With the development of electric vehicles, the number of discarded lithium (Li)-ion batteries is expected to increase in the future. Waste Li-ion batteries contain cobalt (Co), nickel (Ni), and Li, which are valuable metals and, if not appropriately handled, will cause irreparable harm to the environment. Therefore, the recycling of waste Li-ion batteries is an important topic. In this study, we employed the Taguchi method to explore the impact of temperature, solid-to-liquid (S/L) ratio, time, acid concentration, and the amount of added hydrogen peroxide (H2O2) on the leaching rate. The optimized process parameters were initially obtained by the Taguchi method to be a S/L ratio of 10 g L−1, H2O2 addition of 1.5 vol.%, an acid concentration of 2 mol L−1, a temperature of 60 ℃, and a time of 45 min. Because interactions may occur between the various factors, confirmation experiments were carried out according to the order of importance of the effect of the five parameters on the leaching rate. The optimum leaching parameters were ultimately found to be a S/L ratio of 25 g L−1, H2O2 addition of 1.5 vol.%, an acid concentration of 2 mol L−1, a temperature of 60 ℃, and a time of 15 min. For these parameters, the leaching rates of Li, Co, Ni, and Mn were 96.41, 82.53, 89.25, and 99.99%, respectively. Finally, through kinetic analysis, we found that the activation energies of Li, Co, Ni, and Mn were 3.74, 24.81, 37.82, and 24.01 kJ mol−1, respectively. Co obtained by leaching can be used in electrochemical sensors.