Jian Li

Microstructures and Mechanical Properties of Hot-Pressed MoSi2-Matrix Composites Reinforced with SiC and Si3N4 Particles

MoSi2-matrix composites reinforced with Si3N4 and SiC particles were fabricated by means of wet-mixing and heat-pressing process. Scanning electron microscope (SEM), X-ray diffractometry (XRD), polarizing microscopy, Vickers hardness tester, with a universal materials testing machine were used to investigate the morphology, grain size, hardness, fracture toughness, and bending strength of the synthesized composites. Notable effects on the bending strength and fracture toughness of MoSi2 caused by the addition of SiC and Si3N4 particles were found. The MoSi2 composite with 20u2009vol.% SiC and 20u2009vol.% Si3N4 particles has the highest strength and toughness, which is about 100% and 340%, respectively, higher than that of pure MoSi2. The grain size of MoSi2 decreases gradually with the volume content of SiC and Si3N4 particles increasing from 0% to 40%, and MoSi2-20u2009vol% SiC-20u2009vol% Si3N4 composite exhibits the minimum grain size of MoSi2. The relationship between the grain size of MoSi2 and bending strength is not entirely fit with Hall-Petch equation. The strengthening mechanisms of the composite include fine-grain strengthening and dispersion strengthening. The toughening mechanisms of the composite include fine grain, microcracking, crack deflection, crack microbridging, and crack branching.

Anode material NbO for Li-ion battery and its electrochemical properties

The NbO electrode materials were successfully synthesized by high-temperature solid-phase method using Nb powders and Nb2O5 powders as raw materials. The crystalline structure, morphology, and electrochemical properties of the obtained materials were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), dynamic light scattering instrument (DLSA), half-cell charge–discharge tests, and cyclic voltammetry (CV). The reaction mechanism of lithium with NbO was investigated by ex-situ XRD studies. The results show that material average Li storage voltage is nearly located at 1.6xa0V, and the lithium intercalation into NbO remains a single-phase process. For the first discharge, a capacity of 355xa0mAh·g−1 is obtained at a current rate of 0.1C, and 293xa0mAh·g−1 is maintained after 50 cycles, whereas a capacity of 416xa0mAh·g−1 is obtained at a current rate of 0.1C after ball milling. And 380xa0mAh·g−1 reversible capacity remains for the ball milling sample.

Electrochemical performance of Al2O3 pre-coated spinel LiMn2O4

Al2O3-coated spinel LiMn2O4 cathode materials, presintered LiMn2O4 (P-LMO), and calcined LiMn2O4 (C-LMO) were synthesized by chemical deposition and thermal treating method using presintered and calcined LiMn2O4 as precursors. The crystal structure, morphology, the thickness of the coating layer, and particle size of prepared samples were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), and Malvern instruments. The average particle size of P-LMO with like-spheres (0.3xa0μm) is much smaller than that of C-LMO (0.5xa0μm). The Al2O3 layer of P-LMO can effectively reduce the charge transfer resistance and inhibit the Mn dissolution. The electrochemical performance of P-LMO is better than that of C-LMO. It is found that the LiMn2O4 cathode materials have excellent electrochemical cyclability by coated 2xa0mol% Al2O3 at the surface of presintered material. The initial discharge capacity of the material with 2xa0mol% Al2O3-coated is 114.0 mAh·g−1 at 0.1C rate and 55xa0°C, and the capacity retention is 87.3xa0% at 0.5C rate.