The lithiation mechanism of the intermetallic compound Al2Cu as anode materials for lithium-ion batteries during lithium intercalation/deintercalation was studied in this paper. The Gibbs free energy changes for five possible electrochemical reactions of Li intercalated into Al2Cu electrode have been calculated based on the first-principles plane-wave pseudopotential method in conjunction with thermodynamic principles. The reaction Li+Al2Cu -> LiAl+AlCu that possesses the most negative value of the Gibbs free energy change per unit lithium on average among all the five reactions was claimed to be the lithiation mechanism of Al2Cu electrode. In order to warrant the speculation, the 2032-type coin cells with Al2Cu and lithium metal as the testing and the counter electrode, respectively, was assembled. The electrochemical performance of the cells and the phase changes in Al2Cu electrode were examined. Finally, it is found that the experimental results were consistent with the calculated ones, indicating that the first-principles calculations can be used to investigate the lithiation mechanism of the intermetallic compounds. (c) 2006 Elsevier B.V. All rights reserved.