Nitrogen-doped hollow carbon@tin disulfide as a bipolar dynamic host for lithium-sulfur batteries with enhanced kinetics and cyclability.

Lithium-sulfur batteries (LSBs) are promising next-generation electrochemical energy storage systems owing to high theoretical specific capacity (1675 mAh/g) and low cost. However, the shuttling effect of soluble polysulfides with slow conversion kinetics has deferred their commercial applications. The feasible design and synthesis of composite cathode hosts offer a promise solution to improving their electrochemical performances. In this work, tin disulfide (SnS2) nanosheets were anchored on nitrogen-doped hollow carbon with mesoporous shells, forming a bipolar dynamic host ("SnS2@NHCS"). It can efficiently confine the polysulfides and promote their conversion during (dis)charge. The as-assembled LSBs delivered a high capacity, superior rate and cyclability. This work presents a new view on the exploration of novel composite electrode materials for various rechargeable batteries with emerging applications.

Highly Reversible Sodiation/Desodiation from a Carbon-Sandwiched SnS2 Nanosheet Anode for Sodium Ion Batteries.

The further improvement of sodium ion batteries requires the elucidation of the mechanisms pertaining to reversibility, which allows the novel design of the electrode structure. Here, through a hydrogel-embedding method, we are able to confine the growth of few-layer SnS2 nanosheets between a nitrogen- and sulfur-doped carbon nanotube (NS-CNT) and amorphous carbon. The obtained carbon-sandwiched SnS2 nanosheets demonstrate excellent sodium storage properties. In operando small-angle X-ray scattering combined with the ex situ X-ray absorption near edge spectra reveal that the redox reactions between SnS2/NS-CNT and the sodium ion are highly reversible. On the contrary, the nanostructure evolution is found to be irreversible, in which the SnS2 nanosheets collapse, followed by the regeneration of SnS2 nanoparticles. This work provides operando insights into the chemical environment evolution and structure change of SnS2-based anodes, elucidating its reversible reaction mechanism, and illustrates the significance of engineered carbon support in ensuring the electrode structure stability.

Deterministic Two-Dimensional Polymorphism Growth of Hexagonal n-Type SnS2 and Orthorhombic p-Type SnS Crystals.

van der Waals layered materials have large crystal anisotropy and crystallize spontaneously into two-dimensional (2D) morphologies. Two-dimensional materials with hexagonal lattices are emerging 2D confined electronic systems at the limit of one or three atom thickness. Often these 2D lattices also form orthorhombic symmetries, but these materials have not been extensively investigated, mainly due to thermodynamic instability during crystal growth. Here, we show controlled polymorphic growth of 2D tin-sulfide crystals of either hexagonal SnS2 or orthorhombic SnS. Addition of H2 during the growth reaction enables selective determination of either n-type SnS2 or p-type SnS 2D crystal of dissimilar energy band gap of 2.77 eV (SnS2) or 1.26 eV (SnS) as a final product. Based on this synthetic 2D polymorphism of p-n crystals, we also demonstrate p-n heterojunctions for rectifiers and photovoltaic cells, and complementary inverters.