Sun Kyoung Jeoung

Efficient lithium storage from modified vertically aligned carbon nanotubes with open-ends

Herein, we report the use of vertically aligned carbon nanotubes (VA-CNTs) with controlled structure and morphology as an anode material for lithium-ion batteries. The tailored surface structure and open-end morphology of VA-CNTs made by ion milling and transfer processes increases the accessibility of Li ions, and allows Li ions to diffuse inside as well as on the surface of the CNTs through the generated surface defects, leading to the significantly improved lithium ion storage capacity compared to as-grown close-end VA-CNTs. The irreversible discharge capacity of the modified VA-CNTs anode reaches up to 2350 mA h g−1 at 2 C in the first cycle and the reversible capacity is in the range of 1200–557 mA h g−1 for the 2nd–20th cycles. The second insertion capacity of the modified CNTs electrode was 4 times higher than that of the as-grown CNTs and 3.2 times higher than that of a previously reported CNTs electrode for a commercial graphite device.

Flame retardancy and thermal stability of polyurethane foam composites containing carbon additives

Polyurethane (PU) is an important class of polymers that have wide application in a number of different industrial sectors. The goal of this work was the synthesis of flame-retarded PU foam with expandable graphite (EG) or commercial graphene. The flame retardancy and thermal stability of the foams has been studied through cone calorimeter analysis, the limited oxygen index and thermal conductivity. The presence of expandable graphite brings an improvement in fire behavior. In particular, the limited oxygen index increases in a linear way and the highest limited oxygen index values are obtained for EG-PU foams. The results from the cone calorimeter are in agreement with those of oxygen index; EG filled foams show a considerable decrease of maximum-heat release rate (M-HRR) with respect to unfilled foams. The results of thermal conductivity show that an increase in expandable graphite amount in PU foams lead to an increased conductivity.

Study on properties of CFRP fabricated by VA-RTM process

Carbon fiber reinforced plastics (CFRP) have a lot of attention from industry and academia due to its excellent mechanical property. It has been used for aircraft, automotive and so on, since it can replace metallic materials and reduce total weight with increased physical properties. However, the manufacturing process and the material cost are still challenging to be commercialized in the automotive market. Therefore, many researchers are trying to minimize materials and process cost for broadening their applications. In this study, thermoset epoxy resins were used for binder of CFRP. Epoxy resins were investigated in order to figure out optimized curing speed under vacuum assisted resin transfer molding (VARTM) processing condition. Mechanical properties of CFRP with different carbon fiber orientation and woven carbon fiber were compared to mathematically simulated results. In order to develop the application of automobile component, reliability tests of CFRP were carried out. Tensile strength of CFRP i...