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Layered transition metal oxide Na 0·67 Fe 0·5 Mn 0·5 O 2 is considered as a promising cathode material of sodium-ion batteries because of its naturally elemental abundance and high energy density. However, low rate capability and poor structural reversibility of Na 0·67 Fe 0·5 Mn 0·5 O 2 greatly hinder its large scale application. In this study, V-substituted Na 0·67 Fe 0·5 Mn 0·5 O 2 cathode material with improved electrochemical performance is successfully synthesized via a sol-gel method. The effects of V-substitution on chemical composition, crystal structure and morphology of Na 0·67 Fe 0·5 Mn 0·5 O 2 are studied in detail. Furthermore, modification mechanisms on the improved electrochemical performance by V-substitution are investigated. The results demonstrate that the rate capability and cycle stability of Na 0·67 Fe 0·5 Mn 0·5 O 2 cathode material is significantly elevated by V-substitution. And the enhanced electrochemical properties are mainly attributed to the improved Na+ diffusion rate and structural reversibility. This study suggests that introducing V ions into the lattice of Na 0·67 Fe 0·5 Mn 0·5 O 2 crystals is a favorable strategy to improve its electrochemical properties. [ABSTRACT FROM AUTHOR]

[Display omitted] • Surface phosphorylated TiO 2 nanofibers with binary-phase are fabricated successfully. • The reactivity of TiO 2 nanofibers is boosted by surface phosphorylation treatment. • The synthesized SP-TiO 2 -A/B shows significantly improved electrochemical performance. TiO 2 -based nanostructure has been reported as one of the most developable anode materials for sodium-ion batteries, but its low capacity and poor rate capability bring an unavoidable challenge and impede the practical application. In this study, surface phosphorylated TiO 2 nanofibers with anatase/bronze binary-phase are fabricated using ion exchange-annealing treatment and subsequent phosphorylation. The resulting nanofibers can serve as an efficient electrode material for sodium storage, affording a reversible capacity of 224.7 mAh g−1 at 200 mA g−1 and a superior high-rate cycling capability of 108.9 mAh g−1 at 2000 mA g−1 after 1000 cycles. XPS and HRTEM reveal that the synthesized SP-TiO 2 -A/B nanofibers present heterojunction-boundary between anatase/bronze binary-phase and well-crystallized internal-structure with disordered/amorphous surface, and a high ratio of active surface was motivated through phosphorylation and Na+ ion storage behavior was efficiently modulated. The surface phosphorylation engineering provides a promising strategy to develop Na-storage electrodes with superior electrochemical performance. [ABSTRACT FROM AUTHOR]

• Nanoporous Na 2 Fe 1- x Mn x PO 4 F/C composites are synthesized by spray drying method. • Na 2 Fe 0.6 Mn 0.4 PO 4 F/C cathode shows much enhanced sodium storage performance. • Reaction kinetics of Na 2 Fe 0.6 Mn 0.4 PO 4 F/C is revealed by EIS for the first time. • Strategies to enhance the properties of Na 2 Fe 0.6 Mn 0.4 PO 4 F/C are concluded. It is a challenge to develop a facile and scaleable approach to boost the application of high-energy fluorinated iron/manganese phosphate cathode materials for sodium-ions batteries. In this study, for the first time, the porous Na 2 Fe 1- x Mn x PO 4 F/C (x = 0.2, 0.4, 0.6, 0.8) nanocomposites are successfully designed via spray drying, following in-situ pyrolytic carbonization process. To examine this synergetic design, the rate capability, cycling stability, and reaction kinetics of the cathode materials are investigated in detail. It is found that the solid solution Na 2 Fe 0.6 Mn 0.4 PO 4 F/C cathode delivers the high discharge capacities of 94.8 and 30.0 mAh g−1 at 0.05 C and 1.0 C, respectively, and a reversible capacity of 51.0 mAh g−1 after 100 cycles at 0.2 C with a capacity retention of 89.3%. Particularly, the cycling stability as well as rate capability of Na 2 Fe 0.6 Mn 0.4 PO 4 F/C are superior to those of the other Na 2 Fe 1- x Mn x PO 4 F/C solid solutions and the two-phase mixture of Na 2 MnPO 4 F/C and Na 2 FePO 4 F/C. Furthermore, the potential strategies to further improve the electrochemical performance of Na 2 Fe 0.6 Mn 0.4 PO 4 F/C cathode are proposed based on the kinetics analysis of its electrochemical impedance spectroscopy spectra at various charge/discharge depths. It is expected that our research strategies and findings can be extended to other electrode materials in Li+/Na+ storage and beyond. [ABSTRACT FROM AUTHOR]

In view of the inferior specific capacity and low rate capability of titanium dioxide with individual-phase, multi-sized anatase/bronze nanoribbons with heterojunction structure are prepared by a hydrothermal ion exchange method in this study. The effects of calcination temperature on the crystallographic structure, architecture morphology and electrochemical properties of anatase/bronze nanoribbons are investigated. The results show that the prepared anatase/bronze nanoribbons present one-dimensional nanostrips structure with a bandwidth of about 100 nm, and nanofibers are attached to the surface. It is found that calcination temperature is critic in the crystallographic structure, architecture morphology and electrochemical performance of anatase/bronze nanoribbons. The multi-sized anatase/bronze nanoribbons prepared at 300 °C show improved electrochemical performance with superior specific capacity, outstanding rate capability and long cycle life. At the current density of 200 mA·g−1, the specific discharge capacity of the first circle reaches 728 mAh·g−1. Moreover, the specific discharge capacity remains 92.5 mAh·g−1 after 2000 charge-discharge cycles 2000 mA·g−1. The design of anatase/bronze heterojunction structure supplies a potential strategy to develop titanium-based anode with advantageous electrochemical performance. [Display omitted] • Multi-sized anatase/bronze nanoribbons with heterojunction was prepared. • Multi-sized architecture and heterojunction promote sodium storage. • As-obtained anatase/bronze nanoribbons showed good electrochemical performance. [ABSTRACT FROM AUTHOR]

[Display omitted] • A novel pure bimetallic-polyanion Na 4 Fe 2.82 Ni 0.18 (PO 4) 2 P 2 O 7 cathode is produced. • Ni-substituting inhibits the generation of NaFePO 4 impurity during the synthesis. • Ni-substituting and N-doping significantly improve the conductivity of cathode. • The Na 4 Fe 2.82 Ni 0.18 (PO 4) 2 P 2 O 7 @C-N exhibits superior sodium-storage performance. Na 4 Fe 3 (PO 4) 2 P 2 O 7 , with the advantages of strong structural stability, suitable voltage window, low cost and green pollution-free, is considered as a highly researchable cathode material for sodium-ion batteries. However, the low conductivity of Na 4 Fe 3 (PO 4) 2 P 2 O 7 and the inevitable electrochemical inertia from maricite-NaFePO 4 impurity during the preparation process lead to the low reversible capacity and poor cycling stability. In this work, a new bimetallic-polyanion cathode material Na 4 Fe 2.82 Ni 0.18 (PO 4) 2 P 2 O 7 capped with an in-situ nitrogen-doped carbon layer is proposed. Ni-substituting inhibits the generation of electrochemical inert maricite-NaFePO 4 impurity and enhances the Na+ ion conductivity. Meanwhile, a lower volume-change during the charging/discharging process can be achieved in Na 4 Fe 2.82 Ni 0.18 (PO 4) 2 P 2 O 7 electrode compared with conventional Na 4 Fe 3 (PO 4) 2 P 2 O 7 electrode. With the synergistic effect of in-situ N-doping and Ni-substituting, an ultra-high initial discharge capacity (128.4 mAh g−1 at 0.2C), superior rate performance (62.5 mAh g−1 at 50C) and significant long-term cycle life (capacity retention rate of about 83 % after 3000 cycles at 10C) can be achieved in the optimal Na 4 Fe 2.82 Ni 0.18 (PO 4) 2 P 2 O 7 @C-N (Ni6-NFPP@C-N) cathode. This study suggests a practical strategy to produce Na 4 Fe 3 (PO 4) 2 P 2 O 7 -based electrode material with no impurities and superior electrochemical properties for sodium-ion batteries. [ABSTRACT FROM AUTHOR]

We designed and engineered the construction of conductive PPy-decorated hydrangea-type 1T-MoS 2 as a cathode host material for high-energy-density and long-life Li-S batteries. [Display omitted] • PPy-encapsulated hydrangea-type 1 T-MoS 2 sulfur host was successfully prepared. • 1 T-MoS 2 @PPy shows favorable catalytic activities to LiPSs/Li 2 S redox reactions. • The synergistic effect of 1 T-MoS 2 and PPy promoted the conversion of LiPSs. • Hierarchical architecture of 1 T-MoS 2 @PPy is benefit to electron/ion transfer. • 1 T-MoS 2 -S@PPy cathode exhibits high-rate and ultra-stable cycling performance. Lithium-sulfur batteries are regarded as promising candidates for next-generation energy storage applications owing to their high theoretical specific capacity, low cost, and eco-friendliness. However, the poor conductivity, large volume variation of sulfur species during the charging/discharging process, complicated conversion reactions of sulfur species, shuttle effect of lithium polysulfide, and low sulfur loading greatly hinder the practical application of lithium-sulfur batteries. In this study, we propose an efficient approach to design polypyrrole (PPy)-encapsulated 1T-MoS 2 microspheres with a hydrangea-like structure as catalytic sulfur hosts for lithium-sulfur batteries. The catalytic effect of 1T-MoS 2 and the high conductivity of the PPy layer accelerated the adsorption/conversion of lithium polysulfides. The hydrangea-like structure of the 1T-MoS 2 microspheres provided adequate number of active sites and sufficient space for sulfur loading. Meanwhile, the specific inter-porous/outer-coating layer structure could also restrain the expansion of sulfur electrode during the electrochemical reaction process. The obtained 1T-MoS 2 -S@PPy cathode material exhibited outstanding electrochemical performance with an excellent reversible capacity of 1434 mAh g−1 at 0.1C rate, a considerable capacity of 1023 mAh g−1 at 1C rate, and excellent cycling stability for over 800 cycles with a low cycling decay rate of 0.051% per cycle. [ABSTRACT FROM AUTHOR]