Tae-Heum Nam

Electrochemical Performance of Li-Ion Batteries Containing Biphenyl, Vinyl Ethylene Carbonate in Liquid Electrolyte

This paper investigated the electrochemical behavior and thermal properties of vinyl ethylene carbonate (VEC) and biphenyl (BP) additives with triphenyl phosphate (TPP)-based, nonflammable electrolytes for Li-ion batteries. Mesocarbon microbeads and LiCoO 2 were used as the anode and cathode materials, respectively. The main analysis tools were cyclic voltammetry, differential scanning calorimetry, electrochemical impedance spectroscopy, and scanning electron microscopy. The results showed that the oxidizing potential of VEC and BP is about 4.9 and 4.6 V vs LilLi + , respectively, in TPP-containing electrolytes. Consequently, we found that the addition of 0.1 wt % BP to TPP-based electrolytes improved the cell performance and thermal stability of electrolytes for Li-ion batteries.

Corrosion Behavior of Aluminum Alloy for Heat Exchanger in an Exhaust Gas Recirculation System of Diesel Engine

This study examines the corrosion behavior of aluminum alloys in condensed water containing different concentrations of anions for a heat exchanger in an automotive exhaust gas recirculation (EGR) system of a diesel engine. Electrochemical measurements and bulk analyses revealed that the aluminum alloy is protected by the adsorption of increased nitrite and nitrate ions contained in condensed water, despite increased detrimental sulfate ions at high EGR rates. The mechanism of the beneficial anions, which are nitrite and nitrate on aluminum alloy in condensed water, was spontaneous physical adsorption (physisorption).

Mechanism of Corrosion Fatigue Cracking of Automotive Coil Spring Steel

The AISI 300M ultra-high strength steel was applied for the automotive suspension coil spring. Recently, some premature failures were reported, which caused by synergistic effect of cyclic mechanical stress and corrosion, namely corrosion fatigue cracking. In this study, the accurate mechanism of corrosion fatigue cracking for coil spring steel was studied for the proper prevention method against the catastrophic failure. Fatigue life was evaluated in 5 wt% NaCl solution under the anodic dissolution and hydrogen embrittlement conditions, which is simulated by applying constant potentials. Scanning electron microscopy and energy dispersive X-ray spectroscopy analysis indicated that the corrosion fatigue cracking was initiated at the MnS inclusion of the pit initiation site. The calculation of hydrogen production corresponding to each corrosion fatigue test condition revealed the two operating mechanisms of the cracking process. The corrosion fatigue cracking failure of coil spring steel was mainly caused by the anodic dissolution combined with hydrogen embrittlement.