Jun Song Chen

Constructing Hierarchical Spheres from Large Ultrathin Anatase TiO2 Nanosheets with Nearly 100% Exposed (001) Facets for Fast Reversible Lithium Storage

Synthesis of nanocrystals with exposed high-energy facets is a well-known challenge in many fields of science and technology. The higher reactivity of these facets simultaneously makes them desirable catalysts for sluggish chemical reactions and leads to their small populations in an equilibrated crystal. Using anatase TiO(2) as an example, we demonstrate a facile approach for creating high-surface-area stable nanosheets comprising nearly 100% exposed (001) facets. Our approach relies on spontaneous assembly of the nanosheets into three-dimensional hierarchical spheres, which stabilizes them from collapse. We show that the high surface density of exposed TiO(2) (001) facets leads to fast lithium insertion/deinsertion processes in batteries that mimic features seen in high-power electrochemical capacitors.

Nanostructured metal oxide-based materials as advanced anodes for lithium-ion batteries.

The search for new electrode materials for lithium-ion batteries (LIBs) has been an important way to satisfy the ever-growing demands for better performance with higher energy/power densities, improved safety and longer cycle life. Nanostructured metal oxides exhibit good electrochemical properties, and they are regarded as promising anode materials for high-performance LIBs. In this feature article, we will focus on three different categories of metal oxides with distinct lithium storage mechanisms: tin dioxide (SnO(2)), which utilizes alloying/dealloying processes to reversibly store/release lithium ions during charge/discharge; titanium dioxide (TiO(2)), where lithium ions are inserted/deinserted into/out of the TiO(2) crystal framework; and transition metal oxides including iron oxide and cobalt oxide, which react with lithium ions via an unusual conversion reaction. For all three systems, we will emphasize that creating nanomaterials with unique structures could effectively improve the lithium storage properties of these metal oxides. We will also highlight that the lithium storage capability can be further enhanced through designing advanced nanocomposite materials containing metal oxides and other carbonaceous supports. By providing such a rather systematic survey, we aim to stress the importance of proper nanostructuring and advanced compositing that would result in improved physicochemical properties of metal oxides, thus making them promising negative electrodes for next-generation LIBs.

Quasiemulsion-Templated Formation of α-Fe2O3 Hollow Spheres with Enhanced Lithium Storage Properties

α-Fe(2)O(3) hollow spheres with sheet-like subunits are synthesized by a facile quasiemulsion-templated method. Glycerol is dispersed in water to form oil-in-water quasiemulsion microdroplets, which serve as soft templates for the deposition of the α-Fe(2)O(3) shell. When tested as anode materials for lithium-ion batteries, these α-Fe(2)O(3) hollow spheres manifest greatly enhanced Li storage properties.

SnO2‐Based Nanomaterials: Synthesis and Application in Lithium‐Ion Batteries

The development of new electrode materials for lithium-ion batteries (LIBs) has always been a focal area of materials science, as the current technology may not be able to meet the high energy demands for electronic devices with better performance. Among all the metal oxides, tin dioxide (SnO₂) is regarded as a promising candidate to serve as the anode material for LIBs due to its high theoretical capacity. Here, a thorough survey is provided of the synthesis of SnO₂-based nanomaterials with various structures and chemical compositions, and their application as negative electrodes for LIBs. It covers SnO₂ with different morphologies ranging from 1D nanorods/nanowires/nanotubes, to 2D nanosheets, to 3D hollow nanostructures. Nanocomposites consisting of SnO₂ and different carbonaceous supports, e.g., amorphous carbon, carbon nanotubes, graphene, are also investigated. The use of Sn-based nanomaterials as the anode material for LIBs will be briefly discussed as well. The aim of this review is to provide an in-depth and rational understanding such that the electrochemical properties of SnO₂-based anodes can be effectively enhanced by making proper nanostructures with optimized chemical composition. By focusing on SnO₂, the hope is that such concepts and strategies can be extended to other potential metal oxides, such as titanium dioxide or iron oxides, thus shedding some light on the future development of high-performance metal-oxide based negative electrodes for LIBs.

SnO2 nanosheets grown on graphene sheets with enhanced lithium storage properties

We demonstrate a new hydrothermal method to directly grow SnO(2) nanosheets on a graphene oxide support that is subsequently reduced to graphene. This unique SnO(2)/graphene hybrid structure exhibits enhanced lithium storage properties with high reversible capacities and good cycling performance.

Top-Down Fabrication of α-Fe2O3 Single-Crystal Nanodiscs and Microparticles with Tunable Porosity for Largely Improved Lithium Storage Properties

In this work, we report a facile top-down approach to fabricate uniform single-crystal α-Fe(2)O(3) nanodiscs via selective oxalic acid etching. Phosphate ions are employed as a capping agent to control the etching to along the [001] direction. We also show that α-Fe(2)O(3) melon-like microparticles with contrasting textural properties can be generated using the same approach. The etched particles exhibit a much larger total pore volume and average pore size compared to the pristine ones, thus serving as the possible origin for their greatly enhanced capacity retention when tested as potential anode materials for lithium-ion batteries.

SnO2 hollow structures and TiO2 nanosheets for lithium-ion batteries

As an important energy storage platform for portable electronics, lithium-ion batteries (LIBs) have been challenged by steadily growing demands for better performance, improved safety, and enhanced reliability. A variety of nanomaterials has emerged with good electrochemical properties and can be regarded as promising electrode materials for LIBs. In this feature article, we will specifically discuss two nanomaterials systems with unique structures, which show particular promise as anode materials for LIBs: tin dioxide (SnO2) hollow spheres and anatase titanium dioxide (TiO2) nanosheets (NSs) with exposed (001) high-energy facets. For both systems, we survey approaches for synthesizing the unique nanostructured materials required for improved LIB performance and subsequently review their lithium storage properties. By focusing on SnO2 and TiO2, we seek to provide rational understanding of the relationship between proper nanostructuring and enhanced physicochemical properties of the active anode material in LIBs; hopefully uncovering new possibilities to generate advanced materials for next generation rechargeable batteries.

Hierarchical nickel sulfide hollow spheres for high performance supercapacitors

Hierarchical NiS hollow spheres assembled from ultrathin nanosheets are synthesized by an efficient template-engaged conversion method. Silica nanospheres were used as templates, and SiO2@nickel silicate core-shell nanostructures were first prepared. In the presence of Na2S, the nickel silicate shell completely transformed into NiS nanosheetsvia a hydrothermal treatment, accompanied by the total dissolution of the inner SiO2 core. This gives rise to uniform hollow nanospheres whose shells are assembled from ultrathin NiS nanosheets. In virtue of the large surface area and enhanced structural stability, the as-prepared NiS hollow spheres exhibit excellent electrochemical performance as electrode materials for supercapacitors.

Controlled synthesis of hierarchical NiO nanosheet hollow spheres with enhanced supercapacitive performance

In this work, we report a facile strategy for the controlled synthesis of nickel oxide (NiO) hollow spheres (HSs) assembled from nanosheets (NSs). The Ni2CO3(OH)2 NSs are first grown on sulfonated polystyrene (sPS) hollow spheres by a low-temperature solution route. NiO HSs with well preserved morphology are then obtained by calcining the as-prepared sPS@ Ni2CO3(OH)2 NSs composite HSs. Because of the hollow interior and hierarchical structure, these NiO nanosheet hollow spheres have a relatively high specific surface area of 62 m2 g−1. When evaluated for supercapacitive performance, these hierarchical NiO HSs demonstrate improved electrochemical properties with a high capacitance of 415 F g−1 even at a high charge–discharge current rate of 3 A g−1 and 91% of which can be retained after 1000 charge–discharge cycles.

Porous Co3O4 nanowires derived from long Co(CO3)0.5(OH)·0.11H2O nanowires with improved supercapacitive properties

Porous Co(3)O(4) nanowires with large aspect ratio have been obtained by annealing long Co(CO(3))(0.5)(OH)·0.11H(2)O precursor nanowires synthesized by a facile hydrothermal method. The results show that the amount of the additive (urea) has an important impact on the morphology of the as-synthesized cobalt-carbonate-hydroxide intermediate, where the uniformity and the overall structure can be controlled by changing the urea concentration. After the heat treatment, the as-obtained phase-pure Co(3)O(4) nanowires with a well retained structure are applied as the electrode material for supercapacitors, and the sample exhibits excellent performance with a high specific capacitance of 240 F g(-1) after 2000 charge/discharge cycles, corresponding to a retention of 98% of the initial capacitance.