A Li/Composite polymer electrolyte(CPE)/FeS2, 10 mu-thick-cathode battery had a cathode reversible capacity of 625 mAh/g (2.8 e/FeS2), which is five times that of the LixCoO2 cathode (120 mAh/g). The theoretical energy density of the Li/FeS2 couple, based on 2.8 e/FeS2 and on an average voltage of 1.6 V, is close to 860 Wh/kg, which is almost twice that of the Li/LiCoO2 cell. For 45 mu-thick cathodes, 3.9 mAh/cm(2) reversible capacity was achieved. On the basis of this value, the projected specific energy for a bipolar Li/CPE/FeS2 battery is 170 Wh/kg and 250 Wh/kg is the long-term projection value. The effect of binders (such as PEG, PVDF, PBD; polystyrene, polycarbonate resin) and operating conditions on performance, cycle life and thermal characteristics of thin FeS2-based composite cathodes at 130 degrees C were studied. In most cases, composite LiI-P(EO)(n)-Al2O3 polymer electrolytes were used. It was found that 100% first discharge utilization was achieved in PEO and PVDF-bound cathodes. The degradation rate at i>0.3 mA/cm(2) did not exceed 1.5% per cycle for most of the cathodes under investigation. An extension of the end of the charge voltage from 2.25 to 2.4 V was followed by an overcharge protection mechanism. Replacement of I- by imide yielded very similar (almost identical) charge-discharge curves indicating that LiI is an "inert" electrolyte and is not involved in the cathodic reactions. DSC and TCA-DTA thermograms exhibit full compatibility of pyrite with the polymer electrolyte and a high thermal stability of the composite cathode and the LiI-based polymer electrolytes.