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The safety of energy storage equipment has always been a stumbling block to the development of battery, and sodium ion battery is no exception. However, as an ultimate solution, the use of non‐flammable electrolyte is susceptible to the side effects, and its poor compatibility with electrode, causing failure of batteries. Here, we report a non‐flammable electrolyte design to achieve high‐performance sodium ion battery, which resolves the dilemma via regulating the solvation structure of electrolyte by hydrogen bonds and optimizing the electrode–electrolyte interphase. The reported non‐flammable electrolyte allows stable charge‐discharge cycling of both sodium vanadium phosphate@hard carbon and Prussian blue@hard carbon full pouch cell for more than 120 cycles with a capacity retention of >85 % and high cycling Coulombic efficiency (99.7 %). [ABSTRACT FROM AUTHOR]

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

The utilization of oxygen vacancies (OVs) in sodium ion batteries (SIBs) is expected to enhance performance, but as yet it has rarely been reported. Taking the MoO3− x nanosheet anode as an example, for the first time we demonstrate the benefits of OVs on SIB performance. Moreover, the benefits at deep-discharge conditions can be further promoted by an ultrathin Al2O3 coating. A series of measurements show that the OVs increase the electric conductivity and Na-ion diffusion coefficient, and the promotion from ultrathin coating lies in the effective reduction of cycling-induced solid-electrolyte interphase. The coated nanosheets exhibited high reversible capacity and great rate capability with the capacities of 283.9 (50 mA g−1) and 179.3 mAh g−1 (1 A g−1) after 100 cycles. This work may not only arouse future attention on OVs for sodium energy storage, but also open up new possibilities for designing strategies to utilize defects in other energy storage systems. [ABSTRACT FROM AUTHOR]

Transition metal selenides are considered as one of the most promising anode materials for sodium-ion batteries (SIBs) on account of their high theoretical specific capacity. However, the poor conductivity, sluggish kinetics and volume expansion during the (de)sodiation process hinder its application. Herein, a novel heterostructure of CoSe 2 /Sb 2 Se 3 nanocrystals embedded into nanocage-in-nanofiber carbon framework is designed and constructed via electrospinning, carbonization, ion exchange and selenization processes. In this structure, bimetallic selenide heterostructure accelerates electron/ion transfer kinetics and Na+ adsorption capacity, carbon nanocages structure alleviates the volume expansion and maintains structural integrity during the (de)sodiation process, and carbon nanofibers connect the nanocages in series to shorten the electron transmission path and enhance electrical conductivity. As a self-supporting anode for SIBs, as-synthesized CoSe 2 /Sb 2 Se 3 @C@CNF shows a high reversible capacity of 406 mAh g-1 at 0.2 A g-1 after 200 cycles and displays excellent rate capability. More remarkably, the CoSe 2 /Sb 2 Se 3 @C@CNF anode manifests an outstanding cycling stability for over 2000 and 12,000 cycles at 1 and 5 A g-1, with the capacity retention being 97 % and 103 % respectively. Meanwhile, the excellent sodium storage performance is revealed by kinetic analysis, energy level analysis and density functional theory calculations. [Display omitted] • Heterostructure CoSe 2 /Sb 2 Se 3 nanocrystals embedded into nanocage-in-nanofiber carbon framework is constructed. • CoSe 2 /Sb 2 Se 3 heterostructure accelerates electron/ion transfer kinetics and Na+ adsorption capacity. • Nanocage-in-nanofiber carbon framework increases the conductivity and alleviates volume expansion. • CoSe 2 /Sb 2 Se 3 @C@CNF exhibits a remarkable long-term cycling stability after 12,000 cycles. • Energy level analysis and DFT calculations demonstrate the excellent sodium storage performance. [ABSTRACT FROM AUTHOR]

Abstract An original electrode, 3D TiO 2 @C core/shell nanobelt arrays with controllable carbon coating thickness, was successfully constructed in this work. The 3D TiO 2 nanobelts were directly grown on Ti foil, and then were coated with a layer of metal-organic framework (MOF). After thermal annealing, a porous carbon layer with tunable thickness was coated onto the 3D TiO 2 nanobelts through changing the MOF thickness. The as-prepared TiO 2 @C-2 h with 5-nm-thick carbon layer presented an excellent discharge capacity of 210.5 mAh g−1 after 100 cycles at a current density of 50 mA g−1, which is 38% higher than that of pure TiO 2 electrode without carbon coating. Moreover, it can maintain a reversible capacity of 141 mAh g−1 after 1000 cycles at a current density of 200 mA g−1, and a good rate performance with 33% of capacity retention when the current density increasing from 50 to 5000 mA g−1. All the results indicate that the TiO 2 @C core/shell nanobelt array is a promising anode for sodium-ion batteries. Highlights • 3D TiO 2 nanobelt arrays possess short ion transport distance. • Coating of porous carbon layer can solve low rate capability and poor stability. • Carbon coating can be tuned by MOF thickness to get optimal performance. • Ideal 3D TiO 2 @C nanobelt-SIB exhibit superior reversible capacity and rate capability. [ABSTRACT FROM AUTHOR]

• A mixed-ion/electron-conducting interface layer was constructed by a conversion reaction. • The interface layer can improve the affinity with Na metal, leading to dendrite-free Na deposition. • The full cells based on the designed layer show a very stable cycling over 1000 cycles. Sodium metal has been regarded as one of excellent candidates of anode materials for the next-generation high-energy sodium-ion batteries owing to its low redox potential, low cost, and high theoretical capacity. However, the poor reversibility and the dendrite growth of Na anode on cycling have significantly hindered the practical application of sodium metal anodes (SMAs). Herein, we report that a mixed-ion/electron-conducting interface (MIECI) layer, in-situ generated through the conversion of CuP 2 into the mixed conductor of Cu and Na 3 P, enable dendrite-free Na plating/stripping in ether-based electrolyte. The MIECI layer can significantly improve the affinity with the deposited Na, homogenize the Na+ flux, and reduce the local current density. The MIECI layer enables Coulombic efficiency (CE) of Na plating/stripping as high as 99.71% over 420 cycles at 2 mA h cm−2 and 2 mA cm−2 as well as the Na||Na cell to stably cycle for 1200 h (300 cycles) with a depth of discharge of 33.33 % at 2 mA h cm−2. It is found that the current density plays a greater influence on the SMA stability. The in-situ construction of MIECI buffer layer opens up a simple and facile avenue to stabilize SMAs. [ABSTRACT FROM AUTHOR]

Sodium-ion batteries (SIBs) have recently attracted intensive attentions as a potential alternative to LIBs for large-scale energy storage applications. However, one of the major challenges to the commercialization of SIBs is the limited choice of anode materials that can offer high rate capability. In this regard, we report intertwined Cu 3 V 2 O 7 (OH) 2 ·2H 2 O nanowires/carbon fibers composite, fabricated by a facile hydrothermal method, as the anode material for SIBs. It shows s a highly reversible Na-ion storage capacity of 287.4 mAh g −1 after 50 cycles at a large current density of 0.5 A g −1 , and excellent rate performance of delivering 206.5 and 127.7 mAh g −1 after 50 cycles at high current densities of 5 and 10 A g −1 , respectively. The promising performance is ascribed to both the crystal structure of Cu 3 V 2 O 7 (OH) 2 ·2H 2 O with a large interlayer spacing, and unique intertwined network morphology of CuVOH-NWs/CFs composite in which CuVOH-NWs and CFs synergistically functioned. This work will pave a way to develop more metal vanadates materials as anodes for high-performance SIBs. [ABSTRACT FROM AUTHOR]

Sodium ion batteries (SIBs) representan effective energy storagetechnology with potentially lower material costs than lithium ionbatteries. Here, we show that the electrochemical performance of SIBs,especially rate capability, is intimately connected to the electrodedesign at the nanoscale by taking anatase TiO2as an example.Highly ordered three-dimensional (3D) Ni-TiO2core–shellnanoarrays were fabricated using nanoimprited AAO templating techniqueand directly used as anode. The nanoarrays delivered a reversiblecapacity of ∼200 mAh g–1after 100 cyclesat the current density of 50 mAh g–1and were ableto retain a capacity of ∼95 mAh g–1at thecurrent density as high as 5 A g–1and fully recoverlow rate capacity. High ion accessibility, fast electron transport,and excellent electrode integrity were shown as great merits to obtainthe presented electrochemical performance. Our work demonstrates thepossibility of highly ordered 3D heterostructured nanoarrays as apromising electrode design for Na energy storage to alleviate thereliance on the materials’ intrinsic nature and provides aversatile and cost-effective technique for the fabrication of suchperfectly ordered nanostructures. [ABSTRACT FROM AUTHOR]

[Display omitted] • A feasible strategy is developed the multicomponent Fe 3 O 4 /Fe 1-x S@C@MoS 2 @C composite. • MoS 2 nanosheets with expanded interlayer spacing are confined between carbon layers. • The Fe 3 O 4 /Fe 1-x S@C@MoS 2 @C composite exhibits outstanding sodium storage capabilities. Considering the natural reserves, distribution and cost of sodium resources, sodium-ion batteries (SIBs) have been regarded as a potential alternative to lithium-ion batteries. However, it remains challenging to develop the excellent electrode materials for SIBs owing to larger Na ionic radius. Herein, multicomponent Fe 3 O 4 /Fe 1-x S@C@MoS 2 @C hybrid has been designed by using bone-like Fe 3 O 4 @C particles and carbon-coated MoS 2 nanosheets as the core and shell, respectively, followed by sulfurization. On one hand, several high-capacity active materials are well organized together, which can fully exert the synergies among them. Meanwhile, ultrathin MoS 2 nanosheets with expanded interlayer spacing of 0.80 nm are confined between two carbon layers, resulting in the high conductivity and good structural stability of the whole electrode. Consequently, the prepared Fe 3 O 4 /Fe 1-x S@C@MoS 2 @C anode for SIBs exhibits a large reversible capacity of 589.8 mA h/g at 100 mA/g after 200 cycles. Even at a higher current density of 2 A/g, it still keeps a high specific capacity of 503.7 mA h/g. The theoretical calculations further show that the surface of Fe 1-x S is more advantageous for Na+ adsorption in comparison to that of Fe 3 O 4 , due to the stronger charge transfer between Na and neighboring S atoms, which greatly boosts the sodium storage capability of Fe 3 O 4 /Fe 1-x S@C@MoS 2 @C. [ABSTRACT FROM AUTHOR]

Strategy of constructing flexible Sodium-Ion Battery based on Natural Renewable Polymer Materials. [Display omitted] • The concept of green sustainable development based on flexible sodium-ion batteries is put forward. • Flexible organic electrode materials and flexible carbon materials derived from polymer materials are summarized. • The selection strategy and preparation method of flexible electrode materials are discussed. • The challenges of renewable polymer materials for flexible sodium- ion batteries are reviewed. Sodium-ion batteries have been developing rapidly in recent years due to abundant sodium resources. Organic polymers and their derived carbon materials are abundant in resources, with small environmental footprint and controllable structural design, and can be directly used in the positive and anode of sodium ion batteries, which is of great significance for green and sustainable development. Organic polymers also offer great advantages in flexible Sodium-ion batteries due to their inherent flexibility. The research progress of flexible organic polymer materials and flexible polymer derived carbon materials in sodium ion batteries are reviewed. Among them, flexible organic polymer materials will be divided into flexible organic polymer carbonyl molecules and their composites with graphene/carbon nanotubes. For polymer-derived carbon materials, we will introduce several different precursors and preparation methods. Perspectives are envisioned for the further development of flexible renewable polymer materials. [ABSTRACT FROM AUTHOR]