Preparation Of TiO₂ Non Carbon Current Collector And Its Application Research In Lithium Air Battery

Lithium-air battery has a high theoretical energy density of 11425 Wh/kg?excluding oxygen?, which close to the energy density of gasoline. Up to now, the lithium-air battery was considered as the largest energy storage system, so it has received great attention all over the world. Therefore, a series of problems such as environmental pollution resulted from the combustion of fossil fuels and serious shortages of energy would be solved through the research and utilization of lithium-air battery.As a matter of fact, current collector is indispensable in the lithium-air battery, owing to it can collect current from electrochemical reaction. At present, carbon paper is the current collector most commonly used for lithium-air battery. However, with the development of non-carbon current collector, titanium foam and nickel foam have become a great alternative to the carbon paper for lithium-air battery. In this work, a non-carbon current collector based on TiO₂ was synthesized successfully and it was utilized as excellent current collector for lithium-air battery. Firstly, the parameters of preparing TiO₂ nanotubes was investigated and their physical properties and electro-chemical properties in non-aqueous lithium-air battery were studied systematically. Secondly, three kinds of cathodes were prepared by spraying active materials?Ag, Ketjenblack?KB?and Ag+KB respectively? on the TiO₂ nanotubes synthesized former step. Meanwhile, the effect of three air cathodes on lithium-air battery was researched through the charge/discharge test. The experiment results as follows:1. TiO₂ nanotubes were synthesized on titanium foam through anodic oxidation method. The experiment mainly investigated the morphologies of TiO₂ nanotubes, which synthesized through different voltage conditions. During the process of anodic oxidation, the experimental temperature was set up to 50 ? for 2 h. It can be seen from SEM results that under 45 V voltage, the morphology of TiO₂ nanotubes was flawless, independent of each other and almost round or oval. After anodic oxidation, the prepared TiO₂ nanotubes were calcined at high temperature. The XRD results are shown that two kinds of crystal structure, rutile and anatase, were obtained after high temperature calcine for TiO₂ nanotubes.2. The lithium-air battery prepared was testified in dry air condition. The air cathode was prepared by ultrasonic spraying three different active material including Ag?KB and KB+Ag respectively on the current collector with TiO₂ nanotubes surface. The SEM results were shown that the ideal air cathode structure was obtained through ultrasonic spraying. As the electrochemical performance, it is found that the cathode only contained KB can deliver largest discharge capacity and excellent cycle performance. Specifically, the discharge capacity of the cell contained KB could reach 12556.33 mAh/g at the current densities of 0.03 mA/cm2 and the cell also could undergo 32 cycles with a fixed specific capacity of 1000 mAh/g at the current density of 0.1 mA/cm2. This was mainly attributed to the ultra-largespecific surface area that can be provided by KB. so as to form a suitable structure for lithium-air battery. Thus the cathode with TiO₂ nanotubes and KB could provide more storage volume for the deposition of discharged products and act as a better diffusion path for O₂ and electrolyte. In addition, proper current density would result in better performance of lithium-air battery. For example, each circle?discharging and charging? time that the cell reach the fixed specific capacity must take prolonged by reducing the current densities. At small current densities, such as 0.05 mA/cm2, the more CO₂ and H2 O in ambient air could enter into the lithium air battery due to the circle time was longer at small current densities, which resulting in lithium metal anode was decayed. Hence, many byproducts were generated and they were difficult to decompose, which resulting to the decline of cycle performance. In addition, TiO₂ nanotubes, foam nickel and carbon paper were used as the current collector of lithium-air battery, respectively and compared the electrochemical performance among them, it is found that the best performance of the lithium-air battery was obtained by using TiO₂ nanotubes as the current collector.3. After charging and discharging, the surface of the air cathode was covered with a lot of massive materials, blocking the channel of the air cathode. The SEM and XRD test results were shown that the surface of the cathode covering material was mainly Li2O₂ generated by discharged process. The Li2O₂ can't be fully decomposed during long time cycle so it will be accumulated in the surface of cathode, leading to the blocking of the pores of cathode. O₂ can't diffuse into cathode and finally lead to the invalidation of lithium-air battery.