Application In Sodium-ion Batteries Research Articles

Covalent Organic Frameworks (COFs): Characteristics and Applications for Lithium-Ion Batteries (LIBs) and Sodium Ion Batteries (SIBs)

Covalent organic frameworks (COFs) belong to a family of porous organic materials that form 2D or 3D tuned structures via a covalent bond formation between organic blocks. COFs exhibit a remarkable array of characteristics that make them highly promising materials for various applications. COFs are characterized by their chemical and physical stability, their highly porous structure, and their easy structural tunability. They emerged as promising candidates for electrode materials in advanced energy storage devices such as sodium-ion batteries (SIBs) and lithium-ion batteries (LIBs). COFs can be precisely customized for each application via pore engineering and framework functionalization as well as the pre- and post-synthesis. Research has been conducted to examine the effect of various functional groups, active redox sites, pore size, and interlayer distances on the performance of COFs as electrode materials. Herein, this review reports the most recent advances in using COFs as electrode materials in both LIBs and SIBs. It also discusses the synthesis of COFs, structural engineering, and pore engineering. The main advantages and challenges that arise with the application of COFs in rechargeable batteries are presented. This review concluded that COFs do have the potential as anode materials in both LIBs and SIBs by virtue of their crystalline structure and high porosity that enable efficient ion diffusion and storage. COFs provided enhanced battery electrochemical performance, improved energy density, and prolonged cycle life.

Designing hollow Ti3C2@TiSe2 composites for long cycle life of sodium-ion storage

The construction of an anode material with high electrical conductivity and long cycle stability was essential for the practical application of Sodium-ion batteries (SIBs). Hollow Ti3C2@TiSe2 composites were successfully synthesized using in situ selenization methods from MXene-derived materials. The composites obtained in this study exhibited an impressive reversible capacity, attaining a specific capacity of 561 mAh g−1 when tested at a current density of 0.1 A g−1.The specific capacity remained stable at 201 mAh g−1 through 12,000 cycles at a high current density of 10 A g−1. When utilizing Na3V2(PO4)3@C (NVP@C) as the cathode in a full cell, it demonstrated a sustained specific capacity of 138 mAh g−1 over 50 cycles at a current density of 100 mA g−1. Additionally, a capacity of 98 mAh g−1 was maintained over 500 charge-discharge cycles at a higher current density of 1000 mA g−1. The reaction mechanism of Na+ was confirmed through reaction kinetics and ex-situ XRD test. This study demonstrated that the special hollow structure comprised of Ti3C2 and TiSe2 enhanced the material's structural stability as well as the surface activity.

3D flower-like hollow MXene@MoS2 heterostructure for fast sodium storage

Constructing an anode with fast electron transport and high cycling stability is important but challenging for large-scale applications of sodium-ion batteries (SIB). In this study, hierarchical flower-like MXene structures were synthesized using poly (methyl methacrylate) (PMMA) microsphere as templates. Subsequently, a straightforward hydrothermal reaction was utilized to anchor small-sized MoS2 nanosheets. The resulting MXene@MoS2 heterostructure exhibits a distinctive three-dimensional (3D) porous hollow architecture. This structure effectively addresses challenges related to self-aggregation of MoS2 nanosheets and volume expansion of the electrode material during Na+ insertion/extraction processes. Furthermore, the robust hetero-interface supports fast and stable electron transfer, thereby enhancing electrochemical reaction kinetics. The prepared MXene@MoS2 electrode demonstrates the specific capacity of 682.1 mA h g−1 at 0.2 A/g and the reversible capacity of 494.4 mA h g−1 after 1000 cycles at 5 A/g. It is noteworthy that the full battery assembled with the composite material as the anode can still maintain the capacity of 456.2 mA h g−1 after 80 cycles at 0.5 A/g. This outstanding reversible capacity and sustained stability over numerous cycles highlights its potential for a wide range of applications.

Structural regulation enabled stable hollow molybdenum diselenide nanosheet anode for ultrahigh energy density sodium ion pouch cell

For the continued use of sodium-ion batteries (SIBs), which require matching anode materials, it is crucial to create high energy density energy storage devices. Here, hollow nanoboxes shaped carbon supported sulfur-doped MoSe2 nanosheets (S-MoSe2@NC) are fabricated by in situ growth and heterodoping strategy. This ensures that the MoSe2 nanosheets are tightly anchored to the nanoboxes carbon, and the structure can effectively buffer the volume stress caused by sodium ion (de)intercalation, as well as providing abundant ion/electron migration transportations. As anode for SIBs, the S-MoSe2@NC shows a higher rate capability and excellent cycling stability (431.1 mAh/g after 1100 cycles at 10 A/g). This excellent cycle life and high rate ability are due to the structural stability and outstanding electronic conductance with reduced band gap of the S-MoSe2@NC, as evidenced by the diffusion analysis and theoretical calculation. In order to promote the application of SIBs, the S-MoSe2@NC and NaNi1/3Fe1/3Mn1/3O2 were assembled into a pouch cell, and the test found that besides the excellent cycle rate performance, the ultrahigh energy density of 256 Wh kg−1 and flexible characteristics can be achieved. This study has proven that building a structure with a rock-steady foundation and quick ion migration may efficiently control sodium storage and pave the way for novel applications of high-performance transition metal dichalcogenides in sodium storage.

Two-dimensional layered In2P3S9: A novel superior anode material for sodium-ion batteries

Developing reliable and efficient anode materials is essential for the successfully practical application of sodium-ion batteries. Herein, employing a straightforward and rapid chemical vapor deposition technique, two-dimensional layered ternary indium phosphorus sulfide (In2P3S9) nanosheets are prepared. The layered structure and ternary composition of the In2P3S9 electrode result in impressive electrochemical performance, including a high reversible capacity of 704 mA h g−1 at 0.1 A g−1, an outstanding rate capability with 425 mA h g−1 at 5 A g−1, and an exceptional cycling stability with a capacity retention of 88% after 350 cycles at 1 A g−1. Furthermore, sodium-ion full cell also affords a high capacity of 308 and 114 mA h g−1 at 0.1 and 5 A g−1. Ex-situ X-ray diffraction and ex-situ high-resolution transmission electron microscopy tests are conducted to investigate the underlying Na-storage mechanism of In2P3S9. The results reveal that during the first cycle, the P–S bond is broken to form the elemental P and In2S3, collectively contributing to a remarkably high reversible specific capacity. The excellent electrochemical energy storage results corroborate the practical application potential of In2P3S9 for sodium-ion batteries.

An effective strategy to prepare non-graphitic carbon with increased pseudo-graphitic content for sodium-ion battery anode with enhanced plateau capacity

The practical application of sodium-ion batteries is mainly hindered by relatively low energy density, which can be effectively overcome by increasing the pseudo-graphitic content in non-graphitic carbon (NGC) anodes. Herein, a simple and efficient strategy was reported to promote the growth of pseudo-graphitic domains in NGC thanks to the synergistic effect of pre-carbonization and NaOH etching using semi-coke as precursor. Based on pre-carbonization at 800 °C and NaOH etching with NaOH/carbon ratio of 0.5 at 600 °C, the resultant NGC (FC-800–0.5–600) exhibits a 13 % increase in percentage of pseudo-graphitic structure meanwhile 14 % decrease for graphite-like structure, but similar content of highly disordered structure compared with its counterpart. Notably, although similar in sloping capacity, FC-800–0.5–600 possesses much higher plateau capacity (<0.1 V) of 218.6 mAh g−1 than its counterpart (174.9 mAh g−1), which is attributed to the enhanced “interlayer intercalation” effect related with pseudo-graphitic structure. Thus, FC-800–0.5–600 can deliver an impressive reversible capacity of 326.8 mAh g−1 at 20 mA g−1, together with a considerable ICE of 84.7 %. This work proposed an effective strategy to increase pseudo-graphitic structure content in NGC, providing a rational guide for designing high-performance anodes in SIBs for practical use.

High-performance ε-VOPO4 cathode materials for sodium ion battery applications

The nanoscale ε-VOPO4 materials were successfully prepared by hydrothermal synthesis of H2VOPO4 precursors and further calcination. XRD and AFM characterization showed that the prepared nano-ε-VOPO4 belonged to monoclinic crystalline system with high purity of physical phase and an average particle size of 150 nm. FT-IR spectroscopy showed that the characteristic peak of the H2VOPO4 precursor (at 797 cm−1) disappeared after calcination and a characteristic peak representing ε-VOPO4 was captured at 914 cm−1. Furthermore, the XPS results showed that the V in the prepared ε-VOPO4 was mainly +5 valence. In order to further evaluate the potential of ε-VOPO4 as an energy storage material, it was applied as cathode material in sodium ion battery system. Electrochemical tests have demonstrated that ε-VOPO4 has satisfactory electrochemical performance as cathode material for sodium ion batteries. The initial capacities of ε-VOPO4 electrode materials reached 162.3, 135.1, 86.7, 51.4, and 29.7 mAh g−1 at 0.05, 0.2, 1, 2, and 5 C, respectively, and the long-cycle performance results showed that the electrochemical stability was still superior after 200 cycles at a current density of 0.5 C. Meanwhile, the density functional theory calculation shows that the optimized lattice constants (a = 7.279 Å, b = 6.896 Å and c = 7.268 Å) are in good agreement with the experimental data. Notably, the experimental ε-VOPO4 material has a higher voltage plateau than the theoretical calculation, which shows the potential advantage of ε-VOPO4 as a new generation electrode material for high energy storage systems.

A topological nodal surface carbon honeycomb for sodium-ion battery anode

Motivated by the successful synthesis of three-dimensional (3D) graphene monoliths, we propose a 3D carbon honeycomb structure, tC40, composed of graphene-nanoribbons linked with 5-5-8 defects based on first-principles calculations. This structure is not only dynamically, thermally, and mechanically stable, but also possesses interesting electronic properties, including the multiple topological nodal surfaces on the high-symmetry plane k3=0 with double and quadruple degeneracies of bands in the reciprocal space, and the nontrivial surface states connecting different topological nodal surfaces parallel to the z-axis. By using the k·p model, we further show that, unlike previously reported nodal surfaces, the energy dispersion of the quadruply degenerated nodal surface is proportional to the k32, while the Hamiltonian of the doubly degenerated nodal surface is formed by the essential degeneracy of the valence and conduction bands. In addition, we explore the application of this nodal surface carbon as an anode material for sodium-ion batteries (SIBs), and find that tC40 exhibits good performance with a high reversible capacity of 186 mAh·g−1, a low sodium ion migration barrier of 0.1 eV, and a small charging/discharging volume change of 0.79 %. This work expands the family of topological carbon materials and their applications in SIBs.

Binary Metallic CuCo5 S8 Anode for High Volumetric Sodium-Ion Storage.

With the rapid improvement of compact smart devices, fabricating anode materials with high volumetric capacity has gained substantial interest for future sodium-ion batteries (SIBs) applications. Herein, a novel bimetal sulfide CuCo5 S8 material is proposed with enhanced volumetric capacity due to the intrinsic metallic electronic conductivity of the material and multi-electron transfer during electrochemical procedures. Due to the intrinsic metallic behavior, the conducting additive (CA) could be removed from the electrode fabrication without scarifying the high rate capability. The CA-free CuCo5 S8 electrode can achieve a high volumetric capacity of 1436.4 mA h cm-3 at a current density of 0.2 A g-1 and 100 % capacity retention over 2000 cycles in SIBs, outperforming most metal chalcogenides, owing to the enhanced electrode density. Reversible conversion reactions are revealed by combined measurements for sodium systems. The proposed new strategy offers a viable approach for developing innovative anode materials with high-volumetric capacity.

The ultralong Mo4O11 nanoribbons: Ultrasonic synthesis and topotactic transformation toward high-performance sodium-ion batteries

The design and synthesis of two-dimensional layered transitional metal oxides (TMOs) have been of great interest for their potential application in sodium-ion batteries (SIBs), due to the advantages such as multivalent ions and tunable interlayer spacing. However, achieving a well-defined crystal structural topology and geometric morphology in TMOs still remains a significant challenge, particularly in tailoring their polyhedral structures. Herein, the ultralong Mo4O11 nanoribbons (Mo4O11-NR) were prepared by a simple aniline-assisted sonochemical method for the first time. The resulting nanoribbons possess a unique tunnel structure and exhibit topologically frustrated arrangements of MoO6 octahedra and MoO4 tetrahedra. When used as anodes for SIBs, multielectron redox reactions of Mo4O11-NR allow for high-capacity energy storage. The buffered volume expansion of the nanoribbons accommodates the strain that occurs during cycling, thereby boosting cycling stability. The topologically frustrated arrangements of the polyhedra further contribute to the efficient storage and transfer of ions and electrons. As a result, Mo4O11-NR anode achieves a reversible specific capacity of 101 mA h g−1 after 2,000 cycles, when subjected to a high current density of 5 A g−1. This exceptional performance highlights the potential of Mo4O11-NR material as an advanced anode material for high-power devices.

Anion-derived cathode interface engineering enables ether-based electrolytes for sodium-ion batteries

High-performance sodium-ion batteries (SIBs) require not only non-aqueous electrolytes with high ion conductivity but also high interfacial compatibility with both electrodes. Ether-based electrolytes are considered one of the most promising electrolyte systems for SIBs due to the advantages of high reduction stability and weakly desolvating power. However, conventional ether-based electrolytes are easy to decompose and deteriorate on the cathode/electrolyte interface under high voltage, which greatly restricts their practical application in SIBs. Herein, a novel and effective interfacial stabilization strategy is proposed and systemically investigated. A homogeneous and compact cathode electrolyte interphase (CEI) film rich in fluorides and borides can be successfully constructed on the cathode surface by pre-cycling of NVP@C cathode in the NaODFB-DEGDME electrolyte. The ODFB anion-derived CEI film can effectively inhibit the continuous oxidation decomposition of NaPF6-DEGDME electrolytes. As a result, the Na||NVP@C half-cell can stably cycle for 1500 cycles with high average Coulombic efficiency (CE, >99.7 %) at 5C. This work illustrates the significance of the composition and structure of CEI film for improving the interfacial stability of high-voltage SIBs with ether-based electrolytes.

A novel Na8Fe5(SO4)9@rGO cathode material with high rate capability and ultra-long lifespan for low-cost sodium-ion batteries

Sodium-ion batteries (SIBs) are regarded as the most promising technology for large-scale energy storage systems. However, the practical application of SIBs is still hindered by the lack of applicable cathode materials. Herein, a novel phase-pure polyanionic Na8Fe5(SO4)9 is designed and employed as a cathode material for SIBs for the first time. The Na8Fe5(SO4)9 has an alluaudite-type sulfate framework and small Na+ ion diffusion barriers. As expected, the as-synthesized Na8Fe5(SO4)9@rGO exhibits a high working potential of 3.8 ​V (versus Na/Na+), a superior reversible capacity of 100.2 mAh g−1 at 0.2 ​C, excellent rate performance (∼80 mAh g−1 at 10 ​C, ∼63 mAh g−1 at 50 ​C), and an ultra-long cycling life (91.9% capacity retention after 10,000 cycles at 10 ​C, 81% capacity retention after 20,000 cycles at 50 ​C). We use various techniques and computational methods to comprehensively investigate the electrochemical reaction mechanisms of Na8Fe5(SO4)9@rGO.

Research progress of organic liquid electrolyte for sodium ion battery.

Electrochemical energy storage technology has attracted widespread attention due to its low cost and high energy efficiency in recent years. Among the electrochemical energy storage technologies, sodium ion batteries have been widely focused due to the advantages of abundant sodium resources, low price and similar properties to lithium. In the basic structure of sodium ion battery, the electrolyte determines the electrochemical window and electrochemical performance of the battery, controls the properties of the electrode/electrolyte interface, and affects the safety of sodium ion batteries. Organic liquid electrolytes are widely used because of their low viscosity, high dielectric constant, and compatibility with common cathodes and anodes. However, there are problems such as low oxidation potential, high flammability and safety hazards. Therefore, the development of novel, low-cost, high-performance organic liquid electrolytes is essential for the commercial application of sodium ion batteries. In this paper, the basic requirements and main classifications of organic liquid electrolytes for sodium ion batteries have been introduced. The current research status of organic liquid electrolytes for sodium ion batteries has been highlighted, including compatibility with various types of electrodes and electrochemical properties such as multiplicative performance and cycling performance of electrode materials in electrolytes. The composition, formation mechanism and regulation strategies of interfacial films have been explained. Finally, the development trends of sodium ion battery electrolytes in terms of compatibility with materials, safety and stable interfacial film formation are pointed out in the future.

Poly(p-phenylenediamine)-Coated Metal-Organic Frameworks for High-Performance Sodium-Ion Batteries: The Balance of Capacity and Stability.

Metal-organic frameworks (MOFs) with well-defined porous structures and highly active frameworks are considered as promising electrode materials for sodium-ion batteries (SIBs). However, the structure pulverization upon sodiation/desodiation impacts on their practical application in SIBs. To address this issue, poly(p-phenylenediamine) (PPA) was uniformly coated onto the surface of MIL-88A, a typical Fe-based MOF through in situ polymerization initiated by the metal ions (Fe3+) of MIL-88A. Used as an anode material for SIBs, the PPA-coated MIL-88A, denoted as PPA@MIL-88A, showed significantly improved electrochemical performance. A reversible capacity as high as 230 mAh g-1 was achieved at 0.2 A g-1 even after 500 cycles. MIL-88A constructed with electrochemically active Fe3+ and fumaric acid ligands guarantees the high specific capacity, while the PPA polymer coating effectively inhibits the pulverization of MIL-88A. This work provides an efficient strategy for improving the structure and cycling stability of MOFs-based electrode materials.

Kinetically well-matched porous framework dual carbon electrodes for high-performance sodium-ion hybrid capacitors

Sodium-ion hybrid capacitors (SIHCs) have attracted extensive interest due to their applications in sodium-ion batteries and capacitors, which have been considered expectable candidates for large-scale energy storage systems. The crucial issues for achieving high-performance SIHCs are the reaction kinetics imbalances between the slow Faradic battery-type anodes and fast non-Faradaic capacitive cathodes. Herein, we propose a simple self-template strategy to prepare kinetically well-matched porous framework dual-carbon electrodes for high-performance SIHCs, which stem from the single precursor, sodium ascorbate. The porous framework carbon (PFC) is obtained by direct calcination of sodium ascorbate followed by a washing process. The sodium-ion half cells with PFC anodes exhibit high reversible capacity and fast electrochemical kinetics for sodium storage. Moreover, the as-obtained PFC can be further converted to porous framework activated carbon (PFAC) with rich porosity and a high specific surface area, which displays high capacitive properties. By using kinetically well-matched battery-type PFC anodes and capacitive PFAC cathodes, dual-carbon SIHCs are successfully assembled, which can work well in 0–4 V. The optimal PFC//PFAC SIHC exhibits high energy density (101.6 Wh kg−1 at 200 W kg−1), power density (20 kW kg−1 at 51.1 Wh kg−1), and cyclic performance (71.8 % capacitance attenuation over 10,000 cycles).

The Future of Energy Storage: Detailed Description of Layered Structure and Porosity of Hard Carbons

The effort of commissioning green and renewable energy with the growing list of critical raw materials demands innovations in energy storage and conversion [1]. The research on sodium-ion batteries (SIBs) has proved promising for large-scale stationary energy storage. Therefore, the crucial need for material research for SIB applications has motivated the studies on hard carbon anodes that have shown high reversible capacity and low working potential[2]. Nevertheless, the exact sodium storage mechanism in hard carbons remains uncertain, inspiring the detailed study of the structure of non-graphitized carbons. Yet, the structure of hard carbons has no long-range order, which complicates the exact characterization. Thus, we present a study focusing on the chemically activated hard carbons' porous and graphite-like structures with complementary wide- and small-angle scattering methods (Figure 1). The current presentation examines the exact impact of the ratio of activating agents on the structure of hard carbons and how the structure affects the ability to store sodium ions. The studied materials were synthesized from D-glycose via hydrothermal carbonization and activated with zinc chloride with different ratios[3]. The evaluation of the layered structure of carbons from wide-angle x-ray scattering (WAXS) data was carried out with Ruland and Smarsly algorithm[4], which is more suitable for non-graphitic carbons than the typically used approaches. The porous structure was described with small-angle neutron scattering (SANS) data model-free analysis, combining Schiller, Mering, Perret, and Ruland approaches[5].This presentation reveals exciting results from the detailed data analysis that opens new perspectives to the material development for SIB hard carbon anodes. During activation of the hard carbon materials activated with zinc chloride with ratios 1:1.5 and 1:2 significant differences in the interlayer arrangement, pore sizes, and the degree of disorder appeared. The presented results indicate the role of different structural parameters on the charge-discharge plateau and sloping regions, guiding to the better understanding of the sodium storage mechanism in hard carbon anode. The presentation demonstrates the interpretation of the results with a focus on improving energy storage capability. It is discussed: is the detailed structural analysis for the non-graphitic carbons a comprehensive and new sight into the future of energy storage?[1] Critical Raw Materials for Strategic Technologies and Sectors in the EU A Foresight Study, (2020).[2] A. Adamson, R. Väli, M. Paalo, J. Aruväli, M. Koppel, R. Palm, E. Hark, J. Nerut, T. Romann, E. Lust, A. Jänes, Peat-Derived Hard Carbons for High Capacity Sodium-Ion Batteries: Synthesis and Characterization, ECS Meet. Abstr., MA2020-02 (2020) 78.[3] M. Härmas, T. Thomberg, A. Jänes, Effect of Zinc Chloride Activation on D-Glucose Derived Carbons Based Capacitors Performance in Ionic Liquid, J. Electrochem. Soc., 167 (2020) 080533.[4] W. Ruland, B. Smarsly, X-ray scattering of non-graphitic carbon: an improved method of evaluation, J. Appl. Crystallogr., 35 (2002) 624–633.[5] E. Härk, M. Ballauff, Carbonaceous Materials Investigated by Small-Angle X-ray and Neutron Scattering, C, 6 (2020) 82. Figure 1

An impact of sea sponge-derived hard carbon with the symbiosis of sodium ion battery and biomedical applications

BackgroundSodium is pervasive and enormous compared to that of lithium. SIBs have turned out to be factual competitors to LIBs besides storage purposes, the power battery technology intended for electric vehicle transport. The choice of selecting SIBs is effective due to their alluring properties of biomaterials for synthesizing electrode materials. Hard carbon, (HC) owing to its amorphous and highly porous nature of the material leads to the intercalation/deintercalation of sodium ions. MethodsIn this work, the sea sponge (SS) was carbonized by the chemical-activating pyrolysis method. The as-prepared HCs using different chemical activating agents (KOH, NaOH, ZnCl2) reveals the diversified sodium-ion storage behaviors. Significant findingsSS attained a charge capacity of 347.39 mAh g−1 at a 0.1 C rate. The half maximal (IC50) of sea sponge-derived hard carbon was found to be 11.5, 11.4, 10.7 μg/mL against breast cancer cells (MDA MB - 231). The present work communally addressed the potential anode material and effective cancerous activity of sea sponge-derived hard carbon material.

Practical Cathodes for Sodium‐Ion Batteries: Who Will Take The Crown?

AbstractIn recent decades, sodium‐ion batteries (SIBs) have received increasing attention because they offer cost and safety advantages and avoid the challenges related to limited lithium/cobalt/nickel resources and environmental pollution. Because the sodium storage performance and production cost of SIBs are dominated by the cathode performance, developing cathode materials with large‐scale production capacity is the key to achieving commercial applications of SIBs. Therefore, developing host materials with high energy density, long cycling life, low production cost, and high chemical/environmental stability is crucial for implementing advanced SIBs. Among the developed cathode materials for SIBs, O3‐type sodiated transition‐metal oxides have attracted extensive attention owing to their simple synthesis methods, high theoretical specific capacity, and sufficient Na content. However, the relatively large Na‐ion radius leads to sluggish diffusion kinetics and inevitable complex phase transitions during the deintercalation/intercalation process, resulting in poor rate capability and cycling stability. Therefore, this review comprehensively summarizes the research progress and modification strategies for O3‐type cathodes, including the component design, surface modification, and optimization of synthesis methods. This work aims to guide the development of commercial layered oxides and provide technical support for the next generation of energy‐storage systems.

Electrospinning Polyanionic Materials for High‐Rate Na Storage

AbstractAs emerging energy storage devices, sodium‐ion batteries (SIBs) are perceived as promising alternatives to lithium‐ion batteries (LIBs) due to their low cost and high safety. The cathodic side plays a crucial role in determining the energy density as well as the service life of SIBs, and the polyanionic cathode materials are featured by excellent cycle stability, flexible operating voltage and suitable overall electrochemical properties. However, the intrinsic inferior electronic conductivity limits their rate performance. Recently, the possibility of employing advanced electrospinning techniques to fabricate polyanionic materials has been explored. The facile electrospinning can greatly facilitate the ionic and electronic conduction of cathodes by constructing three‐dimensional (3D) conductive networks with the one‐dimensional (1D) nanofibers, and thus improves their electrochemical performance. In this review, we summarize the research progress of the electro‐spun polyanionic cathodic materials and their applications in SIBs, and present future prospects as well as challenges of the electro‐spun polyanions faced to the ever‐increasing demand of advanced energy storage.

Revealing the structural chemistry in Na6−2xFex(SO4)3 (1.5 ≤ x ≤ 2.0) for low-cost and high-performance sodium-ion batteries

Fe-based polyanionic sulfate materials are one of the most promising candidates for large-scale applications in sodium-ion batteries due to their low cost and excellent electrochemical performance. Although great achievements have been gained on a series of Na6−2xFex(SO4)3 (NFSO-x, 1.5 ≤ x ≤ 2.0) materials such as Na2Fe2(SO4)3, Na2Fe1.5(SO4)3, and Na2.4Fe1.8(SO4)3 for sodium storage, the phase and structure characteristics on these NFSO-x are still controversial, making it difficult to achieve phase-pure materials with optimal electrochemical properties. Herein, six NFSO-x samples with varied x are investigated via both experimental methods and density functional theory calculations to analyze the phase and structure properties. It reveals that a pure phase exists in the 1.6 ≤ x ≤ 1.7 region of the NFSO-x, and part of Na ions tend to occupy Fe sites to form more stable frameworks. The NFSO-1.7 exhibits the best electrochemical performance among the NFSO-x samples, delivering a high discharge capacity (104.5 mAh g−1 at 0.1 C, close to its theoretical capacity of 105 mAh g−1), excellent rate performance (81.5 mAh g−1 at 30 C), and remarkable cycle stability over 10,000 cycles with high-capacity retention of 72.4%. We believe that the results are useful to clarify the phase and structure characteristics of polyanionic materials to promote their application for large-scale energy storage.