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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]

P2-Na 2/3 Fe 1/2 Mn 1/2 O 2 is successfully synthesized via a facile spray-drying method followed by calcining at low temperature. The obtained material shows excellent discharge capacity, high rate capability and outstanding cycle ability. • P2-types Na 2/3 Fe 1/2 Mn 1/2 O 2 is synthesized by spray-drying method. • The temperature in the calcining process is decreased significantly. • The sample shows high capacity, excellent rate capability and cycle stability. Owing to its high theoretical capacity, P2-type Na 2/3 Fe 1/2 Mn 1/2 O 2 has been considered as a kind of promising cathode material. However, the practical application is limited due to excessively high calcining temperature during traditional preparation processes. Here, we report the synthesis of P2-Na 2/3 Fe 1/2 Mn 1/2 O 2 by using a facile spray-drying method followed by calcining at low temperature. Under the optimal conditions, the well-crystallized P2-Na 2/3 Fe 1/2 Mn 1/2 O 2 material with excellent rate capability and cycle ability is obtained. And the sample exhibits the initial discharge capacities of 217.9, 171.3 and 117.4 mAh g−1 at 0.1 C, 0.5 C and 2 C rate, respectively. The developed Na 2/3 Fe 1/2 Mn 1/2 O 2 material, synthesized by a new spray drying-calcining procedure, may potentially be used as a suitable cathode in sodium ion batteries. [ABSTRACT FROM AUTHOR]

[Display omitted] Na 4 Fe 3 (PO 4) 2 (P 2 O 7) is regarded as a promising cathode material for sodium-ion batteries due to its affordability, non-toxic nature, and excellent structural stability. However, its electrochemical performance is hampered by its poor electronic conductivity. Meanwhile, most of the previous studies utilized spray-drying and sol–gel methods to synthesize Na 4 Fe 3 (PO 4) 2 (P 2 O 7), and the large-scale synthesis of the cathode material is still challenging. This study presents a composite cathode material, Na 4 Fe 2.94 Al 0.04 (PO 4) 2 (P 2 O 7)/C, prepared via a straightforward ball-milling technique. By substituting Al3+ minimally into the Fe2+ site of NFPP, Fe defects are introduced into the structure, hindering the formation of NaFePO 4 and thereby enhancing Na-ion diffusion kinetics and conductivity. Additionally, the average length of Al O bonds (2.18 Å) is slightly smaller than that of Fe O bonds (2.19 Å), contributing to the superior structural stability. The smaller ionic radii of Al3+ induce lattice contraction, further enhancing the structural stability. Moreover, the surface of material particles is coated with a thin layer of carbon, ensuring excellent electrical conductivity and outstanding structure stability. As a result, the Na 4 Fe 2.94 Al 0.04 (PO 4) 2 (P 2 O 7)/C cathode exhibits excellent electrochemical performance, leading to high discharge capacity (128.1 mAh g−1 at 0.2 C), outstanding rate performance (98.1 mAh g−1 at 10 C), and long cycle stability (83.7 % capacity retention after 3000 cycles at 10 C). This study demonstrates a low-cost, ultra-stable, and high-rate cathode material prepared by simple mechanical activation for sodium-ion batteries which has application prospects for large-scale production. [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]

Na 2 MnPO 4 F has become a promising cathode candidate for next generation sodium ion batteries by virtue of its high working potential and theoretical capacity, but its electrochemical performance is restricted by its low electronic conductivity and sluggish Na+ diffusion. In this study, Na 3 V 2 (PO 4) 2 F 3 is introduced into the Na 2 MnPO 4 F cathode material to improve the electron/ionic conductivity by generating lattice defects and providing active sites for Na+ transportation. The structure, morphology and electrochemical properties of x Na 2 MnPO 4 F· y Na 3 V 2 (PO 4) 2 F 3 /C materials are investigated thoroughly. It is found that the electrochemical performance of Na 2 MnPO 4 F is significantly elevated by the modification of Na 3 V 2 (PO 4) 2 F 3. The optimized lotus root-like porous Na 2 MnPO 4 F·Na 3 V 2 (PO 4) 2 F 3 /C cathode material delivers the first specific discharge capacity of 126.6 mAh·g−1 at 0.05C, which is close to the theoretical specific capacity. Furthermore, the Na 2 MnPO 4 F·Na 3 V 2 (PO 4) 2 F 3 /C cathode material also presents good rate performance (76.9 mAh·g−1 at 1C rate), and remains 93.2% capacity retention after 400 cycles. This paper demonstrates a promising guide to construct Na 2 MnPO 4 F-based cathode materials with superior electrochemical performance for sodium ion batteries. [Display omitted] [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]