Preparation Of The Materials With Hollow/Porous Structure And Their Electrochemical Lithium Storage Properties

The energy and environmental problems gradually become the main problem in the present-day society. With the development of chemical energy, lithium-ion batteries have gained wide recognition because of their high value and great advantage. Since transition metal compounds and alloy materials have many advantages such as good lithium storage performance, low cost, environmental friendliness and abundant resources, they have attracted a lot of attention. However, the low electrical conductivity and the poor electrochemical cycle stability limit their industrial applications. In order to solve these problems, we fabricate hollow/porous materials and characterize their structures and electrochemical lithium storage properties.The hollow structured Mn_xFe_?3-x?O₄ is obtained through the simple solvothermal reaction followed by heat treatment under Ar atmosphere. The morphology and microstructure of Mn_xFe_?3-x?O₄ are characterized by XRD, Raman, AAS, SEM and TEM. This material exhibits excellent lithium storage capacity. The electrode presents a reversible capacity of 1130 mAh g^-1 after 100 cycles at a current density of 0.2 A g^-1. The reversible capacities at the current densities of 0.2,0.5,1,2 and 3 A g^-1 are 970, 710,578,461 and 377 mAh g^-1, respectively. The excellent lithium storage performance of Mn_xFe_?3-x?O₄ sample is mainly due to its unique hollow structure and nano-chipped surface, which provides a larger surface specific area and increases contact between active substance and electrolyte. In addition, this hollow structure can buffer against the large volume change during charging and discharging process, improving the electrochemical cycle stability of the material. Based on previous results, the effects of water and glucose on the structure of Mn_xFe_?3-x?O₄ are also studied. With increasing water content, the hollow structure of the material becomes more obvious. While, the addition of glucose in solvent compacts the surface of the hollow material, which reduces the specific surface area and further leads to worse battery performance.Using Si-Al powders as raw material, the complexation of aluminum ions with 1,4-naphthalenedicarboxylic acid through simple solvothermal method may achieve the precursor material with a core-shell structure. A porous core-shell Si-based material is further prepared by heat treatment in Ar atmosphere followed by acid etching. This method can be extended to the fabrication of other materials with core-shell structures. The porous core-shell structure with larger specific surface area is highly accessible to Li+-containing liquid electrolyte, thus resulting in the enhanced lithium storage capacity. Meanwhile, this kind of porous core-shell structure may buffer tremendous volume change associated with the lithiation/delithiation processes, demonstrating the improved rate performance and good cycle stability of the material.