Nanocarbon-enabled mitigation of sulfur expansion in lithium–sulfur batteries

Significant lithiation-induced sulfur expansion hinders the development of commercial lithium–sulfur (Li–S) batteries, highlighting a pressing need to comprehend the sulfur lithiation mechanism. Coupled molecular dynamics (MD) and finite element analysis (FEA) simulations were used to unveil the chemo-mechanics of rate-dependent sulfur anomalous volumetric changes. The lithiation-induced sulfur transition was found to proceed in four stages, ranging from sulfur lithiation to the formation of Li2S. Lithiation induced sulfur swelling and shrinking, which were accompanied by increased and decreased lithiation stresses, respectively. Although the precipitation of Li2S4, Li2S2, and Li2S resulted in partial lithiation of the sulfur, the formation of these precipitates in turn buffered sulfur expansion by 48.64 %. A high current density was able to mitigate lithiation-induced sulfur expansion with trade-off in battery-specific capacity degradation. Nanocarbons, characterized by high porosity and outstanding mechanical properties, were robust enough to guide sulfur expansion along their open ends, thus effectively buffering sulfur volume change. Our findings provide a new mechanism for previously unexplained experimental observations, advance the understanding of sulfur expansion-caused cathode deterioration, and offer a new design guideline for high-performance Li–S batteries.