Simulation Study of Sulfurized Polyacrylonitrile (SPAN) as Cathode Material for Li-Sulfur Batteries: Guidelines for Electrode and Cell Design

Kurzfassung

Li-Sulfur (Li-S) batteries are considered promising contenders for the next generation of batteries due to a number of advantages: high specific energy, high abundance of sulfur, and the absence of scarce elements such as nickel or cobalt. Unfortunately, Li-S batteries are known to have low coulombic efficiency and rapid self-discharge due to the polysulfide shuttle. Several mitigation strategies have been developed for Li-S batteries to reduce the polysulfide shuttle effect. One of the most promising approaches is to covalently bond the sulfur to a polymer backbone. Long cycle life and high specific capacities have been demonstrated for sulfurated poly(acrylonitrile) (SPAN) cathodes in lithium-based batteries. In this work, we present a novel continuum model for Li-SPAN batteries that includes redox reactions of sulfur covalently bonded to the polymer backbone of SPAN. In addition, we consider transport and electrochemical reactions of the polysulfides in solution. The model requires a number of parameters that can be obtained from structural and electrochemical characterization of the materials. We parameterize and validate the model with measured charge and discharge curves. Based on the simulations, we analyze the charge and discharge mechanism of the SPAN material and study the impact of different parameters and processes on the cell performance. Furthermore, we found that in the current electrode design, transport in the electrolyte does not limit cell performance. However, in cell designs targeting high energy density, our simulations show that the morphology and microstructure of the SPAN cathode will be critical to achieve practical C-rates. The newly developed SPAN model can be considered as a design tool for Li-SPAN batteries. It will guide the development of new materials and the up-scaling of electrode and cell concepts.