However, experimental evidences suggest that even the first discharge capacity is appreciably lower than the theoretical limit. This non-ideality is usually associated with the so-called “polysulfide shuttle effect”. On the cathode side, solid sulfur dissolves in the electrolyte and undergoes successive reduction to different intermediate and reduced-order sulfide ions. Due to the underlying potential and concentration gradients, these negative ions travel toward the anode and chemically oxidize the lithium metal, while being reduced simultaneously. Theoretical capacity is achieved when sulfur undergoes complete electrochemical reduction; hence the above chemical reaction(s) limit the available capacity.
Lithium sulfide (Li2S) is the final discharge product which forms when the ionic product exceeds the solubility limit. This can passivate the surface, block the porous structure and may lead to the reacting species starvation in the cathode.
The shuttle effect is a resultant manifestation of these coupled phenomena. In this work, a computational study is presented in order to quantify the influence of shuttle effect on the Li-S cell capacity. The model correlates concentration evolution and microstructural changes with cell performance. Based on this understanding, electrode modifications such as, cathode coating and microstructure properties are studied in order to fundamentally understand the deleterious influence of the “shuttle effect” on cell performance.