National Basic Research Program of China (973 program) [2011CB935903]; National Natural Science Foundation of China [21233004, 21021002]; City University of Hong Kong Seed Grant [7003023] ; Novel three-dimensional (3D) hierarchical NiSix/Co3O4 core-shell nanowire arrays composed of NiSix nanowire cores and branched Co3O4 nanosheet shells have been successfully synthesized by combining chemical vapor deposition and a simple but effective chemical bath deposition process followed by a calcination process. The resulting hierarchical NiSix/Co3O4 core-shell nanowire arrays directly serve as binder- and conductive-agent-free electrodes for lithium ion batteries, which demonstrate remarkably improved electrochemical performances with excellent capacity retention and high rate capability on cycling. They can maintain a stable reversible capacity of 1279 mA h g(-1) after 100 cycles at a current density of 400 mA g(-1) and a capacity higher than 340 mA h g(-1) even at a current density as high as 8 A g(-1). Such superior electrochemical performance of the electrodes made by directly growing electro-active highly porous Co3O4 on a nanostructured NiSix conductive current collector makes them very promising for applications in high-performance lithium ion batteries.