Nickel sulfide synthesized by ball milling as an attractive cathode material for rechargeable lithium batteries

Nickel sulfide (NiS) powders were prepared by ball milling and melting as cathode materials for a lithium rechargeable battery which was charged and discharged at room temperature (30 degreesC). The NiS powders prepared by melting were composed of several phases such as Ni3S2, Ni7S6, NixS6, and Ni3S4, as derived from XRD. In order to synthesize a homogeneous nickel sulfide (NiS) phase, ball milling (BM) was adopted. A homogeneous NiS phase was easily formed after ball milling up to 12 h under an At atmosphere. The ball milled NiS particles were relatively large compared to those of the starting materials and they had a nanocrystalline structure. The initial discharge capacity of the NiS positive electrode prepared by ball milling is 580 mAh/g-NiS, at 1.4 V vs. Li/Li+. The NiS powders synthesized by ball milling show a better cycling property than NiS prepared by melting and also had a better rate capability. It exhibited 87% of its theoretical capacity at a current rate of 2C, comparable with that of 1/6C. This may be related with the small sized grains of NiS prepared by ball milling. (C) 2002 Elsevier Science B.V. All rights reserved.