Chucheng Lin

Flexible free-standing hollow Fe3O4/graphene hybrid films for lithium-ion batteries

Flexible free-standing hollow Fe3O4/graphene (H-Fe3O4/GS) films were fabricated through vacuum filtration and thermal reduction processes, in which graphene formed a three-dimensional conductive network, with hollow and porous Fe3O4 spindles being captured and distributed homogeneously. Using the films as binder-free and free-standing electrodes for lithium-ion batteries, H-Fe3O4/GS with 39.6 wt% graphene exhibited a high specific capacity (1555 mA h g−1 at 100 mA g−1), enhanced rate capability and excellent cyclic stability (940 and 660 mA h g−1 at 200 and 500 mA g−1 after 50 cycles, respectively). The superior electrochemical performance of this novel material can be attributed to two factors. One is that the three dimensional (3D) graphene network formed is very helpful for keeping H-Fe3O4 in good electrical contact. Another is the short transport length for both lithium ions and electrons due to the porous nature which accommodates volume change and favors electrolyte penetration. It is believed that the strategy for preparing free-standing H-Fe3O4/GS films presented in this work will provide new insight into the design and synthesis of other metal oxide/GS electrodes for flexible energy storage devices.

Solvothermal‐Induced Self‐Assembly of Fe2O3/GS Aerogels for High Li‐Storage and Excellent Stability

A novel solvothermal-induced self-assembly approach, using colloid sol as precursor, is developed to construct monolithic 3D metal oxide/GS (graphene sheets) aerogels. During the solvothermal process, graphene oxide (GO) is highly reduced to GS and self-assembles into 3D macroscopic hydrogels, accompanying with in situ transformation of colloid sol to metal oxides. As a proof of concept, Fe2 O3 /GS aerogels are synthesized based on Fe(OH)3 sol, in which GS self-assemble into an interconnected macroporous framework and Fe2 O3 nanocrystals (20-50 nm) uniformly deposit on GS. Benefitting from the integration of macroporous structures, large surface area, high electrical conductivity, and good electrode homogeneity, the hybrid electrode manifests a superior rate capability (930, 660 and 520 mAh g(-1) at 500, 2000 and 4000 mA g(-1), respectively) and excellent prolonged cycling stability at high rates (733 mAh g(-1) during 1000 charge/discharge cycles at 2000 mA g(-1)), demonstrating its great potential for application in high performance lithium ion batteries. The work described here provides a versatile pathway to construct various graphene-based hybrid aerogels.

Morella-rubra-like metal–organic-framework-derived multilayered Co3O4/NiO/C hybrids as high-performance anodes for lithium storage

Co3O4/NiO/C microspheres with a multilayered ball-in-ball hollow nanoarchitecture were synthesized via carbonization and oxidation treatments of Morella-rubra-like CoNi-based metal–organic frameworks (CoNi-MOFs). The shell walls of each ball were entirely composed of uniform nanorods. This unique multilayered hollow structure can strongly mitigate the change in the volume of the electrodes, which maintains the structural integrity of the Co3O4/NiO/C hybrids during the lithiation–delithiation process. In addition, the C scaffolds improve the conductivity of the electrode and function as a buffer material to mitigate the pulverization of Co3O4 and NiO nanoparticles. Therefore, in Li-ion cells, the multilayered Co3O4/NiO/C hybrids exhibit a high reversible capacity (864 mA h g−1 at 1 A g−1), an excellent rate capacity (421 mA h g−1 at 4 A g−1), and a long-lifetime cycling performance (776 mA h g−1, even after 1000 cycles at 1 A g−1) for Li storage.

Fabrication and Tribological Evaluation of Vacuum Plasma-Sprayed B4C Coating

B4C coating was fabricated by vacuum plasma spraying and the tribological properties of the coating against WC-Co alloy were evaluated by sliding wear tests. Al2O3 coating, one of the most commonly used wear-resistant coatings, was employed as comparison in the tribological evaluation. The results obtained show that, the B4C coating is composed of a large amount of nanostructured particles along with some amorphous phases. Both of the friction coefficient and wear rate of the B4C coating are much lower than those of the Al2O3 coating, and the tribological evaluation reveals a decreasing trend for the B4C coating in friction coefficient as well as wear rate with increasing normal load, which is explained in terms of the formation of a protective transfer layer on its worn surface. Tribofilm wear is found to be the dominant wear mechanism involved in the B4C/WC-Co alloy friction pair.

Determining E 1 and E 2 values for yttrium aluminum garnet ceramics using the Duane-Hunt limit

A major challenge when performing scanning electron microscopy and X‐ray analysis on many ceramic materials is their electrical insulation properties, which leads to buildup of the surface charge and reduced contrast in the secondary electron image. A new procedure was established to quantitatively determine the neutral state values, E1 and E2, of yttrium aluminum garnet (YAG) ceramics using the Duane‐Hunt limit (EDHL) of Bremsstrahlung, in order to eliminate this charge effect. Thirty‐eight EDHL values were linearly fitted with the last portion of X‐ray spectra acquired under the incident energy, E0, from 0.35 to 5.0 kV. According to the distribution of EDHL, two piecewise linear fitting was first employed with a breakpoint of 1.0 kV. Consequently, two intersection points of 0.54 and 2.48 kV, which correspond to E1 and E2 for YAG ceramics, were directly determined using a theoretical curve (EDHL = E0). As a result, the high‐resolution images of the YAG ceramic grain structure were successfully obtained using the calculated E1 and E2 values.