Closed-loop regeneration of battery-grade FePO4 from lithium extraction slag of spent Li-ion batteries via phosphoric acid mixture selective leaching

Abstract

• Li extraction slag of spent Li-ion batteries is recycled into battery-grade FePO 4 . • The selective leaching process using H 3 PO 4 -HCl solution is discussed. • The leaching conditions for recovering battery-grade FePO 4 were optimized. • Re-synthesized LiFePO 4 possesses an excellent charge/discharge capacity. FePO 4 regeneration from lithium extraction slag (LES) is a key link in the closed-loop recycling of LiFePO 4 , but this link has not yet been effectively achieved. This study presents a selective leaching treatment for removing impurities from LES, and then the battery-grade FePO 4 is recovered. The leaching efficiency of impurity elements such as Ni, Cu, and Mn can reach up to 99.53%, 98.08%, and 97.65%, respectively, while the main element of Fe and P remain as low as 0.3% and 1.6%, and recovered FePO 4 (R-FePO 4 ) conformed to China Chemical Industry Standard for battery-grade FePO 4 (HG/T 4701–2014). The leaching experiment shows that H 3 PO 4 treatment contributes to obtaining excellent crystalline FePO 4 , while the addition of HCl mainly enhanced the leaching performance of metal impurities. The optimal conditions for recovering battery-grade FePO 4 were: 1.5 mol/L H 3 PO 4 , H 3 PO 4 /HCl molar ratio of 3:1, a liquid–solid ratio of 10 mL/g, leaching at 90 °C for 3 h. The thermodynamics of the leaching reactions was analyzed to determine the feasibility of leaching impurities and crystallizing FePO 4 from LES. The composition and structure of the regenerated FePO 4 were restored, and the electrochemical performance reached the same level as commercial materials. In addition, the cost of R-FePO 4 is calculated to be $1.35 kg −1 , which is about 32.5% lower than the cost of commercial FePO 4 (C-FePO 4 , $2.0 kg −1 ). This work presents a potential “waste-to-wealth” approach to guide the efficient and environmentally friendly recycling of spent Li-ion batteries (LIBs).