Lithium–sulfur batteries (LSBs) offer high energy density and eco-friendly sulfur cathodes, but commercialization is hindered by slow sulfur redox kinetics and the “shuttle effect”, which limit capacity and cycle life. This study used inverse photoemission spectroscopy and ultraviolet photoelectron spectroscopy (IPES/UPS) to investigate the S redox mechanism. The BNOC matrix, with fully occupied electron states near the Fermi level, enhances conductivity and oxygen covalency by downshifting the lowest unoccupied molecular orbital (LUMO) to hybridize with the highest occupied molecular orbital (HOMO). This matrix traps lithium polysulfides (LiPSs), where loosely bound oxygen atoms facilitate S redox, particularly the key Li₂S ↔ LiPSs conversion. Additionally, the strong covalent B–N bonds, synergizing with the hollow BNOC cages, confine S redox reactions within structurally stable nanoscale spaces, effectively mitigating the shuttle effect. As a result, the LSB in our study delivers extended 1300 cycles at 4 C, maintaining 337.8 mAh·g⁻¹ specific capacity. It also possesses a high areal capacity of 7.76 mAh·cm⁻² at a high sulfur loading of 5.6 mg·cm⁻², and is capable of powering a pouch-type LSB at a current density of 8 mAh·cm⁻² for over 15 cycles. This study lays a foundation for the rational design and performance enhancement of future LSB.