LiMnPO4 cathode materials of various sizes and shapes are synthesized by a hydrothermal method. In order to control the morphology of the LiMnPO4 particles, a nonionic surfactant or a cationic surfactant has employed as a key additive to the reactant solution. LiMnPO4 nanoparticles of grain-shape and rod-shape can be made with sizes between about 100 and 300 nm by adding a nonionic large polymer surfactant. Micrometer-sized LiMnPO4 particles of cuboid shape result from the reaction with a cationic surfactant. LiMnPO4 spheres of about 20 μm diameter are produced when no surfactant is added. The cathode composed of nanocrystalline (about 100 nm size) LiMnPO4 exhibited the best performance with the specific capacity of 153 mAhg-1 for the first battery cycle.