Efficient lithium recovery from spent ternary lithium-ion batteries via sulfuric acid roasting: Reaction mechanisms and gas emission control.

The increasing demand for lithium-ion batteries (LIBs) has introduced significant challenges related to efficient and environmentally sustainable lithium recycling. Recovering cathode materials from spent LIBs via sulfuric acid roasting and subsequent leaching requires a comprehensive understanding of reaction mechanisms and gas emission behaviors to facilitate industrial application. In this study, thermodynamic calculations were conducted using HSC 6.0 software, and real-time gas evolution was analyzed through thermogravimetric mass spectrometry (TG-MS). Gas products were further identified indirectly using ion chromatography (IC) after absorption in an alkaline solution. Material characterization was performed by employing X-ray diffraction (XRD), scanning electron microscopy with energy-dispersive spectroscopy (SEM-EDS), and X-ray photoelectron spectroscopy (XPS). The reaction mechanisms and gas release behaviors of graphite-containing Li1.15(NixCoyMn1-x-y)0.85O2 during sulfuric acid roasting were systematically investigated to optimize the roasting-leaching process.The results revealed a two-stage reaction mechanism: at low temperatures (approximately room temperature to 400 °C), the cathode material reacts with sulfuric acid to form lithium sulfate and transition metal sulfates; during the medium-to-high temperature stage (400-700 °C), lithium sulfate remains thermally stable, while transition metal sulfates decompose or are reduced to water-insoluble oxides or metallic phases, enabling selective lithium extraction. Elevated roasting temperatures also lead to substantially increased emissions of SO2 and CO2. These findings establish a thermodynamically informed roasting-leaching process, facilitating selective lithium recovery while effectively mitigating gas emissions. Additionally, the study provides valuable mechanistic insights into sulfuric acid roasting, presenting a scalable and sustainable strategy for environmentally friendly recycling of spent LIBs.