Nickel hydroxide/sulfide hybrids: halide ion controlled synthesis, structural characteristics, and electrochemical...

Focusing on the synthesis of nickel-based materials (such as nickel sulfides, nickel hydroxides, and nickel oxides) is an urgent need in the fields of batteries, supercapacitors, and catalysis. However, their controlled synthesis still remains a great challenge because of the inadequate understanding of the control factor of their synthesis. A two-step solvo-/hydrothermal process with halide ion embedding/releasing was proposed to understand the effect of the halide ions on the synthesis and sulfidation of nickel hydroxy-halides. We find that the halide ions determine the formation, growth, and evolution of nickel hydroxy halides and promote them to form unique architectures and morphologies, leading to obvious differences in structural characteristics, including conductivity and electrochemical activity. Because of the presence of halide ions, a series of hybrids with multiple interfaces, which consist of hydroxides and sulfides and have various morphologies, such as flower-like balls, solid balls, porous balls, schistose, and thorny balls, with capacities ranging from 100.7 to 261.2 mA h g^-1, can be easily obtained. It is fully demonstrated that the halide anion plays a core role in the synthesis process of nickel-based materials, and this finding will provide more chances for controllably synthesizing high-activity electrode materials.