Green and sustainable recycling of spent lithium batteries: synergistic leaching of SLFP and SLMO for valuable metal extraction and environmental benefits†

With the burgeoning development of lithium batteries, the global lithium battery industry is now facing a multitude of issues regarding spent lithium batteries. The slow and inefficient disposal of these spent batteries will inevitably cause environmental pollution and a waste of valuable resources. In response to this, the current study proposes a green and highly efficient recycling method that eliminates the necessity of adding oxidizing or reducing agents in a low-acid environment. Taking spent lithium iron phosphate (SLFP) and spent lithium manganate (SLMO) as raw materials, we firmly validated the theoretical feasibility of the synergistic leaching process using thermodynamic analysis. Experimental results reveal that at a sulfuric acid concentration of 0.6 mol L⁻¹, a temperature of 40 °C, a SLFP : SLMO molar ratio of 1, a slurry density of 100 g L⁻¹, and a reaction time of 120 min, the leaching efficiencies of lithium and manganese reached as high as 99.99% and 70.02%, respectively. Meanwhile, the leaching rates of iron and phosphorus were merely 0.46% and 1.84%, respectively, and they mainly entered the slag phase in the form of (Mn,Fe)PO₄. The findings from kinetics and reaction mechanism analyses indicated that the redox driving force during the reaction process was quite strong. Specifically, Fe²⁺ generated after the dissolution of SLFP could rapidly react with the high-valence Mn produced following the dissolution of SLMO. By carefully controlling the pH of the filtrate, Li and Mn can be utilized to manufacture Li₂CO₃ and Mn₃O₄ products, respectively. This proposed technique can effectively reduce the consumption of chemical reagents, mitigate environmental pollution to a certain extent, and achieve the green and efficient extraction of valuable metals from spent lithium batteries, thus holding great promise for the sustainable development of the lithium battery recycling industry.