Ballistic ion transport through hierarchically-ordered-structure polymer binder

Abstract

Since its discovery in the 1970s, solid-state ion conduction within polymers has primarily relied on polymer segmental motion to drive ion diffusion. However, ion transport based on polymer dynamics features low ionic conductivity (usually <10⁻⁵ S cm⁻¹) at room temperature and highly depends on temperature, which influences performance by controlling the ratio of amorphous to crystalline composition in polymers. A faster ion transport mechanism, independent of polymer dynamics, has long been sought but remains inaccessible. Here, we report a ballistic ion transport mechanism in a mixed electronic-ionic conductive (MEIC) polymer binder, where its hierarchically ordered structure facilitates ion diffusion and achieves solid-state Li⁺ conductivity in the range of 10⁻⁴ to 10⁻³ S cm⁻¹ from −20 to 70 °C. This mechanically robust MEIC polymer is a versatile ionic conductor, allowing Li⁺, Na⁺, or K⁺ to diffuse through the polymer matrix, with their cationic charges counterbalanced by electrons on conjugated polymer backbones. Traditional polymer binders have typically been classified as inactive materials due to their negligible capacity. In contrast, this polymer binder features a high Li⁺ ion capacity of nearly 1000 mA h g⁻¹, transforming it into an active material and providing a method to enhance energy density. This work establishes a foundation and inspires a design principle for engineering multifunctional polymer binders with superionic conductivity, high electronic conductivity, high capacity, and mechanical robustness, thereby extending their applications in the field of solid-state energy.