Recycling of cathode material from spent lithium ion batteries using an ultrasound-assisted DL-malic acid leaching system

•Ultrasound enhancement is novely applied for leaching process.•A closed-loop process is developed to recycle spent cathode materials.•The mechanism of ultrasound-assisted leaching is explained. Herein, a novel process involving ultrasound-assisted leaching developed for recovering Ni, Li, Co, and Mn from spent lithium-ion batteries (LIBs) is reported. Carbonate coprecipitation was utilized to regenerate LiNi0.6Co0.2Mn0.2O2 from the leachate. Spent cathode materials were leached in DL-malic acid and hydrogen peroxide (H2O2). The leaching efficiency was investigated by determining the contents of metal elements such as Li, Ni, Co, and Mn in the leachate using atomic absorption spectrometry (AAS). The filter residue and the spent cathode materials were examined using Fourier transform infrared (FTIR) and scanning electronic microscopy. The leaching efficiencies were 97.8% for Ni, 97.6% for Co, 97.3% for Mn, and 98% for Li under the optimized conditions (90 W ultrasound power, 1.0 mol/L DL-malic acid, 5 g/L pulp density, 80 °C, 4 vol% H2O2, and 30 min). The leaching kinetics of the cathode in DL-malic acid are in accordance with the log rate law model. The electrochemical analysis indicates that the LiNi0.6Co0.2Mn0.2O2 regenerated at pH 8.5 has good electrochemical performance. The specific capacity of the first discharge at 0.1 C is 168.32 mA h g−1 at 1 C after 50 cycles with a capacity retention of 85.0%. A novel closed-loop process to recycle spent cathode materials was developed, and it has potential value for practical application and for contributing to resource recycling and environmental protection.