High-performance lithium-rich-layered oxide is regarded as a promising candidate for lithium-ion battery (LIB) cathode materials because of its outstanding high specific capacity. Despite in-depth research over the past decade, there are still a number of serious problems limiting its commercialization. Here, we report a simple morphological design and size-controllable material preparation strategy to enhance the electrochemical performance of LIB cathode materials. We use a simple solvothermal method to obtain a carbonate precursor material with different morphologies by adjusting the solvent ratio of the system, which will be conveniently formed into Li1.2Mn0.54Ni0.13Co0.13O2 by calcination. Moreover, further relation between the morphology and electrochemical performance of cathode materials is systematically investigated. The microsphere cathode material with suitable size exhibits superior electrochemical performances among all samples in terms of initial reversible capacity (280.4 mA h g-1 at 0.1 C) and cycle performance (87.67% retention after 200 cycles at 1 C). Even at 5 C, a high discharge capacity of 150.8 mA h g-1 can be obtained. In addition, this work provides a feasible and effective approach to controllable synthesis of stable structures and high-performance oxide electrode materials for LIBs.