• KEPCO Journal on Electric Power and Energy
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• 제6권4호
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• pp.461-466
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• 2020

There are many application fields of electrical energy storage such as load shifting, integration with renewables, frequency or voltage supports, and so on. Especially, the frequency regulation is needed to stabilize the electric power system, and there have to be more than 1 GW as power reserve in Korea. Ni-rich layered oxide cathode materials have been investigated as a cathode material for Li-ion batteries because of their higher discharge capacity and lower cost than lithium cobalt oxide. Nonetheless, most of them have been investigated using small coin cells, and therefore, there is a limit to understand the deterioration mode of Ni-rich layered oxides in commercial high energy Li-ion batteries. In this paper, the pouch-type 20 Ah-scale Li-ion full cells are fabricated using Ni-rich layered oxides as a cathode and graphite as an anode. Above all, two test conditions for the application of frequency regulation were established in order to examine the performances of cells. Then, the electrochemical performances of two types of Ni-rich layered oxides are compared, and the long-term performance and degradation mode of the cell using cathode material with high nickel contents among them were investigated in the frequency regulation conditions.

• Bulletin of the Korean Chemical Society
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• 제31권8호
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• pp.2304-2308
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• 2010

A $LiNi_{0.8}Co_{0.15}Al_{0.05}O_2$ (LNCAO/C) active material composite cathode was coated with carbon. The conductive carbon coating was obtained by addition of surfactant during synthesis. The addition of surfactant led to the formation of an amorphous carbon coating layer on the pristine LNCAO surface. The layer of carbon coating was clearly detected by FE-TEM analysis. In electrochemical performance, although the LNCAO/C showed similar capacity at low C-rate conditions, the rate capability was improved by the form of the carbon coating at high current discharge state. After 40 cycles of charge-discharge processes, the capacity retention of LNCAO/C was better than that of LNCAO. The carbon coating is effectively protected the surface structure of the pristine LNCAO during Li insertion-extraction.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2000년도 하계학술대회 논문집 C
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• pp.1628-1630
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• 2000

Vertically aligned multiwalled carbon nanotubes are grown on silicon oxide substrate at 950$^{\circ}C$ by thermal chemical vapor deposition using $C_{2}H_2$. Three catalytic metals such as iron(Fe), cobalt (Co), and nickel(Ni) are used as catalyst, we found that the growth rate of carbon nanotubes for three catalyst particles are in an order of Fe > Ni > Co. All carbon nanotubes are revealed to have bamboo structure with no encapsulated catalytic particles, the diameter of carbon nanotubes depend on the catalyst, the tip and the compartment sheets of bamboo structure also depend on the shape of catalytic particles.

• Journal of Electrochemical Science and Technology
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• 제12권4호
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• pp.415-423
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• 2021

For a battery module where single cells are connected in series, the single cells should each have a similar state of charge (SOC) to prevent them from being exposed to an overcharge or over-discharge during charge-discharge cycling. To detect the existence of unbalanced SOC cells in a battery module, we propose a simple measurement method using a single-frequency response of electrochemical impedance spectroscopy (EIS). For a commercially available graphite/nickel-cobalt-aluminum-oxide lithium-ion cell, the cell impedance increases significantly below SOC20%, while the impedance in the medium SOC region (SOC20%-SOC80%) remains low with only minor changes. This impedance behavior is mostly due to the elementary processes of cathode reactions in the cell. Among the impedance values (Z, Z', Z"), the imaginary component of Z" regarding cathode reactions changes heavily as a function of SOC, in particular, when the EIS measurement is performed around 0.1 Hz. Thanks to the significant difference in the time constant of cathode reactions between ≤SOC10% and ≥SOC20%, a single-frequency EIS measurement enlarges the difference in impedance between balanced and unbalanced cells in the module and facilitates an ~80% improvement in the detection signal compared to results with conventional EIS measurements.

• 마이크로전자및패키징학회지
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• 제12권2호
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• pp.149-154
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• 2005

궁극적으로 게이트를 저저항 복합 실리사이드로 대체하는 가능성을 확인하기 위해 70 nm 두께의 폴리실리콘 위에 각 20nm의 Ni, Co를 열증착기로 적층순서를 달리하여 poly/Ni/Co, poly/Co/Ni구조를 만들었다. 쾌속열처리기를 이용하여 실리사이드화 열처리를 40초간 $700{\~}1100^{\circ}C$ 범위에서 실시하였다. 복합 실리사이드의 온도별 전기저항변화, 두께변화, 표면조도변화를 각각 사점전기저항측정기와 광발산주사전자현미경, 주사탐침현미경으로 확인하였다. 적층순서와 관계없이 폴리실리콘으로부터 제조된 복합실리사이드는 $800^{\circ}C$ 이상부터 급격한 고저항을 보이고, 두께도 급격히 얇아졌다. 두께의 감소는 기존의 단결정에서는 없던 현상으로 폴리실리콘의 두께가 한정된 경우 금속성분의 inversion 현상이 커서 폴리실리콘이 오히려 실리사이드 상부에 위치하여 제거되기 때문이라고 생각되었고 $1000^{\circ}C$ 이상에서는 실리사이드가 형성되지 못하였다. 이러한 결과는 나노급 두께의 게이트를 저저항 실리사이드로 만 들기 위해서는 inversion과 두께감소를 고려하여야 함을 의미하였다.

• 자원리싸이클링
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• 제22권4호
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• pp.62-69
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• 2013

$Li(NCM)O_2$계 폐리튬전지 공정 스크랩의 재활용 연구의 일환으로서 리튬화합물의 회수와 NCM전구체를 제조하기 위한 침출거동에 대하여 살펴보았다. 우선 탄소를 이용하여 층상 구조의 NCM계 산화물 분말을 분해시켰으며, $600^{\circ}C$ 이상의 탄소반응으로 리튬은 탄산리튬으로 변화시켰다. 탄산리튬은 수세 후 농축과정을 거쳐 순도 99% 이상의 탄산리튬 분말로 회수하였다. 그리고 탄소에 의한 환원 반응율은 $800^{\circ}C$에서 약 88%을 나타내었으며, 탄소환원 처리 후 분말에 대한 황산 침출 결과, 2M 이상의 황산농도에서 코발트, 니켈, 망간의 침출율은 99% 이상이었다.

• Journal of Electrochemical Science and Technology
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• 제14권3호
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• pp.262-271
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• 2023

For electrode stability and the electrochemical performance of the Li-ion cell, it is essential that the active ingredients and unique additives in the polymer binder be well dispersed with the solvent-based slurry. The efficient procedure used to create the slurry affects the rheological characteristics of the electrode slurry. When successively adding different steps of Nmethyl-2-pyrrolidone (NMP) solvent to the cathode composition, it is evenly disseminated. The electrochemical performance of the Li-ion cells and the electrodes made with slurry formed by single step and multiple steps of addition of NMP solvent are examined. To preform rheological properties of cathode electrode slurry on Ni-rich Lithium Nickel-Cobalt-Aluminum Oxide (LiNi_0.80Co_0.15Al_0.05) (NCA). Also, we investigate different step addition of electrode formation and mechanical strength characterization like peel strength. According to the EIS study, a multi-step electrode slurry has lower internal resistance than a single-step electrode slurry, which results in better electrical characteristics and efficiency. Further, microstructure of electrodes is obtained electrochemical performance in the 18650 cylindrical cells with targeted capacity of 1.5 Ah. The slurry of electrodes prepared by single step and multiple steps of addition of NMP solvent and its effect on the fabrication of 1.5 Ah cells. A three-step solvent addition on slurry has been found to be a lower internal resistance than a single-step electrode slurry as confirmed by the EIS analysis, yielding improved electrical properties and efficiency.

• 한국산학기술학회논문지
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• 제8권1호
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• pp.25-32
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• 2007

코발트 니켈 합금형 실리사이드 공정에서 단결정실리콘과 다결정실리콘 기판에 자연산화막이 있는 경우 나노급 두께의 코발트 니켈 합금 금속을 증착하고 실리사이드화하는 경우의 반응 안정성을 확인하였다. 4인치 P-type(100)Si 기판 전면에 poly silicon을 입힌 기판과 single silicon 상태의 두 종류 기판을 준비하고 두께 4 nm의 자연산화막이 있는 상태에서 10 nm 코발트 니켈 합금을 니켈의 상대조성을 $10{\sim}90%$로 달리하며 열증착하였다. 통상의 600, 700, 800, 900, 1000, $1100^{\circ}C$ 각 온도에서 실리사이드화 열처리를 시행 후 잔류 합금층을 제거하고, XRD(X-ray diffraction)및 FE-SEM(Field emission scanning electron microscopy), AES(Auger electron spectroscopy)를 사용하여 실리사이드가 생겼는지 확인하였다. 마이크로라만 분석기로 실리사이드 반응시의 실리콘 층의 잔류 스트레스도 확인하였다. 자연산화막이 존재하는 경우 실리사이드 반응이 진행되지 않았고, 폴리실리콘 기판과 고온에서는 금속과 산화층의 반응잔류물이 생성되었다. 단결정 기판의 고온열처리에서는 실리사이드 반응이 없더라도 핀홀이 발생할 수 있는 정도의 열스트레스가 존재하였다. 코발트 니켈 복합실리사이드 공정에서는 자연산화막을 제거하는 공정이 필수적이었다.

• 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.

• 한국분말재료학회지
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• 제29권5호
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• pp.411-417
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• 2022

Environmental issues such as global warming due to fossil fuel use are now major worldwide concerns, and interest in renewable and clean energy is growing. Of the various types of renewable energy, green hydrogen energy has recently attracted attention because of its eco-friendly and high-energy density. Electrochemical water splitting is considered a pollution-free means of producing clean hydrogen and oxygen and in large quantities. The development of non-noble electrocatalysts with low cost and high performance in water splitting has also attracted considerable attention. In this study, we successfully synthesized a NiCo₂O₄/NF electrode for an oxygen evolution reaction in alkaline water splitting using a hydrothermal method, which was followed by post-heat treatment. The effects of heat treatment on the electrochemical performance of the electrodes were evaluated under different heat-treatment conditions. The optimized NCO/NF-300 electrode showed an overpotential of 416 mV at a high current density of 50 mA/cm² and a low Tafel slope (49.06 mV dec^-1). It also showed excellent stability (due to the large surface area) and the lowest charge transfer resistance (12.59 Ω). The results suggested that our noble-metal free electrodes have great potential for use in developing alkaline electrolysis systems.