• Carbon letters
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• 제26권
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• pp.81-87
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• 2018

Morphological differences in multi-layered graphene flakes or graphene nanoplatelets prepared by oxidative (rGO-NP, reduced graphene oxide-nanoplatelets) and non-oxidative (GIC-NP, graphite intercalation compound-nanoplatelets) routes were investigated with various analytical methods. Both types of NPs have similar specific surface areas but very different structural differences. Therefore, this study proposes an effective and simple method to identify structural differences in graphene-like allotropes. The adsorptive potential peaks of rGO-NP attained by the density functional theory method were found to be more scattered over the basal and non-basal regions than those of GIC-NP. Raman spectra and high resolution TEM images showed more distinctive crystallographic defects in the rGO-NP than in the GIC-NP. Because the R-ratio values of the edge and basal plane of the sample were maintained and relatively similar in the rGO-NP (0.944 for edge & 1.026 for basal), the discrepancy between those values in the GIC-NP were found to be much greater (0.918 for edge & 0.164 for basal). The electrical conductivity results showed a remarkable gap between the rGO-NP and GIC-NP attributed to their inherent morphological and crystallographic properties.

• 융합정보논문지
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• 제8권5호
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• pp.95-100
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• 2018

금속 산화물/그래핀 형태의 복합 나노소재는 높은 전기용량을 갖는 2차 전지의 전극용 소재 또는 고감도 가스 센서의 감지물질 등으로 활용되는 매우 유용한 기능성 소재이다. 본 논문에서는 열 화학기상증착(CVD, Chemical Vapor Deposition)으로 Cu Foil 위에 대면적으로 합성된 CVD 그래핀 및 고정렬 열분해 흑연(HOPG, Highly Oriented Pyrolytic Graphite)으로부터 기계적으로 박리된 그래핀 기판 위에 이산화바나듐($VO_2$) 나노구조물을 기상수송방법으로 직접 성장시키는 연구를 수행하였다. 연구결과 CVD 그래핀 기판의 경우, 그래핀 결정 경계에서 상대적으로 많이 존재하는 기능기들이 $VO_2$ 나노구조물에서 핵형성의 씨앗으로 작용하는 것이 확인되었다. 반면에 HOPG에서 기계적으로 박리된 그래핀 나노시트 표면에는 기능기가 균일하게 분포하기 때문에, 2차원과 3차원 형태로 $VO_2$ 나노구조물이 성장되었다. 이러한 연구결과는 고기능성 $VO_2$/그래핀 나노복합소재를 이용하여 높은 전기용량을 갖는 2차 전지 전극소재 및 고감도 가스 센서의 감지물질 합성에 유용하게 활용될 것으로 전망된다.

• 전기화학회지
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• 제11권4호
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• pp.242-255
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• 2008

1991년 lithium-ion battery(LIB)가 상용화된 이후, 초기 전해질은 주로 lithium cobalt oxide($LiCoO_2$) 양극과 graphite 음극의 특성에 집중되어 연구되어 왔다. 또한 전극과 전해질 간의 적합성에 대한 다양한 연구들이 이들 간의 계면에서 활발히 진행되었다. 이후 Si, Sn 등의 비탄소계 음극소재와 3성분(Ni, Mn, Co)계, spinel, olivine 등의 양극 소재를 리튬 2차전지에 채용하려 함에 따라 기존 전해질 재료들도 많은 도전에 직면하게 되었다. 특히, 안전성 문제가 최근 심각하게 부각됨에 따라 전해질의 요구특성은 점점 복잡해지고 까다로워지고 있다. 본 고에서는 이러한 전극소재 변화에 따른 전해질 소재의 다양한 변화와 그 특성에 대하여 구성요소 별로 연구 및 개발 동향을 정리하였다.

• 공업화학
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• 제24권5호
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• pp.489-493
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• 2013

기존의 EDLC용 활성탄소 대신 리튬이차전지용 탄소류 음전극(천연흑연, 인조흑연, 하드카본, MCMB)을 이용해 리튬이온 커패시터를 구성하면 리튬의 층간 삽입반응으로 인해 기존의 물질보다 에너지 밀도가 큰 전극소재를 개발할 수 있을 것이다. 이 실험에서는 기존 리튬이차전지 음극용 탄소 물질을 대칭 전극으로 사용하여 코인형 커패시터를 제조하여 성능을 측정하였다. 또한 리튬을 미리 삽입시킨 탄소류 전극을 이용한 커패시터를 제조한 후 성능을 측정한 결과, 축전현상이 일어나는 것을 알 수 있었다. 즉 전해액에서 전하분리에 의한 리튬이온의 이동을 보충할 수 있다면 기존의 리튬이온은 탄소류 전극의 층간으로 확산되어 들어가 기존의 대칭성 탄소류 전극의 경우에 비해 축전 용량이 증가한다. 또한 표면적이 매우 큰 graphene oxide를 사용하여 위와 같이 실험한 결과 용량이 크게 나왔으며 이로부터 슈퍼커패시터 전극용 물질에는 높은 비표면적이 중요한 요소로 작용한다는 것을 알 수 있었다.

• 한국재료학회:학술대회논문집
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• 한국재료학회 2012년도 춘계학술발표대회
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• pp.73-73
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• 2012

Modern technology-driven society largely relies on hybrid electric vehicles or electric vehicles for eco-friendly transportation and the use of high technology devices. Lithium rechargeable batteries are the most promising power sources because of its high energy density but still have a challenge. Graphite is the most widely used anode material in the field of lithium rechargeable batteries due to its many advantages such as good cyclic performances, and high charge/discharge efficiency in the initial cycle. However, it has an important safety issue associated with the dendritic lithium growth on the anode surface at high charging current because the conventional graphite approaches almost 0 V vs $Li/Li^+$ at the end of lithium insertion. Therefore, a fundamental solution is to use an electrochemical redox couple with higher equilibrium potentials, which suppresses lithium metal formation on the anode surface. Among the candidates, $Li_4Ti_5O_{12}$ is a very interesting intercalation compound with safe operation, high rate capability, no volume change, and excellent cycleability. But the insulating character of $Li_4Ti_5O_{12}$ has raised concerns about its electrochemical performance. The initial insulating character associated with Ti4+ in $Li_4Ti_5O_{12}$ limits the electronic transfer between particles and to the external circuit, thereby worsening its high rate performance. In order to overcome these weak points, several alternative synthetic methods are highly required. Hence, in this presentation, novel ways using a synergetic strategy based on 1D architecture and surface coating will be introduced to enhance the kinetic property of Ti-based electrode. In addition, first-principle calculation will prove its significance to design Ti-based electrode for the most optimized electrochemical performance.

• 한국세라믹학회지
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• 제35권11호
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• pp.1155-1161
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• 1998

브라운관 funnel glass 내며의 흑연 피막의 저항에 관하여 연구하기 위하여 흑연이 함유된 도전성 도료를 제조하여 flow coating 방법으로 28" wide TV용 funnel glass 내면에 도포하고 흑연피막의 특성과 브라운관의 동작 특성을 평가하였다. 고형분 농도가 증가함에 따라 도전성 도료의 점도와 흑연피막의 두께는 증가하였으며 흑연피막의 전기저항은 감소하였다. 도포 후 건조조건에 따라서도 도전막의 표면상태, 전기저항 및 브라운관의 초기동작 특성등이 다르게 나타났다. 도전성 도료의 고형분 농도는 27%, 점도는 13 cps 전후에서 안정한 흑연피막을 제조할 수 있었으며, 이 때 진공특성이 최적의 상태로 나타났다. 그리고 도전성 도료의 상태와 제조조건에 따라서 브라운관의 다른 전지적 특성들도 변할 수 있기 때문에 브라운관 전체의 특성을 동시에 평가를 해야한다고 생각한다. 그리고 funnel glass에서의 부의 별 저항산포 차리를 줄이기 위해서는 도포 시에 도전성 도료를 주입하는 위치, 건조 조건, funnel glass의 예열 온도 등에 대한 조사도 이루어져야 한다고 생각한다.

• Carbon letters
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• 제14권4호
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• pp.251-254
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• 2013

In this study, poly(amic acid) was prepared via a polycondensation reaction of 3,3'-dihydroxybenzidine and pyromellitic dianhydride in an N-methyl-2-pyrrolidone solution; reduced graphene oxide/polybenzoxazole (r-GO/PBO) composite films, which significantly increased the electrical conductivity, were successfully fabricated. GO was prepared from graphite using Brodie's method. The GO was used as nanofillers for the preparation of r-GO/PBO composites through an in situ polymerization. The addition of 50 wt% GO led to a significant increase in the electrical conductivity of the composite films by more than sixteen orders of magnitude compared with that of pure PBO films as a result of the electrical percolation networks in the r-GO during the thermal treatment at various temperatures within the films.

• Carbon letters
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• 제13권4호
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• pp.230-235
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• 2012

In this study, reduced graphene oxide/polyimide (r-GO/PI) composite films, which showed significant enhancement in their electrical conductivity, were successfully fabricated. GO was prepared from graphite using a modified Hummers method. The GO was used as a nanofiller material for the preparation of r-GO/PI composites by in-situ polymerization. An addition of 20 wt% of GO led to a significant decrease in the volume resistivity of composite films by less than nine orders of magnitude compared to that of pure PI films due to the electrical percolation networks of reduced GO created during imidization within the films. A tensile test indicated that the Young's modulus of the r-GO/PI composite film containing 20 wt% GO increased drastically from 2.3 GPa to 4.4 GPa, which was an improvement of approximately 84% compared to that of pure PI film. In addition, the corresponding tensile strength was found to have decreased only by 12%, from 113 MPa to 99 MPa.

• Bulletin of the Korean Chemical Society
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• 제34권11호
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• pp.3269-3273
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• 2013

Graphene oxide (GO) has been of particular interest because it provides unique properties due to its high surface area, chemical functionality and ease of mass production. GO is produced by chemical exfoliation of graphite and is decorated with oxygen-containing groups such as phenol hydroxyl, epoxide groups and ionizable carboxylic acid groups. Due to the presence of those functional groups, GO can be utilized as a novel platform for hybrid nanocomposites in chemical synthetic approaches. In this work, GO-$SnO_2$ nanocomposites have been prepared through the spontaneous formation of molecular hybrids. When $SnO_2$ precursor solution and GO suspension were simply mixed, $Sn^{2+}$ was spontaneously formed into $SnO_2$ nanoparticles upon the deoxygenation of GO. Through further chemical reduction by adding hydrazine, reduced GO-$SnO_2$ hybrid was finally created. Our investigation for the electrocapacitive properties of hybrid electrode showed the enhanced performance (389 F/g), compared with rGO-only electrode (241 F/g). Our approach offers a scalable, robust synthetic route to prepare graphene-based nanocomposites for supercapacitor electrode via spontaneous hybridization.

• Bulletin of the Korean Chemical Society
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• 제35권4호
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• pp.1067-1072
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• 2014

In this study, we report a new approach for $Mn_3O_4$-graphene nanocomposite by ex situ method. This nanocomposite shows two-dimensional aggregation of nanoparticle, and doping effect by decorated manganese oxide ($Mn_3O_4$), as well. The graphene film was made through micromechanical cleavage of graphite on the $SiO_2/Si$ wafer. Manganese oxide ($Mn_3O_4$) nanoparticle with uniform cubic shape and size (about $5.47{\pm}0.61$ nm sized) was synthesized through the thermal decomposition of manganese(II) acetate, in the presence of oleic acid and oleylamine. The nanocomposite was obtained by self-assembly of nanoparticles on graphene film, using hydrophobic interaction. After heat treatment, the decorated nanoparticles have island structure, with one-layer thickness by two-dimensional aggregations of particles, to minimize the surface potential of each particle. The doping effect of $Mn_3O_4$ nanoparticle was investigated with Raman spectra. Given the upshift in positions of G and 2D in raman peaks, we suggest that $Mn_3O_4$ nanoparticles induce p-doping of graphene film.