracturing. Conchoidal fracturing makes this material a prospective matrix material due to the morphology and dilation regress from the viewpoint of the strain relaxation. We can assume that conchoidal fracturing effectively in randomizes the stress distribution by restraining the formation and propagation of crystalline cleavage. We adopted the melt-spinning method, which is commonly used for fabrication of permanent magnets nanocomposite. [13][14][15] Experimental Preparation of a composite material.-A Si-Ti-Fe ingot was prepared by the arc-melting of the constituent elements at a weight percent ratio of 57.1:19.4:23.5 in an argon atmosphere. The sample was then melt-spun by casting it onto a cold blade at 45 m/s in order to fabricate a ribbon-type nanocomposite. Powder Neutron DiffractionA room-temperature neutron diffraction experiment was performed using a Ge(331) monochromator at a 90 • take-off angle with the HANARO HRPD(High Resolution Powder Diffractometer) at the Korea Atomic Energy Research Institute. Rietveld refinement of the powder pattern was performed with the F...