In situ characterizations of advanced electrode materials for sodium-ion batteries toward high electrochemical performances

Energy storage is an ever-growing global concern due to increased energy needs and resource exhaustion.Sodium-ion batteries(SIBs)have called increasing attention and achieved substantial progress in recent years owing to the abundance and even distribution of Na resources in the crust,and the predicted low cost of the technique.Nevertheless,SIBs still face challenges like lower energy density and inferior cycling stability compared to mature lithium-ion batteries(LIBs).Enhancing the electrochemical performance of SIBs requires an in-deep and comprehensive understanding of the improvement strategies and the underlying reaction mechanism elucidated by in situ techniques.In this review,commonly applied in situ techniques,for instance,transmission electron microscopy(TEM),Raman spectroscopy,X-ray diffraction(XRD),and X-ray absorption near-edge structure(XANES),and their applications on the representative cathode and anode materials with selected samples are summarized.We discuss the merits and demerits of each type of material,strategies to enhance their electrochemical performance,and the applications of in situ characterizations of them during the de/sodiation process to reveal the underlying reaction mechanism for performance improvement.We aim to elucidate the composition/structure-per formance relationship to provide guidelines for rational design and preparation of electrode materials toward high electrochemical performance.

Advances in Mn‑Based Electrode Materials for Aqueous Sodium‑Ion Batteries

Aqueous sodium-ion batteries have attracted extensive attention for large-scale energy storage applications,due to abundant sodium resources,low cost,intrinsic safety of aqueous electrolytes and eco-friendliness.The electrochemical performance of aqueous sodium-ion batteries is affected by the properties of electrode materials and electrolytes.Among various electrode materials,Mn-based electrode materials have attracted tremendous attention because of the abundance of Mn,low cost,nontoxicity,eco-friendliness and interesting electrochemical performance.Aqueous electrolytes having narrow electrochemical window also affect the electrochemical performance of Mn-based electrode materials.In this review,we introduce systematically Mn-based electrode materials for aqueous sodium-ion batteries from cathode and anode materials and offer a comprehensive overview about their recent development.These Mn-based materials include oxides,Prussian blue analogues and polyanion compounds.We summarize and discuss the composition,crystal structure,morphology and electrochemical properties of Mn-based electrode materials.The improvement methods based on electrolyte optimization,element doping or substitution,optimization of morphology and carbon modification are highlighted.The perspectives of Mn-based electrode materials for future studies are also provided.We believe this review is important and helpful to explore and apply Mn-based electrode materials in aqueous sodium-ion batteries.

Computational design of promising 2D electrode materials for Li-ion and Li–S battery applications

Lithium-ion batteries(LIBs)and lithium-sulfur(Li–S)batteries are two types of energy storage systems with significance in both scientific research and commercialization.Nevertheless,the rational design of electrode materials for overcoming the bottlenecks of LIBs and Li–S batteries(such as low diffusion rates in LIBs and low sulfur utilization in Li–S batteries)remain the greatest challenge,while two-dimensional(2D)electrodes materials provide a solution because of their unique structural and electrochemical properties.In this article,from the perspective of ab-initio simulations,we review the design of 2D electrode materials for LIBs and Li–S batteries.We first propose the theoretical design principles for 2D electrodes,including stability,electronic properties,capacity,and ion diffusion descriptors.Next,classified examples of promising 2D electrodes designed by theoretical simulations are given,covering graphene,phosphorene,MXene,transition metal sulfides,and so on.Finally,common challenges and a future perspective are provided.This review paves the way for rational design of 2D electrode materials for LIBs and Li–S battery applications and may provide a guide for future experiments.

Effects of current density on preparation and performance of Al/conductive coating/α-PbO_2-Ce O_2-TiO_2/β-Pb O_2-MnO_2-WC-ZrO_2 composite electrode materials

Al/conductive coating/α-Pb O2-Ce O2-Ti O2/β-PbO 2-MnO 2-WC-Zr O2 composite electrode material was prepared on Al/conductive coating/α-PbO 2-Ce O2-Ti O2 substrate by electrochemical oxidation co-deposition technique. The effects of current density on the chemical composition, electrocatalytic activity, and stability of the composite anode material were investigated by energy dispersive X-ray spectroscopy（EDXS）, anode polarization curves, quasi-stationary polarization（Tafel） curves, electrochemical impedance spectroscopy（EIS）, scanning electron microscopy（SEM）, and X-ray diffraction（XRD）. Results reveal that the composite electrode obtained at 1 A/dm2 possesses the lowest overpotential（0.610 V at 500 A/m2） for oxygen evolution, the best electrocatalytic activity, the longest service life（360 h at 40 °C in 150 g/L H2SO4 solution under 2 A/cm2）, and the lowest cell voltage（2.75 V at 500 A/m2）. Furthermore, with increasing current density, the coating exhibits grain growth and the decrease of content of Mn O2. Only a slight effect on crystalline structure is observed.

Recent advances in electrospun electrode materials for sodium-ion batteries

Sodium-ion batteries(SIBs)have been considered as an ideal choice for the next generation large-scale energy storage applications owing to the rich sodium resources and the analogous working principle to that of lithium-ion batteries(LIBs).Nevertheless,the larger size and heavier mass of Na^(+)ion than those of Li^(+)ion often lead to sluggish reaction kinetics and inferior cycling life in SIBs compared to the LIB counterparts.The pursuit of promising electrode materials that can accommodate the rapid and stable Na-ion insertion/extraction is the key to promoting the development of SIBs toward a commercial prosperity.One-dimensional(1 D)nanomaterials demonstrate great prospects in boosting the rate and cycling performances because of their large active surface areas,high endurance for deformation stress,short ions diffusion channels,and oriented electrons transfer paths.Electrospinning,as a versatile synthetic technology,features the advantages of controllable preparation,easy operation,and mass production,has been widely applied to fabricate the 1 D nanostructured electrode materials for SIBs.In this review,we comprehensively summarize the recent advances in the sodium-storage cathode and anode materials prepared by electrospinning,discuss the effects of modulating the spinning parameters on the materials’micro/nano-structures,and elucidate the structure-performance correlations of the tailored electrodes.Finally,the future directions to harvest more breakthroughs in electrospun Na-storage materials are pointed out.

Functional porous carbon-based composite electrode materials for lithium secondary batteries

The synthetic routes of porous carbons and the applications of the functional porous carbon-based composite electrode materials for lithium secondary batteries are reviewed. The synthetic methods have made great breakthroughs to control the pore size and volume, wall thickness, surface area, and connectivity of porous carbons, which result in the development of functional porous carbon-based composite electrode materials. The effects of porous carbons on the electrochemical properties are further discussed. The porous carbons as ideal matrixes to incorporate active materials make a great improvement on the electrochemical properties because of high surface area and pore volume, excellent electronic conductivity, and strong adsorption capacity. Large numbers of the composite electrode materials have been used for the devices of electrochemical energy conversion and storage, such as lithium-ion batteries （LIBs）, Li-S batteries, and Li-O2 batteries. It is believed that functional porous carbon-based composite electrode materials will continuously contribute to the field of lithium secondary batteries.

Preparation and electrochemical characterization of C/PANI composite electrode materials

Taking the nano-sized carbon black and aniline monomer as precursor and （NH4）2S2O6 as oxidant, the well coated C/polyaniline（C/PANI） composite materials were prepared by in situ polymerization of the aniline on the surface of well-dispersed nano-sized carbon black for supercapacitor. The micro-structure of the C/PANI composite electrode materials were analyzed by SEM. The electrochemical properties of C/ PANI and PANI composite electrode were characterized by means of the galvanostatic charge-discharge experiment, cyclic voltammetric measurement and impedance spectroscopy analysis. The results show that by adding the nano-sized carbon black in the process of chemical polymerization of the aniline, the polyaniline can be in situ polymerized and well-coated onto the carbon black particles, which may effectively improve the aggregation of particles and the electrolyte penetration. What’s more , the maximum of specific capacitance of C/PANI electrode 437.6F·g -1 can be attained. Compared with PANI electrode, C/PANI electrode shows more desired capacitance characteristics, smaller internal resistance and better cycle performance.

Characterization methods of organic electrode materials

The development of novel organic electrode materials is of great significance for improving the reversible capacity and cycle stability of rechargeable batteries.Before practical application,it is essential to characterize the electrode materials to study their structures,redox mechanisms and electrochemical performances.In this review,the common characterization methods that have been adopted so far are summarized from two aspects:experimental characterization and theoretical calculation.The experimental characterization is introduced in detail from structural characterization,electrochemical characterization and electrode reaction chara cterization.The experimental purposes and working principles of various experimental characterization methods are briefly illustrated.As the auxilia ry means,theoretical calculation provides the theoretical basis for characterizing the electrochemical reaction mechanism of organic electrode materials.Through these characterizations,we will have a deep understanding about the material structures,electrochemical redox mechanisms,electrochemical properties and the relationships of structure-property.It is hoped that this review would help researchers to select the suitable characterization methods to analyze the structures and performances of organic electrode materials quickly and effectively.

Carbon materials from melamine sponges for supercapacitors and lithium battery electrode materials: A review

With the increasing energy demand together with the deteriorating environment and decreasing fossil fuel resources,the development of highly efficient energy conversion and storage devices is one of the key challenges of both fundamental and applied research in energy technology.Melamine sponges(MS)with low density,high nitrogen content,and high porosity have been used to design and obtain three‐dimensional porous carbon electrode materials.More importantly,they are inexpensive,environment‐friendly,and easy to synthesize.There have been many reports on the modification of carbonized MS and MS‐based composites for supercapacitor and lithium battery electrode materials.In this paper,recent studies on the fabrication of electrode materials using MS as raw materials have been mainly reviewed,including carbonation,doping activation,and composite modification of MS,and expectations for the development of porous carbon materials for energy storage as a reference with excellent performance,environment‐friendliness,and long life.

Research progress in rare earths and their composites based electrode materials for supercapacitors

Supercapacitor is an imminent potential energy storage system,and acts as a booster to the batteries and fuel cells to provide necessary power density.In the last decade,carbon and carbonaceous materials,conducting polymers and transition metal oxide/hydroxide based electrode materials have been made to show a remarkable electrochemical performance.Rare-earth materials have attracted significant research attention as an electrode material for supercapacitor applications based on their physicochemical properties.In this review,rare earth metals,rare earth metal oxides/hydroxides,rare-earth metal chalcogenides,rare-earth metal/carbon composites and rare-earth metal/metal oxide composites based electrode materials are discussed for supercapacitors.We also discuss the energy chemistry of rare-earth metal-based materials.Besides the factors that affect the performance of the electrode materials,their evaluation methods and supercapacitor performances are discussed in details.Finally,the future outlook in rare-earth-based electrode materials is revealed towards its current developments for supercapacitor applications.

Halogen Storage Electrode Materials for Rechargeable Batteries

The ever-increasing demand for rechargeable batteries with high energy density,abundant resources,and high safety has pushed the development of various battery technologies based on cation,anion,or dual-ion transfer.The use of halogen storage electrode materials has led to new concept battery systems such as halide-ion batteries(HIB)and dual-ion batteries(DIB).This review highlights the recent progress on these electrode materials,including metal(oxy)halides,layered double hydroxides,MXenes,graphite-based materials,and organic materials with carbon or nitrogen redox centers.The reversible electrochemical halogen storage of halide ions(e.g.,F^(−),Cl^(−),and Br^(−)),dual halogen(e.g.,Br_(m)Cl_(n) and [ICl_(2)]^(−)),or binary halide anions(e.g.,PF_(6)^(−),AlCl_(4)^(−),[ZnCl_(x)]^(2−x),and [MgCl_(x)]^(2−x)) in the electrodes is covered.The challenges and mechanisms of halogen storage in various electrode materials in HIBs and DIBs are summarized and analyzed,providing insights into the development of high-performance halogen storage electrode materials for rechargeable batteries.

First-principles study of high performance lithium/sodium storage of Ti3C2T2 nanosheets as electrode materials

Ti3C2Tx nanosheet,the first synthesized MXene with high capacity performance and charge/discharge rate,has attracted increasingly attention in renewable energy storage applications.By performing systematic density functional theory calculations,the theoretical capacity of the intrinsic structure of single-and multi-layered Ti3C2T2(T=F or O)corresponding to M(M=Li and Na)atoms are investigated.Theoretical volumetric capacity and gravimetric capacity are obtained,which are related to the stacking degree.The optimal ratios of capacity to structure are determined under different stacking degrees for understanding the influence of surface functional groups on energy storage performance.Its performance can be tuned by performing surface modification and increasing the interlayer distance.In addition,the reason for theoretical capacity differences of M atoms is analyzed,which is attributed to difference in interaction between the M-ions and substrate and the difference in electrostatic exclusion between adsorbed M-ions.These results provide an insight into the understanding of the method of efficiently increasing the energy storage performance,which will be useful for designing and using high performance electrode materials.

Electrode materials for aqueous multivalent metal-ion batteries: Current status and future prospect

In recent years,the pursuit of high-efficiency electrochemical storage technology,the multivalent metalion batteries (MIBs) based on aqueous electrolytes have been widely explored by researchers because of their safety,environmental friendliness,abundant reserves and low price,and especially the merits in energy and power densities.This review firstly expounds on the problems existing in the electrode materials of aqueous multivalent MIBs (Zn^(2+),Mg^(2+),Al^(3+),Ca^(2+)),from the classical inorganic materials to the emerging organic compounds,and then summarizes the design strategies in bulk and interface structure of electrodes with favorable kinetics and stable cycling performance,especially laying the emphasis on the charge storage mechanism of cathode materials and dendrite-free Zinc anode from the aspect of electrolyte optimization strategies,which can be extended to other aqueous multivalent MIBs.Ultimately,the possible development directions of the aqueous multivalent MIBs in the future are provided,anticipating to provide a meaningful guideline for researchers in this area.

Designing electrode materials for aluminum-ion batteries towards fast diffusion and multi-electron reaction

Since the electrochemical energy storage was invented, mobile has brought us a new world without wires for more electronic devices [1–4]. Aluminum ion batteries(AIBs) were born with the requirements of electrochemical energy storage towards high capacity, safe and low cost.

One-Step Hydrothermal Synthesis of a CoTe@rGO Electrode Material for Supercapacitors

CoTe@reduced graphene oxide(CoTe@rGO)electrode materials for supercapacitors were prepared by a one-step hydrothermal method in this paper.Compared with that of pure CoTe,the electrochemical performance of CoTe@rGO was significantly improved.The results showed that the optimal CoTe@rGO electrode material has a remarkably high specific capacitance of 810.6 F/g at a current density of 1 A/g.At 5 A/g,the synthesized material retained 77.2%of its initial capacitance even after 5000 charge/discharge cycles,thereby demonstrating good cycling stability.Moreover,even at a high current density of 20 A/g,the composite electrode retained 79.0%of its specific capacitance at 1 A/g,thus confirming its excellent rate performance.An asymmetric supercapacitor(ASC)with a wider potential window and higher energy density was assembled by using 3 M KOH as the electrolyte,the CoTe@rGO electrode as the positive electrode,and active carbon as the negative electrode.The operating voltage of the supercapacitor could be increased to 1.6 V,and its specific capacitance could reach 112.6 F/g at 1 A/g.The specific capacitance retention rate of the fabricated supercapacitor after 5000 charge/discharge cycles at 5 A/g was 87.1%,which confirms its excellent cycling stability.In addition,the ASC revealed a high energy density of 40.04 W·h/kg at a power density of 799.91 W/kg and a high power density of 4004.93 W/kg at an energy density of 33.43 W·h/kg.These results collectively show that CoTe@rGO materials have broad application prospects.

Preparation of nano-PANI@MnO_2 by surface initiated polymerization method using as a nano-tubular electrode material:The amount effect of aniline on the microstructure and electrochemical performance

In this study,nano-polyanline and manganese oxide nanometer tubular composites（nano-PANI@MnO2）were prepared by a surface initiated polymerization method and used as electrochemical capacitor electrode materials; and the effect of aniline amount on the microstructure and electrochemical performance was investigated. The microstructures and surface morphologies of nano-PANI@MnO2 were characterized by X-ray diffraction,scanning electron microscopy and fourier transformation infrared spectroscope. The electrochemical performance of these composite materials was performed with cyclic voltammetry,charge–discharge test and electrochemical impedance spectroscopy,respectively. The results demonstrate that the feed ratio of aniline to MnO2 played a very important role in constructing the hierarchically nano-structure,which would,hence,determine the electrochemical performance of the materials. Using the templateassisted strategy and controlling the feed ratio of aniline to MnO2,the nanometer tubular structure of nanoPANI@MnO2 was obtained. A maximum specific capacitance of 386 F/g was achieved in aqueous 1 mol/L Na NO3 electrolyte with the potential range from 0 to 0.6 V（vs. SCE）.

Organic Electrode Materials for Non-aqueous K-Ion Batteries

The demands for high-performance and low-cost batteries make K-ion batteries(KIBs) considered as promising supplements or alternatives for Li-ion batteries(LIBs). Nevertheless, there are only a small amount of conventional inorganic electrode materials that can be used in KIBs, due to the large radius of K^+ ions. Diff erently, organic electrode materials(OEMs) generally own sufficiently interstitial space and good structure flexibility, which can maintain superior performance in K-ion systems. Therefore, in recent years, more and more investigations have been focused on OEMs for KIBs. This review will comprehensively cover the researches on OEMs in KIBs in order to accelerate the research and development of KIBs. The reaction mechanism, electrochemical behavior, etc., of OEMs will all be summarized in detail and deeply. Emphasis is placed to overview the performance improvement strategies of OEMs and the characteristic superiority of OEMs in KIBs compared with LIBs and Na-ion batteries.

Aplication of Corncob-Based Activated Carbon as Electrode Material for Electric Double-Layer Capacitors

To investigate the influence of expansion pretreatment for materials on carbon structure, activated carbons （ACs） were prepared from corncob with/without expansion pretreatment by KOH activation, the structure properties of which were determined based on N2 adsorption isotherm at 77 K. The results show that the expansion pretreatment for corncobs is beneficial to the preparation of ACs with high surface area. The specific surface area of the AC derived from corncob with expansion pretreatment （AC-1） is 32.5% larger than that without expansion pretreatment （AC-2）. Furthermore, to probe the potential application of corncob-based ACs in electric double-layer capacitor （EDLC）, the prepared ACs were used as electrode materials to assemble EDLC, and its electrochemical performance was investi- gated. The results indicate that the specific capacitance of AC-I is 276 F/g at 50 mA/g, which increases by 27% com- pared with that of AC-2 （217 F/g）. As electrode materials, AC-1 presents a better electrochemical performance than AC-2, including a higher voltage maintenance ratio and a lower leakage current.

Review on recent advances of inorganic electrode materials for potassium-ion batteries

Rechargeable potassium-ion batteries(PIBs)have great potential in the application of electrochemical energy storage devices due to the low cost,the abundant resources and the low standard reduction potential of potassium.As electrode materials are the key factors to determine the electrochemical performance of devices,relevant research is being carried out to build high-performance PIBs.In recent years,significant progress has been made in the study of the design of inorganic electrode materials.Herein,we review the cathode materials(Prussian blue and its analogues,layered oxides and poly anionic compounds)and the anode materials(antimony-based,selenium-based and bismuth-based compounds).On the basis of previous work,the structural design principles for improving the performance of electrode materials are reasonably summarized.At the same time,the problems that need to be solved in the preparation of electrode materials and the direction of future research and improvement are pointed out.

Advanced organic electrode materials for aqueous rechargeable batteries

Organic electrode materials take advantages of potentially sustainable production and structural tunability compared with present commercial inorganic electrode materials.However,their applications in traditional rechargeable batteries with nonaqueous electrolytes suffer from the premature failure and safety concerns.In comparison,aqueous rechargeable batteries based on organic electrode materials have received extensive attentions in recent years for low-cost and sustainable energy storage systems due to their inherent safety.This review aims to provide a comprehensive summary on the recent progress in advanced organic electrode materials for aqueous rechargeable batteries.We start from the overview of working principles and general design strategies of organic electrode materials in aqueous rechargeable batteries.Then the research advances of organic electrode materials in various aqueous rechargeable batteries are highlighted in terms of charge carriers(monovalent ions,multivalent ions,and anions).We emphasized the characteristics of organic electrode materials in various charge carriers.Finally,the critical challenges and future efforts of aqueous organic rechargeable batteries are discussed.More organic electrode materials with better electronic conductivity and fast reaction kinetics are still needed to build advanced aqueous batteries for commercial applications.