In view of the importance of environmental protection and resource recovery, recycling of spent lithium-ion batteries (LIBs) and electrode scraps generated during manufacturing processes is quite necessary. An environmentally sound leaching process for the recovery of Li, Ni, Co, and Mn from spent LiNi1/3Co1/3Mn1/3O2-based LIBs and cathode scraps was investigated in this study. Eh–pH diagrams were used to determine suitable leaching conditions. Operating variables affecting the leaching efficiencies for Li, Ni, Co, and Mn from LiNi1/3Co1/3Mn1/3O2, such as the H2SO4 concentration, temperature, H2O2 concentration, stirring speed, and pulp density, were investigated to determine the most efficient conditions for leaching. The leaching efficiencies for Li, Ni, Co, and Mn reached 99.7% under the optimized conditions of 1M H2SO4, 1vol% H2O2, 400rpm stirring speed, 40g/L pulp density, and 60min leaching time at 40°C. The leaching kinetics of LiNi1/3Co1/3Mn1/3O2 were found to be significantly faster than those of LiCoO2. Based on the variation in the weight fraction of the metal in the residue, the “cubic rate law” was revised as follows: θ(1− f)1/3 =(1− kt/r 0 ρ), which could characterize the leaching kinetics optimally. The activation energies were determined to be 64.98, 65.16, 66.12, and 66.04kJ/mol for Li, Ni, Co, and Mn, respectively, indicating that the leaching process was controlled by the rate of surface chemical reactions. Finally, a simple process was proposed for the recovery of valuable metals from spent LiNi1/3Co1/3Mn1/3O2-based LIBs and cathode scraps.