Papers by Author: Shi Xi Zhao

Abstract: In this paper, to improve the elevated temperature performance of spinel LiMn2O4 as cathode materials, the cation/anion co-doping and surface modification together were adopted. The SiO2 coated Li1.02Co0.1Mn1.9O4−xSx spinels were synthesized by the solid-state reaction method and Sol-gel coating process. The samples are characterized by XRD, SEM, galvanostatic charge-discharge. The results show that the Li1.02Co0.1Mn1.9O3.98S0.02 exhibits the best initial discharge capacity of 122mAh/g, and capacity retention rate gets to 92% after 100 cycles at room temperature (25 °C). The substitution of Co and S for Mn and O in LiMn2O4 can enhance the crystal structure stability and overcomes the Jahn-Teller distortion, but cannot resolve the elevated temperature cycling issue of the spinel cathode materials. The capacity loss of Li1.02Co0.1Mn1.9O3.98S0.02 without SiO2 coating gets to 38% after 50 cycles, whereas the 2.0wt.% SiO2-coated Li1.02Co0.1Mn1.9O3.98S0.02 cathode material has only 5.0% capacity loss after 50 cycles at elevated temperature (55°C). It indicates that nano SiO2 coating could suppress Mn dissolution in the electrolyte during cycles. So combining cation/anion co-doping and surface modification is best way to improve the elevated temperature cycling performance of spinel LiMn2O4 as cathode materials.

Abstract: Cathode materials Li-[MnxNi1/2-x/2Co1/2-x/2]-O (x=0.333, 0.4, 0.6, 0.8, 0.9) were fabricated by lithium salts (LiNO3) and manganese-nickel-cobalt hydroxide precursors using the required amounts of Mn, Ni, Co for a given value of x. When Mn content is between 0.5 and 0.8, layered and spinel structure co-existed. Meanwhile the rate Li/M is also a key factor for synthesis of layered-spinel intergrowth structure cathode materials without other impurities. Li-[Ni0.2Co0.2Mn0.6]-O and Li-[Ni0.1Co0.1Mn0.8]-O were synthesized by a Two-step Co-precipitation method.

Abstract: Pb(Mg1/3Nb2/3)O3-PbTiO3 (PMN-PT) solid solutions with composition near the morphotropic phase boundary (MPB) (33mol% PT) were successfully synthesized by the molten salt synthesis (MSS) method at 800°C for 30min using Li2SO4-Na2SO4 and NaCl-KCl molten salts as a medium of reaction, respectively. The influences of processing parameters, such as temperature, time, and type of salts, on the formation and the micrographs characteristics of the PMN-PT powders were discussion. It was found that the PMN-PT powder obtained by the MSS method has a relatively uniform size distribution and a better dispersivity of particle, and an average size of PMN-PT particles with smooth surface was around 0.3∼0.5 μm. With other conditions being kept same, chloride molten salt is more propitious to the formation of PMN- PT solid solutions, and improving the compositional homogeneity of PMN-PT powders.

Abstract: Single perovskite phase PMN-PT powders had been synthesized using molten salts method. The powders of PMN-PT synthesized by MSS had submicrometer particle size and high sinterability, which beneficial to an enhancement of the densification process and a decrease of the sintering temperatures. These advantages have an important bearing on the dielectric properties of these materials. The density of ceramics sintered at 1175°C was up to 98% of the theoretical density. These ceramics had excelled dielectric and piezoelectric properties.