Ni3S2 with different morphologies (nanoflakes, nanosheets, nanoparticles) have been synthesized by simply altering the sulphur sources (thioacetamide, thiourea and sodium thiosulfate) of a hydrothermal process. The obtained three carbon-free nanostructures are evaluated as negative electrode materials for lithium ion batteries. Ni3S2 nanoflakes exhibit the best cycle and rate performance among the samples prepared, which is benefited from their small particle size and porous structure. It maintains a reversible capacity of 861 mA h g−1 after 70 cycles at a current density of 0.4 A g−1, and a reversible capacity of 514 mA h g−1 even at a current density as high as 4.0 A g−1. These features make Ni3S2 nanoflakes a promising candidate as high performance negative electrode material for lithium ion batteries.