Carbon nanosphere@vanadium nitride electrode materials derived from metal-organic nanospheres self-assembled by NH4VO3, chitosan, and amphiphilic block copolymer

Porous hard carbon spheres derived from biomass for high-performance sodium/potassium-ion batteries

Hard carbon is the most attractive anode material for electrochemical sodium/potassium-ion storage. The preparation of hard carbon spheres directly from the broad sources of biomass is of great interest but barely reported. Herein, we developed a simple two-step hydrothermal method to construct porous carbon microspheres directly from the original waste biomass of camellia shells. The porous carbon microspheres have high specific capacities of 250 mAh g^-1and 264.5 mAh g^-1at a current density of 100 mA g^-1for sodium-ion batteries and potassium-ion batteries, respectively. And it has excellent cycle stability for sodium ions and potassium ions outperforming most reported hard carbons, which is mainly attributed to the microporous structure and spherical morphology. The work paves a way to prepare porous hard carbon spheres directly from biomass for alkali metal-ion batteries.

Emerging trends in anion storage materials for the capacitive and hybrid energy storage and beyond

Electrochemical capacitors charge and discharge more rapidly than batteries over longer cycles, but their practical applications remain limited due to their significantly lower energy densities. Pseudocapacitors and hybrid capacitors have been developed to extend Ragone plots to higher energy density values, but they are also limited by the insufficient breadth of options for electrode materials, which require materials that store alkali metal cations such as Li⁺ and Na⁺. Herein, we report a comprehensive and systematic review of emerging anion storage materials for performance- and functionality-oriented applications in electrochemical and battery-capacitor hybrid devices. The operating principles and types of dual-ion and whole-anion storage in electrochemical and hybrid capacitors are addressed along with the classification, thermodynamic and kinetic aspects, and associated interfaces of anion storage materials in various aqueous and non-aqueous electrolytes. The charge storage mechanism, structure-property correlation, and electrochemical features of anion storage materials are comprehensively discussed. The recent progress in emerging anion storage materials is also discussed, focusing on high-performance applications, such as dual-ion- and whole-anion-storing electrochemical capacitors in a symmetric or hybrid manner, and functional applications including micro- and flexible capacitors, desalination, and salinity cells. Finally, we present our perspective on the current impediments and future directions in this field.

Transition metal nitrides for electrochemical energy applications

This review comprehensively summarizes the progress on the structural and electronic modulation of transition metal nitrides for electrochemical energy applications.

Fabrication of a vanadium nitride/N-doped carbon hollow nanosphere composite as an efficient electrode material for asymmetric supercapacitors

Low-cost materials and facile processes to obtain novel electrode materials for assembling asymmetric supercapacitors (ASCs) are urgently needed. Herein, a vanadium nitride/nitrogen-doped carbon nanosphere (VN/NCS) composite composed of VN nanoparticles and N-doped carbon (NC) covering the surface of VN has been prepared by the nitridation of a V₂O₃/C nanocomposite. The hollow VN/NCS composite with a mesoporous structure and the dispersion of VN NPs in N-doped carbon result in a VN/NCS composite with good electrochemical behavior. Moreover, the N-doped carbon layer on the surface of VN effectively inhibits the oxidation of VN during cycling in an alkaline electrolyte. With the VN/NC composite utilized as a novel active electrode material for SCs, good rate capability, specific capacitance, and cycling stability are exhibited. Strikingly, using the VN/NCS composite as a negative electrode and its precursor, the V₂O₃/C composite, as a positive electrode, an asymmetric supercapacitor (ASC) device, with a good energy density of 19.8 W h kg^-1 at 801 W kg^-1 and a short charging time of 89 s, was assembled.

Study on the preparation and mechanism of chitosan-based nano-mesoporous carbons by hydrothermal method

In this paper, the hydrothermal method to synthesize and characterize nano-mesoporous carbons and their synthesis mechanism are reported. Using tri-block Pluronic F127 as a structuring agent and chitosan (CS) as a carbon source, the nano-mesoporous carbons were synthesized by a one-step sol polymerization and hydrothermal process, followed by carbonization at high temperature. The pore structure of the carbon materials was characterized by physical adsorption analyzer, and the morphology was characterized by SEM and TEM. Fourier-transform infrared, Raman and x-ray photoelectron spectroscopy were used to study the synthesis mechanism. The results showed that the self-assembly polymerization reaction between CS and F127 in a weakly acidic system was only implemented driven by the hydrogen bond auxiliary electrostatic interactions initiated by protonated amino groups. The nitrogen from amino groups and acetylamino groups, the oxygen in acetylamino groups, hydroxyl groups and the glycosidic bonds of CS, and the oxygen from the hydrophilic segments of F127 were the main active sites. The mesoporous material possesses a high Brunauer-Emmett-Teller surface area (163 m²/g) and large pore volume (0.462 cm³/g) with pore diameter around 2.1 nm. The nitrogen content was 1.08% and existed in the pore wall as the form of pyridine, pyrrole and quaternary nitrogen.

Accelerated polysulfide conversion on hierarchical porous vanadium-nitrogen-carbon for advanced lithium-sulfur batteries

With high theoretical specific density, low cost, and non-toxicity, Li-S batteries are regarded as a promising candidate for next-generation energy storage systems. However, the shuttling of soluble Li polysulfides (LiPSs) results in self-discharge and rapid capacity degradation. Herein, nitrogen-doped hierarchical porous carbon with embedded highly dispersed vanadium (v)-N_x sites (V-N-C) is developed as a high-performance Li-S battery cathode for the first time. The metal-organic polymer supramolecule structure formed by the electrostatic/hydrogen bond interaction of chitosan-VO₃^- strongly stabilizes V to generate a high density of V-N_x/C sites. During the discharge/charge process, the unique V-N_x/C active sites can serve as efficient catalysts to accelerate the redox kinetics of LiPSs, while the hierarchical porous carbon structure of V-N-C benefits the diffusion/transfer of Li⁺/e^- and suppresses the shuttling of LiPSs. As a result, the S/V-N-C composite delivers a high specific capacity of 1111.2 mA h g^-1 at 0.5C and maintains 573.6 mA h g^-1 at 5C with a low capacity decay rate of 0.087% per cycle (over 500 cycles at 1C). The rate performance of the developed V-N-C cathode in Li-S batteries is superior to that of most of the reported M-N-C and carbon material/metal compound composite electrodes.

Study on the voltage drop of vanadium nitride/carbon composites derived from the pectin/VCl3 membrane as a supercapacitor anode material

The adsorption of metal ions and the further utilization of adsorbent materials help solve serious environmental pollution; therefore, transforming them into supercapacitor electrode materials could be a promising possibility.

Hierarchical Nanosheets/Walls Structured Carbon-Coated Porous Vanadium Nitride Anodes Enable Wide-Voltage-Window Aqueous Asymmetric Supercapacitors with High Energy Density

The energy density of aqueous asymmetric supercapacitors (ASCs) is usually limited by low potential windows and capacitances of both anode and cathode. Herein, a facile strategy to fabricate hierarchical carbon-coated porous vanadium nitride nanosheet arrays on vertically aligned carbon walls (CC/CW/p-VN@C) as anode for aqueous ASCs is reported. The potential window of CC/CW/p-VN@C electrode can be stably extended to -1.3 to 0 V (vs Ag/AgCl) with greatly improved specific capacitance (604.8 F g-1 at 1 A g-1), excellent rate capability (368 F g-1 at 60 A g-1), and remarkable electrochemical stability. To construct ASCs, a Birnessite Na0.5MnO2 nanosheet arrays (CC/CW/Na0.5MnO2) cathode is similarly built. Benefiting from the matchable potential windows and high specific capacitances of the rationally designed anode and cathode, aqueous CC/CW/p-VN@C||CC/CW/Na0.5MnO2 ASCs with a wide voltage window of 2.6 V are fabricated. Moreover, the ASCs showcase an ultrahigh energy density up to 96.7 W h kg-1 at a high power density of 1294 W kg-1, and excellent cycling stability (92.5% retention after 10 000 cycles), outperforming most of previously reported ASCs and even comparable to that of organic electrolyte supercapacitors (SCs). This efficient strategy for fabricating 2.6 V aqueous ASCs suggests a promising research system for high energy density SCs.

Block copolymers for supercapacitors, dielectric capacitors and batteries

Block copolymer-based energy storage emerges as an active interdisciplinary research field. This topical review presents a survey of the recent advances in block copolymers for energy storage. In the first section, we introduce the background of electrochemical energy storage and block copolymer thermodynamics. In the second section, we discuss the current understandings of block copolymer chemistry, processing, pore size, and ionic conductivity. In the third section, we summarize the design principles and state-of-the-art applications of block copolymers in three energy storage devices, namely, supercapacitors, dielectric capacitors, and batteries. Lastly, we present our perspectives on future possible breakthroughs and associated challenges that are essential to propel the development of advanced block copolymers for energy storage. We expect the review to encourage innovative studies on integrating block copolymers into energy storage applications.

A Novel Hierarchical Porous 3D Structured Vanadium Nitride/Carbon Membranes for High-performance Supercapacitor Negative Electrodes

Transition-metal nitrides exhibit wide potential windows and good electrochemical performance, but usually experience imbalanced practical applications in the energy storage field due to aggregation, poor circulation stability, and complicated syntheses. In this study, a novel and simple multi-phase polymeric strategy was developed to fabricate hybrid vanadium nitride/carbon (VN/C) membranes for supercapacitor negative electrodes, in which VN nanoparticles were uniformly distributed in the hierarchical porous carbon 3D networks. The supercapacitor negative electrode based on VN/C membranes exhibited a high specific capacitance of 392.0 F g^-1 at 0.5 A g^-1 and an excellent rate capability with capacitance retention of 50.5% at 30 A g^-1. For the asymmetric device fabricated using Ni(OH)₂//VN/C membranes, a high energy density of 43.0 Wh kg^-1 at a power density of 800 W kg^-1 was observed. Moreover, the device also showed good cycling stability of 82.9% at a current density of 1.0 A g^-1 after 8000 cycles. This work may throw a light on simply the fabrication of other high-performance transition-metal nitride-based supercapacitor or other energy storage devices.

Nanocomposites based on hierarchical porous carbon fiber@vanadium nitride nanoparticles as supercapacitor electrodes

In this study, a hybrid electrode material for supercapacitors based on hierarchical porous carbon fiber@vanadium nitride nanoparticles is fabricated using the method of phase-separation mediated by the PAA-b-PAN-b-PAA tri-block copolymer.