Abstract
Clean and efficient recycling of spent lithium-ion batteries (LIBs) has become an urgent need to promote sustainable and rapid development of human society. Therefore, we provide a critical and comprehensive overview of the various technologies for recycling spent LIBs, starting with lithium-ion power batteries. Recent research on raw material collection, metallurgical recovery, separation and purification is highlighted, particularly in terms of all aspects of economic efficiency, energy consumption, technology transformation and policy management. Mechanisms and pathways for transformative full-component recovery of spent LIBs are explored, revealing a clean and efficient closed-loop recovery mechanism. Optimization methods are proposed for future recycling technologies, with a focus on how future research directions can be industrialized. Ultimately, based on life-cycle assessment, the challenges of future recycling are revealed from the LIBs supply chain and stability of the supply chain of the new energy battery industry to provide an outlook on clean and efficient short process recycling technologies. This work is designed to support the sustainable development of the new energy power industry, to help meet the needs of global decarbonization strategies and to respond to the major needs of industrialized recycling.
© 2024 Institute of Process Engineering, Chinese Academy of Sciences. Publishing services by Elsevier B.V. on behalf of KeAi Communications Co., Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.Org/licenses/by-nc-nd/4.0/).
Keywords: Spent LIBs; Transformative recycling; LCA analysis; Policy guidance; High value utilization
(ProQuest: ... denotes formulae omitted.)
1. Introduction
Green energy and environmental friendliness have become the global goal of actively seeking sustainable and rapid development. Developing a circular economy and realizing green transformation facilitate blood circulation of the world economy and energy [1]. The global consumption of fossil fuels in 2021 reached 595.15 EJ, accounting for 82% of the total primary energy in 2020. Although statistics show that fossil fuels still occupy the leading position in the global energy consumption, it is encouraging that the growth rate of fossil fuel consumption is extremely low every year [2]. According to the World Energy Outlook of the International Energy Agency (IEA), it is estimated that the total energy demand under the State Policies Scenario (STEPS) will increase to 743.9 EJ in 2050, of which renewable energy will only account for 25.8% (Fig. la) [3]. However, as a pillar of the global energy demand, the consumption of fossil fuels inevitably releases a large amount of greenhouse gases. In 2021, the global energy-related total CO2 emissions rebounded significantly to 36.3 Gt. The use of fossil fuels has led to a significant increase in carbon emissions, which has aggravated the greenhouse effect [4]. To solve the environmental, energy and security problems due to fossil energy combustion, many new energy sources, such as solar photovoltaic, wind, water, biomass, and geothermal energy, have been created and converted into flexible electric energy to reduce the carbon emissions associated with fossil energy and to improve energy sustainability (Fig. lb) [3]. However, since the conversion of new energy from the natural environment into direct energy highly depends on environmental conditions, new energy exhibits obvious intermittent characteristics when supplied to humans. In response, the government and enterprises are the best options for employing carbon-neutral electric transport facilities on a large scale in transportation electrification. Therefore, researchers have made great efforts to develop advanced electric energy storage facilities and improve the service lifespan of electric vehicles (EVs).
To maintain a sustainable harmony between energy and the environment, energy-efficient and environmentally friendly lithium-ion batteries (LIBs) stand out among power sources. Many countries hope that this advanced technology can provide a strong impetus for their development within the context of carbon neutrality, reduce the use of local fossil fuels, and provide corresponding incentive policies. To date, the market shares of LIBs in certain industries, such as electric vehicles (EVs), portable devices, and defense, are significantly increasing annually. A total of 6.6 million battery electric vehicles (BEVs) and plug-in hybrid electric vehicles (PHEVs) were sold worldwide in 2021, with the most significant growth in BEVs reaching approximately 70% (Fig. 1c) [5]. In particular, the 3.3 million EVs on the road in China in 2021 exceeded the global sales of EVs in 2020. This increase is closely linked to various actions in China, including rapidly building charging infrastructure and creating economic subsidies. Europe has exhibited a notable growth trend since 2020, with EVs accounting for 65% of the total vehicles on the road. The U.S. saw a 60% increase in sales during the first quarter of 2022 relative to the first quarter of 2021. Within the context of the Announced Pledges Scenario (APS) EV30@30, the EV inventory is expected to exceed 85 million units in 2025 and 270 million units in 2030. The demand for batteries will reach 3.5 TWh, and the demand for cathode materials will reach 20 Mt. Such a significant increase in EV sales will lead to a tight supply chain of minerals for manufacturing batteries (Fig. Id) [5].
Thus, the strategy for carbon reduction in electricity faces the challenges of limited mineral resources and high prices, increasing the national demand for more efficient EVs and continuously driving the battery industry toward LIBs sustainability. According to the United States Geological Survey (USGS), 8900 kt of lithium resources exist in the world; in recent years, mining has exceeded 10 kt to meet the high demand in the LIBs market [6,7]. The lifespan of both EVs and portable devices is approximately 5 years, and the bull market of LIBs will likely generate many spent LIBs and widespread environmental pollution, hence the growing concern for clean and efficient recycling systems. According to global spent LIBs recovery market forecast, from 2021 to 2030, the spent LIBs recovery market will grow from US $4.6 billion to US $22.8 billion [8]. According to GII statistics, the theoretical decommissioning volume of LIBs in China reached 512,000 tons in 2021, with 49.5% recycled and 8% laddered, and the remaining unknown amount of LIBs were recycled by small workshops or abandoned as garbage [9]. Moreover, there are fire safety threats stemming from stacked spent batteries and noncompliant recycling methods, personal health threats and groundwater contamination resulting from toxic electrolyte leakage. Therefore, the proper disposal of spent LIBs and efficient recycling of electrode materials are crucial to for the sustainable development of a harmonious coexistence between humans and the environment in within the context of carbon neutrality policies.
Lithium and cobalt, which are expensive metals, exhibit the characteristics of low relative abundance and high demand in the field of LIBs. Therefore, studies on spent LIBs electrode materials have focused on methods for developing an efficient, inexpensive and pollution-free recovery system. However, the variety of LIBs is rapidly changing, and the corresponding recycling processes are facing unprecedented challenges. Over the past five years, research into the recycling of used batteries has rapidly progressed. There has been an increase in research related to the recycling of spent batteries in laboratories and industry (Fig. 2). However, a sustainable recycling strategy is greatly limited once economic, political, environmental and safety factors are taken out of the equation.
Therefore, when considering the high value and urgency of recycling spent LIBs, it is imperative to enable more interdisciplinary and innovative technologies to fully understand the existing key recycling equipment for transforming the future direction of recycling technologies and for achieving the sustainable development goal of disruptive and clean recovery of all components. It is vital to promote the rapid development of society, economy, science and technology. First, based on the recycling of spent LIBs electrode materials, the importance of spent battery recycling is explained in depth from several key perspectives, including development, application, safety, environment, process and policy. Recent advances in different recovered cathode materials are highlighted, including traditional hydrometallurgy and pyrometallurgy, in particular transformative organic leaching and bioleaching, thereby summarizing the challenges and latest developments in various recovery systems and proposing sustainable development strategies for the corresponding recovery technologies. Finally, the above aspects are systematically analyzed using life-cycle assessment (LCA) to further propose future directions for the spent LIBs recycling system based on the four roles of the government, suppliers, consumers and recyclers and to holistically provide an outlook on future recycling methods.
2. Spent LIBs failure mechanism
2.1. LIBs progress
Commercial LIBs first appeared in the 1970s. The anode and cathode are defined in Eqs. (1) and (2), respectively.
... (1)
... (2)
After the success of primary LIBs, there has been an increase in secondary charging LIBs. From the first release of rechargeable titanium disulfide (TiS) batteries [10] to the commercialization of LiCoO2 (LCO) [11], the energy density, lifetime, and safety of LIBs have been rapidly improved. The discharge reaction processes of the anodes and cathodes of rechargeable batteries can be expressed as Eqs. (3) and (4), respectively.
... (3)
... (4)
Rechargeable batteries have become key means supporting information technology, strategic deployment, decarbonized electricity, and energy storage. Common commercial LIBs are compared Table 1, from various aspects for battery types comprising of various material systems that have emerged. In contrast, there are no perfect LIBs yet. LCO became popular in portable electronic devices, followed by Tesla's first generation of electric sports cars; however, E Vs placed a greater emphasis on the battery cycle time and energy density, while EV suppliers later subsequently replaced the battery type with LiNi1_x_yCoxMnyO2(NCM) or LiNixCoyAlzO2 (NCA) [12,13]. These materials have the advantages of three types of metal materials, including the excellent cycle performance of LCO, the high specific capacity of LiNiO2 and the notable stability of LiMn2O4(LMO) [14]. LCO is expensive, which greatly limits its large-scale commercialization. However, compared to LCO, LiFePO4 (LEP) and LMO dominate the main EV market due to their lower prices. LMO batteries were the preferred power batteries for early EVs, with certain advantages in terms of rate capability and manufacturing costs. However, the high-temperature and cycling capacity disadvantages limited their long-term development. LEP is widely sought after in today's EV and energy storage system markets due to its long cycle life, low cost, and high safety performance [15,16]. Na+ batteries (NIBs) (Fig. 3a) [17,18], К batteries (KIBs) (Fig. 3b) [19,20], Mg2+ batteries (MIBs) (Fig. 3d) [21-25], and Al-based batteries (AIBs) (Fig. 3c and e) [26,27] show the possibility of replacing LIBs in the commercial development of batteries because of their outstanding advantages. For example, Contemporary Amperex Technology (CTAL) launched a new generation of ultrahigh energy density NIBs in 2021 [28]. However, due to the lack of lithium's ultra-high specific capacity (3860 mAh g-1), low redox reaction potential (-3.04 eV vs. standard hydrogen electrodes), and other advantages that make LIBs stand out in the battery industry (Fig. 3f). Therefore, it has been established that metallic lithium is an essential component of rechargeable batteries [29]. Recently, LiF nanocrystalenriched solid-state electrolyte membranes (SEIs) have been utilized in anode-free lithium metal batteries (LMBs), suppressing Li dendrite growth and facilitating rapid Li+ transfer [30]. The research and development of ultralong-lifespan LMBs have opened possibilities for the LIBs market in the future.
However, the vigorous development of LIBs is accompanied by large amounts of spent LIBs, and the service life and failure are the main reasons for spent. Therefore, ascertaining the failure mechanisms of LIBs is very important for optimizing the recycling of spent LIBs.
2.2. Failure mechanisms
The main feature of scrapped LIBs is electrochemical performance failure, and the failure state is closely related to the recovery technology in the pretreatment process and the metallurgical technique. For example, Fig. 4 shows a diagram of the electrochemical performance failure mechanism, which is mainly due to the failure of key materials such as the cathode, anode, electrolyte, and diaphragm [31-34]. The reaction triggers can be divided into mechanical, electrochemical and thermal triggers (Fig. 4a). The side reaction of gas production increases; under the influence of the internal pressure, the outer packaging can burst; and overcharging and overdischarging can cause the risk of heat generation (Fig. 4b). The decomposition of lithium salt LiPF6, solvolysis, or the consumption of decomposed solvent molecules embedded in the graphite layer can explain electrolyte failure (Fig. 4c).
In general, regarding spent LIBs, the focus should be on confirming the failure state and dividing the failure level to realize efficient cleaning and recycling of available spent battery components. Therefore, it is very important to explore the failure mechanism of LIBs and establish failure models for efficient dismantling and recycling of spent LIBs.
3. Traditional to transformative LIBs recycling technology
Based on a thorough understanding of traditional recycling technologies, we should comprehensively improve key factors, such as the environment, economy, safety, and technology, transform traditional recycling technologies, and establish a novel clean and efficient recycling system for all components of spent LIBs.
3.1. Environment
The whole entire recycling process of spent power batteries retired from EVs can be divided into three stages, entailing the consumption of multiple types of energy (Fig. 5a) [35], namely, collection and transport (Stage 1), pretreatment and dismantling (Stage 2), and recycling and integrated use (Stage 3). These stages generate a multifaceted coupled adverse impact. At Stage 1, the use of rail and truck transport reduces greenhouse gas (GHG) emissions by 23%-45%. The potential threat of thermal runaway from spent LIBs, the high weights of LIBs, and the high GHG emissions resulting from the electrolytic corrosion of railway equipment make long-distance rail transport to recycling facilities unattractive (Fig. 5c) [36,37]. In addition, Thomas and colleagues skillfully combined LCA and geographical profiles and conducted modeling analysis to comprehensively understand the impact of recycling infrastructure on the environment. The trucking of spent LIBs and the use of advanced dismantling infrastructure, based on the identification of optimal locations for recycling facilities, could significantly increase the economic benefits of recycling. At Stage 2, pyrometallurgy and hydrometallurgy have been evaluated in regard to end-of-life (EoL) battery recycling systems. The results show that the final recovery of valuable materials from both metallurgical methods could reduce the environmental damage of LIBs production. Notably, Yang et al. [38] systematically analyzed the GHG emissions of components of recycled and spent LIBs; they found that recycled aluminum could release higher GHG emissions. From detailed data of GHG emissions, pyrometallurgy releases higher GHG emissions than hydrometallurgy (Fig. 5b) [38].
Pyrometallurgical recovery methods (pyrometallurgy, vacuum reduction roasting and inert gas reduction roasting) and hydrometallurgical recovery methods (inorganic acid leaching and organic acid leaching) have been compared using OpenLCA software to evaluate the environmental impacts of the different recovery methods, with the global warming potential (GWP) as the midpoint and quantitative analysis based on the total GHG emissions [39]. The GWP can be assessed by two parameters, i.e., the energy reduction rate (ξE) and the GHG reduction rate (ξG), which can be calculated with Eqs. (5) and (6), respectively:
... (5)
... (6)
where Ev is the raw material production energy consumption, Er is the recycling energy consumption, Gv is the raw material production process of GHG emissions and Gr is the recycling process of GHG emissions. Quantitative results have indicated that the differences in the GHG emissions resulting from the recovery of 1 functional unit (FU) of ECO between the two methods are not significant, ranging from 80.5-361.5 CO2-eq FU-1. The GHG emissions resulting from the recycling of 1 FU are significantly lower than those produced by industry resulting from the production of an equivalent amount of ECO from virgin materials. These results demonstrate the significant potential of recovering LIBs in terms of GHG emission reduction. A sensitivity analysis was conducted of the extent and trend of the impacts of two key factors-the metal ion recovery rate and energy mix-on the system energy consumption and GHG emissions. These quantities can be calculated with Eqs. (7) and (8), respectively:
... (7)
... (8)
where E0 and G0 denote the initial values of the system energy consumption and GHG emission indicators, respectively, Ei and Gi denote the corresponding system energy consumption and GHG emissions, respectively, after key factor variation, and δe and δg denote the rates of change of the system energy consumption and GHG emission indicator values, respectively. Dunn and colleagues found that the energy consumption associated with the production of ECO from new materials is 147 MJ kg-1 [40]. Furthermore, there were no significant differences between the various methods at the collection and transport stage. The energy consumption of the different recovery methods is identical at Stages 1 and 2, at 781 and 474 MJ FU-1, respectively, accounting for 3% (hydrometallurgy) to 8% (pyrometallurgy) of the total energy consumption (Fig. 5e). Regarding pyrometallurgy, both the conversion and regeneration phases are major contributors to energy consumption. In general, sound recovery of spent LIBs should involve a combination of the advantages of multiple recovery methods. For example, by combining the advantages of multiple metallurgical methods for LIBs recovery and applying LCA to a corporate LIBs recovery system, the advantages of each recovery method can be weighted and combined to establish an optimal recovery technology [41-44]. Accurec Recycling GmbH Co., Ltd., uses vacuum roasting to recover and treat spent LIBs [45]. Pyrometallurgy and hydrometallurgy were combined in pretreatment, and the sintered cobaltbased alloy was recycled [46]. Sony and Sumitomo adopted a technical partnership approach to the recycling of spent LIBs [47]. Sony completed the preprocessing dismantling magnetic separation step via calcination at 1000 °C to remove plastic and electrolyte materials. The electrode material was hydrometallurgically recycled by Sumitomo into high-purity CoO that meets the standard for the direct preparation of new cells. The combination of these technologies demonstrated outstanding advantages in terms of reduced waste liquid and water consumption during hydrometallurgical recovery and reduced waste gas and electricity consumption during thermal recovery.
3.2. Economic factors
The economic viability of recovery technology determines the potential for large-scale LIBs recovery, and recovery technology constitutes the cornerstone of large-scale commercialization. Relative to long-distance rail transport, road transport allows a more flexible approach for recycling, such as loading spent batteries at smaller recycling sites when traveling to the recycling site to increase the recycling revenue. However, the issue of high costs over long distances must still be addressed. For example (Fig. 5d), when comparing the costs of heavy truck transportation in different countries, the trend exponentially increases with distance traveled [35].
The economic benefits of spent LIBs recovery result from the cascade utilization and recovery of electrode materials. Generally, the evaluation method of discounted cash flow economic benefits is used to analyze the economic feasibility through the relationship between the availability price and the market price for each battery structure [48,49]. First, this can be achieved based on the reserves, market price, and recovery cost of producing LIBs resources. Then, combined with the discount rate, the economic feasibility can be evaluated based on the price relationship between the recovery and treatment costs and benefits. Finally, the discounted cash flow method can be used to analyze the availability in each year. This method can provide considerable support for achieving the double carbon target and formulating recycling policies from national economic strategy and social and human environment perspectives. The resource availability price can be calculated with Eqs. (9) and (10), where W is the resource stock of each type of spent LIBs, CR is the average recycling treatment cost, i is the discount rate (5%), n is the year and P is the resource availability price.
... (9)
... (10)
Based on Commodity Futures Trading Commission metal prices, the treatment cost and availability price range for each type of resource in the recovered spent LIBs can be calculated, where Crij is the resource recovery cost, Cr is the average recovery treatment cost and Wy is the resource quality. Based on research data of recycling waste battery enterprises and combined with the above equations, the cost and availability price range values of eight resources for the recycling and processing of mainstream LIBs can be calculated, as summarized in Table 2. By assuming that the collected ternary lithium batteries, i.e., LFP and LMO batteries, are of the same quality and all weigh one ton, they are mechanically pretreated, after which they are processed by pyro- or hydrometallurgical methods to obtain various valuable resources [50,51]. The recovery profit considers material, security, labor and environmental costs. Clearly, ternary lithium batteries gain approximately 28% of the market price cost due to the relatively high Co and Li contents. The average cost of LFP batteries reaches a maximum value of $76,408.92, recovering 14% of the cost. Ref. [52] suggested that the more common acetic acid leaching process chosen for LFP batteries is the best option for improving economics. The profit difference between the LMO and LFP recovery methods of Li is not significant. However, the cost to recover 1 t of LMO for obtaining Mn is $3114.57, which is much higher than the direct purchase price of $2200.40. According to the above calculations, the low or even negative profits due to Mn recovery can be avoided in the recycling process. Additionally, new challenges are encountered in the development of efficient and inexpensive LFP and LMO recovery technologies. The prices and reserves of Li and Co indicate that ternary LIBs rich in these metals are of high economic value. However, the manufacturing of LFP batteries does not require Co addition, which significantly reduces the manufacturing cost. By comparing the costs of plastic (polyethylene (PE)) and Mn, LFP batteries exhibit a very high economic potential for recycling. Furthermore, EVs that use LFP batteries as power cells could exhibit significant EoL needs. Therefore, the recycling of LFP batteries has a very promising value.
NCM batteries suffer from low thermal stability and notable waste liquid generation, which renders safe mechanical dismantling extremely challenging and reduces the economic nature of recycling. Ma et al. [53] calculated that one regenerated NCM battery could save $2510 t-1. They determined that the cost of recovering 1 t of NCM at full load was $2742. However, the role of Mn and Co in the cathode remains controversial, and numerous issues have limited their market adoption on a large scale and reduced the recovery scale [54]. NCM batteries require high temperatures for pyrometallurgical recovery and complex and lengthy hydrometallurgical recovery processes, and few detailed economic analysis studies have been performed targeting the recovery process. Direct leaching with inorganic acids, by exploiting the low price and high efficiency of leaching, is the main method used by companies to recover valuable substances from NCM batteries. In terms of recovering Co, extraction can generate a relatively high yield of C°CO3 [55]. From economic, efficiency and green recycling perspectives [56], predicted that the future NCM recycling process system should be as follows: alkaline solution dissolution → calcination pretreatment → H2SO4 leaching → H2O2 reduction NCM coprecipitation regeneration.
Under the LFP scenario, Li reaches a maximum availability of 85,200 t at an availability price of $76,428.67. Cu, Al and Fe are available at prices above the market price, and all indicate unavailability. Overall, the resource availability prices of Ni/Co/Mn under three scenarios are much lower than the market prices. The resource availability levels of LIBs under the baseline and LFP scenarios show clear advantages by improving the resource recovery efficiency, which is closely related to the types of metals contained in LIBs.
In summary, the metal content, structure, and cost of the different spent LIBs vary. The recycling scale is positively related to recycling economic benefits. Appropriate recycling methods should be selected according to the capacity of the spent LIBs and the scale of recycling enterprises to improve the economic benefits. Pyrometallurgy is often difficult to apply for collecting high-purity metal materials, and the products are mostly alloys of Ni, Co, and Mn. To recover a single metal, one often must combine hydrometallurgy with other processes. Compared to spent ternary LIBs, LMO and LFP batteries contain less expensive metals and exhibit a high production value within the context of LCA. Therefore, the combination of mechanochemical pretreatment, roasting, leaching, coprecipitation, and reloading could achieve the goal of efficiently recovering the valuable target materials.
3.3. Traditional to transformative recycling processes
The goal of recycling spent LIBs is the laddering of EoL batteries or the conversion of valuable components into valuable materials at maximum recovery rate. Similar to the recycling of electrode materials, academia and the business community are constantly seeking to maximize ladder utilization rates. Our comprehensive review of the literature on the treatment of spent LIBs today falls into two broad technology categories: ladder utilization and material extraction. At the early stages of research on the recycling of spent LIBs, cells are typically inactivated at the pretreatment stage, eliminating potential thermal and electrocution risks, e.g., through discharge treatment [61,62] and low-temperature stripping and dismantling in an inert environment. Cryogenic inert gas technology is widely used in companies to eliminate the thermal risk of the residual charge occurring in warehouses and transportation. However, through a ladder utilization approach, when the battery EoL stage is reached after energy exhaustion, batteries are physically dismantled or chemically roasted. Then, precursor materials are recovered through different metallurgical and impurity removal techniques to finally complete the reloading and reuse of spent LIBs, forming a closed recycling loop, as shown in Fig. 6.
3.3.1. Ladder utilization and pretreatment
Before recycling, spent LIBs are subjected to ladder utilization according to their remaining capacity, degree of damage and remaining lifetime, aiming to maximize the recycling of reusable individual cells from used battery packs and increase the battery life cycle [43]. Obsolete power packs that have reached the end of their useful life have low energy levels and power densities, and they cannot properly propel EVs. However, dismantled battery modules can be used in energy storage devices, household appliances and portable electronic devices. Ladder utilization has been vigorously promoted by the business community and the government and has been included in compulsory measures. Ref. [36] found that 1000 tons of batteries was utilized in echelons, reducing the battery supply by 2%. Industry has tended to opt for more automated mechanical crushing, and the crushed mixed fraction is screened and subjected to flotation and magnetic separation, which is conducive to obtaining positive and negative materials [63-71]. However, ladder utilization inevitably involves the use of manual disassembly, which increases the cost [72].
In laboratory studies, spent LIBs have been manually disassembled in a safe environment; binder removal is difficult during the separation of collector fluid from the electrode material. Organic adhesives, such as polyvinylidene fluoride (PVDF), are often used, and organic solvents, such as Nmethyl-pyrrolidone (NMP) [73-75], dimethylformamide (DMF) [76], and dimethylacetamide (DMAC) [77], are commonly used. However, organic solvents are expensive and toxic, and the cathode material is encapsulated in organic material, making dewatering very difficult and preventing its widespread adoption by industry. Heat treatment methods are widely employed in industrial production; however, the generation of large amounts of exhaust gases and the high energy consumption remain unresolved [78-80]. Moreover, alkaline solutions could explode due to the hydrogen produced in the recovery process, and the large equipment requires a high corrosion resistance. For this reason, strong alkaline leaching is limited to the laboratory scale [81]. With the continuous innovation of technology, the use of electromagnetic waves with frequencies ranging from 300 MHz to 300 GHz to stimulate intermolecular interactions-microwave-assisted enhanced disassembly-has been widely adopted [82-84].
In general, ladder utilization increases the recycling and use values of spent LIBs and reduces the processing capacity and pollution due to the recycling process. Additionally, spent LIBs are closely structured with various valuable components and exhibit a diverse electrolyte composition, and these battery-specific problems add to the recycling challenge. Research on the electrolytes of spent LIBs should focus on maximizing the value of the recovered electrolyte for other applications or modifying it into other industrial byproducts, rather than producing complex electrolytes and reloading batteries. Manual dismantling maximizes the recovery rate, but this method is not widely adopted by the industry due to the high cost and inefficiency.
3.3.2. Transformative technology for extracting valuable materials
3.3.2.1. Cathode. High-temperature pyrometallurgy. Hightemperature pyrometallurgical recovery technology aims to pretreat spent LIBs with high-temperature roasting for molten metal recovery or hydrometallurgical separation recovery from the treatment product. To date, thermal treatment is divided into three main categories based on the recovery technology: high-temperature cracking, high-temperature reduction roasting and low-temperature molten salt roasting. Umicore Co., Ltd. directly places scrap batteries in their original form in a smelting furnace and collects Co-Ni-Cu (Mn) alloy metal products [85]. However, the boiling point of Li is relatively low, and the high temperatures and lengthy recovery processes increase the amount lost. Bak et al. [86] investigated the migration preferences of cations in high-temperature roasted ternary electrode materials at the spinel structure position, where Co ions preferentially migrated to the tetrahedral 8a position of the spinel structure at times. He analyzed the effect of different high-temperature environments on crystal structure transformation and the fugacity of valuable metals, laying the foundation for pyrometallurgical recovery of spent ternary LIBs. Pyrolysis is a recovery technology that involves the use of high temperatures to convert previously unstable electrode materials into stable states. Ref. [87] reduced LiNixCoyMni_x_yO2 to metal Co and Ni at high temperatures ranging from 500 to 700 °C. Zhang et al. [88] employed high-temperature calcination of spent LCO batteries at 550 °C to ultimately recover 30% Li and 50% Co and obtained stable LCO precursor materials Li2CO3 and Co3O4. This indicates that when using high-temperature recovery of spent LIBs, it is necessary to select an appropriate temperature range based on the thermodynamic stability zone of the metal. However, high temperatures could generate significant energy consumption. To reduce the reaction energy consumption, researchers have often added inexpensive reducing agents to reduce the high-temperature reduction energy consumption and increase the recovery efficiency. Hu et al. [89,90] mixed cathode LCO material with anode graphite material and used halide doping (CaF2 and CaCl2) as a variable condition to reduce and calcine the positive electrode material. Co ions were reduced to monomers and recovered by magnetic separation. Li was recovered in gaseous and halide forms (LiF and LiCl, respectively). Vacuum roasting of anode graphite and cathode LMO materials at 800 °C yielded 91.3% LCO, confirming the notable role of spent graphite in pyrometallurgical recovery of valuable cathode metals [91]. To further reduce energy consumption and improve the recovery rate, researchers have continuously adjusted the doping ratio and temperature interval of the electrode material and reducing agent for roasting purposes and have recovered valuable metals by water leaching [91-93], evaporation crystallization [94], and acid solution leaching [95]. The reduction roasting techniques all yielded metal recovery rates exceeding 90%. From a crystal structure perspective, the high affinity of graphite for oxygen is more likely to destabilize the oxygen octahedra of LCO. Moreover, regarding the coupled reaction of graphite combustion and metal compound pyrolysis, the reaction pathway is expressed in Eqs. (12)-(14), and the mechanism of lamellar structure decomposition collapse is shown in Fig. 7a and b.
... (11)
... (12)
... (13)
... (14)
The recycling idea of recovering cathode waste through reduction with anode graphite waste is more widely adopted in reduction roasting technology versus purchasing additional reducing agents. In addition, the dismantling of spent LIBs yields binders, aluminum foil, electrolyzed organic material, diaphragms, and high-sulfur flue gas from boiler houses, coal and slag. All of these solid wastes can be used to reduce cathode materials to metal oxides, monomers, alloys, acid salts and other forms. Low-cost waste biomass as a reducing agent is a future direction for the recycling of spent LIBs. However, attention should be given to the impact of their complex organic structures on ecological stability. Moreover, the shortcomings of pyrometallurgy, such as high energy consumption, difficult collection of metallic materials and polluting gases, and dependence of biomass reduction on high temperatures, limit its application. Consequently, to further improve the technology, these shortcomings can be overcome by coupling multiple recycling techniques. At present, combined pyrometallurgical and hydrometallurgical recovery techniques have been developed and supplemented with external conditions, such as microwaves, ultrasound and heating, to compensate for the shortcomings of these two traditional recovery techniques (Table 3).
The principle of low-temperature molten salt roasting technology is to use the transformation reaction of the cathode material in the molten salt environment, where insoluble compounds are reduced in valence and converted into soluble salts and oxides. SO3 is usually adopted to enhance solubility, while reducing sulfates (Na2S2O7, NaHSO4, K2S2O7, and KHSO4) are employed for roasting with the cathode material to reduce the metal valence. The product is subjected to hydrometallurgy and roasting to prepare precursor and electrode materials [98,99]. Nevertheless, the complex process and the introduction of impurity metal ions make it difficult to separate and purify the cathode metal material [98,100]. To further address the interference of waste gas, Na and K, researchers have applied leaching reagents in separation and purification. Lin et al. [101] conducted concentrated sulfuric acid roasting after LCO pretreatment to selectively separate LiSO4 and CO3O4, yielding a very high Li leaching rate and trace amounts of Co. The entire roasting process is environmentally friendly and produces no toxic or harmful emissions. Furthermore, no acidic or alkaline wastewater is produced in the leaching process. Fan et al. [102] added NH4CI in the roasting process to obtain watersoluble chloride salts of Li and Co by water immersion.
Transformative teaching: Leaching is a common technical technique for dissolving stable-state valent metals and converting them into their ionic forms in a solution medium of a negative metal material for subsequent metal separation and purification. Transformative leaching technology has been developed for using plants, tea (wood cellulose), orange peel, and grape seed materials as leaching agents, these kitchen waste products after enzymatic fermentation of glucose and ethanol as reducing agents. The mechanisms of several transformative leaching techniques are shown in Fig. 8.
Traditional reagents for leaching spent LIBs electrode materials include acids, bases and organic solvents. On this basis, the incorporation of auxiliary methods, such as acoustic, mechanical force and chemical methods, has yielded brilliant results in improving recovery rates and reducing energy consumption levels. However, the discharge of highly concentrated sodium salt effluent, the lengthy process and the large number of impurities in the enrichment solution are the largest challenges for leaching.
Inorganic acids: In conventional hydrometallurgical leaching techniques, the commonly used inorganic strong acid leaching agents H2SO4 [118-120], HC1 [55,121,122] and HNO3 [55,123] are well established and widely used for dissolving various electrode materials. Similar to pyrometallurgical recovery, these three types of acid leach recovery systems introduce inorganic reducing agents, such as Na2S2O3 [124], Na2SO3 [125] or hydrazine sulfate [126], biomass reducing agents, such as grape seeds, tea pomace, glucose, ascorbic acid and straw, ultrasonication, microwave-assisted conditions, and conventional H2O2 reducing agents to increase leaching rates. Notably, sodium bisulfite [127] achieves better leaching in the H2SO4 system, which may be related to the generation of SO2 gas, as expressed in Eq. (15); gas escape enhances the reactivity in the local environment, increasing the perturbation between the positive material and reducing agent and increasing the heat released during the reaction. The lifting mechanism is similar to that of ultrasonic treatment.
... (15)
The leaching agent dosage, reducing agent quantity, temperature, time and auxiliary leaching parameters can be adjusted to obtain the optimal process conditions for acid leach recovery. Then, a separation process can be used to separate and extract or regenerate spent LIBs for preparing precursors, achieving full recovery and utilization of valuable metals. Even though these inorganic strong acids are extremely efficient at leaching metals, the standards are high for certain factors, such as the operating environment and equipment and the treatment of wastewater and acidic fumes. In addition to commonly used inorganic strong acids, hydrofluoric acid can be used to leach Li and Co from LCO due to its self-coupling ionization at high concentrations [128]. The leaching solution is precipitated using NaOH to adjust the pH, and it is roasted and concentrated through evaporation to remove F ions as CaF2, resulting in a final recovery of 98% Li and 80% Co. However, the low acidity and nonoxidizing, nonreducing acidic nature of HF at low concentrations reduces the leaching rate. In recent studies, the use of chemically stable H3PO4 leaching systems has been replaced to solve the problem of volatile acidic fumes. Notably, the NCM cathode material was roasted at 60 °C for 60 min with a H3PO4 concentration of 2 mol L-1, a solid-to-liquid ratio (L/S) of 20 mL g-1 and a H2O2 volume fraction of 4%. The leaching rates of Li, Ni, Mn and Co all exceeded 96%, and in some cases, Li could even be completely recovered. Moreover, researchers have added metal ions to the leaching solvent and obtained a recyclable phosphoric acid solution after coprecipitation. More importantly, the influence strengths of the leaching factors for the phosphoric acid system are as follows: reducing agent > phosphoric acid concentration > time ~ solid-liquid ratio > leaching temperature. Many scholars have compared the leaching effects of various types of strong acids, and the HC1 system is the best leaching agent in terms of cost [129-131]. The systems for LCO, LFP, and LMO leaching differ in the temperature, nitric acid concentration, and reductant dosage. Therefore, further research is needed on the composition of spent LIBs and the application of recovery systems.
Green organic acids'. The trivalent waste of the inorganic acid leaching system damages the environment and is contrary to today's green recycling concept of sustainability. To solve this problem, Li's group first proposed the use of organic acids to recycle spent LIBs by exploiting their eco-friendliness and degradability; they comprehensively investigated the leaching mechanisms and acid dissociation constants (pKa) of organic acid functional groups [132]. This system shifts the focus of future hydrometallurgical recovery research to green organic acid leaching to increase the leaching efficiency and reduce the contamination level. By using the chelating function between tween the functional groups of organic acids and metal elements and the reducing properties of certain specific groups, the main organic acids with chelating functions are citric acid [132], aspartic acid [133], succinic acid [134] and malic acid [135]. Reducing functional organic acids can be used with less of the reducing agent H2O2; ascorbic acid [136] and lactic acid [137] are commonly used. Except aspartic acid, each chelated functional organic acid can leach over 90% of Li and Co for spent LCO recovery. Oxalic acid [138] and carrot acid [139], which provide precipitation functions, can be recovered by a mechanism that uses organic groups to leach valuable metals to produce precipitates. The leaching properties follow the order of succinic acid > citric acid > ascorbic acid acid > aspartic acid. Citric acid exhibits excellent leaching properties and is inexpensive and readily available.
Other functional organic acids: Natural biomass rich in acids is extracted from acidic solutions for leaching, such as rich complexing agents in citrus juice and apple juice. When recovering NCM, certain counter ions, such as Na+, Mg2+, and Ca2+, can indirectly improve the leaching efficiency of organic acids. The recovery rates of valuable metals can exceed 94%. Acid leaching methods for maleic acid [140], acetic acid [140], tartaric acid [141], trichloroacetic acid [142], benzenesulfonic acid [143], formic acid [144], iminodiacetic acid [145], etc., have gradually entered the research field of spent LIBs recycling.
However, Li recovery could be guaranteed to exceed 90%, while the leaching rates of all other metals are low. From the perspective of recycling, organic acids are more environmentally friendly. However, the leaching process has high quirements on acid concentration and dosage, inhibiting the industrial application of organic acidic wastewater that cannot be quickly degraded, while the ecological species balance cannot be maintained, which remain real challenges for large-scale applications.
Selective extraction and chemical precipitation: After the cathodically active material of spent LIBs is acid leached by inorganic/organic acids, valuable metals are enriched in the leaching solution. Afterward, the separation, recovery, purification, dehybridization and preparation of precursors are realized to finally achieve valuable metal recovery of spent LIBs. The leaching solution contains Ni, Co, Mn, Li and other valuable metal ions and Fe, Al, Cu and other impurity metal ions. To date, the methods for separating various valuable metals are selective extraction, precipitation, ion exchange and electrolytic deposition.
Selective extraction: Spent LIBs are extracted mainly in liquid-liquid form, consisting of organic extractants and reactive reagents (Fig. 9a), which can selectively extract specific metal ions from the aqueous phase to the organic phase to achieve selective separation. The frequently used selective extraction techniques are listed in Table 4.
The extraction effect is closely related to the reaction kinetic condition parameters. Ref. [146] used 3% isodecanol as a phase modifier in Cyanex272 and kerosene system extraction and obtained 99.99% cobalt in vapor extraction relative to 95% in the extract. More importantly, an extremely acidic environment does not indicate an extremely high extraction rate. In PC-88A and kerosene extraction systems, the separation of Co and Ni cations becomes increasingly effective with increasing pH; however, the separation effectiveness decreases with decreasing pH [147]. In particular, according to the relevant mechanism of metal extraction technology (Fig. 9b), nickel and cobalt are located very close to each other in the periodic table, and both are transition elements. Separating these metals is extremely challenging and requires high costs. However, the expensive extractant and harsh extraction operating environment reduce the profits of recycling spent LIBs. Therefore, it is possible to combine multiple extraction systems and separation techniques to obtain inexpensive extraction materials for reducing the recovery cost and improving the purification and separation rates.
Chemical precipitation: The properties of valuable metal cations in the leaching solution, which can yield insoluble compounds in various anionic precipitators, can be utilized to separate, purify and remove impurities from the substances in the leaching solution. The method for separating and recovering valuable metals from the leaching solution of cathode materials is usually determined based on the differences in the occurrence states of metal elements in different pH ments. In the process, Li usually exists in the form of Li2CO3 [148], LiF [149], and Li3PO4 [150,151]. Specific elements, such as Ni, Co, and Mn, with similar chemical properties commonly occur in the form of CO2-3, CO2-3 , PO3-4, OH-, and organic chelates [145,150-156]. Fe, Al and Cu, as impurities, can be removed as Fe(OH)3 [157], Fe2(C2O4)3 [158], A1F3 [158], A1(OH)3 [158] and Cu(OH)2 [159], and purification is finally achieved. By adjusting the pH, temperature, ratio of the oil phase to the water phase and other parameters in the chemical precipitation process, high-efficiency and inexpensive separation and purification can be achieved. However, the heterogeneous nucleation phenomenon during metal ion precipitation reduces the product purity.
Clean and efficient combined purification: Scholars have applied various precipitation and extraction methods sequentially to increase the product purity. Chen et al. [162] balanced the pH to 6 in the leaching solution of recovered waste NCM. After adding dimethylglyoxime reagent, approximately 98% of Ni could be selectively precipitated, and Co2+ was precipitated as C°C2O4 when the temperature was adjusted to 55 °C. Therefore, it is very important to combine multiple recovery methods for purification and separation.
Electrochemical deposition: After an electric field is applied to the leaching solution, the valuable metals in the solvent can be deposited on the electrode through redox reactions and then purified and recovered. Strauss et al. [163] used the electrochemical deposition method to obtain Ni and Co, adjusted the pH value of the leaching solution, used Dowex M4195 resin as the extraction agent, and finally extracted 99.0% nickel, 98.5% cobalt and Li/Mn-rich products. However, the application of an electric field does not significantly improve the recovery relative to the use of a chemical reducing agent for final metal recovery [164]. Moreover, reuse of the leaching solution and the residual electricity of the spent LIBs prevent the single consumption of chemical reagents and secondary waste liquid [165].
Liquid membrane separation: Similar to chemical precipitation, the separation of impurity metals mainly depends on the different dissolution and diffusion capabilities of electrode materials in liquid membrane media. Hoshino et al. [166] developed a new method for lithium recovery by electrodialysis using PP13-TFSI ionic liquid, effectively filtering impurity ions, such as Na, Mg, Ca and K; Li+ was selectively concentrated on the cathode side. Yuliusman et al. [167] set the ratio between the emulsion film and electrode waste to 1:2, and the temperature was 80 °C. Cyanex 272 and SPAN 80 extractants were selected to carry metal elements through the liquid film, and approximately 83% Co was recovered by leaching.
The combined method provides a new idea for selective separation and purification. However, the complex technical requirements make it difficult to apply in large-scale recycling of spent LIBs electrode materials. We suggest defining the future research goal of purification and separation as the use of residual electricity to perform electrochemical deposition of the leachate to achieve green and low-consumption separation and purification. Based on traditional mineral metallurgy technology, we established a complete recycling framework system, determined an innovative recycling technology system that could be applied to large-scale production and realized the most economical and environmentally friendly regeneration of electrode materials.
Microbiological green leaching'. Valuable metals in spent LIBs can be extracted by using the metabolic functions of microorganisms or the actions of their metabolites. The types of leaching microorganisms can be divided into autotrophic and heterotrophic bacteria. Autotrophic bacteria include sulfur- and Fe-oxidizing bacteria, and heterotrophic bacteria include Aspergillus and Pénicillium [168-174]. The most common method involves the use of Acidithiobacillus ferrooxidans and Lepto spirillum ferriphilum, S and Fe2+ as energy products, biological oxidation of acidophilus and a low-pH environment to recover spent LIBs. Naseri et al. [175] used a single A. ferrooxidans solution with a pulp density of 10% and a warm environment with pH = 2 in nutrient media of 9 K and FeSO4·7H2O; Li was completely leached to obtain 88% Co. Based on the research results of Roy et al. Ref. [176] used the nutrient media of modified 9 K and FeSO4·7H2O to increase the solid-liquid ratio to 150 g L-1; then, more than 90% of Co, Ni and Mn and 80% of Li and Co could be leached and recovered. The mechanism of bioleaching is closely related to redox and complexation reactions. Autotrophic bacterial leaching occurs as follows: a) relying on the change in the valence state of Fe and S, leaching directly occurs after contacting valuable metals, and b) biological bacteria play a catalytic role in accelerating the redox rate of Fe and S but do not directly react with the metals in the spent LIBs leaching solution [177-179]. Improving the efficiency of bioleaching electrode materials requires special attention to the optimization of the metabolic rate of microorganisms. Therefore, environmental parameters for leaching include the conventional experimental parameters of hydrometallurgy and are closely related to various factors, including biological nutrients [180], carbon and oxygen supply levels [181], biopotential [182], and metal tolerance [180]. However, the toxic metal waste liquid, low leaching power, and inability to use large-scale enterprises have become the greatest threats restricting the growth and metabolic characteristics of biological cells. Researchers have continued to explore the adaptive conditions of biological flora, including reducing the concentration when recycling spent LIBs and increasing the pulp density [183,184]. Leaching kinetics can be upgraded as follows: (a) additives: the use of inorganic low-valence metal salt additives or combined leaching with multiple flora (Fig. 10a) [185]; (b) assisted leaching: ultrasonication can assist leaching, enhancing the penetration of biota into the solid phase material (Fig. 10b) [186]; and (c) genetic modification: altering the metabolic pathways and tolerance levels of bacteria [187], which is a modification technique similar to that used to improve conventional hydrometallurgical recovery (Fig. 10c) [188]. However, there is a lack of research on the recovery of spent anode materials, electrolytes and collectors, and further research is needed on the tolerance of biological cells and efficient metabolic generation. The concept of low-consumption, end-of-pipe low-carbon treatment should be vigorously developed for large-scale corporate applications (Fig. 10d) [189].
Alkali leaching'. Alkaline solvents provide a more limited range of dissolved metals than acidic solvents, and they are limited by the mechanisms of metal and alkali leaching of cathode materials. When selecting leaching solutions, only amino solutions with metal coordination synthesis of stable metal complexes can be chosen for selective leaching with electrochemical and extraction methods for efficient recovery. Ammonia leaching exhibits the advantages of selective metal recovery, reuse and simple recovery. As a result, alkaline leaching is increasingly recognized as a more cost-effective technology than acidic leaching, which agrees with the strategic objective of sustainable energy development. Leaching solvents are often amino-alkaline solutions, including acid ammonium salts formed with SO2-4 [190], CO2-3 [191], Cl [192], HCO3 [193], SO2-3 [194] and NH3*H2O [195]. In particular, the ammonia leaching process depends on mixing the solution with the pretreated electrolyte to obtain fluorine and lithium salts in a stable state. These two salts are rendered harmless according to the composition of the electrolyte, and they can be recycled and reused. However, the trends of ion migration, enrichment and evolution of metallic elements in hydrometallurgical leaching systems remain unclear, and the relevant mechanisms have not been studied in depth. In addition, from the perspective of the reaction mechanism of the alkali leaching process, the molecular dynamics of the leaching process are poor, and the leaching system is incomplete, which is the main bottleneck limiting the recovery rate of alkali leaching. In addition to optimizing the alkali leaching conditions, the degree of difficulty of the leaching conditions should be significantly reduced at the pre treatment stage through pretreatment techniques, such as mechanical activation.
Other methods'. Activation leaching is an effective method for increasing the activity of positive materials by reducing the apparent activation energy of the reaction through physical and chemical activation, with the advantages of acoustic waveassisted treatment. For example, EDTA-2Na can be activated by ball milling with LFP prior to acid leaching, and the valuable metals in LFP can be leached out with H2SO4 [196]. Direct oxidative leaching, involving the use of Е-pH diagrams to obtain the optimum high temperature and low redox potential for hydrothermal synthesis of LFP, enables short-range efficient recovery of positive materials by directly increasing the oxidation potential. The high solubility of deep eutectic solvents (DESs), similar to that of ionic liquids, can be used for recovery purposes. Through economic and technical analyses, DESs represent a green, inexpensive and efficient leaching method. However, various drawbacks, such as hightemperature experimental conditions, low recovery rates, complex purification processes and high prices, have greatly limited the large-scale application of this solvent [197,198]. We must select the optimal acid leaching process conditions, construct an acid leaching kinetic model, establish the control steps for efficient leaching, explore pathways and related mechanisms for selective and efficient migration and transformation of metals in short-range leaching of organic acids, and solve key problems, such as long processes, high chemical reagent consumption and damage to equipment, during traditional hydrometallurgical leaching of valuable metals.
3.3.2.2. Anodes. As the first commercial anode material for LIBs, graphite provides the advantages of high capacity, stable structure and favorable electrical conductivity. Depending on the type of LIBs and the range of applications, the graphite content is more than 11 times that of metallic Li, and the percentage of graphite in EVs is even higher. The SEIs formed by the charging and discharging of LIBs and the unembedded Li+ in the graphite layer are the main sources of Li in the anode material.
There are two main recovery techniques to date. One is the use of pyro- or hydrometallurgical recovery to remove trace metal impurities from graphite when recovering the anode current collector. The other is selective extraction of lithium salts using thermal evaporation and supercritical CO2 extraction methods. Ref. [199] adjusted the microwave calcination temperature and time to obtain an initial Coulombic efficiency of 83.4% at 0.1 °C and a charge specific capacity of 354.1 mAh g-1. The capacity retention rate increased to 98.3% after 60 cycles, recovering graphite with excellent electrochemical properties. Chen et al. [200] used cobalt salts to catalyze the anode material after pretreatment with H2SO4 to obtain highpurity graphite and to recover the metal Co as a salt to close the loop (Fig. lie).
Residual electrolyte in the anode material is a major factor limiting the reuse of graphite and its recovery on an industrial scale. Expensive extraction techniques and energy-intensive pyrolysis methods have disappeared from the recovery field. Rothermel et al. [201] employed several methods for eliminating electrolyte from the anode material and concluded that the subcritical CO2 extraction method performed the best, recovering more than 90% of the electrolyte with conductive salts. Capacity decay and poor cycling stability of the anode material are the main challenges in recycling waste graphite and using it for preparing battery cathodes (Fig. 11a) [201]. Recent studies have shown that adjusting the electrochemical activity of waste graphite and reconstituting graphite layers can solve these problems. However, the technical difficulties are too high to widely use waste graphite in industrial-scale production (Fig. 11d) [202,203]. However, this line of thinking provides an important reference value for future applications and recycling prospects for similar Na- and К-based alkaline batteries. In addition to regenerating negative electrode materials, peroxymonosulfate-activated catalysts can be obtained by recycling waste graphite (Fig. 11b) [204], improving the Hummers method to achieve high-purity graphene (Fig. 11c) [205-207], and mixing graphite with diaphragms to acquire high-tensile-strength polymer-graphite composite films (Fig. 11lf) [208]. The dismantled graphite negative electrodes of spent LIBs can be recycled by the existing recycling process to achieve near-zero waste emission resource comprehensive use, reduce a large amount of solid waste, increase the value of the recycling process and meet regional environmental emission standards. However, contradictions still exist between efficient recovery of all components, recycling treatment and minimization of environmental hazards. Future work should focus on the development of efficient recycling technologies for waste anode materials.
The complexity of battery electrode components is a great challenge for hydrometallurgical leaching technology. Most products after industrial large-scale disassembly and separation are black powders with an ambiguous composition. The coupling of multiple material components with leaching agents and reaction parameters should be explored, and dynamic monitoring of composition ratios and intelligent parameter regulation techniques should be established to avoid single leaching parameters that reduce the recovery rate.
3.3.2.3. Electrolyte. In addition to the cathode material, the electrolyte is an abundant source of lithium. However, lithium is mostly present in the electrolyte as a salt with toxic properties. Furthermore, the multiple processes involved in thermal treatment to recover spent LIBs can drastically degrade the composition of the electrolyte. Therefore, the adsorption of porous electrodes, complex composition and low safety are more notable challenges for electrolyte recovery technology than the high recycling cost of other battery components. Today, progress has been made in the laboratory and in smallscale industrial production.
Usually, physical and chemical methods are adopted for recovering electrolytes, with physical methods including cryogenic and mechanical methods. The Atomic Energy Authority (AEA) in the UK used cryogenic crushing of spent LIBs and then extracted the electrolyte with acetonitrile to recover PVDF, Cu, Al, PE and CoO2 using other process technologies [209]. He et al. [210] dissolved cores with a custom prepared exfoliating extractant instead of an organic solvent and then used a mechanical method to obtain the electrolyte and electrode material using a high-speed rotating device that dissolved the anode binder for separating graphite and copper foil. Toxic LiPF6 can be precipitated from ethylene carbonate and propylene carbonate. The physical method is used on a large scale in industry and exhibits the advantages of a simple process that is environmentally friendly and easy to control. However, certain disadvantages, such as low separation after electrolyte freezing, high energy consumption, easy decomposition of LiPF6 and low purity, have become the main economic considerations for companies when recycling.
Chemical methods can be divided into vacuum pyrolysis and extraction methods. Vacuum pyrolysis is a similar process to pyrometallurgy, where the electrolyte and organic binder are pyrolyzed into fluorocarbon organic compounds at high temperatures. The products are evaporated and condensed for recovery after adjusting the vacuum pressure, effectively avoiding equipment corrosion and toxic fluoride hazards, and the cathodic active material on the collector is completely stripped during organic binder removal. However, the disadvantages of high-temperature pyrometallurgy are inevitable.
Extraction methods include supercritical methods. The relationship between the thermodynamic parameters of supercritical CO2 (temperature and pressure) and the solubility capacity has been exploited by adjusting the thermodynamic parameters to dissolve the electrolyte. Spectroscopic and chromatographic techniques were used to determine that the electrolyte degradation aging products are esters (diethyl carbonate (DEC), dimethyl-2,5-dioxhexane dicarboxylic acid ester (DMDOHC), methyl-2,5-dioxhexane dicarboxylic acid ethyl ester (EMDOHC), and diethyl-2,5-dioxhexane dicarboxylic acid ester (DEDOHC)). An ester-based organic solvent was used to soak the cores, and the electrolyte was dissolved in an organic solvent to separate the electrolyte and core. At the early stages of the process, a supercritical helium pressure head CO2 was used to extract electrolytes from spent LIBs. However, the recovery of trace amounts of LiPF6 was only possible with a high cost and low recovery rate.
Therefore, to overcome these drawbacks, researchers have changed CO2 to a supercritical state or a liquid state, where linear and chain carbonates are extracted in these two states, respectively. Furthermore, since CO2 is an inorganic solvent, LiPF6 can be effectively extracted from electrolytes by increasing the solubility of nonpolar solvents relative to polar solvents by adding corresponding inexpensive modifiers, entraining agents (liquid alcohols) and cointegrating agents (small gaseous alkanes). For instance, in the liquid CO2 extraction method, the entrainer ACN:PC ratio can be adjusted to 3:1 to obtain 89.1 ± 3.4 wt.% [211]. However, the experimental results showed that the type of diaphragm affects the extraction efficiency, with the differences between the extraction efficiencies of the PE diaphragm and the porous glass fiber adsorbed electrolyte reaching nearly double, with values of 73.5 ± 3.6 wt.% and 36.7 ±1.6 wt.%, respectively. The effect of supercritical extraction is mainly influenced by temperature, pressure, time and entrainment agent. In terms of the supercritical CO2 extraction mechanism, external factors mainly affect the extraction behavior by increasing the polarity of CO2.
Today, closed-loop electrolyte recycling remains challenging. Liu et al. [212] developed a technique involving the recovery of supercritical CO2 from the electrolyte and obtained an electrical conductivity of 0.19 mS cm-1 and an initial discharge capacity of 115 mAh g-1 after a series of processes, including extraction, molecular sieve dehydration and component replenishment. The electrolyte obtained from recycling was reloaded into the battery, and the electrochemical properties were measured to ensure that the standards for normal use were met. Although the recovery of electrolytes that meet the standards for battery use provides a new idea for closed-loop efficient recycling of spent LIBs, it is difficult to establish a complete recycling system due to the complexity of both the recycling process and electrolyte composition. Furthermore, certain factors, such as electrolyte purity, removal of hexafluorophosphate impurities, LiPF6 purification, economics of recovery, and unrecovered CO2, after use remain major challenges for a closed-loop recovery strategy.
3.3.3. Future recycling strategies for spent LIBs
Technological advances have accelerated the rate of change of high-energy density power battery types, and the need to explore new recycling technologies for retired batteries is imminent. There is a need to improve the safety and cycle time, the relationship between clean and efficient recycling technologies and the quality and cost of reinstalled batteries to meet the EoL of spent LIBs.
Modern recycling technology for spent LIBs can be suitably applied to nickel- and lead-acid batteries. In the future, recycling technology should focus on the close link with the way batteries are manufactured and designed. Future recycling technology for spent LIBs can adopt a similar basic approach to modern technology. Cooperation is needed between recycling companies and battery manufacturers to develop relevant policies and industry standards, unified classification codes, various battery structures, and full life-cycle traceability management of the different components of batteries. For example, the University of Grasse has developed new recyclable 3D printed batteries in which biodegradable polylactic acid (PLA) materials are applied, further enabling green recycling.
The recycling of LIB s requires full-component recycling of the key energy metals, such as Li, Ni, Co and Mn, in short processes. Nickel-based power batteries require special attention to the recycling of scarce element Ni, while lead-acid batteries should focus on the high lead content and highquality plastic casings. The metal components of the three types of spent batteries can be recovered using clean and efficient hydrometallurgical techniques, the electrolyte can be extracted using supercritical CO2, and graphite-based materials can be applied to adsorb heavy metals from wastewater. The organic material components of batteries should be replaced by environmentally friendly and easily degradable organic materials, and the electrolytes should comprise safe and stable solid phase materials.
4. LCA prediction and recycling optimization
The main mainstream LCA software options available today are OpenLCA [213], Apeironpro [214], SUSB-LCA [215], PLCAT [216], Eco-LCA [217] and GPLCD [218], which enable quantitative evaluation studies of waste treatment, production, transport, energy consumption, and social and environmental relationships. LCA methods for recycling spent LIBs mostly consider energy consumption and GHG emissions for assessment, including vehicle dismantling, vehicle recycling, battery recycling, and tire seat recycling. In particular, battery recycling is a major contributor to GHG emission reduction. However, the negative impacts of energy consumption and three-waste discharge associated with multitype recycling technologies, whether the output is higher than the input, whether the environmental protection is greater than the environmental damage, and the relationship between profit and the environment must still be revealed via LCA.
In general, the recycling of spent batteries can mitigate most environmental impact categories. Lin et al. [219] used LCA to compare three systems of organic water leaching, inorganic acid (HNO3) leaching and organic acid (citric acid) leaching. Citric acid and organic water require lower activation energy and GWP levels when recycling spent LIBs, significantly reducing environmental pollution; the leaching rate of the inorganic acid system is similar. Sun et al. [220] employed biological strain hydrometallurgy technology to recycle EoL waste Zn-Mn batteries. The only environmental impacts are human and marine ecotoxicity. Relative to traditional hydrometallurgy and pyrometallurgy technologies, the overall environmental impacts can be significantly reduced. After optimizing the pretreatment stage, higher environmental gains could be achieved. Rinne et al. [221] compared the impacts of spent LIBs on the environmental footprint in the recycling process. The use of waste as a reducing agent could further reduce the chemical consumption of hydrometallurgical recycling, and H2O2 was deemed unsuitable as a reducing agent for large-scale recycling. Kallisis et al. [222] demonstrated that the recycling of Ni, Co, and Mn cathode materials is the main contributor to environmental safety, with the burden of over 85% of all environmental impact categories reduced to 35%. Al, Cu, and Fe are the main burden in the recycling chain, leading to toxicity (Fig. 12a). Raugei et al. [223] calculated that 23 MJ kg-1 of primary energy is lost per kWh of battery energy recovered and that the reduction in CO2 emissions is reflected in the recovery of graphite and valuable metals (Fig. 12b). Planning a green recycling chain and reducing emissions, energy consumption and use of raw materials through LCA at the EoL stage could effectively offset the environmental impact of the production chain. Today, LEP batteries still account for the majority of retired batteries, and by using LCA, the recycling of 50% of the LEP batteries could fully offset the environmental impact, and 100% recycling could yield energy savings of 313.02 kg CO2-eq and 270.89 kg oil-eq of GHG emissions (Fig. 12c) [224]. The EoL phase of recycling has a more prominent contribution to compensating for environmental change, mitigating the high demand for fossil energy and biological health. However, transport, cling three-waste impurities and complex battery composition pose several negative challenges to the recycling of spent LIBs. Recycling strategies are an important part of GHG emission and disease risk reduction, and losses from recycled metals could be significantly reduced but not completely offset [225].
Among the various recovery technologies, from an LCA perspective, hydrometallurgical recovery and organic acid recovery are the most effective means to reduce environmental burdens to date. However, it is still necessary to reduce the energy consumption of leaching at the pretreatment stage to improve the environmental benefits. Comparing the full lifecycle carbon emissions of NCM, LMO, and LEP battery packs provides advantages, but it is difficult to determine which battery is more advantageous [226-228]. Therefore, reducing the overall emissions must be approached from the perspective of recycling cathodes while enhancing the cleanliness of the power mix. Upgrading battery preparation technology and developing renewable and clean energy sources could improve the overall environmental benefits of vehicles, reducing emissions and energy consumption [229]. Furthermore, recycling cathode waste could greatly contribute to protecting the environment, mitigating toxic organic solvents, mining rare minerals, resolving heavy metal pollution, and promoting sustainability. In addition, data on the impacts of transporting battery materials obtained through custom specialized recycling of spent LIBs, such as trucks and trains, is a valuable method for establishing cascading use and recycling networks.
Future of sustainable battery LCAs Considering the impact on environmental benefits, clean fuels, such as hydrogen fuel and compressed natural gas, have recently become the main trend in batteries. Clean fuel cells produce zero emissions. However, hydrogen-fueled electric vehicles (FCVs) are accompanied by pollutant emissions during manufacturing, hydrogen energy acquisition, storage and transportation from an LCA perspective, with carbon emissions ranging from 36 to 112 kg CO2 eq-kW-1 (Fig. 12d) [230-232]. Improving the fuel cell performance and reducing the loss of key components throughout the process contributes to the life-cycle carbon emissions of the fuel cell system and is an important method for improving the environmental benefits of FC Vs.
In response to geographical climate differences, the share of hybrid vehicles in the market is gradually expanding. According to a comparison of vehicle LCA results encompassing different power sources, renewable fuels have a greater potential to reduce life-cycle carbon emissions than low-carbon electricity portfolios. By considering advances in vehicle powertrain technology and changes in electricity and fuel supplies, PHEVs and HEVs produce lower life-cycle carbon emissions than internal combustion engine vehicles (ICEVs) and significantly higher emissions than BEVs. However, the fine particulate matter (PM2.5) and SO2 emissions of ICEVs are low, and vehicle infrastructure can be identified as a major source of the environmental burden.
With the rapid growth in the lithium market, transition metal minerals are consumed in large quantities, and various low-carbon alternative batteries have been developed. For example, NIBs, Li-S batteries, and Li-air batteries have high energy densities [233-235]. Future LCA research should focus on the recycling of these types of batteries. This research has considerably contributed to promoting the long-term sustainable development of these batteries, improving performance, reducing the use of nonrenewable energy, and decreasing the impact of environmental climate change. There are few studies on the potential impacts of potassium-ion batteries, aluminumion batteries, magnesium-ion batteries, and sodium-ion batteries on the environment. According to their composition and LIBs similarity characteristics, the heavy metal content in the cathode can be reduced, and most of the compositions and structures of batteries can be made compatible with the environment to the highest degree. Energy efficiency and reducing the loss of key equipment are key goals for reducing EoL environmental burdens.
Therefore, the recycling of used batteries should be regarded as an important part of battery LCA, especially because the positive impact of recycling on battery production cannot be ignored. Moreover, the environmental impacts of the best options for recycling various types of batteries should be compared. Finally, the impact of each link on the recycling of spent LIBs should be analyzed in detail. Based on a comparison of multiple evaluation studies, an LCA dynamic model of spent LIBs recycling was formulated, and the undiscovered forwardlooking problems were dynamically evaluated. Further warning of the environmental impacts of various recycling technologies could provide theoretical support for large-scale recycling technology routes and policy decisions for enterprises. In terms of recycling technology, certain variables, such as heating conditions and acid-base concentrations and types, could be coupled to obtain the optimal leaching method. The recycled components and products in the recycling chain should be increased to increase recycling profits.
Countries worldwide have focused on the management of recycling large quantities of EoL LIBs. To achieve the development of a circular economy and green transition, major battery-consuming countries, such as the USA, China, Japan and the EU, have adopted systems and regulations based on the principle of production chain responsibility through subsidies, levies, tax subsidies, incentives-penalties, depositsreturns, etc., thus generating significant social, economic and environmental benefits.
4.1. Existing proposals
USA: Optimizer of recycling policies.
The implementation schemes include the extended producer responsibility system and the deposit system. Regarding the recycling of used batteries, the International Battery Association has been established, and different battery recycling laws and regulations and deposit, trade-in, mandatory recycling and retailer recycling labeling systems have been developed on each continent for the battery supply chain and the consumer side. For example, the government can use financial incentives to subsidize public E Vs; through a policy of immediate access to tax rebates, low-income sellers can receive a tax credit of US $2,630, providing additional benefits to many customers [236]. To develop a sound system for recycling used batteries, legislation is enacted at the federal, continental and prefectural levels and regulated by each other. At the federal level, the Resource Conservation and Recycling Act, the Act Relating to the Reduction in Lead Exposure, the Federal Act on Batteries and the General Waste Management Act have been established to legislate the entire life cycle of batteries. Recycling recommendations provided by the International Battery Association are mostly adopted at the continental level, with a deposit mechanism to guide consumers and a time mechanism to regulate retailers. Nonprofit public service organizations for battery recycling have emerged in the private sector, such as the U.S. Rechargeable Battery Recycling Corporation, which has established separate programs for the collection and transportation of renewable batteries in the retail, community, corporate business and public sectors. Manufacturers have established a uniform code for batteries to be recycled through sales. Retailers are required to pay a deposit of at least $10 for each battery at the time of purchase and deliver it to the retailer within a specified time limit. Otherwise, the deposit is not returned.
In response to geographical climate differences, the share of hybrid vehicles in the market is gradually expanding. According to a comparison of vehicle LCA results including different power sources, renewable fuels have a greater potential to reduce life-cycle carbon emissions than low-carbon electricity portfolios. Consumers are obliged to provide batteries to the seller, the manufacturer or the Battery Association. All parties are subject to severe penalties if they do not comply with these regulations. This model of recycling in the U.S. has successfully addressed the front-end challenges of low efficiency and poor economics of spent LIBs recycling.
Europe: The world's first advocate of recycling battery norms.
The approach taken by the EU relies on the Union System's 1988 Production Responsibility Scheme and the enactment of the Batteries and Accumulators Containing Certain Hazardous Substances Directive issued back in 1991, which provides the recycling of 3 C batteries and leadacid batteries.
A series of relevant directives, such as 2006/66/EC and 2013/56/EU, have been introduced for recycling management of all spent LIBs, with a detailed division of battery production, collection and treatment aspects according to the different subjects applying batteries. Additionally, the EU requires all collected spent LIBs materials in all member states to be recycled at the end of their useful life using a time-lapse approach and clean and efficient methods, especially for certain materials, such as valuable metals. Within Europe, the target Li metal recovery rate should reach 50% by 2027 and 80% by 2031. Between 2024 and 2028, the EU will use a large amount of statistical data to build a new regulatory framework for batteries, replacing the 2006 battery directive that has been in place ever since [237]. On the economic side, Germany has adopted fund and deposit mechanisms to build a recycling system and has legislated that the battery sales side must take responsibility for recycling used batteries that have been sold, delivering the recovered used batteries centrally to a designated institution. Furthermore, the EU has created a legislative framework for sustainable LCA of LIBs, established a common recycling system fund, set up approximately 200,000 recycling sites for half of Germany's production of spent LIBs and defined minimum thresholds for recycling companies regarding the recycling of the various components of used batteries [238].
China: Beginners in recycling technology and recycling policy.
The development and improvement in battery recycling policies draw on the experiences of developed countries, with the extension of the production chain responsibility as a basic principle. In 2018, the state, the Ministry of Industry and Information Technology, the Ministry of Environmental Protection, the Ministry of Science and Technology, the Ministry of Transport, the Ministry of Commerce, the General Administration of Quality Supervision, Inspection and antine, the Bureau and seven other ministries and commissions jointly issued the Interim Measures for the Management of the Recycling of New Energy Vehicle Power Batteries. These measures clearly stipulate that in the recycling process, EV manufacturers bear the main responsibility for power batteries, recycling dismantling and comprehensive utilization enterprises, etc., as a way of ensuring the effective use and environmentally friendly disposal of power batteries [239].
In July of the same year, the Ministry of Industry and Information Technology also issued the Interim Provisions on the Management of New Energy Vehicle Power Battery Recycling and Traceability, which strictly stipulates the need to upload traceability information on recycled battery life cycles, time nodes, technical requirements and other clear requirements for unified coding, information collection and management of power batteries [240]. Additionally, to accelerate the recommended standardization work requirements in the field of new energy battery recycling, the Ministry of Industry and Information Technology is establishing a standardization working group for the new energy battery recycling industry to strengthen the relevant standardization construction team efforts [240]. In April 2020, the Ministry of Industry issued the Management Measures for Gradient Utilisation of New Energy Vehicle Power Batteries, with a focus on the gradient utilization method of waste LIBs and how to promote large-scale gradient utilization, which is the focus of application in business models. On the economic side, the Shanghai government provides a subsidy of RMB 1,000 to recycling companies for used EVs when each is sold by the selling company. Shenzhen has established a special accrual fund to give half of the subsidy funds to recycling companies by reviewing the charging standards.
Japan: A pioneer in advanced recycling technology.
Affected by various natural disasters, such as earthquakes and tsunamis, and the limitations of its land area, Asia's earliest concentrated research and commercialization of hybrid vehicle battery recycling technology occurred in Japan. Moreover, it is also the first country in Asia to implement relevant policies for the battery recycling industry and hosts a world-leading battery recycling system [241]. The well-defined, sound and step-by-step circular economy legislation system has laid the foundation for the development of a circular economy in Japan. The Japanese government has formulated the basic system of a recycling society based on relevant regulations of the battery production chain. In addition, in public media and policy documents, enterprises are actively guided to follow the concept of a circular economy and achieve a suitable awareness of voluntary recycling among the people [242].
Six Japanese firms, including Sumitomo Metal Mining, JX Nippon Mining and Metals, Sumitomo Chemical, Kanto Denka Kogyo, Jera and Nissan Motor, are now cooperating to develop a highly sophisticated recycling technology to recover rare metals, mainly from used storage batteries for EVs [243]. Manufacturers have established a battery recycling system of "battery production-sales-recycling". Moreover, the consideration of locations where batteries frequently emerge, such as battery sellers, EV sales stores, or large-scale charging service facilities, to establish a spent battery recycling service network fully reflects convenience and economy.
4.2. Transformative proposals
With large quantities of EVs in use, a booming recycling industry, and the continued increase in metal prices, the recycling of spent LIBs can be profitable to the tune of $1000 or more per ton. Moreover, recycling valuable metals is considered profitable. Therefore, the government should focus on considering various LCA data, enhancing the awareness of active recycling among managers across all levels, balancing the interests of all parties, increasing policy support and supervision, and establishing mandatory recycling methods for recycling processes that threaten human health and the environment. To develop a circular economy and achieve green transformation, governments must fulfil an important role in the supply chain characterized by the recycling of spent LIBs from a battery life-cycle management perspective. Based on the provided review, a future strategy for closed-loop battery recycling is proposed (Fig. 13):
Consumers: Consumers can choose a strategy to ladder or replace their spent LIBs depending on the health status of the batteries used, thus maximizing benefits at the consumer end.
Government: (i) The government can introduce policies to increase incentives and penalties to promote corporate enthusiasm for the recycling of spent LIBs to increase recycling rates. However, a punitive policy not in line with the economic benefits to businesses will most likely result in a reluctance on the battery supply side to provide the recycling side with the required convenient composition structure at the battery assembly stage. Therefore, the government should develop relevant optimization strategies based on the energy, economic and environmental impacts of the spent LIBs recovery phase, as outlined in this paper, coupled with the establishment of relevant reward and penalty factors. The interests of the supply and recycling sides and political performance can be safeguarded in many ways, (ii) In terms of the economic structure or energy reserves, the recycling strategy should be firmly based on a harmonious coexistence between humans and the environment, thus enhancing the recycling rate. Recycling policies should keep pace with the recycling of spent LIBs technology, which is constantly evolving, and policies must keep pace with the continuous development of recycling technology, (iii) More policy benefits should be shifted in favor of consumers, with incentives to submit retired batteries through subsidies. Through various legislative measures, such as subsidies, taxes, tax subsidies, reward penalties, and deposit refunds, we should improve the interrelationship between sales, use, and recovery and implement a policy involving parallel enforcement and incentives, (iv) We should develop regulations related to the transportation and storage of spent LIBs and encourage the development of lightweight and convenient battery testing systems.
Sellers: Sellers of LIBs are responsible for LIB recycling and disposal at or below capacity thresholds, and optimization decisions should focus on battery recycling rates and government subsidies to protect the environment. Sellers should work with car repairers to increase the price of spent LIBs recycling, accurately rate the battery capacity in customer repairs and give advice to customers to increase their enthusiasm to actively return spent LIBs. The government should regulate the recycling rate, while the sellers are given recycling subsidies. This two-pronged regulation and subsidy policy approach, which is mandatory and incentive-based, could ensure that the recycling rate of spent LIBs meets government requirements, confirming that sellers obtain sufficient profits and increasing the subsidy efficiency.
By summarizing the mature laws and regulations of countries in terms of spent LIBs recycling and by analyzing their well-established policies, this study could serve as a reference for governments initially starting to adopt LIBs on a large scale and for countries about to encounter a wave of EoL power battery recycling policies. By considering the recent implementations of the production responsibility system in such battery developing countries and the existing problems, we propose a green supply chain recycling system for spent LIBs, as shown in Fig. 14. In this system, we consider legal, technical, model and theoretical knowledge and various factors that arise in regard to transportation, profit and the environment.
5. Conclusions and future outlooks
The increasing use of decarbonized electrical energy in the automotive industry has presented unique opportunities for this sector. However, the increasing consumption of LIBs has resulted in a significant increase in the volume of spent batteries. If not managed properly, this consumption could pose significant risks to the economy, the environment, and human health. In light of the potential threats posed by this situation, there is a pressing need for research on the entire process of managing spent batteries, from collection to recycling and pollution control. In this article, we describe recent research efforts in this area and explore the key issues surrounding clean and efficient recycling technologies and their industrialization. To promote sustainable development within our society, a strategic approach that emphasizes the redesign, reuse, and recycling of batteries must be jointly pursued by governments, consumers, recyclers and suppliers.
(i) Recycling: Recyclers are the key links for the recycling of spent LIBs. a) The development of unmanned dismantling technologies and lines should be given higher priority to ensure the safe and efficient operation of other processes, b) Whether GHG emissions or energy consumption, the recycling of spent LIBs provides obvious advantages over the production of LIBs from new raw materials, especially hydrometallurgical recycling, c) The recycling scale is directly proportional to the recycling benefits. Enterprises should choose the appropriate recycling process according to the scale, and thermal runaway should be eliminated in every link, d) Spent electrolytes should be studied to determine methods for applying them in fields other than recycling, e) Organic acid leaching and bioleaching are techniques with the highest potential to move from the laboratory to industrial applications in the future, f) Exploring clean, highefficiency, and low-energy recovery technology options is as important as controlling pollutant discharge technologies. It is especially important to eliminate the potential threat of trivalent toxic waste in the relationship between toxic electrolytes, storage, fine dismantling, metallurgical recovery, dissociation and purification.
(ii) Supply: a) An application design should be invented for electrode materials and other components that can be easily disassembled, assembled, and used in stages. Regional energy endowment should be effectively used to build factories, b) Heavy metal content and manufacturing energy consumption should be reduced, and biodegradable binders and fluorine-free electrolytes should be selected to reduce environmental pollution factors at the source, c) Battery companies should work closely with downstream vehicle companies and upstream raw material companies to compile a complete whole life-cycle database, d) The main ingredients must be labeled on multiple sides of battery outer packaging to facilitate recycling.
(iii) Policies: a) It is necessary to uniformly plan network construction of recycling enterprises and force the elimination of old recycling technologies, b) A battery traceability LCA network database should be established to implement the main responsibilities of each recycling link, control from the production source, cease treatment monitoring, and provide transparent closed-loop recycling-specific processes, c) A favorable public opinion and publicity atmosphere for spent LIBs recycling should be created to guide consumers to actively cooperate with recycling activities, d) The key technologies for hydrometallurgical recovery in the closed-loop industrial chain require the formulation of proprietary subsidy policies.
(iv) Consumption: a) Participation should be actively supported in waste battery recycling activities executed by the government and social organizations, the implementation of the extended producer responsibility system should be supported, and a circular economy and low-carbon development should be promoted, b) Formal waste battery recycling channels should be chosen, waste batteries should be properly stored, and rechargeable or environmentally friendly batteries should be adopted.
Conflict of 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 financially supported by the National Key R&D Program of China, China (2022YFC3902600), CAS Project for Young Scientists in Basic Research, China (YSBR044), Guangdong Basic and Applied Basic Research Foundation, China (2021B1515020068), and China Postdoctoral Science Foundation, China (2023M733510). We would like to thank AJE (https://www.aje.cn/services/editing) for its linguistic assistance during the preparation of this manuscript.
Received 16 May 2023; revised 10 September 2023; accepted 24 September 2023
Available online 27 September 2023
* Corresponding author. Guangzhou Institute of Energy Conversion, Chinese Academy of Sciences (CAS), Guangzhou, 510640, China.
E-mail address: [email protected] (H. Yuan).
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Abstract
Clean and efficient recycling of spent lithium-ion batteries (LIBs) has become an urgent need to promote sustainable and rapid development of human society. Therefore, we provide a critical and comprehensive overview of the various technologies for recycling spent LIBs, starting with lithium-ion power batteries. Recent research on raw material collection, metallurgical recovery, separation and purification is highlighted, particularly in terms of all aspects of economic efficiency, energy consumption, technology transformation and policy management. Mechanisms and pathways for transformative full-component recovery of spent LIBs are explored, revealing a clean and efficient closed-loop recovery mechanism. Optimization methods are proposed for future recycling technologies, with a focus on how future research directions can be industrialized. Ultimately, based on life-cycle assessment, the challenges of future recycling are revealed from the LIBs supply chain and stability of the supply chain of the new energy battery industry to provide an outlook on clean and efficient short process recycling technologies. This work is designed to support the sustainable development of the new energy power industry, to help meet the needs of global decarbonization strategies and to respond to the major needs of industrialized recycling.
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1 Guangzhou Institute of Energy Conversion, Chinese Academy of Sciences (CAS), Guangzhou, 510640, China