A high-performance asymmetric supercapacitors based on hydrogen bonding nanoflower-like polypyrrole and NiCo(OH)2 electrode materials

Ultrafast Microwave-Assisted Synthesis of Porous NiCo Layered Double Hydroxide Nanospheres for High-Performance Supercapacitors

Currently, new clean energy storage technology must be effective, affordable, and ecologically friendly so as to meet the diverse and sustainable needs of the energy supply. In this work, NiCo-LDH containing intercalated EG was successfully prepared within 210 s using an ultrafast microwave radiation technique. Subsequently, a series of characterization and systematic electrochemical tests were conducted to analyze the composition, structure, and energy storage mechanism of the NiCo-LDH material. The Ni:Co ratio of 5:5 results in the highest capacitance value of 2156 F/g at 1 A/g and an outstanding rate performance of 86.8% capacity retention rate at 10 A/g. The results demonstrated that the unique porous structure of NiCo-LDH and large layer spacing were conducive to more electrochemical reactions. Additionally, an electrochemical test was carried out on the NiCo-LDH as a hybrid supercapacitor electrode material, with NiCo-LDH-5:5 serving as the positive electrode and activated carbon as the negative electrode, the asymmetric supercapacitor can achieve a maximum energy density of 82.5 Wh kg-1 and power density of 8000 W kg-1. The NiCo-LDH-5:5//AC hybrid supercapacitors own 81.5% cycle stability and 100% coulombic efficiency after 6000 cycles at 10 A/g.

3D Hierarchically Structured Tin Oxide and Iron Oxide-Embedded Carbon Nanofiber with Outermost Polypyrrole Layer for High-Performance Asymmetric Supercapacitor

Herein, unique three-dimensional (3D) hierarchically structured carbon nanofiber (CNF)/metal oxide/conducting polymer composite materials were successfully synthesized by combinations of various experimental methods. Firstly, base CNFs were synthesized by carbonization of electrospun PAN/PVP fibers to attain electric double-layer capacitor (EDLC) characteristics. To further enhance the capacitance, tin oxide (SnO₂) and iron oxide (Fe₂O₃) were coated onto the CNFs via facile hydrothermal treatment. Finally, polypyrrole (PPy) was introduced as the outermost layer by a dispersion polymerization method under static condition to obtain 3D-structured CNF/SnO₂/PPy and CNF/Fe₂O₃/PPy materials. With each synthesis step, the morphology and dimension of materials were transformed, which also added the benign characteristic for supercapacitor application. For the practical application, as-synthesized CNF/SnO₂/PPy and CNF/Fe₂O₃/PPy were applied as active materials for supercapacitor electrodes, and superb specific capacitances of 508.1 and 426.8 F g^-1 (at 1 A g^-1) were obtained (three-electrode system). Furthermore, an asymmetric supercapacitor (ASC) device was assembled using CNF/SnO₂/PPy as the positive electrode and CNF/Fe₂O₃/PPy as the negative electrode. The resulting CNF/SnO₂/PPy//CNF/Fe₂O₃/PPy device exhibited excellent specific capacitance of 101.2 F g^-1 (at 1 A g^-1). Notably, the ASC device displayed a long-term cyclability (at 2000 cycles) with a retention rate of 81.1%, compared to a CNF/SnO₂//CNF/Fe₂O₃ device of 70.3% without an outermost PPy layer. By introducing the outermost PPy layer, metal oxide detachment from CNFs were prevented to facilitate long-term cyclability of electrodes. Accordingly, this study provides an effective method for manufacturing a high-performance and stable supercapacitor by utilizing unique 3D hierarchical materials, comprised of CNF, metal oxide, and conducting polymer.

A 2H-MoS2/carbon cloth composite for high-performance all-solid-state supercapacitors derived from a molybdenum dithiocarbamate complex

A molecular complex Mo₂O₂(μ-S)₂(Et₂dtc)₂ (dtc = dithiocarbamate) is prepared and loaded onto carbon cloth (CC) through facile solvothermal treatment, followed by subsequent single-source pyrolysis. This results in a highly porous 2H-MoS₂/CC composite with a sponge-like stacked lamellar morphology. Due to its high porosity and unique nano/microstructure, the MoS₂/CC composite exhibits a specific capacitance of 550.0 F g^-1 at 1 A g^-1, outperforming some 1T-MoS₂ based electrodes. The composite is further assembled into a symmetric all-solid-state supercapacitor, which can be operated stably at a wide potential window and shows a specific capacitance of 127.5 F g^-1 at 1 A g^-1. In addition, the device delivers a high energy density of 70.8 W h kg^-1 at 1 kW kg^-1, which still remains 15.0 W h kg^-1 at 18.0 kW kg^-1. 75% of the performance of the device can be retained after 8000 cycles. Such remarkable electrochemical performance is attributed to its novel nano/microstructures with a large surface area, convenient ion transport pathways, enhanced conductivity, and improved structural stability. Thus, this work demonstrates a highly promising dithiocarbamate-based single-precursor pyrolysis route towards the fabrication of metal sulfides/carbon composites for energy storage applications.

Polypyrrole-Based Metal Nanocomposite Electrode Materials for High-Performance Supercapacitors

Metallic nanostructures (MNs) and metal-organic frameworks (MOFs) play a pivotal role by articulating their significance in high-performance supercapacitors along with conducting polymers (CPs). The interaction and synergistic pseudocapacitive effect of MNs with CPs have contributed to enhance the specific capacitance and cyclic stability. Among various conjugated heterocyclic CPs, polypyrrole (PPy) (prevalently knows as “synthetic metal”) is exclusively studied because of its excellent physicochemical properties, ease of preparation, flexibility in surface modifications, and unique molecular structure–property relationships. Numerous researchers attempted to improve the low electronic conductivity of MNs and MOFs, by incorporating conducting PPy and/or used decoration strategy. This was succeeded by fine-tuning this objective, which managed to get outstanding supercapacitive performances. This brief technical note epitomizes various PPy-based metallic hybrid materials with different nano-architectures, emphasizing its technical implications in fabricating high-performance electrode material for supercapacitor applications.

True Meaning of Pseudocapacitors and Their Performance Metrics: Asymmetric versus Hybrid Supercapacitors

The development of pseudocapacitive materials for energy-oriented applications has stimulated considerable interest in recent years due to their high energy-storing capacity with high power outputs. Nevertheless, the utilization of nanosized active materials in batteries leads to fast redox kinetics due to the improved surface area and short diffusion pathways, which shifts their electrochemical signatures from battery-like to the pseudocapacitive-like behavior. As a result, it becomes challenging to distinguish "pseudocapacitive" and "battery" materials. Such misconceptions have further impacted on the final device configurations. This Review is an earnest effort to clarify the confusion between the battery and pseudocapacitive materials by providing their true meanings and correct performance metrics. A method to distinguish battery-type and pseudocapacitive materials using the electrochemical signatures and quantitative kinetics analysis is outlined. Taking solid-state supercapacitors (SSCs, only polymer gel electrolytes) as an example, the distinction between asymmetric and hybrid supercapacitors is discussed. The state-of-the-art progress in the engineering of active materials is summarized, which will guide for the development of real-pseudocapacitive energy storage systems.

A polypyrrole-adorned, self-supported, pseudocapacitive zinc vanadium oxide nanoflower and nitrogen-doped reduced graphene oxide-based asymmetric supercapacitor device for power density applications

Herein, a distinctive approach has been implemented for exploiting a typical battery material zinc vanadium oxide (ZV) as a supercapacitor electrode material.

Interlayer Hydrogen-Bonded Metal Porphyrin Frameworks/MXene Hybrid Film with High Capacitance for Flexible All-Solid-State Supercapacitors

2D metal-porphyrin frameworks (MPFs) are attractive for advanced energy storage devices. However, the inferior conductivity and low structural stability of MPFs seriously limit their application as flexible free-standing electrodes with high performance. Here, for the first time, an interlayer hydrogen-bonded MXene/MPFs film is proposed to overcome these disadvantages by intercalation of highly conductive MXene nanosheets into MPFs nanosheets via a vacuum-assisted filtration technology. The alternant insertion of MXene and MPFs affords 3D interconnected "MPFs-to-MXene-to-MPFs" conductive networks to accelerate the ionic/electronic transport rates. Meanwhile, the interlayer hydrogen bonds (F···HO and O···HO) contribute a high chemical stability due to a favorable tolerance to volume change caused by phase separation and structural collapse during the charge/discharge process. The synergistic effect makes MXene/MPFs film deliver a capacitance of 326.1 F g^-1 at 0.1 A g^-1 , 1.64 F cm^-2 at 1 mA cm^-2 , 694.2 F cm^-3 at 1 mA cm^-3 and a durability of about 30 000 cycles. The flexible symmetric supercapacitor shows an areal capacitance of 408 mF cm^-2 , areal energy density of 20.4 µW h cm^-2 , and capacitance retention of 95.9% after 7000 cycles. This work paves an avenue for the further exploration of 2D MOFs in flexible energy storage devices.