Preparation Technology And Performance Of Cobalt Disulfide Thin-film Cathode For Li-thermal Battery

Nowadays, the most conventional used electrode preparation process for CoS₂cathode thermal batteries is pressed-powder. However, the process has many disadvantages to limit the automation and large-scale production of thermal batteries, including low production efficiency, strict ambient requirement and tedious preparation processes. In order to overcome the above shortcomings of current preparation processce, the thesis designed and prepared a series of CoS₂thin-film cathode electrodes based on different substrate material s by coating method. And then, the parameters related to th e thin-film preparation process were explored and optimized. Finally the discharge performances of the single cells with CoS₂thin-film cathode electrodes were observed.In this thesis, four solvents using as pasting agents were studied, including H-1, polyvinylidene fluoride?PVDF?, sodium silicate and water respectively. The prepared thin-film was characterized by X-ray diffraction?XRD? and scanning electron microscopy?SEM?. Combining with the discharge performances, the results showed that the cell which was made of thin-film cathode using H-1 as pasting agent displayed remarkable performances. Further four substrate materials were studied, including graphite paper, aluminum foil, nickel foam and copper foam respectively. Combining with the performances of thermal battery and the practical production requir ements, finally graphite paper and nickel foam as the substrate materials were selected. And due to the low load, the graphite paper substrate is to satisfy the demand of the high-power and short lifetime thermal batteries; In contrast, considering the heavy load, the nickel foam substrate is best suited for the high-power and long lifetime thermal batteries.In this work, the preparation processes and the discharge performances with graphite paper and nickel foam as substrates for CoS₂thin-film cathode electrodes were investigated. At the meantime, the process parameters were explored and optimized, including solvent volume, ball-milling time, drying conditions and pressed-powder pressure through the surface morphology and the discharge performances of the single cells. Further, the influence of the discharge temperature and the current density for the single cells was studied. The results showed that the discharge temperature had great influence on the discharge performances and the graphite paper substrate was suitable for high current density, in contrast, nickel foam substrate was suitable for low current density. Compared with pressed-powder process, the process of thin-film could effectively improve specific capacity of cathode positive material, and reduce the resistance of the batteries. In addition, the coating method is more suitable for automatic production, and its operating environment is relatively easy to achieve. Therefore, the coating method could provide the possibility for large-scale production for thermal batteries.At last, the mechanism of voltage spike in the thin-film process was preliminarily explored. And we analyzed related reasons causing the voltage spike by adding a series of impurities to the cathode materials. The results showed that moisture in the preliminary drying was the main factor and LiCoO₂ was the main impurity of voltage spike. Finally, the influence of the amount of LiCoO₂ for voltage spike was explored by ac impedance method. The results showed that the voltage spike and the impedance increased with the LiCoO₂ increasing.