Stretchable Energy Storage Devices Research Articles

Highly Compressible Cross-Linked Polyacrylamide Hydrogel-Enabled Compressible Zn-MnO2 Battery and a Flexible Battery-Sensor System.

The fast advancement in flexible and wearable electronics has put up with new requirements on the energy storage device with improved tolerance to deformation apart from offering power output. Despite the tremendous progress in stretchable energy storage devices, the compressional energy storage devices have indeed received limited research attention. In this work, an intrinsically compressible rechargeable battery was proposed using the Zn-MnO2 chemistry and a cross-linked polyacrylamide hydrogel electrolyte. Interestingly, the battery exhibited not only good energy storage performances but also excellent tolerance against large compressional strain without sacrificing the energy storage capability. It was also found that the ionic conductivities of the hydrogel increased with the values of the compressional strain, leading to an enhanced electrochemical performance. More importantly, upon dynamic compression, the voltage output of the battery can be very stable and reliable. Consequently, the battery assembled using the hydrogel electrolyte can be used to power a luminescent panel even with a 3 kg load on top of it. It was also demonstrated that the flexible sensor powered by our compressible battery exhibited similar and stable sensory signals compared with the same sensor powered by two commercial alkaline batteries. Furthermore, because of the excellent mechanical property of our battery, a smart wristband fabricated by integrating two battery packs and the flexible piezoresistive sensor could be powered and used to monitor the pressure exerted, demonstrating the battery's potential as the wearable power source for the flexible and wearable devices.

A Stretchable and Self-Healing Energy Storage Device Based on Mechanically and Electrically Restorative Liquid-Metal Particles and Carboxylated Polyurethane Composites.

Stretchable and self-healing (SH) energy storage devices are indispensable elements in energy-autonomous electronic skin. However, the current collectors are not self-healable nor intrinsically stretchable, they mostly rely on strain-accommodating structures that require complex processing, are often limited in stretchability, and suffer from low device packing density and fragility. Here, an SH conductor comprising nickel flakes, eutectic gallium indium particles (EGaInPs), and carboxylated polyurethane (CPU) is presented. An energy storage device is constructed by the two SH electrodes assembled with graphene nanoplatelets sandwiching an ionic-liquid electrolyte. An excellent electrochemical healability (94% capacity retention upon restretching at 100% after healing from bifurcation) is unveiled, stemming from the complexation modulated redox behavior of EGaIn in the presence of the ligand bis(trifluoromethanesulfonyl)imide, which enhances the reversible Faradaic reaction of Ga. Self-healing can be achieved where the damaged regions are electrically restored by the flow of liquid metal and mechanically healing activated by the interfacial hydrogen bonding of CPU with an efficiency of 97.5% can be achieved. The SH conductor has an initial conductivity of 2479 S cm-1 that attains a high stretchability with 700% strain, it restores 100% stretchability even after breaking/healing with the electrical healing efficiency of 75%.

Inkjet-printed metal oxide nanoparticles on elastomer for strain-adaptive transmissive electrochromic energy storage systems

ABSTRACTThe emergence of soft energy devices provides new possibilities for various applications, it also creates significant challenges in the selection of structural design and material compatibility. Herein, we demonstrate a stretchable transmissive electrochromic energy storage device by inkjet-printing single layer of WO3 nanoparticles on an elastomeric transparent conductor. Such hybrid electrode is highly conductive and deformable, making it an excellent candidate for the application: large optical modulation of 40%, fast switching speed (<4.5 s), high coloration efficiency (75.5 cm2 C−1), good stability and high specific capacity (32.3 mAh g−1 and 44.8 mAh cm−3). The device consists of WO3-based hybrid electrode and polyaniline/carbon nanotubes composite electrode. It maintains excellent electrochromic and energy storage performance even when stretched up to 50%, and achieves a maximum areal energy density of 0.61 μWh cm−2 and power density of 0.83 mW cm−2, which is one of the highest values in stretchable transparent energy storage devices. A device featuring stretchable transparent nanowires based electrode is illustrated as an energy indicator in which the stored energy can be monitored via reversible color variation. This high performance and multifunctional electrochromic energy storage device is a promising candidate for deformable and wearable electronics.

Fully laser-patterned stretchable microsupercapacitors integrated with soft electronic circuit components

Stretchable energy storage devices are prerequisites for the realization of autonomous elastomeric electronics. Microsupercapacitors (MSCs) are promising candidates for this purpose due to their high power and energy densities, potential for miniaturization, and feasibility of embedding in circuits; however, efforts to realize stretchable MSCs have mostly relied on strain-accommodating materials and have suffered from limited stretchability, low conductivity, or complicated patterning processes. Here, we designed and fabricated a stretchable MSC based on reduced-graphene-oxide/Au heterostructures patterned by facile and versatile direct laser patterning. An interconnected and stable 3D network composed of vertically oriented heterostructures was realized by high-repetition-rate femtosecond laser pulses. Upon transferring to polydimethylsiloxane (PDMS), the 3D network achieved a high conductivity of ~105 S m−1, and the conductivity could be maintained at ~104 S m−1 even at 50% strain. A fully laser-patterned stretchable electronics system was integrated with embedded MSCs, which will find applications in soft robotics, wearable electronics, and the Internet of Things.

Mechanical deformation effects on ion conduction in stretchable polymer electrolytes

Flexible and stretchable energy storage devices, including batteries, supercapacitors, and ionic piezoelectrics, have garnered substantial research interest in recent years to address a wide range of applications such as smart textiles and medical implants. These devices are intended to undergo mechanical deformation, and the impact of deformation on electrochemical performance is not well understood. One important area of focus is studying how mechanical deformation influences ion conduction in polymer electrolytes. In this work, a dual theoretical and experimental approach is taken to further evaluate this phenomenon. A stretchable solid polymer electrolyte film subjected to tensile deformation (approximately 48% strain), through which ion diffusion occurs, is analyzed using a continuum approach treating ion diffusion and mechanical deformation as coupled. Thermodynamic laws are applied to obtain governing multiphysics equations accounting for large deformation mechanics and material nonlinearity. The theoretical solution obtained demonstrates how through-plane ionic conductivity changes when the polymer is subjected to stretching. Evolutionary materials deformation of the polymer electrolyte is considered to elucidate the underlying driving physical mechanisms of ion conduction. An experiment was also conducted to measure change in through-plane ionic conductivity with applied uniaxial strain in a sample of polyethylene oxide (PEO), a material commonly used as the electrolyte in solid polymer electrolyte lithium ion batteries. The experimental results show a greater than 1600% ionic conductivity enhancement for approximately 48% strain. The theoretical and experimental results are in good agreement and show that ion conduction is enhanced with increasing strain following an exponential function for a PEO electrolyte.

Stretchable Lithium Metal Anode with Improved Mechanical and Electrochemical Cycling Stability

Summary Stretchable are key components of stretchable/flexible electronic devices. However, they typically exhibit low energy density due to the low storage capability. Lithium (Li) metal is the ideal anode material, but it is ductile and the unstable electrochemical performance further hinders its practical applications. Herein, for the first time, a stretchable Li metal anode with stable mechanical and electrochemical performance is fabricated. It consists of one-entity 3D-patterned Li metal microdomains connected by highly elastic polymer rubbers. Upon stretching, the rubber absorbs the mechanical energy while the electroactive Li domains are not mechanically strained. Moreover, the whole electrode is fabricated by simply winding one single Cu wire, which is facile and cost-effective. The stretchable Li metal anode is a key step in the development of novel stretchable lithium batteries rather than traditional stretchable lithium-ion batteries to boost the energy density of stretchable energy-storage devices.

Facile Preparation of High‐Performance Stretchable Fiber‐Like Electrodes and Supercapacitors

AbstractA facile preparation method was proposed to fabricate core‐sheath structured elastic cord/carbon nanotube (CNT)/polyaniline (PANI) composite fibers with excellent electrochemical performance and good mechanical stretchability. Specifically, we developed a “surface melting for stable attachment” strategy to combine CNT/PANI composite film tightly with elastic cord fiber. The fabricated fiber‐like elastic cord/CNT/PANI composite electrode displays a large gravimetric capacitance of 394 F g−1(corresponds to a linear specific capacitance of 15.4 mF cm−1) and superior rate capability. The electrode capacitance has no obvious decrease when the electrode was stretched from original state to a large stretch ratio of 100%, and the capacitance maintains 98% after 100 stretch‐release cycles; besides, the electrode at stretching state possesses almost same cycling stability and rate capability as it at original state. These results indicate robust micro‐structure and outstanding stretchability of our fiber‐like elastic cord/CNT/PANI composite electrode. Consequently, all‐solid‐state supercapacitors assembled based on the fiber‐like electrode also exhibit impressive stretchability. Overall, the proposed facile method for producing stretchable fiber‐like electrodes/supercapacitors is believed to further boost the practical application of stretchable and wearable energy storage devices.

Silicones for Stretchable and Durable Soft Devices: Beyond Sylgard-184.

This paper identifies and characterizes silicone elastomers that are well-suited for fabricating highly stretchable and tear-resistant devices that require interfacial bonding by plasma or UV ozone treatment. The ability to bond two or more pieces of molded silicone is important for creating microfluidic channels, chambers for pneumatically driven soft robotics, and other soft and stretchable devices. Sylgard-184 is a popular silicone, particularly for microfluidic applications. However, its low elongation at break (∼100% strain) and moderate tear strength (∼3 N/mm) make it unsuitable for emerging, mechanically demanding applications of silicone. In contrast, commercial silicones, such as Dragon Skin, have excellent mechanical properties yet are difficult to plasma-bond, likely because of the presence of silicone oils that soften the network yet migrate to the surface and interfere with plasma bonding. We found that extracting silicone oligomers from these soft networks allows these materials to bond but only when the Shore hardness exceeds a value of 15 A. It is also possible to mix highly stretchable silicones (Dragon Skin and Ecoflex) with Sylgard-184 to create silicones with intermediate mechanical properties; interestingly, these blends also only bond when the hardness exceeds 15 A. Eight different Pt-cured silicones were also screened; again, only those with Shore hardness above 15 A plasma-bond. The most promising silicones from this study are Sylgard-186 and Elastosil-M4130 and M4630, which exhibit a large deformation (>200% elongation at break), high tear strength (>12 N/mm), and strong plasma bonding. To illustrate the utility of these silicones, we created stretchable electrodes by injecting a liquid metal into microchannels created using such silicones, which may find use in soft robotics, electronic skin, and stretchable energy storage devices.

Vanadium dioxide-anchored porous carbon nanofibers as a Na+ intercalation pseudocapacitance material for development of flexible and super light electrochemical energy storage systems

The development of a flexible binder free electrode based on 3D vanadium dioxide (VO2) nano-architectures has materialized as an effective strategy for fabrication of advanced wearable, portable, and stretchable electronic devices. However, most of the stretchable energy storage devices based on VO2 suffer from a relatively low operating voltage, high weight, low specific capacitance, and thus low energy density. Here, a novel binder free supercapacitor electrode composed of hierarchical VO2 nanosheet arrays grown on porous carbon nanofibers (VO2@PCNFs) is designed using a simple hydrothermal method followed by annealing treatment. The electrochemical evaluation confirmed that the energy storage mechanism of the prepared VO2@PCNFs is based on the intercalation pseudocapacitance properties. The resulting VO2@PCNFs electrode displays a wide operation voltage (−1.0 to 1.1V in three electrode systems), maximum specific capacitance of 778Fg−1 (at 1Ag–1), and excellent rate capability. Moreover, a novel all-solid-state asymmetric supercapacitor with good flexibility is assembled in a neutral Na2SO4− poly(vinyl alcohol) (Na2SO4/PVA) gel electrolyte using the VO2@PCNFs film as a positive electrode and PCNFs as a negative electrode. Due to the high capacitances and excellent rate performances of VO2@PCNFs and PCNFs, as well as the synergistic effects of the two electrodes, such asymmetric cell could be cycled reversibly in the voltage range of 0–1.7V, and presents maximum energy density of 75.06Whkg−1, and excellent cycling durability, with 92.4% retaining in its specific capacitance even after 4000 cycles. These encouraging results confirm a great potential of our proposed electrode in developing energy storage devices based on VO2 electrode materials with superior performances for practical applications.

Stretchable Electrode Based on Laterally Combed Carbon Nanotubes for Wearable Energy Harvesting and Storage Devices

AbstractCarbon nanotubes (CNTs) are a promising material for use as a flexible electrode in wearable energy devices due to their electrical conductivity, soft mechanical properties, electrochemical activity, and large surface area. However, their electrical resistance is higher than that of metals, and deformations such as stretching can lead to deterioration of electrical performances. To address these issues, here a novel stretchable electrode based on laterally combed CNT networks is presented. The increased percolation between combed CNTs provides a high electrical conductivity even under mechanical deformations. Additional nickel electroplating and serpentine electrode designs increase conductivity and deformability further. The resulting stretchable electrode exhibits an excellent sheet resistance, which is comparable to conventional metal film electrodes. The resistance change is minimal even when stretched by ≈100%. Such high conductivity and deformability in addition to intrinsic electrochemically active property of CNTs enable high performance stretchable energy harvesting (wireless charging coil and triboelectric generator) and storage (lithium ion battery and supercapacitor) devices. Monolithic integration of these devices forms a wearable energy supply system, successfully demonstrating its potential as a novel soft power supply module for wearable electronics.

Preparation of high strain porous polyvinyl alcohol/polyaniline composite and its applications in all-solid-state supercapacitor

Impacted by the rapid development of the wearable and portable devices, the demands for excellent flexibility and high specific capacitance have highlighted an urgent need for developing flexible energy storage devices. In this paper, we prepare a porous polyvinyl alcohol (PVA)/polyaniline (PANI) composite with perfect mechanical performance (strain deformations of 696%). Due to its three-dimensional (3D) porous structure, deformation of the PANI can be avoided when the composite is bent or stretched. The electrochemical performance of the porous PVA/PANI composite can be maintained so that it holds promise for stretchable energy storage devices. As a proof of concept, an all-solid-state supercapacitor is fabricated by using the porous PVA/PANI composite and exhibits a high areal capacitance of 300.9 mF cm−2 and long-life stability of 85% capacitance retention after 10,000 charge/discharge cycles. In particular, the supercapacitor can also withstand repeated bending and stretching with minimal effect on the electrochemical performance when no current collector is employed. The research presents a design approach of high strain porous composite and shows great promise for the development of stretchable energy storage devices.

Toward Soft Skin‐Like Wearable and Implantable Energy Devices

AbstractThe development of ultra‐compliant power sources is crucial for their seamless integration with next‐generation skin‐like wearable and implantable biomedical systems for long‐term health monitoring. Toward this goal, stretchable energy storage and conversion devices (ESCDs), including supercapacitors, lithium‐ion batteries (LIBs), solar cells, and generators are now attracting intensive worldwide research efforts. The purpose of this review is to discuss the latest achievements in the development of such stretchable energy devices in the context of biomedical applications. We first review the viable strategies and methodologies of fabricating stretchable energy storage and conversion devices. Then, we focus on description of various types of soft energy devices from a materials point of view. Furthermore, we discuss the challenges and opportunities in the design of truly conformal soft energy systems, including various key parameters, such as energy density, stability, and scalability.

An All-Stretchable-Component Sodium-Ion Full Battery.

Stretchable energy-storage devices receive considerable attention due to their promising applications in future wearable technologies. However, they currently suffer from many problems, including low utility of active materials, limited multidirectional stretchability, and poor stability under stretched conditions. In addition, most proposed designs use one or more rigid components that fail to meet the stretchability requirement for the entire device. Here, an all-stretchable-component sodium-ion full battery based on graphene-modified poly(dimethylsiloxane) sponge electrodes and an elastic gel membrane is developed for the first time. The battery exhibits reasonable electrochemical performance and robust mechanical deformability; its electrochemical characteristics can be well-maintained under many different stretched conditions and after hundreds of stretching-release cycles. This novel design integrating all stretchable components provides a pathway toward the next generation of wearable energy devices in modern electronics.

Ag/Au/Polypyrrole Core-shell Nanowire Network for Transparent, Stretchable and Flexible Supercapacitor in Wearable Energy Devices

Transparent and stretchable energy storage devices have attracted significant interest due to their potential to be applied to biocompatible and wearable electronics. Supercapacitors that use the reversible faradaic redox reaction of conducting polymer have a higher specific capacitance as compared with electrical double-layer capacitors. Typically, the conducting polymer electrode is fabricated through direct electropolymerization on the current collector. However, no research have been conducted on metal nanowires as current collectors for the direct electropolymerization, even though the metal nanowire network structure has proven to be superior as a transparent, flexible, and stretchable electrode platform because the conducting polymer’s redox potential for polymerization is higher than that of widely studied metal nanowires such as silver and copper. In this study, we demonstrated a highly transparent and stretchable supercapacitor by developing Ag/Au/Polypyrrole core-shell nanowire networks as electrode by coating the surface of Ag NWs with a thin layer of gold, which provide higher redox potential than the electropolymerizable monomer. The Ag/Au/Polypyrrole core-shell nanowire networks demonstrated superior mechanical stability under various mechanical bending and stretching. In addition, proposed supercapacitors showed fine optical transmittance together with fivefold improved areal capacitance compared to pristine Ag/Au core-shell nanowire mesh-based supercapacitors.

Highly Stretchable Micro‐Supercapacitor Arrays with Hybrid MWCNT/PANI Electrodes

Stretchable energy storage devices are required to fit for stretchable electronic devices, forming a fully stretchable system for comfortable and body‐attachable electronic devices. Herein, highly stretchable micro‐supercapacitors are fabricated by designing wave‐shaped hybrid multiwalled carbon nanotubes/polyaniline electrodes. As‐fabricated stretchable devices exhibit a large areal capacitance of 44.13 mF cm−2 and offer a power density of 0.07 mW cm−2 at an area energy density of 0.004 mW h cm−2. Owing to the designed wavy electrode structure, the electrochemical performances of the stretchable micro‐supercapacitors are almost invariably under different stretching stations ranging from 5% to 40%. By fabricating stretchable micro‐supercapacitors arrays, a red light‐emitting diode can be easily lighted under different conditions including stretching, twisting, crimping, and winding. All these results confirm the outstanding stability and mechanical strength of stretchable micro‐supercapacitors, demonstrating its potential application in skin‐patchable electronics or portable/wearable devices.

Alkali-Resistant Quasi-Solid-State Electrolyte for Stretchable Supercapacitors.

Research on stretchable energy-storage devices has been motivated by elastic electronics, and considerable research efforts have been devoted to the development of stretchable electrodes. However, stretchable electrolytes, another critical component in stretchable devices, have earned quite little attention, especially the alkali-resistant ones. Here, we reported a novel stretchable alkali-resistant electrolyte made of a polyolefin elastomer porous membrane supported potassium hydroxide-potassium polyacrylate (POE@KOH-PAAK). The as-prepared electrolyte shows a negligible plastic deformation even after 1000 stretching cycles at a strain of 150% as well as a high conductivity of 0.14 S cm-1. It also exhibits excellent alkali resistance, which shows no obvious degradation of the mechanical performance after immersion in 2 M KOH for up to 2 weeks. To demonstrate its good properties, a high-performance stretchable supercapacitor is assembled using a carbon-nanotube-film-supported NiCo2O4 (CNT@NiCo2O4) as the cathode and Fe2O3 (CNT@Fe2O3) as the anode, proving great application promise of the stretchable alkali-resistant electrolyte in stretchable energy-storage devices.

Recent advances and challenges of stretchable supercapacitors based on carbon materials

Stretchable energy storage devices are essential for the development of stretchable electronics that can maintain their electronic performance while sustain large mechanical strain. In this context, stretchable supercapacitors (SSCs) are regarded as one of the most promising power supply in stretchable electronic devices due to their high power densities, fast charge-discharge capability, and modest energy densities. Carbon materials, including carbon nanotubes, graphene, and mesoporous carbon, hold promise as electrode materials for SSCs for their large surface area, excellent electrical, mechanical, and electrochemical properties. Much effort has been devoted to developing stretchable, carbon-based SSCs with different structure/performance characteristics, including conventional planar/textile, wearable fiber-shaped, transparent, and solid-state devices with aesthetic appeal. This review summarizes recent advances towards the development of carbon-based SSCs. Challenges and important directions in this emerging field are also discussed.

3 V omni-directionally stretchable one-body supercapacitors based on a single ion–gel matrix and carbon nanotubes

Stretchable supercapacitors often have laminated structures consisting of electrode, electrolyte, and supporting layers. Since the layers are likely to be composed of different materials, delamination is a major cause of failure upon stretching. In this study, we demonstrate delamination-free stretchable supercapacitors where all the component layers are prepared with a single matrix, which is composed of a polymer, poly(vinylidene fluoride-hexafluoropropylene) and an ionic liquid, 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide. Since the ionic liquid in the composite plays a role as both an electrolyte and a plasticizer, this composite can be used as an electrolyte and a supporting layer in the stretchable supercapacitor. The electrode layer can be fabricated by incorporating carbon nanotubes in the common matrix. Then, all the layers can be seamlessly fused into one body by dissolving the surface of the composite with acetone, which evaporates after the integration, leaving no borders between the layers. This one-body stretchable supercapacitor not only has high durability against repetitive stretches but also is stretchable in all directions. This feature clearly distinguishes them from conventional stretchable supercapacitors fabricated using buckled structures, which are stretchable only in one or two directions. Moreover, this supercapacitor has high cell voltage (∼3 V) owing to the ionic liquid-based gel electrolytes. Our demonstration of isotropically stretchable high-durability supercapacitors may have a great implication in the development of stretchable energy storage devices for real applications.

2-Dimensional Supercapacitor Wires to Overcome Intrinsic Low Energy Density

Although a large number of reports on 2D flexible and stretchable energy storage devices have emerged within the past decade, 1D structure systems such as wires for higher flexibility, bio-compatibility and wearability have been desired for broader application of electronics. As a result of these requirements, wire-shaped devices among the cutting edge technologies in energy storage field are taking center stage for application to postmodern electronics and various fields such as fashion and culture. In view of mechanics, plane structures in 2D essentially have a unidirectional folding characteristics. On the other hand, wires with 1D structure have an omnidirectional serpentine structure in the other axes. In contrast to 2D planar formats, it is much easier for wire types to be integrated into more sophisticated structures such as woven textiles that can be used in our daily life. Although wire systems have a large structural potential, some fundamental obstacles hinder the use of wire-type energy storage. Electrochemical performances of wires are still underneath those of 2D plane cells. Many researchers have made efforts to overcome these barriers of wire-type energy storage devices. Most of them suggests ways to shape electrodes into cylindrical wires and a choice of material to maximize the performance as high as possible. In this study, however, we did not stick to using superb materials or constructing a cylinder, but theoretically analysed the origin of undefeatable charge-storage property of 2D plane over 1D wire. Based on this analysis we verified that a difference between wire-type and conventional planar supercapacitors induced the fundamental limits of wire-type supercapacitors. This limit is termed “energy lag effect.” With these derived information, we have first proposed the simultaneous incorporation of favorable electrochemical performance of 2D system and high flexibility of 1D system into solely one device. To exclude the identified limits, we designed a supercapacitor thread in unique structure that completely differs from conventional wire-type energy storage systems. The supercapacitor thread was designed as a dual plane-helix structure and proved not to show energy lag effects, experimentally or analytically.

Novel Flexible Supercapacitors Fabricated by Simple Integration of Electrodes, Binders, and Electrolytes into Glass Fibre Separators

s : We report novel and simple structure of supercapacitors fabricated by using flexible glass fibre separators as templates. This method does not require separate electrodes, binders and high pressure/temperature to build the supercapacitor unit cells as required by the conventional technology. The supercapacitors were fabricated by drop-casting solution mixtures of carbonaceous active materials/gel electrolytes onto two sides of glass fibre separators. Two carbonaceous materials (nanoscaled activated carbons, multi-walled carbon nanotubes) were investigated as electrode materials. The electrochemical measurements reveal that the separatorbased supercapacitors using ACs successfully demonstrated significant mass specific capacitance (22.3 F g−) and energy density (9.7 Wh kg−), indicating this method can be useful in fabricating flexible, wearable and stretchable energy storage devices in more straightforward and cost-effective way than current technology.