Anode carbonaceous material recovered from spent lithium-ion batteries in electric vehicles for environmental application
Graphical abstract
Introduction
Lithium-ion batteries (LIBs) have many advantages over other common types of batteries owing to their high energy density and voltage, long lifetime, wide range of operating temperatures, and minimal memory effect (Dunn et al., 2014). They are considered crucial elements for reducing the dependence on fossil fuels (Frischknecht and Flury, 2011, Dunn et al., 2012). After nearly three decades of commercialization, LIBs are used to power a variety of portable electronic devices (e.g., smartphones) and battery, hybrid, fuel-cell, and plug-in hybrid electric vehicles (EVs) (Dunn et al., 2012, Dunn et al., 2014). According to the International Energy Agency (IEA, 2019), the EV manufacturing capacity has rapidly increased over the last decade, with the global stock of EVs exceeding 5 million in 2018, which is an increase of 63% with respect to the previous year. The production of EVs is predicted to reach 44 million vehicles per year by 2030 (IEA, 2019), and the demand for LIBs in handheld electronics and EVs has increased because they reduce costs and improve the battery performance. In addition, the use of EVs can reduce greenhouse-gas emissions (IEA, 2019).
An LIB consists of an anode (typically made from graphitic carbon) and a cathode, which are separated by a liquid organic electrolyte. Lithium is the main component in LIBs; the other materials currently used for LIB cathodes are cobalt, nickel, aluminum, and manganese. These elements provide compounds with high energy densities and, therefore, result in suitable batteries for portable electronics and automotive fields (Olivetti et al., 2017). According to reports from the British Geological Survey (BGS, 2018), between 2017 and 2025, the demand for nickel, cobalt, and lithium for EVs will increase annually by 39%, 25%, and 26%, respectively. The predicted demand for nickel and cobalt for EVs in 2030 is 1.1 and 0.3 million tonnes, respectively. In addition, large quantities of spent LIBs will be disposed as electronic waste, which may severely damage the environment owing to the toxicity of nickel and cobalt (Dunn et al., 2012, Ziemann et al., 2012, Miedema and Moll, 2013, Richa et al., 2014, Mellino et al., 2017). To ease the demand for raw materials for LIB production and address potential environmental impacts, most researchers have focused on improving the LIB performance and remanufacturing spent LIBs because the storage capacity of spent LIBs can reach 80%. Although the need to recycle spent LIBs is growing, only approximately 5% were recycled as of 2018. Moreover, it was predicted that the LIB recycling market will grow at an annual rate of 30.5% between 2017 and 2025, and>11 million tonnes of spent LIB packs are expected to be discarded between 2017 and 2030 (Natarajan and Aravindan, 2018). Lithium-ion battery (LIB) cathode components contain several recoverable and economically valuable metals, including lithium, cobalt, nickel, and manganese (Chagnes and Pospiech, 2013, Ahmadi et al., 2015). By recycling these metal components, environmental risks can be reduced, and shortages of raw materials can be relieved.
Graphite, which is usually the main component of LIB anodes and accounts for 12% to 21% of a battery’s weight, is a carbon-based material and an efficient conductor of heat and electricity (Dunn et al., 2014). Kikkawa (2018) predicted that the demand for flake graphite for LIB anodes is expected to significantly increase from 150,000 tonnes in 2017 to 800,000 tonnes by 2025. Carbon materials experience only minor aging after use in LIB anodes (Rothermel et al., 2016). Graphite recovered during recycling retains a storage capacity of 345 mAh/g, which is comparable to the 347 mAh/g of commercial graphite (Rothermel et al., 2016, Wang et al., 2019, Yang et al., 2019). However, recovered graphite cannot be used directly in an LIB anode owing to high purity requirements (99.9%) (Wissler, 2006). In addition, commercial graphite from other sources is abundant and inexpensive, making recycling LIB anode materials and upgrading recovered carbon powder from anodes relatively expensive operations because anode carbonaceous material (ACM) has no recognized additional value or other economically benefits.
The research group of this study has examined various carbon materials, including graphite, activated carbon, and various types of biochar as sorbents and catalysts for environmental remediation processes (Oh and Seo, 2014, Oh and Seo, 2016a, Oh and Seo, 2016b, Oh et al., 2017). In addition, a feasibility study of possible environmental applications of recovered ACM from LIBs was conducted. In this study, the performance of ACM as a sorbent and catalyst was evaluated based on previously published graphite and biochar data recorded under identical conditions (Oh and Seo, 2016a, Oh and Seo, 2016b, Oh et al., 2017). It was assumed that ACM can act as a catalyst or sorbent in the removal of toxic metals and organic compounds. Batch experiments were conducted to evaluate the sorption capacities for lead, cadmium, barium, 2,4-dinitrotoluene (DNT), 2,4,6-trinitrotoluene (TNT), hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), and 2,4-dichlorophenol (DCP). To determine the role of electron-transfer mediators in long-term reduction reactions, ACM was applied as a catalyst in the reduction of DNT and RDX with thiol (-SH) reductants, dithiothreitol (DTT) and hydrogen sulfide (H2S). Moreover, the catalytic potential of ACM in persulfate oxidation was evaluated.
Section snippets
Chemicals
DCP (>99%), DNT (>97%), 2-amino-4-nitrotoluene (2A4NT, 95%), 2-nitro-4-aminotoluene (2N4AT, 98%), 2,4-diaminotoluene (≥99%), lead chloride (CaCl2, > 98%), cadmium chloride hydrate (CdCl2·H2O > 98%), barium chloride hydrate (BaCl2·H2O, > 99%), formaldehyde solution (≥34.5%), and DTT (≥99%) were purchased from Sigma Aldrich (Milwaukee, WI, USA); TNT and RDX were provided by Hanhwa Co. (Seoul, South Korea), and TNT and RDX standard stock solutions (1000 μg/mL in acetonitrile, respectively) were
Characteristics of ACM
The properties of ACM and other types of carbon materials are summarized in Table 1. The pH (6.73) and PZC (6.70) were slightly acidic, thus higher than those of commercial graphite (3.73 and 4.94, respectively) and lower than those of rice straw-derived biochar (9.1 and 8.22, respectively) (Table 1) (Oh and Seo, 2014). The surface area was 15.7 m2/g, which is similar to that of rice straw-derived biochar (16.7 m2/g, Oh and Seo, 2016b). Moreover, the CEC was 75.8 meq/100 g, which is much higher
Environmental implications and conclusions
Anode carbonaceous material (ACM) is a by-product from the recovery of spent LIBs. Previous reports have indicated that the environmental impact of LIBs depends on their quantity of toxic heavy metals and the remaining storage capacity (Sullivan and Gaines, 2012). Mineral processing and the extraction of metals such as cobalt, copper, aluminum, manganese, and nickel from ores are associated with major environmental impacts, including soil contamination, greenhouse-gas emissions, loss of
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgments
This work was supported by Upbringing Business with Innovative Urban Public Institutions by the Ministry of Trade, Industry and Energy (Korea) [project name: Establishment of Battery/ESS-Based Energy Industry Innovation Ecosystem]. In addition, this study was supported by the National Research Foundation of Korea (NRF) grant funded by the Korean Government (MOE and MSIT) (2016R1D1A1B03931048, 2020R1A2C1010855).
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