Preparation And Electrochemical Properties Of TiO₂ And SnO₂ Hollow Spheres

Lithium ion battery is a new generation green non-pollution battery when it was used in the 1990s. It is widely used in portable electron apparatus and cars due to its highlights, such as high voltage, large specific capacity, long cycle life, low discharge rate by itself, no memory effect and pollution-free to environment, but the anode materials for lithium ion batteries are the key to constrain its whole performance. The lithium ion batteries which used early almost select carbon/graphite as the anode material. However, as the voltage of lithium intercalation into carbon materials closes to lithium metal, some Li-ions may deposit on the surface of the anode leading to lithium dendrite and hence safety concerns. On the other hand, SEI (Solid Electrolyte Interface) Film is essential to form for carbon electrode on the first discharge and charge cycle. What's more, the SEI film formation may increase the impedance of electrode/electrolyte interface, and doesn't facilitate the reversible insertion and extraction of Li-ions.The anode materials of present have reached their ultimate properties, what's more, these disadvantages of carbon materials improve the development of a new material technology becomes an urgent task for the lithium ion batteries. So looking for new type anode materials with better safety performance, higher specific capacity and longer cycle life, becomes hotspot in the research for lithium ion batteries.Transition metal oxides, such as WO₃, MoO₃, V₂O₅, NiO and TiO₂, have been extensively studied as anode materials for lithium ion batteries. Among these oxides, TiO₂ is paid more attention because of its advantages such as high theoretical specific capacity (335 mAh·g^-1), low cost, no toxicity. Lithium-ion battery supplying stabilized 2-2.5 V can be constructed by TiO₂ and cathode materials providing 4 V, because of its convenient formal potential is about 1.8 V (vs. Li⁺/Li). SnO₂ is paid more attention because of its advantages such as high theoretical specific capacity (781 mAh·g^-1) and low-voltage(below ca. 0.5 V versus. Li⁺/Li). A method to improve the electrochemical performance of Li-ion batteries is to increase the contact area between the active materials and electrolyte, hence making the Li⁺ insertion/extraction more sufficiently. For this purpose, keeping more porosity and less agglomeration of the active materials through assembling them into three-dimensional architecture seems to be an effective way. Metal oxide hollow spheres have been synthesized successfully by various methods, such as templating method, polymer-induced method, sol-gel method, hydrothermal method and so on. The most-applied method for the synthesis of hollow spheres is by far the templating of larger colloidal carbon spheres prepared by dehydrating glucose or sucrose under hydrothermal conditions, the surface of the carbon spheres have a distribution of -OH groups and -C=O groups, which makes surface modification unnecessary. The electrochemical properties of TiO₂ and SnO₂ with varied morphologies, for instance, nanocrystallines, nanorods, nanotubes and nanowires have been studied by many previous researchers. However, the electrochemical features of them have been reported rarely.In this thesis, we synthesized TiO₂ and SnO₂ hollow spheres successfullly by a sol-gel route using carbon spheres as template. The electrochemical properties were investigated by galvanostatic cycling and cyclic voltammetry. The study has been done about the electrochemical properties of lithium insertion into TiO₂ and SnO₂ hollow spheres electrode as follows:1. Carbon spheres with different diameter were prepared by hydrothermal treatment. Uniform TiO₂, SnO₂ and ZnO hollow spheres have been successfully synthesized on a large scale using the as-prepared carbon spheres as template. The results indicated that the diameter and the shell thickness of the metal dioxide hollow spheres can be controlled by using carbon spheres template of different diameter and different concentration.2. The electrochemical performance of TiO₂ hollow spheres prepared by sol-gel was studied. The experimental results showed that the TiO₂ hollow spheres exhibited a high initial discharge capacity and excellent cycling performance. However, there are still large irreversible capacities in the first cycle and the specific capacities need some improvement.3. The electrochemical performance of SnO₂ hollow spheres prepared by sol-gel was studied. The experimental results showed that the SnO₂ hollow spheres exhibited a high initial discharge capacity and excellent cycling performance. However, there are still large irreversible capacities in the first cycle and the cycling performance need some improvement.