Flexible three-dimensional carbon cloth/carbon fibers/NiCo2O4 composite electrode materials for high-performance all-solid-state electrochemical capacitors

Well-designed sophisticated structure of sandwich-like CC@NiAl-LDH@GO@NiCo-LDH material with unique advantages for high performance and practicality hybrid quasi-solid-state supercapacitors

A sandwich-like flexible architecture electrode material composed of NiAl-LDH nanoplates grown on carbon cloths (CC), coupled with GO interlayer and NiCo-LDH nanowire on the interlayer was successfully assembled via hydrothermal and chemical bath deposition (denoted as CC@NiAl-LDH@GO@NiCo-LDH). The promising combination of NiAl-LDH, graphene and NiCo-LDH forming a multilayer structure through electrostatic absorption and in-situ growth process which endow a high mass loading superiority and synergistic effect for supercapacitors. In addition, the interspace inside the sandwich-like architecture constructed by the graphene and the NiAl-LDH/ NiCo-LDH nano-flakes contribute to alleviate of the volume expansion during the cycling process and promote the diffusion rate of ions. The CC@NiAl-LDH@GO@NiCo-LDH material demonstrates excellent electrochemical performance which exhibit remarkable specific capacitance of 2359.8F·g^-1 (14.2F·cm^-2) at 1 A·g^-1 (6 mA·cm^-2) and outstanding capacitance retentions of 93.1% after 1500 cycles. Subsequently, the CC@NiAl-LDH@GO@NiCo-LDH material was used as cathode material to fabricate a hybrid quasi-solid-state supercapacitor that exhibits a high energy density of 52.0 Wh·kg^-1 at 796.7 W·kg^-1 and 38.4 Wh·kg^-1 at 12015 W·kg^-1, revealing its potential and viability for commercial applications. Furthermore, the hybrid quasi-solid-state supercapacitor can be applied under different extreme operating conditions such as bending, twisting, sour/alkali soaking, ice bathing, warm bathing, hammering and cutting conditions. It is predictable that the unique sandwich-like structure will be an extremely promising electrode material for high-performance supercapacitors.

Preparation of Electrode Materials Based on Carbon Cloth via Hydrothermal Method and Their Application in Supercapacitors

Supercapacitors have the unique advantages of high power density, fast charge and discharge rates, long cycle life, high safety, and reliability, and are increasingly being used for applications including automobiles, rail transit, communication equipment, digital electronics, and aerospace equipment. The supercapacitor industry is currently in a stage of rapid development; great breakthroughs have also been made in improving the performance of supercapacitors and the expansion of their application. Electrode technology is the core of supercapacitors. Transition-metal compounds have a relatively high theoretical capacity and have received widespread attention as electrode materials for supercapacitors. In addition, there is a synergistic effect between the different components of various electrode composite materials. Due to their superior electrochemical performance, supercapacitors are receiving increasing research attention. Flexible supercapacitors have been hailed for their good plasticity, resulting in a development boom. This review article mainly outlines the development process of various electrode materials, including carbon materials, conductive polymers, metal compounds, and composite materials, as well as flexible electrode materials based on carbon cloth.

Carbon Transition-metal Oxide Electrodes: Understanding the Role of Surface Engineering for High Energy Density Supercapacitors

Supercapacitors store electrical energy by ion adsorption at the interface of the electrode-electrolyte (electric double layer capacitance, EDLC) or through faradaic process involving direct transfer of electrons via oxidation/reduction reactions at one electrode to the other (pseudocapacitance). The present minireview describes the recent developments and progress of carbon-transition metal oxides (C-TMO) hybrid materials that show great promise as an efficient electrode towards supercapacitors among various material types. The review describes the synthetic methods and electrode preparation techniques along with the changes in the physical and chemical properties of each component in the hybrid materials. The critical factors in deriving both EDLC and pseudocapacitance storage mechanisms are also identified in the hope of pointing to the successful hybrid design principles. For example, a robust carbon-metal oxide interaction was identified as most important in facilitating the charge transfer process and activating high energy storage mechanism, and thus methodologies to establish a strong carbon-metal oxide contact are discussed. Finally, this article concludes with suggestions for the future development of the fabrication of high-performance C-TMO hybrid supercapacitor electrodes.

Achieving High Lithium Storage Capacity and Long-Term Cyclability of Novel Cobalt Germanate Hydroxide/Reduced Graphene Oxide Anodes with Regulated Electrochemical Catalytic Conversion Process of Hydroxyl Groups

To develop ternary transition-metal germanate anodes with superior lithium storage performances for lithium-ion batteries, a novel capacity counterbalance approach in one compound is designed by introducing an electrocatalytic conversion-type component with a positive cycling trend to compensate the negative cycling trend of the GeO₂ component. Novel cobalt germanate hydroxide (CGH) nanoplates chemically bonded on reduced graphene oxide (RGO) sheets are thus synthesized with a mild one-pot hydrothermal approach, constructing maximal face-to-face contact interfaces with interfacial bonds to boost the electrochemical conversion reactions. Furthermore, the hydroxyl groups (Co-OH) of CGH nanoplates are regulated by thermal annealing treatments, thus controlling the capacity contribution resulting from the electrocatalytic conversion reaction of LiOH to exactly offset the capacity fading of GeO₂. The results on the CGH electrodes at different cycling potentials confirm the stepwise electrochemical reactions of Co, GeO₂, and LiOH. The equilibrium of these electrochemical reactions ensures a stable cycling capacity without obvious fluctuations. Consequently, the optimal CGH/RGO hybrid anode delivers a reversible capacity as high as 1136 mA h g^-1 at 0.1 A g^-1 until 100 cycles. It also exhibits a long cyclability with a retained capacity of 560 mA h g^-1 at 1 A g^-1 until 1000 cycles. This work demonstrates a general and efficient capacity counterbalance method to highly boost lithium storage performances in terms of high capacity and long-term cyclability.

Formation of Nanodimensional NiCoO2 Encapsulated in Porous Nitrogen-Doped Carbon Submicrospheres from a Bimetallic (Ni, Co) Organic Framework toward Efficient Lithium Storage

Recently, rock-salt NiCoO₂ (NCO) with desirable electronic conductivity has drawn enormous interest worldwide for energy-related applications. However, the intrinsically sluggish kinetics and electrode aggregation/volumetric change/pulverization during Li-insertion/-extraction processes hugely limit its applications in Li-ion batteries (LIBs). In the contribution, we first devise a bottom-up method for scalable fabrication of the nanodimensional NCO particles encapsulated in porous nitrogen-doped carbon submicrospheres (NCS), which are derived from a bimetal (Ni, Co) metal-organic framework. The porous NCS, as a flexible conductive skeleton, can buffer distinct volume expansion as an efficient buffering phase, restrain agglomeration of nanoscaled NCO, and enhance electronic conductivity and wettability of the electrode. Benefiting from the synergistic functions between the nanodimensional NCO and porous NCS, the obtained NCO@NCS anode (∼74.5 wt % NCO) is endowed with remarkable high-rate reversible capacity (∼403.0 mAh g^-1 at 1.0 A g^-1) and cycling behaviors (∼371.4 mAh g^-1 after being cycled for 1000 times at 1.0 A g^-1) along with a high lithium diffusion coefficient and remarkable pseudocapacitive contribution. Furthermore, the NCO@NCS-based full LIBs exhibit competitive lithium-storage properties in terms of energy density (∼217.0 Wh kg^-1) and cyclic stability. Furthermore, we believe that the methodology is highly promising in versatile design and construction of binary metal oxide/carbon hybrid anodes for advanced LIBs.

A facile approach to prepare a flexible sandwich-structured supercapacitor with rGO-coated cotton fabric as electrodes

In recent years, the energy supply problem of wearable electronic equipment has become a topic of increasing concern. It is necessary to develop energy storage equipment with environmental protection, flexibility, a light quality and excellent performance. In this work, a solid, flexible and symmetrical supercapacitor based on graphene coated cotton fabric was fabricated. The flexible electrode materials were prepared through an environmentally friendly “dry-coating” method and subsequent “two step reduction” method of chemical and microwave reduction, the method is simple and convenient. The morphology and structure of prepared flexible electrode materials were characterized by scanning electron microscopy, X-ray diffraction, and Raman spectrometry. The supercapacitor was assembled in a sandwich structure and packaged and its electrochemical performance was investigated. The flexible sandwich structure (FSS) supercapacitor exhibits high capacitance (464 F g⁻¹ at 0.25 A g⁻¹), good cycling stability (91.6% capacitance retention after 1000 charge and discharge cycles) and excellent electrochemical stability. This supercapacitor with easy fabrication, flexible and excellent electrochemical performance has potential to be used as a wearable device.

In recent years, the energy supply problem of wearable electronic equipment has become a topic of increasing concern. In this work, a solid, flexible and symmetrical supercapacitor based on graphene coated cotton fabric was fabricated.

Interlaced NiMn-LDH nanosheet decorated NiCo2O4 nanowire arrays on carbon cloth as advanced electrodes for high-performance flexible solid-state hybrid supercapacitors

3D hierarchical NiCo₂O₄@NiMn-LDH nanowire/nanosheet arrays have been successfully fabricated on carbon cloth as superior battery-type electrode for high-performance flexible solid-state HSC devices.

Fabrication of three-dimensional composite textile electrodes by metal-organic framework, zinc oxide, graphene and polyaniline for all-solid-state supercapacitors

Textile electrode materials have attracted intense attention in the flexible supercapacitor field due to their flexibility, light weight, hierarchical porosity and mechanical robustness. However, their electrochemical performance is not good due to the low conductivity, ineffective ion diffusion and small electroactive surface area. In this study, a three-dimensional (3D) textile electrode material was constructed by utilizing ZIF-8 (Zeolitic Imidazolate Framework), metal oxides, conductive polymers and graphene sheets. The polyaniline/ZnO/ZIF-8/graphene/polyester textile electrode exhibited good electrochemical performance with a high areal capacitance of 1.378 F/cm² at 1 mA/cm² and high stability under different mechanical deformations. A flexible all-solid-state symmetric supercapacitor device was further fabricated, which can provide a high energy density of 235 μWh/cm³ at a power density of 1542 μW/cm³.

Hybrid MnO2@NiCo2O4 nanosheets for high performance asymmetric supercapacitors

In this work, hybrid MnO₂@NiCo₂O₄ nanosheets grown on Ni foam have been synthesized through a facile hydrothermal approach. The MnO₂@NiCo₂O₄ electrode delivers a high specific capacitance of 3086 mF cm⁻² at a current density of 2 mA cm⁻².