FABRICATION AND CHARACTERIZATION OF AMORPHOUS LITHIUM ELECTROLYTE THIN-FILMS AND RECHARGEABLE THIN-FILM BATTERIES

Amorphous oxide and oxynitride lithium electrolyte thin films were synthesized by r.f. magnetron sputtering of lithium silicates and lithium phosphates in Ar, Ar+O2, Ar+N2, or N2. The composition, structure, and electrical properties of the films were characterized using ion and electron beam, X-ray, optical, photoelectron, and a.c. impedance techniques. For the lithium phosphosilicate films, lithium ion conductivities as high as 1.4x10(-6) S/cm at 25-degrees-C were observed, but none of these films selected for extended testing were stable in contact with lithium. On the other hand, a new thin-film lithium phosphorus oxynitride electrolyte, synthesized by sputtering Li3PO4 in pure N2, was found to have a conductivity of 2x10(-6) S/cm at 25-degrees-C and excellent long-term stability in contact with lithium. Thin-films cells consisting of a 1 mum thick amorphous V2O5 cathode, a 1 mum thick oxynitride electrolyte film, and a 5 mum thick lithium anode were cycled between 3.7 and 1.5 V using discharge rates of up to 100 muA/cm2 and charge rates of up to 20 muA/cm2. The open-circuit voltage of 3.6 to 3.7 V of fully-charged cells remained virtually unchanged after months of storage.