One challenge of battery model development is that many parameters necessary for the battery model are difficult to measure or quantify. For example, the effective diffusion coefficient of lithium ions within the cell is affected by the electrode thickness. This diffusion coefficient, however, was usually treated as a constant in previous work.
This work develops an improved physics-based battery model. The model is developed based on the principles of mass and charge conservation, as well as the electrochemical kinetics for an NCM111 half-cell. The model treats the lithium ion diffusion coefficient as a function of the electrode thickness. The relationship between the lithium ion diffusion coefficient and the electrode thickness is determined by fitting the model with the experimental data. Four half cells are fabricated and tested, and the positive electrode for each cell has a thickness of 46um, 64um, 73um, and 130um, respectively. The lithium diffusion coefficient is found to increase linearly with the electrode thickness. The model is validated at various discharge rates for the cells with different positive electrode thicknesses. It is found that, the utilization of the cell capacity decreases slowly with the increase of the electrode thickness at a low discharge rate. At high discharge rates, the cell with a thick electrode has much poorer rate capability than that with the thin electrode. The physics-based model proposed in the research can be extended to include more cell design parameters. Thus it allows for a better understanding of the influence of cell design parameters on battery performance, and will enable the engineer to more easily design a cell with optimal performance.