Young-Ugk Kim

Prospective materials and applications for Li secondary batteries

Li-ion batteries have been employed successfully in various small electronic devices for the last two decades, and the types of applications are currently expanding to include electric vehicles (EVs), power tools, and large electric power storage units. In order to be implemented in these emerging markets, novel materials for negative and positive electrodes as well as electrolytes need to be developed to achieve high energy density, high power, and safe lithium rechargeable batteries. Here, the trends of the market and development of materials for each application are introduced, and some of next generation Li-ion batteries are discussed.

Quartz (SiO2): a new energy storage anode material for Li-ion batteries

SiO2 is one of the most abundant materials on Earth. It is cost-effective and also environmentally benign when used as an energy material. Although SiO2 was inactive to Li, it was engineered to react directly by a simple process. It exhibited a strong potential as a promising anode for Li-ion batteries.

Core-shell structured silicon nanoparticles@TiO2-x/carbon mesoporous microfiber composite as a safe and high-performance lithium-ion battery anode.

A core-shell structured Si nanoparticles@TiO2-x/C mesoporous microfiber composite has been synthesized by an electrospinning method. The core-shell composite exhibits high reversible capacity, excellent rate capability, and improved cycle performance as an anode material for Li-ion batteries. Furthermore, it shows remarkable suppression of exothermic behavior, which can prevent possible thermal runaway and safety problems of the cells. The improved electrochemical and thermal properties are ascribed to the mechanically, electrically, and thermally robust shell structure of the TiO2-x/C nanocomposite encapsulating the Si nanoparticles, which is suggested as a promising material architecture for a safe and reliable Si-based Li-ion battery of high energy density.

Reaction Mechanism of Tin Phosphide Anode by Mechanochemical Method for Lithium Secondary Batteries

Nanosized Sn 4 P 3 with a layered structure was synthesized by a mechanochemical method, and electrochemical and local structural characteristics of tin phosphide during charge/discharge were studied for its use as an anode material for lithium secondary batteries. As the amount of lithium insertion increased, tin phosphide was converted into lithium phosphides followed by lithiumtin alloy formation, which was confirmed by differential capacity plots and X-ray absorption spectroscopic (XAS) analysis. Based on X-ray diffraction, XAS, and electrochemical data, a three-step reaction mechanism of Sn 4 P 3 with lithium was suggested. Tin phosphide showed a good cyclability and retained a fairly large capacity of 370 mAh/g up to 50 cycles when cycled within a limited voltage window.

Multifunctional TiO2 coating for a SiO anode in Li-ion batteries

A titanium dioxide (TiO2) surface coating was applied to improve both the electrochemical and thermal properties of SiO as a high energy density anode for Li-ion batteries. A nano-scale, thin anatase TiO2 coating was achieved using a facile sol–gel process, and coated and non-coated SiO were characterized using various analytical methods. Increased initial Coulombic efficiency and reversible capacity were observed in the TiO2-coated SiO, which resulted in a 30% increase in the volumetric energy density as compared to that of bare SiO. Furthermore, the TiO2 coating remarkably suppressed the high-rate exothermic reactions observed in lithiated bare SiO and carbon-coated SiO, which could retard thermal runaway and the safety problems that it produces. Hence, an interfacial layer of TiO2 could be an alternative or supplementary coating material to carbon for safety-guaranteed and higher energy density Si-based Li-ion batteries.

Nanosize Si anode embedded in super-elastic nitinol (Ni–Ti) shape memory alloy matrix for Li rechargeable batteries

A nanosize Si embedded in super-elastic Nitinol alloy matrix composite was synthesized in large-scale using arc melting followed by a rapid quenching method. Both X-ray diffraction and high resolution transmission electron microscope with energy dispersive spectroscopy analyses confirmed that approximately 50 nm Si crystallites were surrounded by the Ni–Ti matrix. Ex situsynchrotron XRD was performed to elucidate the phase transition of active materials during lithiation and delithiation. The local structural changes of the Ni–Ti inactive matrix during cycling were investigated by ex situX-ray absorption spectroscopy analyses. This anode material showed an excellent electrochemical stability since the elastic behavior of the inactive Nitinol matrix absorbed the stress generated due to the volume expansion during lithiation of the nanosized Si embedded.

The Reaction Mechanism of Lithium Insertion in Vanadium Tetraphosphide A Possible Anode Material in Lithium-Ion Batteries

Lithium-free vanadium tetraphosphide was synthesized and electrochemical characterizations during cycling were carried out. Based on differential capacity plots (DCP) and X-ray analyses, a four-step reaction mechanism wassuggested. The reaction sequences are topotactic lithium insertion into the VP 4 , phase transformation from monoclinic Li 3 VP 4 to cubic Li 6 VP 4 phase, Li 3 P and VP formation by decomposition, and another lithium insertion into VP as the potential is lowered. Volume expansion of active material was expected from crystallographic data, and confirmed by scanning electron microscope observation during the second reaction step. In monoclinic sustaining range, VP 4 showed an excellent cycling performance with a relatively large reversible capacity.

Investigation of effective-medium approximation, alloy, average-composition, and graded-composition models for interface analysis by spectroscopic ellipsometry

We critically test the capabilities of the effective-medium approximation (EMA) and alloy models to describe multilayer samples with gradual interfaces by analyzing spectroscopic ellipsometric (SE) data of two AlGaAs samples grown expressly for this purpose. The dielectric functions e of the interfaces are calculated in the EMA and alloy models, and the interfaces themselves simulated either as a single layer of Al0.5Ga0.5As or a stack of layers of AlxGa1−xAs with x increasing or decreasing between 0.1 and 0.9 in increments of 0.1. The EMA essentially fails completely for either interface representation. For the alloy model the stepwise-graded representation is significantly better, not only simulating the data more accurately but also yielding thicknesses in essential agreement with those obtained by cross-sectional transmission electron microscopy. The results highlight the types of errors that are encountered with the different models, and show that the analysis of SE data can provide information about...

Effect of Lithium Bis(oxalate)borate as an Electrolyte Additive on Carbon-coated SiO Negative Electrode

As an electrolyte additive, the effects of lithium bis(oxalate)borate (LiBOB) on the electrochemical properties of a carbon-coated silicon monoxide (C-coated SiO) negative elec- trode are investigated. The used electrolyte is 1.3 M LiPF6 that is dissolved in ethylene car- bonate (EC), fluoroethylene carbonate (FEC), and diethyl carbonate (DEC) (5:25:70 v/v/v) with or without 0.5 wt. % LiBOB. In the LiBOB-free electrolyte, the film resistance is not so high