The electrochemistry of superdense 'LiC2' prepared by ball-milling has been investigated in EC-DMC solutions I M LiClO4. A primary capacity very close to 1115 mAhg(-1) per carbon atom was observed during the first deintercalation cycle at constant current. The following intercalation-deintercalation cycles yielded capacity close to the theoretical value of 372 mAhg(-1), typical of natural graphite. Electrochemical ac-impedance spectroscopy demonstrates that a solid electrolyte interface (SEI) is formed spontaneously upon immersion of the electrode in the electrolyte. Due to the complex nature of the compound prepared by ball-milling (a mixture of lithium metal, LiC3 and LiC6) the mechanism of the first deintercalation is rather complex. It involves the oxidation of lithium metal at about 22 mV versus Li, followed by the decomposition of the superdense phase LiC3 and of LiC6 at potentials that corresponds to the normal electrochemical lithium deintercalation from LiC6. Lithium metal in 'LiC2' easily reacts with nitrogen to yield alpha-Li3N that irreversibly de-intercalates about 1.8+/-0.1 lithium before decomposing. (C) 2003 Elsevier Science Ltd. All rights reserved.