A universal performance-enhancing method for Li-S batteries: the cathode material of Li₂S@Li₂S₂@Li₂S₆ double-shell structure

Lithium sulfide (Li₂S) as a cathode material for lithium-sulfur (Li-S) batteries, one of the most promising advanced batteries in the future, has received tremendous attention in the past decades. However, developing the practical Li₂S cathode confronts challenges of low conductivity for Li-ions and electrons, high sensitivity to environmental moisture, big overpotential barrier to electrochemical activation, and poor cyclability due to the shuttle effect of intermediate species. This article herein reports a simple and effective strategy for making Li₂S@Li₂S₂@Li₂S₆ double-shelled microparticles, which can significantly mitigate these problems. They are synthesized by dissolving Li₂S together with S in dimethoxyethane, then drying off the solvent, and finally calcining the collected solid. Compared with pure Li₂S, such a double-shell material presents a 26.7% improvement in cycling capacity, 0.5 V lower in activation overpotential, and prolonged tolerance in the ambient environment. The density functional theory calculation shows that the performance enhancement lies in the higher stability of Li₂S₆ in contact with moisture and some autocatalytic effect of Li₂S₂@Li₂S₆. Such a double-shell structure becomes a universal performance-enhancing approach when being combined with other means, such as cathodes composited with catalytic MoS₂, separators modified with selenium-doped sulfurized-polyacrylonitrile/montmorillonite, electrolytes containing fluorenone additive, and Li anodes coated with a layer of Li₃N. The corresponding capacity retention shows up to 80% improvement compared with pure Li₂S.