Xiaoping Tan

Metal–organic framework-templated two-dimensional hybrid bimetallic metal oxides with enhanced lithium/sodium storage capability

Two-dimensional (2D) porous hybrid bimetallic transition metal oxide (TMO) nanosheets demonstrated promising applications in the energy field due to their large surface areas, porous structure, and synergistic effects. However, the synthesis of these materials is still a big challenge. In this study, we rationally designed a facile strategy to prepare 2D porous hybrid bimetallic TMO (Co3O4/ZnO) nanosheets with novel structural and electrochemical synergistic effects. Derived from bimetallic MOF nanosheets, the porous hybrid nanosheets possess high surface areas and large pore volume. In particular, they are rich in oxygen vacancies, which provide more active sites for electrochemical reaction. Moreover, the harmonious multi-step conversion reaction between Co3O4 and ZnO was helpful for volume buffering, leading to an outstanding cyclic stability. With remarkable structural features and harmonious electrochemical behaviors, the Co3O4/ZnO hybrids exhibit excellent electrochemical performances as anodes for both lithium-ion batteries (LIBs) and sodium-ion batteries (SIBs). This study also introduces a new strategy to prepare 2D porous hybrid bimetallic TMO nanosheets, which can find wide applications in energy storage, catalysis, sensors, and information storage devices.

Hydrothermal synthesis of Ag/β-AgVO3 nanobelts with enhanced performance as a cathode material for lithium batteries

An efficient and scalable strategy has been developed for the synthesis of Ag nanoparticles anchored on β-AgVO3 nanobelts via a template-free hydrothermal reaction. The Ag/β-AgVO3 nanobelts demonstrate enhanced lithium intercalation capacity, rate capability and cyclic stability.

Facile synthesis of nanosheet-structured V2O5 with enhanced electrochemical performance for high energy lithium-ion batteries

Nanosheet-structured vanadium pentoxide (V2O5) has been fabricated by a sol-gel method. As revealed by the TEM, the as-synthesized V2O5 crystallites are composed of layer-by-layer stacked nanosheets. As a cathode material for lithium batteries, it exhibits much better electrochemical performance than the starting commercial V2O5 powders. A high specific discharge capacity of 264 mA h g−1 can be obtained for the nanosheet-structured electrodes, which retains the capacity of 90% after 50 cycles. However, the commercial V2O5 only delivers a specific discharge capacity of 206 mA h g−1 with a capacity retention of 64% after 50 cycles. Moreover, the nanosheet-structured V2O5 electrodes show much-improved C-rate capability. The superior cycling performance demonstrates that the nanosheet-structured V2O5 is a promising cathode material in lithium-ion battery applications.

Carbon wrapped hierarchical Li3V2(PO4)3 microspheres for high performance lithium ion batteries

Nanomaterials are extensively studied in electrochemical energy storage and conversion systems because of their structural advantages. However, their volumetric energy density still needs improvement due to the high surface area, especially the carbon based nanocomposites. Constructing hierarchical micro-scaled materials from closely stacked subunits is proposed as an effective way to solve the problem. In this work, Li3V2(PO4)3@carbon hierarchical microspheres are prepared by a solvothermal reaction and subsequent annealing. Hierarchical Li3V2(PO4)3 structures with different subunits are obtained with the aid of polyvinyl pyrrolidone (PVP). Moreover, excessive PVP interconnect and form PVP-based hydrogels, which later convert into conductive carbon layer on the surface of Li3V2(PO4)3 microspheres during the annealing process. As a cathode material for lithium ion batteries, the 3D carbon wrapped Li3V2(PO4)3 hierarchical microspheres exhibit high rate capability and excellent cycling stability. The electrode has the capacity retention of 80% after 5000 cycles even at 50C.

General synthesis of three-dimensional alkali metal vanadate aerogels with superior lithium storage properties

Three-dimensional (3D) aerogel materials assembled from simplex nanostructures have many advantages in the energy field, but the synthesis of alkali metal vanadate aerogels remains challenging. Herein, we demonstrate a general method for the preparation of a series of 3D alkali metal vanadate aerogels, including NaV3O8, NaV6O15, and K0.25V2O5. The aerogels with a large porous structure built from cross-linked ultra-long nanofibers can be prepared via the hydrothermal self-assembly route followed by a freeze-drying process. The resulting aerogels, e.g. NaV3O8, NaV6O15, and K0.25V2O5, exhibit excellent Li+ storage properties in terms of high specific capacity, good rate capability, and outstanding cyclic stability as cathodes for lithium batteries. Importantly, the NaV3O8 aerogel demonstrates an excellent long-life cyclic performance of 600 cycles at 1000 mA g−1 with no capacity fading. To account for the mechanisms that affect the electrochemical properties, a systematic study is conducted. The superior performances may be due to the superior mechanical stability, good reversibility of lithium insertion/de-insertion and excellent interior structural stability. It is believed that our strategy could probably be extended to prepare other metal vanadate aerogel materials with great promise for various applications.

Mechanical properties and structure of zirconia-mullite ceramics prepared by in-situ controlled crystallization of Si-Al-Zr-O amorphous bulk

Abstract Zirconia-mullite nano-composite ceramics were fabricated by in-situ controlled crystallization of Si-Al-Zr-O amorphous bulk, which were first treated at 900–1 000 °C for nucleation, then treated at higher temperature for crystallization to obtain ultra-fine zirconia-mullite composite ceramics. The effects of treating temperature and ZrO 2 addition on mechanical properties and microstructure were analyzed. A unique structure in which there are a lot of near equiaxed t-ZrO 2 grains and fine yield-cracks has been developed in the samples with 15% zirconia addition treated at 1 150 °C. This specific microstructure is much more effective in toughening ceramics matrix and results in the best mechanical properties. The flexural strength and fracture toughness are 520 MPa and 5.13 MPa·m 1/2 , respectively. Either higher zirconia addition or higher crystallization temperature will produce large size rod-like ZrO 2 and mullite grains, which are of negative effect on mechanical properties of this new composite ceramics.

Template-free synthesis of highly porous V2O5 cuboids with enhanced performance for lithium ion batteries

Highly porous hierarchical V2O5 cuboids have been synthesized by a template-free PVP-assisted polyxol method and the formation mechanism is studied. The cuboids are assembled from numerous mesoporous nanoplates and the preferred orientation of each single nanoplate exposes the 〈110〉 facets, facilitating lithium-ion diffusion by offering a prior channel. This material exhibits a high capacity of 143 mA h g(-1), high rate capacity of 10 C and long life cycling performance up to 1000 cycles. The excellent electrochemical performance of V2O5 cuboid electrodes is due to its unique porous cuboid morphology and optimized structural stability upon cycling. This research provides an effective route to the construction of complex porous architectures assembled from nanocrystals through a surfactant-assisted synthesis method.

Template-free synthesis of β-Na0.33V2O5 microspheres as cathode materials for lithium-ion batteries

In this work, hierarchical three-dimensional (3D) β-Na0.33V2O5 microspheres have been synthesized for the first time by a simple solvothermal reaction with subsequent annealing treatment. The hierarchical microspheres are self-assembled from nanosheet subunits during the solvothermal process. Simultaneously, various hierarchical microspheres with different subunits can be produced by altering the solvothermal solution. After annealing in air, the solvothermal product can be converted into β-Na0.33V2O5 with a well-retained structure. As cathode materials for lithium ion batteries, the as-prepared 3D microspheres exhibit high capacity and good rate capability. The superior electrochemical performance is attributed to the unique three-dimensional hierarchical microstructures, which mimic the advantages of nano- and micro-structures.

Structural evolution of ZrO2–mullite nanocomposites from the Si–Al–Zr–O amorphous bulk

ZrO2–mullite nanocomposites were fabricated by in-situ-controlled crystallization of Si–Al–Zr–O amorphous bulk at 800–1250°C. The structural evolution of the Si–Al–Zr–O amorphous, annealed at different temperatures, was studied by X-ray diffraction, infrared, Laser Raman spectroscopy, field emission scanning electron microscopy, and high-resolution transmission electron microscopy. The materials consisted of an amorphous phase up to 920°C at which phase separation of Si-rich and Al, Zr-rich clusters occurred. The crystalline phases of t-ZrO2 and mullite were observed at 950°C and 1000°C, respectively. Mullite with a tetragonal structure, formed by the reaction between Al–Si spinel and amorphous silica at low temperature, changed into an orthorhombic structure with the increase of temperature. It was the phase segregation that improved crystallization of the Si–Al–Zr–O amorphous bulk. The anisotropic growth of mullite was observed and the phase transformation from t-ZrO2 to m-ZrO2 occurred when the temperature was higher than 1100°C.