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Electrochemical studies of molybdate-doped LiFePO4 as a cathode material in Li-ion batteries.
Kim, Ketack,Kam, Daewoong,Kim, Yeonjoo,Kim, Sinwoong,Kim, Minsoo,Kim, Hyun-Soo American Scientific Publishers 2013 Journal of Nanoscience and Nanotechnology Vol.13 No.5
<P>The use of molybdate as a new anionic dopant that replaces phosphate in LiFePO4 was studied. When a small amount of molybdate (0.5 mol%) was used as a dopant, the olivine structure was maintained, while the lattice volume increased by 0.4%. The expanded volume facilitates ionic transfer, because of which the capacity of doped LiFePO4 at high current discharge rates is higher than that of pure LiFePO4. The discharge value increased by 25.2% at a charge rate of 5 C when the material was doped with 0.5 mol% molybdate ions. The slight expansion of the lattice volume in the olivine structure facilitates a fast redox reaction by lowering the charge transfer resistance. The current values from cyclic voltammetry indicate that the oxidation (charge) process of the cathode material is more improved than the corresponding reduction (discharge) process. Increasing the level of doping beyond 0.5 mol% had no effect on the results. At some discharge rates, the discharge capacity became worse. Because molybdate is divalent while phosphate is trivalent, a large number of molybdate ions in the lattice can exert considerable stress on the structure.</P>
Park, Sieun,Kim, Ketack Elsevier 2017 Journal of Power Sources Vol.338 No.-
<P><B>Abstract</B></P> <P>Tetramethylammonium (TMA) ion is the smallest quaternary ammonium ion (QAI) that can be used in electrochemical double layer capacitor (EDLC) applications. Small ions improve the capacitance of EDLCs by increasing the adsorbed ionic density. Herein, we first report the utilization of TMA BF<SUB>4</SUB> in EDLCs and the properties of the smallest QAI are investigated. However, because of the poor solubility of TMA BF<SUB>4</SUB>, it must be combined with another salt, forming a binary-salt electrolyte. In this study, the maximum TMA BF<SUB>4</SUB> concentration used was 5 mol%. These binary salt mixtures contain a conventional electrolyte salt such as tetraethylammonium BF<SUB>4</SUB>, trimethylethylammonium BF<SUB>4</SUB>, or spiro-bipyrrolidinium BF<SUB>4</SUB>. In addition, 4–5 mol% TMA BF<SUB>4</SUB> was added to the conventional salt solution and a binary-salt electrolyte was obtained, leading to 12–13% increase in the capacitance compared to that of a 100 mol% conventional electrolyte at 10 A g<SUP>−1</SUP>. This work proposes a new method to improve the performance of EDLCs by using binary-salt electrolytes.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Poorly soluble TMA BF<SUB>4</SUB> is usable in EDLCs as a component of binary-salt electrolytes. </LI> <LI> TMA BF<SUB>4</SUB> changes conventional electrolytes into high-performance materials. </LI> <LI> Improvement of the performance by TMA BF<SUB>4</SUB> is investigated. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
Ahn, Seyoung,Kim, Ketack,Kim, Hyunsoo,Nam, Sangyong,Eom, Seungwook Royal Swedish Academy of Sciences 2010 Physica scripta Vol.2010 No.t139
<P>We prepared La<SUB>0.7</SUB>Sr<SUB>0.3</SUB>Co<SUB>1−<I>x</I></SUB>Fe<SUB><I>x</I></SUB>O<SUB>3</SUB> (<I>x</I>=0.1–0.4) catalysts for a zinc air battery by using the citrate method under controlled pH. The prepared precursor powder was heat treated at the calcination temperature of 700 °C and examined for the optimum structure of the cathode. The structure and performance of the catalysts were examined by x-ray diffraction and a scanning electron microscope. The air electrode was prepared by blending the catalyst, Vulcan XC-72R (carbon black), and (polytetrafluoroethylene PTFE) suspension. The oxygen reduction reaction and the oxygen evolution reaction were examined by linear sweep voltammetry. The results showed that La<SUB>0.7</SUB>Sr<SUB>0.3</SUB>Co<SUB>0.7</SUB>Fe<SUB>0.3</SUB>O<SUB>3</SUB> (LSCF0.7) is an excellent catalyst for the zinc air secondary battery.</P>
Various Alcohols as Electrolysis Suppressants in Zn-air Secondary Batteries
Yang, Soyoung,Kim, Ketack The Korean Electrochemical Society 2018 Journal of electrochemical science and technology Vol.9 No.4
The gelling agent used in Zn-air cells plays a role in improving battery life. It prevents the evaporation of water and diffusion of $Zn^{2+}$ ions away from the current collector. Additional functionality was incorporated by replacing some of the gelling agents with new materials. Alcohols with moderate viscosity, namely maltose, sucrose, poly ethylene glycol 600, and 2-hydroxyethyl cellulose, were used to replace some gelling agents in this work. Among these alcohols, poly ethylene glycol 600 and 2-hydroxyethyl cellulose improved the cycle life of full cells. This improved cycle life was attributed to the inhibition of water electrolysis and the improved cycle life of the anode.
Observation of Water Consumption in Zn-air Secondary Batteries
Yang, Soyoung,Kim, Ketack The Korean Electrochemical Society 2019 Journal of electrochemical science and technology Vol.10 No.4
Zn-air battery uses oxygen from the air, and hence, air holes in it are kept open for cell operation. Therefore, loss of water by evaporation through the holes is inevitable. When the water is depleted, the battery ceases to operate. There are two water consumption routes in Zn-air batteries, namely, active path (electrolysis) and passive path (evaporation and corrosion). Water loss by the active path (electrolysis) is much faster than that by the passive path during the early stage of the cycles. The mass change by the active path slows after 10 h. In contrast, the passive path is largely constant, becoming the main mass loss path after 10 h. The active path contributes to two-thirds of the electrolyte consumption in 24 h of cell operation in 4.0 M KOH. Although water is an important component for the cell, water vapor does not influence the cell operation unless the water is nearly depleted. However, high oxygen concentration favors the discharge reaction at the cathode.
황병현,김기택,Hwang, Byunghyun,Kim, Ketack 한국전기화학회 2013 한국전기화학회지 Vol.16 No.3
레독스 플로우 전지(RFB)는 대형에너지 장치로서 신재생 에너지와 같은 전력발생이 일정하지 못한 상황이나 전력수요가 급증감하여 효율적인 에너지의 운용이 요구될 때 효과적으로 사용할 수 있는 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, crossover, 이온 선택성, 용해도 등의 개선을 통해서 새로운 레독스 플로우 전지의 탄생을 기대할 수 있다. 용량의 개선을 위해서 다양한 수계 및 비수계 레독스 쌍의 연구가 되고 있는데 crossover에 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. Redox flow batteries are attractive energy-storage devices for renewable energy and peak-power energy control. Even though some prototypes are available already, many new materials are under development for new battery systems. In this reports, redox pairs and theirs properties are explained, by which one can understand issues with redox pairs, such as contaminations, cross-over, ionic selectivity, and solubility. Batteries that have the same redox pairs in both electrode compartments can be operated longer than those with different redox pairs due to the prevention form the cross-contamination. There are undivided redox flow batteries that have no membrane, which is another direction improving cycle life of the batteries.
Hong, Jeehoon,Hwang, Byunghyun,Lee, Junghye,Kim, Ketack The Korean Electrochemical Society 2017 Journal of electrochemical science and technology Vol.8 No.1
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 10-20%), 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.