• Journal of the Korean Electrochemical Society
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• v.17 no.4
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• pp.237-244
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• 2014

We report novel and simple structure of supercapacitors fabricated by using flexible glass fibre separators as templates. This method does not require separate electrodes, binders and high pressure/temperature to build the supercapacitor unit cells as required by the conventional technology. The supercapacitors were fabricated by drop-casting solution mixtures of carbonaceous active materials/gel electrolytes onto two sides of glass fibre separators. Two carbonaceous materials (nanoscaled activated carbons, multi-walled carbon nanotubes) were investigated as electrode materials. The electrochemical measurements reveal that the separatorbased supercapacitors using ACs successfully demonstrated significant mass specific capacitance ($22.3F\;g^{-1}$) and energy density ($9.7Wh\;kg^{-1}$), indicating this method can be useful in fabricating flexible, wearable and stretchable energy storage devices in more straightforward and cost-effective way than current technology.

• Nano
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• v.13 no.12
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• pp.1850138.1-1850138.6
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• 2018

Two-dimensional (2D) or layered materials have a great potential for applications in energy storage, catalysis, optoelectronics and gas separation. Fabricating novel 2D or quasi-2D layered materials composed of relatively abundant and inexpensive atomic species is an important issue for practical usage in industry. Here, we suggest the layer-structured AlOOH (Boehmite) as a promising candidate for such applications. Boehmite is a well-known layer-structured material and a single-layer can be exfoliated from the bulk boehmite by breaking the interlayer hydrogen bonding. We study atomic and electronic band structures of both bulk and single-layer boehmite, and also obtain the single-layer exfoliation energy using first-principles calculations.

• Applied Chemistry for Engineering
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• v.29 no.6
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• pp.635-644
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• 2018

Lithium ion batteries have been broadly used in various applications to our daily life such as portable electronics, electric vehicles and grid-scale energy storage devices. Significant efforts have recently been made on developing electrode materials for lithium ion batteries that meet commercial needs of the high energy density, light weight and low cost. In this review, we summarize the principles and recent research advances in cathode and anode materials for lithium ion batteries, and particularly emphasize electrode material designs and advanced characterization techniques.

• Journal of Electrochemical Science and Technology
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• v.12 no.2
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• pp.212-216
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• 2021

We investigated the feasibility of hydrogen storage with electrochemically formed VO₂ nanotubes. The VO₂ nanotubes were fabricated through the anodization of vanadium metal in fluoride ion-containing organic electrolyte followed by an annealing process in an Ar-saturated atmosphere at 673 K for 3 h at a heating rate of 3 K /min. During anodization, the current density significantly increased up to 7.93 mA/cm² for approximately 500 s owing to heat generation, which led to a fast-electrochemical etching reaction of the outermost part of the nanotubes. By controlling the anodization temperature, highly ordered VO₂ nanotubes were grown on the metal substrate without using any binders or adhesives. Furthermore, we demonstrated the hydrogen sorption properties of the anodic VO₂ nanotubes.

• Applied Chemistry for Engineering
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• v.34 no.4
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• pp.365-382
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• 2023

A lithium metal anode with high energy density has the potential to revolutionize the field of energy storage systems (ESS) and electric vehicles (EVs) that utilize rechargeable lithium-based batteries. However, the formation of lithium dendrites during cycling reduces the performance of the battery while posing a significant safety risk. In this review, we discuss various strategies for achieving dendrite-free lithium metal anodes, including electrode surface modification, the use of electrolyte additives, and the implementation of protective layers. We analyze the advantages and limitations of each strategy, and provide a critical evaluation of the current state of the art. We also highlight the challenges and opportunities for further research and development in this field. This review aims to provide a comprehensive overview of the different approaches to achieving dendrite-free lithium metal anodes, and to guide future research toward the development of safer and more efficient lithium metal anodes.

• Carbon letters
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• v.12 no.4
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• pp.236-242
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• 2011

The oxyfluorination effects of activated carbon nanofibers (OFACFs) were investigated for $CO_2$ storage. Electrospun CFs were prepared from a polyacrylonitrile/N,N-dimethylformamide solution via electrospinning and heat treatment. The electrospun CFs were chemically activated in order to generate the pore structure, and then oxyfluorination was used to modify the surface. The samples were labeled CF (electrospun CF), ACF (activated CF), OFACF-1 ($O_2:F_2$ = 7:3), OFACF-2 ($O_2:F_2$ = 5:5) and OFACF-3 ($O_2:F_2$ = 3:7). The functional group of OFACFs was investigated using X-ray photoelectron spectroscopy analysis. The C-F bonds formed on surface of ACFs. The intensities of the C-O peaks increased after oxyfluorination and increased the oxygen content in the reaction gas. The specific surface area, pore volume and pore size of OFACFs were calculated by the Brunauer-Emmett-Teller and density functional theory equation. Through the $N_2$ adsorption isotherm, the specific surface area and pore volume slightly decreased as a result of oxyfluorination treatment. Nevertheless, the $CO_2$ adsorption efficiency of oxyfluorinated ACF improved around 16 wt% due to the semi-ionic interaction effect of surface modificated oxygen functional groups and $CO_2$ molecules.

• Journal of Hydrogen and New Energy
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• v.7 no.2
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• pp.181-191
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• 1996

Samples with the compositions of Mg-10wt.%Ni and Mg-25wt.%Ni were prepared by mechanical alloying in a planetary mill. $Mg_2Ni$ phase was formed in the mixture with hydriding dehydriding cycling. The activation of Mg-10wt.%Ni and Mg-25wt.%Ni was completed after n=7 and n=6 around, respectively, at 583K, $0{\sim}8barH_2$. Mg-10wt.% Ni and Mg-25wt. %Ni are considered as excellent hydrogen-storage materials with very high hydriding rates, high dehydriding rates and relatively large hydrogen-storage capacity. The effets of mechanical alloying and hydriding dehydriding cycling are considered the augmentation in the density of active nucleation sites and the diminution in the particle size.

• Korean Chemical Engineering Research
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• v.51 no.5
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• pp.602-608
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• 2013

Gas hydrate studies are attracting attention of many researchers as an innovative, economic and environmentally friendly technology when it is applied to $CO_2$ capture, transport, and storage. In this study, we investigated whether $CO_2$ hydrate shows the self-preservation effect or not, that is the key property for developing a novel $CO_2$ transport/storage method. Especially the degree of self-preservation effect for $CO_2$ hydrate was studied according to the particle size of $CO_2$ hydrate samples. We prepared three kinds of $CO_2$ hydrate samples varying their particle diameter as millimeter, micron and nano size and measured their change of weight at $-15{\sim}-30^{\circ}C$ under atmospheric pressure during 3 weeks. According to our experimental result, the lower temperature, larger particle size, and compact structure for higher density are the better conditions for obtaining self-preservation effect.

• The Transactions of the Korean Institute of Power Electronics
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• v.23 no.3
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• pp.161-167
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• 2018

In battery-operated systems, an isolated converter is used to interface the utility grid with the system to increase stability when charging and discharging batteries. Systems such as vehicle-to-grids (V2Gs), on-board chargers, and energy storage systems (ESSs) have recently become popular, and the roles of isolated converters have become important considerations in fabricating such devices. A fixed-frequency LLC converter, which is a type of isolated converter, presents the advantages of high efficiency and high power density by performing zero-voltage switching (ZVS) over wide frequency ranges. However, the magnetizing inductance of the LLC converter should be designed to enable ZVS in all switching devices. Therefore, in this study, the operating characteristics of the LLC circuit are analyzed, and an optimal design method for ZVS operation is established. Moreover, an 8 kW LLC high-efficiency and high-power-density resonant converter is designed and tested for ESS application. The LLC converter achieves 98% efficiency at rated power.

• Advances in materials Research
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• v.1 no.4
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• pp.245-268
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• 2012

Results of isothermal torsional oscillation tests are reported on melts of linear low density polyethylene and isotactic polypropylene. Prior to rheological tests, specimens were annealed at various temperatures ranging from $T_a$ = 180 to $310^{\circ}C$ for various amounts of time (from 30 to 120 min). Thermal treatment induced degradation of the melts and caused pronounced decreases in their molecular weights. With reference to the concept of transient networks, constitutive equations are developed for the viscoelastic response of polymer melts. A melt is treated as an equivalent network of strands bridged by junctions (entanglements and physical cross-links). The time-dependent response of the network is modelled as separation of active strands from and merging of dangling strands with temporary nodes. The stress-strain relations involve three adjustable parameters (the instantaneous shear modulus, the average activation energy for detachment of active strands, and the standard deviation of activation energies) that are determined by matching the dependencies of storage and loss moduli on frequency of oscillations. Good agreement is demonstrated between the experimental data and the results of numerical simulation. The study focuses on the effect of molecular weight of polymer melts on the material constants in the constitutive equations.