Oxygen-free calcination for enhanced leaching of valuable metals from spent lithium-ion batteries without a reductant

Drawbacks such as reductant need in leaching process or high energy consumption in pre-treatment step exist in current approaches for recycling spent lithium-ion batteries (LIBs). Here, we report an energy-saving pre-treatment process that can increase the metals leaching efficiency of spent LiNixCoyMn1-x-yO2 LIBs in H2SO4 solution. In the proposed process, the spent electrode material was calcined in a nitrogen (oxygen-free) atmosphere, resulting in the easy leaching of metals by H2SO4 without adding reductant. Calcination conditions were examined, and calcination at 350 degrees C for 1.5 h resulted in the optimal leaching rates of Li, Ni, Co, and Mn (>99%). Mechanism analysis revealed how calcination improves the leaching efficiency. We found the proposed calcination pre-treatment can destroy the well-defined layered crystal structure of spent LiNixCoyMn1-x-yO2 without changing its original phase composition. As a result, refinement of crystalline size, increase of defect, amorphization, and specific surface area (with the emergence of cracks and voids) of the cathode particles enhance the leaching of metals. This study may provide an energy-saving and cost-effective pre-treatment process that can remarkably improve metals leaching rates from spent LIBs without adding reductants.