A fast and efficient method for selective extraction of lithium from spent lithium iron phosphate battery

Abstract

A new recovery method for fast and efficient selective leaching of lithium from lithium iron phosphate cathode powder is proposed. Lithium is expelled out of the Oliver crystal structure of lithium iron phosphate due to oxidation of Fe 2 + into Fe 3 + by ammonium persulfate. 99% of lithium is therefore leached at 40 °C with only 1.1 times the amount of ammonium persulfate without the help of acid treatment. The use of ammonium persulfate also avoids the necessity to remove other metal ions in the later purification process. Various characterization methods including SEM, XPS, XRD are used to explore the experimental leaching mechanism. Theoretical investigations are performed which reveals the E-pH diagram of Fe–P–Li–H 2 O thermodynamic equilibrium. It confirms the possibility and suggests appropriate pH range allowing direct conversion from lithium iron phosphate to iron phosphate with great energy saving and reduced use of acid and base. Based on the experimental and theoretical results, a green and efficient closed-loop recycling route for lithium iron phosphate is proposed. • A fast efficient leaching of LiFePO 4 is achieved via oxidation by (NH 4 ) 2 S 2 O 8 . • 99% of lithium is leached without acid due to oxidation of LiFePO 4 to FePO 4 . • Mechanism studies are conducted to establish principles for recycling LiFePO 4 .