Microwave-Assisted Sulfation Method for Lithium Recovery from Spent LiNi_xCo_yMn_zO₂ Cathode Material: Process Intensification and Conversion Mechanism

The recovery rate of lithium from spent lithium-ion batteries (LIBs) is only about 50% by the conventional hydrometallurgical process in industry, which results in huge waste of lithium resources. Therefore, this paper proposes a novel method to selectively recover lithium from the cathode material of spent LIBs via microwave sulfation roasting. The thermodynamic predominant region diagram of the Li–Ni–Co–Mn–S–O system was drawn for the first time to analyze the rules of phase conversion in the sulfation roasting process. The effects of important variables on the leaching rate of Li were investigated by leaching experiments. Additionally, in situ X-ray diffraction, time-of-flight secondary ion mass spectrometry, etc. were employed to clarify the conversion mechanism of the microwave sulfation roasting process. The results show that after roasting with only a theoretical dosage of H2SO4 in a microwave at 550 °C for only 1 h, over 97% of Li is leached by water leaching, while only 2.9% Mn and trace Ni and Co are leached. Compared with the sulfation process using the conventional roasting method, microwave roasting has the advantages of a shorter operation time and a higher extraction rate of Li. This study provides a more efficient and low-carbon technology for the recycling of spent LIBs.