Lithium manganese oxide spinel (LiMn2O4) with a high rate capability was synthesized for rechargeable lithium-ion batteries. This material consisted of a,agglomerates (15 mum on an average) formed from smaller primary particles (ca. 0.5-3 mum). The rate performance of the spinel was examined in an electrochemical test cell where the spinel was the positive electrode and metallic Lithium was the (negative) counter electrode. The specific power output of the cell was found to be more than 8000 W per kilogram of spinel during about 100 s at a discharge rare of 20 C, or more than 400 W per kilogram of spinel during about 1 h at a discharge rare of C/1.