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Mun, Junyoung,Oh, Duk-Jin,Park, Min Sik,Kwon, Ohmin,Kim, Hyung-Tae,Jeong, Seonghun,Kim, Young Gyu,Lee, Myung-Jin The Electrochemical Society 2018 Journal of the Electrochemical Society Vol.165 No.2
<P>Nonaqueous redox flow batteries (RFBs) with an organic electrolyte can work at voltages higher than 2.1 V, thanks to the excellent electrochemical stability of such electrolytes. However, the biggest challenge related to nonaqueous RFBs is that the electrochemically active salts used in these batteries exhibit lower solubilities in organic electrolytes compared to those in aqueous electrolytes. In this study, bis(trifluoromethanesulfonyl) imide (TFSI) is investigated as the counter anions for the complexes of iron and nickel tris(2,2'-bipyridine) ((Bpy)(3)) for use as electrolytes in high-energy RFBs. The synthesized salts were characterized systematically through ab-initio calculations, nuclear magnetic resonance (NMR), inductively coupled plasma mass spectrometry (ICP-MS) and electrochemical analyses. Ni(Bpy)(3)(TFSI)(2) and Fe(Bpy)(3)(TFSI)(2) containing bulky imide anions exhibit the improved solubility by weakening inter-anion Coulombic interactions, via charge delocalization. (c) 2018 The Electrochemical Society.</P>
New dry carbon nanotube coating of over-lithiated layered oxide cathode for lithium ion batteries
Mun, Junyoung,Park, Jin-Hwan,Choi, Wonchang,Benayad, Anass,Park, Jun-Ho,Lee, Jae-Myung,Doo, Seok-Gwang,Oh, Seung M. The Royal Society of Chemistry 2014 Journal of Materials Chemistry A Vol.2 No.46
<▼1><P>For high rate capability and energy density of lithium ion batteries, over-lithiated layered cathodes coated by multiwall carbon nanotube were prepared by a novel dry method without decay in the structure.</P></▼1><▼2><P>Carbon serves as one of the best coating materials for the cathode in lithium ion batteries. This is because it can solve two main problems, which are surface deterioration and poor electrical conductivity. However, the conventional carbon coating procedures and, chemical carbonization processes, are especially difficult to implement for the oxide cathode, which could thereby deteriorate the oxide structure. We prepared a new dry 100 nm-thick homogeneous multi-walled carbon nanotube (MWCNT) coating on the high-capacity oxide cathode material, Li1.17Ni0.17Co0.1Mn0.56O2, by applying shear stress without breaking down the crystal structure or morphology of the cathode. The electronic conductivity of the carbon composite with the coated sample is 170 mS cm<SUP>−1</SUP>, which is over 40 times as much as the conductivity of the pristine cathode containing the same amount of carbon. In addition, at a high current condition of 2450 mA g<SUP>−1</SUP>, a specific capacity of 103 mA h g<SUP>−1</SUP> is observed even with 3 percent of the carbon (in weight) constituting the coated MWCNT. The unconventionally improved performances are explained by the suppression of the electronic resistance and surface charge transfer resistance by electrochemical analyses.</P></▼2>
Kang, Seok Mun,Park, Jae-Hyuk,Jin, Aihua,Jung, Young Hwa,Mun, Junyoung,Sung, Yung-Eun American Chemical Society 2018 ACS APPLIED MATERIALS & INTERFACES Vol.10 No.4
<P>Although sodium ion batteries (NIBs) have gained wide interest, their poor energy density poses a serious challenge for their practical applications. Therefore, high-energy-density cathode materials are required for NIBs to enable the utilization of a large amount of reversible Na ions. This study presents a P2-type Na0.67Co1-x,TixO2 (x < 0.2) cathode with an extended potential range higher than 4.4 V to present a high specific capacity of 166 mAh g(-1). A group of P2-type cathodes containing various amounts of Ti is prepared using a facile synthetic method. These cathodes show different behaviors of the Na+/vacancy ordering. Na0.67CoO2 suffers severe capacity loss at high voltages due to irreversible structure changes causing serious polarization, while the Ti-substituted cathodes have long credible cycleability as well as high energy. In particular, Na0.67Co0.90Ti0.10O2 exhibits excellent capacity retention (115 mAh g(-1)) even after 100 cycles, whereas Na0.67CoO2 exhibits negligible capacity retention (<10 mAh g(-1)) at 4.5 V cutoff conditions. Na0.67Co0.90Ti0.10O2 also exhibits outstanding rate capabilities of 108 mAh g(-1) at a current density of 1000 mA g(-1) (7.4 C). Increased sodium diffusion kinetics from mitigated Na+/vacancy ordering, which allows high Na+ utilization, are investigated to find in detail the mechanism of the improvement by combining systematic analyses comprising TEM, in situ XRD, and electrochemical methods.</P>
Tron, Artur,Mun, Junyoung The Korean Electrochemical Society 2022 Journal of electrochemical science and technology Vol.13 No.1
Owing to the rising concern of global warming, lithium-ion batteries have gained immense attention over the past few years for the development of highly efficient electrochemical energy conversion and storage systems. In this study, alpha-phase VOPO<sub>4</sub>·2H<sub>2</sub>O with nanosheet morphology was prepared via a facile hydrothermal method for application in high-performance lithium-ion batteries. The X-ray diffraction and scanning electron microscopy (SEM) analyses indicated that the obtained sample had an alpha-2 (αII) phase, and the nanosheet morphology of the sample was confirmed using SEM. The lithium-ion battery with VOPO<sub>4</sub>·2H<sub>2</sub>O as the anode exhibited excellent long-term cycle life and a high capacity of 256.7 mAh g<sup>-1</sup> at room temperature. Prelithiation effectively improved the specific capacity of pristine VOPO<sub>4</sub>·2H<sub>2</sub>O. The underlying electrochemical mechanisms were investigated by carrying out AC impedance, rate capability, and other instrumental analyses.