Flexible Supercapacitors Research Articles

Scalable slot-die coated flexible supercapacitors from upcycled PET face shields.

Upcycling Covid19 plastic waste into valuable carbonaceous materials for energy storage applications is a sustainable and green approach to minimize the burden of waste plastic on the environment. Herein, we developed a facile single step activation technique for producing activated carbon consisting of spherical flower like carbon nanosheets and amorphous porous flakes from used PET [poly(ethylene terephthalate)] face shields for supercapacitor applications. The as-obtained activated carbon exhibited a high specific surface area of 1571 m2 g-1 and pore volume of 1.64 cm3 g-1. The specific capacitance of these carbon nanostructure-coated stainless steel electrodes reached 228.2 F g-1 at 1 A g-1 current density with excellent charge transport features and good rate capability in 1 M Na2SO4 aqueous electrolyte. We explored the slot-die coating technique for large-area coatings of flexible high-performance activated carbon electrodes with special emphasis on optimizing binder concentration. Significant improvement in electrochemical performance was achieved for the electrodes with 15 wt% Nafion concentration. The flexible supercapacitors fabricated using these electrodes showed high energy and power density of 21.8 W h kg-1 and 20 600 W kg-1 respectively, and retained 96.2% of the initial capacitance after 10 000 cycles at 2 A g-1 current density. The present study provides a promising sustainable approach for upcycling PET plastic waste for large area printable supercapacitors.

GO Regulated Hydrogel Electrolytes with Superior Conducing and Antiswelling Ability for Flexible Supercapacitors

GO Regulated Hydrogel Electrolytes with Superior Conducing and Antiswelling Ability for Flexible Supercapacitors

Interfacial-engineered robust and high performance flexible polylactic acid/polyaniline/MXene electrodes for high-perfarmance supercapacitors

Flexible supercapacitors with high mechanical strength, excellent flexibility, and high performance are highly desired to meet the increasing demands of flexible electronics. However, the trade-off between mechanical and electrochemical properties remains challenging. In this context, an interface-engineered strategy approach was proposed to construct polylactic acid (PLA)/polyaniline (PANI)/MXene (PPM) film electrodes for flexible supercapacitor applications. In the PPM electrode, the porous PLA prepared from the nonsolvent-induced-phase-separation method served as an ideal flexible substrate, providing excellent flexibility and high mechanical strength, whereas PANI as the coupling agent, enhanced the interfacial strength between PLA and the electroactive MXene that was firmly anchored and deposited on PLA through a facile layer-by-layer dip coating method. The tensile strength at break, elongation at break, and toughness of PPM are 53.09 MPa, 11.09 %, and 4.12 MJ/m3, respectively, much higher than those of pure MXene (29.36 MPa, 4.62 %, and 0.75 MJ/m3). At an optimum mass loading density of 3 mg cm−2 for MXene, the fabricated PPM3 film electrode achieved a high specific capacitance of 290.8 F g−1 at a current density of 1 A g−1 in the three-electrode setup, approximately 1.5 times that of 190.8 F g−1 for pure MXene. Meanwhile, the symmetric all-solid-state supercapacitor based on PPM3 film electrodes delivers a high specific capacitance of 193.7 F g−1 at a current density of 0.25 A g−1, with a corresponding high energy density of 9.3 Wh kg−1 at a power density of 291.3 W kg−1. The SC retains 86 % of its original capacitance even bent at 120° and also possesses an excellent fire-retardant ability, demonstrating its great potential for flexible and safe wearable electronics.

Flexible films with three-dimensional ion transport channels: Carbon nanotubes@MnO2 as interlayer spacers in porous graphene electrodes for high-performance supercapacitors

Flexible supercapacitors have a high potential for application in wearable electronics and microdevices, but their commercial appeal is limited because of low energy density. To overcoming this challenge, this paper proposes a strategy to fabricate dense films with high specific capacitance. A composite film with rapid ion diffusion channels and a high density of 0.86 g cm–3 was synthesized by combining porous graphene nanosheets (PGNs), carbon nanotubes (CNTs), and MnO2 nanosheets. The incorporation of CNTs@MnO2 between graphene layers effectively mitigated aggregation and enhanced electrolyte ion diffusion within the dense graphene structure. PGNs and CNTs synergistically established a three-dimensional pathway for efficient ion transport while optimizing electron dynamics. In 1 mol L–1 Na2SO4 electrolyte, the material exhibited a gravimetric capacitance of up to 320 F g–1 at 1 A g–1 and a volumetric capacitance reached 275 F cm–3. Furthermore, the assembled asymmetric supercapacitors, PGNs-CNTs@MnO2//PGNs-CNTs, exhibited a gravimetric energy density of up to 26.4 Wh kg–1 and a volumetric energy density of up to 22.7 Wh L–1. These findings offer insights into advancing flexible supercapacitor technology for diverse applications.

Flexible Supercapacitor Electrodes Based on Nitrogen-Doped Carbon Derived from Polyimide/Graphene

Flexible Supercapacitor Electrodes Based on Nitrogen-Doped Carbon Derived from Polyimide/Graphene

Polyaniline nanoarrays grown on holey graphene constructed by frozen interfacial polymerization as binder−free and flexible gel electrode for high−performance supercapacitor

Compared with disordered structures, electrode materials with nanoarray structures can effectively improve the energy storage capacity of supercapacitors. Therefore, the construction of nanoarrays structures is an important research direction. Here, one kind of frozen interfacial polymerization was used to create a polyaniline (PANI) nanoarrays grown on holey graphene (HG). Long polyaniline nanoarrays were constructed with the promotion of ice crystal growth and the abundant pores of the HG. It is demonstrated that the formation of PANI array and hierarchical nanofiber structures is not only conducive to shorten charge transport, but also can effectively alleviate interfacial side reactions. Moreover, benefiting from the abundant active sites and hierarchical porous structure of the HG, highly oriented growth of PANI arrays, efficient charge diffusion and electrolyte infiltration can be achieved. As a result, specific capacitance, reversibility and cycling stability could be significantly improved. Especially, the PANI/HG−10 exhibited the maximum specific capacitance of 793.7 F g−1 at a current density of 1 A g−1. The all−solid−state flexible symmetric supercapacitor assembled by gel electrode possesses the energy density of 32.5 Wh kg–1 at a power density of 326.5 W kg–1, and maintained an excellent cycle retention approaching 90.5 % after 5000 cycles. This work expands the ideas for array structure construction and electrode fabrication.

GO based nanocomposite hydrogel enabled high performance wearable all-solid supercapacitor based on hierarchical structure electrodes derived from ZIF-67

The flexible and wearable supercapacitors have attracted wide interest because of their widespread application in smart electronic devices with rapid charging and discharging. As an important part of supercapacitor, the electrode materials with a hollow structure, especially those with hierarchical structures that provide an array of continuous hollow cages, are considered promising. Because of its porous shell which is rich in redox reaction sites for supercapacitors. In this work, we fabricated a ZIF-67 derived hollow Co3O4 growth on the surface of 1D NiCo2O4 to assemble into a beaded structure. In this case, NiCo precursor acted as a structure-directing agent to grow a ZIF-67, a promising electroactive material of electrochemical capacitors to provide capacitance after calcination. Combined with the grapheneoxide (GO) based high conductivity hydrogel as the solid electrolyte, the capacitance of the flexible supercapacitor exhibited a high specific capacitance of 90F g−1 at 0.5 A/g, and it was sturdy and durable. There was no significant loss of capacitance while suffering from bending and pressing. The outstanding electrochemical properties of the all-solid supercapacitor can be attributed to the unique nanostructure of the electrode that created more reactive active sites, increased the diffusion pathway for electrolyte ions, along with the high conductivity of the hydrogel electrolyte.

Self-healable PVA-Borax-K2SO4 hydrogel electrolyte for flexible symmetric supercapacitors

The self-healing hydrogel materials are formed from the reaction between polyvinyl alcohol (PVA) and sodium tetraborate (Borax). The O-B-C vibration peak from the FT-IR spectrum is used to confirm the formation of the self-healing hydrogel structure. With 0.5 M concentration K2SO4, the resistivity of PVA-Borax-K2SO4 material is evaluated by Bode cure and obtained at 4.13 Ω.cm. With the improvement in hybrid structure, the flexible supercapacitor (FSS) devices were fabricated from two carbon fiber fabrics as symmetric electrodes with a self-healing hydrogel material (PVA-Borax-K2SO4) as electrolyte and separator. The electrochemical performances of flexible symmetric supercapacitor (FSS) devices are measured by cyclic voltammetric, charge/discharge, and impedance tests. The specific capacitance of FSS obtained 1.725 mF/cm2 at 0.05 mA/cm2 discharge current. Moreover, the stability of the FSS device attained confirmation by the comparison of the specific capacitance at 2 and 50 cycles.

Flexible Supercapacitor with Wide Electrochemical Stable Window Based on Hydrogel Electrolyte.

Hydrogel electrolyte can endow supercapacitors with excellent flexibility, which has developed rapidly in recent years. However, the water-rich structures of hydrogel electrolyte are easy to freeze at subfreezing and dry at high temperatures, which will affect its energy storage characteristics. The low energy density of micro supercapacitors also hinders their development. Herein, a strategy is proposed to reduce the free water activity in the hydrogel to improve the operating voltage and the energy density of the device, which is achieved through the synergistic effect of the hydrogel skeleton, N, N'-dimethylformamide (DMF), NaClO4 and water. High concentrations of DMF and NaClO4 are introduced into sodium alginate/polyacrylamide (SA/PAAM) hydrogel through solvent exchange to obtain SA/PAAM/DMF/NaClO4 hydrogel electrolyte, which exhibited a high ionic conductivity of 82.1 mS cm-1, a high breaking strength of 563.2kPa, and a wide voltage stability window of 3.5V. The supercapacitor devices are assembled by the process of direct adhesion of the hydrogel electrolyte and laser induced graphene (LIG). The micro-supercapacitor exhibited an operating voltage of 2.0V, with a specific capacitance of 2.41 mF cm-2 and a high energy density of 1.34 µWh cm-2, and it also exhibit a high cycle stability, good flexibility, and integration performance.

Boron Doped Laser-Induced Graphene: A Suitable Substrate for Flexible and Wearable Sensor and Supercapacitor

Boron Doped Laser-Induced Graphene: A Suitable Substrate for Flexible and Wearable Sensor and Supercapacitor

Effect of fluoride (CoF2) based electrode material for high energy and power density asymmetric flexible supercapacitors

Herein, an asymmetric supercapacitor (ASC) device was assembled by employing the pristine CoF2 as active positive electrode material and activated carbon (AC) as negative electrode material. The CoF2 electrode exhibited an outstanding electrochemical behavior with enhanced specific capacitance (Cs) of 872 F/g at 1 A/g current density in three electrode configurations. The reversible Faradaic redox reactions in CoF2 instigate the formation of cobalt-oxyfluorides and generating the mixed valence state of Co (Co2+ and Co3+) which improves its electrical conductivity and electrochemical behaviors. Furthermore, the room temperature paramagnetic nature of CoF2 increases the gradient force of ions which could possibly increase the redox reactions at the electrolyte/electrode interface. The constructed asymmetric device structure of CoF2//AC revealed a quasi-rectangular shaped cyclic voltametric curve and symmetrical semi-triangular shaped galvanostatic charge-discharge profiles, respectively, which affirms the combined electric double layer capacitance and pseudocapacitive nature by its hybrid assembly. Hence, the constructed CoF2//AC ASC demonstrated a remarkable specific capacitance of 141 F/g, energy density of 44.06 Wh.Kg−1, and power density of 422.97 W.Kg−1 at 1 A/g with the high cell voltage of 1.5 V. The CoF2//AC ASC device retained c.a. 92 % of its initial capacitance and attained over 96 % of Coulombic efficiency after 2000 cycles of charge-discharge profiles at 1 A/g, which suggests the high electrochemical stability. This admirable electrochemical performance and the origin towards the magneto-capacitance of CoF2 could pave a new way to explore next generation high-performance supercapacitors.

3D printing of hydrogels for flexible micro‐supercapacitors

AbstractAdvances in hydrogel technology have paved the way for novel and valuable capabilities that are being applied to a diverse spectrum of energy storage applications. Hydrogels, originally renowned for their biomedical applications, are now finding translation into the energy storage domain. These versatile materials exhibit promising potential for various energy‐related applications, including but not limited to acting as highly flexible electrolytes, facilitating the development of flexible supercapacitors, and contributing to advancements in energy conversion devices. The tunable properties of hydrogels, their high ion accessibility, and desirable mechanical characteristics position them as promising candidates for enhancing the performance and efficiency of energy storage systems. In this review, we emphasize the integration of hydrogels into flexible micro‐supercapacitors through 3D printing technology, unraveling the charge transport mechanisms inherent in hydrogels. We discuss methods for developing hydrogels with enhanced physicochemical properties, such as improved mechanical strength, flexibility, and charge transport, offering new prospects for next‐generation energy storage devices. With a deeper understanding of gelation chemistry, we showcase significant progress in fabricating stimuli‐responsive, self‐healing, and highly stretchable hydrogels. Furthermore, we present compelling examples highlighting the versatility of hydrogels, including tailorable architectures, conductive nanostructures, 3D frameworks, and multifunctionalities. The application of innovative 3D printing techniques in hydrogel design is poised to yield materials with immense potential in the realm of energy storage.

Preparation and electrochemical performances of core-shell microtubular PPy/CNT/MOF ternary composites with spherical Co-MOF as sacrificial template

Here we developed PPy/CNT/MOF ternary composites with microtubular structure, which was triggered by both the disassembly of Co-MOF and the reassembly of phosphomolybdate acid (PMA) and the released ligand. As a result, the CNTs and polypyrroles (PPys) are intertwined and deposited on the surface of the composites, forming a core-shell structure. Among the ternary composites, the PM/CNT/MOF-2 electrode (PMA concertation of 5 mM) provides a specific capacitance of 650 F g−1 at 1 A g−1. The assembled flexible supercapacitor device delivered a high energy density of 68.9 μWh cm−2 (45.9 Wh kg−1) at power density of 800 μW cm−2 (800 W kg−1), a good long-term cyclic stability, and superior mechanical flexibility.

Scalable one-step synthesis of reduced graphene oxide: Towards flexible transparent conductive films and active supercapacitor electrodes

The reduced graphene oxide (rGO) thin films have attracted much attention in flexible electronic devices and supercapacitors (SCs). However, the chemical reduction mechanism of GO needs to be clarified, and the one-step process at low temperatures for preparing high-quality rGO thin films from GO dispersions is still blank in the research field. Here, we propose a one-step operation to spray GO dispersions onto substrate or current collector under a hydroiodic acid (HI) atmosphere while simultaneously achieving the preparation of rGO thin films. This pioneering metal-free, transfer-free, fast, low-temperature, environmentally friendly, and scalable spraying technology enables large-scale production of high-quality rGO. This method realizes the preparation of highly conductive and high transmittance rGO thin films on flexible polyimide and polyethylene terephthalate substrates, as well as the preparation of rGO thin films on current collectors as SCs electrodes. Density functional theory calculations show that oxygen-containing functional groups on the surface of GO exhibit a stronger adsorption energy for HI, and have a low energy barrier during reduction by HI. Ab initio molecular dynamics simulated the possible reduction reaction path between GO and HI at 90 °C, demonstrating that HI molecules can effectively reduce GO. Furthermore, the sheet resistance of the transparent conductive film created using the method developed in this study reaches approximately 1000 Ω/sq (80 % transparency), and the specific capacitance of the SCs electrode film created in this method is 433.2 F/g (5 mV/s, 1 M H2SO4). Our study not only validates the efficacy of the one-step synthesis method for rGO thin films but also provides theoretical insights into the underlying reaction mechanism. This work holds significant promise for advancing applications in various electronics by facilitating large-scale production of high-quality rGO thin films.

Tunable durian seed gum-derived eutectogel as a novel coating material: Rheological, thermal, textural and barrier properties for enhanced food preservation

As a promising green and sustainable coating material, gum was extracted from durian seed to produce eutectogel, which the properties were tunable using natural deep eutectic solvent (NADES). Ten different eutectogels were successfully synthesized using durian seed gum (DSG) and xanthan gum (XG) gelators at different composition (5, 10, 15 %) to gel choline chloride-glucose (1:1), choline chloride-fructose (1:2) and betaine-glucose-water (1:1:1) NADESs. Results revealed that eutectogel was non-Newtonian and weak gel material with excellent thermostability up to 200 °C. When the gum content increased, the resulted eutectogel showed higher viscosity, yield stress, hardness, gumminess, adhesiveness, and weight holding capacity. In overall, choline chloride-fructose (1:2) NADES and 10 % of DSG formed an excellent eutectogel which remained stable and compatible upon 12 weeks of storage. It displayed superior viscoelastic, texture, gases and moisture barrier properties which were beneficial for food coating application. This eutectogel was able to extend the shelf life of fresh-cut apples during storage with lower weight loss and higher total phenolic content (TPC). The potential future of this well-characterized tunable DSG-derived eutectogel includes, but not limited to, food and pharmaceutical industries, smart sensing, flexible wearable electronics, water purification, supercapacitors and batteries.

Recent Advances in Biopolymer-Based Hydrogel Electrolytes for Flexible Supercapacitors.

Growing concern regarding the impact of fossil fuels has led to demands for the development of green and renewable materials for advanced electrochemical energy storage devices. Biopolymers with unique hierarchical structures and physicochemical properties, serving as an appealing platform for the advancement of sustainable energy, have found widespread application in the gel electrolytes of supercapacitors. In this Review, we outline the structure and characteristics of various biopolymers, discuss the proposed mechanisms and assess the evaluation metrics of gel electrolytes in supercapacitor devices, and further analyze the roles of biopolymer materials in this context. The state-of-the-art electrochemical performance of biopolymer-based hydrogel electrolytes for supercapacitors and their multiple functionalities are summarized, while underscoring the current technical challenges and potential solutions. This Review is intended to offer a thorough overview of recent developments in biopolymer-based hydrogel electrolytes, highlighting research concerning green and sustainable energy storage devices and potential avenues for further development.

Flexible supercapacitors based on carbon fiber cloth coated copper hexacyanoferrate nanoparticles as positive electrode material

Herein, we report fabrication of a new electrode material based on copper(II) hexacyanoferrate(II) nanoparticles coated on flexible and light weight carbon fiber cloth (CuHCF-NPs@CC) for supercapacitors application. Uniform spherical CuHCF-NPs are successfully synthesized through a simple chemical co-precipitation technique at ambient temperature. The CuHCF-NPs were physically examined by different characterizations, for example, FT-IR, UV–Visible, Raman, XRD, XPS, FE-SEM, EDAX and TEM. The CuHCF-NPs@CC is an excellent electrode material that has an open framework structure that can accommodate a wide variety of ions. The electrochemical characteristics of pseudocapacitive behavior of the material were characterized by cyclic voltammogram (CV), galvanostatic charge-discharge (GCD) and electrochemical impedance spectroscopy (EIS) on two different electrolytes such as K2SO4 and Na2SO4. The CuHCF-NPs@CC exhibits a good reversible cycle in the range of 0 to 0.9 V and excellent charge-discharge performance with a specific capacity of 42.96C g−1 and 24.2C g−1 at 0.2 A g−1 of current density in K2SO4 and Na2SO4 electrolyte, respectively. The low cost, simple preparation methodology, and an outstanding electrochemical behavior of CuHCF-NPs@CC considering a viable candidate for the future energy storage system.

Low-salt organohydrogel electrolytes for wide-potential-window flexible all-solid-state supercapacitors

Flexible supercapacitors have received increasing attention due to their high power density, long cycle life and excellent safety, however, their limited energy density restrains their practical applications. Here, a designed organohydrogel electrolyte strategy boosted the electrochemical potential window (ESW) for flexible all-solid supercapacitor was demonstrated, by which a record-high ESW of 5 V is achieved, accompanied by improved cyclic stability and wider temperature adaptability. Hydrogen-bond of water to DMSO was found to be competitive with cationic hydration, and a wide ESW was achieved at lower salt and DMSO concentrations. DMSO-H2O/alginate/PAAm hydrogel electrolytes were prepared by simple solvent exchange, and it was found that the synergistic interactions between DMSO, water and hydrogel significantly reduced water activity in the hydrogel and realized the high ESW. Moreover, Dimethyl sulfoxide forms abundant hydrogen bonds with water and the hydrogel skeleton, which significantly improves the mechanical properties, freezing resistance, and temperature adaptability of the hydrogel electrolyte. The flexible all-solid-state supercapacitor assembled based on DMSO-H2O/alginate/PAAm hydrogel electrolyte and interdigital electrodes exhibits 2.4 V ESW, stability under different folding angles, adaptability to different temperatures ranging from −20 to 70 °C, and integration performance. The device demonstrates excellent cycling stability and retains 98.66% of capacitance after 10,000 cycles, suggesting that it has the potential to meet the requirements of flexible electronics.

Enhancing Electron/Ion Transport in SnO2 Quantum Dots Decorated Polyaniline/Graphene Hybrid Fibers for Wearable Supercapacitors with High Energy Density.

Fiber-based supercapacitors are the potential power sources in the field of wearable electronics and energy storage textiles due to their unique advantages of electrochemical properties and mechanical flexibility, but achieving high energy density and practical energy supply still presents some challenges. In this study, we reported an approach of microfluidic assisted wet-spinning to fabricate SnO2 quantum dots encapsulated polyaniline/graphene hybrid fibers (SnO2 QDs@PGF) by incorporating uniformly polyaniline into graphene fibers and covalently bridging SnO2 quantum dots. The assembled SnO2 QDs@PGF fiber-typed flexible supercapacitors exhibit an ultralarge specific areal capacitance of 925 mF cm-2 in PVA/H2SO4, superior rate capabilities, and capacitance retention of 88% after 8000 cycles, indicating that the SnO2 QDs@PGF possess near-ideal capacitance properties, efficient ion transfer rate, and good cycling stability. In the EMITFSI/PVDF-HFP electrolyte system, SnO2 QDs@PGF realize a wide operating potential window of 2.5 V, a specific areal capacitance of 678.4 mF cm-2, and an energy density of 147.2 μWh cm-2 at 500 μW cm-2, which can be utilized to power an alarm clock, an electronic timer, and a desk lamp with a requirement of a 3 V battery. The exceptional performance of the SnO2 QDs@PGF can be attributed to the molecular-level homogeneous composite of granular polyaniline and graphene nanosheets and the interfacial C-O-Sn covalent coupling strategy employed between SnO2 QDs and PGF. These avenues not only effectively prevent the undesirable restacking of graphene nanosheets but also increase the interlayer electroactive sites, ordered ion diffusion channels, and strong interfacial charge transfer.

Binder-free laser induced graphene-MnO2 composite electrodes for high areal energy density flexible supercapacitors

The synthesis of Laser-Induced Graphene (LIG) through the laser ablation process of carbon-containing materials is a rapid and scalable process which enables the production of graphene in a cost-effective manner. In recent years, metal oxide – graphene composite electrodes have gained a lot of importance due to their use in various Energy Storage Devices (ESDs). In our investigation, we manufacture composite electrodes of manganese dioxide (MnO2) and LIG through a hydrothermal process and use it as electrodes in Flexible Supercapacitors. This method deviates from traditional procedures as it eliminates the requirement for binders in creating composite electrodes, given that MnO2 can be directly deposited onto the LIG electrodes. The assembled all-Flexible Supercapacitor (FSC), featuring unique LIG-MnO2 composite electrodes, showcased a remarkable areal capacitance of 66.5 mF cm−2 at 5 mV s−1 scan rate. The device also exhibited a very high areal energy density (2.3 mWh cm−2) and power density (19.7 mW cm−2) at 0.2 mA cm−2 current density. Also, 82 % capacitance retention was observed at the end of 2000 cycles and the device also exhibited a good flexibility during bending tests, as evidenced by an 80 % capacitance retention after 100 bending cycles.