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[Display omitted] With the proposal of carbon peaking and carbon neutrality goals, clean energy storage is attracting more and more attentions. In view of the lack of lithium resource in our earth, sodium-ion batteries are considered as the emerging and promising next-generation energy storage devices. Appropriate high-performance anode materials play a vital role in the development of sodium-ion batteries. Here, a core-shell hollow Ni-Co-P nanopolyhedron interconnected by oxygen defect TiO 2 (Ni-Co-P@TiO 2- x) is reported, which is synthesized by ion etching-hydrolysis and subsequent phosphatization/hydrogenation treatment using ZIF-67 as template and hybrid carbon source. The achieved Ni-Co-P@TiO 2- x material has several distinct advantages including hollow core-shell structure, flexible conductive carbon matrix, stable electroactive coating layer, and efficient pseudocapacitive behavior, resulting in high reversible capacities, remarkable rate capability and excellent cycle stability. The synergetic battery-capacitor characteristic of Ni-Co-P@TiO 2- x material makes it become a promising anode for sodium-ion batteries. [ABSTRACT FROM AUTHOR]

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]

[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]

[Display omitted] • Na 4 MnCr(PO 4) 3 /C is firstly prepared by a facile modified solid phase method. • The chelating effect of citric acid is benefit to synthesis pure Na 4 MnCr(PO 4) 3. • 3D porous architecture can improve the conductivity of Na 4 MnCr(PO 4) 3. • Suitable carbon layers can improve the structural stability of Na 4 MnCr(PO 4) 3. Na 4 MnCr(PO 4) 3 is a promising cathode material with high redox potential and high energy density, but the intrinsic poor electronic conductivity and substandard structural stability restrict its practical application. Herein, porous Na 4 MnCr(PO 4) 3 /C with conductive networks and improved electrochemical properties is synthesized by a facile modified solid-state process using citric acid as a multifunctional additive. The results reveal that citric acid can be used as a grinding aid to make the raw materials mix more evenly and speed up the efficiency of ball milling. Besides, 3D conductive network and porous structure originated from polycondensation and carbonization of citric acid can promote the electrochemical properties of Na 4 MnCr(PO 4) 3 /C by enhancing the electronic/ionic conductivity and (de)intercalation reaction kinetics. As expected, the optimal Na 4 MnCr(PO 4) 3 /C delivers a high reversible capacity of 130.5 mAh g−1 at 0.1C rate, and exhibits a capacity retention of 82.62% at 10C rate after 500 cycles. In addition, the reversible biphasic reaction of the cathode is confirmed by the constant galvanostatic intermittent titration technique and ex-situ XRD, which shows great potential of the synthesized Na 4 MnCr(PO 4) 3 /C for practical applications. [ABSTRACT FROM AUTHOR]

Searching for affordable and efficient anode materials is of great significance for the development of sodium-ions batteries. Anatase-based electrode material has demonstrated reasonably voltage and outstanding cyclability. However, low specific capacity and poor Na+ transmission efficiency of conventionally prepared anatase material restrain its practical application. To achieve anatase-based electrode material with superior sodium storage, pompon-villus shaped hydrogen titanate/anatase composite with heterostructure is synthesized by a facile method. Thanks to the cooperative effect of unique pompon-villus architecture, open channel of hydrogen titanate, and specific heterostructure, the synthesized composite displays excellent rate performance and long cycle performance: the discharge specific capacity is remains 157.8 mAh·g−1 after 200 cycles at 0.1 A·g−1, and the discharge specific capacity is maintaining 104.1 mAh·g−1 after 1000 cycles at 2 A·g−1. This work supplies new fundamental strategy and paves an encouraging avenue in designing anatase-based electrode with improved electrochemical performance for sodium-ions batteries. [Display omitted] • Pompon-villus shaped hydrogen titanate/anatase was prepared for the first time. • Heterostructure was constructed between hydrogen titanate and anatase. • As-obtained hydrogen titanate/anatase showed good electrochemical performances. [ABSTRACT FROM AUTHOR]