Viologen-based polymers with extended π-conjugation structure to boost zinc-iodine battery performance by constructing efficient electric double layers

Highly cost-effective and safe aqueous zinc-iodine (Zn-I₂) batteries remain hindered by the so-called polyiodide ion shuttle effect. In this study, a series of viologen-based polymers (VIPA-I, VIPB-I, and VIPC-I) were developed as cathodes for Zn-I₂ batteries based on the “electric double layer (EDL)” concept. The electrostatic interaction between EDL and polyiodide can be well modulated by extending the π-conjugated structure of the polymer, thus effectively inhibiting the shuttling of polyiodide and improving the electrochemical performance of the Zn-I₂ battery. By taking the VIPC-I cathode as an optimal example, it exhibits excellent reversible redox behavior, a high specific capacity of 169.8 mAh g⁻¹ at a current density of 0.1 A g⁻¹, and excellent rate performance (0.2 A g⁻¹-146.9 mAh g⁻¹, 3.0 A g⁻¹-119.0 mAh g⁻¹). This work provides a new strategy to develop intrinsically safe, high-rate, and long-lifespan Zn-I₂ batteries by tuning the EDL structures of polymeric cathodes.