|Carbon-silicon nanocomposite anodes for energy storages
|Zhou, Limin (ME)
|Hong Kong Polytechnic University -- Dissertations
Lithium ion batteries -- Materials
|Faculty of Engineering
|118 pages : color illustrations
|Lithium ion batteries (LIBs) is a kind of newly emerging batteries with excellent properties of high energy density, high working voltage, high charging speed, long cycle life, safe and non-pollution which has already been widely used in recent years. Silicon is one of the most popular anode materials of Li-ion battery due to its high theoretical storage capacity. However, because of its poor electrical conductivity and dramatic capacity fading caused by the large volume expansion/contraction during the electrochemical reaction process, this material encounters great obstacles on the way to large-scale commercialization. In this thesis, two core-shell structures were prepared as reference objects. As carbon materials possess a better electrical conductivity and a more stable structure in the charge-discharge reaction, we used silicon nanoparticle-based composites, coating with a carbon layer to constrain the large volume expansion of silicon during the lithiation. The electrical analysis showed that, comparing with the pure silicon nanoparticles electrode, this structure could prevent the SEI films from continually forming, and improve the electrochemical performance to some extent. Besides carbon shell, a new TiO₂ layer was also studied to replace the carbon shell in the core-shell structure because the TiO₂ layer possesses a higher strength than carbon shell. And the electrochemical test result showed that the TiO₂ layer even did better in keeping the cycle stable. A novel yolk-shell structure was studied to improve the anode properties. It is a structure with a preexistent void between silicon nanoparticles and outer shell. In this thesis, carbon shell and TiO₂ shell were used to form the yolk-shell structure. With the TEM observation, the final composites had a yolk shell structure and the thickness of preexistent void and carbon shell were 50 nanometers and 15 nanometers, respectively while the thickness of preexistent void and TiO₂ shell were 50 nanometers and 30 nanometers. The optical microscope images demonstrated that this yolk-shell structure could efficiently eliminate the pulverization of electrode due to the silicon expansion. And electrical analysis also showed that the yolk-shell silicon nanocomposites electrode had a good electrochemical performance with high capacity, excellent rate capability, and cycle stability.
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