Study Of Lithium Storage Properties Based On Metal Oxide Three-Dimensional Integrated Electrodes

Lithium-ion battery, as one of energy storage devices through lithium-ion insertion/deinsertion in cathodes and anodes, has been widely used in our daily life. As with the broad of applied fields, more requirements such as the choice of active materials, the design of electrode structures and unique characteristics of devices have been presented for the future lithium-ion battery. Thus the seeking for energy storage devices and integrated devices with high performances has been the key development direction for the future batteries.Based on the choice of active materials, construction of electrode structure and design of energy integrated devices, this thesis aims at fabricating lithium-ion batteries with high performances. As for the active materials, SnO2and Co3O4with high specific capacities are the better choice; As for the design of electrode structures, carbon cloth was used as current collector to form a3-D integrated electrode structure; As for energy integrated devices, SnO2with wide characteristics acted as active material can realize SnO2/carbon cloth lithium-ion batteries to power SnO2cloth photodetectors. The main contents are described as follows:To avoid the problem of nanostructure materials self-aggregation, nanosheets-assembled Co3O4microspheres have been successfully fabricated with single reactant, which can take advantage of nanostructure with high performances and microstructure with less self-aggregation. Nanosheets assembled microspheres with high specific area perform better electrochemical properties compared to nanoparticles assembled microspheres. The specific capacity of nanosheets assembled microspheres electrodes can remain1000mAh/g after50charge/discharge cycles at a current density of100mA/g, when current density was set at500mA/g the capacity can reach850mAh/g after80cycles.The Co3O4nanosheets arrays/carbon cloth can be prepared by the same method with microspheres, the carbon cloth can be directly used as current collector to realize the formation of3-D electrodes, simplifying the fabricating process of batteries and providing a3-D transmission path for electrons to increase the lithium-ion storage properties. The Co3O4/carbon cloth integrated electrodes can remain a high areal capacity of3.5mAn/cm2after60cycles at a current density of800μA/cm2and have excellent rate performances.The MnCo2O4nanosheets arrays/carbon cloth can be fabricated with the mixture of two metallic ions and the3-D integrated electrodes can perform excellent lithium storage properties. MnCo2O4can be regarded as the partial replacement of approximate1/3Co by Mn when compared to Co3O4, because of their same crystal structure, approximate lattice constant and same valence states of metal cations. MnCo2O4combines the excellent lithium storage properties of Co-based oxides and low voltage plateau of Mn-based oxides, and the synergistic effect of two metal cations makes MnCo2O4better full cell performances in a certain voltage window. In addition, MnCo2O4/carbon cloth3-D integrated electrodes perform excellent lithium-ion diffusion with no influence from the poor performances of Mn-based oxides. Then the partial replacement of Co by Mn to form MnCo2O4can improve the performances of Co3O4in full cells.Flexible lithium-ion batteries and flexible photodectors have been fabricated with one active material of SnO2. As for lithium-ion batteries, current collector carbon cloth avoids the self-aggregation of SnO2nanoparticles; As for photodetectors, SnO2cloth retain the3-D woven structure of carbon cloth and its microtubes can provide a direct transmission path for electrons. Then a self-powered energy device with combination the flexible lithium-ion battery and flexible photodector can realize the function of photodector.To improve the cycling stability of SnO2nanoparticles, the SnO2@TiO2/carbon cloth3-D integrated electrodes have been prepared because their same crystal structure, approximate lattice constant and excellent cycling performances of TiO2. The electrodes remain high specific capacities of700mAh/g after100cycles at a current density of200mA/g and better rate performances, the initial coulomb efficiency can reach above80%, presenting that the composite electrodes avoid tremendously the inreversible reaction in the first cycle.