High-performance Lithium-ion Battery Electrode Materials And Thin Film Electrode

Rechargeable Li-ion cells are key components of the portable entertainment, computing and telecommunication equipment required by today's information-rich and mobile society. Miniaturization and development towards large power sources are two important directions for the lithium ion battery research. In this thesis, the author mainly conducted the research on thin-film electrodes fabricated by Electrostatic Spray Deposition (ESD) technique, which can be used in fabricating microbatteries. Besides, electrodes materials LiMn₂O₄ and graphite was improved in their electrochemical performance to fit for the use in high power sources.In Chapter 1 the working principle of lithium ion battery and various electrode materials were introduced. Also, a film preparation technique i.e. Electrostatic Spray Deposition was introduced. The author explained the working principle of ESD and showed the applications of this technique. In Chapter 2. the process of coin-type cells assembly and some related experimental methods used in this thesis were introduced.The realization of thin-film lithium-ion batteries requires the successful fabrication of thin-film components of cathode, anode and electrolyte. Electrostatic spray deposition (ESD) technique has proved to be a versatile film formation method, owing to its simplicity, non-vacuum deposition condition, and easy film-morphology control. In this thesis study, it was used to prepare cathode and anode films for lithium ion batteries. In Chapter 3 we prepared LiCoPO₄ electrode films. LiCoPO₄ represents a new class of high-energy cathode material for its higher working voltage at 4.8V, but the lithium-ion diffusion is very slow in it. Its achievable capacity is comparatively low and drops very rapidly after a limited number of cycles, especially in the commonly used LiPF₆ (EC-DEC) electrolyte systems. With an excess of lithium in the initial nominal compositions Li_1+xCoPO₄ (x=0～1), a LiCoPO₄-Li₃PO₄-Co₃O₄ ternary composite can be obtained after heat treatment. Li₃PO₄ and Co₃O₄ were introduced and homogeneously distributed in the LiCoPO₄ matrix. We have obtained distinct two-step feature of the voltage plateaus at 4.8V and 4.9V, high specific...