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

Abstract

Harvesting body heat using thermoelectricity provides a promising path to realizing self-powered, wearable electronics that can achieve continuous, long-term, uninterrupted health monitoring. This paper reports a flexible thermoelectric generator (TEG) that provides efficient conversion of body heat to electrical energy. The device relies on a low thermal conductivity aerogel–silicone composite that secures and thermally isolates the individual semiconductor elements that are connected in series using stretchable eutectic gallium-indium (EGaIn) liquid metal interconnects. The composite consists of aerogel particulates mixed into polydimethylsiloxane (PDMS) providing as much as 50% reduction in the thermal conductivity of the silicone elastomer. Worn on the wrist, the flexible TEGs present output power density figures approaching 35 μWcm−2 at an air velocity of 1.2 ms−1, equivalent to walking speed. The results suggest that these flexible TEGs can serve as the main energy source for low-power wearable electronics.

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

“…[ 30 ] More recently, flexible LM‐based TEGs with low thermal conductivity aerogel‐silicone composites have been developed for wearable applications. [ 31 ] While these novel device architectures show great potential for stretchable thermoelectric systems, scalable fabrication and higher power generation are required to reach the full potential of TEGs for wearable applications.…”

Highly Integrated, Wearable Carbon‐Nanotube‐Yarn‐Based Thermoelectric Generators Achieved by Selective Inkjet‐Printed Chemical Doping

“…performances of the previously reported flexible TEGs, [ 5,7,8,12,15,20–22,38,41–48 ] considering the temperature differences given in each report. The power densities of the TEGs were calculated over the entire device area (closed markers) and the TE leg area in contact with the heat source (open markers).…”

“…Note that although the generated voltages gradually decrease when thermal equilibrium is reached after ≈70 s (Figure 5b and S10b, Supporting Information), the output power densities of our body‐heated CNTY‐based TEG are 0.91 and 16 µW cm −2 when normalized by the total device area and TE legs area, respectively, 2–5 orders of magnitude higher than those of previously reported printed or inherently flexible TEGs [ 49–54 ] (Figure 5c and Table S6, Supporting Information). Although this power density is still slightly lower than those of inorganic‐based TEGs, [ 39,44–46,48,55–57 ] a significant improvement has been achieved compared to the previous organic‐based TEGs. Most recent inorganic‐based TEGs adopted flexible heat sinks to increase and prolong Δ T generated‐…”

Multifunctional liquid metal polymer composites

“…(E) Image showing the compactness and flexibility of the LMPC TEG sensor device. Reproduced with permission, 124 copyright 2021, Springer Nature. (F) Schematic contrasting the heat transfer path in shear mixed EGaIn microparticles to surface‐modified EGaIn nanoparticles (SMEE) under compression.…”

“…By integrating low thermal conductivity silicone into the center of the device, heat flow can be directed through the semiconductors instead of the middle layer (Figure 8E). 124 This was done by mixing aerogel particles into PDMS, enabling the enhanced silicone elastomer insulator to achieve a 50% reduction in thermal conductivity over pure PDMS. In a more recent study, by modifying the surface of LM nanoparticles with carboxylic acid terminated polydimethylsiloxane (COOH‐PDMS‐COOH), heat transfer in LMPCs (transverse to the direction of stretching) has been improved 125 .…”