The waste-management hierarchy considers re-use to be preferable to recycling (Fig. 1). As considerable value is embedded in manufactured LIBs, it has been suggested that their use should be cascaded through a hierarchy of applications to optimize material use and life-cycle impacts2. Energy stored over energy invested (ESOI)—the ratio between the energy that must be invested into manufacturing the battery and the electrical energy that it will store over its useful life—is a metric used to compare the efficacy of different energy-storage technologies. Clearly, ESOI figures will improve if end-of-life electric-vehicle batteries can be used in second-use applications for which the battery performance is less critical.

Profitable second-use applications also provide a potential value stream that can offset the eventual cost of recycling, and already a healthy market is developing in used electric-vehicle batteries for energy storage in certain localities, with demand potentially outstripping supply. For the moment the economics of the decision whether to recycle or re-use are set firmly in favour of re-use. The main factors are (1) the refurbishment cost of putting the battery into a second-use application and (2) any credit that would accrue as the result of recycling the battery instead; if the second-use price were to fall below the sum of the refurbishment cost and the recycling credit, then recycling would be the economically favoured option19. In time, it is anticipated19 that the supply of used electric-vehicle batteries will far exceed the quantity that the second-use market can absorb. It must be remembered, therefore, that—if disposal to landfill is to be avoided—recycling must be the ultimate fate of all LIBs, even if they first have a second use.

Given that stockpiling of waste batteries is potentially unsafe and environmentally undesirable, if direct re-use of an LIB module is not possible, it must be repaired or recycled. End-of-life LIB recycling could provide important economic benefits, avoiding the need for new mineral extraction20 and providing resilience against vulnerable links21 and supply risks22 in the LIB supply chain. For most remanufacture and recycling processes, battery packs must be disassembled to module level at least. However, the hazards associated with battery disassembly are also numerous23,24. Disassembly of battery packs from automotive applications requires high-voltage training and insulated tools to prevent electrocution of operators or short-circuiting of the pack. Short-circuiting results in rapid discharge, which may lead to heating and thermal runaway. Thermal runaway may result in the generation of particularly noxious byproducts, including HF gas25, which along with other product gases may become trapped and ultimately result in cells exploding23. The cells also present a chemical hazard owing to the flammable electrolyte, toxic and carcinogenic electrolyte additives, and the potentially toxic or carcinogenic electrode materials.

Diagnostics of battery pack, modules and cells

‘State of health’ is the degree to which a battery meets its initial design specifications. Over time as the battery degrades, its performance varies from its initial condition. The units are percentage points, with 100% indicating a state of health that is identical to that of a new battery meeting its design specification. (Some new batteries may leave the factory deviating from design specifications, and having less than 100% state of health.) The ‘state of charge’ is the degree to which a battery is charged or discharged. Again, the units are percentage points, with 0% indicating empty and 100% indicating full).

Battery repurposing—the re-use of packs, modules and cells in other applications such as charging stations and stationary energy storage—requires accurate assessment of both the state of health, to categorize whether batteries are best suited for re-use (and if so, for which applications), remanufacture or recycling, and the state of charge, for safety reasons in some recycling processes. For high-throughput triage and gateway testing of batteries at scale, the optimal approach involves in situ techniques for monitoring cells in service to enable advance warning of possible cell replacement, and module or pack reconditioning, rather than complete repurposing at a low level of state of health owing to a few failing cells.

Electrochemical impedance spectroscopy can give information on the state of health of cells, modules and, potentially, full packs26, and also an indication of aging mechanisms such as lithium plating. Such measurements have the potential to inform a decision matrix for re-use or disassembly and processing and, importantly, to identify potential hazards that would have further consequences for downstream processing. Electrochemical impedance spectroscopy has been researched for gateway testing in primary production, for example, in a large battery production plant in the UK27,28. A number of electric-vehicle manufacturers plan to use similar technologies to manage and maintain electric-vehicle battery packs through the identification and replacement of failing modules in the field. Substantial advantages in cost, safety and throughput time are anticipated if this process can be mostly or fully automated27,29. In future, more advanced diagnostic functionality will be embedded in battery management systems, providing data that can be interrogated at end-of-life.

Challenges of pack and module disassembly

Different vehicle manufacturers have adopted different approaches for powering their vehicles, and electric vehicles on the market possess a wide variety of different physical configurations, cell types and cell chemistries. This presents a challenge for battery recycling. Figure 2 details three different types of battery cell design, and their respective packs from electric vehicles in the marketplace from model year 2014. It can be seen that the three vehicles possess very different physical configurations, requiring different approaches for disassembly, particularly regarding automation. It can be seen in Fig. 2 that at the different scales of disassembly, the format and relative size of the different components differ, presenting challenges for automation. The differing form factors and capacities may also restrict applications for re-use. And finally, Fig. 2 illustrates that manufacturers employ varying cell chemistries (see Fig. 3), which will necessitate different approaches to materials reclamation and strongly affect the overall economics of recycling. Whereas the prismatic and pouch cells have planar electrodes, the cylindrical cells are tightly coiled, presenting additional challenges to separating the electrodes for direct recycling processes.

Fig. 2: Examples of three different battery packs and modules (cylindrical, prismatic and pouch cells) in use in current electric cars. The three designs examined are from model year 2014; this is based on the availability of information from vehicle teardowns, and also because older vehicles are more likely to be closer to end-of-life than today’s new cars. The breakdowns include material content in a cell, layout and content of the module and pack and the proportion of critical elements (high economic importance, but at risk of short supply) and strategic materials (either high economic importance or risk of short supply) used. The Nissan pouch cells from Automotive Energy Supply Corporation (AESC) exhibit a mixed cathode chemistry with substantial manganese content and relatively low levels of cobalt. The Tesla cylindrical 18650 cells from Panasonic and the BMW prismatic cells from Samsung SDI both contain high cobalt levels. Each cell has particular recycling challenges. Cylindrical cells are often bonded into a module using epoxy resin (difficult to remove or recycle); fuses at each end may be blown, making cell discharge challenging; and the cell geometry can be difficult to dismantle for direct recycling. Prismatic cells require ‘can opening’ (requiring special tools) to remove the contents. These large cells are under considerably more pressure than are the pouch or cylindrical cells, and can therefore be hazardous to open if the contents have degassed. The high manganese content of the Nissan pouch cells makes pyrometallurgical recycling less cost-effective, because manganese is cheap, but these cells are the least problematic to open and physically separate for direct recycling. Full size image

Fig. 3: LIB cathode chemistries. The term LIB covers a range of different battery chemistries, each with different performance attributes. The basic concept of a LIB is that lithium can intercalate into and out of an open structure, which consists of either ‘layers’ or ‘tunnels’. Generally the anode is graphite but the cathode material may have different chemistries and structures, which result in different performance attributes and there are trade-offs and compromises with each technology. The cathode chemistries of LIBs have a large impact on the performance of LIBs, and these chemistries have evolved and improved. Fig. 3 presents a summary of the different LiB cathode chemistries. Full size image

For repurposing and second-use applications, automotive battery packs are currently dismantled by hand for either the second use of the modules or for recycling. The weights and high voltages of traction batteries mean that qualified employees and specialized tools are required for such dismantling25. This is a challenge for an industry in transition with a shortage of skills. An Institute of the Motor Industry survey found only 1,000 trained technicians in the UK capable of servicing electric vehicles30, with another 1,000 in training. Given there are 170,000 motor technicians in the UK, this represents less than 2% of the workforce. There is concern that untrained mechanics may risk their lives repairing electric vehicles31, and these concerns logically extend to those handling vehicles at the end-of-life. Additionally, it has been suggested32 that manual dismantling, in countries with high labour costs, is uneconomic with respect to revenues from extracted materials or components. Vehicle design has to strike compromises between crash safety, centre of gravity and space optimization, which must be balanced against serviceability25. These conflicting design objectives often result in designs that are not optimized for recyclability, and that can be time-consuming to disassemble manually25.

Automating battery disassembly

Robotic battery disassembly could eliminate the risk of harm to human workers, and increased automation would reduce cost, potentially making recycling economically viable. This is being piloted in a number of current research projects33,34,35,36. Importantly, automation could also improve the mechanical separation of materials and components, enhancing the purity of segregated materials and making downstream separation and recycling processes more efficient. The automation of the dismantling of automotive batteries, however, presents major challenges. This is because robotics and automation in the manufacturing sector rely on highly structured environments, in which robots make pre-programmed repetitive actions with respect to exactly known objects in fixed positions. In contrast, the development of robotic systems that can generalize to a variety of objects, and handle uncertainty, remains a major challenge at the frontier of artificial intelligence research. It is important to consider the complexity of vehicle battery disassembly from this perspective.

At present there is no standardization37 of design for battery packs, modules or cells within the automotive sector, and it is unlikely that this will happen in the near future. Other battery-reliant products, such as mobile phones, have seen an exponential proliferation of different sizes, shapes and types of battery over the past two decades. At present, much of the factory assembly of these batteries is done by human workers and remains unautomated. Their disassembly and waste-handling typically involve even less structured environments, with much greater uncertainties, than a manufacturing assembly line.

Nevertheless, some progress has been made towards automated sorting of consumer batteries. The Optisort system38,39 uses computer vision algorithms to recognize the labels on batteries, and then pneumatic actuators to segregate batteries into different bins according to their type of chemistry. However, Optisort is currently limited to AA and AAA batteries, and a large amount of pre-sorting by hand is needed to separate these from mixed batches of waste batteries, prior to entering the Optisort machine.

The Society for Automotive Engineers and the Battery Association of Japan have both recommended labelling standards for electric-vehicle batteries. Recent algorithms from computer vision research have some capability to recognize objects and materials on the basis of features such as size, shape, colour and texture. However, it could be advantageous for recycling if manufacturers were to (some manufacturers already do) include labels, QR Codes, RfID tags or other machine-readable features on key battery components and sub-structures. Where these provide a reference to an external data source, its utility in aiding the recycling process will depend on the accessibility and format of that data. If proprietary and private, such data are of limited use, but there may be initiatives to move towards standardization and open data formats. A number of companies are considering blockchain technologies to provide whole-life-cycle tracking of battery materials, including information and transparency on provenance, ethical supply chains, battery health and previous use40. China has signalled its intention to track battery materials.

Automated disassembly of electrical goods has also been implemented to some extent in other sectors. For example, Apple has implemented an automated disassembly line for the iPhone 641 that can handle 1.2 million phones per year. This line has 22 stations linked on a conveyor system and can take the iPhone apart in 11 seconds. However, this system can only deal with an iPhone 6 model. Intact phones, of this exact model, must be positioned at the start of the disassembly line, which then uses pre-programmed motions of 29 robots in 21 different cells to dismantle the phone into 8 discrete parts. The LIB is removed by heating the glue which holds the battery in place. Owing to the potential fire hazard, this must take place inside a thermal event protection system, while monitoring the battery using a thermal imaging system.

Unfortunately, 1.2 million phones per year is a drop in the ocean and the Apple disassembly line has been created using conventional industrial automation methods, making it inflexible and incapable of keeping up adaptively with new models and varieties of phones. But building a flexible and adaptable robot disassembly line need not be prohibitively expensive. The challenge is to create control algorithms and software that can make cheap hardware (robot arms cost only several thousands to several tens of thousands of dollars and costs have been steadily decreasing, can work all the time, and have very long service lifetimes) behave flexibly and intelligently to handle hugely complex disassembly problems. If those artificial intelligence challenges can be solved, then the capital investment required to respond to new and changing models could be kept remarkably low (mainly software updates would be needed). Making robots behave intelligently will rely heavily on sensors to enable advanced robotic perception, especially computer vision using three-dimensional RGB-D imaging devices, combined with bespoke sensors from materials and battery experts. The robots will also require tactile and force-sensing capabilities to handle the complex dynamics problems of forceful interactions between the robots and the materials being disassembled.

Owing to the complexity of automotive battery packs, the possibility of collaborative human–robot co-working using a new generation of force-sensitive ‘co-bot’ robot arms33,42 has been suggested. Unlike conventional industrial robots, these co-bots can safely share a workspace with humans, and Wegener33 suggests that the robot could be taught tasks such as unscrewing bolts, while the human handles cognitively more complex tasks. However, this approach does not protect the human worker from battery hazards and even the task of locating a bolt, moving a tool to engage with it, unscrewing and removing it represents a cutting-edge research challenge in robotics and machine vision. Using current industrial robotics methods, the problem only becomes attemptable (but still difficult) provided that the position of the bolt head is always exactly fixed, in a known pose relative to the robot, with very high precision.

State-of-the-art robotics, computer vision and artificial-intelligence capabilities for handling diverse waste materials do exist, and these systems have demonstrated sufficient robustness and reliability to gain acceptance by the UK nuclear industry, for example, in the deployment of artificial-intelligence-controlled, machine-vision-guided robotic manipulation for cutting of contaminated waste material in radioactive environments43. These technologies are now being adapted to the demanding problem of robotic battery disassembly. At different scales of disassembly—pack removal, pack disassembly, module removal and cell separation—different challenges and barriers to automation exist. Some of these are set out in Fig. 4. Computer-vision algorithms are being developed that can identify diverse waste materials and objects44, reliably track objects in complex, cluttered scenes45, and dynamically guide the actions of robot arms46. Dismantling requires forceful interaction between robots and objects, engendering complex dynamics and control problems, such as simultaneous force and motion control47, which is needed for robotic cutting or unscrewing. Dismantled materials must be grasped and manipulated, including fragmented or deformable materials, which pose challenges both to vision systems and autonomous grasp planners. Adjigble et al.48 have recently demonstrated state-of-the-art performance in autonomous, vision-guided robotic grasping of arbitrary objects from random, cluttered heaps. These advances in computer vision, artificial intelligence and robotics fundamentals offer exceptionally promising tools with which to approach the extremely difficult open research challenge of automated disassembly of electric-vehicle batteries.

Fig. 4: Diagram showing challenges of disassembly at different levels of scale. Electric-vehicle battery packs are complex in design, containing wiring looms, bus bars, electronics, modules, cells and other components. There are also many different types of fixtures and fastenings, including screws, bolts, adhesives, sealants and solders, which are not designed for robotic removal. Full size image

Stabilization and passivation of end-of-life batteries

Once LIBs have been designated for recycling, the three main processes involved consist of stabilization, opening and separation, which may be carried out separately or together. Stabilization of the LIB can be achieved through brine or Ohmic discharge. In-process stabilization during opening, however, is the current route preferred in industry, as it minimizes costs. This consists of shredding or crushing the batteries in an inert gas such as nitrogen, carbon dioxide, or a mixture of carbon dioxide and argon. State-of-the art physical processing of LIBs in Europe and North America includes the Recupyl8 (France), Akkuser49 (Finland), Duesenfeld50 (Germany) and Retriev51 (USA/ Canada) processes. Large-scale European processes do not currently use stabilization techniques prior to breaking cells open, instead opting for opening under an inert atmosphere of carbon dioxide or argon (with less than 4% molecular oxygen). Opening under carbon dioxide allows for the formation of a passivating layer of lithium carbonate on any exposed lithium metal. The Retriev process differs from the European processes in that it uses a water spray during the opening step51. The water hydrolyses any exposed lithium and acts as a heatsink, preventing thermal runaway during opening.

Discharging through salt solutions or ‘brine’ (seawater has been used previously52,53) is an alternative method that is supposed to render the cells safe via the corrosion and subsequent water leaching into the cells that passivates the internal cell chemistries. Aqueous solutions of halide salts have been shown to result in substantial corrosion at the battery terminal ends, whereas alkali metal salts, such as sodium phosphate, produce much less corrosion with no water penetration, offering the possibility that cells could be assessed and re-used53. This represents a considerably safer discharging method than using seawater; however, competing electrochemical reactions do occur. Oxygen, hydrogen and other gases, such as chlorine (depending upon the salts in the brine), will form at the anode and cathode terminals, and can potentially be collected, though the dangers and difficulties associated with this should not be underestimated. The time for complete discharge is dependent on the solubility of the salt and hence the conductivity of the solution; increasing the temperature will also shorten the discharge time. Once discharge is complete, the cell components can be separated into different materials streams for further processing: steel can or laminated aluminium, separator, anode (graphite, copper, conductive additive), binder and cathode (active material, aluminium, carbon black, binder).

The brine discharge method is not suitable for high-voltage modules and packs, owing to the high rate of electrolysis and vigorous evolution of gases that would occur. However, for low-voltage modules and cells (or once a high-voltage pack has been dismantled into its constituent components) where the electrolysis can be more carefully controlled, this could, in principle, offer a method of discharge in which the hydrogen and oxygen could be recovered for other applications, adding to the cost-effectiveness of the process54. The downside, however, is that contamination of the cell contents threatens to complicate the downstream chemical processes or compromise the value of processed materials streams.

An alternative to the use of salt solutions is direct Ohmic discharge of the battery through a load-bearing circuit. If the electricity can be reclaimed from the discharge, this could offset some of the cost of further processing. To put it into context, the domestic consumption of a standard UK home is up to 4,600 kWh per year. So a 60-kWh battery pack at a 50% state of charge and a 75% state of health has a potential 22.5 kWh for end-of-life reclamation, which would power a UK home for nearly 2 hours. At 14.3 p per kWh, this equates to UK£3.22 per pack, which may seem a modest gain that does not warrant the cost of investing in equipment. However, if it is unrecovered, the energy from discharge must be dissipated, and this will add to the cooling burden of the facility, creating additional costs. Furthermore, an economy of scale is to be anticipated when recycling electric vehicle batteries in bulk. Similarly, reclaimed energy might make a useful contribution to the profitability of repurposing for second use (see section ‘Battery assessment and disassembly’).

LIB cells can be shredded at various states of charge, and from a commercial point of view, if discharged modules or cells are to be processed in this way, discharge prior to shredding adds cost to the processes. Furthermore, exactly what the optimum level of discharge might be remains unclear. Depending on cell chemistry and depth of discharge, over-discharging of cells can result in copper dissolution into the electrolyte. The presence of this copper is detrimental for materials reclamation as it may then contaminate all the different materials streams, including the cathode and separator. If the voltage is then increased again or ‘normal’ operation resumed55, this can be dangerous because copper can reprecipitate throughout the cell, increasing the risks of short-circuiting and thermal runaway.

Current LIB-processing technologies essentially bypass these concerns by feeding end-of-life batteries directly into a shredder or high-temperature reactor. Industrial comminution technologies can passivate batteries directly but recovered battery materials then require a complex set of physical and chemical processes to produce usable materials streams. Pyrometallurgical recycling processes (see section ‘Stabilization and passivation of end-of-life batteries’) at scale may be able to accept entire electric-vehicle modules without further disassembly. However, this solution fails to capture much of the embodied energy that goes into LIB manufacture, and leaves chemical separation techniques with much to do as the battery materials become ever more intimately mixed.