Serk-Won Jang

Characteristics of carbon-coated graphite prepared from mixture of graphite and polyvinylchloride as anode materials for lithium ion batteries

Abstract A carbon-coated graphite is investigated as the negative electrode for Li-ion batteries. The carbon-coated graphite particles are prepared by simple heat-treatment of mixtures of graphite and poly(vinyl chloride), PVC, at 800–1000°C in an argon flow. The carbon coating reduces significantly the initial irreversible capacity of the graphite in a propylene carbonate-based electrolyte, by suppressing the solvated lithium ion intercalation, and also improves the initial charge–discharge coulombic efficiency. By carbon coating, the specific surface area of graphite particles is greatly increased. These findings can be explained by assuming that a turbostratic structure of PVC-carbon resists irreversible side-reactions which are controlled predominantly by active, edge surface sites.

Lithium storage properties of nanocrystalline Ni3Sn4 alloys prepared by mechanical alloying

Abstract Nanocrystalline Ni 3 Sn 4 alloy powders prepared by high energy ball milling are examined as an anode for lithium-ion batteries. Ex situ X-ray diffraction (XRD) and differential capacity plots show that crystalline Ni 3 Sn 4 has a low affinity for lithium. In the case of well-developed nanocrystalline Ni 3 Sn 4 , the lithium atoms reversibly react with tin atoms in the grain boundaries with no capacity fading for extended cycling.

Nanostructured Ni3Sn2 thin film as anodes for thin film rechargeable lithium batteries

Abstract Thin film Ni 3 Sn 2 anodes were deposited on a Cu substrate by e-beam evaporator at room temperature. The deposited films were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). They were tested as anodes for thin film rechargeable lithium batteries. These film electrodes exhibited an excellent cycle performance over 500 cycles. Ni 3 Sn 2 films remained without undergoing any crystallographic phase change during cycling.

SUBSTRATE EFFECT ON THE MICROSTRUCTURE AND ELECTROCHEMICAL PROPERTIES IN THE DEPOSITION OF A THIN FILM LICOO2 ELECTRODE

An LiCoO2 thin-film cathode was deposited onto sintered alumina and Si/SiO2 substrates. After annealing at 800°C in O2 for 30 min, the film deposited on alumina consisted of large particles with several cracks, whereas the film deposited on the Si substrate was composed of very small and uniform particles. The films deposited on Si showed improved electrochemical properties, such as peak potential divergence and rate capability, over those for the alumina substrate electrode, which can be attributed to differences of the particle size, surface morphology, and the low electrical resistance of the current collector.

Effects of catalytic surface layer on Zr-based alloy getters for hydrogen absorption

Hydrogen sorption characteristics of Zr-based alloy getters fabricated in the forms of bulk were investigated. Non-evaporable getters (NEGs) have been widely used in vacuum devices, but thermal activation process at high temperature and high vacuum environment is inevitably required for efficient sorption rate. In order to solve this problem and improve sorption kinetics, we developed and characterized Ni-coated NEGs. Ni-coated NEGs show good gettering performance and fast sorption kinetics without any activation process, compared to conventional Zr-based NEGs. It is mainly caused by the catalytic effect of surface Ni layer. Surface Ni plays an important role as a catalyst that enables hydrogen to dissociate on surface more easily and also as a protection layer against oxidation. Consequently, Ni-coated NEGs can be easily applicable to vacuum devices because those need not go through the activation process and show fast hydrogen sorption kinetics.