| Since the commercialization of Li-ion batteries as a new type of mini energy storage device in 1990, they have been widely applied in our daily lives. Nowadays, because of the impact of the growing energy shortage crisis on the automobile industry, people have higher demands for li-ion batteries with largely improved energy density, power density and safety. Intercalation reaction is the most representative mechanism in Li-ion batteries for smaller polarization and higher coulombic efficiency than other mechanisms. Based on two kinds of intercalation anodes with different structures, this Ph.D thesis focuses on improving the performance of spinel Li4Ti5O12 (one of the anode materials in current li-ion batteries research) by modification. Meanwhile, it investigates the relationship of the structure and lithium intercalation capability of the layered compounds LiMO2 (M=Ni, Co, V) in order to find general rules for the exploration of this new type of intercalation anode materials.Chapter 1 gives a brief introduction about the structure and working mechanism of lithium ion batteries, and summarizes the literature work on the anode materials from the viewpoint of mechanism. Moreover, the research status of Li4Ti5O12, as an intercalation anode material, is mainly introduced at the end of this chapter. Chapter 2 presents the experimental reagents, processes and test equipments used in the thesis. The detailed procedure of coin cell assembling in laboratory is described, as well as the general characterization methods of materials and electrochemical analysis.In Chapter 3, nano-Li4Ti5O12 powders are synthesized by a simple gel route with acrylic acid. By means of optimizing the calcination temperature, we have found that the 750℃-calcined powder with about 120 nm particle size exhibits the optimal electrochemical performance: a high capacity of over 160 mAh/g after 100 cycles at 0.4C rate and a good rate capability with a capacity of 122 mAh/g even at 10C rate.In Chapter 4, Ti-based anode materials with nominal compositions Li4Ti5CuxO12+x (x=0,0.075,0.15,0.3,0.6,1.2 and 1.67) are synthesized by a solid state reaction process. The color, electronic conductivity and X-ray diffraction analyses indicate that the sintered samples are mainly composed of intergrowth spinel-type Li4Ti5O12 and Li2CuTi3O8. Electrochemical test, ex situ XRD analysis and HRTEM images indicate that the first-cycle lithiation of the doped phase leads to the in-situ production of Cu that can significantly improve the rate performance of Li4Ti5CuxO12+x. Moreover, the structure is not destroyed after the Cu extrusion, so that Li4Ti5CuxO12+x keeps zero strain characteristic and exhibits good cycling performance during the following cycles. With the compromise between the capacity and rate capability, the optimal composition is found to be Li4Ti5Cu0.15O12.15. In addition, the structure and electrochemical performance of new phase - Li2CuTi3O8 are also preliminarily characterized in this chapter.Considering the possibility of lithium ion batteries working in low temperature environment in the future, Chapter 5 investigates and improves the low temperature performance of Li4Ti5O12 by optimizing four factors: amount of conductive carbon, calcination atmosphere, Cu doping and synthesis route. It is found that the addition of conductive carbon can partly improve the low temperature performance, while the Li4Ti5O12 powder synthesized in N2 exhibits relatively better low temperature performance because of smaller particle size. The Cu-doped phase synthesized by solid state reaction, although with big particle size, achieves the better low temperature performance because the in-situ Cu production reduces the charge transfer resistance. The Cu-doped Li4Ti5O12 synthesized from the gel route with acrylic acid exhibits the best low temperature performance because of the smaller particle size and the reduced charge transfer resistance contributed by the in-situ Cu extrusion. At 0.4C rate, the Cu-doped Li4Ti5O12 (gel route) electrode delivers a high discharge capacity of above 140 mAh/g at 0°C, around 120 mAh/g at -10°C, respectively. Besides, the phenomenon that Li4Ti5O12 exhibits large difference with different charge-discharge rate modes is also analyzed at the end of this chapter. Layered O3 compounds with the composition of LiMO2, which are usually used as cathode materials, are a primary focus of material research for lithium ion batteries. In Chapter 6 and Chapter 7, we extensively investigate the relationship of its layered structure and lithium intercalation capability at low potentials whenLiMO2 (M=Ni, Co, V) are used as anode materials. In Chapter 6, we focus on the structural changes of non-stoichiometric LiMO2 (M=Ni, Co) and its effect on lithium intercalation capability by changing the ratio of Li and M. X-ray diffraction, Raman and electrochemical analysis indicate that there is a close relationship between the lithium intercalation capability at low potential and the cation ordering in layered structure. The more ordered cation ions the material has, the more difficult for lithium intercalation which leads to the reduced capacity of intercalation. In Chapter 7, the process of lithium intercalation/deintercalation into Li1+xV1-xO2 is somewhat more delicately investigated. By ex-situ XRD and electrochemical characterization, we find that the reaction above 0.2V during the discharging process derives from the production of SEI film, while there is an intermediate phase which always exists in the intercalation/deintercalation process. But for LiMO2 (M=Ni, Co), no intermediate phase can be found. This indicates that the intercalation mechanism of Li1+xV1-xO2 is different from that of LiMO2 (M=Ni, Co), and the existence of transition metal ions with lower oxidation state in the transition metal layer favors the occurrence of lithium intercalation at such a low potential.Finally, in Chapter 8, the author gives an overview on the achievements and the deficiency of this thesis. Moreover, some prospects and suggestions of the possible future research are given.
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