A Systematic Review of Battery Recycling Technologies: Advances, Challenges, and Future Prospects

Toro, Luigi; Moscardini, Emanuela; Baldassari, Ludovica; Forte, Flavia; Falcone, Ilario; Coletta, Jacopo; Toro, Lorenzo

doi:10.3390/en16186571

Open AccessReview

A Systematic Review of Battery Recycling Technologies: Advances, Challenges, and Future Prospects

¹

Eco Recycling s.r.l., Via Francesco Siacci 4, 00197 Roma, Italy

²

Technosind s.r.l., Viale Palmiro Togliatti 1639, 00155 Roma, Italy

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Author to whom correspondence should be addressed.

Energies 2023, 16(18), 6571; https://doi.org/10.3390/en16186571

Submission received: 31 July 2023 / Revised: 7 September 2023 / Accepted: 8 September 2023 / Published: 12 September 2023

(This article belongs to the Section D2: Electrochem: Batteries, Fuel Cells, Capacitors)

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Abstract

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As the demand for batteries continues to surge in various industries, effective recycling of used batteries has become crucial to mitigate environmental hazards and promote a sustainable future. This review article provides an overview of current technologies available for battery recycling, highlighting their strengths and limitations. Additionally, it explores the current challenges faced by the industry and discusses potential future advancements. Through an in-depth analysis of the state-of-the-art recycling methods, this review aims to shed light on the progress made in battery recycling and the path ahead for sustainable and efficient battery waste management.

Keywords:

battery recycling; lithium-ion batteries; recycling technologies; challenges; resource recovery; circular economy; environmental impact; policy; challenges sustainability

1. Introduction

Batteries play an indispensable role in the modern world by providing portable energy storage and supply capabilities. From consumer electronics to electric vehicles to grid-scale energy storage systems, batteries enable technologies that are transforming society [1]. However, the widespread proliferation of batteries also creates complex challenges; as battery usage continues to grow exponentially across industries, the need for effective battery recycling technologies has become increasingly urgent [2]. Improperly discarded batteries contribute to electronic waste accumulation, while valuable and scarce materials locked inside are lost instead of being recycled. At the same time, the manufacturing of a myriad of battery types to meet booming demand places pressure on critical material supplies [3,4,5,6]. These intertwined issues necessitate the development of effective and sustainable battery recycling processes on a global scale.

Battery recycling recovers valuable minerals and metals in spent batteries that can be reused in manufacturing new batteries or other products. Metals, like cobalt, lithium, nickel, and manganese, are essential ingredients in the electrodes and electrolytes of common rechargeable lithium-ion batteries [3,7]. Battery recycling creates opportunities to reclaim these materials to reduce the environmental footprints of battery production, lower demands for continued resource mining [8], decrease manufacturing costs by utilizing recycled metals, and mitigate potential environmental contamination and human exposures from improper battery disposal [3,7,9,10]. Additionally, establishing functioning battery recycling systems and infrastructure is a pivotal component of transitioning to a circular economy for batteries [4,7,11,12]. In a circular model, materials are continuously looped back into the production system at end-of-life instead of entering the waste stream. However, major obstacles remain that hinder recycling rates and progress toward circularity [6,13,14].

This comprehensive review aims to provide an overview of the current technologies available for battery recycling, focusing on the major battery chemistries, such as alkaline, lead-acid, nickel-cadmium, nickel-metal hydride, and lithium-ion batteries. The review explores the strengths and limitations of existing recycling methods and investigates emerging technologies that show promise in addressing the challenges of battery waste management. Additionally, it identifies the current challenges faced by the industry and discusses potential future advancements and strategies to overcome these challenges.

By presenting a holistic view of the current state of battery recycling technologies, this review aims to contribute to the advancement of sustainable practices in the management of battery waste, foster innovation in recycling processes, and inform policymakers, industry stakeholders, and researchers on the potential pathways to a circular economy for batteries.

2. Overview of Battery Types

Batteries can be broadly categorized into primary batteries and secondary batteries based on their ability to be recharged. Primary batteries, also known as disposable batteries, are designed to be used once until depleted, after which they are discarded. Secondary batteries, commonly referred to as rechargeable batteries, can be recharged and reused multiple times [2,15,16]. This section provides an overview of the key types, characteristics, and applications of both primary and secondary batteries.

2.1. Primary Batteries

Primary batteries (Figure 1) are non-rechargeable batteries commonly used in applications where long shelf life, portability, and low self-discharge are critical [17]. They have a one-time use lifecycle—once discharged, they cannot be recharged for reuse [18,19]. Primary batteries are widely used for low-drain electronics, like remote controls, toys, flashlights, and clocks, as well as for novelty greeting cards, laser pointers, and hearing aids [16,17,20]. Some common types of primary batteries include alkaline batteries, zinc-carbon batteries, and lithium primary batteries, and these are discussed as follows:

Alkaline batteries are one of the most widely used primary batteries, containing manganese dioxide as the cathode, zinc powder as the anode, and an alkaline potassium hydroxide electrolyte [1,18,21,22]. They offer high energy density, stable voltage output, long shelf life (5–7 years), and tolerance to high-drain devices. They are commonly used in flashlights, remote controls, toys, and other portable electronics [1].
Zinc–carbon batteries, also known as carbon–zinc or dry cell batteries. They contain a zinc anode, a carbon cathode, and an electrolyte gel [1,2,22]. Zinc–carbon batteries are inexpensive, deliver 1.5 V voltage, and have a shelf life of 5 years [1,22]. Their low energy density makes them suitable for low-power devices, like remote controls, toys, radios, and smoke detectors [1,2].
Lithium primary batteries use lithium metal as the anode and have non-aqueous organic electrolytes [17]. Lithium batteries offer high energy density, 3 V voltage, wide temperature operation (−55 to 150 °C), and long shelf life (10–15 years) [17,20]. They are commonly used in watches, calculators, thermometers, cardiac pacemakers, and other specialty applications [1,17,20]. Popular chemistries are lithium–manganese dioxide (LiMnO₂) and lithium–iron disulfide (LiFeS₂) [1,17].

2.2. Secondary Batteries

Secondary batteries (Figure 2), also known as rechargeable batteries, can be recharged and reused multiple times. They are widely used in applications that require higher energy densities and longer operational lifetimes. The most commonly used secondary batteries include lead–acid batteries, nickel–cadmium batteries, nickel metal hydride batteries, and lithium-ion batteries. Examples of secondary batteries are as follows:

Lead–acid batteries are one of the oldest and most mature rechargeable battery technologies [1]. They consist of lead electrodes immersed in a sulfuric acid electrolyte. Lead–acid batteries are known for their high power output and affordability, making them ideal for certain applications, such as automotive starting batteries, backup power systems, and uninterruptible power supplies (UPS). However, they have low specific energy (25–50 Wh/kg) and a limited lifecycle (500–2000 cycles) [1,2].
Nickel–cadmium (Ni-Cd) batteries use a nickel oxide hydroxide cathode, metallic cadmium anode, and alkaline potassium hydroxide electrolyte [1,2,20]. NiCd batteries offer robust cycle life (>2000 cycles), high power delivery, tolerance to overcharging/deep discharging, and operation at low temperatures [1,2]. They are commonly used in power tools, emergency lighting, radio-controlled toys/models, and cordless appliances, and they have a specific energy of 30–80 Wh/kg [1,2]. However, cadmium toxicity has resulted in a restriction in their overall use [17].
Nickel–metal hydride (Ni-MH) batteries are an improvement over Ni-Cd batteries while, at the same time, eliminating the use of toxic cadmium. They use a hydrogen-absorbing alloy as the negative electrode and a nickel oxide hydroxide as the positive electrode, with a potassium hydroxide electrolyte. NiMH batteries offer good high-temperature tolerance, lower self-discharge than NiCd, good tolerance to overcharge/discharge, and offer a higher specific energy of 40–120 Wh/kg. However, this type of battery still faces challenges in terms of high cost, poor low-temperature performance, and high self-discharge [1,2]. Ni-MH batteries have found widespread use in hybrid electric vehicles (HEVs), portable electronics, and renewable energy storage systems [2].
Lithium-ion (Li-ion) batteries, first commercialized in 1991 [17], are one of the most popular modern rechargeable batteries due to their high energy density, efficiency, cycle life, and versatility [1,2,17]. Li-ion batteries use layered lithium compound cathode and graphite anode materials that allow lithium-ion intercalation. Different chemistries are utilized, such as lithium nickel cobalt aluminum oxide (NCA) and lithium iron phosphate (LiFePO₄) [17]. Their advantages include high specific energy (80–265 Wh/kg), high cell voltage (3.6–3.7 V), long cycle life (1000–3000 cycles), and low self-discharge [1,2,17]. They are widely used in consumer electronics, electric vehicles, and grid-scale energy storage [17,20]. The Li-ion battery market was estimated at $44 billion in 2020, with projections reaching $135 billion by 2030 [23].

Several other secondary battery chemistries are gaining attention for specific applications, such as the following:

Lithium polymer batteries (Li-Po) utilize polymer electrolytes instead of liquid electrolytes used in conventional lithium-ion batteries [17,24]. Their key component is the polymer electrolyte, which serves as both the separator between the electrodes and the medium for lithium ion transport. Polymer electrolytes offer several advantages over liquid electrolytes that make them attractive for commercial batteries. These include better safety due to the absence of volatile organic solvents, excellent flexibility and processability in thin films, the ability to suppress lithium dendrite growth, and the potential for all-solid-state battery configurations [24]. However, developing polymer electrolytes with high ionic conductivity comparable to liquid electrolytes along with adequate mechanical strength remains a key challenge [17,24].
Sodium-ion batteries (SIBs) are being explored as a potential low-cost alternative to Li-ion batteries for stationary energy storage [1]. SIBs offer certain advantages, including the potential for high-performance electrode materials, rapid sodium ion diffusion, lower manufacturing costs, and improved safety properties. However, SIBs also face challenges, such as their lower operation voltage, structural changes during sodium insertion, and the reactivity of sodium metal [25].
Lithium–sulfur (Li-S) batteries have attracted great interest owing to sulfur’s high theoretical capacity of 1675 mAh/g enabling significantly higher energy density compared to lithium-ion batteries [26]. The low cost and abundance of sulfur also confer economic advantages. However, Li-S batteries face multiple challenges, including the insulating nature of sulfur, dissolution of intermediate polysulfides into electrolytes, causing capacity loss, and volume changes during cycling degrading the cathode [27]. Considerable research has focused on addressing these issues through nanostructured sulfur–carbon composite cathodes, interlayers to inhibit the polysulfide shuttle effect [26], and protective coatings for the lithium metal anode. New strategies are required to enable Li-S batteries for real-world applications, including conductive and robust cathode hosts, catalytic promoters to facilitate redox kinetics, tailored multi-component electrolytes, and sustainable protection of lithium anodes [28].
Lithium–selenium (Li-Se) batteries are also being studied as alternatives owing to selenium’s high electrical conductivity compared to sulfur in Li-S batteries [29,30]. However, similar shuttle effect challenges arise from dissolved lithium polyselenide intermediates. In [29], this issue was addressed through a strategy of manipulating the redox pathway using the organoselenide electrolyte additive diphenyl diselenide (DPDSe). Optimizing the DPDSe to Se ratio improved the battery performance, resulting in over 1000 mAh/g initial capacity and 600 mAh/g retention over 250 cycles. In [30], selenium’s poor electrical conductivity and its large volume changes during cycling leading to capacity fading were addressed by using novel graphitized hierarchical porous carbon (HPC)/selenium composites as cathode hosts. This resulted in enhanced conductivity, elastic buffering of volume changes, and uniform dispersion of selenium.

Beyond lithium-based chemistries, there is a growing exploration of alternative battery chemistries. In particular, potassium-ion batteries (KIBs) are now being investigated as a promising sustainable alternative [31]. Potassium is orders of magnitude more abundant than lithium, and potassium salts are more affordable than lithium salts. KIBs can potentially deliver higher voltage and energy density compared to lithium-ion batteries owing to potassium’s lower redox potential. KIBs are still in the early research stage but show strong potential as a low-cost sustainable technology well-suited for large-scale stationary energy storage applications. Realizing viable KIBs requires systematic optimization of electrodes, electrolytes, and binders, and addressing safety concerns related to the reactive potassium metal anode [31].

Understanding the characteristics and applications of different battery types is crucial for implementing effective recycling strategies [12]. The subsequent sections of this review will delve into the recycling technologies associated with each battery type, examining their strengths, limitations, and advancements, to address the challenges and promote sustainable battery waste management.

3. Battery Recycling Technologies

Recycling technologies play a crucial role in the sustainable management of battery waste and the recovery of valuable materials. Rechargeable batteries, such as nickel–cadmium (NiCd), nickel–metal hydride (NiMH), and lithium-ion (Li-ion), have become increasingly prevalent in modern society, powering a wide array of portable consumer electronics as well as electric vehicles. At the same time, single-use primary batteries based on alkaline chemistries continue to be widely utilized in lower-power devices. The growing production and utilization of these batteries also lead to increasing volumes reaching end-of-life each year. Effective recycling technologies are, therefore, crucial for recovering valuable materials from spent batteries and reducing the environmental impacts associated with disposal.

This section provides a focused analysis of current and emerging recycling processes for four key battery chemistries: NiCd, NiMH, Li-ion, and alkaline. Although other battery types also warrant attention, these four represent most of the current market demand and environmental impact. NiCd, NiMH, and Li-ion are all high-performance secondary batteries essential for portable electronics and electric mobility. Meanwhile, alkaline batteries still dominate the single-use primary battery market.

As highlighted by Figure 3 and Figure 4, the overall recovery approaches are conceptually similar across these four battery chemistries. All currently used systems combine mechanical, hydrometallurgical, and pyrometallurgical processing steps in various arrangements, despite the distinct target materials contained in each battery type. However, substantial differences exist in the specific operating parameters, equipment utilized, and procedural details applied for recycling the different battery types.

The overview of recycling technologies for these important battery types given in this section highlights the different approaches used and their advantages and limitations.

3.1. Alkaline, Ni-Cd, and Ni-MH Battery Recycling

3.1.1. Mechanical Separation

Mechanical separation techniques are commonly used as the initial step in battery recycling processes. These techniques involve the physical separation of battery components based on their size, shape, and density. The main goal is to separate the metallic components, such as electrodes and current collectors, from non-metallic components, like plastic casings and electrolytes. The advantage of mechanical separation techniques is their ability to handle a wide range of battery types. However, these techniques do not recover metals in their pure form and often require further processing steps to refine and purify the materials.

In the case of alkaline batteries, mechanical separation improves material purity for subsequent metallurgical extraction of target materials, such as zinc, manganese, cadmium, and nickel [22]. A common mechanical separation technique is shredding, where batteries are broken down into smaller pieces to facilitate subsequent separation processes. Shredding can be followed by sieving, which uses screens with different mesh sizes to separate materials based on particle size. Magnetic separation [22] extracts ferrous components, while eddy current separation recovers non-ferrous metals based on conductivity.

Mechanical separation techniques have the flexibility to handle a wide range of battery types. However, these techniques do not recover metals in their pure form and generally represent an initial pretreatment step in a sequence of processing steps to refine and purify the target materials [22,32].

An example of a specialized mechanical process for the recovery of alkaline batteries is the one developed by Gasper et al. [32]. This process involves first shredding the batteries to uniform small sizes and then drying them at 425 °C in a rotary oven to remove moisture and evaporate any mercury present. The vaporized mercury is captured by a scrubber.

The dried material is then screened to create a fine fraction and a coarse fraction. The fine fraction contains the battery electrode powders and electrolyte powder, which can potentially be separated based on density differences using a gravity separator.

The coarse fraction undergoes magnetic separation to remove steel casing pieces, which are washed, briquetted, and sold as scrap steel. The remaining non-ferrous portion goes through gravity separation to recover brass, while plastics and paper float to the top for energy recovery.

The described mechanical separation process is designed to handle 1 metric ton per hour of spent batteries. This process offers a rate of 98% diversion from landfills, with a recovery rate of 87% of reuse of battery material [32]. While there is still an initial pre-processing step, this process shows how optimizing mechanical systems can improve metal enrichment before metallurgical processing.

3.1.2. Pyrometallurgical Processes

Pyrometallurgy utilizes high temperatures to extract metals from battery materials [22]. Pyrometallurgical techniques, like roasting, smelting, and thermal desorption have been widely studied for recycling spent alkaline batteries [22] In these processes, batteries are subjected to thermal treatment, such as smelting or roasting, to decompose organic binders, burn off organic electrolytes, and convert metal compounds into a molten or gaseous state [16].

Roasting between 500–800 °C can remove moisture and decompose metal compounds, like MnO₂ to oxides or reduced species. Direct smelting above 1000 °C separates Zn and Mn metals from slag but has issues, like Zn losses [33]. Thermal desorption can selectively vaporize and recover mercury at 300–500 °C without extensive heating [22].

Smelting is a commonly used pyrometallurgical process where the battery materials are heated in a furnace to separate the metals from other components. During smelting, the metals melt and are collected, while other materials form a slag or waste product. The metals recovered from smelting can undergo further refining to achieve higher purity levels [19]. Ni-Cd battery recycling predominantly employs high-temperature pyrometallurgical processes above 1000 °C [16]. Vacuum distillation can recover 99.95% purity Cd metal from Ni-Cd scrap by heating to 850–900 °C in a closed system, leaving an Ni-Fe alloy residue [16].

Industrial Ni-Cd battery recycling predominantly employs high-temperature pyrometallurgical processes above 1000 °C. Major industrial pyro-processes include SNAM, SAB-NIFE, and INMETCO. SNAM and SAB-NIFE use closed furnace distillation at 900 °C. INMETCO reduces CdO with carbon and then condenses the Cd vapor [16]. While effective at recovering Cd, these processes have high energy needs.

NiMH batteries contain significant amounts of rare earth elements (REEs), like lanthanum, cerium, neodymium, and praseodymium, along with nickel, cobalt, and other metals [34]. Pyrometallurgical treatments are usually insufficient to extract marketable REEs from waste NiMH since they result in a mixture of REEs in a slag form [34]. The main challenges of pyrometallurgical processes are the high energy needs, the potential release of harmful emissions, and the generation of hazardous waste [22]. Proper emission control systems and waste treatment measures are essential to minimize the environmental impact.

3.1.3. Hydrometallurgical Processes

Hydrometallurgical processes involve the use of aqueous solutions to extract metals from battery materials. These processes rely on chemical reactions to dissolve metals into a solution, followed by separation and purification steps to recover the metals. Hydrometallurgical processes offer the advantage of selective metal recovery and can be tailored to specific battery chemistries. However, they often require complex chemical processes and generate significant volumes of wastewater, which need to be properly treated to avoid environmental contamination [18].

Recently, an ultrasonication-assisted process was reported to synthesize graphene oxide from the graphite cathode waste of ZnC batteries [35]. The graphite powder obtained after battery dismantling, washing, and crushing was subjected to a modified Hummer’s oxidation using H₂SO₄, KMnO₄, and sonication. This produced high-quality graphene oxide while avoiding issues, like explosions and toxic gas release, encountered in standard Hummer’s synthesis. The graphene oxide showed excellent electrochemical behavior.

Leaching [33,36] is a common hydrometallurgical process used in battery recycling. It involves the use of acid or alkaline solutions to dissolve metals from the battery materials. The main leaching process types include the following [18]:

Alkaline Leaching: Uses a strong base, like NaOH, to selectively leach Zn but not Mn. Around 38–83% Zn extraction is reported, but less than 1% Mn extraction, which confirms high selectivity for Zn.
Complexation Leaching: Uses ligands, like ammonium compounds, to form soluble Zn complexes, enabling selective Zn leaching under mild conditions. Up to 83% Zn extraction was achieved.
Acid Leaching: The most common acid is H₂SO₄. Partially dissolves Zn and Mn oxides, extracting 13–40% Mn and >86% Zn. Not selective for either metal.
Reductive Acid Leaching: Adds a reducing agent, like glucose, to fully reduce and dissolve Mn oxides. Achieves up to 98% Mn and 100% Zn extraction.

Acid leaching is commonly used for the recovery of metals, like cobalt, nickel, and copper [18]. The resulting leach solution is then subjected to purification and/or electrolysis [37,38] to recover individual metals.

Acid leaching of Ni-Cd scrap using inorganic acids, like H₂SO₄, HCl, and HNO₃, or organic acids, like citric acid, has been widely investigated. Over 95% Cd extraction can be achieved from Ni-Cd scraps at 100 °C with 2.3–2.7 M H₂SO₄ [16].

Subsequent solvent extraction that uses organophosphorus compounds, like Cyanex 272, can separate Cd and Ni from the leachate into concentrated solutions for recovery as high-purity metal salts via precipitation or electrowinning [37,38]. Ion exchange or precipitants, like Na₂CO₃, can also purify the Cd. Electrodeposition and crystallization have obtained >90% Cd at high purity [16]. Such multi-stage hydrometallurgy routes allow comprehensive Cd recovery. However, this multistage operation results in an increase in complexity and costs.

Recycling companies, like Umicore, have developed processes to recover REEs from NiMH batteries with up to 98% efficiency. The recycled REEs can be directly reused in new batteries. However, large-scale recycling capacity currently remains limited [34]. Alkaline leaching is another hydrometallurgical approach, particularly suited for the recovery of zinc from spent alkaline batteries. Alkaline solutions, such as sodium hydroxide, are used to dissolve zinc from the battery materials, and the resulting solution is further processed to obtain pure zinc.

Hydrometallurgical processes offer the advantage of selective metal recovery and can be tailored to specific battery chemistries. However, they often require complex chemical processes and generate significant volumes of wastewater, which need to be properly treated to avoid environmental contamination.

3.1.4. Biotechnological Approaches

Biotechnological approaches, also known as bioleaching, utilize microorganisms to extract metals from battery materials. Certain bacteria, fungi, and archaea possess the ability to selectively leach metals from various sources, including battery components [39,40,41,42]. Bioleaching of alkaline batteries involves the cultivation of specific microorganisms, such as iron- and sulfur-oxidizing bacteria, like Acidithiobacillus ferrooxidans, in the presence of battery materials. These microorganisms produce enzymes that break down metal compounds, releasing the metals into a solution. They can extract Cd and Ni from battery paste at moderate temperatures of around 30–40 °C, eliminating the need for high temperatures or concentrated inorganic acids [39].

Organic acids, such as citric acid produced by fungi, like Aspergillus, can also mobilize Cd through complexation leaching. Further optimization of certain parameters, like pulp density, can improve the kinetics and efficiency of Ni-Cd battery bioleaching [39].

Biotechnological approaches offer the advantage of being environmentally friendly and energy efficient [39]. They can selectively target specific metals, reducing the need for extensive chemical processing. However, the implementation of biotechnological approaches in large-scale battery recycling operations is still in the early stages, and further research is needed to optimize their efficiency and scalability.

Figure 3 summarizes the different approaches for recycling spent alkaline, Ni-Cd, and Ni-MH batteries.

Figure 3. Typical direct, pyrometallurgical, and biotechnological recycling methods for the recovery of spent battery active materials.

3.2. Lithium-Ion Battery Recycling

Lithium-ion battery recycling recovers lithium, cobalt, nickel, manganese, copper, aluminum, and steel. Different recycling technologies target the diverse materials present. A number of recycling technologies are common between lithium batteries and alkaline batteries, though the details of the processes differ.

3.2.1. Mechanical Preprocessing

As for the alkaline batteries, shredding is the prevalent mechanical separation method, which breaks down batteries into smaller fragments to enable further sorting processes. While traditional mineral processing technologies can be applied, the pretreatment of LIBs presents unique challenges due to hazardous electrolytes, the risk of fire/explosion, and the diversity of cell/module designs [43]. For this reason, cryogenic shredding techniques are being developed and studied [44]. After shredding, sieving can separate shreds according to size using screens with varying mesh apertures [45]. Magnetic separation is also used to divide ferrous substances from non-ferrous ones, since many batteries incorporate magnetic parts. Moreover, eddy current separation can sort non-ferrous metals from non-metallic materials based on their electrical conductivity. Sieving, magnetic separation, and eddy current separation can all be used in subsequent steps for separating non-metallic and non-ferrous metals from the target materials.

However, additional metallurgical processing remains necessary to extract the metals in their pure form.

3.2.2. Pyrometallurgical Treatment

The goals of thermal processing include the following:

Decomposing and burning off volatile organic compounds, like electrolytes, binders, and plastics, that are present within lithium-ion batteries. This prepares the material for high-temperature smelting [7,46].
Removing moisture and passivating reactive components, like lithium salts, to prevent uncontrolled reactions during smelting [7,46].
Pre-concentrating metals by converting compounds, like metal oxides or phosphates, to metals through pyrolysis and reduction reactions at elevated temperatures [47].
Partially separating materials with different volatility, like plastics and metals, before smelting [7,46].

Pretreatment methods, like incineration, pyrolysis, or calcination, are first used to remove organic components, like plastics, from the spent batteries and to enrich the metal fraction [7,46]. This facilitates the subsequent pyrometallurgical steps. Roasting or calcination then heats the cathode powder with additives, like salts or carbon, at 500–1000 °C to decompose the lithium transition metal oxides into metals or simpler compounds [7]. For example, carbothermic reduction roasting at 700–1000 °C has been used to reduce LiCoO₂ cathode material and recover Co, Li₂CO₃, and graphite. Roasting LiCoO₂ with Al at 600 °C produces Li₂O and Co. Vacuum pyrolysis, chlorination, and nitration roasting with NH₄Cl, NaCl, or HNO₃ have been investigated to obtain Co and Li as chlorides, carbonates, or oxides [47].

Thermally treated battery scrap can undergo direct smelting, which involves heating shredded whole batteries at 1300–1500 °C to liquefy and separate the metals into an alloy phase and slag [7,47,48]. At these high temperatures, the metals originally present in the battery electrodes and current collectors liquefy to form an alloy phase that separates from a top slag layer. The metal alloy can contain iron, nickel, cobalt, copper, manganese, and other transition metals that were present in the original battery materials [7]. However, lithium and manganese are commonly lost to the slag during direct smelting [7]. This alloy can then undergo electrolytic processing to separately recover metals, like copper, nickel, cobalt, and iron. The use of precipitation or solvent extraction is also an option [48].

Companies, like Umicore, Glencore, Accurec, and Retriev Technologies, operate pyrometallurgical recycling at up to 20,000 tons/year capacity. Processes differ in feed pretreatment, furnace types, slag design, and gas treatment. Most recover Cu, Co, and Ni, while Li and Mn are lost to slag or emissions [48].

Pyrometallurgical processes represent high throughput methods for an initial recovery and metal extraction of spent lithium-ion batteries, serving as a preprocessing step before further hydrometallurgical refining. Integrated processes combining pyro- and hydrometallurgy are being developed to optimize lithium-ion battery recycling [11,12].

While productive for material recovery on a large scale, key limitations of pyrometallurgical recycling include high energy use, generation of hazardous emissions, and losses of lithium and manganese to slags or off-gases [7,47].

3.2.3. Hydrometallurgical Recycling

For lithium-ion battery recycling, hydrometallurgical methods are currently being developed to selectively separate battery materials through leaching, precipitation, solvent extraction, and other techniques [8,11,12,13,14,43,46,49,50,51,52,53].

Acid leaching typically uses hot concentrated sulfuric acid to dissolve lithium, cobalt, nickel, manganese, and copper into the solution [8]. Alkaline leaching with ammonia can also be used to selectively extract high-purity lithium, nickel, and cobalt [50].

The type of lixiviant and operating conditions, like acid concentration, temperature, and oxygen level, can be tailored to focus dissolution on specific battery metals based on their chemistry [50]. The metal-rich leach solution obtained undergoes subsequent purification to separate the dissolved metals from other impurities. Chemical precipitation, cementation, ion exchange, solvent extraction, or membrane separations can be applied for this step [13]. Selective solvent extraction is widely used, where immiscible organic extractants transfer targeted metals. For example [8], nickel can be selectively precipitated using dimethylglyoxime (DMG) reagent, D2EHPA extracts manganese [8,54], while cobalt and lithium can be sequentially precipitated using ammonium oxalate and sodium carbonate solutions.

In addition to these conventional solvent extraction approaches, recent research on selective solvent extraction processes for recycling valuable metals from spent lithium-ion batteries has yielded several promising advances. Tailored nanosorbents, like lithium manganese oxide (Li_1.1Mn_1.9O₄) nanotubes, have exhibited excellent stability, recyclability, and lithium uptake capacity over repeated adsorption–desorption cycles using oxidant eluents, like ammonium peroxodisulfate ((NH₄)2S₂O₈) instead of acids [55]. For mixed cathode materials, deep eutectic solvents composed of choline chloride–formic acid (ChCl-FA) combined with mechanochemical pretreatment can achieve highly selective leaching of lithium, nickel, cobalt, and manganese under mild conditions by exploiting proton and chloride complexation and redox effects [56]. Selective extraction systems involving the use of carboxyl-functionalized ionic liquid coupled with tributyl phosphate (TBP) as a co-extractant have also been investigated and optimized to directly extract lithium from multi-metal leach solutions with high efficiency and selectivity [57].

Effective strategies for upcycling and resynthesizing cathode materials from waste LIBs have been demonstrated in recent works [51,52]. In one study [52], the simultaneous synthesis of reduced graphene oxide (rGO) and lithium–manganese-rich (Li_1.2Mn_0.55Ni_0.15Co_0.1O₂) cathode material directly from the electrode powder recovered after mechanical pretreatment of mixed end-of-life LIBs was investigated. Extraction of target metals (Co, Ni, Mn) and oxidation of graphite to graphene oxide (GO) was achieved. The resulting Mn-rich metal solution was used directly to synthesize the Li- and Mn-rich cathode material. Meanwhile, the filtered GO was reduced to graphene oxide (rGO) using ascorbic acid.

In another paper [51], the resynthesis of LiNi_1/3Mn_1/3Co_1/3O₂ (NMC111) cathode materials from the leachate obtained by acid-reductive leaching of waste LIB powder was demonstrated. After selective precipitation of metal impurities, the Ni-, Mn-, and Co-containing solution was used directly to synthesize the NMC111 precursor hydroxide, avoiding costly metal separation steps. The recycled NMCs showed comparable specific capacity to those synthesized from pure reagents under the same conditions.

Currently, several industrial-scale recycling technologies make use of at least an intermediate hydrometallurgical step in their process. These include the following, among others [11]:

Umicore ValéasTM: Developed by Umicore in Belgium, this process has a capacity of 7000 tons/year. It involves pyrometallurgy (smelting in a shaft furnace) followed by hydrometallurgy (leaching) to recover cobalt, nickel, copper, and iron. Other materials, like aluminum, lithium, and graphite are lost.
Sumitomo–Sony: Developed jointly by Sumitomo Metal Mining and Sony in Japan, this process has a capacity of 150 tons/year. It uses calcination followed by pyrometallurgical smelting and hydrometallurgical leaching to recover cobalt oxide and a cobalt–nickel–iron alloy. Lithium and other materials are lost.
Retriev Technologies: Originally called Toxco, this US-based process has a capacity of 4500 tons/year. It uses mechanical processing followed by precipitation to recover lithium carbonate, metal oxides, steel, copper, and cobalt. Plastics are lost.
Recupyl Valibat: Developed in France, this process has a capacity of 110 tons/year. It uses mechanical processing followed by hydrolysis and leaching to recover lithium carbonate, lithium phosphate, steel, copper, and cobalt. Graphite is lost.

Other emerging LIB recycling processes which include hydrometallurgical steps are as follows [11]:

Accurec: Developed in Germany, this process combines mechanical, pyrometallurgical, and hydrometallurgical methods to recover lithium carbonate and a cobalt–nickel–manganese alloy. Polymers and graphite are lost.
Battery Resources: This US process uses mechanical processing and hydrometallurgy to recover lithium carbonate and nickel–manganese–cobalt hydroxide suitable for cathode production. Electrolyte is lost.
LithoRec: Developed in Germany with a capacity of 2000 tons/year, this process focuses on recycling traction LIBs. It uses extensive mechanical processing and hydrometallurgy to recover lithium salts and metal oxides. Electrolyte is lost.
OnTo Technology: This US process aims to recover cathode, anode, and metals using mechanical, pyrometallurgical, and hydrometallurgical steps. Only polymers are lost.
Aalto University Process: A theoretical Finnish process using mechanical, pyrometallurgical, and hydrometallurgical operations to recover almost all LIB materials. Only minor losses occur.

Innovative processes are being developed within the frame of European co-funded projects, such as LIFE LiBAT [58], LIFE DRONE [59], CROCODILE [60], and RHINOCEROS [61]. These are described as follows:

LIFE LiBAT (LIFE16 ENV/IT/000389) [58] aimed to develop and demonstrate an innovative technological solution for recycling primary lithium batteries, particularly lithium–manganese batteries. It integrated mechanical pretreatment with a hydrometallurgical treatment in a prototype plant in Italy, with a processing capacity of 50 kg per day. The project team achieved 67% lithium recovery at 99.8% purity along with 70% total material recovery, exceeding targets set in the Battery Directive. Compared to conventional pyrometallurgical recycling, the process reduced energy consumption by 82% and greenhouse gas emissions by 91%. Economic analysis showed the process is profitable at scales above 500 tons per year. The technology has the potential to be adapted for recycling lithium-ion batteries as well.
LIFE DRONE (LIFE19 ENV/IT/000520) [59] aims to develop a novel hydrometallurgical recycling process for lithium-ion batteries to recover graphite and directly resynthesize nickel–manganese–cobalt (NMC) cathode material. This avoids having to separate individual metals, reducing costs. A prototype plant will treat 1350 kg of electrode powder from 3 tons of batteries to produce 660 kg of NMC oxide. The process is expected to increase Ni, Co, and Mn recovery to 90% at 99% purity while reducing operating costs by 75% and wastewater by 85% compared to current methods.
CROCODILE projects (H2020 GAn°776473) [60] demonstrated a zero-waste European cobalt value chain combining advanced primary and secondary resource metallurgy that enhances sustainability, competitiveness, and strategic autonomy. The project developed and demonstrated innovative metallurgical systems to recover cobalt from diverse European primary and secondary sources, including waste streams, like spent batteries and catalysts. The project showcased synergistic technologies based on advanced pyrometallurgy, hydrometallurgy, biohydrometallurgy, ion metallurgy, and electrometallurgy that can be integrated into existing industrial cobalt recovery processes, enhancing the efficiency, economics, and sustainability of European cobalt production.
The RHINOCEROS project (H2020 GAn°101069685) [61] aims to develop and demonstrate smart robotic sorting and dismantling technology to enable the automation of a lithium-ion battery repurposing production line. When direct reuse of batteries is not feasible, the project will research innovative recycling routes to recover all materials in lithium-ion batteries including metals, graphite, fluorinated compounds, electrolytes, polymers, and electrode materials. The project will utilize end-of-life electric vehicles and stationary storage batteries as feedstocks. By showing an integrated European recycling value chain for these key lithium-ion battery applications, RHINOCEROS can help decrease EU dependence on imported critical raw materials, like lithium, cobalt, and graphite.

Other projects aimed at innovating the European battery market include BATRAW (H2020 GAn° 101058359) [62] and RESPECT (H2020 GAn°101069865) [63]. These are described as follows:

The BATRAW project [62] aims to develop and demonstrate two recycling systems for end-of-life electric vehicle batteries and portable consumer batteries. These systems will contribute to generating secondary streams of critical raw materials and battery materials with strategic importance for the rapidly growing EU battery market. BATRAW also plays a role in reducing EU dependence on imported critical raw materials.
Beyond recycling, the project promotes overall battery sustainability and circularity through new procedures for battery repair, reuse, eco-design, and supply chain transparency via a blockchain raw material tracking platform. Guidelines will also be provided for safe battery transport and handling.
Through its dual recycling pilots, complementary sustainability initiatives, and comprehensive stakeholder engagement, BATRAW aims to foster a circular battery value chain in Europe that enhances strategic autonomy for critical materials while aligning with the EU’s sustainability goals.
The RESPECT project [63], funded under the EU’s Horizon Europe and BATT4EU partnership, aims to transform and strengthen lithium-ion battery recycling in Europe by taking a holistic approach covering the entire recycling value chain from collection logistics to innovative treatment processes. RESPECT considers diverse lithium-ion battery types, states of health, and applications as feedstocks. Its key objective is developing a flexible, safe recycling process at the module level. This encompasses pretreatment, like deactivation, accessing active materials, hydrometallurgy, and direct recycling based on green innovations. The goals of the project include achieving over 90% weight recovery efficiency and reinforcing the security of supply and strategic autonomy by enabling a sustainable circular battery economy in Europe.

In summary, key advantages of hydrometallurgy include high selectivity, high-purity products, and the potential to directly recover battery-grade precursors. However, the multi-stage operations have high reagent consumption and generate large volumes of corrosive effluents [5,8]. The processes also need careful optimization for different battery chemistries.

Hydrometallurgical processes provide promising alternatives to high-temperature pyrometallurgical processes for lithium-ion battery recycling. Further research and development are needed to improve process efficiency and economics on a commercial scale.

3.2.4. Emerging Technologies

Direct Recycling

Direct recycling aims to reclaim and restore the functionality of lithium-ion battery components instead of fully breaking down batteries into metals. The goal is to reduce processing steps and material losses [64,65]. In [64], a two-stage thermal re-lithiation process was developed to directly restore the structure and electrochemical performance of delithiated lithium nickel manganese cobalt oxide (NMC) cathode material, representing an end-of-life cathode. Coating the cathode with lithium hydroxide followed by a low-then high-temperature annealing protocol successfully re-lithiated the cathode and regained its original capacity and cycling stability. This optimized direct recycling approach avoids the costs and waste of fully resynthesizing the cathode material.

In [65], the cathode material lithium cobalt oxide (LCO) was selectively recovered from shredded batteries using aqueous delamination, avoiding the use of harsh solvents that could damage its structure. A hydrothermal “cathode-healing” treatment was able to reintroduce lithium into the recovered LCO powder, restoring its original layered crystal structure and electrochemical capacity. Testing showed that the recycled LCO regained its initial crystallinity, morphology, and specific capacity after the healing process. Froth flotation using just water and a surfactant easily separated the healed LCO powder from the recycled graphite powder, avoiding decomposition issues associated with high-temperature pyrolysis of binders typically required to liberate the powders. The recycled graphite recovered 340 mAh/g capacity after hydrothermal cleaning, compared to 300 mAh/g in its initial unprocessed state. Full lithium-ion cells were demonstrated with the direct recycled LCO cathode versus the recycled graphite anode, showing good capacity retention, though at a slightly reduced rate compared to entirely new materials.

These direct recycling techniques can potentially restore 80–90% of a lithium-ion battery’s initial capacity [64]. However, these processes need further enhancement for commercial viability [65].

Biotechnological Methods

Bio-hydrometallurgy employs microorganisms to selectively extract and concentrate metals from spent lithium-ion batteries. Bioleaching uses bacteria, like Acidithiobacillus ferrooxidans, or fungi, such as Aspergillus niger, that can mobilize metals through various metabolisms [39]. Both bacterial and fungal bioleaching have been explored for spent LIBs. Fungal bioleaching seems more effective due to higher metal tolerance and the production of multiple organic acids as leaching agents [41].

The bacterium Acidithiobacillus ferrooxidans was used [42] for ultrasonic-assisted bioleaching of the metals from spent LIB powder obtained from discarded cell phones.

While biotechnological methods, like bioleaching, show promise for recycling lithium-ion batteries, their application at an industrial scale is still in the preliminary phases, and additional research and development are required to enhance their performance and potential for expansion to large-scale battery recycling facilities.

3.3. Lithium-Polymer Battery Recycling

Lithium-ion batteries with polymer electrolytes represent an emerging battery technology that poses unique challenges for recycling and establishing closed material cycles, as discussed in a recent review article on eco-friendly recycling of future lithium battery generations [66]. Polymer electrolytes in both the cathode and separator lead to difficulties separating and recovering the individual material components. As outlined in [66], currently there are two potential options for handling the polymer electrolyte in recycling, both with drawbacks.

Thermal processing, such as the burning of the polymer electrolyte, allows materials, like the cathode active material, to be recovered, similar to the recycling of conventional lithium-ion batteries [66]. However, this route results in an irrecoverable loss of the polymer electrolyte, which detracts from the sustainability and circularity of the process [67].

Alternatively, complex wet chemical processes could be applied to dissolve the polymer electrolyte in a suitable solvent and enable its recovery [66]. While this would allow retrieving the polymer for reuse, current knowledge gaps exist around whether dissolution can effectively separate the polymer with sufficient purity for battery reuse [68]. The multi-step wet chemistry route is also not expected to be economically or environmentally viable on a commercial scale, despite marginally higher material recovery [66].

Thus, both current recycling options for lithium-polymer batteries are suboptimal from either a sustainability or economic feasibility perspective. This creates barriers to closed material loops and an effective circular economy model for this emerging battery type [66]. Further process innovation is needed to allow efficient retrieval of both the polymer electrolyte and cathode active material.

Research is still needed to engineer recycling processes capable of recovering both polymer electrolytes and electrode materials from lithium batteries at high efficiency, purity, and appropriate economics. This includes developing innovative dissolution solvents, advanced separation techniques, polymer re-isolation methods, electrode material purification, and recycling-friendly battery designs [68].

Figure 4 summarizes the different approaches for recycling Li-ion batteries, while Table 1 summarizes the recycling technologies for all the battery types, discussed with their advantages and disadvantages.

Figure 4. Typical direct, pyrometallurgical, hydrometallurgical, and biotechnological recycling methods for the recovery of Li-ion battery active materials.

4. Current Challenges in Battery Recycling

While battery recycling is crucial for sustainability, several key challenges must be addressed to improve recycling rates, economics, and overall system performance. Major current challenges include economic factors, environmental impacts, safety issues, collection logistics, policy frameworks, and infrastructure limitations.

4.1. Economic Challenges

The economics of battery recycling significantly impact its viability and adoption. Key economic challenges include the following:

High upfront capital cost [3,11,32,69,70,71]: Constructing recycling plants requires extensive initial investments estimated between $100–500 million for large facilities. Significant funding is needed for specialized equipment, facilities, permits, and skilled personnel. This necessitates strategic partnerships and substantial financing.
High operating costs [32,72]: Battery recycling incurs ongoing costs for skilled labor, energy, chemicals, maintenance, compliance, and waste management. For hydrometallurgy, acids, and organic reagents contribute significantly to expenses. Pyrometallurgy is highly energetically demanding and requires extensive emission control systems. Cost-optimization across diverse battery chemistries is essential.
Low material value recovery [7,11,72]: Recycling processes often cannot recover the full material value due to losses from slag, emissions, or low-purity products. This leads to lower revenues compared to mining costs. Improving yields and purity through emerging techniques, like direct recycling, is critical to enhancing value.
Lack of economies of scale [3,6,8,11,12,70,71]: Most recycling facilities remain small-scale demonstrations or pilots, unable to realize the benefits of scale. Modular plants could allow incremental capacity increases responsive to regional battery waste volumes. Automation and process intensification are also needed.

4.2. Environmental Impacts

While greener than mining, battery recycling has several environmental aspects that must be managed, as follows:

Air emissions [7,11,14,39]: Pyrometallurgy and thermal operations generate particulate matter, acidic gases, and metal fumes requiring extensive gas treatment. Dust and VOC emissions also occur during mechanical processing. Emission control costs are substantial.
Wastewater discharges [6,39]: Hydrometallurgy produces large volumes of metal-laden acidic or alkaline wastewater. Costly multistage neutralization and purification are needed before discharge. Some methods, like bioleaching, can operate at near-neutral pH.
Energy intensity [7,12,14,39]: Recycling processes, like shredding and smelting, are energy intensive. The use of renewable energy and heat integration improves sustainability. Hydrometallurgy also relies heavily on electricity for agitation and electrowinning.
Reagent consumption [6]: Strong inorganic acids, organics, like kerosene, and specialty solvents are used in large quantities, especially in hydrometallurgical recovery. Scaling recycling technologies with lower reagent intensity is vital.
Secondary waste generation [6,7,11,12]: Hazardous slags, filter cakes, and treatment residues are produced which require careful disposal. Recycling and reuse within the plant, e.g., for construction, is being evaluated along with stabilization methods before landfilling.

4.3. Safety Concerns

Battery recycling poses inherent occupational and process safety risks from fire, explosion, and exposure, as follows:

Fire and explosion hazards [4,7,44]: Finely divided metals, like lithium and cobalt, can be reactive and combustible. Thermal runaway of damaged lithium-ion batteries can lead to fires during processing. Preheating, passivation, deluge systems, and explosion containment help manage risks during shredding and sorting.
Electrolyte hazards [73]: Electrolytes contain corrosive and toxic salts, like LiPF6. Worker exposure must be minimized during dismantling. Moderate temperatures with ventilation are needed when opening cells to avoid gas releases.
Waste treatment risks: Sludges washed with sulfuric acid to remove metals can undergo exothermic acid–sulphate reactions, releasing toxic SO₂, if not properly neutralized [74]. Chemical incompatibility awareness is critical.

4.4. Collection and Sorting Methods

Efficient battery collection and sorting is pivotal yet challenging, and includes the following issues:

Diffused waste streams [3]: Myriad consumer devices and industrial uses, besides electric vehicles, generate geographically dispersed waste batteries. Effective collection infrastructure and public participation incentives are essential.
Identification and diagnostics [75]: Proper sorting requires clear battery labeling, barcodes, and marking. Performance diagnostics would allow selective secondary use or recycling but add complexity in dismantling. Standardization would benefit recycling facilities.
Commingled waste [12]: Municipal waste streams can blend various battery types and brands. Identifying, selectively dismantling, and routing specific batteries to optimized recycling processes is difficult. Advanced sensor-based sorting technology could assist in separation.
Illegal dumping [76]: Lack of treatment options motivates illegal dumping of spent batteries, resulting in environmental contamination and resource losses. Strong regulations with compliance monitoring and enforcement are critical.
Cross-border flows [4]: Complex transboundary movements of battery waste occur between nations. Harmonizing international collection and shipping regulations while prohibiting illegal trafficking improves recycling access.

4.5. Regulations and Policy Frameworks

Clear policy and regulatory frameworks are needed internationally, including the following:

Responsibility attribution [75]: Policies should establish unambiguous producer versus consumer responsibility for battery recycling costs and logistics.
Recycling targets [4]: Many nations are starting to stipulate mandatory recycling rates for rechargeable batteries between 50 to 70%. Achieving high collection and recycling targets requires coordinated regulatory efforts.
Recycled content mandates [75]: Requiring minimum recycled content thresholds in new batteries, like the proposed 10% for the EU Battery Regulation, would drive demand and improve recycling economics.
Safety and environmental standards [4]: Consistent standards for facility emissions, occupational exposure limits, waste handling, and transportation safeguards tailored for batteries should be instituted while allowing technological flexibility.

4.6. Limited Infrastructure

Suitable recycling infrastructure remains lacking in many regions, resulting in the following issues:

Few commercial facilities [12]: Most recycling plants remain pilot-scale operations focused on demonstrating technologies instead of processing large volumes. Wider deployment of commercial recycling facilities globally is essential.
Underdeveloped logistics networks [72]: Optimized collection points, reverse logistics channels, and transportation infrastructure are needed to link waste batteries to recycling hubs while minimizing costs and emissions.
Immature technologies [14,42]: While emerging techniques seem promising, most are only at the laboratory or prototype stage. Mature technologies suitable for regional waste streams must be fostered through further applied R&D.

In summary, advancing battery recycling requires a concerted multidimensional approach addressing economic, environmental, safety, regulatory, and infrastructure-related challenges across the recycling value chain.

5. Future Prospects and Emerging Technologies

This section delves into the potential future directions of battery recycling, taking a closer look at solutions that encompass improved collection methods, advanced battery design, novel separation techniques, integration into circular economy models, and the application of automation.

5.1. Enhanced Sorting and Collection Techniques

Efficient battery collection and sorting are crucial to maximizing recycling rates and material recovery. Emerging techniques aim to automate these processes for higher throughput.

Dual-energy X-ray transmission can identify battery chemistry and internal structure, allowing automated sortation into precise categories [77]. Spectroscopic techniques, like laser-induced breakdown spectroscopy (LIBS), can rapidly characterize alloy composition [78]. Sensors, like radio-frequency identification (RFID) tags on individual cells, can track batteries for targeted collection [79]. Improved disassembly methods can detach cells and modules while minimizing damage and contamination [45,73].

Enhanced collection infrastructure is also key. Installation of public battery drop-off kiosks with automated sorting units can divert batteries from landfills. Partnerships with retailers for take-back programs can tap into consumer foot traffic. Door-to-door services and expanded hazardous waste collection routes can gather batteries directly from households and businesses. Implementing financial incentives, like disposal fees or recycling rebates, may further motivate proper battery disposal and collection [3,75].

5.2. Advanced Battery Design for Recycling

Future battery designs could be optimized for recyclability. For lithium-ion batteries, reducing heterogeneity in cathode chemistries would simplify recycling processes. Standardized disassembly features, like tabs, scores, and snap fits, could facilitate automated dismantling. Avoiding adhesives and solders would reduce contamination [12,53].

Battery engineers should consider recyclability as a key design criterion alongside performance and safety [72]. Manufacturers can collaborate with recycling firms early in the design process to incorporate these features [53]. Designing for recyclability while maintaining cost competitiveness remains an ongoing challenge.

5.3. Innovative Separation and Recovery Processes

Emerging separation processes aim to recover pure materials from battery manufacturing scrap and end-of-life batteries.

As already mentioned in Section 3, hydrometallurgical techniques, like solvent extraction and selective precipitation, can separate metal salts [8,51,52,80]. Solutions of leached cathode material can undergo sequential precipitation steps to isolate individual metals, like cobalt, nickel, manganese, and lithium. Organic solvents that selectively bind target metals enable their separation from other dissolved salts. Developing high-performance polymers or ionic liquids as extraction agents could enhance separation efficiency and purity.

Optimizing these separation processes will maximize the yields and purity of recovered materials for battery production.

5.4. Battery-to-Battery Recycling

Closed-loop battery-to-battery recycling aims to recover materials in sufficient quality and quantity to directly re-enter lithium-ion cell manufacturing. This requires an integrated process combining optimized collection networks, disassembly, separation, and synthesis of new cathode materials.

Direct recovery methods [64,65], like direct cathode recycling, can rejuvenate and re-lithiate extracted cathode powders to a functional grade with minimal processing steps. Closed-loop hydrometallurgical and pyrometallurgy systems that directly supply recovered metals and compounds into cell fabrication could also minimize costs and waste [12,46,51,52].

Achieving this goal will require substantial progress in sorting, separation, and reprocessing technologies. It will also require consolidation within the currently fragmented recycling industry to integrate operations. Strong collaboration along the value chain, from battery designers to manufacturers, recyclers, and miners, will be essential to construct closed material loops [12,53].

5.5. Automation and Robotics in Recycling Facilities

Automated robotic recycling lines can improve efficiency, productivity, and safety. Robots equipped with sensor arrays, AI-guided vision, and recognition software can accurately sort batteries and dismantle them consistently. This level of precision and speed exceeds manual approaches [81].

Automated disassembly using grinding, shredding or laser cutting produces consistent particles or sections. Robotic arms can manipulate batteries and components with force control to minimize damage. Automated modular reconfigurable work cells allow flexibility in handling diverse battery chemistries and formats. Advanced automation can also assist material separation and synthesis processes. AI-based process control systems can optimize operational parameters for high yields.

However, considerable research and development are still required to implement end-to-end automation [45,73]. Large capital investments may restrict adoption by smaller recycling firms. Additional risks from system faults need to be addressed.

5.6. Technological Integration and Process Optimization

A key priority is integrating emerging technologies into optimized, automated recycling lines. This requires a systems approach examining how each component process affects the overall performance. Standardized interfaces between the collection, sorting, disassembly, separation, and synthesis modules can streamline recycling lines. This integrated systems approach will maximize economic viability and material recovery [12,72].

5.7. Circular Economy Approaches

Transitioning to a circular economy for batteries can systematically reduce waste and resource consumption. It entails shifting from linear take–make–dispose models to circular designs that extend product lifetimes and regenerate materials at end-of-life. Strategies include product-as-service business models where manufacturers retain ownership of batteries and manage reuse [14].

Modular and reconfigurable battery design could enable replacing only degraded components [53]. Repurposing batteries from vehicles to low-power stationary storage applications can lengthen service life.

Implementing battery passports that digitally track components, materials, and lifecycle data can optimize handling along the value chain. More localized recycling infrastructure and supply chains can reduce transport impacts.

6. Conclusions

Batteries provide essential energy storage capabilities across diverse applications from consumer electronics to electric vehicles. However, improper battery disposal can lead to environmental pollution and resource depletion. Implementing optimized recycling processes is crucial for enabling a sustainable circular economy. This review has provided a comprehensive overview of current recycling technologies for major battery types, like lead–acid, nickel–cadmium, nickel–metal hydride, and lithium-ion batteries. Key points are recapped below:

Mechanical preprocessing, like shredding and sieving facilitates, the separation and sorting of battery components. Magnetic, density and sensor-based methods further enable targeted material streams.
Pyrometallurgy exploits high-temperature processing to recover metals. Steps, like smelting and thermal treatment, extract an alloy for refining. However, extensive emissions controls are necessitated.
Hydrometallurgy involves aqueous chemistry techniques to selectively dissolve and separate battery metals. Leaching, solvent extraction, precipitation, and electrolysis are implemented for purification.
Biohydrometallurgy employs microbes for cleaner and more targeted metal extractions but requires process optimization. Electrochemical methods also increasingly assist separations.
Lithium-ion battery recycling poses challenges due to diverse cathode chemistries and reactivity. Cryogenic shredding, direct cathode rejuvenation, and biotechnologies are emerging alternatives.
Economic factors, infrastructure limitations, policy frameworks, environmental impacts, and safety risks pose key challenges for advancing battery recycling.
Future prospects encompass automation, process intensification, battery design for recycling, closed-loop integration, and circular economy business models.

This broad overview of recycling technologies, current capabilities and limitations, and emerging trends lays the groundwork for tackling existing obstacles and guiding future progress.

6.1. Summary of Current Challenges

Realizing the immense potential of battery recycling requires addressing salient technical, economic, regulatory, and social challenges, such as the following:

High capital and operating costs make it difficult for recycling economics to compete with primary mining. Low material value recovery further hinders revenues.
Processes, like pyrometallurgy and hydrometallurgy, have high energy, water, and chemical use leading to environmental burdens. Slags and effluents require extensive treatment.
Safety risks from battery fires, explosions, reactive dust, and toxic exposures necessitate stringent controls during handling and recycling.
Diffused waste streams, commingled sources, and illegal dumping impede efficient collection. Advanced sorting is also needed at facilities.
Unclear regulatory frameworks regarding producer versus consumer liability limit investment. Mandates for recycling rates and recycled content can drive growth.
Infrastructure limitations, like few commercial facilities, underdeveloped logistics networks, and insufficient training programs, restrict widespread adoption.
Immature recycling technologies, especially for emerging battery chemistries and form factors, require further applied R&D to scale up.

Resolving these interconnected challenges demands systems-level solutions across the battery lifecycle, engaging key stakeholders.

6.2. Future Directions and Recommendations

Realizing a sustainable circular economy for batteries will rely on continued efforts in several key areas, as follows:

Improving economics via increased scale, automation, modularization, and diversified revenue streams for recycling facilities.
Advancing technologies, like direct cathode recovery, bioleaching, electrolysis, and integrated recycling lines to enhance efficiency.
Designing future batteries for recycling through modularity, disassembly features, and standardized components.
Expanding collection networks through consumer incentives and industry partnerships for takeback programs.
Developing policies that set ambitious yet feasible recycling targets along with recycled content mandates.
Fostering R&D across lithium-ion chemistries as well as emerging battery types to broaden recyclability.
Embracing circular economy thinking and business models, like product-as-service and reuse/remanufacturing.

Furthermore, key stakeholder groups should adopt the following targeted strategies:

Recyclers can demonstrate integrated pilot facilities and pursue modularization, automation, and process optimization.
Battery manufacturers need to engage recyclers early in the design process to consider recyclability.
Government agencies should institute standards mandating recycling rates, facility emissions limits, and material disclosures.
Corporations can partner with recyclers on battery takeback logistics and provide consumer recycling education.
Academia can develop recycling training programs and collaborate with the industry on applied R&D.

To realize the promise of battery recycling for sustainable development requires active engagement from diverse stakeholders to tackle multifaceted technical and socioeconomic challenges through continued innovation, policy evolution, and systems-level solutions.

Author Contributions

Conceptualization, L.T. (Lorenzo Toro) and L.B.; writing, L.T. (Lorenzo Toro), L.B., F.F., I.F. and J.C., with support from L.T. (Luigi Toro) and E.M.; supervision, E.M., with support from L.B.; validation, L.T. (Luigi Toro) and E.M. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Conflicts of Interest

The authors declare no conflict of interest.

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Figure 1. Example of the structure of a primary battery (alkaline battery).

Figure 2. Example of the structure of a secondary battery.

Table 1. Summary of recycling technologies for different types of batteries.

Battery Type	Recycling Technology	Advantages	Disadvantages
Alkaline, Ni-Cd, Ni-MH	Mechanical separation	Can handle diverse battery types and chemistries Separates metals from non-metals Scalable and flexible process	Does not recover pure metals Further refining steps needed Dismantling and size reduction required first
	Pyrometallurgy	Effective for large-scale metal recovery	High energy consumption Hazardous emissions Slag waste generation
	Hydrometallurgy	Selective metal recovery High purity products	Multi-stage, complex processes High reagent consumption Effluent treatment required
Lithium-Ion	Mechanical separation	Can handle diverse battery types and formats Separates metallic and non-metallic materials Facilitates further processing	Does not recover pure metals or compounds Further refining steps needed Pre-processing and size reduction required first
	Pyrometallurgy	High throughput capability	High energy consumption Hazardous emissions Material losses to slag
	Hydrometallurgy	Selective recovery of materials High purity products	Complex multi-stage processes High reagent consumption Effluent treatment requirements
All Battery Types	Biotechnological Methods	Environmentally friendly Energy efficient Selective leaching	Early development stage Process optimization required
All Battery Types	Direct Recycling	Reduces processing steps Maintains material value	Limited commercial viability currently

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Toro, L.; Moscardini, E.; Baldassari, L.; Forte, F.; Falcone, I.; Coletta, J.; Toro, L. A Systematic Review of Battery Recycling Technologies: Advances, Challenges, and Future Prospects. Energies 2023, 16, 6571. https://doi.org/10.3390/en16186571

AMA Style

Toro L, Moscardini E, Baldassari L, Forte F, Falcone I, Coletta J, Toro L. A Systematic Review of Battery Recycling Technologies: Advances, Challenges, and Future Prospects. Energies. 2023; 16(18):6571. https://doi.org/10.3390/en16186571

Chicago/Turabian Style

Toro, Luigi, Emanuela Moscardini, Ludovica Baldassari, Flavia Forte, Ilario Falcone, Jacopo Coletta, and Lorenzo Toro. 2023. "A Systematic Review of Battery Recycling Technologies: Advances, Challenges, and Future Prospects" Energies 16, no. 18: 6571. https://doi.org/10.3390/en16186571

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A Systematic Review of Battery Recycling Technologies: Advances, Challenges, and Future Prospects

Abstract

1. Introduction

2. Overview of Battery Types

2.1. Primary Batteries

2.2. Secondary Batteries

3. Battery Recycling Technologies

3.1. Alkaline, Ni-Cd, and Ni-MH Battery Recycling

3.1.1. Mechanical Separation

3.1.2. Pyrometallurgical Processes

3.1.3. Hydrometallurgical Processes

3.1.4. Biotechnological Approaches

3.2. Lithium-Ion Battery Recycling

3.2.1. Mechanical Preprocessing

3.2.2. Pyrometallurgical Treatment

3.2.3. Hydrometallurgical Recycling

3.2.4. Emerging Technologies

Direct Recycling

Biotechnological Methods

3.3. Lithium-Polymer Battery Recycling

4. Current Challenges in Battery Recycling

4.1. Economic Challenges

4.2. Environmental Impacts

4.3. Safety Concerns

4.4. Collection and Sorting Methods

4.5. Regulations and Policy Frameworks

4.6. Limited Infrastructure

5. Future Prospects and Emerging Technologies

5.1. Enhanced Sorting and Collection Techniques

5.2. Advanced Battery Design for Recycling

5.3. Innovative Separation and Recovery Processes

5.4. Battery-to-Battery Recycling

5.5. Automation and Robotics in Recycling Facilities

5.6. Technological Integration and Process Optimization

5.7. Circular Economy Approaches

6. Conclusions

6.1. Summary of Current Challenges

6.2. Future Directions and Recommendations

Author Contributions

Funding

Conflicts of Interest

References

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