Expediting Stepwise Sulfur Conversion via Spontaneous Built-In Electric Field and Binary Sulfiphilic Effect of Conductive NbB2-MXene Heterostructure in Lithium-Sulfur Batteries

Fabricating metal boride heterostructures and deciphering their interface interaction mechanism on accelerating polysulfide conversion at atomic levels are meaningful yet challenging in lithium-sulfur batteries (LSBs). Herein, novel highly-conductive and binary sulfiphilic NbB2-MXene heterostructures are elaborately designed with spontaneous built-in electric field (BIEF) via a simple one-step borothermal reduction strategy. Experimental and theoretical results reveal that Nb and B atoms can chemically bond with polysulfides, thereby enriching chemical anchor and catalytic active sites. Meanwhile, the spontaneous BIEF induces interfacial charge redistribution to make more electrons transferred to surface NbB2 sites, thereby weakening its strong adsorption property yet accelerating polysulfide transfer and electron diffusion on hetero-interface, so providing moderate polysulfide adsorb-ability yet decreasing sulfur-species conversion energy barriers, further boosting the intrinsically catalytic activity of NbB2-MXene for accelerated bidirectional sulfur conversion. Thus, S/NbB2-MXene cathode presents high initial capacity of 1310.1 mAh g(-1) at 0.1 C, stable long-term lifespan with 500 cycles (0.076% capacity decay per cycle) at 1 C, and large areal capacity of 6.5 mAh cm(-2) (sulfur loading: 7.0 mg cm(-2) in lean electrolyte of 5 mu L mg(s)(-1)) at 0.1 C. This work clearly unveils the mechanism of interfacial BIEF and binary sulfiphilic effect on accelerating stepwise sulfur conversion at atomic levels.