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Microstructure and Electrochemical Performance on Nano Sb-based Alloy Anode Materials

Author: WangYanYi
Tutor: YiGuoBin
School: Guangdong University of Technology
Course: Applied Chemistry
Keywords: lithium ion battery anode material alloy composites chemicalreduction CNTs lithiation and delithiation performance SnSb-Ag alloy
CLC: TM912
Type: Master's thesis
Year: 2012
Downloads: 35
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Abstract

Improving the energy capacity and cycle life of lithium-ion batteries is an important target, and as such, research on lithium-ion battery anode materials has generated much interest. Compared with graphite anodes, alloy anode materials have a high theoretical capacity and a fast charge/discharge rate, making alloys a class of very promising high-specific energy Li-ion battery anode materials. Both Sn and Sb in SnSb alloy anode materials have the capacity to store lithium, resulting in a higher theoretical specific capacity than other active/inert systems, such as SnCu and SnNi materials, and have been widely studied. Alloy anode materials undergo severe structural and volume changes during the charge/discharge cycle process across large sizes, resulting in uneven ion distribution, serious agglomeration and poor cycle stability.Nano-SnSb and micro-sized Ag alloy composite anode materials were synthesized using chemical reduction method. The addition of Ag made SnSb-Ag composite alloy anode materials, which formed a laminated structure with irregular gap sizes on the surface and interior of the structure after several cycles of insertion-extraction of lithium ions. This approach greatly shortened the lithium ion diffusion distance, reduced the trapping of lithium in the active materials, and increased the space available for volume expansion. As a result, powder drop off during the volume expansions was prevented, resulting in greatly improved cycle stability for the SnSb-Ag composite alloy anode materials.The SnSbAgo.2composite alloy anode material showed excellent electrochemical performance with a50-cycle capacity of518mAh/g, with a reversible capacity retention rate of82.04%between0.1V and1.5V.Recent research has demonstrated that the electrochemical performance of some Sn-based metals and nanoparticles can be significantly improved using CNTs (carbon nanotubes) as compounds. The SnSb-Ag/CNT composites, using L60-100nm CNTs and dispersing CNTs in NaBH4aqueous solution, will get good cycle performance with a50-cycle capacity of573.8mAh/g.Ag and CNTs play an important part in electrochemical properties by comparing the micro structures before and afer cycling, the CV curves, charge and discharge profiles. Silver was used to promote the entire charge-discharge process in the complex multi-step reaction process and, to some extent, alleviate the reunion of the nanoparticles in the reaction process, fully promote the reaction and improve the cycling performance. During the Li intercalation process, CNTs, with a large space volume and formed a network structure, prevented particle aggregation and increased the buffer space between the alloy particles, which greatly reduced the diffusion distance of lithium ions and the occurrence of lithium trapping in the active electrode materials. CNTs also have excellent mechanical properties and toughness, they effectively buffer enormous stresses during the volume expansion of alloy particles, weakening the forces between the particles and reducing the rate of formation of powder particles, resulting in good electrochemical performance. The SnSbAg0.1/6%CNT composite anode exhibited excellent cycle life by controlling the lithiation of the anode material. The reversible capacity for the50th cycle was639.6mAh/g between0.05and1.5V.

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