| Lithium ion rechargeable batteries with LiCoO2 cathode have high energy density, excellent cycle life and sufficient safety characters. The introduction by SONY in 1990 of the world's first commercially successful rechargeable lithium battery represented a revolution in the power source industry. But the cobalt is quit expensive as well as toxic. There has been much interest in manganese oxides and vanadium oxides as cathode candidates for rechargeable lithium batteries. Manganese and vanadium are cheaper and easier derived from Earth's own mineral formation processes.; The research work of this thesis is focused on two projects about Lithium Battery. The goal of the first project concentrates on the development of layered transition metal vanadium oxides with new structures. The purpose of developing these new compounds is to apply them as cathode materials in lithium rechargeable batteries. The high free energy of reaction with lithium and their low cost makes vanadium oxides attractive materials to replace the expensive LiCoO2 cathode in the commercial lithium batteries. Recently, soft chemistry (“Chimie Douce”) was shown to be an effective method for the preparation of high surface area transition metal oxides that offer many advantages as cathodes in rechargeable lithium batteries. Hydrothermal reactions occur naturally in the crust of the earth aiding in the formation of minerals. The goal in using mild hydrothermal reactions is to precipitate new solids from the reaction nutrient which may have open crystalline structures different from the thermodynamically stable phases formed under normal high temperature synthesis conditions. Several synthetic routes aimed at the formation of novel transition metal vanadium oxide compounds have been examined, all of which incorporate the hydrothermal method. The stoichiometry, phase, and structure of the compounds have been examined as a function of deposition conditions using XRD, DCP, TGA, FTIR, SEM and EDS.; These compounds are: (a) Manganese vanadium oxides: pipe ideal structure Mn7(OH)3(VO4)4 γ-type MnV 2O5, and δ-type [N(CH3)4] zMnyV2O5, (b) Zinc vanadium oxides: Zn0.4V2O5·0.27H2O, Zn 3(OH)2(V2O7)·2H2O, and Zn2(OH)3(VO3), (c) Iron vanadium oxides: [N(CH3)4]0.33]Fe0.12V 2O5·1.33H2O, (d) Nick vanadium oxides: (eda)2NiV6O14.; They readily react with buty-lithium solutions. Galvanostatic cycling of composite electrodes based on these compounds revealed a high charge capacity and promising cyclability. Electrochemical properties and rate capabilities of the materials used as cathodes for lithium cells were shown good results.; The second project is exploring the synthesis of manganese oxides using low temperature synthesis. Manganese oxides, such as LiMn2O 4, are of particular interest, because they readily intercalate lithium into their structures. However, only 0.5 lithium can bicycled per manganese atom so that their energy densities are not sufficiently high. We synthesized hexagonal LixMnO2 by hydrothermal reaction, and pillared structure compound, (VO)xMnO2, by ion-exchange reaction. The objective of this project is finding means of stabilizing the layered manganese dioxide structure. This stabilization will be designed to deter the diffusion of manganese ions into the interlayer region and the formation of spinel-like phases, and if possible to attain a hexagonal packing of the oxygen ions. |
