Shape control synthesis and shape dependent electrochemical performances of CuO/Cu₂O nanoparticles

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Shape control synthesis and shape dependent electrochemical performances of CuO/Cu₂O nanoparticles

 

Author: Yu, Haolong
Title: Shape control synthesis and shape dependent electrochemical performances of CuO/Cu₂O nanoparticles
Degree: M.Sc.
Year: 2011
Subject: Lithium ion batteries.
Copper oxide.
Nanoparticles.
Hong Kong Polytechnic University -- Dissertations
Department: Dept. of Mechanical Engineering
Pages: xi, iii, 157 leaves : ill. (some col.) ; 30 cm.
Language: English
InnoPac Record: http://library.polyu.edu.hk/record=b2507575
URI: http://theses.lib.polyu.edu.hk/handle/200/6528
Abstract: Rechargeable Li-ion batteries are attractive power sources for a variety of electric energy storage applications, such as in electric vehicles, smart grids or power storage from solar or wind electricity. Some transition-metal oxides (Fe, Co, Ni, Cu, etc.) have already been extensively investigated as anode materials for lithium ion batteries (LIBs) due to various advantages, such as, high stability which cannot burn compared with carbon when the temperature is high. Cu₂O and CuO are interesting materials with significant potential applications in solar energy conversion, catalysis, gas sensor, and also as the negative electrode material for lithium-ion batteries. Cuprous oxide can be grown as having different kinds of morphology, including spherical, cubic, octahedral, dodecahedra, 26-facet polyhedral, nanowire, nanocage, multipod, and hierarchical structures. The size and morphology of inorganic materials have strong effects on their widely varying physical and chemical properties due to the quite distinctive surface characteristics that are highly dependent on the particle size and shape. Different geometries of copper oxide may demonstrate very different electrochemical performances used as electrode materials for rechargeable lithium ion batteries. In this paper, we have developed low-temperature chemical strategies to synthesize copper oxide nanoparticles having controllable particle shapes and sizes. Cu₂O nanoparticles with various specific morphologies including cubes, spheres, hollows, octahedrons and polyhedrons have been successfully fabricated. We have extensively investigated the electrochemical performances of the Cu₂O nanoparticles as a function of particle size and morphology. Firstly, charge-discharge capacity was measured. Octahedral Cu₂O presents the best capacity at the current of 50mA/g and the spherical Cu₂O shows best at the current of 500mA/g and 5A/g. Moreover, 6th charge-discharge curve at the current density of 50mA/g indicates that the spherical Cu₂O react with Li+ in a wider voltage range than other Cu₂O, certifying spherical Cu₂O presenting best charge-discharge capacity. Cyclic voltammetric measurement and ac impendence spectra were tested for more evidences. From C-V results, spherical Cu₂O own a strong cathodic peak which corresponds to the transformation from Cu₂O to Cu and strong anodic peaks which can be ascribed to the decomposition of SEI and Li₂O. EIS results indicate that spherical Cu₂O present the small value of Rf and Rct which demonstrate that spherical Cu2O show the higher electro-activity than other shapes. From the charge-discharge capacity, 6th charge-discharge curve, C-V, EIS results, the spherical Cu₂O is demonstrated to be the best morphology owns the most outstanding electrochemical performance. And the fundamental reasons leading to this electrochemical activity difference will be described based on the thesis. In order to improve the specific capacity, coating carbon method is adopted.

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