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The shell structure design has been recognized as a highly efficient strategy to buffer the severe volume expansion and consecutive pulverization of conversion‐type anodes. Nevertheless, construction of a functional shell with a stabilized structure that meets the demands of both high electronic conductivity and feasible pathways for Na+ ions has been a challenge so far. Herein, we design a two‐in‐one shell configuration for bimetal selenides to achieve fast sodium storage within broadened voltage windows. The hybridized shell, which benefits from the combination of titanium dioxide quantum dots and amorphous carbon, can not only effectively buffer the strain and maintain structural integrity but also allow facile and reversible transport of electrons and Na+ uptake for electrode materials during sodiation/desodiation processes, resulting in increased reaction kinetics and diffusion of sodium ions, conferring many benefits to the functionality of conversion‐type electrode materials. As a representative material, Ni‐CoSe2 with such structural engineering shows a reversible capacity of 515 mAh g−1 at 0.1 A g−1 and a stable capacity of 416 mAh g−1 even at 6.4 A g−1; more than 80% of the capacity at 0.1 A g−1 could be preserved, so that this strategy holds great promise for designing fast‐charging conversion‐type anodes in the future. [ABSTRACT FROM AUTHOR]

Prussian blue analogs (PBAs) are promising cathode materials for sodium‐ion batteries (SIBs) due to their low‐cost, similar energy density comparable with that of LiFePO4 in lithium‐ion batteries, and long cycle life. Nevertheless, crystal water (≈10 wt%) in PBAs from aqueous synthesis environments can bring significant side effects in real SIBs, especially for calendar life and high temperature storage performance. Therefore, it is of great importance to eliminate crystal water in PBAs for future commercial applications. Herein, a facile heat‐treatment method is reported in order to remove water from Fe‐based PBAs. Although the heat‐treated sample can be easily rehydrated in air, it still exhibits a stable cycling performance over 2000 times under controlled charge cut‐off voltage. In situ synchrotron high‐temperature powder X‐ray diffraction demonstrates that the as‐prepared sample is maintained at a new trigonal phase after dehydration. Moreover, the redox reaction of low‐spin Fe2+/Fe3+ is activated and the high‐temperature storage performance of as‐prepared sample is significantly improved after removal of water. [ABSTRACT FROM AUTHOR]

Iron-based Prussian blue analogs are promising low-cost and easily prepared cathode materials for sodium-ion batteries. Their materials quality and electrochemical performance are heavily reliant on the precipitation process. Here we report a controllable precipitation method to synthesize high-performance Prussian blue for sodium-ion storage. Characterization of the nucleation and evolution processes of the highly crystalline Prussian blue microcubes reveals a rhombohedral structure that exhibits high initial Coulombic efficiency, excellent rate performance, and cycling properties. The phase transitions in the as-obtained material are investigated by synchrotron in situ powder X-ray diffraction, which shows highly reversible structural transformations between rhombohedral, cubic, and tetragonal structures upon sodium-ion (de)intercalations. Moreover, the Prussian blue material from a large-scale synthesis process shows stable cycling performance in a pouch full cell over 1000 times. We believe that this work could pave the way for the real application of Prussian blue materials in sodium-ion batteries. Here the authors deploy a scalable synthesis route to prepare sodium-rich Na2−xFeFe(CN)6 cathode materials for sodium-ion battery. The highly reversible structural evolution during cycling between rhombohedral, cubic and tetragonal phases is the key to enable the good performance. [ABSTRACT FROM AUTHOR]

Low‐cost layered oxides free of Ni and Co are considered to be the most promising cathode materials for future sodium‐ion batteries. Biphasic Na0.78Cu0.27Zn0.06Mn0.67O2 obtained via superficial atomic‐scale P3 intergrowth with P2 phase induced by Zn doping, consisting of inexpensive transition metals, is a promising cathode for sodium‐ion batteries. The P3 phase as a covering layer in this composite shows not only in excellent electrochemical performance but also its tolerance to moisture. The results indicate that partial Zn substitutes can effectively control biphase formation for improving the structural/electrochemical stability as well as the ionic diffusion coefficient. Based on in situ synchrotron X‐ray diffraction coupled with electron‐energy‐loss spectroscopy, a possible Cu2+/3+ redox reaction mechanism has now been revealed. [ABSTRACT FROM AUTHOR]

A novel sodium titanate-carbon (Na 2 Ti 3 O 7 /C) composite has been successfully synthesized via a rheological phase method. The homogeneous-dispersed carbon not only sheathes the single Na 2 Ti 3 O 7 particle but also combines all individual Na 2 Ti 3 O 7 particles to a stable union, as characterized by X-ray diffraction, scanning electron microscopy (SEM), and high-resolution transmission microscopy (HRTEM). The uniformly distributed carbon forms a good network of electrically conductive paths among the Na 2 Ti 3 O 7 particles, which is closely interlinked with each other. So Na 2 Ti 3 O 7 active material can get electrons from all directions and be fully utilized for sodium ion insertion and extraction reactions, which can improve sodium storage properties with enhanced rate capability and super cycling performance. The Na 2 Ti 3 O 7 /C composite exhibits much better electrochemical performance than bare Na 2 Ti 3 O 7 , which displays a stable discharge capacity of 111.8 mAh g −1 at 1C after 100 cycles, while only 48.6 mAh g −1 for bare Na 2 Ti 3 O 7 at the same conditions. Furthermore, the composite shows relatively stable storage capacities during long term cycling even at 5C. The remarkably improved cycling performance and rate capability of Na 2 Ti 3 O 7 are attributed to the tight integration between carbon and Na 2 Ti 3 O 7 which may enhance the electronic conductivity, decrease the charge transfer resistance and improve the electrochemical stability during cycling, thus making a compelling case for its development as an advanced anode material for sodium ion batteries. [ABSTRACT FROM AUTHOR]

Cobalt (II) fluoride begins to enter into the horizons of people along with the research upsurge of metal fluorides. It is very significative and theoretically influential to make certain its electrochemical reaction mechanism. In this work, we discover a new and unrevealed reversible interfacial intercalation mechanism reacting below 1.2 V for cobalt (II) fluoride electrode material, which contributes a combined discharge capacity of about 400 mA h g −1 with the formation of SEI film at the initial discharge process. A highly reversible storage capacity of 120 mA h g −1 is observed when the cell is cycled over the voltage of 0.01-1.2 V at 0.2 C, and the low-potential voltage reaction process has a significant impact for the whole electrochemical process. Electrochemical analyses suggest that pure cobalt (II) fluoride shows better electrochemical performance when it is cycled at 3.2-0.01 V compared to the high range (1.0-4.5 V). So, we hold that cobalt (II) fluoride is more suitable to serve as anode material for lithium ion batteries. In addition, we also try to reveal the relevant performance and reaction mechanism, and realize the possibility of cobalt (II) fluoride as anode material for sodium ion batteries. [ABSTRACT FROM AUTHOR]