Tailoring carbon shell thickness in graphene–Li ₂ S–carbon nanocomposite cathodes for enhanced polysulfide control and electrochemical stability

Lithium-sulfur (Li-S) batteries are promising next-generation energy storage systems due to their high theoretical energy density and the abundance of sulfur; however, their practical application is severely limited by the poor electrical and ionic conductivity of Li₂S and the dissolution of intermediate polysulfides. In this work, a comprehensive multiphysics simulation study is conducted to investigate the influence of carbon shell thickness (0-20 nm) on the electrochemical, thermal, and ionic performance of graphene-Li₂S-carbon nanocomposite cathodes under experimentally realizable conditions (1C discharge rate and 35 °C). The model, developed using COMSOL Multiphysics, couples heat transfer, ion transport, and electric current conservation to capture the complex interactions governing cathode behavior. To ensure experimental relevance and reliability, the simulation results are rigorously validated against reported experimental voltage-capacity data for graphene-Li₂S-carbon cathodes, achieving a low root mean square error of 0.09 V. The results reveal that a carbon shell thickness of approximately 10 nm provides an optimal balance between polysulfide confinement and lithium-ion transport, leading to minimized temperature rise, reduced ionic resistance, and improved current-density uniformity. By establishing a quantitative agreement with experimental literature, this study offers a predictive and experimentally grounded framework for the rational design and optimization of high-performance Li-S battery cathodes.