Yanqing Fu

Porous hollow α-Fe2O3@TiO2 core–shell nanospheres for superior lithium/sodium storage capability

Porous hollow α-Fe2O3@TiO2 core–shell nanospheres for use as anode materials in lithium-ion batteries (LIBs) and sodium-ion batteries (SIBs) have been successfully fabricated by a simple template-assisted method, which has been rarely reported before. Scanning electron microscopy (SEM), transmission electron microscopy (TEM) and N2 adsorption–desorption isotherms reveal that the as-prepared α-Fe2O3@TiO2 is composed of a hollow inner cavity and an outer shell with massive mesopores. This porous hollow structure is capable of buffering the large volume variation of α-Fe2O3 during cycling and preventing the electrode from pulverization and aggregation, as well as providing sufficiently large interstitial space within the crystallographic structure to host alkalis (Li and Na). As a consequence, this hybrid composite exhibits outstanding electrochemical properties, e.g., high specific capacity, excellent cyclability, satisfactory rate performance, and splendid initial coulombic efficiency for both LIBs and SIBs.

A facile synthesis of Fe3O4 nanoparticles/graphene for high-performance lithium/sodium-ion batteries

In this study, a facile, simple, and inexpensive co-precipitation method is used to fabricate diamond-like Fe3O4 nanoparticle/graphene composites for use as lithium-ion batteries (LIBs) and sodium-ion batteries (SIBs) electrode materials. In our synthesis, high-temperature treatment and complicated procedures and apparatus are avoided. Physical characterizations reveal that the as-prepared product is composed of a large fraction of diamond-like Fe3O4 nanoparticles uniformly distributed on thin graphene nanosheets. Compared to bare Fe3O4 and most of the previously reported studies, the as-obtained Fe3O4/graphene composite exhibits greatly enhanced electrochemical properties for both LIBs and SIBs, including excellent reversible capacity, superior cyclability and good rate performance. Specifically, when tested as an anode for LIBs, the Fe3O4/graphene composite shows specific capacity of 1430 mA h g−1 after 100 cycles at 200 mA g−1. The initial discharge capacity tested in SIBs is 855 mA h g−1, and after 40 cycles, the discharge capacity stabilizes at ∼210 mA h g−1 for 250 cycles. The excellent performance can be attributed to the greatly improved electrical conductivity, large surface area and excellent stability of the electrode material.

Effect of magnesium doping on properties of lithium-rich layered oxide cathodes based on a one-step co-precipitation strategy

A Mg-doped lithium-rich layered oxide material is successfully synthesized via a co-precipitation process and a subsequent high-temperature solid state method. The chemical composition, structural characteristics and elemental distribution of the Mg-doped lithium-rich layered oxide material are investigated by inductively coupled plasma optical emission spectroscopy (ICP-OES), scanning electron microscopy (SEM), X-ray diffraction (XRD) and energy-dispersive X-ray spectroscopy (EDXS). The results show that Mg is effectively and equably doped into the samples, which can replace partially Li+ in the cathode material. The electrochemical properties of the Mg-doped lithium-rich layered oxide material are evaluated and compared with those of the conventional Li1.5[Mn0.75Ni0.25]O2+δ cathode material. It can be found that the Mg-doped lithium-rich layered oxide material exhibits excellent electrochemical performance. It can deliver a high initial discharge capacity of 248.6 mA h g−1 and an improved initial coulombic efficiency of 87.9% at 0.1C with a cut-off voltage of 2.0–4.6 V. Moreover, the capacity retention reaches a relatively high value of 94.2% after 200 cycles at 0.5C. In contrast, the capacity retention of conventional Li1.5[Mn0.75Ni0.25]O2+δ is only 59.6%. In addition, the Mg-doped lithium-rich layered oxide material also shows excellent rate capability, which can display a discharge capacity of 130.1 mA h g−1 even at 10C and a capacity retention of 92.6% after 100 cycles at 5C. The enhanced electrochemical properties of the Mg-doped lithium-rich layered oxide material could be attributed to the introduction of Mg, which can effectively mitigate the structural deterioration of the material and facilitate the diffusion coefficient of Li+ during cycling.

An Fe3O4@(C–MnO2) core–double-shell composite as a high-performance anode material for lithium ion batteries

An Fe3O4@(C–MnO2) composite with a cube-like core–double-shell structure has been successfully designed and prepared by a combination of the hydrothermal method and a layer-by-layer (LBL) self-assembly technique. This novel hybrid composite was characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray (EDX) spectroscopy and electrochemical tests. It has been found that this material has a cube-like morphology with a core–double-shell structure. Compared with the bare α-Fe2O3 and Fe3O4–C materials, the as-prepared composite has a significantly enhanced electrochemical performance, with a high capacity, good rate capability, and excellent cycling stability as an anode material for lithium ion batteries (LIBs). At a current density of 100 mA g−1, the as-obtained Fe3O4@(C–MnO2) composite electrode delivers a reversible capacity exceeding 1000 mA h g−1 and retains 979 mA h g−1 after 150 cycles. In contrast, the discharge capacities of the bare α-Fe2O3 and Fe3O4–C show only 111 mA h g−1 and 282 mA h g−1 at a current density of 100 mA g−1 after 150 cycles, respectively. This improved electrochemical performance can be attributed to the high theoretical capacity and larger specific surface area of the MnO2 layer, as well as the high electrical conductivity of the carbon layer, which acts as both the linker and the stabilizer between Fe3O4 and MnO2.

Preparation and performance of β-MnO2 nanorod @ nanoflake (Ni, Co, Mn) oxides with hierarchical mesoporous structure

The rational design and facile synthesis of transition metal oxides are necessary to improve their application in supercapacitors. Herein three kinds of hierarchical mesoporous structured transition metal oxides, which are composed of a β-MnO2 nanorod core and one of three different nanosheet hybrid (Ni, Co, Mn) oxide shells, are facilely synthesized via a novel in situ nucleation and growth of transition metal oxides on the surface of the β-MnO2 nanorods. The crystallographic analyses demonstrated that the three kinds of hybrid oxide shells consisted of cobalt manganese oxide (CMO), nickel manganese oxide (NMO), and nickel cobalt manganese oxide (NCMO). These transition metal oxides are evaluated as electrodes for high performance supercapacitors (SCs). The results reveal that β-MnO2@CMO exhibits a good rate capability of 35% capacity retention even at 20 A g−1, while β-MnO2@NMO displays a high pseudocapacitance of 560 F g−1 at 1 A g−1. However, β-MnO2@NCMO combined the advantages of both β-MnO2@CMO and β-MnO2@NMO, and exhibits a high specific capacitance of 675 F g−1 at 1 A g−1 with excellent rate performance (about 30% capacity retention at 20 A g−1) and cycling stability (83% capacity retention after 3000 cycles). The improved electrochemical performance can be attributed to the unique hierarchical architecture and the synergistic effect of different components.

Nanoflaky MnO2 grown in situ on carbon microbeads as an anode material for high-performance lithium-ion batteries

A flower-like MnO2 encapsulated carbon microbead (MnO2@CMB) nanocomposite is firstly synthesized via in situ nucleation and growth of birnessite-type MnO2 on the surface of monodisperse carbon microbeads. The structure, morphology and performance of the samples are characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), and galvanostatic charge/discharge. The results reveal that the flower textured MnO2@CMB nanocomposite is composed of a CMB core and a MnO2 nanosheet shell. As the anode material for lithium-ion batteries, the MnO2@CMB nanocomposite exhibits excellent electrochemical performance. It shows a good rate capability of 230 mA h g−1 at a current density of 1500 mA g−1 and a large reversible capacity of 620 mA h g−1 without capacity fading for the 80th cycle at 100 mA g−1, which is much better than those of pure MnO2 and graphite. The superior electrochemical performance can be attributed to the unique hierarchical architecture and the combinative effects of the MnO2 nanosheet and carbon matrices.