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.