Hoon-Taek Chung

Effects of Al doping on the microstructure of LiCoO2 cathode materials

Abstract LiCo 1− x Al x O 2 (0≤ x ≤0.3, R 3 m ) powders by the emulsion drying method and their microstructure studies were carried out in order to understand Al-doping effect on the electrochemical properties. Through X-ray diffraction experiment, we confirmed that Co was well substituted by Al while maintaining the α-NaFeO 2 layer structure type. The substitution of Al was effective on suppressing cobalt dissolution at 4.5 V versus Li/Li + and on diminishing changes in a - and c -axes during lithium intercalation. For x =0.1, the open-circuit voltage was slightly higher than that of undoped LiCoO 2 . Chemical diffusion coefficient of lithium in LiCo 1− x Al x O 2 was higher than that of LiCoO 2 because of a smaller variation in the longer c -axis.

Fabrication of LiMn2O4 thin films by sol–gel method for cathode materials of microbattery

Abstract LiMn2O4 thin films have received considerable attention as cathode materials for thin-film microbatteries. In this work, LiMn2O4 thin films are prepared by a sol–gel method using a spin coator. The precursor powder is investigated by TG–DTA and mass spectroscopy analysis in order to study the decomposition process prior to deposition. The coated films are dried at 310 to 360°C, and annealed at 700 to 800°C to obtain a spinel structure. Films annealed under appropriate conditions exhibit good crystallinity, smooth surface morphology, high capacity, and good rechargeability. This film is therefore suitable for use as a cathode for thin-film microbatteries.

Preparation of LiMn2O4 thin films by a sol-gel method

Abstract LiMn2O4 thin films were prepared by a sol–gel method using spin-coating and annealing processes. Anhydrous Mn(CH3COCHCOCH3)3 (manganese acetylacetonate) and LiCH3COCHCO–CH3 (lithium acetylacetonate) were chosen as source materials. The film electrochemical properties depended on the drying temperature even when subjected to the same annealing conditions. The discharge capacity of annealed film increased as the drying temperature was increased. However, the rate of capacity fading during cycling increased as the drying temperature was increased.

Capacity fading of LiMn2O4 electrode synthesized by the emulsion drying method

We adapted the emulsion drying method to obtain highly crystalline spinel LiMn2O4 phase using LiNO3 and Mn(NO3)2·6H2O as starting materials. The emulsion-dried powders were calcined at various temperatures for 24 h in air, and their crystalline phases were identified as a cubic spinel structure with the space group Fd3m by X-ray diffraction study. The initial discharge capacity of the samples calcined at 650°C, 750°C and 850°C were approximately 120 mA h/g, irrespective of calcination temperature. However, their capacity fadings were significantly dependent on the calcination temperature. To investigate the structural changes in the oxide cathode, XRD experiment was carried out as functions of lithium content and charge–discharge cycling number. Through the SEM observation, it was found that particles were disrupted, and the degree of disruption increased with lithium content and cycling.

Characterization of tin oxide/LiMn2O4 thin-film cell

An amorphous, thin film of tin oxide is tested as an anode to replace lithium metal in a thin-film battery. Tin oxide shows irreversible discharge capacity in its initial state, and this gives rise to capacity loss on the first charge–discharge process. Thus, in terms of electrochemical properties, lithium metal is better than tin oxide as an anode for a thin-film battery. In some applications, however, thin-film batteries must withstand high fabrication temperatures (over 250°C to 260°C). Lithium metal film cannot be applied in such conditions due to its low melting point (181°C). Tin oxide is not only able to endure high fabrication temperatures but can also preserve its capacity for a large number of cycles after the initial discharge process. In this study, a thin film of amorphous tin oxide has been prepared by means of a sputtering method. Its suitability as an anode for a thin-film battery is examined. A thin film of LiMn2O4, prepared by a sol–gel method is used for the cathode.

Dependence of the lithium ionic conductivity on the B-site ion substitution in (Li0.5La0.5)Ti1−xMxO3 (M=Sn, Zr, Mn, Ge)

Abstract The dependence of the ionic conductivity on the B-site ion substitution in (Li0.5La0.5)Ti1−xMxO3 (M=Sn, Zr, Mn, Ge) system has been studied. The same valence state and various electronic configurations and ionic radii of Sn4+, Zr4+, Mn4+ and Ge4+ (4d10 (0.69 A), 4p6 (0.72 A), 3d10 (0.54 A) and 3d3 (0.54 A), respectively) induced the various crystallographic variations with substitutions. So it was possible to investigate the crystallographic factors which influence the ionic conduction by observing the dependence of the conductivity on the crystallographic variations. We found that the conductivity increased with decreasing the radii of B-site ions and vice versa and octahedron distortion disturbs the ion conduction. The reason for this reciprocal relationship of conductivity on the radius of B-site ions has been examined on the basis of the interatomic bond strength change due to the cation substitutions. The results were in good agreement with the experimental results. Therefore it could be concluded that interatomic bond strength change due to the cation substitutions may be one of the major factors influencing the lithium ion conductivity in the perovskite (Li0.5La0.5)TiO3 system.

Electrochemical properties of LiMn2O4 thin films: suggestion of factors for excellent rechargeability

Abstract LiMn 2 O 4 thin films are prepared by the sol–gel method. The discharge capacity and cycling performance of the films are determined to investigate the electrochemical properties. By controlling the fabrication conditions, the excellent rechargeability is observed in a test cell which contains the LiMn 2 O 4 thin film. Possible factors which have been reported as causes for capacity loss with cycling are reviewed and those producing excellent rechargeability of the LiMn 2 O 4 thin films are identified. Attention is especially focused on the relaxation of the stress, which is generated during intercalation/de-intercalation process.

Preparation and electrochemical characterization of LiCoO2 by the emulsion drying method

Fine powders of LiCoO2 were successfully synthesized through an emulsion drying method. The oxide powders were characterized by thermogravimetric-differential thermal analyses, X-ray diffractometry, scanning electron microscopy, elemental analysis and electrochemical method including charge–discharge cycling. By post-annealing the powders obtained by the emulsion drying method in the temperature range 600 ∼ 900 ∘C, we obtained LiCoO2 powder which has a layer structure (R3¯m) and consists of fine particles with submicrometre order in diameter. The charge–discharge characteristics as a cathode for lithium ion battery depended on the post-annealing temperature. LiCoO2 powder made by the emulsion drying method displays a good electrochemical performance, suggesting that this soft chemistry approach has the potential to synthesize a high quality electrode material.

Preparation and characterization of LiMn2O4 powders by the emulsion drying method

Abstract Spinel-type lithium manganese oxide is evaluated as a positive electrode material for lithium-ion batteries. Powders of lithium manganese oxide are prepared by the emulsion drying method which is simplified by omitting the toluene washing stage. We investigated the powder and electrochemical characteristics of LiMn 2 O 4 with lithium salts such as LiNO 3 and LiOH·H 2 O.

Fabrication of LiCoO2 thin films by sol-gel method and characterisation as positive electrodes for Li/LiCoO2 cells

Abstract LiCoO 2 thin films are receiving attention as positive electrodes (cathodes) for thin-film microbatteries. In this study, LiCoO 2 thin films are fabricated by a sol–gel spin-coating method and a post-annealing process. The thermal decomposition behaviour of the precursor is investigated by thermogravimetry/differential thermal analysis TG/DTA and mass spectroscopy. The crystallinity, microstructure and electrochemical properties of the final films are also studied by X-ray diffraction (XRD), scanning electron microscopy (SEM) and galvanostatic charge-discharge cycling tests. Films heat-treated under appropriate conditions exhibit high capacity and good crystallinity and are therefore considered to be candidates as cathodes for thin-film microbatteries.