Herein, we demonstrate a novel amorphous composite layer-protected nanocrystalline NiO with superior long-term cyclability as an anode material for Li-ion batteries. Amorphous nickel and lithium carbon oxides form on nickel oxide (NiO nanoparticulate crystals with d < 15 nm) at room-temperature by mechanically milling a mixture of NiO and LiH under a CO2 atmosphere. The amorphous composite layer on the surface of NiO nanocrystal contains lithium carbonate (Li2CO3), nickel carbonate (NiCO3) and nickel acetate (NiC2O4). The NiO-0.4LiH sample milled under an atmosphere of 3 bar of CO2 delivers 770 mAh g−1 of specific capacity with nearly no capacity decrease from 2nd to 565th cycle at 100 mA g−1. Even operating at a high rate of 2 A g−1, the specific capacity remains at 530 mAh g−1, which is remarkably superior to that of pristine NiO (∼393 mAh g−1). The cycling stability is attributed to the amorphous carbon oxide layer effectively buffering the volume expansion of the anode during lithiation and stabilizing the solid electrolyte interphase (SEI) film during cycling of the NiO anode. The facile preparation process and favourable electrochemical performance of the composite NiO anode indicate this is a promising anode for a Li-ion battery.