Micro-/Nano-Structured Materials For Lithium-ion Batteries: Design, Preparation And Property Study

As an environmentally friendly energy source, lithium-ion batteries have attracted extensive attention due to their particular features, such as high working voltage and energy density, good cycling performance, no memory effect and small self-discharge. The development and large-scale applications of the Li-ion batteries have been limited by their electrode materials. So, how to produce the electrode materials with superior performance and low cost has been the key factor for the commercialization process of lithium-ion batteries. Nanomaterials exhibit improved electrochemical performance compared to those of their bulk counterpartes, while crystal structure, size, and morphology of nanostructured electrodes have important influence on electrochemical performance. Therefore, it is a significative research topic for the synthesis of nanostructured electrode materials and systemical study of the optimized relationship between the nanostructured electrode materials and electrochemical performance. The primary content of this paper is as following:1. By the solvothermal methode, the hierarchically dumbbell-like LiFePO₄ microstructures self-assembled by nanoplates have been successfully synthesized by using PVP as the surfactant in benzyl alcohol system. The research results show that PVP plays an important role in the construction of the hierarchically self-assembled microstructures. A reasonable formation mechanism for the special LiFePO₄ microstructures is proposed on the basis of the result of time-dependent experiments. The formation of LiFePO₄ microstructures can be considered as a dissolution–recrystallization process, along with the phase transformation from one material to another material. Finally, we investigated the electrochemical property. Compared with the commercial LiFePO₄, the obtained LiFePO₄ shows an excellent cycling stability almost without capacity fading up to 70 cycles.2. LiMnPO₄ has also been synthesized by the same solvothermal methode. In addition, Fe-doped LiMnPO₄ samples{LiMn_yFe_1-yPO₄ (y=0.2-0.6)} have been successfully obtained and achieved the controllable synthesis of different doping proportions. The effect of different Fe-doped proportions on the structure and morphology of products has been systemically discussed by the means of XRD, ICP, SEM, and lattice parameters. The result reveals that the structure of LiMn_yFe_1-yPO₄ (y=0.2-0.6) samples gradually transforms from cuboid to dumbbell, along with the increase of Fe doping.3. The uniform, well-dispersed Zn_xCo_3-xO₄ nanocubes have been synthesized by hydrothermal method. By tailoring the reaction parameters, such as the amount of PVP and ammonia, the concentration of reactants and reaction time, Zn_xCo_3-xO₄ nanostructures with controllable size, morphology, and Zn-doped proportion have been obtained. Then the Zn_xCo_3-xO₄ samples with different sizes are investigated on the electrochemical and gas sensing properties. The results show that the cycling performance of the sample with 250-300 nm is better than that of the 30-40 nm sample. This result suggests that for each metal oxide system there is an optimum range of particle size and smaller is not better, from which it can just achieve the best electrochemical performance. For the gas sensing property, smaller Zn_xCo_3-xO₄ particle has higher sensitivity to ethanol and gasoline than that of bigger particle.