Taejoo Lee

Measurement and Analysis of Adhesion Property of Lithium-Ion Battery Electrodes with SAICAS

The adhesion strength of lithium-ion battery (LIB) electrodes consisting of active material, a nanosized electric conductor, and a polymeric binder is measured with a new analysis tool, called the Surface and Interfacial Cutting Analysis System (SAICAS). Compared to the conventional peel test with the same electrode, SAICAS gives higher adhesion strength owing to its elaborate cutting-based measurement system. In addition, the effects on the adhesion property of the polymeric binder type and content, electrode density, and measuring point are also investigated to determine whether SAICAS provides reliable results. The findings confirm SAICAS as an effective and promising tool to measure and analyze the adhesion properties of LIB electrodes.

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.

A facile approach to prepare biomimetic composite separators toward safety-enhanced lithium secondary batteries

A mussel-inspired polydopamine (PDA) coating turns radio-frequency (RF) Al2O3 sputtering – which thus far has not been appropriate for the surface treatment of porous polyolefin-based separators – into a damage-free, reliable, and cost-efficient process. Due to the thermally resistive PDA layers, polyethylene (PE) separators can sustain high-power Al2O3 sputtering conditions over 75 W, which significantly reduces processing time. Furthermore, compared to the as-prepared separators, PDA/Al2O3-coated PE separators also reveal improved thermal stability and cycle performance for lithium secondary batteries. PDA/Al2O3-coated PE separators retained their original size when exposed to temperatures of 145 °C over 30 min, while the bare PE separators shrank to 9% of their original size. At a temperature of 25 °C, the unit cell (LiMn2O4/separator/Li metal) employing the PDA/Al2O3-coated PE separators maintained 94.8% (103.4 mA h g−1) of the initial discharge capacity after 500 cycles at C/2 rate and 51.7% (56.7 mA h g−1) at 25 C rate, while the corresponding values for the bare PE separators were 89% (98.6 mA h g−1) at C/2 rate and 24.5% (27.2 mA h g−1) at 25 C rate.