Photothermally Powered Wearable Thermal Battery Through Segmental Polymer Motion‐Driven, Solid‐Solid Phase Change with Durable and High Energy Density

Thermal batteries, designed for storing and on-demand releasing of heat, require multifunctional materials that can directly charge using sunlight and provide high energy density and power density over repeated charge-discharge cycles. Accordingly, we describe a hybrid polymer through a single-pot cross-linking of soft, flexible polyethene glycol (PEG) chains with thermally rigid polystyrene co-allyl alcohol framework, in the presence of graphene oxide (GO). The resulting graphene oxide incorporated poly (ethylene glycol)-toluene diisocyanate-poly(styrene-co-allyl alcohol) (GO-PTP) exhibits a reversible, crystalline-amorphous phase transition between 323 and 333 K, with an enthalpy of 121 J/g. Uniform incorporation of GO within PTP enhances its thermal conductivity by 2.5 times (@4 wt.% loading of GO) and, importantly, supports direct photo-thermal charging with excellent heat-storage efficiency (97%). Detailed temperature-dependent diffraction and NMR analysis reveal a constrained (-15°C to +15°C) and thermally-labile (>+15°C) PEG-chain dynamics. Importantly, this overcomes a fundamental mutual exclusivity with both high energy density (50 Wh/kg) and excellent power density (129 W/kg), with stable behavior over 300 continuous cycles, surpassing DoE targets for phase-change based thermal storage. Finally, seamless inclusion of GO-PTP onto cotton, wearable patch that rapidly charges under sunlight (∼360 s) and discharges in dark (∼900 s), achieving personalized thermal comfort.