Lithium-ion batteries, which have been widely used to power portable electronic devices, are on the verge of being applied to new automobile applications. To expand this emerging market, however, an electrode that combines fast charging capability, long-term cycle stability, and high energy density is needed. Herein, we report a novel layered lithium vanadium fluorophosphate, Li1.1Na0.4VPO4.8F0.7, as a promising positive electrode contender. This new material has two-dimensional lithium pathways and is capable of reversibly releasing and reinserting ~1.1 Li+ ions at an ideal 4 V (versus Li+/Li) to give a capacity of ~156 mAh g−1 (energy density of 624 Wh kg−1). Moreover, outstanding capacity retentions of 98% and 96% after 100 cycles were achieved at 60°C and room temperature, respectively. Unexpectedly high rate capability was delivered for both charge and discharge despite the large particle size (a few microns), which promises further enhancement of power density with proper nano-engineering.

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...