Extraordinary electrochemical performance of lithium-sulfur battery with 2D ultrathin BiOBr/rGO sheet as an efficient sulfur host.

There are many challenges such as the shuttling effect of soluble lithium polysulfides species (LiPSs) and the slow solid-state conversion between LiS and LiS in the development process of lithium-sulfur battery (LSB), so it is vital how to design and fabricate sulfur hosts with strong adsorption and good electrocatalysis. In this work, BiOBr in-situ forms onto both sides of reduced graphene oxide (rGO) to obtain a novel ultrathin BiOBr/rGO sheet, then self-constructing a hydrogel cylinder in shape, via a one-step hydrothermal process. The BiOBr/rGO composite with sandwich structure not only shows the outstanding adsorption effect on LiPSs, resulting from a strong bonding interaction between BiOBr/rGO and LiS demonstrated by XPS technique, but also exhibits the extraordinary electrocatalytic performance on both the LiPSs conversion reaction in cyclic voltammetry experiment of symmetric cell and the LiS nucleation process in potentiostatic deposited experiment, which will significantly improve the electrochemical performance of LSB. The S@BiOBr/rGO electrodes deliver the superior capacity and long cyclic stability with 882.2 mA h g at 0.5 C after 1000 cycles, as well as displays the excellent rate performance with 823.9, 692.6 and 554.2 mA h g at 1 C, 3 C and 5 C, respectively, after 400 cycles. Even though the sulfur loading reaches 4.9 mg cm, the reversible specific capacity of 424.6 mA h gcan be maintained at 0.5 C after 400 cycles. Based on the in-situ X-ray diffraction and in-situ Raman spectroscopy, it could be revealed that the initial discharge process of active sulfur on the BiOBr/rGO cathode is α-S → LiS → LiS → LiS → LiS → LiS, while the charging progress is the corresponding reverse reaction, but the final substance is β-S. This research not only shows that the two-dimensional ultrathin BiOBr/rGO hybrid is successfully developed in LSB with excellent electrochemical performances, but also provides a strategy for exploring the construction of sulfur host materials.