Lithium cobalt phosphate (LiCoPO4), a cathode material for 5 V high-voltage lithium-ion batteries, has limited its practical application due to its low conductivity and ionic diffusion. In this research, a pure-phase LiCoPO4 with core-shell structure is successfully synthesized by oleylamine-assisted ethanol solvothermal method, and the influence of different solvothermal reaction times on the properties of the material is fully studied. The results show that pure-phase LiCoPO4 can be prepared by calcination under pure N2, and carbon layers (3 nm ∼ 8 nm) with different thickness are formed on the surface of LiCoPO4 particles synthesized under different solvothermal reaction times (1 h ∼ 18 h). The LiCoPO4 prepared under the condition of solvothermal reaction time of 12 h has good crystallization properties and morphology characteristics, and the thickness of the carbon layer formed on the surface is about 6 nm. Electrochemical tests show that it has the largest initial discharge capacity, the best performance and the best cycle stability. Adjusting the reaction conditions enables the formation of a suitable thickness of carbon coating on the surface of LiCoPO4, which improves the conductivity, ion diffusion and stability of the material in high voltage environments, thereby improving the electrochemical performance of high-voltage LiCoPO4.