Sung Yeol Kim

Postdoctoral Associate
Ph.D. in Biomedical Engineering, Brown University (Providence, RI)
in Mechanical Engineering, KAIST (Dae-Jeon, Korea)
in Mechanical Engineering, KAIST

Layer-by-layer (LbL) assembly of nanomaterials for energy storage applications

Electric vehicles (EVs) and plug-in hybrid electric vehicles (PHEVs) are immerging as clean alternatives to the conventional internal combustion engine vehicles (ICEVs), reducing the emissions of green house gases and the consumption of oil. The success of EVs and PHEVs critically depends on the performance of the electrochemical energy devices (e.g. batteries, supercapacitors) powering these new vehicles.

Our ultimate goal is to develop an electrochemical energy storage device for EV and PHEV applications; the desired performance characteristics of such device include high energy density (>500Wh/l), high power density (>2.5W/l), good cycle life (>1000 cycles), and calendar life (>10 years). Also, to store and deliver enough energy (~2Ah to 4Ah) for the EV and PHEV applications, active materials coated on the electrodes have to be thick (~100um). To this end, we will use a spray-LbL technique to fabricate a thick electrode coating composed of nanomaterials (e.g. carbon nanotubes, graphene).

Carbon nanotube (CNT) is an attractive material for the energy devices because its favorable properties - high electronic conductivity, porous structure with high surface area, chemical and mechanical stability - can afford an electrode with high energy, high power, and excellent stability. The recent work in our group has successfully demonstrated that a thin multilayer of CNT (<3um) assembled thorough a dip-LbL method outperforms the most advanced electrode materials reported.1

The dipping method is only suitable for depositing thin LbL coatings due to its long process time, whereas a spray-LbL method is more efficient way of fabricating thick coatings.2 Therefore, in this project, a spray-LbL technique will be used to build up a thick CNT electrode for EV and PHEV applications. We will first investigate the effect of the process parameters of the spraying technique (e.g. spray pressure, pH of solution) on the growth and the structure of the CNT coating, and then the correlation between the structure (and the thickness) and the performance of the coating.

1. Lee, S. W.; Yabuuchi, N.; Gallant, B. M.; Chen, S.; Kim, B. S.; Hammond, P. T.; Shao-Horn, Y., High-power lithium batteries from functionalized carbon-nanotube electrodes. Nat. Nanotechnol. 2010, 5 (7), 531-537. 2. Krogman, K. C.; Lowery, J. L.; Zacharia, N. S.; Rutledge, G. C.; Hammond, P. T., Spraying asymetry into functional membranes layer-by-layer. Nat. Mater. 2009, 8 (6), 512-518.