Technological options and design evolution for recycling spent lithium‐ion batteries: Impact, challenges, and opportunities

The lithium‐ion battery (LIB) market is growing, driven by consumer demand and the imperative to reduce greenhouse gas (GHG) emissions. The socio‐environmental impacts of LIBs production are vast; thus, it is of paramount importance to acquire knowledge about the consequences of lithium metal mining on human health, farming and the overall ecosystem. The materials embedded in spent LIBs have high industrial value. To minimize environmental impacts and conserve declining natural resources, the global supply chain for the raw materials for LIBs should not rely solely on mining. Rather, manufacturers should have access to the critical materials recovered from waste, as a sustainable and reliable secondary source of valuable materials. It is also crucial to study the hazards and economic considerations associated with waste LIB management from disassembly to final recycling stage. This article evaluates and highlights various current approaches to recycling and reuse of LIBs, as well as potential future developments. The pros and cons of different technological options for recycling spent LIBs, and opportunities to use small‐scale recycling technology to overcome the associated barriers, are also discussed.

significantly increased.Research published in 2021 reported that around 7.19 billion mobile phones, one billion laptops, and one billion tablets were in use till 2021 (Costa et al., 2021).It is likely that demand for consumer electronics will continue to cause LIB production to grow.The automotive industry is also a potential booming field for LIBS, as it transitions from fossil fuels to electric vehicles (EVs; Hannan et al., 2017).This significant growth in lithium-based products will not only place demand on dwindling natural resources but cause environmental impacts through mining and mineral processing activities.These impacts include GHG emissions, soil pollution ground pollution, and other detrimental effects to ecosystems (Garole et al., 2020;Pandhija et al., 2010).Recovering and reusing lithium and other valuable minerals, such as cobalt, from waste LIBs would decrease reliance on natural resource reserves and reduce the environmental impacts of mining.Recycling LIBs not only helps to preserve the environment and creates economic benefits by conserving natural resources, but also helps reduce the volume of waste being generated.On average, most mobile phones are replaced within 12-18 months, despite of their service condition.The rate of recycling of spent LIBs from discarded mobile phone within last 4 years has improved from 5% to higher percentage but still the rate is less than 10% (Costa et al., 2021).It is estimated that recycling processes can reduce natural resource extraction up to 51.3% (Dewulf et al., 2010).Recycling also helps reduce the amount of fossil fuels and nuclear energy required to fuel the lithium production and extraction processes.Recycling waste LIBs do not completely eliminate the use of materials from virgin resources, as the demand of the growing market is higher than the materials available for recycling processes.Another challenge for LIB recycling is economic viability.The cathode of the LIB contains most of the valuable materials, and this part is removed at the last stage of battery disassembly (Kim et al., 2021).The process of recovering the cathode is expensive and the cost is increasing due to the complexity of disassembly.Batteries produced by different manufacturers have different materials, shapes, battery types, proportions, and morphologies.These variations in battery manufacturing require to develop a unique battery recycling technique which can recycle all types of batteries (Kwade et al., 2018).The recycling industry also has room to improve on the implementation of good environmental practices.For example, most people do not remove the batteries from their spent electronic goods at the end of life (EoL).This prevents the battery from being recycled and having its materials recovered.
This review mainly focuses on the materials of LIBs at various stages of their lifecycle, also concentrating on the end-of-life phase of the battery.The scarcity of the resources used in LIBs is discussed, with a review of the design perspective and current state-of-art techniques in the process of recycling.Recent developments and the pros and cons of current processes are also discussed.One of the main objectives of this article is to highlight the benefits of implementing recycling processes for LIBs, at an environmental level and economic level by reducing the associated cost of the transformation and extraction of the materials.These benefits are especially significant in the automotive industry, with the current shift toward EVs.The spotlight is on cathode materials, as they have high-value materials with difficulties in recycling their components effectively, making this part of a wide study area in battery components.This article also addresses the immediate requirement of standardizing battery components and their conformation.The necessity of applying legislation to incentivize battery recycling processes is also covered.

| Impact of lithium production for LIBs
The socio-environmental impacts of lithium production can be easily understood by considering the modes of lithium production.
To produce one ton of lithium, it is necessary to mine 250 tons of spodumene or 750 tons of mineral rich brine (Ambrose & Kendall, 2020a, 2020b).Lithium extraction from brine directly decreases the water level, as it involves drilling of numerous holes in the salt flat to pump the mineral-rich solution to the surface (Figure 1).Argentina, Bolivia, and Chile are famous for lithium production.In those nations, lithium production has heavily affected farming, wildlife, and ecosystems.The average precipitation in the lithium triangle region is very low, at 100-200 mm per year.The rate of evaporation is 1300-1700 mm per year.As the region is very rich in avifauna and vegetation, a small change in the water supply can greatly affect its biodiversity (Kaunda, 2020).These impacts can be limited by extracting lithium from spent LIBs to reduce the demand of lithium extraction from primary sources.One ton of lithium can be produced from 28 tons of spent LIBs.This equates to approximately 256 spent LIBs batteries from EVs (Meng et al., 2021).

| Impact of cobalt production for LIBs
The Democratic Republic of Congo has one of the world's largest reserves of cobalt.However, the political instability of this nation has led cobalt consumers to seek alternative sources (Schmuch et al., 2018).Access to cobalt reserves in the Congo have also been complicated by short-term price fluctuations, and social, environmental and ethical concerns due to child labor in mining (Schmuch et al., 2018).Researchers have found adverse effects of cobalt exposure in the blood and urine of the children in the region.The DNA damage among the children in that region can be correlated with cobalt contamination of soil, water, and air.Heavy metal particles that are released during cobalt extraction from mines can cause cancer, vision problems, nausea, vomiting, heart diseases, and thyroid problems.Long-term exposure or breathing high concentration of cobalt can cause health issues including asthma and pneumonia.Besides human health, cobalt also affects the ecosystem.Plants that grow in cobalt-contaminated soil contain cobalt in fruit and seeds.During mining, cobalt comes into contact with soil, water, plants, and rocks.Once cobalt enters the environment, it becomes almost impossible to remove (Farjana et al., 2019;Fordyce, 2013;Ruokonen et al., 1996).One typical spent LIBs contain 5%-20% Co of its total elemental composition, say for example, one EV battery (NMC 532 type battery) contains around 14 kg of cobalt (Castelvecchi, 2021).According to report, more than 50% of Co from spent LIBs can be recycled and at optimal recycling condition this rate can go beyond 90% (Gaines & Nelson, 2009;Hossain et al., 2021;Zeng et al., 2014).Support from the international community to extract cobalt from recycled LIBs and the creation of a circular economy would help to alleviate some of these concerns by reducing the need for use of virgin resources.

| Applications and disposal of waste LIBs
Effective recycling of LIBs requires a hierarchy of applications that optimizes material usage and lifecycle impacts.The energy required to produce the battery needs to be evaluated correctly against the energy delivered by the battery to determine whether it can be repurposed at the end of its initial life.Reuse of the battery can offset the recycling cost.For example, there is a significant public demand to reuse second-hand batteries from EVs in household applications.The process of reusing the batteries is more firmly selected over recycling currently, following the factors (a) less price for the refurbishment of incorporating the battery in second-use applications, (b) having more credits for recycling over reuse.If the reusing and recycling options show similar economic benefits then recycling should be the favored option, considering the environmental impact.This is because, over time, the batteries from used EVs will be in greater supply for second-use applications.To avoid the landfilling or stockpiling of the batteries, it is favorable to undergo a recycling process even after the second use.Stockpiling of spent LIBs is hazardous to the environment.Unless it has an option of directly deploying it for a second use, LIB modules must be either repaired or recycled.The need for new minerals extracted can be avoided by end-of-life LIB recycling, which also provides more economic benefits such as avoiding risks of misbalance in demand-supply chain of material of LIB production.

| DISMANTLING OF LIBs FOR RECYCLING
Disassembling complex LIBs from products such as EVs is very hazardous and requires training in high-voltage operations.It is mandatory to use only insulated apparatus for recycling purposes to avoid short-circuits and electrical accidents (Dunn et al., 2012;Meng et al., 2021).The heat generated from the short circuits of the battery while dismantling can produce hazardous gases including hydrogen fluoride, due to the presence of flammable electrolyte.The expansion and excessive accumulation of the gas can lead to an explosion (as shown in Figure 2a; Fei et al., 2021).The electrode materials are also toxic and carcinogenic (Larsson et al., 2017).Batteries must meet an initial design specification called the "state of health."Over time, batteries start to degrade which affects their performance.The units used for a battery's state of health here are percentage points.For example, a battery with a 100% state of health is a fresh cell that fulfills the design specification, although there are a few batteries that may be slightly deviated from the design specifications by having a state of health of less than 100% when dispatched from the factory.The state of charge in the battery specification refers to a degree of charge or discharge, where 100% indicates full charge and 0% indicates empty.

| Battery repurposing
The packs, cells, and modules of used LIBs are reused in other applications such as stationary energy storage and charging stations, which requires a fine assessment for their state of health, state of charge, recycling, remanufacturing, and reusable capabilities.To achieve higher efficiency, instead of replacing the whole battery pack due to the failure of few battery cells, the rapid monitoring system can be built up in situ to recognize the low performing cells selectively which need to be replaced or to identify whether there is need for the module or pack reconditioning.

| Battery aging and hazard identification
Electrochemical impedance spectroscopy is used to measure the state of health and aging mechanism of used batteries.With the help of the data obtained, it provides a decision matrix for the process of reusing or disassembling and helps in identifying the potential hazards which may impact the downstream processing.The electrochemical impedance is also used in a gateway testing process of the primary production of battery, for example, in large production plants (Attidekou et al., 2014(Attidekou et al., , 2017)).Major EV manufacturing companies are planning to use this technology for identifying and replacing the failing modules, which helps in the maintenance and management of the EV (Cerdas et al., 2018).The future of battery management technology is expected to be reliant on diagnostic functionality embedded into battery management systems, which helps gather data for interrogation at end-of-life.

| Diagnostics of LIB cell design
The physical configurations, cell chemistries and cell types of LIBs vary from module to module, which makes battery recycling more complicated and challenging.Figure 2b represents the different cell designs of LIBs.It is evident from Table 1 that the manufacturers employ a range of different cell chemistries, which requires various approaches to the reclamation of materials.The dismantling and separation line of LIBs are greatly affected by the material chemistry, cell array, layout, set, and the amount of dangerous chemicals.As a consequence, the costs associated with recycling are increased by the need to accommodate the wide range of manufacturing variations.Usually, flat electrodes are used in pouch and prismatic cells, whereas the cylindrical cells are coiled tightly, which causes difficulty in the separation of electrodes in the direct recycling process.For example, the Automotive Energy Supply Corporation (AESC) manufactures Nissan pouch cells, which contain a low level of cobalt and a high level of manganese.The cylindrical cells of Tesla EVs (manufactured by Panasonic) and prismatic cells of BMW EVs (manufactured by Samsung SDI) contain high levels of cobalt.These cylindrical cells are mostly bonded by an epoxy resin which is challenging to recycle or remove.Another common difficulty faced during recycling is fusion among the cells.In most of the cases the cells inside the battery pack get fused with each other, which makes the recycling process more complicated and challenging.Also, during dismantling, cell geometry is considered to be an important factor, particularly for direct recycling.

| Diagnostics of active material chemistries in LIBs
LIBs cover a large variety of chemistries.The fundamental working mechanism of LIBs can be described as intercalation and deintercalation of Li + in a tunnel-or layer-like structure.Graphite is mostly used as anode, but the cathode chemistry varies from battery to battery.These cathode chemistries in LIBs are largely responsible for the performance of the battery and research into battery chemistry has led to the development and evolution of improved cathode materials.Table 1 describes the different cathode chemistries found in LIBs.
Cathode active materials used in Li-ion battery manufacturing can be allocated to four categories.These are: lithium-based layered transition metal oxide, spinel oxide, conversion type, and polyanion cathode materials.All of these cathode-active materials have a distinctive crystal structure.The high charge capacity and operating voltage of lithium-based transition metal oxide and polyanion cathode materials make them the most dominating of the cathode materials (Kotal et al., 2022).

| CURRENT SCENARIO FOR BATTERY DISMANTLING
Figure 3 shows the various stages of assembly, which makes automation challenging.Most LIBs are dismantled by hand for recycling or reuse.The weight (EV packs usually weigh 300-700 kg; Kurdve et al., 2019) of LIBs and their high voltage (320-360 V; Belharouak et al., 2020) requires highly qualified employees and specialized tools for dismantling.To make the situation more challenging, there is a shortage of sufficiently qualified employees in the global industry.For example, a survey by an Institute of the motor industry has found that in the United Kingdom, less than 2% of the workforce is capable of servicing the LIBs installed in EVs (Skeete et al., 2020).Manual battery dismantling incurs a high labor cost, which makes the revenue from extracted materials less economically viable.The design of LIBs must be focused on crash safety, space optimization, and center of gravity, balanced against ease of service.These design F I G U R E 3 An example of the assembly of a battery cell, module, pack, and battery system.
constraints result in further challenges to the process of recycling, as they make the manual disassembly of the battery more time-consuming.

| Diagnostics for automated battery disassembly
Using robotic technology to disassemble batteries can eliminate danger to employees and make the process of automation more economically viable.This process has been piloted in several research projects (Harper et al., 2019;Helu et al., 2012;Wegener et al., 2015).The automation process helps maintain the purity of segregated materials and yields higher recycling efficiency.In recent years, the sorting process for consumer batteries has moved toward automation.
One example is the Optisort system (Hellmuth et al., 2021).The Optisort system uses a computer vision algorithm to analyze battery labels and sort them into bins based on their chemistry with pneumatic actuators.However, this process requires mixed batches of waste batteries to be presorted by hand before entering the Optisort machines.Recent developments in the computer vision algorithm have also provided some capabilities for recognizing materials and objects based on features including shape, size, texture, and color.To facilitate automatic processing of waste batteries, the authors recommend that a standard is developed for battery labelling, to provide additional information to sorting databases.Developing a robot that uses artificial intelligence (AI) for automation of LIB recycling processes with the capability to work on multiple process stages would be extremely challenging.For example, the robot would need to be equipped with sensors to detect different levels of materials, as well as computer vision 3D RGB-D imaging devices.To work properly, the robot would also need special features including the ability to measure applied forces and convert them into electrical signals, and tactile capabilities to manage the various activities involved in the disassembly process.
Rather than fully automating the process, the complexity of battery disassembly lends itself more readily to robots and humans working side by side.This has led to the creation of force-sensitive "co-bot" robotic arms (Cassioli et al., 2021;Rujanavech et al., 2016;Wegener et al., 2015).These co-bots can be used to complete some simple tasks, for example, unscrewing a bolt.This frees up human workers to carry out more complex tasks.Robots with AI and computer vision capabilities to handle various waste streams are currently being used in many industries (Audi AG, Electrorecycling GmbH, Automotive Research Center Niedersachsen) in the battery disassembly field (Wegener et al., 2015;Zhou et al., 2021).Some of the more difficult challenges in automated disassembly of LIBs batteries may be overcome with emerging advances in AI, computer vision, and robotic fundamentals.For example, one computer vision algorithm currently under development can identify various types of waste materials (Ramsurrun et al., 2021).It can also reliably track objects and guide the actions of robotic arms in cluttered scenes and complex conditions.This algorithm involves a forceful interaction between objects and robotic arms-for example, when forceful movement of robotic arms in the process of unscrewing or cutting.The need to grip and handle disassembled components may also cause challenges to the autonomous grasp planners and vision systems.

| Discharging and separation of components
During the recycling process, a LIB goes through three important stages: (a) stabilizing the battery, (b) opening the battery, and (c) separation, which are either carried out together or separately.First, batteries are stabilized using ohmic discharge or brine.Then the battery is opened.The opening process mainly consists of shredding or crushing the batteries, under inert atmospheric conditions.Techniques for LIB processing vary in different parts of the world.For example, North America and Europe practice the Recupyl method (Tedjar, 2014), the Akkuser method is used in France (Pudas et al., 2015), the Duesenfeld technique is used in Finland (Zenger et al., 2010), and Retriev technique in Germany (Smith & Swoffer, 2013).However, most large European recyclers skip the stabilization stage before opening the batteries (Harper et al., 2019).This is possible because seawater has been used previously to discharge the batteries (Li et al., 2016;Shaw-Stewart et al., 2019).Saltwater discharges the cell safely by corroding and passivating the cell's inner chemistry.But using alkali metal salts (such as sodium phosphate) in this process has less effect on corrosion.This makes the cells to be assessed and re-used, as the alkali solution penetrate the cell without significant amount of corrosion (Shaw-Stewart et al., 2019).High-voltage modules and packs are not suitable for the brine discharging method because of higher electrolysis rate and gas generation.Low-voltage modules and cells, however, use brine discharging, as the electrolysis rate is lower and easily controllable (Al-Thyabat et al., 2013).One drawback of brine discharging is that it can contaminate the cell chemistry and make the downstream chemical processes more complicated.
An alternative method for discharging batteries, is ohmic discharge (Chen et al., 2018).In this process, the battery is placed in a load-bearing circuit for discharge.LIBs can be shredded at any state of discharge, however, the optimum level of discharge for shredding has not yet been experimentally determined.However, it is known that overdischarging can contaminate the electrodes and separators by dissolving the copper into the electrolyte.This copper reprecipitates if the battery voltage is raised again or if the battery is subjected to usual operation.As a result, the possibility of short-circuiting and thermal runaway is increased.After complete discharge, the components of the battery cell are separated into different material streams for further processing.These streams are: laminated aluminum or steel cans, separators, anode (copper, graphite, conductive additives), cathode (aluminum, binder, active-material, carbon black), and binder.

| Pyrometallurgical technique
In the pyrometallurgical process, metals are recovered as metal alloys from metal oxides using a high-temperature furnace (Makuza et al., 2021).This high-temperature technique is known as "smelting," and used for commercial recycling of LIBs (Hu, Mousa, Tian, et al., 2021;Hu, Mousa, & Ye, 2021).This smelting process is aided mostly by the current collector, with the advantage of using the whole cell or modules without a prior passivation step (Makuza et al., 2021).
The pyrometallurgical processing outputs are metallic alloys, gases, and slags.Using a hydrometallurgical process, the metal alloys are separated in the form of metallic components and slag, which contains lithium, aluminum, and manganese (refer to the hydrometallurgical section later in this article).LIBs contain electrolytes and plastics (approximately 40%-50% of battery weight).These electrolytes and plastics exhibit an exothermic property during smelting and help to reduce energy consumption.In pyrometallurgy, little importance is given to electrolyte, plastic, and lithium-salt recovery.This is because these materials are volatile at low temperatures and require additional hydrometallurgical steps, which involves higher energy cost.Therefore, pyrometallurgical processes are most often used to collect valuable metals like cobalt and nickel (Hossain et al., 2021).

| Physical separation process
During the physical separation process, materials are separated after a low-temperature thermal reduction.This recovery process is largely dependent on the output properties and variations in the materials, such as the density of the materials, the particle size of the elements, hydrophobicity, and ferromagnetism characteristics.The end-product of this process is mainly electrode coating powders, with a small fraction of metal foils, and the coarse fractions of casing materials and plastics.Magnetic materials and plastics are separated from the mixture by a magnetic separation method and principle of density difference respectively.The rest of the residual products are black mass, which contains graphite and metal oxides.Graphite is separated from black mass using the froth flotation technique (Zhan et al., 2018).The most challenging parts of this process are removing the binder, and separation of electrode materials from current collectors.To improve recyclability, battery manufacturers are aiming to use water-soluble binders instead of fluorinated binders in the future (Nguyen & Oh, 2013).Multiple studies are investigating the development and use of nonsoluble styrene-butadiene rubber (Buqa et al., 2006), water-based binder solutions, and cellulose-and lignin-based binders, but these studies are still in the lab-based scale research stage (Nirmale et al., 2017).

| Metal reclamation via hydrometallurgy
In the hydrometallurgical technique, an aqueous solution is used as a leaching medium to leach metals from battery cathodes.Research has indicated that H 2 SO 4 /H 2 O 2 is the most common effective reagent combination (Ferreira et al., 2009).Various studies have been carried out to alter the leaching parameters and find optimum leaching efficiency (Jo et al., 2018;Peng et al., 2021;Zheng et al., 2017).Results have indicated that H 2 O 2 helps to attain a higher leaching efficiency.This is because H 2 O 2 works as a reductant which helps in the conversion of insoluble Co 3+ to soluble Co 2+ (Meshram et al., 2014).After leaching, the metal components are recovered from the solution by reactions and precipitations which vary the pH value.Typically, cobalt is recovered in the form of sulfate (Vieceli et al., 2021), hydroxide (Schiavi et al., 2021), carbonate (Jung et al., 2021), or oxalate (Verma et al., 2021).Lithium is recovered as carbonate or phosphate (Liu et al., 2019).The mechanochemical technique is an alternative method for recycling.The mechanochemical technique produces water-soluble cobalt salt by mixing the cathode materials with a complex agent or chlorinated compounds.The mixture is then washed with water to separate the insoluble fractions (Yun et al., 2018).Recycled materials may be used to resynthesize cathode materials (Meng et al., 2018).Alternatively, the recovered materials can be used to synthesize materials for other applications, such as photocatalysts (Mekonnen et al., 2019;Santana et al., 2017), metal alloys (Hossain et al., 2021), or sensors (Ribeiro et al., 2021).

| Direct recycling
Direct recycling reuses reconditioned anode and cathode material removed from electrodes for remanufacturing LIBs.
With very few changes in the crystal morphology of active material, the mixed metal-oxide cathode materials can be used in the process of making new cathode electrodes.In parallel to reusing the battery cathodes, it is necessary to restore the amount of lithium to its initial level to counter lithium loss due to material degradation.Graphite anodes, when separated mechanically for reusing, may perform well with properties similar to pristine graphite (Sabisch et al., 2018).The direct recycling process eliminates expensive and lengthy purification processes, and most of the battery components can be reused and recovered after a few modifications.However, the direct recycling process has some challenges and obstacles.For instance, batteries with a low state of health are less advantageous to recycle using this process.To attain higher efficiency, the direct recycling method must be manipulated on specific cathode formulation.Contamination due to the presence of other metals in the cathode material makes the direct recycling method highly sensitive and affects the results of electrochemical performance (Li et al., 2017).

| Biological metals reclamation
A process of using bacteria in recovering valuable metals is called bioleaching, and this process has been successfully carried out in the mining industry (Roy, Madhavi, et al., 2021;Smith et al., 2017).This is an emerging technology in LIB recycling and reclamation of valuable metals.Bioleaching can be used as a complementary process to pyrometallurgical and hydrometallurgical processes for extracting metals, as separation of cobalt and nickel is complex and requires additional solvent-extraction processes.In this process, microorganisms digest the metallic oxides from the cathode very specifically.Then metals are recovered from the metallic oxides by reducing the oxides (Jegan Roy et al., 2021;Roy, Cao, et al., 2021).
There is very little literature on the topic of using biological organisms for reclamation, leaving plenty of scope for future research.Figure 4 represents the comparison of the recycling methods.

| ENVIRONMENTAL IMPACT OF RECYCLING TECHNOLOGIES AND LIFE CYCLE ASSESSMENT MEASUREMENT
Li-ion batteries are one of the major parts of EVs, therefore much attention has been paid to the environmental performance of LIBs (Ellingsen et al., 2014).In most of the available environmental studies regarding LIBs and EVs till date, the EoL phase is missing.The reason behind this could be, in comparison to other industrial affairs and technologies, the LIBs recycling technology is still at its cradle (Rajaeifar et al., 2020).Thus, recycling can be considered as an emerging technology, as very few small, medium, and large-scale industries around the globe are operating LIB recycling.Usually, the recycling is considered beneficial when the environmental credits of recycled materials overshadowed the environmental impacts of recycling (Baars et al., 2021;Islam et al., 2022).
Life cycle assessment (LCA) is a well stablished and well-known method for evaluating the potential environmental impacts created by a product, system, service, or technology from its "cradle" to its "grave."Through the LCA analysis, it is possible to know the environmental feasibility of LIB recycling, whether the recycling increases the environmental burdens or decreases the environmental impacts.In Figure 5, the LCA of Li-ion battery from its "cradle" to "grave" has been depicted.
Only a few numbers of life cycle assessments of Li-ion batteries containing EoL phase are available in the literature and these LCA analysis are different from each other regarding their objectives, scope, type of battery chemistry, and the assessment methods used for the analysis.For example, Elwert et al. analyzed the environmental impact of hydrometallurgical recycling of NMC type Li-ion battery.They reported that most of the environmental benefits of recycling are coming due to the recycling of metal casing, and to some extent credits go to cathode recycling (Elwert et al., 2015).Rajaeifar et al. (2021) studied the LCA of pyrometallurgical technologies for recycling the nickel-manganese-cobalt (NMC111) based cathode materials from spent LIBs.They compared the environmental feasibility of open and close loop recycling.According to the results, closed loop recycling emits less GHG.The reduction in GHG by closed loop recycling is due to the re-entrance of recovered materials in LIBs manufacturing with simple treatment, meanwhile in the open loop recycling method the recycled materials are converted into new raw materials which is used in same or different manufacturing process.Mohr et al. summarized the net environmental impacts for various recycling techniques (current pyrometallurgical, current hydrometallurgical, and advanced hydrometallurgical technique) and different cell chemistries (NCA, NMC, and LFP).They reported that advanced hydrometallurgical recycling reduced the global warming potential (GWP) impacts of batteries by 12%-25%.Same reducing impact is observed for abiotic resource depletion potential (ADP) related with NMC and NCA type battery, but in case of LFP type battery, instead of decreasing the impacts hydrometallurgical recycling increases the environmental burden.In comparison with hydrometallurgical technique, the pyrometallurgy shows higher environmental burdens (high net impact) due to high temperature processing of the materials, higher energy consumption, and loss of Li in slag (Peters et al., 2020).Now a days LiFePO 4 and Li(NiCoMn)O 2 type Li-ion batteries are mostly used batteries in EVs.Xiang et al. assessed the environmental impact of different phases of LFP and NMC batteries by measuring 11 potential pollution aspects of these two batteries (Shu et al., 2021).The impact categories/aspects are summarized in Table 2.
The above table shows that recycling offsets environmental pollution in comparison with other phases of battery life.But it is not true always.Depending on battery chemistry, sometimes recycling can add environmental burden.Say F I G U R E 4 A layout of the processes followed by different industries around the world.
for example, recycling of NMC type battery caused toxicity (human, fresh water, and marine) rather than offsetting (Table 2).Batteries with different cathode chemistries have different environmental impacts.However, still there is a huge gap of knowledge regarding the environmental assessment of Li-ion battery recycling.Proper and rigorous LCA analysis of LIB, from its cradle to grave can lead us to correct pathway in the field of LIB recycling.

| OPPORTUNITIES AND CHALLENGES FOR RECYCLING OF SPENT LIBs
Many companies around the globe are piloting methods to reuse LIBs from various applications for a second purpose.In particular, spent EV batteries are being reused for applications in energy storage.Reuse is generally considered to be above recycling in the hierarchy of waste management systems, in order to extract the maximum economic value and minimize environmental impacts.However, even after calculating the benefits and possibilities of the second use of the batteries, recycling is the only alternative to landfilling process when this second use is at an end.Another consideration is that the environmental and economic viability of battery recycling relies on the rapid improvement of batteries, as the recycling process is currently dependent on the cobalt content of the battery.Due to global economic concerns, cathodes are currently produced with lower cobalt content.This provides minimal advantages and reduces the value of materials recovery using current recycling methods.The rise in the volume of the batteries brings up questions concerning the economic scale of recycling processes.The pyrometallurgical process is energy intensive and expensive, so other methods must be implemented to recover the bulk of components from spent LIBs, rather than focusing on a recycling process that only recovers components which have high economic value.
There are many potential opportunities for future recycling of spent LIBs.These opportunities include: increasing the range of recovery processes by incorporating automation in the disassembly process, smart evaluating, and selecting used batteries which are suitable for remanufacture, recycle, and reuse processes.This step provides many beneficial effects such as reduced cost, avoiding the risk of harming the human workers and providing a higher value to the recovered material.Existing designs of battery packs-particularly the adhesive compounds used, bonding techniques and fixtures-are not suitable for machine or hand deconstruction.Current cell-breaking processes involve milling or shredding of LIBs followed by sorting of material.This process reduces the financial value of the recovered materials.But this financial value can be restored if the materials are presorted.The direct recycling method can produce high purity materials by reducing contamination in the breaking stage, but this method is currently in the laboratory testing phase and requires manual disassembly of the battery.It is not currently feasible to implement direct recycling on commercial processing lines.There are also opportunities for battery manufacturers to improve the design of their products to make F I G U R E 5 Life cycle assessment (LCA) of Li-ion battery from its "cradle" to "grave."them more suitable for recycling at the end of their service life.For example, using water-soluble binders to allow the cathode to be easily separated during recycling.The bulk of this article has focused on experimental studies around the scientific considerations in LIB recycling.There are also several nontechnical challenges which influence the parameters of the recycling process of LIBs.These factors include: battery transportation, battery storage, and logistic factors for collecting end-to-life LIBs, and nature of their collection.These processes vary from country to country and place to place and follow various jurisdictions.Research is underway as part of the Faraday Institution ReLiB Project (UK) (Mrozik, 2019); the ReCell Project, (USA) (Mann, 2019); at the Commonwealth Scientific and Industrial Research Organization (CSIRO) in Australia (King et al., 2018), and is incorporated in several European Union projects including ReLieVe, Lithorec, and AmplifII (Pool, 2020).

| Small scale MICROfactories™ for LIB recycling
The innovative concept of small-scale "microrecycling" technologies can convert problematic spent LIBs into a range of value-added resources which could be used as feedstock for industrial applications.Researchers have demonstrated that LIBs waste can be reformed via selective thermal transformation of microrecycling technologies to provide a range of metal alloys that have enormous market value.For example, valuable cobalt, lithium, copper, and aluminum can be recovered simultaneously from spent LIBs using microrecycling techniques such as thermal disengagement followed by selective thermal transformation (Hossain et al., 2021;Hossain & Sahajwalla, 2022).The microrecycling technique, applies a combination of a range of recycling technologies (thermal, chemical, and direct) in a feasible manner and on small scale.Currently, the LIB recycling industry is struggling to maintain reasonable profit margins and economic sustainability as a consequence of low volumes of waste available for processing.Large-scale, industrial processing operations are expensive and energy intensive.These processes also depend on extensive collection and transport operations to deliver waste to recycling centers.This obstacle can be overcome by adopting microrecycling-based, small-scale microfactory technologies.Providing smaller operators with technology to process most of their own waste locally would reduce the need for transport and use of raw materials-as well as producing value-added, recycled, and reformed renewable materials.This is a win-win situation for society, the economy, and the environment.The novel MICROfactories™ could be established in cities as well as small towns, and rural and remote areas to reduce their reliance on centralized recycling industries.Decentralized MICROfactories™ could transform battery waste into valueadded materials at a local level via selective thermal transformation and contribute to global supply chains as well as meet local manufacturing needs with locally recovered materials.These solutions could contribute to "economies of purpose" by empowering the small operators.

| CONCLUSION
The rise in production and disposal of LIBs will continue as we navigate the continued demand for evolving consumer electronics and the transition from fossil fueled vehicles to EVs.The EV industry will have a global responsibility to reduce waste and extract value from end-of-life LIBs by designing, managing, and decommissioning the vehicles to make the most of this valuable secondary resource and reduce the social and environmental impacts of mining virgin materials such as cobalt.End-of-life waste should be kept to a minimum for social, environmental and safety reasons, and regional solutions for recycling spent LIBs would reduce the need for stockpiling, landfill and transporting of spent batteries.This could include small-scale solutions, such as microrecycling, when there is not sufficient waste volume to make large scale recycling economically viable.There are several processes for reuse and recycling of spent LIBs, including reusing spent batteries in a second application (e.g., energy storage for spent EV batteries).However, the batteries must be recycled after the second use to avoid being landfilled.Among all the existing recycling techniques, direct recycling is an emerging technique which could reduce the effect of metal contamination from electrode casing.Bioleaching has the potential to be used in conjunction with the pyrometallurgical technique, and developments in computer vision, AI and robotics will increase opportunities to further automate battery disassembly in the coming years.It is a very essential requirement for the spent LIBs specially from EVs to recycle at the EoL for various reasons.As there is not much significant research and advancement on LIBs recycling from EVs have been achieved till today, this leads to invent convenient and profitable processes in the recycling of LIBs from EVs In most countries, the materials from battery components are not completely accessible, which can add value to the supply chain of the economy.These critical materials are used as a valuable secondary resource in EVs.The future automobile industries have a key factor in making the batteries more sustainable if the manufactured batteries are easier to recycle and maintained in a controlled manner.
DATA AVAILABILITY STATEMENT Data will be available on request.

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I G U R E 1 Water level depletion due to pumping of mineral rich solution (L opez Steinmetz & Fong, 2019).
Consequences of heat generated from a short circuit during battery dismantling; (b) different cell designs of LIBs.
Common cathode active materials in LIBs.