Yongming Sun

Electrospun porous ZnCo2O4 nanotubes as a high-performance anode material for lithium-ion batteries

Porous ZnCo2O4 nanotubes were synthesized for the first time by an easy single-nozzle electrospinning strategy combined with subsequent heating treatment. The ZnCo2O4 nanotubes are polycrystalline with diameters of 200–300 nm and lengths up to several millimeters. The walls are ∼50 nm thick, comprising interconnected ZnCo2O4 nanocrystals (∼30 nm) and numerous nanopores (∼3 nm). When tested as an anode material for lithium-ion batteries, the resulting ZnCo2O4 nanotubes exhibit superior electrochemical lithium-storage performances with high specific capacity, good cyclability, and excellent rate capability. A high reversible capacity of 1454 mAh g−1 at 100 mA g−1 is achieved, and even reaches 794 mAh g−1 at a current density as high as 2000 mA g−1 after 30 discharge/charge cycles, indicating a promising anode candidate for lithium-ion batteries.

Morphosynthesis of a hierarchical MoO2 nanoarchitecture as a binder-free anode for lithium-ion batteries

A simple and cost-effective morphogenetic route has been developed for the fabrication of a hierarchically nanostructured “cellulose” MoO2 monolith in large qualities, whereby the cotton texture acts as both a template and a stabilizer. The MoO2 monolith possesses hierarchical porosity and an interconnected framework, which is demonstrated to be useful as a binder-free anode in rechargeable lithium-ion batteries with both high specific capacity of 719.1 mA h g−1 and good reversibility. Our single-component anode for lithium-storage devices also benefits from a simplified fabrication process and reduced manufacturing cost, in comparison with conventional multicomponent electrodes that are fabricated from a mixture of polymer binders and active materials. The present morphogenetic strategy is facile but effective, and therefore it is very promising for large-scale industrial production. It can be extended to prepare other metal oxides with elaborate textural characteristics.

Ultrafine MoO2 nanoparticles embedded in a carbon matrix as a high-capacity and long-life anode for lithium-ion batteries

A composite of ultrafine MoO2 nanoparticles homogeneously distributed in a carbon matrix has been fabricated on a large scale by an easy impregnation–reduction–carbonization route. Firstly, a cotton/PMA composite was formed by incorporating phosphomolybdate clusters into a cotton framework. Then it was treated in a H2/Ar atmosphere at 500 °C for 5 h and in situ reduced/carbonized into a black monolith comprising ultrafine MoO2 nanoparticles (<2 nm) embedded in the carbon matrix. The electrochemical tests demonstrate that the as-formed MoO2/C hybrid exhibits high capacity and excellent capacity retention as an anode material for lithium-ion batteries. The specific discharge capacity is as high as 1207 mA h g−1 in the first cycle and 734 mA h g−1 over 350 cycles at a current density of 50 mA g−1.

Porous carbon-modified MnO disks prepared by a microwave-polyol process and their superior lithium-ion storage properties

A rapid and economical route based on an efficient microwave-polyol process has been developed to synthesize a disk-like Mn-complex precursor. It can be topotactically converted into porous C-modified MnO disks by post-heating treatment. The as-formed porous C–MnO disks with an average thickness of ∼50 nm and diameters up to 3 μm possess a large specific surface area of 75.3 m2 g−1. Interestingly, each C–MnO disk has a single-crystal-like nature, which is built up by the assembly of carbon-modified MnO nanocrystals of ∼12 nm through the same crystallographic orientation. The as-synthesized C–MnO nanocomposite exhibits high capacity and excellent cycling stability when used as an anode material for lithium-ion batteries, which can be attributed to the unique assembled nanoarchitecture involving three-dimensionally interconnected nanopores and carbon modification as well as small particle sizes of MnO nanocrystals. This work provides a simple and efficient pathway to self-organized porous C–MnO nanohybrids without using any templates or seeds.

Self-assembled mesoporous CoO nanodisks as a long-life anode material for lithium-ion batteries

Even after a decade of intensive efforts, achieving conversion-type anode materials with superior stability via a simple process still remains a great challenge. This work describes a facile solution process at room temperature combined with subsequent annealing to prepare unprecedented self-assembled mesoporous CoO nanodisks on a large scale. The hierarchically nanostructured CoO assemblies consist of orderly self-stacked mesoporous nanodisks of less than 10 nm in thickness and 3–5 μm in diameter. Each CoO nanodisk is built up by extremely fine primary nanoparticles (∼5 nm). When evaluated as an anode material for lithium-ion batteries, the synergistic effects of the unique nanoarchitectures endow the self-assembled CoO nanodisks with superior electrochemical performances, including a high reversible lithium storage capacity (1118.6 mA h g−1 after 50 discharge–charge cycles at 200 mA g−1) and excellent cycling performance (633.5 mA h g−1 after 400 discharge–charge cycles at 800 mA g−1).

Flexible fiber-shaped supercapacitors based on hierarchically nanostructured composite electrodes

A novel all-solid-state, coaxial, fiber-shaped asymmetric supercapacitor has been fabricated by wrapping a conducting carbon paper on a MnO2-modified nanoporous gold wire. This energy wire exhibits high capacitance of 12 mF·cm−2 and energy density of 5.4 μW·h·cm−2 with excellent cycling stability. Hierarchical nanostructures and coaxial architectural design facilitate effective contacts between the two core@sheath electrodes and active layers with high flexibility and high performance. This work provides the first example of coaxial fibershaped asymmetric supercapacitors with an operation voltage of 1.8 V, and holds great potential for future flexible electronic devices.

Microwave‐Induced In Situ Synthesis of Zn2GeO4/N‐Doped Graphene Nanocomposites and Their Lithium‐Storage Properties

Zn2GeO4/N-doped graphene nanocomposites have been synthesized through a fast microwave-assisted route on a large scale. The resulting nanohybrids are comprised of Zn2GeO4 nanorods that are well-embedded in N-doped graphene sheets by in situ reducing and doping. Importantly, the N-doped graphene sheets serve as elastic networks to disperse and electrically wire together the Zn2GeO4 nanorods, thereby effectively relieving the volume-expansion/contraction and aggregation of the nanoparticles during charge and discharge processes. We demonstrate that an electrode that is made of the as-formed Zn2GeO4/N-doped graphene nanocomposite exhibits high capacity (1463 mA h g(-1) at a current density of 100 mA g(-1)), good cyclability, and excellent rate capability (531 mA h g(-1) at a current density of 3200 mA g(-1)). Its superior lithium-storage performance could be related to a synergistic effect of the unique nanostructured hybrid, in which the Zn2GeO4 nanorods are well-stabilized by the high electronic conduction and flexibility of N-doped graphene sheets. This work offers an effective strategy for the fabrication of functionalized ternary-oxide-based composites as high-performance electrode materials that involve structural conversion and transformation.

Surface modification of electrospun TiO2 nanofibers via layer-by-layer self-assembly for high-performance lithium-ion batteries

An economical route based on electrospinning and layer-by-layer (LBL) self-assembly processes has been developed to synthesize unique MoO2-modified TiO2 nanofibers, comprising a core of TiO2 nanofibers and a thin metal-like MoO2 nanolayer. The thickness of the MoO2 nanolayer can be tuned by altering the precursor concentration or the LBL cycles. When evaluated for their lithium-storage properties, the MoO2-modified TiO2 nanofibers exhibit a high discharge capacity of 514.5 mA h g−1 at 0.2 C over 50 cycles and excellent rate capability, demonstrating that enhanced physical and/or chemical properties can be achieved through proper surface modification.

Hierarchical self-assembly of Mn2Mo3O8–graphene nanostructures and their enhanced lithium-storage properties

Hierarchically nanostructured Mn2Mo3O8–graphene nanocomposites have been successfully synthesized in large quantities through a facile two-step reduction approach. The unique Mn2Mo3O8–graphene nanohybrids are composed of graphene-wrapped secondary microspheres of ∼3–5 μm in diameter that are built from many Mn2Mo3O8 nanosheets with thicknesses of 10–15 nm and widths of 80–120 nm. The as-formed Mn2Mo3O8–graphene nanohybrids have been applied as anodes for lithium-ion batteries, and show better lithium storage performance compared to the bare Mn2Mo3O8 nanostructures. The enhanced capacity and cycling performance of the Mn2Mo3O8–graphene nanoarchitectures may benefit from the synergistic effects of the nanohybridization. Graphene layers can hinder the agglomeration and enhance the electronic conductivity of the active materials. This facile strategy may be extended to fabricate other nanostructured graphene-encapsulated ternary metal oxides with elaborate secondary architectures.

Self-assembly of hybrid Fe2Mo3O8–reduced graphene oxide nanosheets with enhanced lithium storage properties

Self-assembled Fe2Mo3O8–reduced graphene oxide (RGO) nanosheets are fabricated by a facile route, whereby crystalline Fe2Mo3O8 nanoparticles are grown on RGO nanosheets. The electrode made of the as-formed hybrid Fe2Mo3O8–RGO nanosheets exhibits a high specific capacity of 835 mA h g−1 after 40 discharge–charge cycles at 200 mA g−1. Even at a current density as high as 3000 mA g−1, the specific capacity reaches 574.8 mA h g−1, much larger than the theoretical capacity of graphite. The high lithium-reaction reversibility and durability of the hybrid Fe2Mo3O8–RGO nanosheets are investigated in detail. Based on in situ XRD analyses, a possible Li-cycling mechanism is proposed. Results show that the reversible conversion reaction involves the decomposition of Fe2Mo3O8 and the formation of metallic Mo, Fe and Li2O upon cycling. The presented synthetic strategy and the excellent lithium-storage performances make the unique hybrid Fe2Mo3O8–RGO nanosheets attractive as a promising anode candidate for next-generation high-performance lithium-ion batteries.