Yan-Mei Jiang

Hierarchical Li4Ti5O12/TiO2 composite tubes with regular structural imperfection for lithium ion storage.

Hierarchical Li4Ti5O12/TiO2 tubes composed of ultrathin nanoflakes have been successfully fabricated via the calcination of the hydrothermal product of a porous amorphous TiO2 precursor and lithium hydroxide monohydrate. The hierarchical tubes are characterized by powder X-ray diffraction, nitrogen adsorption/desorption, scanning electron microscopy and transmission electron microscopy techniques. These nanoflakes exhibit a quite complex submicroscopic structure with regular structural imperfection, including a huge number of grain boundaries and dislocations. The lithium ion storage property of these tubes is evaluated by galvanostatic discharge/charge experiment. The product shows initial discharge capacities of 420, 225, and 160 mAh g−1 at 0.01, 0.1, and 1.0 A g−1, respectively. After 100 cycles, the discharge capacity is 139 mAh g−1 at 1.0 A g−1 with a capacity retention of 87%, demonstrating good high-rate performance and good cycleability. The high electrochemical performance is attributed to unique structure and morphology of the tubes. The regular structural imperfection existed in the nanoflakes also benefit to lithium ion storage property of these tubes. The hierarchical Li4Ti5O12/TiO2 tubes are a promising anode material for lithium-ion batteries with high power and energy densities.

Lithiation mechanism of hierarchical porous MoO2 nanotubes fabricated through one-step carbothermal reduction

A one-step carbothermal reduction method has been developed for the preparation of hierarchical porous materials. In this method, CMK-3 acts both as a template casting the hierarchical porous structure and as a reducing agent for the carbothermal reaction. Hierarchical MoO2 nanotubes prepared through this method exhibit high charge/discharge capacities and rate capabilities when used as an anode material for lithium ion batteries. Cycled at current densities of 0.1 and 1.0 A g−1, the material delivers discharge capacities of 720 and 530 mA h g−1 after 70 cycles, respectively. The Li-ion insertion and extraction processes of MoO2 nanotubes have been investigated by using an in situ X-ray diffraction technique for the first time to elucidate the Li-ion storage mechanism for the MoO2 material. We demonstrate that the discharge capacity increase of MoO2 during the first 30 cycles is attributed to the lithiation transformation of MoO2.

Uniform hierarchical MoO2/carbon spheres with high cycling performance for lithium ion batteries

Uniform hierarchical MoO2/C spheres have been prepared through calcination of a MoO3/resin precursor generated via a simple hydrothermal method in the presence of resorcinol, formaldehyde and (NH4)6Mo7O24·4H2O. The carbon spheres formed in situ by the carbonization of resorcinol–formaldehyde resin in a N2 atmosphere reduce MoO3 into MoO2 nanoparticles. The MoO2/C spheres have been characterized by XRD, SEM, HR-TEM and TGA. Used as an anode material, these spheres exhibit not only good rate capability but also high cycling performance. These hierarchical MoO2/C spheres are a promising anode material for high performance lithium ion batteries.

Hierarchical porous carbon spheres as an anode material for lithium ion batteries

Hierarchical porous carbon spheres are prepared by the carbonization of a D201 anion-exchange resin. These carbon spheres are characterized by X-ray diffraction, Raman spectroscopy, nitrogen adsorption–desorption and electron microscopy. The lithium ion storage capacity of these carbon spheres is evaluated by galvanostatic measurements. The initial discharge–charge capacities of the material are 1213 and 798 mA h g−1 at a current density of 0.1 A g−1, respectively. A discharge capacity of 506 mA h g−1 is still retained when charge–discharged at 1.0 A g−1 for 50 cycles. The large reversible capacity, high rate performance and good cycleability are attributed to the unique hierarchical porous structure featured by large surface area, readily accessed porous channels and the highly graphitized carbon shells. The carbonization of a cheap anion-exchange resin can be easily scaled-up, making the hierarchical porous carbon spheres a promising low-cost anode material for high performance lithium ion batteries.

Distinct effect of hierarchical structure on performance of anatase as an anode material for lithium-ion batteries

Hierarchically structured titania materials composed of anatase nanoparticles have been prepared via a template-free light-driven fabrication route by employing titanium glycolate (TG) as a precursor. These materials are characterized by electron microscopy, X-ray powder diffraction, and nitrogen adsorption–desorption measurements. The lithium storage properties of the materials are evaluated by galvanostatic charge–discharge, cyclic voltammetry, and electrochemical impedance techniques. At a current density of 0.1 A g−1, the initial lithium insertion/extraction capacities of the hierarchically structured titania reach 262 and 221 mA h g−1, respectively. A discharge capacity of approximately 149 mA h g−1 is retained after being cycled at 1.0 A g−1 for 100 cycles, demonstrating the superior rate performance and high cycleability of the materials. The structural hierarchy featured by the well-defined morphology, high specific surface area, narrow pore size distribution, and high crystallinity has a significant influence on the electrochemical properties of the titania materials. The introduction of a hierarchical structure is envisaged as an efficient approach for the development of novel electrode materials for high performance lithium-ion batteries.