The electrochemical reaction of lithium with the skutterudite-type CoP3 compound has been studied. To follow the reaction mechanism, X-ray diffraction (XRD), 7 Li nuclear magnetic resonance (NMR) and X-ray absorption (XAS) experiments have been carried out. During the first reaction of the CoP3 phase, cobalt is reduced and lithium-phosphide is formed. The reversible process observed during subsequent cycles consists of the formation of Li3P from its elements, giving a maximum in reversible gravimetric capacity of 487mAh/g.