Herein, the method of hydrometallurgy is adopted to recycle the precious metal cobalt in spent lithium ion batteries (LIBs). The best experimental conditions for leaching cobalt ions in sulphuric acid–hydrogen peroxide system are studied. The best leaching operation condition is an H₂SO₄ concentration of 3.0 mol L⁻¹, liquid–solid ratio of 7 : 1 and hydrogen peroxide dosage of 1.6 mL g⁻¹ for 2.5 h at 70 °C. Using the extraction characteristics of D2EHPA (di-(2-ethylhexyl) phosphoric acid) and PC-88A (2-ethylhexyl phosphonic acid mono-2-ethylhexyl ester) for a specific ion in different pH value leaching solutions, the best experimental conditions are D2EHPA and PC-88A saponification rates of 20% and 30%, respectively, sulfonated kerosene volume of 70%, oil–water (O/A) ratio of 1 : 1, and extraction time of 10 min. Two extractions are applied, the first extraction occurs at pH 2.70 and the second extraction is done at pH 2.60 using D2EHPA to remove copper and manganese ions. After the extraction operation, PC-88A is used to further extract the leaching solution and maintain the pH at 4.25, so that cobalt and nickel ions are effectively separated, then cobalt ions are separated by oxalic acid and cobalt oxalate is obtained. The purity of cobalt is as high as 99.50%.