NICKEL-MOLYBDENUM SULFIDE NI2MO6S7.9 AS THE CATHODE OF LITHIUM SECONDARY BATTERIES

Nickel-molybdenum sulfide Ni2Mo6S7.9 (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 (LixNi2Mo6S7.9) when the current density was smaller than 0.5 mA/cm2. No evidence of nickel deposition 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 αr 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.