Battery Next Generation – Simulation and validation methods to accelerate detection of performance parameters of single cells and united cell structures for battery systems in heavy utility vehicles

The BNG joint project is funded by the Bavarian Ministry of Economic Affairs, Regional Development and Energy and is aimed at researching and developing new generations of battery systems for battery electric utility vehicles with a production start after 2030.

In Germany up to 75 % of road transport uses utility vehicles. Travel distances of battery electric utility vehicles are in the range of around 400 km. In the future, however, utility vehicles with battery electric drives in combination with quick charging stations will need to be able to cover distances of up to 800 km daily. Therefore, over the lifetime of a utility vehicle, battery systems must be able to complete multiple quick charge processes and numerous partial and full cycles. This translates into high requirements for the calendrical and cyclical lifespan of the battery system. At the same time, the systems also face high requirements for the energy and power density as well as safety. Current, known battery systems can only meet these requirements to a limited extent.

The BNG project aims to develop cell-specific test procedures that are appropriate for obtaining valid assessments of degradation and durability in real applications. Tests with exaggerated currents and temperatures provide information about the expected service life of lithium-ion cells in real applications more quickly. To minimise test duration, strong shirring effects, as they occur in combinatorial loading, are required.

Besides an SEI layer, the deposition of metallic lithium (anodic precipitation), corrosion of current collectors also appears as degradation mechanisms and failure modes. The consequences are reduced charge capacities and increased battery cell impedance. To detect these characteristics during the test procedures in the individual cells, non-destructive capacitance measurements and electrochemical impedance spectroscopy are used in the experimental setup.

The main goal of the accelerated degradation of lithium-ion cells in the test is to amplify the degradation effects within a shortened test duration. This goal shall be accomplished by using a model-based extrapolation of the outcomes of the experimentally determined degradation within the shorter test duration.

Project lead: Prof. Frank Opferkuch, Dr-Ing.

Researchers: Timur Issayenko, M.Sc.

Project partners: MAN Truck & Bus SE, E-T-A GmbH

Funded by: Bavarian Ministry of Economic Affairs, Regional Development and Energy

Funding period: 1 Jan 2023 - 31 Dec 2025

Battery Next Generation (BNG) – Investigating and testing a radio-based battery management system (wireless Battery Management System, wBMS) for battery systems in heavy utility vehicles.

The BNG joint project is funded by the Bavarian Ministry of Economic Affairs, Regional Development and Energy and is aimed at researching and developing new generations of battery systems for battery electric utility vehicles with a production start after 2030.

Besides the necessary and ongoing research and development measures relating to actual cell and battery structure, an essential aspect for further development and improvement of battery systems is the subsequent battery monitoring and control. Therefore, one section of the BNG project is focused on the investigation, testing, and implementation of a radio-based variant of a battery management system (wireless Battery Management System, wBMS). The radio communication that occurs between the cell monitoring controllers (CMC) and the battery management controller (BMC) is a special challenge in the field of heavy utility vehicles.

In automotive applications, the battery structure consists of several cell modules on one level, which are installed on the car chassis. The battery structure in utility vehicles, however, is designed over several superimposed levels. “Battery packs” are the result of this layering, which distributes the number of required cell modules over several layers, with several cell modules installed on each layer. These layers are mostly separated from each other, which means there are only narrow connection points for radio communication. This results in difficult operating conditions for a wBMS, which must fulfil high and new requirements related to data security and reliability.

To test the potential use of a wBMS and to gain information about the radio wave distribution within a battery pack, the high-frequency radio communication is being investigated and tested both in simulation and with technical measurements in a real system. The knowledge gained through this project will subsequently be incorporated into the wBMS concept and design and in the construction of the battery pack.

Project lead: Prof. Frank OpferkuchProf. Armin Dietz

Researchers: Andre Merx, M.Sc.

Project partners: MAN Truck & Bus SE, E-T-A GmbH

Funded by: Bavarian Ministry of Economic Affairs, Regional Development and Energy

Funding period: 1 July 2023 - 31 December 2025

Formation and stabilisation mechanisms of defects in carbon-doped and self-doped titanate nanotubes

In this project, funded by the German Research Foundation, details of the defect structure of titanate nanotubes are being investigated. Such nanotubes have potential applications in hydrogen technology. For example, the material could function as a catalyst carrier, i.e., as a substrate for the platinum particles in PEM fuel cells. To this end, it should have a highly specific surface area and be electronically conductive. Currently, carbon black is used as a catalyst carrier, which meets these requirements, but is not stable in the long-term under the electrochemical conditions in a fuel cell. The degradation of the catalyst carrier leads to agglomeration or even discharge of platinum particles, which leads to a loss of active surface in the cell. Using a material that has an adequately high specific surface area, is electronically conductive, and is also stable against oxidation processes could be a solution to this problem. At the end of the 1990s, a Japanese research group showed that a tubular nanomaterials, titanate nanotubes, can be produced from titanium dioxide using a relatively simple process. As this material is already in oxidised form, it is expected to have better stability compared to carbon black in fuel cells. Without further modification, however, titanate nanotubes are not sufficiently conductive. Therefore, a process has been developed at the Ohm to introduce carbon into the structure without losing the high specific surface area. Electrical characterisations show that the nanotubes display a significantly improved conductivity, which is within the magnitude-range required for fuel cells.

However, it has not yet been researched in detail, to what this conductivity can be attributed. One conjecture is that during the production process Ti⁴⁺ is reduced to Ti³⁺ , which is stabilised by carbon. The project aims to investigate whether such defect states exist and whether they cause electrical conductivity by specifically modifying the material and by comparing carbon-containing and pure, undoped titanate nanotubes. X-ray diffraction, scanning electron microscopy, thermal analysis methods, and spectroscopic procedures are used as methods for investigation. The project will run over three years (2021-2024). Doctoral candidates will carry the research out. The research associates will be supported by student assistants, who will benefit from the opportunity to gain insight into research and development early in their academic careers.

Project leader: Prof. Uta Helbig

Researchers: Dominik Eitel, M.Sc.

Funded by the German Research Foundation

Funding period: Mar 2021 - Mar 2024

Micro and nanostructured functional materials

In this project, the German Research Foundation is providing support for new equipment for the purpose of knowledge-oriented research. With this major instrumentation funding, a multipurpose powder diffractometer with interchangeable tubes and a coupled AFM-Raman microscope with multiple excitation wavelengths and detectors will be procured. The instruments will be used, for example, for the chemical-structural analysis of nanomaterials for fuel cells and of steels for hydrogen technologies.

First and foremost is the development and investigation of alternative electrode and catalyst carrier materials for the polymer electrolyte fuel cells (PEMFCs). In addition to the materials for PEMs, the influence of residual stresses on the embrittlement of steels will be investigated. Steel will play an important role in the transport and storage of hydrogen, e.g., as a container material. Hydrogen is known to cause embrittlement of steel, so it can be assumed that residual stresses in steel will have an influence on the stability of the material.

Both new instruments will also support valuable contributions in the field of medical technology, for example, in analysing stresses in implants and recognising defects in materials. Furthermore, the both devices will support the continued development of bioactive glasses or recyclable silicones.

The major instruments will be procured in 2023 and be available for use as of mid-2024.

Project leader: Prof. Uta Helbig

Funded by the German Research Foundation

Smart monitoring of degradation and regeneration of truck H2 fuel cells using neural networks and impedance tomography

In the SMART.H2 project, funded by the Federal Ministry of Education and Research (BMBF), the degradation and regeneration of truck H2 fuel cells is being investigated. Hydrogen/air polymer electrolyte membrane fuel cells (PEMFCs) present promising potential for powering electric motors in heavy-duty vehicles. Compared to battery-electric drive systems, PEMFCs have a longer mileage per fuel charge and a shorter refuelling time. Furthermore, they are scalable for high engine power and have a higher system efficiency than combustion engines. PEMFC-based electric motors are free of local pollutant and greenhouse gas emissions. Investigating the degradation and regeneration of PEMFCs not only increases our understanding of underlying deactivation processes under realistic operating conditions, but will also help to improve PEMFC lifespan, which will enable the technology to compete with conventional combustion engines.

The project is focused on the development of accelerated degradation tests and instrumental analytical and theoretical methods to identify causal relationships between specific operating conditions in heavy-duty vehicles and the degradation processes in fuel cells. The project has three aims:

1) The development and operation of a laboratory test stand on which single cells and small stacks of up to 2.5 kilowatts of power can be operated and various degradation influences can be investigated. Accelerated degradation tests and regeneration procedures will be developed by means of comparison with synchronous tests on fuel cell systems of up to 100 kilowatts in industrial test rigs.

2) The development and use of a method for the spatially resolved characterisation of fuel cell membrane unit degradation with the aim of using this method to develop a system for the onboard monitoring of fuel cell systems in vehicles.

The modelling of degradation with machine learning methods and the simulation of cells in actual driving operation with the aim of diagnosing degradation conditions in the vehicle itself, efficient controlling of the cells in driving operation, and developing regeneration cycles and procedures for already degraded cells.

Project lead: Prof. Maik Eichelbaum

Project partners: MAN Truck & Bus SE, Prof. Frank Opferkuch (TH Nürnberg), Prof. Raimund Horn (TU Hamburg), Prof. Marc-Georg Willinger (TU München)

Funded by: Federal Ministry of Education and Research (BMBF)

Funding period: 1 Oct 2022 - 30 Apr 2027

SynchronBlow – development of an innovative cross-flow fan with a outlet velocity of 180 km/h

Description of the subject:

For driving simulations on vehicle test benches, air fans are used to simulate the effect of the airflow on the vehicle. Areas of application are exhaust gas tests, chassis dynamometers, or climate chamber tests. The air fan provides the missing airstream in dynamometers and driving simulations. The airflow created by the fan is directed towards the vehicle radiator and under the vehicle. This simulates the cooling effect of the airflow on the engine temperature of the vehicles being tested. Due to the confined space and limited outlet cross-sections in vehicle test benches, current airflow fans can only reach a simulated speed of 160 km/h at most. A simulation of an airflow speed of 180 km/h is urgently needed in order to be able to simulate the influence of higher driving speeds on vehicles and individual components. Asynchronous motors are currently used to drive cross-flow fans. To achieve higher energy efficiency, the project is using a synchronous reluctance machine.

Project aims:

The main aim of the SynchronBlow cooperation is to develop a cross-flow fan with a outlet velocity of 180 km/h with a very compact device construction by using an innovative and optimised synchronous reluctance motor. WMB, a partner in the project, is developing the new cross-flow fan. For the synchronous reluctance motor, an optimised stator and rotor as well as the overall design are being developed to achieve the speed of 2300 rpm concurrently with an increase in efficiency. BEN, another partner, is responsible for the mechanical design, technical production, and investigating the vibration behaviour of the synchronous reluctance motor. At the Technische Hochschule Nürnberg, besides the electromagnetic design and simulation of the synchronous reluctance machine, optimisation to the required target values will be carried out using the institution’s own simulation program for electrical machines. This involves both an analytical calculation using reluctance networks and the use of numerical FEM for the targeted optimisation.

Project lead: Prof. Armin Dietz

Researcher: Michael Schmidt, M.Eng.

Project partners: BEN Buchele Elektromotoren GmbH, WMB Ventilatoren GmbH

Project management organisation of the BMWi ZIM joint project

Project duration: 2.5 years

V²-DoRR - variable venturi nozzle for precise dosing of reactants in hydrogen drives for high quality of control under highly dynamic operating conditions

Both in fuel cell drives or H₂ engines and in thermochemical reactions in general, there is a great effort to increase overall efficiency. One of the essential tasks in these machines and processes is to dose the reaction gases in the reaction volumes with high precision, dynamically, and with as little loss as possible. Technologies used so far for this purpose are mostly calibrated at stationary points and therefore behaviour in changing operation is to some extent unknown. Due to highly dynamic fluidic effects, the physical conditions can only be represented with difficulty linearly - which, however, is the basis of common system calibrations.

A dosing system, for which a European patent has been applied for through BayPAT, is based on the principle of a variable venturi nozzle and includes a device for rapidly changing the effective flow cross-section. This dosing system should offer a higher degree of efficiency compare to conventional technologies.

1. This should be realised using diffuser technology, which enables partial recovery of the pressure losses. In addition, a flow-optimised design provides for lower losses from the outset.
2. The system should offer significantly higher dynamics, which in turn enables more precise control in changing operating conditions. Using a variable venturi nozzle promises high dynamics and precision at the same time, which is the basic prerequisite for use in the variable range of many applications.
3. The system’s application-specific design and dimensioning should provide for load or mass flow requirements and – by means of a transfer function – be associated with an effective flow cross-section. The aim is to achieve a linear actuator behaviour that enables simultaneous use of the actuator as a feedback sensor for the mass flow value.
4. By means of the development of simplified parameterisable equation structures and using real-time capable parameter estimation methods to determine unknown parameters, physically interpretable real-time models (digital twins) will be developed. The models will be able to adjust their parameters constantly during operation, which increases the quality of control. (Keywords: degradation behaviour, component interplay, environmental conditions)

The investigations of the team around Prof. Bikas into the dosing system’s dynamics, precision, and efficacy are supported within the framework of “Validation of research results and inventions” funding from the Bayern Innnovativ GmbH and funded by the Bavarian Ministry of Economic Affairs, Regional Development and Energy. The main focus of their work is on demonstrating the advantages over competitor products in the areas of dynamics, flow losses, quality of control, and calibration robustness.

Project leader:              Prof. Georgios Bikas, Dr-Ing.

Researchers:               Thomas Untheim, B.Eng., Peter Weigand, M.Sc.

Project partners:          Bayerische Patentallianz GmbH, Micro-Epsilon Messtechnik GmbH & Co. KG, UltraZohm, Vectoflow GmbH

Funded by:                   Bayern Innovativ

Funding period:            Jan 2023 - Jun 2024