| Compared with traditional secondary batteries, e.g., Pb-PbO2 battery, Ni-Cd battery, Ni-MH battery, etc., Lithium-Ion Battery (LIB) shows greater advantages at the aspect of rate capability, energy density, and charge-discharge performance. Moreover, LIB also shows the advantages of long cycling life, low self-discharge rate, and amity to the environment. Now LIB has been broadly used in portable electrics, and actively used in space technology, national defence industry, electric vehicles (EV), UPS, etc. As we know, the key to the commercialization of LIB is the successful development of the intercalated electrode materials. This thesis introduced the cathode materials of LIB hi detail, especially in the development status of LiCoO2, and a summary of the LIB development about technology status and development tendency was also given. The effect mechanism of LiCoOi on the performance of the LIB was discussed from the viewpoint of the primary principle of electrochemistry. Furthermore, the fabrication technique and performance of LIB were studied, and LIB for EV was also studied primarily.The crystal structure, physicochemical properties, and morphology of four commercial LiCoO2 specimens were studied by using modem analytic techniques, e.g., XRD, BET, SEM and laser particle size analysis. Various electrochemical methods were used to study the dynamic characteristic of the LiCoO2 electrode reaction. In the process of comparing crystal structure of different LiCoO2 specimens, the ratio of the intensity of diffraction peak (003) and (104), IOOS/IIM, were used. Li+ ion diffusion coefficient was measured using step-potential method (300mV), and it can be found that LC2# LiCoO2 specimen with higher ratio of I003/I104 shows the largest Li+ ion diffusion coefficient. This means that the higher ratio of I003/I104> the better crystal structure the LiCoOi material should show. Based on the proposed LiCoCh sphere electrode diffusion model, and the expression of Li+ diffusion coefficient -DU+ was deduced by using the second law of Pick.Line sweep was used to measure the exchange current density (i? of the LiCoO2 electrode at lower overpotential (5mV) when the LiCoO2 electrode was electrochemically polarized. It was found that the i?was very small when the electrode was not active, and LiCoO2 material showed a feature of semiconductor; but the i?was increased sharply after small scale of Li deintercalation from electrode, at this moment the electrode exhibited the feature of conductor. With the further deintercalation of Li from the LiCoO2 electrode, i?decreased partially because of the density of Li+ in the LiCoO2 electrode falling down.The interface phenomena of LiCoO2 electrode was studied by AC impedance method. From the Nyquist spectrum of LiCoO2 electrode, we found that the spectrum was made up of three part: the highest frequency part was a small radius circle, which was generated by the Li2CO3 thin film on the surface of the LiCoO2 electrode and the radius did not change withthe potential change; the medium frequency part was a large radius circle, which was generated by the electrochemistry polarization and the radius changed with the electrode potential change; and the low frequency was a line generated by the Li+ slow diffusion in the LiCoOi electrode, which has an angle of 45?from the real axis. From the Nyquist spectrum the i?was also calculated, and the value consisted with the above.The charge-discharge performance of the LiCoOa electrode was also studied. From the result we can see that the LiCoOi material, which has good kinetics behavior, especially has high Li+ diffusion coefficient, possesses good charge-discharge performance and long cycling life.The fabrication technique of the LIB was studied in detail. The process flow and some key procedure such as: the fabrication of cathode and anode, and the selection of the electrolyte were studied also. In order to adapt different circumstance, we introduced normal blending and high temperature blending. For improving the adhesive performa... |
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