Research on fast and high-precision float current technology as an alternative to conventional calendar ageing tests on lithium ion cells and research on fast parameterizable ageing prognosis simulations

• Applicants: Dr. Meinert Lewerenz; Professor Dr. Dirk Uwe Sauer
• Subject Area: Electrical Energy Systems, Power Management, Power Electronics, Electrical Machines and Drives
• Term: from 2020 to 2026
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 440701024

• Final Report Year: 2024

Final Report Abstract

Floater hardware that is ideally suited to the application of float currents and fulfils high requirements was successfully developed. The physico-chemical model was able to simulate the overhang effect of the anode. Positive float currents were observed for different combinations of active materials: NMC, NCA, LFP, graphite, graphite-silicon and LTO. It was possible to establish a general link between the float currents and ageing, i.e. the capacity loss, which was supported by 3-electrode measurements. A distinction can be made between anodic and cathodic ageing. While anodic ageing via SEI has already been well researched, cathodic ageing and electrolyte decomposition have hardly been researched at all. The CID was activated in three cells, which was previously signalled by an increase in the float current. This is probably due to overcharging at very high voltages. Float currents enable reliable ageing tests from as low as 5°C. By varying the temperature (steps and ramps), the stability of the cell can be examined for different states of charge. Findings on additional modelling variables, such as entropy, could be determined with a high degree of accuracy, thereby confirming previous assumptions on entropy. Thanks to the findings and the funding from the DFG project, funding was successfully obtained for the junior research group I-BasE led by Dr Meinert Lewerenz. Here, the basic principles from this project will be further advanced towards industrialisation.

Publications

• Float Current Analysis for Fast Calendar Aging Assessment of 18650 Li(NiCoAl)O2/Graphite Cells. Batteries, 7(2), 22.
  Theiler, Michael; Endisch, Christian & Lewerenz, Meinert
  
• Poster: Fast Characterization of Calendar Aging using Float Currents, AABC Mainz 2022
  Meinert Lewerenz, Michael Theiler & Christian Endisch
  
• Poster: Modeling and Measurement of the Transient Process at the Beginning of the Float Current Analysis (FCA), Batterieforum Berlin 2022
  Mohamed Azzam, Christian Endisch & Meinert Lewerenz
  
• Evaluating the Aging-Induced Voltage Slippery as Cause for Float Currents of Lithium-ion Cells. Batteries, 10(1), 3.
  Azzam, Mohamed; Endisch, Christian & Lewerenz, Meinert
  
• Long-Term Self-Discharge Measurements and Modelling for Various Cell Types and Cell Potentials. Energies, 16(9), 3889.
  Azzam, Mohamed; Ehrensberger, Moritz; Scheuer, Reinhard; Endisch, Christian & Lewerenz, Meinert
  
• Poster: Measuring Temperature Dependence of Entropy via Temperature Ramps using Float Current Analysis, ECS Meeting Göteborg 2023
  Meinert Lewerenz*, Mohamed Azzam, Moritz Ehrensberger, Reinhard Scheuer & Christian Endisch
  
• Vortrag: Finding the Calendar Aging Mechanisms Causing Float Currents, Kraftwerk Batterie Aachen 2023
  Meinert Lewerenz, Fan Xue & Christian Endisch
  
• Poster: Comparison of dU/dQ, Voltage Decay and Float Currents via Temperature Ramps, Kraftwerk Batterie Münster 2024
  Mohamed Azzam, Moritz Ehrensberger, Christian Endisch, Dirk-Uwe Sauer & Meinert Lewerenz
  
• Poster: Exploring Ageing Mechanisms in Lithium Ion Battery Cells: Correlating Voltage Hold Current with Traditional Ageing Indicators, Kraftwerk Batterie Münster 2024
  Maya Strautmann, Gereon Stahl & Dirk Uwe Sauer