Electrospinning carbon nanofibers encapsulating transition metal carbides/oxides nanoparticles for high performance lithium ion battery anodes

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Electrospinning carbon nanofibers encapsulating transition metal carbides/oxides nanoparticles for high performance lithium ion battery anodes

 

Author: Lyu, Linlong
Title: Electrospinning carbon nanofibers encapsulating transition metal carbides/oxides nanoparticles for high performance lithium ion battery anodes
Degree: M.Sc.
Year: 2016
Subject: Lithium ion batteries.
Carbon nanofibers.
Hong Kong Polytechnic University -- Dissertations
Department: Faculty of Engineering
Pages: xi, 101 pages : illustrations (some color)
Language: English
InnoPac Record: http://library.polyu.edu.hk/record=b2917033
URI: http://theses.lib.polyu.edu.hk/handle/200/8606
Abstract: In response to the global warming and energy crisis in coming future, dedicated efforts have been devoted to explore, research, and development of renewable and sustainable energy source aiming at sharing the burden on the shoulder of fossil energy source, and gradually or eventually replacing it. In this regard, wind power, tide power, geothermal power, nuclear power and metallic ion batteries appeared and made a difference. Among those, lithium ion batteries (LIBs) power and occupy the market of portable electronic devices, furthermore play a major role in (hybrid) electrical vehicles. Generally speaking, LIBs are the indispensable in those fields. However, anticipated to be lighter weight and longer lifespan, meanwhile support heavier electrical loading, "traditional" LIBs wouldn't satisfy. Graphite, commercial anode material, contribute only 372 mAh/g theoretically, which couldn't meet the high capacity requirement. Therefore, significant works have been done to upgrade anode with better performance. Transition metal carbides (TMCs) and transition metal oxides (TMOs) showed much higher gravimetrical capacity in comparison with graphite. Accordingly, TMCs and TMOs have been widely studied as anode for LIBs. Nevertheless, on the road to commercialization of TMCs or TMOs and replacement of graphite, poor cyclic performance caused by the significant volume change of TMCs and TMOs, which leads to the pulverization of the anode materials and detachment of anode materials from the current collector. Luckily, the nanoscale material, with excellent mechanical property comparing with the bulk counterpart, could efficiently mitigate the tension and contraction force during lithiation and delithiation. Though, nanoscale materials own above-mentioned merits, they are easily agglomerate together in order to decrease its high surface energy. Therefore, the carbon based materials occur as the outer-confinement for TMCs and TMOs, which provides an effective solution. The carbon based materials could successfully suppress the expansion of TMCs and TMOs, and more importantly, offer good electrical conductivity, especially for TMOs. Among wide range of carbon materials, carbon nanofibers (CNFs) suppress the volume expansion while function as the electrical conductor locally and globally. Locally, the CNFs give TMCs/TMOs a uniform distribution, and, globally, the CNFs provide an inter-connected conducting net structurally. Amorphous CNFs encapsulating molybdenum carbide (Mo2C, a potential anode material) nanoparticles (NPs) was synthesized through a one-step electrospinning followed by simple thermal treatment. The as-prepared materials showed enhanced Li-storage ability, superior electrical conductivity, and long lifespan. Specifically, the as-synthesized materials show 900 mAh/g reversible gravimetrical capacity (hereinafter, without specific explanation, capacity refers to the gravimetrical capacity not the volumetric capacity) which is nearly 2.4 times of theoretical capacity of graphite when tested at 0.2C. Meanwhile, the materials demonstrate the efficient suppression upon the significant volume change of combination of nanoscale material and CNFs outer-confinement by showing a relative high capacity of 635 mAh/g @ 0.2C at 400th cycle.

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