Kwon-Koo Cho

Electrochemical properties of sulfur electrode containing nano Al2O3 for lithium/sulfur cell

To prevent the dissolution of lithium polysulfides into liquid electrolyte and to promote the lithium/sulfur redox reaction, nano-sized Al2O3 particles having large specific surface area were added into sulfur electrode. The effects of nano-sized Al2O3 particles on the electrochemical properties of sulfur electrode for lithium/sulfur battery were investigated using CV measurements, charge/discharge tests and ionic conductivity measurements of liquid electrolyte. From the results, the sulfur electrode containing nano Al2O3 particles showed good cycle performance and higher discharge capacity of 660 mAh g−1-sulfur than that of the sulfur electrode without nano Al2O3. It is therefore concluded that the addition of nano-sized Al2O3 particles gives the beneficial effects of preventing the dissolution of lithium polysulfides into liquid electrolyte.

Nitrogen‐Doped Mesoporous Carbon: A Top‐Down Strategy to Promote Sulfur Immobilization for Lithium–Sulfur Batteries

The loss of active sulfur material is a challenge in the application of lithium-sulfur (Li-S) batteries. To immobilize sulfur, a nitrogen-doped mesoporous carbon (PMC) was synthesized with polyaniline (PANi) as the carbon source, which was used for development of Li-S batteries. The nitrogen content and pore system of the PMCs were modulated by varying the pyrolysis temperature to impart good electrochemical properties to the Li-S cells. As a result, the optimal capacity reversibility was obtained with the PMC synthesized at 700 °C that consisted of 12.8 % nitrogen. The enhanced cycle performance of Li-S cells was also validated at high sulfur contents up to 70 % and high C-rates up to 2 C. Furthermore, such sulfur/PMC cathodes could alleviate volume expansion during the discharge process. The results suggest that our synthesized nitrogen-doped PMCs prepared by this top-down strategy are promising materials to immobilize active sulfur in Li-S batteries.

Effect of sulfur electrode composition on the electrochemical property of lithium/PEO/sulfur battery

The lithium/sulfur cell is very attractive because of its high theoretical specific capacity and low production cost. The sulfur electrode is prepared from sulfur, with carbon as an electronic conductor and PEO as an ionic conductor. We changed the carbon content of a 50 wt.% sulfur electrode from 10 wt.% to 40 wt.%. The lithium/PEO/sulfur cell showed two plateau potential regions (2.4 V, 2.1 V) and high discharge capacity, i.e., 1484 mAh/g (88% utilization) for optimum composition. The discharge capacity decreased drastically by charge-discharge cycling. The degradation rate as well as the first discharge capacity depended on the composition of the sulfur electrode. The optimum composition of the 50 wt.% sulfur electrode was 30 wt.% carbon and 20% PEO.

Recovery from self-assembly: a composite material for lithium–sulfur batteries

A highly ordered mesoporous carbon, AlCMK, with an assembly of carbon rods and a bimodal pore system is used for sulfur encapsulation, and the AlCMK/S composite is observed to be able to accommodate volume expansion during a discharge process and recover its original structure when recharged. It is proved that the assembly structure of AlCMK makes it “breath” during the redox reaction of lithium and sulfur. Such a novel ability greatly benefits the maintenance of electrode construction during a repeated discharge–charge process. Moreover, a long heating time (e.g. 20 h) at 300 °C in a two-step melt diffusion method is found to contribute to the uniform dispersion of sulfur in the AlCMK carbon matrix. Using this featured composite, a Li–S cell retains 627 mA h g−1 after 450 cycles at 0.1 C-rate with a coulombic efficiency close to 100% and also shows good rate capability up to 5 C-rate, demonstrating a significant improvement of reversible capacity and cycle stability of Li–S cells.

Electrochemical properties of magnesium electrolyte with organic solvent

Three kinds of electrolytes are investigated to find out the proper electrolyte for magnesium battery. Propylene carbonate electrolyte using magnesium salt of Mg(ClO4)2 shows a higher ionic conductivity than that of dimethyl carbonate and tri(ethyleneglycol dimethyl)ether (TRGDME) but low decomposition potential. The TRGDME electrolyte with 0.5?M Mg(ClO4)2 has a higher ionic conductivity of 6 ? 10?4 ?S?cm?1 than that of dimethyl carbonate, but the decomposition voltage of the electrolyte is over 3.0?V which can be used for Mg/S cell.

Lithium/Sulfur Secondary Batteries: A Review

Lithium batteries based on elemental sulfur as the cathode-active material capture great attraction due to the high theoretical capacity, easy availability, low cost and non-toxicity of sulfur. Although lithium/sulfur (Li/S) primary cells were known much earlier, the interest in developing Li/S secondary batteries that can deliver high energy and high power was actively pursued since early 1990’s. A lot of technical challenges including the low conductivity of sulfur, dissolution of sulfurreduction products in the electrolyte leading to their migration away from the cathode, and deposition of solid reaction products on cathode matrix had to be tackled to realize a high and stable performance from rechargeable Li/S cells. This article presents briefly an overview of the studies pertaining to the different aspects of Li/S batteries including those that deal with the sulfur electrode, electrolytes, lithium anode and configuration of the batteries.

Structure and dye-sensitized solar cell application of TiO2 nanotube arrays fabricated by the anodic oxidation method

Well-ordered TiO2 nanotube arrays were fabricated by the potentiostatic anodic oxidation method using pure Ti foil as a working electrode and ethylene glycol solution as an electrolyte with the small addition of NH4F and H2O. The influence of anodization temperature and time on the morphology and formation of TiO2 nanotube arrays was examined. The TiO2 nanotube arrays were applied as a photoelectrode to dye-sensitized solar cells. Regardless of anodizing temperature and time, the average diameter and wall thickness of TiO2 nanotube arrays show a similar value, whereas the length increases with decreasing reaction temperature. The conversion efficiency is very low, which is due to a morphology breaking of the TiO2 nanotube arrays in the manufacturing process of a photoelectrode.

Electrochemical properties of Li–Fe–S ternary metal sulfide (lithium iron sulfide) synthesized via the molten salt method

Li–Fe–S ternary metal sulfide (lithium iron sulfide) powder was synthesized by the molten salt method. The physical and electrochemical properties of synthesized lithium iron sulfide were also investigated. From the results of XRD analysis, the chemical composition of synthesized lithium iron sulfide powder was Li1.7Fe1.17S2 with a hexagonal crystal structure. The Li/Li1.7Fe1.17S2 cell showed a first charge capacity of 153 mAh g−1-Li1.7Fe1.17S2, corresponding to 48% of theoretical capacity. To understand the charge/discharge reaction behaviors of the Li/Li1.7Fe1.17S2 cell, Li/FeS2,Li/Fe and Li/AB cells were tested. From these results, the charge/discharge mechanism of the Li/Li1.7Fe1.17S2 cell was suggested.

Electrochemical and interfacial properties of (PEO)10LiCF3SO3−Al2O3 nanocomposite polymer electrolytes using ball milling

Electrochemical and interfacial properties of (PEO)10LiCF3SO3−Al2O3 composite polymer electrolytes (CPEs) prepared by either ball milling or stirring are reported. Ball milling was introduced into a slurry preparative technique utilizing PEO, lithium salt and Al2O3 powder ranging from 5 to 15 wt.%. The ionic conductivity was increased by ball milling over a range of temperatures. In particular, a significant increase at low temperature below the melting point of crystalline PEO was observed. Interfacial stability between lithium electrode and CPE was significantly improved by the addition of alumina as well as by ball milling. The electrochemical stability window produced by (PEO)10LiCF3SO3−Al2O3 ball milling was higher than that of stirring, which was about 4.4 V. Charge/discharge performance of Li/CPE/S cells with (PEO)10LiCF3SO3−Al2O3-12 hr ball milling was superior to that of a pristine polymer electrolyte due to the low interface resistance and high ionic conductivity.

Electrochemical Properties of Electrode Comprising of Si Nanopowder Inserted in an Enclosed Structure in C-Coated AAO by Using a Facile Method

Si, Sn, Al, Ge, and their compounds are some of the potential candidates for use as anodic materials in Li-ion secondary batteries. Especially, Si is a promising anode material for Li-ion batteries due to the high theoretical capacity of 4200 mAh/g-based on the formation of Li4.4Si phase. However, the formation of Li4.4Si induces a large volume expansion in the electrode and leads to a rapid drop in capacity. To overcome this problem many experiments and theoretical efforts have been focused on enhancing structural stability of an Si in electrode. Several methods have been also reported for the fabrication of three-dimensional electrode arrays. In this study, we report an improvement of the cycling performance of an Si-nanopowder-based electrode. Si-nanopowder was inserted and confined on the C-coated anodic aluminum oxide by using a new method. It is confirmed from this study that cycling behavior of the Si-powder electrode can be significantly improved by using the method proposed in this study.