High Volumetric Capacitance Research Articles

Air-Stable Conductive Polymer Ink for Printed Wearable Micro-Supercapacitors.

Printed electronics are expected to facilitate the widespread distributed wearable electronics in the era of the Internet of things. However, developing cheap and stable electrode inks remains a significant challenge in the printed electronics industry and academic community. Here, overcoming the weak hydrophilicity of polyaniline, a low-cost, easy-fabricating, and air-stable conducting polymer (CP) ink is devised through a facile assemble-disperse strategy delivering a high conductivity in the order of 10-2 S cm-1 along with a remarkable specific capacitance of 386.9 F g-1 at 0.5 A g-1 (dehydrated state). The additive-free CP ink is directly employed to print wearable micro-supercapacitors (MSCs) via the spray-coating method, which deliver a high areal capacitance (96.6 mF cm-2 ) and volumetric capacitance (26.0 F cm-3 ), outperforming most state-of-the-art CP-based supercapacitors. This work paves a new approach for achieving scalable MSCs, thus rendering a cost-effective, environmentally friendly, and pervasive energy solution for next-generation distributed electronics.

Liquid‐Crystal Mediated Assembly of Iodinated Graphene Oxide for Ultra‐Dense Supercapacitors as Safe Power Source for Internet of Things Data Transmission

AbstractDense iodinated reduced graphene oxide (rGO) with outstanding electrical and electrochemical properties is produced through a green method comprising liquid crystal‐mediated assembly of polyiodides and GO, and subsequent UV irradiation. The dense rGO electrode (1.46 g/cm3) exhibited a very high volumetric capacitance of 226 F/cm3, a factor of three larger than commercial activated carbon, and amongst the highest reported for graphene. The scalability is demonstrated by the fabrication of supercapacitor pouch cells that realized a volumetric energy density of 0.94 Wh/l, comparable to market products with similar footprint, while advantageously using a safe and green aqueous electrolyte. Our pouch cell powered battery‐less Internet of Things (IoT) sensor nodes and demonstrated sensing and transmission of over 40 temperature and relative humidity data packets. Our work establishes the critical advantages graphene‐based materials have over activated carbons in terms of ease of fabrication, tailorability, and enhanced volumetric energy density to advance the state‐of‐art in supercapacitor device research.

A top-down cutting method for construction of high-performance fiber-shaped quasi-solid-state asymmetric supercapacitors

Fiber-shaped asymmetric supercapacitors (FSASCs) have great potential as a future wearable energy storage system because of good weavability, a wide operating voltage window, and high energy density. Conventional bottom-up construction methods for fiber supercapacitors are time-consuming or highly costly. This work proposes a novel facile top-down cutting method to construct FSASCs. FSASCs with desired sizes can be rapidly constructed and easily scaled up by cutting a thin-film supercapacitor into fiber-shaped devices. Serial and parallel FSASCs free of external wire connection were assembled by cutting stacked film supercapacitors and multiplying the cutting width, respectively. Besides, the as-prepared FSASCs exhibit superior comprehensive electrochemical performance, including a high volumetric capacitance of 14.7 F/cm3, a high energy density of 93.5 μWh/cm2, and excellent flexibility. The cutting method with advantages of high simplicity, low cost, and high efficiency may be a general construction method for fiber-shaped energy storage devices.

Carbon-carbon dense network composite with hierarchical structure for additive-free and high volumetric performance supercapacitor

High density carbon composite (AC3/G) with hierarchical porous structure is prepared by packing biomass-based carbon (ACs) into graphene network (rGO), via microwave-assisted hydrothermal treatment followed by capillary evaporation-induced drying. Graphene oxide is reduced during the treating process and acts as frame network to embed the ACs. ACs are packed into the network with a density up to 1.23 g/cm3 for AC3/G. ACs can prevent the agglomeration of rGO, and channels formed between rGO sheets and ACs facilitate the hierarchical porous structure. When AC3/G is used as a binder and conductive additive-free electrode in the three-electrode system, a high volumetric capacitance of 775 F/cm3 at 0.5 A/g is achieved with excellent cycling stability of 97.05%. When assembled into a flexible solid-state supercapacitor device with lignin hydrogel electrolytes, the high-density electrode delivers high volumetric and gravimetric energy densities of 9.7 W h/L and 7.9 W h/kg, with volumetric capacitance of 326 F/cm3 at 0.5 A/g. Remarkably, the study paves a new idea for preparation of energy devices with high volumetric performance using biomass resources.

Development of high performance alpha-Co(OH)2/reduced graphene oxide microfilm for flexible in-sandwich and planar micro-supercapacitors

Herein, a series of alpha-Co(OH)2/reduced graphene oxide (rGO) microfilms and film-based nanodevices were developed via a new scalable technique. Due to the unique hexagonal nanoplates of ultrathin alpha-Co(OH)2 and the intrinsically conductive nature of rGO sheets, such thin films not only can improve the conductivity of alpha-Co(OH)2 and prevent the re-stacking of alpha-Co(OH)2 and rGO sheets but also short the transport routes of electrons and ions between the electrode and the electrolyte. The optimized alpha-Co(OH)2/rGO flexible electrode presents high specific capacitance (273.86 mF/cm2 at 0.1 mA/cm2), advanced rate capability, and excellent coulombic efficiency. Simultaneously, in-sandwich symmetric and asymmetric supercapacitors assembled with polyvinyl alcohol-KOH gel as the solid-state electrolyte achieved high areal and volumetric specific capacitances. Furthermore, a self-assembled planar alpha-Co(OH)2/rGO micro-supercapacitor (MSC) delivers high specific area capacitance (130F/cm2 at 0.5 mA/cm2) and excellent energy density (20 mWh/cm3@56 mW/cm3), which are superior to most of the recently reported carbon-based and metal hydroxides/oxides/sulfides-based planar MSCs. Also, our planar MSC shows excellent cycling performance, good flexibility, and mechanical stability. This work promotes the syntheses of other two-dimensional metal hydroxides/rGO composite film for high-performance flexible micro-electronics.

Self-Healing and Highly Stretchable Hydrogel for Interfacial Compatible Flexible Paper-Based Micro-Supercapacitor.

Most reported wearable electronic devices lack self-healing chemistry and flexible function to maintain stable energy output while irreversible damages and complex deformations. In this work, we report a dual-dynamic network electrolyte synthesized by micellar elastomers introduced into strong hydrogel matrix. The gel electrolyte is fabricated by physically cross-linking the borax-polyvinyl alcohol (B-PVA) network as tough matrix and poly (ethylene oxide) (PEO)-poly (propylene oxide) (PPO)-poly (ethylene oxide) (Pluronic) to frame elastic network, followed by immersion in potassium chloride solution. Under the action of dynamic borate ester bond and multi-network hydrogen bond, the as-prepared electrolyte exhibits high stretchability (1535%) and good self-healing efficiency. Based on the electrolyte, we assemble the interfacial compatible micro-supercapacitor (MSC) by multi-walled carbon nanotubes (MWCNT) interdigital electrode printed on cellulosic paper by direct ink writing (DIW) technique. Thanks to the large specific area and compressive deformation resistance of cellulosic paper, the MSC with tightly interfacial contact achieves high volumetric capacitance of 801.9 mF cm−3 at the current density of 20 μA cm−2. In the absence of stimulation of the external environment, the self-healing MSC demonstrates an ideal capacity retention (90.43%) after five physical damaged/healing cycles. Our research provides a clean and effective strategy to construct wearable MSC.

Superior volumetric capacitance of nitrogen and fluorine Co-doped holey graphene/PANI composite film for supercapacitor electrodes

For the development of small portable energy storage devices with limited space, high volumetric capacitance which representing the chance of reducing the volume is becoming the most critical factor to the real industrial applications. Herein, we introduce a novel simple strategy to fabricate a free-standing binder-free N and F co-doped holey graphene/PANI (NFHG/PANI) composite film, in which the doping of nitrogen and fluorine in holey graphene nanosheets boosts the electron transfer efficiency and facilitates the polymerization and growth of aniline on the graphene surface in the form of nanoparticles. The NFHG/PANI performed a gravimetric capacitance of 580 F g−1 at a current density of 0.5 A g−1 and long-term cycling stability, more importantly, it delivered 828 F cm−3 superior volumetric capacitance at a high packing density. Apparently, such a free-standing NFHG/PANI composite film with excellent performance is of great significance for the development of miniaturized portable energy storage devices.

Graphene Nanosphere as Advanced Electrode Material to Promote High Performance Symmetrical Supercapacitor.

To get carbon electrode with both excellent gravimetric and volumetric capacitances at high mass loadings is critical to supercapacitors. Herein, cracked defective graphene nanospheres (GNS) well meet above requirements. The morphology and structure of the GNS are controlled by polystyrene sphere template/glucose ratio, microwave heating time, and Fe content. The typical GNS with specific surface area of 2794 m2 g-1 , pore volume of 1.48 cm3 g-1 , and packing density of 0.74g cm-3 performs high gravimetric and volumetric capacitances of 529 F g-1 and 392 F cm-3 at 1A g-1 with a capacitance retention of 62.5% at 100 A g-1 in a three-electrode system in 6mol L-1 KOH aqueous electrolyte. In a two-electrode system, the GNS possesses energy density of 18.6Wh kg-1 (13.8Wh L-1 ) at the power density of 504 W kg-1 , which is higher than all reported pure carbon materials in gravimetric energy density and higher than all reported heteroatom-doped carbon materials in volumetric energy density, in aqueous solution, as far as it is known. A structural feature of carbon materials that possess both high energy density and high power density is pointed out here.

Exploring the impact of MoS2 on the performance of the planar solid micro-supercapacitor

A symmetric micro-supercapacitor (MSC) is constructed by electrochemically co-depositing molybdenum disulfide nanoflakes and poly-naphthalenemethylamine onto micro-patterned (100 μm track/gap) palladium current collectors over a plastic substrate. Within this structure, the polymer/MoS2 nanocomposite provides the percolating framework necessary to facilitate the charge transport and intercalation of ions through the entire electrode volume and functional chemical groups and/or defects, increasing the pseudocapacitance contribution. The hybrid MSC gave a high volumetric capacitance of 130 mF/cm3 at a scan rate of 5 mV/s, affording a 3.1 V potential window using a PVA-H2SO4 solid gel electrolyte. Overall, the strategy developed in this work on commercial interdigitated electrodes is based on an easily scalable technology, and further fine-tuning of the electrode design or active material volume can lead to supplementary improvement of the MSC's performance and cycling stability.

Hierarchical porous carbon materials obtained by Cu–Al double hydroxide templates with high gravimetric and volumetric capacitance

The hard-template method belongs to an effective route for preparing porous carbon materials with ideal hierarchical pores. In this work, a kind of hierarchical porous carbon (HPC) with high gravimetric and volumetric capacitance is fabricated by the use of Al–Cu double hydroxides (Al–Cu DHs) as hard templates and polyethylene glycol-200 as carbon precursors. It is found that the Al/Cu molar ratio has a profound influence on the morphology and composition of Al–Cu DHs and the obtained hierarchical porous architecture of HPCs owing to the template and catalyst functions of both Cu and Al2O3. For Al/Cu molar ratios of 5:1 and 7:1, the prepared HPC-05 and HPC-07 display a large specific surface area and appropriate hierarchical porous architecture. They can be used as the electrode materials of supercapacitors without any activation. The HPC-05 exhibits gravimetric capacitance (296.9 F g−1) and high volumetric capacitance (183.3 F cm−3). Moreover, the capacitance retention is 105% in 1 M Na2SO4 electrolyte with an ultrahigh gravimetric energy density of 16.32 W h kg−1 and a volumetric energy density of 10.09 W h l−1. This paper provides a tunable double-hydroxide-template way to construct HPC materials with high gravimetric and volume capacitance.

Layer-by-Layer Assembly of Reduced Graphene Oxide and MXene Nanosheets for Wire-Shaped Flexible Supercapacitors.

As the demand for wearable electronic devices increases, interest in small, light, and deformable energy storage devices follows suit. Among these devices, wire-shaped supercapacitors (WSCs) are considered key components of wearable technology due to their geometric similarity to woven fiber. One potential method for creating WSC devices is the layer-by-layer (LbL) assembly technique, which is a "bottom-up" method for electrode fabrication. WSCs require conformal and adhesive coatings of the functional material to the wire-shaped substrate, which is difficult to obtain with other processing techniques such as vacuum filtration or spray-coating. However, the LbL assembly technique produces conformal and robust coatings that can be deposited onto a variety of substrates and shapes, including wires. In this study, we report WSCs made using the LbL assembly of alternating layers of positively charged reduced graphene oxide functionalized with poly(diallyldimethylammonium chloride) and negatively charged Ti3C2Tx MXene nanosheets conformally deposited on activated carbon yarns. In this construct, the added LbL film enhances capacitance, energy density, and power density by 240, 227, and 109%, respectively, relative to the uncoated activated carbon yarn, yielding high specific and volumetric capacitances (237 F g-1, 2193 F cm-3). In addition, the WSC possesses good mechanical stability, retaining 90% of its initial capacity after 200 bending cycles. This study demonstrates that LbL coatings on carbon yarns are promising as linear energy storage devices for fibrous electronics.

Densely Packed and Highly Ordered Carbon Flower Particles for High Volumetric Performance

Carbon materials with high specific surface areas are ideal support materials for many applications. However, high specific surface area and large pore volume usually render them with low bulk density, which is undesirable for applications aiming at high volumetric performance. Low bulk density stems from large interparticle‐free volume caused by inefficient random packing within the materials. Herein, a simple synthesis and assembly method is reported to afford dense carbon pellets with both high specific surface area and high bulk density, obtained from the ordered packing of low polydispersity carbon flower particles. The densely packed carbon flower particles exhibit similar specific surface area to their pressed powder analogs, while exhibiting a 66–84% increase in bulk density (0.815 g cm−3), and an ultrahigh volumetric surface area (1081 m2 cm−3). The advantages of our materials are demonstrated by supercapacitors, which achieve a high volumetric capacitance of up to 153 F cm−3. The results reinforce the importance of controlling particle size and shape for porous materials to reduce their bulk volume. The developed materials possessing high volumetric surface area will be useful for many applications, such as gas storage, supercapacitors, and batteries.

Polydiketopyrrolopyrroles Carrying Ethylene Glycol Substituents as Efficient Mixed Ion‐Electron Conductors for Biocompatible Organic Electrochemical Transistors

AbstractA comprehensive investigation of four polydiketopyrrolopyrroles (PDPPs) with increasing ethylene glycol (EG) content and varying nature of comonomer is presented, and guidelines for the design of efficient mixed ion‐electron conductors (MIECs) are deduced. The studies in NaCl electrolyte‐gated organic electrochemical transistors (OECTs) reveal that a high amount of EG on the DPP moiety is essential for MIEC. The PDPP containing 52 wt% EG exhibits a high volumetric capacitance of 338 F cm−3 (at 0.8 V), a high hole mobility in aqueous medium (0.13 cm2 V−1 s−1), and a μC* product of 45 F cm−1 V−1 s−1. OECTs using this polymer retain 97% of the initial drain‐current after 1200 cycles (90 min of continuous operation). In a cell growth medium, the OECT‐performance is fully maintained as in the NaCl electrolyte. In vitro cytotoxicity and cell viability assays reveal the excellent cell compatibility of these novel systems, showing no toxicity after 24 h of culture. Due to the excellent OECT performance with a considerable cycling stability for 1200 cycles and an outstanding cell compatibility, these PDPPs render themselves viable for in vitro and in vivo bioelectronics.

Nitrogen and oxygen co‐doped carbon microspheres with partially graphitic structures: Integrated high volumetric capacitance, mass loadings and rate capability for supercapacitors

AbstractSynthesis of porous carbon electrodes with high volumetric capacitance and excellent rate capability, especially for a higher mass loading of 10 mg cm–2, remains a challenge and is important for wide applications of the new generation supercapacitors. We report unprecedented volumetric capacitance of 942.9 F cm–3 in 2 M H2SO4 for partially graphitized carbon microspheres co‐doped with N and O prepared by simple hydrothermal route followed by direct cobalt catalytic pyrolysis, which is comparable to the expensive metal oxide and MnO2‐based pseudo‐capacitors. The resulted carbon also shows excellent rate capability (65.4% and 52.2% capacitance retention as the current density increases from 1 to 20 A g–1 in 2 M H2SO4 and 6 M KOH, respectively) and cyclic stability with a higher mass loading of 9.84 mg cm–2 in acidic/basic electrolytes. More importantly, the high volumetric energy density (22.39 Wh L–1) of the assembled symmetrical supercapacitors in 6 M KOH makes it possible to compete with even some Ni metal hydride batteries. This work offers a way to develop advanced porous carbon materials with ultrahigh volumetric capacitance/mass loadings and fast charge rates for supercapacitors.

Catechol-Coordinated Framework Film-based Micro-Supercapacitors with AC Line Filtering Performance.

Coordination polymer frameworks (CPFs) have broad applications due to their excellent features, including stable structure, intrinsic porosity, and others. However, preparation of thin-film CPFs for energy storage and conversion remains a challenge because of poor compatibility between conductive substrates and CPFs and crucial conditions for thin-film preparation. In this work, a CPF film was prepared by the coordination of the anisotropic four-armed ligand and CuII at the liquid-liquid interface. Such film-based micro-supercapacitors (MSCs) are fabricated through high-energy scribing and electrolytes soaking. As-fabricated MSCs displayed high volumetric specific capacitance of 121.45 F cm-3 . Besides, the volumetric energy density of MSCs reached 52.6 mWh cm-3 , which exceeds the electrochemical performance of most reported CPF-based MSCs. Especially, the device exhibited alternating current (AC) line filtering performance (-84.2° at 120 Hz) and a short resistance capacitance (RC) constant of 0.08 ms. This work not only provides a new CPF for MSCs with AC line filtering performance but also paves the way for thin-film CPFs preparation with versatile applications.

Redox Molecule Adsorbed Graphene Films with Compact Structure for Electrochemical Energy Storage

Graphene films with compact structure and high ion accessible surface are essential to achieve dense energy storage with high-performance. Thus we prepared hydroquinone (HQ) adsorbed reduced graphene oxide (HQ-rGO) films with high packing density by capillary pressure. Hence, sulphuric acid was pre-intercalated between graphene sheets to reduce ion transport resistance, and adsorbed HQ molecules provide abundant pseudocapacitance. Finally, the two materials play a synergistic effect, significantly improving the capacitance performance. The resulting HQ-rGO films exhibit high volumetric capacitance of ~189.4F cm−3 at 1mA cm−2, and after current density increase to 30mA cm−2, its capacitance retention can achieve 54% of original value, which demonstrates excellent rate performance of the device. Clearly, this strategy is great promising for fabrication of electrode material with high performance.

Monolithic flexible supercapacitors drawn with nitrogen-doped carbon nanotube-graphene ink

We demonstrate a facile strategy to fabricate flexible paper-based supercapacitors, in which all the components are integrated onto a paper with poly (vinyl alcohol)/H3PO4 as the gel electrolyte. The electrodes are drawn on both sides of the paper in a mirror image with a surfactant-free ink of nitrogen-doped carbon nanotubes and graphene. The resultant supercapacitors present a high volumetric capacitance of 0.45 F cm−3 and an energy density of 40.0 μWh cm−3. Moreover, this strategy is intrinsically scalable toward flexible energy devices while maintaining their electrochemical and mechanical performance.

Sequentially Bridged Ti3C2Tx MXene Sheets for High Performance Applications

AbstractThe outstanding electrical conductivity and high specific capacitance of 2D Ti3C2Tx MXene have made them promising materials for a wide range of applications including wearable electronics, energy storage, sensors, and electromagnetic interference shielding. However, the fabrication of MXene architectures, both pure and composite, often results in a trade‐off in properties. Here, it is reported that sequential bridging of MXene sheets significantly enhances the mechanical properties of its free‐standing films, with improvements in strength and toughness of up to ≈339 MPa and ≈12.0 MJ m−3, respectively, while simultaneously retaining both high conductivity (≈4850 S cm−1) and volumetric capacitance (≈1220 F cm−3). This sequential bridging strategy permits surface modification of MXene sheets while still yielding stable colloidal dispersions so that the subsequent MXene films comprise of aligned, evenly‐spaced, and interconnected sheets, which are critical for the development of robust energy storage devices and other high performance applications.

Gelam Tree-Derived Carbon Nanosheets as Thick and Free-Standing Electrode for Supercapacitor

Most electrodes for supercapacitors are prepared as thick layer electrodes. Compact, thick and free-standing electrodes are needed for supercapacitor with high volumetric capacitance and energy density. Carbon nanosheets were obtained from treating the bark of the Gelam tree (Melaleuca cajuput Powell) via hydrothermal and microwave processes. The XRD results showed the presence of graphitic carbon in the Gelam tree-derived carbon nanosheet. The carbon nanosheet (the thickness of 0.01 cm) was mixed with graphite and poly(aniline) as conducting binder to fabricate a supercapacitor electrode. Conductivity as high as 3.67 x 10-2 S cm-1 were obtained from the electrode using the carbon nanosheet to graphite the ratio of 3:7. The electrode with this composition had a porous structure. The electrode with a carbon nanosheet to graphite the ratio of 7:3 had a granular morphology with a low conductivity of 0.8 x 10-3 S cm-1. Cyclic voltammetry tests were conducted in lithium chloride and ammonium cyanate-based electrolytes. Both types of electrodes (ratio 3:7 and 7:3) had the same trend of capacitance and voltage window in lithium chloride and ammonium cyanate-based electrolytes. Capacitance as high as 0.0618 F was obtained from the electrode using the 7:3 ratios nanosheet in 10 % ammonium cyanate electrolyte. A novel supercapacitor with high capacitance designed using a thick layer electrode can readily be prepared from the carbon nanosheets derived from the agricultural wood waste.

Sword/scabbard-shaped asymmetric all-solid-state supercapacitors based on PPy-MWCNTs-silk and hollow graphene tube for wearable applications

Fiber-shaped supercapacitors (FSSCs) have attracted increasing attention for wearable electronics. Herein, an asymmetrical fiber-shaped supercapacitor, AFSSCs-ICS, with an innovative encapsulated core-sheath architecture has been successfully constructed for the first time. The sword-scabbard inspired AFSSCs-ICS was fabricated by simply inserting a ‘sword’ positive electrode, PPy-MWCNTs-silk, into one tubular graphene ‘scabbard’ negative electrode with H2SO4/PVA gel as electrolyte. Notably, our newly designed PPy-MWCNTs-silk electrode had an ultrahigh length specific capacitance of 15.3 mF cm−1 (corresponding to high areal or volumetric capacitance of 676.9 mF cm−2 or 376.3 F cm−3), representing one of the highest levels among the fabric yarn derived electrodes, while the hollow graphene tube depicted a superior linear capacitance of 19.1 mF cm−1, which could match well with that of the PPy-MWCNTs-silk electrode. Benefiting from the innovative yet rational structure, and ideally balanced charges, the AFSSCs-ICS had an extended operating potential of 1.6 V, and an outstanding length specific capacitance of 2.3 mF cm−1 with a very admirable energy density of 0.8 μWh cm−1, dramatically surpassing numerous reported FSSCs. Moreover, the AFSSCs-ICS device also afforded superb electrochemical and mechanical stabilities with retentions of 81% after 3000 charging-discharging cycles and 95–105% under bending degrees from 0 to 150°. This study may pave a new way for constructing coaxial fiber-shaped energy source unit for next-generation wearable and portable miniaturized electronics.