Source of raw materials instead of hazardous waste

In order for recycling plants to work safely and economically, the batteries must first be transferred to the process in a controlled and risk-free manner. A key prerequisite for this is precise metrological monitoring right from the pre-treatment stage. This is because lithium-ion batteries are considered potentially dangerous due to their high energy density - especially if they are damaged, deeply discharged or thermally unstable. The first step is therefore to safely inactivate the old batteries. For industrial applications such as UPS systems, driverless transport systems or traction batteries, controlled discharge under defined environmental conditions is essential. In a logistics company, for example, this step takes place in a closed discharge area under a nitrogen atmosphere. Here, pressure, temperature and oxygen sensors monitor critical operating variables in real time. As soon as limit values are exceeded - such as a sudden rise in temperature due to internal cell reactions - the system can intervene automatically, for example by shutting off, flushing or raising the alarm. The continuous analysis of gas concentrations in the room also serves to detect potential dangers at an early stage, for example from escaping electrolyte vapors.

Shredding and sorting

Unloading is followed by mechanical shredding. End-to-end monitoring systems are required to ensure that this process runs efficiently and smoothly. Fill level sensors in feed containers ensure that conveyor systems work evenly without overfilling or running empty. There are then two main ways of recovering the ingredients: the pyrometallurgical and hydrometallurgical processes.

In pyrometallurgical recycling, shredded battery residues are melted at temperatures above 1,500 °C. Metals such as cobalt, nickel and copper remain in the slag, while organic components burn. The method is particularly robust with regard to material streams of different compositions, but is very energy-intensive. Precise process control is therefore crucial. By using precise temperature and pressure measurement as well as adjustable control of the oxygen supply with the help of flow meters, energy consumption can be reduced by up to 10 % and emissions noticeably lowered.

Hydrometallurgy: Complexity under control with sensor technology

The hydrometallurgical process, on the other hand, relies on chemical extraction processes to selectively extract valuable metals from the so-called black mass. Compared to pyrometallurgical recycling, this method offers a higher recovery rate of the individual components and consumes less energy overall. However, this method involves additional process steps. After mechanical shredding, the material is first separated and sorted. Two main fractions are formed. The first fraction is a dry fraction consisting of pieces of metal and plastic, which can be sorted by type and fed directly back into the material cycle. The second fraction is a moist, deep black mass consisting of the formerly active battery materials and liquid components such as the electrolyte. Drying takes place using a filter press or vacuum. The separated electrolyte can also be fed directly back into the material cycle.

The resulting dry black mass is separated in chemical leaching and precipitation processes. However, the use of chemical solutions brings with it new challenges. A decisive factor for efficient leaching processes is the precise dosing and control of the chemicals used, as aggressive acids are used for metal dissolution and precipitation reagents for product recovery. The reliable recording of pH value, conductivity, flow rate and temperature ensures stable process conditions and contributes significantly to the selectivity and quality of raw material recovery as well as the economical use of resources.

The hydrometallurgical process results in either pure products or defined mixtures that can be used directly in the production of new lithium-ion batteries.

Closing the loop for batteries and rechargeable batteries

In order to achieve a true circular economy for batteries and rechargeable batteries, the so-called "closed loop", the active materials, plastics and metal foils used in battery production should be almost completely recovered. The entire recycling process can be simplified by rethinking the design, use and disposal of batteries. For example, the introduction of a battery passport, which tells the recycling company the composition of the battery, or standards for the design would be beneficial. Sustainable battery management is an important prerequisite for establishing a closed-loop system that maximizes the reuse of valuable resources.

Despite the rapid advances in both the process and the associated technologies, there are still challenges to overcome. However, through continuous innovation and collaboration, the industry is increasingly building closed-loop systems that maximize the value of used batteries.

Dr. rer. nat. Dustin Kubas, Product Manager Sales Marketing at Endress+Hauser