Byeong-Chul Yu

Reaction mechanism and enhancement of cyclability of SiO anodes by surface etching with NaOH for Li-ion batteries

SiO has been considered as one of the most promising anodes, the reaction mechanism of SiO with Li is still not well understood. High energy mechanical milling (HEMM) followed by etching of the SiO surface with NaOH solution was carried out in this study to enhance cycle performance. X-ray photoelectron spectroscopy (XPS) analyses showed the different compositions of the Si valence state before and after sputtering, and the atomic ratio of O/Si at the surface differed from that of the inside bulk SiO. Using high resolution transmission electron microscopy (HRTEM), the reaction mechanism of a SiO electrode was investigated. During the first discharge, Li2Si2O5 and Li6Si2O7 phases were identified as well as Li4SiO4 and Li rich amorphous binary LixSi phases. The surface etched SiO showed significantly better cyclability with the reversible capacity of 1260 mA h g−1 over 50 cycles.

Reversible storage of Li-ion in nano-Si/SnO2 core–shell nanostructured electrode

A core–shell nanostructured composite material consisting of nano-Si as the core and SnO2 as the shell is synthesized by a sol–gel method. The reaction mechanism between Li and a nano-Si/SnO2 core–shell nanostructured electrode is investigated, the partial reversible reaction between Li and SnO2 during the first cycle is identified, and the reactivity of the Si core is investigated by ex situ analyses. The nano-Si/SnO2 core–shell nanostructured electrode shows a reversible capacity of ca. 1000 mA h g−1 and good cycle retention close to 80% of the first charge capacity over 50 cycles.

Nanostructured cobalt oxide-based composites for rechargeable Li-ion batteries

Cobalt oxide-based nanocomposites are prepared using Co3O4, various metals (Al, Mg), carbon powders, and a simple high-energy mechanical milling technique. X-ray diffraction, X-ray photoelectron spectroscopy, and high-resolution transmission electron microscopy show that the cobalt oxide-based composites are mainly composed of nanostructured CoO/Al2O3, CoO/MgO, and Co3O4/C composites, respectively. Based on concepts related to the enhanced electrical conductivity of the Co3O4/C nanocomposite using conducting carbon matrix and to the resistance of inactive ceramic matrices (Al2O3, MgO) against active CoO particle growth during cycling, various nanostructured cobalt oxide-based composites are tested for use as anode materials. Among the composites, the Co3O4/C nanocomposite anode exhibits good electrochemical characteristics, such as high-capacity, good initial Coulombic efficiency, and long cycle behavior for Li-ion batteries.

Effect of oxide layer thickness to nano–Si anode for Li-ion batteries

Oxide thickness controlled amorphous SiO2/nano-Si core–shell structure anode for Li ion batteries was easily prepared by etching with NaOH solution using commercial nano-Si with a native oxide. Based on X-ray diffraction patterns and analysis of high resolution transmission microscope images, the electrode which consists of amorphous SiO2/amorphous Si/core crystalline Si after the first cycle showed a self-limiting reaction behavior. Due to this unique dual core–shell structure for a short diffusion path, a high reversible capacity of about 1800 mAh g−1 over 50 cycles and excellent rate capability could be achieved.