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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, Yongwon,Lee, Tae Kyung,Kim, Saehun,Lee, Jeongmin,Ahn, Youngjun,Kim, Koeun,Ma, Hyeonsu,Park, Gumjae,Lee, Sang-Min,Kwak, Sang Kyu,Choi, Nam-Soon Elsevier 2020 Nano energy Vol.67 No.-
<P><B>Abstract</B></P> <P>Li metal anodes and Ni-rich layered oxide cathodes with high reversible capacities are promising candidates for the fabrication of high energy density batteries. However, low Coulombic efficiency, safety hazards from likely vertical Li growth, and morphological instability of Ni-rich cathodes hinder the practical applications of these electrodes. Here, we report that fluorinated compounds can be employed as interface modifiers to extend the applicable voltage range of ether-based electrolytes, which have been used specifically so far for lithium metal batteries with charging cut-off voltages lower than 4 V (vs. Li/Li<SUP>+</SUP>). A complementary electrolyte design using both 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether and fluoroethylene carbonate in concentrated ether-based electrolytes significantly improves the capacity retention (99.1%) in a Li|LiNi<SUB>0.8</SUB>Co<SUB>0.1</SUB>Mn<SUB>0.1</SUB>O<SUB>2</SUB> full cell, with a high Coulombic efficiency of 99.98% after 100 cycles at 25 °C. Thus, the modified electrolyte system is promising for addressing the reductive and oxidative decompositions of labile ether-based electrolytes in high energy density Li metal batteries with Ni-rich cathodes.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Ether-based electrolyte formulation for 4V-class Li metal batteries is presented. </LI> <LI> FEC and TTE are employed as the electrode–electrolyte interface modifiers. </LI> <LI> Fluorine-enriched interfaces enable high-performance Li metal batteries. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
Lee, Seungmin,Lee, Yohan,Lee, Jaehyoung,Lee, Huen,Seo, Yongwon American Chemical Society 2013 Environmental science & technology Vol.47 No.22
<P>The methane (CH<SUB>4</SUB>) – carbon dioxide (CO<SUB>2</SUB>) swapping phenomenon in naturally occurring gas hydrates is regarded as an attractive method of CO<SUB>2</SUB> sequestration and CH<SUB>4</SUB> recovery. In this study, a high pressure microdifferential scanning calorimeter (HP μ-DSC) was used to monitor and quantify the CH<SUB>4</SUB> – CO<SUB>2</SUB> replacement in the gas hydrate structure. The HP μ-DSC provided reliable measurements of the hydrate dissociation equilibrium and hydrate heat of dissociation for the pure and mixed gas hydrates. The hydrate dissociation equilibrium data obtained from the endothermic thermograms of the replaced gas hydrates indicate that at least 60% of CH<SUB>4</SUB> is recoverable after reaction with CO<SUB>2</SUB>, which is consistent with the result obtained via direct dissociation of the replaced gas hydrates. The heat of dissociation values of the CH<SUB>4</SUB> + CO<SUB>2</SUB> hydrates were between that of the pure CH<SUB>4</SUB> hydrate and that of the pure CO<SUB>2</SUB> hydrate, and the values increased as the CO<SUB>2</SUB> compositions in the hydrate phase increased. By monitoring the heat flows from the HP μ-DSC, it was found that the noticeable dissociation or formation of a gas hydrate was not detected during the CH<SUB>4</SUB> – CO<SUB>2</SUB> replacement process, which indicates that a substantial portion of CH<SUB>4</SUB> hydrate does not dissociate into liquid water or ice and then forms the CH<SUB>4</SUB> + CO<SUB>2</SUB> hydrate. This study provides the first experimental evidence using a DSC to reveal that the conversion of the CH<SUB>4</SUB> hydrate to the CH<SUB>4</SUB> + CO<SUB>2</SUB> hydrate occurs without significant hydrate dissociation.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/esthag/2013/esthag.2013.47.issue-22/es403542z/production/images/medium/es-2013-03542z_0012.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/es403542z'>ACS Electronic Supporting Info</A></P>
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, 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>
2-Propanol as a co-guest of structure II hydrates in the presence of help gases.
Lee, Youngjun,Lee, Seungmin,Park, Sungwon,Kim, Yunju,Lee, Jong-Won,Seo, Yongwon American Chemical Society 2013 The journal of physical chemistry. B, Condensed ma Vol.117 No.8
<P>The enclathration of 2-propanol (2-PrOH) as a co-guest of structure II (sII) hydrates in the presence of CH4 and CO2 was experimentally verified with a focus on macroscopic phase behaviors and microscopic analytical methods such as powder X-ray diffraction (PXRD) and NMR spectroscopy. 2-PrOH functioned as a hydrate promoter in the CH4 + 2-PrOH systems, whereas it functioned as an apparent hydrate inhibitor in the CO2 + 2-PrOH systems despite the inclusion of 2-PrOH in the hydrate lattices. From the PXRD patterns, both double CH4 + 2-PrOH and double CO2 + 2-PrOH hydrates were identified to be cubic (Fd3m) sII hydrates. From the (13)C NMR spectra, it was found that, at a lower 2-PrOH concentration, the small 5(12) cages of the sII hydrate were occupied by CH4 molecules only, whereas the large 5(12)6(4) cages were shared by CH4 and 2-PrOH molecules. However, at a stoichiometric concentration, the large cages were occupied by 2-PrOH molecules only, and the corresponding chemical formula for this concentration is 1.50CH40.98 2-PrOH17H2O.</P>
Lee, Bo Ram,Sa, Jeong-Hoon,Hong, Sang Yeon,Lee, Ju Dong,Lee, Kun-Hong,Seo, Yongwon,Sum, Amadeu K. American Chemical Society 2019 The Journal of Physical Chemistry Part C Vol.123 No.6
<P>The current knowledge of guest-guest interactions and co-occupation in clathrate hydrates is exclusive for the same guests (H<SUB>2</SUB> or N<SUB>2</SUB>) at moderate pressure. Here, we introduce the unusual co-occupation of distinct guests in the metastable state of hydrates. With controlled hydrate fraction, particle size, and intensification of the sintering of SF<SUB>6</SUB> hydrate particles formed from water and SF<SUB>6</SUB> gas as a help gas, we observed an abnormal but unique synchronous behavior in Raman intensities of two guest molecules (SF<SUB>6</SUB> and N<SUB>2</SUB>/H<SUB>2</SUB>) in hydrates consistently and repeatedly; over time, the scattering intensity for the guests (i) increases, (ii) decreases, and (iii) finally reaches the stable level. Without a concentration change of SF<SUB>6</SUB>, this abnormal behavior must arise from the possible changes in the scattering cross section of the molecules, suggesting that N<SUB>2</SUB>/H<SUB>2</SUB> strongly interacts with SF<SUB>6</SUB> in the large cages, resulting in a possible co-occupation during the metastable transition. These observations on the metastability of gas hydrate attest the importance of the sintering effect as a barrier to prevent fast gas diffusion for reaching equilibrium, which could have significant implication in increasing overall gas storage in clathrate hydrates.</P> [FIG OMISSION]</BR>
Lee, Hyun Ho,Nam, Dongsik,Kim, Choon-Ki,Kim, Koeun,Lee, Yongwon,Ahn, Young Jun,Lee, Jae Bin,Kwak, Ja Hun,Choe, Wonyoung,Choi, Nam-Soon,Hong, Sung You American Chemical Society 2018 ACS APPLIED MATERIALS & INTERFACES Vol.10 No.12
<P>Here, we report the first electrochemical assessment of organophosphonate-based compound as a safe electrode material for lithium-ion batteries, which highlights the reversible redox activity and inherent flame retarding property. Dinickel 1,4-benzenediphosphonate delivers a high reversible capacity of 585 mA h g<SUP>-1</SUP> with stable cycle performance. It expands the scope of organic batteries, which have been mainly dominated by the organic carbonyl family to date. The redox chemistry is elucidated by X-ray absorption spectroscopy and solid-state <SUP>31</SUP>P NMR investigations. Differential scanning calorimetry profiles of the lithiated electrode material exhibit suppressed heat release, delayed onset temperature, and endothermic behavior in the elevated temperature zone.</P> [FIG OMISSION]</BR>