The formation of crystalline lithium sulfide on electrocatalytic surfaces in lithium–sulfur batteries

Lithium–sulfur (Li–S) battery is highly regarded as a promising next-generation energy storage device but suffers from sluggish sulfur redox kinetics. Probing the behavior and mechanism of the sulfur species on electrocatalytic surface is the first step to rationally introduce polysulfide electrocatalysts for kinetic promotion in a working battery. Herein, crystalline lithium sulfide (Li₂S) is exclusively observed on electrocatalytic surface with uniform spherical morphology while Li₂S on non-electrocatalytic surface is amorphous and irregular. Further characterization indicates the crystalline Li₂S preferentially participates in the discharge/charge process to render reduced interfacial resistance, high sulfur utilization, and activated sulfur redox reactions. Consequently, crystalline Li₂S is proposed with thermodynamic and kinetic advantages to rationalize the superior performances of Li–S batteries. The evolution of solid Li₂S on electrocatalytic surface not only addresses the polysulfide electrocatalysis strategy, but also inspires further investigation into the chemistry of energy-related processes.