Wearable Energy Storage Devices Research Articles

Self‐Gelling Quinone‐Based Wearable Microbattery

AbstractWearable power sources are envisioned since their development promises to speed up the widespread application of wearable devices in different areas, such as healthcare, smart‐city management, and robotics. Here, the 4′‐((9,10‐anthraquinone‐2‐yl)oxy)butyrate (2‐BEAQ), an anthraquinone derivative, is synthesized, and further applied for producing a redox‐active shear‐thinning hydrogel (BEAQ‐gel). The gel comprises cylindrical aggregates of 2‐BEAQ molecules dispersed within a water matrix, interconnected through ionic, ion‐dipole, and hydrogen bonding interactions. BEAQ‐gel also presents interesting rheological characteristics and composition tunability since it can be produced in a large range of concentrations. This improved redox 3D hierarchical network also makes the network capable of retaining high quantities of potassium hydroxide, thereby enhancing conductivity. By coupling BEAQ‐gel with Ferricyanide the development of a wearable battery is demonstrated, which exhibits an output voltage of 0.89 V even when bent at a 180° angle, making it suitable for powering wearable devices. This work presents an innovative alternative for the production of wearable devices, from the design of the anode and cathode materials to the wearable casing and demonstrates the use of redox‐active low‐molecular‐weight‐gel (LMWG) as an active material of a microbattery giving a valuable glimpse to the further development of wearable energy storage devices.

Unlocking Maximum Synergy: Screen-Printing Fabrication of Heterostructured Microsupercapacitor Stacks.

A cost-effective and scalable approach for the fabrication of heterostructured microsupercapacitors (MSCs) employing screen-printing followed by sequential electrochemical and microspray deposition techniques has been demonstrated. The microsupercapacitor electrode (MSC) that composed of stacked layers of mesoporous carbon, polyaniline (PANI), and MXene hold significant promise for wearable electronics. By adjusting the deposition and spray cycles, the MSC can be readily coated with PANI and MXene. The sequentially stacked two layers of MXene and PANI on the mesoporous carbon spheres (PMPM-MSC) yielded a specific capacitance of 1003 mF cm-2 at 0.5mA cm-2, surpassing the performance of PANI/mesoporous carbon electrode by 1.6 times (771 mF cm-2). After 10,000 cycles of charge and discharge, PMPM-MSCs retained more than 86% of their initial capacitance. In-situ Raman spectroscopy confirmedthe synergistic effects between MXene and PANI within the heterostructured stacked PMPM-MSC electrodes, including enhanced electronic conductivity and improved electrolyte ion dissociation, which aligned with the electrochemical measurement results, such as fast charge/discharge rates and reduced internal and mass transport resistance. This study demonstrates the potential of screen-printed heterostructured MSC stacks with maximum electrochemical synergy for portable and wearable energy storage devices.

Fabrication of highly flexible, wearable, free-standing symmetric supercapacitors with high voltage operation enabled by hierarchical graphene/cerium oxide/polypyrrole hybrid films

Flexible, free-standing supercapacitors play a significant role in the development of future wearable energy storage devices. Herein, we successfully fabricated the highly flexible and free-standing graphene/cerium oxide/polypyrrole hybrid films by thermal reduction of graphene oxide (GO) followed by the sol–gel synthesis of CeO2 and then the addition of PPy. By regulating oxygen functional groups in GO, the electronic conductivity and electroactive sites of the hybrid films are significantly controlled, leading to enhanced energy storage capability. Finally, a symmetric flexible supercapacitor (FSC) device was developed using the prepared films as electrodes. Resulting, the integrated symmetric GO-400/CeO2/PPy FSC manifests excellent areal capacitance of 49.0 mF cm−2 at 1 mA cm−2, with a durability of 83.1 % over 10,000 cycles. Specifically, the FSC exhibited capacitance retention of 77.2 % after 10,000 cycles under bending state with exceptional rate ability. Meanwhile, an impressive energy density of 19.69 µW h cm−2 was attained at a power density of 0.85 mW cm−2. Evidently, the synergistic interactions between GO and PPy nanosheets, along with CeO2 favour the rapid electron movement of electrode material for next-generation wearable, portable electronics.

Asymmetric Coordination of Bimetallic Fe-Co Single-Atom Pairs toward Enhanced Bifunctional Activity for Rechargeable Zinc-Air Batteries.

The advancement of rechargeable zinc-air batteries (RZABs) faces challenges from the pronounced polarization and sluggish kinetics of oxygen reduction and evolution reactions (ORR and OER). Single-atom catalysts offer an effective solution, yet their insufficient or singular catalytic activity hinders their development. In this work, a dual single-atom catalyst, FeCo-SAs, was fabricated, featuring atomically dispersed N3-Fe-Co-N4 sites on N-doped graphene nanosheets for bifunctional activity. Introducing Co into Fe single-atoms and secondary pyrolysis altered Fe coordination with N, creating an asymmetric environment that promoted charge transfer and increased the density of states near the Fermi level. This catalyst achieved a narrow potential gap of 0.616 V, with a half-wave potential of 0.884 V for ORR (vs the reversible hydrogen electrode) and a low OER overpotential of 270 mV at 10 mA cm-2. Owing to the superior activity of FeCo-SAs, RZABs exhibited a peak power density of 203.36 mW cm-2 and an extended cycle life of over 550 h, exceeding the commercial Pt/C + IrO2 catalyst. Furthermore, flexible RZABs with FeCo-SAs demonstrated the promising future of bimetallic pairs in wearable energy storage devices.

Superstrong Ionogel Enabled by Coacervation-Induced Nanofibril Assembly for Sustainable Moisture Energy Harvesting.

Ionogels have grabbed significant interest in various applications, from sensors and actuators to wearable electronics and energy storage devices. However, current ionogels suffer from low strength and poor ionic conductivity, limiting their performance in practical applications. Here, inspired by the mechanical reinforcement of natural biomacromolecules through noncovalent aggregates, a strategy is proposed to construct nanofibril-based ionogels through complex coacervation-induced assembly. Cellulose nanofibrils (CNFs) can bundle together with poly(ionic liquid) (PIL) to form a superstrong nanofibrous network, in which the ionic liquid (IL) can be retained to form ionogels with high liquid inclusion and ionic conductivity. The strength of the CNF-PIL-IL ionogels can be tuned by the IL content over a wide range of up to 78 MPa. The optical transparency, high strength, and hygroscopicity enabled them to be promising candidates in moist-electricity generation and applications such as energy harvesting windows and wearable power generators. In addition, the ionogels are degradable and the ionogel-based generators can be recycled through dehydration. Our strategy suggests perspectives for the fabrication of high-strength and multifunctional ionogels for sustainable applications.

Integrated construction of stretchable supercapacitor with outstanding deformation stability and flame retardancy

The fast development of wearable electronics requires urgently stretchable energy storage devices, but conventional stretchable energy-storage devices suffer from poor dynamic deformation stability. The key is to create a new construction strategy of "electrode/electrolyte interface integration". Herein, we have proposed a clever strategy that combines layer-by-layer electrospinning with a self-selected vapor-phase polymerization (VPP) method to assemble the integrated stretchable supercapacitors (ISSCs). Furthermore, the interface stability enhancement mechanism is revealed through experimental and theoretical simulations, showing that the synergistic effect of molecular chain entanglement and mechanical meshing endows excellent anti-deformation stability of ISSCs. As a result, the as-assembled ISSCs deliver excellent dynamic deformation electrochemical stability with 99.5 % capacitance retention after 500 stretching cycles at strain and outstanding flame retardancy (limiting oxygen index (LOI) up to 48.1 % at a film thickness of only 0.22 mm). The innovative integrated design strategy endows a systematic construction plan for the scalable fabrication of wearable organic energy storage devices.

Synthesis and self-assembly of bottlebrush block copolymer electrolytes for solid-state supercapacitors

All-solid-state supercapacitors have attracted increasing attention in recent decades owing to rapid advancements in safe, flexible, and wearable energy storage devices. This study demonstrates a bottlebrush block copolymer electrolyte consisting of poly(styrene-b-butadiene-b-styrene)-g-poly(ethylene glycol) behenyl ether methacrylate (SBS-g-PEGBEM) (simply SgP) for all-solid-state supercapacitors. Due to the adhesive nature and robust mechanical properties of SgP film, devices can be manufactured without the need for separators or packaging. The nonpolar SBS domains serve as scaffolds within the polymer matrix, while the polar PEGBEM domains offer interactive sites for polar ionic liquids (ILs). The synergy between precisely defined nanostructures and the subsequent well-dissociated ions enhances efficient ion transport through the ionic channels. As a result, the supercapacitor with SgP/IL electrolyte exhibits remarkable electrochemical performance. This includes a wide potential window of 2.4 V, an ionic conductivity of 2.4 mS cm−1, and maximum energy density and power density of 28.1 Wh kg−1 and 3080 W kg−1, respectively. The supercapacitor also demonstrates high cycle stability with 87.7 % capacitance retention after 5,000 cycles. The positive impact of the PEGBEM side chains is investigated via molecular dynamics simulations. Thus, this study presents a novel strategy for solid-state electrolytes, offering potential advancements in next-generation energy storage devices.

Composite of CoS1.97 nanoparticles decorated CuS hollow cubes with rGO as thin film electrode for high-performance all solid flexible supercapacitors

Stretchable flexible thin-film electrodes are extensively explored for developing new wearable energy storage devices. However, traditional carbon-based materials used in such independent electrodes have limited practical applications owing to their low energy storage capacity and energy density. To address this, a unique structure and remarkable mechanical stability thin-film flexible positive electrode comprising CoS1.97 nanoparticles decorated hollow CuS cubes and reduced graphene oxide (rGO), hereinafter referred to as CCSrGO, is prepared. Transition metal sulfide CoS1.97 and CuS shows high energy density owing to the synergistic effects of its active components. The electrode can simultaneously meet the high-energy density and safety requirements of new wearable energy storage devices. The electrode has excellent electrochemical performance (1380 F/g at 1 A/g) and ideal capacitance retention (93.8 % after 10,000 cycles) owing to its unique three-dimensional hollow structure and polymetallic synergies between copper and cobalt elements, which are attributed to their different energy storage mechanisms. Furthermore, a flexible asymmetric supercapacitor (FASC) was constructed using CCSrGO as the positive electrode and rGO as the negative electrode (CCSrGO//rGO), which delivers an energy density of 100 Wh kg−1 and a corresponding power density of 2663 W kg−1 within a voltage window of 0–1.5 V. The resulting FASC can power a light-emitting diode (LED) at different bending and twisting angles, exerting little effect on the capacitance. Therefore, the prepared CCSrGO//rGO FASC devices show great application prospects in energy storage.

Architecting N-doped Carbon Nanotube-Rich Carbon Nanofibers with Biomimetic Vine-Leaf-Whisker Structure as Robust Bifunctional Electrocatalysts for Rechargeable Zn-Air Batteries.

Efficient and durable bifunctional catalysts toward oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are urgently desirable but challenging for rechargeable Zn-air batteries (ZABs), especially flexible wearable ZABs. Inspired by the vine-leaf-whisker structure in nature, we proposed a three-dimensional (3D) hierarchical bifunctional catalyst (denoted as Co-Fe-Zn@N-CNT/CNF) consisting of N-doped carbon nanotubes embedded with abundant CoFe alloy nanoparticles, leaf-shaped N-doped carbon nanoflakes, and porous carbon fibers for rechargeable ZABs. The special biomimetic structure provides a large specific surface area, allowing for high exposure of the active site and ensuring fast mass transport/charge transfer. The close combination of CoFe bimetallic alloys and N-doped carbon nanotubes delivers high electrocatalytic activity, while the coexistence of various active sites such as metal nanoparticles (NPs), metal-Nx, doped N species, and their synergistic interactions endows the catalysts with more active sites. As such, the Co-Fe-Zn@N-CNT/CNF catalyst achieves superior bifunctional catalytic activities for the ORR (a half-wave potential of 0.84 V) and the OER (an overpotential of 326 mV at 10 mA cm-2) in alkaline media, comparable to commercial Pt/C and RuO2. Remarkably, both aqueous and solid-state ZABs assembled with Co-Fe-Zn@N-CNT/CNF catalysts as air electrodes demonstrate excellent charging/discharging performance, high peak power density, and robust long-term cycling stability. More interestingly, the flexible ZAB performs well even under bending conditions, displaying satisfactory device stability and mechanical flexibility. This study presents a new collective morphological-composition-structural engineering strategy for exploiting the efficient bifunctional oxygen electrocatalysts, which is of great significance for high-performance rechargeable ZABs and wearable energy storage devices.

Electrically Conductive Polymers for Additive Manufacturing.

The use of electrically conductive polymers (CPs) in the development of electronic devices has attracted significant interest due to their unique intrinsic properties, which result from the synergistic combination of physicochemical properties in conventional polymers with the electronic properties of metals or semiconductors. Most conventional methods adopted for the fabrication of devices with nonplanar morphologies are still challenged by the poor ionic/electronic mobility of end products. Additive manufacturing (AM) brings about exciting prospects to the realm of CPs by enabling greater design freedom, more elaborate structures, quicker prototyping, relatively low cost, and more environmentally friendly electronic device creation. A growing variety of AM technologies are becoming available for three-dimensional (3D) printing of conductive devices, i.e., vat photopolymerization (VP), material extrusion (ME), powder bed fusion (PBF), material jetting (MJ), and lamination object manufacturing (LOM). In this review, we provide an overview of the recent research progress in the area of CPs developed for AM, which advances the design and development of future electronic devices. We consider different AM techniques, vis-à-vis, their development progress and respective challenges in printing CPs. We also discuss the material requirements and notable advances in 3D printing of CPs, as well as their potential electronic applications including wearable electronics, sensors, energy storage and conversion devices, etc. This review concludes with an outlook on AM of CPs.

Screen-printed MXene-based all-solid-state textile supercapacitors

Textile-based supercapacitors (TSCs) have drawn increasing attention in recent years owing to their potential applications in wearable electronics. However, it remains a critical challenge to increase the energy density of TSCs. Herein, we develop a screen-printing strategy to scalable construct high-performance MXene-based all-solid-state textile supercapacitors, which exhibit excellent electrochemical performance, including high specific capacitance (4979.2 mF cm−2) and energy density (62.2 µWh cm−2). The electrochemical performance of assembled MXene-based TSCs is superior to the-state-of-the-art TSCs. This work provides a new strategy for fabricating high-performance flexible supercapacitors and paves the way for the development of wearable energy storage devices.

Preparation of cellulose acetate based flexible separator and its application in zinc–air batteries

Flexible solid-state zinc–air batteries as a wearable energy storage device with great potential, and their separators, which control ion permeability, inhibit zinc dendrite generation, and regulate catalytic active sites, have been developed as gel electrolyte separators with high retention of electrolyte uptake. However, the gel electrolyte separator still has problems such as poor affinity with the electrolyte and poor ionic conductivity, which limits its further application. In order to further improve the electrolyte absorption, ionic conductivity and mechanical strength of cellulose acetate(CA)/polyvinyl alcohol (PVA) nanofibers, TiO2 was added to CA/PVA to increase the porosity, and glutaraldehyde (GA) was used to modify the CA/PVA/TiO2 separator by acetal reaction with CA and PVA to make the molecules closely linked. The results shows that the optimal mass fractions of TiO2 and GA were 2% and 5%, respectively. At this time, the porosity and absorption rate of the separator increased from 48% to 68.2% and 142.4% to 285.3%, respectively. The discharge capacity reached 179 mA cm−3, and the cycle stability rate was 89% after 7 stable constant current charge/discharge cycles.

Polypyrrole in-situ polymerized MXene/TPU fiber electrode for flexible supercapacitors

Ti3C2Tx-based flexible fibers have great potential and wide applications in the energy storage field of wearable electronic textiles and portable electronic devices. This work reports a Ti3C2Tx-MXene/TPU/polypyrrole(PPy) fiber in which PPy is grown on the surface of Ti3C2Tx/TPU fiber by in-situ polymerization. Through efficient wet spinning and in-situ polymerization, Ti3C2Tx/TPU/PPy fiber exhibit pore structure and abundant active sites, which significantly enhance charge transfer rate and conductivity. The fiber exhibits a capacitance of 41.2 F g−1(5 mV S−1) and excellent rate performance in 1 M H2SO4 electrolyte. Its symmetrical fiber-based flexible supercapacitors(SCs) can provide an energy density of 2.36 mW h g−1. At the same time, the fiber has good flexibility and can be woven into a fabric SCs as a wearable energy storage device to realize power supply applications such as electronic watches and LEDs, which provides a potential strategy for the application of flexible wearable energy storage devices.

Recent progress in non-lithium rechargeable batteries with micro to macro 3D engineered electrode architecture

The increasing demand for flexible and wearable energy storage devices, particularly in the field of 3D printed macrobatteries and microbatteries necessitates extensive research worldwide. While lithium-based batteries have traditionally dominated...

Recent progress in non-lithium rechargeable batteries with micro to macro 3D engineered electrode architecture

The increasing demand for flexible and wearable energy storage devices, particularly in the field of 3D printed macrobatteries and microbatteries necessitates extensive research worldwide. While lithium-based batteries have traditionally dominated...

“All-in-one” polypyrrole pillar hybridization flexible membranes on multimodal tactile sensors for wearable energy-storage devices and human–machine interfaces

We designed an “all-in-one” polypyrrole pillar hybridization flexible membrane for wearable energy-storage devices and human–machine interfaces (HMIs).

Stretchable Zn‐Ion Hybrid Capacitor with Hydrogel Encapsulated 3D Interdigital Structure

AbstractTo enhance the areal energy density of current flexible energy storage devices, hybrid capacitors combining the advantages of supercapacitors and batteries are proposed and further enhanced by incorporating the 3D interdigital structure design. However, uneven electric field distribution and hindered ion diffusion kinetics due to the non‐electroactive components in these devices limit the enhancement of areal electrochemical performances when expanding the electrodes longitudinally. Herein, hydrogels with high ionic conductivity and high mechanical stability are designed to accommodate Zn2+‐containing electrolytes and integrated with Ti3C2Tx‐MXene electrodes to assemble flexible Zn‐ion hybrid capacitors (ZIHCs). Fully encapsulated by ionic conductive hydrogels, 3D interdigital electrodes enable omnidirectional ion transport and unimpeded ionic accessibility, facilitating adequate electrode reactions, rapid energy storage, and uniform energy distribution. Hence, the all‐hydrogel‐encapsulated ZIHC achieved a 50‐fold increase in capacitance with a quadrupled electrode thickness, exhibiting a large areal capacitance of 1432 mF cm−2 and an energy density of 389.7 µWh cm−2 without sacrificing power density and rate performance. Finite element simulations further illustrate the uniform distribution of potential, electric field intensity, and energy density in this structure. In addition, the device shows great stability under deformation, excellent adhesion, and underwater workability, demonstrating great promise for next‐generation wearable energy storage devices.

Advances in Additive Manufacturing Techniques for Electrochemical Energy Storage

AbstractThe increasing adoption of additive manufacturing (AM), also known as 3D printing, is revolutionizing the production of wearable electronics and energy storage devices (ESD) such as batteries, supercapacitors, and fuel cells. This surge can be attributed to its outstanding process versatility, precise control over geometrical aspects, and potential to reduce costs and material waste. In this comprehensive review, major AM processes like inkjet printing, direct ink writing, fused deposition modeling, and selective laser sintering/melting along with possible configurations and architectures, are elaborately discussed for each bespoke ESD. The application of 3D‐printed energy storage devices in wearable electronics, Internet of Things (IoT)‐based devices, and electric vehicles are also mentioned in the review. The role of AM in facilitating the production of solid‐state batteries has also revolutionized the electric vehicle (EV) industry. Recent progress in the field of AM of energy systems with solid electrolytes and potential future directions such as 4D printing to incorporate stimuli‐responsive behavior in 3D‐printed materials, biomimetic design optimization, and additive manufacturing of ESD in a micro‐gravity environment have also been highlighted. Extensive research and continuous progress in this field are expected to enhance the longetivity, industrial scalability, and electrochemical performance of 3D‐printed energy storage devices in future.

Active Material‐Free Continuous Carbon Nanotube Fibers with Unprecedented Enhancement of Physicochemical Properties for Fiber‐Type Solid‐State Supercapacitors

AbstractFiber‐type solid‐state supercapacitors (FSSCs) are gaining traction as wearable energy storage devices, given their adaptability akin to traditional fibers. Carbon nanotube fibers (CNTFs) generated via a liquid crystalline (LC) wet‐spinning process demonstrate outstanding electrical conductivity, mechanical strength, and flexibility. However, their intrinsic “defect‐free” sp2 carbon surface restricts immediate FSSC application, limited by lower specific surface area and scant pseudocapacitive sites. This study develops LC‐spun CNTFs with inherent electrochemical activity, eliminating the need for post‐processing or additional active materials, a requirement typically essential in most previous research. This advancement arises from the wet‐spinning of functionalized CNTs from a LC solution with an exceptionally high concentration of 160 mg mL−1, facilitated by the manipulation of the LC phase transition range. The resultant CNTFs exhibit a refined internal structure, yielding an electrical conductivity of 1.9 MS m−1 and a mechanical strength of 0.93 GPa. Simultaneously, they demonstrate inherent electrical energy storage capabilities with a specific capacitance of 139.4 F g−1 and a volumetric capacitance of 192.4 F cm−3 at 0.5 A g−1. This innovation signifies a step forward in the potential for mass production without the burden of additional materials and steps.

Scalable 2D/2D Assembly of Ultrathin MOF/MXene Sheets for Stretchable and Bendable Energy Storage Devices

AbstractScalable assembly of two dimensional (2D) lamellar nanomaterials for deformable films has potential in wearable energy storage devices, but overcoming the trade‐off in mechanical and energy storage properties is a challenge. Here, a blade‐coating strategy is reported to develop highly stretchable and bendable metal‐organic frameworks/large‐sized Ti3C2Tx MXene (MOF/LMX) composite films on the pre‐stretched elastomer substrates. The LMX sheets serve as conductive scaffolds for loading the small‐sized ultrathin MOF sheets (SUMOFs), resulting in an improved tensile strength (≈97 MPa) of the films, which guarantees their structural integrity when forming a wavy structure on a relaxed substrate. In addition, SUMOFs incorporated in‐between LMX layers not only expose active redox sites by mitigating the intrinsic self‐restacking of MOF but also accelerate the electron transfer in the redox reaction process revealed through the density functional theory calculations. As a result, the composite films deliver high electrical conductivity (3244 S cm−1) and energy storage capability (1238 F g−1). When assembled into an asymmetric supercapacitor device, it also exhibits stable performances under different bending and stretching states. Thus, the development of conducting and deformable MOF‐based films with high mechanical, electrical, and energy storage properties enables their potential commercial applications for wearable electronics.