A new electrolytic manganese dioxide (EMD) suitable for use as a cathode for primary or secondary Li-cells has been developed. The heat-treated product is a high surface area EMD (HSA EMD), which was prepared by anodic deposition from an MnSO4/H2SO4 electrolyte at a high current density. It shows excellent electrochemical behavior as a cathode for Li cells. This electrode material discharges its theoretical capacity during the first discharge process and has satisfactory cycling behavior Measurement indicates that HSA EMD has a quicker open-circuit-voltage (OCV) recovery than common EMD. This suggests that fast Li ion diffusion occurs in this material. A two or more phase reaction occurs during the first discharge in the Li/HSA EMD cell. In contrast, repeated discharge/charges are fundamentally a single phase reaction. The relationship between the OCV voltage plateau during the first discharge and structure of the HSA EMD is discussed.