Ketack Kim

Redox Pairs in Redox Flow Batteries

레독스 플로우 전지(RFB)는 대형에너지 장치로서 신재생 에너지와 같은 전력발생이 일정하지 못한 상황이나 전력수요가 급증감하여 효율적인 에너지의 운용이 요구될 때 효과적으로 사용할 수있는 전지모델이다. 일부 상용화된 종류도 있지만 다양한 레독스 쌍과 소재가 연구됨에 따라 개선의 여지가 많은 전지이다. 본 총설에서는 전지의 레독스 쌍(redox pair)의 종류들에 대한 설명을 통하여 레독스 플로우 전지의 전반적인 이해를 돕고자 한다. 레독스 쌍의 혼합오염, cross-over, 이온 선택성, 용해도 등의 개선을 통해서 새로운 레독스 플로우 전지의 탄생을 기대할 수있다. 용량의 개선을 위해서 다양한 수계 및 비수계 레독스 쌍의 연구가 되고 있는데 cross-over에 의해 다소의 용량손실이 있다고 하더라도 혼합오염이 없는 전지라면 레독스 플로우 전지의 내구성의 장점을 살릴 수 있을 것이라 기대한다. 혼합오염이 없는 레독스 플로우 전지 중에는 멤브레인이 필요 없는 전지도 새로운 연구방향으로 모색되고 있다.Abstract: Redox flow batteries are attractive energy-storage devices for renewable energy andpeak-power energy control. Even though some prototypes are available already, many newmaterials are under development for new battery systems. In this reports, redox pairs and theirsproperties are explained, by which one can understand issues with redox pairs, such as con-taminations, cross-over, ionic selectivity, and solubility. Batteries that have the same redox pairsin both electrode compartments can be operated longer than those with different redox pairsdue to the prevention form the cross-contamination. There are undivided redox flow batteriesthat have no membrane, which is another direction improving cycle life of the batteries.Keywords : Redox flow batteries, Redox pairs, Secondary batteries

Components in Zn Air Secondary Batteries

Zinc air 전지의 구성요소와 전지의 특징을 설명하였다. 리튬 이온 전지에 비해 월등히 높은 에 너지 밀도를 가지고 있지만, 충전의 비가역성으로 인한 낮은 용량 유지 특성 때문에 zinc air 이차전지는 아직 상용화되지 못하였다. Zinc air 전지는 충방전에 관여하는 반응들의 속도가 느 려서 그 반응들의 속도를 촉진해야 하는 특징이 있는가 하면 동시에 부식과 수소발생 반응의 속 도는 오히려 느리게 해야 하는 까다로운 조건을 만족해야 한다. 기존의 전지들과 비교하면, 기초 연구뿐 아니라, 전지의 기계적구조, 부식, 복합소재적인 요소의 적용이 더욱 필요한 연구분야라고 하겠다. 출력개선과 부식방지 그리고 공기의 공급에 대비한 물의 증발의 억제 등은 상충하는 성 질을 동시에 만족해야 하는 복합소재의 특성이다.Abstract : Components of zinc-air battery and their problems are explained. Energy density of zinc air battery is superior to other commercial ones including Li-ion batteries. Cycle life of the zinc air batteries is poor because of irreversible redox reactions on both electrodes. In order to improve the performance of the zinc air battery, catalysts, passivation, and the new structure of electrodes should be developed to optimize several reactions in an electrode. Multidisci-plinary efforts, such as mechanics, corrosion science, composite materials are necessary from the beginning of the research to obtain a meaningful product. Keywords : Metal air batteries, Zinc air batteries, Secondary batteries

Neutral Red and Ferroin as Reversible and Rapid Redox Materials for Redox Flow Batteries

Neutral red and ferroin are used as redox indicators (RINs) in potentiometric titrations. The rapid response and reversibility that are prerequisites for RINs are also desirable properties for the active materials in redox flow batteries (RFBs). This study describes the electrochemical properties of ferroin and neutral red as a redox pair. The rapid reaction rates of the RINs allow a cell to run at a rate of 4 C with 89 % capacity retention after the 100th  cycle. The diffusion coefficients, electrode reaction rates, and solubilities of the RINs were determined. The electron-transfer rate constants of ferroin and neutral red are 0.11 and 0.027 cm s-1 , respectively, which are greater than those of the components of all-vanadium and Zn/Br2 cells.

Effects of Cyclic Structure of Ammonium Ions on Capacitance in Electrochemical Double Layer Supercapacitors

The conductivity of the electrolyte used plays a critical role in the optimization of the performance of electrochemical double layer capacitors. However, when the difference in the conductivities of different electrolytes is not significant (only 1020%), the conductivity has little effect on the capacitance. On the other, unlike the conductivity and viscosity of the electrolyte, the cation size directly influences the capacitance. Cyclic ions have a smaller effective radius than that of the corresponding acyclic ions because the acyclic alkyl groups have a greater number of conformational degrees of freedom, such as the rotational, bending, and stretching modes. Consequently, because of the smaller effective size of the cyclic ions, cells containing electrolytes with such ions exhibit higher capacitances than do those with their acyclic counterparts.

1-Ethyl-1-Methyl Piperidinium Bis(Trifluoromethanesulfonyl)Imide as a Co-Solvent for Li-ion Battery Electrodes

In the study, a room temperature ionic liquids as a co-solvent was used to evaluate the feasibility with various electrodes in Li-ion batteries. 1-Ethyl-1-methyl piperidinium bis(tri- fluoromethanesulfonyl)imide(PP12 TFSI) is an ionic liquid that melts at 85 o C. Pure PP12 TFSI is not able to be used as an electrolyte because it is a solid salt at room temperature. PP12 TFSI is mixed with EC/DEC(1/1 vol.%) to prepare mixed solvents. The electrolyte 1.5 M LiPF6 in a mixed solvent having 44 wt.% PP12 TFSI is prepared to evaluated the various electrodes. The electrolytes provides good cycles life of cells with LiNi0.5Mn1.5O4(LNMO), LiFePO4(LFP), Li4Ti5O12(LTO) and artificial graphite. Further improvement of the cell performances can be accomplished by enhancing wettability of electrolytes to electrodes.