DEPOSITION AND CHARACTERIZATION OF LI2O-SIO2-P2O5 THIN-FILMS

Amorphous lithium electrolyte thin films, xLi2O.ySiO2.zP2O5, were depo sited by rf magnetron sputtering of pure and mixed-phase lithium silic ate, lithium phosphate, SiO2, Li2O, and Li2CO3 targets, and their comp ositions were determined using proton-induced gamma-ray emission spect roscopy, energy-dispersive X-ray analysis, Rutherford backscattering s pectrometry, and atomic-emission spectroscopy. The deposition conditio ns were chosen to assure thermalization of the sputtered flux, which p roved to be necessary in order to obtain a homogeneous distribution of Si and P in the films. Optical absorption and ac impedance measuremen ts showed that glass-in-glass phase separation occurred in a large SiO 2-rich domain of the composition diagram. In contrast to bulk glasses, all of the Li2O-SiO2 films were phase-separated, including those with lithia contents larger than lithium disilicate. High-performance liqu id chromatography measurements revealed that, analogous to bulk glasse s, the addition of SiO2 to Li2O-P2O5 compositions reduced the number o f phosphate anion dimers, trimers, and higher anion polymers in the fi lms through the formation of -Si-O-P- bonds. However, in contrast to b ulk glasses, the distribution of phosphate anion polymers followed clo sely the Flory distribution, with the fraction of anion polymers decre asing monotonically with increasing chain length.