Heteroatom engineering in hyper-cross-linked polymer electrolytes for stable quasi-solid-state sodium batteries

Quasi-solid-state sodium-ion batteries (SSSIBs) hold great promise for next-generation energy storage owing to their high safety and abundant reserves, but are limited by the low conductivity and interfacial instability of quasi-solid-state electrolytes (SSEs). This study reports a series of porous hyper-crosslinked polymers (HCPs) constructed from heteroaromatic monomers (thiophene, furan, pyrrole) as high-performance quasi-solid electrolytes. Heteroatoms such as sulfur (S), oxygen (O), and nitrogen (N) within the polymer backbone can induce enhanced localized positive charges, strengthening the electrostatic attraction toward ClO₄⁻ anions and promoting anion-ordered migration, thereby effectively reducing the energy barrier for Na⁺ transport. Notably, the S atom in the thiophene structure facilitates Na⁺ migration while anchoring ClO₄⁻ anions, endowing the electrolyte with a high ionic conductivity of 2.75 × 10⁻³ S cm⁻¹, a low activation energy of 0.15 eV, and a wide electrochemical window of 4.70 V. A Na|TP-HCP-E (thiophene-based HCP electrolyte)| Na₃V₂(PO₄)₃ (NVP) full cell exhibits a capacity retention of 62.03% after 4000 cycles at 1C and demonstrates stable charge-discharge performance even at a low temperature of −25 °C. This work elucidates the modulation mechanism of heterocyclic structures on ion transport behavior and interfacial stability at the atomic scale, providing an important foundation for designing novel high-performance SSEs.