Xiao-Fei Liu

Graphene/single-walled carbon nanotube hybrids: one-step catalytic growth and applications for high-rate Li-S batteries.

The theoretically proposed graphene/single-walled carbon nanotube (G/SWCNT) hybrids by placing SWCNTs among graphene planes through covalent C-C bonding are expected to have extraordinary physical properties and promising engineering applications. However, the G/CNT hybrids that have been fabricated differ greatly from the proposed G/SWCNT hybrids because either the covalent C-C bonding is not well constructed or only multiwalled CNTs/carbon nanofibers rather than SWCNTs are available in the hybrids. Herein, a novel G/SWCNT hybrid was successfully fabricated by a facile catalytic growth on layered double hydroxide (LDH) at a high temperature over 950 °C. The thermally stable Fe nanoparticles and the uniform structure of the calcined LDH flakes are essential for the simultaneously catalytic deposition of SWCNTs and graphene. The SWCNTs and the CVD-grown graphene, as well as the robust connection between the SWCNTs and graphene, facilitated the construction of a high electrical conductive pathway. The internal spaces between the two stacked graphene layers and among SWCNTs offer room for sulfur storage. Therefore, the as obtained G/SWCNT-S cathode exhibited excellent performance in Li-S batteries with a capacity as high as 650 mAh g(-1) after 100 cycles even at a high current rate of 5 C. Such a novel G/SWCNT hybrid can serve not only as a prototype to shed light on the chemical principle of G/CNT synthesis but also as a platform for their further applications in the area of nanocomposites, heterogeneous catalysis, drug delivery, electrochemical energy storage, and so on.

Hydrothermal evolution, optical and electrochemical properties of hierarchical porous hematite nanoarchitectures

Hollow or porous hematite (α-Fe2O3) nanoarchitectures have emerged as promising crystals in the advanced materials research. In this contribution, hierarchical mesoporous α-Fe2O3 nanoarchitectures with a pod-like shape were synthesized via a room-temperature coprecipitation of FeCl3 and NaOH solutions, followed by a mild hydrothermal treatment (120°C to 210°C, 12.0 h). A formation mechanism based on the hydrothermal evolution was proposed. β-FeOOH fibrils were assembled by the reaction-limited aggregation first, subsequent and in situ conversion led to compact pod-like α-Fe2O3 nanoarchitectures, and finally high-temperature, long-time hydrothermal treatment caused loose pod-like α-Fe2O3 nanoarchitectures via the Ostwald ripening. The as-synthesized α-Fe2O3 nanoarchitectures exhibit good absorbance within visible regions and also exhibit an improved performance for Li-ion storage with good rate performance, which can be attributed to the porous nature of Fe2O3 nanoarchitectures. This provides a facile, environmentally benign, and low-cost synthesis strategy for α-Fe2O3 crystal growth, indicating the as-prepared α-Fe2O3 nanoarchitectures as potential advanced functional materials for energy storage, gas sensors, photoelectrochemical water splitting, and water treatment.

Hierarchical nanostructured composite cathode with carbon nanotubes as conductive scaffold for lithium-sulfur batteries

Abstract Carbon nanotubes (CNTs) are excellent scaffolds for advanced electrode materials, resulting from their intrinsic sp2 carbon hybridization, interconnected electron pathway, large aspect ratio, hierarchical porous structures, and low cost at a large-scale production. How to make full utilization of the mass produced CNTs as building blocks for nanocomposite electrodes is not well understood yet. Herein, a composite cathode containing commercial agglomerated multi-walled CNTs and S for Li-S battery was fabricated by a facile melt-diffusion strategy. The hierarchical CNT@S coaxial nanocables exhibited a discharging capacity of 1020 and 740 mAh ·g–1 at 0.5 and 2.0 C, respectively. A rapid capacity decay of 0.7% per cycle at the initial 10 cycles and a slow decay rate of 0.14% per cycle for the later 140 cycles were detected. Such hierarchical agglomerated CNT@S cathodes show advantages in easy fabrication, environmentally benign, low cost, excellent scalability, and good Li ion storage performance, which are extraordinary composites for high performance Li-S battery.

N-Methyl-2-pyrrolidone-assisted solvothermal synthesis of nanosize orthorhombic lithium iron phosphate with improved Li-storage performance

Exploring an efficient and effective way for synthesis of lithium iron phosphate (LiFePO4) with good Li-storage performance is a good way to fully demonstrate their applications for Li-ion batteries. In this contribution, LiFePO4 nanoparticles were synthesized by a facile solvothermal process with water/N-methyl-2-pyrrolidone (NMP) solvent system at a moderate temperature of 180 °C. The product was determined as single-phase orthorhombic LiFePO4, and the presence of crystal growth inhibitor NMP was favourable for the formation of smaller-sized LiFePO4 particles with improved electrochemical properties. After a carbon coating process, the LiFePO4/C sample afforded a reversible capacity of 140 mA h g−1 at 0.5 C, 106 mA h g−1 at 5.0 C at room temperature, and 163 mA h g−1 at 0.5 C, 153 mA h g−1 at 5.0 C at the higher temperature of 60 °C, respectively. The long cycle test at 0.2 C showed that no noticeable capacity fading was observed. The present LiFePO4 obtained by the facile solvothermal process had good thermal and electrochemical stability, which were attributed to facile Li ion diffusion and a good electron transfer pathway in the solvothermal LiFePO4 product.