Shengchun Mao

Graphene oxide sheets-induced growth of nanostructured Fe3O4 for a high-performance anode material of lithium ion batteries

Nanostructured Fe3O4 is intrinsically prone to aggregation, which hinders insertion and extraction of lithium ions. To overcome this problem, we adopt graphene oxide sheets (GOS) and induce growth of nanostructured Fe3O4 on the GOS in the presence of hexamethylenetetramine (HMT). During the synthetic process, GOS provides a template to regulate the growth of nanostructured Fe3O4 and the HMT is able to coordinate with Fe3+ and control its hydrolysis rate. After the annealing process, GOS is reduced to GS (graphene sheets), and Fe3O4/GS composite is obtained. In this hierarchical structure, GS is capable of enhancing the electronic transport of Fe3O4, and the Fe3O4/GS composite has superior electronic conductivity (106 S m−1). Benefitting from the uniform dispersion of the nanosized Fe3O4 on GS and the superior electronic conductivity, the obtained Fe3O4/GS exhibits prolonged cycling stability (1002 mA h g−1 after 175 cycles at a current density of 0.50 A g−1) and excellent rate capability (715, 647 and 535 mA h g−1 at 1.6, 3.2 and 5.0 A g−1, respectively).

Polypyrrole films electrochemically doped with dodecylbenzenesulfonate for copper protection

Polypyrrole films doped with dodecylbenzenesulfonate (PPy-DBS) were prepared for effective copper protection by galvanostatical method on an underlayer of polypyrrole doped with oxalate (PPy-C 2 O 4 ), because PPy-DBS could not be obtained directly on the copper surface by electrochemical methods. Their anticorrosion performance in 3.5% NaCl solution was compared with that of the bilayer PPy-C 2 O 4 coatings with equal thickness. The well-protected time is more than 500 h even for PPy-DBS films with a thickness of only 15 μm, which is 5 times longer than that of PPy-C 2 O 4 films. Furthermore, the corrosive current on PPy-DBS electrode drops by 2 orders of magnitude compared with PPy-C 2 O 4 electrode. It could be that DBS - is difficult to eject from PPy films because of its large size. Consequently, it obstructs the corrosion ions (Cl - ) from penetrating the PPy films and hinders the oxalate from escaping so that the healing ability of PPy could be maintained for a long term. The obstructing effect was confirmed by electrochemical impedance spectroscopy and energy-dispersive X-ray spectroscopy. The results demonstrate that PPy-DBS films on an underlayer of PPy-C 2 O 4 have a potential application to protect copper.

Towards low-cost, high energy density Li2MnO3 cathode materials

The extremely sluggish Li-ion diffusion rate at the activation plateau (∼4.5 V) in the initial charging is an activation bottleneck of Li2MnO3, which seriously restricts its discharge capacity (energy density) and rate performance. Herein, a targeted strategy is proposed where a few fluorines are substituted for oxygen (Li2MnO3−xFx, x = 0.00, 0.015, 0.03, 0.045). F-substitution reduces the deintercalation barrier of Li+ from the crystal structure by weakening the Li–O bond, and improves the electronic transmission performance by inducing more Mn3+ and oxygen vacancies. Therefore, a major breakthrough is made for the activation bottleneck as the lithium-ion diffusion coefficient at 4.5 V is increased by more than two orders of magnitude. Meanwhile, F-ions inhibit the grain growth along the (001) direction and decrease the primary particle sizes. In the narrow electrochemical window of 2.0–4.6 V, a first discharge capacity of 299 mA h g−1 with a high energy density of 934 W h kg−1 at 0.05 C, and a capacity of 200 mA h g−1 at 1 C with a retention ratio of 92% after 100 cycles are achieved.

Enhanced capacitance performance of Al2O3–TiO2 composite thin film via sol–gel using double chelators

Titanium dioxide (TiO2) is usually introduced into dielectric layer of aluminum electrolytic capacitor to enhance capacitance performance via forming Al2O3-TiO2 composite film. However, there is a big obstacle caused by high crystallization temperature of TiO2 to capacitance enhancement. In present work, a facile route was proposed to synthesize crystalline TiO2 with the size of 3-10 nm at room temperature using lactic acid (LA) and acetylacetone (Acac) as double chelators. After being introduced into the surface of etched aluminum foils as dielectric layer, TiO2 boosted the specific capacitance by about 24% compared to that without TiO2, and about 11% compared to that with TiO2 using lactic acid as only chelator.

Simple thermal decomposition method to synthesize LiTi2(PO4)3/C core–shell composite for lithium ion batteries

Polyanionic LiTi2(PO4)3 material with 3D framework structure is intensively investigated to be used in lithium ion batteries. However, the LiTi2(PO4)3-based materials suffer from poor electronic conductivity hindering the application as electrode active materials. This work describes an effective and simple strategy to synthesize LiTi2(PO4)3/C core–shell structure without the addition of external carbon sources. This approach is achieved by a simple one-step solid state reaction using organometallic salt as raw material. The as-prepared LiTi2(PO4)3 exhibits uniform and thin carbon coating on the particle surface. The electrochemical properties of the LiTi2(PO4)3/C composite are investigated, and the results demonstrate that the as-prepared LiTi2(PO4)3/C shows good cycling performance and rate capability.