Reducing the cathode Thiele modulus to promote the discharge capacity of lithium–sulfur batteries

Lithium–sulfur (Li–S) batteries exhibit exceptional high theoretical energy density. However, their practical application is hindered by premature termination of discharge, which severely limits the discharge capacity and achievable energy density even at low discharge rates. This contribution identifies blocked mass transfer as the primary limitation through relaxation analysis. Both X-ray computed tomography and finite element simulation manifest that the preferential solid deposition at the working cathode surface obstructs the mass transfer pathway and triggers premature discharge termination. The Thiele modulus of a thick cathode is utilized to elucidate the disparity between electrochemical reaction and mass transfer rates, underscoring internal diffusion limitations as the root cause. This understanding affords a theoretical framework for optimizing cathode structures. By reducing the Thiele modulus, an enhanced energy density of 436 Wh kg⁻¹ is achieved in Li–S pouch cells. This work advances the understanding of multi-phase reactions in Li–S batteries and offers insights to electrochemical systems involving multi-phase conversions.