A green process for recycling and synthesis of cathode materials LiMn₂O₄from spent lithium-ion batteries using citric acid

Abstract

In view of the reducing reagent consumption and secondary pollution caused by recycling spent lithium-ion batteries (LIBs), a relatively green process has been proposed, because the complex process to separate metals and the use of a large number of environmentally unfriendly chemical reagents are not involved. This process combines acid leaching with the resynthesis of the cathode material to recycle LiMn₂O₄ (LMO) from spent LIBs. The leaching efficiencies of Li and Mn exceeded 94% under the conditions of 1.0 M citric acid concentration, solid-liquid ratio of 60 g L^-1, and 60 min leaching time. After the leaching process, spinel LMO was successfully resynthesized by the sol-gel process using leachate. The sample calcined at 700 °C has the best electrochemical performances, and the initial discharge capacity at a 2C rate and capacity retention after 100 cycles were 87.85 mA h g^-1 and 93.63%, respectively. The resynthesized cathode material possessed excellent cycling performance, which may result from Al doping. Furthermore, the mechanism of overall reaction and the formation process of complex Mn(C₆H₆O₇)·H₂O in the leaching process were explored. This study indicates that citric acid is an effective reagent for recycling cathode materials and the process is feasible.