Layered manganese dioxide (MnO2) films intercalated with Li+, Na+ or Mg2+ ions were synthesized by a one-step electrochemical method. The electrodeposition was potentiostatically performed by applying an anodic potential of 1.0 V vs. Ag/AgCl in an aqueous MnSO4 solution containing a perchlorate salt of the cation. The electrodeposited oxide films have a birnessite-type layered structure with alkali cations and water molecules between manganese oxide layers. The galvanostatic charge-discharge experiments performed in I M LiPF6-DME/PC solution indicated that the Mg2+-intercalated MnO2 electrode exhibits an initial discharge capacity as large as 140 mAh g(-1) and it shows a better capacity retention during cycling as compared with the Li+- or Na+-intercalated MnO2 electrode. (C) 2007 Elsevier B.V. All rights reserved.