Terminal sulfur atoms formation via defect engineering strategy to promote the conversion of lithium polysulfides

Abstract

The defect engineering shows great potential in boosting the conversion of lithium polysulfides intermediates for high energy density lithium-sulfur batteries (LSBs), yet the catalytic mechanisms remain unclear. Herein, the oxygen-defective Li4Ti5O12-x hollow microspheres uniformly encapsulated by N-doped carbon layer ([email protected]) is delicately designed as an intrinsically polar inorganic sulfur host for the research on the catalytic mechanism. Theoretical simulations have demonstrated that the existence of oxygen deficiencies enhances the adsorption capability of spinel Li4Ti5O12 towards soluble lithium polysulfides. Some -S-S- bonds of the Li2S6 on the defective Li4Ti5O12 surface are fractured by the strong adsorption force, which allows the inert bridging sulfur atoms to be converted into the susceptible terminal sulfur atoms, and reduces the activation energy of the polysulfide conversion in some degree. In addition, with the N-doped carbon layer, secondary hollow microspheres architecture built with primary ultrathin nanosheets provide a large amount of void space and active sites for sulfur storage, adsorption and conversion. The as-designed sulfur host exhibits a remarkable rate capability of 547 mAh g−1 at 4 C (1 C=1675 mA g−1) and an outstanding long-term cyclability (519 mAh g−1 after 1000 cycles at 3 C). Besides, a high specific capacity of 832 mAh g−1 is delivered even after 100 cycles under a high sulfur mass loading of 3.2 mg cm−2, indicating its superior electrochemical performances. This work not only provides a strong proof for the application of oxygen defect in the adsorption and catalytic conversion of lithium polysulfides, but offers a promising avenue to achieve high performance LSBs with the material design concept of incorporating oxygen-deficient spinel structure with hierarchical hollow frameworks.