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Despite the clear benefits of Na and S active materials, Na–S hybrid energy storage devices have yet to be exploited, and existing Na–S batteries cannot provide fast kinetics and long-term stabilit...

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.

Carbon is a simple, stable and popular element with many allotropes. The carbon family members include carbon dots, carbon nanotubes, carbon fibers, graphene, graphite, graphdiyne and hard carbon, etc. They can be divided into different dimensions, and their structures can be open and porous. Moreover, it is very interesting to dope them with other elements (metal or non-metal) or hybridize them with other materials to form composites. The elemental and structural characteristics offer us to explore their applications in energy, environment, bioscience, medicine, electronics and others. Among them, energy storage and conversion are extremely attractive, as advances in this area may improve our life quality and environment. Some energy devices will be included herein, such as lithium-ion batteries, lithium sulfur batteries, sodium-ion batteries, potassium-ion batteries, dual ion batteries, electrochemical capacitors, and others. Additionally, carbon-based electrocatalysts are also studied in hydrogen evolution reaction and carbon dioxide reduction reaction. However, there are still many challenges in the design and preparation of electrode and electrocatalytic materials. The research related to carbon materials for energy storage and conversion is extremely active, and this has motivated us to contribute with a roadmap on 'Carbon Materials in Energy Storage and Conversion'.

Monoclinic vanadium dioxide (VO2(B)) is considered as a promising cathode material for lithium ion batteries (LIBs) owing to its high capacity, short ion diffusion channel, and multiple oxidation states. However, VO2(B) is technically limited due to its low electronic conductivity and large volume expansion. In order to resolve these drawbacks, we develop a mesoporous composite of reduced graphene oxide (rGO) and VO2(B) for enhanced rate capability and cycle life of LIB cathode. The uniform deposition of VO2(B) nanorods onto the mesoporous surface of the rGO architecture provides a facile access of Li ions to the storage site, large accessible area, short diffusion pathway, and chemical and mechanical stabilities. The VO2(B)/rGO composite electrode achieves a high capacity of 226 mA h g−1 at current density of 50 mA g−1 and superior capacity retention of 67.5% even at 40 times increase in current density up to 2000 mA g−1. In addition, this composite electrode demonstrates long cyclic stability of 88.5% after 500 cycles at 1000 mA g−1. In situ synchronous X-ray absorption spectroscopic data confirms a reversible change of the local structure and valence state evolution during a charging and discharging process.

Sodium ion batteries are an emerging candidate to replace lithium ion batteries in large-scale electrical energy storage systems due to the abundance and widespread distribution of sodium. Despite the growing interest, the development of high-performance sodium cathode materials remains a challenge. In particular, polyanionic compounds are considered as a strong cathode candidate owing to their better cycling stability, a flatter voltage profile, and stronger thermal stability compared to other cathode materials. Here, we report the rational design of a biomimetic bone-inspired polyanionic Na3V2(PO4)3-reduced graphene oxide composite (BI-NVP) cathode that achieves ultrahigh rate charging and ultralong cycling life in a sodium ion battery. At a charging rate of 1 C, BI-NVP delivers 97% of its theoretical capacity and is able to retain a voltage plateau even at the ultra-high rate of 200 C. It also shows long cycling life with capacity retention of 91% after 10 000 cycles at 50 C. The sodium ion battery cells with a BI-NVP cathode and Na metal anode were able to deliver a maximum specific energy of 350 W h kg−1 and maximum specific power of 154 kW kg−1. In situ and postmortem analyses of cycled BI-NVP (including by Raman and XRD spectra) HRTEM, and STEM-EELS, indicate highly reversible dilation–contraction, negligible electrode pulverization, and a stable NVP-reduced graphene oxide layer interface. The results presented here provide a rational and biomimetic material design for the electrode architecture for ultrahigh power and ultralong cyclability of the sodium ion battery full cells when paired with a sodium metal anode.

Sodium ion hybrid capacitor (SIHC) has much attention because of abundance of sodium source and low cost. To improve the performance of SIHC stability, the poly-Acrylic Acid (PAA) cross-linked with Vinyl Silica Nano Particle (VSNP) was used as gel electrolyte. The VSNP was used as cross-linker and synthesized by Sol-Gel method with Vinyltriethoxysilane (VTES) to improve the mechanical strength of gel. Fourier-Transform Infrared Spectroscopy (FTIR) and Scanning Electron Microscope (SEM) was used to analyze C=C bond and morphology of VSNP. PAA gel was polymerized by radical polymerizaiotn with VSNP cross-linker. To measure electrochemical property, SIHC was fabricated with Na3V2(PO4)3 (NVP) cathode material and Activated Carbon (YP50F) anode material. Electrochemical Impedance Spectroscopy (EIS) was used to analyze interfaces-contact with electrode and electrolyte. After measure electrochemical property, X-ray Diffraction was measured to characterize the NVP crystallinity. By this research, It can propose the way how apply to flexible sodium ion hybrid capacitor and gel electrolyte SIHC

Due to high ionic conductivity of Na3V2(PO4)3 (NVP), stable three-dimensional structure and high theoretical capacity, NVP is attracting much attention as cathode material of Na-ion system. However, NVP has poor electronic conductivity which causes poor rate capability and cycle stability. The aim of this research is to further improve electronic conductivity and structural stability, thereby improving the rate capability and cycle stability. rGO has the characteristics of excellent electronic conductivity, large surface area, which make rGO a suitable material for the conductive network. Electrochemical tests show that NVP/rGO composites has much more excellent cycle stability and rate capability than pristine NVP. The results show that NVP/rGO can be considered as a candidate for cathode materials with high rate capability and stability in sodium ion storage systems and that forming a composite with rGO can improve rate & cycle performance of electrode materials.

Among vanadium-based materials, VO2(B), sharing octahedral VO6 structure with cavities, are considered as cathode materials due to their high capacity and multiple oxidation state. However, it has its own limitations such as low cyclic stability and sluggish charge storage kinetics arising from large structural deformation and poor electrical conductivity. In order to resolve these problems, we report a microsphere of thread like structured VO2(B) consisting of interconnected particles each other, providing continuous and facile electron and ion transport pathway. The robust internetworked microspherical structure leads to prevent the drastic volume variation during Li insertion/de-insertion process. More specifically, the as-synthesized VO2(B) displays high capacity of 225.6 mAh g−1 at 50 mA g−1 with a Columbic efficiency of 98%, high rate retention of 70% at 300 mA g−1, and good cycle stability of 72% after 350 cycles at 300 mA g−1. In addition, their structural and phase reversibility are confirmed by the in-situ XRD of VO2(B), where position of crystalline (002) peak after several electrochemical processes nearly returns on the origin position during Li insertion/de-insertion.

Vanadium pentoxide is considered as a candidate of cathode material for lithium-ion batteries owing to its high specific capacity, large potential window, and short diffusion pathway. However, vanadium pentoxide has its own limitations such as insufficient electronic conductivity, sluggish ion diffusion, and volume expansion. In order to resolve these problems, we demonstrate spray frozen assembly into hierarchically structured open-porous vanadium pentoxide/reduced graphene oxide composite microballs for high performance lithium-ion battery cathodes. The uniform distribution of vanadium pentoxide particles immobilized onto the open-porous surface of reduced graphene oxide microballs is associated with the short ion diffusion pathway, the percolated electronic conduction, and the buffering space. Accordingly, vanadium pentoxide/reduced graphene oxide composite microballs achieve the initial discharge capacity of 273 mAh g−1 at 100 mA g−1 which is higher than those of reduced graphene oxide (78 mAh g−1) and vanadium pentoxide (214 mAh g−1). When the current density increases from 100 to 1000 mA g−1, the capacity retention of vanadium pentoxide/reduced graphene oxide composite microballs is 51.3%, much greater than 36.4% of vanadium pentoxide particles. The capacity retention of 80.4% with the Coulombic efficiency of 97.1% over 200 cycles is twice greater than that of V2O5 particles, indicating improved cyclic stability.