Areal Power Density Research Articles

High-Performance Solid-State Micro-Supercapacitor of Sharp-Edged Electrode Geometry from Metal-Oxide Nanoparticles Loaded Carbon Foam

The demand for miniaturization of energy storage systems has accelerated development of on-chip micro-power devices, for integration into portable electronic devices. Micro-supercapacitors can suitably cater to this need by functioning as efficient miniaturized energy storage devices with high power density, fast charge-discharge rates, and long cyclic lifetime. The parameters that affect performance metrics of micro-supercapacitors are electrode materials, electrolytes, device architecture, and microfabrication techniques. By effective utilisation and tuning of these critical parameters, we report a novel sharp-edged electrode geometry for the in-plane micro-supercapacitors by spray coating of porous carbon foam loaded with iron-oxide nanoparticles (Fe2O3). The high specific surface area of carbon foam facilitated extensive mass loading of metal oxide nanoparticles to exhibit both pseudocapacitance and electric double-layer capacitance. Also, it is imperative to rationally design electrodes with sharp edges as it would lead to an increase of charge density at the corners due to curved surfaces. Utilising this concept of edging effect, we have designed a sharp-edged electrode geometry that exhibited a 68% enhancement of the electric field at the electrodes' corner edges compared to conventional interdigitated electrodes as obtained by COMSOL multiphysics simulation. This increase in the electric field contributed to a high areal capacitance of 12.4 mF/cm2 at 5 mV/s with an enhancement of 235% as compared to conventional interdigitated electrodes. Also, excellent cyclic stability (~ 99.5%) over 10000 charge-discharge cycles was achieved. More notably, the sharp-edged micro-supercapacitor show an excellent areal energy density of 1.73 µWh/cm2 and areal power density of 1425 µW/cm2. Thus, this high-performance in-plane architecture of sharp-edged electrodes possesses enormous potential for numerous energy storage applications.

Nanosilver-Particles Integrated Ni3 Sn2 S2 -CoS Composite as an Advanced Electrode for High Energy Density Hybrid Cell.

An ion-exchange process is a promising approach to design advanced electrode materials for high-performance energy storage devices. Herein, a nanostructured Ni3 Sn2 S2 -CoS (NSS-CS) composite is fabricated by successive hydrothermal and ion-exchange processes. Since the incorporation of redox-rich cobalt element enables the NSS-CS composite to be more electrochemically active, its impact on the electrochemical performance is therefore extensively studied. Particularly, the NSS-CS-0.2g electrode material delivered a high areal capacity of 830.4µAhcm-2 at 5mAcm-2 . Additionally, a room-temperature wet-chemical approach is employed to anchor nanosilver (nAg)-particles on the NSS-CS-0.2g (nAg@NSS-CS-0.2g) to further exalt its electrokinetics. Consequently, the nAg@NSS-CS-0.2g electrode shows a higher areal capacity of 948.5µAhcm-2 (193.5mAhg-1 ) than that of the NSS-CS-0.2g. Furthermore, its practicability is also examined by assembling a hybrid cell. The assembled hybrid cell delivers a high areal capacity of 969.2µAhcm-2 (49.2mAhg-1 ) at 7mAcm-2 and maximum areal energies and power densities of 0.784mWhcm-2 (40.8Whkg-1 ) and 45mWcm-2 (2347.4Wkg-1 ), respectively. The efficiency of the hybrid cells is also tested by harvesting solar energy, followed by energizing electronic components. This work can pave the way for significant attraction in designing advanced electrodes for energy-related fields.

Electrodeposited with FeOOH and MnO2 on laser-induced graphene for multi-assembly supercapacitors

The performance of the electrode material for supercapacitor depends not only on its structure but also on the potential window. In this work, we have demonstrated a two-steps method to prepare the integrated electrode materials. Firstly, Ni@PES films are scribed at CO2 laser induction and Ni@PES-LIG is obtained. Secondly, the subsequent electrodeposition of FeOOH and MnO2 are carried out in three-electrode system. The MnO2/Ni@PES-LIG and FeOOH/Ni@PES-LIG electrodes exhibit high pseudocapacitances of 205 and 210 mF cm−2, respectively. By using The MnO2/Ni@PES-LIG and FeOOH/Ni@PES-LIG electrodes as the anode and cathode, respectively, we have successfully fabricated the free-standing asymmetric supercapacitor (ASC) device, which has wider potential range over 2.0 V. The Ni@ASC device delivers high areal capacitance (110 mF cm−2), high areal energy density (41.6 μWh cm−2), and high areal power density (136 mW cm−2). Additionally, the Ni@ASC assembling with the integrated electrodes reveals a much higher capacitance and wider potential window than other single symmetric and asymmetric supercapacitors due to its multiple energy stored mechanisms.

Facile hydrothermal deposition of Copper-Nickel sulfide nanostructures on nickel foam for enhanced electrochemical performance and kinetics of charge storage

In this study, novel binder-free copper-nickel-sulfur (CNS) nanostructures are deposited on 3D Ni foam (CNS/Ni) by a facile hydrothermal technique. A step-wise evaluation of the CNS nanostructures is systematically carried out by varying the hydrothermal reaction times (3, 6, 9, 18, and 27 h). The structural phase, chemical composition, and morphological evolution were analyzed by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and field emission scanning electron microscopy (SEM) respectively. The CNS deposited at 18 h shows interconnected 2D nanoflakes that provide maximum porosity, fast surface redox reaction sites, and improved ionic and electronic conductivity. The electrochemical measurements for CNS-18 show high areal capacitance (2589 mFcm−2), energy density (0.22 mWhcm−2), and power density (7.8 mWcm−2) at a current density of 20 mAcm−2 owing to its high diffusion-controlled contribution (97 %) to the total current as compared to the other CNS samples. The kinetics of the electrochemical measurements are undertaken by the Dunn and Trasatti method. The CNS-18 sample shows long cyclic stability of approximately 81 % up to 7500 cycles. A CNS/AC asymmetric capacitor was fabricated to demonstrate its practical performance. It is surmised that CNS deposited on Ni foam can be used as an efficient electrode in energy storage applications.

Aqueous Inks of Pristine Graphene for 3D Printed Microsupercapacitors with High Capacitance.

Three-dimensional (3D) printing is gaining importance as a sustainable route for the fabrication of high-performance energy storage devices. It enables the streamlined manufacture of devices with programmable geometry at different length scales down to micron-sized dimensions. Miniaturized energy storage devices are fundamental components for on-chip technologies to enable energy autonomy. In this work, we demonstrate 3D printed microsupercapacitor electrodes from aqueous inks of pristine graphene without the need of high temperature processing and functional additives. With an intrinsic electrical conductivity of ∼1370 S m–1 and rationally designed architectures, the symmetric microsupercapacitors exhibit an exceptional areal capacitance of 1.57 F cm–2 at 2 mA cm–2 which is retained over 72% after repeated voltage holding tests. The areal power density (0.968 mW cm–2) and areal energy density (51.2 μWh cm–2) outperform the ones of previously reported carbon-based supercapacitors which have been either 3D or inkjet printed. Moreover, a current collector-free interdigitated microsupercapacitor combined with a gel electrolyte provides electrochemical performance approaching the one of devices with liquid-like ion transport properties. Our studies provide a sustainable and low-cost approach to fabricate efficient energy storage devices with programmable geometry.

One-Pot Hydrothermal-Derived NiS2 -CoMo2 S4 with Vertically Aligned Nanorods as a Binder-Free Electrode for Coin-Cell-Type Hybrid Supercapacitor.

Transition bimetallic sulfides are exploited as high-capacity electrode materials in energy storage devices owing to their abundant electroactive sites and relatively high electrical conductivity compared with metal oxides. Here, an in situ conversion of metal ions into NiS2 -CoMo2 S4 vertically aligned nanorod arrays on nickel foam (NS-CMS NRAs@NF) using a one-step hydrothermal technique to address the "dead-mass" limitation and multi-step preparation methods is reported. An in situ-converted NS-CMS NRAs obtained for 12 h of reaction time (NS-CMS NRAs-12 h@NF) delivers a superior areal capacity of 780 μAh cm-2 to the other NS-CMS electrodes synthesized for 6 h (543.1 μAh cm-2 ) and 18 h (636.7 μAh cm-2 ) at 7mA cm-2 . A coin-cell-type hybrid supercapacitor (HSC) is also fabricated to unveil the practical adaptability of NS-CMS NRAs-12 h@NF electrode. Utilizing its structural and active material intriguing features, assembled coin-cell-type HSC achieves a high areal capacitance of 246.2 mF cm-2 (5mA cm-2 ) along with maximum areal energy density (147 μWh cm-2 ) and power density (21.3mW cm-2 ), respectively. Furthermore, the capability of coin-cell-type HSC in real-time applications is also inspected. This work promotes in situ deposition strategy to fabricate metal sulfide-based nanostructures for high-performance electrochemical capacitors.

Low-crystalline birnessite-MnO2 nanograins for high-performance supercapacitors

Crystallized transition metal oxides were widely used as the electrode materials for the electrochemical energy storage devices. However, their electrochemical performance including the capacitance and rate capability was greatly hindered due to ion penetrating long distances into the bulk regimes during the electrochemical process. Herein, low-crystalline birnessite-MnO2 nanograins are obtained, which can enhance the ion diffusion kinetics and electrochemical activity significantly due to the structural disorder and defects. The resultant electrode features a superior electrochemical performance with an areal capacitance up to 1154 mF/cm2 at 2 mA/cm2 and rate retention of 69 % when the current density increasing 10 times to 20 mA/cm2 with a commercial standard mass loading about 4.58 mg/cm2. And the cycle stability measurement shows no attenuation after 10000-cycle charge/discharge operation. Moreover, assembled asymmetric supercapacitor device (wide operation voltage of 2.3 V) delivers a maximum areal energy density of 0.36 mWh/cm2 with the areal power density of 5.57 mW/cm2. The electrochemical behavior studies and in-situ Raman reveal that the structural disorder in the low-crystalline nanograins greatly facilitate the reversible ion intercalation/deintercalation process during the electrochemical cycling process. Our results will provide an instructive route for the formulation of the design principle for the high-performance of transition metal oxides electrode material.

High areal energy density structural supercapacitor assembled with polymer cement electrolyte

Structural supercapacitors (SSCs) have attracted increasely interests due to tremendous demand of zero-energy buildings. Yet the challenge of SSCs remains in well balancing the electrochemical energy storage and load-bearing capacity. Herein, an integrated electro-mechanical SSC with high areal energy density and mechanical strength is developed using carbon fiber and building materials. The rGO/CuO on carbon fiber incorporates excellent electrochemical energy storage behaviors of redox-active material and carbon based material. The electrolytes in the form of PAA-PC-LiOTf composites are fabricated to expand the operating voltage of SSCs, which further boost energy density. By regulating the contents of PAA and LiOTf, the polymer cement electrolyte presents the optimal multifunctionality with a compressive strength of 23.65 MPa and ionic conductivity of 7.48 mS cm−1. An assembled SSC with the polymer cement electrolyte can not only bear high external load, but also extend to a voltage window of 4 V, exhibiting maximum areal energy density of 0.65 mWh cm−2 at areal power density of 0.58 mW cm−2. It has the best multifunctionality among the reported SSCs in the form of civil engineering even better than most reported solid-state supercapacitors, which brings new insights into the high performance SSCs.

Site-Selective Transformation for Preparing Tripod-like NiCo-Sulfides@Carbon Boosts Enhanced Areal Capacity and Cycling Reliability.

Flexible power supply systems for future wearable electronics desperately require high areal capacity (Ca) and robust cycling reliability due to the limited surface area of the human body. Transition metal sulfides are preferred as cathode materials for their improved conductivity and rich redox centers, yet their practical applications are severely hindered by the sluggish charge transport kinetics and unavoidable capacity decay due to the phase transformation during charge/discharge processes. Herein, we develop a site-selective transformation strategy for preparing tripod-like NiCo-sulfides@carbon (T-NCS@C) arrays on carbon cloth. The mass loading of active materials is balanced with charge (electron and ion) transport efficiency. The optimized T-NCS@C delivers a superior Ca of 494 μA h/cm2 (corresponding to 235 mA h/g) at 3 mA/cm2. Due to the protection of the carbon layer that is derived from transformed metal-organic framework (MOF) sheath, the T-NCS@C displays excellent stability with 92% retention over 5000 charge/discharge cycles. The flexible full cell adopting Fe2O3 as the anode and T-NCS@C as the cathode exhibits an improved Ea (areal energy density) of 389 μW h/cm2 at a Pa (areal power density) of 4.22 mW/cm2 together with robust cycling reliability.

Polypyrrole/Organic Sulfonic Acid Coated Activated Carbon Fiber Felt as Flexible Supercapacitor with High-performance

Polypyrrole (PPy) was deposited onto carbon fiber felt (CFF) by in-situ polymerization to prepare CFF/PPy composite textile as free-standing and flexible electrode for supercapacitor. Electrochemical performance was characterized by cyclic voltammetry (CV), electrochemical impedance (EIS) and constant current charge-discharge technology. The results show that the doping of organic sulfonic acid further improved the electrochemical performance of electrode materials. Areal capacitance, energy density and power density of the CFF/PPy/TsOH are as high as 5943 mF·cm−2, 1739 µWh·cm−2, 1450 µW·cm−2, respectively (at a current density of 0.8 mA·cm−2). Overall, this flexible textile electrode is promising to be used as wearable electronic device.

Direct ink writing preparation of LiFePO4/MWCNTs electrodes with high-areal Li-ion capacity

The combination of 3D printing technology and electrode materials make the design and manufacture of electrode structures more convenient and faster. Electrodes with the 3D structure have a large surface area and multiple ion transmission paths, which help the batteries to achieve a high areal capacity, energy density and power density. Here, we designed the 3D printed electrodes with a structure of square grid by Direct Ink Writing, and achieved an improvement of areal capacity (1.44 mA h cm−2 at 0.5C), better areal-energy density (18.06 J cm−2) and cycling stability (preserving ~80% capacity after 500 cycles at 5 C).

Novel Conductive Ag-Decorated NiFe Mixed Metal Telluride Hierarchical Nanorods for High-Performance Hybrid Supercapacitors.

Mixed metal chalcogenide nanoarchitectures have been attracting enormous attention as battery-type electrodes for hybrid supercapacitors (HSCs) owing to their enhanced electrochemical (EC) performance. Despite having high electrical conductivity and good EC properties, tellurium has not been fully utilized in metal chalcogenide electrodes as much as sulfur and selenium. Herein, a facile strategy for the fabrication of nickel and iron (NiFe) mixed metal telluride hierarchical nanorods (MMT HNRs) on nickel foam (NF) is proposed. Furthermore, conductive silver (Ag) is decorated on MMT HNRs (AMMT HNRs) to improve the conducting channels, thereby EC performance. Benefitting from the combined advantages of electroactive NiFe mixed metal, conductive tellurium and Ag, and hierarchical nanorod-like nanomorphology, the AMMT HNR electrode has delivered high areal capacity (1.1 mAh cm-2). Finally, the AMMT based HSC with activated carbon coated NF (AC/NF) as a negative electrode exhibited the highest areal capacitance (1176.5 mF cm-2) with high areal energy density (0.669 mWh cm-2) and power density (64 mW cm-2). Moreover, the HSC device has maintained good cycling stability (86% capacity retention) even after 5000 cycles. New findings of this study definitely shed light on the development of telluride-based mixed metal chalcogenide supercapacitors.

Thermal Design Rules of AlGaN/GaN-Based Microwave Transistors on Diamond

Reliable operation of high power GaN amplifiers at maximum performance relies on the mutual optimization of several design parameters constrained by a defined thermal budget. On high thermal conductivity, substrates, such as SiC and diamond, undergo small changes within the design that can lead to drastic changes in channel temperature. We utilize finite element simulations to provide design rules for device structures for GaN-on-diamond amplifiers, benchmarked against GaN-on-SiC. At 8 W/mm power density, a 13 μm gate pitch GaN-on-diamond design compared to a commonly employed 40 μm gate pitch GaN-on-SiC design results in ~40 °C and ~20 °C cooler peak channel temperature, i.e., 182 °C for single and 201 °C for polycrystalline diamond (PCD) substrates despite the 3× larger areal power density. The simulations were validated with 1.25 mm wide, 10-finger GaN-on-diamond high-electron-mobility transistors (HEMT) devices of 13 and 40 μm gate pitch, with good electrical performance in pulsed I-V measurements and Raman thermography measurements. The commonly used Au-Sn die-attach is determined as the next limiting factor for GaN-on-Diamond technologies which require the development of new die-attach materials.

Ink transfer for printed flexible microsupercapacitors

Printed microsupercapacitors (MSCs) with graphene rapidly evolved into one of the promising energy supplies for future flexible integrated electronic device. Gravure printing, as a leading technology, is promising for the large-scale manufacture of printed MSCs. However, ink transfer, a seemingly simple operation that is still not well understood. Herein, ink rheological principles and corresponding ink dynamic transfer are investigated by corresponding printing detail based on a kind of hierarchical porous graphene microsphere ink. Through modifying the rheological properties and ink bridge’s slipping, high quality MSCs were printed with the hierarchical porous graphene microsphere ink. Benefiting from abundant ion accessible channels, the printed MSCs achieved the diffusion rate (9.2 × 10−10 cm2 s−1) of H+ ion, leading to the high areal special capacitance of 43.5 mF/cm2. The areal energy density of 6.1 μWh cm−2 is achieved at areal power density of 3.6 mW cm−2.

Sulfur-doped laser-induced graphene derived from polyethersulfone and lignin hybrid for all-solid-state supercapacitor

Developing a simple and effective high-performance all-solid-state graphene-based mircosupercapacitor (MSC) by using biomass wastes as raw materials has attracted excellent interest. Here we report a scalable approach for producing sulfur-doped porous three-dimensional (3D) graphene materials from lignin and polyethersulfone (PES) films by using a facile laser direct writing (LDW) technique. In the lignin-PES (L-P) film, lignin, a waste by-product generated in paper industry, was served as a sustainable and economic carbon source, while PES was employed as a sulfur source and adhesive. The lignin-PES film can be transformed into sulfur-doped laser-induced graphene (LIG) by scribing under CO2 laser in ambient condition. Furthermore, the MSCs were fabricated directly using two L-P LIG electrodes as electrode materials, and H2SO4/PVA gel as electrolyte. The results indicate L-P LIG MSCs exhibit excellent electrochemical performances, namely, high areal capacitance (22 mF cm−2), superhigh areal energy density of 1.53 mwh cm−2 at the areal power density of 25.4 mw cm−2, which outperform many LIG-based supercapacitors. The concept of designing MSCs obtained with a simple laser-induced technology can inspire both the building MSCs, preparation of graphene, and the sustainable application of lignin.

Micro-supercapacitor characteristics using a micro-ring space-time control circuit

A micro-ring space-time control circuit is proposed for micro-supercapacitor application. The center micro-ring circuit consists of sandwiched titanium dioxide (TiO2) thin film. The input light fed into the circuit via the input port is of 1.55 µm wavelength. The input space source is multiplexed with time at the add port to form the space-time function. A whispering-gallery mode is formed using suitable parameters, which results from the nonlinearity effect induced by the small rings at the sides of the center micro-ring. The light that excites the gold metal surface leads to electron cloud oscillations that form the electron density, which can be transported via wireless connection by employing the whispering-gallery mode or via cable connection. Areal specific capacitance of 0.4 F cm−2 and areal power density of 0.31 MW cm−2 are obtained. In application, the micro-ring circuit can be employed in microsystems that require high specific capacitance and high power for their operations.

High performance flexible micro-supercapacitor for powering a vertically integrated skin-attachable strain sensor on a bio-inspired adhesive

We report on the fabrication of a high performance flexible micro-supercapacitor (MSC) for powering a vertically integrated skin-attachable strain sensor on a gecko-inspired micro-structured adhesive. Combined utilization of the mixed manganese/vanadium (Mn/V) oxide grown on MWCNT electrode and the sulfone-based electrolyte, PC/SL/LiClO4/PMMA, enhances both the capacitance and operation voltage up to 2 V of MSC. Thus, the fabricated MSC exhibits excellent electrochemical performance with an areal capacitance of 11.8 mF cm−2 and an areal energy density of 6.58 µWh cm−2 at an areal power density of 200 µW cm−2. The MSC shows mechanical stability over 1000 repetitive bends at a bending radius of 3.7 mm. The strain sensor made of fragmentized graphene foam embedded in PDMS film provides a high gauge factor of 12.6 up to 50% strain to detect strains due to various bio-signals. Our gecko-inspired adhesive made of PDMS micropillars inked with a mixture of PDMS and Silbione to have spatula tips exhibits not only high adhesion property but also high durability over repeated cycles of attachment-detachment and negligible skin irritation. After vertical integration of the MSC, strain sensor, and the adhesive film, bio-signals such as an arterial pulse, swallowing, and frowning of the brow are successfully detected using energy stored in the MSC.

Tunable capacitance in all-inkjet-printed nanosheet heterostructures

Heterostructures constructed from two-dimensional (2D) building blocks have shown promise for field-effect transistors, memory devices, photosensors and other electronic applications. 2D nanosheet crystals are typically constructed into multilayer heterostructures using layer-by-layer methods, which cannot be used to fabricate large-scale and thick heterostructures, due to the time-consuming nature and low efficiency of the process. An alternative approach to deposit different 2D materials in the controllable fashion is by inkjet printing. Here we show the fabrication of supercapacitors based on 2D heterostructures by inkjet printing Ti3C2Tx MXene nanosheets as electrodes, followed by inkjet printing graphene oxide nanosheets as solid-state electrolyte. The free water molecules trapped between graphene oxide sheets facilitate proton movement through the layered solid electrolyte. The as-made heterostructures show high areal capacitance, good cycling stability and high areal energy and power densities comparable with existing printed supercapacitors. Moreover, the specific capacitance can be increased further by addition of liquid electrolytes.

Functionalized and tip-open carbon nanotubes for high-performance symmetric supercapacitors.

Carbon nanotubes (CNTs) have been widely studied for use in supercapacitor electrodes because of their excellent conductivity, high aspect ratio, excellent mechanical properties, chemical stability, and large specific surface area. However, the electrochemical performance of CNTs is usually limited by their closed tips and fewer active sites. Therefore, a facile and efficient chemical-acid-etching method was employed to open the tips of CNTs and introduce functional groups. Different types of ions (Li+, Na+, and Mg2+) in aqueous electrolytes were investigated using the functionalized and tip-open CNTs (FTO-CNTs), and the Li+-based electrolyte has the best electrochemical performance. The areal capacitance when using FTO-CNTs as positive and negative electrodes could reach 542 mF cm-2 and 410 mF cm-2, respectively, at a scan rate of 10 mV s-1, and the positive electrode reached the highest areal capacitance of 903 mF cm-2 at a current density of 1 mA cm-2. The symmetric supercapacitor-based FTO-CNTs electrode delivered a superior areal energy density of 39 μW h cm-2 and an areal power density of 10.2 mW cm-2, with remarkable cycling stability.

Harnessing Interfacial Electron Transfer in Redox Flow Batteries

Summary Redox flow batteries (RFBs) have garnered increasing attention for their potential to enable the widespread adoption of renewable electricity. However, a critical need associated with the continued development of this technology involves designing electrode-electrolyte interfaces that exhibit rapid, stable electron transfer kinetics. This targeted review outlines key challenges associated with measuring and enhancing the electron transfer kinetics of established and emerging flow battery active materials. We discuss several promising opportunities for advancing flow battery science and technology using the tools of applied electroanalysis and catalysis science. These challenges and opportunities are broadly relevant for future research directed at advancing the commercial adoption of RFBs for grid-scale energy storage.