Recycling end-of-life lithium-ion batteries has attracted widespread attention due to their potential environmental hazards and the importance of key metal supplies. However, the previously reported research methods are intended only for spent Ni-Co-Mn (NCM)-based lithium-ion batteries or spent lithium iron phosphate batteries. In this letter, a new method is proposed for recovering the mixed cathode materials of LiFePO4 and LiNi0.5Co0.2Mn0.3O2 from spent lithium-ion batteries by sole Fe-2(SO4)(3). According to our design, ferric iron itself acts as a Lewis acid and facilitates LiFePO4 to release the reducing agent of ferrous iron to reduce LiNi0.5Co0.2Mn0.3O2. Additionally, the environmentally friendly and efficient leaching process has been achieved for Ni, Co, Mn, and Li by reasonably adjusting the ratio of trivalent iron, LiFePO4, and LiNi0.5Co0.2Mn0.3O2. This method of processing mixed spent lithium-ion battery cathode materials significantly reduces the amount of reducing agent or oxidant usage. Also,it is effective at reducing time, energy consumption, and water consumption. It provides a new solution to recycling used lithium-ion batteries.