Recycling of Spent Lithium Nickel Cobalt Manganese Oxides via Sulfuric Acid Roasting: Revealing the Product Evolution Mechanism

To mitigate the environmental impacts of spent lithium-ion batteries and enhance the sustainability of relative industry, the recovery of lithium nickel cobalt manganese oxide (LiNi_xCo_yMn_zO₂) cathode materials is of paramount importance. Sulfation roasting is a powerful recycling method of LiNi_xCo_yMn_zO₂ cathode but industrially restricted by the generation of AB₂O₄-type spinel transition metal oxides, sulfides or sulfur oxides (SO_x), and the product formation process (especially of transition metal sulfides) is not well understood. In this paper, we reveal the intermediate reactions and products of the roasting process. We investigate the impacts of sulfide generation on recycling and make certain attempts to eliminate the hazardous side reactions. The temperature and graphite are two key parameters determining the formation of sulfides and the roasting products evolved from sulfates to oxides and then to sulfides with the temperature increasing. Under optimized experimental conditions, we suppress the generation of sulfides and AB₂O₄-type spinel oxides and obtain a Li leaching efficiency of over 98%, minimal SO_x emission and negligible loss of transition metals (less than 3%), achieving the clean and effective recycling of LiNi_xCo_yMn_zO₂ cathode materials.