Bottom-up, hard template and scalable approaches toward designing nanostructured Li2S for high performance lithium sulfur batteries

Abstract

Li₂S with a high theoretical capacity of 1166 mA h g⁻¹ and the capability to pair with lithium free anodes has drawn much attention for lithium sulfur (Li–S) battery applications. However, the fast battery decay and the low capacity retention due to dissolution of intermediate polysulfides in electrolytes limit its development. Designing a nanosized and nanostructured host for Li₂S through facile techniques is one of the ways to alleviate the dissolution and improve Li–S battery performance; nevertheless, it is technically difficult to synthesize nanosized and nanostructured hosts for Li₂S because Li₂S is highly sensitive to moisture and oxygen. Herein, a novel technique, i.e., a bottom-up, hard template and scalable method, is proposed to engineer nanoLi₂S composites with core–shell structures as cathodes of Li–S batteries. The size of the as-prepared nanostructured Li₂S is around 100 nm. With the assistance of FETEM, HRTEM and EFTEM elemental mapping, an excellent core–shell structure has been confirmed and the outside carbon shell has a thickness of 20–50 nm, effectively retarding polysulfide outflow and dissolution. A high initial capacity of 915 mA h g⁻¹ at 0.2 C has been achieved upon electrochemical cycling and the battery still has exceptional capacity retention after prolonged 200 cycles with a limited decay of 0.18% per cycle. Also, at 0.5 C the electrode exhibits 60% capacity retention with a long life of 300 cycles. We attribute these good performances to the nano-architecture constructed by the novel and facile method.