Search

Hollow nitrogen (N)-doped Fe 3 O 4 /carbon (C) nanocages with hierarchical porosities have been successfully synthesized by carbonizing polydopamine (PDA)-coated Prussian blue (PB). Scanning electron microscopy, transmission electron microscopy, X-ray powder diffraction, X-ray photoelectron spectroscopy and N 2 adsorption/desorption isotherms were employed to characterize the hollow N-doped Fe 3 O 4 /C superstructures. Owing to their well-defined hierarchical porous structure and high electric conductivity originated from N-doped carbon matrix, the unique hollow nanocages as anode materials for Lithium ion batteries (LIBs) exhibited a specific capacity of 878.7 mA h g −1 after 200 cycles at the specific current of 200 mA g −1 , which is much better than that of N-doped Fe 3 O 4 /C derived from pure PB (merely 547 mA h g −1 ). The novel construction with hollow interior nanoarchitecture, hierarchical porosity, high electrical conductivity, N-doped carbon, and the Fe 3 O 4 nanoparticles incorporated into porous interconnected carbon framework make the special nanocomposites be very promising Fe 3 O 4 -based anode materials. [ABSTRACT FROM AUTHOR]

The search of advanced anodes has been an important way to satisfy the ever-growing demands on high rate performance lithium-ion batteries (LIBs). It was observed that the capacity of Fe 3 C as an anode is larger than its theoretical one, which might be attributed to the pseudocapacity on the interface between the carbide and electrolyte. In this work, a novel carbon sphere doped with Fe 3 C nanoparticles was fabricated and tested as the anode in LIBs. In the first place, iron precursors were embedded in the cross-link polymer resorcinol-formaldehyde (RF) spheres via a facile hydrothermal reaction, in which RF served as the carbon source and ethanol as a dispersant agent. Consequently, the hydrothermal products were carbonized successively at 700 °C under inert atmosphere to obtain porous carbon spheres doped with Fe 3 C. When the composite severed as an anode in LIBs, its discharge capacity increased to the largest during the first 250-400 cycles, then dropped down to a similar level of that after 1000 cycles at different current rates. The discharge capacity of the composite increased from ∼300 mAh g −1 to ∼540 mAh g −1 at the current of 100 mA g −1 during the initial hundreds cycles, and even a discharge capacity of ∼230 mAh g −1 at the current of 2000 mA g −1 . Moreover, it was observed that a discharge plateau gradually appeared between 0.7∼1.1 V during the first hundreds of cycles. The electrochemical behaviors of the anode before 1000 discharge/charge cycles were compared with that after 1000 discharge/charge cycles by cyclic voltammetry and electrochemical impedance spectroscopy to find out the differences between their features. The high rate performance of LIBs might result from the decomposition of electrolyte and the pseudocapacity behavior presented on the interfacial (surface) lithium storage of the active materials. [ABSTRACT FROM AUTHOR]

Novel porous cage-like carbon (C)/nano-Si nanocomposites as anode materials for lithium-ion batteries (LIBs) was prepared based on nano-Si@zeolitic imidazolate frameworks (ZIF-8)-templated method. In this strategy, p-aminobenzoic acid was initially grafted onto nano-Si to form benzoic acid-functionalized nano-Si, and then nano-Si@ZIF-8 was constructed by alternately growing Zn(NO 3 ) 2 ·6H 2 O and 2-methylimidazolate on benzoic acid-functionalized nano-Si under ultrasound. The novel porous cage-like nano-Si/C nanocomposites were fabricated by pyrolyzing the resulted nano-Si@ZIF-8 and washing with HCl to remove off ZnO. Scanning electron microscopy, transmission electron microscopy, X-ray powder diffraction, Raman spectra and N 2 adsorption/desorption isotherms were employed to characterize the porous cage-like nano-Si/C nanocomposites. The resulted nano-Si/C nanocomposites as anode materials for LIBs showed a high reversible capacity of ∼1168 mA h g −1 at 100 mA g −1 after 100 cycles, which was higher than many previously reported Si/C nanocomposites. The porous nanostructure, high specific surface area and good electrical conductivity of the cage-like nano-Si/C nanocomposites contributed together to the good performance for LIBs. It might open up a new way for application of silicon materials. [ABSTRACT FROM AUTHOR]