It is well-known that electrochemical impedance spectra (EIS) can provide important information about the diffusion and reaction processes in Li-S systems. While there is a large amount of experimental characterization of Li-S batteries using EIS, the theoretical modeling is mostly limited to simplified models based equivalent circuits. While these simplified models provide important information about the resistance of the electrolyte, the charge transfer resistance, and double layer capacitance, they fail to provide a more detailed physical understanding of the electrochemical processes inside the battery. Such an understanding can be provided by physics-based models, in particular by finite element models.

In this work we present for the first time a numerical method for the computation of electrochemical spectra in Li-S batteries based on finite element simulations. The model has the advantage that it is entirely framed in terms of measurable quantities, such as ion mobilities and diffusivities, reaction rate parameters, and double layer capacitance. The model is formulated in the form of a nonlinear system of partial differential equations derived from our previous work¹ and which can be easily implemented numerically in standard battery simulators. In addition, the model can accurately describe the depressed semicircles of the EIS. More details about the numerical implementation of the method and a comparison with experimental results will be presented at the conference.

References

1. P. Andrei, C. Shen, and J. P. Zheng, Electrochim. Acta, 284, 469–484 (2018)