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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>
Lee, Jaegi,Lee, Jimin,Ryu, Dongmin,Lee, Hochan,Ye, Sung-Joon Institute of Physics in association with the Ameri 2018 Physics in medicine & biology Vol.63 No.19
<P>A Fano cavity test was performed for four general-purpose Monte Carlo codes, EGSnrc, PENELOPE, MCNP6 and Geant4 to evaluate the accuracy of their electron transport algorithms in magnetic fields. In the simulations, a plane-parallel ionization chamber was modelled as a circular gas disk sandwiched between two circular solid wall disks. It was assumed that an isotropic and uniform line source per unit mass along the central axis of the gas and solid emits mono-energetic electrons with energies 0.01, 0.1, 1.0 and 3.0 MeV at different magnetic field strengths 0, 0.35, 1.0, 1.5 and 3.0 T in the electron transport mode (no Bremsstrahlung). The relative difference between the calculated dose to the gas region and the initial total energy of emitted electrons per unit mass was defined as the accuracy of Monte Carlo codes. In all results, EGSnrc with the enhanced electric and magnetic field (EEMF) macros was not considerably sensitive to the step size parameters and showed accuracy less than 0.18% ± 0.06% with a coverage factor <I>k</I> = 2. The other codes could not achieve competent accuracy with their default settings of step size parameters, compared to EGSnrc with the EEMF macros. With the step size parameters carefully selected, the accuracy of PENELOPE and MCNP6 was within 1.0% and 0.4%, respectively. However, Geant4 showed accuracy within 1.7% except in 3.0 T. EGSnrc with the EEMF macros achieved the best accuracy for the Fano test at the electron energies and the magnetic field strengths investigated in this study and thus, would be recommended to simulate dose responses of ionization chambers in the presence of magnetic fields.</P>
Lee, Yongwon,Lee, Jaegi,Lee, Jeongmin,Kim, Koeun,Cha, Aming,Kang, Sujin,Wi, Taeung,Kang, Seok Ju,Lee, Hyun-Wook,Choi, Nam-Soon American Chemical Society 2018 ACS APPLIED MATERIALS & INTERFACES Vol.10 No.17
<P>Sodium (Na) metal anodes with stable electrochemical cycling have attracted widespread attention because of their highest specific capacity and lowest potential among anode materials for Na batteries. The main challenges associated with Na metal anodes are dendritic formation and the low density of deposited Na during electrochemical plating. Here, we demonstrate a fluoroethylene carbonate (FEC)-based electrolyte with 1 M sodium bis(fluorosulfonyl)imide (NaFSI) salt for the stable and dense deposition of the Na metal during electrochemical cycling. The novel electrolyte combination developed here circumvents the dendritic Na deposition that is one of the primary concerns for battery safety and constructs the uniform ionic interlayer achieving highly reversible Na plating/stripping reactions. The FEC-NaFSI constructs the mechanically strong and ion-permeable interlayer containing NaF and ionic compounds such as Na<SUB>2</SUB>CO<SUB>3</SUB> and sodium alkylcarbonates.</P> [FIG OMISSION]</BR>
Lee, Jaegi,Park, Jong Min,Wu, Hong‐,Gyun,Kim, Jin Ho,Ye, Sung‐,Joon unknown 2015 Journal of applied clinical medical physics Vol.16 No.6
<P>The purpose of the study was to investigate the dosimetric effect defining the body structure with various Hounsfield unit (HU) threshold values on the dose distributions of volumetric‐modulated arc therapy (VMAT) plans. Twenty patients with prostate cancer and twenty patients with head and neck (H&N) cancer were retrospectively selected. For each patient, the body structure was redefined with HU threshold values of −180(<SUB>Body180</SUB>), −350(<SUB>Body350</SUB>), −700(<SUB>Body700</SUB>), and −980(<SUB>Body980</SUB>). For each patient, dose‐volumetric parameters with those body structures were calculated using identical VMAT plans. The differences in dose‐volumetric parameters due to the varied HU threshold values were calculated. For the prostate boost target volume, the maximum dose, mean dose, <SUB>D95%</SUB>, and <SUB>D5%</SUB> with <SUB>Body180</SUB> were higher than those with <SUB>Body980</SUB> by approximately 0.7% (p<0.001). For H&N target volumes, the changes in <SUB>D95%</SUB> of the targets receiving 67.5 Gy, 54 Gy, and 48 Gy between <SUB>Body180</SUB> and <SUB>Body980</SUB> were −1.2%, −0.9%, and −1.2%, respectively (p<0.001). The differences were larger for H&N VMAT plans than for prostate VMAT plans due to the inclusion of an immobilization device in the irradiated region in H&N cases. To apply all attenuating materials to dose calculation, the body structure would be defined with −980 HU. Otherwise, systematic error of about 1%, resulting in underdosage of the target volume, can occur.</P><P>PACS number: 87.55.ne</P>
Lee, Jaegi,Kim, Jung-In,Ye, Sung-Joon,Kim, Hak Jae,Carlson, Joel,Park, Jong Min British Institute of Radiology 2015 The British journal of radiology Vol.88 No.1055
<P>To evaluate the dosimetric effects of roll-rotational setup errors of stereotactic ablative radiotherapy (SABR) for lung cancer using volumetric modulated arc therapy (VMAT).</P>
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>