Iron and nickel phosphorus trisulfides as electroactive materials for primary lithium batteries

Abstract

The theoretical specific capacities of a family of layered compounds MPX 3 (M = Fe, Co, Ni; X = S, Se) for current-producing reactions involving 1.5, 2, 6 and 9 lithium atoms per MPX 3 molecule have been estimated. These data show that FePS 3 and NiPS 3 are good electroactive materials for primary lithium cells. Conditions which allow one to shorten substantially the synthesis time of iron and nickel phosphorus trisulfides in ampoules are presented. According to conductivity measurements in the 293–673 K temperature range, NiPS 3 is an intrinsic and FePS 3 an extrinsic semiconductor. The discharge characteristics of Li/MPS 3 (M = Fe, Ni) cells with an organic electrolyte have been studied; they confirmed that the participation of nine electrons in the redox process is possible. For a primary button cell of the standard size 2325, with a FePS 3 cathode, the specific capacity and specific energy values obtained in a discharge 1.2–1.8 V range at load resistances of 3.0 to 30 kΩ were 500–1160 Ah/kg and 700–1770 Wh/kg (on a pure FePS 3 basis), respectively.