Shuming Zhang

Template-free formation of various V2O5 hierarchical structures as cathode materials for lithium-ion batteries

Various V2O5 hierarchical structures were successfully synthesized via a template-free method by annealing diverse morphological VO2 sub-microspheres which can be facilely tailored by adjusting the solvothermal reaction duration. The VO2 sub-microspheres undergo a solid → yolk–shell → hollow → yolk–shell structure process with increasing time, which is believed to result from an unusual Ostwald-ripening process. After the annealing process, multi-structural VO2 sub-microspheres changed into hierarchical structures including fist-type structures consisting of nanorods, yolk–shell and hollow sub-microspheres composed of nanorods and a yolk–shell construction made up of nanoplates. As the cathode materials for lithium-ion batteries, among them, yolk–shell sub-microspheres comprised of nanoplates exhibited high reversible capacity, excellent cycling stability at high currents and good rate capacities. Without doping and compositing, the electrode delivered reversible capacities of 119.2 and 87.3 mA h g−1 at high current densities of 2400 and 3600 mA g−1, respectively, as well as a capacity retention of 78.31% after 80 cycles at 1200 mA g−1. The excellent electrochemical performance could be attributed to the purity of the phase and synergistic effect between the yolk–shell structure and hierarchical structure of the sub-microspheres, which make the yolk–shell V2O5 hierarchical structure a promising candidate for the cathode material for lithium-ion batteries.

Synthesis of novel ammonium vanadium bronze (NH4)0.6V2O5 and its application in Li-ion battery

A novel ammonium vanadium bronze (NH4)0.6V2O5 has been successfully synthesized via a simple hydrothermal treatment and its electrochemical performance is investigated. The as-synthesized material was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared (FTIR) spectrum, Raman spectrum, X-ray photoelectron spectroscopy (XPS), element analysis (EA), cyclic voltammetry (CV) and galvanostatic charge/discharge cycling test. The results revealed that a pure novel phase (NH4)0.6V2O5 was obtained with square brick-like morphology. Preparation conditions such as amount of reducing agent, temperature and reaction time have been investigated to obtain the pure phase. (NH4)0.6V2O5 square bricks are tested as a cathode material for lithium-ion batteries. It has an excellent lithium ion insertion/extraction ability with a high specific discharge capacity of 280.2 mA h g−1 and 244.3 mA h g−1 during 1.0–3.8 V at the current densities of 10 mA g−1 and 20 mA g−1, respectively.

Long straczekite δ-Ca0.24V2O5·H2O nanorods and its derived β-Ca0.24V2O5 nanorods as novel host materials for lithium storage with excellent cycling stability

Nanorods of δ-Ca0.24 V2 O5 ⋅H2 O, a straczekite group mineral with an open double-layered structure, have been successfully fabricated by a facile hydrothermal method and can be transformed into the tunnel β geometry (β-Ca0.24 V2 O5 ) through a vacuum annealing treatment. The generated β-Ca0.24 V2 O5 still preserves the nanorod construction of δ-Ca0.24 V2 O5 ⋅H2 O without substantial sintering and degradation of the nanostructure. As cathode materials, both calcium vanadium bronzes exhibit high reversible capacity, good rate capability, as well as superior cyclability. Compared with the hydrated vanadium bronze, the β-Ca0.24 V2 O5 nanorods show better cycling performance (81.68 and 97.93 % capacity retention after 200 cycles at 100 and 400 mA g-1 , respectively) and excellent long-term cyclic stability with an average decay of 0.035 % per cycle over 500 cycles at 500 mA g-1 . Note that the double-layered δ-Ca0.24 V2 O5 ⋅H2 O electrode irreversibly converts into β-Cax V2 O5 phase during the initial Li+ insertion/extraction process, while in contrast, the β-phase calcium vanadium bronze electrode shows excellent structural stability during cycling. The excellent electrochemical performance demonstrates that the two calcium vanadium bronzes are potential cathode candidates for rechargeable lithium-ion batteries.

Development of a macroporous-spherical polyanionic compound (TiO)2P2O7 as a novel anode material for sodium ion batteries

The phosphate-based polyanionic compound with the formula (TiO)2P2O7 was synthesized by a simple precipitation method with a soft template as a novel anode material for sodium ion batteries for the first time. The polyanionic compound (TiO)2P2O7 with a macroporous-spherical structure exhibited an initial specific capacity of 293.0 mA h g−1 at 0.1C in the voltage range of 0.01–2.5 V vs. Na+/Na. The reversible capacity remained at 200.9 mA h g−1 after 100 cycles. It is attractive that the macroporous-spherical (TiO)2P2O7 delivered an extremely stable cycling performance at a high charge rate of 2.5C. A high capacity retention of 85.1% was obtained after 1100 cycles with an initial specific capacity of 112.7 mA h g−1. The ex situ XRD and XPS analysis indicates that the excellent cycle stability and high rate capability are attributed to the intrinsic 3D framework structure and well-connected macroporous-spherical morphology of (TiO)2P2O7. The macroporous-spherical (TiO)2P2O7 is a promising anode for sodium ion batteries.