Silicon nanoparticle-based composite as anode material for lithium ion batteries

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Silicon nanoparticle-based composite as anode material for lithium ion batteries

 

Author: Wang, Qian
Title: Silicon nanoparticle-based composite as anode material for lithium ion batteries
Degree: M.Sc.
Year: 2015
Subject: Lithium-ion batteries.
Nanosilicon.
Hong Kong Polytechnic University -- Dissertations
Department: Dept. of Mechanical Engineering
Pages: xii, 102 leaves : illustrations ; 30 cm
Language: English
InnoPac Record: http://library.polyu.edu.hk/record=b2817852
URI: http://theses.lib.polyu.edu.hk/handle/200/8046
Abstract: Lithium ion batteries (LIBs) considered as a kind of newly emerging and greenest chemical batteries have been widely used in recent years. However, the existing storage capacity of LIBs can hardly satisfy the high energy consumption products, such as the intelligent electronic devices and electric vehicles, etc. Therefore, developing an electrode material with a large-volume has led to a popular research field. Silicon, with a high theoretical storage capacity, cannot been put into large-scale commercialization due to its poor electrical conductivity and dramatic capacity fading caused by the large volume expansion/contraction during the electrochemical reaction process. In order to improve the electrochemical properties of silicon, a new kind of binder called sodium alginate (SA) which has a relatively strong binding with silicon nanoparticles was used, and it could improve the capacity and stability on pure silicon nanoparticles electrode in the contrast with PVDF, a commercial binder. As carbon materials have a better electrical conductivity and a more stable structure in the charge-discharge reaction, we also studied a silicon nanoparticle-based composites, coating with a carbon layer to constrain the large volume expansion of silicon during the delithiation. 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. In this dissertation, we also developed an improved method to fabricate a special silicon nanoparticles-based yolk-shell structure, with a preexistent void between silicon nanoparticles and carbon shell outside. In order to control the dispersity, thickness of the void and carbon layer, a lot of conditional experiments had been made. With the TEM observation, the final composites had a yolk shell structure and the thickness of preexistent void and carbon shell were 44 nanometers and 6 nanometers, respectively. 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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