Thin-iron sulfide films were deposited electrochemically on nickel current collector, and used as cathodes in lithium/composite polymer electrolyte cells. X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) tests showed that 0.6–1μm thick FeS1+ x films were amorphous, with the Fe:S stoichiometry of the films invariant with depth. A Li/CPE/FeS1+ x cells ran at i d = i ch = 50μA/cm2 (c/1 rate) and 125°C for over 650 charge/discharge cycles with 0.06% per cycle capacity loss and 100% Faradaic efficiency.