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Niobium oxides have fascinated numerous interests for ultrafast sodium‐ion batteries due to their impressive stability, fast pseudocapacitive kinetics, and high safety features. However, the poor intrinsic electronic conductivity and unrevealed mechanisms largely limit their further applications. Here, inspired by density functional theory (DFT) calculations, the introduction of conductor heterostructure (Nb2O5/NbSe2) can largely decrease the bulk phase inserted energy of Na+ from 9.88 to −3.54 eV, as well as promote the delocalization of electron, greatly improving the electrical conductivity of Nb2O5. As expected, the as‐obtained orthorhombic niobium pentoxide (T‐Nb2O5‐x‐NbSe2@C) delivers a high conductivity of 3.69 S cm−1, exhibiting a great improvement of four orders magnitude than that of the parent Nb2O5 (1.87 × 10−4 S cm−1). Impressively, T‐Nb2O5‐x‐NbSe2@C possesses a high reversible capacity of 249 mAh g−1 at 0.1 A g−1, as well as excellent rate performance of 63 mAh g−1 at 5.0 A g−1, nearly twins the capacity of parent porous Nb2O5. Furthermore, the periodic evolutions of the main peaks for targeted electrodes during repeated charging/discharging processes have been further revealed by in situ XRD, demonstrating a highly reversible inserted/extracted storage mechanism of Na+. This work provides a novel method to improve the conductivity of materials by constructing conductor heterojunction. [ABSTRACT FROM AUTHOR]

Sodium layered oxides feature in high capacity and diverse composition, however, are plagued by various issues including limited kinetics and interfacial instability with residual alkali. Conventional substitution/doping and heterogeneous coating are promising to tackle the problems of bulk and surface, respectively, but normally insufficient to address both. Herein, a post‐substitution strategy is proposed to modify primary sodium‐layered‐oxide particles that can simultaneously deal with bulk and surficial issues. As a typical example, post Ti‐substitution for O3‐NaNi1/3Fe1/3Mn1/3O2 is successfully performed by adjusting thermodynamic driving force, resulting in depth‐controllable Ti infusion from surface to bulk, as proved by energy dispersive spectroscopy maps collected at the cross‐section. Residual alkali species are efficiently diminished and benefited from the surface‐to‐bulk osmotic reaction, significantly improving Coulombic efficiency. Moreover, remarkable enhancements in reversible capacity (135 mAh g−1 at C/10), rate capability (74% retention at 5 C), and long‐term cycling stability (80% retention after 300 cycles at 2 C) are achieved by manipulating gradient‐like Ti distribution in a primary particle that brings with increased kinetics and strengthened interfacial stability, surpassing those given by rough heterotic coating and homogeneous Ti‐substitution. Such post‐substitution is expected to provide a universal strategy to modify primary layered‐oxide particles for developing advanced cathode materials of SIBs. [ABSTRACT FROM AUTHOR]

Fe‐Mn based layered oxides are recognized as promising cathode materials for sodium‐ion batteries (SIBs) with high capacities and earth‐abundant ingredients. However, their real‐world applications are still constrained by fast capacity decay accompanied with the requirements of deeper insights into the principles behind. Herein, taking O3‐NaxFe1/2Mn1/2O2 as a classic sample, the capacity fading mechanism of Fe‐Mn based layered oxides is comprehensively investigated through combined techniques. For the first time, it is revealed that Fe migration is merely triggered after the oxidation of ≈0.3 mol Fe3+ based on solid proofs from ex situ X‐ray absorption spectroscopy and Mössbauer spectroscopy, which implies the crucial role of the accumulated structural distortion induced by Jahn–Teller active Fe4+. O3‐P3 phase transition during cycling is obviously constrained along with Fe migration as evidenced by in situ/ex situ X‐ray diffraction, well interpreting the intensified polarization and the resulting large capacity loss. More importantly, within the desodiation depth (≈80% of sodium extraction) where Fe migration is almost absent, the capacity fading is dominantly rooted in the Fe4+ activated and Mn‐dissolution aggravated surface passivation as confirmed by mass/X‐ray spectroscopies and electrochemical analysis. These renewed understandings of the fast capacity decay in Fe‐Mn based layered oxides offer clearer clues for designing desirable cathodes for SIBs. [ABSTRACT FROM AUTHOR]

Antimony (Sb) is considered a promising anode material for sodium‐ion batteries due to its high specific capacity and moderate working potential. However, the non‐negligible volume variation leads to the rapid decay of capacity, which hinders the practical application of Sb anode materials. Here, an economical and scalable route with high yield is proposed to obtain Sb ultrafine nanocrystals embedded in a porous carbon skeleton. Notably, the synergetic effect of the heterogeneous structure is maximized by inducing the interfacial coupling SbOC and creating buffering space for the volume effect of Sb. The high‐entropy phase interface creates the doping site breaking the periodicity of atoms and alters the electronic structure, also bridging the slip of intergranular defects. Thus, the electronic conductivity and phase interface structural stability are reinforced. The mechanism of accelerating electron migration at the heterogeneous phase interface is visualized through the density functional theory method, and the mass/charge‐transfer kinetics is analyzed via the calculation of surface‐induced capacitive contribution. [ABSTRACT FROM AUTHOR]

Heteroatom‐doping is an effective approach to modify the microstructure of carbon‐based materials toward enhanced electrochemical energy storage performance. Nevertheless, it is a great challenge to obtain a specific heteroatom‐doped carbon material with hierarchical structure as a general doping strategy is missing. Herein, carbon materials doped with P, S and both of them are designed and precisely prepared through in‐situ polymerization. Used as anode for sodium‐ion batteries, the best performing material displays a high specific capacity of 368.6 mAh g−1 at a current density of 0.1 A g−1 after 100 cycles. A high capacity of 159.8 mAh g−1 is achieved at a large current density of 5 A g−1. Impressively, this material also delivers robust storage performances for lithium. According to the first‐principles method and detailed experimental data, the expanded interlayer distance and enhanced electronic conductivity of the microcrystalline region can be attributed to C−S and P−C bonds, while the high surface capacitance contribution can be assigned to surface C−S species and highly exposed edges of the microcrystalline region. This work sheds light on a promising method for the exploitation of versatile heteroatom modified hierarchical carbon materials. [ABSTRACT FROM AUTHOR]

Abstract: Designing potential anodes for sodium‐ion battery with both remarkable durability and high‐rate capability has captured enormous attention so far. The engineering of size and morphology is deemed as an effective manner to boost the electrochemical properties. Owing to the anisotropic self‐assembly of iron selenide, rod‐like FeSe2 coates with nitrogen‐doped carbon is prepared through the thermal reaction of Prussian blue with selenium. Notably, the cyano groups are effectively transformed into N‐doped carbon with FeNC bonds, which uniformly coats FeSe2, prompting Na+ transportations. Interestingly, the particle size is tailored by heating rates, along with increased carbon content, leading to broadened energy levels for redox reaction. Bestowed by these advantages, the FeSe2/N‐C as Na‐storage anode delivers impressive electrochemical properties. Even at a rather high rate of 10.0 A g−1, a considerable capacity of 308 mAh g−1 is yielded over 10 000 loops. Supported by the detailed analysis of kinetic features, reduced size of particles could bring about the enhanced contributions of pseudocapacitive and quickening rate of ions transferring. The phase evolutions are further investigated by in situ EIS and ex‐situ technologies. The work is expected to provide a new strategy to prepare metal‐selenide with controllable size and induce the faster kinetic of high‐rate materials. [ABSTRACT FROM AUTHOR]

Abstract: Hierarchical nanoscale carbons have received wide interest as electrode materials for energy storage and conversion due to their fast mass transfer processes, outstanding electronic conductivity, and high stability. Here, heteroatom (S, P, and N) doped hierarchical vesicular carbon (HHVC) materials with a high surface area up to 867.5 m2 g−1 are successfully prepared using a surface polymerization of hexachloro‐cyclotriphosphazene (HCCP) and 4,4′‐sulfonyldiphenol (BPS) on the ZIF‐8 polyhedrons. Significantly, it is the first time to achieve a controllability of the wall thickness for this unique carbon, ranging from 18 to 52 nm. When utilized as anodes for sodium ion batteries, these novel carbon materials exhibit a high specific capacity of 327.2 mAh g−1 at 100 mA g−1 after 100 cycles, which can be attributed to the expanded interlayer distance and enhanced conductivity derived from the doping of heteroatoms. Importantly, a high capacity of 142.6 mAh g−1 can be obtained even at a high current density of 5 A g−1, assigning to fast ion/electronic transmission processes stemming from the unique hierarchical vesicular structure. This work offers a new route for the fabrication/preparation of multi‐heteroatom doped hierarchical vesicular materials. [ABSTRACT FROM AUTHOR]

Abstract: Different dimensions of carbon materials with various features have captured numerous interests due to their applications on the tremendous fields. Restricted by the raw materials and devices, the controlling of their morphology is a major challenge. Utilizing the catalytic features of the intermediates from the low‐cost salts and polymerization of 0D carbon quantum dots (CQDs), 0D CQDs are expected to self‐assemble into 1/2/3D carbon structures with the assistance of temperature‐induced intermediates (e.g., ZnO, Ni, and Cu) from the salts (ZnCl2, NiCl2, and CuCl). The formation mechanisms are illustrated as follows: 1) the “orient induction” to evoke “vine style” growth mechanism of ZnO; 2) the “dissolution–precipitation” of Ni; and 3) the “surface adsorption self‐limited” of Cu. Subsequently, the degree of graphitization, interlayer distance, and special surface area are investigated in detail. 1D structure from 700 °C as anode displays a high Na‐storage capacity of 301.2 mAh g−1 at 0.1 A g−1 after 200 cycles and 107 mAh g−1 at 5.0 A g−1 after 5000 cycles. Quantitative kinetics analysis confirms the fundamentals of the enhanced rate capacity and the potential region of Na‐insertion/extraction. This elaborate work opens up an avenue toward the design of carbon with multidimensions and in‐depth understanding of their sodium‐storage features. [ABSTRACT FROM AUTHOR]

Abstract: Antimony holds a high‐specific capacity as a promising anode material for Na‐ion batteries (SIBs) and much research is focused on solving the poor cycling stability issue associated with its large volume expansion during alloying/dealloying processes. Here, self‐thermal‐reduction method is successfully applied to prepare antimony/carbon rods (Sb/C rods) utilizing potassium antimony(III)‐tartrate (C8H10O15Sb2K2) as a dual source of carbon matrix and metallic antimony. According to theory calculations and experiment results, the formation process is explicitly explored as follows: C8H10O15Sb2K2 → Sb2O3/C → Sb2O3/Sb/C → Sb/C rods. Notably, organic ligands in C8H10O15Sb2K2 can be gradually turned into amorphous carbon with simultaneous reduction of Sb3+ to metal Sb. Moreover, potassium chloride acts as an activator and a template during the course of carbonization, and synchronous reduction is introduced. Consequently, an antimony/carbon electrode material denoted as SbOC/C is formed, exhibiting a unique dual‐carbon‐modified structure and extensive SbOC bridge bonds that give rise to outstanding cycling performance and rate capacity. Specifically, the capacity is maintained at 404 mA h g−1 with 89% retention after 700 cycles at 500 mA g−1. The low‐cost, self‐thermal‐reduction method and excellent electrode performances of electrode material make it attractive for large‐scale energy storage systems. [ABSTRACT FROM AUTHOR]

Antimony sulfide (Sb 2 S 3 ) has been shown as a promising candidate for sodium ions batteries, in considering the gravimetric energy density and high theoretical capacity. Hollow-sphere Sb 2 S 3 coated with carbon are successfully designed through Oswald ripening process. The Sb 2 S 3 /C utilized as SIBs anode displays excellent electrochemical properties, delivering a high charge capacity of 693.4 mAh g −1 at 0.2 A g −1 between 0.01 and 3.0 V (vs. Na + /Na). Its reversible capacity can keep 545.6 mAh g −1 , with a retention of ∼80% after 100 cycles. Even the current densities return from 6.4 to 0.2 A g −1 , the Sb 2 S 3 /C still maintains 550.8 mAh g −1 after 70 cycles. Combining the large void space with carbon layer, the advantages are noticed when the increased electrolyte penetration area, improved electronic conductivity and shortened Na + diffusion length are attained concurrently, resulting in the excellent specific capacity and cycling stability. The study provides an effect strategy in improving the electrochemical performances of metal sulfides as anode for SIBs. [ABSTRACT FROM AUTHOR]

The ever-increasing demand of lithium-ion batteries (LIBs) caused by the rapid development of various electronics and electric vehicles will be hindered by the limited lithium resource. Thus sodium-ion batteries (SIBs) have been considered as a promising potential alternative for LIBs owing to the abundant sodium resource and similar electrochemical performances. In recent years, significant achievements regarding anode materials which restricted the development of SIBs in the past decades have been attained. Significantly, the sodium storage feasibility of carbon materials with abundant resource, low cost, nontoxicity and high safety has been confirmed, and extensive investigation have demonstrated that the carbonaceous materials can become promising electrode candidates for SIBs. In this review, the recent progress of the sodium storage performances of carbonaceous materials, including graphite, amorphous carbon, heteroatom-doped carbon, and biomass derived carbon, are presented and the related sodium storage mechanism is also summarized. Additionally, the critical issues, challenges and perspectives are provided to further understand the carbonaceous anode materials. [ABSTRACT FROM AUTHOR]

Transition-metal carbides (TMCs) are emerging as promising electrode materials for electrochemical energy storage devices, owing to their good conductivity and stability. Herein, Mo2C nanoparticles have been successfully encapsulated into a porous N-doped carbon matrix through in situ confined carbonization. When evaluated as an anode material for sodium-ion batteries (SIBs), the resultant Mo2C/N-doped composite (Mo2C-NC) exhibited a high rate capability and excellent cycle stability with a high capacity retention of 95.4 % after 2500 cycles. The prominent sodium storage performances can be attributed to its special nanoarchitecture, which provides a synergistic effect to offer shortened Na+/e− transfer pathways, highly effective restraint through particle agglomeration, and a buffer for the drastic volume change during the prolonged cycles. Owing to the efficient one-pot procedure and high electrochemical performances, the porous Mo2C/N-doped carbon hybrids are great potential anode materials for rechargeable SIBs. [ABSTRACT FROM AUTHOR]

Rod-like α-MoO 3 is successfully designed by alternating voltage induced electrochemical synthesis (AVIES) approach. The morphology and texture of MoO 3 is effectively controlled by applying various calcination temperature of 300–600 °C. Notably, the α-MoO 3 microrods growing along [001] direction have the high aspect ratio, and the randomly stacked structure can facilitate the charge transfer and offer more active sites for sodium storage. When utilized for sodium-ion batteries, it presents the high charge capacities of 305 mAh g −1 at 1C and 143 mAh g −1 at 10C. Even after 3000 cycles at 10C, a significant capacity of 108 mAh g −1 is still delivered, highlighting its marvelous electrochemical properties. This work may be a compelling exploration for developing metal/metal oxides materials for sodium storages by AVIES. [ABSTRACT FROM AUTHOR]

Yolk-like TiO2 are prepared through an asymmetric Ostwald ripening, which is simultaneously doped by nitrogen and wrapped by carbon from core to shell. It presents a high specific surface area (144.9 m2 g−1), well-defined yolk-like structure (600-700 nm), covered with interweaved nanosheets (3-5 nm) and tailored porosity (5-10 nm) configuration. When first utilized as anode material for sodium-ion batteries (SIBs), it delivers a high reversible specific capacity of 242.7 mA h g−1 at 0.5 C and maintains a considerable capacity of 115.9 mA h g−1 especially at rate 20 C. Moreover, the reversible capacity can still reach 200.7 mA h g−1 after 550 cycles with full capacity retention at 1 C. Even cycled at extremely high rate 25 C, the capacity retention of 95.5% after 3000 cycles is acquired. Notably, an ultrahigh initial coulombic efficiency of 59.1% is achieved. The incorporation of nitrogen with narrowing the band gap accompanied with carbon uniformly coating from core to shell make the NC TiO2-Y favor a bulk type conductor, resulting in fast electron transfer, which is beneficial to long-term cycling stability and remarkable rate capability. It is of great significance to improve the energy-storage properties through development of the bulk type conductor as anode materials in SIBs. [ABSTRACT FROM AUTHOR]

3D porous carbon encapsulated SnO 2 nanoparticles composite (SnO 2 -PC) prepared by an efficient in situ methodology was applied as anode for sodium ion batteries (SIBs). It delivered a high reversible specific capacity of 280.1 mAh g −1 after 250 cycles at a current density of 100 mA g −1 , with ultrahigh capacity retention of 91.63%. Notably, it can Exhibit 100 mAh g −1 after 1000 cycles even at a high current density of 1600 mA g −1 . These greatly enhanced electrochemical properties of SnO 2 -PC composite can be attributed to the superior structure that the electrical conductivity of the composite was improved by the porous carbon matrix, moreover, it can serve as a cushion during the process of Na ion insertion/extraction into the composite. Significantly, this kind of in situ synthesis method is portable for other similar composite. [ABSTRACT FROM AUTHOR]

S odium t itanate (Na 2 Ti 6 O 13 ) cuboid is successfully prepared and employed for anode electrode materials in sodium-ion batteries (SIBs). Their sodium storage properties are presented by undertaking polyvinylidene fluoride (PVDF), carboxymethyl cellulose (CMC) as different binders. At a current density of 0.1 C, the sodium titanate cuboid with CMC and PVDF exhibits discharge capacity of 269.5 mAh g −1 and 251.0 mAh g −1 , respectively. At the 200th charge/discharge cycle, the reserved discharge capacity for Sodium titanate cuboid electrode with CMC binder is 173.6 mAh g −1 , amounting to a capacity retention of 94.4%, much higher than that employing PVDF as binder (the discharge capacity of 69.3 mAh g −1 and the capacity retention of 54.1%). The rate capability test and the Coulombic efficiency data also manifest that the Sodium titanate cuboid utilizing CMC as binder is superior to the ones with PVDF. These enhanced electrochemical performance mainly derive from the strong cohesive strength of CMC binder and the swellability of PVDF binder, verifying the importance of a binder to the optimization of sodium storage behavior. [ABSTRACT FROM AUTHOR]

Bimetallic oxides of different metal species and well‐defined nanostructure could lead to a new generation of polymetallic oxide in the energy storage field. Exceptional 1D nanostructured materials are favorable in the electronic transmission of the kinetic processes and confinement effects of electronic structures deriving from the nanoscale dimensions. In this work, an Sb2MoO6 nanorod is successfully prepared for the first time through a facile metathesis reaction process. Then, a thin polyaniline (PANI) layer is coated via the in situ oxidative polymerization of aniline. The Sb2MoO6‐based nanorods are first utilized as anode material for sodium‐ion batteries (SIBs). Benefiting from the synergistic effect of PANI coating and 1D nanostructure, the Sb2MoO6@PANI nanorod electrode presents enhanced sodium storage performances, and a reversible specific capacity of 370.2 mAh g−1 can be retained after 100 cycles. Ex situ electrochemical impedance spectra (EIS) and transmission electron microscopy (TEM) are used to study the evolution process, demonstrating that the PANI coating can alleviate the pulverization of the rod structure and reflect better cycle stability. This work reveals the sodium storage activity of novel Sb2MoO6 nanorods and proposes an efficient strategy to promote its electrochemical properties; it is in great favor of extending the development of anode materials for SIBs. [ABSTRACT FROM AUTHOR]

Black phosphorus, an attractive anode material for sodium‐ion batteries (SIBs), has aroused grand attention because of its high theoretical capacity. Nevertheless, its practical exploration is limited by large volume swelling, followed by rapid capacity decaying. Herein, both large‐area few‐layer phosphorene and low‐defect graphene are obtained by electrochemical exfoliation. The sandwich‐structured phosphorene–graphene hybrid with the simultaneous introduction of PC and POC bonds through chemical activation is employed to heighten the performance of SIBs, leading to a high specific capacity of 2311 mA h g−1 (based on the mass of phosphorene) at 0.1 A g−1 with a capacity retention of 83.9% after 100 loops, which can be ascribed to the flexible space of graphene layers that alleviates the volumetric expansion of phosphorene. Moreover, the stable chemical bonds as the bridge for electrons transferring can immobilize phosphorene and protect phosphorene from cracking during the sodiation/desodiation process. Expectedly, the anode exhibits excellent cycle performance of 200 loops with retained capacities of 1582.6 and 1120.6 mA h g−1 at 1 and 5 A g−1, respectively. Therefore, this electrochemical approach provides a guide for the preparation of other sandwiched 2D materials, which can be applied in high‐performance energy‐storage devices. A sandwich structured phosphorene–graphene hybrid is well‐designed through chemical activation with electrochemically exfoliated phosphorene and graphene. Simultaneously, the formation of PC and POC bonds can protect phosphorene from cracking, and graphene offers an elastic buffer to accommodate the volumetric expansion of phosphorene. This work may provide a guide for the future design of high‐performance anode material for sodium‐ion batteries (SIBs). [ABSTRACT FROM AUTHOR]

As a result of its high‐energy density, metal–selenides have demanded attention as a potential energy‐storage material. But they suffer from volume expansion, dissolved poly‐selenides and sluggish kinetics. Herein, utilizing' thermal selenization via the Kirkendall effect, microspheres of NiSe2 confined by carbon are successfully obtained from the self‐assembly of Ni‐precursor/PPy. The derived hierarchical hollow architecture increases the active defects for sodium storage, while the existing double N‐doped carbon layers significantly alleviate the volume swelling. As a result, it shows ultrafast rate capability, delivering a stable capacity of 374 mAh g−1, even after 3000 loops at 10.0 A g−1. These remarkable results may be ascribed to the NiOC bonds on the interface of NiSe2 and the carbon film, which leads to the faster transfer of ions, the effective trapping of poly‐selenide, and the highly reversible conversion reaction. The kinetic analysis of cyclic voltammetry (CV) demonstrates that the electrochemical process is mainly dominated by pseudocapacitive behaviors. Supported by the results of electrochemical impedance spectroscopy (EIS), it is confirmed that the solid–electrolyte interface films are reversibly formed/decomposed during cycling. Given this, this elaborate work might open up a potential avenue for the rational design of metal‐sulfur/selenide anodes for advanced battery systems. Hierarchial hollow‐structured NiSe2/N‐C with double carbon films are designed from the self‐assembled clew‐like Ni‐Pr by the Kirkendall effect. And it is found that incorporation of NiOC into the carbon layers enables tailoring of the interfacial traits, inducing the fascinating electrochemical behaviors. This elaborate work might open up a potential avenue for these rational TMDs anodes designs for advanced battery storage systems. [ABSTRACT FROM AUTHOR]

The sodium storage performance of NiS2 suffer from low initial coulombic efficiency and poor cycling stability which are ascribed to the volume expansion and collapse of the structure during the charge/discharge transformation process. Compared with composites, encapsulating NiS2 in carbon framework is more effective in buffering for the volume expansion and enhancing the electronic conductivity of sodium‐ion batteries. In this work, NiS2 decorated with bifunctional carbon (NiS2@C@C), where nickel dimethylglyoxime and polyaniline are employed as the precursor and carbon source, respectively, are obtained. Since the introduced carbon layer suppresses the volume expansion and enhances both the electronic conductivity and charge transfer of Na+, the attained NiS2@C@C displays outstanding sodium storage performance. At a current density of 0.1 A g−1, a high reversible specific capacity of 580.8 mAh g−1 remains even after 100 cycles. The first coulombic efficiency (79.65%) and rate performance (448 mAh g−1 at 1.6 A g−1) of NiS2@C@C are also remarkable. Extraordinarily, the excogitation of NiS2 decorated with bifunctional carbon is also significant for the preparation of similar materials. Through the sulfuration of nickel dimethylglyoxime wrapped with polyaniline, bifunctional carbon decorated NiS2 (NiS2@C@C) is prepared. Benefitting from the ingenious design, the sodium storage performance of NiS2@C@C electrodes is greatly superior to undecorated NiS2 electrodes. This work might supply an effective excogitation for the practical application of transitional metal sulfides in sodium‐ion batteries. [ABSTRACT FROM AUTHOR]

Antimony-based materials represent promising anode materials for sodium ion batteries (SIBs) owing to their high theoretical capacity, however, the large volume expansion and low ionic conductivity during the electrochemical process prohibit them from reaching their theoretical expectations. In this work, Sb 2 S 3 @C and Sb 2 Se 3 @C nanodots with uniform diameters of 19.0 nm and 20.7 nm were synthesized by H 2 /C thermal reduction and co-sulfurization (selenization) of sodium stibogluconate. Each Sb 2 S 3 and Sb 2 Se 3 nanodot was coated by an interconnecting carbon network with weak graphitization, which further crosslinked together to form a high conductive framework. When applied as anode for SIBs, they exhibited desired sodium storage properties, especially the excellent cycling stability of Sb 2 Se 3 @C nanodots with a reversible capacity of 316.1 mA h g−1 after 100 cycles at 100 mA g−1 and 269.1 mA h g−1 after 200 cycles at 1 A g−1, which was consistent with the calculated result of theoretical volume changes (264% and 246%) and density functional theory (DFT) calculation for both materials during the Na+ intercalation processes, as expected. [Display omitted] • Sb 2 S 3 (Sb 2 S 3) nanodots/C composites have been successfully fabricated. • The volume changes of two materials during the Na+ insertion/deintercalation process have been calculated and analyzed in details. • The satisfactory sodium storage properties are achieved, which is consistent with the result of theoretical calculation. [ABSTRACT FROM AUTHOR]

Here we show that P2/O3 biphasic layered structure is originated from internal heterogeneity of "cationic potential" induced by locally compositional non-uniformity, which largely depends on the temperature-driven reaction thermodynamics and kinetics. The clarified material-formation mechanism enables facile design and preparation of P2/O3 biphasic materials with much-improved sodium-storage performances than single-phase one, promoting the exploration of advanced cathodes for sodium-ion batteries. [Display omitted] Sodium layered oxides generally suffer from deep-desodiation instability in P2 structure and sluggish kinetics in O3 structure. It will be great to design P2/O3 biphasic materials that bring the complementary merits of both structures. However, such exploration is hindered by the ambiguous mechanism of material formation. Herein, supported by theoretical simulations and various spectroscopies, we prove that P2/O3 biphasic structures essentially originate from the internal heterogeneity of cationic potential, which can be realized by constraining the temperature-driven ion diffusion during solid-state reactions. Consequently, P2/O3 biphasic Na 0.7 Ni 0.2 Cu 0.1 Fe 0.2 Mn 0.5 O 2– δ with well-designed quaternary composition is successfully obtained, exhibiting much-improved rate capabilities (62 mAh g−1 at 2.4 A g−1) and cycling stabilities (84% capacity retention after 500 cycles) than its single-phase analogues. Furthermore, synchrotron-based diffraction and X-ray absorption spectroscopy are employed to unravel the underlying sodium-storage mechanism of the P2/O3 biphasic structure. This work presents new insights toward the rational design of advanced layered cathodes for sodium-ion batteries. [ABSTRACT FROM AUTHOR]

The ultrathin TiO 2 nanosheets doped by nitrogen tightly attaching on carbon nanotubes are designed and evaluated as anode for sodium ion batteries. The TiO 2 nanosheets attaching on carbon nanotubes composite shows a high specific capacity of 248.5 mAh g −1 at the rate of 0.5 C, and it can still deliver a specific capacity of 100.9 mAh g −1 at a high rate of 20 C, which verifies an outstanding sodium storage capacity and an excellent rate capability. More encouragingly, at a rate of 10 C, the specific capacity can be still kept at 154.2 mAh g −1 after 3500 cycles, displaying a remarkable long-term cyclic stability. Note that the corresponding kinetics analysis suggests that the pseudocapacitive behaviour is responsible for the updating sodium storage performances of TiO 2 nanosheets composite. Additionally, the cooperation effects of carbon nanotubes preservation and nitrogen modification can provide fast electronic pathways, and the TiO 2 nanosheets can promote sodium ions transport and increase the active sites for sodium storage. The merits of multiple functional and tailor-designed strategies make contributions to develop high-performance TiO 2 anodes in sodium ion batteries. [ABSTRACT FROM AUTHOR]

By reason of rich sodium resources, sodium-ion batteries have excited enormous consideration for adhibition in the developing energy-storage stations. And not surprisingly, the exploration of cost-effective anode materials for SIBs have been a conspicuous topic. Herein, iron trioxide embedded in the nitrogen-doped carbon matrix with strong oxygen-bridge bonds is synthesized by using the iron based metal organic framework as template. The obtained composite delivers excellent electrochemical properties, such as specific capacity of 473.7 mAh g −1 at the current density of 100 mA g −1 after 100 cycles. Besides, the reversible capacity still remains at 155.3 mAh g −1 at the high density of 4000 mA g −1 . This remarkable sodium-ion storage capability could be attributed to the incorporation of nitrogen atoms into carbon matrix and the strong chemical bonds between iron trioxide and carbon matrix, which can restrain electrode pulverization and also retain an interparticle connection even after long cycling that could offer a good electronic conductive pathway. This engineer strategy for preparing iron trioxide possess strong interfacial interaction with nitrogen-doped carbon matrix can be applied to other metal phosphides and metal oxide materials. [ABSTRACT FROM AUTHOR]

Na 3 V 2 (PO 4 ) 3 (NVP) is a very promising cathode material in sodium ion battery for rapidly emerging large-scale energy storage with its classical 3D NASCION structure. However, the cycling life and rate performances are restricted its low electronic conductivity. To overcome these, the double carbon-wrapped Na 3 V 2 (PO 4 ) 3 composite is firstly designed through rheological phase approach, delivering enhanced electrochemical properties. The unique double carbon layers are composed of uniform amorphous carbons as protecting framework for stabilizing the structure, as well as the graphitized carbon sheets playing the role of conductive network for better electronic conductivity. This double carbon-wrapped Na 3 V 2 (PO 4 ) 3 composite exhibits a high reversible capacity of 99.8 mAh g −1 over 500 cycles at 1 C (110 mA g −1 ), yielding the coulombic efficiency of ∼99.8%. Meanwhile, it displays an initial capacity of 73 mAh g −1 at 100 C and remains 55 mAh g −1 at an ultra-rate of 200 C. Even after cycling at 200 C over 12 000 cycles, the Na + -storage capacity of 40 mAh g −1 with a retention of 72.7% is still obtained, highlighting its excellent long cycling life and remarkable rate performances. [ABSTRACT FROM AUTHOR]

Hard Carbons (HCs) are widely investigated as anode materials for Sodium-ion batteries (SIBs), for the abundance of the precursors and their easy synthesis. However, the intercalation of Na+ in the HCs is a big challenge for the design of high-performance SIBs. Heteroatom-doping can effectively facilitate the intercalation of Na+ in the anode material. Herein, a series of double and triple-atom phosphorus-nitrogen, phosphorus-sulfur, nitrogen-sulfur and phosphorus-nitrogen-sulfur in the camphor wood (Cmph) derived-HCs are fabricated, and their electrochemical performances as anodes for SIBs are investigated. The P–N–S-Cmph delivers high initial coulombic efficiency (ICE) of 70.74%%, an outstanding rate performance and good cycling stability, maintaining a specific capacity of 280 mAh g−1 at 2000 mA g−1 after 500 cycles. The excellent performances of the anode materials are assigned to the synergetic effect of the heteroatom-doping of S, N and P enlarging the interlayer spacing of the doped-Cmph-HCs, increasing the intercalation/deintercalation rate of Na+ in the HCs; disposing more active sites for the Na+ storage. In addition, sulfur can reversibly react with Na+, reducing the irreversible consumption of Na+ by the surface functional groups. This work presents a simple and effective method of designing high performance anode materials for SIBs. • P, N and S co-doping in the biomass hard carbon anodes are developed. • P, N and S-doping increased the Na+ intercalation rate in the anode materials. • S-doping provided more active sites for Na+ storage in the hard carbon anodes. [ABSTRACT FROM AUTHOR]

Cube-shaped porous carbon (CPC) was obtained from the carbonization of MOF-5 (Zn 4 O(OOCC 6 H 4 COO) 3 ) crystals and shows abundant micro/mesopores, high mechanical strength, largest surface area (2316 m 2 g −1 , BET method) and good electrical conductivity (a high weight ratio 98.17/1.83 of C/O). When utilized as anode material for sodium-ion batteries, the CPC presents a high overall sodium storage capacity ∼240 mAh g −1 at a current density of 100 mA g −1 after 100 cycles, and maintains a high specific capacity of 100 mAh g −1 after 5000 cycles at a current density of 3200 mA g −1 . For the advantages of this unique carbon framework structure, the CPC might be a promising anode material for the application of SIBs. [ABSTRACT FROM AUTHOR]

• Bi/GO composites with different Bi content were synthesized by a novel and efficient electrochemical method. • Bi 2 O 2 2+and reduced graphene oxide, which make Bi/GO composites possess high ionic and electrical conductivity, were generated during the reaction. • The small volume expansion of Bi/GO composite during sodiation is attributed to the existence of GO. • The Bi/GO composite anode displays superior rate performance and excellent cycling stability. Bismuth, a promising attribute for sodium-ion batteries, which have been attracting significant attention owing to their advantages of high volumetric capacity and suitable operating potential. However, most traditional Bi-based materials are suffered from pulverization and fracture of the electrodes caused by dramatic volume variation, consequently diminishing the cycle stability. Herein, in this work, bismuth embedded within graphene oxide matrices have been obtained by utilizing a novel and efficient electrochemical method. Through the strong reducing properties of Zintl clusters Bi 2 2−, GO is partially reduced to generate reduced graphene oxide with better electrical conductivity. Simultaneously, Bi is strongly loaded on the GO through Bi-O-C bonding, which can form Bi 2 O 2 2+ with excellent ionic conductivity. Moreover, the volume expansion of Bi during sodiation can be effectively buffered in the GO matrices. As a result, this Bi/GO composite exhibits excellent electrochemical performances in sodium-ion batteries (SIBs), including a high specific capacity of 258 mAh g−1 at 10 A g−1 and an excellent cycle stability with high retained capacity of 315 mAh g−1 after 500 cycles at 2 A g−1. This work paves the way to prepare designated promising electrode materials for high-performance SIBs, and thoroughly understands mechanism of electrochemical methods for preparing materials. [Display omitted] [ABSTRACT FROM AUTHOR]

P2–Na 2/3 Ni 1/3 Mn 2/3 O 2 as a promising cathode material for sodium ion batteries (SIBs) has attracted much attention owing to high capacity and wide operation voltage. However, it suffers from inferior rate and cycling performances due to P2–O2 phase transition and Na+/vacancy ordering during charge/discharge process. Herein, a Fe/Ti co-substitution strategy is successfully utilized to mitigate these issues. Notably, as probed by In-situ X-ray diffraction, the substitution of Ni with Fe significantly stabilizes the interlayer framework by impeding slab glide during deep Na+ extraction, resulting in reversible P2-OP4 phase transition with smaller volume change of host structure compared to P2–O2 transition. Meanwhile, synchrotron X-ray diffraction shows that, the Na+/vacancy ordering is greatly suppressed by further replacing Mn with Ti, which breaks down the long-range ordering of Ni/Mn distribution, promoting Na ion transport. In addition, the charge compensation mechanism of Fe/Ti co-substituted P2–Na 0.67 Ni 0.23 Fe 0.1 Mn 0.57 Ti 0.1 O 2 (NFMT) revealed by Ex-situ X-ray absorption spectroscopy demonstrates that the incorporation of Fe3+/4+ redox couple largely improve the working voltage. Consequently, the obtained NFMT cathode delivers a high energy density over 420 Wh/kg within 4.3–2.6 V, accompanied with remarkably enhanced kinetics and capacity retention. Such co-substitution strategy provides a promising approach to develop high-voltage and cycle-stable cathode materials for SIBs. [Display omitted] • Fe/Ti co-substitution is proposed to modify the P2–Na 2/3 Ni 1/3 Mn 2/3 O 2 cathode. • Fe substitution can prevent the P2–O2 phase transition. • Ti substitution disrupts cation ordering and Na+/vacancy ordering. • Fe/Ti co-substitution can stabilize the reversible OP4 phase. [ABSTRACT FROM AUTHOR]

• Sodium-containing layered metal oxides are studied at the single particle scale. • Electrochemical performance of single particles and bulk material is different. • Internal Na+ ion diffusion in O3-phase particles is faster than in P2-phase particles. An electrochemical collision method is utilized to compare the sodium de-insertion process in particles of quarternary sodium-containing layered metal oxides Na x TMO 2 (TM = Fe, Mn, Ni, Cu) in the O3 phase and the P2 phase. The electrochemical behavior of the two types of materials is found to be different. The diffusion of Na+ inside an individual particle occurs more readily in O3-type oxides than in P2-type oxides, which is contrary to the conventional wisdom that P2-type oxides usually provide higher Na-ion conductivity than their O3 analogs. These results provide a more detailed analytical perspective for assessing battery materials. [ABSTRACT FROM AUTHOR]

The impacts of Cu substitution upon the cycling stability of Na x MO 2 (M = Fe, Mn) cathodes are systematically studied. Evidenced by CuO segregation and XPS analysis, the average valence of Mn can hardly reach +4, possibly owing to the production of Mn(II). It is proposed that, Cu substitution can efficiently enhance the cycling stability by reducing the content of Mn(III) and suppressing the electrochemical activities of Mn4+/3+ redox couple. • Cycling stability of Na x MO 2 (M = Cu, Fe, Mn) cathodes are systematically studied. • CuO segregation is evidenced to be associated with the limited valent state of Mn. • Adding Cu2+ actually lower Mn valence by decreasing Mn(III) and generating Mn(II). • Cu2+-substitution may enhance the cycling stability mainly by suppressing Mn(III). Adding Cu2+ has substantially boosted the practical potentiality of Fe/Mn-based layered cathodes for sodium ion batteries (SIBs) owing to the enhanced stabilities, which were previously ascribed to the raised valence of Mn. Herein, the roles of Cu2+ are verified by investigating Cu2+-substituted materials with the stoichiometry of Na 0.5+x Cu x Fe 0.5-x Mn(IV) 0.5 O 2. Surprisingly, it is found that Mn valence can hardly reach the expected value (IV) even by adjusting Cu2+ content. For the first time, the separation of CuO, which has been previously detected but rarely explained, is ascribed to the restrained chemical states of Mn. Detailed analyses show that, Mn(II) is generated while Mn(III) is decreased in pace of Cu2+ substitution, actually lowering down the oxidation states of Mn. Moreover, Mn4+/3+ redox can be efficiently restricted by importing Cu2+. Albeit the loss of capacity, the cycling stability is greatly enhanced, achieving a high capacity retention of 92.3% after 200 cycles within 4.2–2.5 V. Therefore, the suppression of Jahn-Teller Mn(III) should be intrinsically responsible for the superior cycling stability after Cu2+ substitution. These findings may present a new sight to probe the roles of Cu in layered Na x MO 2 system for the design of advanced cathodes for SIBs. [ABSTRACT FROM AUTHOR]

Nitrogen or phosphorus doping is a commonly used method to ameliorate the electrochemical properties of carbonaceous material. In this study, nitrogen-rich carbon nanosheets are first prepared and then annealed with NaH 2 PO 4 to synthesize phosphorus doping nitrogen-rich carbon nanosheets. Two obtained materials are utilized as anodes of sodium-ion batteries and potassium-ion batteries, revealing that phosphorus doping can improve sodiation capacity (247.9 vs. 175.1 mA h g−1) and lower potassiation capacity (207.2 vs. 242.6 mA h g−1). To explore the inner reason for this phenomenon, Na+ and K+ diffusion coefficients are surveyed through galvanostatic intermittent titration technique, showing that the electrode with large ion diffusion coefficient delivers a large capacity. This work provides some use for reference in introduction of heteroatoms to carbonaceous anode materials of sodium-ion batteries and potassium-ion batteries. Image 1 • Carbon nanosheets with high P and N contents were prepared. • P-doped N-rich carbon nanosheets exhibited higher sodiation capacity. • N-rich carbon nanosheets performed better in K-storage than Na-storage. • The electrode with large ion diffusion coefficient delivers a large capacity. [ABSTRACT FROM AUTHOR]