1. Introduction
Recently, the use of lithium-ion batteries (LIBs) has increased sharply owing to the popularization of electric vehicles (EVs) and portable devices. In particular, in the case of EVs, usage is increasingly rapid, and unlike portable devices, large-capacity batteries are used [
1]. According to the International Energy Agency (IEA), the usage of EVs is expected to increase rapidly. Furthermore, EV-related policies and total cost of ownership (TOC) savings are expected to greatly increase the EV market size. The number of electric vehicles on the road is estimated to reach 220 million by the 2030s [
2,
3].
In the case of EVs and portable devices, lithium-ion secondary batteries, which have the characteristics of high energy density and low weight, are mainly used [
4,
5]. Therefore, research on the treatment and re-materialization of spent LIBs has become crucial amid the increase in battery market size.
Materialization technology for recycling of spent batteries can mitigate material shortages and price increases, further leading to cost savings of major materials. Recycling technology can reduce the cost of cathode materials (NCM: nickel, cobalt, manganese) from USD 25/kg to USD 10/kg. In general, the recycling of cobalt (Co), nickel (Ni), and manganese (Mn) found in LIBs is actively carried out [
6]. On the other hand, Li, which accounts for about 4–7% of battery content, has not been recovered for economic reasons, but research on Li recovery is now underway because of the recent increase in Li prices [
7,
8,
9].
In the case of existing processes, one drawback is that the removal of impurities is difficult when Li is recovered from black powder because Li is extracted after recovering other valuable metals (Co, Ni, Mn, etc.). Because of this problem, research on selective Li leaching technology has been conducted, and its overview information is shown in
Figure 1 [
10].
In selective Li leaching, roasting is performed to convert Li compounds and allow Li leaching in water. After leaching Li, vacuum evaporation or entraining gas evaporation is performed to facilitate the recovery of Li compounds. This requires a chemical reaction in which a portion of Li in the active material (LiCoO
2 or LCO) reacts with C and changes to Li
2CO
3 [
11,
12].
This has the implication that when an organic material containing C exists, LiNi
xCo
yMn
zO
2 can be reduced to Li
2CO
3, Ni, Co, and MnO by the carbon reduction reaction [
10,
13]. After roasting, Li
2CO
3 can be selectively leached in deionized (DI) water. However, Li
2CO
3 is known to have very low solubility (12.9 g/L, 25 °C) [
14]. Therefore, it is necessary to study the optimal roasting conditions and selection of the liquid-to-solid (L/S) ratio.
For effective Li leaching and recovery, this study conducted an experimental design based on the Taguchi method to analyze the effects of selective Li leaching and investigate the optimal conditions. Through these studies, it is possible to establish optimal conditions for the selective lithium leaching.
Author Contributions
Conceptualization, Y.J.J., S.C.P., B.Y.Y., and S.H.S.; Data curation, Y.J.J.; Formal analysis, Y.J.J.; Investigation, S.C.P. and B.Y.Y.; Methodology, Y.J.J.; Project administration, S.H.S.; Supervision, S.H.S.; Validation, S.H.S. and B.Y.Y.; Visualization, S.C.P.; Writing—original draft, Y.J.J.; Writing—review and editing, S.H.S. All authors have read and agreed to the published version of the manuscript.
Funding
This study was supported by the Technology Innovation Program (Development of Material Component Technology) (Project No. 2011183) funded by the Ministry of Trade, Industry and Energy, Republic of Korea.
Acknowledgments
The authors are thankful for the support by the Ministry of Trade, Industry and Energy, Republic of Korea.
Conflicts of Interest
There is no conflict of interest to declare.
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