Rare metals recycling from spent NCM cathode materials and simultaneous dehydrofluorination of polyvinylidene fluoride (PVDF) in subcritical water

Abstract

Several studies have examined the recovery of lithium (Li), nickel (Ni), cobalt (Co), and manganese (Mn) from used lithium-ion batteries (LIBs). However, the environmentally friendly and cost-effective leaching and efficient separation of rare metals from the active cathode material of LIBs remains a challenge. In this study, we present a novel route for the extraction of high-value metals from the NCM cathode material of spent LIBs using subcritical water-containing polyvinylidene fluoride (PVDF). The experimental parameters such as reaction temperature, time, liquid–solid and mass ratios, were carefully investigated. The raw cathode material and the solid residues before and after leaching were characterized using ICP-OES, XRD, FT-IR and SEM-EDS analyses. Results showed that the maximum extraction efficiencies of Li, Ni, Co, and Mn of (98.69, 98.24, 97.52, and 99.04) %, respectively, were achieved under the optimized conditions of 350 °C, 2 h, 1:3 mass ratio, and 60:1 mL/g liquid–solid ratio. Meanwhile, the experimental results of leaching kinetics revealed that the reaction in the system was controlled by the surface chemical reaction model with the linear fitting degree of (R2 = 0.97–0.99) and the calculated activation energies of 63.72 kJ/mol (for Li), 73.55 kJ/mol (for Ni), 74.99 kJ/mol (for Co), and 71.88 kJ/mol (for Mn). The overall findings of this research concluded that the PVDF-assisted subcritical water extraction process is a beneficial and a promising alternative to other existing methods.