Preparation And Properties Of Negative Electrode Composites For Silicon-based Lithium Ion Batteries

For anode materials with high specific capacity, Si has attracted much attention because of its highest lithium storage capacity?4200mAhg-1?, good safety due to the lower lithium extraction potential?0.4V?, which is a little higher than that of the graphite. However, the limited cycling life resulted from the significant volume changes during the lithium insertion and extraction process, as well as the lower conductivity, greatly restricts its practical use in LIBs. To solve the problems mentioned above, Si based composites were prepared and studied in this work.Firstly, the Si/Li₄Ti₅O₁₂ composite with a larger reversible capacity of 550mAh/g compared with that of the pure Si was prepared by the hydro-thermal method. After 30 cycles, the specific capacity retention was 310mAh/g. On the basis of the EIS results, it was found that the resistance for the composite was lower than that of the pure Si, and the lithium-ion diffusion coefficient was higher than that the pure Si. Scanning electron microscopy?SEM? and Energy Disperse Spectroscopy?EDS?results showed that the surface and the space among the Si particles were filled by the Li₄Ti₅O₁₂ particles, which could buffer the volume expansion for Si during the process of charging and discharging due to the nearly zero strain effect for Li₄Ti₅O₁₂, furthermore, the cycling performance for Si/ Li₄Ti₅O₁₂ composite was improved.Then, the Si/TiO₂ composite with different molar ratios was prepared by the so-gel method. SEM and transmission electron microscope?TEM? results showed that the surface and the space among the Si particles were filled by the TiO₂ particles, which could buffer the volume expansion for Si during the process of charging and discharging due to the smaller strain effect of the TiO₂.According to the X-ray diffraction?XRD?, it could be found that there are no impurity phases in the composite. On the basis the electrochemical tests, the Si/TiO₂ composite with the molar ratio of 1:3 had a specific capacity of 750mAh/g after 30 cycles. Moreover, compared with the pure Si, its resistance was lower and the lithium-ion diffusion coefficient was higher.Finally, the Si/C composites with different Si weight ratio were prepared by the electrostatic spinning method. At the same time, influence of different carbon source on the electrochemical performance for Si/C composites was studied. It was found that the charge and discharge specific capacity were 2189 and 2151mAh/g for the first cycle, corresponding to a coulomb efficiency of 98%, which was much higher than that of the commercial grphite. As a result of the carbon inclusion acting as the buffering agent for the Si volume expansion, the specific capacity retention was 250mAh/g after 30 cycles, which was nearly zero for the pure Si.