Functional Polymers for Ionic Thermoelectrics: Multiscale Design Strategies for Ion Dynamics, Mechanics, and Energy Harvesting.

The efficient conversion of dissipated heat into useful electrical energy has emerged as a promising approach for sustainable energy technologies. Ionic thermoelectrics (iTEs) are particularly attractive because they generate substantial thermo-voltages, effectively harvest low-grade heat, and offer advantages such as cost-effectiveness, easy scalability, and remarkable performance. Unlike liquid-state platforms, quasi-solid-state iTEs exhibit properties that are critically governed by the polymer matrix and polymer-ion interactions, which are closely related to the overall device performance. Consequently, the use of functional polymers effectively improves the characteristics and performance of quasi-solid-state iTEs. Therefore, this paper highlights the impact of the polymer matrix on performance and mechanical properties in iTEs from molecular-, micro-, to macro-scale engineering. Particular emphasis is placed on clarifying the role of polymers at various scales to provide an in-depth understanding of performance enhancement. Furthermore, the current challenges and prospective research directions are discussed, offering guidance toward the development of next-generation iTE-based energy harvesting platforms.