Silicon Quantum Dots-Carbon Nanotube Composite as Anode Material for Lithium Ion Battery
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Silicon Quantum Dots-Carbon Nanotube Composite as Anode Material for Lithium Ion Battery Lanlan Zhong1, Andi Xie2, Lorenzo Mangolini1,2 1 Materials Science and Engineering Program, University of California, Riverside 2 Mechanical Engineering Department, University of California, Riverside ABSTRACT Silicon is a very promising material for anodes of lithium ion batteries. It exhibits a high theoretical capacity of 3579 mAh/g. However, during the lithiation and de-lithiation, silicon materials experience up to a 300% volume change, leading to poor cyclability [1-2]. Research shows that reducing the silicon particle size can mitigate this problem. Carbon nanotubes (CNTs) function well as electrode materials in electrolytic cells because of their high electrical conductivity and surface area. In this work, we combine silicon nanoparticles (Si NPs) and CNTs as anode materials. Si NPs are generated using a plasma-enhanced chemical vapor deposition technique and their surface is modified with a 12-carbon long aliphatic chain to impart solubility in non-polar solvents. They are applied onto a nanotube-based layer using a wet-phase deposition technique. SEM and TEM analysis confirm that they form a conformal coating onto the nanotube surface. The CNTs - Si NPs composite active material is tested in half-cells where lithium foil acts as counter electrode. We have achieved an average of 810 mAh/g discharge capacity for composites with a CNTs to Si NPs weight ratio of 1:1. We expect to be able to increase the discharge capacity by increasing the Si NPs weight content. INTRODUCTION Lithium ion batteries are the most widely used energy storage technology in portable electronic devices because of their light-weight, high energy capacity, low self-discharge properties. Despite this, continuous improvements in their performance are needed especially to enable their use in automotive applications. Silicon is a very promising alternative anode material, however it experiences large volume variations during battery charge/discharge resulting in pulverization of the active layer, leading to poor cyclability and rapid capacity fading. Moreover, there are additional issues that affect negatively the cycling ability of siliconbased anodes. These are the formation of a solid electrolyte interface (SEI) [3] and the loss of electrical contact between active materials and the current collector [4]. Nanostructured silicon is expected to experience less mechanical stress upon lithium insertion/extraction. It has been shown that reducing the particle size to less than ~150 nm effectively solves the pulverization issue [5]. Thus, the combination of silicon nanostructures with a conductive material is a widely investigated approach for the realization of novel anode structures with superior performance. The approaches in literature can be classified in two main categories. In a first approach, onedimensional structures such as silicon nanowires and silicon nanotubes are investigated as potential anode material. They are typically grown on conductive
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