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

The theoretical specific capacities of a family of layered compounds MPX3 (M = Fe, Co, Ni; X = S, Se) for current-producing reactions involving 1.5, 2, 6 and 9 lithium atoms per MPX3 molecule have been estimated. These data show that FePS3 and NiPS3 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, NiPS3 is an intrinsic and FePS3 an extrinsic semiconductor. The discharge characteristics of Li/MPS3 (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 FePS3 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 FePS3 basis), respectively.