The results of a study of the reactivity of lithium intercalated into petroleum coke (Conoco) in a PC/EC/DMC (1/1/3 volume) mixture and LiCF3SO3 as the lithium salt are presented here. We show the loss of intercalated lithium is due to its reactivity with the electrolyte and increases quasi-linearly during 1000 h of storage, and thereafter becomes less important as the storage time increases. The storage of passivated petroleum coke electrodes without any lithium content allowed us to determine the rates of the precipitation and dissolution reactions involving the passivating layer.