Figure 1 shows the variation of cell capacity with cycle number for a plug-in electric-vehicle (PHEV) LIB with energy density of 170 Wh/kg cycled at 25oC with 1C charge and 2C discharge. At this moderate operating condition it is usually believed that lithium plating is not a concern. However, we found in our experiment that cell capacity dropped abruptly after ~3000 cycles, which is in consistence with the recently reported nonlinear aging behavior by Schuster et al. (4). The model presented in this study well captures this nonlinear behavior, as shown in Fig. 1a, and this abrupt drop in cell capacity is attributed to the rapid rise of lithium plating rate after extended cycling as shown in Fig. 1b.
The model is then applied to predict the cycle life of the above PHEV cell at different ambient temperatures, as shown in Fig. 2a. It is found that the cell at 20oC has the longest cycle life. Either increasing or lower the temperature would accelerate cell aging. These results are in accordance with the recent experiment findings by Waldmann et al (3).
The effects of electrode thickness on the cycle life are also investigated, as shown in Fig. 2b. These cells are cycled at 25oC with 1C charge and 1C discharge. Even at this moderate operating condition, cells with thicker electrode have much poorer life as shown in Fig. 2b, which is because lithium plating is more prone to occur with the increase of electrode thickness. This result has a profound implication on high-energy, thick-electrode cells for all electric vehicles (EV).
Details about the model development, and about the effects of cell design parameters and operating conditions on cell aging due to lithium plating will be given in this presentation. Finally, we shall propose some novel strategies to significantly extend the cycle life and increase fast rechargeability of energy-dense EV batteries.
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2. M. B. Pinson and M. Z. Bazant, J. Electrochem. Soc., 160, A243 (2013).
3. T. Waldmann, M. Wilka, M. Kasper, M. Fleischhammer and M. Wohlfahrt-Mehrens, J. Power Sources, 262, 129 (2014).