A dihydroquinoline-conjugated polymer cathode with a hierarchical structure and abundant redox-active sites for aluminum-ion batteries

Abstract

Redox-active organic polymers have shown promise as sustainable cathode elements for aluminum-ion batteries (AIBs) owing to their multi-electron redox capability, high theoretical capacity, and elevated redox potential. However, the low density of redox-active sites, low intrinsic conductivity, and dissolution-induced shuttle effects frequently restrict their practical use. In this work, a novel dihydroquinoline-based conjugated polymer with a hierarchical structure, denoted as NaphPz, was designed and synthesized as a cathode material for AIBs. Benefiting from its large specific surface area, high density of redox-active sites, and dual p-type redox behavior characteristics, the NaphPz cathode delivered excellent electrochemical performance. The assembled Al-NaphPz battery achieved a high discharge capacity of 245 mAh g⁻¹ and a coulombic efficiency of 97.2% at 0.1 A g⁻¹. Even at a high current density of 0.8 A g⁻¹, the battery retained a capacity of 115 mAh g⁻¹ with a coulombic efficiency exceeding 99%. Furthermore, the use of multi-walled carbon nanotubes and graphene oxide-coated separators (MCNT-GO-S) effectively mitigated the dissolution of NaphPz, significantly improving the cycling stability. The battery incorporating MCNT-GO-S retained 91.8% of its initial capacity after 500 cycles at 0.8 A g⁻¹. This study presents a feasible method for creating high-performance organic cathode materials and highlights the enormous potential of dihydroquinoline-based organic polymers in AIBs.