Thin films have been deposited by radio-frequency magnetron sputtering, using LiCoO2, LiNiO2 and LiNi0.7Co0.3O2 targets, in argon or Ar/O-2 gas mixture. The composition of the thin films has been determined by proton induced gamma-ray emission (PIGE) analysis and by Rutherford backscattering spectroscopy (RBS). The oxygen partial pressure in the plasma influences the composition of the thin films; these results an discussed with regard to the film morphology.