Thermodynamically Driven Phase Separation for Wearable Ionic Thermoelectrics

Abstract

The integration of high thermoelectric performance, mechanical compliance, and self-healing capability in ionic conductors remains a fundamental challenge for wearable energy technologies. Here, these limitations are overcome through the thermodynamic design of phase-separated ionic gels. By precisely modulating the interactions between the in situ polymerizable hydrophilic matrix (PDAC) (Poly([2-(Acryloyloxy)ethyl]dimethylammonium chloride)) and the hydrophobic ionic liquid (EMIM:TFSI) (1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide), spontaneous formation of bicontinuous microstructures is achieved that simultaneously deliver record-high thermopower (30.80 mV K−1), exceptional mechanical properties (762% strain, 2862.51 kJ m−3 toughness), and self-healing efficiency (85% thermal voltage retention). The microstructure emerges from balanced enthalpic-entropic contributions as predicted by Flory-Huggins theory, creating percolated ion-selective transport channels within a deformable polymer skeleton while maintaining interfacial stability. This approach overcomes the long-standing trade-offs among ionic thermophoresis, mechanical robustness, and reparability in conventional ionic thermoelectrics. As a demonstration, 3D-printed stretchable thermoelectric wristbands with outstanding energy-harvesting performance are fabricated. The work establishes a paradigm for multifunctional ionic materials, with immediate applications in wearable thermal energy harvesting and adaptive sensors, while providing a framework for next-generation soft electronics.