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The addition of Ni3+ ions causes a change in the electron distribution of surrounding ions, which further lead to the decreased diffusion energy barrier and increased adsorption energy of Na+ ions. The above factors make P2-Na 0.67 Mn 0.45 Ni2+ 0.12 Ni3+ 0.10 Co 0.33 O 2 (Ni-R1) get a higher and stable specific capacity of 114 mA h/g in the voltage range of 2.0–4.25 V, with a capacity retention ration of 80% after 1000 cycles. It provides a new idea for development of a practical sodium ion battery. [Display omitted] For transition metal oxide materials, high Ni content is an effective method to obtain a high specific capacity. However, the theoretical capacity is determined due to the certain amount of variable charges of transition metal ions. The increased capacity in specific voltage window may attribute to the easier transport of alkali ions, instead of more active elements. Borrowing the theory of Ni-rich materials in LIB, excess Ni elements were added into P2-type layered oxide material to form the Jahn-Teller active Ni3+ ions. About 25%-61% Ni3+ ions can effectively promote de-/intercalation of Na+ ions due to the decreased diffusion energy barrier and increased adsorption energy of Na+. The preferred "Ni-rich" material Na 0.67 Mn 0.45 Ni 0.22 Co 0.33 O 2 (Ni-R1) shows a reversible specific capacity of 114 mA h g−1 in the voltage range of 2.0–4.25 V. In addition, it shows an excellent cycle stability, the capacity retention ration is 80% after 1000 cycles at a current density of 1 A g−1. The in-depth study proves that, Jahn-Teller active Ni3+ ions can effectively regulate the valence electron distribution of surrounding ions in synthesis stage. However, it will promote Jahn-Teller distortion when the Ni3+ content is increased to 74%, which makes the rate performance deteriorate dramatically. The present work provides a simple and efficient way to increase the capacity in suitable voltage range for application. [ABSTRACT FROM AUTHOR]

Co shows excellent performance in the high voltage range for layered oxide cathode materials for sodium ion batteries (SIBs). However, its high cost and toxicity are significant disadvantages.Co‐free cathodes with high performance are urgently needed for development. Herein, cheap Mg and Ti elements are preferred to replace Co elements. A P2‐Na0.67Mn0.53Ni0.30Mg0.085Ti0.085O2 (Ni30MgTi) cathode shows a high reversible specific capacity of 118 mA h g−1 at a current density of 50 mA g−1 in 2.0–4.25 V, which is even higher than that in the base sample with Co. Moreover, Mg and Ti raise the median discharge voltage from 3.21 to 3.59 V, which raises the energy density from 325 to 410 Wh kg−1. On the other hand, ex situ XPS and in situ differential electrochemical mass spectrometry tests indicate that Ni30MgTi has a stable anionic redox reaction with reversible capacity in the high voltage range. The concept of bimetallic co‐substitution offers a simple and effective Co‐free strategy to reduce the cost and increase the energy density of layered oxide cathode materials simultaneously for SIBs. [ABSTRACT FROM AUTHOR]

Sodium‐ion batteries (SIBs) have attracted much attention due to their abundance, easy accessibility, and low cost. P2‐type layered oxide materials, as one of the most potential cathode candidates for SIBs, have been widely studied. However, various kinds of structural evolution during cycling are harmful to the stability. In the present Minireview, the phase transitions occurring in the process of charge/discharge are summarized, and the mechanism of structural rearrangement and phase transition are introduced. This Minireview is aimed at helping researchers understand the detailed structural evolution, and propose strategies of designing the P2‐type layered oxide cathodes with low strain. [ABSTRACT FROM AUTHOR]

Most P2‐type layered oxides exhibit a large volume change when they are charged into high voltage, and it further leads to bad structural stability. In fact, high voltage is not the reason which causes the irreversible phase transition. There are two internal factors which affect structural evolution: the amount and distribution of Na ions retained in the lattice. Hereon, a series of layered oxides Na2/3MnxNix−1/3Co4/3−2xO2 (1/3≤x≤2/3) were synthesized. It is observed that different components have different structural evolutions during the charge/discharge processes, and further researches find that the distribution of Na ions in layers is the main factor. By controlling the distribution of Na ions, the phase transition process can be well controlled. As the referential component, P2‐Na2/3Mn1/2Ni1/6Co1/3O2 cathode with uniform distribution of Na ions is cycled at the voltage window of 1.5–4.5 V, which exhibits a volume change as low as 1.9 %. Such a low strain is beneficial for cycling stability. The current work provides a new and effective route to regulate the structural evolution of the promising P2‐type layered cathode for sodium ion batteries. [ABSTRACT FROM AUTHOR]

Most P2‐type layered oxides exhibit a large volume change when they are charged into high voltage, and it further leads to bad structural stability. In fact, high voltage is not the reason which causes the irreversible phase transition. There are two internal factors which affect structural evolution: the amount and distribution of Na ions retained in the lattice. Hereon, a series of layered oxides Na2/3MnxNix−1/3Co4/3−2xO2 (1/3≤x≤2/3) were synthesized. It is observed that different components have different structural evolutions during the charge/discharge processes, and further researches find that the distribution of Na ions in layers is the main factor. By controlling the distribution of Na ions, the phase transition process can be well controlled. As the referential component, P2‐Na2/3Mn1/2Ni1/6Co1/3O2 cathode with uniform distribution of Na ions is cycled at the voltage window of 1.5–4.5 V, which exhibits a volume change as low as 1.9 %. Such a low strain is beneficial for cycling stability. The current work provides a new and effective route to regulate the structural evolution of the promising P2‐type layered cathode for sodium ion batteries. [ABSTRACT FROM AUTHOR]

Most P2‐type layered oxides exhibit a large volume change when they are charged into high voltage, and it further leads to bad structural stability. In fact, high voltage is not the reason which causes the irreversible phase transition. There are two internal factors which affect structural evolution: the amount and distribution of Na ions retained in the lattice. Hereon, a series of layered oxides Na2/3MnxNix−1/3Co4/3−2xO2 (1/3≤x≤2/3) were synthesized. It is observed that different components have different structural evolutions during the charge/discharge processes, and further researches find that the distribution of Na ions in layers is the main factor. By controlling the distribution of Na ions, the phase transition process can be well controlled. As the referential component, P2‐Na2/3Mn1/2Ni1/6Co1/3O2 cathode with uniform distribution of Na ions is cycled at the voltage window of 1.5–4.5 V, which exhibits a volume change as low as 1.9 %. Such a low strain is beneficial for cycling stability. The current work provides a new and effective route to regulate the structural evolution of the promising P2‐type layered cathode for sodium ion batteries. [ABSTRACT FROM AUTHOR]

Most P2‐type layered oxides exhibit a large volume change when they are charged into high voltage, and it further leads to bad structural stability. In fact, high voltage is not the reason which causes the irreversible phase transition. There are two internal factors which affect structural evolution: the amount and distribution of Na ions retained in the lattice. Hereon, a series of layered oxides Na2/3MnxNix−1/3Co4/3−2xO2 (1/3≤x≤2/3) were synthesized. It is observed that different components have different structural evolutions during the charge/discharge processes, and further researches find that the distribution of Na ions in layers is the main factor. By controlling the distribution of Na ions, the phase transition process can be well controlled. As the referential component, P2‐Na2/3Mn1/2Ni1/6Co1/3O2 cathode with uniform distribution of Na ions is cycled at the voltage window of 1.5–4.5 V, which exhibits a volume change as low as 1.9 %. Such a low strain is beneficial for cycling stability. The current work provides a new and effective route to regulate the structural evolution of the promising P2‐type layered cathode for sodium ion batteries. [ABSTRACT FROM AUTHOR]

Sodium‐ion batteries (SIBs) are the most promising candidates as alternatives to lithium‐ion batteries (LIBs), owing to the natural abundance of sodium salt and the low cost. However, the commercial application of SIBs is principally hampered by the absence of suitable cathode materials. Herein, a novel Na2FeP2O7@carbon/expanded graphite (NFPO@C/EG) composite with a unique microstructure was developed through a scalable sol‐gel process followed by a ball‐milling procedure with expanded graphite. Benefiting from the multiscale carbon‐modified structure, the NFPO@C/EG effectively improves the electronic conductivity and, at the same time, shortens the path of sodium ion transmission. As a consequence, the NFPO@C/EG cathode presents a much higher specific capacity and more stable cycling stability than NFPO@C and NFPO. The unique design of NFPO@C/EG endows a high ratio of pseudocapacitance contribution and a large Na+ diffusion coefficient. As a consequence, the NFPO@C/EG cathode displays stable cycle performance (82 mAh g−1 over 400 cycles at 232 mA g−1) and superior rate capability (60 mAh g−1 at a high charge/discharge density of 2320 mA g−1). This multiscale carbon‐modified design concept builds an avenue for the practical application of polyanionic cathode materials and promotes the development of low‐cost SIBs. [ABSTRACT FROM AUTHOR]

Graphical abstract Novel anode of ternary FeS@TiO 2 @C nanotubes has been successfully fabricated via a general MOF-derived solid sulfuration method. Due to the porous carbon-wrapped hollow nanostructure and electroactive stable TiO 2 modification layer, this anode displays a stable cycling performance and superior rate capability for Na-ion batteries. Highlights • FeS@TiO 2 @C nanotubes were synthesized via a MOF-derived sulfuration method. • FeS@TiO 2 @C nanotubes show superior rate capability and cycling performance. • Carbon-encapsulated porous structure enhances the electrochemical performance. Abstract Na-ion batteries (SIBs) have now attractive extensive attention due to the wide-spread preserve of sodium resources and low cost, which have the potential as the alternative for Li-ion batteries and suitable for large energy station application. Herein, we have rationally synthesized uniform nanotube-structured FeS@TiO 2 @C anode with metal-organic framework (Fe-MOF) rods as the self-support template. Such uniform ternary FeS@TiO 2 @C nanotubes were facilely prepared by sulfuration of FeTiO 3 @C nanotubes, which were obtained by a one-pot annealing of TiO 2 -coated Fe-MOF nanorods. This carbon-wrapped hollow nanostructure could effectively mitigate the volume expansion, improve the electronic conductivity and provide more channels and active sites for Na+ transporting. In detail, these uniform FeS@TiO 2 @C nanotubes achieve superior rate capability (with a high reversible capacity of 387, 390, 376, 348, 325, and 286 mA h g−1 at the current density of 0.1, 0.2, 0.5, 1.0, 2.0, and 5.0 A g−1, respectively) and excellent cycling performance (with a reversible capacity of 454 mA h g−1 after 120 cycles at 0.2 A g−1 and 406 mA h g−1 after 150 cycles at 1.0 A g−1). [ABSTRACT FROM AUTHOR]

• P2-LNMTCOF has higher sodium content due to the basis material with the component of O3-type cathode material. • The LiF additive can promote the formation of P2-type cathode material. • The LiF additive can realize the co-doping of anions and cations at the same time. • The voltage drop during cycling has been suppressed due to the more stable TM-O (F) octahedron. • The TOF-SIMS techniques provide novel and powerful tools for exploring the binding state between elements. Element doping is a common and effective method for improving the electrochemical performance of cathode materials, and typically it can be divided into cation ion and anion ion doping. Among the cathode materials of sodium-ion batteries, the important layered oxide cathodes mainly include those of O3 and P2 types, according to the sites of Na ions and the number of oxide layer packings. Hereon, the successful transformation of O3-type cathode NaNi 0.45 Mn 0.4 Ti 0.1 Co 0.05 O 2 (O3-NMTCO) into P2-type cathode of NaNi 0.45 Mn 0.4 Ti 0.1 Co 0.05 O 2 -0.08LiF (P2-LNMTCOF) is achieved via a facile Li/F co-doping route. The modified P2-type cathode (P2-LNMTCOF) have main three advantages over the traditional P2-type cathode Na 0.7 Ni 0.45 Mn 0.4 Ti 0.1 Co 0.05 O 2 (P2-NMTCO): higher Na content, solid solution reaction in high-voltage range, and stronger TM-F bond. As a result, the current P2-LNMTCOF cathode shows the best cycling performance, with the initial capacity of about 160 mA h g−1 and the capacity retention of 61% after 200 cycles. In addition, because of the more stable TM-O (F) octahedron, the voltage drop during cycling has been effectively suppressed. This study provides a new idea and reference for synthesizing high performance P2-type layered oxide cathode materials for sodium-ion batteries. [ABSTRACT FROM AUTHOR]

Keywords: aqueous batteries; cathode materials; manganese; quinone cathodes; storage mechanisms; vanadium; Zn-ion batteries EN aqueous batteries cathode materials manganese quinone cathodes storage mechanisms vanadium Zn-ion batteries 1 1 1 01/18/21 20210113 NES 210113 B Aqueous zinc ion batteries (ZIBs) b are the most promising rechargeable batteries for the grid energy storage and industrial energy storage for its lower cost and higher safety. The cathode materials consist of Mn-based materials, V-based materials, Prussian blue analogous (PBAs), Quinone and the others materials. Aqueous batteries, cathode materials, manganese, quinone cathodes, storage mechanisms, vanadium, Zn-ion batteries. [Extracted from the article]

A scalable and facile polymer-blowing and galvanic replacement route for 3D porous carbon framework embedded with uniform Sb nanoparticles have been synthesized Such designed electrode architecture provides porous structure, high structure stabilities, high electronic conductivity and robust buffer layers, which could solve the issue of poor ionic and electronic transport in electrode materials and accommodate the large volume expansion. • 3D porous Sb ⊂ 3DPC was synthesized via a scalable and facile polymer-blowing and galvanic replacement route. • 3D porous Sb ⊂ 3DPC anode show superior rate capability and cycling performance. • Such 3D porous interconnected carbon-encapsulated structure enhances the electrochemical performance. The development of high-performance Na-ion batteries in order to meet the increasing demand of the industrial applications of energy storage requires low cost and large-scale preparation methods for battery electrodes with outstanding performance. In this work, we have designed a novel anode of three-dimensional porous interconnected carbon matrix embedded with Sb nanoparticles (Sb ⊂ 3DPC) via a scalable and facile polymer-blowing and galvanic replacement route. This designed electrode architecture provides large surface areas, large pore volumes and interconnected pore frameworks, supplying enlarged interface of the electrolyte and electrode, reducing the diffusion pathway and inhibiting the volume expansion of Sb during cyclic movement. The as-prepared Sb ⊂ 3DPC anode shows high Na-storage performance, such as an outstanding cycle stability (461 mA h g−1 at 100 mA g−1 over 200 cycles) and exceptional high rate capability (349 mA h g−1 at 5000 mA g−1). As for the application in the full Na-ion batteries, the assembled Sb ⊂ 3DPC//Na 3 V 2 (PO 4) 3 full cell also shows remarkable rate capability. Such polymer-blowing-based approach provides a low cost, uncomplicated and large scale preparation method for porous and stable electrode materials and opens up a wide horizon in other electrochemical applications. [ABSTRACT FROM AUTHOR]