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

摘要

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, NJ_7S_6, and Ni_xS_6. The nickel sulfide-carbon composite powders prepared from a spray solution containing 0.1 M sucrose have a main crystal structure of Ni_7S_6 phase with small impurity peaks of Ni_xS_6 phase. A nickel oxide-carbon composite powder is first formed as an intermediate product in the front part of the reactor at 800 ℃. 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%.