Research On The Preparation Of Lithium Cobalt Oxide Thin Films By Electrochemical And Hydrothermal Method

In this thesis, LiCoO₂ thin films were prepared directly on cobalt substrates by electrochemical method and hydrothermal method. By means of modern analysis technique, such as XRD,SEM and XPS, the influences of electrochemical conditions (include temperatures, current density, concentration of electrolyte and reaction duration) and hydrothermal conditions (temperatures, concentration of electrolyte and reaction duration) on the formation of the thin films were investigated, respectively. The main conclusion acquired from the present work as follows:(1) LiCoO₂ thin films were prepared directly on cobalt substrates by constant current electrochemical method and hydrothermal method.(2)The current density is the driving force for electrochemical reaction in the thin films formation process. The current density is too small to meet the need of reaction to grow thin film. On the contrary, the greater the current density, the quicker the electrochemical reaction; but the thin film in this case, will adsorbs a lot of water and impurity, and result in the quality of the as-prepared LiCoO₂ films in inferior.The temperature is the key factor for the growth of LiCoO₂ thin film. In the same condition, the higher the temperature, the quicker the aggradation of LiCoO₂ grains, and the production will make the nuclei format and have no obvious configuration because that it has adsorb a lot of water and impurity. Configuration 30℃and 90℃, the as-grown thin films are compact and uniform at 30℃.The feasible concentration of electrolyte recommended as 3mol/L. The reaction duration is too short to meet the need for the growth of LiCoO₂ thin film. If the electrochemical reaction is too long, it will result in dissolving of the as-prepared LiCoO₂ films. In this case, there is no LiCoO₂ film adhered on the substrates, or the orienting growth of the films is destroyed, and the films are disordered. For the nonce, the feasible parameters of electrochemical method are: keep the current density of 0.5mA/cm2, the concentration of LiOH solution of 3mol/L and electrochemical reaction duration of 50h.(3) In the hydrothermal processing, accompanied with the increasing of the concentration of LiOH solution. The reaction temperature is risen; and results in the formation of LiCoO₂ in very different. In this case, the number of the characteristic reflection peaks increases, and the unidentified peaks increase too; furthermore the morphologies of the as-prepared LiCoO₂ films are more disordered and no simpler grains formed. It is consisted with that in electrochemical processing; the increasing of reaction temperature and reaction time is inferior to the growth LiCoO₂ films.The feasible parameters of hydrothermal method are the reaction temperature of 140℃, the concentration of LiOH solution of 4mol/L and the reaction duration of 20h.