• 접착 및 계면
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• 제22권1호
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• pp.1-7
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• 2021

신재생 에너지 발전을 통한 안정적인 전력 공급을 위해 대용량 에너지 저장 장치의 중요성이 최근 부각되고 있다. 이러한 관점에서 차세대 이차 전지인 Na-air battery (NAB)는 풍부하고 저렴한 원재료를 통해 대용량을 구현할 수 있어 많은 관심을 받고 있다. 본 연구에서는 Hybrid type Na-air battery를 위한 활성탄 기반 촉매들을 제조하여 이들의 특성을 비교 분석하였다. 특히, 자원 재활용의 관점에서 버려진 오렌지 껍질을 사용하여 활성탄(Orange-C)과 이를 질소를 이용하여 도핑한 활성탄(N-doped-Carbon, Nd-C)을 제조하였으며, 널리 사용되고 있는 Vulcan카본과 성능을 비교하였다. 또한, 제조한 활성탄(Nd-C)이 지지 촉매로 활용 가능한지 확인하기 위해 수정된 폴리올법을 사용하여 Pt/C 촉매(homemade-Pt/C, HM-Pt/C)를 합성하였으며, 상용화된 Pt/C 촉매(Commercial Pt/C)와 전기화학적 성능을 비교하였다. 제조된 Orange-C와 Nd-C는 전형적인 H3 타입 BET isotherm을 보였으며, 이는 마이크로 기공과 메조기공이 존재한다는 증거이다. 또한, HM-Pt/C의 경우, 활성탄(Nd-C) 지지 촉매 위에 Pt 입자가 고르게 분포하고 있음을 TEM 분석을 통해 확인할 수 있었다. 특히, HM-Pt/C 기반의 NAB의 경우, 1st galvanostatic charge-discharge 시험에서 가장 작은 Voltage gap (0.224V)과 우수한 Voltage efficiency (92.34%)를 보였다. 또한, 20사이클 동안 진행한 사이클 성능 시험에서도 가장 안정적인 성능을 보였다.

• Bulletin of the Korean Chemical Society
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• 제34권2호
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• pp.433-436
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• 2013

Carbon-coated $Li_3V_2(PO_4)_3-LiMnPO_4$ composite cathode materials are first reported in this work, prepared by the mechanochemical process with a complex metal oxide as the precursor and sucrose as the carbon source. X-ray diffraction pattern of the composite material indicates that both olivine $LiMnPO_4$ and monoclinic $Li_3V_2(PO_4)_3$ co-exist. We further investigated the electrochemical properties of our $Li_3V_2(PO_4)_3-LiMnPO_4$ composite cathode materials using galvanostatic charging/discharging tests, where our $Li_3V_2(PO_4)_3-LiMnPO_4$ composite electrode materials exhibit the charge/discharge efficiency of 91.9%, while $Li_3V_2(PO_4)_3$ and $LiMnPO_4$ exhibit the efficiency of 87.7 and 86.7% in the first cycle. The composites display unique electrochemical performances in terms of overvoltage and cycle stability, displaying a reduced gap of 141.6 mV between charge and discharge voltage and 95.0% capacity efficiency after $15^{th}$ cycles.

• 전기화학회지
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• 제21권4호
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• pp.61-67
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• 2018

새로운 전자 기기들이 등장함에 따라 시판되고 있는 리튬 이온 배터리 (lithium ion battery, LIB)는 다양한 문제에 직면해 있으며, 이와 관련하여 많은 해결 노력들이 시도되어 왔다. 차세대 이차 전지의 개발이라는 관점에서 LIB의 문제들을 해결하기 위해, 우리는 mesoporous carbon based on waste biomass (MCWB) 와 Polypyrrole (PPY) hydrogel과 같은 두 가지 종류의 촉매를 성공적으로 개발하였다. MCWB와 PPY hydrogel 촉매들은 전형적인 H3 타입 BET isotherm을 나타내었으며, 이는 micropore와 mseopore가 존재한다는 증거이다. 특히 PPY hydrogel을 기반으로 하는 해수 전지(seawater battery, SWB)의 경우, galvanostatic charge-discharge 시험에서 voltage efficiency성능은 MCWB를 적용한 battery보다 높았지만 Pt/C를 적용한 battery보다는 낮았다. 더욱 흥미롭게도, PPY hydrogel 기반의 SWB는 20 사이클(480hrs) 동안 우수한 가역적인 충/방전 특성을 나타내었으며, voltage efficiency성능은 70.32%에서 77.35% 범위의 우수한 특성을 나타내었다. 상기 연구 결과는 차세대 이차 전지를 위한 비귀금속 촉매 개발에 기여하는 결과라고 사료된다.

• Carbon letters
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• 제17권1호
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• pp.39-44
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• 2016

The work presented in this report was a detailed comparative study of the electrochemical response exhibited by graphite anodes in Li-ion batteries having different physical features. A comprehensive morphological and physical characterization was carried out for these graphite samples via X-ray diffraction and scanning electron microscopy. Later, the electrochemical performance was analyzed using galvanostatic charge/discharge testing and the galvanostatic intermittent titration technique for these graphite samples as negative electrode materials in battery operation. The results demonstrated that a material having a higher crystalline order exhibits enhanced electrochemical properties when evaluated in terms of rate-capability performance. All these materials were investigated at high C-rates ranging from 0.1C up to 10C. Such improved response was attributed to the crystalline morphology providing short layers, which facilitate rapid Li⁺ ions diffusivity and electron transport during the course of battery operation. The values obtained for the electrical conductivity of these graphite anodes support this possible explanation.

• 폴리머
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• 제36권3호
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• pp.321-325
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• 2012

본 연구에서는 화학적으로 활성 흑연나노섬유를 제조하여 그에 따른 전기화학적 거동을 확인하였다. 활성화제로 KOH를 사용하였으며, KOH와 흑연나노섬유의 비를 무게비로 각각 0, 1, 2, 4, 및 5로 처리하여 표면과 기공특성을 연구하였고, 그에 따른 전기화학적 거동을 살펴보았다. 활성화된 흑연나노섬유의 결정구조와 표면특성은 각각 X-선 회절분석법(XRD), 주사전자현미경(SEM) 분석방법을 이용하여 확인하였으며, 기공 특성은 비표면적 장치(BET)를 이용하였으며 질소흡착 등온선에 의해 조사하였다. 전기화학적 특성은 10 mV/s의 주사속도로 순환전류전압(cyclic voltammetry)을 통한 곡선으로 고찰하였으며 정전류법(galvanostatic method)으로 측정된 충방전 곡선을 통해 비축전용량을 계산하였다. 실험 결과로부터, 활성 흑연나노섬유의 전기화학적 거동은 KOH 양이 증가함에 따라 향상되었으며, 4 배 처리된 활성 흑연나노섬유가 최대의 비축전용량을 가진 것으로 나타났다. 이것은 KOH 활성화에 의해 활성 흑연나노섬유의 비표면적과 기공부피가 증가하기 때문인 것으로 사료된다.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2010년도 춘계학술대회 초록집
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• pp.163.2-163.2
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• 2010

In this work, nano-flake shaped nickel oxide (NiO) films were synthesized by chemical bath deposition technique for electrochemical capacitors. The deposition was carried out for 1 and 2 h at room temperature using nickel foam as the substrate and the current collector. The structure and morphology of prepared NiO film were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). And, electrochemical properties were characterized by cyclic voltammetry, galvanostatic charge-discharge, and AC impedence measurement. It was found that the NiO film was constructed by many interconnected NiO nano-flakes which arranged vertically to the substrate, forming a net-like structure with large pores. The open macropores may facilitate the electrolyte penetration and ion migration, resulted in the utilization of nickel oxide due to the increased surface area for electrochemical reactions. Furthermore, it was found that the deposition onto nickel foam as substrate and curent collector led to decrease of the ion transfer resistance so that its specific capacitance of a NiO film had high value than NiO nano flake powder.

• Journal of Electrochemical Science and Technology
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• 제8권4호
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• pp.314-322
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• 2017

The electrolyte plays one of the most significant roles in the performance of electrochemical supercapacitors. Most liquid organic electrolytes used commercially have temperature and potential range constraints, which limit the possible energy and power output of the supercapacitor. The effect of elevated temperature on a lithium bis(oxalate)borate(LiBOB) salt-based electrolyte was evaluated in a symmetric supercapacitor assembled with activated carbon electrodes and different electrolyte blends of acetonitrile(ACN) and propylene carbonate(PC). The electrochemical properties were investigated using linear sweep voltammetry, cyclic voltammetry, galvanostatic charge-discharge cycles, and electrochemical impedance spectroscopy. In particular, it was shown that LiBOB is stable at an operational temperature of $80^{\circ}C$, and that, blending the solvents helps to improve the overall performance of the supercapacitor. The cells retained about 81% of the initial specific capacitance after 1000 galvanic cycles in the potential range of 0-2.5 V. Thus, LiBOB/ACN:PC electrolytes exhibit a promising role in supercapacitor applications under elevated temperature conditions.

• 한국표면공학회지
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• 제51권1호
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• pp.47-53
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• 2018

Sn-based lithium-ion batteries have low cost and high theoretical specific capacity. However, one of major problem is the capacity fading caused by volume expansion during lithiation/delithiation. In this study, 3-dimensional foam structure of Cu-Sn alloy is prepared by co-electrodeposition including large free space to accommodate the volume expansion of Sn. The Cu-Sn foam structure exhibits highly porous and numerous small grains. The result of EDX mapping and XPS spectrum analysis confirm that Cu-Sn foam consists of $SnO_2$ with a small quantity of CuO. The Cu-Sn foam structure electrode shows high reversible redox peaks in cyclic voltammograms. The galvanostatic cell cycling performances show that Cu-Sn foam electrode has high specific capacity of 687 mAh/g at a current rate of 50 mA/g. Through SEM observation after the charge/discharge processes, the morphology of Cu-Sn foam structure is mostly maintained despite large volume expansion during the repeated lithiation/delithiation reactions.

• Corrosion Science and Technology
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• 제20권1호
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• pp.15-21
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• 2021

Through a simple filtration process, followed by carbonization within a reductive environment, coffee waste grounds can be transformed into a non-porous hard carbon for use in multiple contexts. This resulting coffee-waste carbon has been evaluated as an eco-friendly and cost-effective replacement for conventional graphite. When compared with different types of carbon, our study found that the coffee-waste carbon fell into the category of hard carbon, as verified from the galvanostatic charge/discharge profiles. The coffee-waste carbon showed a superior rate capability when compared to that of graphite, while compromising smaller capacity at low C rates. During electrochemical reactions, it was also found that the coffee-waste carbon is well exposed to electrolytes, and its disordered characteristic is advantageous for ionic transport which leads to the low tortuosity of Li ions. Finally, the high irreversible capacity (low initial Coulombic efficiency) of the coffee-waste carbon, which if also often observed in amorphous carbon, can be adequately resolved through a solution-based prelithiation process, thereby proving that the coffee-waste carbon material is quite suitable for commercial use as an anode material for quickly-chargeable electrodes.

• 공업화학
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• 제30권3호
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• pp.324-330
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• 2019

Petal-like nickel cobaltite ($NiCo_2O_4$)/reduced graphene oxide (rGO) composites with different $rGO-to-NiCo_2O_4$ weight ratios were synthesized using a simple hydrothermal method and subsequent thermal treatment. In the $NiCo_2O_4/rGO$ composite, the $NiCo_2O_4$ 3-dimensional nanomaterials contributed to the improvement of electrochemical properties of the final composite material by preventing the restacking of the rGO sheet and securing ion movement passages. The composite structure was examined by field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), and Fourier-transform infrared (FT-IR) spectroscopy. The FE-SEM and TEM images showed that petal-like $NiCo_2O_4$ was supported on the rGO surface. Cyclic voltammetry (CV), galvanostatic charge-discharge (GCD), and electrochemical impedance spectroscopy (EIS) were used for the electrochemical analysis of composites. Among the prepared composites, $0.075g\;rGO/NiCo_2O_4$ composite showed the highest specific capacitance of $1,755Fg^{-1}$ at a current density of $2Ag^{-1}$. The cycle performance and rate capability of the composite material were higher than those of using the single $NiCo_2O_4$ material. These nano-structured composites could be regarded as valuable electrode materials for supercapacitors that require superior performance.