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Summary: Polyaniline‐derived N‐doped carbon‐composited Na3V2(PO4)3 (NVP@NC) are synthesized by a rheological phase reaction followed by calcination. The NVP@NC composite displays improved cycling and rate properties. Its discharge capacity remains 118.7 mAh g−1 at the 400th cycle at 0.3 C. It also obtains invertible capacities of 93.7 and 91.1 mAh g−1 at 5 and 10 C after 1000 cycles, with capacity retention rates of 92.7% and 98.4%, respectively. These enhanced results due to the N‐doped carbon layer (NC), which restrains the expansion and deformation of the crystal structure, reduce the transport length of sodium ion and electrons and improves the electroconductibility of NVP. [ABSTRACT FROM AUTHOR]

Summary: Graphene‐wrapped poly 2,5‐dihydroxy‐1,4‐benzoquinone‐3,6‐methylene (PDBM) nanocomposites with three‐dimensional nanoflower structures have been successfully prepared through the ultrasonic exfoliation and reassembly process in methanol. Compact distribution of graphene into the nanocomposite has established a three‐dimensional conductive network, which contributes to improved properties on discharge capacity and cycle performance. Composite with 20 wt% graphene was proved the best ratio when used in sodium‐ion batteries. Its initial discharge capacity can achieve 210 at 30 mA g−1. After 100 cycles, the capacity is stable at 121 mAh g−1. The composite featuring highly conductive channels and multidimensional electron transport pathway is synthesized by an easy ultrasonic way, which may be applied in large scales for sodium‐ion batteries. [ABSTRACT FROM AUTHOR]

[Display omitted] • This work summarizes the application of vanadium oxides as aqueous ZIBs cathodes. • Electrochemical properties and energy storage behavior of different types of vanadium oxide cathodes. • Current challenges and expected development foregrounds of vanadium oxides cathodes in aqueous ZIBs are proposed. The rapid development of science and technology, as well as the trend toward intelligence, has resulted in a surge in the demand for excellent energy storage devices for smart devices. At present, the most widely used lithium ion batteries have limited further development because of their high cost and various disadvantages of electrolytes (flammable and toxic). In spite of the low costs and safety of aqueous zinc-ion batteries, the high radius of the zinc ions and strong electrostatic interactions make cathode materials without excellent performance difficult to find. Various oxidation states, structural diversity, excellent multiplicity performance and high capacity have attracted researchers to vanadium-based oxides in recent years. However, vanadium-based oxides have disadvantages such as poor structural stability and low electrical conductivity, so this paper summarizes the progress of research on vanadium oxide cathode materials such as V 2 O 5 , VO 2 , V 2 O 3 , etc., and provides an outlook on future development directions. [ABSTRACT FROM AUTHOR]

The impacts of Cu substitution upon the cycling stability of Na x MO 2 (M = Fe, Mn) cathodes are systematically studied. Evidenced by CuO segregation and XPS analysis, the average valence of Mn can hardly reach +4, possibly owing to the production of Mn(II). It is proposed that, Cu substitution can efficiently enhance the cycling stability by reducing the content of Mn(III) and suppressing the electrochemical activities of Mn4+/3+ redox couple. • Cycling stability of Na x MO 2 (M = Cu, Fe, Mn) cathodes are systematically studied. • CuO segregation is evidenced to be associated with the limited valent state of Mn. • Adding Cu2+ actually lower Mn valence by decreasing Mn(III) and generating Mn(II). • Cu2+-substitution may enhance the cycling stability mainly by suppressing Mn(III). Adding Cu2+ has substantially boosted the practical potentiality of Fe/Mn-based layered cathodes for sodium ion batteries (SIBs) owing to the enhanced stabilities, which were previously ascribed to the raised valence of Mn. Herein, the roles of Cu2+ are verified by investigating Cu2+-substituted materials with the stoichiometry of Na 0.5+x Cu x Fe 0.5-x Mn(IV) 0.5 O 2. Surprisingly, it is found that Mn valence can hardly reach the expected value (IV) even by adjusting Cu2+ content. For the first time, the separation of CuO, which has been previously detected but rarely explained, is ascribed to the restrained chemical states of Mn. Detailed analyses show that, Mn(II) is generated while Mn(III) is decreased in pace of Cu2+ substitution, actually lowering down the oxidation states of Mn. Moreover, Mn4+/3+ redox can be efficiently restricted by importing Cu2+. Albeit the loss of capacity, the cycling stability is greatly enhanced, achieving a high capacity retention of 92.3% after 200 cycles within 4.2–2.5 V. Therefore, the suppression of Jahn-Teller Mn(III) should be intrinsically responsible for the superior cycling stability after Cu2+ substitution. These findings may present a new sight to probe the roles of Cu in layered Na x MO 2 system for the design of advanced cathodes for SIBs. [ABSTRACT FROM AUTHOR]