Flexible Micro-supercapacitors Research Articles

Printed flexible solid-state microsupercapacitor with highly-stable aqueous cobalt-based inks

Cobalt-based nanomaterials are among the most noticed candidates for manufacturing supercapacitive electrodes. Inkjet-printing is an emerging technique for fabricating miniaturized devices. In this work, highly flexible microsupercapacitors (MSCs) are manufactured, using a pseudocapacitive (C = 900 F‌ g−1 at 1 A g−1) Co-oxide-hydroxide water-based and ultra-stable (up to 12 months) ink on paper. The synthesized capacitive active material consists of cobalt-oxide nanocubes and cobalt-hydroxide hexagonal nanoflakes. Conductive (Rs = 13 Ω/□) silver nanowire networks serve as current collectors, and the morphology of cobalt oxide-hydroxide structures and the developed ink features, allow for printing well-detailed and homogeneous patterns. The inkjet-printed symmetric and asymmetric devices show notable areal specific capacitances of 35.68 mF cm−2 and 23.60 mF cm−2 at a current density of 0.1 mA cm−2, respectively. The asymmetric devices deliver impressive energy and power densities of 2.76 μW h cm−2 (4.10 W h kg−1) and 646 μW cm−2 (959 W kg−1), respectively. A thorough study on the cyclic and mechanical stability of the flexible devices resulted in perfect capacitance maintenance of 94.3 % after 10,000 charge and discharge cycles and retention of over 80 % even after 1000 cycles of successive bending and folding. The extensive study of capacitance retention following folding under various obtuse and reflex angles, which can be regarded as an important step toward characterizing flexible devices suitable for being utilized in wearable electronics, is carried out for the first time to the best of our knowledge. The findings of this study clearly illustrate the prospects of using the inkjet-printing technique to fabricate high-performance MSC devices appropriate for integration with flexible and wearable electronics.

Manufacturing Shape-Controllable Flexible PEDOT/rGO Composite Electrodes for Planar Micro-Supercapacitors.

Flexible electronic products, with their characteristics of flexibility and wearability, have attracted significant attention and have become an important direction in the research and development of the electronics industry. Planar micro-supercapacitors (MSCs) with flexible composite electrodes can provide reliable energy support for these products, propelling their further development. The research employed a quick, effective, and environmentally friendly method of laser scribing to create shape-controllable flexible composite electrodes on composite films of Poly(3,4-ethylenedioxythiophene) and graphene oxide (PEDOT/GO), which were subsequently assembled into MSCs. An analysis of the composite electrode morphology, structure, and elemental distribution was conducted through the utilization of SEM, TEM, and XPS techniques. Following this, a comprehensive evaluation of the electrochemical performance of the flexible MSCs was carried out, which included cyclic voltammetry (CV), galvanostatic charge/discharge (GCD), and assessment of cyclic stability. The analysis of the CV results indicated that the MSCs achieved the areal capacitance of 5.78 mF/cm2 at 5 mV/s. After 5000 cycles at a current density of 0.05 mA/cm2, the capacitance retention rate was 85.4%. The high areal capacitance and strong cycle stability of MSCs highlight the potential of PEDOT/reduced graphene oxide (PEDOT/rGO) electrodes in electrode applications.

Laser-induced fabrication of porous graphene for flexible planar microsupercapacitors with wide voltage window

Herein, laser-induced graphene (LIG) derived from polyimide (PI) is demonstrated to construct a flexible planar interdigital microsupercapacitors (MSCs) device with wide voltage window through simple laser-direct-writing method. The mechanism study of LIG derived from PI show that the photon energy of the laser is absorbed by the electrons and converted into heat energy, and the rapid energy accumulation produces extremely high temperatures leading to the graphitization of PI film. At the same time, the internal expansion and gas escape from the interior, the graphitized carbon material grows upward, resulting in the formation of porous graphene. As a demonstration of the supercapacitor application, the as-prepared LIG MSCs device show excellent supercapacitance performance, wide voltage window (0–1.8 V) and good mechanical flexibility. When the laser power is 2.75 W, that is, 50 % of the maximum power, the resulting LIG MSCs device has a high specific capacitance of 20.85 mF cm−2, a maximum energy density of 9.38 μWh cm−2, and good cycle stability with a capacitance retention rate of 101.09 % after 15,000 cycles. This work provides a simple method to prepare graphene-based MSCs and demonstrates great potential of the LIG MSCs in flexible wearable electronic devices.

Flexible zinc-ion hybrid micro-supercapacitors with polymeric current collector for integrated energy storage in wearable devices

The ubiquity of conventional micro-fabrication techniques has encountered impediments in constructing cost-effective micro-devices, thereby constraining their broad deployment. Concurrently, the suboptimal energy density inherent to supercapacitors exacerbates this challenge. This study presents a straightforward assembly methodology for the fabrication of a mechano-electrochemically-efficient micro-zinc ion hybrid supercapacitor (M−ZSC), alongside the introduction of an innovative polymeric current collector. The M−ZSC is fabricated through a process involving masked spray deposition of a novel adhesive current collector and the electrode materials, and electroplating of zinc nanosheets onto the anode finger, creating an electrochemically performant and mechanically robust device. The resulting M−ZSC exhibits a notable areal capacitance of 52.2 mF/cm2 and an energy density of 18.5 µWh/cm2 for the normal mass-loading of 3.6 mg/cm2, which is amongst the highest reported values for energy storage. The masked spray deposition/hot pressing technique enabled us to fabricate free-standing thick electrodes with a loading density of up to 56.1 mg/cm2, facilitating the achievement of an ultrahigh areal capacitance of 227 mF/cm2 and an energy density of 80.5 µWh/cm2. Furthermore, the M−ZSC exhibits a robust retention of 95 % capacitance at 1 mA/cm2. Critical to its flexibility, the device is constructed using purely additive deposition methods on flexible substrates and is therefore well-tailored for deployment in flexible electronics and on-chip applications. These micro-devices are well-poised for seamless integration within a singular electronics package or chip architecture.

Research and development of double layer P-doped laser induced graphene thin film electrode for flexible micro-supercapacitor applications

Laser-induced graphene (LIG) has garnered significant attention for its cost-effectiveness and high efficiency in fabricating flexible micro-energy storage devices. In this study, we devised a simple method to fabricate double layer P-doped LIG electrodes through repetitive laser induction technology for high-performance flexible energy storage applications. Instead of utilizing commercial polyimide (PI) thin film, we optimized the formation process of P-doped PI thin film and achieved a highly flexible double layer P-doped LIG thin film electrode with a uniformly porous structure and the high porosity through repeated laser induction processes. Experimental results demonstrated that the developed double layer P-doped LIG thin film electrode exhibits high porosity, high specific areal capacitance of 180 mF cm-2, and high energy density of 0.025 mWh cm-2. Furthermore, an all-solid-state micro-supercapacitor utilizing hydrogel electrolyte was assembled, demonstrating a high areal capacitance of 62 mF cm-2 and excellent cycling stability with 95% capacitance retention after 6000 charging/discharging cycles. Moreover, the developed all-solid-state micro-supercapacitor successfully powered a light-emitting diode, showcasing its significant potential for practical energy storage applications.

Laser-assisted synthesis of MnOx and 3D graphene composites for wide-voltage flexible planar microcapacitors

Herein, we propose a simple and eco-friendly strategy based on laser direct writing technology to regulate the valence state of Mn-based oxides nanoparticles anchored on three-dimensional(3D) framework of laser-induced graphene (LIG) for the application of high-performance flexible planar interdigital microsupercapacitors (MSCs). Under the laser radiation, a polyimide (PI) and MnO2 composite film was directly converted into 3D graphene and MnOx (MnO, MnO2 and Mn3O4 mixture). Furthermore, the results reveal that LIG/MnOx MSCs device exhibits a high specific capacitance of 23.3 mF cm−2, which is about 29 times higher than that of LIG MSCs (0.8 mF cm−2). Moreover, LIG/MnOx MSCs possess a high energy density of 7.28 μWh cm−2, outstanding cycle stability with the capacitance retention rate of 97.4 % after 10,000 cycles, and excellent mechanical flexibility. Therefore, this preparation strategy of LIG/MnOx provides a reference for the performance regulation of Mn-based oxides and the low-cost construction of MSCs devices with high energy density, which carries significant research implications for diverse flexible wearable electronic applications in the forthcoming days.

Self-charging V2CTx/CNT-based zinc ion micro-supercapacitor for wearable electronics

The flexible self-charging zinc ion micro-supercapacitors (ZIMSC) that can be effectively charged by harvesting ubiquitous energy from the air, not only achieve power supply anytime and anywhere but also improve the integrated degree without external charging plug or cable, enabling it a promising candidate for the wearable electronic device in various environmental scenarios. Herein, we reported a chemically self-charging ZIMSC based on a free-standing V2CTx/CNT electrode. Introducing 1D CNT into 2D V2CTx fundamentally overcomes the self-stacking problem of the nanosheets while providing additional ion transport paths and improving the conductivity of active electrodes. The area-specific capacity of V2CTx/CNT-based ZIMSC achieves 117.2 mF cm−2 after 8.0 h self-charging. The excellent self-charging performance is attributed to the oxidation of vanadium in the V2CTx-based cathode stimulated by ambient oxygen, accompanied by the Zn2+ deintercalation process. The flexible ZIMSC exhibited an optimal area capacitance of 246.88 mF cm−2 at a current density of 0.5 mA cm−2. Additionally, the self-charging ZIMSC is integrated with the V2CTx-based pressure sensors for a self-powering wearable system that exhibits excellent stability over 50,000 loading/unloading cycles. This work provides a rational design for constructing highly efficient self-charging energy storage devices and broadens the horizons of flexible wearable devices.

Emerging Vanadium-Doped Cobalt Chloride Carbonate Hydroxide for Flexible Electrochromic Micro-Supercapacitor: Charged-State Prediction from RGB Input by ANN Model.

Multifunctional devices integrated with electrochromic and supercapacitance properties are fascinating because of their extensive usage in modern electronic applications. In this work, vanadium-doped cobalt chloride carbonate hydroxide hydrate nanostructures (V-C3H NSs) are successfully synthesized and show unique electrochromic and supercapacitor properties. The V-C3H NSs material exhibits a high specific capacitance of 1219.9Fg-1 at 1mVs-1 with a capacitance retention of 100% over 30000 CV cycles. The electrochromic performance of the V-C3H NSs material is confirmed through in situ spectroelectrochemical measurements, where the switching time, coloration efficiency (CE), and optical modulation (∆T) are found to be 15.7 and 18.8s, 65.85cm2C-1 and 69%, respectively. A coupled multilayer artificial neural network (ANN) model is framed to predict potential and current from red (R), green (G), and blue (B) color values. The optimized V-C3H NSs are used as the active materials in the fabrication of flexible/wearable electrochromic micro-supercapacitor devices (FEMSDs) through a cost-effective mask-assisted vacuum filtration method. The fabricated FEMSD exhibits an areal capacitance of 47.15mFcm-2 at 1mVs-1 and offers a maximum areal energy and power density of 104.78Whcm-2 and 0.04mWcm-2, respectively. This material's interesting energy storage and electrochromic properties are promising in multifunctional electrochromic energy storage applications.

Fabrication of flexible nitrogen-doped graphene micro-supercapacitors by laser-induced self-made precursors

Fabrication of flexible nitrogen-doped graphene micro-supercapacitors by laser-induced self-made precursors

One-step sustainable preparation of laser induced S-doped graphene for assembly of high-performance supercapacitors

Lignin, an industrial by-product that is abundant, renewable and has aromatic ring characteristics, is regarded as an ideal raw material for the synthesis of two-dimensional graphene materials. However, the sustainable development of graphene produced from lignin faces thorny challenges such as environmental pollution, low yield, cumbersome steps and harsh conditions. In this study, low-energy, green, large-scale one-step preparation of sulfur-doped graphene was achieved by co-blending lignin and sodium alginate into a fully biomass-based film, followed by easy-to-operate laser etching. Among them, alkaline lignin not only served as a carbon source but also acted as a sulfur doping source, avoiding the use of additional sulfur doping reagents. The results showed that the sheet resistance of graphene gradually decreased with the increase of laser power. The sheet resistance of graphene prepared when the laser power was 90% was as low as 8 Ω sq−1, which provided an inherent advantage for the subsequent assembly of flexible micro-supercapacitors. The specific capacitance and high energy density of the resulting supercapacitor were as high as 88.29 mF cm−2 and 12.26 μW h cm−2, respectively. This method successfully developed a sustainable and low-energy graphene preparation method, paving the way for the sustainable development of flexible energy storage devices.

Rationally engineered interdigitated electrodes with heteroatom doped porous graphene and improved surface wettability for flexible micro-supercapacitors

Micro-supercapacitors (mSCs) are crucial components for the miniaturization of electronic devices and the growing demand for portable, wearable, and Internet-of-things (IoT) technology. Among these, electric double-layer mSCs (EDL mSCs) stand out with their rapid charge/discharge capability and extended lifespan. Porous graphene structure has been utilized to EDL-mSCs due to their compatibility with various substrates and ease of integration. However, methods to increase the performance of the EDL-mSCs based on the porous graphene electrode needs to be considered to achieve high performance flexible mSCs. In this study, we introduce rationally designed, heteroatom doped porous graphene electrodes, incorporating highly electrochemical active nitrogen sites (such as pyrrolic-, pyridinic-, and graphitic-N sites), that greatly enhances the performance of the flexible mSCs. The method involves directly laser scribing polyimide film coated with a phthalocyanine-based dopant, resulting in a remarkable 254 % increase in capacitance and an impressive volumetric energy density of 2.5 mWh cm−3 compared pristine EDL-mSC. This heteroatom-doping strategy improves conductivity and surface wettability and creates more active sites for specific capacitance. Additionally, the heteroatom-doped mSCs exhibit excellent capacitance retention under strain and bending tests, demonstrating their suitability for practical circuit applications. This work offers a simple and effective approach to design flexible and high-performance mSCs, meeting the energy-storage demands of modern electronics and IoT devices.

High-performance micro supercapacitor assembled by laser-induced graphene electrode and hydrogel electrolyte with excellent interfacial wettability for high capacitance

In this work, we demonstrate a facile, rational and novel strategy to assemble micro-supercapacitors (MSCs) via employing laser-induced graphene (LIG) microelectrodes and sodium alginate/polyacrylamide hydrogel electrolytes soaked in sulfuric acid solution (SA/PAAM-H2SO4). The microelectrodes are conductive graphene materials with porous structure that use laser direct writing technology to carbonize insulating polyimide (PI) sheets. The importance of good wetting of the electrode material by the electrolyte on the performance of the device is explained. There is good compatibility and interfacial contact between electrode and electrolyte. Impressively, the SA/PAAM-H2SO4 hydrogel electrolyte with high ionic conductivity (574.7 mS cm−1) also exhibit good water retention capability and performs normally even after 60 h of exposure to air. The capacitance of LIG-MSCs based on SA/PAAM-H2SO4 hydrogel is comparable to that of PVA/H2SO4 hydrogel. The LIG-MSCs exhibit high areal capacitance of 7.12 mF cm−2 and outstanding cycling stability. Moreover, our LIG-MSCs displays excellent mechanical flexibility and stable performance, the capacitance is almost unaffected even in highly bent states and during continuously hammering. Furthermore, the LIG-MSCs can be arbitrarily connected in series and in parallel without the requirement of metal-based interconnects for high-voltage and high-capacitance output. Our design strategy aims to provide new insights for the development of flexible MSCs.

Low-Temperature, Universal Synthetic Route for Mesoporous Metal Oxides by Exploiting Synergistic Effect of Thermal Activation and Plasma.

Mesoporous metal oxides exhibit excellent physicochemical properties and are widely used in various fields, including energy storage/conversion, catalysis, and sensors. Although several soft-template approaches are reported, high-temperature calcination for both metal oxide formation and template removal is necessary, which limits direct synthesis on a plastic substrate for flexible devices. Here, a universal synthetic approach that combines thermal activation and oxygen plasma to synthesize diverse mesoporous metal oxides (V2O5, V6O13, TiO2, Nb2O5, WO3, and MoO3) at low temperatures (150-200°C), which can be applicable to a flexible polymeric substrate is introduced. As a demonstration, a flexible micro-supercapacitor is fabricated by directly synthesizing mesoporous V2O5 on an indium-tin oxide-coated colorless polyimide film. The energy storage performance is well maintained under severe bending conditions.

Hierarchically Structured Nb2O5 Microflowers with Enhanced Capacity and Fast-Charging Capability for Flexible Planar Sodium Ion Micro-Supercapacitors

HighlightsHierarchically structured Nb2O5 microflowers consiste of porous and ultrathin nanosheets.Nb2O5 microflowers exhibit enhanced capacity and rate performance boosting Na ion storage.Planar NIMSCs with charge and kinetics matching show superior areal capacitance and lifespan.Planar Na ion micro-supercapacitors (NIMSCs) that offer both high energy density and power density are deemed to a promising class of miniaturized power sources for wearable and portable microelectronics. Nevertheless, the development of NIMSCs are hugely impeded by the low capacity and sluggish Na ion kinetics in the negative electrode. Herein, we demonstrate a novel carbon-coated Nb2O5 microflower with a hierarchical structure composed of vertically intercrossed and porous nanosheets, boosting Na ion storage performance. The unique structural merits, including uniform carbon coating, ultrathin nanosheets and abundant pores, endow the Nb2O5 microflower with highly reversible Na ion storage capacity of 245 mAh g−1 at 0.25 C and excellent rate capability. Benefiting from high capacity and fast charging of Nb2O5 microflower, the planar NIMSCs consisted of Nb2O5 negative electrode and activated carbon positive electrode deliver high areal energy density of 60.7 μWh cm−2, considerable voltage window of 3.5 V and extraordinary cyclability. Therefore, this work exploits a structural design strategy towards electrode materials for application in NIMSCs, holding great promise for flexible microelectronics.

Highly stable aqueous carbon-based conductive ink for screen-printed planar flexible micro-supercapacitor

In this study, we have successfully developed a series of low-cost, environmentally friendly, and high-performance carbon-based conductive inks with a three-dimensional micro-nano structure through a simple dispersion and ball-milling process, offering an array of desirable characteristics. Significantly, the carbon-based conductive inks remained stable even after a 30-day settling period. Furthermore, the conductive film, produced using screen printing techniques, demonstrated an impressive conductivity of 1.99 × 103 S/m. This remarkable conductivity highlights the ability of the films to consistently maintain a robust conductivity network, even when subjected to 5000 mechanical bending/releasing tests. Expanding on the success of our carbon-based conductive inks, we harnessed their potential in the production of all-solid-state flexible Micro-supercapacitors (MSCs) with an interdigital structure, utilizing screen-printing technology. The resulting MSCs exhibited outstanding performance metrics, including a notable areal energy density of 1.47 µWh cm-2 and an area power density of 0.2 mW cm-2. Moreover, these MSCs demonstrated remarkable cycle stability, retaining 96.3% of their capacitance after 20,000 cycles. Additionally, their excellent mechanical flexibility was evident as they experienced only a minor 2.98% capacitance degradation after undergoing 5000 bending/releasing cycles. These findings highlight the enormous potential of our work in facilitating the scalable production of wearable and portable electronic products.

A high performance selectively grown nano-octahedral Mn3O4 on lignin derived laser scribed graphene for microsupercapacitor applications

Porous graphene infused with mixed valency metal oxide as a supercapacitor material has received much attention. However, the existing approach to directly infusing mixed valency metal oxide such as Mn3O4 on graphene electrodes results in poor electrochemical performance. We report the facile fabrication of oil palm lignin derived laser scribed graphene with sol-gel hydrothermal grown nano-octahedral shaped Mn3O4 nanoparticles to boost the electrochemical performance of the flexible hybrid microsupercapacitor. The newly formed Mn3O4 nanoparticles (Mn3O4 NPs) were octahedral shaped and 15 to 30 nm in size, without any agglomeration and detrimental effect on the porosity of the laser scribed lignin-graphene. Further, the addition of Mn3O4 NPs grown for 3 h increased the specific surface area of the lignin-graphene by 66 %, which improved the microsupercapacitor's areal capacitance by five times to 136.19 mFcm−2 at 0.08 mAcm−2 measured in PAAS/K2SO4 gel electrolyte. The resulting highly stable and pliable microsupercapacitor retained 93.4 of its initial capacitances over 5000 charge-discharge cycles at 0.5 mAcm−2 and 97 % over 400 bending cycles at 50 mVs−1, respectively. The direct synthesis of Mn3O4 on IDE-patterned lignin-derived LSG electrodes presents new possibilities in energy storage applications.

Flexible micro-supercapacitors with organic gel electrolytes based on screen-printable CuO-ink

In recent years, due to the increase in the demand for miniaturized devices, there has been a massive increase in research to develop flexible, thin and scalable rechargeable energy storage micro-devices. Micro-supercapacitors (MSCs) with high charge-discharge rates and power density are excellent options for small, lightweight, easy-to-incorporate, flexible energy storage devices. However, the main problem with modern MSCs is their low energy density and money-intensive, time taking, sophisticated construction methods. Screen-printing is a simple, cost-effective and scalable method for fabricating MSCs. Using silver as the current collector, copper oxide as the active material, and gel electrolyte, we present a screen-printable method for constructing flexible MSCs on a PET substrate. The printed MSC was found to give 10.13 mA h cm−3 of volumetric specific capacity and energy density of 10.1 mW h cm−3 with an excellent stability of 99.5% over 3000 cycles and very small capacity degradation even with 120° bending deformation, suggesting outstanding mechanical flexibility and operation stability. Additionally, by connecting numerous MSC devices in series and parallel, the output voltage and current are intelligently adjusted to meet the requirements of varied applications. This study offers an efficient and economical approach to generate MSCs characterized by a substantial energy density. This breakthrough opens avenues for incorporating these MSCs into upcoming wearable technologies.

Controlling surface oxygen vacancies in 3D networked MnO2 based nanocomposites for high performance flexible in-plane micro-supercapacitors

The rising demand for portable, flexible, and eco-friendly electronic devices has spurred the development of micro-supercapacitors (mSCs) as compact and versatile energy storage components. Electric double-layer (EDL)-mSCs incorporating graphene electrodes offer swift and reversible charge/discharge processes, making them suitable for sustainable device systems. To greatly enhance the electrochemical performance of mSCs, we present a direct synthesis and fabrication of surface oxygen vacancy-controlled MnO2 with a Faradaic capacitive behavior on a porous graphene electrode with 3D networked framework. Surface oxygen vacancies in MnO2 were created through hydrogen peroxide (H2O2) treatment, which led to an increase in the electrode's conductivity and facilitating electrochemical reactions due to creation of the local electric field at the vacancy sites. We achieved 251 % and 163 % increase in capacitance of surface oxygen vacancy controlled MnO2/graphene nanocomposite electrode compared to the porous graphene electrode and pristine MnO2/graphene electrode, respectively, and exhibited a volumetric energy density of 3.61 Wh/L. Furthermore, the mSCs demonstrated excellent cyclic stability and mechanical flexibility under various strain conditions. This surface oxygen vacancy-controlled MnO2/graphene nanocomposite electrode represents a simple and efficient strategy for high-performance and versatile energy storage components, with potential applications in electronic devices and sustainable energy systems.

Analysis of the potential of nickel selenide micro-supercapacitors as energy storage device

Microsupercapacitors (MSCs) are emerging as compelling electrochemical energy storage solutions, particularly for miniaturized portable electronics. Their appeal lies in their high-power density and exceptional cycling stability, making them promising alternatives to traditional batteries. However, current microfabrication techniques often involve costly steps that result in materials with structural defects, ultimately limiting their energy density. This research introduces an innovative approach by harnessing screen-printing technology, which offers an additive and cost-effective production process while reducing waste generation. The study centers on the assessment of three distinct electrode materials—NiSe2, Ni3Se4, and NiSe—synthesized via a hydrothermal process for their suitability in supercapacitor applications. Among these materials, NiSe emerges as a standout candidate, showcasing remarkable energy storage capabilities. It achieves an impressive specific capacity of 93.3 mAh g−1 at a current density of 12 A g−1 in three-electrode measurements and demonstrates outstanding cycling stability, retaining 98 % of its capacity over an impressive 30,000 charge-discharge cycles. The resulting flexible symmetric micro-supercapacitor (NiSe-MSC) exhibits a remarkable volumetric capacitance of 81.44 F cm−3 at a current density of 6 A g−1, accompanied by impressive power density (822.86 W cm−3) and energy density (5.28 mWh cm−3).

Deposition of MnO2 on KOH-activated laser-produced graphene for a flexible planar micro-supercapacitor

Deposition of MnO2 on KOH-activated laser-produced graphene for a flexible planar micro-supercapacitor