Influence of Switching on the Aging of High Power Lithium-Ion Cells

• Published in: Batteries (Basel) Vol. 8; no. 4; p. 33
• Main Authors: Ngaleu, Guy, Theiler, Michael, Straßer, Xenia, Hanzl, Christian, Komsiyska, Lidiya, Endisch, Christian, Lewerenz, Meinert
• Format: Journal Article
• Language: English
• Published: Basel MDPI AG 01-04-2022
• Subjects: 18650; Aging; Aging (artificial); Converters; Discharge; Electric cells; Electrochemical impedance spectroscopy; frequency; Graphite; Homogeneity; Lithium-ion batteries; multilevel inverter; NCA; Parameters; Rechargeable batteries; Rollover; Signal quality; Switching
• ISSN: 2313-0105; 2313-0105
• DOI: 10.3390/batteries8040033

For intelligent battery systems that are able to control the current flow for each individual cell, the multilevel inverter is an interesting approach to replace the bidirectional AC/DC-converter and improve flexibility of charging system and signal quality in both directions. Therefore, the cells are modulated by switching varying the duty cycle, the current and the frequency up to the kHz-range. This is only beneficial if the switching does not lead to a significant additional aging. The scientific gap to assess and understand the impact of switching is investigated in this paper by testing 22 high-power 18650 lithium-ion cells (Samsung 25R). The cells are tested at 50 Hz and 10 kHz switching frequency during charge, discharge and charge/discharge at 50% duty cycle. The tests are compared to eight reference tests with continuous current flow performed at the average and the maximum current for charge and discharge, respectively. The results are obtained by evaluating the remaining capacity, resistance, electrochemical impedance spectroscopy and dV/dQ analysis. Before reaching rollover, the investigated cells lose homogeneity and cathode capacity but no significant difference for the aging parameters are found. After rollover, the cell-to-cell variation is greater than the aging induced by the different cycling parameters.