As a promising cathode for next-generation lithium-ion batteries, the morphology dependence, size preference and electron/ion conductance of manganese-based lithium transition-metal phosphate (MLTP) compounds were comprehensively analyzed via synergistic strategies including the surfactant-assisted solvothermal method and surface modification. Variations of morphology, (particle, crystallite and lattice) size and electron/ion conductivity selectively modulated their electrochemical properties. For MLTP cathode materials, the as-prepared small-sized particle with large crystallite and large lattice greatly optimized the cycling stability, reversible capacity and polarization performance, whereas irregular particle morphology mainly inhibited the specific capacity. Meanwhile, the RGO-decorated MLTP-EG12/C cathode material could further unlock the high-rate capability and thermal stability without polarization differences. These regulation mechanisms of morphology, size and conductivity described in this work can be helpful in the development of high-performance cathode materials for lithium-ion batteries.