ABSTRACT
Flexible wearable thermoelectric (TE) devices hold great promise for a wide range of applications in human thermal management and self-powered systems. Currently, the main challenge faced by flexible TE devices is the inadequate dissipation of heat, which hinders the maintenance of significant temperature differences over prolonged periods. Most existing heat sinks, being rigid in nature, compromise the overall flexibility of the device. Therefore, the challenge lies in maintaining device flexibility while ensuring effective heat dissipation. In this study, we developed a flexible phase-change material (FPCM) heat sink to address this issue and enhance the heat dissipation capabilities of TE devices (FPCM-TED). When used as a thermoelectric cooler (TEC), the FPCM heat sink efficiently absorbs heat from the hot end, enabling long-lasting and high-performance cooling of the TEC. This capability effectively reduces body temperature by up to 11.21 °C and can be sustained for at least 300 s. Additionally, when employed as a thermoelectric generator (TEG), the FPCM absorbs heat at the cold end, thereby increasing the temperature difference between the hot and cold ends and enhancing the output performance of the device. By integrating FPCM-TED into a fabric wristband, we successfully developed a self-powered wireless pedometer sensing system. This breakthrough lays a solid foundation for the application of wearable, smart clothing.
ABSTRACT
Flexible thermoelectric generators (f-TEGs) offer an opportunity to realize wearable, self-powered electronic devices. A typical f-TEG consists of flexible electrodes and rigid thermoelectric (TE) legs in a flexible package. In the realm of f-TEGs utilizing flexible electrodes and TE cuboids, our unwavering objective lies in the attainment of enhanced flexibility and elevated energy conversion efficiency. In this paper, we employ a quasi-three-dimensional thermal model to design an f-TEG with a rhombus gap structure (E/A-RhTEG) with its optimized performance validated by simulation and experiment. Additionally, the lateral and vertical thermal resistances are introduced to further explain the optimizing principle in the f-TEG's output performance. Compared with the conventional TEG with a rectangular air gap structure (E/A-ReTEG), E/A-RhTEG demonstrates improved energy conversion efficiency to some extent. Simulation results indicate that the output power and energy conversion efficiency of a 25-np-pair E/A-RhTEG at a 30 K temperature gradient reach 8.45 mW and 2.55%, which represent a performance improvement of 3.09 and 6.28%, respectively, compared to E/A-ReTEG. To further elucidate the optimization principle in the performance of f-TEGs, additional considerations are given to the lateral and vertical resistances. In this study, E/A-RhTEG comprising 25 np pairs is fabricated utilizing TE cuboids. Experimental findings indicate that E/A-RhTEG exhibits a voltage output of 127.07 mV when subjected to a temperature difference of 30 K, which demonstrates a performance enhancement of 4.06% compared to E/A-ReTEG. Furthermore, this study also demonstrates its implementation when wrapped around a curved surface and successfully achieves a self-powered device system after device performance optimization.