• 멤브레인
• /
• 제30권5호
• /
• pp.307-318
• /
• 2020

기존의 바나듐 레독스 흐름전지(vanadium redox flow battery, VRFB)에서 사용하고 있는 과불소계이오노머인 나피온(Nafion)은 전해질에 존재하는 바나듐 이온의 투과도가 높아, 바나듐 이온이 분리막을 투과하여 반대쪽 전해질로 교차 이동하는 문제를 갖고 있다. VRFB에서 바나듐 이온의 투과는 서로 다른 산화수를 갖는 바나듐 이온이 부반응을 일으켜 충전, 방전 용량의 감소를 야기하고, 장기적인 성능 감소를 일으키는 원인이 된다. 이러한 문제를 해결하기 위해 본 연구에서는 SiO₂에 3-aminopropyl group이 도입된 나노입자(fS)를 Nafion에 분산시켜 바나듐 이온의 투과를 감소시키고, VRFB의 장기적인 성능의 향상을 도모하고자 하였다. SiO₂에 붙어 있는 아민기(-NH₂)가 Nafion의 술폰산 음이온(SO₃^-)과 이온결합을 형성함과 동시에, 암모늄 양이온(-NH₃⁺)의 양전하가 바나듐 이온에 대해 Gibbs-Donnan 효과를 나타내어 낼 것이라고 기대하였다. fS를 섞은 Nafion 용액의 pH와 Nafion-fS 막의 IEC 측정을 통해 암모늄 양이온과 술폰산 음이온의 이온결합이 존재하는 것을 확인하였고, fS의 양이 많아질수록 바나듐 이온의 투과도가 감소하는 것을 확인하였다. VRFB 단위 전지에 제조한 복합막을 도입하였을 때, 150 mA/㎠의 전류밀도에서 충방전 사이클을 200회 반복 진행하여도 방전용량을 최대 80%까지 유지할 수 있었다.

• Bulletin of the Korean Chemical Society
• /
• 제30권8호
• /
• pp.1733-1737
• /
• 2009

A new cathode material based on Li$Ni_{0.8}Co_{0.15}Al_{0.05}O_2$ (LNCA)/polyaniline (Pani) composite was prepared by in situ self-stabilized dispersion polymerization in the presence of LNCA. The materials were characterized by fourier transform infrared spectroscopy (FT-IR), ultraviolet-visible spectroscopy (UV-Vis), X-ray diffraction (XRD), and scanning electron microscopy (SEM). Electrochemical properties including galvanostatic charge-discharge ability, cyclic voltammetry (CV), capacity, cycling performance, and AC impedance were measured. The synthesized LNCA/Pani had a similar particle size to LNCA and exhibited good electrochemical properties at a high C rate. Pani (the emeraldine salt form) interacts with metal-oxide particles to generate good connectivity. This material shows good reversibility for Li insertion in discharge cycles when used as the electrode of lithium ion batteries. Therefore, the Pani coating is beneficial for stabilizing the structure and reducing the resistance of the LNCA. In particular, the LNCA/Pani material has advantageous electrochemical properties.

• 한국해양공학회지
• /
• 제16권6호
• /
• pp.60-64
• /
• 2002

This paper describes the machining characteristics of the MoSi$_2$--based composites through the process of electric discharge drilling with various tubular electrodes. In addition to hardness characteristics, microstructures of Nb/MoSi$_2$laminate composites were evaluated from the variation of fabricating conditions, such as preparation temperature, applied pressure, and pressure holding time. MoSi$_2$-based composites have been developed in new materials for jet engines of supersonic-speed airplanes and gas turbines for high-temperature generators. These high performance engines may require new hard materials with high strength and high temperature-resistance. Also, with the exception of grinding, traditional machining methods are not applicable to these new materials. Electric discharge machining (EDM) is a thermal process that utilizes a spark discharge to melt a conductive material. The tool electrode is almost -unloaded, because there is n direct contact between the tool electrode and the work piece. By combining a non-conducting ceramic with more conducting ceramic, it was possible to raise the electrical conductivity. From experimental results, it was found that the lamination from Nb sheet and MoSi$_2$ powder was an excellent strategy to improve hardness characteristics of monolithic MoSi$_2$. However, interfacial reaction products, like (Nb, Mo)SiO$_2$and Nb$_2$Si$_3$formed at the interface of Nb/MoSi$_2$, and increased with fabricating temperature. MoSi$_2$composites, with which a hole drilling was not possible through the conventional machining process, enhanced the capacity of ED-drilling by adding MbSi$_2$, relative to that of SiC or ZrO$_2$reinforcements.

• 한국세라믹학회지
• /
• 제43권2호
• /
• pp.121-125
• /
• 2006

[ $LiFePO_4$ ] is one of the promising materials for cathode material of secondary lithium batteries due to its high energy density, low cost, environmental friendliness and safety. $LiFePO_4$ was synthesized by the solid-state reaction method at 500 - 800°C. The crystal structure of $LiFePO_4$ was analyzed by X-ray powder diffraction. The samples synthesized at 600 and $700^{\circ}C$ showed a single phase of a olivine structure. The particle sizes were increased and the specific surface areas were decreased with heating temperatures. The electrochemical performance was investigated by coin cell test. The discharge capacities at 0.1 C-rate were 118 mAh/g and 112 mAh/g at $600^{\circ}C,\;700^{\circ}C$, respectively. In an attempt to improve the electrical conductivity of cathode materials, $LiFePO_4/graphite$ composite was prepared with various graphite contents. The electrical conductivity and discharge capacity were increased with increasing the graphite contents in composite samples. The rate capabilities at high current densities were also improved.

• 한국지반신소재학회논문집
• /
• 제8권2호
• /
• pp.41-46
• /
• 2009

본 논문에서는 연약지반개량을 위한 다짐말뚝공법들의 압밀촉진효과를 파악하기 위하여 일련의 실내모형실험을 실시하였다. 모형실험에서는 다짐말뚝의 재료로써 모래, 쇄석, 모래질 쇄석을 사용하여 치환율이 10%인 복합지반을 조성하였다. 각각의 복합지반에 하중을 재하 한 후 시간의 경과에 따른 침하량 및 점토부의 과잉간극수압 소산 거동을 관측하였으며 간극막힘 현상에 대한 검토를 위하여 압밀 종료 후 각각의 다짐말뚝에 대한 점토 혼입 양상을 관찰하였다. 실험 결과 쇄석다짐말뚝에 의한 침하저감효과와 압밀촉진효과가 가장 크게 나타났으며 압밀 종료 후 세 가지의 다짐말뚝 모두 점토의 혼입 양상은 관측되지 않았다.

• Progress in Superconductivity
• /
• 제14권1호
• /
• pp.60-65
• /
• 2012

A superconductor flywheel energy storage system (SFES) is an electro-mechanical battery which transforms electrical energy into mechanical energy for storage, and vice versa. A 35 kWh class SFES module was designed and constructed as part of a 100kWh/1MW class SFES composed of three 35 kWh class SFES modules. The 35 kWh class SFES is composed of a main frame, superconductor bearings, a composite flywheel, a motor/generator, electro-magnetic bearings, and a permanent magnet bearing. The high energy density composite flywheel is levitated by the permanent magnet bearing and superconductor bearings, while being spun by the motor/generator, and the electro-magnetic bearings are activated while passing through the critical speeds. Each of the main components was designed to provide maximum performance within a space-limited compact frame. The 35 kWh class SFES is designed to store 35 kWh, with a 350 kW charge/discharge capacity, in the 8,000 ~ 12,000 rpm operational speed range.

• Korean Chemical Engineering Research
• /
• 제55권4호
• /
• pp.483-489
• /
• 2017

The loss of the sulfur cathode material through dissolution of the polysulfide into electrolyte causes a significant capacity reduction of the lithium-sulfur cell during the charge-discharge reaction, thereby debilitating the electrochemical performance of the cell. We addressed this problem by using a chemical and physical approach called reduction of polysulfide dissolution through direct coating functional inorganic (graphene oxide) or organic layer (polyethylene oxide) on electrode, since the deposition of external functional layer can chemically interact with polysulfide and physically prevent the leakage of lithium polysulfide out of the electrode. Through this approach, we obtained a composite electrode for a lithium-sulfur battery (sulfur: 60%) coated with uniform and thin external functional layers where the thin external layer was coated on the electrode by solution coating and drying by a subsequent heat treatment at low temperature (${\sim}80^{\circ}C$). The external functional layer, such as inorganic or organic layer, not only alleviates the dissolution of the polysulfide electrolyte during the charging/discharging through physical layer formation, but also makes a chemical interaction between the polysulfide and the functional layer. As-formed lithium-sulfur battery exhibits stable cycling electrochemical performance during charging and discharging at a reversible capacity of 700~1187 mAh/g at 0.1 C (1 C = 1675 mA/g) for 30 cycles or more.

• 한국지반공학회:학술대회논문집
• /
• 한국지반공학회 2006년도 춘계 학술발표회 논문집
• /
• pp.1148-1154
• /
• 2006

Composite discharge capacity tests and smear effect tests are carried out to estimate the parameters for the reliability-based design of vertical drain method. Also the probabilistic and deterministic solutions of radial consolidation theory are presented. It compared to the result of reliability-based design and that of deterministic design using the tested and estimated parameters. The results indicated that the drain spacing is larger the deterministic method than the probabilistic method because the former is not considered the uncertainties in the properties of soil. The divergence of methods is dependent on the probability of achieving target degree of consolidation by a given time and the coefficient of variation(COV) of the coefficient of horizontal consolidation$(c_h)$.

• Macromolecular Research
• /
• 제10권5호
• /
• pp.273-277
• /
• 2002

Ultra-thin polymer films containing cobalt(II) meso-tetraphenylporphyrin(CoTPP) have been prepared by vacuum codeposition of the metal complex and trans-2-butene as an organic monomer using an inductively coupled RF glow discharge operating at 7-9 Watts. The polymer films were characterized by sorption measurements. Sorption data obtained for polymer films containing CoTPP indicate that the CoTPP molecules are capable of reversibly binding oxygen molecules. It was found that the adjacent CoTPP molecules in the aggregated metal complex phase could irreversibly share the oxygen molecules. A dispersion of the metal complex molecules in the polymer matrix was made to maintain the reversible reactivity of the metal complex molecules with oxygen in the polymer films via vacuum evaporation process. The Henry mode solubility constant, the Langmuir mode capacity constant, the amount of binding oxygen, and the dissociation equilibrium in the dual mode sorption theory were discussed.

• 대한전기학회:학술대회논문집
• /
• 대한전기학회 1997년도 하계학술대회 논문집 C
• /
• pp.1609-1611
• /
• 1997

We fabricated five type of electric double layer capacitor(EDLC) with extremely stable activated carbon as a positive and negative electrodes. The electrodes consisted of activated carbon and several different conductor layers on aluminium foil. Cyclic voltammogram of activated carbon electrodes at scan rate 5mV/sec was reversable redox reaction. The discharge capacity of activated carbon-KS 6 composite electrode was higher than that of activated carbon electrode without KS 6.