The lithium Li-rich cathode material Li1.2Ni0.15Co0.10Mn0.55O2 was prepared by one combined method of coprecipitation and solid phase sintering. The morphology, phase and electrochemical properties of the samples at different precipitation times were tested by SEM, XRD, battery test system and electrochemical workstation. The results show that the morphology and electrochemical properties of the prepared cathode materials can be effectively controlled by controlling the precipitation time during the coprecipitation process. At the precipitation time of 8h, the precursor prepared has regular morphology and the best dispersibility. Under the voltage range of 2.0-4.8V and 0.1C, the retention rate at 50-cycle capacity is 80.0%, and the discharge specific capacity at 5C can reach 131 mAh·g-1; at the same time, the sample prepared at this precipitation time has a lower electrochemical transfer resistance of 159 O. Through this study, it is verified that the control of the precipitation time in the coprecipitation process can effectively regulate the structure of the cathode material and improve its electrochemical performance.