Songhun Yoon

Electric Double‐Layer Capacitor Performance of a New Mesoporous Carbon

A new mesoporous carbon (NMC) was prepared, and its performance in an electric double-layer capacitor (EDLC) was compared to that of a conventional carbon (a molecular-sieving carbon, MSC25). The effect of pore size and pore connection pattern on EDLC performance was demonstrated. To prepare NMC, phenol resin was synthesized inside the pores of an inorganic template, Mobile Composite Material 48 (MCM48), and the resulting resin-template composite was carbonized at 700°C under Ar atmosphere. A coke-like carbonaceous material was obtained after removing the inorganic template by HF treatment. The surface area of NMC was 1257 m 2 g -1 which is smaller than that of MSC25 (1970 m 2 g -1 ) NMC had three-dimensionally interconnected mesopores (2.3 nm average diam), but randomly connected cage-like micropores (<2.0 nm) were dominant in MSC25. The difference in the pore size and pore connection pattern between the two carbons gave rise to a remarkable difference in their EDLC performances. NMC exhibited a smaller specific capacitance (about 120 F g - 1 ) than MSC25 as a result of its smaller surface area, but it showed a higher critical scan rate than the MSC25 electrode due to a smaller resistance-capacitance (RC) time constant. The specific charging capacity of the NMC electrode was about 20 mAh g -1 and was largely invariant vs. the charge-discharge rate. This was contrasted by MSC25 which showed a steadily decreasing capacity with an increase in rate. As a result, the NMC electrode outperformed the MSC25 based on rate capability. The smaller RC time constant and better rate capability of the NMC electrode apparently arises from the lower electrolyte resistance in pores, which in turn stems from the faster ionic motion in larger pores.

Synthesis of a new mesoporous carbon and its application to electrochemical double-layer capacitors

A mesoporous carbon with regular three-dimensionally interconnected 2 nm pore arrays using AlMCM-48 as a template has been synthesised; the mesoporous carbon exhibited excellent performance as an electrochemical double layer capacitor.

Advanced Hybrid Supercapacitor Based on a Mesoporous Niobium Pentoxide/Carbon as High-Performance Anode

Recently, hybrid supercapacitors (HSCs), which combine the use of battery and supercapacitor, have been extensively studied in order to satisfy increasing demands for large energy density and high power capability in energy-storage devices. For this purpose, the requirement for anode materials that provide enhanced charge storage sites (high capacity) and accommodate fast charge transport (high rate capability) has increased. Herein, therefore, a preparation of nanocomposite as anode material is presented and an advanced HSC using it is thoroughly analyzed. The HSC comprises a mesoporous Nb2O5/carbon (m-Nb2O5-C) nanocomposite anode synthesized by a simple one-pot method using a block copolymer assisted self-assembly and commercial activated carbon (MSP-20) cathode under organic electrolyte. The m-Nb2O5-C anode provides high specific capacity with outstanding rate performance and cyclability, mainly stemming from its enhanced pseudocapacitive behavior through introduction of a carbon-coated mesostructure within a voltage range from 3.0 to 1.1 V (vs Li/Li(+)). The HSC using the m-Nb2O5-C anode and MSP-20 cathode exhibits excellent energy and power densities (74 W h kg(-1) and 18,510 W kg(-1)), with advanced cycle life (capacity retention: ∼90% at 1000 mA g(-1) after 1000 cycles) within potential range from 1.0 to 3.5 V. In particular, we note that the highest power density (18,510 W kg(-1)) of HSC is achieved at 15 W h kg(-1), which is the highest level among similar HSC systems previously reported. With further study, the HSCs developed in this work could be a next-generation energy-storage device, bridging the performance gap between conventional batteries and supercapacitors.

Facile Synthesis of Nb2O5@Carbon Core–Shell Nanocrystals with Controlled Crystalline Structure for High-Power Anodes in Hybrid Supercapacitors

Hybrid supercapacitors (battery-supercapacitor hybrid devices, HSCs) deliver high energy within seconds (excellent rate capability) with stable cyclability. One of the key limitations in developing high-performance HSCs is imbalance in power capability between the sluggish Faradaic lithium-intercalation anode and rapid non-Faradaic capacitive cathode. To solve this problem, we synthesize Nb2O5@carbon core-shell nanocyrstals (Nb2O5@C NCs) as high-power anode materials with controlled crystalline phases (orthorhombic (T) and pseudohexagonal (TT)) via a facile one-pot synthesis method based on a water-in-oil microemulsion system. The synthesis of ideal T-Nb2O5 for fast Li(+) diffusion is simply achieved by controlling the microemulsion parameter (e.g., pH control). The T-Nb2O5@C NCs shows a reversible specific capacity of ∼180 mA h g(-1) at 0.05 A g(-1) (1.1-3.0 V vs Li/Li(+)) with rapid rate capability compared to that of TT-Nb2O5@C and carbon shell-free Nb2O5 NCs, mainly due to synergistic effects of (i) the structural merit of T-Nb2O5 and (ii) the conductive carbon shell for high electron mobility. The highest energy (∼63 W h kg(-1)) and power (16 528 W kg(-1) achieved at ∼5 W h kg(-1)) densities within the voltage range of 1.0-3.5 V of the HSC using T-Nb2O5@C anode and MSP-20 cathode are remarkable.

Preparation of Nanotube TiO2-Carbon Composite and Its Anode Performance in Lithium-Ion Batteries

This research was supported by a grant from the Fundamental Research and Development Program for Core Technology of Materials funded by the Ministry of Knowledge Economy, Republic of Korea.

TiO2 nanodisks designed for Li-ion batteries: a novel strategy for obtaining an ultrathin and high surface area anode material at the ice interface

A rapid and relatively large-scale production of ultrathin TiO2 nanodisks was achieved under mild conditions by developing a novel and simple sol–gel process occurring at the interface of an organic solvent and ice. Owing to the ultrathin structure and unusually high surface area (>400 m2 g−1), the TiO2 nanodisks exhibited high reversible capacity (191.4 mA h g−1 at 0.2 C) and excellent rate performance (58% capacity retention at 20 C) as an anode in lithium ion batteries.

Ordered mesoporous WO3-x possessing electronically conductive framework comparable to carbon framework toward long-term stable cathode supports for fuel cells

We report on the successful synthesis of ordered mesoporous WO3−X with a high conductivity comparable to a mesoporous carbon framework. Ordered mesoporous WO3−X was prepared using KIT-6 as a hard template. Some WO3−X particles have negative replica structures of KIT-6 template and the other particles are generated by asymmetric incorporation of phosphotungstic acid inside channels of KIT-6 template. The wall of this mesostructured WO3−X has a single crystalline structure, which might be responsible for its high conductivity (1.76 S cm−1) comparable to ordered mesoporous carbons (3.0 S cm−1). Pt/mesoporous WO3−X exhibits a significant tolerance to cycling between 0.6 and 1.3 VNHE in 0.5 M H2SO4 solution, preserving 87% of its initial electrochemical surface area (ECSA) after 1000 cycles. On the contrary, the ECSA of the Pt/C decreased significantly with the number of cycles, resulting in loss of 74% of its initial ECSA.

Reverse micelle synthesis of colloidal nickel-manganese layered double hydroxide nanosheets and their pseudocapacitive properties.

Colloidal nanosheets of nickel-manganese layered double hydroxides (LDHs) have been synthesized in high yields through a facile reverse micelle method with xylene as an oil phase and oleylamine as a surfactant. Electron microscopy studies of the product revealed the formation of colloidal nanoplatelets with sizes of 50-150 nm, and X-ray diffraction, energy dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy studies showed that the Ni-Mn LDH nanosheets had a hydrotalcite-like structure with a formula of [Ni3 Mn(OH)8 ](Cl(-) )⋅n H2 O. We found that the presence of both Ni and Mn precursors was required for the growth of Ni-Mn LDH nanosheets. As pseudocapacitors, the Ni-Mn LDH nanosheets exhibited much higher specific capacitance than unitary nickel hydroxides and manganese oxides.

Method of Preparation for Particle Growth Enhancement of LiNi0.8Co0.15Al0.05O2

Herein, a preparation method of a Ni-rich cathode material in a lithium-ion battery is presented. Using the separate addition of A1 hydroxide sol to a Ni/Co sulfate solution, monodispersed large particles of Ni 0.8 Co 0.15O Al 0.05 hydroxide were prepared in a shorter retention time within a continuously stirred tank reactor. The electrochemical test of a cathode fabricated with as-prepared material exhibited a good discharge capacity (190 mA g -1 ), high initial efficiency (90.3%), high rate capability, and stable cyclability even though it was composed of larger particles. The improved performances in this work were probably attributable to the uniform dispersion of A1 atoms within LNi 0.8 Co 0.15 Al 0.05 O 2 particles and the well-developed layered structure.

Influence of Particle Size on Rate Performance of Mesoporous Carbon Electric Double-Layer Capacitor (EDLC) Electrodes

Herein, mesoporous carbon materials with different particle sizes were prepared using the direct templating method. To control particle size, the concentration of surfactant/silicate dissolved in aqueous solution was varied. According to a decrease in the concentration, a larger surface area and a smaller particle size were observed, whereas pore size and connectivity remained invariant. From the investigation of electric double-layer capacitor performance, specific capacitance was proportional to surface area. From electrochemical impedance spectroscopy analysis, a resistance relevant to pseudocapacitive faradaic reaction on electrode surface became larger, but a decrease in the total electrolyte resistance in pores was observed as a function of particle size decrease. This contradictory behavior of two resistances resulted in an existence of optimal particle size for the minimum equivalent series resistance (1.40 Ω cm 2 ), which was comparable with the ordered mesoporous carbon electrode from the MCM-48 template.