Soon-Ho Chang

Electrochemical and structural properties of HT-LiCoO2 and LT-LiCoO2 prepared by the citrate sol-gel method

Abstract LT-LiCoO 2 has a slightly modified structure but significantly different electrochemical properties compared to LiCoO 2 prepared at high temperature. In this study, the structure and electrochemical properties of LT-LiCoO 2 have been evaluated using Raman spectroscopy, X-ray absorption spectroscopy (XANES and EXAFS), and electrochemical methods. According to the structural analysis, LT-LiCoO 2 has an intermediate structure between a layered and a spinel structure. The first discharge capacity of LT-LiCoO 2 is ∼80 mAh/g (100 μA/cm 2 ).

Synthesis and electrochemical properties of V2O5 intercalated with binary polymers

Abstract We have synthesized a new inorganic/organic hybrid material, which comprises vanadium pentoxide (V 2 O 5 ) and the binary polymers poly(2,5-dimercapto-1,3,4-thiadiazole) (PDMcT) and polyaniline (PANI), and have investigated its electrochemical property. Fourier transform infrared spectra (FT-IR) confirms that both 2,5-dimercapto-1,3,4-thiadiazole (DMcT) and aniline molecules are oxidatively intercalated into the interlayer of V 2 O 5 xerogel, and result in a binary polymers/V 2 O 5 hybrid material. X-ray diffraction (XRD) shows that intercalation of polymers expands the V 2 O 5 interlayer distance by 4.8xa0A. V K-edge X-ray absorption near-edge structure spectroscopic analysis shows no significant change in VO 6 octahedral symmetry, but a slight reduction of the V(5+) state. Electrochemical investigations in the 4–2xa0V range versus Li/Li + using non-aqueous electrolyte cells show that as-synthesized binary polymers/V 2 O 5 material exhibits an initial discharge capacity of ∼190xa0mAhxa0g −1 while an oxygen-treated sample exhibits an initial capacity of about 220xa0mAhxa0g −1 and a better reversibility for lithium insertion/de-insertion.

Electrochemical properties of cobalt-exchanged spinel lithium manganese oxide

Abstract Cobalt-exchanged LiCo y Mn 2− y O 4 ( y =0.0, 0.1, 0.2, 0.3, 0.4, 0.5) is prepared at 800°C in air. The crystal symmetry of the LiCo y Mn 2− y O 4 is determined as cubic spinel with space group Fd3m . The lattice parameter and the discharge capacity decrease with increase in substituted Co content, but the cycle performance is enhanced. The first discharge capacity of LiCo 0.2 Mn 1.8 O 4 is 96 mAh g −1 in the 3.7–4.3 V range and 109 mAh g −1 in the 3.7–5.1 V range. A Mn(II) peak is observed in the cyclic voltammogram for spinel LiMn 2 O 4 . It is difficult to remove this Mn(II) with conventional preparation methods. The peak disappears in cobalt-exchanged spinel sample, LiCo y Mn 2− y O 4 ( y >0.1), and the cycle performance is enhanced.

Preparation of single-phase Pb(Mg1/3Nb2/3)O3 samples utilizing information from solubility relationships in the Pb–Mg–Nb–citric acid–H2O system

The optimum pH for preparing single-phase Pb(Mg1/3Nb2/3)O3(PMN) powder can be estimated from the solubility vs. pH diagrams for the corresponding metal ions in hydroxide, carbonate and citrate media. The homogeneous and stoichiometric citrate PMN precursor could be prepared from the system Pb–Mg–Nb–citric acid–H2O by adjusting the pH of the solution to 6. Ultrafine (0.05–0.3 µm) and stoichiometric PMN powder could be obtained through the thermal decomposition of the citrate precursor at the relatively low temperature of 900 °C.

The Effect of Lithium Intercalation on the Crystal Structure and Magnetic Property of Layered FeWO4Cl

LiFeWO4Cl has been prepared by reductive intercalation of lithium into FeWO4Cl. FeWO4Cl crystallizes into a tetragonal system (space group P4/nmm) with cell dimensions of a=6.677(5) A and c=5.270(5) A, while lithium intercalation gives rise to the formation of a monoclinic phase ( P21/m) with cell dimensions of a=7.050(0) A, b=6.926(2) A, c=5.043(0) A and β=92.54(2)°. Infrared (IR) spectroscopic analyses of FeWO4Cl and LiFeWO4Cl show that the symmetry of the tetrahedral WO42- group in FeWO4Cl becomes reduced as the lithium intercalate into its two-dimensional lattice, indicating an alternately ordered lithium occupancy of half of the octahedral interlayer sites. The effective magnetic moments of FeWO4Cl and LiFeWO4Cl were estimated to be 5.95 and 5.10 B.M., respectively, which can be attributed to the selective reduction of a high-spin ferric ion to a high-spin ferrous one upon lithium intercalation. It was also found that the two-dimensional magnetic property of FeWO4Cl was changed to a three-dimensional one in LiFeWO4Cl owing to the c-axis contraction.