Fixture-free omnidirectional prestretching fabrication and integration of crumpled in-plane micro-supercapacitors

Omnidirectionally Stretchable High-Performance Microbatteries Based on Nanocomposite Current Collectors

Stretchable electronics are transforming next-generation wearables and robotics, creating a significant demand for compatible energy storage devices. Microbatteries, known for their compact and flat design, hold great promise but often face limitations of low strain tolerance and unidirectional stretchability. Here, we introduce omnidirectionally stretchable Zn-MnO2 microbatteries featuring innovative nanocomposite current collectors. These current collectors comprise serpentine-patterned silver nanowire and carbon nanotube nanocomposites embedded in a soft elastomer, which effectively dissipate strain across all directions. The resulting microbattery achieves impressive performance, including a high capacity (>1.5 mAh cm-2), excellent rate capability (up to 5.0 mA cm-2), and robust operation under omnidirectional/biaxial strains. Additionally, multiple microbattery cells are successfully integrated with a wireless charging circuit and a soft LED array, forming a wearable system that seamlessly conforms to body movements. This work establishes a novel design framework for deformable energy storage devices, merging superior electrochemical performance with multidirectional stretchability.

2D-Supported Vertical MXenes for Ultrafast Filtering with Ultralow Inductance

Filtering supercapacitors (SCs) are promising for miniaturized power filter electronics due to their high capacitance and robust high-power performance. However, their adoption is limited by a poor low-frequency response in planar porous electrodes, causing mismatched operating frequencies and overheating risks. To address this, we develop MXene-based SCs using a novel vitamin C-assisted solution-thermal method to assemble Ti3C2Tx MXenes into 2D-supported vertical structures, enhancing the dynamic response for linear filtering. These SCs achieve an ultrafast frequency response of 13.8 kHz at a phase angle of -45°, with electric inductance 1/2000 that of commercial aluminum electrolytic capacitors (AECs). They exhibit high areal and volumetric capacitances and effectively smooth random AC waveforms into stable DC signals. Their practicality is demonstrated by replacing bulky AECs and parallel capacitors in a Bluetooth audio amplifier, delivering wireless audio playback without tone quality loss and highlighting their transformative potential for next-generation electronics.

Deformation-tolerant, wireless-charging microbatteries for seamlessly integrated omnidirectional stretchable electronics

Wireless-charging in-plane microbatteries (MBs) with conformal shape and high-capacity hold substantial promise in advancing the practical applications of complexly configured electronic devices. However, integrating these MBs seamlessly with flexible electronic system remains a challenge as it requires a rational structure design and reasonable materials engineering for the micropower system, ensuring both high compatibility and robust mechanical stability. Here, we present stretchable and wireless-charging dual-plating MBs that integrate seamlessly into circuits through an omnidirectional stretch-contraction strategy coupled with mask-assisted printing. The strain-induced folding structures and no active-material design endow the wireless-charging MBs with reliable deformation-tolerant capabilities, which can sustain ~200% omnidirectional strains and have advantages of an order of magnitude in terms of power and energy densities, compared to the existing in-plane MBs. With the exceptional compatible and elastic properties, a wirelessly charging stretchable display integrated circuit and even intelligent electronic skin are achieved, capable of mimicking human touch to sense the weight, temperature, and shape of objects.

Cost-effective fabrication of submicron-scale patterns enabled by microcontact printing with a pre-strained soft elastomeric stamp

While photolithography and e-beam lithography remain the predominant techniques for nanoscale patterning, their high costs and inherent complexity have limited their accessibility for certain applications. Recently, shrink lithography has emerged as a promising technique for reducing pattern dimensions through substrate contraction, offering a simpler and cost-effective alternative to existing methods. In this study, we propose a method combining microcontact printing with a pre-stretched soft elastomeric stamp to achieve scalable pattern reduction. We introduce the pre-stretching and releasing of the Ecoflex-based soft elastomeric stamp in microcontact printing processes, leveraging its excellent stretchability and elasticity. This approach allows for the reduction of the original pattern dimensions by up to 60%. Furthermore, by experimentally quantifying the shrinkage with respect to the applying strain, we characterize the degree of pattern reduction, which offers a promising alternative for fabricating sub-micron scale features, with potential applications in scalable nano-manufacturing.

Covalent organic frameworks and their composites as enhanced energy storage materials

The advancement in materials chemistry promoted the growth of energy storage systems such as capacitors, supercapacitors and batteries. Covalent organic frameworks and nanomaterials have significantly improved the performance of various energy storage systems. Because of the unique properties of these materials, like high surface area, tunable architectures, and enhanced conductivity, researchers have developed effective and durable energy storage solutions for multiple applications. These findings are significant for meeting the demand for reliable and sustainable energy storage materials in order to save energy for a better future of mankind. As the demand for reliable and sustainable energy storage materials is increasing, the scientific community is more focussed towards the development of covalent organic frameworks (COFs). The high surface area, thermal and chemical stability, structural tunability, porosity, and low density of COFs make them appropriate for energy storage applications. Their potential to produce advanced energy storage devices with better performance and durability is further reinforced by their ability to be customized for specific applications and amplified for conductive materials. This review covers the designs and synthetic techniques of COFs and their composites specifically suitable for energy storage uses. It further highlights their use as cathode and anode materials in supercapacitors, COF based electrolytes and batteries. The review further includes the flexibility and efficiency of COFs in energy storage applications. Furthermore, it addresses the challenges and their potential solutions regarding the use of COFs in energy storage devices. By providing a comprehensive understanding of the advantages and limitations of COFs, this review aims to inform and inspire future advancements in energy storage technologies.

Facile Preparation of High-Performance Free-Standing Micro-Supercapacitors by Optimizing Oxygen Groups on Graphene

Free-standing micro-supercapacitor (MSC) devices without substrate or current collectors are promising for practical applications. However, it is still difficult to prepare high-performance free-standing MSC devices because of the requirement of optimized active sites, conductivity, ion diffusion, controlled patterns, moisture susceptibility, etc. Here, it is proposed that the optimization of oxygen level on graphene is promising to solve these requirements because of the balance of sp2 and sp3 hybridization. Using the medium-oxidized graphene, the flexible, conductive, hydro-stable, easy-processing film can be facilely obtained, which facilitates the preparation of free-standing MSC electrodes. After constructing with gel electrolyte, the free-standing MSC device shows a high capacitance of 898.4 mF cm-2 using aqueous-gel electrolyte and 383.6 mF cm-2 using ion-gel electrolyte with mass loading of ca. 10 mg cm-2. Correspondingly, the MSC device can achieve a landmark energy density of 42.6 µWh cm-2 at 0.85 mW cm-2 (7.1 mWh cm-3 at 141.7 mW cm-3). The advantages of high performance, facile preparation, and low inactive components make the free-standing MSC device promising for practical applications.

On-Demand Picoliter-Level-Droplet Inkjet Printing for Micro Fabrication and Functional Applications

With the advent of Internet of Things (IoTs) and wearable devices, manufacturing requirements have shifted toward miniaturization, flexibility, environmentalization, and customization. Inkjet printing, as a non-contact picoliter-level droplet printing technology, can achieve material deposition at the microscopic level, helping to achieve high resolution and high precision patterned design. Meanwhile, inkjet printing has the advantages of simple process, high printing efficiency, mask-free digital printing, and direct pattern deposition, and is gradually emerging as a promising technology to meet such new requirements. However, there is a long way to go in constructing functional materials and emerging devices due to the uncommercialized ink materials, complicated film-forming process, and geometrically/functionally mismatched interface, limiting film quality and device applications. Herein, recent developments in working mechanisms, functional ink systems, droplet ejection and flight process, droplet drying process, as well as emerging multifunctional and intelligence applications including optics, electronics, sensors, and energy storage and conversion devices is reviewed. Finally, it is also highlight some of the critical challenges and research opportunities. The review is anticipated to provide a systematic comprehension and valuable insights for inkjet printing, thereby facilitating the advancement of their emerging applications.

Carbon Micro/Nano Machining toward Miniaturized Device: Structural Engineering, Large-Scale Fabrication, and Performance Optimization

With the rapid development of micro/nano machining, there is an elevated demand for high-performance microdevices with high reliability and low cost. Due to their outstanding electrochemical, optical, electrical, and mechanical performance, carbon materials are extensively utilized in constructing microdevices for energy storage, sensing, and optoelectronics. Carbon micro/nano machining is fundamental in carbon-based intelligent microelectronics, multifunctional integrated microsystems, high-reliability portable/wearable consumer electronics, and portable medical diagnostic systems. Despite numerous reviews on carbon materials, a comprehensive overview is lacking that systematically encapsulates the development of high-performance microdevices based on carbon micro/nano structures, from structural design to manufacturing strategies and specific applications. This review focuses on the latest progress in carbon micro/nano machining toward miniaturized device, including structural engineering, large-scale fabrication, and performance optimization. Especially, the review targets an in-depth evaluation of carbon-based micro energy storage devices, microsensors, microactuators, miniaturized photoresponsive and electromagnetic interference shielding devices. Moreover, it highlights the challenges and opportunities in the large-scale manufacturing of carbon-based microdevices, aiming to spark further exciting research directions and application prospectives.

Trunk-Inspired SWCNT-Based Wrinkled Films for Highly-Stretchable Electromagnetic Interference Shielding and Wearable Thermotherapy

Nowadays, the increasing electromagnetic waves generated by wearable devices are becoming an emerging issue for human health, so stretchable electromagnetic interference (EMI) shielding materials are highly demanded. Elephant trunks are capable of grabbing fragile vegetation and tearing trees thanks not only to their muscles but also to their folded skins. Inspired by the wrinkled skin of the elephant trunks, herein, we propose a winkled conductive film based on single-walled carbon nanotubes (SWCNTs) for multifunctional EMI applications. The conductive film has a sandwich structure, which was prepared by coating SWCNTs on both sides of the stretched elastic latex cylindrical substrate. The shrinking-induced winkled conductive network could withstand up to 200% tensile strain. Typically, when the stretching direction is parallel to the polarization direction of the electric field, the total EMI shielding effectiveness could surprisingly increase from 38.4 to 52.7 dB at 200% tensile strain. It is mainly contributed by the increased connection of the SWCNTs. In addition, the film also has good Joule heating performance at several voltages, capable of releasing pains in injured joints. This unique property makes it possible for strain-adjustable multifunctional EMI shielding and wearable thermotherapy applications.

Moisture-Electric-Moisture-Sensitive Heterostructure Triggered Proton Hopping for Quality-Enhancing Moist-Electric Generator

Moisture-enabled electricity (ME) is a method of converting the potential energy of water in the external environment into electrical energy through the interaction of functional materials with water molecules and can be directly applied to energy harvesting and signal expression. However, ME can be unreliable in numerous applications due to its sluggish response to moisture, thus sacrificing the value of fast energy harvesting and highly accurate information representation. Here, by constructing a moisture-electric-moisture-sensitive (ME-MS) heterostructure, we develop an efficient ME generator with ultra-fast electric response to moisture achieved by triggering Grotthuss protons hopping in the sensitized ZnO, which modulates the heterostructure built-in interfacial potential, enables quick response (0.435 s), an unprecedented ultra-fast response rate of 972.4 mV s-1, and a durable electrical signal output for 8 h without any attenuation. Our research provides an efficient way to generate electricity and important insight for a deeper understanding of the mechanisms of moisture-generated carrier migration in ME generator, which has a more comprehensive working scene and can serve as a typical model for human health monitoring and smart medical electronics design.

Localized Electron Density Regulation Effect for Promoting Solid-Liquid Ion Adsorption to Enhance Areal Capacitance of Micro-Supercapacitors

The development of flexible microelectronic systems requires the construction of high-energy-output planar micro-supercapacitors (MSCs). Herein, the localized electron density, by introducing graphene quantum dots (GQDs) on the surface of electrodes, is regulated. The enhanced local field intensity promotes ion electrostatic adsorption at the solid-liquid interface, which significantly improves the energy density of MSCs in the confined space. Local electronic structure has been investigated from the perspective of the topological analysis of the electron localization function (ELF) and the electron density. Impressively, the edges of the simulated structure exhibit a higher electron density distribution than the CC skeleton. This finding indicates that the introduced GQDs reinforce the intrinsic electrical double-layer capacitance (EDLC) and the oxygen-bearing functional groups at the edge, further increasing the pseudocapacitance performance. Moreover, the edge electron aggregation effect enables the all-carbon-based symmetric MSCs to exhibit ultra-high areal capacitance (21.78 mF cm-2 ) and excellent cycle stability (86.74% retention after 25 000 cycles). This novel surface local charge regulation strategy is also applied for intensifying ion electrostatic adsorption on Zn-ion hybrid MSCs (polyvalent metal ions) and ion-gel electrolyte MSCs (non-metallic ions). With excellent planar integration, this device demonstrates excellent flexibility and has potential applications in timing and environmental monitoring.

Sea-Cucumber-like Microstructure Polyoxometalate/TiO2 Nanocomposite Electrode for High-Performance Electrochromic Energy Storage Devices

The key challenge in the practical application of electrochromic energy storage devices (EESDs) is the fabrication of high-performance electrode materials. Herein, we deposited K7[La(H2O)x(α2-P2W17O61)] (P2W17La) onto TiO2 nanowires (NW) to construct an NW–P2W17La nanocomposite using a layer-by-layer self-assembly method. In contrast to the pure P2W17La films, the nanocomposite exhibits enhanced electrochromic and electrochemical performance owing to the 3D sea-cucumber-like microstructure. An EESD using the NW–P2W17La film as the cathode exhibited outstanding electrochromic and energy storage properties, with high optical modulation (48.6% at 605 nm), high switching speeds (tcoloring = 15 s, tbleaching = 4 s), and high area capacitance (5.72 mF cm−2 at 0.15 mA cm−2). The device can reversibly switch between transparent and dark blue during the charge/discharge process, indicating that electrochromic contrast can be used as a quantitative indicator of the energy storage status.

Recent advances in polyaniline-based micro-supercapacitors

The rapid development of the Internet of Things (IoTs) and proliferation of wearable electronics have significantly stimulated the pursuit of distributed power supply systems that are small and light. Accordingly, micro-supercapacitors (MSCs) have recently attracted tremendous research interest due to their high power density, good energy density, long cycling life, and rapid charge/discharge rate delivered in a limited volume and area. As an emerging class of electrochemical energy storage devices, MSCs using polyaniline (PANI) electrodes are envisaged to bridge the gap between carbonaceous MSCs and micro-batteries, leading to a high power density together with improved energy density. However, despite the intensive development of PANI-based MSCs in the past few decades, a comprehensive review focusing on the chemical properties and synthesis of PANI, working mechanisms, design principles, and electrochemical performances of MSCs is lacking. Thus, herein, we summarize the recent advances in PANI-based MSCs using a wide range of electrode materials. Firstly, the fundamentals of MSCs are outlined including their working principle, device design, fabrication technology, and performance metrics. Then, the working principle and synthesis methods of PANI are discussed. Afterward, MSCs based on various PANI materials including pure PANI, PANI hydrogel, and PANI composites are discussed in detail. Lastly, concluding remarks and perspectives on their future development are presented. This review can present new ideas and give rise to new opportunities for the design of high-performance miniaturized PANI-based MSCs that underpin the sustainable prosperity of the approaching IoTs era.

Ultrafast Synthesis of Metal-Layered Hydroxides in a Dozen Seconds for High-Performance Aqueous Zn (Micro-) Battery

Efficient synthesis of transition metal hydroxides on conductive substrate is essential for enhancing their merits in industrialization of energy storage field. However, most of the synthetic routes at present mainly rely on traditional bottom-up method, which involves tedious steps, time-consuming treatments, or additional alkaline media, and is unfavorable for high-efficiency production. Herein, we present a facile, ultrafast and general avenue to synthesize transition metal hydroxides on carbon substrate within 13 s by Joule-heating method. With high reaction kinetics caused by the instantaneous high temperature, seven kinds of transition metal-layered hydroxides (TM-LDHs) are formed on carbon cloth. Therein, the fastest synthesis rate reaches ~ 0.46 cm2 s-1. Density functional theory calculations further demonstrate the nucleation energy barriers and potential mechanism for the formation of metal-based hydroxides on carbon substrates. This efficient approach avoids the use of extra agents, multiple steps, and long production time and endows the LDHs@carbon cloth with outstanding flexibility and machinability, showing practical advantages in both common and micro-zinc ion-based energy storage devices. To prove its utility, as a cathode in rechargeable aqueous alkaline Zn (micro-) battery, the NiCo LDH@carbon cloth exhibits a high energy density, superior to most transition metal LDH materials reported so far.

Bending Resistance Covalent Organic Framework Superlattice: "Nano-Hourglass"-Induced Charge Accumulation for Flexible In-Plane Micro-Supercapacitors

Covalent organic framework (COF) film with highly exposed active sites is considered as the promising flexible self-supported electrode for in-plane micro-supercapacitor (MSC). Superlattice configuration assembled alternately by different nanofilms based on van der Waals force can integrate the advantages of each isolated layer to exhibit unexpected performances as MSC film electrodes, which may be a novel option to ensure energy output. Herein, a mesoporous free-standing A-COF nanofilm (pore size is 3.9 nm, averaged thickness is 4.1 nm) with imine bond linkage and a microporous B-COF nanofilm (pore size is 1.5 nm, averaged thickness is 9.3 nm) with β-keto-enamine-linkages are prepared, and for the first time, we assembly the two lattice matching films into sandwich-type superlattices via layer-by-layer transfer, in which ABA-COF superlattice stacking into a "nano-hourglass" steric configuration that can accelerate the dynamic charge transportation/accumulation and promote the sufficient redox reactions to energy storage. The fabricated flexible MSC-ABA-COF exhibits the highest intrinsic CV of 927.9 F cm-3 at 10 mV s-1 than reported two-dimensional alloy, graphite-like carbon and undoped COF-based MSC devices so far, and shows a bending-resistant energy density of 63.2 mWh cm-3 even after high-angle and repeat arbitrary bending from 0 to 180°. This work provides a feasible way to meet the demand for future miniaturization and wearable electronics.