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Lee, Jaegi,Lee, Yongwon,Lee, Jeongmin,Lee, Sang-Min,Choi, Jeong-Hee,Kim, Hyungsub,Kwon, Mi-Sook,Kang, Kisuk,Lee, Kyu Tae,Choi, Nam-Soon American Chemical Society 2017 ACS APPLIED MATERIALS & INTERFACES Vol.9 No.4
<P>We present an ultraconcentrated electrolyte composed of 5 M sodium bis(fluorosulfonyl)imide in 1,2-dimethoxyethane for Na metal anodes coupled with high-voltage cathodes. Using this electrolyte, a very high Coulombic efficiency of 99.3% at the 120th cycle for Na plating/stripping is obtained in Na/stainless steel (SS) cells with highly reduced corrosivity toward Na metal and high oxidation durability (over 4.9 V versus Na/Na+) without corrosion of the aluminum cathode current collector. Importantly, the use of this ultraconcentrated electrolyte results in substantially improved rate capability in Na/SS cells and excellent cycling performance in Na/Na symmetric cells without the increase of polarization. Moreover, this ultraconcentrated electrolyte exhibits good compatibility with high-voltage Na4Fe3(PO4)(2)(P2O7) and Na-0.7(Fe0.5Mn0.5)O-2 cathodes charged to high voltages (>4.2 V versus Na/Na+), resulting in outstanding cycling stability (high reversible capacity of 109 mAh g(-1) over 300 cycles for the Na/Na4Fe3(PO4)(2)(P2O7) cell) compared with the conventional dilute electrolyte, 1 M NaPF6 in ethylene carbonate/propylene carbonate (5/5, v/v).</P>
Hyungsub Lee,Gwan-Su Yi,Yoonkey Nam 대한의용생체공학회 2023 Biomedical Engineering Letters (BMEL) Vol.13 No.4
Modularity is one of the important structural properties that affect information processing and other functionalities of neuronalnetworks. Researchers have developed in-vitro clustered network models for reproducing the modularity, but it is stillchallenging to control the segregation and integration of several sub-populations of them. We cultured clustered networkswith alginate patterning and collected the electrophysiological signals to investigate the changes in functional propertiesduring the development. We built inter-connected neuronal clusters using alginate micro-patterning with a circular shape onthe surface of the micro-electrode array. The neuronal clusters were enabled to be connected at 3 or 10 days-in-vitro (DIV)by removing the barrier. The neuronal signals from different types of networks were collected from 16 to 34 DIV, and functionalcharacteristics were examined. Connectivity and burst motif analysis were carried out to find out the relation betweenthe structure and function of the networks. Neuronal networks with clustered structure showed different activity propertiesfrom the random networks along the development. The clustered networks had more short-range connections compared tothe random networks. In the network burst motif analysis, the clustered networks showed more various patterns and a slowerpropagation of the activation patterns. In this study, we successfully cultured neuronal networks with clustered structure,and the structure affected the functional properties. The network model suggested in this study will be a good solution forobserving the effect of structure on function during their development.
Lee, Yongwon,Lee, Jaegi,Kim, Hyungsub,Kang, Kisuk,Choi, Nam-Soon Elsevier 2016 Journal of Power Sources Vol.320 No.-
<P><B>Abstract</B></P> <P>Employing linear carbonates such as dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) as electrolyte solvents provides an opportunity to design appropriate electrolyte systems for high-performance sodium-ion batteries (SIBs). However, in practice, the use of linear carbonate-containing electrolytes is quite challenging because linear carbonates readily decompose at Na metal electrodes or sodiated anodes. One of the promising approaches is using an electrolyte additive to resolve the critical problems related to linear carbonates. Our investigation reveals that remarkable enhancement in electrochemical performance of Na<SUB>4</SUB>Fe<SUB>3</SUB>(PO<SUB>4</SUB>)<SUB>2</SUB>(P<SUB>2</SUB>O<SUB>7</SUB>) cathodes with linear carbonate-containing electrolytes is achieved by using a fluoroethylene carbonate (FEC) additive. Importantly, the initial Coulombic efficiency of the Na deposition/stripping on a stainless steel (SS) electrode is drastically improved from 16% to 90% by introducing the FEC additive into ethylene carbonate (EC)/propylene carbonate (PC)/DEC (5/3/2, v/v/v)/0.5 M NaClO<SUB>4</SUB>. The underlying mechanism of FEC at the electrode-electrolyte interface is clearly demonstrated by <SUP>13</SUP>C nuclear magnetic resonance (NMR). In addition, the Na<SUB>4</SUB>Fe<SUB>3</SUB>(PO<SUB>4</SUB>)<SUB>2</SUB>(P<SUB>2</SUB>O<SUB>7</SUB>) cathode in EC/PC/DEC (5/3/2, v/v/v)/0.5 M sodium perchlorate (NaClO<SUB>4</SUB>) with FEC delivers a discharge capacity of 90.5 mAh g<SUP>−1</SUP> at a current rate of C/2 and exhibits excellent capacity retention of 97.5% with high Coulombic efficiency of 99.6% after 300 cycles at 30 °C.</P> <P><B>Highlights</B></P> <P> <UL> <LI> The FEC additive forms a surface film on the Na metal electrode and the cathode. </LI> <LI> The FEC additive allows the use of linear carbonates in sodium-ion batteries. </LI> <LI> FEC-added electrolytes improve cycling performance of Na<SUB>4</SUB>Fe<SUB>3</SUB>(PO<SUB>4</SUB>)<SUB>2</SUB>(P<SUB>2</SUB>O<SUB>7</SUB>) cathodes. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
Highly Stable Iron- and Manganese-Based Cathodes for Long-Lasting Sodium Rechargeable Batteries
Kim, Hyungsub,Yoon, Gabin,Park, Inchul,Hong, Jihyun,Park, Kyu-Young,Kim, Jongsoon,Lee, Kug-Seung,Sung, Nark-Eon,Lee, Seongsu,Kang, Kisuk American Chemical Society 2016 Chemistry of materials Vol.28 No.20
<P>The development of long-lasting and low-cost rechargeable batteries lies at the heart of the success of large-scale energy storage systems for various applications. Here, we introduce Fe- and Mn-based Na rechargeable battery cathodes that can stably cycle more than 3000 times. The new cathode is based on the solid-solution phases of Na4MnxFe3-x(PO4)(2)-(P2O7) (x = 1 or 2) that we successfully synthesized for the first time. Electrochemical analysis and ex situ structural investigation reveal that the electrodes operate via a one phase reaction upon charging and discharging with a remarkably low volume change of 2.1% for Na4MnFe2(PO4)(P2O7), which is one of the lowest values among Na battery cathodes reported thus far. With merits including an open framework structure and a small volume change, a stable cycle performance up to 3000 cycles can be achieved at 1C and room temperature, and almost 70% of the capacity at C/20 can be obtained at 20C. We believe that these materials are strong competitors for large-scale Na-ion battery cathodes based on their low costs, long-term cycle stability, and high energy density.</P>
Anomalous Jahn–Teller behavior in a manganese-based mixed-phosphate cathode for sodium ion batteries
Kim, Hyungsub,Yoon, Gabin,Park, Inchul,Park, Kyu-Young,Lee, Byungju,Kim, Jongsoon,Park, Young-Uk,Jung, Sung-Kyun,Lim, Hee-Dae,Ahn, Docheon,Lee, Seongsu,Kang, Kisuk The Royal Society of Chemistry 2015 ENERGY AND ENVIRONMENTAL SCIENCE Vol.8 No.11
<P>We report a 3.8 V manganese-based mixed-phosphate cathode material for applications in sodium rechargeable batteries; i.e., Na4Mn3(PO4)(2)(P2O7). This material exhibits a largest Mn2+/Mn3+ redox potential of 3.84 V vs. Na+/Na yet reported for a manganese-based cathode, together with the largest energy density of 416 W h kg (1). We describe first-principles calculations and experimental results which show that three-dimensional Na diffusion pathways with low-activation-energy barriers enable the rapid sodium insertion and extraction at various states of charge of the Na4-xMn3(PO4)(2)(P2O7) electrode (where x = 0, 1, 3). Furthermore, we show that the sodium ion mobility in this crystal structure is not decreased by the structural changes induced by Jahn-Teller distortion (Mn3+), in contrast to most manganese-based electrodes, rather it is increased due to distortion, which opens up sodium diffusion channels. This feature stabilizes the material, providing high cycle stability and high power performance for sodium rechargeable batteries. The high voltage, large energy density, cycle stability and the use of low-cost Mn give Na4Mn3(PO4)(2)(P2O7) significant potential for applications as a cathode material for large-scale Na-ion batteries.</P>
In-Situ Annealing Study on the Thermal Stability of Nickel Germanides
Jae-Wook Lee,양철웅,고대홍,Dongwon Lee,Hyungsub Kim,Kyung-Hwan Kwak 한국물리학회 2007 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.50 No.3
This study investigated the formation and the thermal stability of Ni germanides formed in Ni/Ge and Ni$_{0.9}$Ta$_{0.1}$/Ge systems. At temperatures above 550 $^\circ$C, the sheet resistance of the germanides in the Ni$_{0.9}$Ta$_{0.1}$/Ge system was lower than that in the Ni/Ge system. The microstructure of the phases formed by the reaction was examined by using analytical electron microscopy (AEM), and convergent beam electron diffraction (CBED) techniques were used to identify the phase of Ni germanide. In addition, in-situ annealing in transmission electron microscopy (TEM) was used to examine the formation and the morphological evolution of Ni germanides in the Ni/Ge and the Ni$_{0.9}$Ta$_{0.1}$/Ge systems as functions of temperature. The addition of Ta atoms inhibited the agglomeration of Ni germanide and improved the thermal stability of Ni germanide. This study investigated the formation and the thermal stability of Ni germanides formed in Ni/Ge and Ni$_{0.9}$Ta$_{0.1}$/Ge systems. At temperatures above 550 $^\circ$C, the sheet resistance of the germanides in the Ni$_{0.9}$Ta$_{0.1}$/Ge system was lower than that in the Ni/Ge system. The microstructure of the phases formed by the reaction was examined by using analytical electron microscopy (AEM), and convergent beam electron diffraction (CBED) techniques were used to identify the phase of Ni germanide. In addition, in-situ annealing in transmission electron microscopy (TEM) was used to examine the formation and the morphological evolution of Ni germanides in the Ni/Ge and the Ni$_{0.9}$Ta$_{0.1}$/Ge systems as functions of temperature. The addition of Ta atoms inhibited the agglomeration of Ni germanide and improved the thermal stability of Ni germanide.
Electrospun uniaxially-aligned composite nanofibers as highly-efficient piezoelectric material
Lee, Caroline,Wood, David,Edmondson, Dennis,Yao, Dingyu,Erickson, Ariane E.,Tsao, Ching Ting,Revia, Richard A.,Kim, Hyungsub,Zhang, Miqin Elsevier Science B.V., Amsterdam. 2016 CERAMICS INTERNATIONAL Vol.42 No.-