Kang-Seop Yun

Enhanced Water Splitting by Fe2O3-TiO2-FTO Photoanode with Modified Energy Band Structure

The effect of TiO2 layer applied to the conventional Fe2O3/FTO photoanode to improve the photoelectrochemical performance was assessed from the viewpoint of the microstructure and energy band structure. Regardless of the location of the TiO2 layer in the photoanodes, that is, Fe2O3/TiO2/FTO or TiO2/Fe2O3/FTO, high performance was obtained when α-Fe2O3 and H-TiNT/anatase-TiO2 phases existed in the constituent Fe2O3 and TiO2 layers after optimized heat treatments. The presence of the Fe2O3 nanoparticles with high uniformity in the each layer of the Fe2O3/TiO2/FTO photoanode achieved by a simple dipping process seemed to positively affect the performance improvement by modifying the energy band structure to a more favorable one for efficient electrons transfer. Our current study suggests that the application of the TiO2 interlayer, together with α-Fe2O3 nanoparticles present in the each constituent layers, could significantly contribute to the performance improvement of the conventional Fe2O3 photoanode.

Microstructural Effect of Carbon Blacks for the Application in Lithium Ion Batteries

Carbon blacks commercially available (Super P, SP and Ketjen black, KB) and synthesized by a liquid phase plasma process (SC) were compared for the lithium ion battery applications as an anode material. All the carbon black samples were spherical with sizes in the range of 30–50 nm. The Brunauer–Emett–Teller (BET) specific surface areas of the SP, KB, and SC samples were measured to be 62, 1452, and 895 m2/g, respectively. The overall fraction of the ordered structure, represented by the ratio of the G-band to the D-band (G/D raio) from Raman spectra, was highest for the SC sample. A large specific surface area of the samples was found to play an important role in storing lithium ions, contributing to high initial charge capacities, 2050 mAh/g for KB and 1542 mAh/g for SC. The initial charge–discharge coulombic efficiency of the samples was strongly influenced by the solid electrolyte interface (SEI) formation behavior. The behavior of SEI formation seemed to be affected by the microstructural characteristics of the carbon blacks such as crystallinity and G/D ratio. The SC sample having a high G/D ratio and a slight variation without a peak of dQ/dV with potential showed a small initial capacity irreversibility.

Simulation Protocol for Prediction of a Solid-Electrolyte Interphase on the Silicon-based Anodes of a Lithium-Ion Battery: ReaxFF Reactive Force Field

We propose the ReaxFF reactive force field as a simulation protocol for predicting the evolution of solid-electrolyte interphase (SEI) components such as gases (C2H4, CO, CO2, CH4, and C2H6), and inorganic (Li2CO3, Li2O, and LiF) and organic (ROLi and ROCO2Li: R = -CH3 or -C2H5) products that are generated by the chemical reactions between the anodes and liquid electrolytes. ReaxFF was developed from ab initio results, and a molecular dynamics simulation with ReaxFF realized the prediction of SEI formation under real experimental conditions and with a reasonable computational cost. We report the effects on SEI formation of different kinds of Si anodes (pristine Si and SiOx), of the different types and compositions of various carbonate electrolytes, and of the additives. From the results, we expect that ReaxFF will be very useful for the development of novel electrolytes or additives and for further advances in Li-ion battery technology.

Electrochemical properties of the TiO2(B) powders ball mill treated for lithium-ion battery application

BackgroundBelt or wire shaped TiO2(B) particles were synthesized for lithium ion battery application by a hydrothermal and heat treatment process. In order to facilitate TiO2(B)/C composites fabrication, the synthesized TiO2(B) particles were crushed into smaller sizes by ball milling.ResultsBall mill treated TiO2(B) particles of less than 1.0 μm with a fraction of anatase phase, compared to as-synthesized TiO2(B) particles with about 24 μm in average particle size, showed a significant improvement in the electrochemical properties. They showed a much improved stability in the charge–discharge cycles and irreversibility. They maintained about 98% of the initial capacity during 50 cycles while as-synthesized sample before ball mill treatment showed a gradual decrease in the capacity with the cycles. The irreversibility of 12.4% of as-synthesized sample was also greatly improved to 7% after ball milling treatment.ConclusionsOur results indicate ball mill treatment can be an economical way to improve electrochemical properties of TiO2(B) anode materials for lithium ion battery application.

Electrochemical properties of chemically processed SiO x as coating material in lithium-ion batteries with Si anode.

A SiOx coating material for Si anode in lithium-ion battery was processed by using SiCl4 and ethylene glycol. The produced SiOx particles after heat treatment at 725°C for 1 h were porous and irregularly shaped with amorphous structure. Pitch carbon added to SiOx was found to strongly affect solid electrolyte interphase stabilization and cyclic stability. When mixed with an optimal amount of 30 wt% pitch carbon, the SiOx showed a high charge/discharge cyclic stability of about 97% for the 2nd to the 50th cycle. The initial specific capacity of the SiOx was measured to be 1401 mAh/g. On the basis of the evaluation of the SiOx coating material, the process utilized in this study is considered an efficient method to produce SiOx with high performance in an economical way.

Effect of Processing Parameters on the Microstructure and Band Gap Energy of 1D-Na 2 Ti 6 O 13

Nano-structured one-dimensional particles were synthesized by a molten salt process. Effects of processing parameters on the microstructure and band gap energy of the powder were studied in this paper. For the synthesis of the particles, two different raw materials of tubular shaped Na-titanate (Na-TiNT) and spherical shaped were utilized. Synthesizing with the raw material of Na-TiNT, around 70nm thick 1D- with the bandgap energy of 3.5 eV was obtained at . Below or without the presence of NaCl, 1D- was in a relatively short in length and agglomerated state. With the processing temperature increased, the thickness of the 1D- was also observed to be increased. On the other hand, when was employed as a raw material, the mixed amount of played an important role in transforming the morphology and phase of the raw material, affecting the bandgap energy of the synthesized product. Specific surface area of the synthesized 1D- was significantly affected by the raw and mixed materials as well as processing temperature. When Na-TiNT was processed at with NaCl, the specific surface area of the 1D- showed the best value of 30.63 .