Wearable Power Sources Research Articles

Filling the gap between topological insulator nanomaterials and triboelectric nanogenerators

Reliable energy modules and higher-sensitivity, higher-density, lower-powered sensing systems are constantly required to develop wearable electronics and the Internet of Things technology. As an emerging technology, triboelectric nanogenerators have been potentially guiding the landscape of sustainable power units and energy-efficient sensors. However, the existing triboelectric series is primarily populated by polymers and rubbers, limiting triboelectric sensing plasticity to some extent owing to their stiff surface electronic structures. To enrich the current triboelectric group, we explore the triboelectric properties of the topological insulator nanofilm by Kelvin probe force microscopy and reveal its relatively positive electrification charging performance. Both the larger surface potential difference and the conductive surface states of the nanofilms synergistically improve the charge transfer behavior between the selected triboelectric media, endowing the topological insulator-based triboelectric nanogenerator with considerable output performance. Besides serving as a wearable power source, the ultra-compact device array demonstrates innovative system-level sensing capabilities, including precise monitoring of dynamic objects and real-time signal control at the human-machine interface. This work fills the blank between topological quantum matters and triboelectric nanogenerators and, more importantly, exploits the significant potential of topological insulator nanofilms for self-powered flexible/wearable electronics and scalable sensing technologies.

Mechanical study of perovskite solar cells: opportunities and challenges for wearable power source

We provide a review of current understandings of mechanical properties and fracture behaviors of perovskites that are essential for flexible and stretchable solar cell (SC) applications. We first review the mechanical failure modes in perovskites. We further discuss the underlying mechanisms of mechanical failure and its impact on device degradation in flexible perovskite solar cells (PSCs). Then, we examine the strategies to mitigate these mechanical issues in flexible PSCs. Lastly, we assess the elevated challenges and present recommendations for future research directions to advance the technology towards a fully stretchable and wearable energy source.

Interface engineered silver nanoparticles decorated g-C3N4 nanosheets for textile based triboelectric nanogenerators as wearable power sources

Textile based mechanical energy harvesting devices have emerged out as potential power sources for wearable electronics. For the first time, we report the fabrication of a textile based triboelectric nanogenerator (T-TENG) composed of an active layer of silver (Ag) nanoparticles loaded graphitic carbon nitride (g-C3N4) nanosheets on carbon fibres. The triboelectric characteristics has been found to be dramatically enhanced upon combinatorial effect of Ag nanoparticles loading and interfacial engineering with the introduction of a nylon layer between nanosheets and carbon cloth fibres. With teflon as a counter triboelectric material, under mechanical agitation, the AgCN/nylon bi-layer T-TENG can generate an open circuit voltage of as high as ~ 200 V and charges a commercial capacitor up to ~85 V in only 30 s. The improvement in triboelectric characteristics of the AgCN based bi-layer T-TENG is attributed to Ag nanoparticles induced modifications of surface area, dielectric properties and intrinsic resistivity of the host material. Apart from mechanical impact, the T-TENG can generate electrical output under minute mechanical forces originating from sources like air flow and biomechanical actions when integrated to wearable clothing and the output data can be accessed remotely. The AgCN/nylon-teflon based bi-layer T-TENG is not only stable at higher operating temperatures but also exhibits a higher power conversion efficiency at an elevated temperature (up to ~65 °C), which could be explained by the energetics of the composite system. The superior output characteristics as well as thermal stability of AgCN/nylon based triboelectric nanogenerator makes it a potential candidate for integration into textile based wearable electronic devices.

Stretchable thermoelectric generator for wearable power source and temperature detection applications

Wearable thermoelectric generators are attracting tremendous interest due to their capability of converting the human body heat into electricity for powering electronics. In order to reduce the parasitic thermal resistance and enhance the efficiency of the energy harvesting process, the compliance of the device is required by introducing stretchable structures or materials. Thus, in this work, we present a novel stretchable thermoelectric generator (STEG) with 50 pairs of bulk thermoelectric legs connected by the kirigami-inspired flexible electrodes. The device was fabricated by a sacrificial layer assisted soldering fabrication method and its generation performances were characterized under natural and forced convection, as well as constant temperature difference conditions, respectively. The results indicated that the generated power density of the STEG under convection was enhanced by improving the cold-side air velocity, and the power density of the device under constant temperature difference conditions could be promoted with order of magnitudes to 2.7 mW/cm2 at ΔT = 50 K. Besides, the STEG features reliable during the cycling of 30 % tensile strain load and bending with a radius of 5 mm, respectively. Finally, various practical applications of the STEG were investigated including the wearable power supply and temperature detector for human proximity/contact testing and high-temperature alert. Our results demonstrate that the proposed STEG configuration displays high output performance that could be utilized for wearable electronics applications.

Frontiers and Structural Engineering for Building Flexible Zinc-Air Batteries.

With the development of flexible devices, the demand for wearable power sources has increased and gradually become imperative. Zinc–air batteries (ZABs) have attracted lots of research interest due to their high theoretical energy density and excellent safety properties, which can meet the wearable energy supply requirements. Here, the flexibility of energy storage devices is discussed first, followed by the chemistries and development of flexible ZABs. The design of flexible electrodes, the properties of solid‐state electrolytes (SSEs), and the construction of deformable structures are discussed in depth. The researchers working on flexible energy storage devices will benefit from the work.

The direct use of enzymatic biofuel cells as functional bioelectronics

Enzymatic biofuel cells (EBFCs) are a subgroup of fuel cells that use enzymes as catalysts. EBFCs that utilize physiological substrates such as glucose or lactate are of great interest as implantable or wearable power sources to activate medical devices. This contribution introduces the working principles of EBFCs and summarizes recent progress in EBFC-enabled biosensors, pulse generators, and therapy. Biosensors with self-powered characteristic enjoy high selectivity, leading to potential “instrument-free” or “expensive-instrument-free” measurement. Autonomous pulse generation is based on the hybrid of EBFC and supercapacitor, which is promising for the application in medical related electrostimulation. By providing the direct electrical stimulation, or controllably releasing drug, EBFCs can also be used for self-powered therapeutic system. The further combination of self-powered sensing and treating enables EBFC as a possible platform of diagnostics and therapeutics. Future efforts can be focused on resolving the limited power density and lifetime of EBFC.

Wearable Ultrahigh Current Power Source Based on Giant Magnetoelastic Effect in Soft Elastomer System.

In this study, we present the observation of the giant magnetoelastic effect that occurs in soft elastomer systems without the need of external magnetic fields and possesses a magnetomechanical coupling factor that is four times larger than that of traditional rigid metal-based ferromagnetic materials. To investigate the fundamental scientific principles at play, we built a linear model by using COMSOL Multiphysics, which was consistent with the experimental observations. Next, by combining the giant magnetoelastic effect with electromagnetic induction, we developed a magnetoelastic generator (MEG) for biomechanical energy conversion. The wearable MEG demonstrates an ultrahigh output current of 97.17 mA, a low internal impedance of around ∼40 Ω, and an intrinsic waterproof property. We further leveraged the wearable MEG as an ultrahigh current power source to drive a Joule-heating textile for personalized thermoregulation, which increased the temperature of the fiber-shaped resistor by 0.2 °C. The development of the wearable MEG will act as an alternative and compelling approach for on-body electricity generation and arouse a wide range of possibilities in the renewable energy community.

Alkaline sodium polyacrylate-starch hydrogels with tolerance to cold conditions for stretchable zinc-air batteries

With the advancement of wearable electronic devices, it is critical to create a flexible power source that is high performing, cost effective, and safe. The flexible zinc-air battery as a promising candidate has been widely concerned, while most hydrogel electrolytes lose their stretchability in a strong alkaline environment. Herein, a sodium polyacrylate-starch double-network hydrogel is prepared by simple solution copolymerization and swelling techniques. Not only does the hydrogel exhibit exceptional mechanical strength, toughness, and ionic conductivity, but it also exhibits an exceptional freezing-tolerance capability. The stretchable zinc-air battery with sandwich construction has a high energy efficiency of 68%, a high energy density of 67.5 mW cm −2 , and a high degree of dependability in stretched modes. Additionally, the battery performs well mechanically and electrochemically at a cold environment (−20 °C). The batteries can be incorporated into a range of energy-consuming gadgets, suggesting that they are very practicable as wearable power sources. • a hydrogel electrolyte based on sodium polyacrylate and starch was prepared. • Air cathode and Zn anode were designed based on stainless-steel knitted fabric. • The stretchable zinc-air battery operated both under room and cold conditions.

Synergistically Improving Flexibility and Thermoelectric Performance of Composite Yarn by Continuous Ultrathin PEDOT:PSS/DMSO/Ionic Liquid Coating.

Combining fabrics with a poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) coating is the most promising method to fabricate wearable thermoelectric (TE) devices. However, the high modulus, low strain, and low TE performance of PEDOT:PSS coating lead to poor flexibility and low power generation efficiency. In this study, dimethyl sulfoxide (DMSO) and ionic liquids (ILs) were selected as a modifier to enhance the flexibility and TE performance of PEDOT:PSS. Different from the penetrating structure and coil conformation of pristine PEDOT:PSS coating, a flexible continuous ultrathin layer of PEDOT:PSS/DMSO/1-ethyl-3-methylimidazolium dicyanamide (P/D/ED) with a linear conformation forms on the surface of cotton yarn. The morphology and structure of PEDOT:PSS and P/D/ED coating were characterized by FESEM, XPS, and Raman spectroscopy. Compared with the pristine PEDOT:PSS film, the P/D/ED film shows significantly reduced modules and enhanced strain and bending stability. Moreover, the TE performance of P/D/ED-coated yarn is significantly enhanced with nearly half mass loading. Based on this, a large-area wearable TE fabric with enhanced flexibility and TE performance was prepared. The output power density is 136.1 mW/m2 at ΔT = 40.8 K, which is a typically high value compared with the former reported composite TE fabrics. This study provides a new way to synergistically enhance the flexibility and TE performance of composite yarn, and the prepared TE fabric has great potential as a wearable power source.

Fabrication of Millimeter Thick Polymer‐Based Thermoelectric Devices by Solvent‐Free Printing

AbstractSolution‐processable polymer‐based materials allow the fabrication of flexible, light‐weight, and large‐area thermoelectric devices (TEDs). However, solution fabrication processes of polymer‐based materials involve the drying of an organic solvent, which induces an unfavorable material orientation and hinders the formation of a thick thermoelectric layer. These limitations significantly deteriorate the performance of polymer‐based TEDs. In this paper, a polymer‐based TED, fabricated by solvent‐free printing (SFP)—a technique that eliminates the solvent drying process—is reported. A carbon nanotube (CNT)–polymer composite, which is a typical polymer‐based thermoelectric material, has been fabricated by a two‐step process. The deposition of a suspension, composed of CNTs and a liquid polymer precursor, on a substrate is followed by the solidification of the liquid polymer precursor via a cross‐linking reaction. This technique does not involve the drying of organic solvents. Therefore, thermoelectric materials with random material orientation and thicknesses of greater than 1 mm are obtained. The SFP‐fabricated polymer‐based TED exhibits an electric power that is more than four orders of magnitude higher than that of a thin‐layered TED fabricated via a conventional solution process. This work facilitates the realization of various applications of polymer‐based TEDs, such as wearable power sources that can convert body heat to electricity.

Wearable Thermoelectric Materials and Devices for Self-Powered Electronic Systems.

The emergence of artificial intelligence and the Internet of Things has led to a growing demand for wearable and maintenance-free power sources. The continual push toward lower operating voltages and power consumption in modern integrated circuits has made the development of devices powered by body heat finally feasible. In this context, thermoelectric (TE) materials have emerged as promising candidates for the effective conversion of body heat into electricity to power wearable devices without being limited by environmental conditions. Driven by rapid advances in processing technology and the performance of TE materials over the past two decades, wearable thermoelectric generators (WTEGs) have gradually become more flexible and stretchable so that they can be used on complex and dynamic surfaces. In this review, the functional materials, processing techniques, and strategies for the device design of different types of WTEGs are comprehensively covered. Wearable self-powered systems based on WTEGs are summarized, including multi-function TE modules, hybrid energy harvesting, and all-in-one energy devices. Challenges in organic TE materials, interfacial engineering, and assessments of device performance are discussed, and suggestions for future developments in the area are provided. This review will promote the rapid implementation of wearable TE materials and devices in self-powered electronic systems.

Fiber-shaped stretchable triboelectric nanogenerator with a novel synergistic structure of opposite Poisson's ratios

The rapid advancement of flexible and stretchable electronics has attracted intensive attention in recent decades. However, challenges still remain in developing wearable and sustainable power sources with comparable portability and stretchability. Here, a novel type of stretchable fiber-shaped triboelectric nanogenerator (AXF-TENG) was fabricated by inserting a negative Poisson-ratio auxetic fiber into a positive Poisson-ratio hollow circular sleeve, forming a synergistic structured TENG composed of opposite Poisson's ratios. Owing to the advanced structural designs, the inner auxetic fiber would expand in all directions to more effectively contact with the shrunk outer steel wire sleeve under stretching. The peak-to-peak voltage and transfer charge of composite based AXF-TENG could reach up to 42 V and 12.5 nC, respectively. The fabricated AXF-TENG can be used as a self‐powered multifunctional sensor to detect human motions and be woven into an energy‐harvesting fabric to scavenge biomechanical energy. With open-circuit voltage of 46 V and maximum instantaneous power density of 52.36 mW/m2, the AXF-TENG fabric was capable of lighting up 20 light emitting diodes (LEDs), charging commercial capacitors, powering an electronic watch and a calculator. All of these merits of the proposed AXF-TENGs suggest their promising potentials for versatile applications in biomechanical energy harvesting and self-powered sensing.

Double-network thermocells with extraordinary toughness and boosted power density for continuous heat harvesting

Double-network thermocells with extraordinary toughness and boosted power density for continuous heat harvesting

Autonomously Adhesive, Stretchable, and Transparent Solid‐State Polyionic Triboelectric Patch for Wearable Power Source and Tactile Sensor

AbstractRobust power supplies and self‐powered sensors that are extensible, autonomously adhesive, and transparent are highly desirable for next‐generation electronic/energy/robotic applications. In the work, a solid‐state triboelectric patch integrated with the above features (≈318% elongation, >85% average transmission, ≈44.3 N m−1 adhesive strength) is developed using polyethylene oxide/waterborne polyurethane/phytic acid composite (abbreviated as PWP composite) as an effective current collector and silicone rubber as tribolayer. The PWP composite is optimized systematically and corresponding single‐electrode device can supply a power density of 2.3 W m−2 at 75% strain. The triboelectric patch is capable of charging capacitors and powering electronics by efficiently harvesting biomechanical energies. Moreover, it can be autonomously attached to nonplanar skin or apparel substrates and used as a tactile sensor or an epidermal input touchpad for physiological motion detection and remote control of appliances, respectively. Even after dynamic deformation, tailoring, and prolonged use, the patch can maintain good stability and reliability of electrical outputs. This work provides a novel solid‐state and liquid‐free polyionic electrode‐based triboelectric nanogenerator integrated with adhesiveness, stretchability, and transparency, which can meet wide application needs from transparent electronics, artificial skins, to smart interfaces.

Vanadium metal-organic framework derived 2D hierarchical VO2 nanosheets grown on carbon cloth for advanced flexible energy storage devices

The design and creation of binder-free hierarchical porous structure on flexible substrate based on metal oxides derived from metal-organic frameworks (MOFs) has become as a desirable approach for developing advanced wearable and portable power sources. Herein, a novel flexible electrode was elaborately designed based on vanadium dioxide (VO2) nanosheets anchored on carbon cloth (CC) through the formation of vanadium MOF nanosheets on CC and then transformation to mesoporous VO2. The resulting binder free VO2@CC derived from V-MOF composite was directly used as a flexible electrode in energy storage application. For better understanding the role of V-MOF precursor, another novel electrode was fabricated by a simple hydrothermal growth of vanadium precursor on CC and then transformation to mesoporous VO2. The results confirmed that the type of precursor plays an important role in preparing the final VO2 nanostructures and the V-MOF precursor leads to the preparing highly mesopores VO2 with large surface area, which significantly enhanced the energy storage capability. Benefiting from the intriguing structural properties, high specific capacitance (470 F g−1 at 1 A g−1) and wide potential window (about 2 V), the VO2@CC derived from V-MOF was directly used as both positive/negative electrodes for fabrication of flexible all-solid-state symmetric supercapacitors, which provide high energy density (63.45 Wh kg−1 at 0.9 kW kg−1) and high power density (9.0 kW kg−1 at 50.4 Wh kg−1) with superior flexibility and outstanding cycling stability (about 95.% capacitance retention over 5000 cycles at 1.0 A g−1), which comparable to or higher than most of the previous reported devices based on VO2 nanostructures, indicating a great capability of our designed electrode in creating and developing next-generation high-performance supercapacitors for the future.

A humidity-resistant, stretchable and wearable textile-based triboelectric nanogenerator for mechanical energy harvesting and multifunctional self-powered haptic sensing

Textile-based triboelectric nanogenerators (t-TENGs) have attracted extensive attention in wearable power source and movement monitoring. However, the electrical output performance and environmental adaptability of t-TENGs in single-electrode mode are still unsatisfactory, which significantly limits their applications. This limitation is especially more pronounced in humid environments. In the present study, a humidity-resistant and stretchable single-electrode t-TENG (abbreviated as PFL@WFCF-TENG) consisting of the porous flexible layer (PFL) and waterproof flexible conductive fabric (WFCF) has been designed to improve the output performance. Considering the three-dimensional structure and excellent superhydrophobicity of PFL and superior conductivity of WFCF, the resultant PFL@WFCF-TENG (2 × 4 cm2 area) has high outputs (~135 V, ~7.5 μA, 26 μC/m2, 631.5 mW/m2) and favorable humidity-resistant (80% RH). Based on these excellent features, the proposed PFL@WFCF-TENG is expected to be applied for intelligent alarming, haptic sensing, and energy harvesting. Moreover, combined with the microelectronic module, a portable and wearable self-powered haptic controller based on the PFL@WFCF-TENG has been designed for various human–machine interface (HMI) scenarios, such as controlling of the lamp, electronic badge, computer application, and humidifier. The PFL@WFCF-TENG proposed in this study not only provides a feasible solution for developing wearable electronic devices with high electrical output even in high-humidity environments but also shows promising applications in a variety of areas, including wearable power supply, portable computer peripherals, intelligent robots and security systems.

Flexible lithium metal capacitors enabled by an in situ prepared gel polymer electrolyte

The rapid development of next-generation flexible electronics stimulates the growing demand for flexible and wearable power sources with high energy density. Li metal capacitor (LMC), combining with a Li metal anode and an activated carbon cathode, exhibits extremely high energy density and high power density due to the unique energy storage mechanism, thus showing great potential for powering wearable electronic devices. Herein, a flexible LMC based on an in situ prepared PETEA-based gel polymer electrolyte (GPE) was reported for the first time. Owing to the high ionic conductivity of PETEA-based GPE (5.75 × 10−3 S/cm at 20 °C), the assembled flexible LMC delivers a high capacitance of 210 F/g at 0.1 A/g within the voltage range from 1.5 V to 4.3 V vs. Li/Li+, a high energy density of 474 Wh/kg at 0.1 A/g and a high power density of 29 kW/kg at 10 A/g. More importantly, PETEA-based GPE endows the LMC with excellent flexibility and safety, which could work normally under abuse tests, such as bending, nail penetration and cutting. The in situ prepared PETEA-based GPE simplifies the fabrication process, avoids the risk of leakage and inhibits the growth of Li dendrite, making LMC a promising flexible energy storage device for the flexible electronic field.

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A fully transient, safe and wearable power source can help reduce electronic wastes. In article number EOM212073, Zifeng Wang and co‐workers reported a fully degradable battery made entirely of environmentally friendly materials, such as fruit juice, gelatin, and cellulose. Using kirigami techniques, the device exhibits good mechanical flexibility against bending, twisting, and stretching. The proposed battery shows promising application in powering various wearable sensors. image

Highly conductive locust bean gum bio-electrolyte for superior long-life quasi-solid-state zinc-ion batteries.

Rechargeable aqueous zinc-ion batteries (ZIBs) are promising wearable electronic power sources. However, solid-state electrolytes with high ionic conductivities and long-term stabilities are still challenging to fabricate for high-performance ZIBs. Herein, locust bean gum (LBG) was used as a natural bio-polymer to prepare a free-standing quasi-solid-state ZnSO4/MnSO4 electrolyte. The as-obtained LBG electrolyte showed high ionic conductivity reaching 33.57 mS cm−1 at room temperature. This value is so far the highest among the reported quasi-solid-state electrolytes. Besides, the as-obtained LBG electrolyte displayed excellent long-term stability toward a Zn anode. The application of the optimized LBG electrolyte in Zn–MnO2 batteries achieved a high specific capacity reaching up to 339.4 mA h g−1 at 0.15 A g−1, a superior rate performance of 143.3 mA h g−1 at 6 A g−1, an excellent capacity retention of 100% over 3300 cycles and 93% over 4000 cycles combined with a wide working temperature range (0–40 °C) and good mechanical flexibility (capacity retention of 80.74% after 1000 bending cycles at a bending angle of 90°). In sum, the proposed ZIBs-based LBG electrolyte with high electrochemical performance looks promising for the future development of bio-compatible and environmentally friendly solid-state energy storage devices.

Flexible, fiber-shaped, quasi-solid-state Zn-polyaniline batteries with methanesulfonic acid-doped aqueous gel electrolyte

Although quasi-solid-state fiber-shaped Zn-polyaniline batteries (Fs-ZPBs) are safe and potentially wearable power sources, they exhibit severe capacity degradation due to the inherently low electrolyte conductivity, soluble quinone formation in the cathode, and anode corrosion. In this study, these problems are mitigated by supplementing a polyvinyl alcohol-based gel-type electrolyte with methanesulfonic acid, which forms intermolecular hydrogen bonds to connect polyvinyl alcohol chains with each other and link the polyaniline surface with the electrolyte. The establishment of these linkages increases the ionic conductivity of the electrolyte and enhances charge transfer at the polyaniline/electrolyte interface. The relatively large molecular size of methanesulfonic acid hinders the access of water to the active materials (polyaniline and Zn) while allowing polyaniline to be efficiently doped with small-radius Cl− anions. The effects of dual anion doping and water capture suppress polyaniline degradation and Zn corrosion, resulting in excellent battery performance, namely, 88.1% capacity retention after 2000 cycles and 92.7% capacity retention after 500 bending cycles at a 2.5 mm bending radius. Furthermore, an all-carbon-yarn Fs-ZPB is developed for applications requiring practical wearability.