Necklace‐Like Structures Composed of Fe3N@C Yolk–Shell Particles as an Advanced Anode for Sodium‐Ion Batteries

It is of great importance to develop cost‐effective electrode materials for large‐scale use of Na‐ion batteries. Here, a binder‐free electrode based on necklace‐like structures composed of Fe₃N@C yolk–shell particles as an advanced anode for Na‐ion batteries is reported. In this electrode, every Fe₃N@C unit has a novel yolk–shell structure, which can accommodate the volumetric changes of Fe₃N during the (de)sodiation processes for superior structural integrity. Moreover, all reaction units are threaded along the carbon fibers, guaranteeing excellent kinetics for the electrochemical reactions. As a result, when evaluated as an anode material for Na‐ion batteries, the Fe₃N@C nano‐necklace electrode delivers a prolonged cycle life over 300 cycles, and achieves a high C‐rate capacity of 248 mAh g^?1 at 2 A g^?1.     

Hierarchically Porous Fe2CoSe4 Binary‐Metal Selenide for Extraordinary Rate Performance and Durable Anode of Sodium‐Ion Batteries

Owing to high energy capacities, transition metal chalcogenides have drawn significant research attention as the promising electrode materials for sodium‐ion batteries (SIBs). However, limited cycle life and inferior rate capabilities still hinder their practical application. Improvement of the intrinsic conductivity by smart choice of elemental combination along with carbon coupling of the nanostructures may result in excellence of rate capability and prolonged cycling stability. Herein, a hierarchically porous binary transition metal selenide (Fe₂CoSe₄, termed as FCSe) nanomaterial with improved intrinsic conductivity was prepared through an exclusive methodology. The hierarchically porous structure, intimate nanoparticle–carbon matrix contact, and better intrinsic conductivity result in extraordinary electrochemical performance through their synergistic effect. The synthesized FCSe exhibits excellent rate capability (816.3 mA h g^?1 at 0.5 A g^?1 and 400.2 mA h g^?1 at 32 A g^?1), extended cycle life (350 mA h g^?1 even after 5000 cycles at 4 A g^?1), and adequately high energy capacity (614.5 mA h g^?1 at 1 A g^?1 after 100 cycles) as anode material for SIBs. When further combined with lab‐made Na₃V₂(PO₄)₃/C cathode in Na‐ion full cells, FCSe presents reasonably high and stable specific capacity.     

Mesoporous NiS2 Nanospheres Anode with Pseudocapacitance for High‐Rate and Long‐Life Sodium‐Ion Battery

It is of great importance to exploit electrode materials for sodium‐ion batteries (SIBs) with low cost, long life, and high‐rate capability. However, achieving quick charge and high power density is still a major challenge for most SIBs electrodes because of the sluggish sodiation kinetics. Herein, uniform and mesoporous NiS₂ nanospheres are synthesized via a facile one‐step polyvinylpyrrolidone assisted method. By controlling the voltage window, the mesoporous NiS₂ nanospheres present excellent electrochemical performance in SIBs. It delivers a high reversible specific capacity of 692 mA h g^?1. The NiS₂ anode also exhibits excellent high‐rate capability (253 mA h g^?1 at 5 A g^?1) and long‐term cycling performance (319 mA h g^?1 capacity remained even after 1000 cycles at 0.5 A g^?1). A dominant pseudocapacitance contribution is identified and verified by kinetics analysis. In addition, the amorphization and conversion reactions during the electrochemical process of the mesoporous NiS₂ nanospheres is also investigated by in situ X‐ray diffraction. The impressive electrochemical performance reveals that the NiS₂ offers great potential toward the development of next generation large scale energy storage.     

A 1D Honeycomb‐Like Amorphous Zincic Vanadate for Stable and Fast Sodium‐Ion Storage

Developing nanomaterials with synergistic effects of various structural merits is considered to be an effective strategy to improve the sluggish ion kinetics and severe structural degradation of sodium‐ion battery (SIB) anodes. Herein, honeycomb‐like amorphous Zn₂V₂O₇ (ZVO‐AH) nanofibers as SIBs anode material with plentiful defective sites, complex cavities, and good mechanical flexibility are reported. The fabrication strategy relies on the expansive and volatile nature of the organic vanadium source, based on a simple electrospinning with subsequent calcination. Originating from the synergies of amorphous nature and honeycomb‐like cavities, ZVO‐AH shows increased electrochemical activity, accelerated Na‐ion diffusion, and robust structure. Impressively, the ZVO‐AH anode delivers superior cycle stability (112% retention at 5 A g^?1 after 5000 cycles) and high rate capability (150 mAh g^?1 at 10 A g^?1). The synthetic versatility is able to synergistically promote the practical application of more potential materials in sodium‐ion storage.     

Unique Cobalt Sulfide/Reduced Graphene Oxide Composite as an Anode for Sodium‐Ion Batteries with Superior Rate Capability and Long Cycling Stability

Exploitation of high‐performance anode materials is essential but challenging to the development of sodium‐ion batteries (SIBs). Among all proposed anode materials for SIBs, sulfides have been proved promising candidates due to their unique chemical and physical properties. In this work, a facile solvothermal method to in situ decorate cobalt sulfide (CoS) nanoplates on reduced graphene oxide (rGO) to build CoS@rGO composite is described. When evaluated as anode for SIBs, an impressive high specific capacity (540 mAh g^?1 at 1 A g^?1), excellent rate capability (636 mAh g^?1 at 0.1 A g^?1 and 306 mAh g^?1 at 10 A g^?1), and extraordinarily cycle stability (420 mAh g^?1 at 1 A g^?1 after 1000 cycles) have been demonstrated by CoS@rGO composite for sodium storage. The synergetic effect between the CoS nanoplates and rGO matrix contributes to the enhanced electrochemical performance of the hybrid composite. The results provide a facile approach to fabricate promising anode materials for high‐performance SIBs.     

Advanced Se3P4@C Anode with Exceptional Cycling Life for High Performance Potassium‐Ion Batteries

Potassium‐ion batteries have attracted increasing attention for next‐generation energy storage systems due to their high energy density and abundance of potassium. However, the lack of suitable anode highly hampers its practical application due to the large ionic radius of K⁺. Herein, a Se₃P₄@mesoporous carbon (Se₃P₄@C) composite is reported as a high‐performance anode for potassium‐ion batteries. The Se₃P₄@C composite is synthesized through an in situ combination reaction between red phosphorus and Se within a porous carbon matrix. In this way, the nano‐sized Se₃P₄ is well confined in the porous carbon and thus exhibits a close contact with the carbon matrix. This can significantly improve the conductivity and alleviate the volume change during the cycling process. As a result, the Se₃P₄@C exhibits a high reversible initial capacity of 1036.8 mAh g^?1 at a current density of 50 mA g^?1 as well as an excellent cycle performance with a capacity decay of 0.07% per cycle over 300 cycles under 1000 mA g^?1. In terms of high specific capacity and stable cycling performance, the Se₃P₄@C anode is a promising candidate for advanced potassium‐ion batteries.     

A Salt‐Templated Strategy toward Hollow Iron Selenides‐Graphitic Carbon Composite Microspheres with Interconnected Multicavities as High‐Performance Anode Materials for Sodium‐Ion Batteries

In this work, a facile salt‐templated approach is developed for the preparation of hollow FeSe₂/graphitic carbon composite microspheres as sodium‐ion battery anodes; these are composed of interconnected multicavities and an enclosed surface in‐plane embedded with uniform hollow FeSe₂ nanoparticles. As the precursor, Fe₂O₃/carbon microspheres containing NaCl nanocrystals are obtained using one‐pot ultrasonic spray pyrolysis in which inexpensive NaCl and dextrin are used as a porogen and carbon source, respectively, enabling mass production of the composites. During post‐treatment, Fe₂O₃ nanoparticles in the composites transform into hollow FeSe₂ nanospheres via the Kirkendall effect. These rational structures provide numerous conductive channels to facilitate ion/electron transport and enhance the capacitive contribution. Moreover, the synergistic effect between the hollow cavities within FeSe₂ and the outstanding mechanical strength of the porous carbon matrix can effectively accommodate the large volume changes during cycling. Correspondingly, the composite microsphere exhibits high discharge capacity of 510 mA h g^?1 after 200 cycles at 0.2 A g^?1 with capacity retention of 88% when calculated from the second cycle. Even at a high current density of 5.0 A g^?1, a high discharge capacity of 417 mA h g^?1 can be achieved.     

O3‐Type Layered Ni‐Rich Oxide: A High‐Capacity and Superior‐Rate Cathode for Sodium‐Ion Batteries

Inspired by its high‐active and open layered framework for fast Li⁺ extraction/insertion reactions, layered Ni‐rich oxide is proposed as an outstanding Na‐intercalated cathode for high‐performance sodium‐ion batteries. An O3‐type Na_0.75Ni_0.82Co_0.12Mn_0.06O₂ is achieved through a facile electrochemical ion‐exchange strategy in which Li⁺ ions are first extracted from the LiNi_0.82Co_0.12Mn_0.06O₂ cathode and Na⁺ ions are then inserted into a layered oxide framework. Furthermore, the reaction mechanism of layered Ni‐rich oxide during Na⁺ extraction/insertion is investigated in detail by combining ex situ X‐ray diffraction, X‐ray photoelectron spectroscopy, and electron energy loss spectroscopy. As an excellent cathode for Na‐ion batteries, O3‐type Na_0.75Ni_0.82Co_0.12Mn_0.06O₂ delivers a high reversible capacity of 171 mAh g^?1 and a remarkably stable discharge voltage of 2.8 V during long‐term cycling. In addition, the fast Na⁺ transport in the cathode enables high rate capability with 89 mAh g^?1 at 9 C. The as‐prepared Ni‐rich oxide cathode is expected to significantly break through the limited performance of current sodium‐ion batteries.     

Size‐, Water‐, and Defect‐Regulated Potassium Manganese Hexacyanoferrate with Superior Cycling Stability and Rate Capability for Low‐Cost Sodium‐Ion Batteries

Potassium manganese hexacyanoferrate (KMHCF) is a low‐cost Prussian blue analogue (PBA) having a rigid and open framework that can accommodate large alkali ions. Herein, the synthesis of KMHCF and its application as a high‐performance cathode in sodium‐ion batteries (NIBs) is reported. High‐quality KMHCF with low amounts of crystal water and defects and with homogeneous microstructure is obtained by controlling the nucleation and grain growth by using a high‐concentration citrate solution as a precipitation medium. The obtained KMHCF exhibits superior cycling and rate performance as a NIB cathode, showing 80% capacity retention after 1000 cycles at 1 C and a high capacity of 95 mA h g^?1 at 20 C. Unlike conventional single‐cation batteries, the hybrid NIB with KMHCF as cathode and Na as anode in Na‐ion electrolyte displays three reversible plateaus that involve stepwise insertion/extraction of both K⁺ and Na⁺ in the PBA framework. In later cycling, the K⁺–Na⁺ cointercalated phase is partially converted into a cubic sodium manganese hexacyanoferrate (NaMHCF) phase due to the increasing replacement of Na⁺ for K⁺.     

High‐Performance Flexible Freestanding Anode with Hierarchical 3D Carbon‐Networks/Fe7S8/Graphene for Applicable Sodium‐Ion Batteries

Sodium‐ion batteries (SIBs) have gained tremendous interest for grid scale energy storage system and power energy batteries. However, the current researches of anode for SIBs still face the critical issues of low areal capacity, limited cycle life, and low initial coulombic efficiency for practical application perspective. To solve this issue, a kind of hierarchical 3D carbon‐networks/Fe₇S₈/graphene (CFG) is designed and synthesized as freestanding anode, which is constructed with Fe₇S₈ microparticles well‐welded on 3D‐crosslinked carbon‐networks and embedded in highly conductive graphene film, via a facile and scalable synthetic method. The as‐prepared freestanding electrode CFG represents high areal capacity (2.12 mAh cm^?2 at 0.25 mA cm^?2) and excellent cycle stability of 5000 cycles (0.0095% capacity decay per cycle). The assembled all‐flexible sodium‐ion battery delivers remarkable performance (high areal capacity of 1.42 mAh cm^?2 at 0.3 mA cm^?2 and superior energy density of 144 Wh kg^?1), which are very close to the requirement of practical application. This work not only enlightens the material design and electrode engineering, but also provides a new kind of freestanding high energy density anode with great potential application prospective for SIBs.     

Graphitic Carbon Nitride (g‐C3N4)‐Derived N‐Rich Graphene with Tuneable Interlayer Distance as a High‐Rate Anode for Sodium‐Ion Batteries

Heteroatom‐doped carbon materials with expanded interlayer distance have been widely studied as anodes for sodium‐ion batteries (SIBs). However, it remains unexplored to further enlarge the interlayer spacing and reveal the influence of heteroatom doping on carbon nanostructures for developing more efficient SIB anode materials. Here, a series of N‐rich few‐layer graphene (N‐FLG) with tuneable interlayer distance ranging from 0.45 to 0.51 nm is successfully synthesized by annealing graphitic carbon nitride (g‐C₃N₄) under zinc catalysis and selected temperature (T = 700, 800, and 900 °C). More significantly, the correlation between N dopants and interlayer distance of resultant N‐FLG‐T highlights the effect of pyrrolic N on the enlargement of graphene interlayer spacing, due to its stronger electrostatic repulsion. As a consequence, N‐FLG‐800 achieves the optimal properties in terms of interlayer spacing, nitrogen configuration and electronic conductivity. When used as an anode for SIBs, N‐FLG‐800 shows remarkable Na⁺ storage performance with ultrahigh rate capability (56.6 mAh g^?1 at 40 A g^?1) and excellent long‐term stability (211.3 mAh g^?1 at 0.5 A g^?1 after 2000 cycles), demonstrating the effectiveness of material design.     

In Situ Formation of Hierarchical Bismuth Nanodots/Graphene Nanoarchitectures for Ultrahigh‐Rate and Durable Potassium‐Ion Storage

Metallic bismuth (Bi) has been widely explored as remarkable anode material in alkali‐ion batteries due to its high gravimetric/volumetric capacity. However, the huge volume expansion up to ≈406% from Bi to full potassiation phase K₃Bi, inducing the slow kinetics and poor cycling stability, hinders its implementation in potassium‐ion batteries (PIBs). Here, facile strategy is developed to synthesize hierarchical bismuth nanodots/graphene (BiND/G) composites with ultrahigh‐rate and durable potassium ion storage derived from an in situ spontaneous reduction of sodium bismuthate/graphene composites. The in situ formed ultrafine BiND (≈3 nm) confined in graphene layers can not only effectively accommodate the volume change during the alloying/dealloying process but can also provide high‐speed channels for ionic transport to the highly active BiND. The BiND/G electrode provides a superior rate capability of 200 mA h g^?1 at 10 A g^?1 and an impressive reversible capacity of 213 mA h g^?1 at 5 A g^?1 after 500 cycles with almost no capacity decay. An operando synchrotron radiation‐based X‐ray diffraction reveals distinctively sharp multiphase transitions, suggesting its underlying operation mechanisms and superiority in potassium ion storage application.