Showing papers on "Supercapacitor published in 2020"

Tuning the interlayer spacing of graphene laminate films for efficient pore utilization towards compact capacitive energy storage

Abstract: Supercapacitors have shown extraordinary promise for miniaturized electronics and electric vehicles, but are usually limited by electrodes with rather low volumetric performance, which is largely due to the inefficient utilization of pores in charge storage. Herein, we design a freestanding graphene laminate film electrode with highly efficient pore utilization for compact capacitive energy storage. The interlayer spacing of this film can be precisely adjusted, which enables a tunable porosity. By systematically tailoring the pore size for the electrolyte ions, pores are utilized optimally and thereby the volumetric capacitance is maximized. Consequently, the fabricated supercapacitor delivers a stack volumetric energy density of 88.1 Wh l−1 in an ionic liquid electrolyte, representing a critical breakthrough for optimizing the porosity towards compact energy storage. Moreover, the optimized film electrode is assembled into an ionogel-based, all-solid-state, flexible smart device with multiple optional outputs and superior stability, demonstrating enormous potential as a portable power supply in practical applications. The volumetric performance of supercapacitors needs to be improved, but the usual trade-off between porosity and density is a problem. Here the authors develop a graphene laminate film with tunable porosity that leads to a volumetric energy density of 88.1 Wh l−1 at the device level.

An aqueous hybrid electrolyte for low-temperature zinc-based energy storage devices

Abstract: Aqueous zinc-based energy storage (ZES) devices are promising candidates for portable and grid-scale applications owing to their intrinsically high safety, low cost, and high theoretical energy density. However, the conventional aqueous electrolytes are not capable of working at low temperature. Here we report a frigostable, cost-effective, safe and eco-friendly hybrid electrolyte with high zinc-ion conductivity (6.9 mS cm−1 at −40 °C), and high reversibility of Zn plating/stripping, which consists of water, ethylene glycol (EG) and zinc sulfate salt (ZnSO4). Experiments together with theoretical calculations demonstrated that the unique solvation interaction of Zn2+ with EG can effectively enhance the hydrogen bonding between EG and H2O and weaken the solvation interaction of Zn2+ with H2O, thus providing the hybrid electrolyte with a lower freezing point and reversible Zn/Zn2+ chemistry. As a proof-of-concept, both Zn-ion hybrid supercapacitors (ZHSCs) and Zn-ion batteries (ZIBs) with the hybrid electrolytes delivered high energy densities (36 W h kg−1 for the ZHSC and 121 W h kg−1 for the ZIB), high power densities (3.1 kW kg−1 for the ZHSC and 1.7 kW kg−1 for the ZIB) and long-cycle life (5500 cycles over 110 days for the ZHSC and 250 cycles for the ZIB) at −20 °C. This work provides a new option for low-temperature energy storage devices.

Heteroatom-Doped and Oxygen-Functionalized Nanocarbons for High-Performance Supercapacitors

Abstract: Electrochemical capacitors (best known as supercapacitors) are high‐performance energy storage devices featuring higher capacity than conventional capacitors and higher power densities than batteries, and are among the key enabling technologies of the clean energy future. This review focuses on performance enhancement of carbon‐based supercapacitors by doping other elements (heteroatoms) into the nanostructured carbon electrodes. The nanocarbon materials currently exist in all dimensionalities (from 0D quantum dots to 3D bulk materials) and show good stability and other properties in diverse electrode architectures. However, relatively low energy density and high manufacturing cost impede widespread commercial applications of nanocarbon‐based supercapacitors. Heteroatom doping into the carbon matrix is one of the most promising and versatile ways to enhance the device performance, yet the mechanisms of the doping effects still remain poorly understood. Here the effects of heteroatom doping by boron, nitrogen, sulfur, phosphorus, fluorine, chlorine, silicon, and functionalizing with oxygen on the elemental composition, structure, property, and performance relationships of nanocarbon electrodes are critically examined. The limitations of doping approaches are further discussed and guidelines for reporting the performance of heteroatom doped nanocarbon electrode‐based electrochemical capacitors are proposed. The current challenges and promising future directions for clean energy applications are discussed as well.

Carbon-Based Fibers for Advanced Electrochemical Energy Storage Devices

Abstract: Advanced electrochemical energy storage devices (EESDs) that can store electrical energy efficiently while being miniature/flexible/wearable/load-bearing are much needed for various applications ranging from flexible/wearable/portable electronics to lightweight electric vehicles/aerospace equipment. Carbon-based fibers hold great promise in the development of these advanced EESDs (e.g., supercapacitors and batteries) due to their being lightweight, high electrical conductivity, excellent mechanical strength, flexibility, and tunable electrochemical performance. This review summarizes the fabrication techniques of carbon-based fibers, especially carbon nanofibers, carbon-nanotube-based fibers, and graphene-based fibers, and various strategies for improving their mechanical, electrical, and electrochemical performance. The design, assembly, and potential applications of advanced EESDs from these carbon-based fibers are highlighted. Finally, the challenges and future opportunities of carbon-based fibers for advanced EESDs are discussed.

Layered Transition Metal Dichalcogenide-Based Nanomaterials for Electrochemical Energy Storage.

Abstract: The rapid development of electrochemical energy storage (EES) systems requires novel electrode materials with high performance. A typical 2D nanomaterial, layered transition metal dichalcogenides (TMDs) are regarded as promising materials used for EES systems due to their large specific surface areas and layer structures benefiting fast ion transport. The typical methods for the preparation of TMDs and TMD-based nanohybrids are first summarized. Then, in order to improve the electrochemical performance of various kinds of rechargeable batteries, such as lithium-ion batteries, lithium-sulfur batteries, sodium-ion batteries, and other types of emerging batteries, the strategies for the design and fabrication of layered TMD-based electrode materials are discussed. Furthermore, the applications of layered TMD-based nanomaterials in supercapacitors, especially in untraditional supercapacitors, are presented. Finally, the existing challenges and promising future research directions in this field are proposed.

Ti3C2Tx MXene-Reduced Graphene Oxide Composite Electrodes for Stretchable Supercapacitors.

Abstract: The development of stretchable electronics requires the invention of compatible high-performance power sources, such as stretchable supercapacitors and batteries. In this work, two-dimensional (2D) titanium carbide (Ti3C2Tx) MXene is being explored for flexible and printed energy storage devices by fabrication of a robust, stretchable high-performance supercapacitor with reduced graphene oxide (RGO) to create a composite electrode. The Ti3C2Tx/RGO composite electrode combines the superior electrochemical and mechanical properties of Ti3C2Tx and the mechanical robustness of RGO resulting from strong nanosheet interactions, larger nanoflake size, and mechanical flexibility. It is found that the Ti3C2Tx/RGO composite electrodes with 50 wt % RGO incorporated prove to mitigate cracks generated under large strains. The composite electrodes exhibit a large capacitance of 49 mF/cm2 (∼490 F/cm3 and ∼140 F/g) and good electrochemical and mechanical stability when subjected to cyclic uniaxial (300%) or biaxial (200% × 200%) strains. The as-assembled symmetric supercapacitor demonstrates a specific capacitance of 18.6 mF/cm2 (∼90 F/cm3 and ∼29 F/g) and a stretchability of up to 300%. The developed approach offers an alternative strategy to fabricate stretchable MXene-based energy storage devices and can be extended to other members of the large MXene family.

Graphene and graphene oxide based aerogels: Synthesis, characteristics and supercapacitor applications

Abstract: Graphene and graphene-based materials have a high potential, especially in energy storage technology. Thanks to the three-dimensional (3D) structures developed with this material, their importance in the production and application of energy storage devices has increased. Studies on supercapacitor applications of graphene-based aerogels have begun to arouse interest in recent years. In this study, recent studies on aerogel supercapacitors, in which researchers have shown great interest, have been compiled and collected. In this study, production methods and properties of graphene oxide, properties and production of aerogels, production and applications of graphene/graphene oxide aerogels are discussed. In this way, the data is presented and discussed in an organized way for the researchers who study or who want to study in this field.

An Ultrafast Conducting Polymer@MXene Positive Electrode with High Volumetric Capacitance for Advanced Asymmetric Supercapacitors

Abstract: Pseudocapacitors or redox capacitors that synergize the merits of batteries and double-layer capacitors are among the most promising candidates for high-energy and high-power energy storage applications. 2D transition metal carbides (MXenes), an emerging family of pseudocapacitive materials with ultrahigh rate capability and volumetric capacitance, have attracted much interest in recent years. However, MXenes have only been used as negative electrodes as they are easily oxidized at positive (anodic) potential. To construct a high-performance MXene-based asymmetric device, a positive electrode with a compatible performance is highly desired. Herein, an ultrafast polyaniline@MXene cathode prepared by casting a homogenous polyaniline layer onto a 3D porous Ti3 C2 Tx MXene is reported, which enables the stable operation of MXene at positive potentials because of the enlarged work function after compositing with polyaniline, according to the first-principle calculations. The resulting flexible polyaniline@MXene positive electrode demonstrates a high volumetric capacitance of 1632 F cm-3 and an ultrahigh rate capability with 827 F cm-3 at 5000 mV s-1 , surpassing all reported positive electrodes. An asymmetric device is further fabricated with MXene as the anode and polyaniline@MXene as the cathode, which delivers a high energy density of 50.6 Wh L-1 and an ultrahigh power density of 127 kW L-1 .

Electrode material–ionic liquid coupling for electrochemical energy storage

Abstract: The development of new electrolyte and electrode designs and compositions has led to advances in electrochemical energy-storage (EES) devices over the past decade. However, focusing on either the electrode or electrolyte separately is insufficient for developing safer and more efficient EES devices in various working environments, as the energy-storage ability is determined by the ion arrangement and charge and/or electron transfer at the electrode–electrolyte interface. In this Review, we assess the fundamental physicochemical and electrochemical properties at the electrode–electrolyte interfaces in Li-ion batteries and supercapacitors using safe and electrochemically stable ionic-liquid electrolytes. Key reactions and interactions at the electrode–electrolyte interface, as well as geometric constraints and temperature effects, are highlighted. Building on the fundamental understanding of interfacial processes, we suggest potential strategies for designing stable and efficient ionic-liquid-based EES devices with emerging electrode materials. The development of efficient, high-energy and high-power electrochemical energy-storage devices requires a systems-level holistic approach, rather than focusing on the electrode or electrolyte separately. In this Review, we discuss the interfacial reactions and ion transport in ionic-liquid-based Li-ion batteries and supercapacitors, and summarize their impact on device performance.

3D-Printed Structure Boosts the Kinetics and Intrinsic Capacitance of Pseudocapacitive Graphene Aerogels.

Abstract: The performance of pseudocapacitive electrodes at fast charging rates are typically limited by the slow kinetics of Faradaic reactions and sluggish ion diffusion in the bulk structure. This is particularly problematic for thick electrodes and electrodes highly loaded with active materials. Here, a surface-functionalized 3D-printed graphene aerogel (SF-3D GA) is presented that achieves not only a benchmark areal capacitance of 2195 mF cm-2 at a high current density of 100 mA cm-2 but also an ultrahigh intrinsic capacitance of 309.1 µF cm-2 even at a high mass loading of 12.8 mg cm-2 . Importantly, the kinetic analysis reveals that the capacitance of SF-3D GA electrode is primarily (93.3%) contributed from fast kinetic processes. This is because the 3D-printed electrode has an open structure that ensures excellent coverage of functional groups on carbon surface and facilitates the ion accessibility of these surface functional groups even at high current densities and large mass loading/electrode thickness. An asymmetric device assembled with SF-3D GA as anode and 3D-printed GA decorated with MnO2 as cathode achieves a remarkable energy density of 0.65 mWh cm-2 at an ultrahigh power density of 164.5 mW cm-2 , outperforming carbon-based supercapacitors operated at the same power density.

Synthesis and Characterization of a NiCo2O4@NiCo2O4 Hierarchical Mesoporous Nanoflake Electrode for Supercapacitor Applications

Abstract: In this study, we synthesized binder-free NiCo2O4@NiCo2O4 nanostructured materials on nickel foam (NF) by combined hydrothermal and cyclic voltammetry deposition techniques followed by calcination at 350 °C to attain high-performance supercapacitors. The hierarchical porous NiCo2O4@NiCo2O4 structure, facilitating faster mass transport, exhibited good cycling stability of 83.6% after 5000 cycles and outstanding specific capacitance of 1398.73 F g−1 at the current density of 2 A·g−1, signifying its potential for energy storage applications. A solid-state supercapacitor was fabricated with the NiCo2O4@NiCo2O4 on NF as the positive electrode and the active carbon (AC) was deposited on NF as the negative electrode, delivering a high energy density of 46.46 Wh kg−1 at the power density of 269.77 W kg−1. This outstanding performance was attributed to its layered morphological characteristics. This study explored the potential application of cyclic voltammetry depositions in preparing binder-free NiCo2O4@NiCo2O4 materials with more uniform architecture for energy storage, in contrast to the traditional galvanostatic deposition methods.

Probing the energy conversion process in piezoelectric-driven electrochemical self-charging supercapacitor power cell using piezoelectrochemical spectroscopy.

Abstract: The design and development of self-charging supercapacitor power cells are rapidly gaining interest due to their ability to convert and store energy in an integrated device. Here, we have demonstrated the fabrication of a self-charging supercapacitor using siloxene sheets as electrodes and siloxene-based polymeric piezofiber separator immobilized with an ionogel electrolyte. The self-charging properties of the fabricated device subjected to various levels of compressive forces showed their ability to self-charge up to a maximum of 207 mV. The mechanism of self-charging process in the fabricated device is discussed via “piezoelectrochemical effect” with the aid of piezoelectrochemical spectroscopy measurements. These studies revealed the direct evidence of the piezoelectrochemical phenomenon involved in the energy conversion and storage process in the fabricated device. This study can provide insight towards understanding the energy conversion process in self-charging supercapacitors, which is of significance considering the state of the art of piezoelectric driven self-charging supercapacitors. Devices that are capable of energy harvesting and storage are attractive for meeting daily energy demands, however they are limited by efficiency. Here the authors fabricate a siloxene-based self-charging supercapacitor power cell and probe the piezoelectrochemical effect involved in the charging process.