Wan-Keun Kim

Effect of Al2O3 Coatings Prepared By RF Sputtering on Polyethylene Separators for High Power Lithium-Ion Batteries

In this study, we demonstrated the effects of aluminum oxide (Al2O3)-based ceramic coatings deposited by radio-frequency (RF) magnetron sputtering on commercial polyethylene (PE) microporous separators. Due to the superb thermal stability of the ceramic materials themselves, the Al2O3 coatings solved the chronic thermal shrinkage problem of PE separators. Separators with sputtered Al2O3 coatings maintained their initial dimensions even after high temperature exposure at 140 °C for 30 min. The sputtered Al2O3 layer effectively changed the surface of a PE separator from being hydrophobic to hydrophilic too, improving its wettability with liquid electrolyte. Additionally, a sputtered Al2O3 coating can improve the rate capability (~130%) compared with a bare PE separator under a high current density (7.75 mA cm-2, 5 C rate) because the layer does not require additional use of polymeric binder materials, which usually inhibit the formation of pore structures in microporous membranes.

Proton Conducting Membrane Based on Crosslinked Sulfonated Polyimide for Direct Methanol Fuel Cell

Crosslinked membrane based on sulfonated polyimide was prepared by the introduction of crosslinkable monomer in polymerization process and crosslinking during membrane casting. Crosslinked membranes showed different properties from non-crosslinked membranes. Crosslinking decreased methanol crossover and therefore unit cell using crosslinked membrane showed increased open circuit voltage, 0.81 V, in comparison with unit cell using noncrosslinked membrane, 0.71 V. In addition, water uptake of crosslinked membrane, 40.5%, was lower than that of non-crosslinked membrane, 57.0%, and this resulted in improved dimensional stability. However, proton conductivity of crosslinked membranes showed rather low relative to non-crosslinked membrane due to reduced water uptake.