Batteries & Energy Storage
Research areas, projects and highlights from the fields of electrochemistry and battery technologyCopyright: © ISEA
Our research areas follow the path from materials to battery systems that can be used in the field. Each of the research areas can work on independent questions in the respective field. But in all cases research at CARL is oriented towards supporting material development for batteries, generating statements on achievable lifetime and reliability in the shortest possible time for both, the development of production processes and the applications, or contributing to the construction and operation of optimal battery systems. To give you an insight into the research areas, the available laboratory equipment, the participating chairs of the CARL team and the models and data analysis methods used, you will find a description of our research fields after a few highlights of our work. Furthermore, you will also find some ongoing projects that we are working on together with our partners in academia or industry.
- cell analytics
In our analytical laboratory, a wide variety of battery cell types can be analyzed for their physical and chemical properties. This allows both a detailed characterization of new cells and the identification of fundamental aging mechanisms. The knowledge gained here serves as a basis for developing and improving our battery models in order to map battery behavior over the entire life cycle and can also provide important feedback directly to cell production.
- model development
Based on laboratory analysis and extensive cell testing, battery models are developed and parameterized at CARL to analyze and predict battery behavior. The work ranges from the development and parameterization of physicochemical models that represent the fundamental processes in the battery cell to impedance models and empirical aging models. Each of these models incorporates different aspects of the key relationships revealed by the experiments and at the electrode and cell levels. Such models can then be the basis for battery system design for various applications, as well as for online diagnostic algorithms. Empirical, data-driven, or mechanistic models at different size scales are used, depending on the problem at hand.
- design and operation strategies and management systems for battery systems
At the system and application level, the various single cell models serve as the basis for quantitative system models for various applications such as electric cars, buses, trains, ships, or stationary applications. The central task is to understand and optimize the battery system. This is achieved in three main areas:
1) Reduction of aging by optimizing the operating conditions including online diagnostic procedures that determine the state of the batteries at any time and allow e.g. minimizing the charging times without reducing the lifetime.
2) Optimization of the battery system design considering thermal management, temperature gradients, statistical variations of cell quality, the impact of cell interconnection concepts, integration with power electronics and robustness against mechanical impacts such as shocks, pressure or other environmental stresses.
competence cluster battery utilization (Batterienutzung)
The Battery Utilization Concepts (BattNutzung) cluster is funded by the German Federal Ministry of Education and Research (BMBF) with around 20 million euros and a total of 29 project partners in 13 projects, each scheduled to run for 3 years. The focus is on research into new battery concepts and applications.
With the increasing market penetration of the lithium-ion battery and the resulting increase in the supply of battery cells, the need for cell concepts tailored to the specific requirements of selected applications is also growing. In addition, the increasing use of lithium-ion batteries in the automotive sector in combination with increasing life expectancies of the cells ensures enormous quantities of cells with the potential of a second use after the use in the vehicle. All these topics are to be addressed within the framework of the Battery Utilization Concepts (BattNutzung) competence cluster created by the BMBF.
The Battery Utilization Concepts cluster is led by the cluster coordinators Prof. Dr. rer. nat. Dirk Uwe Sauer (Institute for Power Electronics and Electrical Drives ISEA, RWTH Aachen University) as spokesperson and with a focus on the topic area "Aging and Lifetime Prognosis", Prof. Dr.-Ing. Andreas Jossen (Chair for Electrical Energy Storage Technology EES, Technical University of Munich) with a focus on the topic area "Safety and Performance" and Prof. Dr. rer. nat. habil. Axel Müller-Groeling (Fraunhofer Institute for Silicon Technology ISIT, Itzehoe) with a focus on the topic area "Battery System Evaluation".
The focus of the cluster is on research into methods for the comprehensive evaluation of new materials and cells after production and in operation. In this context, possible 2nd-use applications, i.e. further use in other applications, are also taken into account and comprehensive life cycle assessments are carried out, including an estimation of the availability of raw materials. By means of all these newly developed methods, the development focus is to be directed towards the application requirements already in the early phases of the development pipelines for new cells and cell materials within the framework of the BMBF umbrella concept "Research Factory Battery".
The aim of InOPlaBat is the spatially and temporally resolved detection of lithium plating (accumulation of metallic lithium) in lithium-ion batteries. Lithium plating is a safety-critical phenomenon especially in fast charging processes of electric vehicles, which is caused on the anode by the limited capacity of lithium ions to be absorbed at the desired rate. In order to optimize battery lifetime and safety for all requirement profiles, it is central to detect the formation of metallic lithium and dendrites at an early stage. Reversible as well as irreversible plating can be accompanied by the formation of dendrites and lead to safety-critical short circuits. Irreversible plating additionally leads to a significant capacity loss due to loss of cyclizable lithium.
In order to capture the structure of electrode materials and their changes, in particular the plating of lithium on the anode during charging, across scales from nanometer to centimeter dimensions, various optical, electron microscopic (FIB, SEM and TEM) and X-ray (micro-CT, nano-CT) techniques in combination with spectroscopic techniques (NMR, EPR, EIS) will be used in the project. Based on findings from post-mortem investigations, suitable in situ/operando experimental facilities will be set up for the respective methods in order to investigate the charging/discharging processes directly in a battery cell under operating conditions. This should make it possible to analyze plating processes with high resolution in the cell in situ and thus correlate structural changes with spectroscopically detected dynamic processes.
To understand the processes taking place, as well as their fundamental causes, the measurements will be closely linked to coupled atomistic simulations and macroscopic modeling. A bidirectional flow of information is central, since a deeper physical understanding can only be achieved through successful multiscale simulation of the processes taking place, while experimental data provide the basis for formulation, parameterization and validation of the simulation systems. Subsequently, modeling at the macroscopic level provides a transfer path towards commercial cells and ensures direct applicability of the results in industrial applications.
The knowledge thus gained is expected to provide both rapid and accurate feedback on the impact of process and material changes in cell production. In addition, through the further development of electrical tests, a random, low-cost examination of cells will be made possible. This will improve the sustainability of cells developed and produced in this way by increasing cell life and reducing safety risks and thus potential containment measures in the battery pack.
In this project, a highly automated test bench for extensive cell characterization before and after aging tests of battery cells will be built and put into operation at the Center for Ageing, Reliability and Lifetime Prediction of Electrochemical and Power Electronic Systems (CARL) at RWTH Aachen University. This will be combined with an automatically controlled cyclization test bench, which allows individual loading and measurement of the cells during aging tests at defined temperatures. The aim is to characterize battery cells regularly, comparably and in detail. This will allow the effects of material and process changes in cell production to be investigated, quantified and reflected back. In addition to the classic parameters such as weight, voltage and 1kHz resistance, data from other measurements will also be recorded in a standardized and automated measurement procedure. These are from electrical measurements in addition to the cell capacitance also complete measurements of the electrochemical impedance (EIS) and additionally during the measurement cycle optically recorded heat and expansion information. The electrical measurements are supplemented by imaging images using a computer tomograph to investigate internal, mechanical effects. The high level of automation of the entire test sequence allows new cell samples from cell manufacturing facilities such as the Fraunhofer FFB to be recorded and characterized on a daily basis. We are not aware of a comparable system like this anywhere in the world.
The automated assembly and contacting of the battery cells on standardized cell holder boards including ID-based test management enables an efficient, traceable and comparable transfer to the aging test. The aging test takes place with highly accurate, efficient test equipment for setting environmental conditions, electrical cycling, and measurement under variable load profiles. Following the aging test, the cells are measured again using the standardized characterization procedure to perform a before-and-after comparison of the data. Due to the central storage in a database system, the evaluation of the recorded data can be carried out on the one hand with classical evaluation methods, which have been developed at ISEA for many years, and on the other hand by means of machine learning methods. The results obtained can be incorporated into the production process in the shortest possible way by establishing direct interfaces to the production site. At CARL, extensive, highly specialized laboratory equipment is available for further characterization of the morphology and chemical changes of the active materials and the electrolyte.