Electrochemical properties of bare nickel sulfide and nickel sulfide-carbon composites prepared by one-pot spray pyrolysis as anode materials for lithium secondary batteries

Spherical bare nickel sulfide and nickel sulfide-carbon composite powders are prepared by a one-step spray pyrolysis. Submicron bare nickel sulfide particles with a dense structure have mixed crystal phases of NiS, Ni ₇S₆, and Ni_xS₆. The nickel sulfide-carbon composite powders prepared from a spray solution containing 0.1 M sucrose have a main crystal structure of Ni₇S₆ phase with small impurity peaks of Ni_xS₆ phase. A nickel oxide-carbon composite powder is first formed as an intermediate product in the front part of the reactor at 800 C. Fast decomposition of thiourea at this high temperature results in the evolution of hydrogen sulfide gas, which then forms the nickel sulfide-carbon composite powders by direct sulfidation of nickel oxide under the reducing atmosphere. Nickel sulfide nanocrystals with a size of a few nanometers are uniformly distributed inside the spherical carbon matrix. The nickel sulfide-carbon composite powders prepared with 0.1 M sucrose have an excellent discharge capacity of 472 mA h g^-1 at a high current density of 1000 mA g^-1, even after 500 cycles, with the corresponding capacity retention measured after the first cycle being 86%.