TY - JOUR A1 - Williams Ngaleu, Guy A1 - Theiler, Michael A1 - Straßer, Xenia A1 - Hanzl, Christian A1 - Komsiyska, Lidiya A1 - Endisch, Christian A1 - Lewerenz, Meinert T1 - Influence of Switching on the Aging of High Power Lithium-Ion Cells JF - Batteries N2 - 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. UR - https://doi.org/10.3390/batteries8040033 KW - 18650 KW - NCA KW - graphite KW - switching KW - multilevel inverter KW - frequency KW - cycle life Y1 - 2022 UR - https://doi.org/10.3390/batteries8040033 UR - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:573-22861 SN - 2313-0105 VL - 8 IS - 4 PB - MDPI CY - Basel ER - TY - JOUR A1 - Straßer, Xenia A1 - Williams Ngaleu, Guy A1 - Hanzl, Christian A1 - Azzam, Mohamed A1 - Endisch, Christian A1 - Lewerenz, Meinert T1 - Influence of Switching on the Aging of High Energy Lithium-Ion Cells JF - Batteries N2 - An AC-battery or multilevel inverter used to increase safety and flexibility is realizable by switching the cells and modules on and off in a defined way and thus can replace the bidirectional converter. Assessing possible additional aging due to switching, the results of a previous study for a high-power optimized cell showed no influence on the current rates or the switching. In this paper, a highly energy-optimized LG 18650-cell is investigated to discuss the influence of switching during the charge and discharge process, respectively, as well as combining both processes together with clear performance differences when applying higher charge and discharge currents. Moreover, the influence of switching is discussed for the two frequencies (50 Hz and 10 kHz) and different duty cycles. The aging is analyzed by capacity loss and resistance increase, by dV/dQ analysis, and by electrochemical impedance spectroscopy. We found no clear negative influence of switching but a positive effect if the cells are switched during charge. The best performance is found for switching during charge as well as during discharge. The cell aging during switching is clearly determined by the average and not the maximum current applied. This work shows no negative effects of multilevel inverter applications on the tested cells. UR - https://doi.org/10.3390/batteries9020139 KW - 18650 KW - NMC811 KW - Graphite KW - switching KW - multilevel inverter KW - frequency KW - cycle life Y1 - 2023 UR - https://doi.org/10.3390/batteries9020139 UR - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:573-41074 SN - 2313-0105 VL - 9 IS - 2 PB - MDPI CY - Basel ER -