Seung-Wan Song

Low temperature preparation of β-LiFe5O8 fine particles by hydrothermal ball milling

Abstract Lithium ferrite, β-LiFe 5 O 8 , fine particles with a 100–120 nm size were successfully prepared by hydrothermal ball milling at the low temperature of 170 °C for 2 h without any post annealing. The lithium ferrite fine particle formation was confirmed by characterization using XRD, SEM, XPS and magnetization measurements. The experimental results strongly support the idea that ball milling can accelerate the reaction not only between the solid and solid phases but also between the solid and liquid phases. We believe hydrothermal ball milling can open a new era for the low temperature synthesis and fabrication of homogeneous fine particles both in composition and size.

Effect of LiOH concentration change on simultaneous preparation of LiCoO2 film and powder by hydrothermal method

Abstract LiCoO2 film and powder applicable to rechargeable lithium microbatteries have been directly prepared at the same time by hydrothermal treatment of a cobalt metal plate in a concentrated LiOH solution. The effect of LiOH concentration (0.1–6 M) on the structural change in film and powder has been examined using the XRD, micro-Raman and SEM analyses. It is found that all the powders with a layered hexagonal structure are precipitated by homogeneous nucleation regardless of LiOH concentration, whereas the dependence of film structure on the concentration is revealed by a selection of phase such as cobalt hydroxide species, hexagonal or cubic spinel phases formed by heterogeneous nucleation.

In situ visible Raman spectroscopic study of phase change in LiCoO2 film by laser irradiation

Abstract A phase change in LiCoO2/Co films in a spot of 1 μm diameter has been investigated under ambient conditions using 514.5 nm radiation by laser Raman spectroscopy. Laser irradiation resulted in a remarkable phase change of the film from hexagonal to cubic spinel, forming a lithium deficient phase Li1−xCoO2, which was enhanced with laser power. Based on comparative Raman studies, incorporation of cobalt atoms from the Co substrate by the local heating effect of laser irradiation has been suggested for the phase change. The in situ tool is expected to be useful for applications in control of micro-structure of cathode films for micro-batteries and micro-structural analysis.

Soft Solution Processing for direct fabrication of LiMO2 (M=Ni and Co) film

Abstract LiMO2 (M=Ni and Co) films were directly fabricated in a concentrated LiOH solution at fixed temperatures, between 100 and 200 °C, using Soft Solution Processing. Film formation mechanism studies elucidate the key role of hydroxyl group in obtaining the LiCoO2 films and of electrochemical anodic process in obtaining the LiNiO2 films. It is also found that the formation of the LiMO2 (M=Ni and Co) is fully based on dissolution–precipitation model. Successful preparation of LiMO2 (M=Ni and Co) films using the newly designed experimental conditions based on the elucidation of the microstructuring mechanism shows a good example of how to introduce more economical, energy and material efficient, and environment-friendly synthetic route.

Single-step fabrication of Li1−xNi1+xO2 and LiCoO2 films by Soft Solution-Processing at 20–200°C

Abstract Li 1− x Ni 1+ x O 2 and LiCoO 2 films as cathodes for lithium rechargeable microbatteries were fabricated in a concentrated LiOH solution at 20–200°C using different Soft Solution-Processing methods. While LiCoO 2 films can be obtained by a purely hydrothermal reaction, a supplementary electrochemical charge with the same hydrothermal conditions is necessary to produce Li 1− x Ni 1+ x O 2 films. A film formation mechanism study elucidated the necessity of such different activation methods for the preparation of Li 1− x Ni 1+ x O 2 and LiCoO 2 films.

Direct fabrication of crystallized LiCoO2 films on paper by artificial biomineralization with electrochemically activated interfacial reactions

Abstract We have developed a new method to directly fabricate lithium cobalt oxide (LiCoO 2 ) films onto porous films by an electrodeposition method in solutions at low temperature. A set of porous substrate films consisting of a PTFE membrane-filter and paper was placed between a LiOH solution and a CoSO 4 solution. Cobalt compounds were deposited on the substrates under electrical currents of ∼1 mA/cm 2 using carbon electrodes. As a result, we found that LiCoO 2 films on the porous filter were successfully fabricated at 120 °C. Furthermore, the LiCoO 2 films did not cover the entire substrate, but formed only in the shape of the anode.