Selective recovery of lithium and efficient leaching of transition metals from spent LiNixCoyMnzO2 batteries based on a synergistic roasting process

A novel process was developed for the selective extraction of Li and efficient leaching of transition metals (TMs) from spent LiNixCoyMnzO2 (NCM) batteries coupled with the synergistic disposal of Na2SO4 byproducts generated from lithium battery industry. The NCM cathode was transformed into water-soluble LiNaSO4 and acid-dissolved divalent oxides of (NiO)m(MnO)n and CoO based on the synergy between self-reduction of graphite anode and Na2SO4 roasting. >85% Li was selectively extracted from the roasted product by water leaching. Subsequently, >95% Ni, >99% Mn and >99% Co were leached by H2SO4 solution without additional reductant. During the self-reduction roasting of graphite anode, the addition of Na2SO4 transformed Li from Li2CO3 to LiNaSO4 with higher solubility and also prevented the overreduction of Ni and Co oxides to the metallic states, which are prone to the deterioration of their acid leaching performance. Through the precise regulation of NCM phases during the synergistic roasting process, the efficient cascade extraction of Li and TMs from spent NCM batteries was realized, and a new way for the comprehensive utilization of the Na2SO4 byproducts was determined. Moreover, the emission of toxic gases SO2 and NOx generated in the acid roasting was avoided. The proposed process obeys the principles of circular economy and green chemistry.