Boosting Sodium Storage in TiO2 Nanotube Arrays through Surface Phosphorylation

Sodium‐ion batteries (SIBs) offer a promise of a scalable, low‐cost, and environmentally benign means of renewable energy storage. However, the low capacity and poor rate capability of anode materials present an unavoidable challenge. In this work, it is demonstrated that surface phosphorylated TiO₂ nanotube arrays grown on Ti substrate can be efficient anode materials for SIBs. Fabrication of the phosphorylated nanoarray film is based on the electrochemical anodization of Ti metal in NH₄F solution and subsequent phosphorylation using sodium hypophosphite. The phosphorylated TiO₂ nanotube arrays afford a reversible capacity of 334 mA h g^?1 at 67 mA g^?1, a superior rate capability of 147 mA h g^?1 at 3350 mA g^?1, and a stable cycle performance up to 1000 cycles. In situ X‐ray diffraction and transmission electron microscopy reveal the near‐zero strain response and robust mechanical behavior of the TiO₂ host upon (de)sodiation, suggesting its excellent structural stability in the Na⁺ storage application.     

Construction of Inorganic/Organic Hybrid Layer for Stable Na Metal Anode Operated under Wide Temperatures

Sodium metal battery is supposed to be a propitious technology for high-energy storage application owing to the advantages of natural abundance and low cost. Unfortunately, the uncontrollable dendrite growth critically hampers its practical implementation. Herein, an inorganic/organic hybrid layer of NaF/C F/CC on the surface of Na foil (IOHL-Na) is designed and synthesized through the in situ reaction of polyvinylidene fluoride (PVDF) and metallic sodium. This protective layer possesses satisfactory Young's modulus, good kinetic property, and sodiophilicity, which can distinctly stabilize Na metal anode. As a result, the symmetric IOHL-Na cell achieves a lifespan of 770 h at 1 mAh cm⁻²/1 mA cm⁻² in carbonate electrolyte. The assembled full battery of IOHL-Na||Na₃V₂(PO₄)₃ delivers a high discharge capacity of 85 mAh g⁻¹ at 10 C after 600 cycles under ambient temperature. Furthermore, the IOHL-Na||Na₃V₂(PO₄)₃ cell still can steadily operate at 10 C for 600 cycles at 55 °C. And when testing at an ultralow temperature of −40 °C, the full cell achieves 40 mAh g⁻¹ at 0.5 C with a prolonged lifespan of 450 cycles. This work offers a new approach to protect the metal sodium anode without dendrite growth under wide temperatures.     

Fe2VO4 Hierarchical Porous Microparticles Prepared via a Facile Surface Solvation Treatment for High‐Performance Lithium and Sodium Storage

Preventing the aggregation of nanosized electrode materials is a key point to fully utilize the advantage of the high capacity. In this work, a facile and low‐cost surface solvation treatment is developed to synthesize Fe₂VO₄ hierarchical porous microparticles, which efficiently prevents the aggregation of the Fe₂VO₄ primary nanoparticles. The reaction between alcohol molecules and surface hydroxy groups is confirmed by density functional theory calculations and Fourier transform infrared spectroscopy. The electrochemical mechanism of Fe₂VO₄ as lithium‐ion battery anode is characterized by in situ X‐ray diffraction for the first time. This electrode material is capable of delivering a high reversible discharge capacity of 799 mA h g^?1 at 0.5 A g^?1 with a high initial coulombic efficiency of 79%, and the capacity retention is 78% after 500 cycles. Moreover, a remarkable reversible discharge capacity of 679 mA h g^?1 is achieved at 5 A g^?1. Furthermore, when tested as sodium‐ion battery anode, a high reversible capacity of 382 mA h g^?1 can be delivered at the current density of 1 A g^?1, which still retains at 229 mA h g^?1 after 1000 cycles. The superior electrochemical performance makes it a potential anode material for high‐rate and long‐life lithium/sodium‐ion batteries.     

Synergizing Phase and Cavity in CoMoOxSy Yolk–Shell Anodes to Co‐Enhance Capacity and Rate Capability in Sodium Storage

Sodium‐ion batteries (SIBs) have been recognized as the promising alternatives to lithium‐ion batteries for large‐scale applications owing to their abundant sodium resource. Currently, one significant challenge for SIBs is to explore feasible anodes with high specific capacity and reversible pulverization‐free Na⁺ insertion/extraction. Herein, a facile co‐engineering on polymorph phases and cavity structures is developed based on CoMo‐glycerate by scalable solvothermal sulfidation. The optimized strategy enables the construction of CoMoO_xS_y with synergized partially sulfidized amorphous phase and yolk–shell confined cavity. When developed as anodes for SIBs, such CoMoO_xS_y electrodes deliver a high reversible capacity of 479.4 mA h g^?1 at 200 mA g^?1 after 100 cycles and a high rate capacity of 435.2 mA h g^?1 even at 2000 mA g^?1, demonstrating superior capacity and rate capability. These are attributed to the unique dual merits of the anodes, that is, the elastic bountiful reaction pathways favored by the sulfidation‐induced amorphous phase and the sodiation/desodiation accommodatable space benefits from the yolk–shell cavity. Such yolk–shell nano‐battery materials are merited with co‐tunable phases and structures, facile scalable fabrication, and excellent capacity and rate capability in sodium storage. This provides an opportunity to develop advanced practical electrochemical sodium storage in the future.     

Porous BN Nanofibers Enable Long‐Cycling Life Sodium Metal Batteries

Sodium metal anode, featuring high capacity, low voltage and earth abundance, is desirable for building advanced sodium‐metal batteries. However, Na‐ion deposition typically leads to morphological instability and notorious chemical reactivity between sodium and common electrolytes still limit its practical application. In this study, a porous BN nanofibers modified sodium metal (BN/Na) electrode is introduced for enhancing Na‐ion deposition dynamics and stability. As a result, symmetrical BN/Na cells enable an impressive rate capability and markedly enhanced cycling durability over 600 h at 10 mA cm^?2. Density functional theory simulations demonstrate BN could effectively improve Na‐ion adsorption and diffusion kinetics simultaneously. Finite element simulation clearly reveals the intrinsic smoothing effect of BN upon multiple Na‐ion plating/stripping cycles. Coupled with a Na₃V₂O₂(PO₄)₂F/Ti₃C₂X cathode, sodium metal full cells offer an ultrastable capacity of 125/63 mA h g^?1 (≈420/240 Wh kg^?1) at 0.05/5 C rate over 500 cycles. These comprehensive analyses demonstrate the feasibility of BN/Na anode for the establishment of high‐energy‐density sodium‐metal full batteries.     

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.     

Hierarchical Porous Nanosheets Constructed by Graphene‐Coated,Interconnected TiO2 Nanoparticles for Ultrafast Sodium Storage

Sodium‐ion batteries (SIBs) are considered promising next‐generation energy storage devices. However, a lack of appropriate high‐performance anode materials has prevented further improvements. Here, a hierarchical porous hybrid nanosheet composed of interconnected uniform TiO₂ nanoparticles and nitrogen‐doped graphene layer networks (TiO₂@NFG HPHNSs) that are synthesized using dual‐functional C₃N₄ nanosheets as both the self‐sacrificing template and hybrid carbon source is reported. These HPHNSs deliver high reversible capacities of 146 mA h g^?1 at 5 C for 8000 cycles, 129 mA h g^?1 at 10 C for 20 000 cycles, and 116 mA h g^?1 at 20 C for 10 000 cycles, as well as an ultrahigh rate capability up to 60 C with a capacity of 101 mA h g^?1. These results demonstrate the longest cyclabilities and best rate capability ever reported for TiO₂‐based anode materials for SIBs. The unprecedented sodium storage performance of the TiO₂@NFG HPHNSs is due to their unique composition and hierarchical porous 2D structure.     

Stable Metal Anode enabled by Porous Lithium Foam with Superior Ion Accessibility

Lithium (Li) metal anodes have attracted much interest recently for high‐energy battery applications. However, low coulombic efficiency, infinite volume change, and severe dendrite formation limit their reliable implementation over a wide range. Here, an outstanding stability for a Li metal anode is revealed by designing a highly porous and hollow Li foam. This unique structure is capable of tackling many Li metal problems simultaneously: first, it assures uniform electrolyte distribution over the inner and outer electrode's surface; second, it reduces the local current density by providing a larger electroactive surface area; third, it can accommodate volume expansion and dissipate heat efficiently. Moreover, the structure shows superior stability compared to fully Li covered foam with low porosity, and bulky Li foil electrode counterparts. This Li foam exhibits small overpotential (≈25 mV at 4 mA cm^?2) and high cycling stability for 160 cycles at 4 mA cm^?2. Furthermore, when assembled, the porous Li metal as the anode with LiFePO₄ as the cathode for a full cell, the battery has a high‐rate performance of 138 mAh g^?1 at 0.2 C. The beneficial structure of the Li hollow foam is further studied through density functional theory simulations, which confirms that the porous structure has better charge mobility and more uniform Li deposition.     

In Situ Formation of Polysulfonamide Supported Poly(ethylene glycol) Divinyl Ether Based Polymer Electrolyte toward Monolithic Sodium Ion Batteries

Sodium ion battery is one of the promising rechargeable batteries due to the low‐cost and abundant sodium sources. In this work, a monolithic sodium ion battery based on a Na₃V₂(PO₄)₃ cathode, MoS₂ layered anode, and polyether‐based polymer electrolyte is reported. In addition, a new kind of polysulfonamide‐supported poly(ethylene glycol) divinyl ether based polymer electrolyte is also demonstrated for monolithic sodium ion battery via in situ preparation. The resultant polymer electrolyte exhibits relatively high ionic conductivity (1.2 mS cm^?1) at ambient temperature, wide electrochemical window (4.7 V), and favorable mechanical strength (25 MPa). Moreover, such a monolithic Na₃V₂(PO₄)₃/MoS₂ sodium ion battery using this polymer electrolyte delivers outstanding rate capability (up to 10 C) and superior cyclic stability (84%) after 1000 cycles at 0.5 C. What is more essential, such a polymer electrolyte based soft‐package monolithic sodium ion cell can still power a red light emitting diode lamp and run finite times without suffering from any internal short‐circuit failures, even in the case of a bended and wrinkled state. Considering these aspects, this work no doubt provides a new approach for the design of a high‐performance polymer electrolyte toward monolithic sodium ion battery with exceptional rate capability and high safety.     

Boosting the Reversibility of Sodium Metal Anode via Heteroatom‐Doped Hollow Carbon Fibers

Sodium (Na) metal anodes stand out with their remarkable capacity and natural abundance. However, the dendritic Na growth, infinite dimensional changes, and low Coulombic efficiency (CE) present key bottlenecks plaguing practical applications. Here, heteroatom‐doped (nitrogen, sulfur) hollow carbon fibers (D‐HCF) are rationally synthesized as a nucleation‐assisting host to enable a highly reversible Na metal. The “sodiophilic” functional groups introduced by the heteroatom‐doping and large surface area (≈1052 m² g^?1) synchronously contribute to a homogenous plating morphology with dissipated local current density. High “sodiophilicity” of the D‐HCF is confirmed by first‐principle calculations and experimental results, where strong adsorption energy of ?3.52 eV with low Na⁺ nucleation overpotential of 3.2 mV at 0.2 mA cm^?2 is realized. As such, highly reversible plating/stripping is achieved at 1.0 mA cm^?2 with average CE approximating 99.52% over 600 cycles. The as‐assembled Na@D‐HCF symmetric cells exhibit a prolonged lifetime for 1000 h. A full‐cell paired with Na₃V₂(PO₄)₃ cathode further demonstrates stable electrochemical behavior for 200 cycles at 1 C along with excellent rate performance (102 mAh g^?1 at 5 C). The results clearly show the effectiveness of the D‐HCF in manipulating Na⁺ deposition and thus the significance of nucleation control in realizing dendrite‐free metal anodes.     

High Areal Capacity and Lithium Utilization in Anodes Made of Covalently Connected Graphite Microtubes

Lithium metal is an attractive anode material for rechargeable batteries because of its high theoretical specific capacity of 3860 mA h g^?1 and the lowest negative electrochemical potential of ?3.040 V versus standard hydrogen electrode. Despite extensive research efforts on tackling the safety concern raised by Li dendrites, inhibited Li dendrite growth is accompanied with decreased areal capacity and Li utilization, which are still lower than expectation for practical use. A scaffold made of covalently connected graphite microtubes is reported, which provides a firm and conductive framework with moderate specific surface area to accommodate Li metal for anodes of Li batteries. The anode presents an areal capacity of 10 mA h cm^?2 (practical gravimetric capacity of 913 mA h g^?1) at a current density of 10 mA cm^?2, with Li utilization of 91%, Coulombic efficiencies of ≈97%, and long lifespan of up to 3000 h. The analysis of structure evolution during charge/discharge shows inhibited lithium dendrite growth and a reversible electrode volume change of ≈9%. It is suggested that an optimized microstructure with moderate electrode/electrolyte interface area is critical to accommodate volume change and inhibit the risks of irreversible Li consumption by side reactions and Li dendrite growth for high‐performance Li‐metal anodes.     

Facile Synthesis of Ultrasmall CoS2 Nanoparticles within Thin N‐Doped Porous Carbon Shell for High Performance Lithium‐Ion Batteries

Cobalt sulfide (CoS₂) is considered one of the most promising alternative anode materials for high‐performance lithium‐ion batteries (LIBs) by virtue of its remarkable electrical conductivity, high theoretical capacity, and low cost. However, it suffers from a poor cycling stability and low rate capability because of its volume expansion and dissolution of the polysulfide intermediates in the organic electrolytes during the battery charge/discharge process. In this study, a novel porous carbon/CoS₂ composite is prepared by using nano metal–organic framework (MOF) templates for high‐preformance LIBs. The as‐made ultrasmall CoS₂ (15 nm) nanoparticles in N‐rich carbon exhibit promising lithium storage properties with negligible loss of capacity at high charge/discharge rate. At a current density of 100 mA g^?1, a capacity of 560 mA h g^?1 is maintained after 50 cycles. Even at a current density as high as 2500 mA g^?1, a reversible capacity of 410 mA h g^?1 is obtained. The excellent and highly stable battery performance should be attributed to the synergism of the ultrasmall CoS₂ particles and the thin N‐rich porous carbon shells derieved from nanosized MOF precusors.     

Large‐Area,Uniform, Aligned Arrays of Na3(VO)2(PO4)2F on Carbon Nanofiber for Quasi‐Solid‐State Sodium‐Ion Hybrid Capacitors

Sodium–vanadium fluorophosphate (Na₃V₂O_2x(PO₄)₂F_3?2x, NVPF, 0 ≤ x ≤ 1) is considered to be a promising Na‐storage cathode material due to its high operation potentials (3.6–4 V) and minor volume variation (1.8%) during Na⁺‐intercalation. Research about NVPF is mainly focused on powder‐type samples, while its ordered array architecture is rarely reported. In this work, large‐area and uniform Na₃(VO)₂(PO₄)₂F cuboid arrays are vertically grown on carbon nanofiber (CNF) substrates for the first time. Owing to faster electron/ion transport and larger electrolyte–electrode contact area, the as‐prepared NVPF array electrode exhibits much improved Na‐storage properties compared to its powder counterpart. Importantly, a quasi‐solid‐state sodium‐ion hybrid capacitor (SIHC) is constructed based on the NVPF array as an intercalative battery cathode and porous CNF as a capacitive supercapacitor anode together with the P(VDF‐HFP)‐based polymer electrolyte. This novel hybrid system delivers an attractive energy density of ≈227 W h kg^?1 (based on total mass of two electrodes), and still remains as high as 107 Wh kg^?1 at a high specific power of 4936 W kg^?1, which pushes the energy output of sodium hybrid capacitors toward a new limit. In addition, the growth mechanism of NVPF arrays is investigated in detail.     

Nontopotactic Reaction in Highly Reversible Sodium Storage of Ultrathin Co9Se8/rGO Hybrid Nanosheets

Transition metal chalcogenide with tailored nanosheet architectures with reduced graphene oxide (rGO) for high performance electrochemical sodium ion batteries (SIBs) are presented. Via one‐step oriented attachment growth, a facile synthesis of Co₉Se₈ nanosheets anchored on rGO matrix nanocomposites is demonstrated. As effective anode materials of SIBs, Co₉Se₈/rGO nanocomposites can deliver a highly reversible capacity of 406 mA h g^?1 at a current density of 50 mA g^?1 with long cycle stability. It can also deliver a high specific capacity of 295 mA h g^?1 at a high current density of 5 A g^?1 indicating its high rate capability. Furthermore, ex situ transmission electron microscopy observations provide insight into the reaction path of nontopotactic conversion in the hybrid anode, revealing the highly reversible conversion directly between the hybrid Co₉Se₈/rGO and Co nanoparticles/Na₂Se matrix during the sodiation/desodiation process. In addition, it is experimentally demonstrated that rGO plays significant roles in both controllable growth and electrochemical conversion processes, which can not only modulate the morphology of the product but also tune the sodium storage performance. The investigation on hybrid Co₉Se₈/rGO nanosheets as SIBs anode may shed light on designing new metal chalcogenide materials for high energy storage system.     

N‐Doped Carbon Nanofibers with Interweaved Nanochannels for High‐Performance Sodium‐Ion Storage

Although graphite materials have been applied as commercial anodes in lithium‐ion batteries (LIBs), there still remain abundant spaces in the development of carbon‐based anode materials for sodium‐ion batteries (SIBs). Herein, an electrospinning route is reported to fabricate nitrogen‐doped carbon nanofibers with interweaved nanochannels (NCNFs‐IWNC) that contain robust interconnected 1D porous channels, produced by removal of a Te nanowire template that is coelectrospun within carbon nanofibers during the electrospinning process. The NCNFs‐IWNC features favorable properties, including a conductive 1D interconnected porous structure, a large specific surface area, expanded interlayer graphite‐like spacing, enriched N‐doped defects and active sites, toward rapid access and transport of electrolyte and electron/sodium ions. Systematic electrochemical studies indicate that the NCNFs‐IWNC exhibits an impressively high rate capability, delivering a capacity of 148 mA h g^?1 at current density of as high as 10 A g^?1, and has an attractively stable performance over 5000 cycles. The practical application of the as‐designed NCNFs‐IWNC for a full SIBs cell is further verified by coupling the NCNFs‐IWNC anode with a FeFe(CN)₆ cathode, which displays a desirable cycle performance, maintaining acapacity of 97 mA h g^?1 over 100 cycles.     

Self‐Formed Electronic/Ionic Conductive Fe3S4 @ S @ 0.9Na3SbS4⋅0.1NaI Composite for High‐Performance Room‐Temperature All‐Solid‐State Sodium–Sulfur Battery

Fe₃S₄ @ S @ 0.9Na₃SbS₄?0.1NaI composite cathode is prepared through one‐step wet‐mechanochemical milling procedure. During milling process, ionic conduction pathway is self‐formed in the composite due to the formation of 0.9Na₃SbS₄?0.1NaI electrolyte without further annealing treatment. Meanwhile, the introduction of Fe₃S₄ can increase the electronic conductivity of the composite cathode by one order of magnitude and nearly double enhance the ionic conductivities. Besides, the aggregation of sulfur is effectively suppressed in the obtained Fe₃S₄ @ S @ 0.9Na₃SbS₄?0.1NaI composite, which will enhance the contact between sulfur and 0.9Na₃SbS₄?0.1NaI electrolyte, leading to a decreased interfacial resistance and improving the electrochemical kinetics of sulfur. Therefore, the resultant all‐solid‐state sodium–sulfur battery employing Fe₃S₄ @ S @ 0.9Na₃SbS₄?0.1NaI composite cathode shows discharge capacity of 808.7 mAh g^?1 based on Fe₃S₄@S and a normalized discharge capacity of 1040.5 mAh g^?1 for element S at 100 mA g^?1 for 30 cycles at room temperature. Moreover, the battery also exhibits excellent cycling stability with a reversible capacity of 410 mAh g^?1 at 500 mA g^?1 for 50 cycles, and superior rate capability with capacities of 952.4, 796.7, 513.7, and 445.6 mAh g^?1 at 50, 100, 200, and 500 mA g^?1, respectively. This facile strategy for sulfur‐based composite cathode is attractive for achieving room‐temperature sodium–sulfur batteries with superior electrochemical performance.     

Self‐Suppression of Lithium Dendrite in All‐Solid‐State Lithium Metal Batteries with Poly(vinylidene difluoride)‐Based Solid Electrolytes

Polymer‐based electrolytes have attracted ever‐increasing attention for all‐solid‐state lithium (Li) metal batteries due to their ionic conductivity, flexibility, and easy assembling into batteries, and are expected to overcome safety issues by replacing flammable liquid electrolytes. However, it is still a critical challenge to effectively block Li dendrite growth and improve the long‐term cycling stability of all‐solid‐state batteries with polymer electrolytes. Here, the interface between novel poly(vinylidene difluoride) (PVDF)‐based solid electrolytes and the Li anode is explored via systematical experiments in combination with first‐principles calculations, and it is found that an in situ formed nanoscale interface layer with a stable and uniform mosaic structure can suppress Li dendrite growth. Unlike the typical short‐circuiting that often occurs in most studied poly(ethylene oxide) systems, this interface layer in the PVDF‐based system causes an open‐circuiting feature at high current density and thus avoids the risk of over‐current. The effective self‐suppression of the Li dendrite observed in the PVDF–LiN(SO₂F)₂ (LiFSI) system enables over 2000 h cycling of repeated Li plating–stripping at 0.1 mA cm^?2 and excellent cycling performance in an all‐solid‐state LiCoO₂||Li cell with almost no capacity fade after 200 cycles at 0.15 mA cm^?2 at 25 °C. These findings will promote the development of safe all‐solid‐state Li metal batteries.     

A Liquid‐Metal‐Enabled Versatile Organic Alkali‐Ion Battery

Despite the high specific capacity and low redox potential of alkali metals, their practical application as anodes is still limited by the inherent dendrite‐growth problem. The fusible sodium–potassium (Na–K) liquid metal alloy is an alternative that detours this drawback, but the fundamental understanding of charge transport in this binary electroactive alloy anode remains elusive. Here, comprehensive characterization, accompanied with density function theory (DFT) calculations, jointly expound the Na–K anode‐based battery working mechanism. With the organic cathode sodium rhodizonate dibasic (SR) that has negligible selectivity toward cations, the charge carrier is screened by electrolytes due to the selective ionic pathways in the solid electrolyte interphase (SEI). Stable cycling for this Na–K/SR battery is achieved with capacity retention per cycle to be 99.88% as a sodium‐ion battery (SIB) and 99.70% as a potassium‐ion battery (PIB) for over 100 cycles. Benefitting from the flexibility of the liquid metal and the specially designed carbon nanofiber (CNF)/SR layer‐by‐layer cathode, a flexible dendrite‐free alkali‐ion battery is achieved with an ultrahigh areal capacity of 2.1 mAh cm^?2. Computation‐guided materials selection, characterization‐supported mechanistic understanding, and self‐validating battery performance collectively promise the prospect of a high‐performance, dendrite‐free, and versatile organic‐based liquid metal battery.     

Flexible and Binder‐Free Electrodes of Sb/rGO and Na3V2(PO4)3/rGO Nanocomposites for Sodium‐Ion Batteries

Flexible power sources have shown great promise in next‐generation bendable, implantable, and wearable electronic systems. Here, flexible and binder‐free electrodes of Na₃V₂(PO₄)₃/reduced graphene oxide (NVP/rGO) and Sb/rGO nanocomposites for sodium‐ion batteries are reported. The Sb/rGO and NVP/rGO paper electrodes with high flexibility and tailorability can be easily fabricated. Sb and NVP nanoparticles are embedded homogenously in the interconnected framework of rGO nanosheets, which provides structurally stable hosts for Na‐ion intercalation and deintercalation. The NVP/rGO paper‐like cathode delivers a reversible capacity of 113 mAh g^?1 at 100 mA g^?1 and high capacity retention of ≈96.6% after 120 cycles. The Sb/rGO paper‐like anode gives a highly reversible capacity of 612 mAh g^?1 at 100 mA g^?1, an excellent rate capacity up to 30 C, and a good cycle performance. Moreover, the sodium‐ion full cell of NVP/rGO//Sb/rGO has been fabricated, delivering a highly reversible capacity of ≈400 mAh g^?1 at a current density of 100 mA g^?1 after 100 charge/discharge cycles. This work may provide promising electrode candidates for developing next‐generation energy‐storage devices with high capacity and long cycle life.     

CuO Quantum Dots Embedded in Carbon Nanofibers as Binder‐Free Anode for Sodium Ion Batteries with Enhanced Properties

The design of sodium ion batteries is proposed based on the use of flexible membrane composed of ultrasmall transition metal oxides. In this paper, the preparation of CuO quantum dots (≈2 nm) delicately embedded in carbon nanofibers (denoted as 2‐CuO@C) with a thin film via a feasible electrospinning method is reported. The CuO content can be controlled by altering the synthetic conditions and is optimized to 54 wt%. As binder‐free anode for sodium ion batteries, 2‐CuO@C delivers an initial reversible capacity of 528 mA h g^?1 at the current density of 100 mA g^?1, an exceptional rate capability of 250 mA h g^?1 at 5000 mA g^?1, and an ultra‐stable capacity of 401 mA h g^?1 after 500 cycles at 500 mA g^?1. The enhancement of electrochemical performance is attributed to the unique structure of 2‐CuO@C, which offers a variety of advantages: highly conductive carbon matrix suppressing agglomeration of CuO grains, interconnected nanofibers ensuring short transport length for electrons, well‐dispersed CuO quantum dots leading to highly utilization rate, and good mechanical properties resulting in strong electrode integrity.