Qianwen Li

Synthesis of MnO@C core–shell nanoplates with controllable shell thickness and their electrochemical performance for lithium-ion batteries

MnO@C core–shell nanoplates with a size of ∼150 nm have been prepared via thermal treatment deposition of acetylene with the precursor of Mn(OH)2 nanoplates, which has been hydrothermally synthesized. The thickness of the carbon shells varied from ∼3.1 to 13.7 nm by controlling the treatment temperature and reaction duration time. The electrochemical performance of the MnO@C nanoplates, which were synthesized at 550 °C for 10 h with a carbon shell thickness of ∼8.1 nm, display a high reversible capacity of ∼770 mA h g−1 at a current density of 200 mA g−1 and good cyclability after prolonged testing, which is higher than that of MnO@C nanoplates with a carbon shell thickness of ∼3.1, 4.0, 4.2, 10.9 and 13.7 nm.

Synthesis of Mn3O4 nanowires and their transformation to LiMn2O4 polyhedrons, application of LiMn2O4 as a cathode in a lithium-ion battery

Mn3O4 nanowires with diameter of ∼15 nm and a length of up to several micrometres have been hydrothermally synthesized at 200 °C for 15 h without any surfactants. It was investigated that during the formation process of Mn3O4 nanowires the length of the nanowires increased while the diameter did not obviously change. The coercivity of the Mn3O4 nanowires is up to 5600 Oe at 5 K. As these Mn3O4 nanowires were treated with LiOH by solid state reaction at 750 °C for 6 h, interconnected LiMn2O4 polyhedrons were obtained. The achieved discharge capacity of the LiMn2O4 polyhedrons was 115 mAh g−1 and they retained 98.3% of this capacity after 60 cycles at 0.1 C.

Solid state synthesis of a new ternary nitride MgMoN2 nanosheets and micromeshes

In this study, a new ternary nitride MgMoN2 was synthesized by a solid-state reaction of Mo, Mg and NaN3 in a stainless steel autoclave at 700 °C. The crystal structure of MgMoN2 (a = 2.91081 A, c = 10.55029 A, Z = 2) was determined by Rietveld refinement based on the X-ray diffraction data (XRD), which comprises of alternating layers of MgN6 octahedral and MoN6 trigonal prisms. The field-emission scanning electron microscopy (FE-SEM) and the transmission electron microscopy (TEM) show that the obtained MgMoN2 was composed of nanosheets with a diameter of several micrometers and with a thickness of about 30 nm. As Mo was substituted by other molybdenum sources (such as MoO3, (NH4)6Mo7O24·4H2O or Na2MoO4·4H2O), the FE-SEM images, TEM images and the selected-area electron diffraction (SEAD) patterns show that the obtained MgMoN2 was composed of single-crystalline micromeshes with different pore sizes. An oriented aggregation mechanism was considered for the formation of MgMoN2 nanosheets and micromeshes. The as-obtained MgMoN2 micromesh is promising as a catalyst support in chemical filtration and in separations under severe operating conditions.

Solid state synthesis of nitride, carbide and boride nanocrystals in an autoclave

This feature article provides a brief overview of the latest developments in the solid state synthesis of various nitride, carbide and boride nanocrystals in an autoclave at mild temperatures. An additive assisted route was developed for nitride, carbide and boride nanocrystals. In the presence of S powder, 3C–SiC nanocrystals were obtained utilizing waste plastics and Si powder at 350–500 °C. With the assistance of I2, rare-earth and alkaline-earth hexaboride nanocrystals were prepared at temperatures below 400 °C. As N-aminothiourea and iodine were added to the system containing Si and NaN3, β-Si3N4 nanorods and α,β-Si3N4 nanoparticles could be prepared at 60 °C. A ternary nitride of MgSiN2 can also be prepared at 350–500 °C using Si, Mg, and NaN3 as reactants.