Spinel-structured lithium manganese oxide (LiMn(2)O(4)) cathodes have been successfully commercialized for various lithium battery applications and are among the strongest candidates for emerging large-scale applications. Despite its various advantages including high power capability, however, LiMn(2)O(4) chronically suffers from limited cycle life, originating from well-known Mn dissolution. An ironical feature with the Mn dissolution is that the surface orientations supporting Li diffusion and thus the power performance are especially vulnerable to the Mn dissolution, making both high power and long lifetime very difficult to achieve simultaneously. In this investigation, we address this contradictory issue of LiMn(2)O(4) by developing a truncated octahedral structure in which most surfaces are aligned to the crystalline orientations with minimal Mn dissolution, while a small portion of the structure is truncated along the orientations to support Li diffusion and thus facilitate high discharge rate capabilities. When compared to control structures with much smaller dimensions, the truncated octahedral structure as large as 500 nm exhibits better performance in both discharge rate performance and cycle life, thus resolving the previously conflicting aspects of LiMn(2)O(4).