Search

Alloying‐type antimony (Sb) with high theoretical capacity is a promising anode candidate for both lithium‐ion batteries (LIBs) and sodium‐ion batteries (SIBs). Given the larger radius of Na+ (1.02 Å) than Li+ (0.76 Å), it was generally believed that the Sb anode would experience even worse capacity degradation in SIBs due to more substantial volumetric variations during cycling when compared to LIBs. However, the Sb anode in SIBs unexpectedly exhibited both better electrochemical and structural stability than in LIBs, and the mechanistic reasons that underlie this performance discrepancy remain undiscovered. Here, using substantial in situ transmission electron microscopy, X‐ray diffraction, and Raman techniques complemented by theoretical simulations, we explicitly reveal that compared to the lithiation/delithiation process, sodiation/desodiation process of Sb anode displays a previously unexplored two‐stage alloying/dealloying mechanism with polycrystalline and amorphous phases as the intermediates featuring improved resilience to mechanical damage, contributing to superior cycling stability in SIBs. Additionally, the better mechanical properties and weaker atomic interaction of Na−Sb alloys than Li−Sb alloys favor enabling mitigated mechanical stress, accounting for enhanced structural stability as unveiled by theoretical simulations. Our finding delineates the mechanistic origins of enhanced cycling stability of Sb anode in SIBs with potential implications for other large‐volume‐change electrode materials. [ABSTRACT FROM AUTHOR]

Sodium‐ion batteries (SIBs) with wide operating temperature are regarded as promising candidates for large‐scale energy storage systems. However, SIBs operating under elevated temperature aggravate the electrolyte decomposition with unstable cathode‐electrolyte interphase (CEI), causing a rapid capacity degradation. Herein, anion receptor tris(pentafluorophenyl)borane (TPFPB) is selected as electrolyte additive to construct robust NaF‐rich CEI. The strong interactions between anion and TPFPB via the electron‐deficient boron atoms weaken ClO4− solvation and promote the coordination capability between solvents and Na+ cations, demonstrating greatly improved oxidative stability. Na3V2(PO4)3 cathode in TPFPB‐containing electrolyte delivers long‐term stability with a capacity retention of 86.9% after 100 cycles at a high cut‐off voltage of 4.2 V (vs. Na+/Na) and a high temperature of 60 °C. Besides, TPFPB also works well with enhanced performance over a temperature range from −30 to 60 °C. This study proposes a prospective method by manipulating the solvation chemistry for constructing high‐temperature rechargeable SIBs. [ABSTRACT FROM AUTHOR]

Given the merits of affordable cost, superior low‐temperature performance, and advanced safe properties, sodium‐ion batteries (SIBs) have exhibited great development potential in large scale energy storage applications. Among various emerging carbonaceous anode materials applied for SIBs, hard carbon (HC) has recently gained significant attention regarding their relatively low cost, wide availability, and optimal overall performance. However, the insufficient initial Coulombic efficiency (ICE) of HC is the main bottlenecks, which is inevitably hindering their further commercial applications. Herein, an in‐depth holistic exposition about the reasons causing the unsatisfied ICE and the recent advances on effective improvement strategies are comprehensively summarized in this review, which have been divided into two aspects including the intrinsic property (degree of graphitization, pore structure, defect, et al.) and the extrinsic factor (electrolyte, electrode materials, et al.). In addition, future prospects and perspectives on HC to enable practical application in SIBs are also briefly outlined. [ABSTRACT FROM AUTHOR]

Sodium‐ion batteries (SIBs) present great appeal in various energy storage systems, especifically for stationary grid storage, on account of the abundance of sources and low cost. Unfortunately, the commercialization of SIBs is mainly limited by available electrode materials, especially for the cathodes. Prussian blue analogs (PBAs), emerge as a promising alternative for their structural feasibility in the application of SIBs. Decreasing the defects (vacancies and coordinated water) is an effective strategy to achieve superior electrochemical performance during the synthetic processes. Herein, we summarize crystal structures, synthetic methods, electrochemical mechanisms, and the influences of synthesis conditions of PBAs in detail. This comprehensive overview on the current research progresses of PBAs will give guides and directions to solve the existing problems for their application in SIBs. [ABSTRACT FROM AUTHOR]

The development of large‐scale energy storage systems (ESSs) aimed at application in renewable electricity sources and in smart grids is expected to address energy shortage and environmental issues. Sodium‐ion batteries (SIBs) exhibit remarkable potential for large‐scale ESSs because of the high richness and accessibility of sodium reserves. Using low‐cost and abundant elements in cathodes with long cycling stability is preferable for lowering expenses on cathodes. Many investigated cathodes for SIBs are dogged by structural and morphology changes, unstable interphases between the cathode and the electrolyte, and air sensitivity, causing unsatisfactory cycling performance. Therefore, understanding the mechanism of capacity degeneration in depth and developing precise solutions are critical for designing low‐cost cathodes that are highly stable under cycling. Herein, recent progress in long‐cycle‐life and low‐cost cathodes for SIBs is focused on, and a comprehensive discussion of the key points in SIBs toward large‐scale applications is provided. The roots of the unstable cycling performance of low‐cost cathodes are discussed. Also, effective strategies are summarized from the recent progress on long‐cycle‐life and low‐cost cathodes. This review is expected to encourage deeper investigation of long‐lifespan cathodes for SIBs, particularly for potential large‐scale industrialization. [ABSTRACT FROM AUTHOR]

Sodium‐ion batteries (SIBs) are considered as a low‐cost complementary or alternative system to prestigious lithium‐ion batteries (LIBs) because of their similar working principle to LIBs, cost‐effectiveness, and sustainable availability of sodium resources, especially in large‐scale energy storage systems (EESs). Among various cathode candidates for SIBs, Na‐based layered transition metal oxides have received extensive attention for their relatively large specific capacity, high operating potential, facile synthesis, and environmental benignity. However, there are a series of fatal issues in terms of poor air stability, unstable cathode/electrolyte interphase, and irreversible phase transition that lead to unsatisfactory battery performance from the perspective of preparation to application, outside to inside of layered oxide cathodes, which severely limit their practical application. This work is meant to review these critical problems associated with layered oxide cathodes to understand their fundamental roots and degradation mechanisms, and to provide a comprehensive summary of mainstream modification strategies including chemical substitution, surface modification, structure modulation, and so forth, concentrating on how to improve air stability, reduce interfacial side reaction, and suppress phase transition for realizing high structural reversibility, fast Na+ kinetics, and superior comprehensive electrochemical performance. The advantages and disadvantages of different strategies are discussed, and insights into future challenges and opportunities for layered oxide cathodes are also presented. [ABSTRACT FROM AUTHOR]

Hard carbon (HC) anodes have shown extraordinary promise for sodium‐ion batteries, but are limited to their poor initial coulombic efficiency (ICE) and low practical specific capacity due to the large amount of defects. These defects with oxygen containing groups cause irreversible sites for Na+ ions. Highly graphited carbon decreases defects, while potentially blocking diffusion paths of Na+ ions. Therefore, molecular‐level control of graphitization of hard carbon with open accessible channels for Na+ ions is key to achieve high‐performance hard carbon. Moreover, it is challenging to design a conventional method to obtain HCs with both high ICE and capacity. Herein, a universal strategy is developed as manganese ions‐assisted catalytic carbonization to precisely tune graphitization degree, eliminate defects, and maintain effective Na+ ions paths. The as‐prepared hard carbon has a high ICE of 92.05% and excellent cycling performance. Simultaneously, a sodium storage mechanism of "adsorption‐intercalation‐pore filling‐sodium cluster formation" is proposed, and a clear description given of the boundaries of the pore structure and the specific dynamic process of pore filling. [ABSTRACT FROM AUTHOR]

Layered transition metal oxide (NaxTMO2), being one of the most promising cathode candidates for sodium‐ion batteries (SIBs), have attracted intensive interest because of their nontoxicity, high theoretical capacities, and easy manufacturability. However, their physical and electrochemical properties of water sensitivity, sluggish Na+ transport kinetics, and irreversible multiple‐phase translations hinder the practical application. Here, a concept of surface lattice‐matched engineering is proposed based on in situ spinel interfacial reconstruction to design a spinel coating P2/P3 heterostructure cathode material with enhanced air stability, rate, and cycle performance. The novel structure and its formation process are verified by transmission electron microscopy and in situ high‐temperature X‐ray diffraction. The electrode exhibits an excellent rate performance with the highly reversible phase transformation demonstrated by in situ charging/discharging X‐ray diffraction. Additionally, even after a rigorous water sensitivity test, the electrode materials still retain almost the same superior electrochemical performance as the fresh sample. The results show that the surface spinel phase can play a vital role in preventing the ingress of water molecules, improving transport kinetics, and enhancing structural integrity for NaxTMO2 cathodes. The concept of surface lattice‐matched engineering based on in situ spinel interfacial reconstruction will be helpful for designing new ultra‐stable cathode materials for high‐performance SIBs. [ABSTRACT FROM AUTHOR]

Sodium‐ion batteries (SIBs) show tremendous potential for large‐scale energy storage systems due to the high abundance of sodium resources and potentially low cost. Among the discovered anode materials for SIBs, metal selenides with large theoretical capacities are considered as a promising candidate. Nevertheless, metal selenide‐based anodes are trapped by poor ionic/electronic conductivity, low initial Coulombic efficiency, and drastic volume changes during the (de)sodiation process. Herein, the differences in sodium‐storage mechanisms of different metal selenides are first analyzed. Subsequently, the specific challenges and corresponding modification strategies (such as nanostructure design, carbon modification, potential window regulation, electrolyte optimization, and constructing heterostructures) for metal selenides as SIB anodes are discussed in detail, and recent advances are also presented. Finally, the potential research directions of metal selenides in SIBs are comprehensively reviewed. It is believed that this review can provide constructive comments on the optimization and large‐scale application of high‐performance metal selenide‐based anode for SIBs. [ABSTRACT FROM AUTHOR]

With the growing demand for energy storage, layered oxide cathodes (Na x TMO 2) for sodium-ion batteries (SIBs) have become the spotlight for researchers. However, irreversible multiphase transformation and structural degradation, as well as lattice oxygen loss, hindered their commercialization. Electronic structure modulation based on the orbital hybridization concept is an important way to solve key scientific problems. Herein, due to its unique electronic structure, Sn is chosen as the proof of the conceptual element, and its effect on layered oxide cathode is summarized in three aspects: reversible phase transformation, abnormal structural regulation, and stable anionic redox. Firstly, the large size of Sn4+ suppresses the sliding of the transition metal oxide (TMO 2) layer and Na+/vacancy ordering as well as enhances the delocalization of electrons. Secondly, Sn with a similar ionic radius to other TM ions in the structure promotes the stacking of the O3 phase. What's more, the distinctive electronic structure of Sn4+ will enhance the operating voltage. Thirdly, a strong Sn-O bond stabilizes the lattice oxygen, promotes stable anion redox, and improves the energy density of the battery. Therefore, electronic structure modulation can provide technical direction for the development and industrialization of high-performance SIBs. [Display omitted] • Sn inhibits the sliding of the transition metal oxide layer by constructing a stable framework in the structure, leading to reversible phase transitions. • Sn4+ possesses a distinctive electronic structure that promotes the stacking of the O3 phase and enhances average voltage. • A strong Sn-O bond stabilizes lattice oxygen that boosts the stable anionic redox and high energy density. [ABSTRACT FROM AUTHOR]

Prussian blue analogues (PBAs) have attracted extensive attention as cathode materials in sodium‐ion batteries (SIBs) due to their low cost, high theoretical capacity, and facile synthesis process. However, it is of great challenge to control the crystal vacancies and interstitial water formed during the aqueous co‐precipitation method, which are also the key factors in determining the electrochemical performance. Herein, an antioxidant and chelating agent co‐assisted non‐aqueous ball‐milling method to generate highly‐crystallized Na2‐xFe[Fe(CN)6]y with hollow structure is proposed by suppressing the speed and space of crystal growth. The as‐prepared Na2‐xFe[Fe(CN)6]y hollow nanospheres show low vacancies and interstitial water content, leading to a high sodium content. As a result, the Na‐rich Na1.51Fe[Fe(CN)6]0.87·1.83H2O hollow nanospheres exhibit a high initial Coulombic efficiency, excellent cycling stability, and rate performance via a highly reversible two‐phase transition reaction confirmed by in situ X‐ray diffraction. It delivers a specific capacity of 124.2 mAh g−1 at 17 mA g−1, presenting ultra‐high rate capability (84.1 mAh g−1 at 3400 mA g−1) and cycling stability (65.3% capacity retention after 1000 cycles at 170 mA g−1). Furthermore, the as‐reported non‐aqueous ball‐milling method could be regarded as a promising method for the scalable production of PBAs as cathode materials for high‐performance SIBs. [ABSTRACT FROM AUTHOR]

The shell structure design has been recognized as a highly efficient strategy to buffer the severe volume expansion and consecutive pulverization of conversion‐type anodes. Nevertheless, construction of a functional shell with a stabilized structure that meets the demands of both high electronic conductivity and feasible pathways for Na+ ions has been a challenge so far. Herein, we design a two‐in‐one shell configuration for bimetal selenides to achieve fast sodium storage within broadened voltage windows. The hybridized shell, which benefits from the combination of titanium dioxide quantum dots and amorphous carbon, can not only effectively buffer the strain and maintain structural integrity but also allow facile and reversible transport of electrons and Na+ uptake for electrode materials during sodiation/desodiation processes, resulting in increased reaction kinetics and diffusion of sodium ions, conferring many benefits to the functionality of conversion‐type electrode materials. As a representative material, Ni‐CoSe2 with such structural engineering shows a reversible capacity of 515 mAh g−1 at 0.1 A g−1 and a stable capacity of 416 mAh g−1 even at 6.4 A g−1; more than 80% of the capacity at 0.1 A g−1 could be preserved, so that this strategy holds great promise for designing fast‐charging conversion‐type anodes in the future. [ABSTRACT FROM AUTHOR]

Carbonaceous materials are considered strong candidates as anode materials for sodium‐ion batteries (SIBs), which are expected to play an indispensable role in the carbon‐neutral era. Herein, novel braided porous carbon fibres (BPCFs) are prepared using the chemical vapour deposition (CVD) method. The BPCFs possess interwoven porous structures and abundant vacancies. The growth mechanism of the BPCFs can be attributed to the polycrystalline transformation of the nanoporous copper catalyst in the early stage of CVD process. Density functional theory calculations suggest that the Na+ adsorption energies of the mono‐vacancy edges of the BPCFs (−1.22 and −1.09 eV) are lower than that of an ideal graphene layer (−0.68 eV), clarifying in detail the adsorption‐dominated sodium storage mechanism. Hence, the BPCFs as an anode material present an outstanding discharge capacity of 401 mAh g−1 at 0.1 A g−1 after 500 cycles. Remarkably, this BPCFs anode, under high‐mass‐loading of 5 mg cm−2, shows excellent long‐term cycling ability with a reversible capacity of 201 mAh g−1 at 10 A g−1 over 1000 cycles. This study provided a novel strategy for the development of high‐performance carbonaceous materials for SIBs. [ABSTRACT FROM AUTHOR]

Prussian blue analogs (PBAs), as promising cathode materials for sodium‐ion batteries (SIBs), have received extensive research interest due to their appealing characteristics, e.g., the low cost of their raw materials, easy manufacturing, open frameworks, and high theoretical specific capacity. There are some challenges for PBAs cathodes, however, hindering their performance output, making them currently unacceptable for practical applications. To improve the performance and cycling stability of PBAs, a clear in‐depth understanding of the relationship of their electrochemical reaction process to their ion insertion/extraction mechanisms and structural evolution is extremely important. Nowadays, advanced characterization techniques have become an important tool to guide the construction of high‐performance PBAs cathodes. In this review, the various advances by using advanced characterization techniques to reveal the reaction mechanisms for PBAs cathodes are summarized and discussed. By appreciating how the advanced characterization techniques to guide fabrication of high‐performance PBAs or reveal their detailed reaction mechanisms, it is hoped that this review can assist readers to find more valuable and advanced technologies to help to resolve some key problems and enhance their performance so as to accelerate the practical application of PBAs cathode for SIBs. [ABSTRACT FROM AUTHOR]

Organic electroactive compounds hold great potential to act as cathode material for organic sodium‐ion batteries (OSIBs) because of their environmental friendliness, sustainability, and high theoretical capacity. Although some organic electrodes have been developed with good performance, their practical application is still obstructed by some inherent drawbacks such as low conductivity and solubility in organic electrolytes. In addition, research on OSIBs has been mainly focused on the performance of electrodes on the material level and neglected the trade‐off relationship between the high redox potentials and specific capacities. Almost all organic cathodes used in OSIBs lack the ability to be charged first in half‐cells because of the absence of detachable sodium ions, resulting in low attractiveness when assembling full cells with hard carbon as anode. Here, this review presents several existing reaction mechanisms in OSIBs and designs of organic cathode materials. Furthermore, strategies are proposed in order to provide guidelines for improving their performance according to some critical parameters (output voltage, specific capacity, and cycle life) in potential practical OSIBs, and some accounts of organic materials assembled in full cells are summarized. Finally, the challenges and prospects of organic electrodes for OSIBs are also discussed in this review. [ABSTRACT FROM AUTHOR]

Recently, environmental degradation along with the energy crisis has led to an urgent necessity to develop renewable and clean energy storage devices. The sodium ion batteries (SIBs) have become promising candidates in the whole energy storage system, due to its rich and low‐cost sodium resources. To accelerate the commercialization of SIBs, the energy density of SIBs needs to be further improved. Increasing the operating voltage of SIBs is considered to be an effective method, which requires stable and high‐voltage cathode materials. Comparatively, polyanionic sulfate materials (PSMs) with stable skeletons, adjustable structures, operational safety, and the high electronegativity of SO42− are believed to be the most promising high‐energy‐cathodes. In this review, recent progresses on several typical sulfates for SIBs are summarized. What's more, based on their intrinsic characteristics, the structures and kinetic behaviors of PSMs are also discussed. Reported measures to optimize their electrochemical performances and structural stability are summarized and reviewed. The key challenges and corresponding opportunities for PSMs are also discussed. The insights presented in this review may be a guide for designing and developing stable and practical PSMs for room‐temperature SIBs, which is conducive to promoting their industrialization. [ABSTRACT FROM AUTHOR]

Manganese‐based Prussian Blue, Na2−δMn[Fe(CN)6] (MnPB), is a good candidate for sodium‐ion battery cathode materials due to its high capacity. However, it suffers from severe capacity decay during battery cycling due to the destabilizing Jahn–Teller distortions it undergoes as Mn2+ is oxidized to Mn3+. Herein, the structure is stabilized by a thin epitaxial surface layer of nickel‐based Prussian Blue (Na2−δNi[Fe(CN)6]). The one‐pot synthesis relies on a chelating agent with an unequal affinity for Mn2+ and Ni2+ ions, which prevents Ni2+ from reacting until the Mn2+ is consumed. This is a new and simpler synthesis of core–shell materials, which usually needs several steps. The material has an electrochemical capacity of 93 mA h g−1, of which it retains 96 % after 500 charge–discharge cycles (vs. 37 % for MnPB). Its rate capability is also remarkable: at 4 A g−1 (ca. 55 C) it can reversibly store 70 mA h g−1, which is also reflected in its diffusion coefficient of ca. 10−8 cm2 s−1. The epitaxial outer layer appears to exert an anisotropic strain on the inner layer, preventing the Jahn–Teller distortions it normally undergoes during de‐sodiation. [ABSTRACT FROM AUTHOR]

Structural engineering and creating atomic disorder in electrodes are promising strategies for highly efficient and rapid charge storage in advanced batteries. Herein, a nanohybrid architecture is presented with amorphous vanadium oxide conformally coated on layered V2C MXene (a‐VOx/V2C) via tunable anodic oxidation, which exhibits a high reversible capacity of 307 mAh g–1 at 50 mA g–1, decent rate capability with capacity up to 96 mAh g–1 at 2000 mA g–1, and good cycling stability as a cathode for sodium‐ion batteries. The a‐VOx layer enables reversible and fast Na+ insertion/extraction by providing sufficient vacancies and open pathways in the amorphous framework, unlike the irreversible phase transition in its crystalline counterpart, while layered V2C MXene offers abundant electron/ion transfer channels, which are joined together to boost the electrochemical performance. Notably the improved reversibility and structural superiority of the a‐VOx/V2C nanohybrid are clearly revealed by in situ Raman, in situ transmission electron microscopy, in situ synchrotron X‐ray absorption spectroscopy, and density functional theory calculations, demonstrating a reversible V–O vibration and valence oscillation between V4+ and V5+ in the disordered framework, with robust structural stability and unobstructed Na+ diffusion. This work provides a meaningful reference for the elaborate design of MXene‐based nanostructured electrodes toward advanced rechargeable batteries. [ABSTRACT FROM AUTHOR]

High initial coulombic efficiency is highly desired because it implies effective interface construction and few electrolyte consumption, indicating enhanced batteries' life and power output. In this work, a high‐capacity sodium storage material with FeS2 nanoclusters (≈1–2 nm) embedded in N, S‐doped carbon matrix (FeS2/N,S‐C) was synthesized, the surface of which displays defects‐repaired characteristic and detectable dot‐matrix distributed Fe‐N‐C/Fe‐S‐C bonds. After the initial discharging process, the uniform ultra‐thin NaF‐rich (≈6.0 nm) solid electrolyte interphase was obtained, thereby achieving verifiable ultra‐high initial coulombic efficiency (≈92 %). The defects‐repaired surface provides perfect platform, and the catalysis of dot‐matrix distributed Fe‐N‐C/Fe‐S‐C bonds to the rapid decomposing of NaSO3CF3 and diethylene glycol dimethyl ether successfully accelerate the building of two‐dimensional ultra‐thin solid electrolyte interphase. DFT calculations further confirmed the catalysis mechanism. As a result, the constructed FeS2/N,S‐C provides high reversible capacity (749.6 mAh g−1 at 0.1 A g−1) and outstanding cycle stability (92.7 %, 10 000 cycles, 10.0 A g−1). Especially, at −15 °C, it also obtains a reversible capacity of 211.7 mAh g−1 at 10.0 A g−1. Assembled pouch‐type cell performs potential application. The insight in this work provides a bright way to interface design for performance improvement in batteries. [ABSTRACT FROM AUTHOR]

Hard carbon (HC) is recognized as a promising anode material with outstanding electrochemical performance for alkali metal‐ion batteries including lithium‐ion batteries (LIBs), as well as their analogs sodium‐ion batteries (SIBs) and potassium‐ion batteries (PIBs). Herein, a comprehensive review of the recent research is presented to interpret the challenges and opportunities for the applications of HC anodes. The ion storage mechanisms, materials design, and electrolyte optimizations for alkali metal‐ion batteries are illustrated in‐depth. HC is particularly promising as an anode material for SIBs. The solid‐electrolyte interphase, initial Coulombic efficiency, safety concerns, and all‐climate performances, which are vital for practical applications, are comprehensively discussed. Furthermore, commercial prototypes of SIBs based on HC anodes are extensively elaborated. The remaining challenges and research perspectives are provided, aiming to shed light on future research and early commercialization of HC‐based SIBs. [ABSTRACT FROM AUTHOR]

Sodium‐ion batteries have attracted ever‐increasing attention in view of the natural abundance of sodium resources. Sluggish sodiation kinetics, nevertheless, remain a tough challenge, in terms of achieving high rate capability and high energy density. Herein, a sheet‐in‐sphere nanoconfiguration of 2D titania–carbon superlattices vertically aligned inside of mesoporous TiO2@C hollow nanospheres is constructed. In such a design, the ultrathin 2D superlattices consist of ordered alternating monolayers of titania and carbon, enabling interpenetrating pathways for rapid transport of electrons and Na+ ions as well as a 2D heterointerface for Na+ storage. Kinetics analysis discloses that the combination of 2D heterointerface and mesoporosity results an intercalation pseudocapacitive charge storage mechanism, which triggers ultrafast sodiation kinetics. In situ transmission electron microscope imaging and in situ synchrotron X‐ray diffraction techniques elucidate that the sheet‐in‐sphere architecture can maintain robust mechanical and crystallographic structural stability, resulting an extraordinary high rate capability, remarkable stable cycling with a low capacity fading ratio of 0.04% per cycle over 500 cycles at 0.2 C, and exceptionally long‐term cyclability up to 20 000 cycles at 50 C. This study offers a method for the realization of a high power density and long‐term cyclability battery by designing of a hierarchical nanoarchitecture. [ABSTRACT FROM AUTHOR]

Titanium‐based polyanions have been intensively investigated for sodium‐ion batteries owing to their superior structural stability and thermal safety. However, their low working potential hindered further applications. Now, a cation and anion dual doping strategy is used to boost the redox potential of Ti‐based cathodes of Na3Ti0.5V0.5(PO3)3N as a new cathode material for sodium ion batteries. Both the Ti3+/Ti4+ and V3+/V4+ redox couples are reversibly accessed, leading to two distinctive voltage platforms at ca. 3.3 V and ca. 3.8 V, respectively. The remarkably improved cycling stability (86.3 %, 3000 cycles) can be ascribed to the near‐zero volume strain in this unusual cubic symmetry, which has been demonstrated by in situ synchrotron‐based X‐ray diffraction. First‐principles calculations reveal its well‐interconnected 3D Na diffusion pathways with low energy barriers, and the two‐sodium‐extracted intermediate NaTi0.5V0.5(PO3)3N is also a stable phase according to formation energy calculations. [ABSTRACT FROM AUTHOR]

Over the past decades, porous carbonaceous and carbon‐incorporated composites have aroused tremendous attention owing to their unique properties such as high surface area, excellent accessibility to active sites, tunable morphologies and structures, and superior mass transport and diffusion. They have been widely investigated and applied in various fields, such as energy storage, absorption, water filtration, drug delivery, catalysis, and sensing. In the energy storage area, rechargeable sodium‐ion batteries (SIBs) have attracted tremendous attention as the next‐generation power plants for large‐scale energy storage systems (EESs). However, their low energy density and power density, as well as their poor cyclability, are still the main challenges for SIBs, especially for the anode, which acts as a bottleneck. With the incorporation of appropriate porous carbonaceous materials, the disadvantages of large volume shrinkage and low electron conductivity of alloying‐ and conversion‐based anode materials have been significantly alleviated. This review points out and summarizes the most recent developments in synthesis strategies and morphology control of porous carbonaceous materials and the corresponding carbonaceous‐material‐incorporated high performance anodes for SIBs. Furthermore, the remaining challenges associated with these composites and effective routes to enhance their performance are discussed. [ABSTRACT FROM AUTHOR]

Structural evolution of the cathode during cycling plays a vital role in the electrochemical performance of sodium‐ion batteries. A strategy based on engineering the crystal structure coupled with chemical substitution led to the design of the layered P2@P3 integrated spinel oxide cathode Na0.5Ni0.1Co0.15Mn0.65Mg0.1O2, which shows excellent sodium‐ion half/full battery performance. Combined analyses involving scanning transmission electron microscopy with atomic resolution as well as in situ synchrotron‐based X‐ray absorption spectra and in situ synchrotron‐based X‐ray diffraction patterns led to visualization of the inherent layered P2@P3 integrated spinel structure, charge compensation mechanism, structural evolution, and phase transition. This study provides an in‐depth understanding of the structure‐performance relationship in this structure and opens up a novel field based on manipulating structural evolution for the design of high‐performance battery cathodes. [ABSTRACT FROM AUTHOR]

With the unprecedentedly increasing demand for renewable and clean energy sources, the sodium‐ion battery (SIB) is emerging as an alternative or complementary energy storage candidate to the present commercial lithium‐ion battery due to the abundance and low cost of sodium resources. Layered transition metal oxides and Prussian blue analogs are reviewed in terms of their commercial potential as cathode materials for SIBs. The recent progress in research on their half cells and full cells for the ultimate application in SIBs are summarized. In addition, their electrochemical performance, suitability for scaling up, cost, and environmental concerns are compared in detail with a brief outlook on future prospects. It is anticipated that this review will inspire further development of layered transition metal oxides and Prussian blue analogs for SIBs, especially for their emerging commercialization. [ABSTRACT FROM AUTHOR]

Emerging rechargeable sodium‐ion storage systems—sodium‐ion and room‐temperature sodium–sulfur (RT‐NaS) batteries—are gaining extensive research interest as low‐cost options for large‐scale energy‐storage applications. Owing to their abundance, easy accessibility, and unique physical and chemical properties, sulfur‐based materials, in particular metal sulfides (MSx) and elemental sulfur (S), are currently regarded as promising electrode candidates for Na‐storage technologies with high capacity and excellent redox reversibility based on multielectron conversion reactions. Here, we present current understanding of Na‐storage mechanisms of the S‐based electrode materials. Recent progress and strategies for improving electronic conductivity and tolerating volume variations of the MSx anodes in Na‐ion batteries are reviewed. In addition, current advances on S cathodes in RT‐NaS batteries are presented. We outline a novel emerging concept of integrating MSx electrocatalysts into conventional carbonaceous matrices as effective polarized S hosts in RT‐NaS batteries as well. This comprehensive progress report could provide guidance for research toward the development of S‐based materials for the future Na‐storage techniques. [ABSTRACT FROM AUTHOR]

An in‐depth understanding of the electrochemical behavior of cathode materials in a complex chemical environment is critical for the development of state‐of‐the‐art sodium‐ion batteries. Advanced synchrotron‐based characterization is a powerful tool for collecting valuable information on complicated reaction mechanisms. X‐ray absorption spectroscopy can be used to precisely monitor the valence state and corresponding changes during cycling of various elements. Information on the local structure, such as coordination number and bond information can also be extracted from the fitting data in Fourier transform extended X‐ray absorption fine structure. In this review, we summarize findings on state‐of‐the‐art cathode materials using ex‐situ/in‐situ X‐ray absorption spectroscopy to probe fundamental discoveries on sodium‐ion battery systems and what important and valuable results have been obtained. Further possible improvements and practical operating advice are also discussed in detail. [ABSTRACT FROM AUTHOR]

Two‐dimensional (2D) superlattices offer promising technological opportunities in tuning the intercalation chemistry of metal ions. Now, well‐ordered 2D superlattices of monolayer titania and carbon with tunable interlayer‐spacing are synthesized by a molecularly mediated thermally induced approach. The 2D superlattices are vertically encapsulated in hollow carbon nanospheres, which are embedded with TiO2 quantum dots, forming a 0D‐2D‐3D multi‐dimensional architecture. The multi‐dimensional architecture with the 2D superlattices encapsulated inside exhibits a near zero‐strain characteristic and enriched electrochemical reactivity, achieving a highly efficient Na+ storage performance with exceptional rate capability and superior long‐term cyclability. [ABSTRACT FROM AUTHOR]

Structural modulation and surface engineering have remarkable advantages for fast and efficient charge storage. Herein, we present a phosphorus modulation strategy which simultaneously realizes surface structural disorder with interior atomic‐level P‐doping to boost the Na+ storage kinetics of TiO2. It is found that the P‐modulated TiO2 nanocrystals exhibit a favourable electronic structure, and enhanced structural stability, Na+ transfer kinetics, as well as surface electrochemical reactivity, resulting in a genuine zero‐strain characteristic with only approximately 0.1 % volume variation during Na+ insertion/extraction, and exceptional Na+ storage performance including an ultrahigh rate capability of 210 mAh g−1 at 50 C and a strong long‐term cycling stability without significant capacity decay up to 5000 cycles at 30 C. Take the strain: A phosphorus modulation of anatase TiO2 simultaneously triggers a surface phase transition, which gives structural disorder, and interior atomic‐level P‐doping. These two beneficial changes result in a zero‐strain characteristic during sodium‐ion insertion/extraction which occurs with only about 0.1 % volume variation and thus enables an exceptional sodium‐storage performance. [ABSTRACT FROM AUTHOR]

Low‐cost layered oxides free of Ni and Co are considered to be the most promising cathode materials for future sodium‐ion batteries. Biphasic Na0.78Cu0.27Zn0.06Mn0.67O2 obtained via superficial atomic‐scale P3 intergrowth with P2 phase induced by Zn doping, consisting of inexpensive transition metals, is a promising cathode for sodium‐ion batteries. The P3 phase as a covering layer in this composite shows not only in excellent electrochemical performance but also its tolerance to moisture. The results indicate that partial Zn substitutes can effectively control biphase formation for improving the structural/electrochemical stability as well as the ionic diffusion coefficient. Based on in situ synchrotron X‐ray diffraction coupled with electron‐energy‐loss spectroscopy, a possible Cu2+/3+ redox reaction mechanism has now been revealed. The P2@P3 Na0.78Cu0.33−xZnxMn0.67O2 composite induced by Zn doping with revealed redox behavior of Cu2+/3+ is a promising cathode for Na ion batteries. Zn doping not only induces the formation of a P3 phase, which shows a distinct crystal and atomic arrangement with nanoscale thickness, but also offered a high and flat voltage profile, leading to improvement in both structural/electrochemical stability and humidity resistance. [ABSTRACT FROM AUTHOR]

Abstract: The cathode materials in the Na‐ion battery system are always the key issue obstructing wider application because of their relatively low specific capacity and low energy density. A graphene oxide (GO) wrapped composite, Na2Fe2(SO4)3@C@GO, is fabricated via a simple freeze‐drying method. The as‐prepared material can deliver a 3.8 V platform with discharge capacity of 107.9 mAh g−1 at 0.1 C (1 C = 120 mA g−1) as well as offering capacity retention above 90% at a discharge rate of 0.2 C after 300 cycles. The well‐constructed carbon network provides fast electron transfer rates, and thus, higher power density also can be achieved (75.1 mAh g−1 at 10 C). The interface contribution of GO and Na2Fe2(SO4)3 is recognized and studied via density function theory calculation. The Na storage mechanism is also investigated through in situ synchrotron X‐ray diffraction, and pseudocapacitance contributions are also demonstrated. The diffusion coefficient of Na+ ions is around 10−12–10−10.8 cm2 s−1 during cycling. The higher working voltage of this composite is mainly ascribed to the larger electronegativity of the element S. The research indicates that this well‐constructed composite would be a competitive candidate as a cathode material for Na‐ion batteries. [ABSTRACT FROM AUTHOR]

Abstract: Sodium‐ion batteries (SIBs) have been considered as the most promising candidate for large‐scale energy storage system owing to the economic efficiency resulting from abundant sodium resources, superior safety, and similar chemical properties to the commercial lithium‐ion battery. Despite the long period of academic research, how to realize sodium‐ion battery commercialization for market applications is still a great challenge. Thus, from the perspective of future practical application, this review will identify the factors that are restricting commercialization, and evaluate the existing active materials and sodium‐ion‐based full‐cell system. The design and development trends that are needed for SIBs to meet the requirements of practical applications in large‐scale energy storage will also be discussed in detail. [ABSTRACT FROM AUTHOR]

Considering that the high capacity, long-term cycle life, and high-rate capability of anode materials for sodium-ion batteries (SIBs) is a bottleneck currently, a series of Co-doped FeS2 solid solutions with different Co contents were prepared by a facile solvothermal method, and for the first time their Na-storage properties were investigated. The optimized Co0.5Fe0.5S2 (Fe0.5) has discharge capacities of 0.220 Ah g−1 after 5000 cycles at 2 A g−1 and 0.172 Ah g−1 even at 20 A g−1 with compatible ether-based electrolyte in a voltage window of 0.8-2.9 V. The Fe0.5 sample transforms to layered Na xCo0.5Fe0.5S2 by initial activation, and the layered structure is maintained during following cycles. The redox reactions of Na xCo0.5Fe0.5S2 are dominated by pseudocapacitive behavior, leading to fast Na+ insertion/extraction and durable cycle life. A Na3V2(PO4)3/Fe0.5 full cell was assembled, delivering an initial capacity of 0.340 Ah g−1. [ABSTRACT FROM AUTHOR]

A facile, one-step, soft chemistry approach is developed to synthesize ClO 4 -doped polypyrrole coated Na 1+ x MnFe(CN)6 composite as a cathode material (NMHFC@PPy) for SIBs. PPy plays multiple important roles in the composite. First, PPy serves as a conductive coating layer which can increase the electronic conductivity of NMHFC to improve the rate capability. Second, PPy can act as a protective layer to reduce the dissolution of Mn in the electrolyte to improve the cycling performance. Finally, the PPy doped with ClO 4 − can act as active materials to increase the capacity of the composite. NMHFC@PPy shows high energy density (428 W h kg −1 ), enhanced cycling performance (67% capacity retention after 200 cycles), and excellent rate capacity (46% capacity for 40 C rate). [ABSTRACT FROM AUTHOR]

Sodium-ion energy storage, including sodium-ion batteries (NIBs) and electrochemical capacitive storage (NICs), is considered as a promising alternative to lithium-ion energy storage. It is an intriguing prospect, especially for large-scale applications, owing to its low cost and abundance. MoS2 sodiation/desodiation with Na ions is based on the conversion reaction, which is not only able to deliver higher capacity than the intercalation reaction, but can also be applied in capacitive storage owing to its typically sloping charge/discharge curves. Here, NIBs and NICs based on a graphene composite (MoS2/G) were constructed. The enlarged d-spacing, a contribution of the graphene matrix, and the unique properties of the MoS2/G substantially optimize Na storage behavior, by accommodating large volume changes and facilitating fast ion diffusion. MoS2/G exhibits a stable capacity of approximately 350 mAh g−1 over 200 cycles at 0.25 C in half cells, and delivers a capacitance of 50 F g−1 over 2000 cycles at 1.5 C in pseudocapacitors with a wide voltage window of 0.1-2.5 V. [ABSTRACT FROM AUTHOR]

Recently, room‐temperature stationary sodium‐ion batteries (SIBs) have received extensive investigations for large‐scale energy storage systems (EESs) and smart grids due to the huge natural abundance and low cost of sodium. The SIBs share a similar "rocking‐chair" sodium storage mechanism with lithium‐ion batteries; thus, selecting appropriate electrodes with a low cost, satisfactory electrochemical performance, and high reliability is the key point for the development for SIBs. On the other hand, the carefully chosen elements in the electrodes also largely determine the cost of SIBs. Therefore, earth‐abundant‐metal‐based compounds are ideal candidates for reducing the cost of electrodes. Among all the high‐abundance and low‐cost metal elements, cathodes containing iron and/or manganese are the most representative ones that have attracted numerous studies up till now. Herein, recent advances on both iron‐ and manganese‐based cathodes of various types, such as polyanionic, layered oxide, MXene, and spinel, are highlighted. The structure–function property for the iron‐ and manganese‐based compounds is summarized and analyzed in detail. With the participation of iron and manganese in sodium‐based cathode materials, real applications of room‐temperature SIBs in large‐scale EESs will be greatly promoted and accelerated in the near future. State‐of‐the‐art high‐abundance and low‐cost metal‐based cathode materials for sodium‐ion batteries are comprehensively summarized and analyzed, providing a step toward the real‐life, commercial application of sodium‐ion batteries. Constructive suggestions and guidance are provided and future prospects regarding this promising field are discussed. [ABSTRACT FROM AUTHOR]

Iron sulfides draw much attention as electrode candidates for sodium-ion batteries (SIBs) due to the rich chemical stoichiometries and high capacity. However, they usually exhibit poor cycling performance due to the large volume change during sodiation/desodiation process. In this work, we embed Fe 7 S 8 nanoparticles into sulfur, nitrogen-doped carbon (S/N–C) nanofibers through electrospinning/sulfurization processes. The heteroatom doped carbon matrixes could effectively protect the Fe 7 S 8 from structural collapse, obtaining a stable cycling performance. Moreover, the conductive matrixes with 1D structure can facilitate the diffusion of electrons, leading to good rate capability. As results, the as-designed Fe 7 S 8 @S/N–C nanofibers present a discharge capacity of 347 m Ah g−1 after 150 cycles at 1 A g−1 and a high rate capacity of 220 m Ah g−1 at 5 A g−1 in virtue of unique structural characteristics. • The S/N-doped carbon nanofibers can enhance the conductivity of Fe 7 S 8. • Fe 7 S 8 nanoparticles are embedded into the doped carbon nanofibers. • The Fe 7 S 8 @S/N–C nanofibers present a capacity of 347 mA h g−1 after 150 cycles. [ABSTRACT FROM AUTHOR]