A High Energy Density Asymmetric Supercapacitor from Nano‐architectured Ni(OH)2/Carbon Nanotube Electrodes

The demand for advanced energy storage devices such as supercapacitors and lithium‐ion batteries has been increasing to meet the application requirements of hybrid vehicles and renewable energy systems. A major limitation of state‐of‐art supercapacitors lies in their relatively low energy density compared with lithium batteries although they have superior power density and cycle life. Here, we report an additive‐free, nano‐architectured nickel hydroxide/carbon nanotube (Ni(OH)₂/CNT) electrode for high energy density supercapacitors prepared by a facile two‐step fabrication method. This Ni(OH)₂/CNT electrode consists of a thick layer of conformable Ni(OH)₂ nano‐flakes on CNT bundles directly grown on Ni foams (NFs) with a very high areal mass loading of 4.85 mg cm^?2 for Ni(OH)₂. Our Ni(OH)₂/CNT/NF electrode demonstrates the highest specific capacitance of 3300 F g^?1 and highest areal capacitance of 16 F cm^?2, to the best of our knowledge. An asymmetric supercapacitor using the Ni(OH)₂/CNT/NF electrode as the anode assembled with an activated carbon (AC) cathode can achieve a high cell voltage of 1.8 V and an energy density up to 50.6 Wh/kg, over 10 times higher than that of traditional electrochemical double‐layer capacitors (EDLCs).     

High‐Performance Hybrid Supercapacitor Enabled by a High‐Rate Si‐based Anode

A hybrid supercapacitor constructed of a Si‐based anode and a porous carbon cathode is demonstrated with both high power and energy densities. Boron‐doping is employed to improve the rate capability of the Si‐based anode (B‐Si/SiO₂/C). At a high current density of 6.4 A/g, B‐Si/SiO₂/C delivers a capacity of 685 mAh/g, 2.4 times that of the undoped Si/SiO₂/C. Benefiting from the high rate performance along with low working voltage, high capacity, and good cycling stability of B‐Si/SiO₂/C, the hybrid supercapacitor exhibits a high energy density of 128 Wh/kg at 1229 W/kg. Even when power density increases to the level of a conventional supercapacitor (9704 W/kg), 89 Wh/kg can be obtained, the highest values of any hybrid supercapacitor to date. Long cycling life (capacity retention of 70% after 6000 cycles) and low self‐discharge rate (voltage retention of 82% after 50 hours) are also achieved. This work opens an avenue for development of high‐performance hybrid supercapacitors using high‐performance Si‐based anodes.     

Advances on Emerging Materials for Flexible Supercapacitors: Current Trends and Beyond

The progressive size reduction of electronic components is experiencing bottlenecks in shrinking charge storage devices like batteries and supercapacitors, limiting their development into wearable and flexible zero‐pollution technologies. The inherent long cycle life, rapid charge–discharge patterns, and power density of supercapacitors rank them superior over other energy storage devices. In the modern market of zero‐pollution energy devices, currently the lightweight formula and shape adaptability are trending to meet the current requirement of wearables. Carbon nanomaterials have the potential to meet this demand, as they are the core of active electrode materials for supercapacitors and texturally tailored to demonstrate flexible and stretchable properties. With this perspective, the latest progress in novel materials from conventional carbons to recently developed and emerging nanomaterials toward lightweight stretchable active compounds for flexi‐wearable supercapacitors is presented. In addition, the limitations and challenges in realizing wearable energy storage systems and integrating the future of nanomaterials for efficient wearable technology are provided. Moreover, future perspectives on economically viable materials for wearables are also discussed, which could motivate researchers to pursue fabrication of cheap and efficient flexible nanomaterials for energy storage and pave the way for enabling a wide‐range of material‐based applications.     

A High‐Performance Sodium‐Ion Hybrid Capacitor Constructed by Metal–Organic Framework–Derived Anode and Cathode Materials

Sodium‐ion hybrid capacitors (SIHCs) can potentially combine the virtues of high‐energy density of batteries and high‐power output as well as long cycle life of capacitors in one device. The key point of constructing a high‐performance SIHC is to couple appropriate anode and cathode materials, which can well match in capacity and kinetics behavior simultaneously. In this work, a novel SIHC, coupling a titanium dioxide/carbon nanocomposite (TiO₂/C) anode with a 3D nanoporous carbon cathode, which are both prepared from metal–organic frameworks (MOFs, MIL‐125 (Ti) and ZIF‐8, respectively), is designed and fabricated. The robust architecture and extrinsic pseudocapacitance of TiO₂/C nanocomposite contribute to the excellent cyclic stability and rate capability in half‐cell. Hierarchical 3D nanoporous carbon displays superior capacity and rate performance. Benefiting from the merits of structures and performances of anode and cathode materials, the as‐built SIHC achieves a high energy density of 142.7 W h kg^?1 and a high power output of 25 kW kg^?1 within 1–4 V, as well as an outstanding life span of 10 000 cycles with over 90% of the capacity retention. The results make it competitive in high energy and power–required electricity storage applications.     

Fabrication of Hybrid Supercapacitor by MoCl5 Precursor-Assisted Carbonization with Ultrafast Laser for Improved Capacitance Performance

Hybrid supercapacitors use electric double-layer capacitance and Faradaic pseudocapacitance as energy storage mechanisms. This type of supercapacitor is becoming a prime candidate for next-generation energy storage devices, with advantages in terms of energy density, specific capacitance, and life cycle. However, reducing the electrode area and increasing the specific capacitance of hybrid supercapacitors remain challenging. In this study, a MoCl₅ Precursor-assisted Ultrafast Laser Carbonization (MPAULC) method to fabricate symmetric hybrid supercapacitors with improved capacitance and reduced size is proposed. The method uses an ultrafast laser to induce the formation of carbon/MoO₃ composite with the assistance of the MoCl5 precursor. This ultrafast laser carbonization method exhibited high processing precision. The role of the precursor in laser processing is studied using time-resolved imaging and temperature calculations. The specific area capacitance of the C/MoO₃ hybrid supercapacitor is 11.85 mF cm⁻², 9.2 times higher than that of the laser-induced carbon supercapacitor without precursor. The MPAULC method provides a reliable pathway for fabricating miniaturized hybrid supercapacitors with carbon/metal oxide composite electrodes on polymer substrates.     

Preparation of MnCo2O4@Ni(OH)2 Core–Shell Flowers for Asymmetric Supercapacitor Materials with Ultrahigh Specific Capacitance

Supercapacitors have attracted much interest in the past decades owing to their important applications, but most of them are focused on solitary or simple metal oxides. Here, a novel supercapacitor electrode composed of multicomponent MnCo₂O₄@Ni(OH)₂ belt‐based core–shell nanoflowers is reported by a facile and cost‐effective method. This hybrid electrode exhibits a significantly enhanced specific capacitance. An asymmetric supercapacitor based on this unique hybrid nanoflowers as anode and an activated carbon film as cathode demonstrates high energy density, high power density, and long cycling lifespan.     

Fast and Large Lithium Storage in 3D Porous VN Nanowires–Graphene Composite as a Superior Anode Toward High‐Performance Hybrid Supercapacitors

Li‐ion hybrid capacitors (LIHCs), consisting of an energy‐type redox anode and a power‐type double‐layer cathode, are attracting significant attention due to the good combination with the advantages of conventional Li‐ion batteries and supercapacitors. However, most anodes are battery‐like materials with the sluggish kinetics of Li‐ion storage, which seriously restrict the energy storage of LIHCs at the high charge/discharge rates. Herein, vanadium nitride (VN) nanowire is demonstated to have obvious pseudocapacitive characteristic of Li‐ion storage and can get further gains in energy storage through a 3D porous architecture with the assistance of conductive reduced graphene oxide (RGO). The as‐prepared 3D VN–RGO composite exhibits the large Li‐ion storage capacity and fast charge/discharge rate within a wide working widow from 0.01–3 V (vs Li/Li⁺), which could potentially boost the operating potential and the energy and power densities of LIHCs. By employing such 3D VN–RGO composite and porous carbon nanorods with a high surface area of 3343 m² g^?1 as the anode and cathode, respectively, a novel LIHCs is fabricated with an ultrahigh energy density of 162 Wh kg^?1 at 200 W kg^?1, which also remains 64 Wh kg^?1 even at a high power density of 10 kW kg^?1.     

Low-Cost,Safe, and Ultra-Long Cycle Life Zn–K Hybrid Ion Batteries

Zinc-ion batteries (ZIBs) are viewed as a promising energy storage system for large-scale applications thanks to the low cost and wide accessibility of Zn-based materials, the high theoretical capacity of Zn anode, and their high level of safety. However, the practical application of ZIBs is hindered by the rapid performance degradation. Herein, a Zn–K hybrid ion battery design is proposed using a high-quality Prussian blue cathode and a nonflammable Zn–K hybrid ion electrolyte. The electrochemical process is divided into two parts, with K⁺ insertion/extraction occurring at the cathode side and Zn²⁺ plating/stripping occurring at the anode side, which avoids structure destruction caused by Zn²⁺ insertion in the cathode. The non-flammable electrolyte not only ensures high safety but also effectively suppresses dendrite growth on the Zn anode. The hybrid cells demonstrate a high capacity of 151.0 mAh g⁻¹, a high voltage of 1.74 V (vs Zn²⁺/Zn), and an ultra-long cycle life of 15 000 cycles. Combining the nonflammable nature of the electrolyte, the abundance of raw materials, and good electrochemical performance, the Zn–K hybrid ion battery system promises a promising future for renewable energy storage applications.     

A High‐Energy Lithium‐Ion Capacitor by Integration of a 3D Interconnected Titanium Carbide Nanoparticle Chain Anode with a Pyridine‐Derived Porous Nitrogen‐Doped Carbon Cathode

Lithium‐ion capacitors (LICs) are hybrid energy storage devices that have the potential to bridge the gap between conventional high‐energy lithium‐ion batteries and high‐power capacitors by combining their complementary features. The challenge for LICs has been to improve the energy storage at high charge?discharge rates by circumventing the discrepancy in kinetics between the intercalation anode and capacitive cathode. In this article, the rational design of new nanostructured LIC electrodes that both exhibit a dominating capacitive mechanism (both double layer and pseudocapacitive) with a diminished intercalation process, is reported. Specifically, the electrodes are a 3D interconnected TiC nanoparticle chain anode, synthesized by carbothermal conversion of graphene/TiO₂ hybrid aerogels, and a pyridine‐derived hierarchical porous nitrogen‐doped carbon (PHPNC) cathode. Electrochemical properties of both electrodes are thoroughly characterized which demonstrate their outstanding high‐rate capabilities. The fully assembled PHPNC//TiC LIC device delivers an energy density of 101.5 Wh kg^?1 and a power density of 67.5 kW kg^?1 (achieved at 23.4 Wh kg^?1), and a reasonably good cycle stability (≈82% retention after 5000 cycles) within the voltage range of 0.0?4.5 V.     

A High‐Energy Li‐Ion Battery Using a Silicon‐Based Anode and a Nano‐Structured Layered Composite Cathode

High capacity electrodes based on a Si composite anode and a layered composite oxide cathode, Ni‐rich Li[Ni_0.75Co_0.1Mn_0.15]O₂, are evaluated and combined to fabricate a high energy lithium ion battery. The Si composite anode, Si/C‐IWGS (internally wired with graphene sheets), is prepared by a scalable sol–gel process. The Si/C‐IWGS anode delivers a high capacity of >800 mAh g^?1 with an excellent cycling stability of up to 200 cycles, mainly due to the small amount of graphene (～6 wt%). The cathode (Li[Ni_0.75Co_0.1Mn_0.15]O₂) is structurally optimized (Ni‐rich core and a Ni‐depleted shell with a continuous concentration gradient between the core and shell, i.e., a full concentration gradient, FCG, cathode) so as to deliver a high capacity (>200 mAh g^?1) with excellent stability at high voltage (～4.3 V). A novel lithium ion battery system based on the Si/C‐IWGS anode and FCG cathode successfully demonstrates a high energy density (240 Wh kg^?1 at least) as well as an unprecedented excellent cycling stability of up to 750 cycles between 2.7 and 4.2 V at 1C. As a result, the novel battery system is an attractive candidate for energy storage applications demanding a high energy density and long cycle life.     

Micro‐Supercapacitors Based on Interdigital Electrodes of Reduced Graphene Oxide and Carbon Nanotube Composites with Ultrahigh Power Handling Performance

A novel method for fabricating micro‐patterned interdigitated electrodes based on reduced graphene oxide (rGO) and carbon nanotube (CNT) composites for ultra‐high power handling micro‐supercapacitor application is reported. The binder‐free microelectrodes were developed by combining electrostatic spray deposition (ESD) and photolithography lift‐off methods. Without typically used thermal or chemical reduction, GO sheets are readily reduced to rGO during the ESD deposition. Electrochemical measurements show that the in‐plane interdigital design of the microelectrodes is effective in increasing accessibility of electrolyte ions in‐between stacked rGO sheets through an electro‐activation process. Addition of CNTs results in reduced restacking of rGO sheets and improved energy and power density. Cyclic voltammetry (CV) measurements show that the specific capacitance of the micro‐supercapacitor based on rGO–CNT composites is 6.1 mF cm^?2 at 0.01 V s^?1. At a very high scan rate of 50 V s^?1, a specific capacitance of 2.8 mF cm^?2 (stack capacitance of 3.1 F cm^?3) is recorded, which is an unprecedented performance for supercapacitors. The addition of CNT, electrolyte‐accessible and binder‐free microelectrodes, as well as an interdigitated in‐plane design result in a high‐frequency response of the micro‐supercapacitors with resistive‐capacitive time constants as low as 4.8 ms. These characteristics suggest that interdigitated rGO–CNT composite electrodes are promising for on‐chip energy storage application with high power demands.     

Kinetics Enhanced Nitrogen‐Doped Hierarchical Porous Hollow Carbon Spheres Boosting Advanced Potassium‐Ion Hybrid Capacitors

Potassium‐ion hybrid capacitors (PIHCs) shrewdly combine a battery‐type anode and a capacitor‐type cathode, exhibiting an energy density close to that of potassium ion batteries and a comparable power density of supercapacitors. However, the rosy scenario is compromised by the sluggish kinetics in the PIHCs device. Herein, the kinetics enhanced nitrogen‐doped hierarchical porous hollow carbon spheres (NHCS) are synthesized and successfully applied to PIHCs. As for the K half‐cell, NHCS anchored with sodium alginate delivers excellent electrochemical performance. Further evaluation shows that the binder can significantly affect the potassium storage performance of NHCS by adjusting the coatability and ionic conductivity of the NHCS anode. Moreover, kinetic analysis and density functional theory calculations reveal the origin of the superior electrochemical properties of NHCS. As expected, an advanced PIHC device is assembled with a NHCS anode and an activated NHCS cathode, demonstrating an exceptionally high energy/power density (114.2 Wh kg^?1 and 8203 W kg^?1), along with a long‐life capability. The successful construction of high‐performance PIHCs in this work opens a new avenue for the development and application of PIHCs in the future.     

High‐Performance Sodium‐Ion Hybrid Supercapacitor Based on Nb2O5@Carbon Core–Shell Nanoparticles and Reduced Graphene Oxide Nanocomposites

Sodium‐ion hybrid supercapacitors (Na‐HSCs) have potential for mid‐ to large‐scale energy storage applications because of their high energy/power densities, long cycle life, and the low cost of sodium. However, one of the obstacles to developing Na‐HSCs is the imbalance of kinetics from different charge storage mechanisms between the sluggish faradaic anode and the rapid non‐faradaic capacitive cathode. Thus, to develop high‐power Na‐HSC anode materials, this paper presents the facile synthesis of nanocomposites comprising Nb₂O₅@Carbon core–shell nanoparticles (Nb₂O₅@C NPs) and reduced graphene oxide (rGO), and an analysis of their electrochemical performance with respect to various weight ratios of Nb₂O₅@C NPs to rGO (e.g., Nb₂O₅@C, Nb₂O₅@C/rGO‐70, ‐50, and ‐30). In a Na half‐cell configuration, the Nb₂O₅@C/rGO‐50 shows highly reversible capacity of ≈285 mA h g^?1 at 0.025 A g^?1 in the potential range of 0.01–3.0 V (vs Na/Na⁺). In addition, the Na‐HSC using the Nb₂O₅@C/rGO‐50 anode and activated carbon (MSP‐20) cathode delivers high energy/power densities (≈76 W h kg^?1 and ≈20 800 W kg^?1) with a stable cycle life in the potential range of 1.0–4.3 V. The energy and power densities of the Na‐HSC developed in this study are higher than those of similar Li‐ and Na‐HSCs previously reported.     

A Printable Metallic Current Collector for All‐Printed High‐Voltage Micro‐Supercapacitors: Instantaneous Surface Passivation by Flash‐Light‐Sintering Reaction

Recently, a printable power source that can be implemented on demand in integrated circuitries has gained tremendous attention to facilitate next‐generation, form‐factor free, miniaturized electronic systems. Among various energy storage units, a solid‐state micro‐supercapacitor with in‐plane device architecture has been recognized as a viable candidate with characteristic advantages of long cycle life‐time, high frequency response, and fast charge/discharge rate. However, to date, high performance, all‐printed micro‐supercapacitors have rarely been reported owing to an absence of printable current collector materials that can sustain high voltage conditions. In this study, a multidimensional printable particle mixture comprising Ni nanoparticles, Ni flakes, and a photoreactive polymer, polyvinylpyrrolidone is proposed. The highly conductive, printed metallic current collector is generated with a conductive surface passivation layer in a timescale of 10^?3 s by flash‐light sintering process. It is revealed that the resulting metallic current collector is stable at a voltage as high as 3 V in the carbon electrode‐based device, enabling the fabrication of an all‐printed solid‐state micro‐supercapacitor with an areal energy density of 79–23 mJ cm^?2 at an areal power density of 0.4–12.8 mW cm^?2. Arbitrarily designed device circuits can be generated on demand simply by using a digitally programmable printing process, without incorporation of additional interconnection lines.     

Advanced Asymmetric Supercapacitors Based on Ni(OH)2/Graphene and Porous Graphene Electrodes with High Energy Density

Hierarchical flowerlike nickel hydroxide decorated on graphene sheets has been prepared by a facile and cost‐effective microwave‐assisted method. In order to achieve high energy and power densities, a high‐voltage asymmetric supercapacitor is successfully fabricated using Ni(OH)₂/graphene and porous graphene as the positive and negative electrodes, respectively. Because of their unique structure, both of these materials exhibit excellent electrochemical performances. The optimized asymmetric supercapacitor could be cycled reversibly in the high‐voltage region of 0–1.6 V and displays intriguing performances with a maximum specific capacitance of 218.4 F g^?1 and high energy density of 77.8 Wh kg^?1. Furthermore, the Ni(OH)₂/graphene//porous graphene supercapacitor device exhibits an excellent long cycle life along with 94.3% specific capacitance retained after 3000 cycles. These fascinating performances can be attributed to the high capacitance and the positive synergistic effects of the two electrodes. The impressive results presented here may pave the way for promising applications in high energy density storage systems.     

Fe2O3 Nanoneedles on Ultrafine Nickel Nanotube Arrays as Efficient Anode for High‐Performance Asymmetric Supercapacitors

High performance of electrochemical energy storage devices depends on the smart structure engineering of electrodes, including the tailored nanoarchitectures of current collectors and subtle hybridization of active materials. To improve the anode supercapacitive performance of Fe₂O₃ for high‐voltage asymmetric supercapacitors, here, a hybrid core‐branch nanoarchitecture is proposed by integrating Fe₂O₃ nanoneedles on ultrafine Ni nanotube arrays (NiNTAs@Fe₂O₃ nanoneedles). The fabrication process employs a bottom‐up strategy via a modified template‐assisted method starting from ultrafine ZnO nanorod arrays, ensuring the formation of ultrafine Ni nanotube arrays with ultrathin tube walls. The novel developed NiNTAs@Fe₂O₃ nanoneedle electrode is demonstrated to be a highly capacitive anode (418.7 F g^?1 at 10 mV s^?1), matching well with the similarly built NiNTAs@MnO₂ nanosheet cathode. Contributed by the efficient electron collection paths and short ion diffusion paths in the uniquely designed anode and cathode, the asymmetric supercapacitors exhibit an excellent maximum energy density of 34.1 Wh kg^?1 at the power density of 3197.7 W kg^?1 in aqueous electrolyte and 32.2 Wh kg^?1 at the power density of 3199.5 W kg^?1 in quasi‐solid‐state gel electrolyte.     

Conformal Multifunctional Titania Shell on Iron Oxide Nanorod Conversion Electrode Enables High Stability Exceeding 30 000 Cycles in Aqueous Electrolyte

Iron oxide is promising for use in aqueous energy storage devices due to the high capacity, but one of the most challenging problems is cycling instability within the large potential window that results from the complete quasi‐conversion reaction. Herein, a conformal surface coating strategy toward iron oxide via atomic layer deposition (ALD) is presented and an Fe₃O₄@TiO₂ core–shell nanorod array anode is reported that exhibits remarkable cycling performance exceeding 30 000 times within a wide potential window in neutral lithium salt electrolyte. ALD offers a uniform and precisely controllable TiO₂ shell that not only buffers the inner volume expansion of Fe₃O₄, but also contributes extra capacity through Li⁺ intercalation/de‐intercalation and helps to alleviate the water electrolysis. Furthermore, by pairing with a pseduocapacitive cathode of V₂O₃@carbon and using a hydrogel electrolyte of PVA‐LiCl, a unique flexible quasi‐solid‐state hybrid supercapacitor can be assembled. With a high voltage of 2.0 V, the device delivers high volumetric energy and power densities (2.23 mWh cm^?3, 1090 mW cm^?3), surpassing many recently reported flexible supercapacitors. This work highlights the importance of ALD conformal multifunctional shell to instable nanoarray electrodes in aqueous electrolytes and brings new opportunities to design advanced aqueous hybrid energy storage devices.     

Large‐Area Reduced Graphene Oxide Composite Films for Flexible Asymmetric Sandwich and Microsized Supercapacitors

Asymmetric supercapacitors have attracted tremendous attention in energy storage devices since they have an enhanced energy density in comparison with symmetric supercapacitor devices. Furthermore, the development of diverse and flexible electronic devices requires the asymmetric supercapacitor devices to be flexible and in various configurations. However, it is still a challenge to develop a universal strategy to obtain both capacitive and Faradic electrodes with various architectures. Herein, a spontaneously reducing/assembling strategy in an alkaline condition is developed to fabricate large‐area reduced graphene oxide (RGO) and RGO–metal oxide/hydroxide composite films or microsized structures. As a proof of concept, the large‐area pure RGO and RGO/Mn₃O₄ composite films with porous structure and superior mechanical property are achieved by such strategy. These RGO‐based films can directly serve as the anodes and cathodes of the flexible asymmetric film supercapacitors. Furthermore, the interdigital RGO and RGO/Mn₃O₄ patterns are also obtained via a selectively reducing/assembling process to achieve the asymmetric microsized supercapacitors. These asymmetric supercapacitors with different configurations possess good electrochemical performance and excellent flexibility. Therefore, such reducing and assembling strategy provides a route to achieve large‐area RGO‐based films and microsized structures for the applications in the various fields such as energy storage and photocatalysis.     

High‐Performance Supercapacitor Applications of NiO‐Nanoparticle‐Decorated Millimeter‐Long Vertically Aligned Carbon Nanotube Arrays via an Effective Supercritical CO2‐Assisted Method

Nickel oxide (NiO) nanoparticles are distributed uniformly in the vertically aligned carbon nanotube arrays (VACNTs) with millimeter thickness by an effective supercritical carbon dioxide‐assisted method. The as‐prepared VACNT/NiO hybrid structures are used as electrodes without binders and conducting additives for supercapacitor applications. Due to the synergetic effects of NiO and VACNTs with nanoporous structures and parallel 1D conductive paths for electrons, the supercapacitors exhibit a high capacitance of 1088.44 F g^?1. Furthermore, an asymmetric supercapacitor is assembled using the as‐synthesized VACNTs/NiO hybrids as the positive electrode and the VACNTs as the negative electrode. Remarkably, the energy density of the asymmetric supercapacitor is as high as 90.9 Wh kg^?1 at 3.2 kW kg^?1 and the maximum power density reaches 25.6 kW kg^?1 at 24.9 Wh kg^?1, which are superior to those of the NiO or VACNTs‐based asymmetric supercapacitors. More importantly, the asymmetric supercapacitors exhibit capacitance retention of 87.1% after 2000 cycles at 5 A g^?1. The work provides a novel approach in decorating highly dense and long VACNTs with active materials, which are promising electrodes for supercapacitors with ultrahigh power density and energy density.     

Ternary Hybrids of Amorphous Nickel Hydroxide–Carbon Nanotube‐Conducting Polymer for Supercapacitors with High Energy Density,Excellent Rate Capability,and Long Cycle Life

The utilization of Ni(OH)₂ as a pseudocapacitive material for high performance supercapacitors is hindered by its low electrical conductivity and short cycle life. A coaxial ternary hybrid material comprising of amorphous Ni(OH)₂ deposited on multiwalled carbon nanotubes wrapped with conductive polymer (poly (3,4‐ethylenedioxythiophene)‐poly(styrenesulfonate)) is demonstrated. A thin layer of disordered amorphous Ni(OH)₂ is deposited by an effective “coordinating etching and precipitating” method, resulting in an ultrahigh specific capacitance of 3262 F g^?1 at 5 mV s^?1 and excellent rate capability (71.9% capacitance retention at 100 mV s^?1). More importantly, the polymer layer prevents the degradation of the nanostructure and dis­solution of Ni ion during repeated charge–discharge cycling for 30 000 cycles, a phenomenon which often plagues Ni(OH)₂ nanomaterials. Using the ternary Ni(OH)₂ hybrid and the reduced graphene oxide/carbon nanotube hybrid as the positive and negative electrodes, respectively, the assembled asymmetric supercapacitors exhibit high energy density of 58.5 W h kg^?1 at the power density of 780 W kg^?1 as well as long cycle life (86% capacitance retention after 30 000 cycles). The ternary hybrid architecture design for amorphous Ni(OH)₂ can be regarded as a general approach to obtain pseudocapacitive materials for supercapacitors with both high energy density, excellent rate capability, and long cycle life.