Yifang Zhang

Nitrogen-Doped Yolk–Shell-Structured CoSe/C Dodecahedra for High-Performance Sodium Ion Batteries

In this work, nitrogen-doped, yolk-shell-structured CoSe/C mesoporous dodecahedra are successfully prepared by using cobalt-based metal-organic frameworks (ZIF-67) as sacrificial templates. The CoSe nanoparticles are in situ produced by reacting the cobalt species in the metal-organic frameworks with selenium (Se) powder, and the organic species are simultaneously converted into nitrogen-doped carbon material in an inert atmosphere at temperatures between 700 and 900 °C for 4 h. For the composite synthesized at 800 °C, the carbon framework has a relatively higher extent of graphitization, with high nitrogen content (17.65%). Furthermore, the CoSe nanoparticles, with a size of around 15 nm, are coherently confined in the mesoporous carbon framework. When evaluated as novel anode materials for sodium ion batteries, the CoSe/C composites exhibit high capacity and superior rate capability. The composite electrode delivers the specific capacities of 597.2 and 361.9 mA h g-1 at 0.2 and 16 A g-1, respectively.

Dodecahedron-Shaped Porous Vanadium Oxide and Carbon Composite for High-Rate Lithium Ion Batteries

Carbon-based nanocomposites have been extensively studied in energy storage and conversion systems because of their superior electrochemical performance. However, the majority of metal oxides are grown on the surface of carbonaceous material. Herein, we report a different strategy of constructing V2O5 within the metal organic framework derived carbonaceous dodecahedrons. Vanadium precursor is absorbed into the porous dodecahedron-shaped carbon framework first and then in situ converted into V2O5 within the carbonaceous framework in the annealing process in air. As cathode materials for lithium ion batteries, the porous V2O5@C composites exhibit enhanced electrochemical performance, due to the synergistic effect of V2O5 and carbon composite.

Rational design of multi-shelled CoO/Co9S8 hollow microspheres for high-performance hybrid supercapacitors

Hollow structures with complex interiors are promising to endow electroactive materials with fascinating physical properties, such as low mass density, large surface area and high permeability. Meanwhile, the construction of hollow structures with binary chemical compositions could further enhance the resultant electrochemical properties. Herein, we reported a designed synthesis of multi-shelled CoO/Co9S8 hollow microspheres by calcining a hollow microsphere precursor with S powder in argon gas (Ar). The inherent characteristic of cobalt(II) mono-oxide can benefit the electrochemical activity, while the cobalt sulfide component could improve the electrical conductivity of this cobalt-based composite material. These multi-shelled hollow structures are proved to possess a porous texture with a relatively large specific surface area (SSA = 43.1 m2 g−1), which could provide more active sites for electrochemical reactions. As a result, the as-prepared multi-shelled CoO/Co9S8 hollow microspheres exhibit an enhanced specific capacitance and excellent rate performance when evaluated as electrode materials for hybrid supercapacitors.

Nanorod-Nanoflake Interconnected LiMnPO4·Li3V2(PO4)3/C Composite for High-Rate and Long-Life Lithium-Ion Batteries

Olivine-type structured LiMnPO4 has been extensively studied as a high-energy density cathode material for lithium-ion batteries. However, preparation of high-performance LiMnPO4 is still a large obstacle due to its intrinsically sluggish electrochemical kinetics. Recently, making the composites from both active components has been proven to be a good proposal to improve the electrochemical properties of cathode materials. The composite materials can combine the advantages of each phase and improve the comprehensive properties. Herein, a LiMnPO4·Li3V2(PO4)3/C composite with interconnected nanorods and nanoflakes has been synthesized via a one-pot, solid-state reaction in molten hydrocarbon, where the oleic acid functions as a surfactant. With a highly uniform hybrid architecture, conductive carbon coating, and mutual cross-doping, the LiMnPO4·Li3V2(PO4)3/C composite manifests high capacity, good rate capability, and excellent cyclic stability in lithium-ion batteries. The composite electrodes deliver a high reversible capacity of 101.3 mAh g-1 at the rate up to 16 C. After 4000 long-term cycles, the electrodes can still retain 79.39% and 72.74% of its maximum specific discharge capacities at the rates of 4C and 8C, respectively. The results demonstrate that the nanorod-nanoflake interconnected LiMnPO4·Li3V2(PO4)3/C composite is a promising cathode material for high-performance lithium ion batteries.

Multi-shelled a-Fe2O3 for high rate supercapacitors

Hollow structured metal oxides are extensively studied in energy storage and conversion systems. In this work, we report the fabrication of multi-shelled Fe2O3 microspheres with nanospindles assembly on its exterior shell. The β-FeOOH precursor nanospindles were firstly grown on the surface of carbon microspheres to produce β-FeOOH@carbon composites, which were later converted into multi-shelled Fe2O3 microspheres by calcination in air. As electrode material for supercapacitors, the multi-shelled Fe2O3 microspheres exhibit high capacity and good rate capability. The electrode delivers the specific capacitances of 630 and 510 F g−1 at the current densities of 1 and 5 A g−1, respectively.Abstract中空结构的金属氧化物在能源储存和转化系统中已被广泛研究. 本文报道了纳米纺锤自组装的多层中空α-Fe2O3微米球. β-FeOOH前 驱体纳米锤首先在炭球表面沉积生长得到β-FeOOH@炭球复合材料, 然后在空气中烧结移除模板, 转变为多层中空α-Fe2O3微米球. 该材料 用作超级电容器的电极材料具有高容量和良好的倍率性能. 该电极在1 和5 A g−1的条件下, 可以释放630和510 F g−1的比放电容量.

Self-templating synthesis of double-wall shelled vanadium oxide hollow microspheres for high-performance lithium ion batteries

Hollow structured vanadium pentoxide microspheres with multiple double-walled shells were fabricated from solid vanadium oxide precursors through ascorbic acid-assisted solvothermal growth. The interiors of the vanadium oxide microspheres and number of the novel double-walled shells can be readily controlled by adjusting the combustion of solid vanadium oxide precursors. The formation mechanism of the unique structures is elucidated and attributed to the diffusion controlled oxidation process in air. The obtained V2O5 hollow spheres with triple double-walled shells show improved electrochemical performance compared to single-shelled V2O5 hollow microspheres as electrode materials for lithium-ion batteries.

Heterogeneous NiS/NiO multi-shelled hollow microspheres with enhanced electrochemical performances for hybrid-type asymmetric supercapacitors

Heterogeneous structures with binary chemical compositions could achieve unique chemical properties by modification of the components and interface engineering. Meanwhile, hollow microspheres with complex interiors have been extensively studied in energy storage and conversion systems due to their possibility of adjusting the electrochemical performances. In this work, we report the reliable preparation of heterogeneous (NiO)x(NiS)1−x (0 ≤ x ≤ 1) multi-shelled hollow microspheres derived from carbon sphere@nickel precursor templates. The structural evolution of the multiple shells is carefully studied. Moreover, the effect of sulfurization extent of the (NiO)x(NiS)1−x compounds on the electrochemical performance is also explored. As electrode materials for supercapacitors, the heterogeneous (NiO)0.1(NiS)0.9 multi-shelled hollow microspheres exhibit the best electrochemical performances among a series of nickel oxide/sulfide compounds. The (NiO)0.1(NiS)0.9 sample can deliver a high specific capacitance of 1063 F g−1 at 2 A g−1. Even at a high current density of 50 A g−1, the electrode can still retain a high specific capacitance of 486 F g−1 after 10 000 cycles. Furthermore, a (NiO)0.1(NiS)0.9‖active carbon asymmetric supercapacitor (ASC) exhibits a specific capacitance of 58.5 F g−1 at 2 A g−1 in 2 M KOH solution. The superior electrochemical performances can be attributed to the careful composition regulation and the stable multi-shelled structure.

S-doped porous carbon confined SnS nanospheres with enhanced electrochemical performance for sodium-ion batteries

Stannous based anode materials have been extensively studied for sodium ion batteries due to their high theoretical capacities. However, the large volume changes upon repeated cycling always cause their structural pulverization and capacity fading. Herein, we report the fabrication of S-doped porous hollow carbon confined SnS nanospheres particles and their good electrochemical performance as an anode material for sodium ion batteries. Unlike previous reports, stanniferous solid carbonaceous nanospheres are novelly prepared by a hydrothermal process, and they can be converted into yolk–shell structured Sn@C nanospheres after thermal annealing in a H2/Ar atmosphere. The subsequent sulfidation process can produce S-doped carbon confined SnS hollow nanospheres with high porosity. The obtained SnS@SPC nanospheres possess a large Brunauer–Emmett–Teller (BET) surface area of 135.8 m2 g−1. As an anode material for sodium ion batteries, the obtained yolk–shell SnS@SPC exhibits a high reversible capacity of 512 mA h g−1 at 100 mA g−1 and good cycling stability. The void space between the carbon shell and the SnS yolk can accommodate the volume changes during the charge/discharge process. Meanwhile, the porous carbon shell can serve as a conductive skeleton and a reservoir for the electrolyte.

Effect of nano-segregation phases on electrochemical property of high active Al alloy anode

The effect of nano-segregation phases formed during rolling process on the electrochemical property of Al-Mg-Sn-Bi-Ga-In alloy anode in alkaline solution (80?C, Na2SnO3 + 5mol/L NaOH)was analyzed according to the chronopotentiometry (E-T curves), hydrogen collection tests and modern microstructure analysis. The results show that when controlling the rolling temperature and pass deformation at 370?C and 40% respectively, the Al alloy anode undergoes the dynamic recrystallization, which benefits to the uniform distribution of nano-segregation phases and improvement of electrochemical property of Al alloy anode. The optimum Al alloy anode has the more negative electrode potential of about -1.48V (vs.Hg/HgO) and the lower hydrogen evolution rate of 0.1889mL/ (min?cm2).