Compact Assembly and Programmable Integration of Supercapacitors

An ultrastretchable seamlessly integrated contactless charging microsystem towards skin-attachable wireless microelectronics

For electronics to be wearable, contactless charging and overall deformability are necessary pre-conditions. However, the current heterogeneous integration based on different active materials and separate manufacturing often leads to mechanical mismatch. Here, we report an ultrastretchable all-in-one integrated MXene-based microsystem comprising wireless coils, micro-supercapacitors (MSCs) and strain sensors. The seamless configuration without any connecting interface dramatically improves the structural integrity of the microsystem, and a pre-crumpled structure endows it with superior stretchability. Attributed to these, our MSCs can be wirelessly charged in ~20 s under various types of deformation and are capable of powering strain sensors, responding rapidly to body motion signals. Moreover, the MSCs display a high specific capacitance of 76.82 F cm-3, and superb mechanical stability with 98.5% capacitance retention after biaxial stretching 1000 cycles from 0% to 500% areal strain. Therefore, this work sheds new insights into design and implementation of skin-attachable wireless microelectronics.

Unlocking Self-antioxidant Capability and Processability of Additive-free MXene Ink towards High-performance Customizable Supercapacitors

The solution processing of MXene ink is the feasible strategy to realize its state-of-the-art applications. Nevertheless, achieving high stability and processability of additive-free MXene ink is particularly challenging. Herein, we propose an oxyanion-terminated Ti3C2Tx MXene ink that exhibits excellent self-antioxidant capability and processability. The vertex-connected polyhedrons of oxyanions capping on the Ti3C2 host serve as an in situ antioxidative shield, effectively preventing the attack of free H2O molecules while increasing the robustness of the Ti-C bond and reducing the susceptibility of surface Ti atoms to oxidation. Consequently, the shelf life of MXene ink can be extended up to 5 months at room temperature. Moreover, the high electron accumulation of oxyanions enhances the interlayer interactions among MXene sheets through electrostatic binding, which enables the formation of stable and uniform MXene inks with controlled rheological properties and processability. Inspired by Chinese calligraphy, we utilize the oxyanion-terminated MXene ink to fabricate high-performance and customizable paper supercapacitors, which exhibit exceptional flexibility and stability, allowing them to be tailored to desired capacity, stretchability, and shapes. This in situ surface chemistry strategy of oxyanions can activate the self-antioxidant capability and solution processability of MXene, paving the way for its widespread applications in flexible and wearable electronics.

Recent advances in integrated solar cell/supercapacitor devices: Fabrication, strategy and perspectives

BACKGROUND

Solar cell/supercapacitor integrated devices (SCSD) have made some progress in terms of device structure and electrode materials, but there are still many key challenges in controlling electrode performance and improving the efficiency of integrated devices.

AIM OF REVIEW

It is necessary to study how to balance the photoelectric conversion process and the storage process. From the microscopic mechanism of different functional unit materials to the mechanism of macroscopic devices, it is essential to conduct in-depth research.

KEY SCIENTIFIC CONCEPTS OF REVIEW

Here, the structures and preparation methods of various types of integrated SCSD were introduced. Then, the strategies for improving the overall performance of integrated devices were evaluated. Finally, the key objectives of reducing the cost of materials, increasing the stability and sustainability of devices were highlighted. Better matching of different functional units of devices was also prospected.

Three-dimensional high-aspect-ratio microarray thick electrodes for high-rate hybrid supercapacitors

Hybrid supercapacitors (HSCs) with facile integration and high process compatibility are considered ideal power sources for portable consumer electronics. However, as a crucial component for storing energy, traditional thin-film electrodes exhibit low energy density. Although increasing the thickness of thin films can enhance the energy density of the electrodes, it gives rise to issues such as poor mechanical stability and long electron/ion transport pathways. Constructing a stable three-dimensional (3D) ordered thick electrode is considered the key to addressing the aforementioned contradictions. In this work, a manufacturing process combining lithography and chemical deposition techniques is developed to produce large-area and high-aspect-ratio 3D nickel ordered cylindrical array (NiOCA) current collectors. Positive electrodes loaded with nickel-cobalt bimetallic hydroxide (NiOCA/NiCo-LDH) are constructed by electrodeposition, and HSCs are assembled with NiOCA/nitrogen-doped porous carbon (NiOCA/NPC) as negative electrodes. The HSCs exhibits 55% capacity retention with the current density ranging from 2 to 50 mA cm-2. Moreover, it maintains 98.2% of the initial capacity after long-term cycling of 15,000 cycles at a current density of 10 mA cm-2. The manufacturing process demonstrates customizability and favorable repeatability. It is anticipated to provide innovative concepts for the large-scale production of 3D microarray thick electrodes for high-performance energy storage system.

Evaporate-casting of curvature gradient graphene superstructures for ultra-high strength structural materials

In contemporary manufacturing, the processing of structural materials plays a pivotal role in enabling the creation of robust, tailor-made, and precise components suitable for diverse industrial applications. Nonetheless, current material forming technologies face challenges due to internal stress and defects, resulting in a substantial decline in both mechanical properties and processing precision. We herein develop a processing strategy toward graphene superstructure with a curvature gradient, which allows us to fabricate robust structural materials with meticulously designed functional shapes. The structure consists of an arc-shaped assembly of graphene nanosheets positioned at co-axial curvature centers. During the dehydration-based evaporate-casting process, the assembly is tightened via capillary effect, inducing local bending. By precisely tuning the axis-center distance and tilt angle, we achieve accurate control over the shape of obtained structure. Notably, internal stress is harnessed to reinforce a designed mortise and tenon structure, resulting in a high joining strength of up to ~200 MPa. This innovative approach addresses the challenges faced by current material forming technologies and opens up more possibilities for the manufacturing of robust and precisely shaped components.

Patterned Micro Flexible Supercapacitors based on the Rapid Transfer-Printing Method

Developing a simple and rapidly preparative method for patterned flexible supercapacitors is essential and indispensable for the swift advancement of portable devices integrated with micro devices. In this study, we employed a cost-effective and rapid fabrication method based on transfer-printing technology to produce patterned micro flexible supercapacitors with various substrates. The resulting flexible micro supercapacitors not only allow for customized patterns with strong flexibility and resistance to bending, while maintaining a certain level of performance, but also facilitate the creation of diverse circuits to tailor voltage and current to specific requirements. Patterned micro flexible supercapacitors with a thickness of 0.02 mm, based on accordion-like Ti3C2Tx MXene materials coated on a substrate, demonstrate a specific capacitance of 142.7 mF cm-2 at 0.5 mA cm-2. The devices exhibit satisfactory capacitance retention (91% after 5000 cycles) and superb mechanical flexibility (71% capacitance retention at 180° bending after 2000 cycles). At a power density of 2.9 mW cm-2, the energy density of the sandwich structure device reaches 126.8 μWh cm-2. This study is expected to contribute new ideas for the design and preparation of patterned flexible supercapacitors.

Robust Graphene-based Aerogel for Integrated 3D Asymmetric Supercapacitors with High Energy Density

Three-dimensional asymmetric supercapacitors (3D ASC) have garnered significant attention due to their high operating window, theoretical energy density, and circularity. However, the practical application of 3D electrode materials is limited by brittleness and excessive dead volume. Therefore, we propose a controlled contraction strategy that regulates the pore structure of 3D electrode materials, eliminates dead volume in the 3D skeleton structure, and enhances mechanical strength. In this study to obtain reduced graphene oxide/manganese dioxide (rGO/MnO2) and reduced graphene oxide/carbon nanotube (rGO/CNT) composite aerogels with a stable and compact structure. MnO2 and CNT as nanogaskets, preventing the self-stacking of graphene nanosheets during the shrinkage process. Additionally, the high specific capacitor nanogaskets significantly enhance the specific energy density of the rGO aerogel electrode. The prepared rGO/MnO2//rGO/CNT 3D ASC exhibits a high mass-specific capacitance of 216.15 F g-1, a high mass energy density of 74 Wh kg-1 at 3.5 A g-1, and maintains a retention rate of capacitance at 99.89 % after undergoing 10,000 cycles of charge and discharge at 5 A g-1. The versatile and integrated assembly of 3D ASC units is achieved through the utilization of the robust mechanical structure of rGO-based aerogel electrodes, employing a mortise and tenon structural design.

All Plant-Based Compact Supercapacitor in Living Plants

Biomass-based energy storage devices (BESDs) have drawn much attention to substitute traditional electronic devices based on petroleum or synthetic chemical materials for the advantages of biodegradability, biocompatibility, and low cost. However, most of the BESDs are almost made of reconstructed plant materials and exogenous chemical additives which constrain the autonomous and widespread advantages of living plants. Herein, an all-plant-based compact supercapacitor (APCSC) without any nonhomologous additives is reported. This type of supercapacitor formed within living plants acts as a form of electronic plant (e-plant) by using its tissue fluid electrolyte, which surprisingly presents a satisfying electrical capacitance of 182.5 mF cm-2, higher than those of biomass-based micro-supercapacitors reported previously. In addition, all constituents of the device come from the same plant, effectively avoid biologically incompatible with other extraneous substances, and almost do no harm to the growth of plant. This e-plant can not only be constructed in aloe, but also be built in most of succulents, such as cactus in desert, offering timely electricity supply to people in extreme conditions. It is believed that this work will enrich the applications of electronic plants, and shed light on smart botany, forestry, and agriculture.

Inorganic Hydrogel Based on Low-Dimensional Nanomaterials

Composed of three-dimensional (3D) nanoscale inorganic bones and up to 99% water, inorganic hydrogels have attracted much attention and undergone significant growth in recent years. The basic units of inorganic hydrogels could be metal nanoparticles, metal nanowires, SiO2 nanowires, graphene nanosheets, and MXene nanosheets, which are then assembled into the special porous structures by the sol-gel process or gelation via either covalent or noncovalent interactions. The high electrical and thermal conductivity, resistance to corrosion, stability across various temperatures, and high surface area make them promising candidates for diverse applications, such as energy storage, catalysis, adsorption, sensing, and solar steam generation. Besides, some interesting derivatives, such as inorganic aerogels and xerogels, can be produced through further processing, diversifying their functionalities and application domains greatly. In this context, we primarily provide a comprehensive overview of the current status of inorganic hydrogels and their derivatives, including the structures of inorganic hydrogels with various compositions, their gelation mechanisms, and their exceptional practical performance in fields related to energy and environmental applications.

Nanoparticle-Based Photothermal Therapy for Breast Cancer Noninvasive Treatment

Rapid advancements in materials science and nanotechnology, intertwined with oncology, have positioned photothermal therapy (PTT) as a promising noninvasive treatment strategy for cancer. The breast's superficial anatomical location and aesthetic significance render breast cancer a particularly pertinent candidate for the clinical application of PTT following melanoma. This review comprehensively explores the research conducted on the various types of nanoparticles employed in PTT for breast cancer and elaborates on their specific roles and mechanisms of action. The integration of PTT with existing clinical therapies for breast cancer is scrutinized, underscoring its potential for synergistic outcomes. Additionally, the mechanisms underlying PTT and consequential modifications to the tumor microenvironment after treatment are elaborated from a medical perspective. Future research directions are suggested, with an emphasis on the development of integrative platforms that combine multiple therapeutic approaches and the optimization of nanoparticle synthesis for enhanced treatment efficacy. The goal is to push the boundaries of PTT toward a comprehensive, clinically applicable treatment for breast cancer.

Spatial-Interleaving Graphene Supercapacitor with High Area Energy Density and Mechanical Flexibility

The booming portable electronics market has raised huge demands for the development of supercapacitors with mechanical flexibility and high power density in the finite area; however, this is still unsatisfied by the currently thickness-confined sandwich design or the in-plane interdigital configuration with limited mechanical features. Here, a spatial-interleaving supercapacitor (SI-SC) is first designed and constructed, in which the graphene microelectrodes are reversely stacked layer by layer within a three-dimensional (3D) space. Because each microelectrode matches well with four counter microelectrodes and all 3D spatial-interleaving microelectrodes have narrow interspaces that maintain the efficient ions transport in the whole device, this SI-SC has a prominent liner capacitance increase along with the device thickness. As a result, the high specific areal capacitance of 36.46 mF cm^-2 and 5.34 μWh cm^-2 energy density is achieved on the 100 μm thick device. Especially, the microelectrodes in each layer are interdigitated, ensuring the outstanding mechanical flexibility of SI-SC, with ∼98.7% performance retention after 10⁴ cycles of bending tests, realizing the excellent integration of high area energy density and mechanical flexibility in the finite area. Furthermore, the SI-SC units can be easily integrated into wearable electronics to power wristwatches, light-emitting diodes (LEDs), calculators, and so on for practical applications.

Fast constructing polarity-switchable zinc-bromine microbatteries with high areal energy density

Microbatteries (MBs) are promising candidates to provide power for various miniaturized electronic devices, yet they generally suffer from complicated fabrication procedures and low areal energy density. Besides, all cathodes of current MBs are solid state, and the trade-off between areal capacity and reaction kinetics restricts their wide applications. Here, we propose a dual-plating strategy to facilely prepare zinc-bromine MBs (Zn-Br₂ MBs) with a liquid cathode to achieve both high areal energy density and fast kinetics simultaneously. The Zn-Br₂ MBs deliver a record high areal energy density of 3.6 mWh cm^-2, almost an order of magnitude higher than available planar MBs. Meanwhile, they show a polarity-switchable feature to tolerate confusion of cathode and anode. This strategy could also be extended to other battery systems, such as Zn-I₂ and Zn-MnO₂ MBs. This work not only proposes an effective construction method for MBs but also enriches categories of microscale energy storage devices.

Strain-Driven Auto-Detachable Patterning of Flexible Electrodes

Flexible electrodes that are multilayer, multimaterial, and conformal are pivotal for multifunctional wearable electronics. Traditional electronic circuits manufacturing requires substrate-supported transfer printing, which limits their multilayer integrity and device conformability on arbitrary surfaces. Herein, a "shrinkage-assisted patterning by evaporation" (SHAPE) method is reported, by employing evaporation-induced interfacial strain mismatch, to fabricate auto-detachable, freestanding, and patternable electrodes. The SHAPE method utilizes vacuum-filtration of polyaniline/bacterial cellulose (PANI/BC) ink through a masked filtration membrane to print high-resolution, patterned, and multilayer electrodes. The strong interlayer hydrogen bonding ensures robust multilayer integrity, while the controllable evaporative shrinking property of PANI/BC induces mismatch between the strains of the electrode and filtration membrane at the interface and thus autodetachment of electrodes. Notably, a 500-layer substrateless micro-supercapacitor fabricated using the SHAPE method exhibits an energy density of 350 mWh cm^-2 at a power density of 40 mW cm^-2 , 100 times higher than reported substrate-confined counterparts. Moreover, a digital circuit fabricated using the SHAPE method functions stably on a deformed glove, highlighting the broad wearable applications of the SHAPE method.

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

Multidimensional folded structures with elasticity could provide spatial charge storage capability and shape adaptability for micro-supercapacitors (MSCs). Here, highly crumpled in-plane MSCs with superior conformality are fabricated in situ and integrated by a fixture-free omnidirectional elastic contraction strategy. Using carbon nanotube microelectrodes, a single crumpled MSC holds an ultrahigh volumetric capacitance of 9.3 F cm^-3, and its total areal capacitance is 45 times greater than the initial state. Experimental and theoretical simulation methods indicate that strain-induced improvements of adsorption energy and conductance for crumpled microelectrodes are responsible for the prominent enhancement of electrochemical performance. With outstanding morphological randomicity, the integrated devices can serve as smart coatings in moving robots, withstanding extreme mechanical deformations. Notably, integration on a spherical surface is possible by using a spherical mask, in which a small area of the microdevice array (3.9 cm²) can produce a high output voltage of 100 V.

A Review of Compact Carbon Design for Supercapacitors with High Volumetric Performance

Volumetric performance is of great importance in today's energy storage devices, and is used to evaluate their competitiveness in the markets of miniaturized electronic devices and space-constrained electric vehicles. Supercapacitors suffer from a low volumetric energy density in spite of their high power and long cycle life because of their use of porous but low-density carbons. This review considers compact carbon design strategies for high volumetric performance supercapacitors based on four key electrode parameters: density, thickness, gravimetric capacitance, and nonactive components. A guide is provided for constructing a conductive additive-/binder-free self-supported ultrathick, dense electrode to maximize the volumetric energy density. The research status of emerging micro-supercapacitors and hybrid supercapacitors is then briefly discussed, emphasizing the importance of their volumetric performance and the opportunities as well as challenges they face in the trendy Internet of things applications or larger device systems.

Planar Graphene-Based Microsupercapacitors

With the development of wearable, portable, and implantable electronic devices, flexible and on-chip microsupercapacitors (MSCs) are urgently needed for miniaturized energy storage. Planar MSCs have high power density, fast charge/discharge rate, and long operating lifetime, and can adapt to future flexible, integrated, and miniaturized electronic systems for wide application foreground. Due to the high specific surface area, outstanding electrical conductivity, and excellent electron mobility, graphene shows promising advantages in planar MSCs devices, thus stimulates wide-ranging research in the last few years. Herein, the recent progress of planar graphene-based MSCs, including the intrinsic structure regulation of graphene-based electrode materials, the specific fabrication techniques, the multifunctional integration, and various applications of MSCs as flexible and on-chip energy storage is systematically summarized. The key challenges and prospects of future planar graphene-based MSCs are also discussed targeting to realize their practical applications.

Electro-responsive actuators based on graphene

Electro-responsive actuators (ERAs) hold great promise for cutting-edge applications in e-skins, soft robots, unmanned flight, and in vivo surgery devices due to the advantages of fast response, precise control, programmable deformation, and the ease of integration with control circuits. Recently, considering the excellent physical/chemical/mechanical properties (e.g., high carrier mobility, strong mechanical strength, outstanding thermal conductivity, high specific surface area, flexibility, and transparency), graphene and its derivatives have emerged as an appealing material in developing ERAs. In this review, we have summarized the recent advances in graphene-based ERAs. Typical the working mechanisms of graphene ERAs have been introduced. Design principles and working performance of three typical types of graphene ERAs (e.g., electrostatic actuators, electrothermal actuators, and ionic actuators) have been comprehensively summarized. Besides, emerging applications of graphene ERAs, including artificial muscles, bionic robots, human-soft actuators interaction, and other smart devices, have been reviewed. At last, the current challenges and future perspectives of graphene ERAs are discussed.

A seamlessly integrated device of micro-supercapacitor and wireless charging with ultrahigh energy density and capacitance

Microdevice integrating energy storage with wireless charging could create opportunities for electronics design, such as moveable charging. Herein, we report seamlessly integrated wireless charging micro-supercapacitors by taking advantage of a designed highly consistent material system that both wireless coils and electrodes are of the graphite paper. The transferring power efficiency of the wireless charging is 52.8%. Benefitting from unique circuit structure, the intact device displays low resistance and excellent voltage tolerability with a capacitance of 454.1 mF cm⁻², superior to state-of-the-art conventional planar micro-supercapacitors. Besides, a record high energy density of 463.1 μWh cm⁻² exceeds the existing metal ion hybrid micro-supercapacitors and even commercial thin film battery (350 μWh cm⁻²). After charging for 6 min, the integrated device reaches up to a power output of 45.9 mW, which can drive an electrical toy car immediately. This work brings an insight for contactless micro-electronics and flexible micro-robotics.

Miniaturized energy storage devices integrated with wireless charging bring opportunities for next generation electronics. Here, authors report seamlessly integrated wireless charging micro-supercapacitors with high energy density capable of driving a model electrical car.