Lithium-ion battery recycling
Added: 11. 4. 2022 09:20:42 Views count: 286
11 April 2022
Lithium-ion battery recycling
The rapid growth of the electric car market is essential to meet global targets for reducing greenhouse gas emissions, improving air quality in urban centers and meeting the needs of consumers. Moreover electric vehicles are increasingly popular among drivers.
However, the growing number of electric cars is a serious waste management problem. Nonetheless, depleted batteries also provide an opportunity to gain access to strategic elements and critical materials and are a valuable secondary resource. So there are many incentives to take this issue seriously.
In the article you will find:
- Lithium or lithium-ion batteries cover a whole range of different types of batteries
- What is the current approach to dealing with batteries that are no longer used to power electric cars
- The main challenges of battery recycling
- Current approaches to recycling their advantages and disadvantages
- Mechanical processing
- Hydrometallurgical processing
- Pyrometallurgical processing
- Bio recycling
- Other aspects that need to be considered for battery recycling in the future
Lithium batteries are not alike
Although “lithium batteries” appear to be just one type of battery, in fact, the chemical reactions that take place within each of them can vary widely. Moreover there are many differences in their design and arrangement of individual modules and cells.
The battery generally contains a cathode, an anode, a separator, an electrolyte and a housing with a sealing function. In all lithium batteries, it is the lithium ions that transfer the charge through the electrolyte from the anode to the cathode. But here the similarity of lithium batteries often ends.
Lithium passes through an open structure, which may consist of layers or tunnels. The anode is generally graphite of differing shape, and also the cathode can have different chemical compositions and structures, resulting in different battery properties.
Each technology has its advantages and offers different compromises. In addition, the chemical reactions in the batteries have improved over time and continue to do so.
Batteries for electric vehicles have a complex design, they contain various cable harnesses, buses and electronics. They consist of various modules and cells. There are also many different types of fasteners, including various screws, adhesives, sealants and solders.
Unfortunately, this means that the batteries from two different cars are very different, which must be reflected in how they can be disposed of when they are no longer suitable for use in electric cars.
Why every battery is different
The design and construction of the vehicle and batteries must find a compromise between crash safety, center of gravity, space optimization, serviceability and other demands. These conflicting goals often lead to designs that do not optimize batteries for recyclability and can be extremely difficult to disassemble.
There is currently no standardization of design for batteries, modules or cells and this is unlikely to happen in the near future.
Other battery-dependent products, such as mobile phones, have seen an exponential increase in battery sizes, shapes and types over the last two decades. At present, much of the factory assembly of these batteries is performed by human workers and remains non-automated. Their dismantling and waste management usually involve an even less automated environment with much higher risks than the production assembly line had.
Waste management hierarchy
The basic waste management scheme consists of five stages, each of which is worse from an economic and environmental point of view. Efforts should therefore be made to deal with waste at the highest level possible.
The basic steps of waste management from the most ecological to the least ecological are:
- Prevention - striving to ensure that batteries have the longest possible life, are as light and small as possible, and therefore minimize waste. This step is the responsibility of the engineers who design the batteries.
- Re-use - means that electric vehicle batteries should be used in some other place if they are no longer suitable for the needs of the car. Usually as energy storage in places where it is needed.
- Recycling - seeks to recover as much of the materials used in the batteries as possible.
- Recovery - the use of some battery materials as energy for other recycling processes. At the moment, some battery parts are used as fuel in pyrometallurgy.
- Disposal - means that no value is recovered from the battery and the waste goes to a landfill.
In the waste hierarchy, reuse or second life of batteries is considered much more advantageous than recycling. Over time, however, the supply of used electric vehicle batteries is expected to far exceed the amount that the second-hand market can absorb. So sooner or later, recycling is the inevitable fate of every battery.
Because the accumulation of used batteries is potentially dangerous and very environmentally highly undesirable, recycling must be the last step of every battery in their life cycle.
This is because electrolytes in batteries contain harmful substances, such as organic solvents and lithium salts containing fluorine, which can cause great damage to the environment. Therefore, if unnecessary batteries get directly into the environment, they will cause an irreversible environmental disaster.
In addition to the high environmental burden in case of problems, precious metals contained in batteries, such as lithium, cobalt, nickel, copper, aluminum and others, speak for recycling. In the electrode, the average lithium content is about 5% of its weight, which is much higher than the content in natural ores, and the battery therefore has a considerable recycling value.
Reuse or second life of batteries
Nowadays, when deciding whether to recycle or reuse, reuse clearly wins because it is less expensive and also improves the ratio of energy invested in the production of the battery to the energy that the battery has stored over its lifetime. This will improve the overall efficiency of the energy storage technology.
In second-use applications, battery performance is less critical, making used electric vehicle batteries exceptionally suitable for this purpose.
Energy storage markets are evolving rapidly as energy regulators move to cleaner energy sources in various places. Energy storage is therefore in great demand in areas where a high share of renewable energy requires balancing supply with demand or where weak networks require reinforcement.
A healthy market for used batteries for electric energy storage vehicles in certain locations is already developing, with demand still exceeding supply. Today, these projects are developing mainly in places where there are market regulations.
The main challenges of battery recycling
Sooner or later, each battery will be recycled, which currently presents many different challenges.
Due to the short history of electromobility, a systematic recycling system has not yet been established.
The problem for recycling is mainly:
- high energy density,
- significant danger to staff,
- currently low price of some used elements,
- big differences and variety in batteries.
Some commercial companies are already announcing that they can recycle up to 80% of batteries through a combination of mechanical and chemical recycling processes and recover 95% of their precious metals through a chemical recycling process.
However, the recycling system still does not look so optimistic that it certainly cannot handle all the batteries that travel around the world today.
Battery recycling. Source: https://www.autoweek.com/news/green-cars/a35803612/battery-recycling/
Battery recycling involves both physical (mechanical) and chemical processes. Chemical processes can be divided into pyrometallurgical and hydrometallurgical, which usually involve leaching, separation, extraction and chemical / electrochemical precipitation.
Many different names are used for this recycling step: physical processes, mechanical processing or direct recovery. It is a process of recovering useful components from depleted batteries without the use of chemical methods.
Mechanical processing usually involves previous treatment of batteries. The batteries are usually discharged or stabilized before handling. The modules and cells are then disassembled, broken and sorted. Electrolytes are also mostly extracted from them. Finally, the cathode material is collected.
Mechanical processing makes it possible to recover plastics, aluminum, copper and so-called black matter. The black matter contains critical metals and is collected and then taken over for hydrometallurgical processing. Other materials are recycled in separate processes.
The advantages of mechanical processing are:
- short recovery path,
- low energy consumption,
- environmental friendliness
- and a high recovery rate.
The advantage of direct recycling is that, in principle, all battery components can be recovered and reused after further processing.
However, it is not clear whether the recycled material will achieve the long-term properties of the new material. The efficiency of direct recycling processes correlates with the health of the battery and may not make much sense if this condition is poor.
Once batteries are recycled, three main processes must take place:
- and separation.
These processes can be performed separately or together. Battery stabilization can be achieved with saline or ohmic discharge. However, stabilization during opening is currently the industry's preferred route because it minimizes costs. It consists of crushing batteries in an inert gas such as nitrogen, carbon dioxide or a mixture of carbon dioxide and argon.
Stabilization is not the same as discharge
Battery cells can be shredded at various states of charge, and from a commercial point of view, discharging before crushing increases the costs. In addition, it remains unclear exactly what the optimal discharge level should be. Depending on the chemistry of the cell, excessive discharge of the cells can lead to dissolution of the copper in the electrolyte. The presence of this copper is detrimental to the regeneration of materials, as it can then contaminate other materials, including the cathode and separator.
Hazards and problems associated with mechanical recycling
Different manufacturers have chosen different approaches to powering their vehicles, and electric vehicles on the market have a wide range of different physical configurations, cell types and chemicals.
1. Different types of battery cells
Each battery cell has specific recycling issues. Cylindrical cells are often bonded to the module with an epoxy resin that is difficult to remove or recycle. Prismatic cells require "can opening", which can be achieved only with special tools. The high manganese content of Nissan shell cells, in turn, makes recycling less cost-effective because manganese is cheap. However, these cells are the least problematic to open and physically separate for direct recycling.
2. Recycling automation
Vehicles have very different physical battery configurations that require different disassembly approaches, making automation almost impossible. The format of the batteries and the relative sizes of the various components vary. Different forms and sizes can also limit tool reuse. In addition, manufacturers use different chemical compositions of cells, which also requires different approaches and has a strong impact on the overall recycling economy.
3. Lack of professional staff
The high weight and high voltage of the batteries mean that such disassembly requires qualified personnel and specialized tools, which is a great challenge for the emerging industry.
In addition, disassembling battery packs from electric vehicles requires high voltage training and insulated tools to prevent electric shock or battery short circuit. A short circuit results in a rapid discharge, which can lead to heating and heat leakage. Heat leakage can result in very harmful by-products and, together with other gases, can lead to an explosion.
Pyrometallurgy is widely used for the commercial extraction of cobalt. Commonly used pyrometallurgical processing of used batteries is similar to smelting ore. Before the melting process, the batteries are first disassembled into separate cells and then sent to a heating furnace. The batteries are gradually reduced by preheating, pyrolysis and melting.
This process is particularly suitable for the recycling of conventional consumer batteries, as it can be applied to imperfectly sorted raw materials from battery cells. They can be treated together with other types of waste, which also improves the thermodynamics of the whole process.
This versatility is also valuable with regard to batteries for electric vehicles, because the current collectors also help the melting process. This technique has the important advantage that it can be used with whole cells or modules without the need for prior stabilization.
Pyrometallurgical recycling processes are theoretically able to accept entire electric vehicle modules without further disassembly. However, this solution fails to recycle much of the energy that goes into battery production and, in addition, leaves a lot of work to the techniques of chemical separation (hydrometallurgy) because the battery materials mix even more.
Advantages and disadvantages of pyrometallurgy
There is a relatively small safety risk in this process because the cells and modules are exposed to extreme temperatures with a metal recovery reducing agent. In addition, the combustion of electrolytes and plastics produces heat, thus reducing the energy consumption required for this process.
The disadvantage is that in the pyrometallurgical process:
- usually does not take into account the regeneration of electrolytes and plastics (approximately 40-50% of the battery weight) or other components such as lithium salts.
- Other environmental problems arise as this process produces toxic gases that need to be captured and remediated.
- Subsequent hydrometallurgical processing is required.
- The whole process is highly energy demanding.
Despite all the problems, this process is often used to extract high-value metals such as cobalt and nickel. Thermal metallurgy is highly efficient, especially in the production of cobalt, thus the economics of this method depend to a large extent on the amount of cobalt contained in the batteries used and on fluctuations in its market value.
Given all its problems and, above all, the limited resources of lithium, which is coming to the forefront of raw material recovery, this traditional method does not have much development prospects.
Pyrometallurgical process. Source: https://www.metallurgyfordummies.com/pyrometallurgy.html
The hydrometallurgical recycling process typically comes after the battery has been previously treated. It includes a method of chemical or biological leaching and precipitation, which makes it possible to recover rare minerals from the black matter and can then return them to battery manufacturers for reuse in the production of new batteries.
Hydrometallurgical treatments involve the use of solutions to leach the desired metals from the cathode material. In this process, it is necessary to determine and monitor the whole set of conditions to achieve the optimal leaching rate:
- leaching acid concentration,
- solution temperature,
- solid to liquid ratio
- and adding a reducing agent.
Methods and processes are still being sought to obtain the highest possible yield and purity from battery materials. The processes vary according to the physical and chemical properties of the materials in the batteries, including their morphology, density, magnetism and other properties.
Some processes achieved a recovery rate of 99% for lithium, 93% for cobalt, 91% for nickel and 94% for manganese. Very high results were also achieved using bioleaching, for which bacteria and fungi are used.
Bio recycling of metals
Bioleaching, in which bacteria are used to extract precious metals, is successfully used in the mining industry. It is an emerging technology that can also be used for battery recycling and metal reclamation and is a potential complement to hydrometallurgical and pyrometallurgical processes.
Cobalt and nickel in particular are difficult to separate using normal processes and require additional solvent extraction steps. The process of using microorganisms to selectively digest metal oxides to form metal nanoparticles seems to be a promising path. However, the number of studies performed so far is relatively small.
Conclusions and future prospects
Each of these recycling processes offers certain benefits and presents certain challenges in the future. What is certain is that batteries cannot end up in landfills with other waste, as they are a significant environmental hazard and also contain precious metals, whose natural resources are being significantly depleted.
Recycling is therefore a clear imperative for the future of electric cars.
The main challenge lies not only in the recycling processes themselves, but also in the design of batteries that take into account the need for future recycling. The following options will need to be considered:
- Advanced sensors and improved methods for battery monitoring in the field and end-of-life testing would allow the characteristics of individual batteries to best match the proposed applications for second use. Accompanying advantages would be higher safety and higher market value.
- Proper labeling of batteries and their composition so that recyclers know how best to dispose of them and making sure that the labeling itself is not a hazard to battery operation. It would be ideal to implement labels, QR codes, RfID labels or other machine readable elements on key battery components and substructures.
- The ideal solution would be if battery composition information was publicly available. As long as this information is private, there is only a limited scope of how it can be truly useful to recyclers. Battery classification by electrode type is a minimum requirement.
- Initiatives towards standardization and open data formats would greatly facilitate the whole recycling process. World-class legislative cooperation would be ideal in this regard.
- China has already indicated its intention to monitor battery materials. One solution to recycling problems would be a blockchain that would allow battery materials to be traced throughout the life cycle, including information and transparency on the origin of these materials and ethical supply chains. The information could also include the health of the battery and its previous use.
- Utilization of processes which, in addition to cobalt, will be able to recover nickel, manganese and lithium from the battery, the stocks of which are becoming a major problem.
- We should also focus on recycling and recovering other materials, which may not be as valuable in themselves, but may pose a risk to the environment, such as electrolytes.
- Current recycling processes should also lead to a reduction in greenhouse gas emissions compared to the primary production. More efficient processes are needed to improve both the environmental and economic viability of recycling.
At present, the volumes of electric vehicle batteries that require recycling are still small. As these volumes grow, economies of scale in relation to recycling will need to be addressed. And alternative methods will be needed rather than recycling only the most economically valuable components.