The facile recycling of spent lithium-ion batteries (LIBs) has attracted considerable attention because of its immense significance in environmental protection and resource utilization. The traditional leaching of cathode materials faces various problems, such as high energy consumption, large amounts of reductants, low metal leaching efficiencies, and insufficient safety. This study proposed a novel leaching system using reduced glutathione (GSH) as a reductant to leach cathode materials. The results indicate that the H₂SO₄–GSH leaching process of cathode materials depends on internal diffusion. Moreover, the leaching efficiencies of lithium, nickel, cobalt, and manganese are above 99% by controlling thermodynamic conditions. The leaching results were optimized by using the Box–Behnken experimental design, and a model of metal leaching efficiencies was proposed. Through the coprecipitation method and oxidative roasting process, a spherical LiNi_xCo_yMn_zO₂ (NCM) cathode material was successfully regenerated from the leaching solution. The regenerated NCM cathode material shows good electrochemical performance, and its discharge capacity is 164.5 mA h g⁻¹ at 0.2 C. After 100 cycles, its capacity retention ratio is as high as 94.93%. Economic assessments suggest that the process is profitable. This study substantially reduced the leaching temperature and consumption of chemical reagents, as well as improved the metal leaching efficiencies and safety, which is conducive to the sustainable industrial development of spent LIBs.