Preparation and Electrochemical Characterization of LiCoO 2 Single Crystal Particles prepared by Super Critical Water Sy
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salt at a suitable temperature under air or oxygen atmosphere. The crystallinity and crystal size of these materials are important to obtain a high performance of rechargeable lithium batteries and strongly depend on starting materials and preparation conditions. Therefore, various efforts on transition metal oxide synthesis have been performed by many researchers. In particular, new preparation methods have been applied to obtain good cathode and anode materials in order to realize an excellent electrochemical characteristics of transition metal oxides. Sol-gel method, hydrothermal synthesis, ion exchange method, and so on, have been used to prepare various kinds of oxides for cathode and anode materials of rechargeable lithium batteries [5]. These methods are sometimes very convenient to obtain a high crystalline material with a uniform crystal size. The preparation of various oxides using Super Critical Water have also been reported for various type of electrochemical and electrical devices (for example CeO 2 was prepared for solid oxide electrolyte) [6]. This synthesis is very suitable for the production of highly crystalline fine oxide particles with a uniform distribution of particle size. In this study, LiCoO 2 was prepared using Super Critical Water Synthesis (SCWS) and tested as a cathode material of rechargeable lithium battery. EXPERIMENT SCWS method Figure 1 shows the schematic illustration for the flow type reaction cell of the SCWS used in this study. LiOH and Co(N0 3)2 were used as the starting materials. These salts were dissolved in water with various concentrations and pumped out to the electric furnace (temperature 400 59 Mat. Res. Soc. Symp. Proc. Vol. 575 02000 Materials Research Society
'C). The LiOH and Co(N0 3 )2 aqueous solutions were pressurized at 30 MPa just before the entrance of the electric furnace. These 2Q30 Kft solutions were mixed at the entrance of the main reaction cell. Simultaneously, the super critical water produced by using a preheating electric furnace and a high pressure pump, was also injected in the entrance of the electric furnace. The temperature and pressure of super critical water in the main cell were 400 °C and 30 MPa. Super critical water with H 20 2 was used as an oxygen source for LiCoO 2 production. The Temperature: 400 0C 3 volume of the main cell was 12.15 cm 3 or 21.6 Reactor volume : 21.6 cm cm 3 and the reaction time was 22-12 sec. This Reaction time: 12 sec means that the total process of the oxide preparation is finished within 1 min. This reaction time is much shorter than any other .i' .•! . preparation methods. Under these conditions, the deposition of Co oxides were carried out. The reaction products were analyzed by x-ray diffraction method with Cu Ka radiation. Three Figure 1 Schematic illustration of SCWS main products were observed, LiCoO 2, CO30 4 , process for the preparation of LiCoO 2 cathode and CoO depending on the preparation material for rechargeable lithium batteries. conditions. In all experiments, NO3- ions were reduced to NO 2- ion
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