Low temperature one-step synthesis of carbon co-encapsulated NiS2, NiS and S8 nanocrystals by electrophilic oxidation of nickelocene

A novel method is developed for the synthesis of carbon co-encapsulated near-equiaxed NiS2, NiS and S-8 nanocrystals with core-shell structure by a one-step solid state reaction of nickelocene with ammonium persulphate at 200 degrees C in an autoclave. These nanocrystals have a narrow size distribution ranging from 5 to 19 nm and the median size is 10.99 nm. Both amorphous and graphitizable carbon shell are formed, encapsulating hundreds of nanocrystals as a whole and providing exclusive rooms for these nanocrystals separated from each other. The interaction of nickel with cyclopentadienyl ligands through pi bond results in the formation of core-shell structure. The carbon encapsulated NiS2 and NiS nanocrystal anodes retain a reversible capacity of 517 and 326 mA h/g after 50 cycles at a current density of 208 and 1480 mA/g, respectively. (C) 2014 Elsevier B.V. All rights reserved.