Recycling and optimized raw material cycles, secondary use and a knowledge-based cell design should make lithium-ion batteries more sustainable and safer in the future. Scientists from process engineering and materials science at the Karlsruhe Institute of Technology (KIT) create the basis for this with joint research on the battery life cycle. The new research projects are part of the battery research clusters "greenBatt" and "BattUse" newly created by the Federal Ministry of Education and Research (BMBF).
Battery cells with a long-term high performance can significantly reduce the ecological footprint of applications such as electromobility. It is also conceivable to continue using such cells after use, for example in large network storage systems. However, not all cells are suitable for such “second life scenarios”; long-term operation requires the perfect interaction of numerous components and materials: “When a battery is continuously charged and discharged, undesirable side reactions also inevitably occur,” says Professor Hans Jürgen Seifert from the institute for Applied Materials - Applied Materials Physics at KIT. “If that has a negative impact on their behavior, it is called degradation or aging. It cannot be prevented entirely, but it can be delayed and mitigated by an appropriate cell design. “Seifert and his team analyze the decomposition mechanisms in the particularly reactive electrolyte based on the associated gas formation. High-precision calorimetric measurements are carried out, i.e. the balancing of heat quantities in the operation of a battery as well as its thermodynamic modeling. The aim of the project is precise predictions of cell behavior during use, explains Seifert: "With our models, safe and sustainable batteries can then be developed knowledge-based and quickly brought to market."
A better understanding of the degradation processes also helps to create more reliable service life forecasts for lithium-ion cells. Corresponding test series are extremely time-consuming. “As a solution, test procedures are required in which aging proceeds more quickly,” says Professor Thomas Wetzel from the Institute for Thermal Process Engineering. “The cells' comfort zone is around 25 degrees Celsius. If you expose them to heat or cold, they age significantly faster. ”The complexity of the aging processes and the thermal conditions in the cells have made it difficult to transfer the results of accelerated test procedures to conventional methods. Wetzel and his team now identify suitable conditions and parameters, which trigger as few additional aging mechanisms as possible and are therefore suitable as markers. With the help of this “thermal fingerprint” of a battery cell, it should be possible to reliably predict aging even in accelerated test series.
Another focus of the new clusters is a recycling-friendly battery design and the further development of recycling processes and raw material cycles. “There are currently two ways of recycling lithium batteries. In the pyrometallurgical approach, the cells are melted down at high temperatures. This is robust and safe, but the recycling rate that can be achieved is limited, ”explains Professor Hermann Nirschl from the Institute for Mechanical Process Engineering and Mechanics (MVM) at KIT. “The mechanical approaches, ie shredding and sorting, promise potentially higher recycling rates. However, these are generally associated with higher security risks, and the separation of materials has so far only been moderately selective. “At the MVM, individual process parameters and process chains of mechanical recycling are simulated in high resolution, compared and optimized with the aim of enabling economically viable, environmentally friendly and function-preserving battery recycling. In doing so, they take into account innovative approaches such as shock waves, ultrasound processes or wet grinding, which guarantee high material selectivity, preservation of functional materials and, through the use of water, a high level of safety. In the future, favorable design features for batteries can be derived directly from the simulation results. Ultrasonic processes or wet grinding, which guarantee high material selectivity, preservation of functional materials and, through the use of water, also a high level of safety. In the future, favorable design features for batteries can be derived directly from the simulation results. Ultrasonic processes or wet grinding, which guarantee high material selectivity, preservation of functional materials and, through the use of water, also a high level of safety. In the future, favorable design features for batteries can be derived directly from the simulation results.
Where the current processes for battery recycling reach their limits, the yield can be further increased by a better combination of mechanical and thermal processes. The research team led by Professor Wilhelm Schabel of Thin Film Technology (TFT) at KIT is working on thermal recycling processes for volatile organic components in electrode layers. "We want to recover valuable raw materials that were not sufficiently taken into account in the previous processing of battery cells," says Schabel. “Together with our project partners, we will also optimize the treatment of the shredded material at temperatures of up to 500 degrees Celsius with regard to the recycling rate. “Experiments with new spectroscopic measurement methods should lead to a fundamental understanding of the micro and macro processes in the electrode layers during the recycling process. In addition, a suitable strategy for a further thermal treatment for the separation of high-boiling components and components that diffuse slowly in the layer structures is to be found. "We will consistently transfer our experimental findings into simulation models," emphasizes Schabel. "This is the only way we can contribute to the optimization of future recycling processes." "We will consistently transfer our experimental findings into simulation models," emphasizes Schabel. "This is the only way we can contribute to the optimization of future recycling processes." "We will consistently transfer our experimental findings into simulation models," emphasizes Schabel. "This is the only way we can contribute to the optimization of future recycling processes."
In addition to sustainability, the focus of work in the new research clusters is also the safety of battery systems. Safety-critical defects at cell level rarely occur, but can have serious consequences - such as with lithium plating: "The effect is triggered by the accumulation of metallic lithium in the anode," explains Professor Ulrike Krewer from the Institute for Applied Materials of electrical engineering. “This can lead to a massive loss of capacity, in extreme cases also to short circuits or even to a cell fire.” To prevent this from happening, cells can be monitored and checked during operation. However, such online methods have so far mainly been used in the laboratory and are not very sensitive at the system level. Krewer and her team are now developing improved analysis algorithms for practical use. "In doing so, we take into account non-linear processes when operating a battery; this data has so far hardly been used for diagnosis," says Krewer.
When designing the umbrella concept “Research Factory Battery”, the German government recently created four new competence clusters for battery research, which are funded with a total of 100 million euros. The KIT coordinates nationwide research on flexible production systems in the “InZePro” competence cluster (intelligent battery cell production) and high-performance batteries in the “AQua” cluster (analytics / quality assurance). The contributions of the KIT in the research clusters "greenBatt" (recycling / green battery) and "BattNutzen" (battery usage concepts) are based on the close cooperation of different institutions. Various institutes of the Fraunhofer Society, the Ingolstadt University, the Rheinisch-Westfälische Technische Hochschule Aachen (RWTH),
Further information: https://www.bmbf.de/de/batterieforschung-in-deutschland-662.html