Enhanced Dilation Properties of Silicon-Silicide, Si-TiFeSi2, Nanocomposite as a Lithium Battery Anode

Abstract

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...

The role of thermal annealing on the microstructures of (Ti, Fe)-alloyed Si thin-film anodes for high-performance Li-ion batteries

“…One should note that there have been several reports on the benecial properties of the TiFeSi 2 phase as an electrically conducting and mechanically buffering material. 10,[24][25][26] Fig. 1 X-ray diffraction patterns representing the structural phase evolution in the (Ti, Fe)-alloyed Si thin-film samples annealed at the different temperatures.…”

“…Furthermore, the cyclic performance data demonstrate on average 65% coulombic efficiency (CE) during 1st cycle for all the samples annealed up to 600 C. This problem has also been observed in previous reports on Si-based anodes. 25,26 The initial low CE has been ascribed to the formation of solid electrolyte interphase (SEI) on the surface of the (Ti, Fe)-alloyed Si thin-lm anode and a local loss of electrical contact caused by volumetric variation of the anode. 23,27 Moreover, Fig.…”

Study of the Binder Influence on Expansion/Contraction Behavior of Silicon Alloy Negative Electrodes for Lithium-Ion Batteries

“…1 is that all electrodes severely expand (>180%) upon lithiation (Li-Si alloying) and contract upon delithiation (Li-Si de-alloying), although the extent and behavior of expansion/contraction differ depending upon the selected binders. 22,23,25,35 We note that a non-linear thickness change as function of the run time, that is proportional to capacity, is observed. This is contradictory to the expected linear behavior of Li-Si alloying.…”