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Because of sodium abundance, sodium ion batteries attract a lot of attention for advanced energy storage applications. As the main member of cathodes, NASICON-type structured Na 3 V 2 (PO 4) 3 contributes excellent ion shuttling rate and structure stability. However, the low electrical conductivity (<10−4 S cm−1) of Na 3 V 2 (PO 4) 3 limits its application in high power field. Herein, the Na 3 V 2 (PO 4) 3 nanoparticles anchored in the carbon matrix are successfully prepared through using the V-based metal organic frameworks (MIL-101(V)). As expected, these small Na 3 V 2 (PO 4) 3 grains are uniformly distributed in Na 3 V 2 (PO 4) 3 /carbon composite accompanying with the presence of 3D carbon framework. When used as cathode for sodium ion batteries, Na 3 V 2 (PO 4) 3 /carbon composite delivers a considerable Na-storage capacity of 136.4 mAh g−1 at the current rate of 1 C and in the voltage range of 2.5–3.8 V. Even at the current rate of 5 C and 10 C, the 84.17% and 84.5% of capacity retentions are surprisingly kept after 1,000 cycles, verifying its ultra-long cycling life. Electrochemical impedance spectroscopy substantiates a decreased charge transfer resistance for Na 3 V 2 (PO 4) 3 /carbon composite. Assisting with the detailed kinetic analysis, it is found that the enhanced surface-controlled behaviors mainly lead to the improvement of sodium-storage capability. The ex-situ scanning electron microscope and X-ray powder diffraction analysis demonstrates that unique architecture of as-prepared Na 3 V 2 (PO 4) 3 /carbon composite significantly enhances structural stability during the fast cycling. This work provides insights on design of future advanced electrode materials for sodium ion batteries. Image 1 • M-NVP/C composite is synthesized using MIL-101(V) as both carbon and vanadium source. • NVP nanoparticles are surrounded by 3D carbon framework and conductive network structure. • M-NVP/C composite demonstrates high-rate capability and long-term cyclability. • Pseudocapacitive behavior of M-NVP/C composite is confirmed by kinetics analysis. • Ex - situ SEM and XRD analysis proves the good structure stability of M-NVP/C composite. [ABSTRACT FROM AUTHOR]

Sodium titanate (Na 2 Ti 6 O 13) exhibits great potential as a sodium-ion batteries (SIBs) anode material, nevertheless the limited electronic conductivity markedly hampers its applications. To combat this shortcoming, carbon coating has been widely employed to fabricate Na 2 Ti 6 O 13 /C composites; however, this method requires a high-temperature processing that is energy-intensive releases environmental pollutants. Herein, silver is used as a novel conducting agent, and we demonstrated a simple and efficient method to prepare Ag@Na 2 Ti 6 O 13 composites. We find that nano-sized silver particles (3%) are well distributed on the Na 2 Ti 6 O 13 surface, leading to boosted conductivity of the composites. As a result, the Ag@Na 2 Ti 6 O 13 electrode exhibits an excellent performance for Na+ insertion, where after 100 cycles a discharge capacity of 189 mAh g −1 is achieved, demonstrating superior capacity retention of 97.9%. The result of silver coating on the battery performance was investigated coherently by various techniques, such as electrochemical impedance spectroscopy. Our work provides a feasible approach to prepare electronically conductive compounds for battery applications. [ABSTRACT FROM AUTHOR]

• NVO are prepared using Pluronic-F127 as structure-directing agent. • NVO show unique nanorod structures. • NVO calcined at 400 °C shows high capacity and high rate capability. • Kinetics analysis verifies the pseudocapacitive behavior of R-400. • Outstanding performance is attributed to low resistance and fast Na+ ions intercalation/deintercalation kinetics. In this study, NaV 3 O 8 nanorods are successfully prepared using nonionic surface-active agents Pluronic-F127 as structure-directing agent. The as-prepared NaV 3 O 8 nanorods calcinated at different temperatures are characterized by various techniques, including X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy. The NaV 3 O 8 calcinated at 400 °C for 20 h shows appropriate sizes and uniform morphologies of the nanorods, 4–7 μm in length and 0.2–0.5 μm in diameter. The NaV 3 O 8 nanorods as cathode materials for Na-ion batteries deliver high discharge capacity reaching up 110.4 mAh g−1 at current density of 120 mA g−1, as well as long lifespan by maintaining capacity of 162.1 mAh g−1 after 500 charge-discharge cycles. Also, a high reversible capacity of 83.9 mAh g−1 can be retained after 500 cycles at high rate of 2 A g−1. The obtained outstanding electrochemical performances are associated with the unique micro-nano structures, which does not only facilitate transport of Na+ ion, but also resist erosion from electrolytes. Overall, the results suggest the promise of NaV 3 O 8 nanorods as cathode materials for high capacity, high power and long lifespan Na-ion batteries. This work may open an innovative route to discover diverse electrode materials with nanostructure for energy storage system. [ABSTRACT FROM AUTHOR]

[Display omitted] • Na 2 THBQ were combined with CDs as cathode materials in SIBs for the first time. • o -Na 2 THBQ/CDs-2 performed good cycling stability and rate performance. • The mechanism of o -Na 2 THBQ/CDs-2 was explored by ex-situ tests. • The sodium ion diffusion coefficient of the materials was tested by GITT. Organic compounds are considered auspicious due to their widespread presence in nature, low cost, and sustainability. However, the inherent drawbacks of these organics' compounds, like low-conductivity and high-solubility, restrict their large-scale application. To solve these problems, we innovatively combined carbon quantum dots (CDs) with active substances (tetrahydroxybenzoquinone ortho -disodium salt (o -Na 2 THBQ)) at different mass ratios. The optimized o -Na 2 THBQ/CDs-2 (the mass ratio of o -Na 2 THBQ to CDs is 10:2) exhibited excellent electrochemical performance, the first-cycle discharge specific capacity was 410 mAh g−1 and maintained 182 mAh g−1 after 500 cycles, and the Coulombic efficiency was nearly 100 %. After 1300 cycles, the o -Na 2 THBQ/CDs-2 composite demonstrated a high specific capacity of 63 mAh g−1 at 500 mA g−1. This work provides a reference to design an optimal composite ratio of carbon dots (CDs) and organics to fabricate cathode materials for high-performance sodium-ion batteries. [ABSTRACT FROM AUTHOR]

• Na 2 Ti 6 O 13 nanorods are prepared by the hydrothermal and solid-phase sintering methods. • Na 2 Ti 6 O 13 nanorods has large interlayer spacing (about 0.798 nm). • Na 2 Ti 6 O 13 nanorods exhibit high cycle capacity and high rate capability. • The pseudo-capacitance contribution rate and Na+ diffusion coefficient are calculated. [Display omitted] In this study, Na 2 Ti 6 O 13 nanorods with large interlayer spacing (about 0.798 nm) were synthesized by the hydrothermal and solid-phase sintering methods, and applied to the anode of sodium ion batteries (SIBs). The influence of different calcination temperatures on the electrochemical properties of Na 2 Ti 6 O 13 nanorods were all studied. Benefitting from the nanorods structure and the large interlayer spacing, the Na 2 Ti 6 O 13 prepared at 800 °C possessed fast Na+ diffusion and achieved high discharge capacities of 168.2 and 115.2 mA h g−1 at different current densities of 20 and 500 mA g−1, respectively, and remained at 131.1 and 96.7 mA h g−1 after 100 cycles, which exhibited the best cycling stability, fast Na+ diffusion characteristics, and excellent rate performance. Supported by electrochemical impedance spectroscopy, we found that the value of R ct became larger and the D Na + became smaller with the progress of charge and discharge, which might be the cause of the decrease in the specific discharge capacity. The detailed analysis of cyclic voltammetry test confirmed that the proportion of pseudo-capacitance gradually decreased with the electrochemical reaction process keeping, from 83.8% at the beginning to 60.9% at the 100th cycle. This work establishes a valuable basis for the future study of Na 2 Ti 6 O 13 as outstanding anode material for SIBs. [ABSTRACT FROM AUTHOR]

• NVO material doped by niobium ion (Nb5+) was successfully prepared by the rheological phase method. • Nb-doping lead to an expansion of the lattice volume and increase the intrinsic conductivity. • NaNb 0.018 V 2.982 O 8 demonstrates high-rate capability and long-term cyclability. • Pseudocapacitive behavior of Nb-doped NVO is confirmed by kinetics analysis. In this work, NaNb 0.018 V 2.982 O 8 (NVO-0.018Nb) composite was served as the cathode of sodium-ion batteries (SIBs) to deliver a superior Na-storage capacity of 187 mA h g−1 at the current density of 1 C and voltage range of 1.5–4.0 V, and favorable energy density (419.3 Wh kg−1). Electrochemical impedance spectroscopy (EIS) measurements displayed decreased charge transfer resistance in the NVO-0.018Nb composite. The detailed kinetic analysis revealed enhanced surface-controlled behaviors, leading to improved sodium-storage capability. Scanning electron microscopy (SEM) and X-ray powder diffraction (XRD) analyses demonstrated that NVO-0.018Nb composite exhibited unique structure with significantly enhanced structural stability during fast cycling. In sum, the proposed method looks promising for the design of future advanced electrode materials of SIBs. [ABSTRACT FROM AUTHOR]