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 stretcha… Show more
“…[ 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.…”
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.
“…[ 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.…”
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.
“…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).…”
Section: Resultsmentioning
confidence: 99%
“…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‐…”
Flexible thermoelectrics that enable conformal contact with heat sources of arbitrary shape are indispensable for self‐powered wearable electronics. Scalable integration of flexible thermoelectric (TE) materials into functional devices has improved over the past few years, however, the practical applications of flexible TE materials are still hindered by low performance. Herein, highly aligned carbon‐nanotube yarns (CNTYs) are proposed, combined with selective doping via picoliter scale inkjet printing. Coagulation assisted by van der Waals forces ensures a highly aligned structure of the CNTY, thus achieving the ultrahigh power factors of 4091 and 4739 µW m−1 K−2 for the p‐ and n‐type, respectively. The proposed TE materials can be effortlessly up‐scaled into highly integrated modules via inkjet printing. A highly integrated, flexible CNTY‐based TE generator (TEG) with 600 PN pairs generates unparalleled milliwatt‐scale power at ΔT = 25 K, which is a few orders of magnitude higher than those of previously reported flexible material‐based TEGs. This TEG successfully powers a red light‐emitting diode using body heat alone, requiring no external power sources. For the seamless operation of practical applications requiring high power, this work explores the key design parameters for flexible TEGs with high performance and manufacturability and presents new platforms for self‐powered wearable electronics.
“…(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.…”
Section: Functional Propertiesmentioning
confidence: 99%
“…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 .…”
Liquid metal polymer composites are an emerging class of functional materials with potentially transformative impacts in wearable electronics, soft robotics, and human-computer interactions. By employing different processing methods, room temperature liquid metal inclusions can be embedded in insulating polymers like elastomers to incorporate functional properties of metals while the matrix remains soft and stretchable. These solid-liquid composites offer an interesting, yet complex multifunctional material system. In this review, we present an exclusive overview of the synthesis methods, structural and functional properties, and applications of gallium-based liquid metal polymer composites. Common methods to control the size of liquid metal inclusions and their interaction in polymers are discussed. Moreover, the effect of liquid metal microstructures on the overall properties of the composites is summarized. We also highlight the new trends in terms of material composition, printing process, and novel applications of liquid metal polymer composites in intelligent systems.
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