Porous and heterostructured molybdenum-based phosphide and oxide nanobelts assisted by the structural engineering to enhance polysulfide anchoring and conversion for lithium–sulfur batteries

Abstract

Lithium-sulfur batteries have ultra-high theoretical energy densities, which make them one of the most promising next-generation energy storage systems. However, it is still difficult to achieve large-scale commercialization because of fast capacity fade and poor rate capabilities. These problems are mainly caused by the severe shuttle effect of lithium polysulfide (LiPS) and slow redox kinetics. To solve these barriers, herein a modification strategy of functional separator is prepared by coating heterostructured and defective MoP-MoO2 with porous carbon nanofibers (PCNFs) on the surface of a commercial separator. Moreover, for the first time, we detailly explored the formation processes of various heterojunction (MoP-MoO2, Mo3P-MoO2 and MoP-Mo3P) derived from MoO3 nanobelts and put forward some conceptions for the constituting heterostructured MoP-MoO2 through the phosphorization of MoO3 precursor. The functional coating layer exhibits both satisfactory interception ability for LiPS shuttle and fast LiPS conversion ability due to abundant anchoring sites of heterostructured MoP-MoO2 nanobelts and shortened lithium ion channels of the prepared PCNFs. Benefiting from these advantages, the assembled Li-S battery with MoP-MoO2/PCNFs separator delivered a high specific capacity of 1078.9 mAh g−1 at 1C and 1056.7 mAh g−1 at 2C, excellent cycling stability (856.9 mAh g−1 after 400 cycles at 1C and 630.1 mAh g−1 after 500 cycles at 2C). The cell with MoP-MoO2/PCNFs separator manifested outstanding cycle performance with fading rate of 0.08 % at 0.5C after 300 cycles under a sulfur loading of 4.0 mg cm−2. The novel work will provide a new strategy by which the modified separator with the heterostructured transition metal phosphides and oxides can be applied for high-performance Li–S batteries and shows great potential for practical application.