Tongbin Lan

Additive-free synthesis of unique TiO2 mesocrystals with enhanced lithium-ion intercalation properties

Unique nanorod-like mesocrystals constructed from ultrathin rutileTiO2 nanowires were successfully fabricated for the first time using a low-temperature additive-free synthetic route, and the mesocrystal formation requirements and mechanism in the absence of polymer additives were discussed. The ultrathin nanowires were highly crystalline and their diameters were found to be ca. 3–5 nm. The rutile TiO2 mesocrystals were formed through homoepitaxial aggregation of the ultrathin nanowiresvia face-to-face oriented attachment, accompanied and promoted by simultaneous phase transformation from the precursor hydrogen titanate to rutile TiO2. The rutile TiO2 mesocrystals thus synthesized were subjected to detailed structural characterization by means of scanning and transmission electron microscopy (SEM/TEM) including high-resolution TEM (HRTEM) and selected area electron diffraction (SAED), X-ray diffraction (XRD) and Raman spectroscopy. The rutile TiO2 mesocrystals were tested for lithium-ion intercalation and demonstrated large reversible charge–discharge capacity and excellent cyclic stability, which could be attributed to the intrinsic characteristics of the mesostructured TiO2 constructed from ultrathin nanowires offering large specific surface area for intercalation reaction and easy mass and charge transport, as well as sufficient void space accommodating volume change.

Hierarchically porous TiO2 microspheres as a high performance anode for lithium-ion batteries

Hierarchically porous rutile TiO2 microspheres composed of nanorods were fabricated by using a facile synthetic route. These materials were characterized by X-ray diffraction (XRD), N2 adsorption–desorption, and scanning and transmission electron microscopy (SEM and TEM). Based on a series of experimental results, a self-assembly process for the formation of the hierarchical microspheres was also proposed. Furthermore, the hierarchically porous rutile TiO2 microspheres were used as the negative electrode material in lithium-ion batteries (LIBs) and demonstrated a large reversible charge–discharge capacity of 160.4 mA h g−1 after 100 cycles at 1 C, which was much greater than commercial rutile TiO2 under the same conditions, indicating that these materials had excellent cycling stability and high rate performance.

In situ synthesis of GeO2/reduced graphene oxide composite on Ni foam substrate as a binder-free anode for high-capacity lithium-ion batteries

A GeO2/RGO composite was successfully fabricated via alternating deposition of graphene oxide (GO) and GeO2 on the surface of a Ni foam substrate using a facile dip-coating method cooperated with in situ hydrolysis of GeCl4. This material was directly used as a binder-free anode for LIBs and exhibited high reversible capacity (1716 mA h g−1 at 0.2 A g−1, 702 mA h g−1 at 16 A g−1), good cycling performance (1159 mA h g−1 at 1 A g−1 after 500 cycles) and excellent rate capability. In addition, a reversible capacity as high as 621 mA h g−1 can be retained when cycled to 500 cycles at a rate as high as 8 A g−1.

SPINEL Li2MTi3O8(M = Mg, Mg0.5Zn0.5) NANOWIRES WITH ENHANCED ELECTROCHEMICAL LITHIUM STORAGE

Spinel structural Li2MTi3O8(M = Mg, Mg0.5Zn0.5) nanowires have been successfully synthesized using titanate nanowires as a precursor and then have been used for the first time as anode materials in a rechargeable Li-ion battery. The cell composed of Li2MgTi3O8 nanowires exhibited a discharge capacity of 232 mAhg-1 at the second cycle, while only 159 mAhg-1 was obtained for the bulk prepared by a solid state reaction. The results of electrochemical impedance spectra indicate that spinel structural Li2MTi3O8(M = Mg, Mg0.5Zn0.5) nanowires can significantly reduce the charge transfer impedance, leading to enhanced capability of electrochemical lithium storage.

ULTRATHIN Li4Ti5O12 NANOSHEETS AS A HIGH PERFORMANCE ANODE FOR Li-ION BATTERY

Ultrathin Li4Ti5O12 (LTO) nanosheets were successfully synthesized for the first time using the ultrathin titanate nanowires as a precursor. The synthesized Li4Ti5O12 nanosheets have a large surface area of 159.2m2g-1 and their thickness was found to be ca. 5–7 nm. These nanosheets were highly crystalline and used as anode materials in rechargeable lithium-ion batteries. A stable capacity of 150 mAhg-1 for LTO nanosheets can be retained after 70 cycles at a current density of 1 Ag-1 in the voltage window of 2.5–1.0 V. It is notable that a large capacity of 267.5 mAhg-1 was obtained at the second discharge and 166 mAhg-1 can be retained after 70 cycles at 1 Ag-1 in the voltage range of 2.5–0.02 V. These results indicate that the anode materials made of spinel LTO nanosheets displayed a large reversible capacity at a high charge/discharge rate.

Rutile TiO2 Mesocrystals/Reduced Graphene Oxide with High-Rate and Long-Term Performance for Lithium-Ion Batteries

An in situ hydrothermal route is developed for fabricating rutile TiO2 mesocrystals/reduced graphene oxide nanosheets (TGR) hybrids in the presence of dodecylbenzenesulphonic acid (ADBS). These rutile TiO2 mesocrystals with a Wulff shape are composed of ultra-tiny rod-like subunits with the same oriented direction and closely wrapped by the nanosheets of reduced graphene oxide (RGO). It is found that ADBS played a key role for the formation of mesocrystals during the self-assembly process, which pillared the graphene oxide (GO) nanosheets and involved the aggregation of the mesocrystal subunits. Furthermore, the TGR hybrids are used as an anode material and exhibited a large capacity over 150 mA h g−1 at 20 C after 1000 cycles, and high rate capability up to 40 C. These high performance characteristics may be due to the intrinsic characteristics of rutile TiO2 mesocrystals constructed from ultra-tiny subunits and hybridized with super conductive RGO nanosheets.

Ultrathin TiO2-B nanowires with enhanced electrochemical performance for Li-ion batteries

A facile one-step hydrothermal route was designed for preparing ultrathin TiO2-B nanowires, which were then hybridized with RGO to form a TiO2-B/RGO hybrid via an in situ approach, and both of them have a large BET surface area (231.6 m2 g−1 for TiO2-B nanowires and 256.1 m2 g−1 for the TiO2-B/RGO hybrid). It was found that the synthesized ultrathin nanowires are perpendicular to the [010] direction which is the most open channel in the TiO2-B crystal structure, demonstrating more Li-ion insertion/extraction hosts exposed to the electrolyte. Thus, the cell made of TiO2-B ultrathin nanowires exhibited large reversible lithium-ion charge–discharge capacity, excellent cycling stability and high-rate capability. When combined with RGO, the formed TiO2-B/RGO hybrid exhibited further improved Li storage performance. For instance, a capacity of 205.3 mA h g−1 was obtained at the fourth cycle and then faded slightly to 189.4 mA h g−1 after 300 cycles, demonstrating a surprising low average capacity fading of ca. 0.026% per cycle from 4th to 300th cycles.

Hierarchically porous anatase TiO2 microspheres composed of tiny octahedra with enhanced electrochemical properties in lithium-ion batteries

In the present work, a one-step synthetic route is developed for fabricating hierarchical anatase TiO2 microspheres for the first time. These microspheres are composed of ultrathin rod-like structures in the radial direction, in which ultrathin rods consisted of tiny octahedra via a growth model of oriented attachment. Based on XRD and electron microscopic analyses, a mechanism for the growth of the microspheres is proposed. This material displays a large capacity of 157.3 mA h g−1 at 1 C after 200 cycles and also exhibits high rate performance and excellent cycling stability. These high performance characteristics may be due to the intrinsic characteristics of the hierarchical porous anatase TiO2 microspheres, in which the porous structure can permit facile diffusion of the electrolyte. They can also enhance the contact between the electrode surface and the electrolyte, while the ultrathin rods can shorten the transport distance of Li-ions and electrons during electrochemical cycling. At the same, the porous microsphere can also accommodate volume changes in the charge–discharge process.

One-step hydrothermal synthesis of Nb doped brookite TiO2 nanosheets with enhanced lithium-ion intercalation properties

In the present work, Nb doped brookite TiO2 nanosheets were successfully synthesized via a one-step hydrothermal route. The synthesized samples were characterized by X-ray diffraction (XRD), Raman spectroscopy, scanning and transmission electron microscopy (SEM/TEM) and X-ray photoelectron spectroscopy (XPS). According to the experimental results, a possible mechanism for the formation of Nb doped brookite TiO2 nanosheets was proposed. Furthermore, Nb doped brookite TiO2 nanosheets were used as an anode material for the Li-ion intercalation reaction and it was found that their electronic/ionic conductivity was improved. At the same time, the cell made of Nb doped brookite TiO2 nanosheets also exhibited enhanced lithium-ion intercalation properties. For instance, this material displayed reversible capacities of 119.7 and 104.6 mA h g−1 at 5 C after 100 and 500 cycles, respectively.

Nb-Doped Rutile TiO2 Mesocrystals with Enhanced Lithium Storage Properties for Lithium Ion Battery

A homogeneous Nb-doped rutile TiO2 mesocrystal material was synthesized successfully through a facile hydrothermal route. The incorporation of Nb5+ not only promotes the crystallization of the building subunits of the rutile TiO2 mesocrystal, but also improves the electrochemical performance at higher current rates. A capacity of 96.3 mAh g-1 at a current density as high as 40 C and an excellent long-term cycling stability with a capacity loss of approximately 0.006 % per cycle at 5 C could be achieved when an appropriate amount of Nb5+ was doped into rutile TiO2 mesocrystal. The reasons for the improvement of rate capability may be attributed to the enhancement of electronic conductivity, Li-ion diffusion kinetics, and the surface storage property for the Nb-doped rutile TiO2 mesocrystal.