| In order to meet the needs of high-power batteries, the lithium-rich manganese layered compounds as cathode materials have attracted much attention due to their high specific capacity of more than250mAh g-1. However, the poor rate capability and cycling stability limit their large-scale application in lithium-ion batteries. It is generally known that particle size reduction and surface modification are effective ways to improve the electrochemical performance (lithium storage performance) of the material. In this paper, we focused on fabrication of nanomaterials and surface modification, and the results are as follows:First, we use the gel-assisted combustion method and template method to prepare the disordered and ordered porous lithium-rich manganese layered compounds. For gel-assisted combustion method (polyvinylpyrrolidone (PVP, Mw=130W) as the auxiliary combustion agent), the disordered porous0.4Li2MnO3?0.6LiNi2/3Mn1/3O2sample prepared at600℃shows the best electrochemical performance because of the appropriate degree of crystallinity and the particle size. For instance, the electrode delivers291mAh g-1at the current density of15mA g-1within2.0-4.8V and the capacity retains92.3%after100cycles. In contrast, lithium-rich manganese layered compound with ordered porous structure, using the ordered porous SiO2(KIT-6) as template, shows better rate and cycle performance, i.e., it shows a higher capacity of293.6mAh g-1and higher capacity retention of93.9%after100cycles. When cells were charged at15mA g-1and discharged at200,500and1500mA g-1, ordered (disordered) porous electrodes show229.8(208),112.5(82) and84.7(40.6) mAh g-1, respectively. Obviously, the ordered porous sample shows better electrochemical performance than the disordered.As we all known, the templates in traditional template method usually need to be removed, but the templates in self-template method can also serve directly as the source of certain elements in final product. The latter was more simple and controllable. In this paper, porous MnO2amicrospheres (obtained by calcining MnCO3microspheres) were used as template to prepare hollow0.3Li2Mn03-0.7LiNi0.5Mn0.5O2microspheres, which can be explained by Kekendaer effect (different metal ions with different diffusion velocity). The hollow0.3Li2MnO3·0.7LiNi0.5Mn0.5O2microspheres electrode shows high reversible specific capacity (initial capacity of295mAh g-1), outstanding cycle performance (278mAh g-1after200cycles) and superior rate performance (213.9mAh g-1when discharged at200mA g-1). In addition, the micro-spheroidal morphology can still maintain even after200charge/discharge cycles.Moreover,1-D nanorod structure and3-D microsphere0.3Li2MnO3·0.7LiNi0.5Mno.s02were also prepared by using1-D nanorod β-MnO2and3-D thorn ball γ-MnO2as templates, and the two lithium-rich manganese layered compounds show excellent lithium storage performance. Compared with the1-D nanorods sample, the3-D microspheres sample consisting of1-D nanorods delivers a much higher volumetric capacity. For example, the compact density of the3-D microspheres sample and the1-D nanorods sample are1.68g cm-3and1.16g cm-3, respectively. So the3-D microspheres sample is almost1.5times the volume specific capacity of the1-D nanorods sample at the same current density.At last, surface modification is also used to improve lithium storage performance of the lithium-rich manganese layered compounds. The0.4Li2MnO3·0.6LiNi2/3Mn1/3O2particles were coated with a thin layer of Al2O3by atomic layer deposition technology (ALD), and a typical core-shell structure (i.e.,0.4Li2MnO3·0.6LiNi2/3Mn1/3O2as core, and Al2O3as shell) was obtained. In comparison with the pure0.4Li2MnO3·0.6LiNi2/3Mn1/3O2sample, the core-shell structure0.4Li2MnO3·0.6LiNi2/3Mn1/3O2@Al2O3shows better cycling performance. After150charge/discharge cycles, the capacity retains94.5%for the Al2O3modified electrode, while only retains87.5%for the pristine electrode. |
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