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A rationally designed strategy was employed for the preparation of VN@C hollow structures using ZIF-8 polyhedra as sacrificial templates. Meanwhile, ZIF-8 also plays the role of both nitrogen and carbon sources during the synthetic process. Benefiting from the unique loose hollow structure with high surface area of VN@C, as well as the support of carbon, the product displays an outstanding lithium storage performance. The discharge capacity can reach 495.3 mA h g−1 at 1 A g−1 after 500 cycles. [ABSTRACT FROM AUTHOR]

Zeolitic Imidazolate Framework 67 (ZIF-67) and its derivates have attracted extensive interest for lithium-ion batteries (LIBs). Here, Cerium-doped cobalt phosphide@nitrogen-doped carbon (Ce-doped CoP@NC) with hollow polyhedron structure materials were successfully synthesized via ionic-exchange with Co and Ce ions using the ZIF-67 as a template followed with a facile low-temperature phosphorization treatment. Benefitting from the well-designed hollow polyhedron, steady carbon network, and Ce-doping structural merits, the as-synthesized Ce-doped CoP@NC electrode demonstrated superior performance as the anode in LIBs: a superior cyclability (400 mA h g−1 after 500 cycles) and outstanding rate-capability (590 mA h g−1, reverted to 100 mA g−1). These features not only produced more lithium-active sites for LIBs anode and a shorter Li-ion diffusion pathway to expedite the charge transfer, but also the better tolerance against volume variation of CoP during the repeated lithiation/delithiation process and greater electronic conductivity properties. These results provide a methodology for the design of well-organized ZIFs and rare earth element-doped transition metal phosphate with a hollow polyhedron structure. [ABSTRACT FROM AUTHOR]

• FeS 2 @CF-NS were synthesized by electrostatic spinning with subsequent calcination. • The carbon backbone buffers the volume expansion. • The doped N, S and defect sites facilitate fast and stable Na+/e− exchange. • The FeS 2 nanoparticles and FeS 2 nanoflakes shorten the Na+ diffusion distance. • Capacitive Na+ storage mechanism contributes to the rate performance. FeS 2 is a promising electrode material for sodium ion batteries (SIBs) because of its high theoretical capacity, rich reserves, and eco-friendly nature. In this study, N and S doped (N, S-co-doped) carbon fibers (CFs) encapsulated FeS 2 nanoparticles (5–12 nm) and adherent FeS 2 nanoflakes (denoted as FeS 2 @CF-NS), were synthesized by electrostatic spinning and subsequent thermal treatment. In this structure, the FeS 2 nanoparticles and the FeS 2 nanoflakes shorten the Na+ diffusion distance; the N, S co-doping and defect-rich sites in the carbon fibers accelerate the Na+/e− transmission and buffer the volume expansion during the Na-FeS 2 conversion reaction. These merits synergistically contribute to the notable sodium storage performance of FeS 2 @CF-NS. As anode for Na-ion half batteries, the FeS 2 @CF-NS exhibits high capacity (637.1 mAh/g at 1 A/g after 400 cycles) and excellent rate capacity (431.1 mAh/g at 5 A/g). Kinetic analysis confirms that this composite structure stimulates the pseudocapacitance Na+ storage mechanism and enables a capacitive contribution ratio as high as 92.7% with respect to the total capacity. In combination with Na 3 V 2 (PO 4) 3 -C cathode, the FeS 2 @CF-NS also achieves remarkably high specific capacity (561.1 mAh/g at 1 A/g after 500 cycles) and stable cyclability (338.6 mAh/g at 5 A/g after 5000 cycles) in full cells. [ABSTRACT FROM AUTHOR]

Bi 3 Se 4 is a promising anode material for energy storage owing to its merits of layer structure and high specific capacity, however, it usually faces rapid capacity decay and poor rate performances due to the large volume expansion during ion insertion and extraction processes. Herein, Bi 3 Se 4 @N-doped carbon spheres (Bi 3 Se 4 @NC) were fabricated for the first time as anode material for both lithium ion batteries (LIBs) and potassium ion batteries (PIBs). The obtained Bi 3 Se 4 @NC exhibited notable good rate capability (614.4 mAh g−1 at 0.1 A g−1 and 144.5 mAh g−1 even at 20 A g−1) and excellent cycle stability as anode for LIBs. It also displayed preeminent specific capacity of 359.3 mAh g−1 (at 50 mA g−1) and excellent rate capability (achieve capacity as high as 222.4 mAh g−1 at 300 mAh g−1) when used as anode for PIBs. The contribution of the pseudocapacitance capacity and the low resistance of the electrode material contribute to the origin of excellent rate capability. In addition, the potassium ion storage mechanism of Bi 3 Se 4 @NC has been further examined by ex-situ XRD patterns and HRTEM analyses. The above results reveal that the Bi 3 Se 4 @NC composite is a competitive anode material for LIBs and PIBs. [Display omitted] • Uniform Bi 3 Se 4 @NC spheres were synthesized for the first time by MOF derivative method. • Bi 3 Se 4 @NC spheres possess high structural stability and electronic conductivity. • Bi 3 Se 4 @NC shows excellent cycle stability and rate capability for Li+ and K+ storage. • The electrochemical reaction mechanism was presented by XRD patterns and HRTEM images. [ABSTRACT FROM AUTHOR]