Fast-Charging High-Energy Battery-Supercapacitor Hybrid: Anodic Reduced Graphene Oxide-Vanadium(IV) Oxide Sheet-on-Sheet Heterostructure

Fabrication and investigation of a pentamerous composite based on calix[4]arene functionalized graphene oxide grafted with silk fibroin, cobalt ferrite, and alginate

This paper presents a new scaffold made from graphene oxide nanosheets, calix[4]arene supramolecules, silk fibroin proteins, cobalt ferrite nanoparticles, and alginate hydrogel (GO-CX[4]/SF/CoFe2O4/Alg). After preparing the composite, we conducted various analyses to examine its structure. These analyses included FTIR, XRD, SEM, EDS, VSM, DLS, and zeta potential tests. Additionally, we performed tests to evaluate the swelling ratio, rheological properties, and compressive mechanical strength of the material. The biological capability of the composite was tested through biocompatiblity, anticancer, hemolysis, antibacterial anti-biofilm assays. Besides, the rheological properties and swelling behaviour of the composite were studied. The results showed that the scaffold is biocompatible with Hu02 cells and the cell viability percentages of 85.23 %, 82.78 %, and 80.18 % for were acquired for 24, 48, and 72 h, respectively. In contrast, the cell viability percentage of BT549 cancer cells were obtained 65.79 %, 60.45 % and 58.16 % for same period which confirmed notable anticancer activity of the product composite. Moreover, a significant antibacterial growth inhibition against E. coli and S. aureus species highlights its potential as an effective antibacterial agent. Furthermore, the observed minimal hemolytic effect (6.56 %) and strong inhibition of P. aeruginosa biofilm formation with a low OD value (0.24) indicate notable hemocompatibility and antibacterial activity.

Competitive Redox Chemistries in Vanadium Niobium Oxide for Ultrafast and Durable Lithium Storage

Niobium pentoxide (Nb2O5) anodes have gained increasing attentions for high-power lithium-ion batteries owing to the outstanding rate capability and high safety. However, Nb2O5 anode suffers poor cycle stability even after modified and the unrevealed mechanisms have restricted the practical applications. Herein, the over-reduction of Nb5+ has been demonstrated to be the critical reason for the capacity loss for the first time. Besides, an effective competitive redox strategy has been developed to solve the rapid capacity decay of Nb2O5, which can be achieved by the incorporation of vanadium to form a new rutile VNbO4 anode. The highly reversible V3+/V2+ redox couple in VNbO4 can effectively inhibit the over-reduction of Nb5+. Besides, the electron migration from V3+ to Nb5+ can greatly increase the intrinsic electronic conductivity for VNbO4. As a result, VNbO4 anode delivers a high capacity of 206.1 mAh g-1 at 0.1 A g-1, as well as remarkable cycle performance with a retention of 93.4% after 2000 cycles at 1.0 A g-1. In addition, the assembled lithium-ion capacitor demonstrates a high energy density of 44 Wh kg-1 at 5.8 kW kg-1. In summary, our work provides a new insight into the design of ultra-fast and durable anodes.

Recent Progress of 2D Layered Materials in Water-in-Salt/Deep Eutectic Solvent-Based Liquid Electrolytes for Supercapacitors

Supercapacitors are candidates with the greatest potential for use in sustainable energy resources. Extensive research is being carried out to improve the performances of state-of-art supercapacitors to meet our increased energy demands because of huge technological innovations in various fields. The development of high-performing materials for supercapacitor components such as electrodes, electrolytes, current collectors, and separators is inevitable. To boost research in materials design and production toward supercapacitors, the up-to-date collection of recent advancements is necessary for the benefit of active researchers. This review summarizes the most recent developments of water-in-salt (WIS) and deep eutectic solvents (DES), which are considered significant electrolyte systems to advance the energy density of supercapacitors, with a focus on two-dimensional layered nanomaterials. It provides a comprehensive survey of 2D materials (graphene, MXenes, and transition-metal oxides/dichalcogenides/sulfides) employed in supercapacitors using WIS/DES electrolytes. The synthesis and characterization of various 2D materials along with their electrochemical performances in WIS and DES electrolyte systems are described. In addition, the challenges and opportunities for the next-generation supercapacitor devices are summarily discussed.

Progressive activation of porous vanadium nitride microspheres with intercalation-conversion reactions toward high performance over a wide temperature range for zinc-ion batteries

Rechargeable aqueous zinc-ion batteries have great promise for becoming next-generation storage systems, although the irreversible intercalation of Zn²⁺ and sluggish reaction kinetics impede their wide application. Therefore, it is urgent to develop highly reversible zinc-ion batteries. In this work, we modulate the morphology of vanadium nitride (VN) with different molar amounts of cetyltrimethylammonium bromide (CTAB). The optimal electrode has porous architecture and excellent electrical conductivity, which can alleviate volume expansion/contraction and allow for fast ion transmission during the Zn²⁺ storage process. Furthermore, the CTAB-modified VN cathode undergoes a phase transition that provides a better framework for vanadium oxide (VO_x). With the same mass of VN and VO_x, VN provides more active material after phase conversion due to the molar mass of the N atom being less than that of the O atom, thus increasing the capacity. As expected, the cathode displays an excellent electrochemical performance of 272 mAh g^-1 at 5 A g^-1, high cycling stability up to 7000 cycles, and excellent performance over a wide temperature range. This discovery creates new possibilities for the development of high-performance multivalent ion aqueous cathodes with rapid reaction mechanisms.

Ethanol Solvent Used in Constructing Ultra-Low-Temperature Zinc-Ion Capacitors with a Long Cycling Life

Zinc-ion capacitors (ZICs) gain enormous attraction for their high power density, low cost, and long life, but their poor low-temperature performance is still a challenge due to the dissatisfactory freezing point of aqueous electrolyte solution. It is difficult for them to meet the requirements in cold environments as well as the extreme low temperature and severe temperature fluctuations in aerospace environments. Herein, ethanol (EtOH) solvent with ZnCl₂ is used as an electrolyte to address these issues. Benefiting from the low freezing point (-114 °C) of EtOH, the ZIC with the ZnCl₂/EtOH electrolyte can be operated at an ultralow temperature of -78 °C. It also demonstrates long cycling stability over 30,000 cycles. Such an enhancement is attributed to the unique properties of [ZnCl(EtOH)₅]⁺ that can stabilize the coordination environment of Zn²⁺, slow the diffusivity, and raise the nucleation overpotential, leading to uniform Zn plating/stripping and subsequently suppressing dendrite growth. Meanwhile, the lower activation energy in ZnCl₂/EtOH than that in ZnSO₄/H₂O electrolytes endows the ZIC excellent charge transfer properties. This work provides a fascinating electrolyte and a feasible pathway for ultra-low-temperature ZICs with a long cycling life.

Fabrication and Development of Binder-Free Mn-Fe-S Mixed Metal Sulfide Loaded Ni-Foam as Electrode for the Asymmetric Coin Cell Supercapacitor Device

Currently, the fast growth and advancement in technologies demands promising supercapacitors, which urgently require a distinctive electrode material with unique structures and excellent electrochemical properties. Herein, binder-free manganese iron sulfide (Mn-Fe-S) nanostructures were deposited directly onto Ni-foam through a facile one-step electrodeposition route in potentiodynamic mode. The deposition cycles were varied to investigate the effect of surface morphologies on Mn-Fe-S. The optimized deposition cycles result in a fragmented porous nanofibrous structure, which was confirmed using Field Emission Scanning Electron Microscopy (FE-SEM). X-ray photoelectron spectroscopy (XPS) confirmed the presence of Mn, Fe, and S elements. The energy dispersive X-ray spectroscopy and elemental mapping revealed a good distribution of Mn, Fe, and S elements across the Ni-foam. The electrochemical performance confirms a high areal capacitance of 795.7 mF cm-2 with a 24 μWh cm-2 energy density calculated at a 2 mA cm-2 current density for porous fragmented nanofiber Mn-Fe-S electrodes. The enhancement in capacitance is due to diffusive-controlled behavior dominating the capacitator, as shown by the charge-storage kinetics. Moreover, the assembled asymmetric coin cell device exhibited superior electrochemical performance with an acceptable cyclic performance of 78.7% for up to 95,000 consecutive cycles.

Towards two-dimensional color tunability of all-solid-state electrochromic devices using carbon dots

Electrochromic devices (ECDs) that display multicolor patterns have gradually attracted widespread attention. Considering the complexity in the integration of various electrochromic materials and multi-electrode configurations, the design of multicolor patterned ECDs based on simple approaches is still a big challenge. Herein, it is demonstrated vivid ECDs with broadened color hues via introducing carbon dots (CDs) into the ion electrolyte layer. Benefiting from the synergistic effect of electrodes and electrolytes, the resultant ECDs presented a rich color change. Significantly, the fabricated ECDs can still maintain a stable and reversible color change even in high temperature environments where operating temperatures are constantly changing from RT to 70°C. These findings represent a novel strategy for fabricating multicolor electrochromic displays and are expected to advance the development of intelligent and portable electronics.

Cobalt vanadium chalcogenide microspheres decorated with dendrite-like fiber nanostructures for flexible wire-typed energy conversion and storage microdevices

The increasing energy demand for next-generation portable and miniaturized electronics has drawn tremendous attention to develop microscale energy storage and conversion devices with light weight and flexible characteristics. Herein, we report the preparation of flower-like cobalt vanadium selenide/nickel copper selenide (CoVSe/NiCuSe) microspheres with three-dimensional hierarchical structure of micropore growth on copper wire for a flexible fiber microsupercapacitor (microSC) and overall water splitting. The CoV-LDH microspheres are anchored on the dendrite-like NiCu nanostructured Cu wire using a hydrothermal method (CoV-LDH/NiCu@CW). The sulfidation and selenization of CoV-LDH/NiCu was carried out through the ion-exchange reaction of OH^- with sulfide and selenide ions to obtain CoVS/NiCuS@CW and CoVSe/NiCuSe@CW electrodes, respectively. Benefitting from the unique structure, the flower-like CoVSe/NiCuSe@CW microspheres exhibit better electrochemical performance compared with other as-prepared fiber-shaped electrodes. As an electrode active material for microSC, CoVSe/NiCuSe microspheres exhibit a specific capacitance of 35.40 F cm^-3 at 4 mA cm^-2, and maintain 281.25 F cm^-3 even at a high current density of 83 mA cm^-2, indicating outstanding charge storage capacitance and excellent rate capability. Moreover, the assembled flexible solid-state asymmetric microSCs based on flower-like CoVSe/NiCuSe microspheres-coated Cu wire as the positive electrode and polypyrrole/reduced graphene oxide-coated carbon fiber as the negative electrode manifests a maximum energy density of 20.17 mW h cm^-3 at a power density of 624.32 mW cm^-3 and remarkable cycling stability (96.7% after 5000 cycles) with good mechanical stability. As an electrocatalyst for oxygen and hydrogen evolution reactions in alkaline medium, the CoVSe/NiCuSe electrode delivers an overpotential of 297 mV and 165 mV at 100 mA cm^-2. Furthermore, the CoVSe/NiCuSe-based electrolysis cell for overall water splitting presents a low cell voltage (1.7 V at 50 mA cm^-2) as well as high durability.

Scalable Spray Drying Production of Amorphous V2 O5 -EGO 2D Heterostructured Xerogels for High-Rate and High-Capacity Aqueous Zinc Ion Batteries

Rechargeable aqueous zinc-ion batteries (ZIBs) are promising in stationary grid energy storage due to their advantages in safety and cost-effectiveness, and the search for competent cathode materials is one core task in the development of ZIBs. Herein, the authors design a 2D heterostructure combining amorphous vanadium pentoxide and electrochemically produced graphene oxide (EGO) using a fast and scalable spray drying technique. The unique 2D heterostructured xerogel is achieved by controlling the concentration of EGO in the precursor solution. Driven by the improved electrochemical kinetics, the resultant xerogel can deliver an excellent rate capability (334 mAh g^-1 at 5 A g^-1 ) as well as a high specific capacity (462 mAh g^-1 at 0.2 A g^-1 ) as the cathode material in ZIB. It is also shown that the coin cell constructed based on spray-dried xerogel can output steady, high energy densities over a broad power density window. This work provides a scalable and cost-effective approach for making high performance electrode materials from cheap sources through existing industrialized materials processing.

Fabrication of VO Nanorings on a Porous Carbon Architecture for High-Performance Li-Ion Batteries

Vanadium monoxide (VO) is a promising candidate as an anode for lithium-ion batteries due to its high theoretical capacity, low cost, and considerable electronic conductivity. Unfortunately, a large volume change during electrochemical processes obstructs its practical application. In this work, a composite of VO nanorings grown on a porous carbon architecture is prepared via a topochemical self-reduction approach. When used as an anode for lithium-ion batteries, improved redox kinetics from enhanced electronic conduction and the corresponding fast lithium-ion diffusion is observed to greatly promote the electrochemical performance of lithium-ion batteries. The resulting composite delivered a reversible capacity of 336 mA h g^-1 after 400 cycles at 10 A g^-1 with a capacity retention of 85%, owing to the synergistic effect of VO nanorings and porous carbon in alleviating volume changes that result in a long-term cycling ability at a high current density. At 20 A g^-1, the composite anode exhibited a rate capability of 235 mA h g^-1, superior to all VO-based electrodes reported in the literature. Furthermore, a full cell was first fabricated by employing VO@C-2 as the anode and LiFePO₄ as the cathode, which exhibited a capacity of 213 mA h g^-1 after 100 cycles at 0.1 A g^-1, indicating the potential of VO as an anode for practical application.

Interfacial Engineered Vanadium Oxide Nanoheterostructures Synchronizing High-Energy and Long-Term Potassium-Ion Storage

Potassium ion hybrid capacitors (KICs) have drawn tremendous attention for large-scale energy storage applications because of their high energy and power densities and the abundance of potassium sources. However, achieving KICs with high capacity and long lifespan remains challenging because the large size of potassium ions causes sluggish kinetics and fast structural pulverization of electrodes. Here, we report a composite anode of VO2-V2O5 nanoheterostructures captured by a 3D N-doped carbon network (VO2-V2O5/NC) that exhibits a reversible capacity of 252 mAh g-1 at 1 A g-1 over 1600 cycles and a rate performance with 108 mAh g-1 at 10 A g-1. Quantitative kinetics analyses demonstrate that such great rate capability and cyclability are enabled by the capacitive-dominated potassium storage mechanism in the interfacial engineered VO2-V2O5 nanoheterostructures. The further fabricated full KIC cell consisting of a VO2-V2O5/NC anode and an active carbon cathode delivers a high operating voltage window of 4.0 V and energy and power densities up to 154 Wh kg-1 and 10 000 W kg-1, respectively, surpassing most state-of-the-art KICs.

2D Silicene Nanosheets for High-Performance Zinc-Ion Hybrid Capacitor Application

Supercapacitors possessing fast-charging characteristics and long lifespan are becoming increasingly important for powering portable and smart energy storage devices, and combining capacitive and battery-type materials into an integrated device is an effective method for increasing the overall performance of capacitors. Silicene is being designed as a cathode for the development of enhanced capacitance and ultra-cycle stable zinc-ion hybrid capacitors. Possessing a maximum areal capacity of 14 mF cm^-2, a maximum power density of 9 mW cm^-2, capacitance retention of 112% even after 10 000 cycles, and an unexpectedly high energy density of 23 mJ cm^-2, this achievement of the zinc-ion hybrid capacitor would be superior to that of previously reported silicon-based supercapacitors. The DFT calculations further reveal that Zn ions dominate the capacitive behavior of the silicene electrode. The support association between silicene and zinc-ion hybrid capacitors so that they can take advantage of each other's strengths, which takes electrochemical energy technology to a stage, offering a straightforward proposal for integration and implementation of silicon-based materials.

Zn induced NiCo composites modified by carbon materials as a battery-type electrode material for high-performance supercapacitors

The development of simple preparation and excellent capacity performance electrode materials is the key to energy conversion and storage for supercapacitors. Based on the growth mechanism of crystal, Zn induced NiCo nanosheets and nanoneedles composite structure deposed on Ni foam (ZNC) are successfully attained by a facile one-step method, the growth mechanism of the composite structure is further discussed. Because of its unique composites structure and additional modification of carbon, the carbon modified ZNC (ZNC@C) delivers better energy storage ability (2280 mC cm^-2at 2 mA cm^-2) compare to ZNC. An asymmetric supercapacitor (ASC) is assembled by ZNC@C as the positive electrode and carbonized popcorn as the negative electrode. The ASC exhibits good energy storage performance. Zn also positively affects the adsorption energy to enhance the capacitance property based on Density Functional theory calculation. The simple method for the composite structure by tuning the kinetics behaver of the crystal can provide a new strategy in synthesizing the materials, and the material with a unique structure and high performance will have potential applications in the field of energy storage.

A new potassium dual-ion hybrid supercapacitor based on battery-type Ni(OH)2 nanotube arrays and pseudocapacitor-type V2O5-anchored carbon nanotubes electrodes

Hybrid supercapacitors (HSCs) with the characteristics of high energy density, long cycle life and without altering their power density need to be developed urgently. Herein, a novel dual-ion hybrid supercapacitors (DHSCs) with Ni(OH)₂ nanotube arrays (NTAs) as positive electrode and V₂O₅ directly grown on freestanding carbon nanotubes (CNTs) as negative electrode is assembled. In charging mechanism of DHSCs, K⁺ are inserted into the V₂O₅ negative while OH^- react with Ni(OH)₂ positive; during discharge, the K⁺ and OH^- are released from V₂O₅ negative and Ni(OH)₂ positive, respectively, and return back to the electrolyte, which is quite different from traditional metal ion or alkaline supercapacitors. Because of the merits combining dual-ion mechanism and HSCs, the DHSC displays excellent capacity retention of ∼ 81.4% after 10,000 cycles, high energy density of ∼ 25.4 μWh cm^-2 and high power density of ∼ 4.66 mW cm^-2, indicating the potential applications in the further on flexible wearable electronics.

Ultrafast, Kinetically Limited, Ambient Synthesis of Vanadium Dioxides through Laser Direct Writing on Ultrathin Chalcogenide Matrix

Vanadium dioxide (VO₂) is a strongly correlated electronic material and has attracted significant attention due to its metal-to-insulator transition and diverse smart applications. Traditional synthesis of VO₂ usually requires minutes or hours of global heating and low oxygen partial pressure to achieve thermodynamic control of the valence state. Further patterning of VO₂ through a series of lithography and etching processes may inevitably change its surface valence, which poses a great challenge for the assembly of micro- and nanoscale VO₂-based heterojunction devices. Herein, we report an ultrafast method to simultaneously synthesize and pattern VO₂ on the time scale of seconds under ambient conditions through laser direct writing on a V₅S₈ "canvas". The successful ambient synthesis of VO₂ is attributed to the ultrafast local heating and cooling process, resulting in controlled freezing of the intermediate oxidation phase during the relatively long kinetic reaction. A Mott memristor based on a V₅S₈-VO₂-V₅S₈ lateral heterostructure can be fabricated and integrated with a MoS₂ channel, delivering a transistor with abrupt switching transfer characteristics. The other device with a VS_xO_y channel exhibits a large negative temperature coefficient of approximately 4.5%/K, which is highly desirable for microbolometers. The proposed approach enables fast and efficient integration of VO₂-based heterojunction devices and is applicable to other intriguing intermediate phases of oxides.

Enhanced electrochemical activities of morphologically tuned MnFe2O4 nanoneedles and nanoparticles integrated on reduced graphene oxide for highly efficient supercapacitor electrodes

The morphology of a nanoparticle strongly controls the path of electronic interaction, which directly correlates with the physicochemical properties and also the electrochemical comportment. Combining it with a two-dimensional (2D) material for a layer-by-layer approach will increase its possibilities in applications such as energy conversion and storage. Here, two different morphologies of MnFe2O4, nanoparticles and nanoneedles, are developed by a facile hydrothermal approach and sandwiched with reduced graphene oxide for constructing a 2D/3D sandwiched architecture. The rGO planar structure with abundant hierarchical short pores facilitates the thorough utilization of the utmost surface area to permeate the electrolyte within the structure to minimize the accumulation of rGO nanosheets laterally. The ferrite composited with rGO manifests high specific capacitance as the EDLC behaviour surpasses the faradaic pseudocapacitance boosting electrical conductivity compared to the as-synthesized MnFe2O4 structures. Benefiting from a 3D structure and the synergetic contribution of the MnFe2O4 nanoneedles and electrically conductive rGO layer, the MnFe2O4 nanoneedles@rGO electrode exhibits a high areal capacitance of 890 mF cm-2 and a remarkable specific capacitance of 1327 F g-1 at a current density of 5 mA cm-2. 93.36% of the initial capacitance was retained after 5000 cycles in 1 mol L-1 Na2SO4 indicating its high cycling stability. The synthesis route proves to be beneficial for a comprehensive yield of MnFe2O4@rGO nanosheets of different morphologies for use in the sophisticated design of energy-storing devices. This research strongly suggests that nanoparticle geometry, in addition to two-dimensional carbon-based materials, is a critical factor in a supercapacitor design.

Effect of pomelo seed-derived carbon on the performance of supercapacitors

Electrochemical ultracapacitors derived from green and sustainable materials could demonstrate superior energy output and an ultra-long cycle life, which could contribute to next-generation applications. Herein, we utilize pomelo seeds, a bio-waste from pomelo, in high-energy and high-power supercapacitors by a facile low-cost pyrolysis and activation method. The as-synthesized hierarchically porous carbon is surface-engineered with a large quantity of nitrogen and sulfur heteroatoms to give a high specific capacitance of ∼845 F g-1 at 1 A g-1. An ultra-high stability of ∼93.8% even after 10 000 cycles (10 A g-1) is achieved at room temperature. Moreover, a maximum energy density of ∼85 W h kg-1 at a power density of 1.2 kW kg-1 could be achieved in 1.2 V aqueous symmetrical supercapacitors. The results provide new insights that will be of use in the development of high-performance, green supercapacitors for advanced energy storage systems.

VO2 Nanostructures for Batteries and Supercapacitors: A Review

Vanadium dioxide (VO₂ ) received tremendous interest lately due to its unique structural, electronic, and optoelectronic properties. VO₂ has been extensively used in electrochromic displays and memristors and its VO₂ (B) polymorph is extensively utilized as electrode material in energy storage applications. More studies are focused on VO₂ (B) nanostructures which displayed different energy storage behavior than the bulk VO₂ . The present review provides a systematic overview of the progress in VO₂ nanostructures syntheses and its application in energy storage devices. Herein, a general introduction, discussion about crystal structure, and syntheses of a variety of nanostructures such as nanowires, nanorods, nanobelts, nanotubes, carambola shaped, etc. are summarized. The energy storage application of VO₂ nanostructure and its composites are also described in detail and categorically, e.g. Li-ion battery, Na-ion battery, and supercapacitors. The current status and challenges associated with VO₂ nanostructures are reported. Finally, light has been shed for the overall performance improvement of VO₂ nanostructure as potential electrode material for future application.

In situ synthesis of nitrogen site activated cobalt sulfide@N, S dual-doped carbon composite for a high-performance asymmetric supercapacitor

Cobalt sulfides with high theoretical capacity are considered as potential electrodes for supercapacitors (SCs). However, the insufficient reactive sites and low electrical conductivity of bulky cobalt sulfides restrict their applications. Here, we proposed an efficient approach for in situ formation of nitrogen site activated cobalt sulfide@N, S dual-doped carbon composite (CS@NSC) by vulcanizing the cobalt-glutamine complex (CG) precursor in a tube furnace. The effects of the molecular structure and calcination temperature of CG precursors on the morphology, structure and electrochemical performance of CS@NSC were studied. The designed CS@NSC-2 exhibited a specific capacity of 593 C g^-1 at the current density of 1 A g^-1 and good cyclic stability with 88.7% retention after 2000 cycles. Moreover, an asymmetric supercapacitor (ASC) was fabricated by CS@NSC-2 (positive electrode) and activated carbon (AC) (negative electrode), which delivered ultra-high energy density of 67.8 Wh kg^-1 at a power density of 400 W kg^-1 and possessed 83.1% capacitance retention after 5000 cycles. The eco-friendly method was also suitable for synthesizing nickel sulfide. This work may provide an innovative horizon for the in situ formation of active sites in electrode materials.

Flexible/Stretchable Supercapacitors with Novel Functionality for Wearable Electronics

With the miniaturization of personal wearable electronics, considerable effort has been expended to develop high-performance flexible/stretchable energy storage devices for powering integrated active devices. Supercapacitors can fulfill this role owing to their simple structures, high power density, and cyclic stability. Moreover, a high electrochemical performance can be achieved with flexible/stretchable supercapacitors, whose applications can be expanded through the introduction of additional novel functionalities. Here, recent advances in and future prospects for flexible/stretchable supercapacitors with innate functionalities are covered, including biodegradability, self-healing, shape memory, energy harvesting, and electrochromic and temperature tolerance, which can contribute to reducing e-waste, ensuring device integrity and performance, enabling device self-charging following exposure to surrounding stimuli, displaying the charge status, and maintaining the performance under a wide range of temperatures. Finally, the challenges and perspectives of high-performance all-in-one wearable systems with integrated functional supercapacitors for future practical application are discussed.

Synthesis of a three-dimensional cross-linked Ni-V2O5 nanomaterial in an ionic liquid for lithium-ion batteries

A three-dimensional cross-linked Ni-V₂O₅ nanomaterial with a particle size of 250-300 nm was successfully prepared in a 1-butyl-3-methylimidazole bromide ionic liquid (IL). The formation of this structure may follow the rule of dissolution-recrystallization and the ionic liquid, as both a dissolution and structure-directing agent, plays an important role in the formation of the material. After calcination of the precursor, the active material (Ni-V₂O₅-IL) was used as an anode for lithium-ion batteries. The designed anode exhibited excellent electrochemical performance with 765 mA h g^-1 at a current density of 0.3 A g^-1 after 300 cycles, which is much higher than that of a NiVO-W material prepared via a hydrothermal method (305 mA h g^-1). These results show the remarkable superiority of this novel electrode material synthesized in an ionic liquid.

Ultra-High Energy Density Hybrid Supercapacitors Using MnO2/Reduced Graphene Oxide Hybrid Nanoscrolls

Manganese oxide (MnO2) is a promising material for supercapacitor applications, with a theoretical ultra-high energy density of 308 Wh/kg. However, such ultra-high energy density has not been achieved experimentally in MnO2-based supercapacitors because of several practical issues, such as low electrical conductivity of MnO2, incomplete utilization of MnO2, and dissolution of MnO2. The present study investigates the potential of MnO2/reduced graphene oxide (rGO) hybrid nanoscroll (GMS) structures as electrode material for overcoming the difficulties and for developing ultra-high-energy storage systems. A hybrid supercapacitor, comprising MnO2/rGO nanoscrolls as anode material and activated carbon (AC) as a cathode, is fabricated. The GMS/AC hybrid supercapacitor exhibited enhanced energy density, superior rate performance, and promising Li storage capability that bridged the energy-density gap between conventional Li-ion batteries (LIBs) and supercapacitors. The fabricated GMS/AC hybrid supercapacitor demonstrates an ultra-high lithium discharge capacity of 2040 mAh/g. The GMS/AC cell delivered a maximum energy density of 105.3 Wh/kg and a corresponding power density of 308.1 W/kg. It also delivered an energy density of 42.77 Wh/kg at a power density as high as 30,800 W/kg. Our GMS/AC cell's energy density values are very high compared with those of other reported values of graphene-based hybrid structures. The GMS structures offer significant potential as an electrode material for energy-storage systems and can also enhance the performance of the other electrode materials for LIBs and hybrid supercapacitors.

Ce(OH)3 as a novel negative electrode material for supercapacitors

Novel electrode materials with desired specific capacitances are needed for supercapacitors. Rare-earth (RE)-based materials are fascinating in the field of catalysis and energy. Herein, a series of hydroxides including La, Ce, Pr and Nd was synthesized via in situ precipitation. Interestingly, only Ce(OH)₃ showed a redox peak in both positive and negative ranges. The other RE hydroxides exhibited a redox peak only in the positive range. Therefore, in order to certify that Ce(OH)₃ can be used as a negative electrode, symmetrical supercapacitors consisting of Ce(OH)₃ as both positive and negative electrodes were assembled, and showed a voltage window of 1.3 V. Moreover, asymmetrical supercapacitors were successfully fabricated, in which the positive electrode was composed of La(OH)₃, Pr(OH)₃ or Nd(OH)₃. These results may pave the way to novel negative electrode materials.

Electrode Materials for Supercapacitors: A Review of Recent Advances

The advanced electrochemical properties, such as high energy density, fast charge–discharge rates, excellent cyclic stability, and specific capacitance, make supercapacitor a fascinating electronic device. During recent decades, a significant amount of research has been dedicated to enhancing the electrochemical performance of the supercapacitors through the development of novel electrode materials. In addition to highlighting the charge storage mechanism of the three main categories of supercapacitors, including the electric double-layer capacitors (EDLCs), pseudocapacitors, and the hybrid supercapacitors, this review describes the insights of the recent electrode materials (including, carbon-based materials, metal oxide/hydroxide-based materials, and conducting polymer-based materials, 2D materials). The nanocomposites offer larger SSA, shorter ion/electron diffusion paths, thus improving the specific capacitance of supercapacitors (SCs). Besides, the incorporation of the redox-active small molecules and bio-derived functional groups displayed a significant effect on the electrochemical properties of electrode materials. These advanced properties provide a vast range of potential for the electrode materials to be utilized in different applications such as in wearable/portable/electronic devices such as all-solid-state supercapacitors, transparent/flexible supercapacitors, and asymmetric hybrid supercapacitors.

Lithium-Ion-Based Electrochemical Energy Storage in a Layered Vanadium Formate Coordination Polymer

A vanadium formate (VF) coordination polymer and its composite with partially reduced graphene oxide (prGO), namely VF-prGO, can be applied as anode materials for Li-ion based electrochemical energy storage (EcES) systems in the potential range of 0-3 V (vs Li⁺ /Li). This study shows that a reversible capacity of 329 mAh g^-1 at a current density of 50 mA g^-1 after 50 cycles can be realized for VF along with a high rate capability. The composite exhibits even a higher capacity of 504 mAh g^-1 at 50 mA g^-1 . A good capacity retention is observed even after 140 cycles for both VF and the composite. An ex-situ X-ray photoelectron spectroscopy study indicates the involvement of V³⁺ /V⁴⁺ redox couple in the charge storage mechanism. A significant contribution of this reversible capacity is attributed to the pseudocapacitive behavior of the system.

Electrospun Nb2O5 nanorods/microporous multichannel carbon nanofiber film anode for Na+ ion capacitors with good performance

For the disadvantages of both the slow reaction kinetics and the poor conductivity for Nb₂O₅ electrode materials as sodium-ion capacitors (SICs), Nb₂O₅ NRs/NMMCNF film electrode with good flexibility and high electrochemical property has been fabricated by electrospinning PAN/PMMA/H₂Nb₂O₆·H₂O homogeneous viscous suspension and followed by an annealing treatment, in which the precursor H₂Nb₂O₆·H₂O nanorods are obtained by grinding H₂Nb₂O₆·H₂O nanowires, and Nb₂O₅ nanorods are uniformly embedded in nitrogen doped microporous multichannel carbon nanofiber. Benefiting from the multichannel network structure, Nb₂O₅ NRs/NMMCNF film electrode delivers the fast kinetics of Na⁺-storage and the superior Na-ion storage performance, it delivers outstanding rate capability (101 mAh g^-1 at 4 A g^-1) and ultralong lifespan (91% capacity retention after 10,000 cycles at 2 A g^-1). A Nb₂O₅ NRs/NMMCNF//AC SIC based on the Nb₂O₅ NRs@NMMCNF fiber film anode and the AC cathode is assembled. The energy density of the as-assembled device is as high as 91 Wh kg^-1 and its maximum power density is 7499 W kg^-1. This work offers a new structure design strategy toward intercalation-type metal oxide electrodes for application in SICs.

Electronegativity principles in metal oxides based supercapacitors

To meet growing demands for energy consumptions in modern society, it is necessary to develop different energy sources. Renewable energy such as wind and solar sources are intermittent, therefore, energy storage devices become more and more important to store energy for use when no wind or no light. Supercapacitors play a key role in energy storage, mainly due to their high power density and long cycling life. However, supercapacitors are facing the obstacle of low energy density, one of the most intensive approaches is to rationally design new electrode materials. In this review, we focus on metal oxides-based materials and present an electronegativity criterion for the design and appropriate selection of new electrode chemical compositions. Metal elements with proper electronegativity scale have the potential to transfer electron for energy storage. Suitable positive and negative electrodes matching can enhance many properties of supercapacitors, which may overcome many related obstacles. Furthermore, electronegativity scale may also help people to find novel metal oxides based supercapacitors.