We have developed manganese-based lithium secondary battery technology as a part of a 10-year national project in Japan for The Development of Dispersed-Type Battery Energy Storage Technology. The cell chemistry we developed consisted of a modified graphite anode material containing dispersed Ag particles, and a partially substituted LiMn2O4 cathode with Li in the Mn sites. These materials showed a significant improvement in a cell's cycle life performance. The 250 Wh class single cell with the cell chemistry mentioned above showed energy densities of 131 Wh/kg and 295 Wh/dm3. The 2 kWh class module battery including 8 cells connected in series and a battery management system delivered energy densities of 122 Wh/kg and 255 Wh/dm3 that exceeded the final target of 120 Wh/kg and 240 Wh/dm3 for the project. Most of the target items for the battery performance were accomplished and proved. Thus the basis for practical application was developed, however, some areas concerning the further durability under various circumstances and conditions still remain to be accomplished. Continuous development for mass production and cost reduction is also expected for this technology in order to contribute to industry and society.