Printing Liquid Metal Elastomer Composites for High‐Performance Stretchable Thermoelectric Generators

Abstract

Continuous powering of wearable electronics and personalized biomonitoring systems remains a great challenge. One promising solution is the use of thermoelectric generators (TEGs) that convert body heat to electricity. These energy harvesters must conform to curved surfaces and minimize thermal barriers to maintain efficiency while still exhibiting durability under large deformations. Here, highly efficient, stretchable thermoelectric generators made of inorganic semiconductors and printed multifunctional soft matter are introduced. Liquid metal elastomer composites with tailored microstructures are printed as highly conductive thermal interface materials and stretchable interconnects. Additionally, elastomer composites with hollow microspheres are formulated to print a deformable and lightweight thermal insulator within the device. These stretchable thermoelectric wearables show an excellent performance by generating an open‐circuit voltage of 392 mV and a power density of ≈650 µW cm−2 at ∆T = 60 °C and withstanding more than 15 000 stretching cycles at 30% strain. Furthermore, the additive manufacturing process is leveraged by direct writing of the TEGs on textiles to demonstrate their seamless integration and by 3D printing of stretchable heatsinks to maintain a large temperature gradient across the device and to study the effect of convective heat transfer on device performance.

3D Printing of Liquid Metal Embedded Elastomers for Soft Thermal and Electrical Materials

“…2,9 This makes LMEEs especially useful as thermal interface materials to manage heat generated by microprocessors, electronics, and thermoelectric devices (TEDs). 11,26,40 Here we show that 3D printing can be used to further enhance the thermal management properties of LMEE through the creation of high aspect ratio, mechanically deformable, fin-based heat sinks for flexible thermoelectrics.…”

“…In addition to functioning as an electrically conductive electrode for TENGs, LMEEs can also be engineered as electrical insulators that exhibit an exceptional combination of low mechanical stiffness and high thermal conductivity. , This makes LMEEs especially useful as thermal interface materials to manage heat generated by microprocessors, electronics, and thermoelectric devices (TEDs). ,, Here we show that 3D printing can be used to further enhance the thermal management properties of LMEE through the creation of high aspect ratio, mechanically deformable, fin-based heat sinks for flexible thermoelectrics.…”

“…Han et al demonstrated Seebeck energy harvesting potential with a concentric rectangular 1 mm high printed heat sink. This generated an ≈16.5% increase in performance compared without the heat sink …”

“…This generated an ≈16.5% increase in performance compared without the heat sink. 40 To highlight the compliance and deformability of the 3D printed LMEE heat sink, we further fabricated a wearable wrist worn garment-like Peltier device for limb cooling based on work by Zadan et al (see the Methods section) (Figure 7d). The 3D printed LMEE heat sink adhered to the surface of the wearable thermoelectric device and was able to improve performance by facilitating the convection of heat.…”

X-ray scattering as an effective tool for characterizing liquid metal composite morphology

“…Present techniques utilize imaging, either through optical or electron microscopy, and often image analysis to determine number-averaged size distributions of the inclusions. [25][26][27][28][29] While these procedures are widely accepted, they are time-intensive and are only capable of analyzing a limited number of inclusions that are visible within a particular field of view. A technique for determining bulk, volumeaveraged size distributions is currently lacking.…”