The valuable metals in the cathode of spent lithium-ion batteries (LIBs) have been recovered by a more simple and efficient process. The cathode was leached directly by citric acid without pretreatment such as immersed in N-methyl-pyrrolidone (NMP) or calcined. The leaching conditions of the concentration of citric acid, H2O2 dosage, reaction temperature, reaction time and solid-to-liquid ratio on the leaching efficiency have been discussed. Results show that under the condition of 1.0 M citric acid, 8% (V-hydrogen peroxide/V-citric acid) hydrogen peroxide, reaction temperature of 70 degrees C, leaching time of 70 min and solid-to-liquid ratio of 40 g/L, the leaching rate reached 99%. The leaching solution could be used to prepare new cathode materials of LIBs, and the detached aluminum foil and residue were recycled. The leaching solution has been dried and detected, and the result shows that the product is the mixture of citrate and citric acid. The chelating of the cobalt and lithium ions with the citrate plays an important role in improving the leaching efficiency.