To synthesize the $LiCoO_2$ thin film cathode, sol-gel sping coating process was used. This method offers advantages such as excellent control of stoichiometry, easy control of crystallinity, density and microstructure. Moreover, the fabrication cost is relatively low and the deposition rate is high. In the sol-gel process of film preparation, the drying and annealing temperatures are critical factors to affect the properties of those thin films. To address these issues, we investigated the effects of the heat treatment condition by comparing the electrochemical properties of $LiCoO_2$ thin films which were prepared at various heat treatment condition. And we also investigated the effects of orientation of Pt current collector on the electrochemical properties of $LiCoO_2$ thin-film cathodes.
The $LiCoO_2$ thin-film cathode dried at higher drying temperature shows larger initial capacity due to the its more stoichiometric composition. Oxygen defect was made by abrupt evaporation of organic materials of lithium and cobalt source material. To investigate the effect of the orientation of Pt current collector, $LiCoO_2$ thin films were depositied at Pt(111) and Pt(200) current collector. The material properties and electrochemical properties of $LiCoO_2$ thin films deposited on Pt(200) current collector shows different behavior from that of Pt(111). The initial discharge capacity of $LiCoO_2$ thin film cathode depositied on the Pt(111) show the decrease of discharge capacity as the annealing temperature increases. But the initial discharge capacity decreases as the annealing temperature increases in the case of $LiCoO_2$ thin-film deposited at Pt(200) current collector. Thus, it is found that the discharge capacity of the films prepared by sol-gel spin coating method can be affected by the orientation of current collector. The different amount of (003) orientation and grain size is thought to cause this different electrochemical behavior of above films.
All solid-state thin-film cathode test cell was fabricated by depositing Lipon electrolyte and $SnO_2$ anode with RF magnetron sputtering on the $LiCoO_2$ thin-film cathode prepared by sol-gel spin coating process. $LiCoO_2$ thin-film cathode prepared by sol-gel spin coating process could be a candidate of the cathode film of all solid-state thin-film battery.
