Cost effective synthesis hetero-structured N-doped C-coated Ni9S8/Ni3S2/NiS1.03 nanoparticles attached on 3D reduced graphene oxide anode to exceptional Li-ion performance

•N-NixSy@C/G was synthesized by a facile hydrothermal, freeze-drying and subsequent calcination method.•The system can be endowed with the increased electrical conductivity by in-situ carbon layer and nitrogen doped.•Graphene not only provides an attachment skeleton to avoid agglomeration, but also accelerates electron transport.•N-NixSy@C/G with significantly enhanced synergistic effects demonstrates outstanding lithium ion storage performance.