Dual-locking interface engineering via in-situ grown covalent organic framework for high-rate and stable sulfurized polyacrylonitrile cathodes

Sulfurized polyacrylonitrile (SPAN) is a promising cathode for lithium–sulfur (Li–S) batteries owing to high coulombic efficiency. However, its practical application is hindered by significant volume expansion and sluggish reaction kinetics. This study addresses these limitations by constructing a molecularly engineered coating with a TAPA-TPAL covalent organic framework (TT-COF), designed for integrated dual electronic and chemical regulation. TT-COF's polarized conjugated structure forms electron-rich/deficient domains, lowering its lowest unoccupied molecular orbital (LUMO) energy level below SPAN's highest occupied molecular orbital (HOMO). This enhances charge separation, reduces interfacial resistance, and accelerates reaction kinetics. Covalent grafting via imine linkages further mitigates electrode cracking. By stabilizing the electrode-electrolyte interface, we exploit TT-COF's 1.9 nm uniform pores and intrinsic electric field to establish a model that selectively sieves ions and reorganizes their bonding environments—outperforming conventional physical size-exclusion methods via partial covalent bonding. Integrating these merits, a self-regulating system is developed to relieve mechanical strain: TT-COF dissipates stress through in-situ formed chemically bonded coatings, ensuring stability under extreme conditions. Consequently, SPAN@TT-COF retains 91.6% capacity after 300 cycles at 0.2 C. It also exhibits more stable long-term cycling at 10 C while maintaining its structural integrity. This advancement effectively resolves the longstanding trade-off between rate capability, capacity, and cycle life.