Process for recycling mixed-cathode materials from spent lithium-ion batteries and kinetics of leaching

Abstract

A "grave-to-cradle" process for the recycling of spent mixed-cathode materials (LiCoO₂, LiCo_1/3Ni_1/3Mn_1/3O₂, and LiMn₂O₄) has been proposed. The process comprises an acid leaching followed by the resynthesis of a cathode material from the resulting leachate. Spent cathode materials were leached in citric acid (C₆H₈O₇) and hydrogen peroxide (H₂O₂). Optimal leaching conditions were obtained at a leaching temperature of 90 °C, a H₂O₂ concentration of 1.5 vol%, a leaching time of 60 min, a pulp density of 20 g L^-1, and a citric acid concentration of 0.5 M. The leaching efficiencies of Li, Co, Ni, and Mn exceeded 95%. The leachate was used to resynthesize new LiCo_1/3Ni_1/3Mn_1/3O₂ material by using a sol-gel method. A comparison of the electrochemical properties of the resynthesized material (NCM-spent) with that synthesized directly from original chemicals (NCM-syn) indicated that the initial discharge capacity of NCM-spent at 0.2 C was 152.8 mA h g^-1, which was higher than the 149.8 mA h g^-1 of NCM-syn. After 160 cycles, the discharge capacities of the NCM-spent and NCM-syn were 140.7 mA h g^-1 and 121.2 mA h g^-1, respectively. After discharge at 1 C for 300 cycles, the NCM-spent material remained a higher capacity of 113.2 mA h g^-1 than the NCM-syn (78.4 mA h g^-1). The better performance of the NCM-spent resulted from trace Al doping. A new formulation based on the shrinking-core model was proposed to explain the kinetics of the leaching process. The activation energies of the Li, Co, Ni, and Mn leaching were calculated to be 66.86, 86.57, 49.46, and 45.23 kJ mol^-1, respectively, which indicates that the leaching was a chemical reaction-controlled process.

Keywords: Kinetics; Re-synthesis; Recycle; Spent lithium-ion battery cathodes.