| The rapid development of implanted medical devices, RF smart cards and microelectro-mechanical system has brought unprecedented opportunities and challenges for thin-film solid-state lithium ion batteries (TFSLB). High capacity, long life and high safety electrode materials are the focus of research in the fields of TFSLB. Compared to the compound electrodes, the electrochemical performance of thin film electrode is currently limited due to the low capacity, especially poor rate capability. To improve the electrochemical properties of TFSLB, high-performance LiV3O8 film positive electrodes have been studied systematically in this thesis. Firstly, LiV3O8 films were prepared by radio frequency (RF) magnetron sputtering and the technological parameters were optimalized. From which a mixed amorphous-nanocrystalline LiV3O8 film and a nanostructrued LiV3O8 film with excellent capacity properties can be obtained. Secondly, the influences of Li ion diffusion kinetic behavior on rate capability were discussed based on the kinetics studies for this two different microstructure LiV3O8 films. Finally, the capacity fading mechanism of the LiV3O8 films were investigated intensively.The influence of sputtering parameters on the structure transformation of LiV3O8 film was studied. The results showed that different microstructured LiV3O8 films can be obtained after alteration the sputtering power and oxygen partial pressure, respectively. The film with nanocrystallite zone scattered in amorphous matrix area was received at the sputtering power of 130 W, called the mixed amorphous-nanoctrystalline microstructure LiV3O8 film. When the ratio of argon/oxygen flow setted to 2:1 during sputtering process, the obtained LiV3O8 film was composed of nanoparticles in size of 50 nm and the nanoparticles were connected with each other by amorphous structure of LiV3O8. XRD result showed that this film had a (100) preferred orientation with average grain size of 15 nm.A initial capacity of 382 mAh/g with retention of 84% after 30 cycles in mixed structure thin film was delivered at the current density of 10μA/cm2. The TEM measurement results indicated that the LiV3O8 thin film with mixed structure combined the advantages of amorphous and nanocrystalline phases and thus obviously improved the electrochemical properties. The nanostructrued LiV3O8 film displayed a capacity of 388 mAh/g and rentention capability of 81% after 50 cycles. This excellent electrochemical performance was attributed to the nanosized particles and the amorphous structure beween these particles which provide large surface area and a more stable crystal structure. Besides, the nanostructured LiV3O8 thin film was oriented with its (100) planes, which provided short Li-ion diffusion paths and facilitated the flow of lithium. Therefore, the thin film displayed excellent high-rate capability. At a discharge rate of 3C, the specific capacity of nanostructrued LiV3O8 film is 250 mAh/g, whereas only 78 mAh/g was obtained for mixed structure LiV3O8 film at the same C-rate. Even at an ultrahigh rate of 40C, the nanostructured LiV3O8 film finished one charge-discharge step in only 45 s with a capacity of 102 mAh/g.Kinetics studies showed that the Li-ion displayed different diffusion behaviors depended on electrode potential in different microstructure LiV3O8 films. Li-ion diffusion coefficient (DLi+) of the nanostructured LiV3O8 thin film was found in the range of 10-1110-13 cm2·s-1, accompanying with two minimum values at 2.3 and 2.6 V. However, the DLi+ of the mixed microstructure film kept stable in 10-13 cm2·s-1 in portential range of 2.03.0 V. The differences were induced by the absent of phase transtransformation during lithiation/delithiation process in the mixed microstructure LiV3O8. Furthermore, the diffusion activation energy for the nanostructured LiV3O8 film was lower than that of the mixed microstructure LiV3O8 film, which therefore led to its better rate capability.The capacity fading mechamism of the two kinds of LiV3O8 films was studied. After a prolonged cycling, the capacity fading of the mixed microstructure LiV3O8 film was found to be coupled by the formation of surface layers on film and growing microcracks, which greatly increased the cell resistence. For the nanostructured LiV3O8 film, the capacity fading is caused by the collapse of layerd structure and the pulverlization of the active materials.
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