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고형신,박현우,김근중,이종대 한국화학공학회 2019 Korean Journal of Chemical Engineering Vol.36 No.4
A Ni0.9Co0.05Ti0.05(OH)2 precursor was synthesized with the concentration gradient method. To overcome the Li-ion shortage the problem due to the formation of a solid electrolyte interphase (SEI) layer during the initial charge/discharge process in the cathode material, lithium-excess Li1+xNi0.9Co0.05Ti0.05O2 (0x0.07) cathode materials were investigated by physical and electrochemical analyses. The physical properties of the lithium-excess cathode materials were analyzed using FE-SEM and XRD. A coin type half-cell was fabricated with the electrolyte of 1M LiPF6 dissolved in organic solvents (EC :EMC=1 : 2 vol%). The electrochemical performances were analyzed by the initial charge/discharge efficiency, cycle stability, rate performance and electrochemical impedance spectroscopy (EIS). The initial charge capacity of the cathode material was excellent at about 199.8-201.7mAh/g when the Li/Metal ratio was 1.03-1.07. Additionally, the efficiency of the 6.0 C/0.1 C was 79.2-79.9%. When the Li/Metal ratio was 1.05, the capacity retention showed the highest stability of 97.8% after 50 cycles.
고형신 ( Hyoung Shin Ko ),박현우 ( Hyun Woo Park ),이종대 ( Jong Dae Lee ) 한국화학공학회 2018 Korean Chemical Engineering Research(HWAHAK KONGHA Vol.56 No.5
본 연구에서는 농도구배형 공침합성법을 통해 Ni<sub>0.9</sub>Co<sub>0.05</sub>Ti<sub>0.05</sub>(OH)<sub>2</sub> 전구체를 제조하였다. 높은 니켈함량의 양극 활 물질에서 나타나는 산소 탈리에 따른 구조변화문제를 극복하기 위하여 소성온도 변화에 따른 양극 활물질의 물리적, 전기화학적 분석방법을 사용하여 조사하였다. Li<sub>1.05</sub>Ni<sub>0.9</sub>Co<sub>0.05</sub>Ti<sub>0.05</sub>O<sub>2</sub>의 물리적 특성은 FE-SEM, XRD, TGA를 이용하여 분석하였다. 양극 활물질과 LiPF6(EC:EMC=1:2 vol%) 전해질을 사용하여 제조한 코인셀의 전기화학적 성능은 초기 충·방전 효율, 사이클 유지율 및 율속 테스트를 통해 분석하였다. 제조된 양극재의 초기 충전 용량 및 초기효율은 소성온도 750~760 ℃에서 244.5~247.9 mAh/g, 84.2~85.8%로 우수하였다. 또한 용량 보존율은 50사이클 후에 97.8~99.1%의 높은 안정성을 나타내었다. In this study, the Ni<sub>0.9</sub>Co<sub>0.05</sub>Ti<sub>0.05</sub>(OH)<sub>2</sub> precursor was prepared by the concentration gradient co-precipitation method. In order to overcome the structural change due to oxygen desorption in the cathode active material with high nickel content, the physical and electrochemical analysis of the cathode active material according to the calcination temperature were investigated. Physical properties of Li<sub>1.05</sub>Ni<sub>0.9</sub>Co<sub>0.05</sub>Ti<sub>0.05</sub>O<sub>2</sub> were analyzed by FE-SEM, XRD and TGA. The electrochemical performance of the coin cell using a cathode active material and LiPF6(EC:EMC=1:2 vol%) electrolyte was evaluated by the initial charge/discharge efficiency, cycle retention, and rate capabilities. As a result, the initial capacity and initial efficiency of cathode materials were excellent with 244.5~247.9 mAh/g and 84.2~85.8% at the calcination temperature range of 750~760 ℃. Also, the capacity retention exhibited high stability of 97.8~99.1% after 50cycles.
Core-shell 구조의 MCMB/Li4Ti5O12 합성물을 사용한 하이브리드 커패시터의 전기화학적 특성
고형신 ( Hyoung Shin Ko ),최정은 ( Jeong Eun Choi ),이종대 ( Jong Dae Lee ) 한국화학공학회 2014 Korean Chemical Engineering Research(HWAHAK KONGHA Vol.52 No.1
본 연구에서는 낮은 사이클 안정성을 갖는 MCMB의 단점을 향상시키기 위하여 높은 사이클 안정성과 부피팽창이 없는 장점을 갖는 물질인 Li4Ti5O12를 코팅하여 core-shell 구조의 MCMB/Li4Ti5O12를 합성하고 MCMB-Li4Ti5O12를 음극으로, LiMn2O4, Active carbon fiber를 양극으로 사용하여 단위 셀을 제조하였다. LiPF6 염과 EC/DMC/EMC 용매를 전해질로 사용하여 제조한 하이브리드 커패시터 단위 셀로 충방전, 사이클, 순환전압전류, 임피던스 테스트를 진행 하여 전기화학적 특성을 평가한 결과, MCMB-Li4Ti5O12/LiMn2O4 전극을 사용한 하이브리드 커패시터가 MCMB 전극 의 하이브리드 커패시터 보다 좋은 충/방전 성능을 보였고, 67 Wh/kg, 781 W/kg의 에너지밀도와 출력밀도를 나타내었다. The MCMB-Li4Ti5O12 with core-shell structure was prepared by sol-gel process to improve low cycle capability of MCMB in this study. The electrochemical characteristics were investigated for hybrid capacitor using MCMB-Li4Ti5O12 as the negative electrode and LiMn2O4, Active carbon fiber as the positive electrode. The electrochemical behaviors of hybrid capacitor using organic electrolytes (LiPF6, EC/DMC/EMC) were characterized by charge/discharge, cyclic voltammetry, cycle and impedance tests. The hybrid capacitor using MCMB-Li4Ti5O12/LiMn2O4 electrodes had better capacitance than MCMB hybrid systems and was able to deliver a specific energy with 67 Wh/kg at a specific power of 781 W/kg.
리튬이차전지 음극재로서 Graphite/SiO2 합성물의 전기화학적 특성
고형신 ( Hyoung Shin Ko ),최정은 ( Jeong Eun Choi ),이종대 ( Jong Dae Lee ) 한국공업화학회 2014 공업화학 Vol.25 No.6
The graphite/SiO2 composites as anode materials for lithium-ion batteries were prepared by sol-gel method to improve the graphite`s electrochemical characteristics. The prepared graphite/SiO2 composites were analysed by XRD, FE-SEM and EDX. The graphite surface modified by silicon dioxide showed several advantages to stabilize SEI layer. The electrochemical characteristics were investigated for lithium ion battery using graphite/SiO2 as the working electrode and Li metal as the counter electrode. Electrochemical behaviors using organic electrolytes (LiPF6, EC/DMC) were characterized by charge/discharge, cycle, cyclic voltammetry and impedance tests. The lithium ion battery using graphite/SiO2 electrodes had better capacity than that of using graphite electrodes and was able to deliver a discharge capacity with 475 mAh/g at a rate of 0.1 C. Also, the capacity retention ratio of the modified graphite reaches 99% at a rate of 0.8 C.
수화한 무정형 알루미나로부터 제조된 $\gamma$-Alumina의 특성
김윤섭,고형신,서정권,이정민,하백현,Kim, Yun-Seop,Go, Hyeong-Sin,Seo, Jeong-Gwon,Lee, Jeong-Min,Ha, Baek-Hyeon 한국재료학회 2001 한국재료학회지 Vol.11 No.11
The amorphous alumina was obtained by flash calcination of Bayer gibbsite[$Al(OH)_3$aluminum trihydroxide]. Rehydration and pore characteristics of $r-A1_2O_3$ prepared from rehydrated amorphous alumina were investigated. Crystal phases of pseudo-boehmite and bayerite were changed when amorphous alumina was hydrated at various conditions such as time, the ratio of water/alumina and pH. Specific surface areas and pore volumes of $r- A1_{2O}_3$ were influenced by the reaction time, water/alumina and PH of rehydration. The total pore volume of $r-A1_{2O}_3$increases with increasing the reaction time and ratio of water/alumina. Especially, the pure pseudo-boehmite of single phase could be prepared, when amorphous alumina was hydrated in the range of pH 6.5-8.0 in water/alumina= 10 at $90^{\circ}C$ for 7hr. The $r-Al_{2O}_3$, obtained by calcination of the prepared pseudo-boehmite at $500^{\circ}C$ for 2hrs, is characterized by the specific surface area of $265m^2$/g, total pore volume of $0.75cm^3$/g.
카올린나이트로부터 중기공성 ${\gamma}-Al_2O_3$의 제조 및 특성
이광현,고형신,김윤섭,Lee, Gwang-Hyeon,Go, Hyeong-Sin,Kim, Yun-Seop 한국재료학회 2000 한국재료학회지 Vol.10 No.12
국내산 kaolinite를 소성한 다음 실리카를 선택적으로 추출하여 중기공성 ${\gamma}-Al_2O_3$를 제조하였다. $1000^{\circ}C$에서 24시간 소성된 kaolinite는 소량의 무정형 실리카와 ${\gamma}-Al_2O_3$으로 이루어진 스피넬 상의 미세구조로 전이되었음을 확인하였다. 다공성 ${\gamma}-Al_2O_3$는 $25~90^{\circ}C$의 반응온도, 0.5~4h의 추출시간 및 1~8M의 KOH 농도범위에서 무정형 실리카를 선택적으로 용해하여 제조할 수 있었다. $90^{\circ}C$, 1시간 및 4M의 KOH 농도조건에서 얻어진 ${\gamma}-Al_2O_3$는 약 $40~80{\AA}$ 정도의 매우 좁은 하나의 기공크기 분포를 가지고 있었으며, mesopore의 기공이 많이 생성되었다. 비표면적은 $250\textrm{m}^2/g$이고, 총 기공부피는 $0.654\textrm{cm}^3/g$로 나타났다. Mesoporous ${\gamma}-Al_2O_3$ has been prepared by selective leaching of silica from calcined domestic kaolinite. From XRD and TG-DTA data, it was found that the microstructure of a spinel phase, consisting of ${\gamma}-Al_2O_3$ containing a small mount of amorphous silica, was obtained by calcining kaolinite samples at around $1000^{\circ}C$ for 24h. Porous ${\gamma}-Al_2O_3$ was prepared by selectively dissolving the amorphous silica in KOH solutions of 1~4M at temperatures of $25~90^{\circ}C$ for leaching time of 0.5~4h. In the case of the ${\gamma}-Al_2O_3$ obtained upon KOH treatment of 4M at $90^{\circ}C$ for 1h, it showed a very narrow unimodal pore size distribution, and also formed much mesopore at a diameter of around $40~80{\AA}$. The specific surface area was $250\textrm{m}^2/g$ and the total pore volume was $0.654\textrm{cm}^3/g$.