Preparation Of Naostructured Si/C Composites As Anodes For Lithium Ion Batteries

Nowadays, to explore and use renewable energy and develop pollution-free and high-efficiency energy storage devices has already been an urgent problem for human beings. As a secondary battery, lithium ion batteries have drawn widely attention in the fields of new energy for several decades, which is attributed to their superiority such as high voltage and specific energy, long cycle life, low self discharge and environmental friendliness. As an anode material for lithium ion batteries, silicon exhibits a very high theoretical specific capacity 10 times larger than that of carbon, and its nanostructures have many favorable features. Therefore, nanostructured Si materials become a hot research on anode materials for lithium ion batteries.In this work, we prepared several nanostructured Si/C anodic materials, and studied their composition, structure, morphology and electrochemical performances. In order to obtain better electrochemical properties, we prepared nanostructured Si/C composites, so that C could relieve the severe volume change of Si during cycling. Besides, we also tried to use cheap material and simple methods to prepare nanostructured Si/C anodic materials with good electrochemical performances.In the first part of our work, we prepared Si/C nanowires and nanoparticles via magnesiothermic reduction. The precursor of SiO2/C nanowires were prepared by electrostatic spinning with tetraethyl orthosilicate (TEOS) as Si source, then magnesiothermic reduced to get Si/C nanowires. Likewise, the Si/C nanoparticles were prepared by magnesiothermic reducing palygorskite, a natural and abundant mineral on the earth, and coating with C. The structure and morphology of above two Si/C composites were studied, and the results testified the possibility of magnesiothermic reducing palygorskite. We also analysed the factors that influenced the morphology of reduced palygorskite and its electrochemical properties.In the other part of our work, we prepared Si/C anodes via dip-coating method, and studied the structure, morphology and electrochemical performances. Ni foam substrates were dip-coated in acetone solution of cellulose acetate with Si particles, then heat treated to acquire Si/C anodes with Ni foam as current collector. We prepared Si/C anodes with three different mass fractions of Si, and studied their electrochemical properties that were directly affected by Si mass fraction. The results showed that anode with 75wt% Si presented the best cyclic performance. At a current density of 200mAg-1, the first discharge specific capacity was 1699 mAhg-1.