Selective Recovery of Lithium from Spent Lithium-ion Batteries Synergized by Carbon and Sulfur Elements

Abstract

Recycling of spent lithium-ion batteries (LIBs) has attracted ever-growing attention globally owing to the scarcity of critical metals and potential environmental risk. To solve the bottlenecks including poor selectivity and prominent environmental risks during the recovery of valuable metals from spent LIBs, the work proposed a novel process for selectively recovery of lithium synergized by carbon and sulfur elements. Firstly, H2SO4 was determined as the optimal roasting reagent by systematically investigating the effects of various roasting reagents including NaHSO4, (NH4)2SO4, NH4HSO4 and H2SO4 on the leaching selectivity of lithium from the LiNi1/3Co1/3Mn1/3O2 active material in spent LIBs, environmental impact and cost of reagents. Then, the effect of graphite dosage on the selectivity of lithium from LiNi1/3Co1/3Mn1/3O2 is investigated. Finally, the conversion path and mechanism under the synergistic effect of C and S elements for enhancing the selectivity of lithium is revealed. It is found that the leaching efficiency can achieve 93% under the following optimal conditions: the molar ratio of LiNi1/3Co1/3Mn1/3O2 to H2SO4 of 2: 1, graphite dosage of 20% (w), roasting temperature of 600℃, and roasting time of 120 min. The purity of the precipitated Li2CO3 from the obtained leachate is higher than that of battery grade Li2CO3. Ni, Co and Mn from LiNi1/3Co1/3Mn1/3O2 almost remains in the leaching residue which can be employed as the precursor materials for synthesizing cathode materials after separation and purification treatment. In addition, the separated graphite can be reused as roasting additive during the sulfation roasting of LiNi1/3Co1/3Mn1/3O2. By analyzing the thermal behavior of the mixed powder of LiNi1/3Co1/3Mn1/3O2 and graphite, along with the X-ray diffraction (XRD) characterization of the roasting products, it is found that the roasting temperature can be reduced by the addition of waste graphite, the selectivity of lithium can be enhanced under the synergistic effect of C and S elements. Most importantly, no hazardous gases such as SOx are generated. This work proposed a new solution for simultaneous recycling of cathode and anode materials by combing the advantages of sulfation roasting and carbothermal reduction, thus the efficient, selective and cleaner extraction of lithium and the circulating utilization of waste graphite can be achieved.