The study of the electrochemical reaction mechanism of lithium with NiSb2 intermetallic material is reported here. The nickel diantimonide prepared by classic ceramic route is proposed as possible candidate for anodic applications in Li-ion batteries. The electrochemical characterisation of NiSb2 versus Li+/Li0 shows a reversible uptake of 5 lithium per formula unit, which leads to reversible capacities of 500mAhg−1 at an average potential of 0.9V. From ex situ XRD and 121Sb Mössbauer measurements it was shown that during the first discharge the orthorhombic NiSb2 phase undergoes a pure conversion process (NiSb2 +6 Li+ +6e− →Ni0 +2Li3Sb). During the charge process that follows, the lithium extraction from the composite electrode takes place through an original conversion process, leading to the formation of the high pressure NiSb2 polymorph. This highly reversible mechanism makes it possible to sustain 100% of the specific capacity after 15 cycles.