Soft and Stretchable Thermoelectric Generators Enabled by Liquid Metal Elastomer Composites

Abstract

Stretchable thermoelectric generators (TEGs) capable of harvesting electrical energy from body heat under cold weather conditions have the potential to make wearable electronic and robotic systems more lightweight and portable by reducing their dependency on on-board batteries. However, progress depends on the integration of soft conductive materials for robust electrical wiring and thermal management. The use of thermally conductive soft elastomers is especially important for conforming to the body, absorbing body heat, and maintaining a temperature gradient between the two sides of the TEGs in order to generate power. Here, we introduce a soft-matter TEG architecture composed of electrically and thermally conductive liquid metal embedded elastomer (LMEE) composites with integrated arrays of n-type and p-type Bi 2 Te 3 semiconductors. The incorporation of a LMEE as a multifunctional encapsulating material allows for the seamless integration of 100 thermoelectric semiconductor elements into a simplified material layup that has a dimension of 41.0 × 47.3 × 3.0 mm. These stretchable thermoelectric devices generate voltages of 59.96 mV at Δ10 °C, 130 mV at Δ30 °C, and 278.6 mV and a power of 86.6 μW/cm 2 at Δ60 °C. Moreover, they do not electrically or mechanically fail when stretched to strains above 50%, making them well-suited for energy harvesting in soft electronics and wearable computing applications.

Advanced Wearable Thermocells for Body Heat Harvesting

“…The emergence of wearable electronic devices has stimulated the demand for a flexible, light-weight, and high-efficiency power supply system. [1,2] In contrast to more traditional energy storage systems (e.g., batteries [3] and supercapacitors [4] ), which require manual recharging, flexible energy harvesters (including solar cells, [5] piezoelectric polymer generators, [6,7] triboelectric generators, [8,9] and thermoelectric generators [10][11][12][13] ) convert energy from the local environment, including mechanical motion or temperature gradients from the human body, to electrical charge. [14,15] These energy harvesters are environmentally friendly power sources, which potentially provide a pathway toward the elimination of manual device charging and a reduction in battery waste.…”

“…[10] Among these power sources, thermoelectric generators (TEG) attached to the human body are highly attractive, as the heat continually being emitted by the body (up to 20 mW cm −2 ) enables a constant power supply, in contrast to motion-based, or solar-based energy harvesting technologies. [10][11][12][13]16,17] We have recently discussed the promising prospect of body heat harvesting in the future global market of wearable electronics and provided possible designs for a skin-conformal TEG. [10] However, the relatively low Seebeck coefficient (S e = ∆V/∆T, where ∆V is the open circuit voltage and ∆T is the temperature gradient) on the order of µV K −1 [18] and the reliance on rigid and expensive thermoelectric materials have greatly limited the practical development of TEGs for wearable applications.…”

Ultrastretchable, Wearable Triboelectric Nanogenerator Based on Sedimented Liquid Metal Elastomer Composite

“…Compared to emerging battery technologies that are soft and stretchable, [ 8–11 ] energy harvesting technologies are especially promising since they are renewable and self‐sustaining (i.e., do not require recharging) and have the potential to generate adequate power for operating consumer‐grade wearable electronics. [ 12–16 ] Among various methods for energy harvesting, triboelectric nanogenerators (TENGs) are cost‐effective and sustainable power sources that can transform mechanical energy into electricity by coupling the effect of contact electrification and electrostatic induction. [ 17–20 ] For most wearable electronic applications, TENGs should be soft, flexible, and stretchable so that they can be incorporated into garments and conform to limbs and joints.…”

Flexible thermoelectric generator with liquid metal interconnects and low thermal conductivity silicone filler

“…We have not observed any evidence of EGaIn leakage through the elastomer during repetitive bending cycles. However, in a recent study by Zadan et al, EGaIn droplets embedded in PDMS were used to create the interconnects in a flexible thermoelectric module 60 . The elastomer was mechanically activated in order to create electrically conductive traces.…”