Wednesday, 4 October 2017
Prince George's Exhibit Hall D/E (Gaylord National Resort and Convention Center)
In order to improve the performance of Lithium ion secondary batteries (LiBs) for electric vehicles and hybrid electric vehicles, it is very important to understanding the internal transport phenomena under high rate condition to increase power density. In our previous studies, we focused on the actual porous electrode structure, and the Li ion and electron conductivity was evaluated by the effective conductive path with the actual reconstruction electrode structure . In addition, the charge-discharge performance was simulated with the model of reaction and mass transfer in heterogeneous porous electrode structure . This model was developed with the multi-block method which is the method of coarse graining to keep the information of heterogeneous structure . Furthermore, in order to design high capacity anodes based on volumetrically expanding active materials for lithium-ion batteries, we investigated the effects of the expansion ratio of active materials on the charge capacity by carrying out numerical simulations based on the porous electrode theory . In this simulation, as assumptions, Li concentration and potential distribution in active material (AM) and electrolyte (EL) were calculated with Butler-Volmer equation as the boundary condition of the interface between AM and EL. it was assumed that temperature is constant, the formation of SEI is ignored, binder phase inhibit ionic transfer. From these calculation results, the effect of heterogeneous porous structure, which consist of active material, conductive material and binder, on the cell performance could be evaluated. Especially, we focused on the dynamic effective parameter which means the ratio of the effective ionic conductivity in porous electrode between the local time and the initial condition. In the case of expansion ratios of 0.5, which means the 50 % enlargement of active material at the SOC=100%, this value becomes approximately 0.24. Thus, the effective ionic conductivity decrease about 0.2 times than that at initial condition. However, in order to examine then in detail, there are some subjects. In this study, the effect of various expansion ratio and the aggregate structure of active materials was examined. And also, the validity of this simulation was evaluated with some experimental charge-discharge curve and direct observation of volume expansion. Figure 2 shows the cross section view of cell under charge condition and the change of electrode layer thickness. In our presentation, we will discuss the effect of the micro-scale structure on cell performance with volume expansion and the validity of this simulation.