Soon Ki Jeong

Electrochemical Properties of Multi-Wall Carbon Nanotubes as a Novel Negative Electrode for Calcium Secondary Batteries

We investigated the electrochemical behavior and properties of multi-wall carbon nanotubes (MWCNTs) as a novel negative electrode for calcium ion batteries during charging and discharging. The second charge and discharge capacities were ~63 and ~43 mAh g–1 in propylene carbonate-based electrolyte and ~86 and ~60 mAh g–1 in ethylene carbonate-based electrolyte, respectively. X-ray diffraction analysis results showed that the inter-layer distance of the MWCNTs was increased after charging, indicating that calcium ions were intercalated into the MWCNT graphitic sheets during the charging. The electrochemical performance of the MWCNT electrode was improved by using ball milling to introduce defects.

Electrochemical Properties of NbO as a Negative Electrode Material for Lithium Secondary Batteries

The electrochemical properties of niobium monoxide, NbO, were investigated as a negative electrode material for lithium-ion batteries. Lithium ions were inserted into and extracted from NbO material at potentials < 1.0 V versus Li/Li+, involving formation of a solid electrolyte interface (SEI) on the NbO surface in the first cycle. Its reversible capacity is ~67 mAh g–1 with the capacity retention of ~109% after 50 cycles. The magnitude of charge transfer resistance was greatly decreased by ball-milling the pristine NbO, whereas the ball-milling had no effect on the SEI resistance.

Effect of Electrolyte Concentration on Electrochemical Properties of Zinc Hexacyanoferrate Electrode in Zinc-Ion Batteries

The aqueous rechargeable zinc ion battery (ARZIB) system has been actively studied in the field of energy storage. Prussian blue analogues (PBAs) are considered effective cathode materials in the ARZIB system. In our previous study, Zn(NO3)2 solutions of different concentrations were used as electrolytes in an ARZIB system with a zinc hexacyanoferrate (ZnHCF) electrode. And the effect of electrolyte concentration on the electrochemical performance was studied. In this study, the effect of electrolyte concentration was demonstrated through electrochemical tests and Raman analysis. Charge/discharge tests were conducted at different electrolyte concentrations. And electrochemical performance degradation was observed above a certain electrolyte concentration. This effect was due to the strong interaction between the zinc cations and the nitrate anions, confirmed by the Raman spectroscopy analysis of the Zn(NO3)2 electrolyte.

Electrochemical Decomposition of Poly(Vinylidene Fluoride) Binder for a Graphite Negative Electrode in Lithium-Ion Batteries

To clarify the electrochemical decomposition of poly (vinylidene fluoride) (PVdF) used as a binder for lithium-ion batteries while simultaneously verifying the correlation between electrode resistance and the PVdF content in graphite negative electrodes, in this study, we applied lithium bis (trifluoromethanesulfonyl) imide, which suppresses graphite exfoliation, as a salt. As a result, the electrochemical decomposition of PVdF was observed at a higher potential than that at which the electrolyte was decomposed during the reduction process. Additionally, this study demonstrated (through electrochemical impedance spectroscopy analysis) that electrode resistances such as solid electrolyte interface and charge transfer resistance proportionally increased with the PVdF content.

Electrochemical Redox Reactions of Lithium Ion on Nickel Electrode in Propylene Carbonate-Based Solutions

This study investigated the effect of a co-solvent on the lithium metal negative electrode to understand the growth of dendritic lithium and the battery performance. An electrolyte was prepared by adding a dimethyl carbonate (DMC) co-solvent in a propylene carbonate (PC) solvent. Adding DMC, considerably improved the unstable and low cyclic efficiency in the PC only electrolyte was considerably improved. Scanning electron microscopy showed that the growth of dendritic lithium was affected by the quantity of DMC. The more DMC was added, the more the dendritic lithium formation was suppressed. Fourier transform infrared spectroscopy revealed that the surface component of the deposited lithium was different, depending on the quantity of DMC added. This study successfully demonstrated that DMC co-solvent could suppress dendritic lithium.

Electrochemical Properties of Carbon-Coated NbO2 as a Negative Electrode for Lithium-Ion Batteries

We investigated the electrochemical properties of carbon-coated niobium dioxide (NbO2) as a negative electrode material for lithium-ion batteries. Carbon-coated NbO2 powders were synthesized by ball-milling using carbon nanotubes as the carbon source. The carbon-coated NbO2 samples were of smaller particle size compared to the pristine NbO2 samples. The carbon layers were coated non-uniformly on the NbO2 surface. The X-ray diffraction patterns confirmed that the inter-layer distances increased after carbon coating by ball-milling. This lead to decreased charge-transfer resistance, confirmed by electrochemical impedance spectroscopy, allowing electrons and lithium-ions to quickly transfer between the active material and electrolyte. Electrochemical performance, including capacity and initial coulombic efficiency, was therefore improved by carbon coating by ball-milling.

Electrochemical Properties of Carbon-Coated FeS2 as a Positive Electrode for Lithium Secondary Batteries

The electrochemical properties of carbon-coated FeS2 were investigated as a positive electrode material for lithium secondary batteries. The carbon-coated FeS2 powders were synthesized by ball-milling using polyaniline as the carbon source. The particles in the carbon-coated FeS2 samples were smaller than those in the pristine FeS2 samples. The electrochemical performance, including capacity, of these batteries was improved by carbon-coating by ball-milling. However, the initial coulombic efficiency decreased because of the reduction of the oxidized products on FeS2 surface. The reduction in particle size provides a larger contact area for the electrolyte. Larger quantities of oxidation products were formed by the reduction of FeS2 in the presence of air and water after carbon-coating. Therefore, the poor initial coulombic efficiencies of carbon-coated FeS2 electrodes were caused by the reduction of the oxidized products on the FeS2 surface.

Electrochemical Properties of Li4Ti5O12 as a Negative Electrode for Calcium Secondary Batteries in Ca(TFSI)2/THF Electrolyte

We investigated the electrochemical behavior and properties of lithium titanate oxide as the negative electrode for calcium ion batteries during charge/discharge tests in tetrahydrofuran (THF)-based electrolyte. The reversible charge and discharge capacities of ~150 and ~145 mAh g–1 were observed, respectively, in THF-based electrolyte. They are larger than those obtained in propylene carbonate-based electrolyte. Moreover, interesting charge/discharge curves were observed, which might be attributed to structural changes during the insertion/extraction of calcium ions. These results were confirmed by the charge/discharge curves and scanning electron microscopy images.

Effects of Poly(Vinylidene Fluoride) Content on Electrochemical Properties of a Graphite Negative Electrode in Lithium Secondary Batteries

We investigated the effect of poly (vinylidene fluoride) (PVdF) binder content on graphite negative electrodes for lithium secondary batteries. The negative electrode was prepared by artificial graphite powder and poly (vinylidene fluoride) binder. Scanning electron microscopy, charge/discharge test, and electrochemical impedance microscopy were conducted. As a result of electrochemical analysis, we confirmed that the electrochemical behavior varied according to the PVdF content (5, 10, 15, 50, and 90 wt%). In addition, charge/discharge test and electrochemical impedance microscopy results showed the high irreversible capacities and resistances, observed for electrodes containing PVdF contents of 50 and 90 wt%. This demonstrated that decomposition of the binder was generated during electrochemical analysis.

Effects of Dimethoxyethane as a Co-Solvent on Electrochemical Formation of a Surface Film on Graphite in an Ethylene Carbonate-Based Solution

The electrochemical processes occurring at the surface of a highly ordered pyrolytic graphite electrode were investigated, to understand the effects of dimethoxyethane as a co-solvent on the formation of a surface film. In-situ electrochemical atomic force microscopy revealed that a thin film of ~5 nm thickness was formed on the graphite surface after the first potential cycling. There was no evidence of co-intercalation of the solvent molecules. The cyclic voltammetry analysis revealed that a irreversible reduction peak closely related to the film formation was present at ~1.7 V vs. Li+/Li.