Chil-Hoon Doh

Intercalation of Lithium Ions into Graphite Electrodes Studied by AC Impedance Measurements

Effects of electrolyte concentrations and the level of preintercalation (x values in Li{sub x}C{sub 6}) on the lithium ion intercalation into graphite lattices have been examined in propylene carbonate-ethylene carbonate mixed solutions with LiClO{sub 4} as an electrolyte by ac impedance measurement techniques. Exchange current densities were determined for reductive intercalation of lithium by ac impedance measurements to range between 1.4 and 2.4 mA/cm{sup 2} depending on the amount of intercalated lithium ions with a transfer coefficient ({alpha}) of 0.65. Diffusion coefficients during the deintercalation process have also been determined at various preintercalation levels. The dependence of diffusion coefficients and exchange currents on the x values in Li{sub x}C{sub 6} (x {le} 1) is discussed.

Anodic WO3 mesosponge @ carbon: a novel binder-less electrode for advanced energy storage devices.

A novel design for an anodic WO3 mesosponge @ carbon has been introduced as a highly stable and long cyclic life Li-ion battery electrode. The nanocomposite was successfully synthesized via single-step electrochemical anodization and subsequent heat treatment in an acetylene and argon gas environment. Morphological and compositional characterization of the resultant materials revealed that the composite consisted of a three-dimensional interconnected network of WO3 mesosponge layers conformally coated with a 5 nm thick carbon layer and grown directly on top of tungsten metal. The results demonstrated that the carbon-coated mesosponge WO3 layers exhibit a capacity retention of 87% after completion of 100 charge/discharge cycles, which is significantly higher than the values of 25% for the crystalline (without carbon coating) or 40% for the as-prepared mesosponge WO3 layers. The improved electrochemical response was attributed to the higher stability and enhanced electrical conductivity offered by the carbon coating layer.

Comparative Electrochemical Analysis of Crystalline and Amorphous Anodized Iron Oxide Nanotube Layers as Negative Electrode for LIB

This work is a comparative study of the electrochemical performance of crystalline and amorphous anodic iron oxide nanotube layers. These nanotube layers were grown directly on top of an iron current collector with a vertical orientation via a simple one-step synthesis. The crystalline structures were obtained by heat treating the as-prepared (amorphous) iron oxide nanotube layers in ambient air environment. A detailed morphological and compositional characterization of the resultant materials was performed via transmission electron microscopy (TEM), field-emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), and Raman spectroscopy. The XRD patterns were further analyzed using Rietveld refinements to gain in-depth information on their quantitative phase and crystal structures after heat treatment. The results demonstrated that the crystalline iron oxide nanotube layers exhibit better electrochemical properties than the amorphous iron oxide nanotube layers when evaluated in terms of the areal capacity, rate capability, and cycling performance. Such an improved electrochemical response was attributed to the morphology and three-dimensional framework of the crystalline nanotube layers offering short, multidirectional transport lengths, which favor rapid Li(+) ions diffusivity and electron transport.

SnO2 Pinning: An Approach to Enhance the Electrochemical Properties of Nanocrystalline CuFe2O4 for Lithium-Ion Batteries

A first attempt to synthesize and explore SnO2 pinned CuFe2O4 material as an anode for lithium-ion batteries has been made. The study highlights the approach of exploiting SnO2 pinning to enhance the electrochemical properties of nanocrystalline CuFe2O4 anodes. Virgin CuFe2O4 and SnO2 pinned CuFe2O4 powders were synthesized with 10–30 nm via under a one pot solution combustion method with specific calcination conditions. It is further understood that SnO2 pinning has reduced saturation magnetization and bulk resistance and thereby enhanced the charge-discharge characteristics of native CuFe2O4 anodes significantly in rechargeable lithium cells.

Improved electrochemical performance of doped-LiNi0.5Mn1.5O4 cathode material for lithium-ion batteries

In this paper, the electrochemical performance of doped-LiNi0.5Mn1.5O4 is reviewed. The rate capability, rate performance, and cyclic life of the doped-LiNi0.5Mn1.5O4 materials with various elements are reported. The Fe, Scsubstituted materials exhibited remarkably superior cycling performance and rate capabilities than pristine LiNi0.5Mn1.5O4.

Electrochemical Characteristics of Lithium Transition-Metal Oxide as an Anode Material in a Lithium Secondary Battery

Lithium transition-metal oxides (LiTMOs) such as LiCoO2 and LiMn2O4 were investigated for their use as anode material for the lithium secondary battery. Ni¦Li0¦LiPF6(lM, EC + DEC (1 : l))¦LiTMO¦Cu cell was fabricated and its electrochemical properties were examined. LiCoO2 and LiMn2O4 showed fairly good characteristics as anode material as well as cathode material. At the 1st cathodic process, LiCoO2 had a potential plateau at 1.4 V on open circuit potential line, but LiMn2O4 had two ambiguous potential plateaus between 0.6 and 0.1 V. The specific resistance of Li¦LiCoO2 cell was 8 ohm-g, but that of Li¦LiMn{si2}O{si4} cell decreased gradually while the reaction proceeded. The specific capacities of Li¦LiCoO2 and Li¦LiMn2O4 cells at the 1st discharge were about 300 mAh/g. Capacity retention of Li¦ LiMn2O4 cell during charge-discharge cycling was higher than that of Li¦LiCoO2 cell.

Analysis on the Formation of Li 4 SiO 4 and Li 2 SiO 3 through First Principle Calculations and Comparing with Experimental Data Related to Lithium Battery

The formation of Li-Si-O phases, and from the starting materials SiO and are analyzed using Vienna Ab-initio Simulation (VASP) package and the total energies of Li-Si-O compounds are evaluated using Projector Augmented Wave (PAW) method and correlated the structural characteristics of the binary system SiO- with experimental data from electrochemical method. Despite becomes stable phase by virtue of lowest formation energy calculated through VASP, the experimental method shows presence of as the only product formed when SiO and reacts during slow heating to reach and found no evidence for the formation of . Also, higher density of (2.42 g ) compared to the compositional mixture (2.226 g ) and better cycle capacity observed through experiment proves that as the most stable anode supported by better cycleabilityfor lithium ion battery remains as paradox from the point of view of VASP calculations.

A study on carbon coating to silicon and electrochemical characteristics of Si-C/Li cells

The aim of this paper is to study the electrochemical behavior of Si-C material synthesized by heating a mixture of silicon and polyvinylidene fluoride (PVDF) in the ratios of 5, 20, and 50 wt%. The particle size of the synthesized material was found to be increased with increase in the PVDF ratio. The coexistence of silicon with carbon was confirmed from the XRD analysis. A field emission scanning electron microscope (FESEM) study performed with the material proved the improvement in coating efficiency with increase in the PVDF ratio. Coin cells of the type 2025 were made by using the synthesized material, and the electrochemical properties were studied. An electrode was prepared by using the developed Si-C material. Si-C|Li cells were made with this electrode. A charge|discharge test was performed for 20 cycles at 0.1 C hour rate. Initial charge and discharge capacities of Si-C material derived from 20 wt% of PVDF was found to be 1,830 and 526 mAh|g, respectively. Initial charge/discharge characteristics of the electrode were analyzed. The level of reversible specific capacity was about 216mAh/g at Si-C material derived from 20 wt% of PVDF, initial intercalation efficiency (IIE), intercalation efficiency at initial charge/discharge, was 68%. Surface irreversible specific capacity was 31 mAh/g, and average specific resistance was 2.6 ohm * g.

A preliminary investigation upon the electrochemical behavior of CoO and NiO anodes: Comparative study

Among the variety of alternate anode materials being studied, the research on the exploration of 3d-metal oxide anodes gains paramount importance in the recent time, as it is bestowed with an easy preparation method and a less complicated decomposition mechanism. Towards this direction, an attempt to synthesize the compound CoO and to investigate the electrochemical behavior of the same both individually and in comparison with NiO compounds was made with a view to understand the extent to which the chosen candidates, viz., CoO and NiO can be exploited as high capacity anodes. Between the two oxides, CoO exhibited a specific capacity of at least 550 mAh/g, against NiO with an average capacity of ∼330 mAh/g. Also, the magnitude of irreversible capacity loss and the extent of capacity fade upon cycling corresponding to CoO anode were found to be lesser than NiO anodes. The enhanced specific capacity values and the better cycleability properties of CoO anodes are believed to be due to the inherent electrochemical characteristics of the compound. The type and the nature of SEI formed over the electrode surface and the formation of possible progressive agglomeration of the products of decomposition are expected to be the factors responsible for the difference in the electrochemical behavior of CoO and NiO anodes. In short, electrochemical characterization of the individual oxides are studied and probable reasons for the observed difference in the charge-discharge behavior of CoO and NiO anodes are discussed in this communication.

Application of carbon to anode material for the lithium secondary battery

Summary form only given. We have studied on the electrochemical characteristics of carbon materials(petroleum coke, pyrolyzed furan resin(PFR), graphitized mesocarbon microbeads(MCMB), etc.) as anode material of the lithium secondary battery by cyclic voltammetry and galvanostatic charge/discharge with current density and electrolyte. The carbon electrodes were prepared by the coating the slurry of carbon of 90wt% and polyvinylidene fluoride of lOwt% as the binder on Cu foil. During cyclic voltammetry, PFR and MCNM shows good cycling behavior in the condition of scan rate of 10mV/sec, potential range between 0V and 3V vs. Li/Li/sup +/ in IM LiAsF/sub 6//PC electrolytic solution. In the case of galvanostatic charge/discharge of PFR and MCNM, LiAsF/sub 6///PC electrolytic solution was best of all electrolytic solutions tested in the condition of current density of 1mA/cm/sup 2/ and potential range between 0V and 1.5V vs. Li/Li/sup +/. And its electrochemical properties were better in current density of 2mA/cm/sup 2/ than in current density of 1mA/cm/sup 2/. At current density of 2mA/cm/sup 2/, PFR electrode showed ca. 100% Ah efficiency and stable utilization behavior with cycling. The utilization was 25% at the 50th cycle.