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The phase formation and transition mechanism of lead magnesium niobate–lead titanate [(1−x)Pb(Mg1/3Nb2/3)O3–xPbTiO3, PMN-PT, 0≤x≤1] were investigated by thermal analysis and XRD. The effect of process parameters such as x values, synthesis temperatures, and excess PbO on phase transitions were studied in terms of the diffraction peak splitting. The results show that the perovskite phases undergo the transitions pseudocubic→rhombohedral→coexistence of rhombohedral and tetragonal→tetragonal in the x value range 0–1. At the composition of morphotropic phase boundary, preferential formation of the PMN-PT tetragonal phase was observed and discussed at elevated synthesis temperatures or with enhanced excess PbO.

Two structure types of LiMnO2 were synthesized by sol-gel method and ion-exchange method respectively. The results indicate that orthorhombic phase LiMnO2 is more stable than layered LiMnO2, o-LiMnO2 can be synthesized directly by sol-gel methods followed by heat-treated in argon, but layered LiMnO2 was obtained only by indirect methods such as ion-exchange method. In this paper, we first synthesized layered NaMnO2 by the sol-gel method, and then obtained layered LiMnO2 by the ion-exchange method. The phase, constitution, chemical composition, and images of the products were tested by XRD, AAS (atomic absorption spectroscopy) and SEM. The electrochemical performances of the two structural types of LiMnO2 are obviously different during the initial few cycles, but later they both have a good capacity-retaining ability. The capacity of layered structure LiMnO2 is higher than that of o-LiMnO2.

LiMn2O4−xFx prepared by the sol-gel method has a perfect crystal formation. The crystal particle size of the material was medium and distributed uniformly. The substitution of F for O increased the specific capacity of the material at the cost of the cycleability. The explanation of this results is that the F decreases the valence of Mn, that is, more Mn3+ and less Mn4+ exist in the material. The increase of Mn3+ will improve the initial specific capacity and Mn3+ is the original reason for Jahn-Teller effect that caused the poor cycleability of the cathode material by the micro-distortion of the crystal structure. In addition, the expanded measurement of the crystal lattice is also the reason for the poor cycleability. Therefore, the results of F-substitution and cation-substitution are opposite. If the two methods are combined, they can compensate the inability each other and the satisfactory results may be obtained.

主要研究了纳米氧化铝包覆对磷酸铁锂/C复合正极材料结构和电化学特性的影响。采用溶胶-凝胶方法把纳米氧化铝包覆在商业LiFePO 4 /C颗粒表面。研究了Al 2 O 3 包覆层的量对LiFePO 4 电极在室温和高温充放电性能的影响。结果显示：2wt% Al 2 O 3 包覆层能有效增加电池的循环容量, 能延缓电池在高温条件下充放电的容量衰减, 减小电极的界面阻抗。这归因于氧化铝包覆层对磷酸铁锂晶粒的表面起保护作用, 减少电解液对磷酸铁锂晶粒表面的腐蚀, 从而改善循环过程中磷酸铁锂的表面结构的完整和稳定, 确保锂离子扩散通道的畅通。