Study on efficient and synergistic leaching of valuable metals from spent lithium iron phosphate using the phosphoric acid-oxalic acid system

Recycling valuable metals from spent lithium iron phosphate (LFP) batteries can effectively alleviate resource depletion and reduce environmental pollution. In this work, a short-flow recovery process for efficient leaching of Li and Fe from spent LFP using a mixed acid system is proposed. Response Surface Methodology (RSM) is used to determine the optimal leaching process conditions. The results indicate that under the conditions of 0.65 mol·L−1 H3PO4, 0.33 mol·L−1 H2C2O4, 40 g·L−1 solid/liquid ratio, and 51 min, the leaching rates of Li and Fe are 97.72 % and 98.24 %, respectively. The leaching mechanism analysis shows that the use of H3PO4 released Li and Fe in the olivine crystals, and the chelation of H2C2O4 with Fe (III) in solution promoted the further destruction of the LFP structure. Due to the synergistic effect of the mixed acid, almost all the Li and Fe in the spent cathode are leached into the solution. By adjusting the molar ratio of Li:Fe:P in the leaching solution, a new LFP is synthesized by the spray drying process. The regenerated LFP has a spheroid-like structure with a grain size of about 300–800 nm and abundant Li+ diffusion channels between the particles, which are beneficial to the electrochemical performance of the battery. This study provides a simple and effective technique for the full-component recovery of valuable metals from spent LFP cathodes and the low-cost regeneration of LFP electrode materials.