Current state of science and technology
Lithium-ion batteries have become an integral part of our everyday lives. While they were initially mainly used in portable devices such as cell phones or notebooks, today they can be found - whether permanently installed or replaceable - in almost every area, such as electronic devices, power tools, remote-controlled vehicles and, of course, all areas of electromobility.
The reason for the popularity of these batteries is their high energy density combined with high power density. Depending on the cell chemistry used, around 100 to 200 Wh/kg of energy can be stored, in some cases even up to 250 Wh/kg. This means that a large amount of electrical energy can be stored at a comparatively low weight.
However, the production of these batteries requires at least the lithium that gives them their name and, depending on the cell chemistry, also metals such as nickel and cobalt. Extracting these as primary raw materials is one of the biggest problems for battery production in Europe. The largest deposits of these raw materials are located outside the EU, and in some cases their extraction is linked to environmental damage or human rights violations. In Chile's Salar de Atacama, for example, lithium is extracted by pumping the salty water from underground to the surface and evaporating it in basins. The high water consumption leads to a drop in the groundwater level, with negative consequences for the environment. Cobalt, on the other hand, is mainly produced in the Democratic Republic of Congo. Mining often takes place under precarious conditions in unsecured mines, often using child labor. Efficient recycling is therefore an important factor for the EU, both for economic, environmental and human rights reasons.
European legislation on battery recycling
At the end of 2023, the EU adopted the new Regulation 2023/1542 to bring the legislation on batteries, and waste batteries in particular, up to date. As an EU regulation, it is directly applicable in all EU member states and (unlike EU directives) does not require national legislation.
The new directive specifies minimum recycled content levels that must be achieved for the production of new batteries. This applies to cobalt, lead, lithium and nickel. Recycling efficiencies and material recovery for cobalt, copper, lead, lithium and nickel are also specified. TheCO2 footprint of batteries also plays a major role in the regulation. This is to be determined for the entire life cycle of the battery and therefore also includes recycling.
A major innovation introduced in the EU regulation is the digital battery passport. This should make it possible to retrieve information about each battery and track the status of the battery until it is recycled.
For lithium-ion batteries, specifically batteries for electric cars and rechargeable industrial batteries, the specific requirement is that a recycling efficiency of 65% is achieved from the end of 2025 and 70% from the end of 2030. For material recycling, a value of 90% must be achieved for cobalt, copper and nickel and 50% for lithium from the end of 2027. By the end of 2031, these values will increase to 95% and 80% respectively.
Fundamentals of lithium-ion batteries
Fig. 1: Structure of a lithium-ion battery The typical structure of a lithium-ion battery is shown in Figure 1. Both electrodes consist of a metal foil that serves as a current conductor, which is coated with the actual active material in which the electrochemical reaction takes place. On the cathode side, an aluminum foil is used, which is coated with a mixed metal oxide containing lithium. This is where the largest selection of materials can be used. In most cases, cobalt, nickel and manganese are used alone or in combination, although the proportions can vary. Combinations of all three metals are used most frequently (NMC batteries). Lithium iron phosphate (LFP) is also the most widely used. A copper foil is used on the anode side, which is usually coated with graphite. The electrolyte consists of an organic solvent (a mixture of carbonates and additives) in which the so-called conductive salt is dissolved, usually lithium hexafluorophosphate. Both electrodes are separated from each other by the separator, which is made of polyolefin.
The resulting battery cells have a voltage of 3.2 to 3.7 V. For a higher voltage, several of these cells are connected in series and placed in a housing (known as a module). For electric vehicles, several of these modules are connected in series and housed in a metal frame (the "rack") to form a battery system or pack. Depending on the size, voltages of up to approx. 850 V can be achieved. Some manufacturers do away with the division into modules and instead place the cells directly in the frame (so-called "cell-to-pack design").
When the battery is charged, lithium ions migrate from the cathode (metal oxide) to the anode (graphite) to equalize the charge and are stored there. This does not produce elemental lithium, the ions are only stored in the graphite (so-called intercalation). This process is reversed when discharging.
The recycling of lithium-ion batteries poses a challenge in many respects. To avoid problems, the residual electrical energy in the battery must first be removed. Separating the active materials from the electrodes is another problem. The electrolyte consists of a highly flammable solvent and the conductive salt, which can form hydrogen fluoride through decomposition. Furthermore, the variation in the structure must be taken into account. Li batteries with different cathode materials can be found on the market, meaning that sorting is necessary before recycling. The electrolyte also contains a mixture of solvents. If these are recovered in high purity during recycling, they can be reused in new battery cells.
Current recycling methods
The overall process of recycling lithium-ion batteries consists of discharging, dismantling, pre-treatment (mechanical dismantling, possibly with thermal treatment) and preparation of the black mass (active material). Discharging is not necessary for some processes. Dismantling, on the other hand, is only carried out for battery systems and can be optional.
Discharging
In electrical deep discharge, the battery is connected in series to a discharge system which discharges the electrical energy in a controlled manner (Fig. 2). As the battery management system prevents deep discharging, the battery must be connected directly. When a specified minimum voltage is reached, the battery is automatically short-circuited and can be safely removed from the series connection without interrupting the discharge process of the other batteries. In the optimum case, the electrical energy is recovered and fed into the power grid or stored temporarily. If this is not possible, it can also be converted into heat. Fully discharged batteries can be handled more safely and make subsequent work steps safer.
Another method is salt water discharge. For this, the batteries are placed in a salt water bath in which the electrical energy is discharged. In some cases, the batteries are opened beforehand (sawed or drilled open) so that the electrolyte leaks out and salt water enters the battery. This very simple process enables different cells to be discharged together without any electrical connection. However, the process has a number of problems. The electrical energy is usually not completely dissipated and the black mass obtained at the end of the recycling process is still reactive. If the battery is opened so that the electrolyte and parts of the metal oxides are rinsed out, the conductive salt can also react with water and form hydrofluoric acid, among other things, which must be neutralized. The formation of hydrogen gas is also possible. Both the solvent vapors and the resulting gases require extraction and gas purification. The salt water is also contaminated with electrolytes, metal oxides and reaction products and has to be disposed of at great expense. The process also takes a lot of time.
Fig. 2: Discharge system for battery modules
Dismantling
The dismantling of battery systems down to module level is in most cases a manual process and therefore requires technical personnel and the appropriate tools. Although it is easily possible to process entire battery packs in appropriately sized industrial recycling plants, it generally makes more sense in terms of added value to carry out the dismantling, as around a quarter of the total weight can already be removed in this way. The components recovered in this way can be resold directly into the established recycling cycles (e.g. the battery racks, copper cables or electronic components), which results in further positive added value. At the same time, this avoids having to channel this material through the entire recycling process, which takes up part of the recycling capacity and, in particular, increases wear on the shredder. The cell-to-pack systems already mentioned are problematic in this context. As the cells are glued to the rack here, dismantling is cumbersome or not possible, which is why the battery pack has to be shredded completely.
Automation is desirable due to the high manpower requirements for dismantling. There are numerous projects on this topic at universities and in industry, and some companies are already offering such solutions commercially. The challenge here is the lack of standardization. Each car model has an individual battery system and therefore requires the disassembly process to be adapted, e.g. by programming the robots used (cover image).
Pre-treatment
The shredding of batteries is generally referred to as pre-treatment and always involves a shredding process, possibly combined with thermal treatment. In mechanical-thermodynamic recycling at low temperature, the Duesenfeld process, the batteries are shredded under nitrogen and the solvent of the electrolyte is removed under vacuum at low temperature before mechanical separation is carried out. Thanks to the low temperature, there is no decomposition of the conductive salt to form hydrogen fluoride, which means that no exhaust gas scrubbing is required and the electrolyte is recovered in its pure form. After separation, a heavy fraction, black mass, separator, aluminum, copper and the electrolyte solvent are obtained. The black mass still contains all the conductive salt and graphite and can be processed hydrometallurgically or reused by means of direct reuse. Ultimately, a recycling efficiency of 91 % can be achieved (Fig. 3).
Fig. 3: Output fractions in mechanical-thermodynamic recycling
The only difference between mechanical-thermodynamic recycling at high temperatures is that drying takes place at a higher temperature. This results in decomposition of the conductive salt. The hydrogen fluoride formed must be removed by exhaust gas scrubbing and leads to contamination and partial decomposition of the solvent obtained. The hydrogen fluoride gas can also corrode the system. Lithium fluoride remains in the black mass, a very stable compound from which the lithium is difficult to recover. Heating and cooling phases require additional energy and time. The output fractions after separation are almost identical to the low-temperature process, although the composition of the black mass and electrolyte differ. Combined with the processing of the black mass, recycling rates of 70-90% can be achieved.
In mechanical recycling under water, shredding takes place with the addition of water. By using water as a medium, it is also possible to process charged batteries, although the energy released heats up the circulating medium. The hydrofluoric acid produced by the decomposition of the conductive salt is corrosive and can be bound by adding calcium ions. Most of the calcium fluoride formed in this process ends up in the black mass and can disrupt hydrometallurgical processing. The electrolyte solvent remains in the water and cannot be recovered. The shredder medium must ultimately be disposed of. After the final separation, black mass, plastics, metallic housing parts, aluminum and copper are obtained. However, the black mass is still moist and reactive and is either dried (with the risk of hydrogen fluoride formation) or sold in a moist state. After processing the black mass, a recycling rate of 50-70% is achieved.
The last variant of pre-treatment is pyrolysis. Here, the batteries are deactivated in a vacuum at a high temperature (up to 600 °C) before they are shredded and the material separated. The heat treatment causes the binder within the active materials to decompose, which makes it easier to separate them from the metal foils. However, the separator and the electrolyte also decompose, and the hydrogen fluoride formed must also be removed from the exhaust gas stream by means of gas scrubbing. In addition to the additional energy required for heating, costs are also incurred for the final storage of the filter materials after exhaust gas purification. The fractions obtained after separation are black mass, metallic housing parts, aluminum and copper. Lithium and graphite can only be recovered to a limited extent from the black mass, while the aluminum content is higher. As expected, the recycling rates are lower at 40-60 %, but the process is nevertheless advantageous for small batteries, as these cannot usually be discharged electrically (Fig. 4).
Fig. 4: Flow chart of processes for recycling commercial lithium-ion batteries
Preparation of the black mass
Depending on the process, the black mass from the pre-treatment contains the active material of the cathode and possibly also that of the anode. In order to recover the individual elements from the mixed metal oxides, metallurgical processes are used that have long been established in the field of ore processing and must be adapted to the properties of the black mass.
Hydrometallurgy involves wet-chemical processing of the black mass by first breaking it down using reagents (e.g. sulphuric acid). The dissolved metals are then separated by extraction or precipitation and recovered as salts (e.g. heavy metal sulphates or lithium carbonate). For reuse in lithium-ion batteries, these metal salts can be used to produce the cathode material, which can ultimately be almost 100 % recovered. Various processes are used in hydrometallurgy, which differ in the sequence of individual steps and the chemicals used. This results in different chemical requirements, operating costs,CO2 balances and purities of the fractions obtained.
In pyrometallurgy, black mass or complete batteries are melted down in the furnace. The material is exposed to different temperature ranges from 400 to 1450 °C. The organic compounds are thermally decomposed, while at the same time these and the graphite serve as reducing agents for some of the metal compounds contained in the material as the temperature rises. The elementary metals form an alloy from which iron, copper, cobalt and nickel can be recovered hydrometallurgically. The slag also obtained contains manganese, lithium and aluminum, among others. As hydrometallurgical processing is expensive, the material is usually recycled in road construction. Recycling rates are significantly lower at 32-50%. At the same time, the energy requirement is high, while electrolyte and graphite are incinerated and lead to a poorCO2 balance. In addition, several exhaust gas scrubbing processes are required, waste is produced for final disposal and hydrometallurgy also generates waste water for disposal. Cobalt and nickel salts that are obtained can be reused in cathode materials. Due to high operating costs, pyrometallurgy is not worthwhile for low-cost cell chemistry, e.g. LiFePO4, as the added value is too low.
Outlook: future recycling processes Direct Recycling / Direct Re-Use
In the established processes for processing the black mass, the active material is separated back into the individual metal salts using metallurgical processes, from which the cathode active material must be produced from scratch. In direct recycling or direct re-use, the cathode active material (CAM) is instead converted into a regenerated CAM (rCAM) using various mechanical and chemical processing methods (e.g. re-lithiation). The crystal structure and morphology are retained and the material is "repaired" by adding new lithium. The rCAM obtained in this way can be used directly for the production of new battery cells. The separated anode active material (usually graphite) can also be reused.
Summary
A very positive development in the field of lithium-ion battery recycling has been emerging for several years. Established companies, particularly from Southeast Asia, have been operating recycling plants for this sector for a long time, but to date have focused on high-temperature processes and the correspondingly low recycling rates. Considering the ambitions of battery manufacturers to massively expand production in Europe as well, the demand for raw materials will also increase in the coming years. In the long term, the older, inefficient recycling processes must be replaced by better methods in order to keep as many raw materials as possible in the cycle. The EU has laid an important legal foundation for this with the new Battery Regulation. With the more modern recycling processes available, these ambitions can already be fulfilled today, enabling companies to build an efficient recycling infrastructure in Europe.
The article is based on a presentation given at the Ulm 2025 discussion
