High-performance Electrochemical Energy Storage Devices Research Articles

Unveiling magnetite metal-organic frameworks for asymmetric pseudo-supercapacitor with high energy density and magnetocapacitance

Utilizing innovative techniques for electrode fabrication and incorporating novel energy storage concepts through external stimuli forces is crucial for enhancing the specific capacity and commercial feasibility of energy storage devices. The performance of supercapacitors hinges on both capacitive behavior, which enhances charge-discharge characteristics and power density, and ion-diffusion behavior, which boosts energy density. This study delves into the impact of external magnetic fields on supercapacitor performance by enhancing pseudo-capacitive behavior through a facile redox pathway and promoting the diffusion coefficient of the electrolyte. We presented magneto-electrophoretic deposition (M-EPD) to apply a high-surface-area zeolitic imidazolate framework (ZIF), which serves as a robust binder-free strategy. Specifically, the Fe3O4-ZIF-67 nanocomposite is uniformly supported on ferromagnetic nickel foam (NF) and demonstrates an impressive specific capacitance of 656.7 F g−1 (328.4 C g−1) at 1 A g−1. In addition, coin cell supercapacitors assembled with Fe3O4-ZIF-67/NF as positive and Fe3O4-ZIF-67-MWCNT/CF as negative electrodes achieve outstanding energy density (103.3 W h kg−1) at a power density of 750 W kg−1, coupled with excellent cycling stability (83.61 % capacity retention) after 10,000 cycles at 20 A g−1. Notably, the cell exhibits superior magnetocapacitance and the highest diffusion coefficient under an external magnetic field of 100 mT. The energy density reaches 163.2 W h kg−1 at a power density of 750 W kg−1, with a coulombic efficiency of 77.7 %. This represents a 1.58-fold enhancement compared to the absence of the magnetic field. The results demonstrated that ferromagnetic coupling between metal−oxygen−metal centers is enhanced via oxygen 2p orbitals, thereby creating a facile pseudocapacitance mechanism. The ZIF-67 shell further regulates the charge-discharge behavior of the electrode through the interplay between diffusive and capacitive mechanisms. This work introduces a promising new approach for preparing high-surface-area MOF-based electrodes and stimuli-responsive, high-performance electrochemical energy storage devices.

Electrodeposited Co0.85Se/Ni3Se2 heterostructure as an efficient binder-free cathode for fast electrochemical energy storage devices

In this study, a facile technique was developed to generate a bimetallic Co0.85Se/Ni3Se2 heterostructure through a straightforward one-step electrodeposition process. The resulting structure proved to be an efficient cathode for fast charge/discharge electrochemical energy storage devices. The composition and morphology of the cathode can be easily adjusted by varying the molar ratio of Co/Ni precursors. The optimized Co0.85Se/Ni3Se2 (3:1) electrode demonstrated an impressive specific capacity of 141.9 mAh g−1 at a current density of 1 A g−1. It retained a capacity of 103.5 mAh g−1 at a high current density of 8 A g−1 due to its heterostructure nature. The assembled hybrid supercapacitor (HSC) device based on this optimized cathode achieved remarkable energy and power densities. Additionally, the Co0.85Se/Ni3Se2 (3:1) electrode was successfully demonstrated in micro-HSC (μ-HSC) applications, exhibiting favorable cycling stability during 480-h floating tests. These findings suggest that the synthesized Co0.85Se/Ni3Se2 cathode has great potential for use in high-performance electrochemical energy storage devices.

One-step synthesis of g-C3N4/TiVCTx MXene electrodes for lithium-ion batteries and supercapacitors

The wide-ranging application of lithium-ion batteries (LIBs) is currently restricted by their slow ion dynamics and low capacity, which hinders the development of innovative electrode materials. Herein, the graphitic carbon nitride (g-C3N4)/TiVCTx composite was fabricated through in situ pyrolysis of urea to generate g-C3N4 nanosheets on the surface of TiVCTx nanosheets. The as-prepared g-C3N4 protective layer can reduce the degree of oxidation of TiVCTx MXene, restrain the re-stacking of TiVCTx nanosheets and minimize the risk of undesirable side reactions. As expected, the g-C3N4/TiVCTx electrode exhibits remarkable specific capacity of 1025.3 mAh/g after 150 cycles at 0.1 A/g and 558.3 mAh/g after 1000 cycles at 1.0 A/g for LIBs and a high specific capacitance of 508.9F g−1 in 0.5 M Na2SO4 electrolyte at 1.0 A/g after 7000 cycles for supercapacitors (SCs). Furthermore, the assembled g-C3N4/TiVCTx-30//LiFePO4 full cell presents stable specific capacity of 505.5 mAh/g at 0.1 A/g after 100 cycles and 255.2 mAh/g at 0.1 A/g along with a Coulombic efficiency of 97.9 % after 50 cycles at − 20 °C, demonstrating excellent low temperature tolerance. Density functional theory (DFT) calculation results indicated that the g-C3N4/TiVCTx-30 exhibits strongest adsorption capacity for Li+ with an adsorption energy of −3.85 eV. The introduction of g-C3N4 improves the insertion and extraction kinetics of Li+, effectively reducing the diffusion barrier. Consequently, the g-C3N4/TiVCTx-30 electrode exhibits potential application prospects in high-performance electrochemical energy storage devices. Our work provides valuable insights and significant research implications for improving the specific capacity and stability of TiVCTx MXene in the field of energy storage.

Boosting the pseudocapacitance of BiFeO3 by Zn doping for flexible battery-supercapacitor hybrid devices

Perovskite BiFeO3 (BFO) as a type of battery-type electrode materials, usually suffers from poor electrolyte ion transport in the BFO crystal. We propose a novel strategy of Zn doping to improve the ion transport and boost the faradaic pseudocapacitance of BFO for flexible battery-supercapacitor hybrid (BSH) devices. The Zn-doped BFO (Z-BFO-1) with the low Zn doping content, can maintain the crystal structure of BFO and the uniform distributions of elements. The oxygen vacancy content can be increased from BFO to Z-BFO-1, reflecting the influence of the Zn doping on the crystal structure of BFO. The Z-BFO-1 electrode with the stable crystal structure in the charge/discharge process, can provide the highest specific capacitance (223 F g−1 at 0.2 A/g) and the largest Li+ diffusion coefficient (2.386 × 10−11 cm2 s−1) among these BFO-based electrodes with different Zn doping contents. The first-principles calculations reveal that the Zn doping in BFO can significantly enhance the built-in electric fields and greatly lower the Li+ migration energy barriers (from 2.08 eV to 1.43 eV). This flexible MnO2//Z-BFO-1 BSH device with the high energy density (37.5 Wh kg−1 at 0.23 kW kg−1), opens up a new avenue for developing high-performance electrochemical energy storage devices.

Metal Phosphide Anodes in Sodium-Ion Batteries: Latest Applications and Progress.

Sodium-ion batteries (SIBs), as the next-generation high-performance electrochemical energy storage devices, have attracted widespread attention due to their cost-effectiveness and wide geographical distribution of sodium. As a crucial component of the structure of SIBs, the anode material plays a crucial role in determining its electrochemical performance. Significantly, metal phosphide exhibits remarkable application prospects as an anode material for SIBs because of its low redox potential and high theoretical capacity. However, due to volume expansion limitations and other factors, the rate and cycling performance of metal phosphides have gradually declined. To address these challenges, various viable solutions have been explored. In this paper, the recent research progress of metal phosphide materials for SIBs is systematically reviewed, including the synthesis strategy of metal phosphide, the storage mechanism of sodium ions, and the application of metal phosphide in electrochemical aspects. In addition, future challenges and opportunities based on current developments are presented.

Alternately electrodeposited mesoporous NiCoSe2@MnO2 nanocomposite-anchored Ni-Co layered double hydroxide nanoneedles for hybrid supercapacitors

A rational strategy for preparing effective electrode materials is crucial for high-performance electrochemical energy storage devices. Herein, a facile route is developed to construct hierarchical composite electrodes (NiCoLDH@NiCoSe2@MnO2) consisting of...

Comprehensive characterization of a Mn0.1Mg0.9Fe2O4/CeO2/MgFe2O4 nanocomposite for high-performance supercapacitor applications

Metal oxide nanocomposites have grown in popularity in the field of electrochemical devices due to their numerous advantages, such as a large active surface area and high chemical stability. However, it is crucial to emphasize that the structural properties of these metal oxide nanocomposites are crucial in molding their electrochemical performance. Using solvothermal reflux and auto-combustion techniques (Mn0.1Mg0.9Fe2O4/CeO2/MgFe2O4) comprising Mn0.1Mg0.9Fe2O4, CeO2, and MgFe2O4 was successfully produced. This nanocomposite was used to construct high-performance electrochemical energy storage devices, notably battery-type applications. This nanocomposite crystal structure, morphology, and elemental composition were thoroughly examined. The electrochemical performance of the synthesized nanocomposite was examined using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) using a 6 M KOH electrolyte solution to acquire a thorough grasp of its properties. When tested at a current density of 1 A/g, the composite electrode demonstrated an impressive specific capacity (Cs) of 368.7 C/g. Even after 5000 charge-discharge cycles, the Mn0.1Mg0.9Fe2O4/CeO2/MgFe2O4 nanocomposite electrode retained 93 % of its capacity retention. These findings definitively establish the Mn0.1Mg0.9Fe2O4/CeO2/MgFe2O4 nanocomposite as a top choice for energy storage systems.

Fabrication of ZnSnO3@In2O3 core-shell based 1D microfiber heterostructure for high energy density asymmetric supercapacitors

Core-shell microfibers have witnessed a substantial demand surge in developing supercapacitors (SCs) owing to their enhanced conductivity, high surface area, and structural stability. Here, we report a facile low-cost electrospun ZnSnO3 @In2O3 core-shell microfibers heterostructure for SC application. The distinct fibrous morphology and synergistic incorporation of Zinc (Zn), Tin (Sn), and Indium (In) demonstrate significantly enhanced electrochemical performance while assembled in an asymmetric SC (ASC) by utilizing ZnSnO3 @In2O3 core-shell as positive and activated carbon (AC) as negative electrode. The ASC device exhibits an excellent specific capacitance of 160 F/g at 1 A/g along with a maximum specific energy of 40 Wh/kg. The ASC also records 86.95% capacitance retention with an exceptional 90% coulombic efficiency retention over 15,000 cycles at 15 A/g. This novel ZnSnO3 @In2O3 core-shell//AC signifies great potential in achieving high-performance electrochemical energy storage devices.

Direct Ink Writing 3D Printing for High-Performance Electrochemical Energy Storage Devices: A Minireview.

Despite tremendous efforts that have been dedicated to high-performance electrochemical energy storage devices (EESDs), traditional electrode fabrication processes still face the daunting challenge of limited energy/power density or compromised mechanical compliance. 3D thick electrodes can maximize the utilization of z-axis space to enhance the energy density of EESDs but still suffer from limitations in terms of poor mechanical stability and sluggish electron/ion transport. Direct ink writing (DIW), an eminent branch of 3D printing technology, has gained popularity in the manufacture of 3D electrodes with intricately designed architectures and rationally regulated porosity, promoting a triple boost in areal mass loading, ion diffusion kinetics, and mechanical flexibility. This focus review highlights the fundamentals of printable inks and typical configurations of 3D-printed devices. In particular, preparation strategies for high-performance and multifunctional 3D-printed EESDs are systemically discussed and classified according to performance evaluation metrics such as high areal energy density, high power density, high volumetric energy density, and mechanical flexibility. Challenges and prospects for the fabrication of high-performance 3D-printed EESDs are outlined, aiming to provide valuable insights into this thriving field.

Biological treatment as a green approach for enhancing electrochemical performance of wood derived carbon based supercapacitor electrodes

Wood-derived biochar is an eco-friendly and porous carbon material that can be used to prepare supercapacitor electrodes. For the purpose of addressing the deficiencies in the specific surface area and pore structure of wood-derived carbon as the raw material of electrodes, a biological pre-treatment method was developed to construct the desirable pore structure of wood by leveraging the lignin-degrading property of white-rot fungi. First, white-rot fungi with permeability and biodegradability on lignocellulosic substrates were used to regulate the pore structure of natural paulownia wood, which was then carbonized to produce a porous hyphae/wood-derived carbon conductive substrate. Afterward, manganese dioxide (MnO2) was deposited on the substrate to fabricate the MnO2/hyphae/wood-derived carbon (HWC-3M) electrode by the hydrothermal method. The degradation of lignin by white-rot fungi broke the original pore structure of wood, strengthened effective channels in the cell walls, and facilitated the loading of MnO2 into the channels to improve the ion transport rate. The HWC-3M had richer energy storage sites, more electrolyte ion transport channels, and better electrochemical performance than the control electrode made of untreated wood-derived carbon (HWC-0), showing an excellent areal specific capacitance (3395 mF/cm2 at a current density of 1.0 mA/cm2), moderate gravimetric specific capacitance (138.3 F/g), and good cycling stability (retention of 88.6% after 2000 cycles). The results indicate that pretreating wood-derived carbon composite electrode with white-rot fungi serves as a new green approach to develop high-performance electrochemical energy storage devices.

Nanocellulose-based advanced materials for flexible supercapacitor electrodes

Nanocellulose is sustainable, has excellent properties and a unique structure that can be used to create environmentally friendly supercapacitor electrodes with pore structures. Supercapacitor, as a high-performance electrochemical energy storage device, has the advantages of high power density, long cycle life, fast charging and discharging, and high energy density. Currently, the problem of energy depletion is becoming more and more serious, and in order to solve this problem, people are beginning to replace traditional petroleum-based materials with environmentally friendly biomass-based materials. Nanocellulose, as a derivative of cellulose, the most widely distributed biomass in nature, has high specific surface area, biodegradability, high strength and good dispersibility. This review discusses and summarizes the latest research on nanocellulose-based supercapacitor electrode materials. First, the physical and chemical properties of nanocellulose and the preparation strategy are presented. Second, the types of electrodes are introduced in terms of electrodes with nanocellulose as substrate and those with other support materials. Next, recent studies on the use of these electrodes for flat supercapacitors and fiber-based supercapacitors are presented. Finally, the future prospects and challenges of using nanocellulose in supercapacitor electrode materials are outlined.

MXenes for Zinc-Based Electrochemical Energy Storage Devices.

As an economical and safer alternative to lithium, zinc (Zn) is promising for realizing new high-performance electrochemical energy storage devices, such as Zn-ion batteries, Zn-ion hybrid capacitors, and Zn-air batteries. Well-designed electrodes are needed to enable efficient Zn electrochemistry for energy storage. Two-dimensional transition metal carbides and nitrides (MXenes) are emerging materials with unique electrical, mechanical, and electrochemical properties and versatile surface chemistry. They are potential material candidates for constructing high-performance electrodes of Zn-based energy storage devices. This review first briefly introduces the working mechanisms of the three Zn-based energy storage devices. Then, the recent progress on the synthesis, chemical functionalization, and structural design of MXene-based electrodes is summarized. Their performance in Zn-based devices is analyzed to establish relations between material properties, electrode structures, and device performance. Last, several research topics are proposed to be addressed for developing practical MXene-based electrodes for Zn-based energy storage devices to enable their commercialization and broad adoption in the near future.

Editorial: Interface and structure designs of electrode materials for advanced electrochemical energy storage

The increasing demand for mobile power supplies in electric vehicles has motivated intense research 18 efforts in developing high-performance electrochemical energy storage (EES) devices. However, 19 current EES technologies have not met the requirements for various applications to improve 20 performance and safety, and reduce cost and environmental footprint. Advanced materials, including 21 active anode and cathode materials, inactive carbon and binding additives, metal current collectors, 22 separators, and electrolytes, play the essential role in supporting battery operations. Particularly, the 23 interface engineering of distinct phases or components in composite electrodes and electrolytes, as well 24 as the hierarchical structure design for each component or multi-component device, can address many 25 fundamental issues associated with the charge transport kinetics, electrochemical characteristics, and 26 chemical/physical/mechanical properties. Therefore, it is possible to improve the energy storage 27 performance, reliability, and safety by investigating the interface and structure. 28

Nature-inspired self-activation method for the controllable synthesis of highly porous carbons for high-performance supercapacitors

The specific surface area (SSA) and pore structure are two critical factors that determine the energy storage performance of carbon-based supercapacitors. However, for biobased carbon electrodes, it is difficult to simultaneously control the pore structures and achieve high SSA. Herein, highly porous carbons (HPCs) with ultrahigh SSA and controllable pore structures are produced through hydrogel-controlled carbonization and activation process for glucose. Polyacrylamide (PAM) is used as the pore-forming agent, and pore structures can be regulated by controlling the content of PAM. The highest SSA of the HPCs reaches 3381 m2 g−1 with a 60% PAM content. Compared with the sample without PAM, the specific capacitance of HPCs-60 shows a 63% increase, reaching 441 F g−1 at a current density of 0.25 A g−1. Moreover, a KOH/PVA symmetric supercapacitor assembled from HPCs-60 not only exhibits an excellent energy density (10.9 Wh kg−1 at a power density of 125 W kg−1) but also has high cycling stability (∼10% loss over 20,000 cycles) and good flexibility. The as-prepared supercapacitors can provide stable power supplies for multiple electronic devices, indicating that the HPCs have enormous potential for use in high-performance electrochemical energy storage devices.

Promising sustainable technology for energy storage devices: Natural protein-derived active materials

Electrochemical energy storage devices (EESDs) are critical technologies in modern economy, covering numerous fields such as portable electronics, electric vehicles, etc. The expanding market of EESDs demands for extra requirements such as safety, environmental friendliness and low cost, in addition to increasingly enhanced electrochemical properties. Natural proteins are abundant, versatile bio-macromolecules involving tremendous amount of amino acids/functional groups/heteroatoms, which greatly benefit sustainable technologies for advancing performances of EESDs. Recent years, significant research on utilizing natural proteins including plant/animal proteins to fabricate active materials for enhancing performance of EESDs has been well reported. Therefore, it is important to comprehensively summarize the progress and achievements, analyze the advantages/challenges, and predict the prospective for future protein-based strategies toward high-performance EESDs, which are the contents of this review. The protein-derived active materials include activated carbons, silicon, sulfur, metal alloys, transitional metal compounds, and nonprecious metal catalysts. The resulting EESDs are associated with Li-/Na-/K-ion batteries, metal–air batteries, and redox flow batteries, as well as supercapacitors. The contributions of proteins to stabilizing/protecting electrodes, and thus enhancing performance of EESDs are specifically emphasized. Furthermore, studies on genetical engineering of proteins for directing self-assembly of active material nanoparticles are introduced.

Co-precipitation reaction: A facile strategy for designing hierarchical porous carbon nanosheets for EDLCs and zinc-ion hybrid supercapacitors

Hierarchical porous carbon is a valuable electrode material for electrochemical energy storage devices by virtue of its high specific surface area, excellent conductivity, and large pore volume. Herein, a simple, convenient and cheap self-made Fe-based template strategy is innovated to prepare hierarchical porous carbon employing coal chemical byproducts anthracene as carbon precursor, which is utilized as electrode materials of electrical double layer capacitors (EDLCs) and zinc ions hybrid supercapacitors (ZHSs). Benefiting from the high specific surface area (2085.1 m2 g−1), feasible micropore content (0.28 cm3 g−1), suitable oxygen content (11.57 at%) and two-dimensional nanosheet structure, the optimal sample delivered a high specific capacitance value of 183.5 F g−1 at 0.05 A/g and excellent rate capability (109.5 F g−1 at 20 A/g) for symmetric supercapacitor. Meanwhile, the as-fabricated ZHSs exhibited remarkable specific capacitance (181.67 mAh/g at 0.05 A/g), superior energy density (145.2 Wh kg−1), high power density (14.5 kW kg−1) and splendid cycling stability (∼91.25 % after 40,000 charge/discharge cycles at 2 A g−1). This work affords a new idea for the synthesis of template carbon using a feasible and low-cost co-precipitation reaction route and has great significance for the development of high-performance electrochemical energy storage device.

Biomass-derived two-dimensional carbon materials: Synthetic strategies and electrochemical energy storage applications

Because climate change, environmental pollution and other issues have gradually become the greatest threat to human existence, developing advanced technologies to solve these problems is of vital importance. Electrochemical energy storage devices play an important role in conveniently and efficiently using new energy instead of fossil energy. It is worth noting that biomass is a renewable source of carbon with many advantages, including extensive sources, low cost, and environmental friendliness. Two-dimensional (2D) carbon materials have become significant candidates for electrode materials due to their unique lamellar structure and excellent electrical conductivity. Therefore, the development of 2D carbon materials derived from biomass is a valuable research topic. In particular, biomass-derived 2D carbon materials, a group of promising electrode materials for high-performance electrochemical energy storage devices, have attracted extensive attention because of their high specific surface area, high porosity, and abundant active sites. This review first introduces key synthetic strategies used for developing 2D carbon materials from biomass. Then, applications of biomass-derived 2D carbon materials in a series of electrochemical energy storage and conversion devices, including lithium-ion batteries, lithium-sulfur batteries, sodium/potassium-ion batteries, metal-air batteries, and supercapacitors, are summarized. Meanwhile, various impact factors for their electrochemical performances, such as the biomass source, preparation process and potential development strategies, are noted. Finally, the opportunities and future challenges are discussed.

Interlayer Modulation of Layered Transition Metal Compounds for Energy Storage.

Layered transition metal compounds are one of the most important electrode materials for high-performance electrochemical energy storage devices, such as batteries and supercapacitors. Charge storage in these materials can be achieved via intercalation of ions into the interlayer channels between the layer slabs. With the development of lithium-beyond batteries, larger carrier ions require optimized interlayer space for the unrestricted diffusion in the two-dimensional channels and effectively shielded electrostatic interaction between the slabs and interlayer ions. Therefore, interlayer modulation has become an efficient and promising approach to overcome the problems of sluggish kinetics, structural distortion, irreversible phase transition, dissolution of some transition metal elements, and air instability faced by these materials and thus enhance the overall electrochemical performance. In this review, we focus on the interlayer modulation of layered transition metal compounds for various batteries and supercapacitors. Merits of interlayer modulation on the charge storage procedures of charge transfer, ion diffusion, and structural transformation are first discussed, with emphasis on the state-of-art strategies of intercalation and doping with foreign species. Following the obtained insights, applications of modified layered electrode materials in various batteries and supercapacitors are summarized, which may guide the future development of high-performance and low-cost electrode materials for energy storage.

Toward emerging two-dimensional nickel-based materials for electrochemical energy storage: Progress and perspectives

1 Various 2D Ni-based materials for supercapacitors and batteries are systematically discussed. 2 The connection between different structures and electrochemical performances of 2D Ni-based materials has been given. 3 Strategies for enhancing electrochemical capability of 2D Ni-based materials are outlined. 4 Some perspective about high-performance 2D Ni-Based materials for energy storage applications are presented. Two-dimensional (2D) Ni-based materials have attracted considerable attention due to their distinctive properties, including high electro-activity, large specific surface areas, controllable chemical compositions, and abundant forms of composite materials. Over the last decade, there has been increasing research interest in constructing advanced 2D Ni-based nanomaterials possessing short and open channels with efficient mass diffusion capability and rich accessible active sites for electrochemical energy storage (EES). Herein, the recent advances in developing emerging 2D Ni-based materials involving Ni-based oxides, sulfides, phosphides, selenides, hydroxides, metal-organic framework (MOF), and Ni-rich layered oxides (LiNi x M y M′ z O 2 /NaNi x M y M′ z O 2 ) for EES is reviewed. After a brief summary of crystal structures and synthetic methods of 2D Ni-based materials, design strategies for improving electrochemical performances of 2D Ni-based materials are described in detail through vacancy creation, heteroatoms doping, and 3D nanostructures. Afterward, their applications as electrode materials for EES including supercapacitors, alkali (Li, Na, K)-ion batteries, and multivalent metal (Zn, Mg, Ca)-ion batteries are discussed. This review also discusses the charge storage mechanisms of 2D Ni-based materials by various advanced characterization methods. Finally, the current challenges and research outlook of 2D Ni-based materials toward high performance EES devices are presented.

Hierarchical hybrid electrodes with NiCo2S4 nanosheets and Co4S3 nanocages for high energy density supercapacitors

Transition metal sulfides are gaining attention as a new highly capacitive active material for high-performance supercapacitors, however, it is still a challenge that synthesizes a distinctive structure to enhance the electrochemical characteristics and practical applications. In this work, hierarchical structural hybrid metal sulfides (NiCo2S4/Co4S3) based on nanosheets and nanocages are synthesized by sulfurating the NiCo-LDH/ZIF-67 precursors. The NiCo2S4/Co4S3 electrode with remarkable layered and porous structure effectively increase the electrochemical active surface area and accelerate the charge transfer, achieving a high specific capacitance of 8.43 F cm−2 at a current density of 2 mA cm−2 and good cyclic stability. An assembled asymmetric supercapacitor with activated carbon delivers a high energy density of 0.50 mWh cm−2 at a power density of 1.69 mW cm−2. These results demonstrate that NiCo2S4/Co4S3 is an ideal electrode material for high-performance electrochemical energy storage devices.