Composite nickel nanoparticles and method for producing same

A method for producing composite nickel nanoparticles comprises: A) a step for obtaining a complexed reaction solution by heating a mixture of nickel carboxylic acid and a primary amine at a temperature ranging from 100°C to 165°C; B) a step for obtaining a metallic nickel nanoparticle slurry by heating the complexed reaction solution at a temperature of at least 170°C by microwave irradiation, and reducing nickel ions in the complexed reaction solution such that the nickel ions are covered by the primary amine; and C) a step for obtaining composite nickel nanoparticles, which are covered by the primary amine and elemental sulfur or an elemental-sulfur-containing organic compound, by adding sulfur powder or the elemental-sulfur-containing organic compound, which is capable of replacing the covering primary amine, to the metallic nickel nanoparticle slurry covered by the primary amine.