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Lithium-sulfur batteries have attracted numerous attentions owing to their high theory discharge specific capacity and energy density. However, sulfur cathode usually suffers from poor cycle stability and slow reaction kinetics, caused by its poor conductivity, excessive volume changes during charge/discharge processes, complex sulfur species conversion reaction and the dissolution of polysulfide intermediates. Here, we present a free-standing framework of Mn 3 O 4 nanoparticles combine with polypyrrole (PPy) nanotubes as host materials for lithium-sulfur batteries to overcome these issues. In this construction, PPy nanotubes serve as the excellent container of sulfur and physical barrier for the excessive volume expansion of sulfur during electrochemical reaction processes, and the nanotubes also provide an efficient conductive network for the rapid transmission of electrons and ions, while Mn 3 O 4 nanoparticles facilitate trapping lithium polysulfides. The coordination of PPy nanotubes and Mn 3 O 4 effectively alleviate the shuttle effect as well as enhance the utilization of sulfur. The obtained PPy@Mn 3 O 4 -S sample shows high capacities of 1419.9 and 925.5 mAh g−1 at 0.1 C and 1 C rate, respectively, and exhibits a low capacity fading rate of 0.062% per cycle for 800 cycles at 1 C rate. This work provides a new and effective way for the design of lithium-sulfur batteries with both high rate performance and long cycle stability. [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] 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]

[Display omitted] • Ni, Mn co-doped FePO 4 @C is synthesized by an ion exchange method in aqueous media. • Heating is benefit to increase the delithiation rate of LiFePO 4. • Ni, Mn co-doping can effectively enhance the electronic conductivity of FePO 4. • Ni, Mn co-doping can obviously increase the working voltage of FePO 4 cathode. Olivine FePO 4 is widely regarded as an optimal cathode material for sodium-ion batteries due to its impressive theoretical capacity of 177.7 mAh g−1. Nonetheless, the material's limited application stems from its intrinsic low electronic and ionic conductivities and ion diffusion rate. Previously, most modifications of olivine FePO 4 are conducted through electrochemical or ion exchange processes in organic solvents, which severely restricted its potential for large-scale applications. In this research, a novel water-based ion exchange method is proposed for the synthesis of Ni-doped, Mn-doped, and Ni, Mn co-doped FePO 4 @C, which is non-toxic, cost-effective, and demonstrating promising prospects for various applications. Fe 2.7 Mn 0.2 Ni 0.1 PO 4 @C (0.2Mn0.1Ni-FP@C) is synthesized by a straightforward ion exchange method in aqueous media. The material exhibits a discharge capacity of 154.4 mAh g−1 at 0.1C rate. After 300 cycles at 1C, the capacity retention rate remains at 70.7 %. Numerous tests and calculations conducted in this study demonstrate that 0.2Mn0.1Ni-FP@C, modified through Mn3+ and Ni3+ co-doping, exhibits superior electrochemical performance due to its enhanced electronic conductivity and ion diffusion rate. [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]

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]

[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]

It is a great challenge to develop the cathode materials with high efficiency, long life and low-cost for lithium-sulfur batteries. In this paper, we design a simple hydrothermal method to synthesize MoS 2 wrapped the MOFs-derived N-doped carbon nanorods as an effective sulfur host to improve the electrochemical performance of lithium-sulfur batteries. In the hydrothermal process, the cubic zeolitic imidazolate framework-67 (ZIF67) particles are connected together to form nanorods, and MoS 2 nanosheets are wrapped on the surface of the nanorods. In this composite, the carbon nanorods derived from ZIF67 is the main host for S-loading, while N-doping can change the hybrid orbital form of carbon and significantly improve the chemical adsorption of polysulfide. The elemental cobalt and cobalt oxide derived from ZIF67 can improve the electronic conductivity and polarity of the composite. And MoS 2 coating layer can provide more active sites, accelerate the sulfur redox reactions and effectively restrain the shuttle effect. The synergetic effects of above-mentioned factors make the MoS 2 @CZIF67/S composite cathode material shows excellent electrochemical performance. The composite shows high reversible specific capacities of 1391.9 and 806.1 mAh g−1 at 0.1C and 1C rate, respectively, and exhibits a capacity retention of 70.5% after 400 cycles at 1C rate. [ABSTRACT FROM AUTHOR]