Study On Preparation And Electrochemical Properties Of Li₄Ti₅O₁₂ Anode Thin-film For Lithium Microbatteries

All-solid-state thin-film lithium micromatteries are of considerable current researchinterest. In recent years, considerable attention has been devoted to the investigation of the cathode film. By contrast, there have been few reports on the fabrication thin-film anode materials for lithium-ion batteries. Therefore, to develop high performance, low-cost anode thin film has a very important significance on the development of all- solid-state lithium microbatteries. The anode materials are usually carbon in commercial lithium ion batteries. However, the main drawback for carbonaceous materials is the passivation film formed during the first charging, which consumes lithium from the cathode. And there is still some safty concern. Li₄Ti₅O₁₂ is a promising anode material for lithium-ion batteries. During the process of Li⁺ intercalation and de-intercalation, its crystal form does not change and the total volume change is less than 1%, so it is regarded as a "zero strain" material. The lithium ion battery using Li₄Ti₅O₁₂ material as anode material has excellent reversibility, and the safety and reliability of the material is improved compared with that of carbon electrodes, such as graphite. Therefore, spinel Li₄Ti₅O₁₂ anode material has attracted substantial research interests of many scientists.In order to obtain high specific capacity and improve cyclibility of anode thin film, Li₄Ti₅O₁₂ thin film was prepared by spin coating and RF magnetron sputtering methods. As for target materials for RF magnetron sputtering, Li₄Ti₅O₁₂ powder was synthesized by critic acid-assisted sol-gel combustion method. Herein, the main research works are as follows:Li₄Ti₅O₁₂ powders with narrow size distribution and superior dispersion was successfully synthesized by a sol-gel combustion method using citric acid as a chelating agent and an organic fuel.The influence of annealing temperature, annealing time and the ratio of critic acid to metal ions on the structural and electrochemical properties of Li₄Ti₅O₁₂ powder was investigated. Citric acid can complex with Ti and Li at the same time to realize more uniform distribution of ions in molecular level. This decreased the ions rearrangement energy and distance. The sample synthesized at 750℃for 6h with average particle size of 100nm showed the best cycling behavior.Thin film of spinel Li₄Ti₅O₁₂ was successfully prepared by RF magnetron sputtering technology on Si/SiO₂/ Pt substrate. The characteristics of Li₄Ti₅O₁₂ thin films prepared by RF magnetron sputtering were examined by XRD, SEM, AFM, CV and galvanostatic charge/discharge cycling test. The influence of deposition condition, such as sputtering powers, O₂ to Ar gas ratio and substrate temperature, on the characteristic ofLi₄Ti₅O₁₂ thin films have been studied firstly.Thin film of spinel Li₄Ti₅O₁₂ was successfully prepared by a spin-coating technology used sol-gel method. We studied the effect of the preparation condition such as the initial Li /Ti molar ratios, the drying temperature, the annealing temperature and time on the films by means of TG/DSC, XRD, SEM, AFM and galvanostatic charge/discharge cycling test. Using these tests, we can observe the structure, morphology and electrochemical performance of the Li₄Ti₅O₁₂ thin film.The kinetics behaviors related to Li deintercalation/ intercalation process of spinel Li₄Ti₅O₁₂ were studied by means of electrochemical im spectroscopy (EIS) measurements. The open circuit voltage and the differential capacitance plot for Li₄Ti₅O₁₂ with the change of intercalation compositions have been measured. The lithium ion diffusion coefficients have been obtained by EIS method and the results indicate that its values are change with the change of lithium ion intercalation compositions.