• 자원리싸이클링
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• 제21권5호
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• pp.88-92
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• 2012

중유회로부터 증류수로 용출시킨 중유회 용출액에서 금속 중 $Ni^{2+}$이온의 정량을 분광광도법으로 측정하고자 하였다. 또 중유회용출액 중 다량 존재하는 $V^{3+}$이온이 $Ni^{2+}$이온의 분광광도법적 정량에 미치는 영향을 알아보기 위하여 $Ni^{2+}$이온 ppm 대비 $V^{3+}$이온의 함량을 달리한 시료의 흡광도를 조사한 결과 $V^{3+}$이온의 함량이 $Ni^{2+}$ 함량의 50% 이하인 조건에서는 시료 중 $Ni^{2+}$이온의 정량이 분광광도법으로 가능함을 확인하였다.

• 공업화학
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• 제10권3호
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• pp.491-495
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• 1999

졸겔법에 의하여 리튬전지용 $Ni_{0.2}V_2O_5$ aerogel (ARG) 양극 소재를 개발하여 전기화학적 특성을 조사하였다. ARG는 무정형의 층상화합물로 $400^{\circ}C$ 이상에서 열처리할 경우 orthorhombic 구조로 전환되었으며, 표면구조는 섬유 모양의 단위체가 서로 얽혀 일정한 방향으로 성장하여 비등방성 sheet를 형성하고 있다. 리튬 이온이 층간 삽입될 수 있는 다수의 특정한 에너지 준위의 자리가 ARG내에 존재하며, 전지의 평균전위는 3.1 V (vs. $Li/Li^+$) 이었다. ARG 리튬이차전지의 계면저항은 ARG층 내 리튬 몰분율에 상관없이 일정한 반면, 전하이동저항은 개로전압에서 최대이며 ARG내 리튬 이온의 농도가 증가할수록 증가하였다.

• Korean Chemical Engineering Research
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• 제57권6호
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• pp.832-840
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• 2019

양극 활물질의 전기화학적 성능을 개선하기 위하여, 농도 구배형 전구체를 사용한 boron-doped $LiNi_{0.90}Co_{0.05}Ti_{0.05}O_2$를 합성하였다. 제조된 양극 활물질의 특성은 XRD, SEM, EDS, PSA, ICP-OES 및 전기전도도 측정을 통하여 분석하였다. 초기 충 방전 용량, 사이클, 순환전압전류, 율속 특성 및 임피던스 테스트를 통해 전기화학적 성능을 조사하였다. 붕소가 0.5 mol% 도핑된 $LiNi_{0.90}Co_{0.05}Ti_{0.05}O_2$ 양극 활물질은 2.7~4.3 V (vs. $Li/Li^+$)의 전압 범위에서 0.5 C의 전류를 인가했을 때, 187 mAh/g의 용량을 보이며 50 사이클 이후 94.7%의 용량 유지율을 보였다. 상대적으로 고전압인 2.7~4.5 V (vs. $Li/Li^+$)의 전압 범위에서는 200 mAh/g의 높은 용량을 보이며 50 사이클 이후 80.5%의 용량 유지율을 나타냈다.

• Bulletin of the Korean Chemical Society
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• 제34권9호
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• pp.2577-2582
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• 2013

A novel stick-shaped portable sensing device featuring a microhole array interface between the polyvinylchloride-2-nitrophenyloctylether (PVC-NPOE) gel and water phase was developed for in-situ sensing of perchlorate ions in real water samples. Perchlorate sensitive sensing responses were obtained based on measuring the current changes with respect to the assisted transfer reaction of perchlorate ions by a perchlorate selective ligand namely, bis(dibenzoylmethanato)Ni(II) (Ni(DBM)2) across the polarized microhole array interface. Cyclic voltammetry was used to characterize the assisted transfer reaction of perchlorate ions by the $Ni(DBM)_2$ ligand when using the portable sensing device. The current response for the transfer of perchlorate anions by $Ni(DBM)_2$ across the micro-water/gel interface linearly increased as a function of the perchlorate ion concentration. The technique of differential pulse stripping voltammetry was also utilized to improve the sensitivity of the perchlorate anion detection down to 10 ppb. This was acquired by preconcentrating perchlorate anions in the gel layer by means of holding the ion transfer potential at 0 mV (vs. Ag/AgCl) for 30 s followed by stripping the complexed perchlorate ion with the ligand. The effect of various potential interfering anions on the perchlorate sensor was also investigated and showed an excellent selectivity over $Br^-$, $NO_2{^-}$, $NO_3{^-}$, $CO{_3}^{2^-}$, $CH_3COO^-$ and $SO{_4}^{2^-}$ ions. As a final demonstration, some regional water samples from the Sincheon river in Daegu city were analyzed and the data was verified with that of ion chromatography (IC) analysis from one of the Korean-certified water quality evaluation centers.

• 한국재료학회:학술대회논문집
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• 한국재료학회 2011년도 춘계학술발표대회
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• pp.5-5
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• 2011

The research and development of hybrid electric vehicle (HEV), plug-in hybrid electric vehicle (PHEV) and electric vehicle (EV) are intensified due to the energy crisis and environmental concerns. In order to meet the challenging requirements of powering HEV, PHEV and EV, the current lithium battery technology needs to be significantly improved in terms of the cost, safety, power and energy density, as well as the calendar and cycle life. One new technology being developed is the utilization of composite cathode by mixing two different types of insertion compounds [e.g., spinel $LiMn_2O_4$ and layered $LiMO_2$ (M=Ni, Co, and Mn)]. Recently, some studies on mixing two different types of cathode materials to make a composite cathode have been reported, which were aimed at reducing cost and improving self-discharge. Numata et al. reported that when stored in a sealed can together with electrolyte at $80^{\circ}C$ for 10 days, the concentrations of both HF and $Mn^{2+}$ were lower in the can containing $LiMn_2O_4$ blended with $LiNi_{0.8}Co_{0.2}O_2$ than that containing $LiMn_2O_4$ only. That reports clearly showed that this blending technique can prevent the decline in capacity caused by cycling or storage at elevated temperatures. However, not much work has been reported on the charge-discharge characteristics and related structural phase transitions for these composite cathodes. In this presentation, we will report our in situ x-ray diffraction studies on this mixed composite cathode material during charge-discharge cycling. The mixed cathodes were incorporated into in situ XRD cells with a Li foil anode, a Celgard separator, and a 1M $LiPF_6$ electrolyte in a 1 : 1 EC : DMC solvent (LP 30 from EM Industries, Inc.). For in situ XRD cell, Mylar windows were used as has been described in detail elsewhere. All of these in situ XRD spectra were collected on beam line X18A at National Synchrotron Light Source (NSLS) at Brookhaven National Laboratory using two different detectors. One is a conventional scintillation detector with data collection at 0.02 degree in two theta angle for each step. The other is a wide angle position sensitive detector (PSD). The wavelengths used were 1.1950 ${\AA}$ for the scintillation detector and 0.9999 A for the PSD. The newly installed PSD at beam line X18A of NSLS can collect XRD patterns as short as a few minutes covering $90^{\circ}$ of two theta angles simultaneously with good signal to noise ratio. It significantly reduced the data collection time for each scan, giving us a great advantage in studying the phase transition in real time. The two theta angles of all the XRD spectra presented in this paper have been recalculated and converted to corresponding angles for ${\lambda}=1.54\;{\AA}$, which is the wavelength of conventional x-ray tube source with Cu-$k{\alpha}$ radiation, for easy comparison with data in other literatures. The structural changes of the composite cathode made by mixing spinel $LiMn_2O_4$ and layered $Li-Ni_{1/3}Co_{1/3}Mn_{1/3}O_2$ in 1 : 1 wt% in both Li-half and Li-ion cells during charge/discharge are studied by in situ XRD. During the first charge up to ~5.2 V vs. $Li/Li^+$, the in situ XRD spectra for the composite cathode in the Li-half cell track the structural changes of each component. At the early stage of charge, the lithium extraction takes place in the $LiNi_{1/3}Co_{1/3}Mn_{1/3}O_2$ component only. When the cell voltage reaches at ~4.0 V vs. $Li/Li^+$, lithium extraction from the spinel $LiMn_2O_4$ component starts and becomes the major contributor for the cell capacity due to the higher rate capability of $LiMn_2O_4$. When the voltage passed 4.3 V, the major structural changes are from the $LiNi_{1/3}Co_{1/3}Mn_{1/3}O_2$ component, while the $LiMn_2O_4$ component is almost unchanged. In the Li-ion cell using a MCMB anode and a composite cathode cycled between 2.5 V and 4.2 V, the structural changes are dominated by the spinel $LiMn_2O_4$ component, with much less changes in the layered $LiNi_{1/3}Co_{1/3}Mn_{1/3}O_2$ component, comparing with the Li-half cell results. These results give us valuable information about the structural changes relating to the contributions of each individual component to the cell capacity at certain charge/discharge state, which are helpful in designing and optimizing the composite cathode using spinel- and layered-type materials for Li-ion battery research. More detailed discussion will be presented at the meeting.

• 분석과학
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• 제10권6호
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• pp.427-432
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• 1997

도데실황산나트륨(SDS)이 수식된 유리탄소전극에 의해 철(III) 이온의 정량분석이 선택성 있게 제안되었다. 이것은 SDS와 $Fe^{3+}$의 정전기적 인력으로 착물이 형성되는 데 근거한 것이다. 철(III) 이온의 정량분석은 시차펄스전압전류법(DPV)에 의해 하였고, 그 정량분석을 위한 $(DS^-)_n-Fe^{3+}$의 환원 피크는 +0.466(${\pm}0.002$)volt (vs. Ag/AgCl)였다. 철(III) 이온의 정랑분석을 위한 검량선은 $0.50{\times}10^{-5}{\sim}10{\times}10^{-5}mol/L$의 농도 범위에서 얻었으며, 검출한계는 $0.14{\times}10^{-5}mol/L$였다. $Cu^{2+}$, $Ni^{2+}$, $Co^{2+}$, $Pb^{2+}$, $Zn^{2+}$ 및 $Mn^{2+}$는 철(III) 이온의 정량에 거의 영향을 미치지 않으나, $CN^- $ 및 $SCN^-$은 철(III) 이온의 정량을 크게 방해하였다.

• 전기화학회지
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• 제11권4호
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• pp.284-288
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• 2008

박막 리튬이차전지의 고용량 음극을 개발하기 위하여, Sn(II) 아세테이트를 포함한 유기전해조 도금법을 이용하여 Sn 박막전극을 제조하였다. $Li^+$와 $Sn^{2+}$를 포함한 전해조에 대한 순환전위전류시험 결과 3종류의 환원 반응이 나타났으며, $2.0{\sim}2.5\;V$ 영역이 Ni 집전체 표면에 대한 Sn의 석출 반응에 해당한다. 수계전해액에 대한 $Sn^{2+}$의 표준환원전위는 2.91 V vs. $Li^+/Li^{\circ}$ 인데 반해 유기전해조에서는 보다 낮은 전위에서 환원반응이 일어났다. 이는 유기전해질의 고저항과 $Sn^{2+}$의 낮은 농도에 기인한 과전위의 결과로 생각된다. 제조한 전극의 물리적 특성 및 전기화학적 특성을 연구하였다. 석출한 Sn 전극을 $150^{\circ}C$로 열처리하여 보다 높은 결정성을 얻을 수 있었고, 이를 Sn/Li 전지로 구성하여 전기화학적 실험을 한 결과 0.25 V와 0.75 V에서 각각 합금화-탈합금화 과정을 확인 할 수 있었다. 제조한 전극의 두께를 전기량을 통하여 계산한 바 $7.35{\mu}m$였으며, 가역용량은 $400{\mu}Ah/cm^2$을 얻었다.

• Journal of Electrochemical Science and Technology
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• 제12권2호
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• pp.237-245
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• 2021

Atomic layer deposition (ALD) enhances the stability of cathode materials via surface modification. Previous studies have demonstrated that an Ni-rich cathode, such as LiNi_0.8Co_0.1Mn_0.1O₂, is a promising candidate owing to its high capacity, but is limited by poor cycle stability. In this study, to enhance the stability of the Ni-rich cathode, synthesized LiNi_0.8Co_0.1Mn_0.1O₂ was coated with Al₂O₃ using ALD. Thus, the surface-modified cathode exhibited enhanced stability by protecting the interface from Ni-O formation during the cycling process. The coated LiNi_0.8Co_0.1Mn_0.1O₂ exhibited a capacity of 176 mAh g^-1 at 1 C and retained up to 72% of the initial capacity after 100 cycles within a range of 2.8-4.3 V (vs Li/Li⁺. In contrast, pristine LiNi_0.8Co_0.1Mn_0.1O₂ presented only 58% of capacity retention after 100 cycles with an initial capacity of 173 mAh g^-1. Improved cyclability may be a result of the ALD coating, which physically protects the electrode by modifying the interface, and prevents degradation by resisting side reactions that result in capacity decay. The electrochemical impedance spectra and structural and morphological analysis performed using electron microscopy and X-ray techniques establish the surface enhancement resulting from the aforementioned strategy.

• 전기화학회지
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• 제19권1호
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• pp.1-8
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• 2016

층상구조 삼성분계 $LiNi_{1-x-y}Co_xMn_yO_2$ 양극활물질을 4.3 V 이상 고전압으로 충전시키면 용량 증가를 기대할 수 있으나 기존 전해액의 산화안정성이 낮아 고전압 성능 구현에 제한이 있다. 본 연구에서는 설폰계 전해액 첨가제인 dimethyl sulfone (DMS), diethyl sulfone (DES), ethyl methyl sulfone (EMS)을 사용하여 $LiNi_{0.5}Co_{0.2}Mn_{0.3}O_2$ 양극의 고전압 특성을 향상시키고자 한다. 본 논문은 다양한 선형 sulfone계 첨가제가 포함된 전해액에서 3.0-4.6 V 전압범위에서 양극의 충방전 특성과 양극-전해액간 계면거동과 표면층 분석에 대한 내용으로 이루어져 있다. 특히 Dimethyl sulfone (DMS) 첨가제 사용시, 50 사이클 중 $198-173mAhg^{-1}$의 방전 용량과 87%의 용량유지율을 보여 기존 전해액 대비 상당히 향상된 충방전 안정성을 보였다. 표면조성 분광분석 결과, DMS 첨가제 사용시 양극에 안정한 표면보호층이 형성되고 금속 용출이 억제되어 고전압 충방전 특성이 향상되었음 알 수 있었다.

• 한국결정학회:학술대회논문집
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• 한국결정학회 2002년도 정기총회 및 추계학술연구발표회
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• pp.16-16
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• 2002

The presently commercialized lithium-ion batteries use layer structured LiCoO₂ cathodes. Because of the high cost and toxicity of cobalt, an intensive search for new cathode materials has been underway in recent years. Recently, a concept of a one-to-one solid state mixture of LiNO₂ and LiMnO₂, i.e., Li[Ni/sub 0.5/Mn/sub 0.5/]O₂, was adopted by Ohzuku and Makimura to overcome the disadvantage of LiNiO₂ and LiMnO₂. Li[Ni/sub 0.5/Mn/sub 0.5/]O₂ has the -NaFeO₂ structure, which is characteristic of the layered LiCoO₂ and LiNiO₂ structures and shows excellent cycleability with no indication of spinel formation during electrochemical cycling. Layered Li[Ni/sub x/Co/sub 1-2x/Mn/sub x/]O₂ (x = 0.5 and 0.475) materials with high homogeneity and crystallinity were synthesized using a mechanical alloying method. The Li[Ni/sub 0.475/Co/sub 0.05/Mn/sub 0.475/]O₂ electrode delivers a high discharge capacity of 187 mAh/g between 2.8 and 4.6 V at a high current density of 0.3 mA/㎠(30 mA/g) with excellent cycleability. The charge/discharge and differential capacity vs. voltage studies of the Li[Ni/sub x/Co/sub 1-2x/Mn/sub x/]O₂ (x = 0.5 and 0.475) materials showed only one redox peak up to 50 cycles, which indicates that structural phase transitions are not occurred during electrochemical cycling. The magnitude of the diffusion coefficients of lithium ions for Li[Ni/sub x/Co/sub 1-2x/Mn/sub x/]O₂(x = 0.5 and 0.475) are around 10/sup -9/ ㎠/s measured by the galvanostatic intermittent titration technique (GITT).