LiMn2-xMxO4 (M = Co, Ni, Fe, Cr, Al; x = 0, 0.05, 0.15, 0.2) cathode materials for lithium-ion batteries have been synthesized by an improved solid-state method. Samples were characterized by XRD, SEM, and XPS for their structure, morphology and surface conditions. Their electrochemical performance was also tested. Compared with pristine LiMn2O4, all LiMn2-xMxO4 materials exhibited much better cycling stability between 3.0 V and 4.3 V. LiMn1.85Cr0.15O4 showed a superior cycling stability with a capacity retention of 96.6% after 100 cycles, which is 23% higher than that of the LiMn2O4 phase. The underlying mechanism of the improved cycle performance has been investigated by synchrotron-based X-ray diffraction under operating conditions for batteries. In situ XRD results proved that metal-ion-doped LiMn2O4 could hinder the phase transformation, reduce microstrain and volume shrinkage during cycling and improve their structural stability. The role of the doped metal ions was also confirmed by density functional theory calculations.