The necessity of conditioning 18650 cells using the example of the mobile battery test stand eZTR
Authors:   Otto-von-Guericke Universität Magdeburg, GERMANY, Kretschmann Robert , Lüdecke Stefan , Seidensticker Kai , Bierwirth Florian 
Published: April 2022

The project “Competence centre e-Mobility” (KeM) accepts the structural challenges and develops solutions in key areas of electromobility within the framework of a newly established competence centre. In addition to the primary objective of building and transferring technical know-how, the long-term anchoring of insights gained in employment-efficient economic structures is of particular importance. The focus of research is the use of novel drive systems under real conditions. Focused on the electric storage systems, the longevity and reparability of complete electro mobile systems form the strategic research approach. The work focuses on the development and testing of maintenance-friendly modular energy storage technology, new, simple system architectures for vehicle controls, and the systemic design of specialized applications in battery assembly. Furthermore, the electric drive train has again become the focus of automobile manufacturers due to the so-called diesel-gate. In addition to the electric motor and the necessary power electronics for power conversion and control of the system, the high-voltage battery (HV battery) defined the performance of electric cars during the development and design. Among other things, there is still great potential in rapid, reliable and cost-effective testing of different battery configurations under real conditions. In this area of conflict, the described work should be set with. To investigate the meaningful use of different battery configurations (cell type and arrangement, dimensions, handling, gravimetric and volumetric energy density, contacting, etc.), a mobile battery test stand was set up at the Otto-von-Guericke University Magdeburg. This enables the testing of several expansion stages of HV batteries under real conditions. For this purpose, a ZTR Roadster, a three-wheeled L5e vehicle (see Figure 1), was fitted with an electric powertrain. The entire vehicle was designed so that the compact HV batteries can be removed and replaced with minimal effort. In addition to the challenges involved in the conversion of the powertrain, the different expansion stages of HV batteries are explained. To test the performance of lithium-ion round cells (type 18650), a battery module including current charging technology was designed and integrated into the existing test carrier. To test the battery test bench at the limit under real conditions, participation in the WAVE (electric mobility rally) took place in 2018 and 2019. The focus was on generating measurement data and testing the suitability for the everyday use of non-conditioned lithium-ion storage systems. In the following, the necessary investigations derived from this about the conditioning of round cells are presented. The experiences gained within this experiment are presented in the publication and substantiated with the collected measurement data. Furthermore, it will be discussed which structural changes would be necessary to enable a stable long-term operation and which findings were obtained concerning the conception of energy-dense HV batteries.