LiCoMnO4 with nanosized truncated octahedral structure was prepared via a modified sol–gel route. The single-crystalline subunits grew completely without serious agglomeration. The growth mechanism was discussed in detail. The sample was tested as cathode materials for 5 V Li-ion batteries. Ni doping was also investigated to decrease the content of Mn3+ ions and the Mn dissolution, and then the decomposition of electrolyte was inhibited on the cathode surface. LiCo0.9Ni0.1MnO4 exhibited enhanced cyclic stability compared with the pristine LiCoMnO4.Keywords: cathodes; doping; high voltage; LiCoMnO4; lithium-ion batteries;