Enhanced Built-In Electric Field Facilitates Electron and Ion Transfer for High-Performance Lithium–Sulfur Batteries

The complex and multistep redox reactions of sulfur species result in severe polysulfide shuttling, which remains a key obstacle to the practical development of lithium–sulfur batteries (LSBs). To address this challenge, this study employs a rectifying interface constructed from molybdenum dioxide (MoO2) and nitrogen-deficient carbon nitride (DCN), with the aim of enhancing the catalytic conversion efficiency of lithium polysulfides (LiPSs) by regulating electron and ion transport through increased interfacial charge transfer between built-in electric fields. Kelvin probe force microscopy characterization confirms the increase in the work function difference at the heterojunction interface. In situ ultraviolet–visible spectroscopy findings further verify the significant enhancement of LiPS transformation kinetics by the MoO2-DCN heterojunction. The cell with MoO2-DCN separators demonstrates outstanding cycling stability across a wide temperature range (0 to 60 °C); specifically, after 100 cycles, the average capacity fade rates are as low as 0.082% and 0.21% per cycle, respectively. Notably, the cell achieves a high initial areal capacity of 7.39 mAh cm–2 even at the elevated sulfur loading of 6.09 mg cm–2. This work provides important experimental guidance for designing high-performance LSBs through the regulation of the heterointerfacial built-in electric field.