Ambient temperature synthesis of polycrystalline thin films of lithium cobalt oxide with controlled crystallites' orientations

Polycrystalline thin films of lithium cobalt oxide (nominally LiCoO2) have been deposited by a process which we have named, ion beam directed assembly (IBDA). It is similar to ion assisted deposition (IAD) or ion beam assisted deposition (IBAD), but the major difference is that in IBDA the ion beam directs, via the vector momenta of the ions, rather than merely assists, the growth. Hence, we also term the process directed assembly to distinguish it from self assembly. Also, in directed assembly the ions may or may not become an integral part of the film's composition. In this paper we wish to show that the IBDA process may be capable of controlling microstructure, e.g., in the case of polycrystalline films, control the orientations of the crystallites. For LiCoO2 we have observed this in two ways - by X-ray analysis, and electrochemically, by lithium diffusivity measurements. In particular, we have observed increased lithium diffusivities (greater than or equal to 10(-8) cm(2)/s) in IBDA deposited films as compared to that found for rf sputter deposited films (approximate to 10(-10) cm(2)/s). In addition, the coulometric titration characteristics of an IBDA deposited Li1-yCoO2 are very similar to those of sputtered deposited films (for lithium extraction/insertion y less than or equal to 10.5, and for quasi-equilibrium voltages up to 4.2 volts).