Construction of PEI-Based Sulfur-Containing Polymers Molecular Framework with Enhanced Lithium Diffusion and Long-Term Stability for High-Performance Lithium–Sulfur Batteries

Organic sulfur cathodes for lithium–sulfur (Li–S) batteries hold great promise for suppressing polysulfide shuttling, yet their practical implementation is hindered by sluggish Li + transport kinetics and intricate synthesis processes. Here, we present a catalyst-free solid-state synthesis strategy to construct a sulfur-containing polymer molecular framework (PEI@TPAL@S) by integrating terephthalaldehyde-based motifs (TPAL) and sulfur clusters into a polyethylenimine (PEI) backbone. The designed framework features abundant nitrogen-active sites and hierarchically interconnected nanopores, synergistically enhancing polysulfide confinement and Li + diffusion. The PEI@TPAL@S cathode achieves a sulfur content of 77.0 wt %, a Li + diffusion coefficient 100-fold higher than conventional sulfur-containing polymers and exceptional rate capability (726 mAh g –1 at 5C). Remarkably, it demonstrates ultralong cycling stability with a minimal capacity decay rate of 0.051% per cycle over 500 cycles at 5C. Mechanistic studies reveal that the covalent Li–N bonding and porous architecture facilitate efficient polysulfide adsorption and rapid Li + transport, while density functional theory (DFT) calculations confirm reduced energy barriers for lithium sulfide nucleation. This work provides a scalable pathway for high-performance organic sulfur cathodes and advances the molecular-level design of sulfur-containing polymers for next-generation energy storage systems.