Kwang-il Chung

Catalytic effect of transition metal(II)-N,N′-bis(naphthaldehyde)diimines on reduction of thionyl chloride

Abstract A series of transition metal(II) complexes, such as 1,2-bis(naphthylideneimino)ethane [M(II)(NAPET)], 1,3-bis(naphthylideneimino)propane [M(II)(NAPPR)], 1,4-bis(naphthylideneimino)butane [M(II)(NAPBU)] and 1,5-bis(naphthylideneimino)pentane [M(II)(NAPPE)] (M=Co, Cu, Ni), are synthesized. Catalytic effects of these complexes for the reduction of thionyl chloride on a glassy carbon electrode are evaluated by determining kinetic parameters with cyclic voltammetry. The charge transfer process during the reduction of thionyl chloride is affected by the concentration of catalysts. Some tetradentate Schiff base M(II) complexes show catalytic activities for the reduction of thionyl chloride. The catalytic effects are demonstrated from a shift of the reduction potential for thionyl chloride towards a more positive direction and an increase in peak current. Significant improvements in the cell performance have been noted in terms of both thermodynamic and kinetic parameters for the thionyl chloride reduction. An exchange rate constant, k o , of 1.24×10 −8 cm/s was observed at a bare electrode, while larger values of 0.23–1.69×10 −7 cm/s were observed at the catalyst-supported glassy carbon electrode. Thermodynamic and kinetic parameters for thionyl chloride reduction are affected by the chelate ring size of ligands in the metal(II)–Schiff base complexes used as a catalyst.

Electrochemical properties of passivation film on mesophase pitch-based carbon fiber electrode

Abstract We studied the irreversible capacity in negative carbon electrodes for the Li ion battery. In this work, we focused on electrolyte decomposition which is one of the main effects related to film formation. We investigated the properties of the film and the process of Li + intercalation into the mesophase pitch-based carbon fiber (MPCF) in 1 M LiPF 6 -EC/DEC (1:1, v/v) electrolyte solution. The charge-discharge profile, cyclic voltammetry and impedance spectroscopy showed the electrochemical properties of the film which is formed on the MPCF at the voltage range of 2.4–0.5 V (vs. Li/Li + ) during the first charge. FTIR-ATR spectra confirmed the film composition, which consist of Li 2 CO 3 , ROCO 2 Li, ROLi (R=CH 3 or CH 2 CH 3 ). We discuss a systematic change of the structure of MPCF electrode–electrolyte interface at the first intercalation potentials.

Studies on the effects of coated Li2CO3 on lithium electrode

Abstract Although a lithium metal anode has a high energy density compared with a carbon insertion anode, the poor rechargeability prevents the practical use of anode materials. A lithium electrode coated with Li 2 CO 3 was prepared as a negative electrode to enhance cycleability through the control of the solid electrolyte interface (SEI) layer formation in Li secondary batteries. The electrochemical characteristics of the SEI layer were examined using chronopotentiometry (CP) and impedance spectroscopy. The Li 2 CO 3 –SEI layer prevents electrolyte decomposition reaction and has low interface resistance. In addition, the lithium ion diffusion in the SEI layer of the uncoated and the Li 2 CO 3 -coated electrode was evaluated using chronoamperometry (CA).

Properties of passivation film on carbon electrode in LiPF6/EC+DEC electrolytes

Abstract The co-solvent of ethylene carbonate (EC) and diethyl carbonate (DEC) was used to investigate the decomposition of electrolyte in Li-ion batteries. The electrolyte solutions were prepared by mixing in various volume ratios from pure DEC to 7:3 (EC:DEC). The potentials at which they are decomposed on the anodic electrode were examined using cyclic voltammetry. It was found that some kinds of reduction reactions proceeded and a film on the surface of the anode was formed. The film showed different properties, which were dependent on the mixing ratio of the solvents. From our results, we concluded that the best composition ratio of EC:DEC in 1 M LiPF 6 /(EC+DEC) system was approximately 4:6 (EC:DEC, volume ratio).

Studies on heat-treated MPCF anodes in Li ion batteries

Abstract The intercalation/deintercalation of lithium ions into the heat-treated mesophase pitch-based carbon fibers (MPCF) was carried out in 1 M LiPF6–ethylene carbonate (EC)/diethyl carbonate (DEC) (1:1, volume ratio) solution at room temperature. LiC6 became incorporated into the heat-treated MPCF via an Li+ intercalation process. The transition stage was observed by a charge–discharge curve, impedance spectrum, and X-ray diffraction (XRD) spectrum. From the observed results, we conclude that the initial intercalation of lithium ions proceeds not by a reversible pathway, but rather, an irreversible path. From the deintercalation to the continuous cycles the lithium ion is intercalated and deintercalated via a reversible pathway.