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Nickel-molybdenum sulfide Ni2Mo~Sv.9 (nickel Chevrel phase, NiCP) was tested as the cathode of lithium secondary batteries. The Li/NiCP cell could be galvanostatically discharged up to x = 4 -5 (LixNi2Mo6ST.9) when the current density was smaller than 0.5 mA/cm 2. No evidence of nickel delbosition from the NiCP cathode was observed even after the cell was deeply discharged to x = 4. This resulted in the small distortion of the NiCP crystal lattice upon lithium intercalation, which was clearly observed by the experimental result that the ar value of the rhombohedral lattice parameter hardly changed before and after lithium intercalation. As a result, the NiCP cathodes showed excellent discharge-charge cycling properties. In a deep cycling test carried out between 1.5-2.7V, more than 50% of the initial discharge capacity was maintained even after 200 cycles. In shallow range cycling tests performed in the ranges of 0.5 < x < 1 and 1 < x < 2, the cells were cycled more than 5000 and 1700 times, respectively.Volumetric energy density of a battery (Wh/liter) sometimes becomes more important than gravimetric energy density (Wh/kg), especially when the cell volume is strictly limited as in the case of small-size portable batteries. Ternary molybdenum sulfides M,Mo6Ss-z (M = metal), socalled Chevrel phase compounds (1), are one of the most promising candidates for such high volumetric energy density cells because of their high specific densities: e.g.,

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