Yuhong Oh

Ultrathin Zirconium Disulfide Nanodiscs

We present a colloidal route for the synthesis of ultrathin ZrS(2) (UT-ZrS(2)) nanodiscs that are ~1.6 nm thick and consist of approximately two unit cells of S-Zr-S. The lateral size of the discs can be tuned to 20, 35, or 60 nm while their thickness is kept constant. Under the appropriate conditions, these individual discs can self-assemble into face-to-face-stacked structures containing multiple discs. Because the S-Zr-S layers within individual discs are held together by weak van der Waals interactions, each UT-ZrS(2) disc provides spaces that can serve as host sites for intercalation. When we tested UT-ZrS(2) discs as anodic materials for Li(+) intercalation, they showed excellent nanoscale size effects, enhancing the discharge capacity by 230% and greatly improving the stability in comparison with bulk ZrS(2). The nanoscale size effect was especially prominent for their performance in fast charging/discharging cycles, where an 88% average recovery of reversible capacity was observed for UT-ZrS(2) discs with a lateral diameter of 20 nm. The nanoscale thickness and lateral size of UT-ZrS(2) discs are critical for fast and reliable intercalation cycling because those dimensions both increase the surface area and provide open edges that enhance the diffusion kinetics for guest molecules.

Effective wrapping of graphene on individual Li4Ti5O12 grains for high-rate Li-ion batteries

An effective way of synthesizing graphene-wrapped Li4Ti5O12 particles was developed by solid-state reaction between graphene oxide-wrapped P25 (TiO2) and Li2CO3. Compared to the previously reported graphene/Li4Ti5O12 composites, prior wrapping of TiO2 with subsequent chemical lithiation led to more effectively confined Li4Ti5O12. The Li4Ti5O12 tightly bound by graphene exhibited a remarkable specific capacity of 147 mA h g−1 at a rate of 10 C (1 C = 175 mA g−1) after 100 cycles. This rate capability is one of the highest values among reported Li4Ti5O12 with 150 ± 50 nm grains. The improved rate capability was attributed to the enhanced electronic conductivity of each Li4Ti5O12 grain via uniform graphene wrapping, with single-grain growth during annealing from the initial ∼25 nm TiO2 nanoparticles enclosed by outer graphene sheets. Graphene-eliminated Li4Ti5O12 by thermal decomposition was also directly compared to the graphene-coated sample, to clarify the role of graphene with nearly equivalent particle size/morphology distributions.

Nanoscale interface control for high-performance Li-ion batteries

AbstactLi-ion batteries have attracted great interest for the past decades, and now are one of the most important power sources for portable electronic devices, store electricity, hybrid electric vehicles (HEV), etc. However, Li-ion-battery technologies still have several problems related to the electrochemical performance (cycle-life performance and power density) or safety of the active electrode materials. There have been numerous breakthrough challenges to overcome these problems by extensive research. Among the various methods to improve the battery’s electrochemical properties, nanoscale coating on active materials and control of the nanostructured morphology were proven as effective approaches over the last decade. In this review paper, enhanced electrochemical properties of the cathode and anode materials via nanoscale interface modification and the respective enhancing mechanisms will be discussed.

Next-Generation Electrocatalysts

In this chapter, we provide a comprehensive review of the most recent advances in the field of efficient catalysts for oxygen reduction reaction (ORR ) at fuel-cell cathodes, metal-inorganic nanocomposites. Extensive research has been focused on developing alternative metal-inorganic composites with phosphate compounds. A few examples of ORR catalysts in the aqueous solution will be introduced to help researchers more effectively select composite materials and understand the important reactions involved in fuel cells.