| With the non-renewable fossil energy gradually depleted, such as oil, coal and natural gas, lithium-ion batteries - a kind of efficient and environmental friendly moden energy storage system - become more and more popular. Lithium-ion batteries are playing an important role in the fields of 3C electronics, new energy vehicles, aerospace and large-scale energy storage systems. With the development of intelligent society,electronic devices tend to become miniaturized. As a kind of safe and reliable micro?energy devices, all-solid-state thin-film lithium batteries ?ASSTFLBs? have thus attracted great attention in both academic research and industry.At present, there are still some problems in the fabrication of ASSTFLBs and the performances of them are still insufficient. Due to the multicomponent of the batteries,including the positive and negative electrodes, the electrolyte, the substrate and the encapsulation layer, the gravimetric energy density of ASSTFLBs is very small. Elevating the cutoff votage of the electrode materials is an effective method to increase the energy density, but the high potential will cause unstability of the positive electrode and deterioration of electrochemical performance. On the other hand, ASSTFLBs are assembled in a multi-layer structure and require ultra-low concentration of dust and water in the air, which can lead to the failure of the entire battery. In addition, some electrolyte films are very sensitive to air, which increases the difficulty and fabrication cost of the thin film batteries.The preparation of LiCoO2 film, the modification of Al2O3 coating on the surface of LiCoO2 film and all-solid-state thin-film lithium batteries were investigated in this paper.The research contents are listed as follows:?1? The effects of stainless steels, gold-plated stainless steels and gold-plated quartz glass substrates on the electrochemical performance of LiCoO2 thin films prepared with magnetron sputtering were compared. We further studied the effects of working pressure and sputtering power on the films using gold-plated stainless steel substrates. Finally,LiCoO2 films with the best performance were obtained at 230 W of power and 2.5 Pa of working pressure. The tests showed that the lithium cobalt oxide grains had a strong ?003?preferential orientation. This film was cycled at a current density of 12 ?A cm-2 and the discharge specific capacity was 62.2 ?Ah cm-2 ?m-1 with a charge cut-off voltage of 4.5 V. We further found that electrochemical performances are difference between LiCoO2 film and the target powders because of the differences of their crystallinity and real material composition. Based on the optimized fabrication parameters, the LiCoO2 film was coated with Al2O3 via magnetron sputtering. The final electrochemical tests showed that the sample coated with Al2O3 for 30 minutes had the best cycle stability. The discharge capacity retention of the 50th cycle was improved from 66.6% to 79.3% after the Al2O3 coating.?2? LiPON solid electrolyte thin films were prepared by magnetron sputtering technology under pure nitrogen atmosphere. Electrochemical tests were performed to reveal the properties of the solid electrolyte films. The decomposition voltage of the electrolyte film is over 5 V. The Li+ conductivity is measured to be 1.70×10-6 S cm-1, with the transfer number over 0.991. Applying the basic structure of the all-solid-state thin-film lithium battery, Cu/Li/LiPON/LiCoO2 cells were successfully fabricated with a novel thin-film battery process. The initial discharge specific capacity of the thin-film lithium battery is 45.9 ?Ah cm-2?m-1 when charged to 4.2 V with a current density of 7.64 ?A cm-2, and the cycle life is more than 600 cycles. |
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